| 摘要 |
In a diffraction grating made of a single crystalline silicon substrate, one major plane thereof is provided with a plurality of asymmetric triangular grooves, each having a wall inclined by an angle theta with respect to the major surface so as to satisfy an equation <IMAGE> where theta represents the blaze angle, P the pitch of the groove, lambda B the blazing wavelength, and m the order of diffraction. The walls of each groove receiving incident light is covered with a metal coat. The diffraction grating is prepared by using a {hkl} plane (where h=k) inclined by theta with respect to the {111} plane of the single crystalline silicon as a major surface, and then anisotropic-etching the major surface through an etching mask having stripes having sufficiently smaller width than the grating constant. Preferably, following the anisotropic etching, isotropic etching is made for the major surface.
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