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Photonic crystals can be engineered so that the flow of optical power and the phase of the field are independently controlled. The concept is demonstrated by creating a self-collimating lattice with an embedded cylindrical lens. The device is fabricated in a photopolymer by multi-photon lithography with the lattice spacing chosen for operation around the telecom wavelength of 1550 nm. The lattice is based on a low-symmetry rod-in-wall unit cell that strongly self-collimates light. The walls are varied in thickness to modulate the effective refractive index so light acquires a spatially quadratic phase profile as it propagates through the device. Although the phase of the field is altered, the light does not focus within the device because self-collimation forces power to flow parallel to the principal axes of the lattice. Upon exiting the device, ordinary propagation resumes in free space and the curved phase profile causes the light to focus. An analysis of the experimentally observed optical behavior shows that the device behaves like a thin lens, even though the device is considerably thick.
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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 apertureNA = 0.59 was demonstrated experimentally.
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- Award ID(s):
- 1711356
- PAR ID:
- 10368584
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 47
- Issue:
- 12
- ISSN:
- 0146-9592; OPLEDP
- Format(s):
- Medium: X Size: Article No. 2943
- Size(s):
- Article No. 2943
- Sponsoring Org:
- National Science Foundation
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