Code-division multiple-access encoding and decoding of femtosecond optical pulses over a 2.5-km fiber link

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 1.5-μm communication band. Our CDMA link consists of a femtosecond mode-locked Er-fiber laser and two chirped pulse fiber amplifiers, a pair of low-loss fiber-pigtailed pulse shapers for encoding and decoding, a 2.5-km dispersion-compensated transmission fiber, and an ultrafast nonlinear optical receiver. Our results demonstrate high fidelity transmission of spectrally encoded femtosecond pulses over 2.5 km of fiber, followed by the use of the nonlinear CDMA receiver to discriminate between correctly and incorrectly decoded signals with 20-dB contrast.