The present invention relates to semiconductor lasers, and more specifically to semiconductor lasers having fundamental lateral mode selectivity.
It is a well known fact that the optical radiation emitted from a semiconductor laser consists of radiation having a finite number of transverse modes and lateral modes. The fundamental mode in either the transverse or lateral direction is the mode of optical radiation having no nodes; all other modes in the lateral or transverse direction are known as higher order modes. The prior art has taught that if the active region or recombination region of the semiconductor laser is made thin enough the number of transverse modes could be reduced to only the fundamental transverse mode.
Limiting the radiation in the emitted optical radiation beam to the fundamental mode alone in the lateral direction has proved to be a difficult undertaking. Attempts have been made to achieve single lateral mode operation of lasers by confining the optical gain region to a long, narrow stripe across the body and perpendicular to the cleaved mirrored end surfaces by using narrow stripe electrical contacts near the recombination region. This generally does not provide enough mode selectivity to assure single mode operation, especially at high drive current levels.
The operation of a semiconductor laser in the fundamental lateral and fundamental transverse modes alone is most desirable since the emitted optical radiation beam will be much narrower than radiation containing a finite number of lateral and transverse modes. Single mode laser operation is especially desirable in such applications as fiber optical communications and video disc readout. Therefore, it would be most desirable to be able to operate a semiconductor laser not only in the fundamental transverse mode but also in the fundamental lateral mode.