Eugene I. Gordon

Mode selection in GaAs injection lasers resulting from fresnel reflection

In several recent papers, attention has been given to the Fresnel reflectivity associated with cleaved facets of the laser. The small dimensions of the heterostructure waveguide give rise to a considerable angular spread in the energy incident on the facet. As a result, the mode reflectivity is not given simply by the Fresnel equation, which is only valid for an infinite plane wave. Rather, it is a properly weighted average over the plane-wave distribution of the mode. The differences in mode reflectivity with respect to TE and TM modes, as well as the variations with mode number, have been offered as a possible explanation for the predominant appearance of TE modes and preference for higher order modes in the large optical-cavity (LOC) geometry. However, the considerations to date have ignored the finite extent of the field in the junction plane. This situation is rectified in this paper. It is shown that the splitting in the mode reflectivity values between TE (electric field in the junction plane) and TM (electric field perpendicular to the junction plane) modes is reduced, and under certain conditions TM modes can be favored. In particular, it is shown that if a TE mode is oscillating, then there is a preference for a lowest order mode in the plane of the junction and a highest order mode in the transverse plane. Conversely, if for some reason a TM mode is oscillating, then the preference is for highest order modes in the plane of the junction and lowest order modes in the transverse plane.

Purging: a reliability assurance technique for semiconductor lasers utilizing a purging process

Prior to packaging, semiconductor lasers are purged by being subjected first to high temperature and high current simultaneously so as to suppress stimulated emission and stress the shunt paths which allow leakage current to flow around the active region. A prudent, but nonessential, second step is to lower the temperature and/or current so that the lasers emit stimulated emission (preferably strongly, near the peak output power), thereby stressing the active region. Lasers subjected to such a purge exhibit stabilized degradation rates in short times (of the order of a few hours) and provide a robust population which meets the performance criteria of long lifetime systems.

Electro-optic diffraction grating for light beam modulation and diffraction

The interaction between a strong traveling microwave signal and an optical beam in an electro-optic material is described in the limit of very high microwave dielectric constant. The interaction produces effects analogous to those produced by a moving diffraction grating. When the optical beam is wider than the wavelength of the microwave signal, the first grating order is resolved from the zero-order or main beam. Under this condition two types of devices become possible: 1) a beam deflector which can position an optical maser beam on, for example, 105distinct points with negligible crosstalk and with address times of order 10-7s, 2) a baseband light intensity modulator which is founded on the fact that light deflected into the first-order beam by the microwave signal is removed from the main beam. The amount deflected into the first-order beam is proportional to the microwave power; the intensity modulation follows the microwave envelope. The power required for a given modulation depth is inversely proportional to the seven halfs power of the dielectric Constant. As an example, for a not unrealistic choice of dielectric constant of 104, complete transfer from the zero-order to the first-order beam requires 5 watts of microwave power. The interaction length is of order one centimeter and the interaction bandwidth is essentially unlimited. As a baseband modulator the maximum instantaneous bandwidth is of order 10 percent of the subcarrier frequency. Experimental verification is provided in an earlier paper [1].