Researches On The Key Technologies Of Channel Impairments Inhibition In Direct Detection OFDM-PON

With the development of data traffic, especially for the images and videos, the pursuit of large-capacity network results in the 40 or 100 Gbps data rate 100 km access distance optical transmission system being the main trend for the next generation passive optical network (PON). Orthogonal frequency division multiplexing passive optical network (OFDM-PON) possesses significant research value, since the features of good anti-dispersion properties, high bandwidth, high frequency spectrum efficiency, flexible bandwidth allocation, and flexible scalability. Compared with coherent optical orthogonal frequency division multiplexing, direct detection (DD) OFDM is very attractive for next generation high capacity PON, because of its low cost. Currently, there are still key problems to be resolved in OFDM-PON. For example:the signal to signal intermixing interference (SSII) caused by fiber dispersion and modulator chirp in intensity modulation direct detection OFDM system after fiber transmission; signal to signal beating interference (SSBI) in linear field modulation direct detection OFDM system; the lower electric spectral efficiency in conventional intensity modulation or linear field modulation direct detection system and et al.In this paper, the research mainly focuses on the key key problems. The main work and innovative contributions are listed as follows.1. Arming at the problem of power fading in intensity modulation direct detection OFDM system, we investigate the formation mechanism of power fading by establishing the channel modle. We propose a vestigial-sideband (VSB) DD OFDM scheme by using Fiber Bragg Gratting (FBG) VSB filter to mitigate the power fading. VSB filter could destroy the symmetry of DSB spectrum to mitigate power fading. The amplitude and phase distortion caused by VSB filter and dispersion could be compensate by using frequency domain equalizer.16QAM modulation and 100km standard single mode fiber (SSMF) transmission experiment indicates that the channel bandwidth used for data subcarriers has been improved from 6GHz to lOGHz.2. Power fading could be mitigated by using the VSB filter. However, the system performance is limited by SSII caused by the VSB filter, dispersion and square law detection. We investigate the formation mechanism of SSII and the interaction with dispersion, modulator chirp, and VSB filter. We propose iterative interference cancellation method used in VSB-IMDD OFDM system to mitigate power fading and SSII, simultaneously. To further reduce the computational complexity of ONUs, symbol predistortion method is proposed in this work to mitigate the SSII in VSB-IMDD OFDM system. In this work, we firstly use iterative interference cancellation method in the receiver to reconstruct the OFDM signal at the transmitter, and calculate the SSII. After carrying out the SSII cancellation, the SSII could be mitigated by using iterative interference cancellation method in the receiver. We furtherly propose symbol pre-distortion method to estimate the SSII in the transmitter at the VSB-IMDD OFDM system. Symbol predistortion is more suitable for OFDM-PON downstream scheme.40Gbps data rate,16QAM and 100km standard single mode fiber (SSMF) transmission experiment indicates that the receiver sensitivity is improved 2.4dB for iterative interference cancellation method, and 2.2dB for symbol pre-distortion method.3. Arming at the problem of sigal to signal beating interference in linear field modulation direct detection OFDM system, the input-output relationship of this system is represented and modeled by using the Volterra series for the first time. Then, the SSBI in linear field modulation system could all be mitigated by using the second order Volterra filter. In this work, the transmission performance of Volterra filter, iterative interference cancellation method and symbol predistortion method is analysed. The input-output relationship of this system is represented and modeled by using the Volterra series. The second order Volterra filter is used to mitigate SSBI.40Gbps data rate,16QAM modulation and 100km standard single mode fiber (SSMF) transmission simulation indicates that the receiver sensitivity is improved 5.7dB for the second order Volterra pre-inverse filter, and 5.9dB for the second order Volterra post-inverse filter.4. Arming at the problem of the lower signal to noise ratio after DAC, the higher interference caused by radio frequency-tone (RF-tone) image, and signal to signal beating interference in digital domain generated radio frequency-tone (D-RF-tone) virtual single sideband (VSSB) direct detection optical OFDM downstream scheme. We propose the analog domain generated radio frequency-tone (A-RF-tone) based virtual single sideband (VSSB) direct detection optical OFDM downstream scheme. The VSSB OFDM signal is generated by coupling the RF-tone and the OFDM baseband signal. Symbol pre-distortion method is introduced to mitigate SSBI.40Gbps data rate,16QAM and 100km standard single mode fiber (SSMF) transmission experiment indicates that the signal to noise rate before optical I/Q modulator in the proposed scheme is improved about 8dB, the RF-tone image is mitigated, and the receiver sensitivity is improved 2.9dB.