Abstract: 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.theta.=sin.sup.-1 m.lambda..sub.B /2Pwhere .theta. represents the blaze angle, P the pitch of the groove, .lambda..sub.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.

Abstract: 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 ##EQU1## where .theta. represents the blaze angle, P the pitch of the groove, .lambda..sub.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.

Abstract: A mechanical optical switching device has a plurality of input optical fibers coupled to the input side of the mechanical switching device for receiving incoming light beam signals. Individually associated with each optical fiber is an input collimating lens which is positioned to receive the incoming light beam and to convert it into parallel light beams. Optical path-switching means, having a uniform refractive index, are disposed at the rear or output of the input lens for switching the optical paths of the collimated parallel light beams emerging from the input lens means. A plurality of output optical fibers have individually associated output lenses for focusing the parallel light beams, after they have passed through the position controlled by the optical path-switching means.