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.