Fabrication and Characterization of Spatially-Variant Self-Collimating Photonic Crystals

Spatially-variant photonic crystals (SVPCs) created using materials having a low refractive index are shown to be capable of abruptly controlling light beams with high polarization selectivity. SVPCs are photonic crystals for which the orientation of the unit cell is controllably varied throughout the lattice to control the flow of light. Multi-photon lithography in a photo polymer was used to fabricate three-dimensional SVPCs that direct the flow of light around a 90 degree bend. The optical performance of the SVPCs was characterized using a scanning optical-fiber system that introduced light onto the input face of a structure and measured the intensity of light emanating from the output faces. As a proof-of-concept, SVPCs that can bend a beam at a wavelength of ?0 = 2.94 ?m were fabricated in the photo-polymer SU-8. The SVPCs were shown to direct infrared light of one polarization through a sharp bend, while the other polarization propagated straight through the SVPC, when the volumetric fill-factor is near 50%. The peak-to-peak ratio of intensities of the bent- and straight-through beams was 8:1, and a power efficiency of 8% was achieved. The low efficiency is attributed to optical absorption in SU-8 at ?0 = 2.94 ?m. SVPCs that can bend a beam at telecommunications wavelengths near ?0 = 1.55 ?m were fabricated by multi-photon lithography in the photo-polymer IP-Dip. IP-Dip was chosen over SU 8 to enable fabrication of finer features, as are needed for an SVPC scaled in size to operate at shorter wavelengths. Experimental characterization shows that these particular SVPCs provide effective control of the vertically polarized beam at ?0 = 1.55 ?m, when the volumetric fill-factor is around 46%. The beam bending peak efficiency was found to be 52.5% with a peak-to-peak ratio between the bent- and straight-through beams of 78.7. Additionally, these SVPCs can bend a light beam with a broad bandwidth of 153 nm that encompasses both the C- and S-bands of the telecommunications window. Furthermore, the SVPCs have high tolerance to misalignment, in which an offset of the input beam by as much as 6 ?m causes the beam-bending efficiency to drop no more than 50%. Finally, it is shown that these particular SVPCs can bend beams without significantly distorting the mode profile. This work introduces a new scheme for controlling light that should be useful for integrated photonics. The penultimate chapter discusses nonlinear phenomena that were observed during the optical characterization of the SVPCs using a high peak-power amplified femtosecond laser system. The first of these effects is referred to as super-collimation , in which the beam bending peak efficiency of certain SVPCs increases with input intensity, reaching as high as 68%. The second effect pertains to nonlinear imaging of light at ?0 = 1.55 ?m scattered from an SVPC and detected using a silicon-CCD camera. This effect enables beam bending within the device to be imaged in real time. The dissertation concludes with an outlook for SVPCs, discussing potential applications and challenges that must be addressed to advance their use in photonics