Optical filter

Details Optical filter Optical filter

1981-09-29

1983-10-04

Punter, William H.

350166, G02B 528, G02B 530

Patent

active

044075669

ABSTRACT:
A filter element for a narrow-passband optical filter comprises a birefringent crystal (10) having a rectangular parallelopiped configuration with an entrance face (11), an exit face (12) and side walls (21, 22, 23, 24). The optic axis (25) of the crystal (10) is parallel to the entrance and exit faces (11 and 12). The side walls (21, 22, 23, 24) are polished to provide total internal reflection of optical energy incident thereon at greater than a critical angle as measured from the normal. By covering the side walls (21, 22, 23, 24) with a coating whose index of refraction is given by the algorithm n=(N.sup.2 =sin.sup.2 .theta.).sup.1/2, where n is the index of refraction of the coating, N is the lower index of refraction of the crystal (10), and .theta. is a half-angle defining the maximum field of view in air for the filter element, the critical angle for total internal reflection is made substantially equal to the half-angle defining the maximum field of view. In this way, vignetting is suppressed and a wide field of view is obtained.

REFERENCES:
Willisen, F. K. von, "A Tunable Birefringent Filter", App. Optics, 1-1966, pp. 97-104.
Nestrizhenko, Yu. A., "Total-Internal-Reflection Polarizer as an Interference-Polarization Filter for a Laser", Optics & Spectroscopy, 8-1974, pp. 186-189.
Schineller et al., "Development of a Wide-Angle Narrow-Band Optical Filter", Manf. Optican Intern., 9-968, pp. 148 & 148.

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