Signal processing apparatus for optical gyro

An apparatus for effecting a signal processing for an optical gyro in which light is propagated simultaneously clockwise and counterclockwise through an optical propagation path in cooperation with a rotation axis and receives a phase modulation and then a phase difference of the light based on Sagnac effect is detected to obtain a photoelectric output signal proportional to an input rotation angular velocity, the apparatus comprising:

• a frequency mixing circuit, responsive to digital reference signals in synchronization with a drive signal for the phase modulation, for taking signal components of the same frequency fm as, a frequency 2fm twice, and a frequency 4fm four times that of the drive signal from the photoelectric output signal and converting the respective signal components to a signal of a frequency .DELTA.fm.sub.1, a signal of a frequency .DELTA.fm.sub.2 and a signal of a frequency .DELTA.fm,, respectively, to thereby output first, second and third analog signals, respectively, and for converting fifth, seventh and ninth analog reference signals in synchronization in phase with the drive signal and having frequencies fm, 2fm and 4fm, respectively, to a signal of the frequency .DELTA.fm.sub.1, a signal of the frequency .DELTA.fm.sub.2 and a signal of the frequency .DELTA.fm.sub.3, respectively, to thereby output fourth, sixth and eighth analog signals, respectively;
• an analog/digital converting circuit, responsive to second, seventh and twelfth digital signals in synchronization with the fourth, sixth and eighth analog signals, respectively, for converting the first, second and third analog signals to first, sixth and eleventh digital signals, respectively;
• a digital demodulating means, operatively connected to the frequency mixing circuit and the analog/digital converting circuit, for outputting the second, seventh and twelfth digital signals, generating third, eighth and thirteenth digital signals in synchronization with the fourth, sixth and eighth analog signals, respectively, forming fourth and fifth digital signals in synchronization with the third digital signal and shifted in phase by 90.degree. from each other, ninth and tenth digital signals in synchronization with the eighth digital signal and shifted in phase by 90.degree. from each other, and fourteenth and fifteenth digital signals in synchronization with the thirteenth digital signal and shifted in phase by 90.degree. from each other, effecting digital multiplications between the first digital signal and the fourth and fifth digital signals, between the sixth digital signal and the ninth and tenth digital signals, and between the eleventh digital signal and the fourteenth and fifteenth digital signals, and taking direct current components from results of the respective multiplication to thus output a sixteenth digital signal;
• a polarity discriminating means, responsive to the sixteenth digital signal, for discriminating a polarity of the input rotation angular velocity to thereby output a seventeenth digital signal;
• a phase modulation index computing means, responsive to the sixteenth digital signal, for outputting an eighteenth digital signal for keeping constant a ratio of each amplitude of the signal components corresponding to the frequencies 2fm and 4fm of the photoelectric output signal, and outputting a ninteenth digital signal corresponding to a present phase modulation index;
• and
• an angular velocity computing means, responsive to the sixteenth, seventeenth and ninteenth digital signals, for outputting a twentieth digital signal proportional to the input rotation angular velocity.