Acousto-optic band reject light filter and apparatus using same

Claim 2

In a method for rejecting light of a selected optical frequency from a light beam the steps of, exciting an acoustic wave in an optically anisotropic medium at a selected radiofrequency related to the optical frequency of the light to be rejected, substantially collinearly diffracting the light beam on the acoustic wave within the optically anisotropic medium to diffract light of a first polarization and of the selected optical frequency related to the acoustic frequency into light of a second polarization, analyzing the diffracted light beam to reject from the diffracted light beam light of the second polarization while retaining in the diffracted light beam light of the first polarization, detecting the intensity of the light of the optical frequency which is rejected, and controlling the power density of the acoustic wave in the optically anisotropic medium in response to the intensity of the light of the optical frequency which is rejected.

Claim 3

The method of claim 1 including the step of, passing the diffracted and polarization analyzed light beam of the first polarization into an optical device to be tested, and spectrum analyzing such light obtained from the optical device as modified by passage through the device to provide an indication of the optical transfer characteristics of the device under test.

Claim 4

The method of claim 1 including the step of introducing a beam of white light as the beam of incident light.

Claim 5

In an acousto-optic apparatus, optically anisotropic medium means, means for exciting an acoustic wave in said optically anisotropic medium means at a selected radio frequency related to the optical frequency of light to be rejected, said optically anisotropic medium means being disposed to receive an incident light beam for substantially collinearly diffracting the light beam on the acoustic wave within said optically anisotropic medium means to diffract light of a first polarization and of the optical frequency to be rejected into light of a second polarization, means for polarization analyzing the diffracted light beam to reject, from the diffracted light beam, light of the second polarization while retaining in the diffracted light beam light of the first polarization, means for detecting the intensity of the light of the optical frequency which is rejected, and circuit means for controlling the power density of the acoustic wave in the anisotropic medium means in response to the intensity of the detected light of the optical frequency which is rejected.

Claim 6

In an acousto-optic apparatus, optically anisotropic medium means, means for exciting an acoustic wave in said optically anisotropic medium means at a selected radio frequency related to the optical frequency of light to be rejected, said optically anisotropic medium means being disposed to receive an incident light beam for substantially collinearly diffracting the light beam on the acoustic wave within said optically anisotropic medium means to diffract light of a first polarization and of the optical frequency to be rejected into light of a second polarization, means for polarization analyzing the diffracted light beam to reject, from the diffracted light beam, light of the second polarization while retaining in the diffracted light beam light of the first polarization, means for detecting the intensity of the light of the optical frequency which is rejected, and circuit means for controlling the power density of the acoustic wave in the anisotropic medium means in response to the intensity of the detected light of the optical frequency which is rejected.

Claim 7

The apparatus rejected, claim 4 wherein said circuit means includes means for detecting the intensity of the light of the optical frequency which is rejected and for producing an output representative of the detected intensity, means for producing a reference output corresponding to a desired intensity of the light which is rejected, means for comparing the detected rejected light intensity output with the reference output to derive an error output, and means responsive to the error output for controlling the power density of the acoustic wave in the anisotropic medium means to obtain a substantially constant rejected light intensity as a function of frequency of the rejected light.

Claim 8

The apparatus of claim 4 disposed to apply to an optical device means to be tested the diffracted and polarization analyzed light beam of the first polarization, and comprising spectrum-analyzing means disposed to receive light obtained from an optical device means under test as modified by passage through the device means to provide an indication of the nonlinear optical transfer characteristics of the device means under test.

Claim 9

The apparatus of claim 4 including means for sweeping the frequency of the acoustic wave within said optically anisotropic medium means to obtain a sweep of the optical frequency of the light rejected from the diffracted light beam, and said circuit means includes circuitry for altering the power density of the acoustic wave in the anisotropic medium means to maintain substantially constant rejected light intensity as a function of the optical frequency of the rejected light.

Claim 10

The apparatus of claim 4 including source means for directing a beam of white light into said optically anisotropic medium means as said incident light beam.

Claim 11

In an acousto-optic apparatus, an optically anisotropic medium means disposed to receive a beam of light for propagating the light beam as a particular wave having a first polarization orientation in a birefringent system, said medium means being further capable of propagating a light beam polarized in the second polarization orientation different from the first polarization orientation as another wave of said birefringent system, means coupled to said medium means for developing an acoustic wave of a predetermined frequency in said anisotropic medium means, the frequency of said acoustic wave being selected to define a phase-matched relationship such that the vector sum of the momentum vectors of the incident light beam and the acoustic wave are equal to that of an output light beam oriented at said second polarization, whereby an incident light beam satisfying that condition for a given acoustic wave frequency is diffracted into that second polarization orientation, and means for polarization analyzing the diffracted light beam to reject light of the second polarization while retaining in the diffracted light beam light of the first polarization, whereby an output band reject optical filter response is obtained, means for detecting the intensity of the light of the optical frequency which is rejected, and circuit means for controlling the power density of the acoustic wave in the anisotropic medium means in response to the intensity of the detected light of the optical frequency which is rejected.

Claim 12

In an acousto-optic apparatus, an optically anisotropic medium means disposed to receive a beam of light for propagating the light beam as a particular wave having a first polarization orientation in a birefringent system, said medium means being further capable of propagating a light beam polarized in the second polarization orientation different from the first polarization orientation as another wave of said birefringent system, means coupled to said medium means for developing an acoustic wave of a predetermined frequency in said anisotropic medium means, the frequency of said acoustic wave being selected to define a phase-matched relationship such that the vector sum of the momentum vectors of the incident light beam and the acoustic wave are equal to that of an output light beam oriented at said second polarization, whereby an incident light beam satisfying that condition for a given acoustic wave frequency is diffracted into that second polarization orientation, and means for polarization analyzing the diffracted light beam to reject light of the second polarization while retaining in the diffracted light beam light of the first polarization, whereby an output band reject optical filter response is obtained, means for detecting the intensity of the light of the optical frequency which is rejected, and circuit means for controlling the power density of the acoustic wave in the anisotropic medium means in response to the intensity of the detected light of the optical frequency which is rejected.

Claim 13

The apparatus of claim 9 including means for sweeping the frequency of the acoustic wave within said optically anisotropic medium means to obtain a sweep of the optical frequency of the light rejected from the diffracted light beam, and said circuit means includes circuitry for altering the power density of the acoustic wave in the anisotropic medium means to maintain substantially constant rejected light intensity as a function of the optical frequency of the rejected light.

Claim 14

Acousto-optic apparatus as in claim 9 wherein said anisotropic medium means is capable of propagating a light beam having said first polarization as a particular wave in the birefringent system and of diffracting and propagating a light beam of orthogonal polarization to said first beam as another wave of said birefringent system in response to acoustic waves propagating within said anisotropic medium means in a direction substantially collinear with the direction of propagation of the light beams within said medium means, and the frequency of said acoustic waves is selected to define a phase-matched relationship such that the vector sum of the momentum vectors of the incident light beam and the acoustic waves are equal to that of an output light beam orthogonally oriented to said input light beam, whereby the incident light beam satisfying that condition for a given acoustic wave frequency is diffracted into said orthogonal polarization.

Claim 15

The apparatus of claim 11 including source means for directing a beam of white light into said optically anisotropic medium means as the incident light beam.