High-speed fiber-based modules for TDM/WDM soliton systems

The nonlinear behaviors of a pulse in optical fibers are studied in the framework of fiberoptic communication systems that employ solitons. High-speed fiber-based modules are developed for time-division-multiplexed (TDM) or wavelength-division-multiplexed (WDM) systems. Transmission experiments show that when launched into a low-dispersion, anomalous optical fiber, a chirped high-order soliton can undergo an irreversible pulse breakup. This is the first experimental evidence of the previous analytic predictions. The observed phenomenon has to be taken into consideration in system implementations. Simulations and experiments also show that the nonlinear properties of an optical soliton can be harnessed to design fiber-based devices for TDM/WDM applications. The first demonstrated is a nonlinear optical loop mirror switch that uses repeated collisions between two orthogonally polarized solitons. A switching contrast ratio of 80:1 and a low latency of 10ns are achieved. This is the shortest all-optical switch constructed in fiber. The module exhibits clean-switched pulse profile and timing jitter tolerance, which make it attractive for all-optical pulse regeneration and demultiplexing in TDM networks. The second demonstrated device is a broadband high repetition rate source generated by spectrally spreading the output of a harmonically mode-locked fiber soliton laser. The design for the spectral broadening is optimized with numerical simulations and employs commercially available single mode fiber, dispersion shifted fiber, and an erbium doped fiber amplifier. It greatly simplifies the traditional designs that typically include a pulse compression stage, resulting in a compact, stable and cost-effective source. The obtained 35-nm-wide smooth and flat spectrum is centered around 1550nm and at a repetition rate of 2.5GHz, which make it suitable for spectrum-sliced WDM applications. The final experiments illustrate that the soliton signal recovery can be achieved via the simultaneous operations of a nonlinear amplifying loop mirror (NALM) as a nonlinear amplifier, noise filter and amplitude equalizer. More importantly, the NALM's functionality is, for the first time, extended to a WDM system. Experimental results show that an average gain of 10dB and a power penalty improvement of 2.5dB are obtained for four WDM channels. Issues including the cross phase modulation (XPM) effect on the NALM performance are also discussed.