DIFFRACTIVE OPTICAL ELEMENTS WITH GRADED EDGES

• US 20170003504A1
• Filed: 06/30/2015
• Published: 01/05/2017
• Est. Priority Date: 06/30/2015
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Lauri Sainiemi
• Inventors: Vallius, Tuomas, Sainiemi, Lauri, Levola, Tapani, Mattila, Marco
• Granted Patent: US 9,910,276 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• 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 27/0101 characterised by optical features G02B27/0172 takes precedence
• 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: G02B 5/1819 Plural gratings positioned on the same surface, e.g. array of gratings plural diffractive elements positioned sequentially along the optical path G02B27/4272
• CPC Class Codes: G02B 5/1852 using mechanical means, e.g. ruling with diamond tool, moulding

Abstract

In an optical system that includes a waveguide with multiple diffractive optical elements (DOEs) incorporating diffraction gratings, light exiting a trailing edge of an upstream DOE enters a leading edge of a downstream DOE. One or more of the DOEs may include a leading and/or a trailing edge that have a graded profile. At a graded trailing edge of an upstream DOE, grating height smoothly decreases from full height to shallow height as a function of the proximity to the trailing edge. At a graded leading edge of the downstream DOE grating height smoothly increases from shallow height to full height as a function of distance away from the leading edge. By reducing a sharp boundary at the interface between the upstream and downstream DOEs, the graded profiles of the DOE edges enable optical resolution to be maintained decreasing sensitivity to misalignment between the DOEs that may occur during manufacturing.

Claims

1. An optical system, comprising:

a substrate of optical material;

a first diffractive optical element (DOE) disposed on the substrate and configured as an in-coupling grating to receive, as an input, one or more optical beams that propagate in the first DOE and exit at a trailing edge of the first DOE; and

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

in which the trailing edge of the first DOE is located on the substrate at an interface with the second DOE, wherein the one or more optical beams exiting at the trailing edge, enter a leading edge of the second DOE, and

wherein the trailing edge and leading edge are graded so that a grating height of each of the first DOE and the second DOE increases as a function of distance from the interface.

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

3. The optical system of claim 1 in which the grating height in the first DOE decreases approximately linearly from a full height upstream from the trailing edge to a shallow height at the trailing edge of the first DOE.

4. The optical system of claim 1 in which the grating height in the first DOE decreases approximately linearly from a full height upstream from the trailing edge to zero height at the trailing edge of the first DOE.

5. The optical system of claim 1 in which the grating height in the second DOE increases approximately linearly from a shallow height at the leading edge to a full height downstream from the leading edge.

6. The optical system of claim 1 in which either the first DOE or second DOE is a straight diffraction grating or a slanted diffraction grating.

7. The optical system of claim 1 in which the one or more optical beams received as the input emanate as a virtual image produced by a micro-display or imager.

8. 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 one or more near eye virtual displays with an expanded exit pupil, and

in which light enters at a leading edge of a DOE and exits at a trailing edge of a DOE and at least one of the DOEs has a portion with a graded profile so that grating height linearly increases as a function of distance from the leading edge or the trailing edge over the portion.

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

10. The electronic device of claim 8 in which the structure comprises a waveguide.

11. The electronic device of claim 8 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.

12. The electronic device of claim 8 in which the imager comprises a micro-display operating in one of transmission, reflection, or emission.

13. The electronic device of claim 8 as implemented in a head mounted display device or portable electronic device.

14. The electronic device of claim 8 in which each of the one or more input optical beams is produced by a corresponding one or more sources.

15. A method, comprising:

receiving light at an input-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 output-coupling DOE disposed in the exit pupil expander; and

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

in which light exits the input-coupling DOE at a first graded trailing edge on which full height gratings transition to a smooth surface on the input-coupling DOE adjacent to a first interface between the in-coupling DOE and the intermediate DOE, and

in which light exiting the input-coupling DOE enters the intermediate DOE at a graded leading edge on which a smooth surface on the intermediate DOE adjacent to the first interface transitions to full height gratings, and

in which light exits the intermediate DOE at a second graded trailing edge on which full height gratings transition to a smooth surface on the intermediate DOE adjacent to a second interface between the intermediate DOE and the out-coupling DOE.

16. The method of claim 15 in which the transitions are gradual to minimize discontinuity at the interface so as to reduce impairment of optical resolution or reduce phase change in light coupled between the in-coupling DOE and intermediate DOE or between the intermediate DOE and the out-coupling DOE.

17. The method of claim 15 in which the input-coupling DOE, the intermediate DOE, or the output-coupling DOE is formed with a polymer that is molded from a substrate that is etched using ion beam etching with a moving mask.

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 input-coupling DOE or the intermediate DOE.

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

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