US 5,534,992 AGranted

Optical measuring apparatus

AssigneeHamamatsu Photonics K.K.

InventorsAkira Takeshima, Musubu Koishi, Yoshihisa Warashina, Yoshihiko Mizushima

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Abstract

Laser light from LD (laser diode) is guided through a fiber to be projected onto a reflector. A receiver detects a return beam of modulated light reflected by the object and outputs a signal reflecting a phase difference between the laser light and the modulation signal. The frequency of the modulation signal is changed based on the signal value so as to finally achieve phase lock. When the phase lock fixes the frequency of the modulation signal, the frequency always corresponds to a distance from LD to the reflector or a group index of a substance filling the optical path. Thus, the distance to the object or the group index of the substance filling the optical path at the time of phase lock can be determined in a simple manner and with a high accuracy, based on the output frequency at the time of phase lock.

Claims13

Dependent claims

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.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/298,554Filed 30 Aug 1994
Priority: JP 5-21419930 Aug 1993
Granted: 9 Jul 1996
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

G01S 7/4818
Constructional features, e.g. arrangements of optical elements: using optical fibres
G01S 7/4915
Receivers: time delay measurement, e.g. operational details for pixel components ; Phase measurement
G01S 17/36
Using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated: with phase comparison between the…
G01S 17/88
Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems: lidar systems specially adapted…