Abstract An electro-optical modulator comprising an electro-optic crystal, means for projecting a beam of light through the crystal on to an optical aperture, and means for applying to the crystal a variable electric field which will be substantially non-uniform across the beam of light in any plane transverse to the path of the beam so as to cause a variable spreading of the beam and thereby modulate the amount of illumination passing through the optical aperture. The electric field may be applied to the crystal by means of two narrow linear electrodes on opposite sides of the crystal and parallel to the path of the beam. The optical aperture may be a translucent aperture in an opaque screen, or it may be one end of a fiber-optic light guide. An optical alignment system may be formed of one or two such electro-optic modulator crystals, an optical detector for producing an electrical signal representing the amount of illumination passing through the optical aperture and frequency selective means responsive to the said signal. Servo systems may be provided for adjusting the position of the aperture transversely so as to maximize the output of the frequency selective means.
An electro-optical modulator comprising a first electro-optic crystal with first electrode means for applying a variable electric field thereto, a second electro-optic crystal with second electrode means for applying a variable electric field thereto, the said first and second crystals having their c-axes orthogonal to one another, optical aperture means of predetermined cross-sectional area, means for projecting a beam of light through the first crystal and thence through the second crystal and onto the said optical aperture means, a first modulation signal source means for applying a first alternating signal having a first frequency to the said first electrode means, a second modulation signal source means for applying a second alternating signal having a second frequency to the said second electrode means, optical detector means connected to the said optical aperture means so as to receive light from the said beam of light through the said optical aperture means, servo means connected to position the said optical aperture means in two orthogonal directions, filter means for filtering the output of the optical detector means so as to provide two output signals consequent upon the first and second alternating signals respectively, and means for applying the said two output signals to the servo means to center the said optical aperture means in the said light beam.
Claim 2
Dependent Claim
215 words
An electro-optical modulator comprising a first electro-optic crystal with first electrode means for applying a variable electric field thereto, a second electro-optic crystal with second electrode means for applying a variable electric field thereto, the said first and second crystals having their c-axes orthogonal to one another, optical aperture means of predetermined cross-sectional area, means for projecting a beam of light through the first crystal and thence through the second crystal and onto the said optical aperture means, a first modulation signal source means for applying a first alternating signal having a first frequency to the said first electrode means, a second modulation signal source means for applying a second alternating signal having a second frequency to the said second electrode means, optical detector means connected to the said optical aperture means so as to receive light from the said beam of light through the said optical aperture means, servo means connected to position the said optical aperture means in two orthogonal directions, filter means for filtering the output of the optical detector means so as to provide two output signals consequent upon the first and second alternating signals respectively, and means for applying the said two output signals to the servo means to center the said optical aperture means in the said light beam.