Use of state of polarization transparent scheme for polarization shift keying signal as optical phase conjugator to improve the transmission performance

Transmission characteristics of polarization shift keying (PolSK) signal is experimentally demonstrated in this work. Performance degradation due to transmission is improved using optical phase conjugation (OPC) technique. The wavelength converter based on the proposed state of polarization (SOP) transparent scheme for PolSK signal is effective to use it as mid-link optical phase conjugator and which is difficult to achieve using conventional wavelength conversion scheme. It is found that for fiber transmission, the performance of both of the orthogonal SOPs of the PolSK signal is different for their respective chirping characteristics which can be optimized to be similar using proposed OPC technique.     

Optical packet labeling based on simultaneous polarization shift keying and amplitude shift keying

We propose and demonstrate label encoding-swapping and transmission for an orthogonally labeled packet by use of a 10-Gbit/s amplitude shift keying payload and a 2.5-Gbit/s polarization shift keying (PolSK) label. A simple scheme for demodulating and demultiplexing the PolSK label based on an injection-locked Fabry-Perot laser diode is described. The extinction ratio of the newly added PolSK label can be precisely controlled and maintained after the intermediate node.     

All-optical wavelength conversion and multicasting for polarization-multiplexed signal using angled pumps in a silicon waveguide

We report all-optical wavelength conversion and multicasting for a 20 Gb/s (2×10 Gb/s) polarization-multiplexed (Pol-MUX) nonreturn-to-zero amplitude-shift keying signal using four-wave mixing (FWM) in a silicon waveguide. The temporal waveforms and eye diagrams demodulated from both polarization channels of the converted idler are clearly observed. Moreover, the wavelength multicasting of the Pol-MUX signal is also demonstrated by using two incident pumps.     

Performance analysis of FSO links under strong atmospheric turbulence conditions using various modulation schemes

Strong atmospheric turbulence is a major hindrance in wireless optical communication systems. In this paper, the performance of a wireless optical communication system is analyzed using different modulation formats such as, binary phase shift keying-subcarrier intensity modulation (BPSK-SIM), differential phase shift keying (DPSK), differential phase shift keying-subcarrier intensity modulation (DPSK-SIM), M-ary pulse position modulation (M-PPM) and polarization shift keying (PolSK). The atmospheric channel is modeled for strong atmospheric turbulences with combined effect of turbulence and pointing errors. Novel closed-form analytical expressions for average bit error rate (BER), channel capacity and outage probability for the various modulation techniques, viz. BPSK-SIM, DPSK, DPSK-SIM, PolSK and M-PPM are derived. The simulated results for BER, channel capacity and outage probability of various modulation techniques are plotted and analyzed.     

Reconfigurable photonic generation of microwave hybrid frequency/phase shift keying signals

A photonic approach for the generation of microwave hybrid frequency/phase shift keying (FSK/PSK) signal based on an integrated polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is proposed and demonstrated. In the scheme, the polarization modulator is employed to modulate the linearly polarized lightwave to generate an optical polarization-shift keying (PolSK) signal. Then the PolSK signal is sent to the PDM-DPMZM via a polarization controller to generate optical PSK signal. After photo-detection, a microwave hybrid FSK/PSK signal can be obtained. Simulations are conducted to verify the proposed scheme. As bit rate is set to 1 Gbit/s, a hybrid FSK/PSK signal with frequency of 10/15 GHz and phase shift of\(\pi\)is successfully demonstrated. Hybrid signals with 2-Git/s frequency shift and 1-Git/s phase shift are also implemented. The compression ratio of the generated signal is 25.5 and the main-to-sidelobe ratio is 11.2 dB. The generations of ASK, PSK and FSK signals are discussed, and the impact of the polarization extinction ratio is also analyzed.     

大气激光通信中的偏振调制性能

为充分证明偏振移位键控可有效抑制大气湍流等因素的影响这一观点,对目前大气激光通信系统中广泛采用的几种强度调制和偏振移位键控技术进行详细的分析研究,从各调制方式的功率利用率、带宽需求、传输容量以及差错性能几个方面进行对比。研究结果表明,各调制方式各有千秋,不能一概而论。综合各方面性能考虑,偏振移位键控较其他几种强度调制方式更具优越性,其具有最大传输容量、最小的带宽需求和接收误码率。由此可见,偏振调制方式更适合应用于大气激光通信。     

Polarization insensitive wavelength conversion based on dual-pump four-wave mixing for polarization multiplexing signal in SOA

We have theoretically investigated polarization insensitive all-optical wavelength conversion for polarization multiplexing signal based on dual-pump four-wave mixing (FWM) in a SOA. The simulation result shows that the polarization insensitive converted signal can be separated into two lightwaves without crosstalk when one of the two orthogonal data lightwaves is parallel with one pump and the SOA should be polarization insensitive. Several conditions which affect the conversion efficiency for polarization multiplexing signal are also discussed.     

基于半导体光放大器四波混频效应的多种调制格式的波长转换实验

实验报道了利用半导体光放大器(SOA)的四波混频(FWM)效应实现多种码型的波长转换.其中对于非归零(NRZ)信号实现了从单信道到三信道的多波长转换.调制速率从10 Gb/s到40 Gb/s均实现多波长转换.对于归零(RZ)信号分别实现了20 Gb/s和40 Gb/s的RZ格式的波长转换和40 Gb/s的载波抑制归零(CSRZ)格式的波长转换,利用光纤布拉格光栅(FBG)作为带陷滤波器消除共轭光和抽运光之间的串扰.对于非归零差分相移键控(NRZ_DPSK)信号分别实现了20 Gb/s和40 Gb/s的波长转换,利用实验室自制的光纤延时干涉仪进行NRZ-DPSK信号的解调.基于FWM效应的转换光的输出消光比大于7 dB,转换后消光比退化约为3 dB.     

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.     

Polarization insensitive wavelength conversion based on four-wave mixing for polarization multiplexing signal in high-nonlinear fiber

We have theoretically and experimentally investigated polarization insensitive of all optical wavelength conversion for polarization multiplexing signal based on four-wave mixing (FWM) in nonlinear optical fiber. Optical polarization multiplexing technique can be used to double the transmission bit rate by adding data on each of two orthogonal optical states. At the receiver side, the two orthogonal signals can be obtained by direct detection. The eye diagrams of the original signals have been probed and compared with the converted one in this experiment. The characteristics of the converted signal have been fully studied and a little crosstalk which leads a better corresponding eye diagram has been obtained after polarization demultiplexing.     

Simultaneous multichannel NRZ-to-RZ format conversion of 4-ASK signal based on phase-intensity hybrid modulation and dispersion compensation fiber

We propose and investigate a novel technique to realize non-return-to-zero （NRZ） to return-to-zero （RZ） format conversion of a multichannel 4-ary amplitude shift keying （4-ASK） signal. The proposed format converter composed of two modulators and a dispersion compensating fiber （DCF） is theoretically inves-tigated using numerical simulation as basis. Research shows that a 4-channel 20-Gb/s NRZ-4-ASK signal can be converted to a RZ-4-ASK signal simultaneously without wavelength shifting and signal quality degradation, with the converted signal multiplexed to 40 Gb/s.     

Wide-Band Optical Wavelength Converter Based on Four-Wave Mixing Using Optimized Semiconductor Optical Amplifier

We have simulated 50 nm up and down wavelength conversion for a non-return to zero differential phase shift keying (NRZ-DPSK) signal using four-wave mixing in an optimized semiconductor optical amplifier (SOA) at 10 Gb/s for the first time. For this we optimized the SOA parameters to achieve sufficient quality and enhancement in four-wave mixing effect. This can be done in such a manner that the SOA never saturates and produces maximum four-wave mixing signals with minimum gain fluctuations. The quality of the converted signal is best before the saturation of SOA. Finally, we have numerically simulated cascaded wavelength converters up to 1300 km transmission distance.     

Simultaneous format conversion of parallel multichannel based on FWM in symmetric highly nonlinear fiber loop

A parallel multichannel format conversion scheme for elastic optical networking based on four wave mixing （FWM） in symmetric highly nonlinear fiber loop （S-HNLF-L） is proposed and the performance is evaluated and discussed. Parallel four channels format conversion from quadrature phase shift keying （QPSK） to binary phase shift keying （BPSK） signals at 40 Gb/s is theoretically analyzed and simulated. The results are helpful for the format-adaptive elastic optical networks.     

Wide-Band Optical Wavelength Converter Based on Four-Wave Mixing Using Optimized Semiconductor Optical Amplifier

We have simulated 50 nm up and down wavelength conversion for a non-return to zero differential phase shift keying (NRZ-DPSK) signal using four-wave mixing in an optimized semiconductor optical amplifier (SOA) at 10 Gb/s for the first time. For this we optimized the SOA parameters to achieve sufficient quality and enhancement in four-wave mixing effect. This can be done in such a manner that the SOA never saturates and produces maximum four-wave mixing signals with minimum gain fluctuations. The quality of the converted signal is best before the saturation of SOA. Finally, we have numerically simulated cascaded wavelength converters up to 1300 km transmission distance.     

Optical labeling scheme using polarization shift keying/vestigial sideband carrier-suppressed return-to-zero orthogonal modulation

We propose and experimentally demonstrate a polarization shift keying label and a vestigial sideband carrier-suppressed return-to-zero payload scheme for a 43 Gbit/s all-optical label switching network. This scheme has a narrow channel bandwidth and a low penalty due to polarization mode dispersion impairments, which confirm it as a candidate technique for the next generation of optical networks.     

Numerical analysis for four-wave mixing based wavelength conversion of differential phase-shift keying signals

We numerically investigate the main constrains for high efficiency wavelength conversion of differential phase-shift keying （DPSK） signals based on four-wave mixing （FWM） in highly nonlinear fiber （HNLF）. Using multi-tone pump phase modulation techniques, high efficiency wavelength conversion of DPSK signals is achieved with the stimulated BriIlouin scattering （SBS） effects effectively suppressed. Our analysis shows that there is a compromise between conversion efficiency and converted idler degradation. By optimizing the pump phase modulation configuration, the converted DPSK idler＇s degradation can be dramatically decreased through balancing SBS suppression and pump phase modulation degradation. Our simulation results also show that these multi-tone pump phase modulation techniques are more appropriate for the future high bit rate systems.     

Orthogonal polarization shift keying label rewriting method in an all-optical label switching network

A novel polarization shift keying label rewriting scheme in 43 Gbit/s all-optical label switching network by synchronous polarization modulation is proposed and experimentally demonstrated. The old label can be changed to a new one by just one single step without a label erasure process, which can simplify the network node structure.     

All-optical reconfigurable multi-logic gates based on nonlinear polarization rotation effect in a single SOA

We demonstrate an all-optical reconfigurable logic gate based on dominant nonlinear polarization rotation accompanied with cross-gain modulation effect in a single semiconductor optical amplifier (SOA).Five logic functions,including NOT,OR,NOR,AND,and NAND,are realized using 10-Gb/s on-off keying signals with flexible wavelength tunability.The operation principle is explained in detail.By adjusting polarization controllers,multiple logic functions corresponding to different input polarization states are separately achieved using a single SOA with high flexibility.     

Performance improvement of 10-Gb/s XGM wavelength conversion by using polarization control structure

By utilizing the cross polarization modulation effect in semiconductor optical amplifier(SOA), the extinc tion ratio of cross gain modulation(XGM)wavelength conversion was enhanced, the pattern effect was significantly reduced,and the power penalty of wavelength conversion was reduced by 5 dB simultane-ously. Furthermore, by adjusting the settings of polarization controllers, both inverted and non-inverted wavelength conversion can be achieved right in the same wavelength converter.     

基于光子晶体光纤中FWM的4×10 Gbit/s全光波长转换

 多波长转换对于增强波分复用光网络的灵活性具有重要意义。基于光子晶体光纤中的多四波混频原理,实现了4×10 Gbit/s全光波长转换,深入调查了泵浦功率、光纤长度、信号光与泵浦光偏振失配对波长转换信号质量的影响。结果表明：当泵浦光功率从6 dBm到20 dBm增长的过程中,转换信号Q因子随泵浦光功率增大而增大,最大为82.01,光纤长度从50 m到120 m变化过程中,转换信号Q因子最大为57.41,而随着信号光与泵浦光偏振失配角的增大,转换信号Q因子逐渐降低,当失配角大于60°后,转换信号质量急剧下降。