Demonstration of code-division multiple-access encoding and decoding of femtosecond optical pulses over a 2.5-km dispersion-compensated fiber link
Abstract
Ultrashort pulse code-division multiple-access (CDMA) based on spectral phase encoding and subsequent decoding of coherent femtosecond pulses offers an interesting approach for local area network applications. In this thesis, we report for the first time proof-of-concept transmission experiments for femtosecond pulse Code Division Multiple Access (CDMA) operating over kilometer lengths of optical fiber in the 1550 nm communication band. Our CDMA system integrates several novel components and sub-systems, including a femosecond modelocked Er-fiber laser and two chirped pulse fiber amplifiers, a pair of low-loss fiber-pigtailed pulse-shapers with programmable phase modulators for encoding/decoding and dispersion fine tuning, a 2.5-km dispersion-compensated transmission fiber, and an ultrafast nonlinear optical receiver. Femtosecond pulses generated by the Er-fiber laser are spectrally encoded by the first encoder pulse shaper. Coded pulses (which look like pseudorandom noise-bursts) are then transmitted over a 2.5-km transmission fiber link which is dispersion compensated using a special dispersion-compensating fiber (DCF). The output encoded pulses from the fiber link are sent to the second pulse shaper to decode the transmitted signals. With proper decoding phase codes, the encoded signals can be restored to almost its original pulsewidth. With wrong phase codes, the encoded signals remain as low-intensity noisebursts. A nonlinear fiber-optic thresholder is then used to distinguish properly decoded pulses from improperly decoded signals. This thesis concentrates on the development and study of a few individual component technologies, namely femtosecond pulse laser, dispersion compensation, and a femtosecond pulse encoder/phase compensator, and their integration into a single-user CDMA testbed. Almost distortionless transmission of sub-500-fs pulses over a few kilometers of fibers will be presented using a combination of DCF and a programmable pulse shaper. Because of the great successes of fiber dispersion compensation and spectral phase encoding/decoding, high-fidelity transmission of encoded femtosecond pulses over 2.5-km transmission fiber link is achieved, which leads to high contrast results in the nonlinear thresholder.
Degree
Ph.D.
Advisors
Weiner, Purdue University.
Subject Area
Electrical engineering
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