This work reports the fabrication of micron-scale spatially variant photonic crystals (SVPCs) and their use for steering light beams through turns with bending radius Rbend on the order of ten times the optical wavelength λ0. Devices based on conventional photonic crystals, metamaterials, plasmonics and transformation optics have all been explored for controlling light beams and steering them through tight turns. These devices offer promise for photonic interconnects, but they are based on exotic materials, including metals, that make them impractically lossy or difficult to fabricate. Waveguides can also be used to steer light using total internal reflection; however, Rbend of a waveguide must be hundreds of times λ0 to guide light efficiently, which limits their use in optical circuits. SVPCs are spatially variant 3D lattices which can be created in transparent, low-refractive-index media and used to control the propagation of light through the self-collimation effect. SVPCs were fabricated by multi-photon lithography using the commercially available photo-polymer IP-DIP. The SVPCs were structurally and optically characterized and found to be capable of bending light having λ0 = 1.55 μm through a 90-degree turn with Rbend = 10 μm. Curved waveguides with Rbend = 15 μm and 35 μm were also fabricated using IP-DIP and optically characterized. The SVPCs were able to steer the light beams through tighter turns than either waveguide and with higher efficiency.
A spatially-variant photonic crystal (SVPC) that can control the spatial propagation of electromagnetic waves in three
dimensions with high polarization sensitivity was fabricated and characterized. The geometric attributes of the SVPC
lattice were spatially varied to make use of the directional phenomena of self-collimation to tightly bend an unguided
beam coherently through a 90 degree angle. Both the lattice spacing and the fill factor of the SVPC were maintained to
be nearly constant throughout the structure. A finite-difference frequency-domain computational method confirms that
the SVPC can self-collimate and bend light without significant diffuse scatter caused by the bend. The SVPC was
fabricated using multi-photon direct laser writing in the photo-polymer SU-8. Mid-infrared light having a vacuum
wavelength of λ0 = 2.94 μm was used to experimentally characterize the SVPCs by scanning the sides of the structure
with optical fibers and measuring the intensity of light emanating from each face. Results show that the SVPC is
capable of directing power flow of one polarization through a 90-degree turn, confirming the self-collimating and
polarization selective light-guiding properties of the structures.