Binary-lens-embedded photonic crystals.

A binary-lens-embedded photonic crystal (B-LEPC) was designed for operation at 1550 nm and fabricated by multiphoton lithography. The lens is binary in the sense that optical path difference is generated using unit cells having just two distinct fill factors. The unit cells have a "rod-in-wall" structure that exhibits three-dimensional self-collimation. Simulations show that self-collimation forces light to move through the device without diffracting or focusing, even as the wavefront is reshaped by the lensing region. Upon exiting the device, the curved wavefront causes the light to focus. The thickness of a B-LEPC was reduced threefold by wrapping phase in the style of a Fresnel lens. Embedding a faster-varying phase profile enables tighter focusing, and numerical aperture NA = 0.59 was demonstrated experimentally.