US 5,614,708 AGranted

Optical feedback photodetection apparatus

AssigneeHamamatsu Photonics K.K.

InventorsMusubu Koishi, Kouichi Shirakawa, Akira Takeshima

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Abstract

An optical feedback photodetection apparatus of the present invention achieves high-speed response while minimizing noise to obtain a high S/N ratio and a wide dynamic range. In the apparatus, on the basis of a modulated drive signal from a drive signal output circuit, a semiconductor laser outputs a light beam modulated at a frequency f.sub.0 to irradiate an object to be measured through an optical system, and the light beam reflected by the object is fed back to the semiconductor laser through the optical system. The intensity of the light beam from the semiconductor laser having an optical amplification function varies due to the return light beam. A photoconductive light-receiving device to which a modulated voltage signal at the frequency f.sub.0 from a voltage application unit is applied receives the light beam from the semiconductor laser and having an intensity varying due to the return light beam, thereby performing synchronous detection. A modulated current signal flowing through the photoconductive light-receiving device is converted to a voltage signal by a current/voltage conversion unit, and the low-frequency component of the voltage signal is extracted.

Claims9

Dependent claims

An optical feedback photodetection apparatus, comprising:

an oscillator for oscillating a synchronizing signal at a predetermined frequency;
a drive signal output unit for outputting a drive signal modulated at the predetermined frequency on the basis of the synchronizing signal output from said oscillator;
a light source which receives the drive signal output from said drive signal output unit to emit a light beam intensity-modulated at the predetermined frequency and which optically amplifies a return light beam reflected from an object to be measured;
an optical system for irradiating the light beam emitted from said light source on said object to be measured and for feeding back the return light beam from said object to said light source;
a voltage application unit for outputting an AC voltage signal at the predetermined frequency on the basis of the synchronizing signal output from said oscillator;
a photoconductive light-receiving device for receiving the light beam emitted from said light source and for synchronously detecting the light beam emitted from said light source at the predetermined frequency upon application of the AC voltage signal output from said voltage application unit;
a current/voltage conversion unit for converting a modulated current flowing through said photoconductive light-receiving device to a voltage signal and for outputting the voltage signal;
and
a frequency filter unit for extracting and outputting a low-frequency component of the voltage signal output from said current/voltage conversion unit.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/591,392Filed 25 Jan 1996
Priority: JP 7-1101226 Jan 1995
Granted: 25 Mar 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

G11B 7/127
Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for…
G02B 21/0084
Details of detection or image processing, including general computer control: time-scale detection, e.g. strobed, ultra-fast, heterodyne detection
G11B 7/13
Heads, e.g. forming of the optical beam spot or modulation of the optical beam: optical detectors therefor
H01S 5/50
Semiconductor lasers: amplifier structures not provided for in groups H01S5/02 - H01S5/30