Reverse-order crossed pancake lens with azimuthal compensation

1. A pancake lens block, comprising:

a plurality of optical elements configured to transmit at least a portion of radiation from a radiation source, wherein the plurality of optical elements comprises:

a partial reflector; and

a retarder is configured to convert the portion of radiation from one polarization state to another polarization state;

a spatially patterned optical retardation film coupled between the partial reflector and the retarder, wherein the spatially patterned optical retardation film:

comprises a reactive mesogen having a uniaxial birefringence;

comprises a layer having a thickness that varies in a radial direction; and

is configured to reduce an optical effect of stress birefringence in the plurality of optical elements;

a reflective polarizer configured to reflect the portion of radiation to the partial reflector through the retarder, where the partial reflector reflects a second portion of the radiation from the retarder back to the reflective polarizer; and

an eye-reflection reduction portion configured to:

receive the second portion of radiation from the reflective polarizer after the second portion of the radiation has passed through the retarder; and

reduce back reflections emanating from an eye of a user, the eye-reflection reduction portion comprising:

a polarizer;

a compound retarder comprising a stack of at least three quarter wave plates; and

an anti-reflective material.

2. The pancake lens block of claim 1 , wherein:

the retarder is oriented to a first axis of orientation, where the retarder is configured to selectively transmit the portion of radiation from the radiation source;

the partial reflector receives the portion of radiation from the retarder and transmits the portion of radiation; and

the plurality of optical elements further comprise:

a second retarder oriented to a second axis of orientation that is substantially orthogonal to the first axis of orientation, where the second retarder is configured to transmit the portion of radiation from the partial reflector.

3. The pancake lens block of claim 2 , wherein at least one of the second retarder or the partial reflector comprises a plastic lens.

4. The pancake lens block of claim 3 , wherein the plastic lens is fabricated using an injection molding process.

5. The pancake lens block of claim 3 , wherein the plastic lens comprises a material whose stress optical coefficient is higher than a stress optical coefficient of a cyclic olefin material.

6. The pancake lens block of claim 3 , wherein the spatially patterned optical retardation film has a maximum thickness that is approximately equal to a thickness of the plastic lens.

7. The pancake lens block of claim 1 , wherein an amount of retardation provided by the spatially patterned optical retardation film increases with an increasing radius of the spatially patterned optical retardation film.

8. The pancake lens block of claim 1 , wherein the spatially patterned optical retardation film is fabricated using a non-uniform spin coating process.

9. The pancake lens block of claim 8 , wherein the non-uniform spin coating process comprises:

dispensing a fluid from a fluid source onto a surface of a substrate at a first radial position while spinning the substrate at a first angular velocity; and

dispensing the fluid from the fluid source onto the substrate's surface at a second radial position while spinning the substrate at a second angular velocity.

10. The pancake lens block of claim 9 , wherein the fluid comprises a volatile component and a nonvolatile component, and the volatile component evaporates from the substrate's surface yielding a film on the substrate's surface, the film comprising the nonvolatile component.

11. The pancake lens block of claim 1 , wherein the reactive mesogen comprises at least one of an acrylate, a methacrylate, an epoxy, an oxetane, a vinyl-ether, a styrene, or a thiol.

12. The pancake lens block of claim 1 , wherein the reactive mesogen has pre-tilt that changes with an increasing radius of the layer.

13. A head mounted display (HMD) comprising:

an electronic display configured to emit light; and

a pancake lens block comprising:

a plurality of optical elements configured to transmit at least a portion of the light emitted by the electronic display, wherein the plurality of optical elements comprises:

a partial reflector; and

a retarder is configured to convert the portion of light from one polarization state to another polarization state; and

a spatially patterned optical retardation film coupled between the partial reflector and the retarder, wherein the spatially patterned optical retardation film:

comprises a reactive mesogen having a uniaxial birefringence;

comprises a layer having a thickness that varies in a radial direction; and

is configured to reduce an optical effect of stress birefringence in the plurality of optical elements;

a reflective polarizer configured to reflect the portion of light to the partial reflector through the retarder, where the partial reflector reflects a second portion of the light from the retarder back to the reflective polarizer; and

an eye-reflection reduction portion configured to:

receive the second portion of light from the reflective polarizer after the second portion of light has passed through the retarder; and

reduce back reflections emanating from an eye of a user, the eye-reflection reduction portion comprising:

a polarizer;

a compound retarder comprising a stack of at least three quarter wave plates; and

an anti-reflective material.

14. The HMD of claim 13 , wherein:

the retarder is oriented to a first axis of orientation, where the retarder is configured to selectively transmit the portion of light emitted by the electronic display;

the partial reflector receives the portion of light from the retarder and transmits the portion of light; and

the plurality of optical elements further comprise:

a second retarder oriented to a second axis of orientation that is substantially orthogonal to the first axis of orientation, where the second retarder is configured to transmit the portion of light from the partial reflector.

15. A method of assembling a pancake lens block, the method comprising:

positioning a plurality of optical elements to transmit at least a portion of light from a radiation source, wherein the plurality of optical elements comprises:

a partial reflector; and

a retarder is configured to convert the portion of light from one polarization state to another polarization state;

coupling a spatially patterned optical retardation film between the partial reflector and the retarder, wherein the spatially patterned optical retardation film:

comprises a reactive mesogen having a uniaxial birefringence;

comprises a layer having a thickness that varies in a radial direction; and

is configured to reduce an optical effect of stress birefringence in the plurality of optical elements;

configuring a reflective polarizer to reflect the portion of light to the partial reflector through the retarder, where the partial reflector reflects a second portion of the light from the retarder back to the reflective polarizer; and

configuring an eye-reflection reduction portion to:

receive the second portion of light from the reflective polarizer after the second portion of light has passed through the retarder; and

reduce back reflections emanating from an eye of a user, the eye-reflection reduction portion comprising:

a polarizer;

a compound retarder comprising a stack of at least three quarter wave plates; and

an anti-reflective material.

16. The method of claim 15 , further comprising fabricating the spatially patterned optical retardation film using a non-uniform spin coating process.