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| Liquid crystal light shutter |
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| Audio-visual display device |
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| Active matrix type liquid crystal display apparatus with a projection part in the drain line |
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| Apparatus for setting timing of internal combustion engines |
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Local reference beam generator
| Details |
Inventors: Campbell, Blair F.; Holmes, Richard B.; Ma, Sam S.; Guthals, Dennis M.;
Assignee: Rockwell International Corporation (Seal Beach, CA)
Primary Examiner: Howell; Janice A.
Assistant Examiner: Wong; Don
Attorney, Agent or Firm: Hamann; H. Fredrick, Field; Harry B.
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. |
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DETAILED DESCRIPTION It is an object of the present invention to provide an improved spatial filter and beam generator in which phase variations are filtered from an incident optical beam, particularly in a manner requiring a relatively uncomplicated electrical and optical arrangement.
This and other objects and advantages are achieved with a filtering apparatus which first passes an incident beam of light through a first lens having a first focal length, causing the incident beam of light to be focussed, and then passes the incident beam of light through a pinhole having an opening of a predetermined size.
In accordance with one aspect of the invention, the pinhole is spaced from the first lens 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.
In the illustrated embodiment, the pinhole has a size which may be equal to or significantly larger than the nominal diffraction limited spot size.
The incident beam of light which passes through the pinhole is then directed toward a second lens having a second focal length.
In a preferred embodiment, the second lens is spaced from the pinhole so that the pinhole forms a substantially unresolved source for the second lens.
Because of the increased size of the pinhole and the non-focal length spacing between the pinhole and the first lens, the pinhole 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.
As explained in greater detail below, the filter of the present invention may be used to provide a reference beam for use in optical holography.
This reference beam is derived from an incident signal beam, and through the method of the present invention, a plane wave reference beam is formed that is spatially and temporally coherent with the incident signal beam
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