DIFFRACTIVE OPTICAL ELEMENT USING CROSSED GRATING FOR PUPIL EXPANSION

• US 20170034435A1
• Filed: 07/30/2015
• Published: 02/02/2017
• Est. Priority Date: 07/30/2015
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Vallius, Tuomas
• Granted Patent: US 10,038,840 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 2027/0138 comprising image capture systems, e.g. camera
• CPC Class Codes: G02B 2027/014 comprising information/image processing systems
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0172 characterised by optical features
• 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 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: H04N 23/61 based on recognised objects
• CPC Class Codes: H04N 23/63 by using electronic viewfinders
• CPC Class Codes: H04N 23/80 Camera processing pipelines; Components thereof

Abstract

In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), an in-coupling DOE couples light into the waveguide, an intermediate DOE provides exit pupil expansion in a first direction, and an out-coupling DOE provides pupil expansion in a second direction and couples light out of the waveguide. The intermediate DOE is configured with a crossed grating which is a three-dimensional microstructure that is periodic in two directions. The crossed grating provides multiple optical paths to a given point in the DOE in which differences in optical path lengths are larger than the coherence length. The crossed grating in the intermediate DOE may provide increased display uniformity in the optical display system by reducing the “banding” resulting from optical interference that is manifested as dark stripes in the display. The crossed grating can further enable the optical display system to be more tolerant to manufacturing variations.

Claims

1. An optical system, comprising:

a substrate of optical material;

a first diffractive optical element (DOE) disposed on the substrate, the first DOE having an input surface and configured as an in-coupling grating to receive one or more optical beams as an input; and

a second DOE disposed on the substrate and configured for pupil expansion of the one or more optical beams along a first direction,

wherein at least a portion of the second DOE is configured with a crossed grating that is periodic in two directions.

2. The optical system of claim 1 in which the crossed grating includes one of symmetric or asymmetric features.

3. The optical system of claim 2 in which the asymmetric features include one of slanted gratings or blazed gratings.

4. The optical system of claim 1 further including a third DOE disposed on the substrate, the third DOE having an output surface and configured for pupil expansion of the one or more optical beams along a second direction, and further configured as an out-coupling grating to couple, as an output from the output surface, one or more optical beams with expanded pupil relative to the input.

5. The optical system of claim 4 in which differences among optical path lengths in the second DOE exceed a coherence length so as to improve display uniformity in the third DOE.

6. 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;

an imager operatively connected to the optical engine to form images based on the image data and to generate one or more input optical beams incorporating the images; and

an exit pupil expander, responsive to the one or more input optical beams, comprising a structure on which multiple diffractive optical elements (DOEs) are disposed,

in which the exit pupil expander is configured to provide one or more output optical beams, using one or more of the DOEs, as a near eye virtual display with an expanded exit pupil, and

wherein at least one of the DOEs has a portion configured as a crossed grating with a plurality of grating elements that are periodically arranged along first and second directions that are different from each other.

7. The electronic device of claim 6 in which the portion of the DOE supports multiple optical paths to a given point within the portion of DOE wherein the differences in the multiple optical path lengths exceed a coherence length of an input optical beam.

8. The electronic device of claim 6 in which the exit pupil expander provides pupil expansion in two directions.

9. The electronic device of claim 6 in which the imager includes one of light emitting diode, liquid crystal on silicon device, organic light emitting diode array, or micro-electro mechanical system device.

10. The electronic device of claim 6 in which the imager comprises a micro-display operating in one of transmission, reflection, or emission.

11. The electronic device of claim 6 as implemented in a head mounted display device or portable electronic device.

12. The electronic device of claim 6 in which each of the one or more input optical beams is produced by a corresponding one or more sources.

13. The electronic device of claim 6 in which the structure is curved or partially spherical.

14. The electronic device of claim 6 in which two or more of the DOEs are non-co-planar.

15. A method, comprising:

receiving light at an in-coupling diffractive optical element (DOE) disposed in an exit pupil expander;

expanding an exit pupil of the received light along a first coordinate axis in an intermediate DOE disposed in the exit pupil expander;

expanding the exit pupil along a second coordinate axis in an out-coupling DOE disposed in the exit pupil expander; and

outputting light with an expanded exit pupil relative to the received light at the in-coupling DOE along the first and second coordinate axes using the out-coupling DOE,

in which the intermediate DOE includes gratings configured to provide a periodic contoured surface having a first periodicity along a first direction and a second periodicity along a second direction.

16. The method of claim 15 in which the periodic contoured surface comprises one of quadrangular elements, cylindrical elements, polygonal elements, elliptical elements, pyramidal elements, curved elements, or combinations thereof.

17. The method of claim 15 in which the in-coupling DOE, the intermediate DOE, or the out-coupling DOE is formed with a polymer that is molded from a substrate that is etched using ion beam etching in which the substrate is moveable relative to an ion beam source.

18. The method of claim 15 further in which at least a portion of the out-coupling DOE is an apodized diffraction grating having shallow grooves relative to the in-coupling DOE or the intermediate DOE.

19. The method of claim 15 as performed in a near eye display system.

20. The method of claim 19 in which the output light provides a virtual display to a user of the near eye display system.