Sound measurement apparatus, sound measurement method, and program

Abstract

Provided is a measurement technology of an optical phase modulation amount due to sound without being affected by noise included in average light intensity. The measurement technology includes: an interference light generator that obtains first light including light subjected to optical phase modulation by a sound measurement unit and second light different from the first light and including light subjected to optical phase modulation by the sound measurement unit from light emitted from a light source; a first photodetector that obtains a first electrical signal from the first light; a second photodetector that obtains a second electrical signal from the second light; a differential signal generator that obtains a differential signal that is a difference between the first electrical signal and the second electrical signal; and an optical phase modulation amount adjuster that adjusts an optical phase modulation amount φdue to an element other than sound by fixing an interferometer such that a phase of an interference fringe is in mid-fringe by using the differential signal as an error signal, in which the optical phase modulation amount φdue to sound is measured as a current Δi of the differential signal, and the first photodetector and the second photodetector are adjusted such that output voltages are saturated when light that causes a phase fluctuation exceeding a predetermined range around mid-fringe is input.