DIFFRACTIVE OPTICAL ELEMENT WITH UNCOUPLED GRATING STRUCTURES

• US 20170123208A1
• Filed: 10/29/2015
• Published: 05/04/2017
• Est. Priority Date: 10/29/2015
• 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 9,946,072 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 2027/0118 comprising devices for improving the contrast of the display / brillance control visibility
• CPC Class Codes: G02B 2027/0123 comprising devices increasing the field of view
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• 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 27/286 for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34
• 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 27/4261 having a diffractive element with major polarization dependent properties
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1842 Gratings for image generation G02B5/1847 takes precedence
• CPC Class Codes: G02B 6/0026 Wavelength selective element, sheet or layer, e.g. filter or grating
• CPC Class Codes: G02B 6/005 provided by one optical element, or plurality thereof, placed on the light output side of the light guide
• CPC Class Codes: G06F 3/14 Digital output to display device ; Cooperation and interconnection of the display device with other functional units

Abstract

In an optical display system having a waveguide and 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 exit pupil expansion in a second direction and couples light out of the waveguide. The intermediate DOE includes grating features that are configured to rotate a state of polarization of light perturbations in the intermediate DOE that would otherwise generate optical interference through a closed-loop coupling phenomenon. The polarization state of a perturbed beam is rotated in the intermediate DOE to be orthogonal relative to the polarization state of the main beam used for image display to thereby uncouple the closed loops and make the perturbed beam non-interfering with the imaging beam.

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 includes grating features configured to rotate a state of polarization of light perturbations to be orthogonal relative to a polarization of the input optical beams to reduce coupling between closed loops in the second DOE arising from multiple optical paths to a given location in the second DOE in which path length differences are smaller than a coherence length.

2. The optical system of claim 1 in which the configured grating features include at least one of grating asymmetry, grating depth, or grating fill factor.

3. The optical system of claim 2 in which the grating asymmetry is implemented using 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 with uncoupled grating structures in which a polarization state of optical perturbations is rotated to be non-interfering with the input optical beams.

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 the DOE wherein 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 as an imaging beam 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 grating features configured to change a polarization state of an interfering optical beam to be orthogonal to a polarization state of the imaging beam.

16. The method of claim 15 in which parameters describing the grating features are selected in an iterative process to reduce closed-loop coupling in the intermediate DOE by observing a level of banding in the EPE.

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 including implementing varying depth modulation direction in the intermediate DOE to control whether the interfering optical beam causes constructive or destructive interference.

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.