Fabrication of a focusing grating mirror by electron beam lithography

A focusing grating mirror (FGM), which is a new computer generated holographic grating with functions of focusing lens and diffraction grating mirror, is proposed and fabricated, we believe, for the first time. A high speed and accurate electron beam writing system, based on a multitask minicomputer, 16-bit D/A converters with 64K-word static memories, and a scanning electron beam microscope, is developed and used to fabricate the FGMs comprising grating corrugations with chirp and bend structures. Excellent properties of the FGM are obtained, giving almost diffraction-limited spot size and the expected wavelength dispersion. The fabricated FGM is combined with a laser diode as an external cavity mirror to confirm the functions of direct optical feedback and wavelength selection, and the fundamental operation of an external-cavity laser is demonstrated.