JPS6479723A - Optical modulating device - Google Patents

Abstract

PURPOSE:To reduce the instability of driving including the temperature characteristic of the liquid crystal tilt angle by properly setting a ratio of a length 1L of a low- refractive index part to a length 1H of a high-refractive index part occupied in one cycle of a diffraction grating, which consists of the certain low-refractive index part and the high-refractive index part, and relations to diffraction efficiency. CONSTITUTION:A phase type diffraction grating is constituted by a certain-refractive index material having a refractive index ng and a refractive index varying material which are interposed between surfaces facing each other of two substrates; and when the refractive index of the refractive index varying material is controlled to perform optical modulation, nthetam (=ng) exists at the time of the use if an arbitrary refractive index existing between a maximum refractive index nmax and a minimum refractive index nmin of the refractive index varying material is denoted as ntheta. Relations between lengths 1L and 1H are set to satisfy {1L/(1L+1H)}>0.5 in case of nmin<ntheta<ng and are set to satisfy {1L/(1L+1H)}<0.5 in case of ng<ntheta<nmax. Concretely, a refractive index varying material 1 and a certain-refractive index material 2 are alternately interposed in parallel, and both faces are interposed between substrates 4 having transparent electrodes 3.