非線性失真補償應用於載波間干擾消除於長距離正交分頻多工被動光網路系統

Abstract

隨著未來客戶對頻寬服務需求的增加，被動光網路被視為非常適合的解決方案, 他可以提供很高的頻寬給用戶。 近來，使用正交振幅調變格式於正交分頻多工非常適合作為長距離被動光網路技術的解決方案，因為它可以藉由低頻寬需求的元件提供很高的傳輸速率。此外，具成本效益的強度調變和直接偵測構想是首選，舉例來說，只使用電吸收調變雷射和單一個PIN光接收器。然而，強度調變直接偵測正交分頻多工系統有許多挑戰，例如:power fading和色散造成的失真。除此之外，色散造成的非線性失真，可近似成二次的子載波間互相干擾，它將會使訊噪比變差。因此，一個最新的子載波間干擾消除技術被提出，它可以提升強度調變直接偵測系統中的訊噪比和接收端敏感度。此外，由於正交分頻多工訊號的峰值功率和平均功率的比率很高，使得強度調變直接偵測的系統的OMI將被限制以避免過多的光強度調變器所造成的非線性。 在這篇論文中，一個最新的非線性失真補償於子載波間干擾消除技術被提出並首次於實驗中驗證由電吸收調變器強度調變直接偵測正交分頻多工傳輸系統。而電吸收調變器非線性造成的非線性失真被考慮於我們所提出子載波干擾的模型中。因此,電吸收調變器轉換時的非線性和色散所共同造成的非線性失真可以於接收端即時估計。因此，我們系統的OMI可以增加到更好的效能。而且，子載波間干擾消除在實驗中驗證可以達到5-dB的訊噪比提升和3.3-dB的敏感度提升(FEC限制線上)藉由非線性失真補償模型用於子載間消除技術可以達到36.3-Gbps傳輸速率的正交分頻多工系統傳輸150公里未補償標準單模光纖。

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.