| Summary: | 博士 === 國立交通大學 === 光電工程學系 === 101 === In order to meet the requirements of broadband multimedia services in the near future, FSAN (Full Service Area Networks) has been working on the new standard for next-generation passive optical network (NGPON) and named NGPON2, which can provide 40-Gbps capacity to support 1-Gbps data rate for each optical network unit (ONU), and extend the coverage range from 20-km to 100-km standard single-mode fiber (SSMF). However, current on-off-keying (OOK) based optical transceiver used in 2.5-Gbps GPON and 10-Gbps XGPON cannot be directly upgraded to support 40-Gbps NGPON2, since 40-Gbps OOK modulation will occupy near 40-GHz bandwidth and suffer from server limitation of chromatic dispersion and receiver noise, thus limit the SSMF transmission to be less than 5 km and cannot meet the NGPON2 requirement.
Recently, optical OFDM LR-PON with intensity modulation and direct detection (IMDD), which boasts to offer high spectral efficiency and flexible bandwidth allocation, has been attracted a lot of attention, and is very suitable for NGPON2. However, optical IMDD OFDM LR-PON has two hurdles needed to be crossed. The first one is the RF power fading, which limits the available bandwidth of the 1st passband of 100-km SSMF to be less than 3 GHz, while the second one is the subcarrier-to-subcarrier-intermixing interference (SSII), which generates in-band and out-of-band interferences to degrade the performance of received OFDM signal seriously.
In this thesis, we theoretically and experimentally analyze the RF power fading and SSII effects. Then, we proposed the bias-control low-chirp optical IMDD OFDM scheme, which can adjust the chirp of electro-absorption modulator (EAM) to increase the bandwidth of the first passband. The experimental results demonstrate a superior performance of 21-Gbps OFDM signal transmission over 100-km LR-PONs with spectrally-efficient 3 GHz by using a cost-effective and low-chirp EAM, and adopting the 128-QAM format and adaptive subcarrier preemphasis and post-equalizer.
We also analyze the responses of 20~100-km SSMF and find that secondary passbands can be used to increase the bandwidth. Thus, we develop the dynamic multi-band OFDM with adaptive modulation and bit-loading algorithm to make the best of bandwidth utilization. The experimental results successfully demonstrate a superior performance of at least 40-Gbps OFDM-signal transmission over 20~100-km LR-PONs, which is achieved by using a 10-GHz EAM and direct detection, and adopting the bit-loading algorithm.
Finally, we develop a novel SSII cancellation technique to estimate and eliminate SSII. For the first time, the SSII cancellation technique is experimentally demonstrated in an EAM-based IMDD multi-band OFDM transmission system. Since the characteristics of SSII are seriously affected by the chirp parameter, a simple constant chirp model, we found, cannot effectively remove the SSII. Therefore, a novel dynamic chirp model is developed to obtain better estimation and cancellation of SSII. Compared with 23.6% SSII cancellation by the constant chirp model, our experimental results show that incorporating the dynamic chirp model into the SSII cancellation technique can achieve up to 74.4% SSII cancellation and 2.8-dB sensitivity improvement in a 32.25-Gbps OFDM system over 100-km SSMF.
Based on our proposed dynamic optical multi-band OFDM with adaptive modulation and novel SSII cancellation technique, the optical IMDD OFDM LR-PON will not be limited by the RF power fading and SSII, and become a feasible and economical solution for NGPON2.
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