Studies On Optical Signal Processing And Transmission System Of Converged Fiber-Wireless Wdm-Pon

With the appearance of fixed and mobile broadband services, the bandwidth demand of users is considerably increasing. The capacity of the next generation optical access network (OAN) is required to be greatly improved. It is commonly agreed that wavelength division multiplexed passive optical network (WDM-PON) is highly recognized as the most promising candidate for next generation OAN because of its high-bandwidth provision, good scalability, being transparent to bit-rates and protocol. Meanwhile, as the mobile application of internet services is more and more popular nowadays, the flow rate of wireless services increases tremendously. Radio access network (RAN) can hardly satisfy the demand of the boosting bandwidth services. Therefore, the broadband OAN is developing towards larger capacity, multiple access methods and convergence of wired and wireless services. Currently, the converged WDM-PON and C-RAN has attracted more attention because it can provide multi-services for multi-users in any place at any time. Nevertheless, there remain a number of key issues to be resolved in converged WDM-PON, such as small bandwidth of RSOA-based colorless optical network unit (ONU), poor wavelength adaptability of the radio remote unit (RRU), and the incompatibility of WDM-PON and radio over fiber (RoF) technology.This dissertation focuses on the above-mentioned issues of converged WDM-PON. The main research work and contributions are summarized as follows:Firstly, most existing schemes of phase-modulated RoF signal generation by using external modulation in converged WDM-PON suffer from large phase noise because the two beaten beams travel independently through separated optical paths. To reduce the phase noise, a scheme of phase-modulated RoF signal generation employing polarization-dependent electrical-optical modulator is proposed and demonstrated. The RoF signal is modulated on one polarization-direction of optical carrier and obtained by adjusting polarization controller. The experimental results indicate that both Binary Phase Shift Keying RoF signal and Orthogonal Frequency Division Multiplexing Quadrature Phase Shift Keying (OFDM-QPSK) RoF signal can be generated. Considering the two beaten beams go through the same optical path, there will be no random phase fluctuation between the beams. The error vector magnitude of OFDM-QPSK RoF signal measured in the experiment is only 4% at back-to-back transmission.Secondly, in order to resolve the bandwidth limitation of RSOA-based colorless ONU in WDM-PON, an improved scheme of uplink transmission for RSOA-based colorless ONU with the help of cascaded Mach-Zehnder Interferometers (MZIs) is proposed. Cascaded MZIs with high-pass-filter characteristics can compensate the low-pass-filter characteristics of the RSOA. The simulation results show that the cascaded MZIs equalizer is able to improve the uplink bandwidth of WDM-PON to 10GHz. A better received sensitivity of -23.4dBm at BER of 1.0×10-3 after 25km single mode fiber transmission with cascaded MZIs and more than one order-of-magnitude reductions in BER can be achieved compared with the single MZI.Thirdly, most existing schemes in converged C-RAN-WDM-PON suffer from the high cost of RRUs because wavelength-dependent optical filters and light sources should be installed. In this dissertation, a new wavelength reuse solution in converged RoF-WDM-PON based on a polarization modulation to intensity modulation (PolM-to-IM) convertor is proposed. The downstream millimeter-wave signal and upstream optical carrier can be obtained by adjusting polarization controller because they are working at different modulation regions. Based on the experimental results,54.8GHz millimeter-wave signal without wavelength-dependent filter is recovered in RRU and 1Gbps NRZ upstream signal is received after 25km fiber transmission.Fourthly, to achieve more services transmitted in converged C-RAN-WDM-PON, a scheme of converged RoF-WDM-PON based on a distributed PolM-to-IM convertor is proposed, which can simultaneously support the existing low radio frequency and millimeter-wave wireless services transmission. The experimental results show that the OFDM downstream signals working at 0.3GHz and 54.8GHz are received at the RRU via 25km fiber. Meanwhile, successful transmission of the upstream signal is implemented by reusing the light-wave. In addition, a new scheme of converged RoF-WDM-PON with wavelength reuse to deliver three services is proposed and demonstrated by polarization multiplexing and frequency multiplexing. Based on the experimental results, the traditional 0.3GHz RF signal, 15GHz microwave signal and 60GHz millimeter-wave signal are attained without wavelength-dependent filters in RRU.