Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as a factor of six in quantum-well lasers. They also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while the nonlinear gain compression factor remains largely unaffected by it. The authors present the temperature dependence data for the K factor as further evidence for the effects of carrier transport. >

High speed quantum-well lasers and carrier transport effects

The frequency response of a group of 1.3 μm InGaAsP vapor-phase-regrown buried heterostructure lasers of various cavity lengths is analyzed by fitting the measured response curves. The dependence of resonant frequency f 0 and damping rate \Gamma on bias power is determined. The differential gain coefficient for InGaAsP is determined as 3.5 \times 10^{-16} cm2. The damping rate is found to be proportional to the square of the resonant frequency with a proportionality factor which is independent of device geometry and facet reflectivity. The existence of such a universal relationship between \Gamma and f 0 and the observed magnitude of the damping rate is explained by the interband relaxation model of nonlinear gain.

Frequency response of 1.3&#181;m InGaAsP high speed semiconductor lasers

The gain spectrum in semiconductor lasers is affected by the intensity-dependent nonlinear effects taking place due to a finite intraband relaxation time of charge carriers. We obtain an analytic expression for the nonlinear gain in multimode semiconductor lasers using the density-matrix formalism. In general, the nonlinear gain is found to consist of the symmetric and asymmetric components. The asymmetry does not have its origin in the carrier-induced index change, but is related to details of the gain spectrum. The general expression for the nonlinear gain is used to discuss the range of single-longitudinal-mode operation of distributed feedback lasers. It is also used to obtain an analytic expression for the self-saturation coefficient and to compare the predicted value to the experimental value for both GaAs and InGaAsP lasers. The agreement between the theoretical and the experimental values supports the hypothesis that spectral hole burning is the dominant mechanism for the gain nonlinearities in semiconductor lasers.

Gain nonlinearities in semiconductor lasers: Theory and application to distributed feedback lasers

We investigate the occurrence of instabilities related to possible transitions to chaos in specific configurations based on semiconductor lasers. Various scenarios, such as period doubling, frequency locking, quasiperiodicity, and intermittency, are observed experimentally as functions of the control parameters. These are, respectively, the current modulation, external light injection, and delayed feedback. The experimental findings are described and discussed on the basis of semiconductor-laser rate equations.

Intensity instabilities of semiconductor lasers under current modulation, external light injection, and delayed feedback

The influence of both compressive and tensile strain on semiconductor lasers and optical amplifiers is reevaluated in the light of recent experimental and theoretical work. Strain reduces the three-dimensional symmetry of the lattice and helps match the wave functions of the holes to the one-dimensional symmetry of the laser beam. It can also decrease the density of states at the valence band maximum and so reduce the carrier density required to reach threshold. These two effects appear to adequately explain the TE and TM gain in compressive and tensile structures, including polarization-independent amplifiers, the behavior of visible lasers and the improved frequency characteristics of InGaAs/GaAs lasers. In 1.5 /spl mu/m InGaAsP/InP lasers phonon-assisted Auger recombination appears to remain the dominant current path and can explain why the temperature sensitivity parameter to remains >

Band-structure engineering in strained semiconductor lasers

Recently, the bandwidths of semiconductor lasers, detectors, and optical transmission systems have been dramatically increased. The considerations used to achieve a record 26.5 GHz bandwidth in a 1.3 μm InGaAsP laser at -60°C are described here. The small-signal modulation characteristics of a number of different laser structures are compared. Several large-signal modulation experiments are described with emphasis on the laser response to 8 Gbit/s modulation.

B. Hemenway

Papers

High-speed InGaAsP constricted-mesa lasers