J. E. Ripper

Measurement of Spontaneous Carrier Lifetime from Stimulated Emission Delays in Semiconductor Lasers

An analysis of the delay between the beginning of the excitation of a semiconductor laser and the onset of stimulated emission is carried out. It justifies the use of these delays as a method of measuring the spontaneous carrier lifetime, even when this lifetime is not the same for all carriers. It is also shown that the lifetime thus measured is the average lifetime of all carriers when the population inversion is at the threshold level.

Single longitudinal mode operation of cw junction lasers by frequency‐selective optical feedback

cw oscillation in a single longitudinal mode is reported for stripe‐geometry junction lasers operated at room temperature with frequency‐selective optical feedback. The frequency‐selective feedback, obtained by optically coupling a diffraction grating to the diode, is used to select a single mode of the normally multimode spectrum generated by the diode laser itself. Single‐frequency oscillation is observed for currents up to 30% above threshold. The oscillation frequency has a linewidth determined primarily by the internal dynamics of the diode and is tunable over the entire multimode spectrum. Additional experimental results demonstrate the homogeneous broadening of the radiative line in these lasers.

Suppression of output nonlinearities in double‐heterostructure lasers by use of misaligned mirrors

Nonlinearity (kinks) in the dependence of light output power on current has been effectively eliminated by the use of mirrors aligned at a small angle from the direction perpendicular to the stripe or filament. Such a structure increases confinement of the lasing filament and causes an increase in threshold current density that is smaller than that produced by stripe narrowing.

Behavior of spontaneous emission across threshold in GaAs junction lasers

The spontaneous emission behavior of a cw stripe‐geometry GaAs laser is examined in detail. Contrary to recently published results, a sharp discontinuity of the spontaneous emission growth occurs when the laser reaches threshold. Above threshold, slow increases in the spontaneous emission are observed, coming mostly from the regions where the lasing light intensity is small. Other discontinuity points were, at higher currents, observed corresponding to the onset of higher‐order modes and second‐order mode locking.

Filaments in semiconductor lasers

Filament profiles in cw stripe‐geometry homostructure GaAs lasers are measured from below to well above threshold through their optical spectra. It is shown that the filament appears well below threshold and its dimensions are not a strong function of injection level and consequently of the optical field intensity. These results are at variance with previously published theories.

Effect of uniaxial pressure on the threshold current of double‐heterostructure GaAs lasers

On application of uniaxial pressure perpendicular to the junction, the threshold current of GaAs double‐heterostructure injection lasers at room temperature is observed to increase to a certain critical pressure P0, and then decrease with further increase in pressure. A flip of the polarization of laser light occurs at P0. This behavior can be explained using a model previously proposed to explain the reduction in threshold of homostructure GaAs lasers upon application of uniaxial pressure.

Spectral hole burning in GaAs junction lasers

Spectral hole burning corresponding to a gain reduction of the order of 1% has been observed in GaAs junction lasers. This observation is made possible by the use of the strong superradiant amplification of the spontaneous emission along the junction.

Effect of saturable absorption on the behavior of spontaneous emission in semiconductor lasers

A substantial reduction of the spontaneous emission intensity is observed at the onset of stimulated emission in some injection lasers. It is shown that this effect is caused by the saturation of optically absorbing traps present in the active region. It is suggested that saturable optical absorption is also responsible for previously unexplained similar reduction observed by Nicoll in bulk semiconductor lasers.

Refractive‐index profile and resonant modes in GaAs lasers

We examine the form of the refractive‐index profile that has to exist in the direction parallel to the junction in a semiconductor junction laser in order to explain the experimentally observed spectral separation between adjacent transverse modes parallel to the junction. We show that previously assumed profiles are unsatisfactory. We present a form of profile that results in predicting mode wavelength separation that is in agreement with experimental data.

Dynamics of Electrons in Heavily Doped GaAs

Spontaneous emission measurements in GaAs junction lasers are interpreted assuming long thermalization and recombination times of electrons injected into the p region of the diode. Experimental results qualitatively agree with calculations based on this model.