Extended cavity lasers which utilize semiconductor gain elements and many different types of passive cavities have long been used for both single frequency operation and for short pulse generation by mode-locking. Proper operation of an extended cavity laser requires a semiconductor gain element (which is achieved by high quality AR coatings on the semiconductor laser facets) and a high overall feedback (which requires a high coupling efficiency between the gain medium and the extended passive cavity, a low loss in that cavity, and a high reflection at the cavity end). A major limitation of extended cavity lasers is the limited power levels at which they operate, determined by the relatively low powers of conventional semiconductor lasers. High powers are readily available from laser arrays. Incorporating a laser array in an extended cavity is difficult, however, because the complex radiation pattern complicates the AR coating procedure and more important, does not lend itself to efficient coupling.
© 1990 Optical Society of AmericaPDF Article