Passive scan angle doubling optical system

• US 5,455,708 A
• Filed: 12/19/1994
• Issued: 10/03/1995
• Est. Priority Date: 12/19/1994
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wilson, James M., Harris, Ellis D.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): SCHUBERG, DARREN E
• Application Number:
  US08/357,881
• Time in Patent Office: 288 Days
• Field of Search: 359/196, 359/197, 359/201, 359/205, 359/206, 359/207, 359/208, 359/212, 359/216, 359/217, 359/218, 359/219, 359/223, 359/226, 359/17, 359/558, 359/570, 359/572, 359/574, 358/474, 250/230, 250/236
• US Class Current: 359/226.1
• CPC Class Codes: G02B 26/106 having diffraction gratings as scanning elements, e.g. holographic scanners holographic optical elements G02B5/32, holography G03H

Abstract

A scan angle doubling system using a rotating cylindrical drum with reflective binary diffractive optical element facets, a cylindrical mirror, and a lens to increase the scanning angle available from a rotating mirror polygon of a given size. The properties of the passive components are such that the output light beam from the reflective binary diffractive optical element facets of the rotating cylindrical drum is collimated and normal to the rotating cylindrical drum. The cylindrical drum, cylindrical mirror, and lens are arranged such that the rotating cylindrical drum and the cylindrical mirror are opposed to each other and separated by a distance greater than the sum of the radius of curvature of the cylindrical mirror plus the focal length of the lens, and the lens is interposed between the rotating cylindrical drum and the cylindrical mirror so that the center of the radius of curvature of the cylindrical mirror and the focal point of the lens means are coincident.

Claims

1. A scan angle doubling system comprising:

A) a rotating cylindrical drum with at least one reflective binary diffractive optical element facet and a normal which is perpendicular to said reflective binary diffractive optical element facet,

B) a cylindrical mirror with a scan plane radius of curvature and a center of the radius of curvature,

C) a focussing lens means with a focal length and a focal point,

D) said rotating cylindrical drum, said cylindrical mirror, and said focussing lens means being arranged such that said rotating cylindrical drum and said cylindrical mirror are opposed to each other and separated by a distance greater than the sum of the radius of curvature plus the focal length, and said focussing lens means being interposed between said rotating cylindrical drum and said cylindrical mirror such that the center of the radius of curvature of said cylindrical mirror and the focal point of said focussing lens means are coincident, and

E) said rotating cylindrical drum, said cylindrical mirror, and said focussing lens means being arranged relative to each other to reflect a beam along a first path from said reflective binary diffractive optical element facet, at a first angle measured from the normal, through said focussing lens means to be received by said cylindrical mirror, said cylindrical mirror reflecting the received beam along a second path through said focussing lens means to be received by said reflective binary diffractive optical element facet, said reflective binary diffractive optical element facet reflecting said received beam in a post scan direction, at a second angle measured from the normal which is greater than the first angle.

2. The scan angle doubling system of claim 1 wherein said rotating cylindrical drum, said cylindrical mirror and said focussing lens means are further arranged to substantially maintain beam collimation whenever the beam is reflected from said reflective binary diffractive optical element facet of said rotating cylindrical drum.

3. The scan angle doubling system of claim 1 wherein said focussing lens means is a combination lens.

4. The scan angle doubling system of claim 3 wherein said combination lens uses at least one cylindrical element.

5. The scan angle doubling system of claim 1 wherein the second angle is approximately twice the first angle.

6. A scanning system comprising:

A) a light source for providing a light beam,

B) a first focussing lens means for focussing the light beam,

C) post scan lens means,

D) a photoreceptor medium,

E) scan angle doubling means comprising;

i) a rotating cylindrical drum with at least one reflective binary diffractive optical element facet and a normal which is perpendicular to said reflective binary diffractive optical element facet,

ii) a cylindrical mirror with a scan plane radius of curvature and a center of the radius of curvature,

iii) a second focussing lens means with a focal length and a focal point,

iv) said rotating cylindrical drum, said cylindrical mirror, and said second focussing lens means being arranged such that said rotating cylindrical drum and said cylindrical mirror are opposed to each other and separated by a distance greater than the sum of the radius of curvature plus the focal length, and said second focussing lens means being interposed between said rotating cylindrical drum and said cylindrical mirror such that the center of the radius of curvature of said cylindrical mirror and the focal point of said second focussing lens means are coincident, and

v) said rotating cylindrical drum, said cylindrical mirror, and said second focussing lens means being arranged relative to each other to reflect a beam along a first path from said reflective binary diffractive optical element facet, at a first angle measured from the normal, through said second focussing lens means to be received by said cylindrical mirror, said cylindrical mirror reflecting the received beam along a second path through said second focussing lens means to be received by said reflective binary diffractive optical element facet, said reflective binary diffractive optical element facet reflecting said received beam in a post scan direction, at a second angle measured from the normal which is greater than the first angle,

F) said light source, said first focussing lens means, and said scan angle doubling means arranged relative to each other such that the light beam from said light source passes through said first focussing lens means and becomes focussed on said reflective binary diffractive optical element facet, and

G) said scan angle doubling means, said post scan lens means, and said scanning medium arranged such that the beam reflected in the post scan direction passes through said post scan lens means and is received by said photoreceptor medium.

7. The scanning system of claim 6 wherein said rotating cylindrical drum, said cylindrical mirror and said second focussing lens means are further arranged to substantially maintain beam collimation whenever the beam is reflected from said reflective binary diffractive optical element facet of said rotating cylindrical drum.

8. The scanning system of claim 6 wherein said second focussing lens means is a combination lens.

9. The scanning system of claim 8 wherein the combination lens uses at least one cylindrical element.

10. The scanning system of claim 6 wherein the second angle is approximately twice the first angle.