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本文报导采用国产器件建立的1.5μm波段外差FSK相干光纤通信实验系统。系统中发送光源和本振光源分别采用InGaAsP自聚焦棒(GRINROD)外腔和光栅外腔半导体激光器,笔者对大频偏、单滤波/包络检波系统和小额偏、单滤波/差分—延迟检波系统进行了研究。在这两个系统中,中频(IF)经AFC分别稳定在1.05 GHz4±1 MHz和810MHz±1MHz。140Mbit/s信号经6.4公里单模光纤(损耗约为0.62dB/km)传输后,经光电混频、预放、中放和中频滤波后进行包络检波或差分一延迟检波,检波后的信号经基带放大和基带滤波后进行取样、判决。经测量:系统的误码率BER≤10~(-8)(半小时观测时间),系统的接收灵敏度为-37.7dBm(BER≤10~(-9),系统的损耗余量为24.92dB。实验中,笔者对IF电路进行了优化设计,同时,利用中频谱对发送光源的调频特性进行了深入的研究。实验结果表明,只要选择合适的GRINROD外腔的尺寸,可以得到不同线宽的激光源,进而可以建立不同相干程度的相干光纤通信系统。
This article reports a 1.5μm band heterodyne FSK coherent optical fiber communication experiment system established by domestic devices. In this system, the InGaAsP self-focusing rod (GRINROD) external cavity and the grating external cavity semiconductor laser are respectively used as the transmitting light source and the local oscillation light source. The large offset, single filter / envelope detection system and small offset, single filter / differential- Detection system was studied. In both systems, the intermediate frequency (IF) is stabilized at 1.05 GHz4 ± 1 MHz and 810 MHz ± 1 MHz, respectively, via AFC. 140Mbit / s signal after 6.4 km single-mode optical fiber (loss of about 0.62dB / km) transmission, the optical mixing, pre-amp, intermediate and IF filter envelope detection or differential delay detection, the detected signal After the baseband amplification and baseband filtering sampling, verdict. The measured BER of the system BER≤10 ~ (-8) (half-hour observation time), the receiving sensitivity of the system is -37.7dBm (BER≤10 ~ (-9), the system’s margin of loss is 24.92dB. In the experiment, the author has carried on the optimized design to IF circuit, at the same time, has carried on the thorough research to the frequency modulation characteristic of sending the light source using the middle frequency spectrum.The experimental result indicated that as long as selects the suitable GRINROD external cavity size, Source, which in turn can establish coherent optical fiber communication systems with different degrees of coherence.