All-optical asynchronous detection for a compact integrable incoherent optical CDMA system

In this paper, we investigate all-optical truly asynchronous detection without global clocking in an incoherent optical code-division multiple-access (CDMA) system. The implemented system is designed with an integrable optical source consisting of an electro-absorption modulator for pulse carving, compact coders consisting of fiber Bragg grating arrays for encoding and decoding, and receiver consisting of an all-optical thresholder for data and clock recovery. We compare three detection schemes: 1) synchronous detection with data from a photodetector and clock from an external source; 2) asynchronous detection with data and clock from the all-optically thresholded signal received by a clock and data recovery (CDR) unit; and 3) asynchronous detection with data from a photodetector and clock extracted from the all-optically thresholded signal using CDR. Error-free transmission is obtained for detection schemes 1) and 3). A combination of all-optical thresholding and CDR technology is demonstrated in an optical CDMA system for the first time.