Lateral-mode selectivity in external-cavity diode lasers withresidual facet reflectivity

The relatively flat lateral gain profile across a wide-strip laser diode does not allow sufficient overlap with the Gaussian fundamental mode of an external resonator to achieve saturation of the gain in the wings of the mode profile. Thus, parasitic free-running oscillation of the diode in an external-cavity laser is permitted by residual facet reflectivity of the antireflection-coated diode, and degrades the lateral-mode-selectivity of the external resonator at injection currents exceeding the threshold of the solitary diode. A relation between the maximum injection current at which the external-cavity laser will operate in a single mode and the diode's facet reflectivity is given     

Competing effects of well-barrier hole burning and nonlinear gainon the resonance characteristics of quantum-well lasers

The effects of the quantum capture and release of carriers from quantum wells (QWs) on the resonance response of QW lasers are investigated from a model of well-barrier hole burning with built-in nonlinear gain. Significant similarities and contrasts with the conventional single-mode model are noted in both the large-signal transient behavior and in the small-signal resonance characteristics. The competition between well-barrier hole burning and nonlinear gain is explored by studying of time responses, phase portraits, frequency transfer functions; and contour maps of constant resonance frequency, damping rate, and 3-dB bandwidth in the parameter spaces defined by the nonlinear gain coefficient versus the ratio of relaxation times for capture and release of carriers by the wells. A systematic treatment of the well-barrier model is presented along with these predicted dynamical trends     

Experimental verification of strain benefits in 1.5-μmsemiconductor lasers by carrier lifetime and gain measurements

Recombination processes, gain, and loss have been comparatively studied in both strained and lattice-matched 1.5-μm semiconductor quantum-well lasers using differential carrier lifetime techniques and other measurements. For the first time, some predicted strain benefits to 1.5-μm semiconductor lasers have been verified, including (i) the reduction of the Auger recombination rate in devices with both 0.9% and 1.8% compressive strain; and (ii) a 33% reduction of transparency carrier density in lasers with 0.9% strain compared to lattice-matched lasers. The authors, however, did not observe an increase of the differential gain in strained devices as predicted     

Experimental study of Auger recombination, gain, and temperaturesensitivity of 1.5 μm compressively strained semiconductorlasers

The effect of strain on Auger recombination has been studied using the differential carrier lifetime technique in both lattice matched InGaAs-InP and compressively strained quaternary quantum wells. It is found that Auger recombination is reduced in strained devices. The transparency carrier density and differential gain of both lattice matched and strained devices have been obtained by gain and relative intensity noise measurement. A reduction of the transparency carrier density is observed in the strained device. However, no differential gain increase is seen. The temperature sensitivity of the threshold current density of both lattice matched and strained devices has been fully studied. Physical parameters contributing to the temperature sensitivity of the threshold current density have been separately measured, and it is shown that the change in differential gain with temperature is a dominant factor in determining the temperature sensitivity of both lattice matched and strained devices     

Intracavity optical bistability due to thermally induced changes in absorption and refraction

Optical bistability in the presence of an optically induced absorption is observed when a thin 13 μm CdS sample is inserted between two mirrors of 90 percent reflectivity. In our experiment, a modulated CW laser of about 15 mW peak power is tuned on each side of theAfree exciton resonance in CdS, and the transmission characteristics are studied. A theoretical calculation is presented and good agreement is obtained.     

Dynamics of optically switched bistable diode laser amplifiers

Measurements of the switch-off time of an optically switched Fabry-Perot InGaAsP/InP laser amplifier indicate that the device can turn off in less than the spontaneous carrier lifetime. The switching dynamics of the amplifier are numerically modeled using the van der Pol equation with optical injection and the rate equation for the carrier density. The simulations show that the device switches off faster as its injection current is increased toward the threshold level. A qualitative analytical analysis is presented which shows that this fast switch off is due to the very large cavity finesse of the amplifier when biased near its lasing threshold.     

Observation of mode beating and self-frequency locking in a nearlysingle-mode semiconductor laser

The beat spectra between the adjacent modes of a semiconductor laser having no external cavity are reported. Passive beat-frequency locking is observed at high power without a saturable absorber. This self-induced locking is manifested by the dramatic narrowing (by four orders of magnitude) of the beat spectrum between the dominant and adjacent modes. It is accompanied by the transition from nearly single-mode behavior to a highly structured multifrequency optical spectrum     

Well-barrier hole burning in quantum well lasers

The reported wide variations in the damping behavior of quantum well lasers are explained by a novel theory of nonlinear gain, well-barrier hole burning. In the model a spatial hole develops perpendicular to the active region involving carriers moving between the wells and the barrier/confinement layers. The modified rate equations describing well-barrier hole burning are presented. An analytical approximation for the nonlinear gain coefficient epsilon , valid only under certain conditions, is given. A numerical solution is given for the case of high photon densities and large capture-times. It is shown how well-barrier hole burning explains the measurements of the increased spontaneous emission from the barrier/confinement region above threshold. Various higher-than-expected damping rates reported in some quantum well lasers are shown to be consistent with the model.<>     

Anomalously high damping in strained InGaAs-GaAs single quantum well lasers

Measurements of the relative intensity noise spectra of strained, single-quantum-well, separate-confinement-heterostructure (SCH) InGaAs-GaAs lasers indicate that their frequency response is strongly damped. The ratio of the damping rate to the square of the resonance frequency is k=2.4 ns. This intrinsically limits the 3-dB modulation bandwidths of these lasers to about 4 GHz, negating the predicted increase in modulation bandwidth due to the large differential gain often associated with quantum-well devices. The damping behavior of these lasers is inconsistent with previous predictions of damping in bulk lasers due to spectral hole burning. A structure-dependent damping mechanism is proposed for quantum-well lasers.<>     

High power 980 nm ridge waveguide lasers with etch-stop layer

For the first time, the use of an etch-stop layer to precisely control the mesa height in ridge waveguide InGaAs/GaAs lasers is reported. These 980 nm devices emit up to 180 mW of total power in the fundamental spatial mode and lase in a single frequency with sidemode suppression ratios of greater than 25 dB.<>