General diffractive optics method for expanding an exit pupil

• US 20090303599A1
• Filed: 06/03/2005
• Published: 12/10/2009
• Est. Priority Date: 06/03/2005
• Status: Abandoned Application

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Levola, Tapani
• Application Number:
  US11/921,533
• Publication Number:
  US 20090303599A1
• Time in Patent Office: Days
• US Class Current: 359/567
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0944 Diffractive optical elements, e.g. gratings, holograms gratings per se G02B5/18; holograms used as optical elements per se G02B5/32
• CPC Class Codes: G02B 27/42 Diffraction optics , i.e. systems including a diffractive element being designed for providing a diffractive effectG02B27/60 takes precedence
• CPC Class Codes: G02B 27/4205 having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
• CPC Class Codes: G02B 5/32 Holograms used as optical elements

Abstract

This invention describes a general diffractive optics method that uses a plurality of diffractive elements on an optical substrate for expanding the exit pupil of a display of an electronic device for viewing. The method can be used for optical coupling in an optical device and it is characterized by extending of an exit pupil of an input optical beam in an output optical beam wherein the optical device comprises: an optical substrate and in-coupling, intermediate and out-coupling diffractive element disposed on the optical substrates, wherein periodic lines of the intermediate diffractive element comprise an angle ρ with periodic lines of the in-coupling and of the out-coupling diffractive elements, respectively. The system can support a broad range of rotation angles (e.g., 0<ρ<70°) and corresponding conical angles and remains geometrically accurate.

Claims

1. An optical device, comprising:

a substrate of optical material having a first surface and an opposing second surface;

a first diffractive element disposed on the substrate for receiving an input optical beam defined by a wave-vector k and containing periodic lines with a period d;

a second diffractive element disposed on the substrate in relationship with the first diffractive element and containing further periodic lines with a period d, wherein an angle between said periodic lines and said further periodic lines is 2ρ

; and

an intermediate diffractive element disposed on said substrate adjacent to the first and the second diffractive elements and containing still further periodic lines with the period d/2 cos ρ

, wherein ρ

is an angle between said periodic lines and the still further periodic lines and said angle ρ

is not equal to 45°

, wherein

at least part of the input optical beam is diffracted in the first diffractive element for providing a diffracted optical component to the intermediate diffractive element substantially within the first and second surfaces, and

at least part of the diffracted optical component in the intermediate diffractive element is coupled to the second diffractive element substantially between the first and second surfaces so as to allow at least part of the coupled diffracted optical component to exit the substrate by diffraction in the second diffractive element for providing an output optical beam defined by a further wave-vector k1 having exactly the same direction as the wave-vector k of said input optical beam.

2. The optical device of claim 1, wherein said optical device is for extending of an exit pupil of said input optical beam by providing said output optical beam.

3. The optical device of claim 1, wherein said diffracted optical component is incident and subsequently diffracted to a first diffraction order on the intermediate diffractive element an uneven number of times before providing said at least part of the diffracted light component to said second diffractive element.

4. The optical device of claim 1, wherein said intermediate diffractive element supports only reflective zero and first order diffraction modes, or an index of refraction of said substrate is n>

λ

/d, wherein λ

is a wavelength of the input optical beam.

5. The optical device of claim 1, wherein a second or higher order diffraction modes are unsupported by said intermediate diffractive element, which is enforced by a condition expressed as

$\sqrt{1+8}$



cos 2 

ρ

>

nd λ

,

wherein n is an index of refraction of said substrate, λ

is a wavelength of the input optical beam.

6. The optical device of claim 5, wherein 0<

ρ

<

70°

.

7. The optical device of claim 1, wherein a predetermined condition is maintained, said condition is that transmission diffraction modes are unsupported for said intermediate diffractive element, which is enforced by a condition expressed as λ

/d>

1, wherein λ

is a wavelength of the input optical beam.

8. The optical device of claim 1, wherein said first diffractive element, said second diffractive element or said intermediate diffractive element is disposed on said first surface or on said second surface.

9. A method, comprising:

receiving an input optical beam defined by a wave-vector k at a first diffractive element containing periodic lines with a period d and disposed on a substrate of optical material having a first surface and an opposing second surface;

diffracting at least part of the input optical beam in the first diffractive element for providing a diffracted optical component to an intermediate diffractive element substantially within the first and second surfaces;

further diffracting said diffracted optical component by said intermediate diffractive element; and

coupling at least part of said further diffracted said diffracted optical component in the intermediate diffractive element to a second diffractive element substantially between the first and second surfaces so as to allow at least part of the coupled diffracted optical component to exit the substrate by diffraction in the second diffractive element for providing an output optical beam defined by a further wave-vector k1 having exactly the same direction as the wave-vector k of said input optical beam for extending of the exit pupil of an input optical beam, wherein

said second diffractive element is disposed on said substrate in relationship with the first diffractive element and contains further periodic lines with a period d and wherein an angle between said periodic lines and said further periodic lines is 2ρ and

said intermediate diffractive element is disposed adjacent to the first and the second diffractive elements and contains still further periodic lines with the period d/2 cos ρ

, wherein ρ

is an angle between said periodic lines and the still further periodic lines and said angle ρ

is not equal to 45°

.

10. The method of claim 9, wherein said diffracted optical component is incident and subsequently diffracted to a first diffraction order on the intermediate diffractive element an uneven number of times before said at least part of the diffracted light component is provided to said second diffractive element.

11. The method of claim 9, wherein said intermediate diffractive element is configured to support only zero and first order reflective diffraction modes, or an index of refraction of said substrate is n>

λ

/d, wherein λ

is a wavelength of the input optical beam.

12. The method of claim 9, wherein the intermediate diffractive element is configured not to support a second or higher order diffraction modes, which is enforced by a condition expressed as

$\sqrt{1+8}$



cos 2 

ρ

>

nd λ

,

wherein n is an index of refraction of said substrate, λ

is a wavelength of the input optical beam.

13. The method of claim 12, wherein 0<

ρ

<

70°

.

14. The method of claim 9, wherein the intermediate diffractive element is configured not to support transmission diffraction modes, which is enforced by a condition expressed as λ

/d>

1, wherein λ

is a wavelength of the input optical beam.

15. The method of claim 9, wherein said first diffractive element, said second diffractive element or said intermediate diffractive element is disposed on said first surface or on said second surface.

16. An electronic device, comprising:

a data processing unit;

an optical engine operatively connected to the data processing unit for receiving image data from the data processing unit;

a display device operatively connected to the optical engine for forming an image based on the image data; and

an exit pupil expander comprising;

a substrate of optical material having a first surface and an opposing second surface;

a first diffractive element disposed on the substrate for receiving an input optical beam defined by a wave-vector k and containing periodic lines with a period d;

a second diffractive element disposed on the substrate in relationship with the first diffractive element and containing further periodic lines with a period d, wherein an angle between said periodic lines and said further periodic lines is 2ρ

; and

an intermediate diffractive element disposed on said substrate adjacent to the first and the second diffractive elements and containing still further periodic lines with the period d/2 cos ρ

, wherein ρ

is an angle between said periodic lines and the still further periodic lines and said angle ρ

is not equal to 45°

, wherein

at least part of the input optical beam is diffracted in the first diffractive element for providing a diffracted optical component to the intermediate diffractive element substantially within the first and second surfaces, and

at least part of the diffracted optical component in the intermediate diffractive element is coupled to the second diffractive element substantially between the first and second surfaces so as to allow at least part of the coupled diffracted optical component to exit the substrate by diffraction in the second diffractive element for providing an output optical beam defined by a further wave-vector k1 having exactly the same direction as the wave-vector k of said input optical beam.

17. The electronic device of claim 16, wherein said intermediate diffractive element is configured to support only reflective zero and first order reflective diffraction modes, or an index of refraction of said substrate is n>

λ

/d, wherein λ

is a wavelength of the input optical beam.

18. The electronic device of claim 16, wherein the intermediate diffractive element is configured not to support a second or higher order diffraction modes, which is enforced by a condition expressed as

$\sqrt{1+8}$



cos 2 

ρ

>

nd λ

,

wherein n is an index of refraction of said substrate, λ

is a wavelength of the input optical beam.

19. The electronic device of claim 18, wherein 0<

ρ

<

70°

.

20. The electronic device of claim 16, wherein the intermediate diffractive element is configured not to support transmission diffraction modes, which is enforced by a condition expressed as λ

/d>

1, wherein λ

is a wavelength of the input optical beam.

21. The electronic device of claim 16, wherein said electronic device is a digital camera, a computer game device, a wireless device, a portable device or a mobile terminal.

22. The electronic device of claim 16, further comprising a communications unit for receiving signals containing information indicative of the image data, wherein the data processing unit is operatively connected to the communications unit for receiving the information.