Semiconductor laser spatial mode tailoring using an external cavity mode-selecting mirror.

摘要

The objectives of this dissertation were to theoretically explore and experimentally develop a new external cavity method for tailoring the spatial mode structure of a semiconductor laser array and a wide-stripe semiconductor laser. The general concept of the external cavity stabilization technique is to select a desired spatial mode profile (which by definition becomes the fundamental mode of the laser) and then to fabricate a diffractive optical element (called a Diffractive Mode Selecting Mirror (DMSM)) which has a significant modal reflectivity for only this tailored fundamental mode. Under the proper conditions, significant mode discrimination between the tailored fundamental mode and the next higher-order mode can be achieved.; The research evolved through three phases. In the first phase, general aspects of the DMSM concept were theoretically developed and successfully applied to a Talbot cavity. It was shown that the free space characteristics of the Talbot effect could be modified by an appropriate diffractive optical element (the fore-runner of the DMSM) to achieve a uniquely selected intensity profile as opposed to the naturally occurring Talbot image. This served as the initial proof-of-concept. Motivated by this success, the technique was used to stabilize a tailored spatial mode in an external cavity, one-dimensional, semiconductor array consisting of either 4 or 8 laser diodes. Next, the DMSM method of tailoring a spatial mode in an external cavity semiconductor laser was successfully applied to a laser using a wide-stripe semiconductor amplifier as the gain medium. 2.8 watts of stable output power was achieved over a 600{dollar}mu{dollar}m-wide region of the wide-stripe amplifier. To my knowledge, this is the largest, single transverse mode region ever stabilized in a semiconductor laser.; Finally it must be noted that although the DMSM technique was demonstrated by tailoring the spatial mode of semiconductor lasers, it is generally applicable for tailoring the spatial modes of all classes of lasers.