Spectral Dynamical Behavior in Passively Mode-Locked Semiconductor Lasers (original) (raw)
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Mode-Locking in Semiconductor Fabry-Pérot Lasers
IEEE Journal of Quantum Electronics, 2010
We theoretically study the dynamics and the modelocking properties of semiconductor Fabry-Pérot lasers with intracavity saturable absorber by using a travelling-wave model and a time-domain description of the optical response of the semiconductor materials. Our description enables us to incorporate important features as for instance the abrupt spectral variations of the absorption in the saturable absorber. We analyze the influence of several key parameters that affect the stability of the mode-locking regime and show that this modelling approach can be used, upon proper fitting of the material parameters, for optimization of the design of semiconductor mode-locked lasers.
Detuning and Thermal Effects on the Dynamics of Passively Mode-Locked Quantum-Well Lasers
IEEE Journal of Quantum Electronics, 2000
The impact of the wavelength-dependent properties of quantum-well (QW) saturable-absorbers (SAs) on the modelocked operation of monolithic two-section QW lasers is examined with a travelling-wave description that includes a model for the optical response of the active material at finite temperatures. Good-quality mode-locking regimes occur only in small regions of parameter space due to the wavelength-dependent absorption and saturation energy of the SA section. Joule heating associated with photocurrent generation in the SA section dynamically modifies the relative detuning, and may eventually lead to the disappearance of mode-locking. Either proper thermal management of the absorber section or absorbers with wavelength-independent properties are needed in order to improve the breadth of the regime of good-quality mode-locked operation.
Relaxation Oscillations and Pulse Stability in Harmonically Mode-Locked Semiconductor Lasers
IEEE Journal of Quantum Electronics, 2000
In this paper, we discuss pulse dynamics in harmonically mode-locked semiconductor lasers and present the conditions necessary for stability. In a laser mode-locked at the th harmonic, the pulse energy fluctuations have ( +1) different modes of relaxation oscillations. Different modes correspond to different patterns for the energy fluctuations in the different pulses inside the laser cavity. In the higher order relaxation oscillation modes, the energy fluctuations are negatively correlated in different pulses inside the laser cavity, and these modes can cause instability. Gain saturation on time scales of the order of the pulse width (dynamic gain saturation) stabilizes pulse energy fluctuations with respect to relaxation oscillations. The precise limits on the stable operating regime depend on the gain dynamics at both slow and fast time scales. We also discuss harmonic mode-locking in the presence of a slow saturable absorber. Dynamic loss saturation in a saturable absorber can work against dynamic gain saturation and limit the stability range for harmonic mode-locking.
Theory of mode-locked semiconductor lasers with finite absorber relaxation times
Applied Physics Letters, 1997
We investigate the influence of a finite absorber relaxation time on passively mode-locked semiconductor lasers. We find that the mode-locking mechanism of Haus is surprisingly susceptible to small perturbations and small changes in the parameters. Even when the absorber relaxation time is much larger than the pulse duration, it typically is still short enough to be a crucial part of the physics of mode-locking. Allowing for a finite absorber relaxation time, we find that stable operation of a mode-locked semiconductor is possible over a wide range of parameters. We argue that the pulse duration is inversely proportional to the square root of the pulse energy. © 1997 American Institute of Physics. ͓S0003-6951͑97͒04615-9͔
New regime of inverse saturable absorption for self-stabilizing passively mode-locked lasers
Applied Physics B, 2005
The reflectivity of a semiconductor saturable absorber mirror (SESAM) is generally expected to increase with increasing pulse energy. However, for higher pulse energies the reflectivity can decrease again; we call this a 'roll-over' of the nonlinear reflectivity curve caused by inverse saturable absorption. We show for several SESAMs that the measured roll-over is consistent with two-photon absorption only for short (femtosecond) pulses, while a stronger (yet unidentified) kind of nonlinear absorption is dominant for longer (picosecond) pulses. These inverse saturable absorption effects have important technological consequences, e.g. for the Q-switching dynamics of passively mode-locked lasers. A simple equation using only measurable SESAM parameters and including inverse saturable absorption is derived for the Q-switched modelocking threshold. We present various data and discuss the sometimes detrimental effects of this roll-over for femtosecond high repetition rate lasers, as well as the potentially very useful consequences for passively mode-locked multi-GHz lasers. We also discuss strategies to enhance or reduce this induced absorption by using different SESAM designs or semiconductor materials.
Applied Physics Letters, 1997
Time resolved intracavity gain, saturable absorption dynamics, intracavity intensity pulse profiles, and their corresponding spectrograms, were measured in an external cavity hybrid mode-locked semiconductor diode laser. These measurements were performed to obtain fundamental information of the mode-locking dynamics and to determine their role in the pulse shaping and chirping dynamics. The results of these experiments show that the integrating nonlinearity associated with gain depletion, coupled with group velocity dispersion, leads to asymmetric intensity pulse profiles with predominantly cubic temporal phase, while saturable absorption coupled with group velocity dispersion tends to linearize the chirp. Exploitation of these dynamics may allow researchers to generate optical pulses with higher peak intensities than previously reported.
Locking bandwidth of actively mode-locked semiconductor lasers
IEEE Journal of Quantum Electronics, 1993
The locking bandwidth of an actively mode-locked semiconductor laser is a measure of its tolerance to variations in the input drive frequency. At frequencies outside the locking bandwidth, the output pulses from the laser exhibit large amplitude fluctuations and timing jitter. This paper investigates the locking bandwidths of fundamentally driven and harmonically driven high-repetition-rate actively mode-locked semiconductor lasers. We show that the locking bandwidth is maximized when the cavity length is minimized. The locking bandwidth is related to an important constant, the "pull-in time". Experimental data and numerical modeling show that the pull-in time is a function of the optical bandwidth of the system and the RF drive level.