EP0640846A2
Expired / Lapsed
EP
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Optical measuring apparatus
Assignee: Hamamatsu Photonics KK
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Filing: 1994-08-26
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Granted: —
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Expires: 2014-08-26
Abstract
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.
Inventors
- 👤 Akira Takeshima
- 👤 Musubu Koishi
- 👤 Yoshihisa Warashina
- 👤 Yoshihiko Mizushima
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 10:27
CPC Classifications
G; G01; G01S; G01S7/00; G01S7/48; G01S7/481; G01S7/4818; G01S17/00; G01S17/02; G01S17/06; G01S17/08; G01S17/32; G01S17/36; G01S17/88; G01S7/491; G01S7/4912; G01S7/4915; G01S7/4918
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
173 words
An optical measuring apparatus comprising: a light-transmitting portion for projecting modulated light subjected to intensity modulation toward a target object; a light-receiving portion for receiving reflected, modulated light reflected by said target object and returning thereto and a voltage signal reflecting a waveform of a modulation signal used in the intensity modulation in said light-transmitting portion, directly calculating a product between said reflected, modulated light and said voltage signal, time-averaging a calculation result of said product, and outputting a signal according to a value of a phase difference between said reflected, modulated light and said voltage signal; frequency adjusting means for adjusting a frequency of said modulated light so as to keep an output signal from said light-receiving portion 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 light-receiving portion to the target object, based on the frequency counted by said frequency counting means.
Claim 2
Dependent Claim
30 words
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 light-receiving portion to the target object.
Claim 3
Dependent Claim
31 words
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 light-receiving portion to the target object.
Claim 4
Dependent Claim
27 words
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 5
Dependent Claim
22 words
An optical measuring apparatus according to Claim 1, further comprising a delay unit between said frequency adjusting means and said light-transmitting portion.
Claim 6
Dependent Claim
57 words
An optical measuring apparatus according to Claim 1, wherein said light-receiving portion comprises: a photoconductive receiver for receiving a light signal, to which a voltage reflecting the waveform of said modulation signal is applied; and time-averaging means for receiving an output current from said photoconductive receiver to calculate a time average of values of said output current.
Claim 7
Dependent Claim
25 words
An optical measuring apparatus according to claim 6, wherein said light-receiving portion further comprises adjusting means for adjusting an offset voltage of said photoconductive receiver.
Claim 8
Dependent Claim
113 words
An optical measuring apparatus according to Claim 6 or 7, 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 0V, 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 9
Dependent Claim
16 words
An optical measuring apparatus according to Claim 8, wherein said photoconductive receiver is a metal-semiconductor-metal photodetector.
Claim 10
Dependent Claim
23 words
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 11
Dependent Claim
116 words
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 light-receiving portion, amplifying a value of a difference between a value of said reference voltage and a value of the output signal from said light-receiving portion, 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 12
Dependent Claim
260 words
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 light-receiving portion, amplifying a value of a difference between a value of said reference voltage and a value of the output signal from said light-receiving portion, 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 light-transmitting portion.
Claim 13
Dependent Claim
63 words
Optical measuring apparatus wherein an optical beam is transmitted and received, and a frequency of intensity modulation of the transmitted beam is controllable to enable a predetermined phase relation to be established with the received beam, such that a characteristic of the optical path between transmission and reception can be determined from the modulation frequency once the predetermined phase relation has been established.
References Cited (Backward Citations)
No citation records indexed.
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