APODIZING HOLOGRAPHIC GRATINGS FOR THE MODAL CONTROL OF SEMICONDUCTOR-LASERS

We first present the fabrication technique of apodizing holographic gr atings. Gratings with a spatially variable reflectivity profile were o btained by the interference of two Gaussian beams on a glass plate cov ered with a photoresist. When the exposure time was short enough to av oid saturation of the photoresist, gratings with a quasi-Gaussian refl ectivity profile for the beam reflected in the -1 order were produced; the reflectivity at the center could be as high as 71%, and the half- width of the reflectivity profile at the e(-1) position could be as sm all as 180 mu m. Apodizing gratings were used as the end mirror of the external cavity of a broad-area semiconductor laser. Single longitudi nal- and lateral-mode operation was observed over the full range of al lowed injection currents. (C) 1997 Optical Society of America.