This paper proposes new channel interference cancellation technique using an electrooptic (EO) switch and optical hardlimiters for direct-detection optical code-division multiple-access (CDMA) systems. In the proposed system, the received signal is split into two paths, a signal path and a reference path. The channel interference in a reference path is reduced by double optical hardlimiters. The output of a reference path drives the EO switch to reduce the effect of the channel interference in a signal path. When the reference signal is larger than or equal to the threshold of the driver circuit, the EO switch is turned on, that is, set in the bar state and the signal in a signal path is passed to an avalanche photodiode (APD); Otherwise, the EO switch is turned off, that is, set in the cross state and the signal is not passed to the APD. It is shown that the proposed system is effective to reduce the effect of the channel interference when the received optical power is large and when the effect of the channel interference is large. Moreover, it is shown that the proposed system can improve the floor probabilities of the systems with and without double optical hardlimiters.
Tomoaki Ohtsuki, "Channel Interference Cancellation Using Electrooptic Switch and Optical Hardlimiters for Direct-Detection Optical CDMA Systems," J. Lightwave Technol. 16, 520- (1998)