We discuss mode-locking of low-gain solid-state lasers using a semiconductor saturable Bragg reflector structure. This recently developed low-loss mode-locking device consists of a single quantum well which acts as a saturable absorber incorporated into a high-reflectivity Bragg mirror. Highly stable mode-locking in solid-state lasers results from an ultrafast transient reflectivity in the device that is caused by saturation of the excitonic absorption in near-resonant conditions.

We introduce a new low-loss semiconductor structure for femtosecond intracavity mode locking in low-gain solidstate lasers. This monolithic device can be engineered to exhibit specif ic saturation characteristics desirable for mode locking solid-state lasers. Self-starting 90-fs pulses are obtained with Ti:sapphire and diode-pumped Cr:LiSAF lasers. We discuss mode-locking mechanisms in quantum-well passively mode-locked solid-state lasers.

We present short cavity erbium/ytterbium fiber lasers that are passively mode-locked with a saturable Bragg reflector. The lasers produce sub-500-fs pulses at fundamental cavity repetition rates as high as 300 MHz. Stable passive harmonic operation increases the repetition rate to 2.0 GHz. The mode-locking mechanism in both the normal and anomalous group velocity dispersion regimes is investigated using complete analytical and numerical models and direct comparison with the experimental results. A simple technique for accurately measuring the total cavity dispersion is presented.

A theoretical model is developed for the pulse dynamics in a fiber laser mode locked by a saturable Bragg reflector and operating in regimes beyond the scope of the master mode-locking equation. An asymptotically valid mode-locked evolution equation is derived, which includes a heuristic model for the saturable Bragg reflector dynamics. The model employed allows, for the first time to our knowledge, direct comparison (with no free parameters) of the theoretical predictions of the pulse spectral and temporal profiles with experimental results in both the normal and anomalous dispersion regimes. Extensive numerical simulations of the governing evolution equation, an averaged equation, and analytical solutions are found to be in excellent agreement with experimental results.

We describe an experimental realization of ultralong-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM) transparent optical networks is proposed and implemented, which enables excellent transmission performance while avoiding dispersion compensation on a connection-by-connection basis. We demonstrate "broadcast-and-select" node architectures that take full advantage of this method. Our implementation of signal leveling ensures minimum variations of path-averaged power among the wavelength-division-multiplexing (WDM) channels between the dynamic gain-equalizing nodes and results in uniform nonlinear and spontaneous-emission penalties across the WDM spectrum. We achieve 80 10.7-Gb/s DWDM networking over 4160 km (52 spans 80 km each) of all-Raman-amplified symmetric dispersion-managed fiber and 13 concatenated OADMs or 320 320 wavelength-port OXCs with 320-km node spacing. The WDM channels use 50-GHz grid in band and the simple nonreturn-to-zero (NRZ) modulation format. The measured values exhibit more than a 1.8-dB margin over the forwarderror correction threshold for 10 15 bit-error-rate operation. We compare these results with point-to-point transmission of 80 10-Gb/s NRZ WDM signals over 4160 km without OADM/ OXC and provide detailed characterization of penalties due to optical signal-to-noise-ratio degradation, filter concatenation, and crosstalk. Index Terms-Add-drop multiplexer, dispersion management, optical communication, optical cross-connect (OXC), Raman amplification, transparent optical networks. I. INTRODUCTION T RANSPARENT ultra-long-haul (ULH) network systems have gained strong importance in the past few years, as the longer transparent reach distance of optical circuit connection promises network cost reduction through elimination of costly optical-to-electrical-to-optical (O/E/O) data regenerators.