We investigate second-harmonic generation (SHG) from aperiodic optical superlattices in the regime of pump depletion, where the influence of typical fabrication errors which can be introduced by the random -fluctuation of the thickness for each domain in the simulation is considered according to the actual case. It is found that both the SHG conversion efficiencies calculated in undepleted pump approximation (UPA) and an exact -solution decrease when the fluctuation gets larger. However, the decreasing degree is related to the wavelength of the fundamental wave (FW), and the longer the FW wavelength, the lesser the corresponding conversion efficiency reduction. A relative tolerance with respect to SHG conversion efficiency calculated in UPA and exact solution is defined in a previous work, in which a typical model based on the relative tolerance curves is proposed to estimate the SHG conversion efficiency. The simulation results exhibit that the relative tolerance curves are basically coincident with the standard curve when the random fluctuation is very small (typically below 1%). However, as the fluctuation increases, the relative tolerance curves exhibit a large deviation from the standard one, and the deviation is also determined by the wavelength of the FW.

实验验证了一种结构简单、变换效率高的可调谐偏振不敏感全光波长变换器。光子晶体光纤由于其特殊的纤芯结构，能够保有较高的双折射效应。通过调节抽运光的偏振态,使之与光子晶体光纤的双折射轴成45°夹角入射,则此时信号光与抽运光在光子晶体光纤中进行简并四波混频过程时，其变换效率对信号光偏振态的随机变化不敏感,闲频光输出功率几乎保持不变。实验结果表明,所搭建的全光波长变换器在25 nm变换范围内,闲频光偏振敏感度低于0.6 dB,变换效率优于-15 dB(峰值可达-7.6 dB), 输出闲频光的光信噪比优于40 dB，长时间工作性能稳定，可实现开机自启动，是一种实用性强的偏振不敏感全光波长变换器。

A switchable multiwavelength laser with a continuously tunable spacing is proposed and illustrated based on cascaded interactions of the second harmonic and difference-frequency generations in an aperiodically poled MgO-doped lithium niobate (MgO:APPLN) waveguide. The wavelengths and wavelength spacings of the four outputs are continuously varied and controlled by changing the two input pump wavelengths and spacings within a 3-nm flattop bandwidth of MgO:APPLN. In addition, the switchable states of the four outputs can be selected by inputting proper powers of the two pumps. The number of output wavelengths can also be increased by choosing the proper APPLN structure, the total length of MgO:APPLN, and higher powers of input pump lights.

We propose a scheme for mitigating Rayleigh backscattering noise and demodulating differential phase-shift keying (DPSK) signals in wavelength-division-multiplexed passive optical networks (WDM-PONs) with injection-locked Fabry-Perot laser diodes (FP-LDs). Signal demodulation and wavelength conversion are simultaneously realized on the basis of the frequency deviation and red shift of longitude modes in the FP-LDs. Experimental results demonstrate that the demodulation and wavelength conversion of 2.5-Gb/s DPSK signals are achieved. A power penalty of about 1.6 dB at a bit error rate of 10-9 is measured after transmission over 25-km single mode fiber.

We propose a wavelength conversion scheme for chaotic optical communications (COC) based on a Fabry-Perot (FP) laser diode. The FP laser, as a wavelength converter, is injection-locked at one of longitudinal modes by an external continuous-wave (CW) light. The simulation results demonstrated that the chaos masked signal at wavelength \lambda1, which corresponds to the other longitudinal mode of FP laser, can be converted to the injection-locked mode (wavelength \lambda 2) based on cross-gain modulation in a closed-loop COC link. A 1.2-GHz chaos masked sinusoidal signal is successfully decoded with signal-to-noise ratio (SNR) beyond 8 dB in 15-nm wavelength conversion range, and the effects of SNR on the signal frequency and conversion span are also investigated.