| 摘要 |
A method for fabricating an InP diffraction grating for a distributed feedback semiconductor laser includes the steps of applying an electron beam resist on a semiconductor substrate, giving electron beam exposure to the electron beam resist and controlling heights of resist patterns by using fixed electron beam diameters but by varying incident electron doses. The semiconductor substrate is dry-etched. The electron beam exposure is such that the incident electron doses are made larger at a center portion than at portions towards two sides of the diffraction grating. Due to the proximity effect, the resist patterns after development will have a lower height and a narrower width at portions at which the incident electron doses are increased and, conversely, a higher height and a wider width at portions at which the incident electron doses are decreased. In a method of fabricating a distributed feedback laser using a substrate of the InP diffraction grating fabricated as above, the method includes the step of sequentially growing on the substrate a waveguide layer, an active layer and a cladding layer. The method enables to fabricate a low distortion distributed feedback laser for analog modulation having non-uniform diffraction gratings.
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