OPTICAL RANGE FINDER

PURPOSE: To accurately detect the phase difference of the measured light at the times of emitting and receiving the light and to improve the measuring accuracy of a distance by comparing the pulse height of a homodyne signal with each other corresponding to the switching of the phase modulation of a drive signal. CONSTITUTION: A signal generator 20 outputs a drive signal D0 in which four types of phase modulation are executed in time division to a light source 30, and outputs the signal D1 and reference signals R1 , R2 having the same frequency f0 to homodyne processors 50, 60. Further, the generator 20 outputs a switching signal S0 synchronized with the phase switching of the signal D1 to a phase detector 70 and a gain regulator 80. Thus, the light source 30 irradiates the object 10 to be measured with a measuring light P0 phase- modulated in a time division. Its scattered reflected light is received by a photodetector 40, which outputs a detection signal M0 to the processors 50, 60. The processors 50, 60 synthesizes the signals R1 , R2 and the signal M() to generate an interference signal. As a result, the pulse heights of holding homodyne signals H11 , H12 and inverting homodyne signals H21 , H22 are accurately reflected by the phase difference of the signal M1 and the signals R1 , R2 .