The subcarrier multiplexing/wavelength division multiplexing for radio over fiber

Abstract

In this project, we review the system configurations and performance of high-speed digital optical transmission using sub-carrier multiplexing (SCM) and Wavelength Division Multiplexing (WDM). The systems are setup to gain the performance of channels spacing especially for bandwidth efficiency and compare it by the modulation techniques. A radio-over-fiber (RoF) distribution system incorporating both SCM and WDM technologies is presented. In the system model, the sixteenth input signals are modulated with different electrical carriers at microwave frequencies and then they are merged by using a combiner. The combined of the signal is then modulated by external modulation techniques using Mach Zehnder Modulation that has own bandwidth is 20 GHz. In WDM, each of N different wavelengths is transmitting at N times the individual CW laser speed, providing a significant capacity enhancement. The WDM channels are separated in wavelength to avoid cross-talk when they are demultiplexed by a non-ideal optical fiber. In this scheme, multiple optical carriers are launched into the same optical fiber through the WDM technique. Each optical carrier carries multiple SCM channels using several microwave subcarriers. One can mix analog and digital signals using different subcarriers or different optical carriers. At the receiver end, the optical signal is converted back to an electrical domain by an APD photodetector and filtered by Bandpass Rectangle filter. The particular signals then demultiplexed and demodulated, using conventional detection methods. The outcomes of bandwidth was increased to 60 GHz by applying of 16 channel of SCM combined to WDM in optical fiber link. The combination of WDM and SCM provides the potential of designing broadband passive optical networks capable of providing integrated services (audio, video, data, etc.) to a large number of subscribers.