带前置光放大的星间微波光子链路建模及性能优化

Modelling and optimization of optically preamplified inter-satellite microwave photonics links

考虑到星间微波光子链路中信号经远距离传输损耗大,利用前置光放大来提高链路的信噪比.建立了带前置光放大的星间微波光子链路模型,利用Bessel函数展开和Graf加法定理推导出了信噪比(SNR)的解析表达式.确定了对链路影响最大的主要噪声成分,在不同前置放大器增益的条件下,对调制器直流偏置相移进行了优化,使得在给定SNR要求下所需激光器输出光功率最小,并进一步分析了前置放大器增益对最小激光器输出功率和最优直流偏置相移的影响.数值仿真结果表明:随着前置放大器增益的增加,达到指定SNR所需的激光器输出功率变小,相应的最优直流偏置相移先减小后增大.对于QPSK调制信号,未加前置放大器时,SNR要达到15.56 dB(BER=10-9),激光器输出光功率至少为45 dBm,而前置放大器增益为15 dB时,只需要22.57 dBm.

An optical preamplifier is applied to increase the signal-to-noise ratio （SNR） of inter-satellite mi- crowave photonics links considering the large signal loss in distant propagation. An optically preamplified inter- satellite microwave photonics links model is established and an analytical expression of SNR is derived_with the method of expanding Bessel series and Graf addition theorem. The dominant noise components influence the link performance is confirmed, given the desired SNR, the direct current （DC） bias phase shift of modulator can be optimized so as to minimize the output power of laser diode （LD） under different gain of optical preamplifier, and the effects of the optical preamplifier gain on the minimum output power of LD and optimal DC bias phase shift is also examined. According to the numerical results, the output power of LD needed to achieve the required SNR decreases while increasing the gain of preamplifier, and the corresponding optimal DC bias phase shift decreases first and then increases. For QPSK modulation signal, the output power of LD needed to achieve the SNR of 15.56 dB （BER= 10-9） is at least 45 dBm without an optical preamplifier, while the output power of LD is required only 22.57 dBm as the gain of preamplifier is 15 dB.