Coherent laser radar device

• US 20030133093A1
• Filed: 11/21/2002
• Published: 07/17/2003
• Est. Priority Date: 05/11/2001
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yanagisawa, Takayuki, Hirano, Yoshihito, Asaka, Kimio
• Granted Patent: US 6,765,654 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• 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 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

An object of the invention is to obtain a coherent laser radar device that provides one system of a photo detector and eliminates a blind zone, including a pulsed laser that oscillates at a frequency which is identical with or close to an output light of a local light source as a single frequency; a transmission/reception optical system that irradiates a pulsed laser beam from the pulsed laser toward a target as a transmission light and receives a scattered light from the target as a reception light; a light coupling means that couples the output light from the local light source and the reception light; a photo detecting portion that conducts light coherent detection on a coupled light; and a signal processing device that calculates a speed and a distance of a target in accordance with an output of the detection, in which the photo detecting portion comprises: a photo detecting element that conducts the light coherent detection; a microwave switch that changes over a propagation path of an output from the photo detecting element; a microwave amplifier; and a switch control means that changes over the microwave switch so as to transmit a signal before a reference time as a monitor signal and transmit a signal after the reference time as a reception signal with a time at which the pulse light from the pulsed laser has completely passed through the transmission/reception optical system as the reference time.

Claims

1. A coherent laser radar device comprising:

a local light source that oscillates at a single frequency;

a pulsed laser that oscillates at a frequency which is identical with or close to an output light of said local light source as a single frequency;

a transmission/reception optical system that irradiates a pulsed laser beam from said pulsed laser toward a target as a transmission light and receives a scattered light from the target as a reception light;

a light coupling means that couples the output light from said local light source and said reception light;

a photo detecting portion that conducts light coherent detection on the light coupled by said light coupling means; and

a signal processing device that calculates a speed and a distance of a target in accordance with an output from said photo detecting portion, characterized in that said photo detecting portion comprises;

a photo detecting element that conducts the light coherent detection;

a microwave switch that changes over a propagation path of an output from said photo detecting element;

a microwave amplifier; and

a switch control means that changes over said microwave switch so as to transmit a signal before a reference time to said signal processing device as a monitor signal and transmit a signal after the reference time to said signal processing device as a reception signal with a time at which the pulse light from said pulsed laser has completely passed through said transmission/reception optical system as the reference time.

2. A coherent laser radar device according to claim 1, characterized in that:

said pulsed laser includes an adjusting mechanism that adjusts a cavity length;

said device further comprises a control circuit that controls said adjusting mechanism; and

said control circuit outputs to said adjusting mechanism a control signal that adjusts the cavity length of said pulsed laser on the basis of an error signal from said signal processing device based on a frequency difference between the laser pulse and the local light.

3. A coherent laser radar device according to claim 1, characterized in that:

said microwave amplifier is made up of a pre-amplifier that amplifies a signal from said photo detecting element and a post-amplifier that amplifies an output of the pre-amplifier; and

said microwave switch is disposed between said pre-amplifier and said post-amplifier, outputs a signal that has been amplified by said pre-amplifier as a monitor signal and outputs a signal that has passed through said post-amplifier as a reception signal.

4. A coherent laser radar device according to claim 1, characterized in that:

said microwave amplifier is made up of a pre-amplifier that amplifies a signal from said photo detecting element and a post-amplifier that amplifies an output of the pre-amplifier; and

said microwave switch is disposed between said photo detecting element and said pre-amplifier, outputs a signal from said photo detecting element as a monitor signal and outputs a signal that has passed through said post-amplifier as a reception signal.

5. A coherent laser radar device comprising:

a local light source that oscillates at a single frequency;

a pulsed laser that oscillates at a frequency which is identical with or close to an output light of said local light source as a single frequency;

a transmission/reception optical system that irradiates a pulsed laser beam from said pulsed laser toward a target as a transmission light and receives a scattered light from the target as a reception light;

a light coupling means that couples the output light from said local light source and said reception light;

a photo detecting portion that conducts light coherent detection on the light coupled by said light coupling means; and

a signal processing device that calculates a speed and a distance of a target in accordance with an output from said photo detecting portion, characterized in that said photo detecting portion comprises;

a photo detecting element that conducts the light coherent detection,

a microwave amplifying portion that amplifies an output signal from said photo detecting element; and

a gain control means that controls the gain of said microwave amplifying portion so that an amplitude of the output signal from said microwave amplifying portion does not exceed a given threshold value.

6. A coherent laser radar device according to claim 5, characterized in that:

said pulsed laser includes an adjusting mechanism that adjusts a cavity length;

said device further comprises a control circuit that controls said adjusting mechanism; and

said control circuit outputs to said adjusting mechanism a control signal that adjusts the cavity length of said pulsed laser on the basis of an error signal from said signal processing device based on a frequency difference between the laser pulse and the local light.

7. A coherent laser radar device according to claim 5, characterized in that:

said microwave amplifier is made up of a pre-amplifier that amplifies a signal from said photo detecting element and a gain control amplifier that amplifies an output of the pre-amplifier; and

said gain control means controls the gain of said gain control amplifier.

8. A coherent laser radar device according to claim 5, characterized in that:

said microwave amplifier is made up of a pre-amplifier that amplifies a signal from said photo detecting element and a post-amplifier that amplifies an output of the pre-amplifier; and

said gain control means comprises a microwave variable attenuator disposed between said pre-amplifier and said post-amplifier, and an attenuation control circuit that controls the attenuation of said microwave variable attenuator.

9. A coherent laser radar device characterized by comprising:

a local light source that oscillates at a single frequency;

a pulsed laser that oscillates at a frequency which is identical with or close to an output light of said local light source as a single frequency;

a transmission/reception optical system that irradiates a pulsed laser beam from said pulsed laser toward a target as a transmission light and receives a scattered light from the target as a reception light;

a light coupling means that couples the output light from said local light source and said reception light;

a photo detecting portion that conducts light coherent detection on the light coupled by said optical coupler; and

a signal processing device that detects a speed and a distance of a target in accordance with an output from said photo detecting portion;

a light variable attenuator disposed between said transmission/reception optical system and said photo detecting portion; and

a control means that controls the attenuation of said light variable attenuator in such a manner that an amplitude of the output from said photo detecting portion does not exceed a given threshold value.

10. A coherent laser radar device according to claim 9, characterized in that:

said pulsed laser includes an adjusting mechanism that adjusts a cavity length;

said device further comprises a control circuit that controls said adjusting mechanism; and

said control circuit outputs to said adjusting mechanism a control signal that adjusts the cavity length of said pulsed laser on the basis of an error signal from said signal processing device based on a frequency difference between the laser pulse and the local light.