Holographic optical system including waveplate and aliasing suppression filter

A holographic optical system, comprising:

• a laser light source for emitting a light beam when energized;
• an optical disk, said optical disk having information encoded as reflectance variations on a surface thereof;
• means for rotating the optical disk about a drive axis;
• beam directing means for directing the light beam emitted by said laser light source to the surface of the optical disk, said beam directing means providing a light path including a beam splitter and a quarter-waveplate, said quarter-waveplate including a holographic waveplate comprising first and second volume holograms made from dichromated gelatin, said holograms each having differential diffraction efficiencies relative to selected polarization directions, said first and second holograms being arranged in a multi-layered structural relationship to form a composite bidiffractive element, said bidiffractive element providing a first propagation path for incident light polarized in a first polarization direction and a second propagation path for incident light polarized in a second polarization direction, said first and second volume holograms each being constructed so as to have a thickness T, an average index of refraction n.sub.0 of approximately 1.26, an internal angle of incidence .alpha. calculated on the basis of said average index of refraction n.sub.0 being approximately 1.26 in accordance with the relationship .alpha.=asin (sin/1.26), where .theta..sub.D0 is the external angle of incidence, an internal angle of diffraction .beta. calculated on the basis of said average index of refraction n.sub.0 being approximately 1.26 in accordance with the relationship .phi.=(.pi./2)-(.beta.-.alpha.)/2, where .phi. is Bragg plane tilt, and an external angle of incidence .theta..sub.D0, such that said first and second propagation paths are of unequal length by a multiple of one-quarter wavelength in accordance with the relationship .delta.L(T)=T(1.26((1/cos(.alpha.))-(1/cos(.beta.)))+(tan(.alpha.)+tan(.be ta.)) * sin (.theta..sub.D0)), where .delta.L(T) is the path length difference between radiation polarized in the first and second directions;
• detector means for receiving the light beam after it has been reflected by the optical disk for generating an output signal representative of the information encoded on the optical disk;
• and
• information recovery means for processing the output signal and generating data signals representative of the information encoded on the optical disk.

A holographic optical system, comprising:

• a laser light source for emitting a light beam when energized;
• a magneto-optical disk, said magneto-optical disk having information encoded on a surface thereof as variations in magnetization orientation;
• means for rotating the magneto-optical disk about a drive axis;
• beam directing means for directing the light beam emitted by said laser light source to the surface of the magneto-optical disk, said beam directing means providing a light path including a polarization selective beam splitter and a half waveplate, said half waveplate including a holographic waveplate comprising first and second volume holograms made from dichromated gelatin, said holograms each having differential diffraction efficiencies relative to selected polarization directions, said first and second holograms being arranged in a multi-layered structural relationship to form a composite bidiffractive element, said bidiffractive element providing a first propagation path for incident light polarized in a first polarization direction and a second propagation path for incident light polarized in a second polarization direction, said first and second volume holograms each being constructed so as to have a thickness T, an average index of refraction n.sub.0 of approximately 1.26, an internal angle of incidence .alpha. calculated on the basis of said average index of refraction n.sub.0 being approximately 1.26 in accordance with the relationship .alpha.=asin (sin/1.26), where .theta..sub.D0 is the external angle of incidence, an internal angle of diffraction .beta. calculated on the basis of said average index of refraction n.sub.0 being approximately 1.26 in accordance with the relationship .phi.=(.pi./2)-(.beta.-.alpha.)/2, where .phi. is Bragg plane tilt, and an external angle of incidence .theta..sub.D0, such that said first and second propagation paths are of unequal length by a multiple of one-half wavelength in accordance with the relationship .delta.L(T)=T(1.26((1/cos(.alpha.))-(1/cos(.beta.)))+(tan(.alpha.)+tan(.be ta.)) * sin (.theta..sub.D0)), where .delta.L(T) is the path length difference between radiation polarized in the first and second directions;
• detector means for receiving the light beam after it has been reflected by the magneto-optical disk for generating an output signal representative of the information encoded on the magneto-optical disk;
• and
• information recovery means for processing the output signal and generating data signals representative of the information encoded on the magneto-optical disk.

A holographic optical blur filter system for use with a video detector having a plurality of adjacent detector elements, comprising:

• a first volume hologram mounted on a substrate for receiving an input radiation beam and diffracting a first portion of the input radiation beam as a first beam and transmitting a second portion of the input radiation beam as a second beam;
• a second volume hologram mounted on a substrate for receiving the first and second beams and diffracting one of the beams while transmitting the other beam, said first and second beams being directed at angles that are substantially parallel to each other;
• a spacer positioned between the first and second volume holograms, said spacer's thickness being chosen to provide a selected amount of spatial separation between the first and second beams as they pass through the second volume hologram in accordance with the relationship D(T.sub.g)=T.sub.g (tan .theta..sub.d)+(T(tan .beta.), where D(T.sub.g) is the spatial beam separation for a given spacer thickness, T.sub.g is the spacer thickness, .theta..sub.d is the external angle of incidence and .beta. is the internal angle of diffraction, said selected amount of spatial separation being substantially equal to a dimension of said detector elements;
• and
• wherein the input radiation beam may include first and second polarization components of different direction and the first and second volume holograms have different diffraction efficiencies relative to the first and second polarization components, which different diffraction efficiencies are used to generate the first and second beams.