Local reference beam generator

Details Local reference beam generator Local reference beam generator

1991-08-09

1992-09-15

Howell, Janice A.

Optical: systems and elements

Lens

With light limiting or controlling means

359558, 359740, G06K 908

Patent

active

051483238

ABSTRACT:
A filtering apparatus 30 passes an incident beam of light through a first lens having a first focal length, causing the incident beam of light 32 to be focussed, and then passes the incident beam of light through a pinhole 36 having an opening of a predetermined size. In accordance with one aspect of the invention, the pinhole 36 is spaced from the first lens 34 by a distance which is greater than, or less than, but not equal to the lens' focal length wherein only a portion of the incident beam of light passes through the opening of the pinhole 36. In the illustrated embodiment, the pinhole 36 has a size which is significantly larger than the nominal diffraction limited spot size of the first lens 34. The incident beam of light which passes through the pinhole is then directed toward a second lens 38 having a second focal length. In a preferred embodiment, the second lens 38 is spaced from the pinhole 36 by a distance substantially equal to the second lens' focal length. Because of the increased size of the pinhole and the non-focal length spacing between the pinhole and the first lens 34, the pinhole 36 is able to block substantially all of the phase varying portion of the wavefront of the incident beam yet the sensitivity of the filter to intensity variations and component misalignments is substantially reduced.

REFERENCES:
patent: 3608992 (1971-09-01), Phelps
patent: 3630593 (1971-12-01), Bartelt et al.
patent: 3838903 (1974-10-01), Leith et al.

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