Liquid Crystal Modulated Optical CDMA in a Fiber-based Testbed

Yijing Fu, Frank Barnes, Teresa Ewing, Steven Serati, Xiaowei Xia

Published in SPIE Proceedings Volume 5595, Active and Passive Optical Components for WDM Communications IV; (2004)


In recent years, optical CDMA systems have been proposed for multiple accesses to utilize the vast bandwidth available in optical fiber. Optical CDMA systems are believed to provide asynchronous access for each user in the system, which is especially suitable for usage in LAN. In this paper, we demonstrate a novel optical CDMA scheme in a fiber-based testbed. Using the liquid crystal spatial light modulator (SLM), we are able to construct a reconfigurable optical CDMA system suitable for fiber-optic networks. We address the code for each user in the spectrum domain by using a standard 4-f pulse shaping apparatus. Because of the low coherency of the light source we used in the system, we are able to modulate it in time domain without changing its frequency distribution significantly. We can reconfigure the network connection while keep the information bits un-influenced. Another merit of using analog liquid crystal device is that the transmissions of the different frequency components are analog controllable, we can get a uniform intensity distribution in frequency domain when the spectrum of the light source is not flat. Using the liquid crystal as a programmable optical modulator, the high polarization sensitivity of the components used in the system enables low crosstalk between different codes assigned to different users.

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