A FP filter with high reflection loss is useful in WDM network. Two methods of this kind of filter are proposed in this paper. The property of these filters is studied. It is proved that these two structures are practical in a wide period of frequency. These new kinds of filters can be used to form a non-isolator WDM network.

This paper points out that, in a dynamic optical cross-connect (OXC) of the WDM all optical networks, there exists a kind of coherent crosstalk, the same-source crosstalk. This kind of crosstalk, though originated from the same source but passing through the different light paths, may interference with the signal at the output and impose power penalty on the system. The formulas and their deduction are also given, as well as some examples applying this formulas are presented. The analysis shows that the impact of the same-source crosstalk can cause more severe system degradation than other kinds of same-wavelength crosstalk do. Consequently, it will requires more stringent optical isolation performance of the WDM device as long as conceiving the same-source crosstalk. In this paper, we also proposed a new modification of the OXC structure, in which optical path differences of each wavelength channel are introduced by adding appropriate length of optical fiber. The simulation results show that this new structure can distinctively reduce the impact of the same-source crosstalk, and the crosstalk requirement on optical network elements may be significantly relaxed. Furthermore, the additional hardware cost is very low.

In this paper, we report the successful demonstration of 10 GHz actively mode-locked fiber ring laser for the first time in China. Pulses train as short as 9 ps has been obtained from this laser. The laser can operate at a wide wavelength range, from 1529 nm to 1564 nm. The mean output power is about 2.1 mW at the wavelength of 1545 nm. Nonlinear polarization rotation was utilized to achieve intra-cavity compression.

The spectral characteristics of gain-clamped EDFAs including pump- and laser-controlled was investigated theoretically and experimentally. It is found that if the average population inversion can still be managed, the gain profiles should be also clamped.

An all fiber Q-switched laser with Mach-Zehnder Interferometer configuration has been reported. A fiber Bragg grating is used to achieve frequency-choice and tuning. The laser can generate stable optical pulse at center wavelength 1561nm, peak power 2.6w, pulse width 4.2?s at repetition rate 760Hz, pumped by a laser diode 980nm. Self-mode locking in the Q- switched all fiber laser has been demonstrated. If changing period of fiber grating through adjusting stress or temperature, we can obtain continuous wavelength tunable output optical pulse and the tunable range is about 5nm.

We fabricated a bandpass filter based on Moire Bragg grating in fiber with a uniform phase mask. We employed a stretch and two-exposure technique, in which the fiber was exposed to UV light from a KrF excimer through a phase mask and then the fiber is stretched and given another exposure at the same region. Due to the stretch, the periods of these two grating are slightly different, and there is a transmission between two reflection peaks at the Bragg wavelength of these two gratings. Applying different stretch can control the bandpass width of the filter. We measured the stretch characterization of a uniform Bragg grating and found the Bragg wavelength of the grating shifts linearly with the stretched length. We theoretically analyzed the grating structure and its reflection spectrum. The filter’s characteristics can be optimized by choosing appropriate parameters. We will give a theoretical discussion concerning which parameters and how they affect the filter's operation.

In recent years, growing attention is being focused on wavelength disvision multiplexing optical communication system as a promising means of mass-scale communication. To realize these systems, wideband & temperature-stabilized optical isolators are essential, which in turn require Faraday rotators capable of ensuring a Faraday rotation stable against wavelength and temperature variation. A new wideband & temperature-stabilized optical isolator for 1.5 5 ?m wavelength has been developed using Bi-substituted holmium-ytterbium iron garnet (HoYbBilG) single crystal as a Faraday rotator. The optical isolator features 0.34?m bandwidth, less 0.6 dB insertion loss and over 37 dB backward loss at a wavelength of 1.55?m throughout the temperature range from -10 to 60°C. The Faraday rotation (FR) and optical absorption loss of HoYbBilG have been investigated in the near-infrared wavelength region (?=0.9—1.7?m). The specific Faraday rotation of Ho0.85Yb1.02Bi1.13Fe5O12 is about -767deg/cm at ?=1.55?m. The Faraday rotation wavelength and temperature characteristics of HoYbBilG crystals are also discussed. These results indicate that the Bi-substituted holmium-ytterbium iron garnet single crystals realize a high Faraday rotation stability against temperature and wavelength in the near infrared region

The cascade EDFAs have to be used if the distance between nodes is extremely long in WDM network. However, the gain spectrum of normal EDFA is not flat. This will become much serious as the number of cascade EDFAs is huge. The gain spectrum is studied both theoretically and experimentally in this paper. A special designed FP filter is used to compensate the gain difference after cascade EDFAs used.

The polarization characteristics of a twisted DBR fiber laser are investigated. Analytic formulae for the polarization-mode beat frequency and polarization direction are derived.

In this paper, a new type of re-configurable all optical add/drop multiplexer (OADM) with dynamic gain control function is presented. The channel spacing of the input four-wavelength WDM signal is 3.2nm. The function of adding and dropping any wavelength component of the signal is demonstrated. The total loss is less than ldB (The gain of each SOA is set to about 6dB). Under the control of the gain management unit (GMU), the difference of each channel is less than 0.3dB. Due to the transparency of the OADM, it can add/drop different kinds (such as different format or bit rate) of optical signal. In this paper, we also presented the experimental setup and discussed its results. The highest test bit rate of the WDM signal is 2.5Gbit/s. Its applications in the WDM all optical networks are also discussed.

The power penalty of semiconductor laser diode in a loop mirror (SLALOM) as OTDM optical demultiplexer is numerically assessed in this paper. The calculation shows that the degradation of SLALOM performance is greatly related to amplified spontaneous emission (ASE) of SLA and pattern effect due to SLA's slow recovery time. The operating condition of SLA is discussed to improve the demultiplexer’s performance.

In this paper we present the distance scale calibration of optical fiber Optical Time Domain Reflectometers (OTDR) using the optical time-delay recirculating line approach. Particularly we demonstrate the optical modulation - phase-shift technique to measure the length of the standard fiber which formed the loop of the delay line. Two stages of modulations of 10 KHz and 1 MHz were used to achieve, step-by-step, the final optical length uncertainty of less than 0.02m+1.20 X 10-6. The length measurement results were self-checked and they are well within the quoted uncertainty. With the calibrated delay recirculating-line as a transfer standard the distance scale of the OTDRs is verified to the uncertainty of about 2 x 10-5, depending on the OTDRs’ performance.

A novel scheme of OADM(Optical Add/Drop Multiplexer) is proposed. It has the property of arbitrary add/drop channel compositions ( up to 4 wavelengths). In order to supress more of the homodyne crosstalk, we proposed a novel scheme of utilizing OLM(Optical Loop Mirror) so that we can utilizes the demultiplexer back-and-forth, thus utilizes it both as a demultiplexer and a multiplexer.The results show that we get a 5dB improve on the crosstalk depression, that means a 3 times larger network scale than normal scheme of demultiplexer+switch array+coupler. We found that the reflection on the input port of demultiplexer is the main cause of homodyne crosstalk.

The integrated acoustically-tunable optical filter (IAOTF) is rapidly gaining importance in the field of WDM networks because it has the combined features of narrow bandpass , rapid switching time and broad tuning range . The low loss surface acoustic wave (SAW) transducer and the weigthed acoustic waveguide is studied using coupled-mode theory . It is proved that the theory is effective in the analysis and design of acousto-optic devices .

In this paper, wavelength trimming technique which uses a lens to diverge or converge incident light on the phase mask during the fabrication of fiber Bragg gratings is theoretically analyzed. A more accurate formula for the wavelength shift is obtained and has been verified experimentally.

Shift of Bragg wavelength of UV written fiber gratings due to changes in temperature of the host B/Ge co-doped fiber is studied experimentally in this paper. and thc experimental results are very well fitted by linear functions. The results are coincidence with the theoretical analysis. Farther more, it is discovered that Bragg wavelength of the fiber grating is pcrmanentl shifted to the shorter side of its original position after annealing at relatively higher temperature. and this result is well explained by the color-center model for optical fiber photosensitivity.

Using a cantilever beam tuning device to chirp a uniform fiber Bragg grating(FBG) into a chirped one is carried out in this paper. The device developed in our laboratory can adjust the chirp constant and the center wavelength of a chirped FBG at the same time. The chirped FBG obtained in this way has been used for standard single mode nondispersion shifted fiber(NDSF) dispersion compensation in optical communication system. The principle and experimental results about chirping and dispersion compensation are presented.

Using the high frequency saturation filter effect and dynamic recovery time, the dependence of the frequency chirp and intersymbol interference ( ISI ) of a wavelength converter based on cross-phase modulation in Mach-Zehnder wavelength converter is analyzed. While the extinction ratio is kept the same for diferent probe power, for out phase converting, the poorer performance of the converted signal is due to a longer gain recovery time and the larger intersymbol interference. But for in phase converting, the high probe or fast carrier recovery time is not certain better than that of low probe power.

This paper presents a novel optical circulator configuration which only employs Faraday rotators to complete light polarization plane’s rotation. By using Jones matrices, the insertion loss and isolation are evaluated. The results show that the isolation is obviously increasing with an increase of the rotation errors of the rotators. A 3-port circulator has been fabricated and achieved an insertion loss lower than 0.8dB and an isolation over 45dB.

An in-line detecting method for fiber optic polarization with a fiber Bragg grating was proposed in this paper. The information on the state of polarization of light in the grating was carried on the radiation light from the grating. Their relationship was demonstrated in an experiment. According to this relationship the state of polarization of light in single mode fibers can be measured in line.

The underwater laser communication system is an ideal but difficult programme. The influences of the water depth and channel characteristics on the received signals of underwater laser communication are studied in the paper, it is the reason that causes the degression of communication quality. In the last a programme of adaptive gain control of PMT is presented, and the composed principle frame and the test results are given.

In the paper, an OADM based on fiber gratings and circulators is demonstrated. In order to reduce the interferometric crosstalk severely degrading the system performance in the common structure, a novel structure of cascaded gratings is proposed, which can reduce the power penalty induced by the interferometric crosstalk to the level of noninterferometric crosstalk without the need of raising the peak reflectivity of the fiber gratings. Optical spectra of the related ports in the two structures are measured, which show a 3dB reduction of the crosstalk induced by the dropped signal and complete suppression of the crosstalk induced by the added signal in the novel structure. The temperature compensation technique is used, which can reduce the temperature sensitivity of the fiber gratings to 0.1 lnm/100°C in the range of working ambient temperature. With the fiber gratings annealed for 4 hours in 120°C, the long-term stability of the device is greatly improved.

A concept of Post-fiber-transmission Intensity Noise or Interference Intensity Noise (IIN) is proposed and a formula estimate of maximum Relative Intensity Noise (RIN) for a CATV system induced by laser phase noise and multiple-path- interference (MPI) from fibre-connector reflections has been given out through theoretical analysis and experiment measurement. It is turned out that maximum RIN increases with total number of unqualified connectors and their light reflection coefficients, but decreases with RF frequency increase. For a fixed-length fibre jumper ended with two unqualified connectors, there exists a worst RIN dependent on laser linewidth and RF frequency, also exists another worst RIN dependent on RF frequency and fibre length for a given laser linewidth. It is concluded, only from the point view of depressing RIN induced by connector reflections, that lasers having linewidth within 30-300 MHz had better not be used. Furthermore if no connectors with slant connective end-surface can be got at hand, very limited total number, less than about 4 for example, of fibre connectors with flat connective end-surface can be unquestionably used.

Principle of biconically fused fiber polarization beainsplitters (FPBS) has been introduced in this paper, and a new method for fabricating FPBS has been presented. Compared with the conventional methods in which the first polarization modulation waist point (PMWP) arrived after drawing through many power transfer cycles, the power transfer variation versus the drawn length became fast and the stop point in the drawing process was difficult to control, our method has the advantages of easy fabrication. We use a low temperature heater to fuse and taper the fiber coupler, so the coupling region of the coupler is extremely weakly fused such that the fibers are barely touching. Consequently, the number of power transfer cycles before arriving the first PMWP is greatly reduced, and the first PMWP can be determined easily. In our experiment, the first PMWP in the power transfer curve monitored with unpolarized 1312-nm laser light is taken as the stop point in the coupler drawing process, the experimental results show that, an average extinction ratio of -14.06dB at the throughput port and -14.11dB at the coupled port have been achieved at 1312-nm wavelength. Experimental results show that, this method is simple and convenient.

Numerical analysis of the pulse distortion in dispersion compensation system with linearly chirped fiber gratings(LCFGs) is presented in this paper. The characteristics of distorted pulse including pulse shape, pulse width as well as frequency chirp are given in detail. We find that the subpulses reflected by LCFG are imposed on different frequency chirp which induces their different broadening behaviors.

Two types of four-channel tunable optical add-drop multiplexers(OADM) are demonstrated which are based on fiber Bragg gratings(FBGs),optical circulators and switches. Both of them can dynamically select the drop channel or just bypass all WDM channels. The crosstalk from the adjacent channel is lower than -23dB and the isolation between the drop and add port is higher than 40dB.

This paper proved, for the first time, that in a optical fiber with arbitrary index profile ,which have not any geometrical axes in cross section and changes randomly in longitudinal section, there are a couple of orthogonal axes, called as Principle Polarization Axes(PPA). If a linear polarized light inject from one input PPA, it keeps linear polarization out of an output PPA. Their additional phase shift produced by U matrix are opposite. So, this paper suggests, that we can take the group delay difference of them as PMD (Polarization Mode Dispersion),and the formula is given. In the practical measurement system, linear polarizer are used at both end of a fiber. Because PSP(Principle State of Polarization) is not a linear polarization state, the analyses of this paper maybe even approximate to real results.

We demonstrate an optical time division demultiplexing from 8x2.5Gb/s pseudorandom data stream using a nonlinear optical loop mirror, or nonlinear fiber Sagnac interferometer switch. To ensure good extinction ratio of the demultiplexed signal, some experimental results show it is necessary to adjust carefully the dc bias, modulation current, compression fiber length and switching width and synchronous between the data and control pulses.

Stimulated Brillouin Scattering(SBS) is one of important nonlinear optical effects in optical fiber transmission system, it limits the optical power that can be transmitted through fiber. If input optical power is over SBS threshold, part of power will be changed to backward Stokes wave, this process exacerbates the system transmission characteristic very much. In this paper, SBS effect was systemically studied by experiments. Firstly, backward Stokes wave was observed, we investigated its spectrum and frequency shift to pumping signal wave. Then, the relationship of SBS threshold characteristic with linewidth of light source and modulation formats was discussed, and approved by experiments. The impact on bite error rate characteristic of system due to SBS was also investigated experimentally.

We investigated the possible solutions of the higher order nonlinear Schrödinger (HNLS) equation describing femtosecond optical pulses in an optical fiber system. By using the Hirota direct method, we derived a fundamental solitary wave solution for arbitrary parameters and a N-soliton solution under some conditions. The significance of the soliton solution was discussed.

Reserch on crosstalk of flexible image fiber bundles. The theoretical expression on crosstalk is gotten. This paper describes a new technique to quantitatively measure crosstalk in coherent image fiber bundles using a calibrated optical video system. At the imput end of the fiber bundle, light is coupled into only one angle fiber. At the output end, a large area around the excited fiber is monitored using a video CCD array. Additionally, static MTF measurements to gether with visual inspection was used to correlate the crosstalk to the imaging properties of an optical fiber bundle. Comparison between different samples resulted by the experimental measurements.

We propose a novel kind of switch to construct a class of optical cross-connect (OXC) having both point-to-point and to-multipoint capabilities. The switch is call splitter-and-delivery (SAD) one, which has inherent multicasting capability. It is composed of splitters, 2x1 digital switches and optical gates, and is better implemented in a single silicon board using planar silica waveguide technology. Less than -40 dB crosstalk is achievable by cooperative actions of the digital switches and optical gates. On the basis of the SAD switch, we further propose three OXC architectures having different modular structures. But fundamentally, they are all strictly nonblocking and have multicasting capability. The expanding methods when the number of the fibers and the wavelengths increase a few or by a few times are comparatively demonstrated.

In this article, we analysis the property of mode-converter based on fiber grating and discussed the optimum of parameter of fiber used in the fabrication of mode converter, and the requirement for the tilted angle of stripe of grating.

In this paper, based on the typical example of fiber optical ring resonator which is constructed by connecting single mode fiber depend on fiber optic directional coupler, the resonance depth and finesse are discussed and their equation are derived too. Furthermore, the optimal resonance term are given and illustrated clearly in some curves.

Based on analyzing the shortages of fabricating OTDM devices by means of conventional technology ot fabricating fiber coupler. We propose some novel methods to improve the device performance. Including: more accuracy splitting ratio by using 2X2 coupler, sensor by microbend loss, extending bandwidth of 2 X 2 coupler, increasing its isolation, and putting isolator in OTDM system.

With gain switched quantum well DFB laser generating pulse width 40ps, period 400ps, utilizing 3dB optical fiber directional coupler concatenated and precisely control optical path of each arm, we fabricate 8 X 2.5Gb/s pulse multiplexer. Experimental results show that, This scheme exhibits uniform pulse span, small pulse fluctuation and low loss.

In this paper, the characteristic of thermal induced non-reciprocal phase noise was analyzed theoretically, and the temperature distribution model was derived for the fiber sensing coil. The zero point drift of the fiber optic gyros(FOG) induced by outside temperature fluctuation was simulated numerically and compared for the four type fiber sensing coil manufacture methods (ZYL, SYM, DIP, QUA). The related zero point drift compensated method was proposed.

The effects of the initial chirp of the control soliton pulse on the time shift in the soliton-repulsion logic gate (SRLG) are investigated numerically by split-step Fourier transforms. We discuss the influence of both the positive initial chirp and the negative initial chirp to logic function of SRLG in two-core fibers. The results show that initial chirp of the control pulse seriously affects on the time shift. And the more initial chirp, the less the time shift.

Polarization mode dispersion in fiber seriously limits high-capacity optical fiber communication system. Nonlinear pulse evolution transmitted in fiber was stimulated through computer, we find that nonlinearity can compress pulse and reduce polarization mode dispersion(PMD).

The effects of the position of dispersion compensation fiber on 4 X 10Gb/s WDM systems with different duty cycle are investigated. With the long amplifier spacing and large input power, no matter what the duty cycle is, the performance of the system with DCF-first is worse than that with SMF -first; The best performance can be obtained with duty cycle of 0.5, and it is independent of the position of DCF. With the short amplifier spacing and small input power, the system performance with NRZ format and DCF-first is better than that of other systems. It means that NRZ format and DCF-first should be employed in WDM system with short amplifier spacing.

This paper analyzes in detail the SNR deterioration induced by SLALOM demultiplexer. The slight asymmetry of the coupler will seriously reduce the output SNR. With some pulse delay, the signal-to-clock time delay of a little less than the delay can result in the maximized SNR. Furthermore, increasing pulse delay will degrade the optimal SNR. The optimized configuration of the device is further discussed. It is more suitable to choose the SLA with long carrier lifetime. The optimal time delay between signal and control pulses should be precisely set to be near the control pulsewidth. The SLA can be arbitrarily positioned around any one of a number of periodic sites that equal to the integral times of the control pulse. Through adjusting the optical delay line, SLA’s optical offset to that site should be a little bit less than the control pulsewidth.

The Non-linear Distortion(NLD) in QAM channel of AM/QAM lightwave systems is mainly caused by the clipped Gaussian noise. We use an asymptotic distortion spectrum of clipped Gaussian noise estimating the nonlinear distortion power in AM/M-QAM lightwave system. Also the BER of QAM signal is calculated based on the estimated NLD power. We also compute the BER of QAM signal with the changing of QAM signal power to Gauss noise power ratio(SNRg) and QAM signal power to NLD power ratio(SNLD).

Performances of both 10Gb/s externally modulated optical fiber transmission systems and 2.5Gb/s directly modulated systems with MSSI are investigated by numerical simulation. The results show that the pulse broadening due to the second order fiber dispersion can be perfectly compensated by employing MSSI, no matter the original pulses have or have no chirp. In addition, it is also shown that the signal spectra broadened by self phase modulation in fiber can be renarrowed to its original shape. We also report a transmission experiment of 2.5Gb/s directly modulated optical signal over 200km standard single mode fiber. In this system, a spectral inverter, which is based on the effect of four wave mixing in dispersion shifted fiber to realize spectral inversion, was inserted at the mid-point of the 200km fiber span. By designing and optimizing a novel configuration, a wavelength conversion efficiency of -7dB was obtained. The DFB laser used in our 2.5Gb/s directly modulated optical transmitter has a 1.8dB power penalty after 100km fiber transmission, and a BER floor occurred at 10-6 after 200km transmission without dispersion compensation. In our experiment, by using MSSI, a receiver sensitivity of -28.8dBm at BER=10-10 after 200km transmission was achieved and the power penalty is 2.8dB.

Quasi-soliton exits in optical fibre link with periodical dispersion management and power balance. The analytical approximate expressions for the quasi-soliton are given. The evolution of the optical pulse width has the shape like a saw-tooth. The pulse width at the end of each unit cell is basically dependent on balance the average dispersion and nonlinear effect

The mechanism of the formation of ring shaped pattern of the output light from a multimode optical fiber at the Stokes wavelength of stimulated Raman scattering has been argued in several publications.In this paper,a novel experimental result,i.e.the ring shaped field pattern in backward stimulated Raman scattering is presented to explain the mechanism.lt has been proved that self-focusing plays no role in the formation of the ring shaped structure.The ring shaped pattern is attributed to the refractive index profile of the fiber used in the experiment.The result of numerical calculation shows good agreement with that of the experiment.

Power management is discussed based on a WDM optical test network, in which ring laser clamped EDFAs are used to compensate loss and only the optical attenuators is needed for power regulation. All channels at the output of each node are adjusted to a preset power level, so signal power fluctuations and differences between channels are not passed to the later nodes. The transmission performance is also studied and a simple expression is derived for evaluating the possible input power to the fiber and the possible transmission distance in optical networks. The accumulation of optical amplifier noise and the maximum input power for the stable gain of the lasing-clamped EDFA are the dominant factors limiting the network scale, and restrict the preset input power to the fiber.

A tunable optical orthogonal encoder/decoder is designed and realized by means of programmable memory, optical splitter and combiner, 2X2 optical switches and optical delay lines. It overcomes the poor correlation, small capacities and narrow tunable range of prime-code and 2n code tunable optical encoder /decoder found in the literature abroad. The configuration of the proposed encoder/decoder is simple and it is flexible for application. In addition, it has low optical power loss and very suitable for all-optical code-division multiple access communication system.

This paper presents the test results in the initial phase that we are constructing a self-healing all-optical network testbed, which is called SHAONET. The completed testbed will be used to demonstrate broadband applications based on wavelength routing + WDM + SDH + ATM and Ethernet transport of multimedia signals from multimedia terminal and video server. The design, implementation and performance of the testbed are discussed.

Fiber-optic switches are becoming increasingly important for fiber management, restoration and provisioning applications in dense wavelength division multiplexed (DWDM) long distance telecom networks. Specific applications for optical switches include optical crossconnects and optical add/drop multiplexers.

Recently, there has been a growing interest in IP/ATM/SONET and IP over WDM (Internet Protocol (IP), Asynchronous Transfer Mode (ATM), Synchronous Optical Network (SONET) Wavelength Division Multiplexing) (WDM)) to meet the high bandwidth needs of Internet traffic. This paper presents a network architecture called hyper-cluster employing wavelength-routing, multi-hop packet switching and optical reconfiguration which can be used to support IP over WDM. The proposed architecture is modularly scalable to very large configurations on both hardware and operational bases. A hyper-cluster uses a logical hierarchy for the purpose of addressing but guarantees that all access nodes have a constant number of transceivers. It is a cluster of regular graphs; the clustering structure follows the traffic distribution in a grand granularity. The issue of operational scalability is addressed by presenting a scalable routing protocol When using shuffle-net as the building block, we also present a novel routing scheme called quantified deflection routing, which could improve network performance significantly. The application of the reconfigurability of the proposed architecture to IP over WDM is briefly discussed.

Wide temperature range (typically from -45°C to +85°C) operation of Distributed Feedback (DFB) lasers at 1.3 ?m wavelength has gained increasing interest in recent years. These lasers, when used without thermoelectric coolers in an interactive analog distribution network, provide cost-effective light sources for return path upstream transmission of digital (data) and analog video channels using RF carriers.

Long-haul point-to-point transmission systems based on wavelength division multiplex (WDM) are worldwide being installed today. Optical networks containing optical ADD/DROP multiplexers (OADMs) and optical cross-connects (OXCs) are currently tested within field trials in order to assess the hardware, operational and installation aspects and requirements. Within the ACTS project ’’PHOTON”, a WDM cross-connected network called ’’PHOTONET” with ? 520km transmission length and an optical cross-connect is realized and operated with 2.5 GBit/s and 10 GBit/s transmission. The presentation gives an overview of the project, focuses on the field trial and the applications.

The multichannel wavelength division multiplex technique offers the possibility to use the optical fiber amplifier bandwidth for high capacity transmission whereas single channels are routed via optical crossconnects. Linear and nonlinear fiber effects as well as crossconnect characteristics influence the transmission length of the signal path. These effects are illustrated by the transparency length diagram. The basic knowledge for planning future optical networks is achieved from transmission experiments in recirculating fiber loops accompanied by the development of simulation tools. The loop experiments deliver a deeper insight in physical properties of fiber trunks carrying bundles of optical channels. The influence of crossconnects or single components on the signal quality can also be investigated by a repeated loop transit. The experimental results are used to improve a simulation model on the basis of "Ptolemy". This simulation tool permits a prediction of signal quality degradation during transit through a network path. Another important topic of WDM network research are experiments with installed fiber trunks. As a first attempt the experiments on a replica of the Berlin- Darmstadt intercity connection are presented.

We discuss a simple, self-consistent iterative method for the analysis of rectangular waveguides with strong guidance. We show that this method removes the ambiguity of the conventional effective index method and gives a convergent value of the propagation constant both near and far from cutoff. Near the cut-off region, the accuracy can be improved by including an external effective index correction which takes into account the finite mode effect outside the waveguide.

A detailed numerical investigation has been undertaken of the operating characteristics of Terahertz Optical Asymmetric Demultiplexers (TOADs) devices subject to frequency detuned picosecond control and signal pulses, taking into account both gain saturation and nonlinear gain compression in the Semiconductor Optical Amplifier (SOA). It is shown that the output behaviour of TOADs exihibits significant differences depending on whether the signal and control pulses are at higher relative frequencies (positive detuning) or lower relative frequencies (negative detuning). The analysis indicates that negative frequency detuning can be used to achieve an enhanced output power in the switched region and a reduced width of switching window. Calculations are shown to be in good agreement with available experimental results.

We have examined the main constraints on the design of single-channel, high-capacity soliton communication systems. In the average soliton regime, the Gordon-Haus timing jitter limits the bit rate to about 5 Gb/s for transoceanic fiber links, while for shorter transmission distances the main limitation is fiber perturbations arising from discrete in-line amplification. The use of dispersion-decreasing fibers and of periodic optical phase conjugation for jitter control can increase significantly the capacity of soliton communication systems. We found that the third-order dispersion assumes a prominent role in this case. Reducing this effect sufficiently, the main constraint becomes the soliton-soliton interactions and bit rates superior to 110 Gb/s can be achieved for amplifier spacings less than 80 km. For higher amplifier spacings the bit rate is limited by the Raman induced timing jitter.

This paper reviews Lucent Technologies’ effort to build the state-of-the-art fiber-optic transport networks in China. As the world fastest growing economy for the last decade, China’s demand for telecommunication grows exponentially. Fiber-optic based transport networks as information superhighway is crucial for this telecommunication revolution in China. The first wave of transport network transformation came in 1993 when synchronous digital hierarchy (SDH) was introduced in China. Lucent Technologies has been at the forefront of this effort for the last five years. The second wave of transformation came in 1997 when China’s first dense wavelength division multiplexing (DWDM) systems with transport capacity of 20Gb/s was deployed from Xi’an to Wuhan by Lucent Technologies. This year, Lucent Technologies, selected by China Telecom, is going to massively deploy DWDM technologies in national backbone networks. This effort will increase the transport capacity by an order of magnitude. The effort to increase transport bandwidth is accompanied by the effort to introduce new applications on fiber-optic networks. In December 1997, SDH based fiber-optic transport system is used to distribute compressed digital television signals for the first time in China. Fiber-optic networks are now used for multimedia services.