Pancake lens assembly and optical system thereof

A head-mounted display (HMD), comprising:

• an optical lens assembly that receives an image light from an electronic display and directs the image light to an eye-box, the optical lens assembly comprising:
• a first optical element including a partial reflector and a quarter-wave plate;
• a second optical element including a reflective polarizer;
• and
• a varifocal lens disposed inside a cavity formed by the first optical element and the second optical element, the varifocal lens being an liquid crystal (LC) lens stack comprising a plurality of LC lenses, an LC lens of the plurality of the LC lenses having a plurality of optical states including an additive state that adds optical power to the varifocal lens and a subtractive state that removes optical power from the varifocal lens,
• wherein the plurality of optical states provides a range of adjustment of optical power for the optical lens assembly.