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We propose and experimentally demonstrate a novel scheme which can simultaneously realize wavelength-preserving and phase-preserving amplitude noise compression of a 40 Gb/s distorted non-return-to-zero differential-phase-shift keying (NRZ-DPSK) signal. In the scheme, two semiconductor optical amplifiers (SOAs) are exploited. The first one (SOA1) i...
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Citations
... Compared with the interferometer structure, the new quantumwell SOA (QW-SOA) and quantum-dot SOA (QD-SOA) can regenerate signals with stable structure and can be integrated on a chip. However, its manufacturing process is complex, which makes it unable to be widely used [19,20]. Therefore, further research is still essential to improve the 3 R regeneration scheme used for DPSK signals. ...
This paper presents experimental demonstration of an all-optical 3 R (re-amplification, re-shaping, re-timing) regeneration scheme for differential phase-shift keying (DPSK) signals, which consists of a clock recovery module and a phase-regeneration module. The clock recovery module is based on a mode-locked fiber laser, and the optical clock is extracted with low timing jitter of 29 ps from a degraded 10 Gb/s DPSK signal. The phase regenerator consists of a one-bit delay interferometer demodulation stage and a semiconductor optical amplifier in which cross-phase modulation and nonlinear polarization rotation occur simultaneously. The results show that, after 3 R regeneration, the receiver sensitivity is improved by more than 1.6 dB for a bit error rate of 1 E-9.
... Semiconductor optical amplifiers (SOAs) show significant promise in all-optical signal processing, such as wavelength conversion [1][2][3], logic function [4][5][6], format conversion [7][8][9] and signal regeneration [10][11][12], owing to various nonlinearities, small-footprint, cost-effectiveness, low-driving requirements and ability for on-chip processing. However, the SOAs performance for highdata-rate (greater than 10 Gb/s) operation is limited by the intrinsic carrier lifetime, which is on the order of a few hundred picoseconds in typical SOAs. ...
In this paper, we demonstrated a novel physical mechanism based on the well-barrier hole burning enhancement in a quantum well (QW) semiconductor optical amplifier (SOA) to improve the operation performance. To completely characterize the physical mechanism, a complicated theoretical model by combining QW band structure calculation with SOA’s dynamic model was constructed, in which the carrier transport, interband effects and intraband effects were all taken into account. The simulated results showed optimizing the thickness of the separate confinement heterostructure (SCH) layer can effectively enhance the well-barrier hole burning, further enhance the nonlinear effects in SOA and reduce the carrier recovery time. At the optimal thickness, the SCH layer can store enough carrier numbers, and simultaneously the stored carriers can also be fast and effectively injected into the QWs.
... Semiconductor optical amplifiers (SOAs) are widely used in wavelength conversion [1][2][3][4], logic functions [5][6][7], format conversion [8][9][10], and signal regeneration [11][12][13][14], owing to the advantages of various nonlinearities in SOAs, small footprints, and the ability for on-chip processing. However, their applications for high bitrates are limited by the intrinsic slow recovery time. ...
... Wavelength-converting format conversion from PSK to OOK is also required. Furthermore, while transmitting in LHBNs, due to chromatic dispersion, amplified spontaneous emission (ASE) from optical amplifiers, and other possible effects, the PSK signal may still be degraded [13]. If the distorted PSK signal is directly demodulated to the OOK signal, the amplitude noise and the phase noise of the distorted PSK signal will be transferred to the amplitude noise of the OOK signal. ...
... To characterize ultrafast gain recovery, intraband effects, such as spectrum hole burning, carrier heating, and carrier cooling, should be taken into account. We have developed a comprehensive QW-SOA model, including the band structure calculation and rate equations [13,14]. ...
We propose a scheme to realize gain recovery of the order of a few picoseconds in a typical quantum well semiconductor optical amplifier (QW-SOA) using a pump signal with amplitude dips. In the scheme, the gain recovery is determined by the fast carrier density depletion and carrier temperature heating processes. The ultrafast gain recovery is numerically verified by a completed model combining the QW band structure calculation with rate equations in the QW-SOA. In practice, a pump signal with amplitude dips can be partly characterized by a non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal generated by a Mach–Zehnder modulator. Therefore, we experimentally demonstrate 40 Gb/s wavelength-converting and regenerative format conversion from NRZ-DPSK to return-to-zero on–off keying (RZ-OOK), which may be a key function to connect different kinds of modulation formats at gateway nodes between long-haul backbone networks and metro area networks.
... 40 Gb/s 的 NRZ-DPSK 信号全光 2R 再生 [15] , 并对 SOA 的性能进行了优化. 本文在分析基于 SOA 的 交叉增益调制 (XGM) 获得反码信号并利用 XGC 效应实现光 2R 再生的基础上, 提出了利用 SOA 瞬态交叉相位调制效应 (T-XPM) [14] 获得良好的 反码信号、改进基于 SOA-XGC 效应的 2R 再生方 法, 首次实现了基于 SOA 的有误码率改善支持的 100 Gb/s 归零码 RZ 恶化信号的全光 2R 再生 [16] . ...
Quality of optical signal can be severely degraded after a long distance optical fiber transmission, therefore all-optical 2R (re-amplification, re-shaping) regeneration is required for its low power consumption and good potential of high-speed operation. Semiconductor optical amplifier (SOA) is a very promising candidate for regeneration due to its relatively low nonlinear switching power threshold and possibility of integration. However, speeds of the existing 2R schemes based on SOAs are limited by pattern effects introduced by the long carrier recovery time. So far, most of experimental results for SOA-based regeneration schemes have been limited to 40 Gb/s, only a few demonstrations at 80 Gb/s are available. An effective method to cope with the pattern effects in the SOA is to employ cross gain compression (XGC) effect. Simultaneously injecting two signals of different wavelengths with complementary logics and balanced powers into the SOA leads to an almost constant ability to make the XGC effect intrinsically immune to the pattern effects. Previously, 2R experimental results were demonstrated at 10 Gb/s and 40 Gb/s with XGC respectively, but no further results of higher speed have been presented to date. In this study, we improve the previous two-stage configuration for XGC-based regeneration by introducing a transient cross phase modulation (T-XPM) in the first SOA for generating the high-quality logic-inverted signal, which, as we find, is essential to facilitating the high-speed XGC operation in the next SOA. Firstly, a numerical model of the photon-electron dynamics in an SOA is built with considering the ultrafast intra-band processes, amplified spontaneous emission (ASE) noise at multiple wavelengths, and device segmentation along propagation direction. The quality of the logic-inverted signal with different offsets of the filter wavelength for T-XPM is studied with the model. It is found that the appropriate blue-shift detuning of the filter wavelength greatly helps to improve the quality of the logic-inverted signal. In experiment, the influence of the filter offset on the quality of the logic-inverted signal is also investigated systematically and the best quality and the largest eye-opening of the logic-inverted signal are achieved with a blue-shift of 0.72 nm, which are consistent with the simulation result. With the best logic-inverted signal, XGC effect is deployed in the second SOA. Effective reduction of the amplitude fluctuation can be observed by comparing the eye diagrams of the input degraded with output regenerative signals. Bit error rates (BERs) are also measured for all four tributaries of the degraded and the regenerated signals and the receiving sensitivity at a BER of 10-9 is improved by 1.7-2 dB. Such results show that the XGC-based 2R regeneration scheme is effective even at a speed of as high as 100 Gb/s with the help of high-quality logic-inverted signal. Degraded signals at different wavelengths (from 1535 nm to 1555 nm) are successfully regenerated with Q-factor improvement, demonstrating the wavelength-independent regeneration capability of the XGC-based 2R regenerator.
Quantum-well semiconductor optical amplifiers (QW-SOAs) have been widely used in all-optical signal processing functions because of their various nonlinear effects. For different optical signal processing functions, the requirements for performance of the QW-SOAs are different, and nonlinear effects of the QW-SOAs should be controlled selectively. Engineering nonlinear effects of QW-SOA is very important for different applications in optical signal processing. Here, a comprehensive QW-SOA model by combining the QW band structure calculation with the dynamic model is established to connect the structure parameters with the nonlinear effects of QW-SOA. Those characterized parameters of the QW-SOAs, such as gain coefficient, differential gain coefficient, refractive index change, differential refractive index change, linewidth enhancement factor, third-order susceptibility and polarization dependent gain, are used to characterize the nonlinear effects, and are calculated with different structure parameters based on this developed model. Take the wavelength conversion based on cross gain modulation effect and four wave mixing effect as examples, the structure parameters of the QW-SOAs are optimized for engineering the nonlinear effects and achieving the best output performance. This theoretical work presents a guide for choosing the optimized structure parameters while fabricating the QW-SOAs for different optical signal processing functions
We experimentally investigate the phase-preserving amplitude regeneration based on the optical phase conjugation process in a polarization-selected orthogonal-pump semiconductor optical amplifier (PSOP-SOA) subsystem, enabling the signal-to-noise ratio (SNR) improvement of 1.84dB for QPSK signals.
