Variable attenuator for dual beams

• US 5,311,217 A
• Filed: 12/23/1991
• Issued: 05/10/1994
• Est. Priority Date: 12/23/1991
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Guerin, Jean M., Ibrahim, Abd-El-Fattah A.
• Primary Examiner(s): Reinhart, Mark J.
• Application Number:
  US07/812,294
• Time in Patent Office: 869 Days
• Field of Search: 346/1.1, 346/76 L, 346/107 R, 346/108, 346/160, 358/296, 358/300, 358/302
• US Class Current: 347/246
• CPC Class Codes: G02B 27/281 used for attenuating light intensity, e.g. comprising rotatable polarising elements
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02F 1/13318 Circuits comprising a photodetector
• CPC Class Codes: G02F 2203/48 Variable attenuator
• CPC Class Codes: H04N 1/1135 for the main-scan only
• CPC Class Codes: H04N 1/1911 Simultaneously or substantially simultaneously scanning picture elements on more than one main scanning line, e.g. scanning in swaths

Abstract

A variable attenuator for electronically controlling dual beam intensity comprising a laser source for emitting a light beam, a twisted nematic liquid crystal for exposure control of the light beam, a double-sided multi-layer dielectric thin film coated polarization plate for decreasing the s-component of the light beam to less than or equal to 0.0001 of the light beam emitted from the laser source, and a beam splitting crystal for separating said light beam into two beams of equal intensity.

Claims

1. A variable attenuator for electronically controlling dual beam intensity comprising

a laser source for emitting a light beam,

a liquid crystal for exposure control of said light beam from said laser source,

polarization means for decreasing the s-polarization component of said light beam from said liquid crystal, and

beam splitting means for separating said light beam from said polarization means into two beams of equal intensity.

2. The variable attenuator for electronically controlling dual beam intensity of claim 1 further comprising a Brewster plate and feedback and analyzing means between said polarization means and said beam splitting means, said Brewster plate for separating a portion of said light beam from said polarization means to said feedback and analyzing means to control the voltage applied to said liquid crystal.

3. The variable attenuator for electronically controlling dual beam intensity of claim 1 wherein the intensity of said s-polarization component is decreased to less than or equal to 0.0001 of said light beam emitted from said laser source.

4. The variable attenuator for electronically controlling dual beam intensity of claim 1 wherein said liquid crystal comprises a twisted nematic liquid crystal.

5. The variable attenuator for electronically controlling dual beam intensity of claim 1 wherein said polarization means comprises a double-sided multi-layer dielectric thin film coated polarization plate.

6. The variable attenuator for electronically controlling dual beam intensity of claim 1 wherein said beam splitting means comprises a beam splitting crystal.

7. A variable attenuator for electronically controlling dual beam intensity comprising

a laser source for emitting a light beam,

a twisted nematic liquid crystal for exposure control of said light beam from said laser source,

a double-sided multi-layer dielectric thin film coated polarization plate for decreasing the s-polarization component of said light beam from said twisted nematic liquid crystal, to less than or equal to 0.0001 of said light beam emitted from said laser source,

a Brewster plate and feedback and analyzing means for separating a portion of said light beam from said polarization means to said feedback and analyzing means to control the voltage applied to said twisted nematic liquid crystal, and

a beam splitting crystal for separating said light beam from said polarization plate into two beams of equal intensity.