Femtosecond encoder-decoders and ultrafast nonlinear thresholders and their integration in a femtosecond code division multiple access communication system test-bed
Abstract
Femtosecond code division multiple-access (CDMA) communication systems are an attractive choice for local area network applications due to their unique attributes of optical processing, asynchronous transmission, and the capability of multiple-access. In its simplest form an optical CDMA system can be described as follows. In the transmitter femtosecond pulses generated by a laser source are spectrally encoded into picosecond duration pseudonoise bursts and transmitted over a dispersion compensated fiber channel. Each user in the CDMA system is assigned a unique phase code by which it encodes all its data bits, and assigning different minimally interfering code-sequences to different users accommodates multiple users. The different users can be connected in a simple broadcast and select type architecture where all transmitters are connected to all receivers by a passive star coupler. In the receiver the decoder has knowledge of the phase code of only one particular transmitter. Hence only the encoded data bits that are intended for a particular receiver get properly decoded back into femtosecond pulses, and the encoded data bits of all other users remain as improperly decoded pseudonoise signals. A nonlinear optical thresholder that discriminates on the basis of intensity then detects the properly decoded femtosecond signal pulses and rejects the improperly decoded multi-access interference. This thesis addresses the design and construction of two of the optical CDMA component technologies, namely, femtosecond encoder-decoders, and ultrafast nonlinear thresholders. Both experimental and numerical results will be presented. These sub-systems were successfully integrated to construct an optical CDMA test-bed. The optical CDMA test-bed will be discussed and results demonstrating CDMA transmission over 2.5km of optical fiber will be presented.
Degree
Ph.D.
Advisors
Weiner, Purdue University.
Subject Area
Electrical engineering
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