Head mounted display including a reverse-order crossed pancake lens

A head mounted display (HMD) comprising:

• an electronic display configured to emit light;
• and
• a pancake lens block comprising:
• a first compound retarder comprising a stack of at least three quarter wave plates whose optical axes are oriented in a specific order relative to one another, where the first compound retarder is configured to selectively transmit a portion of the emitted light;
• a partial reflector configured to receive the portion of emitted light from the first compound retarder and transmits the portion of emitted light;
• a second compound retarder comprising an additional stack of at least three quarter wave plates whose optical axes are orthogonal and oriented in a different order that reversely maps to the specific order, where the second compound retarder is configured to selectively transmit the portion of emitted light from the partial reflector;
• a reflective polarizer configured to reflect the portion of emitted light selectively transmitted by the second compound retarder back to the second compound retarder, where the partial reflector reflects a second portion of emitted light from the second compound retarder back to the reflective polarizer;
• and
• an eye-reflection portion configured to:
• receive the second portion of emitted light from the reflective polarizer after the second portion of emitted light has passed through the second compound retarder;
• and
• reduce back reflections emanating from an eye of a user, the eye-reflection portion comprising:
• a polarizer;
• a third compound retarder comprising another stack of at least three quarter wave plates;
• and
• an anti-reflective material.

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

• positioning a partial reflector adjacent to a first compound retarder across an air gap, wherein:
• the first compound retarder comprises a stack of at least three quarter wave plates whose optical axes are oriented in a specific order relative to one another, where the first compound retarder is configured to selectively transmit a portion of radiation from a radiation source;
• and
• the partial reflector is configured to receive the portion of radiation from the first compound retarder and transmit the portion of radiation;
• positioning a second compound retarder adjacent to the partial reflector, the second compound retarder comprising an additional stack of at least three quarter wave plates whose optical axes are orthogonal and oriented in a different order that reversely maps to the specific order, where the second compound retarder is configured to selectively transmit the portion of radiation from the partial reflector;
• positioning a reflective polarizer adjacent to the second compound retarder, the reflective polarizer configured to reflect the portion of radiation selectively transmitted by the second compound retarder back to the second compound retarder, where the partial reflector reflects a second portion of the radiation from the second compound retarder back to the reflective polarizer;
• and
• positioning an eye-reflection portion adjacent to the reflective polarizer, the eye-reflection portion configured to:
• receive the second portion of radiation from the reflective polarizer after the second portion of radiation has passed through the second compound retarder;
• and
• reduce back reflections emanating from an eye of a user, the eye-reflection portion comprising:
• a polarizer;
• a third compound retarder comprising another stack of at least three quarter wave plates;
• and
• an anti-reflective material.