Wavefront sensing with in-field illuminators

1. A head mounted display (HMD) comprising:

a wavefront sensor;

an illumination layer configured to emit infrared illumination light that is collimated or near-collimated to a center of rotation of an eye; and

an optical element configured to receive retina-reflected infrared light and redirect the retina-reflected infrared light to the wavefront sensor, wherein the retina-reflected infrared light is the infrared illumination light reflected by a retina and exiting a pupil of the eye, and wherein the wavefront sensor is configured to generate a wavefront image in response to the retina-reflected infrared light.

2. The HMD of claim 1 , wherein the illumination layer includes an array of infrared in-field illuminators configured to be disposed between 10 mm and 35 mm from the eye when a user of the HMD is utilizing the HMD, and wherein the array of infrared in-field illuminators is visually unnoticeable by the eye when disposed between 10 and 35 mm from the eye.

3. The HMD of claim 2 , wherein an individual infrared in-field illuminator has a footprint of less than 200 microns×200 microns.

4. A near-eye optical system comprising:

a wavefront sensor;

an array of infrared in-field illuminators configured to emit infrared illumination light to a center of rotation of an eye; and

a combiner optical element configured to receive retina-reflected infrared light and redirect the retina-reflected infrared light to the wavefront sensor, wherein the retina-reflected infrared light is the infrared illumination light reflected by a retina and exiting a pupil of the eye, and wherein the wavefront sensor is configured to generate a wavefront image in response to the retina-reflected infrared light.

5. The near-eye optical system of claim 4 , wherein each of the infrared in-field illuminators in the array includes:

an infrared light source emitting the infrared illumination light; and

a beam-forming element configured to direct the infrared illumination light toward the center of rotation of the eye.

6. The near-eye optical system of claim 5 , wherein the beam-forming elements of the infrared light sources are configured to increase an illumination angle of the infrared illumination light as a distance of a particular beam-forming element increases from a middle region of the array of infrared in-field illuminators.

7. The near-eye optical system of claim 4 , wherein the infrared in-field illuminators include at least one of a micro light emitting diode (micro-LED), an edge emitting LED, a vertical cavity surface emitting laser (VCSEL) diode, or a Superluminescent diode (SLED).

8. The near-eye optical system of claim 4 further comprising:

a transparent substrate, wherein the array of infrared in-field illuminators is disposed on the transparent substrate, and wherein the transparent substrate is positioned to pass the retina-reflected infrared light through the transparent substrate to the combiner optical element, the combiner optical element configured to redirect the retina-reflected infrared light back through the transparent substrate toward the wavefront sensor.

9. The near-eye optical system of claim 4 further comprising:

illumination logic configured to selectively activate individual infrared in-field illuminators in the array of infrared in-field illuminators.

10. The near-eye optical system of claim 4 , wherein the wavefront sensor includes:

a camera including an image sensor; and

a lenslet array disposed in an optical path between the combiner optical element and the image sensor, wherein microlenses of the lenslet array focus the retina-reflected infrared light onto the image sensor.

11. The near-eye optical system of claim 10 , wherein the lenslet array is positioned at a plane that is conjugate to a pupil plane of an eye.

12. The near-eye optical system of claim 10 , wherein the camera includes an infrared filter configured to pass the infrared illumination light and reject other light wavelengths.

13. The near-eye optical system of claim 4 , wherein the combiner optical element includes a polarization-selective volume hologram that reflects a first polarization orientation of the retina-reflected infrared light and passes polarization orientations that are other than the first polarization orientation, and wherein the combiner optical element passes visible light.

14. The near-eye optical system of claim 4 , wherein the infrared in-field illuminators in the array are spaced apart so that at least a portion of the infrared in-field illuminators will be positioned to illuminate a retina of the eye, through a pupil of the eye, over a range of eye positions.

15. A method comprising:

illuminating an eye with infrared illumination light, wherein the infrared illumination light is directed to a center of rotation of the eye;

generating a wavefront image of retina-reflected infrared light, wherein the retina-reflected infrared light is the infrared illumination light reflected by a retina and exiting a pupil of the eye; and

determining an accommodative eye state value based at least in part on the wavefront image.

16. The method of claim 15 , wherein generating the wavefront image includes receiving the retina-reflected infrared light with a wavefront sensor including an image sensor and a lenslet array.

17. The method of claim 16 , wherein the lenslet array is positioned at a plane that is conjugate to a pupil plane of the eye.

18. The method of claim 16 , wherein determining the accommodative eye state value includes analyzing a spacing of beam spots of the wavefront image generated by microlenses of the lenslet array focusing the retina-reflected infrared light onto the image sensor.

19. The method of claim 15 further comprising:

adjusting a virtual image presented to the eye by a head mounted display in response to the accommodative eye state value.

20. The method of claim 15 , wherein the infrared illumination light is collimated or near-collimated.