Eye imaging with an off-axis imager
Examples of an imaging system for use with a head mounted display (HMD) are disclosed. The imaging system can include a forward-facing imaging camera and a surface of a display of the HMD can include an off-axis diffractive optical element (DOE) or hot mirror configured to reflect light to the imaging camera. The DOE or hot mirror can be segmented. The imaging system can be used for eye tracking, biometric identification, multiscopic reconstruction of the three-dimensional shape of the eye, etc.
1. An imaging system comprising:
an optical element positioned in front of an eye of a user;
a reflective element that reflects light in a first wavelength range; and
a forward-facing imager sensitive to a subset of light of the first wavelength range, wherein the forward-facing imager is oriented to capture the subset of light of the first wavelength range reflected by the reflective element, wherein the forward-facing imager is on a same side of the optical element as an eye of a user;
a virtual backward-facing imager formed by infrared light propagated from the eye of the user through the optical element corresponding to the infrared light reflected by the reflective element and captured by the forward-facing imager; and
wherein the virtual backward-facing imager and the forward-facing imager are positioned on opposite sides of the optical element and the virtual backward-facing imager and the forward-facing imager are equidistant from the optical element.
2. The imaging system of claim 1 , wherein the reflective element comprises a hot mirror, a holographic optical element (HOE), an off-axis holographic mirror (OAHM), or an off-axis volumetric diffractive optical element (OAVDOE).
3. The imaging system of claim 1 , wherein the first wavelength range comprises an infrared wavelength range.
4. The imaging system of claim 1 , wherein the optical element comprises the reflective element, and wherein the optical element is transmissive to at least 50% of visible light incident on the optical element.
5. The imaging system of claim 1 , wherein the reflective element comprises a plurality of segments.
6. The imaging system of claim 5 , wherein a first segment in the plurality of segments has an optical property that is different from an optical property of a second segment in the plurality of segments.
7. The imaging system of claim 6 , wherein the optical property of the first segment in the plurality of segments or the optical property of the second segment in the plurality of segments comprises a reflection angle or an optical power.
8. The imaging system of claim 5 , wherein two of the plurality of segments are arranged horizontally.
9. The imaging system of claim 5 , wherein two of the plurality of segments are arranged vertically.
10. The imaging system of claim 1 , wherein the forward-facing imager further comprises a perspective control lens assembly comprising a shift lens, a tilt lens, or a shift-tilt lens.
11. The imaging system of claim 1 , wherein the reflective element is transmissive to a second wavelength range that is different from the first wavelength range.
12. The imaging system of claim 1 , wherein the optical element comprises the reflective element, and wherein the optical element is non-transmissive to visible light incident on the optical element.
13. The imaging system of claim 1 , wherein the depth of field for the forward-facing imager is the same as the depth of field of the virtual backward-facing imager based on the virtual backward-facing imager and the forward-facing imager being equidistant from the optical element.
14. The imaging system of claim 1 , wherein depth of field for the virtual backward-facing imager and the forward-facing imager are the same.