The so-called side-exposure method has been widely used in the fabrication of fiber Bragg gratings (FBGs). The effects of the fiber cladding on the wavefronts of the UV writing beams and the interference fringes formed inside the fiber have been addressed in this study. The wavefronts of the UV beams have been analyzed and it has been demonstrated that the existence of the fiber cladding significantly alters the wavefronts of the UV beams in one plane and makes them highly astigmatic. Based on the calculated wavefront radii of the UV beams, a model has been established for prediction of the interference fringe pattern formed in the fiber core area.

We experimentally investigate the simultaneous measurement of bending and temperature using the phase-shifted long-period fiber gratings (LPFGs) based on the resonant wavelength shift and wavelength spacing change by the bending and temperature change, respectively. The phase-shifted LPFGs can be fabricated by UV post-exposure on a half of the grating region. The UV post-exposure has the effect of inducing a positive phase shift for the core mode while decreasing the coupling strength between the core and cladding modes. The spectral evolution of the transmission thus depends on the initial coupling strength of the grating. We applied the phase-shifted LPFG fabricated with the second saturated LPFG to the simultaneous measurement of bending and temperature. The left and right resonant peaks shifted into the longer wavelength due to the variation of the grating period as the bending curvature increased and the wavelength spacing between two peaks was not changed by the bending. However, since the phase-shifted LPFG has two different sections with different photo-induced average indices, the wavelength spacing between left and right peaks decreases as the temperature increases. Based Consequently, it is possible to discriminate two effects between bending and temperature based on the proposed schematics.

A novel pressure sensor with FBG partly packaged by a metal tube is presented. The thermal-strain cross effect can be avoided. Moreover, its pressure sensitivity is -2.44×10^-3/MPa with the range from 0 to 0.44 MPa, which is 1200 times as that of a bare fiber grating. The linearity of this sensor reaches 0.9986.

In this paper, we studied temperature characters of LPFG fabricated with a new designed system, which focuses the CO₂ laser pulse beam on standard single mode fiber with azimuthally symmetric irradiation. A high temperature optical fiber sensor based on such a LPFG has average high temperature sensitivity of 0.16nm/°C, large dynamic range of 0°C to 600°C, good temperature repeatability and simple configuration. Meanwhile, the sensor with different temperature measurement range can be easily obtained by adjusting the fabricating parameter of LPFG. The temperature sensor with those advantages has a potential of measuring temperature as high as 900°C.

Fabrication of a 2 cm long Bragg grating with reflectivity of 99.96 % in the B/Ge codoped fiber is demonstrated by phase mask method under high energy UV pulses. The growth characteristics of grating strength and Bragg wavelength shift are investigated. During UV irradiation, the evolution of the type I grating exhibited typically different stages: growth, saturation and decrease. With further UV exposure, the decrease of the type I grating was followed by the appearance of regenerated grating. But these phenomena were not observed under relatively low energy UV pulses. When the regenerated grating entered into saturation stage again, it became stable and had higher reflectivity and broader bandwidth than the type I grating.

We present a novel forficiform device for both the temperature-compensating package for fiber Bragg gratings(FBGs) and cryogenic FBG temperature sensors. The wavelengths of the reflected light from 1550nm FBGs are measured in the temperature range from 77K to 353K .The temperature sensitivity of FBG sensors can be reduced by more than 10 times, reaching 0.001nm/K in the temperature range from 243K to 353K when the device is used in the temperature-compensating package for FBGs. If the device is used in sensing, the temperature sensitivity of 0.0448nm/K can be obtained at 100K, which is 1.15 times greater than that of a FBG fixed on Teflon substrate. Furthermore, when the FBG in the forficiform device is bonded on an aluminum substrate or a poly substrate, the temperature sensitivity can reach 0.12nm/ K at 100K.

We experimentally demonstrate a simple scheme for tunable repetition rate multiplication based on the fractional Talbot effect using a linearly tunable, chirped fiber Bragg grating. The key component in this scheme is our linearly tunable, chirped FBG without its center wavelength shift, which was fabricated with the S-bending method using a uniform FBG. By simply tuning the GVD of the chirped FBG, we readily multiply an original 8.5 ps, 10 GHz soliton pulse train by a factor of 2 ~ 5 to obtain high quality pulses at repetition rates of 20 ~ 50 GHz without significant system configuration change.

The response of a transmission spectrum to applied axial strain for an in-fiber Mach-Zehnder interferometer that based on two tcascaded long-period fiber gratings is studied theoretically and experimentally. Linear strain-induced wavelength shift with a tuning rate of -0.6 pm per microstrain has been achieved, which suggests that such an optical fiber device can be used as a cost effective, tunable wavelength-division multiplexing (WDM) filter.

In this paper, a novel structure design of all-fiber tunable compressor has been proposed which based on two cascaded uniform fiber Bragg gratings and a Piezoelectric Ceramic is used to make the compressor posses tunable function. By simulating numerically the evolution of picosecond pulses in the compressor, we have found that picosecond pulses can be compressed effectively, if the parameters of gratings and pulses were chosen properly. Additionally, the further study reveals that the width of output pulse could become narrower and the fiber gratings needed would be shorter, if the negative chirp of initial pulse were induced by pulse laser.

A novel 16-channel comb filter based on superstructure fiber Bragg grating (SFBG) is proposed for the first time. It is characterized by single-grating structure, equal reflectivity peaks, narrow channel bandwidth, flat-top, high bandwidth utilization ratio, standard 50 GHz channel-spacing, and realizing dispersion compensation and wavelength filtration simultaneously. Based on ameliorated layer-peeling algorithm, that is adopting channel-by-channel windowing method rather than all-channel integral windowing method, this novel SFBG is synthesized successfully. According to the grating structure of the synthesized SFBG, reflectivity spectrum, group delay and group delay ripper are analyzed based on the method of transfer matrix. The results show this SFBG does an almost perfect job of reproducing the desired spectrum.

The microwave photonic responses of super-structured fibre Bragg gratings in combination with dispersive fibre are investigated theoretically and experimentally. The super-structured gratings are optimised, taking account of the spectral response of the broadband source, EDFA and optical tunable filter to achieve a filter response with side-lobe suppression of more than 60 dB.

The asymmetry index profile in the transverse plane, which could be induced during the writing of fiber Bragg gratings with UV side-exposure techniques, may cause the photo-induced birefringence, as was numerically evaluated by Kokou Dossou et al. But the impact of this photo-induced birefringence on the performance of fiber grating components remains to be determined. In this paper, we numerically analyzed this kind of impact by using a finite-element method with a full vectorial formulation and the coupled-mode equations. It shows how the birefringence affects the reflection spectrum, the group delay. This numerical method will be useful in designing and analyzing fiber gratings.

Driven by the fast development of fiber communication networks, there exists a strong need for a dynamic coupler with a large number of output ports. In our work, we developed a dynamic optical coupler by employing a specially designed Dammann grating that consists of two areas, which are the Dammann-grating area and the blank area. When incoming beams entirely impinge on the Dammann-grating area of the plate, this device demonstrates 1×8 dynamic optical coupler with good uniformity of 0.03 and low insertion loss of about 10.7 dB for each channel as a splitter at the wavelength of 1550 nm. When incoming beams entirely impinge on the blank area of the plate, this device achieves a low insertion loss of 0.43 dB as a combiner. Therefore, this device can achieve the beam splitter and combiner as a switch between them according to the relative shift between two areas of the plate. The experimental results are reported in detail in this paper.

The authors report for the first time clear and stable self mode-locked pulses with Q-switched pulse envelope in diode pumped Yb-doped Q-switched fiber lasers. Self Phase Modulation (SPM) effect is used to explain the generation of self mode-locking. On this basis, the AOM was removed and two gratings were used as the cavity mirrors. An all-fiber F-P cavity mode-locked fiber laser was realized for the first time. Similar mode-locked pulses were observed when using two ring reflectors as the cavity mirrors. SPM effect combining with saturable absorption effect is proposed as an explanation. The all-fiber F-P cavity fiber laser provides a new method to generate mode-locked pulses.

A theoretical investigation of bidirectionally dual-order pumped distributed Raman amplifiers is presented in detail, and comparisons with other Raman amplification schemes, i.e., bidirectional first-order pumping and Raman-plus-erbium-doped fiber hybrid amplification, are carried out at identical nonlinear phase shifts. The results show that symmetric bidirectional dual-order pumping can achieve the best optical signal-to-noise ratio performance by appropriate choice of the second-order pump wavelength and second-to-first-order pump power ratio for both short- and long-span conditions.

Based on a compact 2-D Finite-Difference Time-Domain(FDTD) method, We study the effect of imperfection of transverse periodicity on the leakage loss in photonic crystal fibers(PCFs). Random fluctuations of holes radius and position in PCFs are introduced to analyze their effect on the guiding ability.

In this paper, we described a new type of wideband communication fiber with low water peak. The new fiber has excellent dispersion performance. It allows WDM technology to be applied on the range: E band to L+ band, which wavelength range is from 1370nm to 1650nm. It has relative low relative dispersion slope called as RDS, which makes high bit rate transmission system be easy to realize full dispersion compensation with low cost. Low water peak characteristics of new fiber provide necessary condition to extend operation range to E band. New fiber has moderate effective area, which makes new fiber have flexible amplification choices. Excellent PMD performance makes new fiber be suitable for higher bit rate transmission system.

A tunable, gain-clamped (GC) double-pass Erbium-doped fiber amplifier (EDFA) using only one fiber Bragg grating (FBG) has been demonstrated, which solves the problem existing the conventional GC-EDFA using two FBGs, in which the clamped-gain is very difficult to be tuned. In the new GC-EDFA, the lasing oscillation for clamping the gain is produced between a FBG and a fiber reflection mirror, and a variable optical attenuator (VOA) is used to change the loss of the laser, which is filtered solely from a narrowband filter for tuning the clamped-gain, however it does not change the signal power directly. Meanwhile, the double-pass configuration enhances efficiently the gain, therefore, compared with the single-pass configuration, the maximum possible input signal power for gain-clamping is greatly extended. Furthermore, the FBG can depress the strong backward amplification spontaneous emission in double-pass configuration, so it can reduce the noise figure a certain extent. Finally, a gain-tunable GC-EDFA with a wide dynamic input power range is demonstrated.

A new design of all-optical gain-clamped L-band double-pass (DP) erbium-doped fiber amplifier (EDFA) has been demonstrated, in which, the input port and the odd-channel output port of interleaver are connected with a DP configuration EDF through a circulator to form lasing ring cavity for clamping gain, and the even port is utilized to export the amplified signals. A low NF can be achieved because the lasing co-propagates with the signal, and the lasing is exported separately from the amplified signal thanks to interleaver. Meanwhile, the fiber Bragg grating incorporated in DP configuration suppresses the backward ASE generation, and therefore improves efficiently the gain and lowers the NF. In such a way, the clamped gain of 16.3dB with a variation below 0.2dB and the noise figure below 5dB is achieved on the new L-band gain-clamped EDFA.

All-fiber frequency shifter of polarisation maintaining fiber is of great importance in fiber optics. Previous researchers generally studied one-pass all-fiber frequency shifter of polarisation maintaining fiber. This paper discusses multiple-pass all-fiber frequency shifting of polarisation maintaining fiber theoretically. The solutions of coupled-mode equations for polarisation maintaining fiber when the two orthogonal modes exist is discussed, and the multiple-pass frequency shifting is analyzed. The special issue of the two-pass frequency shifter where the linearly polarized light launching into one polarisation axis of the polarisation maintaining fiber is discussed.

Optical fibers for UV transmission have been under intensive development for medical, industrial and other applications during the past several years. Because of this high-speed growth, the problems associated with the damage and transmission properties of silica fibers in the UV region need to be deeply solved. In this paper, in order to make silica-core fibers with excellent transmission in a UV spectral region, an improved silica-core fiber is fabricated by a new fabrication technology of UV-transmission fibers. The technology of fabricating a UV fiber using silica glass is based on two effects of previous UV irradiation and heat treatment. The structural defects and color centers are purposefully caused in silica glass by irradiation silica glass preform with UV, then the structural defects and color centers are removed by performing heat treatment in drawing tower during drawing optical fiber process. The defect generation mechanism in the silica optical fibers is investigated in the paper, and these defects termination principle is also developed. Finally, UV fibers have been tested. From these tested results, UV fibers fabricated by proposed technology have reached the level of high characteristics.

In this paper, we demonstrate a chirped grating designed to compensate for both second- and third-order fiber dispersion. The fabrication technique of chirped gratings is the phase-mask beam scanning method by using a standard unchirped phase mask and by tapering a fiber in the region of the grating. We have made theoretical analysis on the chirp induced by linear and nonlinear taper profiles. The reflectivity and time delay curve of such fiber Bragg grating have been calculated.

A novel Moire grating in Yb³⁺-doped double-clad fiber is reported. It consists of two intracore Bragg reflection gratings separated by an optical phase shift; the grating was formed through double exposure phase-mask method. An Yb³⁺-doped double-clad fiber laser based on this grating is presented. The laser wavelengths are 1055nm and 1057nm, respectively, with less than 0.1nm line-width, over 40dB signal-to-noise ratio.

Polarization-related impairments have become a critical issue for high-data-rate optical systems, particularly when considering polarization-mode dispersion (PMD). Consequently, compensation of PMD, especially for the first-order PMD is necessary to maintain adequate performance in long-haul systems at a high bit rate of 10 Gb/s or beyond. In this paper, we successfully demonstrated automatic and tunable compensation for first-order polarization-mode dispersion. Furthermore, we reported the statistical assessment of this tunable compensator at 10 Gbit/s. Experimental results, including bit error rate measurements, are successfully compared with theory, therefore demonstrating the compensator efficiency at 10 Gbit/s. The first-order PMD was max 274 ps before PMD compensation, and it was lower than 7ps after PMD compensation.

This paper discusses the reflection of chromatic dispersion in 40Gb/s system. And find a real time adaptive dispersion compensation technique based on BER feedback and fuzzy logic control. At the same time, the paper discusses the relation between BER and chromatic dispersion. In the paper, we do the simulation of 240 km (3 segments) 40Gb/s optical system. In the simulation, we can find the best chromatic dispersion tolerance of the 40Gb/s system. To compensate the CD, the fuzzy logic control is used. We give the fuzzy logic control arithmetic in the paper, put up the rule in the fuzzy logic control. We use the Bragg Gratings to compensate the CD. At last, we summarize the paper.

In this paper, the beam-propagation characteristics of the total internal reflection induced by the thermo-optic effect are investigated. Based on the Fourier heat transmission principle and variable separation method, we derive the analytical transient expression of thermal field for general thermo-optic (TO) devices. Based on the analytical expression, time response and steady-state temperature distribution of thermal-optic devices are presented. The expansion rule of total internal reflection (TIR) in the thermal field is developed mathematically, and quantitative calculation is given about specific expansion value. As an illustration and application of this rule, a X-junction 2×2 TIR switch is designed to accomplish the object of high reflection efficiency. The computer simulation results show the structure presents a high reflection coefficient indeed, the reflection loss is only -0.76dB. The computer simulation results agree with the calculation well.

The serious downturn of optical fiber communication industry in the past three years speeds up the consolidation of passive component manufacturing. Automation activity and investment stopped due to no driving force from the volume demand. A lot of skillful but low cost labors must be needed in the future for manufacturing when the demand comes back. Except MEMS based VOA, most of components based on advanced technology seem to get delayed in most applications. Furthermore, the highly integrated products are also delayed and become uncertain, especially AWG technology. Most of the manufacturing of passive components already moved or are moving to Asia especially China. Browave already built its manufacturing factory and is almost doing all the manufacturing in Zhong Shan. Browave tries to optimize the value of Taiwan plus China, i.e., Tawan provides superior management system, quality systems and manufacturing engineering support where China provides a lot of skillful but low cost labors. Browave is now not only providing the basic elements like Couplers, Isolators, TFF add/drop filter, Thin Film based GFF (Gain Flattened Filters), but also providing "Dedicated Lines" for the components/modules/subsystems for the players who need the value as mentioned above.

The Information Optoelectronic Technology Research Institute (IOTRI) in Tsinghua University brings together research activities and research projects in various optoelectronic devices, integrated photonic devices, optical fiber telecommunication and networks, optical display, optical storage and optical fiber sensing systems. The researches on the optical components for the all optical networks are executed in the area of Fiber Bragg Grating, Wavelength Converters, Tunable filters, Fiber Amplifiers, DFB+EA integrated light source chips and modules, optical nonlinear macromolecule material and its application, Fiber Amplifiers, etc. and the forecast researches on photonic crystal and nanophotonics are also started. Up to now, about 10 research projects on optical component for all optical networks are kept on going in IOTRI with the projects supports by the government through the National High-tech R&D Program ("863" program), the National Fundamental Research and Development Program (“973” Program), the National Natural Science Foundation (NSFC), Tsinghua 985 Project, Foundation project of Tsinghua University, and some cooperated projects. All these projects cover the following research areas: Fiber Bragg Grating and its application in DWDM systems such as broadband dispersion and dispersion slope compensation, polymer optical waveguide and its applications, photonic crystal's theoretical analysis and design, wide-band dynamic gain equalized FRA+EDFA hybrid module and related components, wavelength converters and its application in optical networks, tunable PMD compensators, Fiber optical parametric amplification, Gain Coupling in high-speed integrated light sources, etc. Some projects are just carried on, and some of them achieved a lot. About 30 papers in the above areas are posted in the last 3 years.

Zirconium oxide films were prepared with and without ion beam assisted deposition (IBAD) by an electron beam. The effects of Ar-ion bombardment on the optical inhomogeneity of ZrO₂ films deposited at room temperature were investigated. The results show that all samples are amorphous, and the refractive index of sample A without IBAD randomly changed with the film thickness, while the relative inhomogeneity of samples B, C, D with IBAD nearly zero. It was found that the energy of depositing molecule or atom had an important effect on the optical inhomogeneity of films, and the optical inhomogeneity of amorphous ZrO2 films could be improved by IBAD.

Block copolymers (BCPs), which self-assemble into spatially periodic one-dimensional (1D) ordered lamellar equilibrium structures, can be used as multilayer waveguide materials. In this article, the hybrid modal characteristics of three representative self-assembled BCPs multilayer stripe waveguides were studied with compact 2D finite-difference time-domain (2D-FDTD) method. By comparing our numerical results with those obtained by the N-layer waveguide formalism, it is found that on some occasions the two-dimensional (2D) formalism is a good choice to substitute for the three-dimensional (3D) modal analysis of multilayer waveguide . It is also been proved that if the sequence of the two different index layers is inverted in the structure, the modal analysis results change dramatically and the lamellar width is an important factor that influences the optical field distribution of the waveguide modes. An investigation about the triblock copolymer (tri-BCP) waveguide revealed that its field distribution layered more obviously for the particularity of tri-BCP waveguide core structure.

Fiber-to-the-Premise (FTTP), a keyword in the current fiber and cable industry, leads us variegated directions of the research and development activities. In fact, this momentum of industry seems to be weak yet, since the bandwidth demand by market is still unbalanced to the capacity in the several market segments. However, the recent gradual recovery in metro and access network indicates a positive sign for FTTP deployment projects. It is the very preferable for us to optimize R&D strategy applicable to the current market trend of sequential investment.

We present, in the form of review, the results of our study on the design, fabrication and assembly of optical printed circuit boards (O-PCBs) for VLSI micro/nano-photonic applications. The O-PCBs are designed to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards, substrates or chips, in a manner similar to the electrical printed circuit boards (E-PCBs). We have assembled and constructed O-PCBs using optical waveguide arrays and circuits made of polymer materials and have examined their information handling performances. We also designed power beam splitters and waveguide filters using nano-scale photonic band-gap crystals. We discuss scientific and technological issues concerning the processes of miniaturization, interconnection and integration of polymer optical waveguide devices and arrays for O-PCB and VLSI micro/nano-photonics as applicable to board-to-board, chip-to-chip, and intra-chip integration for computers, telecommunications, and transportation systems.

Surface Acoustic Waves (SAW) propagating in a semi-infinite, anisotropic medium Lithium niobate(LiNbO₃) are discussed. Integrated Acousto-Optical Tunable Filters (AOTF) have demonstrated wide application in various fields of laser technology, spectroscopy, optoelectronics and optical signal processing as well as wavelength division multiplexed (WDM) networks. We fabricated practical quasi-collinear integrated AOTF.

A new polarization beam splitter/combiner is realized as a one dimensional metal grating structure with periods less than the wavelength; one polarization paralleled to the gratings will be reflected while the orthogonal polarization will be transmitted. We fabricate metal-stripe gratings on glass substrate using E-beam nanolithography technique and reactive ion etching process. A detail investigation of the polarization effect at 1550nm wavelength is carried out with theory analyze and experimental results. The polarization beam splitter has uniform performance with wide variations in the angle of incidence and has low insertion loss, high polarization extinction ratios both the reflected and the transmitted beams.

The transfer functions of the vertically coupled microring resonator are derived. The effects of parameters such as: the coupling coefficients, the internal propagation loss and the microring’s radius on the characteristics of the resonator are analyzed theoretically. And the optimum parameters are chosen. The higher order microring resonator is compared with the single ring resonator. At last, a wide wavelength range tunable filter based on microring resonator is proposed and its structure is shown in details.

We developed various optical devices and integrated optical devices based on innovative nano-optical structures and design. The nano-optical devices and integrated devices were fabricated through a nano-manufacturing platform based on wafer level nano-replication with mold and nano-pattern transfer by nano-lithography. The nano-replication process, which based on imprinting a single-layer spin-coated UV curable resist, achieved excellent nano-patterning fidelity and on-wafer uniformity with high-throughput. Excellent wafer level performance and yield were achieved. Nano-optic devices, such as, quarter wave plates and polarizers, and integrated nano-optical devices, such as monolithically integrated semi-isolators, were manufactured with the nano-manufacturing platform. The developed technology is suitable for high-throughput and low cost manufacturing needs for commercializing nano-structure based optical devices and integrated optical devices.

In order to resolve the contradiction between real-time and arithmetic complex in television tracking capture system, the paper discusses a real-time target track processing system which is constructed by high performance DSP chipset TMS320C6416 as core digital processor, huge reprogrammable logic chipset CPLD as system logic controller and field reprogrammable array FPGA as image preprocessing chipset to sampled video digital image. In the same time, the author also improved target capture arithmetic by introducing a kind of fast image correlation matching arithmetic based on evolutionary algorithms. Major parts put on hardware construct, working theory and new image correlation matching algorithms. Furthermore the comparison of the performance provided by this method with conventional matching algorithms is discussed. Theoretical analysis and simulation results show that the proposed algorithm is very effective.

Based on the optical thin film interference theory, a novel thin film multi-half-wave multi-frequency filtering technology applied to DWDM interleaver, a comb-like filter, is proposed in this report. A flexible on-demand design of arbitrary frequency spacing can be easily obtained by this thchnology. The parameters of this thin film structure have been analyzed and optimized, and a specific expression for these thin film structure has been described. 50G-spaced and 100G-spaced DWDM interleavers with flat-top passband consisting of less than 30 layers have been designed and fabricated. The process of fabrication is also discussed in this paper. These thin film interleavers have the advantages of good stability, arbitrary wavelength spacing between the adjacent channels, rectangular shape of the pass-band, less layers, low cost, and easy encapsulation, which would make it more attractive to use in DWDM system. The above-mentioned technology exhibits the flexibility in design and the advantages of thin film coating, which will have more applications besides interleaver.

A brief review of three specially designed types of photonic crystal fiber (PCF) that we recently developed for high performance devices is presented. The first is absolutely single polarization PCF (ASPF), which guides only one polarization mode, the second is dispersion-flattened polarization maintaining PCF for Supercontinuum generation, and the third is a new type of photonic bandgap fiber with a super-lattice structure.

A new dual-pump fiber optical parametric amplifier (FOPA) is investigated, which is composed of three-section photonic crystal fibers (PCF) and theoretically provides a nearly flat gain of 21.54 dB with peak-to-peak gain uniformity of better than 0.2-dB over the 405-nm bandwidth from 1260 nm to 1665 nm. Moreover, the influence of random fluctuations of the second-order dispersion in each fiber segment on the gain spectrum also is analyzed. When the average values of second-order dispersions are maintained close to the constant optimum values, the deviation of gain spectra is not large and the gain ripple is not more than 3 dB in presence of second-order dispersion variations.

In this paper, we proposed a novel SPSM PCF and analyzed its optical properties with a full vector model. Considering the opposite parity of each guided mode in the fiber with symmetric structure, we improved the full vector model we developed previously. The numerical result demonstrated that the algorithm proposed is very efficient for analyzing the PCFs with symmetric structure. It only needs relatively few terms to obtain good results that the computation time can be reduced greatly. It is also confirmed that the fiber structure proposed is very efficient and can operate at SPSM region from the wavelength 1.37mm to 1.70mm.

Full-vectorial finite element method based eigenmode solver and imaginary-distance beam propagation method are developed for analyzing modal leakage characteristics of microstructured fibers and photonic band gap fibers. In both schemes the curvilinear hybrid edge/nodal elements based on linear tangential and quadratic normal vector basis functions are adopted to accomplish the computational window divisions and perfectly matched layer (PML) is incorporated as the boundary condition to absorb waves out of the computational window. The two schemes give consistent results for the numerical examples considered and the validity and usefulness of this work are demonstrated. Comparison with published results is shown.

This paper reports recent advances in photonic functional devices. These devices are being developed for advanced optical networks and are fabricated by using planar lightwave circuit technology. After briefly summarizing the fabrication, properties, and progress of silica based planar lightwave circuits, this work describes lattice-form dynamic devices designed to compensate for unwanted fiber characteristics with respect to high-speed wavelength division multiplexing transmissions. These dynamic devices include adaptive chromatic dispersion, polarization-mode dispersion, and gain non-uniformity compensators. The paper then describes optical signal processing devices for communications use, namely an optical label recognition device, an optical encoder/decoder for time-spreading/wavelength-hopping code division multiple access, and a spectrum synthesis device.

A new arrayed wave-guide demultiplexer is proposed on Proton exchanged X-cut-Y propagating Lithium-niobate substrate. The device simulation is performed at 1550nm central wave length. The simulation is carried out using Optiwave 5.O based on the beam propagation method.and uses effective index method for calculating the propagation constant b.This novel device differs from the conventional AWG MUX/DEMUX. The width of the wave-guides in the array section is varied from 2.5µm to 4.0µm with a step size of 0.1µm keeping the length of all array wave-guides equal. This contributes to the dispersion effect. The small 's' bend. sections are used at the i/p and the o/p array aperture. The dispersive effect at the i/p and o/p bend section is negligible. Hence the dispersion of the Phasar is mainly due to the increase in the width of the wave-guides in the array section. One of the merits of the device is the use of the variable Width wave-guides for controlling the effective index of the wave-guides in the array, which makes the device compact and reduces the optical propagation losses. In the conventional arrayed wave guide DWDM MUX/DEMUX the increase in the channel count Increases the cross talk that can be minimized by increasing the number of wave-guides in the array section, resulting in a complex structure. In the proposed device the spacing between the wave guides in the array section can be easily controlled by the “s” bend sections which in turn minimizes the cross talk [intra channel] without increasing the number of wave-guides in the array structure which limits the phase error. As the device is Lithium niobate based, which exhibits an excellent electro optic behavior, the device can be made tunable contributing to the rapid development of high speed Broadband optical networks such as fiber to the home and Broadband optical networks such as fiber to the home and DWDM, apart from using it as a dynamic switching device.The simulated results at l=1550nm for X- cut Y propagating proton exchanged wave guide {PHASAR} for TE polarized light depicts the free spectral range in the order of THz. The simulation was performed for 4-channel demultiplexer having a channel spacing of 200GHz. Due to the strong confinement in the array wave-guide structure, the field profile at the focusing point in the image plane maintains its shape. The modal field is assumed to be Gaussian and all the measurements are performed at (FWHM). The device has low diffraction order although it is used for broadband optical communication network This results in a low diffraction loss at the central channel. An attempt is made in the design to keep the focal field at the o/p a replica of the modal field at the i/p by choosing the symmetric I/P & O/P MMI coupler and the wave-guides. The non-uniformity is kept minimum by the optimization of position of the waveguides in the i/p and the o/p array aperture apart from using linear tapers at the i/p and o/p.

An optical transversal programmable filter can realize arbitrary filter characteristics in one circuit and can vary the filter characteristic adaptively, so it is a promising device. This filter consists of a variable splitter for splitting a input light to N paths(taps), variable phase shifters, delay lines and a variable combiner for combining the split lights to an output light. We can obtain the desired filter characteristics by setting up the arbitrary tap coefficients and minimize the principle loss by designing a symmetrical arrangement of the variable splitter and the variable combiner with each other. However, in order to set those, it is necessary to control the circuit characteristics accurately with compensating for the fabrication errors. We fabricated the low loss optical transversal programmable filter with the monitor waveguides and a novel method which adjusts the circuit characteristics and compensates the fabrication errors, using silica-based PLC. And we demonstrated three types of filter spectra having a Gaussian-shape, a flat-top-shape and a flat-top-shape with a low loss ripple adaptively using the one optical transversal programmable filter.

This paper has analyzed the random phase errors of AWG (array waveguides grating) induced by fabricate processing and their affects on crosstalk level of AWG between non-adjacent channels theoretically. And a very useful formula which can estimate crosstalk level has been proposed. By using this formula, the DWDM (Dense Wavelength De-multiplexer Multiplexer) components based on AWG can be optimized to reduce their crosstalk level. Finally, a very good design example which non-adjacent crosstalk is -40dB by using this formula has been given.

In this paper we design and fabricate the first mirror-integrated silicon-on-insulator-based (SOI-based) arrayed-waveguide grating (AWG) with working functions. The fabricated AWG has a channel spacing of 1.6 nm centered at 1556 nm. We substitute the bent waveguides array in the traditional AWG configuration by adopting the structure of the mirror-integrated straight waveguides. Theoretical advantages of the new structure are demonstrated. Detailed description of the design procedure and the fabrication process is provided. Test results of both the traditional AWG and this design are delineated and analyzed, which shows that the total length of the waveguide array is reduced from 3.14 cm to 2.53 cm, and the holistic structure also becomes more compact. The crosstalk of the fabricated 1x8 AWG is better than -20 dB. The typical on-chip insertion loss is about 10 dB. Losses caused by the mirrors and the waveguides transmission are about 4.2 dB, both of which resulted from the imprecision in the fabrication process.

At first, we made a approximative λ/4-shifted DFB Yb-doped fiber laser with double exposure method .The length of Yb-doped fiber is 10cm. Secondly, we processed the fiber laser by UV trimming. In addition, the running characteristics of the λ/4 phase-shift DFB Yb³⁺-doped fiber CW lasers were researched. The fiber laser have the following excellent characteristics: Output power of 25mW, fluctuation of less than 2%, 100% single longitudinal mode, 27dB polarization extinction ratio, 60dB signal-to-noise. What is more, the effect on the fiber lasers is also researched from several factors such as temperature, mechanism perturbation and fresnel reflection of fiber end section.

A new linear cavity multi-wavelength erbium-doped fibre laser with enhanced signal-to-noise ratio characteristics is demonstrated. The laser system is developed by two steps from a conventional ring cavity configuration which consists of a frequency-shifted cavity and single multi-wavelength filters. Firstly, the noises characteristic is improved about 2.8 dB on an average with the inset of a dual-pass Mach-Zender interferometer and shifting the station of output coupler However, the output power is suppressed about 1.5 dB on an average by the change. Next, the noises characteristic is further improved by about 4.3dB against the conventional ring cavity configuration and the output power is increased by about 1.8 dB by utilizing a special Bragg grating array replacing the F-P filter to compose a linear cavity configuration.. The emitting range with output flatness better than 3dB covers 20nm wavelengths from 1540 to 1560 nm, with line spacing of 0.8nm and average output power of 0.8dBm.The linear cavity multi-wavelength erbium-doped fibre laser with high signal-to noise ratio can be useful in a wavelength division multiplexing transmission system.

In the paper, the supercontinuum generation in the normal dispersion shifted fiber is investigated using the single-pass and double-pass configurations. The spectral bandwidth of supercontinuum is enhanced from the 90nm with single pass configuration to127nm using the double pass configuration. The enhanced broadening mechanism is mainly due to the collision interaction between counter- traveling pulses, as well as the doubled length of fiber.

The purpose of this paper is to use numerical simulations and experiments to investigate the SCG in HNLF and optimize the SCG according to the parameters of fiber and pump pulse. Complex temporal and spectral characteristics of supercontinuum generation are investigated in the zero-dispersion wavelength (ZDW) region of highly nonlinear fibers. The simulations are based on an extended nonlinear Schrödinger equation (NLSE), which is valid even in circumstances where the bandwidth of the SCG is of the same order as the central frequency of the input pulse, and includes higher order nonlinearity, dispersion and intrapulse stimulated Raman scattering. We developed a finite difference scheme incorporating modified 4-th order Runge-Kutta algorithm to solve the equation. We discuss the SCG by varying the parameters of input pulse, such as pulse width, peak power, and center wavelength, to explore the dynamics of SCG in normal and anomalous dispersion regions. An optimal approach for supercontinuum generation is proposed and proved by experiments and simulations. The measured and calculated spectra are compared and exhibit good qualitative agreements. Our works provide a useful approach to design a practical SC source by using the conventional HNLF and readily available low power fiber laser sources.

An erbium-doped fiber laser with high-power and CW uniform multi-wavelength output was reported. More than 20 laser wavelengths were achieved at room temperature by using a frequency periodic filter and frequency shifter. The output spectral becomes flat after optimizing the laser cavity, the pump power and the length of active fiber. Low threshold and high slope efficiency were realized by the introduction of linear cavity.

A 24 cm gain-shifted Tm³⁺-Yb³⁺-codoped tellurite fibre employing novel high concentration doping technique and using 980 nm diode laser single-wavelength pumping is demonstrated with a maximum gain of 6 dB at 1490 nm and a gain range of 1475~1505 nm.

A novel erbium doped fiber (EDF) designed for high power WDM applications is presented. The fiber design and performance versus numerical aperture and cutoff wavelength are described based on an advanced EDFA model. The optical and spectral characteristics of the high power fiber are shown. Experimental measurement results of this fiber and comparison with typical commercially available EDFs are given. Performance results show that the new EDF is ideal for high power EDFA applications. It features high power conversion efficiency at high pump power, especially with 980nm pumping, extremely flat gain shape, very low splice loss to typical pigtail fibers, and negligible macro-bending loss.

An optical amplifier for metro WDM networks, based on a gain-clamped semiconductor optical amplifier is proposed. The amplifier (RAGCSOA) consists of a low gain Raman fiber amplifier and a gain-clamped semiconductor optical amplifier. The RAGCSOA has over 20 dB gain and a noise figure below 3 dB. In addition, the potentially compact amplifier shows negligible transients under dynamic add-drops. Sixteen channels of 10 Gb/s signals were successfully transmitted over five NZDSF spans of 80 km using RAGCSOAs. RAGCSOAs were also used to successfully transmit sixteen channels of 10 Gb/s WDM signals over four 40km spans of SMF with add-drops. No penalty was observed when 15 out of 16 channels were dynamically add/dropped in all the transmission systems. The RAGCSOA can be very compact when a GCSOA chip and a Raman pump LD chip are packaged in a module.

In this paper, characteristics of erbium-ytterbium co-doped phosphate glass waveguide amplifier integrated with multilayer medium thin film filter is designed theoretically, a S-type geometry waveguide structure is used to achieve a long path in a compact chip, and obtained higher gain with lower Er-doped concentration. The multilayer medium thin film filter is utilized to achieve a broader flattening gain bandwidth. The intrinsical gain spectrum is obtained by solving rate and power propagation equations, the effect of transmittance spectrum of thin film filter on flattening gain is discussed. Average gain of about 17dB is obtained between 1535nm and 1565nm with gain difference of below 3dB.

A new method of gain adjustment of multipump Raman fiber amplifier is proposed and numerically demonstrated. The method utilizes the areas under the pump power evolution curves along the gain fiber as a criterion and the Newton-Raphson method is used to find the appropriate power combination of the pumps to realize the desired gain profile. The proposed method has two merits: First, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual scheme of the amplifier, i.e. it can be used in Raman fiber amplifiers with all kinds of pumping schemes including co-, counter-, or bi-directional pumping. Numerical simulation results are also provided to verify the proposed method and demonstrate its effectiveness.

Fusion splicing is a well-known technique to connect a fiber pair and fusion splicers have been commercially available for this process for a long time. An important feature of a fusion splice is the coupling loss that is influenced by - among other things - the mutual spotsizes of the two fibers involved. Hence, similar fibers such as standard single mode fibers can be spliced to nearly zero loss whereas dissimilar fiber pairs may give higher loss. The latter category covers the splice combinations of erbium doped fibers that are often spliced to other fiber types such as the standard single mode fiber. We have investigated how splice loss of dissimilar fibers is influenced by fiber design with emphasis on this combination. Finally we propose a fiber design suitable for optimizing splicing capabilities of erbium doped fibers. With this design it is possible to keep fiber cutoff below 980 nm, which is of importance for practical applications, a requirement that usually conflicts with the demand for good splicing properties. An actual design, has been manufactured and splicing properties for this and the conventional design are compared.

We present a numerical study of the guidance and amplification properties in an Er³⁺-doped honeycomb photonic bandgap fiber with down-doped core. Our analysis is based on a full-vector plane-wave expansion method and Runge-Kutta iterative algorithm. Overlap integrals between mode profiles and Er³⁺-doped region varies from 0.973 to 0.350 in guiding range of the fiber. The highly efficient amplifier can be designed by using this fiber.

A 980/1600 Wavelength Division Multiplexing (WDM) fiber coupler is a critical component of an L-band (1580 nm to 1620 nm wavelength region) Erbium Doped Fiber Amplifier (EDFA), and the application in the L-band requires low optical loss at 980 nm and 1600 nm for the single mode fiber used in making the coupler. Common single mode fiber, designed for use at 980 nm, would usually have a significantly higher optical loss at these wavelengths. Therefore, a new design may be required. In this paper, we describe our work in fiber design to meet the new requirements and discuss relevant issues, especially fiber attenuation and bend loss performance.

Er³⁺-Yb³⁺ co-doped phosphate glass waveguide amplifier at large signal operation are theoretically studied. By solving the rate and optical power propagation equations describing the Er³⁺-Yb³⁺ co-doped system, quantum conversion efficiency(QCE) at large operation are optimized. It is shown that improvement of Er³⁺-concentration and increase of amplifier length can improve QCE, improvement of Yb³⁺-concentration reduces QCE, the rate of 1~2 of Er³⁺-Yb³⁺ co-doped concentration is available.

Highly uniform multiwavelength erbium-doped fiber ring laser with a sinusoidal phase modulator and line intervals of 0.45 nm is demonstrated. The flat and stable output distribution is realized by optimizing modulation voltage and frequency for the sine phase modulator. Simultaneous 30 lasing lines are obtained in power difference less than 2 dB. In addition, the implemented cavity structure can support unidirectional operation even without optical isolators. The power difference between clockwise and counterclockwise direction is higher than 20 dB, almost independent of pumping powers and lasing wavelengths in lasing operation.

Presented in this paper is the design and fabrication of a novel polarization-insensitive optical circulator with multiport. For an optical circulator with n ports, it guides the signal from port 1 into port 2, port 2 into port 3, and so on, till port n into port 1. As a result, the circulator provides further chromatic dispersion compensation and routing function, etc. In this paper, two designs of circulators concerning with odd and even port compact are presented. The port number regarding to each scheme can be arbitrarily designed according to system requirement. Experiments have been conducted to show the performance of our designs on a 3-port and 4-port loop circulators. Key parameters of each scheme are also presented, including the insertion loss (IL), the polarization dependence (PDL), the isolation performance (IS), return loss (RL) and the crosstalk within its working wavelength. Results from the experiments show that the fabricated circulator provides an excellent performance for each set of system parameters. This circulator provides a new possibility for developing compact nonreciprocal devices in the field of optical communications.

This paper illustrates detailed numerical analysis, lab tests, and field trials of MCI's next generation fiber development process from the years 2000 to 2004. The new Medium Dispersion Fiber (MDF) has dispersion of around 7~8 ps/nm/km, which will satisfy MCI and worldwide next generation transmission fiber technical specifications and requirements at 20 Pb/s*km for "short fat" (20 Tb/s x 1000 km) and "long thin" (6.67 Tb/s x 3000 km) future DWDM and ULH network application and deployment.

This paper reports the fabrication and characterization of a new type latching magnetic optical switch. The basic optical switch has two stable states wherein an optical signal from the input port can be routed to either one of the two output ports. The key component of the optical switch is a cantilever made of soft magnetic material with a reflective surface. The optical switch is bi-stable because the cantilever has a tendency to align with the external magnetic field, and the torque to align the cantilever can be di-directional depending on the angle between the cantilever and the magnetic field. Switching between the two stable states is accomplished by momentarily changing the direction and/or the magnitude of the cantilever's magnetization by passing a short current pulse through a planar coil underneath the cantilever. In either of its stable states, the cantilever is held in its position by the combined influence of permanent external magnetic field and other mechanical forces, such as a physical stop or a mechanical torques produced by torsion flexures supporting the cantilever. Large angle deflection and bi-stable latching operations have been demonstrated. Characterization has been performed for optical switching performances. Computer simulation results were compared to the experimental results. The switching speed is 3.2 ms, optical insertion loss is -4 dB, and the energy consumption is 44 mJ for each switching event.

An exact theory for an optical acousto-optic phase modulator with a ZnO coating (OF-AOPM) has been developed, which is made by considering only the radial strain induced by acoustic wave in the resonator. It has been shown that radial strain alone gives strong modulation in the vicinity of a modulating frequency close to half-wave resonance of the Piezoelectric ZnO Coating. At frequency far from this region, not only radial strain but also axial strain may be counted on for optical modulation. In this paper, phase modulation in OFPM for the entire frequency region is presented by considering both axial and radial strains. The theoretical calculation shows good agreement with the experimental results. The frequency response of the OF-AOPM for optical phase modulation has been investigated using this theory. For broadband frequency responses, both radial and axial strains play important roles in optical phase modulation. At low frequencies below the vicinity of the half-wave resonant frequency of ZnO film, the axial strain is dominant. For the other frequency regions, strong phase modulation arises from the strain and the simplified theory presented in the previous paper [1] can be applied. This theoretical model is expected to be useful in device design as well as for many device applications.

Holographic Optical Elements (HOEs) are gaining much importance and finding newer and better applications in areas of optical fiber communication and optical information processing systems. In contrast to conventional HOEs, optical communication and information systems require smaller and efficient elements of desired characteristics and transfer functions. Such Micro Holographic Optical Elements (MHOEs) can either be an HOE, recorded with two narrow beams of laser light or a segment cut from a larger HOE (SHOEs), and recorded in the conventional manner. In this study, micro holographic couplers, having specific focusing and diffraction characteristics were recorded in different holographic recording media such as silver halide and dichromated gelatin. Wavelength response of the elements was tested at 633 nm and 442 nm. Variation in diffraction efficiency/coupling factor, and insertion loss of the elements were studied. The paper reports in detail about the above results and related design considerations.

KTa_1-xNb_xO₃ crystal exhibits an extremely large quadratic electro-optic effect, which is 20 times greater than that of LiNbO₃. This property makes this crystal attractive for optical signal processing applications. We have successfully prepared a 2-inch KTN crystal that exhibits the largest quadratic electro-optic coefficient ever reported. We have also fabricated a buried optical waveguide with a low transmission loss and demonstrated an optical switch with a driving voltage of 2.6 V and a 92 nsec rise time. This paper reviews the crystal growth, material properties, electro-optic effect, waveguide fabrication, and optical switch operation of KTN crystal.

Single mode tapered waveguide (spot-size converter) can transmit the optical field with low loss. The less loss is very important for highly integrating optic devices. For the integrating optic device use the weak waveguide in order to keep the small ellipse field, like 2-3um. But standard single mode fiber has a large diameter like 9-11um, and a round field. If we want to get the effective coupling, the spot-size converter must be used. These kinds of spot-size converter waveguide are designed so that the effective values of the normalized frequency are nearly the same everywhere and the shape of the mode field is basically kept Gauss. Then it can get the low loss coupling between the integrated waveguide and fiber with Gauss field.[1] In this paper, an optimal method was used to find the lateral of the spot-size converter after give both the end size. It must point out that this paper's conclusion is just the theoretical computation conclusion. In general, the BPM method can be used to design the low loss tapered waveguide. In this paper, under the background of FD-BPM method, the neural network' nonlinear property was used to find the optimal low loss boundary of the taper waveguide through the net learning. This paper describes a process of design a waveguide spot-size converter lateral side. After the process, the spot-size converter waveguide can get low radiation loss and coupling in highly effect. And the paper also presents a method for finding the optimal boundary of the SSCs.

The variable optical attenuator (VOA) has played very important roles in wavelength division multiplexed (WDM) systems, it is an essential optical component aimed to continuously adjust the optical power transmitting in optical networks. In this paper, we began to study a new type of variable optical attenuator using polymer liquid crystal material. We hanged the liquid crystal technologies and MEMS technologies together to design variable optical attenuator. This paper describes the methods and process of the preparation of polymer liquid crystal material, presents some experimental results obtained in laboratory.

This paper describes a Michelson all-fiber acceleration seismic geophone with dual-optic routes. Compared with the single-optic route structure, dual-optic routes geophone exhibits wider frequency response range; meanwhile it also constrains the transverse vibration of the mass, incline and bend of the fiber more efficiently. The seismic geophone consists of Michelson interferometer, sensing element and signal processing system. An alternating current phase tracking (PTAC) homodyne scheme has been used to process output signal of the Michelson interferometer. Experimental results matches well with the theoretical prediction; the working frequency band is 5~535Hz; the acceleration sensitivity is 0.9rad/m/s²; and the non-distortion percentage is smaller than 0.7%.

We have proposed and demonstrated that the optical coherence function can be sythesized into desired shapes by manipulating the optical frequency and the phase of the lightwave. Based upon this unique technique, the synthesis of optical coherence function, various distributed photonic sensing and optical information processing applications have been developed. In this paper, the principle of the synthesis of optical coherence function is summarized. A series of functional optical sensing systems, including fiber-optic reflectometries, distributed stress location sensors, multiplexed FBG sensors, are introduced. Fully distributed fiber optic strain sensing systems per Brillouin frequency shift are highlighted, and synthesized dynamic grating based sensor is also presented. Applications in two- or three-dimensional distributed measurements, such as optical tomography of scattering medium, are also reviewed.

The virtually unlimited bandwidth of optical fibers has caused a great increase in data transmission speed over the past decade and, hence, stimulated high-demand multimedia services such as distance learning, video-conferencing and peer to peer applications. For this reason data traffic is exceeding telephony traffic, and this trend is driving the convergence of telecommunications and computer communications. In this scenario Internet Protocol (IP) is becoming the dominant protocol for any traffic, shifting the attention of the network designers from a circuit switching approach to a packet switching approach. A role of paramount importance in packet switching networks is played by the router that must implement the functionalities to set up and maintain the inter-nodal communications. The main functionalities a router must implement are routing, forwarding, switching, synchronization, contention resolution, and buffering. Nowadays, opto-electronic conversion is still required at each network node to process the incoming signal before routing that to the right output port. However, when the single channel bit rate increases beyond electronic speed limit, Optical Time Division Multiplexing (OTDM) becomes a forced choice, and all-optical processing must be performed to extract the information from the incoming packet. In this paper enabling techniques for ultra-fast all-optical network will be addressed. First a 160 Gbit/s complete transmission system will be considered. As enabling technique, an overview for all-optical logics will be discussed and experimental results will be presented using a particular reconfigurable NOLM based on Self-Phase-Modulation (SPM) or Cross-Phase-Modulation (XPM). Finally, a rough experiment on label extraction, all-optical switching and packet forwarding is shown.

A theoretical and experiment analysis of two-step ion-exchanged glass optical power splitter is reported. In order to facilitate quantitative analysis, we propose the rational model of physics for a 1×4 S-branch power splitter in glass. These surface half-round channel waveguides are fabricated by first performing a thermal exchange in Tl₂SO₄ through a mask patterned on the glass surface. The channel waveguides are then buried by second thermal Na+ exchange, unmasked ion exchange, in melt NaNO₃. A buried optical power splitter of low insertion loss and uniformity loss has been realized.

A novel fast tunable electro-optic (EO) polymer waveguide grating is proposed and designed. Its resonant wavelength can be linearly tuned by first-order EO effect with a high sensitivity of 6.1pm/V. Its spectrum characteristics depend strongly on many grating parameters, such as refractive index modulation, modulation function, grating period and period number. Material selection, fabrication technology, EO tuning ability and polarization dependence of EO polymer waveguide grating are also discussed. This waveguide grating not only overcomes the shortages of optic fiber gratings, such as slow wavelength tuning ability, and large-scale integration inconveniency, but has many advantages, such as high resonant wavelength tune sensitivity, same fabrication technology as semiconductor, and polarization independence.

Three different structures of planar waveguide interleavers are discussed in detail with comparison: Mach-Zehnder interferometer, Mach-Zehnder interferometer with a ring resonator, and AWG(arrayed waveguide grating) . Further, we demonstrated a 1:4 AWG-based interleaver with 50GHz channel spacing, flatten passband and low channel crosstalk can be achieved by proper design.

An effective way of constructing an AWG with a wide passband is to use a configuration with a parabolic horn as the input waveguide to a slab waveguide. This configuration provides good passband control ability and fabrication stability. However, the parabolic waveguide horn may induce chromatic dispersion (CD) in AWGs. In this paper, first the theory of broadening passband and origins of CD in AWG were analyzed, then the influences of the configuration parameters of parabolic horn to broaden spectrum of AWG were discussed through a beam propagation method (BPM) and numerical calculation. A good flat-top AWG was obtained by choosing rationally three parameters: exit width W, broadening coefficient α and length of multimode waveguide. And low CD was achieved through adjusting the length of multimode waveguide slightly.

This paper reviews recent progress and presents new designs and experimental results on single polarization (SP) fibers. The design concept for achieving SP propagation and approaches using either stress induced birefringence or hole-assisted geometrical birefringence for realizing single polarization fibers are described. Designs of hole-assisted SP fibers with either dual holes or a central hole are discussed in details. Effects of fiber parameters on SP fiber performance such as bandwidth, cutoff wavelength, mode field area are analyzed. Results on fabrication and characterization of dual-hole-assisted SP fibers are presented. SP operating windows centered at wavelength from 900 to 1600 mm with bandwidths from 18 to 55 nm are realized. Applications of SP fibers for single mode fiber lasers to produce linear polarized laser output are demonstrated with extinction ratio of 17-20 dB.

We propose an enhanced theory that can be commonly applied to fiber reliability evaluations under various stress and failure probability levels, under prolonged stress and in stressed fiber distribution conditions. In the theory, the inert strength distribution of fibers is composed of two types of Weibull distributions with different slope parameters. We included proof-test conditions that adhere to Mitsunaga's theory in the calculations. New parameters that express the high-strength distribution can be obtained from the tensile strength data using a theoretical equation. We analyzed the static fatigue characteristics under uniform bending and two-point bending using this theory. The experimental results agreed well with the calculated results for bent fibers. We believe that the theory will play a vital role in the design of optical fiber cords for sharp-bending uses and in the minimization of various optical packages.

In order to investigate the effects of processing parameters in thermal poling, an in situ testing system used for thermal poling optical fibers was constructed with an all polarization maintaining fiber Mach-Zehnder interferometer. The in situ monitoring of the thermal poling process was done to investigate the effects of processing parameters in thermal poling, such as poling ambient temperature, applied poling voltage and poling duration, on the linear electrooptic coefficient induced in the optical fiber. Experiments of the in situ monitoring showed that the stronger the electric field in the fiber core was, the higher linear electrooptic coefficient induced in the fiber core could be. But the electrical breakdown of dielectric medium between electrodes limits the maximum applied poling voltage. Considering the limit of electrical breakdown of the structure of side polished fiber, the voltage of 3000 volts could be applied during thermal poling. When a voltage of 3000 volts applied on the device with side polished fiber, the optimum poling duration is about 16 minutes and the optimum ambient temperature for thermal poling is about 190°C. The in situ testing system could also be used for the in situ monitoring of manufacture of thermal poling optical fiber so as to improve the efficiency of manufacture.

The Raman spectra intensity can be enhanced in liquid core optical fiber (LCOF) .The total Raman power emitted by the LCOF is a function of the following parameters: LCOF length, LCOF loss coefficients at the laser and Raman wavelengths, the concentration of analyte and input laser power. The attenuation of the light in CS₂ is small in the range from 1400nm to1700nm. We dissolved liquid CCL₄ into CS₂ and got different solutions of different concentrations. When the analyte concentration was changed, the analyte molecules and the numerical aperture of the LCOF were also changed, so there is an optimum concentration at which the maximum Raman spectrum can be obtained. Our experiment result is in good agreement with the calculated results. Backward Raman scattering is superior to forward Raman scattering in our experiment. Raman intensity first increases to a maximum with fiber length, then decrease because the fiber attenuation becomes dominant. Therefore, there exists the optimum fiber length. In our experiment, we find that higher Raman intensity can be obtained when the fiber length is 2m. The Raman intensity becomes powerful when the input pump power becomes larger. Raman linewidth becomes narrow when the concentration decreased. Our experiment also approves it.

We compare the noise characteristics of optical pulses generated from an actively mode-locked (AML) erbium-doped fiber laser (EDFL) with a semiconductor optical amplifier and an injection-locked EDFL with a gain-switched Fabry-Perot laser diode (FPLD). The mode-locked EDFL pulse exhibits a phase noise of -110.1 dBc/Hz (at 1 MHz offset frequencies from the carrier), the timing jitter of 1.16 ps, and a supermode noise suppression ratio of 47.5 dB. The injection-locked EDFL pulse exhibits a phase noise of -121.1 dBc/Hz (at 1 MHz offset frequencies from the carrier), a timing jitter of 0.31 ps, and a supermode noise suppression ratio of 51 dB. It is demonstrated that the injection-locked EDFL with a gain-switched FPLD has lower noise characteristics than the AML-EDFL.

We have experimentally investigated the soliton interaction in a passively mode-locked fiber soliton ring laser and revealed the existence of three types of strong soliton interaction: a global type of soliton interaction caused by the existence of unstable CW components; a long-range type of soliton interaction mediated through the radiative dispersive waves; and the direct soliton interaction. Based on the soliton interactions we found that the appearance of the various soliton operation modes observed in the passively mode locked fiber soliton lasers could be well explained. Numerical simulations have also confirmed the existence of these soliton interactions and their consequences.

A new nonlinear optical loop mirror (NOLM) constructed from a dispersion decreasing fiber (DDF) and a general fiber is proposed. Numerical simulation shows that a ultra-short pulse with pedestal suppression and small chirp generated by the new optical loop mirror can steadily evolutes over a very long fiber. When the pulse takes the best quality factor, the bigger compression factor is gained and the shorter optical fiber is used comparing to the use of the nonlinear optical loop mirror constructed from dispersion decreasing fiber (DDF-NOLM).

A high efficiency Q-switched and self-mode-locked Er³⁺/Yb³⁺ co-doped fiber ring laser with a Mach-Zehnder interferometer (MZI) is proposed. The fiber laser with threshold of 126.84 mw and linewidth of 0.06nm has been demonstrated. The average power of 62.6mW, the peak power of 1231.8mW of the Q-switched giant pulses with the pulse duration of 2.6μs can be achieved. It is found that in order to generate Q-switched giant pulses, different repetition frequency must be selected as pumping power is changed. This phenomenon is observed for the first time to our knowledge. In the experiment, it is also found that stable passive Q-switch pulses can be observed, which waveform is not the same with the different pump power, although the arms lengths of the interferometer is not changed. When the absorbed pumped power is increased to 591.8mW, a self-mode-locking pulse can be formed and it is given a detailed theoretically illustration in this paper.

Theory and experimental results on the self-starting passive mode-locked Yb fiber ring laser generating short pulse are reported. The relations between the laser cavity parameters and mode-locked pulse characters are discussed. 980nm LD pumped laser is used as the pump source and high concentration Yb³⁺-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained, with center wavelength of 1046nm, 3dB bandwidth of 6.01nm and 20dB bandwidth of 16nm. The mode-locked threshold power is 150mW and output power is 26mW with 50MHz repetition rate.

A novel L-band multi-wavelength erbium-doped fibre ring laser was proposed and studied by numerical method. The numerical model was developed based on a C-band EDFA and the propagation and rate equations of homogeneous broaden in two levels medium. In this L-band model, the excited state absorption was included during computing. The flat multi-wavelength laser in L-band was achieved by lengthening the erbium-doped fibre, and utilizing detrimental backward amplified spontaneous emission as a secondary pump power. The laser emitting spectral region was shifted, to prevent the mode competing at room temperature. This kind of laser can be useful in a wavelength division multiplexing transmission (WDM) system.

Fiber optical parametric amplifiers (OPAs) are based on the third-order nonlinear susceptibility of glass fibers. If two strong pumps and a weak signal are fed into a fiber, an idler is generated. Signal and idler can grow together if pump power is high enough, and phase matching occurs. Gain in excess of 60 dB has been obtained. Fiber OPAs can exhibit a large variety of gain spectra: a gain bandwidth of 400 nm has been demonstrated; tunable narrowband gain regions can also be generated. The idler can be used for wavelength conversion, and spectral inversion. Fiber OPAs have a minimum NF of 3 dB, like EDFAs; this also holds when they are used as wavelength converters. By modulating the pump one can modulate the signal and/or idler at the output, and implement fast signal processing functions, including: demultiplexing of TDM signals; retiming and regeneration. The development of practical devices will require progress in the design and fabrication of fibers with high nonlinearity, dispersion properties suitable for improving phase matching and good longitudinal uniformity. Novel fibers, such as holey fibers, are promising in this respect.

A novel superstructure fiber Bragg grating (SFBG) based comb gain equalizer for fiber optical parametric amplifier (OPA) is proposed. This gain equalizer is characterized by its comb reflectivity spectrum. It can have two functions at least, one is flattening the gain in multi ITU-T regulated channels, the other is it can be used as multi-channel isolation filters taking full advantage of its comb reflectivity spectrum. In addition it can be dispersionless or have dispersion compensation function. A one-bump fiber OPA, 30dB bandwidth >15nm, is designed with one of its peak gains (41dB) located at the center of work wavelengths in a 16-channel 100GHz spaced WDM optical transmission system according to corresponding Chinese criterion (1548.51nm~ 1560.61nm). The object reflectivity spectra of gain equalizer are calculated in two parts independently. Inner channel part for every channel is designed according to the gain spectrum of fiber OPA. As a comb filter, its inter-channel part reflectivities are the smaller the better. But inter-channel part reflectivities can not be simply zeroed, for which would result in the rising and descending edges of reflectivity spectrum being too sharp to be performed by any filter. To split the difference, inter-channel part reflectivities are calculated with Gaussian hypergeometric function (-0.5dB bandwidth 0.1nm, -45dB bandwidth 0.3nm) to obtain slower rising and descending edges than the simply zeroed case, which is very necessary and important to be sure the object reflectivity spectrum not only has sharp enough edges to take the shape of comb but also is physically realizable. Adopting channel-by-channel windowing method to apodize the object reflectivity spectrum, a superstructure fiber Bragg grating is designed with lay-peeling inverse scattering technique. At last, according to the coupling coefficient calculated, reflection spectrum and group time delay are analyzed based on the method of transformation matrix. Calculation results show that this SFBG satisfies all requirements. Further calculation results show that, using this SFBG as comb gain equalizer, the gain of fiber OPA is flattened in every channel to within ±0.4dB among 16 channels, with channel isolation high up to -35dB. It needs to point out that this method can also be used to design gain equalizer for other optical amplifiers.

In this paper, a novel semi-analytical algorithm for calculating backward-pumped Raman amplifier is proposed. The algorithm does not need iteration and can greatly save the computational time. Simulation results for Raman amplifiers with 25 km and 50 km fibers show that the accuracy of the method is quite satisfying in comparison with the shooting algorithm and the deviation is within 0.02 dB.

An adaptive step-size method for the coupled equations of multi-pumped broadband Raman amplifiers is proposed based on Runge-Kutta-Fehlberg methods. This algorithm adjusts the step-size appropriately according to the presupposed precision and the local truncation error of each step. Simulation results indicate that our adaptive step-size method improves the accuracy and the simulating speed efficiently compared with other traditional algorithms and suits the numerical simulation for fiber Raman amplifier.

Multi-Wavelength Fiber Raman Amplifier (MW-FRA) has become an essential component in DWDM system due to its broad bandwidth, flexibility and excellent performance. This paper is first dedicated to an accurate modeling of the MW-FRA for a propagation equation, which includes fiber loss, Stimulated Raman Scattering (SRS), Rayleigh backscattering, spontaneous emission noise and thermal noise. Then based on the reasonably simplified model it focuses on a numerical calculation with initial pump wavelength and power for the acquisition of on-off gain and flatness of signals, which are taken as feedback information to adjust the corresponding pumps. An inheritance algorithm is applied in the process of such iteration, which moves on until the target gain and flatness are achieved. According to the Raman gain spectrum characteristics, we can improve the algorithm to speed up the calculation and to make it more practically applicable. The design idea here is implemented by using C language. With input target gain and flatness, initial value of signals and pumps, the program can output the optimized results of pump wavelength and power. Besides, the simulation results from employing VPI are demonstrated, which proves the algorithm is effective.

Through analyzing the nonlinear phase feature of the three-mirror G-T cavity, a novel unequal passband interleaver using a Michelson interferometer in which one mirror is replaced by an equally-spaced three-mirror G-T cavity is design by imitation. The device split an input beam with channel spacing of 50GHZ into two beams with channel spacing of 100GHZ. At -1dB, the odd channel and the even channel have unequal passband for transmission speed of 40Gb/s and 10Gb/s, respectively. The isolation is more than 30dB. All the possible reflection coefficients of the three-mirror G-T cavity with which the interleavers meet the above need of the DWDM system are searched out by optimization of the computer.

OADM is a key component in DWDM due to many merits such as good performance in low loss, low price, simple and flexible integration structure. One of the critical issues focused on the research of OADM is to design multiplexer/demultiplexer hoping to reduce the insertion loss and improve the propagation efficiency of the total device. In this paper, we present the design of 4×1 and 8×1 multiplexers based on SOI materials. The devices show several advantages including low insertion loss, phase-insensitiveness, polarization independence and compact size. The devices' performances are simulated under different conditions and all exhibit satisfying results. It's ideal to equip them in compact optical system.

We report a new method for writing the dual-wavelength Bragg fiber gratings. The method is based on the photosensitivity of Ge-doped optical fibers. Our double-exposure technique enables a good control over the grating's reflectivity and the separation of the two Bragg wavelengths. A grating with two equal transmission peak of 20.5dB is obtained by using this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, an optical add-drop multiplexer (OADM) that allows dropping two fixed wavelength channels is proposed.

A bidirectionally pumped spectrum pre-sliced multi-wavelength fiber source is presented in the paper. Two 980nm laser diodes (LDs) are engaged to provide the pump power. An optimized double pass Mach-Zehnder interferometer with extinction ratio larger than 41dB is utilized as the comb filter. The extinction ratio of the fiber source is larger than 24.5dB in the whole C band, and almost reaches 29dB at 1530nm. Integral power of each channel is 0.58mW at 1550nm under 112.3mW total pump power. Channel spacing and bandwidth are 0.81nm and 0.30nm, respectively.

We constructed a reflection L-band erbium-doped fiber amplifier based on fiber loop mirror, which reflects the backward ASE to the EDF as a secondary pumping source. A gain of 30 dB increased 6 dB compared to the forward end-pumped EDFA has been achieved in the wavelength region from 1570 to 1603 nm. In order to improve the gain and NF further, we constructed a novel configuration for reflection L-band erbium-doped fiber amplifier via inserting a 980 nm LD in the input part. Adjusting the ratio of power of the two LDs, the gain and NF are greatly improved in different degree in the region from 1565 to 1615 nm. Compared to the configuration pumped by only 1480 nm LD with given power, the gain enhanced 1.5-9.9 dB and the NF decreases 1.3-9.4 dB.

A TDM FBG sensor system with CCD detection was presented for a serial FBG array. Four FBGs were multiplexed and a device based on NOLM technique was adopted for the separation of the pulses. Computer simulation shows that the system provides high sensitivity which is the main factor for a practical FBG sensor.

In this paper, the reflective and transmissive characteristics of the high-birefringence fiber loop mirror (HiBi-FLM), which is composed of arbitrary lengths and sections of high-birefringence fiber (HBF) were theoretically and experimentally investigated in detail. Simple explicit equations to respectively describe the reflectivity and transmissivity of the HiBi-FLM with one-section, two-section and three-section HBF were obtained, while the process of calculating the reflectivity and transmissivity of HiBi-FLM with n-section HBF was given. The experimental results verified the theoretic model.

A measuring principle and method about rotatory element ε' in the tensor dielectric coefficient of a rotatory optical fiber is put forward in this paper. First the rotatory angle ψ and rotatory coefficient V is measured which make us understand the rotatory characteristic of the optic fiber. On the basis of that the ε'; is measured by the one of measurement of ψ, I or Hb. The measuring of ε' is very important for analysis and calculation the rotatory fiber by electromagnetic theory.

A simple technique for the generation of bright and dark pulses train from continuous-wave (cw) light is presented. The principle is based on direct external nonlinear modulation and a simple theoretical explanation was given. Conversion between bright and dark pulses can be obtained by simple adjustment of the bias level and modulation depth of the modulator. The repetition rate of the pulses is twice the driven signal frequency.

A multi-wavelength erbium-doped fiber laser using a Moire Bragg grating in polarization-maintaining fiber is proposed. Two Moire Bragg gratings in Polarization-maintaining fiber are respectively fabricated successfully through stretching and double, triplicate exposure method. The two gratings fabricated respectively have four and six reflection peaks and are respectively incorporated in the linear erbium-doped fiber laser cavities to perform mode-selection and output coupler functions. The proposed laser can be made to operate in simultaneous four-wavelength or six-wavelength operations when the EDF is cooled in liquid nitrogen (77K).

In this paper, we present a noise figure improved double-pass L-band EDFA based on HiBi fiber loop mirror as the ASE suppressor. By utilizing a HiBi fiber loop mirror as the wavelength-dependent reflector, the ASE light has been weakened to a large extend, which increases the inversion ion population at the input end of erbium-doped fiber. Therefore, the noise figure of this double-pass EDFA has been much improved. Compared with that of the conventional double-pass structure based on 3dB fiber loop mirror, the NF of our novel configuration is reduced by 2.06~5.33dB for the ten sampled signal wavelength (1580.84nm~1588.48nm).

The basic theory of rotatory optical fiber was discussed. The electromagnetic field components, basic parameters of the fiber were evaluated as the functions of the argument ε' which is the rotatory element in the tensor dielectric coefficient matrix ε of the fiber .The calculating results were shown by the curves. In addition, a new expression about the relation between ε' and applied magnetic field Hb was demonstrated, by that the tensor dielectric coefficient of the rotatory optical fiber can be easily evaluated.

The absorption efficiency for circular or offset double-clad optical fibers is investigated with modal analysis method. First, calculate the number of all the propagating modes approximately using WKB method and derive the analytic formulas for calculating the number of propagating modes that can't be absorbed by active core. Then the absorption efficiency can be obtained analytically. Comparison of modal method with the ray optics method is made and the condition of using both methods is also discussed.

In this paper, an all-fiber electric voltage sensor based on high birefringence fiber loop mirror is presented. This voltage sensor is composed of a 3dB coupler and ~8m high birefringence (HiBi) fiber, part of which is affixed to a piezoelectric translator (PZT). When the voltage applied on the PZT changes, the transmission spectrum of this HiBi fiber loop mirror will shift accordingly. As the direct current voltage increases to 75.2V, the phase shift of this HiBi fiber loop mirror is nearly π rad and the transmission peak changes by about half of a period. This voltage sensor has a sensitivity of 0.004nm/V and its linearity reaches 0.99878. Moreover, we have theoretically studied transmission spectrum shift of this HiBi fiber loop mirror when the length and refractive index difference of HiBi fiber are altered.

The absorption efficiency of graded-index double-clad fiber lasers or amplifiers is investigated. As ray optics method is no longer valid for graded-index case, the mode analysis method is used in this paper. Calculated results show that absorption efficiency for a graded-index is higher than that for a step-index in symmetric case. In offset core case, the graded-index can achieve the same absorption efficiency with much smaller offset distance. The absorption efficiency for different graded-index profiles of the inner cladding is also calculated and compared.

Full characterization of the sensitivity of the LPFG is a precursor to practical device design, and knowledge of the sensitivity of the Long-period fiber gratings to the parameters of its physical environment processed is clearly important. We present a theoretical and experimental investigation into the sensitivity of long-period fiber gratings as a function of processed parameters by high-frequency CO₂ laser pulses.

The measurement of magneto-optical effects in the fiber core absorption is powerful tool in a number of applications. The polarimetry rotatory angle measurement play a key role in these applications, especially in the case with a tiny rotatory angle. With Faraday magneto-optical modulator of Tb₃Ga₅O₁₂ and the polarizer controlled by step-motor, the accurate measurement is improved of tiny rotation angle of the linearly polarized light. The development is reported here.

The optical properties of near elliptical core polarization maintaining photonic crystal fiber are analyzed by using a full vector model. We classify guided modes in the near elliptical core photonic crystal fibers (PCFs) according to the minimum waveguide sectors and its appropriate boundary conditions. Because the field patterns of the near elliptical core PCF is similar to that of rectangular waveguide, the guided modes are labeled in this PCF in the same way as in rectangular waveguide. The numerical results exhibit that the modal birefringence of elliptical core PCF is at least one order of magnitude higher than the conventional elliptical polarization-maintaining fibers (PMF). Zero walkoff point occur at the longer wavelength than that of convention elliptical PMF. This can restrain the first order polarization mode dispersion. This fiber has a number of potential applications in polarization control and management.

This paper presented a silica-based 1×8 optical power splitter at 0.85μm designed with Multi Mode Interference (MMI). The waveguide material is Si-based SiO₂ doped with Ge and deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition) method. The refractive index of glass substrate is 1.458, and the index difference is 0.75%. The input and output waveguides are optimized considering the characteristics of VCSEL (Vertical Cavity Surface Emitting Lasers). The core pitch on this chip is chosen as 250μm to take the fiber connections into account, and the typical cladding diameter of optical fibers as 125µm. The critical parameters in the fabrication of the MMI power splitter are the multimode section width and length. In general the key performance specifications of the optical power splitter are insertion loss and uniformity. We use a Finite Difference Beam Propagation Method (FDBPM) to simulate accurately the evolution of the fundamental mode power of the input guide incoming to the device, and analyze the relationships of various parameters in detail. The bend output waveguides are sin-bend styles. Compared with the commercial optical power splitter, the simulation results accord with the requirement of our design, containing compact size, low loss, stable splitting ratio, low crosstalk, large optical bandwidth, and good fabrication tolerances. The insertion loss and the uniformity of pilot study are 9.07dB and 0.02dB respectively.

A new method for side-pumping double-cladding fiber was researched. A quartz column of 3mm length was cut away from D-shape double-cladding fiber which has a transverse sectional dimension of 350μm×400μm. Then the column-fiber coupler was fabricated by gluing the column onto the side of inner cladding . The pumping light was coupled into the inner cladding from the end of the D-shape quartz column. When the output power was 1.3W from the forward end of the coupler, the optimum efficiency is 85%. This method can be suitable for pumping the fiber laser and amplifier of several watts output power.