1977-08-11
1978-12-12
Corbin, John K.
G02B 102, G02B 520
Patent
active
041293576
ABSTRACT:
A birefringent filter module comprises, in seriatum, an entrance polarizer, a first birefringent crystal responsive to optical energy exiting the entrance polarizer, a partial polarizer responsive to optical energy exiting the first polarizer, a second birefringent crystal responsive to optical energy exiting the partial polarizer, and an exit polarizer. The first and second birefringent crystals have fast axes disposed .+-. 45.degree. from the high transmitivity direction of the partial polarizer. Preferably, the second crystal has a length 1/2 that of the first crystal and the high transmitivity direction of the partial polarizer is nine times as great as the low transmitivity direction. To provide tuning, the polarizations of the energy entering the first crystal and leaving the second crystal are varied by either rotating the entrance and exit polarizers, or by sandwiching the entrance and exit polarizers between pairs of half wave plates that are rotated relative to the polarizers. A plurality of the filter modules may be cascaded. The first crystal for module (n+1) is 2/3 of the length of the second crystal of module n.
REFERENCES:
harris et al., "Optical Network Synthesis Using Birefringent Crystals"; J. Optical Soc. Am.; vol. 54, p. 1267 (Oct. 1964).
Title; "Improvement in Birefringent Filters", Applied Optics; vol. 15, p. 2871 (Nov. 1976).
Frosch Robert A. Administrator of the National Aeronautics and Space
Title Alan M.
Corbin John K.
Manning John R.
Marchant Robert D.
Rosenberger R. A.
Tresansky John O.
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