Optical Domain Demultiplexing of Subcarrier Multiplexed Cellular and Wireless LAN Radio Signals

Subcarrier multiplexed transmission of cellular (900 MHz), personal communications systems (1.8 GHz) and wireless LAN (2.4 GHz) over the fiber has interesting applications. These multi channel radio over fiber links can connect enhanced wireless hot-spots that will support high speed wireless LAN services or low speed cellular services to different customers from the same antenna. Optical pre-filtering of SCM signals allows the use of inexpensive photodetector and increases network flexibility with fiber based optical filters. However, realizing optical demultiplexing at such low frequencies necessitates optical filters with high selectivity and low insertion loss. In this paper, we implemented a fiber wireless access system, where demultiplexing of subcarrier multiplexed cellular and WLAN signals was demonstrated in optical domain using a sub-picometer bandpass filter. Our novel fiber Bragg grating based bandpass filter has a bandwidth of 120 MHz at -3dB, 360 MHz at -10 dB and 1.5 GHz at -20 dB respectively. We experimentally verified that this filter could adequately isolate signals at as low as 900 MHz from 2.4 GHz. Experimental results show that the designed all optical demultiplexer provides about 25 dB isolation between 900 MHz and 2.4 GHz radio signals.