JPS57120864A - Optical system voltage measuring device - Google Patents

Abstract

PURPOSE:To obtain an optical voltmeter whose temperature characteristic has been improved, by utilizing a temperature change of an angle of rotation of a crystal rotary plate, and compensating a temperature of an electrooptical crystal. CONSTITUTION:A temperature change of an electrooptical crystal 1 is offset by placing a crystal rotary plate 6 in fron of the electrooptical crystal 1 and changing the incident polarization direction in accordance with a temperature. For instance, in case when an incident polarization direction 8 at the time of a low temperature is set to phi= 45 deg., and it has been varied by theta at the time of a high temperature, an optical signal output obtained through a 1/4 wavelength plate 4 and a polarizing prism 3 becomes Palpha sin(V.pi/V ).cos(2theta). In this state, in case when half-wavelength voltage V is decreased by 4% at the time of a high temperature, the first term of said expression becomes almost 1.04 times, but the temperature change component is offset by constituting so that the second term becomes 0.96 at the time of a high temperature. That is to say, in this case, theta becomes equal to 8 deg., and thickness (d) of the crystal rotary plate 6 becomes 28mm. according to the experiment. In this way, when thickness of the crystal rotary plate 6 in accordance with dependence of V of the electrooptical crystal 1, a temperature compensation to various crystals becomes effective.