Pancake lenses using Fresnel surfaces
A head-mounted display includes a pancake lens block. The pancake lens block includes a first waveplate to form first nonlinearly polarized light, a Fresnel surface to reflect and transmit a portion of the first nonlinearly polarized light, a second waveplate to form first linearly polarized light, and a linear reflective polarizer to transmit linear polarized light of a particular polarization rotation direction and to reflect light of other polarization rotation directions.
1. A lens block comprising:
a plurality of optical surfaces positioned such that light from a display is received and takes a folded beam path before being output from the lens block, the plurality of optical surfaces including:
a first waveplate surface positioned to receive the light from the display,
a Fresnel lens surface that is configured to reduce a field curvature of the received light, the Fresnel lens surface including a first set of facets having a reflective coating reflective in a band of light and a second set of facets without the reflective coating transmissive in the band of light,
a second waveplate surface, wherein the Fresnel lens surface is positioned between the first waveplate surface and the second waveplate surface, and
a reflective polarizer surface that is configured to output light of a particular polarization from the lens block, wherein the second waveplate surface is positioned between the Fresnel lens surface and the reflective polarizer surface.
2. The lens block of claim 1 , wherein light transmitted to the Fresnel lens surface has a polarization different than the particular polarization.
3. The lens block of claim 1 , wherein the reflective polarizer surface is a linear reflective polarizer.
4. The lens block of claim 1 , wherein the Fresnel lens surface is overmolded.
5. The lens block of claim 1 , wherein the first waveplate surface is a quarter waveplate.
6. The lens block of claim 5 , wherein the Fresnel lens surface is configured to transmit a portion of the received light that is nonlinearly polarized light.
7. The lens block of claim 6 , 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.
8. The lens block of claim 1 , wherein the optical surfaces are part of a monolithic pancake lens block.
9. The lens block of claim 1 , wherein at least some of the plurality of optical surfaces have different indices of refraction, and the indices of refraction are such that a back optical element including the first waveplate surface and the Fresnel lens surface and a front optical element including the second waveplate surface and the reflective polarizer surface compensate each other to reduce the field curvature.