The relation between the phase shift and the mean optical power (MOP) output from a delay-line interferometer (DLI) port applied for phase-shift keying (PSK) signal demodulation is proven of a cosine law irrelevant to signal modulation condition. The variation amplitude of the MOP is proportional to the transition duration of the modulation pulses. This phenomenon is interpreted as the result of the statistical and waveform characteristics of the PSK. The conclusions verified by simulation and experiment are generalized to other modulation formats and then applied to phase detuning monitoring, delay time judgment of DLI, and independence of modulation data assessment.

A novel architecture of converged radio-over-fiber (RoF) and wavelength division multiplexed passive optical network (WDM-PON) system, namely RoF-WDM-PON, is demonstrated. 20-GHz 1-Gb/s radio frequency (RF) signals and 1-Gb/s baseband (BB) signals are simultaneously generated and transmitted using optical carrier suppression (OCS) modulation techniques. The proposed scheme is compatible with the conventional RoF and PON system. 25-km single-mode fiber (SMF) transmission is successfully achieved.

A method of multi-channel receiving for high bit rate heterodyne direct-detection optical orthogonal frequency-division-multiplexing (OOFDM) system is proposed to reduce the sampling rate demand of analog-to-digital converter (ADC). The sampling rate of ADCs can be reduced to 1/N that of the original signal bandwidth in an N-channel receiving system. Aided by a succeeding digital signal processing (DSP) at the receiver, aliasing free signal can be recovered. A back-to-back experimental result is given for a 4-channel system, based on which, a down conversion process for heterodyne can be reduced. The signal rebuilding algorithm is given and analyzed in its complexity and noise tolerance.

A cost-effective method of multi-receiver optical orthogonal frequency-division multiplexing (OOFDM) system is proposed to reduce the requirement for the speed of the receiver and the size of fast Fourier transform (FFT). The sampling rate of analog-to-digital converters (ADCs) can be reduced to 1/N of the original signal bandwidth in an N-receiver system. Aided by signal predistortion at the transmitter, aliasing-free signal can be retrieved independently and directly at the low speed receivers. A back-to-back experimental result is given for a two-receiver system. The effect of the electrical filters added before the ADC is studied and the analysis for filters optimization is given.

利用光纤无源器件制作了光学90°混频器,实现了混频器90°相移的精确控制与监测,稳定时间达到12 h以上,利用此混频器研究并实现了数字相干光检测。对差分相移键控(DPSK)信号光和本振光进行混频,高速模数转换器(ADC)对混频后的基带信号采样,利用离线数字信号处理算法进行光载波相位估计和色散补偿,利用有限冲击响应(FIR)数字滤波器补偿了经过90 km光纤传输的8 Gb/s速率DPSK信号的色散失真,测量无误码。

提出并实现了用相干自混频方法监测马赫-曾德尔调制器(MZM)零偏置点漂移, 将同一光源所产生的部分未调制光和调制后的光进行混频, 利用混频光功率的最大最小值之比作为监测量监测。相比于监测信号光平均光功率的方法, 可使±5%偏置点漂移下的灵敏度从0.02 dB提高到0.3 dB。利用设计完成的硬件反馈控制系统进行了多次实验, 讨论了影响系统工作的各种因素及相应的解决办法, 结果表明该方法工作有效。

We have studied a function-lock strategy for all-optical logic gate (AOLG) utilizing the cross-polarization modulation (CPM) effect in a semiconductor optical amplifier (SOA). By monitoring the power of logic light, the strategy realized controllable methods to capture OR and NOR functions and switch between them. The strategy has been successfully applied in experiment with 10-Gb/s not-return-to-zero (NRZ) signals, which has a high success-rate above 95% and ensures the high extinction ratio of result light above 11.4 dB. Every step in the strategy has definite numeric evaluation, which provides the potential of automatic implementation.

By utilizing the cross polarization modulation effect in semiconductor optical amplifier (SOA), the extinction 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 simultaneously. Furthermore, by adjusting the settings of polarization controllers, both inverted and non-inverted wavelength conversion can be achieved right in the same wavelength converter.