Study On Key Techniques In Radio Over Fiber Broadband Wireless Access Networks

Radio over Fiber (RoF) broadband wireless access network, the integration of optical fiber and wireless technology, is an emerging research field. It entails the use of optical fiber links to deliver radio frequency (RF) signal, with the advantages including huge bandwidth,low attenuation loss and immunity to RF interference. RoF technique is a powerful solution to provide broadband wireless access services with increased mobility and reduced cost. Our thesis focuses on the researches of the key technologies and system design as follows:1. Photonic generation of high-speed RF signalThe use of high-speed RF signal in the RoF systems is receiving increasing interests since it can be used as RF carrier or local oscillator signal for providing broadband wireless access services. To save costly electrical hardware, all-optical generations of milimeter-wave signals have attracted much attention. We propose three novel schemes for photonic generation of RF signal:1)Photonic generation of six-fold frequency millimetre-wave(MMW): We propose and experimentally demonstrate to generate 60-GHz MMW based on two cascaded 10-GHz single drive Mach-Zehnder modulators (MZMs). The scheme is scalable in frequency band if faster devices are employed, thus up to 240-GHz high speed MMW can be obtained using currently available 40-GHz components.2)Photonic generation of quadruple frequency MMW: We propose and experimentally demonstrate a novel scheme to generate frequency-quadrupled MMW using an integrated dual-parallel Mach-Zehnder modulator (DPMZM). A 40-GHz high-speed MMW is obtained based on a 10-GHz RF signal.3)24-GHz Ultra-Wideband over Fiber System: We propose and experimentally demonstrate a 24-GHz UWB over fiber system with a simple structure using photonic generation and frequency up-conversion technique. The performance of the up- converted UWB pulses after the fiber transmission is also studied.2. OCS-DPSK modulation format in bi-directional RoF systems Optical carrier suppression-differiential phase-shift keying (OCS-DPSK) is an effective modulation format in bi-directional RoF systems to realize flexible applications in future broadband access networks. We propose two novel methods to generate OCS-DPSK using single intensity modulator:1)Generation of OCS-DPSK using ASK to DPSK format conversion: We experimentally demonstrate to produce an OCS-DPSK format using one DPMZM. The proposed scheme is based on ASK to DPSK format conversion by suppressing the spectral tones of an optical carrier suppression-amplitude shift keying (OCS-ASK) signal.2)Generation of OCS-DPSK using one single drive MZM: This scheme realizes three key functions in full-duplex RoF systems: up-conversion of baseband data for downlink wireless service delivery, generation of remote local oscillator (LO) signal for down-conversion of uplink wireless signal, and re-modulation of down-converted uplink data, thus greatly lowering the cost of base stations.3)In addition, based on the OCS-DPSK generation principle, an optical carrier suppression-differiential quadruple phase-shift keying (OCS-DQPSK) signal is also obtained using a DPMZM for simultaneously delivering multiple RoF services at the common RF carrier.3. Convergence of RoF and PON to provide hybide multiple sevicesThe future broadband access networks demand large bandwidths and high data rate for data-intensive multimedia and real-time applications. It is desirable to simultaneously deliver wireline and wireless signals using the same fiber infrastructure with cost-effective configurations. We present three novel schemes to provide hybrid multiple services by convergeing RoF and passive optical network (PON) techniques with centralized wavelength:1)Multiband RoF transmission systems: We propose a novel multi-band RoF system and experimentally demonstrate the simultaneous generation and transmission of the downstream1.25-Gb/s baseband, 20-GHz microwave and 40-GHz millimiter-wave signals and upstream symmetric data. The system uses 10-GHz components to achieve frequency doubling and quadrupling, and without the need of additional light source and wavelength management at the base station.2)Convergence of RoF to deliver high-speed point-to-point downlink data and double broadcast services in wavelength division multiplexing-passive optical network (WDM-PON) systems: We propose and experimentally demonstrate that double broadcast services can be overlaid over high-speed point-to-point downlink data with centralized light sources and shared fiber infrastructure in a WDM-PON system.3)Intergration with RoF to provide one wireless and double wireline services in WDM-PON systems: We propose and experimentally demonstrate a WDM-PON system simulataneously providing triple different services with centralized light source and shared optical-fiber infrastructure based on a single DPMZM.4. Photonic RF signal processing based on silicon micro-ring resonatorPhotonic RF signal processing has particular advantages since it is more efficient, less complex, and less costly than conventional electronic systems, especially at high- speed millimeter wave frequencies. We present and experimentally demonstrate two important photonic RF devices including photonic up-converter and photonic RF phase shifter based on silicon micro-ring resonator:1)Photonic RF up-converter: Based on the free-carrier dispersion effect in a resonance-split silicon microring resonator, we experimentally demonstrate a novel micrometer-scale optical up-converter for up-converting a 1-Gb/s baseband data to 40-GHz millimeter-wave in RoF systems.2) Photonic RF phase shifter: Based on the thermal nonlinear effect of the silicon microring, a prototype of the phase shifter is experimentally demonstrated for a 40-GHz signal with a 4.6-rad tuning range. We also experimenally verify the phase shift response speed of the designed photonic RF phase shifter.