Polarization-type laser detection system

Details Polarization-type laser detection system Polarization-type laser detection system

1999-07-09

2001-12-04

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S221000, C250S222100

Reexamination Certificate

active

06326608

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to laser technology, and more particularly, to a polarization-type laser detection system which is capable of distinguishing between a reflected light signal from a target object and a back-scattered light signal from a mass of suspended particles in the air.
2. Description of Related Art
FIG. 1
is a schematic diagram of a conventional laser detection system. As shown, this laser detection system includes a control unit
10
, a laser emitter
20
, and an optical receiver
30
. This laser detection system is used to detect whether any target object is present nearby. In the case of a target object
40
is present nearby, the laser beam from the laser emitter
20
will be reflected back by the target object
40
and received by the optical receiver
30
. The received light is then analyzed by the control unit
10
to indicate the presence of the target object
40
.
One drawback to the foregoing laser detection system, however, is that, under bad weather conditions when the air is filled with suspended particles, the emitted laser beam from the laser emitter
20
would be scattered back, causing the optical receiver
30
to received a back-scattered light signal that would make the control unit
10
unable to perform the intended target detection. The laser detection system would therefore operate improperly under bad weather conditions.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide a laser detection system, which is capable of distinguishing between a reflected light signal from a target object and a back-scattered light signal from suspended particles in the air, so as to allow the laser detection system to be nevertheless reliably operable under bad weather conditions.
In accordance with the foregoing and other objectives of this invention, a new laser detection system, called polarization-type laser detection system, is provided.
The polarization-type laser detection system of the invention includes the following system components: laser means for generating a linearly-polarized laser beam which is polarized in a first direction; an emitting optical system, coupled to the laser means, for directing the laser beam to a specified direction for target detection; a reception optical system for receiving the echoed light signal from the emitted laser beam, if any; the reception optical system including: an analyzer lens (AL) for blocking a first direction of the echoed light signal and passing a second direction that is perpendicular to the first direction in which the emitted laser beam is polarized; and a Fresnel lens for focusing the emerging light from the AL into a focal point; an optical detection module, including a first optical detector disposed at the focal point of the Fresnel lens; and a second optical detector disposed beside the first optical detector.
The polarization-type laser detection system of the invention further comprises a laser drive circuit, coupled to the laser means, for driving the laser means to produce the linearly-polarized laser beam. The emitting optical system includes a stop, optically coupled to the laser means, for restricting the amount of the laser beam emitted from the laser means; and a collimator, optically coupled to the stop, for collimating the emerging light from the stop, with the collimated light then being outputted from the emitting optical system for target detection. Further, the polarization-type laser detection system of the invention comprises a pre-amplification circuit, coupled to the first and second optical detectors, for amplifying the first and second opto-electrical signals generated by the first and second optical detectors.
The foregoing laser detection system is capable of distinguishing whether the echoed light is a back-scattered light signal from suspended particles in the air or a reflected light signal from a solid target object. This allows the laser detection system to be nevertheless utilizable under bad weather conditions when suspended particles in the air could result in false detection.


REFERENCES:
patent: 3646352 (1972-02-01), Bol et al.
patent: 3788742 (1974-01-01), Garbuny
patent: 4459023 (1984-07-01), Reich et al.
patent: 5076696 (1991-12-01), Cohn et al.
patent: 5471298 (1995-11-01), Moriya
patent: 5815265 (1998-09-01), Moelter et al.

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