| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a Sagnac interference-type photocurrent sensor carrying out stable and high-accuracy measurement, even if the modulation efficiency of a phase modulation element changes, or a light propagation route, especially an extinction ratio between the phase modulation element and a 1/4 wavelength board worsens. <P>SOLUTION: A phase-modulation-element driving circuit controls the phase modulation depth of the phase modulation element so that the amplitude of a second-order harmonic and the amplitude of a fourth-order harmonic become the same, when synchronous detection of a detected light quantity is carried out with a phase modulation angular frequency. The standardization means of an arithmetic circuit calculates a reference value by dividing the amplitude of the third-order harmonic of a signal controlled by the phase-modulation-element driving circuit, by any one of the amplitudes of even-order harmonics of the second-order, fourth-order, and six-order harmonics, or the sum of the amplitudes of the second-order and fourth-order harmonics. Then the standardized reference value is output as a value proportional to the magnitude of a current to be measured. <P>COPYRIGHT: (C)2011,JPO&INPIT |
