Nonlinear distortion compensation employing SSII cancellation in long reach OFDM PON system
|關鍵字:||長距離被動光網路;正交分頻多工技術;子載波互相干擾;long reach PON;OFDM;SSII|
With the increasing of customer needs for broadband services in near furture, passive optical network is considered to be the most promising candidate that can provide high bandwidth to users. Recently, orthogonal frequency-division multiplexing (OFDM) with quadrature amplitude modulation (QAM) format has become one of the most promising candidates in long-reach passive optical network (LR-PON), because it can provide high capacity with the low-bandwidth requirement of components. Besides, the cost-effective intensity modulation and direct-detection (IMDD) schemes are preferred, for instance, using an electro-absorption modulated laser (EMLs) and a single PIN photo-detector. However, there are several challenges in IMDD OFDM systems, such as power fading and dispersion-induced distortion. Besides, dispersion-induced nonlinear distortion, which is approximately modeled as the 2nd-order subcarrier-to-subcarrier intermixing interference (SSII), will worsen the signal-to-noise ratio (SNR). Hence, a novel SSII cancellation technique has been proposed to improve SNR and receiver sensitivity of the IMDD OFDM system. Additionally, due to inherently high peak to average power ratio of OFDM signals, optical modulation index (OMI) of an IMDD system will be sacrificed to avoid severe nonlinearity of optical intensity modulators. In this work, a novel nonlinear distortion compensation employing SSII cancellation technique is proposed and experimentally demonstrated in an EAM-based IMDD OFDM system for the first time. The EAM nonlinearity-induced nonlinear distortion is regarded as part of SSII in the proposed model, so that it can be compensated by the calculated theoretical SSII. Thus, the EAM nonlinearity- and dispersion-induced nonlinear distortion can be eliminated at the receiver simultaneously. Accordingly, the OMI of our system could be increased to reach better performance. Moreover, the SSII cancellation is demonstrated to achieve maximum 5-dB SNR improvement and 3.3-dB sensitivity improvement at FEC limit are demonstrated by incorporating the Nonlinear distortion compensation model into the SSII cancellation technique in 36.3-Gbps OFDM system over 150-km SSMF.