Method and apparatus for light beam scanning using a hologram

• US 4,925,262 A
• Filed: 11/17/1988
• Issued: 05/15/1990
• Est. Priority Date: 04/13/1983
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Hasegawa, Shinya, Ikeda, Hiroyuki, Yamagishi, Fumio
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Parsons, David R.
• Application Number:
  US07/273,624
• Time in Patent Office: 544 Days
• Field of Search: 350/3.71
• US Class Current: 359/18
• CPC Class Codes: G02B 26/106 having diffraction gratings as scanning elements, e.g. holographic scanners holographic optical elements G02B5/32, holography G03H
• CPC Class Codes: G06K 15/1285 Holographic scanning in general G02B

Abstract

A method for constructing a hologram on a transparent disk which includes two steps. First, irradiating a reference wave light beam having a diverging spherical wave front from a first point light source located at a predetermined distance on a center axis of the transparent disk. Second, irradiating an object wave light beam having a diverging spherical wave front from a second point light source located at a predetermined distance on a normal line away from a predetermined distance from the center axis. The result is interference between the reference wave light beam irradiated by the first point light source and the object wave light beam irradiated by the second point light source on the transparent disk and the formation of interference fringes having an extreme value of a spatial frequency as a hologram in one embodiment, a reconstruction beam is irradiated to the position, or in the vicinity of the extreme value.

Claims

1. A method for producing a scanning light beam, comprising the steps of:

(a) forming a hologram on a rotatable disk having a rotation axis by;

(a1) irradiating a reference wave light beam from a first point light source located on the rotation axis at a first predetermined distance from the rotatable disk to provide a construction wave light beam having a diverging spherical wave front;

(a2) irradiating an object wave light beam from a second point light source, located at a second predetermined distance from the rotatable disk and a third predetermined distance from the rotation axis thereof, to produce another construction wave light beam having a diverging spherical wave front and a first wavelength; and

(a3) causing interference between the reference and object wave light beams to produce interference fringes having a spatial variation of spatial frequency, the spatial variation including a minimum rate of change of the spatial frequency;

(b) rotating the rotatable disk after forming the hologram therein; and

(c) directing a reconstruction beam onto the rotatable disk simultaneously with said rotating in step (b) to produce the scanning light beam, the reconstruction beam having a second wavelength longer than the first wavelength and enabling the scanning light beam as output from the rotatable disk to be directly usable in straight-line scanning, the reconstruction beam being incident on the rotatable disk in the vicinity of the minimum rate of change of the spatial frequency.

3. A method as claimed in claim 1,

wherein the first and second predetermined distances are substantially equal, and

wherein step (a2) comprises positioning the second point light source along a first line parallel to the rotation axis at the third predetermined distance therefrom, the hologram being substantially equidistant from the rotation axis and the first line.

2. An apparatus for producing a scanning light beam, comprising:

a rotatable disk having a rotation axis and containing a hologram obtained by interference of a reference wave light beam and an object wave light beam, each of the reference and object wave light beams having a diverging spherical wave front, the reference wave light beam having been produced by a first point light source located on the rotation axis at a first predetermined distance from the rotatable disk and the object wave light having been produced with a first wavelength by a second point light source located at a second predetermined distance from the rotatable disk and a third predetermined distance from the rotation axis thereof, the hologram having interference fringes having spatial variation of spatial frequency, the spatial variation including a minimum rate of change of the spatial frequency;

a light beam source operable to generate a reconstruction beam for irradiating said hologram, the reconstruction beam having a second wavelength longer than the first wavelength and being incident on said rotatable disk in the vicinity of the minimum rate of change of the spatial frequency of the interference fringes of the hologram; and

rotating means for rotating said rotatable disk to shift the hologram and obtain a scanning light beam directly usable in straight line scanning.

4. An apparatus as recited in claim 2, wherein the first and second predetermined distances are substantially equal and the first and second point light sources are arranged symmetrically with respect to a normal line perpendicular to the rotatable disk and passing through the minimum rate of change of the spatial frequency of the hologram.

5. An apparatus as recited in claim 4, wherein the said light beam source is operable to direct the reconstruction beam, independently of the object wave light beam and the reference wave light beam, to form an angle of incidence (θ

_i) of the reconstruction beam on the rotatable disk and an angle of diffraction (θ

_d) meeting the following equations;

##EQU7## where λ

₁ is the first wavelength, λ

₂ is the second wavelength, r is a distance from the rotation axis to a point of incidence of the reconstruction wave light beam, f_A is the first predetermined distance, f_B is the second predetermined distance and R is the third predetermined distance.

6. An apparatus as recited in claim 5,

wherein at least one of the reference and object wave light beams are produced by an argon laser, and

wherein said light beam source comprises a semiconductor laser.

7. An apparatus as recited in claim 6, further comprising means for producing printed output using the scanning light beam.

8. An apparatus as recited in claim 5, further comprising means for producing printed output using the scanning light beam.

9. A method as claimed in claim 8, further comprising the steps of:

(d) providing a transparent disk having a center axis to form the hologram therein;

(e) positioning the first point light source substantially along the center axis of the transparent disk and positioning the second point light source along a first line perpendicular to the plane of the transparent disk, the hologram being substantially equidistant from the center axis and the first line.

10. An apparatus as recited in claim 9, further comprising means for producing printed output using the scanning light beam.

11. An apparatus as recited in claim 4, further comprising means for producing printed output using the scanning light beam.

12. An apparatus as recited in claim 2, wherein the said light beam source is operable to direct the reconstruction beam, independently of the object wave light beam and the reference wave light beam, to form an angle of incidence (θ

_i) of the reconstruction beam on the rotatable disk and an angle of diffraction (θ

_d) meeting the following equations;

##EQU8## where λ

₁ is the first wavelength, λ

₂ is the second wavelength, r is a distance from the rotation axis to a point of incidence of the reconstruction wave light beam, f_A is the first predetermined distance, f_B is the second predetermined distance and R is the third predetermined distance.

13. An apparatus as recited in claim 12,

wherein at least one of the reference and object wave light beams are produced by an argon laser, and

wherein said light beam source comprises a semiconductor laser.

14. An apparatus as recited in claim 13, further comprising means for producing printed output using the scanning light beam.

15. An apparatus as recited in claim 12, further comprising means for producing printed output using the scanning light beam.

16. An apparatus as recited in claim 2,

wherein at least one of the reference and object wave light beams are produced by an argon laser, and

wherein said light beam source comprises a semiconductor laser.

17. An apparatus as recited in claim 16, further comprising means for producing printed output using the scanning light beam.

18. An apparatus as recited in claim 2, further comprising means for producing printed output using the scanning light beam.