Research On Key Problems In Short Range High Data Rate Polymer Optical Fiber Communication

During the past years, recent attention has been focused on polymer optical fibers (POF) due to their several advantage properties such as large core, low cost, robustness and tolerance to extreme bending, immunity to electromagnetic interference, and ease of installation, which establishe the POF as a preferred alternative transmission medium for high-speed short range data communications. However, due to its large modal dispersion, the bandwidth of POF is limited which greatly reduces the transmission capacity. Therefore, how to reduce the dispersion and improve the transmission bandwidth seems to very important for the actual POF communications. Nevertheless, adopting the advanced modulations and signal processing algorithms could overcome the bandwidth limition, achieve the high data rate and improve the system performance. Combining the channel characteristic of polymethyl metacrylate (PMMA) step-index (SI)-POF based on intensity modulated direct detected (IM/DD) structure, the issues of digital modulation technique, transmission capacity enhancement, bandwidth optimization and nonlinearity mitigation are mainly investigated.Aimed at the discrete components of the power spectrum destiny (PSD), the spectral properties of the M-ary Position Phase Shift Keying (MPPSK) modulated signal is derived. The waveform optimization method and full M-ary position modulation are proposed to suppress these discrete components. The theoretical analysis and experimental results demonstrate that the discrete components are greatly suppressed and the spectrum utilization is enhanced.0.3dB～0.7dB in signal to noise ratio (SNR) is saved which demonstrates the feasibility and validity of these two methods.The low-pass frequency behavior of the SI-POF results in larger attenuation at the high frequency region, and the transmission capability and quality is limited. The transmission system in a SI-POF is divided into two frequency regions, a novel composite transmission approach is proposed for an in-home access network combining discrete multitone modulation (DMT) and MPPSK modulation. Hadamard sequence spreading is introduced to suppress the adjacent-channel interference. The experiment verifys that, using the new methodology, an additional bit rate of 39 Mbps in the low SNR region is obtained at a bit error rate (BER) of 1×10-4. It is demonstrated that the proposed scheme can offer better BER performance and make a better compromise with higher transmission rate.Considering the calculation of channel capacity of the SI-POF communication system, the characters of the optimal PSD and the practical PSD of DMT were theoretically analyzed, and an uniform power loading techniques was used to evaluate and calculate the maximum achievable date rate based on the channel model of Gaussian low-pass filter and first-order low-pass filter. Theoretical expressions for the optimal bandwidth and realistic capacity were derived for uncoded DMT of an IM/DD SI-POF system based on SNR gap. Furthermore, the results demonstrate that adopting the optimum bandwidth can effectively enhance the transmission rate. The accurate prediction of capacity is beneficial to the POF system designing.Considering the high Peak-to-Average Power Ratio (PAPR) problem in DMT transmission, approximations of statistical distribution of PAPR for Nyquist-sampling and oversampling DMT are accurately analyzed. A PAPR reduction scheme based on Jacket-Spread (JS) precoding is proposed and introduced in the POF transmission link. Theoretical analysis is presented to show that JS-DMT can gain more efficient PAPR reduction and have the excellent PSD and BER performance. In order to overcome the defects that the transmission rate is sensitive to the bandwidth, an improved multi-band (MB) JS-DMT scheme with split symbol-spread blocks is proposed, thus the same SNR for each subcarrier is avoided. Results demonstrate that MB-JS-DMT is more efficient and can be easily applied to the POF system, in addition, better PAPR performance are also achieved without BER and PSD degradation. It is a promising technique for the practical POF transmission.To mitigate the nonlinearity of resonant cavity light emitting diode (RCLED), the impact of RCLED nonlinear characteristic on DMT transmission is investigated. The parameters including DC bias point of RCLED and the DMT signal power on the communication performance is analyzed. Polynomial pre-distorter and look-up-table (LUT) pre-distorter are proposed in POF system to compensate the RCLED nonlinearity. With the help of new methodologies, both of the pre-distortion schemes are benefiting from higher power efficiency and exhibiting great resistance to nonlinearity, and even could be well demodulated in the strong nonlinearity range, which demonstrates the feasibility and validity of these two methods for RCLED nonlinearity mitigation in POF system.