基于反射式半导体光放大器的OFDM-PON上行通道吞吐潜力

Throughput Potential of Orthogonal Frequency Division Multiplexing Passive Optical Network Uplink Based on Reflective Semiconductor Optical Amplifiers

对正交频分复用无源光网(OFDM-PON)的上行通道物理层的吞吐量进行研究。OFDM-PON在光网络单元(ONU)端采用反射式半导体光放大器(RSOA)作为无色光源,实现双边带光强度调制,并在光线路终端(OLT)采用加半导体光放大器(SOA)前置放大的PIN光二极管做直接检测。基于一个RSOA的窄带相干积分模型,采用对有源区中载流子速率方程和光波传播方程的微扰解对RSOA的动态电光调制特性和频率啁啾特性进行理论与实验探讨,证明RSOA具有低通调制特性,其3dB截止频率关联于偏置电流和输入光功率。利用RSOA的频率啁啾和SOA的高通增益特性,并将RSOA与中心波长蓝移的光滤波器级联,实现光学均衡,把上行通道的3dB截止频率从1.5GHz扩展到2.2GHz。进一步采用自适应比特加载的调制格式,使通过一个RSOA的上行数据吞吐量可以达到4Gb/s以上,则一个包含10个ONU的OFDM-PON的上行吞吐量可达到40Gb/s。

The uplink physical throughput potential of orthogonal frequency division multiplexing passive optical network （OFDM-PON） is discussed. Reflective semiconductor optical amplifiers （RSOAs） are used in optical network units （ONUs） as the colorless resources to produce the dual-sideband intensity modulation, and a PIN photodiode with semiconductor optical amplifier （SOA） as pre-amplifier is used in optical line terminal （OLT） to complete direct detection. Based on a coherent narrowband integral model of RSOA, the weak perturbation solutions of the carrier rate equation and the wave propagation equation are used to investigate the RSOA＇s dynamic electro-optical modulation behavior and frequency chirp characteristic theoretically and experimentally. It is proved that the RSOA is of low-pass modulation characteristics, and its 3 dB cut-off frequency is related to the bias current and the inject optical power. The optical equilibrium is achieved and the 3 dB cut-off frequency of the uplink can be promoted from 1.5 GHz up to 2.2 GHz by taking advantage of RSOA＇ s optical frequency chirp and the high-pass optical gain characteristic of SOA, and cascading a blue-shifted optical band-pass filter with RSOA. Furthermore, by utilizing the adaptive bit loading modulation, the data throughput in one RSOA-based uplink can reach 4 Gb/s and above, which means that the total uplink throughput of an OFDM-PON with ten RSOA-based ONUs can achieve 40 Gb/s.