Pancake lenses using Fresnel surfaces

1. A lens block implemented as a monolithic pancake lens block, the lens block comprising:

a first waveplate surface positioned to receive light coming from a display;

a front optical element having a first flat surface and a second flat surface opposite to the first flat surface, a second waveplate surface placed on the first flat surface and a reflective polarizer surface placed on the second flat surface; and

a Fresnel lens comprising a first set of facets with a partially reflective coating that are reflective in a band of light and a second set of facets without the partially reflective coating that are transmissive in the band of light, the Fresnel lens configured to:

partially transmit first light of a first polarization coming from the first waveplate surface in a first direction, and

partially reflect second light of the first polarization coming from the second waveplate surface in a second direction opposite to the first direction, wherein

the reflective polarizer surface is directly adjacent to an exit pupil and configured to transmit light of a second polarization coming from the second waveplate surface in the first direction, and the second waveplate surface is directly adjacent to the Fresnel lens.

2. The lens block of claim 1 , wherein the first light is circularly polarized light.

3. The lens block of claim 1 , wherein the second waveplate surface is configured to change a polarization of a portion of the first light coming from the Fresnel lens from a circular polarization into a linear polarization.

4. The lens block of claim 1 , wherein the first waveplate surface is a quarter waveplate.

5. The lens block of claim 1 , wherein the second waveplate surface is configured to change a polarization of a portion of light partially reflected in the first direction by the Fresnel lens into the second polarization.

6. The lens block of claim 1 , wherein the reflective polarizer surface is a linear reflective polarizer.

7. The lens block of claim 1 , wherein a surface of the Fresnel lens is overmolded with an immersion layer.

8. The lens block of claim 7 , wherein the immersion layer is index matched to the surface of the Fresnel lens.

9. The lens block of claim 1 , wherein the second waveplate surface has a matching retardance as the first waveplate surface and is rotated such that a slow axis of the first waveplate surface lines up with a fast axis of the second waveplate surface.

10. The lens block of claim 1 , wherein at least some of a plurality of optical surfaces of the lens block have different indices of refraction, and the indices of refraction are such that the front optical element and a back optical element that includes the first waveplate surface and the Fresnel lens compensate each other to mitigate a field curvature of the lens block.

11. The lens block of claim 1 , wherein the lens block is capable of being part of a headset.

12. A method comprising:

receiving light coming from a display at a first waveplate surface in a lens block implemented as a monolithic pancake lens block;

partially transmitting, by a Fresnel lens in the lens block, first light of a first polarization coming from the first waveplate surface in a first direction, the Fresnel lens comprising a first set of facets with a partially reflective coating that are reflective in a band of light and a second set of facets without the partially reflective coating that are transmissive in the band of light;

partially reflecting, by the Fresnel lens, second light of the first polarization coming from a second waveplate surface of a front optical element in the lens block in a second direction opposite to the first direction, the front optical element having a first flat surface and a second flat surface opposite to the first flat surface, the second waveplate surface placed on the first flat surface and a reflective polarizer surface placed on the second flat surface;

changing, by the second waveplate surface, a polarization of a portion of the first light coming from the Fresnel lens from the first polarization into the second polarization; and

transmitting, by the reflective polarizer surface that is directly adjacent to an exit pupil, light of the second polarization coming from the second waveplate surface in the first direction, and the second waveplate surface is directly adjacent to the Fresnel lens.

13. The method of claim 12 , wherein the first light is circularly polarized light.

14. The method of claim 13 , further comprising changing, by the second waveplate surface, the polarization of the portion of the first light from a circular polarization into a linear polarization.

15. A headset comprising:

a display configured to emit image light; and

a lens block implemented as a monolithic pancake lens block, the lens block comprising:

a first waveplate surface positioned to receive the image light,

a front optical element having a first flat surface and a second flat surface opposite to the first flat surface, a second waveplate surface placed on the first flat surface and a reflective polarizer surface placed on the second flat surface, and

a Fresnel lens comprising a first set of facets with a partially reflective coating that are reflective in a band of light and a second set of facets without the partially reflective coating that are transmissive in the band of light, the Fresnel lens configured to:

partially transmit the received image light of a first polarization coming from the first waveplate surface in a first direction, and

partially reflect incident light of the first polarization coming from the second waveplate surface in a second direction opposite to the first direction, wherein

the reflective polarizer surface is directly adjacent to an eye box of the headset and configured to transmit light of a second polarization coming from the second waveplate surface in the first direction toward the eye box, and the second waveplate surface is directly adjacent to the Fresnel lens.