Optical measuring apparatus

Claim 2

An optical measuring apparatus, comprising: a light-transmitting portion for projecting light subjected to intensity modulation according to a modulation signal toward a target object; a photoconductive light-receiving element for receiving said modulation signal and light reflected by said target object said photoconductive light-receiving element directly calculating a product between said reflected light and said modulation signal and outputting a signal according to a value of a phase difference between said reflected light and said modulation signal; time-averaging means for receiving said output signal from said photoconductive light-receiving element and calculating a time averaged value of said output signal; frequency adjusting means for adjusting a frequency of said modulated light so as to keep an output signal from said photoconductive light-receiving element fixed at a reference value; frequency counting means for counting a fixed modulation frequency as adjusted by said frequency adjusting means; and processing means for obtaining a characteristic value of an optical path from said light-transmitting portion and said photoconductive light-receiving element to the target object, based on the frequency counted by said frequency counting means.

Claim 3

An optical measuring apparatus according to claim 1, wherein said characteristic value is a distance of the optical path from said light-transmitting portion and photoconductive light-receiving element to the target object.

Claim 4

An optical measuring apparatus according to claim 1, wherein said characteristic value is a group index of the optical path from said light-transmitting portion and photoconductive light-receiving element to the target object.

Claim 5

An optical measuring apparatus according to claim 1, further comprising a calibration bypass optical path for removing a phase difference intrinsic to the optical measuring apparatus itself.

Claim 6

An optical measuring apparatus according to claim 1, further comprising a delay unit between said frequency adjusting means and said light-transmitting portion.

Claim 7

An optical measuring apparatus according to claim 1, wherein said photoconductive light-receiving element is so arranged that if a quantity of the projected light is constant and a value of applied voltage is an independent variable, an amount of a current flowing in said photoconductive receiver is an odd function of the applied voltage in a predetermined definition area including the value of applied voltage being 0 V, and that the applied voltage is periodic, a value of time average thereof is approximately 0, and an amplitude thereof is an even function of time with the origin at a time of an intermediate point between two adjacent times having an amplitude of 0.

Claim 8

An optical measuring apparatus according to claim 6, wherein said photoconductive light-receiving element is a metal-semiconductor-metal photodetector.

Claim 9

An optical measuring apparatus according to claim 1, wherein said photoconductive light-receiving element further comprises: adjusting means for adjusting an offset voltage of said photoconductive light-receiving element.

Claim 10

An optical measuring apparatus according to claim 8, wherein said photoconductive receiver is so arranged that if a quantity of the projected light is constant and a value of applied voltage is an independent variable, an amount of a current flowing in said photoconductive receiver is an odd function of the applied voltage in a predetermined definition area including the value of applied voltage being 0 V, and that the applied voltage is periodic, a value of time average thereof is approximately 0, and an amplitude thereof is an even function of time with the origin at a time of an intermediate point between two adjacent times having an amplitude of 0.

Claim 11

An optical measuring apparatus according to claim 9, wherein said photoconductive light-receiving element is a metal-semiconductor-metal photodetector.

Claim 12

An optical measuring apparatus according to claim 1, wherein said voltage signal is produced by phase-modulating said modulation signal with another modulation signal.

Claim 13

An optical measuring apparatus according to claim 1, wherein said frequency adjusting means comprises: an error amplifier for receiving a reference voltage and an output signal from said photoconductive light-receiving element, amplifying a value of a difference between a value of said reference voltage and a value of the output signal from said photoconductive light-receiving element, and outputting an amplified voltage signal; a low-pass filter for receiving said amplified voltage signal, reducing an ac component, and outputting a near dc voltage signal; and a voltage control oscillator for receiving said near dc voltage signal, producing an electric signal of a frequency according to a value of said voltage signal, and outputting said electric signal to said light-transmitting portion.

Claim 14

An optical measuring apparatus according to claim 1, wherein said frequency adjusting means comprises: an error amplifier for receiving a reference voltage and an output signal from said photoconductive light-receiving element, amplifying a value of a difference between a value of said reference voltage and a value of the output signal from said photoconductive light-receiving element, and outputting an amplified voltage signal; a low-pass filter for receiving said amplified voltage signal, reducing an ac component, and outputting a first near dc voltage signal; first signal converting means for receiving said first near dc voltage signal and a voltage range instruction signal, and outputting a first near dc electric signal having a value according to a value of a product between a value of said first near dc voltage signal and a value of said voltage range; second signal converting means for receiving a displacement voltage instruction signal and outputting a second near dc electric signal having a value according to a value of said displacement voltage instruction signal; signal adding means for receiving said first near dc electric signal and said second near dc electric signal and outputting a second near dc voltage signal according to a value of a sum between a value of said first near dc electric signal and a value of said second near dc electric signal; and a voltage control oscillator for receiving said second near dc voltage signal output from said signal adding means, producing a signal of a frequency according to a value of said voltage signal, and outputting said signal to said photoconductive light-transmitting element.