A spectral phase encoded time spreading optical code division multiple access testbed
Spectral phase-encode time-spreading (SPECTS) is a promising technique for optical code-division multiple-access (O-CDMA) networks. In SPECTS O-CDMA, users are multiplexed and distinguished with unique phase codes impressed on the spectrum of ultra-short optical signal pulses. The encoding and decoding processes are implemented with grating/lens zero-dispersion pulse-shapers using spatial light phase modulators (SLPMs) in the Fourier plane. The SLPMs add the encoding or decoding O-CDMA phase codes on the spectrum which is spatially spread and then recombined by the grating(s) and lens(es).
In this dissertation, we demonstrate a SPECTS O-CDMA network testbed with large throughputs and high performances. Two types of fiber-pigtailed bulk-optic pulseshapers, 1-D transparent-mode and 2-D reflective-mode, are constructed to be used as SPECTS O-CDMA encoders and decoders in the testbed. In order to support a large number of users, the testbed includes up to eight SPECTS O-CDMA encoding channels and one decoding channel. With the combination of time-slotting and polarization-multiplexing operations, the maximum throughput achieved on the testbed is 32 users (8 O-CDMA channel × 2 time slots × 2 polarizations) at 10 Gb/s/user.
Two nonlinear detecting techniques (thresholding and gating) for coherent SPECTS O-CDMA are discussed in the dissertation. A nonlinear thresholder and a nonlinear optical loop mirror (NOLM) time gate are built in the testbed; each uses a 500-m highly nonlinear fiber(HNLF). An "O-CDMA receiver" including the NOLM and the thresholder followed by an optical-electrical (O-E) converter can distinguish the intended user by demultiplexing the time-slotted signal and then suppressing the multi-user interference (MUI). In the bit-error-rate (BER) statistics experiments, the "O-CDMA receiver" can detect the intended user's signal with error-free or low BER performance in various testbed structures.
Network-layer application experiments including video-transmission, File Transport Protocol (FTP) and TCP application are successfully demonstrated on the testbed. The network performance of the testbed is high in these experiments according to the measurement by the imbedded network-performance analyzer.