We discuss recent progress on ultra-high-speed modulation formats for next-generation optical communications at 160 Gb/s and beyond. In particular, we demonstrate CSRZ, PAP-CSRZ, GAP-CSRZ, RZ-VSB, and DPSK signals at ultra-high data rates.

Optical 3R regeneration is of great interest due to its ability to enhance the system margins in photonic network, because it enables to reset transmission impairments induced by channel interaction distortion, accumulation of amplified spontaneous emission (ASE) noise, chromatic dispersion and non-linearities of optical fibers and so forth. In comparison to electrical 3R regenerators, optical 3R regenerators are expected to be less complex and require less high-speed electronic components owing to simple optical signal processing, leading to small footprint, low power consumption and low cost. In this paper, we describe an optical 3R regenerator operable with carrier-suppressed return-to-zero (CS-RZ) modulation format which will be employed in dense WDM (DWDM) network to increase the efficiency of bandwidth utilization. We have demonstrated 3R regenerative transmission using 100 GHz-spacing 40 Gbit/s 5 WDM CS-RZ signals so as to confirm that a DWDM filtering effect can be drastically mitigated by the 3R regenerator.

This paper reviews silica glass based nonlinear optical fiber designs for signal processing using optical Kerr effect. The requirements for designing nonlinear fibers are described first. Then the design concept is discussed and design examples are shown to illustrate the tradeoffs among the different fiber properties such as effective area, dispersion and attenuation. Furthermore, fiber designs with distributed Brillouin frequency shift to mitigate the effect of simulated Brillouin scattering in nonlinear fibers are discussed in detail. SBS threshold increase of 7 dB over conventional nonlinear fibers is experimentally demonstrated.

We design a kind of dual-cladding photonic crystal fiber (DC-PCF), in which air holes arranged in the vicinity of the core (inner-cladding) is smaller than the other air holes (outer-cladding). By numerical simulation, the dispersion characteristic of this novel PCF is investigated. Dispersion curves will become comparatively flat while gradually reducing the air holes arranged in inner cladding under fixing the air holes of outer cladding. An ultra-flattened dispersion can be realized when the air holes size of inner-cladding dwindling down to an optimum size. As an example, the DC-PCF demonstrates an extraordinary flattened dispersion around 9.8ps/nm.km within ±0.4ps/nm/km fluctuation range in an ultra-broad wavelength range from 1.0μm to 2.0μm . Furthermore, when the air holes arranged in the second layer nearing the core is reduced slightly, the flattened dispersion curve even can parallel shift from 11.8ps/nm/km to 7.8ps/nm/km, 6.2ps/nm/km, 4.0ps/nm/km at the wavelength around 1.55μm.

Group velocity dispersion (GVD) and effective mode area (Aeff) of solid core honeycomb cladding photonic crystal fiber (PCF) with different up/down doping levels are investigated theoretically. Both total internal reflection (TIR) and photonic bandgap (PBG) guiding mechanisms are shown to be available in this fiber structure with gradual change of the doping level. It is noted that the previously overlooked TIR guiding design with up-doping could acquire improved nonlinear property compared with PBG mechanism in short normalized wavelength region. On the other hand, the total GVD is shown to be dominated by waveguide dispersion corresponding to the fiber structure. Numerical results show that HPCF can achieve small Aeff with low air-fill fraction, and doping level in HPCF provides an additional way to change GVD excepting structure parameters. Special cases are given to demonstrate the potential of HPCF in combining design of Aeff and GVD, aiming at applications such as Raman amplification and dispersion compensation around 1550nm.

An optimal design of Photonic crystal waveguide (PCW) directional coupler (DC) with adiabatic coupling is presented in this paper. Planar wave expand (PWE) method and FDTD method are used to analyze and optimize PCW-DC. It is shown that use this PCW-DC can achieve efficient transmission ratio in cross state, bar state and power division state at different coupling length. The simulation results show that the coupling ratio can be higher than 90% in some selective wavelength in these states. With the help of adiabatic coupling and bent PCW, the coupling coefficient of two parallel SMFs whose distance from each other at standard interval of 125μm can be higher than 90%. This also suggests that this device can realize a very efficient add/drop filter device which can be used in WDM system.

Supercontinuum was generated in a polarization-maintaining (PM) PCF. The main advantage with the PM-PCF is the preservation of the state of polarization of the field propagating. For several applications, it is essential that the output has a well-defined polarization. In addition, the preserved polarization enhances the nonlinear interactions so that less power is required to generate the SC. The field patterns, birefringence and nonlinearity in the PM-PCF were simulated using a full-vector finite element method. Spectral broadening was achieved pumped by the optical parameter amplifier system (OPA). It was concluded that the SC generation was depended on the pump wavelength, and the difference group velocities in the two sides of the zero dispersive wavelength of the PCF and the OH absorption at about 1.4μm in the PCF affected the flatness of the generated supercontinuum. When the pump wavelength lied further away from the zero dispersive wavelength, the flatness was reduced, even in the visible region the blue-shift peaks were separated and didn't come into being supercontinuum. Supercontinuum with a broad bandwidth of 300 nm to 1350 nm was generated when the pump wavelength of 1200 nm, and the generated spectral bandwidth was beyond two octaves.

An all-optical tunable wavelength converter using a combination of self-phase modulation (SPM) effects in highly nonlinear microstructure fibers and narrowband spectral filtering is investigated, which is reported for the first time to our knowledge. Wavelength conversion over a±4nm bandwidth of a 10Gb/s date rate is obtained with good efficiency. A 25-m-long microstructure fiber with zero-dispersion wavelength at 800nm is used as the nonlinear medium. The core diameter of microstructure fiber is 2.4μm and the outer diameter is 125μm. The nonlinearity is γ=36km-1W-1, which is 20 times higher that that of a conversional dispersion-shifted fiber. The dispersion at the wavelength of 1550nm is ~+150ps/nm-km and the loss is 40dB/km.

In this presentation, the universal structure of one-dimensional photonic crystal (1-D PC) is constructed, and its optical transmission properties are analyzed by transfer matrix method (TMM). A case that there are two kinds of medium as a period is studied in detail. It is concluded that the reflectivity in photonic band-gap (PBG) increases with the increasing of periodical number, and the bandwidth of PBG has direct relation with the difference between two kinds of dielectric constant, three methods for extending PBG are discussed. When defect layer is inserted, a defect mode appears in the PBG. The concept of optimal periodical number is presented, and it is found that this optimal periodical number is only relative to the ratio of dielectric constant (K). Using multi-objective optimization method, we educe the curve and equation relation between optimal periodical number and K for the first time. In addition, the change in the number of defect mode with the variation of the defect layer's thickness is analyzed, and it is explained by the theory of F-P cavity.

Two group unit cells of second order Sierpinski carpet photonic crystals are constructed, where the dielectric pillars in the unit cells are geometry structure of isosceles triangle. Photonic bands of the fractal photonic crystals are calculated by Order-N method. The result shows that the center frequency of guided bands vary with changing the structure shape of the unit cells, and with variety of the apex angle of the isosceles triangle pillars, it can be seen that the capacity of tuning the frequency of guided bands for big triangle dielectric pillar in the middle of the unit cell is stronger than that for small ones all around the unit cell.

This paper brings forward a new point of view that the quantum effect is a common phenomenon, which emerges not only in atoms but also in any system as long as the size of the system is comparable with the length of incident wave. Analogous to the case of electrons in atoms, light propagating in periodic medium is described as a kind of 'probability wave', modulated by the periodic potential field of refractive index, and an fundamental equation similar to the Schrodinger equation is derived based on the theory of quantum-mechanics. By solving the equation, the band structure of photonic crystal can be understood as a result of quantum effect of the probability wave propagating in the periodic dielectric structure. As an example, two-dimension photonic band structure is discussed.

Microstructure fiber is a new kind of optical fiber. An arrangement of air holes running along the full length of the fiber provides the confinement and guidance of light. The light is confined in the silica core along the fiber axis. This fiber has endlessly single mode, special dispersion characteristics and so on. Using a vectorial effective-index numerical method, we investigated the dispersion characteristics of a microstructure fiber with honeycomb cladding structures. The dispersion, dispersion slope, and Kappa parameter can be designed neatly by changing the air hole size and the separation of the holes in fiber cladding. We demonstrated the Microstructure fiber with large absolute value of normal dispersion and negative dispersion slope at the wavelength of 1550nm. Conventional communication non-shifted single-mode fibers and nonzero-dispersion shifted fibers (NZ-DSF) can be compensated efficiently using the microstructure fiber at the wavelength around 1550nm.

We investigate the beam splitting phenomena under the case that light is incident obliquely on thin film Fabry-Perot filter and the dispersion diagram of Fabry-Perot filter is shown; Gaussian beam propagating in the structure is analyzed by Fourier decomposition in angular field, transmitted band is calculated by characteristic matrix arithmetic in optical thin film theory. At last, the thin film Fabry-Perot filter device was fabricated by e-beam deposition in vacuum and measured from 782 to 787 achieved by the tunable Ti-sapphire laser. We show the variation of the distance between the splitting spots at different wavelengths by the image of splitting beams we detected, demonstrating the distance achieve maximum at the peak transmittance wavelength because of the largest group delay. And the experimental result is in good agreement with our interpretation.

The structure of microstructured optical fiber (MOFs) has a strong impact on its nonlinearity parameter and therefore, could be designed to meet the needs of optical processing applications. By a full-vector finite element method, the nonlinearity coefficient of MOFs with a silica core and two kinds of air hole cladding structures, i.e., the hexagonal lattice and square lattice, is computed respectively. The dependence of the nonlinearity coefficient of MOFs on the structure parameters and the wavelength is analyzed. The results show that, for a given wavelength and a given air-filling fraction, the nonlearity coefficient has a maximum when the pitch of air holes changes, if the air holes are very large, nonlearity coefficient maximum of the hexagonal lattice and the square lattice amount to approximately 77w-1km-1 and 54w-1km-1 respectively; for a given wavelength and a given pitch of air holes, the nonlinearity coefficient increases when cladding air-filling fraction increases; for given structure parameters, the nonlinearity coefficient decreases while the wavelengh increases. The above results are the good reference to investigation and use of the MOFs.

Microstructured optical fiber (MOF) is a new class of optical fiber that has emerged in recent years. It is formed by an array of air holes running along the fiber length. They are fascinating because of various novel properties, including endlessly single-mode operation, scalable dispersion and nonlinearity, and the surprising phenomenon of a short wavelength bend loss edge, etc. These optical characteristics make possible wide-ranging applications in optical communication. In this paper, we investigate the mode coupling characteristics induced by periodic microbending in MOF. Coupling between various modes in normal single mode fiber (SMF) and polarization maintaining fiber (PMF) have already been investigated theoretically as well as experimentally. Periodic microbending created by a corrugated fixture on a SMF is known to induce the mode coupling between a codirectional propagating core (LP01) and cladding mode (LP11). In our experiment, a core-cladding mode coupler was built and tested based on a section of endlessly single mode MOF (fabricated with the stack-and-draw process). The fiber was bended between a pair of identical grooved plates with 250μm periodicity, thus this can be treated as a mechanical-stress-induced long period grating (LPG). The effect of microbending is controlled using stress gauge. The coupling strength is compared between single mode fiber and MOF under the same stress gage condition. The modal coupling coefficient enhancement is observed in MOF because of the complex index distribution.

Mechanism of supercontinuum(SC) spectrum generation due to cross-phase modulation(XPM) in a dispersionflattened/decreasing fiber(DFDF) with low birefringence has been investigated theoretically and experimentally. By using a XPM, the measured SC spectum width becomes 33.6 % broader than that obtained by using only self-phase modulation (SPM). This fact implys that effectiveness and validity of the sc generation using XPM method. Furthermore, dependence of generated sc spectrum broadening on incident power, polarization angle of the input pulses, and modal birefringence are investigated. consequently, it was velifid that when a polarization angle of the input pulses is 45 degrees with regard to the principal axes of the fiber and incident average power is less than 0.147 mW, soliton trapping takes place due to a balance between soliton pulse powers and modal birefringence value. In addition, it was shown experimentally that for a polarization angle of the input pulses of 22.5 degrees, the sc spectrum is enlarged by the same amount as in the case of 45 degrees.

Air-guiding photonic bandgag (PBG) fibers are new kind fibers which are quite different from conventional correspondence ones. In this paper, we studied the light transmission properties and light wave modes of hexagonal air-guiding PBG fibers. The fiber core is 10μm diameter air hole, surrounded by a cladding of 71.5μm diameter. The outer-cladding of the fiber is about 185μm. The experimental results show that when the wavelength ranges from 1430 to 1600 nm, there is merely no attenuation. It means that in these new fibers, light wavelength ranges widely. In addition, light wave mode and fiber core are the same in symmetrical structure. The theoretical results coincide with experimental results exactly.

A theoretical study of flat supercontinuum (SC) generation in a highly nonlinear photonic crystal fiber (PCF) is presented. We propose a chromatic dispersion profile of a highly nonlinear PCF for flatly broadened SC generation around 1550nm. The proposed chromatic dispersion profile of the fiber which is a convex function of wavelengths has small normal group-velocity dispersion at the pump wavelength and the dispersion slope around which is flat. It is found that the fiber with such dispersion characteristics is suitable for generating a relatively flat SC. The initial chirp of the input pulse also has a significant effect on SC generation in photonic crystal fiber. A flatter and wider spectrum can be obtained by the pulse with appropriate positive initial chirp.

An ultra compact, highly integrated photonic switch with 2×3 configuration was designed and fabricated using the thermo-optical effect of polymer materials. By exerting voltage to proper compartment of the electrode, the input light can be switched freely among three output ports. The experiment results show: for the "insufficient reflection" state, the extinction ratio is 16.64dB for the middle output port; for the "bar" state, the extinction ratio for the reflection port is 26.8 dB. The power consumption is on the scale of 100 mW, and varies with different function mode.

A micro high-speed 1×2 magneto-optic switch, which is used in high-speed all-optical network (AON), is designed and analyzed. The theoretical and experimental analysis of the micro high-speed magneto-optic switch mainly involves the parts of optical route, nanosecond impulser and high-speed magnetic field etc. The study of optical route covers design scheme of polarization optical route in the optical switch, the performance analysis of magneto-optic crystal by using Faraday Effect. The research of nanosecond impulser involves the design, simulation and test of electronic circuit diagram of nanosecond pulse. The analysis of high-speed magnetic field consists of magnetic path design in Faraday rotator and analysis of high-speed magnetic field etc. The nanosecond current pulse transient from nanosecond impulser is used to switch the magnetization of the magneto-optic crystal, which propagates a 1550nm optical beam. The experiment results state that nanosecond impulser can output the current pulse with impulse amplitude 10~60V and impulse width 10~ 100ns. The optical beam can be stably switched and the switching time is less than 1μs currently.

An optical switch by Sagnac interferometers (FSI) structure is described in this paper. An analysis shows that the switching properties of the device are polarization-independent. An experimental setup was achieved by using a PLZT electro-optical (EO) ceramic as the control unit. By using this setup, the theoretical analysis model is proved by experiments with different input polarization states. At the same time, the typical performances of the switch realized less than -22dB cross talk and less than 1 switching time. In addition, the Kerr coefficient of the PLZT compound used in experiments was measured about , and the insertion loss of it was found increasing rapidly when external electric field is larger than 600KV/m.

Optical interconnections on printed circuit board (PCB) holds the promise to meet an ever-increasing demand for inter-chip interconnect bandwidth, while the requirement of a stringent alignment between transmitter (normally VCSEL) and the waveguide on PCB exhibits one of obstacles that prohibit immediate implementation of optical interconnections. We demonstrate in this paper a soft lithography based coupling structure with a 0.5x0.5 mm pick-up window interfacing to VCSEL, along with a beam duct connecting to a regular waveguide. The coupling head, beam duct and the regular waveguide for chip-chip transmission were monolithically fabricated with UV-cured optical polymers through a single soft lithography process. The optical alignment was greatly eased by a factor of four comparing with conventional coupling approaches of straight waveguides. The coupling efficiency of the structure was compared with those of two prior schemes by utilizing ZEMAX, and change in transmitted pulse shape due to different beam path length was also analyzed. It was found that time delay as a result of an increased size of coupling structure was only in the order of 10-12 second, suitable for high speed communications in the range of 10Gb/s.

A novel bidirectional 2×2 optical switch technique, based on the conventional erbium-doped fibers (EDFs) with an operation of pumped or unpumped power level, is proposed and demonstrated experimentally. By using the amplification and absorption function of EDFs and a simply architecture design, the input signals can be switched to a suitable position. The response time of wavelength switching will approach about 2 ms. Moreover, the behavior and system performance of the proposed configuration also have been studied.

In this paper, the performance of optical packet switching (OPS) network with coherent time-spreading optical code (OC) label is investigated experimentally. In the experiment, superstructured fiber Bragg grating (SSFBG) is used for the OC-label processing for the first time. Packet routing experiment with 10 Gbps and 40 Gbps payload data has been successfully demonstrated by hybrid using planar lightwave circuit (PLC) and SSFBG as the OC-label encoder and decoder respectively.

The regenerative wavelength conversion of the picosecond short pulse with repetition rate of 10GHz is demonstrated employing a SOA based interferometer. Both up-conversion and down-conversion can be realized with wavelength range from 1535nm to 1555nm. The regenerative capability of this wavelength convertor is also demonstrated with degradated signal.

The optimal matching problem of the nonlinear refractive phase-shift and the nonlinear absorptive phase-shift in optical limiters is studied by means of the Gaussian beam Z-scan diffraction theoretical model. Optical limiting behaviors in the limits of the small nonlinear absorption and the large nonlinear absorption are examined. The Gaussian beam Z-scan diffraction theoretical mode and the method of simulating the optical limiting characteristics are presented, and typical numerical computational findings are given. Our results show that, when the nonlinear absorption of an optical limiting material is negligible, the optical limiting characteristic curve exhibits a kind of slowly attenuating oscillating waveforms. In this case, the optical limiting threshold and the clamped output value of the optical limiter are dependent on the installation position of the sample and the convergence of the incident Gaussian beam. When the phase-shift produced by the nonlinear refraction is comparable with that by the nonlinear absorption, the two optical limiting effects from the nonlinear refraction and the nonlinear absorption cancel out to some extent. Our results also show that the ratio of the nonlinear absorptive phase-shift to the nonlinear refractive phase-shift has a great impact on the optical power entering the far-field receiving aperture. To acquire a satisfactory optical limiting performance, a large enough difference must exist between the nonlinear absorptive phase-shift and the nonlinear refractive phase-shift.

Future network will include wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM) technologies. All-optical format conversion between their respective preferable data formats, non-return-to-zero (NRZ) and return-to-zero (RZ), may become an important technology. In this paper, 10Gbit/s all-optical NRZ-to-RZ conversion is demonstrated based on terahertz optical asymmetric demultiplexer (TOAD) using clock all-optically recovered from the NRZ signal for the first time. The clock component is enhanced in an SOA and the pseudo-return-to-zero (PRZ) signal is filtered. The PRZ signal is input into an injection mode-locked fiber ring laser for clock recovery. The recovered clock and the NRZ signal are input into TOAD as pump signal and probe signal, respectively, and format conversion is performed. The quality of the converted RZ signal is determined by that of the recovered clock and the NRZ signal, whereas hardly influenced by gain recovery time of the SOA. In the experimental demonstration, the obtained RZ signal has an extinction ratio of 8.7dB and low pattern dependency. After conversion, the spectrum broadens obviously and shows multimode structure with spectrum interval of 0.08nm, which matches with the bit rate 10Gbit/s. Furthermore, this format conversion method has some tolerance on the pattern dependency of the clock signal.

Based on cross-gain modulation (XGM) in cascaded semiconductor optical amplifiers (SOAs), all-optical AND and NOR operations at 20Gb/s were both realized in the same configuration for the first time. By controlling the input signal power, the two logic gates can be achieved from different output channels. Single-port-couple SOAs with 1000μm active regions are exploited to improve the output performance. The dependence of the output characteristics on the input signal power and wavelength was also investigated.

A novel all-optical 40Gbit/s NRZ-to-RZ data format conversion scheme based on sum-frequency generation (SFG) interaction in a periodically poled LiNbO³ (PPLN) waveguide is presented for the first time, using a Mach-Zehnder interferometer (MZI). The conversion mechanism relies on the combination of attenuation and nonlinear phase shift Φ_NL induced on the signal field. The performance of the conversion is numerically evaluated, with the result showing that it is more effective to yield Φ_NL when appropriately phase mismatched for SFG process but Φ_NL≈0 when quasi-phase-matching (QPM). Compared with the cascaded second-order nonlinear interactions (SHG+DFG) with the influence of walk-off effect, a high conversion efficiency and good performance are achieved with peak power 500mw and width 2ps of the pump, which can be used in super high-speed situation (40Gbit/s and above). Finally, the inverse process of SFG and corresponding walk-off effect are analyzed and the optimum arrangement of power is proposed, showing that proper power, pump width, and waveguide length are necessary for achieving a satisfied conversion effect.

The majority of optical processing devices that are employed in optical transmission systems are based on optical fibres or planar optical waveguides that rely on basic physical phenomena such as coupling, interference or Bragg grating reflection for their functionality. These devices include, for example, a wide variety of single- and multi-mode couplers and splitters, Mach-Zehnder interferometers, wavelength filters, dispersion compensators, arrayed waveguide gratings (AWGs), resonators, etc. In addition to these devices, there is a further range of devices that rely solely on their geometrical design for their functionality and involve none of the above physical phenomena. Simple examples of these devices include velocity couplers, null couplers, Y-junctions and tapers. Each of these devices relies on the approximately adiabatic propagation of each of its modes along the length of the device. A key feature of such propagation is that each mode essentially conserves both its power and field symmetry. Recent work has demonstrated that it is possible to switch modes passively with wavelength using the approximately adiabatic transformation of one mode into a mode with dissimilar field symmetry. This transformation is achieved through appropriate geometrical design of the device. For example, it is possible to transform the symmetric fundamental mode into the first odd mode of a planar waveguide by employing a two-mode asymmetric Y-junction. Using this and other mode transformations, it is possible to design compact planar devices that will combine or separate 2 or 3 channels in a coarse wavelength division multiplexing (CWDM) system.

In conventional optical packet label banks, recognizing different photonic labels would require the equal number of experiments. We have proposed a tunable multi-port optical spectrum synthesizer composed of NxN arrayed waveguide grating for photonic parallel signal processing. In this paper, the parallel encoding and decoding of 10Gbit/s pulse trains pattern in the spectrum domain using the multi-port optical spectrum synthesizer were experimentally examined. As shown in this research, the proposed N-port multiplexed optical spectrum synthesizer promises to provide a parallel optical processing in the photonic network and other optical signal processing.

This paper proposes a design of polymer Triple Ring Resonators Filter (TRRF) based on silicon substrate. The device structure was demonstrated in order to get wide Free Spectral Ranger (FSR) of the device and a box-like filter response. The transmission equation of the amplitude of input and output lightwaves and coupling coefficients were analyzed by coupling mode theory also.

By numerical simulation, we show that the fourth-order dispersion (FOD) makes sub-picosecond optical pulse broaden as second-order dispersion (SOD), makes optical pulse oscillate simultaneously as third-order dispersion (TOD). Based on above two reasons, sub-picosecond optical pulse will be widely broaden and lead to emission of continuum radiation during propagation. Here, resemble to two- and third-order dispersion compensation, fourth-order dispersion compensation is also suggested in a dispersion-managed optical fiber link, which is realized by arranging two kinds of fiber with opposite dispersion sign in each compensation cell. For sake of avoiding excessively broadening, ultra short scale dispersion compensation cell is required in ultra high speed optical communication system. In a full dispersion compensation optical fiber system which path average dispersion is zero about SOD, TOD, and FOD, even suffering from affection of high order nonlinear like self-steep effect and self-frequency shift, 200 fs gauss optical pulse can stable propagate over 1000 km with an optimal initial chirp. When space between neighboring optical pulse is only 2 picoseconds corresponding to 500 Gbit/s transmitting capacity, eye diagram is very clarity after 1000 km. The results demonstrate that ultra short scale dispersion compensation including FOD is need and effective in ultra-high speed optical communication.

Polarization mode dispersion (PMD) is becoming major system impairment in high speed and long distance optical fiber transmission systems. As the bit rate climbs from 10 to 40Gb/s per channel and beyond, optical pulses are increasingly distorted by 1st and higher order PMD. We report on the experimental mitigation of pulse distortion due to 1st and higher order PMD effect based on one tunable differential group delay (DGD) element, which is a compact concatenation via six magneto-optic polarization rotators (Faraday rotators) of six YVO₄ birefringence crystals whose lengths decrease in a binary power series. Two different experiments are carried out, with and without an electric polarization controller set before the tunable DGD element. Optical pulses with width of 41ps are broadened and distorted by the PMD emulator which generates 1st and 2nd order PMD with mean magnitude of 30.28 ps and 483.31 ps², respectively, and then reshaped by the compensation device. Degree of polarization (DOP) is used as the feedback signal, which is significantly increased from around 0.15 to around 0.85. The experiment results show that pulse distortion due to 1st and higher order PMD is successfully mitigated.

The online dispersion monitoring technique based on XGM between the two sidebands of the optical signal in a semiconductor optical amplifier (SOA) is proposed in this paper. The simulation shows that through the cross gain modulation between the two sidebands of the signal and introducing dither to the time delay between them and extracting the 2nd order frequency component of the dither in the SOA output, the dispersion variation can be obtained and the dispersion monitoring range can be improved.

A feasible and cost-effective online chromatic dispersion (CD) monitoring scheme for high speed optical communication system is demonstrated in this paper. Based on the formerly verified theoretical model, the output electrical power of a specific frequency band is tested to reflect the residual chromatic dispersion online. Thus the microwave devices are selected to form the electrical power detecting circuit, which consists of a PIN photodiode, a microwave power filter and a power detector in tandem. In the experiments, frequency band center were chosen at 5 GHz for the 10 Gbit/s system and 12 GHz for the 40 Gbit/s system. Then the output voltage of the detector was processed and converted to digital signal and the signal was processed to obtain the amount of the chromatic dispersion of the tested systems. For the 40 Gbit/s system, the maximum detectable chromatic dispersion was around 130-ps/nm and a resolution of 5-ps/nm/db was achieved at the chosen frequency band centered at 12 GHz. Performance of the microwave devices and comparison of the experimental results at different frequency bands are also discussed, which verified that the chosen center frequency was suitable for detection of CD in optical communication system beyong 10 Gbit/s speed.

The dispersion compensation theory of the chirped fiber grating (CFG) in externally modulated CATV lightwave system is analyzed by using the time-domain form of the field envelope wave equation, and the analytic expression of the composite second order (CSO) distortion is obtained. The results show that the requirement of dispersion compensation in externally modulated CATV lightwave transmission system is different from that in common digital optical fiber communication system. Moreover, to a certain fiber transmission link, the dispersion compensation effect is not same for different dispersion compensation position of CFG and it exists an optimal position.

Free space laser communication system is composed of laser communication subsystem and Acquisition Pointing and Tracking(APT) subsystem. Laser communication subsystem achieves high rate dates transmission, multiple-axis ATP subsystem accomplish rapid, high acquisition probability and high precision, dynamic tracking. In this paper the structure and principle of typical laser communication system was described briefly at first, and link transmission and system noise characteristic, background light performance, SNR requisition are analyzed about Coarse Pointing Assembly(CPA) links. In order to satisfy demand of acquisition probability, System designation is optimized and important component is selected.

A 2.1 km terrestrial free-space optical data link operating at 5 Gbps by using WDM and 1550 nm fiber communication techniques was established. Two 2.5 Gbps pattern generators are used to directly modulate 1530 nm and 1550 nm DFB lasers respectively. The output of each modulated optical signal are combined by a CWDM, and then amplified by a 20dBm EDFA. The amplified optical signal is then applied to a specially designed transmitting telescope. The received optical signal is focused onto the core of a 62.5μm multi-mode optical fiber using coupling optics within the receive telescope. The coupled optical signal is interfaced to a de-multiplexer to separate the two individual wavelengths, where each of two outputs is then connected to a 2.5 Gbps receiver. The BER and optical stability measurements are presented to quantify and demonstrate link quality for a 2.1 km span. BER and received optical coupled power data is presented to illustrate atmospheric effects associated with typical link performance.

This paper discusses the excursion mechanism of transient in the EDFA and the corresponding impairments to the DWDM. The dynamic amplifier simulation model and simulation results are presented. The technical platform for next-generation intelligent EDFA is introduced and realized. The method is demonstrated to be feasible by the experimental results.

Optical filtering is mostly employed to generate vestigial sideband (VSB) signal in high speed wavelength division multiplexing (WDM) systems. This paper experimentally shows the relationship of VSB filtering impact and bit sequence lengths at 40Gb/s wire rate. Two optical filters and different pseudorandom bit sequence (PRBS) are used in experiment. The results show that he optical filtering impacts the long bit sequence more than the short cases.

This paper reports the progress of the 863 high-technology project of China "Optical Resilient Packet Ring (O-RPR) Based on All-optical Buffering Techniques". In this ring network, for the packet through an intermediate node the conversion of O/E/O is not needed in order to overcome the bottleneck of O/E/O. In all-optical node a Dual Loop Optical Buffer (DLOB) is used to revolve the collision between the packet, which pass through the node, and add packet from local user to ring. The principle of DLOB is introduced. The bit-rate of head of optical frame is lower than the bit-rate of payload in a packet, in order to increase the efficiency of transmission link. This paper will introduce the network topology, layers and the structure of optical node. It includes an optical splitter, optical delay line as input buffer, a SOA as optical switch, which switch the packet dropping down form the ring or pass through the node, a DLOB and an electric buffer. An ARM is used for regulation of different buffers. The experiment results of a demonstrate network including 3 nodes are given.

Quantum key can be theoretically demonstrated to be secure and now commercially available. The bit rate of the quantum key distribution is much lower than that for "one-time pad" needs. The practical bit limitation of the quantum key distribution system is analyzed to explain necessity for bit amplification. The method of bit amplification is also introduced in this paper.

A database is founded to estimate the nonlinear impairments of single channel return-to-zero (RZ) transmission systems with arbitrary parameters. Our link setup consists of multi-span transmission fiber and dispersion compensation component, with dispersion slope full compensating. The total transmission distance and the transmission fiber could be arbitrary, i.e. with arbitrary nonlinear coefficient, attenuation and dispersion. The parameters of input signal could also be arbitrary, i.e. with arbitrary transmission rate, input power, and any duty cycle of RZ pulse. Even the amplification schemes could be single-stage erbium-doped fiber amplifier (EDFA), or double-stage EDFA, or hybrid EDFA-Raman amplification. The database is obtained by numerous numerical simulations, neglecting the amplified spontaneous emission noise, polarization mode dispersion. The performance of transmission system impaired by nonlinear effects is represented by eye opening penalty (EOP). One can use the database to estimate the EOP of single channel transmission systems with bit rate up to 160 Gb/s, and can also evaluate the maximum transmission distance for given system impairment conveniently. For high-bit-rate transmission systems, intra-channel nonlinearity dominates the nonlinear impairments, therefore, the database to asses the nonlinear impairment of single channel transmission link is also valid for high-bit-rate wavelength-division multiplexed (WDM) systems. The accuracy and the limitation of the database are also discussed.

In order to generate a stable and pure 60GHz millimeter-wave signal, a periodically wavelength-swept lightwave signal over a limited wavelength range which center wavelength at 1310nm and frequency-swept rate up to 1GHz is an important component of the whole system. In this paper, we focus on three methods to yield the wanted periodically wavelength-swept lightwave signal, which are sinusoidal wavelength scan, triangular wavelength scan and saw-toothed wavelength scan. We analyze in theory the power characteristics and the spectrum characteristics of the 60GHz millimeter-wave signals relative to the different wavelength-swept lightwave signal generated by different wavelength-swept methods. Furthermore, we simulate the 60GHz radio-over-fiber transmission systems respectively with the three wavelength sweep methods and gain the results in agreement with the analysis in theory.

A time/frequency two-dimensional OCDMA en-/decoding system scheme is presented. The system adopting prime-hop code and fiber Bragg grating (FBG) en-/decoder are experimentally demonstrated. The experimental results show that inputting data at the transmitter can be received accurately at the receiver. It offers a real example for OCDMA technology application in optical communication system.

We propose and demonstrate a simple and cost-effective technique to detect and localize the fiber failures in WDM PON. By reusing the downstream lasers as WDM light sources for the optical time-domain reflectometry, the proposed technique can localize the failures in both feeder and drop fibers without using the expensive tunable laser.

In this paper, we investigate the optimal design of bidirectional pumped FRA with the impact of co-pumping RIN transfer using the quality factor (Q-factor) analysis for multispan long-haul transmission systems. The benefits from low ASE and MPI noise accumulation, impairments due to nonlinearity enhancement caused by signal amplification and the RIN transfer penalty are taken into account. The optimal operation of bidirectional Raman pumped long-haul multispan fiber system (24×100 km) at 10 Gb/s is calculated according to the copumping percentage, total Raman gain and pump RIN intensity. Both RZ and NRZ modulation format are examined. Our analysis provides a useful tool for the optimization process of bidirectional Raman pumping multispan long-haul transmission system including the requirement of pump RIN.

The National Institute of Advanced Industrial Science and Technology (AIST) in Japan has been developing Aimulet, which is a compact low-power consuming information terminal for a personal information services. Conventional Aimulet, which is called Aimulet ver. 1 or CoBIT, has features of location and direction sensitive information service device without batteries. On the other hand, the Aimulet ver. 1 has two subjects, one is multiplex and demultiplex of some contents, and another is operation under sunshine. In Former subject is of solved by the wavelength multiplex technique using LED emitter with different wavelength and dielectric optical filters. Latter subject is solved by new micro spherical solar cells with a visible-light-eliminating optical filter and a new design of light irradiation. These techniques are applied to the EXPO 2005, Aichi Japan and introduced in public. The former technique is applied on Aimulet GH, which is used in Orange Hall of the Global House, scientific museum with a fossil of a frozen mammoth. The latter technique is applied on Aimulet LA, which is used in the Laurie Anderson's WALK project in the Japanese Garden.

We experimentally demonstrate the generation of supercontinuum (SC) with a 12.5GHz DFB/EAM ultrashort optical pulse broadened in the high nonlinear fiber (HNLF). Through longitudinal mode-carving of the SC spectrum, a novel multiwavelength continuous wave (CW) optical source with precise 25GHz channel spacing is realized. The bit error rate (BER) curve and eye diagram show that the multiwavelength CW optical source is promising for dense wavelength division multiplexing (DWDM) systems.

In this paper, a new fabricating strategy for polymer microring resonators vertically coupled to a bus waveguide is developed. A carefully engineered Al masking process is utilized to compensate the local concave of the buried waveguide formed by polymer spin-coating, realizing perfectly flat top surface of the buried bus waveguide. A serial of the vertically coupled polymer microring resonator showing excellent topology was fabricated with this strategy. The resonance phenomenon is oberved in a PMMA-based microring resonators using this fabricating strategy .The suggested approach is suitable to fabricate vertically coupled polymer micro-resonators.

A scheme for generating multi-wavelength fiber source based on erbium-doped fiber amplified spontaneous emission and spectrum sliced technique is demonstrated for potential applications in the dense-wavelength division multiplexing (DWDM) communication systems. A spectrum sliced multi-wavelength fiber source of 140 channels (extinction ratios larger than 13 dB) with 0.57nm channel spacing covering C-band and L-band is obtained by optimizing the erbium-doped fiber length and the pumping ratio of the scheme.

An actively mode-locked fiber ring laser for generating wavelength-tunable optical pulses is demonstrated. An Er-Yb doped waveguide amplifier is used as an optical amplifier, and a Fabry-Perot laser diode is used as a modulator in the fiber laser. Moreover, we add a variable optical delay line to control the cavity length for maintaining a constant repetition frequency and pulsewidth at different wavelengths. The optical side-mode-suppression-ratio is better than 33.5 dB over the wavelength-tunable range of 46 nm.

Incoherent broad-bandwidth cw-pumping at λ_p= 1.52 μm a singly resonant Ti:LiNbO₃ integrated optical parametric oscillator at λ_s= 3.94 μm, in the quasi-phase-matched non-degenerate Type I {eee} configuration, may efficiently generate ultra-coherent signal output by the convection-induced phase-locking mechanism. The incoherence of the pump is absorbed by the idler wave at λ_i = 2.47 μm, propagating at the same group velocity v_i=v_p = O.4557c, while the signal propagating at v_s=O.4455c becomes highly coherent. In such an integrated waveguide configuration one obtains signal spectral widths smaller than 5 x 10 ^-4 times the pump spectral width, and a reduction of the average signal intensity fluctuations by less than a factor 10^-4.

A novel fiber ring laser technique, which covers both C- and L-bands, with the function of wavelength tunability and single-longitudinal-mode oscillation, is proposed and demonstrated experimentally. We propose a two-stage hybrid amplifier, which consists of a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA) with cascade configuration, for the gain profile to achieve C- to L-band (1540 to 1610 nm). A saturated-absorber-based autotracking filter, which composes of an unpumped erbium-doped fiber (EDF) and an optical reflected mirror (ORM), is employed to provide fine mode restriction and guarantee the single-frequency operation. The unpumped EDF must use shorter length to retrieve the stabilized single-frequency operation while the EDF length is between 0.5 to 1 m long. The effectively operation range is from 1542 to 1618 nm. The maximal output power of 5.7 dBm is retrieved at near 1577 nm, and the output power will drop to 3.7 and -0.32 dBm at 1604 and 1616 nm, respectively. The SMSR can be up to 53.2 dB/ 0.05 nm at around 1577 nm. The performance of output power of > 2.1 dBm, power stability of ≤ 0.02 dB, wavelength variation of ≤ 0.01 nm and side-mode suppression ratio (SMSR) of > 31 dB / 0.05 nm has been demonstrated for this single-frequency fiber laser over the wavelength range of 1550 to 1608 nm. The linewidth (RF) spectrum of the proposed structure has also been studied.

The intensity modulation (IM) of a hybrid soliton pulse source (HSPS) utilizing linearly chirped Gaussian apodized fiber Bragg grating is described using electric field approach. The HSPS is modeled by a time-domain solution of the coupled-mode equations. It is shown that resonance peak spectral splitting (RPSS) in the IM spectra does not strongly depends on antireflection coated reflectivity, and gain compression factor. It is also found that RPSS disappears by choosing suitable liner chirp rate in Gaussian apodized FBG.

A theoretical and experimental study of femtosecond supercontinuum generation in short tapered fibers with micrometer diameter waist has been carried out. In our numerical model, an extended nonlinear Schroedinger equation that involves the parameters of dispersion coefficient and effective core area varying along the length of tapered fiber is used to describe the evolution of intense femtosecond pulses centred at 850 nm. As a result, the supercontinuum is generated due to enhanced nonlinear effects in a narrow waist; the octave spanning spectra are found in an optimum structure with only short waist length of 8.0 mm and diameter of 2 μm for an input average power of 100mW. Experimental verification using a femtosecond pulse from a Ti: sapphire laser is then made and compared with the numerical simulations.

Silicate glasses are among the best hosts for rare-earth ions, especially for the development of integrated optic amplifiers and lasers, due to their chemical robustness and adaptability to different waveguide fabrication process. Their application to the manufacturing of optical amplifiers, however, may be limited by the relatively narrow fluorescence bandwidth. Here the results of an in-depth study of the effect of an increasing content of alumina on the broadening of the emission bandwidth are reported. We synthesized and characterized a new set of glasses: their basic composition was of the type SiO₂ - Na₂O - CaO - Al₂O₃, with small percentages of P₂O₅ and K₂O. Alumina content was varied from about 1% to 20 mol%. An almost constant concentration of erbium oxide ( ~ 0.4 mol% ) was also present. The spectroscopic properties of these glasses, namely absorption and emission spectra, radiative and experimental lifetimes, are discussed. The characterization of the optical waveguides, fabricated in these glasses by ion-exchange method, is presented as well.

The criterions for determining the minimum number of arrayed waveguides are presented using the design theory of arrayed waveguide gratings (AWGs) and Fraunhofer diffraction principle for the optimal design of AWGs. In addition, some parameters such as the cross section of waveguides and the waveguide separation between adjacent waveguides are chosen to optimize the AWG structure to satisfy the performance specifications and to match the fabrication conditions in our laboratory. As an example to demonstrate the effectiveness of the proposed method, the simulated results of the designed 16 16 AWGs with silica-based sol-gel material were provided using the beam propagation method (BPM). And the effectiveness of optimal parameters, especially to the selection of the minimum number of arrayed waveguides on the performance of the AWG, has been perfectly verified by comparing the transmission spectra of the designed AWGs. The design methodology can serve as a simple and useful tool for the optimal design of AWG multiplexers/demultiplexers.

An organic-inorganic hybrid sol-gel material by using Tetraethylorthosilicate(Teos) and phenyltriethoxysilane(Phtes) as precursors was synthesized, and a planar optical waveguide was fabricated by using spin-coating on silicon substrate. A rib waveguide was formed by inductively coupled plasma (ICP). A relation between refractive index and composition of the precursors was obtained by M-line method; the optical loss of the planar waveguide was measured to be 0.23dB/cm at 632.8nm wavelength. A directional coupler was also realized.

With the assistance of a focused infrared beam heating, laser-fused fiber taper optical coupler features a significantly smaller package in comparison with conventional flame fused coupler and is readily to fit in modern compact devices. A design of optical fiber microcoupler with a fused length 200μm is presented. As an effort to search for optimal low loss coupling, optical properties of the micro-coupler were studied for various taper lengths from 1000 to 6000 μm as well as for different diameters in coupling region. Beam Propagation Method (BMP) was used to simulate the operation of microcoupler and the theoretical result was compared with measured property. An optimum design for a 3dB microcoupler as example was found at a taper length of about 1320 μm and coupling diameter of 14 μm with an excellent coupling efficiency.

A 32 × 32 arrayed waveguide grating (AWG) multiplexer operating around the 1550 nm wavelength has been designed and fabricated using fluorinated poly (ether ether ketone). The schematic layout is about 3.2×1.7 cm². For our AWG, the total loss of designed AWG multiplexer is calculated to be 4.5 dB. We fabricated the AWG multiplexer by spin coating, photolithographic patterning and reactive ion etching (RIE). The core size is 5×5 μm². The roughness of polymer surface was reduced by 20 nm using a remelting technique. The measured wavelength channel spacing of the fabricated AWG multiplexer is 0.796 nm and center wavelength is 1548 nm. The inserting loss of the AWG is 9.5 dB and crosstalk less than -20 dB.

In this letter, we present an improved coupled-mode theory applied to the optical-fiber directional coupler with a large overlap between the evanescent electromagnetic fields of two fibers. The analysis is based on a method of the quantum mechanics for the hydrogen molecule ion, where a new couple of local orthogonal modes corresponding to the fiber 1 and 2 are introduced. We may obtain the coupled-mode equations of local modes and the simple formulas of the output powers from coupler, in which, the overlap integral between the evanescent fields of two fibers is taken account of as an second order approximation. A new conclusion from this theory is that a coupling ratio with 100% can't be reached for a lossless coupler with a sufficiently small distance between two fibers.

Trapezoid index modulation (TIM) is introduced in long period fiber grating to decrease the index change. The coupled-mode equations of long period grating with trapezoid index modulation have been presented. The coupled interactions considered in these equations include not only the self-coupling of the core mode and the coupling between the fundamental core mode and the cladding modes, but also the self-coupling of the cladding modes. Compared with the long-period fiber grating with rectangle index modulation (RIM), the advantage of this novel grating is that it needs a smaller refractive index change. The value of refractive index change decreases with the increasing of the difference between the top width and the bottom width. When the difference between the top width and the bottom width is 30 μm, the refractive index change is only 80.2% of that of the long-period fiber grating with rectangle index modulation. Trapezoid index modulation can also be applied to the fiber Bragg and sampled grating to decrease the refractive index change. Sixteen uniform channels filtering with small refractive index change are also demonstrated.

This paper numerically studied few-mode TFBG using Volume Current Method (VCM). Polarization dependent scattering (PDS) at some tilted angle were studied and the distribution of radiation field was numerically simulated. calculated Numerical results showed that when incident wavelengths near the resonant one, the power difference between radiation field of S and P polarization was much small for each mode.

A bandwidth-tunable optical fiber Bragg grating filter with a large tuning range of 36 nm (1.8 - 37.8 nm) has been demonstrated, which represents, to the best of our knowledge, the broadest tuning range in reflection bandwidth of any optical fiber Bragg gratings that has been reported. The unique cantilever beam based chirp-rate tuning method used here may produce a changeable and uniform chirp rate along the length of the grating, with simultaneously keeping the center wavelength of the grating fixed. Based on this study, a spacing-tunable comb filter by using a sampled-chirped fiber Bragg grating has also been demonstrated. The change in spacing, with a tuning range up to 2.1 nm (1.2-3.3 nm), is also obtained by using the unique fiber grating chirp-rate tuning technique.

Effect of the cladding-mode coupling losses on the spectrum of multi-channel fiber Bragg grating (FBG) has been numerically investigated on the basis of the extended coupled-mode equations. It has been shown that there exists a reflection slope in the spectrum of both the intra- and inter-channels due to the existences of the cladding-modes. This slope could be larger than 1 dB when the induced index change is about 3x10^-3, which makes the channels especially the one at the shortest wavelength considerably asymmetric. For comparison, a 39-channel linearly chirped FBG with a channel spacing of 0.8 nm and a chromatic dispersion of -850 ps/nm has been designed and fabricated. The experimental results show good agreement with the numerical ones.

We propose the iterative layer-peeling algorithm (LPA) and the genetic algorithm (GA) to numerically optimize the fiber Bragg grating (FBG) design. Fabrication constraints are introduced in the design, such that the designed FBGs satisfy the spectral specifications and are easy to fabricate. The powerful numerical optimization permits removing the phase shifts in the FBGs, so that the gratings can be fabricated with conventional high quality holographic phase masks, without need for custom made phase masks. We introduce the inverse LPA, which is faster than the conventional transfer matrix method by two orders of magnitude for analysis of the FBGs. The synthesis of the FBG using the LPA and the analysis of the FBG using the inverse LPA can be iterated in a loop, which allows applying the constraints in both grating and spectrum spaces. The impact of the applied constraints and the convergence are analyzed. The GA is powerful for achieving the global optimum with a higher probability than that of the iterative algorithm and simulated annealing. Our GA is enhanced by a new Fourier series-based real-valued encoding to provide high degrees of freedom, and a rank-based fitness function. The new GA enables us to remove phase shifts in the gratings. All the designed WDM band-pass gratings with minimum dispersion are fabricated using the holographic phase mask without phase shifts. The experimental gratings with dispersion of ± 33 ps/nm in the 0.33 nm flat-top passband will be shown.

A simple dispersion measurement of fiber gratings using an un-balanced Michelson interferometer is proposed. A broadband source and an optical spectrum analyzer are used to scan the interference spectrum, and then the group time delay can be obtained rapidly by Fourier transform processing the interference spectrum. We measured the group time delays of a uniform-period FBG, a chirped FBG, an arrayed-waveguide grating interleaver, and a thin-film filter type OADM by an un-balanced Michelson and Mach-Zehnder interferometers, respectively. The experimental results excellent match the measured results of the optical network analyzer. The experimental repeatability is shown to be better than 1ps.

The refractive index profile of fiber preform is determined by using shearing interferometry and the fringe analyzing by phase-step method. The experimental results for two different shearing are presented.

A nondestructive technique for determining the refractive indices of the core and the cladding of step index optical fibers is presented. This method involves diffraction of plane wave from an optical fiber and application the iterative method on Fresnel-Kirchhoff integral, the refractive indices of the core and the clad obtained by this method are in good agreement with the results of other techniques.

The refractive index profile of optical fiber preform is measured by a nondestructive technique based on Talbot interferometry. In this technique the preform is placed between two ronchi ruling gratings of 10 lines/mm and the system is illuminated by an expanded and collimated beam of He-Ne laser. In this arrangement the 2nd grating is positioned in the Talbot image of the 1st grating and the preform axis is parallel to the gratings planes. To eliminate the effect of clad on the light beam deflection during the measurements, the preform is immersed in an index matching liquid. The phase front of the laser light over the 2nd grating can be monitored by analysis of the moire pattern which is formed over there. The analysis is done by means of 4-step phase shift technique. In this technique the second grating is moved in four steps of 1/4 of the grating vector and in each step the intensity profile of the moire pattern is recorded. The phasefront can be specified by using the recorded intensities. The refractive index profile of the preform can be calculated from the changes on phasefront while the preform is placed between the gratings respect to the case when it is absent. The whole procedure is automated and computer controlled by using a CCD camera to record the moire fringes, a stepper motor for linear translation of the 2nd grating and a code in MATLAB to control the system and measurements.

The Stimulated Raman scattering spectrum of polymethyl methacrylate(PMMA) plastic fiber was measured and the characteristic of the first order Raman spectrum was studied. The threshold, spectral bandwidth was measured. The formation mechanism of stimulated Raman scattering spectrum was analyzed. The first order Raman spectral bandwidth of plastic optical fiber is less and the volume is 2.8nm or so and it is not changed with the energy of pump light. The Raman frequency shift is 2563 cm-1. Compared with silica fiber, PMMA plastic fiber has smaller spectrum width, bigger Raman frequency shift and lower threshold of energy density. The energy transfer mechanism of silica fiber is the same with PMMA plastic fiber.

We propose a new method to enhance solitons' robustness to polarization-mode dispersion (PMD) in a long-haul conventional single-mode fiber (SMF). The method is based on the utilization of four-wave mixing (FWM) effects of two principal polarization states of optical pulses. An intensively bound state of solitons can be achieved when the FWM effect is taken into account. It is proved numerically that the solitons with FWM are more adaptive to polarization-mode dispersion than the ones without FWM in the standard fiber links.

When an input soliton pass through an optical amplifier, the soliton is boosted along together with the noise signal, and a random variation in the arrival time, called the Gordon-Haus effect, is induced. By the use of programmed chirp and a continuous dispersion profile, as envisaged by Kumar and Hasegawa, it is possible to produce a soliton like pulse called the quasi-soliton. This kind of pulse needs less peak power than the soliton and reduces the soliton-soliton interaction while keeps the benefits of optical solitons. Based on the results obtained by Kumar and Lederer for the Gordon-Haus effect on dispersion managed systems, we studied the influence of this effect in the quasi-soliton propagation. We have obtained an analytical solution for the mean square frequency shift. The expression obtained depends on the dispersion map parameters and the amplifier spacing. The results are shown for different values of the initial chirp.

The slow group-velocity femtosecond autosolitons in a dispersion flattened fiber is investigated, of which third-order dispersion is nil and fourth-order dispersion is existent. For the femtosecond pulse with the half of normal group velocity, it is found that the analytic solutions of the bright soliton and dark soliton. The magnitude of the fourth-order dispersion parameter is related to the higher-order nonlinearity coefficient. The peak power and the period of the soliton are determined by the magnitude of the fourth-order dispersion parameter and the higher-order nonlinearity coefficient.