Study On Enabling Technologies Of Millimeter-Wave Radio-over-Fiber Optical Wireless Access Networks

Recently, optical-wireless access networks based on millimeter-wave (mm-wave) radio-over-fiber (ROF) technology have emerged as a potential solution for next generation optical-wireless networks, due to its great potential to deliver ubiquitous multi-gigabit wireless services through centralized, simplified remote base stations (BS) with low-loss, bandwidth-abundant fiber-optic back-haul connectivity. This thesis focuses on enabling technologies of mm-wave ROF access networks, on the basis of theoretical analysis as well as system simulations and experimentations. The main topics include:1. Optical mm-wave generationA novel optical mm-wave generator based on a double locked Fabry-Perot (FP) laser is proposed. The optical mm-wave generator is locked by two sources:the external optical injection and the driven RF reference frequency. Stable optical mm waves with low phase noise are then generated. There is no need for high-bandwidth devices to support high RF driven frequency in this scheme. Furthermore.neither an external strong optical injection power nor an additional optical filter is required. Here we also give the theoretical and experimental comparisons between the frequency-doubling, tripling and quadrupling cases for the mm-wave generator and RoF system.36-GHz optical mm waves can be experimentally generated in frequency-doubling case, as well as40.2-GHz optical mm waves in frequency-tripling case and40-GHz optical mm waves in frequency-quadrupling case. Error-free transmission of2.25-Gb/s (frequency-doubling case) and2.5-Gb/s (frequency-tripling case and frequency-quadrupling case) OOK signals can be achieved over20-km of standard single mode fiber (SSMF).2. ROF systems with multi-service wireless signals at60-GHz sub-bandsWe propose and demonstrate a novel60GHz multi-band RoF system. In this design, two signals at different intermediate frequencies (IFs) are remotely up-converted to different60-GHz mm-wave sub-bands at a photo-detector (PD), by utilizing a common DFB laser as the optical heterodyne source. A square-law-type detector is used at the user terminal to eliminate the frequency instability and the phase-noise of the two independent heterodyne lights and down-convert the wireless signals to their associated IFs. There is no need for complex system architecture and expensive high frequency clock sources in our scheme. The proposed scheme here can be considered as a single side band (SSB) modulation system, since the two higher sidebands of the signals at mm-wave band can be filtered out by the mm-wave RF devices with limited response band. Compared with conventional60GHz multi-band ROF systems, our scheme is highly tolerant to fiber dispersion so that it can be used in large area coverage networks.3. Convergence of mm-wave ROF technology and optical access networksFirstly, an ultra-dense wavelength division multiplexing (UDWDM) mm-wave RoF access network with integrated wired and wireless services is proposed. In this scheme, the local oscillator laser used for coherent detection can be utilized to up-convert wireless signals to mm-wave band as well as select the desired UDWDM channel (both wired and wireless signals) precisely. On the wireless receiving side, the down-conversion of mm-wave signals can be realized by a self-mixing RF receiver. As a result, there is no complex wireless receiver in our design Theoretical analysis as well as system simulations and preliminary downlink experimentations are carried out. For the wired signal transmission,4Gb/s QPSK signals with channel spacing of7.25GHz can be successfully transmitted over35-km SSMF (BER<lE-3), while for the wireless signal transmission,2Gb/s OOK signals with channel spacing of6.5GHz can be successfully transmitted over35-km SSMF and4-m wireless distance (BER<1E-6).Secondly, a novel peer-to-peer (P2P) interconnection in a60-GHz mm-wave ROF access network is proposed and experimentally demonstrated for the first time. In this scheme, the beating of the lightwaves for downlink and P2P transmissions at the PD can provide signal up-conversion for both signals. The downlink and P2P mm-wave signals can be down-converted simultaneously to their associated IFs by a Schottky RF detector located on the user terminal. No high-frequency clock sources or other high bandwidth devices are required for signal up/down-conversion. Relative received RF power at6GHz of downlink signal versus different received optical power of the P2P signal before the PD is also given in the thesis.