Theory of short-pulse gain saturation in semiconductor laser amplifiers

Theory of nondegenerate four-wave mixing between pulses in a semiconductor waveguide

“…By this, the effects of carrier density changes, carrier heating, and spectral hole burning (SHB) are treated on equal footing. This is reasonable for a single pair of short pulses, since gain saturation calculations [21] show these effects to be comparable for pulses shorter than 10-20 ps. The effects of coupling between the different saturation mechanisms for the material susceptibility itself is not included.…”

“…1. Notice that there are pulsewidth ranges around each of the characteristic scattering times in which this separation cannot be made and where one has to resort to numerical calculations [21].…”

Analysis of Timing Jitter in External-Cavity Mode-Locked Semiconductor Lasers

“…The pulses shorten little above nm. Ultrafast gain dynamics, specially hot carrier thermalization, can inhibit the generation of subnanosecond pulses due to pulsewidth dependent saturation energies of the active media [33]. In addition, self-phase modulation and time-bandwidth product increase that, in turn, reduces the stable region of mode-locking.…”

Pulse properties of external-cavity mode-locked semiconductor lasers

“…The SOA and absorber models describe, in the relaxation rate approximation, deviations from quasi-equilibrium Fermi-Dirac distributions due to spectral-hole burning (SHB) and carrier heating (CH). An effective rate equation model [8] describes the depletion in local carrier density, resonant with the lasing transition, due to SHB and the energetic redistribution of electrons and holes due to CH. In the absorber, the nonlinear dependence of the absorption recovery time with the reverse voltage due to carrier sweep-out is phenomenologically described and it amounts to τ abs 10 ps for V abs ≈ −2 V. Furthermore, bandgap renormalization due to the quantum-confined Stark effect leads to red-shift of the absorption edge, which allows us, in a simple way, to map the unsaturated absorption level into applied reverse voltage.…”

“…These arguments, however, neglect the contribution from ultrafast gain dynamics. The saturation energy of SOA and ABS, determining the pulse shaping strength, have contributions from gain depletion (differential saturation) [7] and non-equilibrium processes [8]. Ultrafast processes are increasingly important when the pulsewidth reaches their characteristic sub-picosecond time scales, specially due to hot carrier thermalization [2].…”