Coherent laser radar system and target measurement method

• US 20010009458A1
• Filed: 01/12/2001
• Published: 07/26/2001
• Est. Priority Date: 01/20/2000
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Sugimoto, Etsuo, Sugimoto, Kyoko, Yanagisawa, Takayuki, Hirano, Yoshihito, Asaka, Kimio, Wadaka, Shusou, Ooga, Yasuisa
• Granted Patent: US 6,469,778 B2
• Time in Patent Office: Days
• US Class Current: 356/28.5
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/486 Receivers

Abstract

A coherent laser radar system includes a pulsed laser oscillating a pulsed laser beam which is split into two parts by an optical divider. A first part of the two is transmitted as a transmitted beam via a beam splitter. A second part is supplied to a delay line via a coupling optics and others to be delayed by a predetermined time as a local beam, and is incident onto an optical coupler. The received beam from the target is incident onto the optical coupler via a scanning optics and so on. A photodetector carries out the coherent detection of the light beam coupled by the optical coupler. A signal processor computes a target velocity and the like from a signal generated by the detection and converted into a digital signal by an A/D converter. This makes it possible to solve a problem of a conventional system in that the system configuration is complicated and expensive.

Claims

1. A coherent laser radar system comprising:

a pulsed laser for oscillating a single wavelength pulsed laser beam;

optical dividing means for dividing the pulsed laser beam oscillated by said pulsed laser, and for outputting first part of the pulsed laser beam as a transmitted beam and second part of the pulsed laser beam as a local beam;

transceiver optical means for transmitting the transmitted beam to a target, and for receiving a light beam from the target as a received beam;

a delay line for delaying the local beam output from said optical dividing means;

optical coupling means for coupling the received beam with the local beam output from said delay line;

a photodetector for carrying out coherent detection of a light beam output from said optical coupling means; and

a signal processor for obtaining physical information about the target from the signal passing through the coherent detection by said photodetector.

2. The coherent laser radar system according to

claim 1

, wherein said delay line comprises an optical fiber with a predetermined length.

3. The coherent laser radar system according to

claim 1

, wherein said delay line comprises:

an optical divider for dividing the local beam output from said optical dividing means into n local beams, where n is a positive integer greater than one;

n delay lines for providing the n local beams with different delay times; and

an optical coupler for coupling the n local beams delayed by said n delay lines.

4. The coherent laser radar system according to

claim 1

, wherein said delay line comprises:

a loop line; and

an optical coupler for guiding the local beam output from said optical dividing means into said loop line, and for dividing part of the local beam traveling around said loop line.

5. The coherent laser radar system according to

claim 4

, wherein said delay line comprises an optical amplifier at a midpoint of said loop line.

6. The coherent laser radar system according to

claim 1

, further comprising an optical amplifier connected between said delay line and said optical coupling means for amplifying the local beam.

7. The coherent laser radar system according to

claim 5

, wherein said optical amplifier is an optical fiber amplifier.

8. The coherent laser radar system according to

claim 5

, wherein said optical amplifier is a semiconductor optical amplifier.

9. The coherent laser radar system according to

claim 5

, wherein said optical amplifier is a laser amplifier composed of a solid-state laser medium.

10. The coherent laser radar system according to

claim 4

, wherein said optical coupler is a variable optical coupler whose dividing ratio is variable.

11. The coherent laser radar system according to

claim 4

, wherein said optical coupler comprises:

an optical switch consisting of an acoustooptic device for supplying said loop line with local beam output from said optical dividing means and the local beam traveling around said loop line; and

an optical divider for dividing the local beam traveling around said loop line.

12. The coherent laser radar system according to

claim 1

, further comprising an A/D converter for converting the signal output from said photodetector into digital data, and for supplying the digital data to said signal processor.

13. The coherent laser radar system according to

claim 12

, wherein said signal processor comprises:

a time gate for enabling the digital data output from said A/D converter to be input to said signal processor as information data in response to the local beam;

an FFT (fast Fourier transform) section for computing a spectrum of the information data; and

a Doppler frequency detector for detecting a Doppler frequency and for computing the physical information of the target from the spectrum output from the FFT section.

14. A target measurement method comprising the steps of:

oscillating a single wavelength pulsed laser beam;

dividing the pulsed laser beam into a first part used as a transmitted beam and a second part used as a local beam;

transmitting the transmitted beam to a target, and receiving a light beam from the target as a received beam;

delaying the local beam;

coupling the received beam with the local beam delayed;

carrying out coherent detection of the coupled light beam; and

obtaining physical information about the target from the signal passing through the coherent detection.