Full-duplex Wavelength Interleaved DWDM Hybrid Access Radio-over-fiber System

Abstract
The paper demonstrate a simplified full-duplex wavelength interleaved (WI)-DWDM hybrid access radio-over-fiber (ROF) system for providing 2 GB/s wired and 1 GB/s wireless downlink and 1 GB/s uplink data data simultaneously. Here we use only one arrayed waveguide grating device to realize both the demultiplexing and multiplexing functions. Because of using only the subcarriers of the single channel to carry both the wired and wireless data, we do not need extra optical components such as interleaver to separate them at the base stations. The experimental results demonstrate that this scheme is feasible and has good transmission performance for the future WI-DWDM hybrid access ROF system.
Keyword:radio–over-fiber (ROF); arrayed waveguide grating (AWG); wavelength interleaving (WI); full-duplex.
I.Introduction
Radio over Fiber (RoF) refers to a technology whereby light is modulated by a radio signal and transmitted over an optical fiber link to facilitate wireless access, such as 3G and WiFi simultaneous from the same antenna.[1] In other words, radio signals are carried over fiber optic cable. Thus, a single antenna can receive any and all radio signals (3G, Wifi, cell, etc..) carried over a single fiber cable to a central location where equipment then converts the signals; this is opposed to the traditional way where each protocol type (3G, WiFi, cell) requires separate equipment at the location of the antenna. In RF-over-Fiber architecture, a data-carrying RF (Radio Frequency) signal with a high frequency (usually greater than 10 GHz) is imposed on a lightwave signal before being transported over the optical link. Therefore, wireless signals are optically distributed to base stations directly at high frequencies and converted from the optical to electrical domain at the base stations before being amplified and radiated by an antenna. As a result, no frequency up/down conversion is required at the various base stations, thereby resulting in simple and rather cost-effective implementation is enabled at the base stations.
The 60GHZ radio–over-fiber (ROF) system, because of its high throughput, high bandwidth and low loss, attracts more and more attentions recently. Since the user’s requirements continue to increase, a hybrid access ROF system that is able to provide wired and wireless services simultaneously is desirable. ROF systems adopting wavelength interleaved (WI) DWDM technology makes the utilization of bandwidth resources more efficient and the corresponding system more competitive.
Experimental Setup:
At the central office (CO), three light carriers with frequencies of 193.02THz, 193.06THz, and 193.1THz enerated by the CW laser array are combined by an ideal MUX component. Their frequency space is 40GHz. Then they are modulated by 30GHz sinusoidal wave using a MZM biased at the half-wave voltage in order to generate 60GHz OCS optical millimeter-wave. Because of the WI characteristic, the bandwidth efficiency of our scheme is improved effectively. A 20/40 IL1 is followed to separate the two side-bands of every WDM channels. In order to improve the performance of the received wired and wireless signals, IL2 and IL3 are followed at the odd and even output ports of IL1 respectively to filter out the undesired side-bands. The right side-bands (S1R, S2R, S3R) outputting from the even port of IL are then IM by 1Gb/s data using a single-arm MZM for providing wireless service.