Spectrally phase coded optical code division multiple access (O-CDMA) system and spectral line-by-line pulse shaping

Multiple access techniques are required to meet the demand for high-speed and large-capacity communications in optical networks, which allow multiple users to share the fiber bandwidth. Optical code-division multiple-access (O-CDMA) is receiving increased attention due to its potential applications for local area optical networks. We experimentally investigate an ultrashort pulse O-CDMA scheme based on spectral phase encoding and decoding of coherent mode-locked laser pulses. Strong interference suppression is achieved by using a novel, ultrasensitive nonlinear optical intensity discriminator based on second harmonic generation (SHG) in a periodically-poled lithium niobate (PPLN) waveguide. We have experimentally demonstrated/investigated: (1) 4-user, 2.5 Gb/s and 10 Gb/s O-CDMA system with ultra-low power (∼30 fJ/bit); (2) reconfigurable all-optical code translation in our O-CDMA testbed; (3) 50 km single mode fiber (SMF) transmission experiments for O-CDMA system; (4) security issues in O-CDMA networks. We have built the first grating-based spectral line-by-line pulse shaper and demonstrated many functionalities: (1) demonstrated line-by-line pulse shaping experiments in which the individual spectral lines present in the output of a mode-locked laser with ∼10 GHz mode spacing are resolved. The shaped pulses overlap in time, which leads to a new way to observe fluctuations of the comb-offset frequency in the time domain; (2) demonstrated line-by-line pulse shaping control for optical arbitrary waveform generation (O-AWG); (3) demonstrated tunable return-to-zero signal generation, return-to-zero to non-return-to-zero format conversion; (4) demonstrated complete intensity and phase measurement of optical pulses using spectral line-by-line pulse shaping; (5) in addition to utilizing the spectral lines generated from a mode-locked laser, we also applied line-by-line pulse shaping control on spectral lines generated from a phase modulated continuous wave (CW) laser. Based on these apparatus, we showed various optical processing functionalities, including CW-to-pulse conversion, width and wavelength tunable return-to-zero pulse generation, pulse-to-CW conversion, wavelength conversion and microwave waveform synthesis