Single Mode Diode Laser For Optical Scanning And Recording

Laser beam scanning with holographic grating has the advantage of low cost, vibration and wobble insensitive and simple mechanical construction. However, it requires that the laser operate at single longitudinal mode with good wavelength stability. This is easily achieved in a gas laser but is difficult thus far to obtain with a semiconductor laser. We have specifically developed a high power laser particularly suitable for use in holographic scanning. Its high power and single transverse mode feature are also useful in optical disc recording. The device is called channeled-substrate narrow stripe laser with double current confinement and large optical cavity. In this structure, stable single longitudinal mode is achieved by strong index guiding and special facet coating. Furthermore, single transverse mode is maintained by good lateral electrical and optical confinements. The high power capability is obtained by the use of large optical cavity. The resultant is a buried crescent-shaped active region with an additional reverse-biased p-n junction. Light output up to 50 mW is obtained at 790 nm in CW operation at room temperature. Threshold current as low as 30 mA and differential quantum efficiency as high as 60% are achieved. Furthermore, high quality beam with minimum astigmatism and a diver-gence angle of 320 x 100 (FWHM) is maintained throughout the whole power range. This laser has been incorporated into our Holoscan laser printer which is now commercially available. It is also being used in a variety of prototype disc recording systems.