Grazing incidence holograms and system and method for producing the same

• US 5,710,645 A
• Filed: 10/23/1995
• Issued: 01/20/1998
• Est. Priority Date: 01/29/1993
• Status: Expired due to Fees

• Current Assignee: Stanley H. Kremen
• Original Assignee: Imedge Technology Incorporated
• Inventors: Coleman, Zane, Phillips, Nicholas J.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US08/546,709
• Time in Patent Office: 820 Days
• Field of Search: 359/3, 359/4, 359/34, 359/1, 359/15, 359/32, 359/35, 359/27, 359/7, 359/13, 359/30, 359/900
• US Class Current: 359/1
• CPC Class Codes: G03H 1/0408 Total internal reflection [TIR] holograms, e.g. edge lit or substrate mode holograms
• CPC Class Codes: G03H 2001/207 with modification of the nature of the hologram, e.g. changing from volume to surface relief or from reflection to transmission
• CPC Class Codes: G03H 2222/47 Evanescent wave
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A method and system for recording and displaying grazing-incidence (i.e., steep reference beam angle) holograms supported on a substrate having thin edge-illuminatable geometry. The system and process of the present invention uses thin edge-illuminated substrates that facilitate optimal coupling of the reference light beam at steep angles approaching grazing incidence. Different recording techniques are employed when the index of refraction of the substrate is greater than that of the recording medium, than when the index of refraction of the substrate is less than that of the recording medium.

Claims

1. A system for producing a volume hologram having slanted fringes, comprising:

a substrate made from an optically transparent material having an index of refraction n_s, said substrate having front and rear surfaces disposed substantially parallel to each other, and an edge surface disposed between said front and rear surfaces;

a holographic recording medium having an index of refraction n_M greater than n_S with the difference of index of refraction therebetween equal to Δ

n, said holographic recording medium having front and rear surfaces, and said rear surface of said holographic recording medium being disposed in direct physical contact with the front surface of said substrate along an interface;

a laser light source for producing a laser beam;

a laser beam splitting means for splitting said produced laser beam into an object beam for propagation along a first optical path, and a reference beam for propagation along a second optical path;

object beam directing means for directing said object beam along an optical path into said recording medium;

reference beam directing means for directing said reference beam along a single-pass optical path extending through said substrate at a grazing angle of incidence of at least about 80 degrees with respect to the normal to said interface;

wherein, during the recording of said slanted fringes in said holographic recording medium, said reference beam is transmitted from said substrate into said holographic recording medium with a predetermined intensity transmittance and interferes with said object beam within said holographic recording medium so as to form a volume hologram with slanted fringes in said holographic recording medium;

wherein said index of refraction of said substrate n_s is matched to the index of refraction of said holographic recording medium n_m by selecting values for n_s and n_m so that the difference of index of refraction therebetween Δ

n is functionally related to said grazing angle of incidence .O slashed._s and the index of refraction of said substrate n_S by the expression;

##EQU17##

2. The system of claim 1, which further comprises polarization means for imparting a predetermined polarization state to at least one of said object beam and said reference beam as said object beam and said reference beam propagate along said first and second optical paths, respectively.

3. The system of claim 2, wherein said predetermined polarization state is the S-mode polarization state.

4. The system of claim 1, wherein said slanted fringes are representative of the spatial structure of an object.

5. The system of claim 1, wherein said slanted fringes are representative of an optical function.

6. The system of claim 1, wherein said difference of index of refraction Δ

n is functionally related to said grazing angle of incidence and said predetermined intensity transmittance by a constraint formed by applying Fresnel relations and Snell'"'"'s Law at said interface.

7. A system for illuminating a volume hologram having slanted fringes comprising:

a substrate of thin construction, made from an optically transparent material having an index of refraction n_S, said substrate having front and rear surfaces disposed substantially parallel to each other, and an edge surface disposed between said front and rear surfaces;

a holographic recording medium made from an optically transparent material having an index of refraction n_M greater than n_S with the difference of index of refraction therebetween equal to Δ

n, said holographic recording medium having front and rear surfaces and a volume hologram with slanted fringes prerecorded therein, and said rear surface of said holographic recording medium being disposed in direct physical contact with the front surface of said substrate along an interface; and

a light source for producing an illumination beam which propagates along a single-pass optical path extending through said substrate at a grazing angle of incidence .O slashed._s of at least about 80 degrees with respect to the normal to said interface, so that said illumination beam couples into said holographic recording medium and interacts with said slanted fringes, wherein said index of refraction of said substrate n_S is matched to the index of refraction of said holographic recording medium n_M by selecting values for n_S and n_M so that the difference of index of refraction therebetween Δ

n is functionally related to said grazing angle of incidence .O slashed._s and the index of refraction of said substrate n_S by the expression;

##EQU18##

8. The system of claim 7, wherein said fringes are representative of the spatial structure of an object.

9. The system of claim 7, wherein said fringes are representative of an optical function.

10. The system of claim 7, wherein said difference of index of refraction Δ

n is functionally related to said grazing angle of incidence and said predetermined intensity transmittance by a constraint formed by applying Fresnel relations and Snell'"'"'s Law at said interface.

11. A method of recording a volume hologram having slanted fringes, comprising the steps of:

(a) selecting

(1) a substrate made from an optically transparent material having an index of refraction of n_S, and

(2) a holographic recording medium having an index of refraction n_M greater than n_S,

wherein the difference of index of refraction therebetween is equal to Δ

n, said substrate has front and rear surfaces disposed substantially parallel to each other and an edge surface disposed between said front and rear surfaces, and said holographic recording medium has front and rear surfaces and said rear surface of said holographic recording medium being disposed in direct physical contact with the front surface of said substrate along an interface;

(b) producing a laser beam from a laser source and splitting said laser beam into an object beam for propagation along a first optical path, and a reference beam for propagation along a second optical path; and

(c) simultaneously directing said object beam along an optical path into said recording medium, and directing said reference beam along a single-pass optical path extending through said substrate at a grazing angle of incidence of at least about 80 degrees with respect to the normal to said interface,

whereby said reference beam is transmitted from said substrate into said holographic recording medium with a predetermined intensity transmittance and interferes with said object beam within said holographic recording medium so as to form a volume hologram with slanted fringes in said holographic recording medium;

wherein during step (a) said index of refraction of said substrate n_s is matched to the index of refraction of said holographic recording medium n_m by selecting values for n_s and n_m so that said difference of index of refraction therebetween Δ

n is functionally related to said grazing angle of incidence .O slashed. the index of refraction of said substrate n_S by the expression;

##EQU19##

12. The method of claim 11, wherein said difference of index of refraction Δ

n is functionally related to said grazing angle of incidence and said predetermined intensity transmittance by a constraint formed by applying Fresnel relations and Snell'"'"'s Law at said interface.

13. The method of claim 11, which further includes the step of arranging polarization means for imparting a predetermined polarization state to at least one of said object beam and said reference beam as said object beam and said reference beam propagate along said first and second optical paths, respectively.

14. The method of claim 13, wherein said predetermined polarization state is the S-mode polarization state.

15. The method of claim 11, wherein said fringes are representative of the spatial structure of an object.

16. The method of claim 11, wherein said fringes are representative of an optical function.