Secure active sensor

Claim 1

In an optical radar system having a transmitting portion for generating an optical radar beam, an optical system directing said beam to a target and collecting the reflected radiation, and a receiving portion having a detector for sensing the reflected radiation, the improvement in said system comprising: a laser transmitter forming said transmitting portion and comprising, a first partially transmissive end reflector and a second substantially totally reflective end reflector positioned to form a laser cavity, a dye cell positioned in said cavity and aligned between said end reflectors, and means for stimulating said dye cell to laser emission to generate said optical radar beam; a single Faraday cell comprising, two polarizers crossed by 90° and separated by a Faraday medium, said Faraday cell having a first portion extending into the laser cavity such that the laser beam must pass through the Faraday cell, and a second portion extending into an optical path between said optical system and said detector such that the reflected beam must pass through the Faraday cell before sensing by the detector; means for establishing a magnetic field surrounding said Faraday cell and randomly varying the magnetic field strength so as to vary the optical frequency passed by said cell; an optical switch and a plurality of spectral filters positioned in the optical path between said second portion of said Faraday cell and said detector; and means coupled to said stimulating means and said optical switch for controlling said switch in conjunction with said laser transmitter to block optical radiation to said detector during lasing and pass optical radiation only during viewing of the reflected beam.

Claim 4

A method of protecting an optical radar system from unwanted or interfering radiation at a radar detector comprising: forming a dye laser having a first partially transmissive end reflector, a second grating end reflector, and a dye cell aligned therebetween to form a cavity; generating a pulsed laser radar beam by stimulating said dye cell to laser emission; inserting a Faraday cell having a first portion extending into the laser cavity to control the frequency of the laser beam; randomly varying the frequency passed by the Faraday cell; transmitting the beam to a target; receiving the reflected beam from the target through a second portion of the same Faraday cell; positioning a radar detector to detect the beam passed by the Faraday cell; inserting an optical switch into the beam path between the second portion of the Faraday cell and the detector; and controlling said switch to block optical radiation to the detector during generation of the beam and to pass optical radiation only during viewing of the reflected beam.

Claim 5

A method of protecting an optical radar system from unwanted or interfering radiation at a radar detector comprising: forming a dye laser having a first partially transmissive end reflector, a second grating end reflector, and a dye cell aligned therebetween to form a cavity; generating a pulsed laser radar beam by stimulating said dye cell to laser emission; inserting a Faraday cell having a first portion extending into the laser cavity to control the frequency of the laser beam; randomly varying the frequency passed by the Faraday cell; transmitting the beam to a target; receiving the reflected beam from the target through a second portion of the same Faraday cell; positioning a radar detector to detect the beam passed by the Faraday cell; inserting an optical switch into the beam path between the second portion of the Faraday cell and the detector; and controlling said switch to block optical radiation to the detector during generation of the beam and to pass optical radiation only during viewing of the reflected beam.