Optical: systems and elements – Polarization without modulation – Polarization by reflection or refraction
Patent
1992-06-01
1993-11-02
Lerner, Martin
Optical: systems and elements
Polarization without modulation
Polarization by reflection or refraction
359566, 359569, 359576, G02B 518, G02B 530, G02B 2728, G02B 2744
Patent
active
052588718
ABSTRACT:
A dual diffraction grating useful in optical disk heads comprises first and second light diffracting surfaces of identical pitch and depth, wherein the diffraction grooves of the first and second diffraction surfaces are angularly oriented with respect to one another. Incident light beams are diffracted into first and second components with the first components being TM polarized components and the second components being TE polarized components. Upon emerging from the dual diffraction grating, the first and second components diverge with respect to one another because the first component is substantially transmitted through the diffraction grating without diffraction while the second component is diffracted. The initial diffraction by the first grating causes the TE component to diverge away from the TM component while the second diffraction grating diffracts the TE component back toward the TM component so as to diverge therefrom by only a slight angle of, for example, about 0.1.degree. to 3.0.degree.. In use, the two components emerging from the dual diffraction grating are focussed on photodetectors to develop reproduction signals and tracking and focus error signals. In a preferred embodiment, the first diffraction grating is etched in a first substrate, and the second diffraction grating is etched on a second substrate. The first and second substrates are then bonded to one another with a layer of optical adhesive. The two gratings are displaced by 0.1.degree.-5.degree. with respect to each other.
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Eastman Kodak Company
Holloway William W.
Lerner Martin
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