We report efficient wave plates with different retardations and orientations of fast axes realized using transmitarrays
composed of a periodic arrangement of amorphous silicon elliptical cylinders on glass. We show that novel polarization
devices which locally rotate the polarization by different angles while preserving the wavefront can be demonstrated
using such a high contrast transmitarray. We present design, fabrication and experimental characterization results for
near infrared transmissive wave retarders with efficiencies in excess of 90%, and discuss the potential applications of atwill
local polarization control enabled by this technology.
We present design, fabrication, and characterization results of high numerical aperture (NA) micro-lenses based on a
high contrast transmitarray platform. The high contrast transmitarray is created by periodic arrangement of amorphous
silicon posts with different diameters on a fused silica substrate. We report near infrared high NA micro-lenses with spot
sizes as small as 0.57λ and focusing efficiencies in excess of 80%. We demonstrate a trade-off relation between NA and
efficiency of high contrast array flat micro-lenses, and attribute it to the spatial discretization of their phase profiles.
We present reflective phase shifters based on high contrast gratings resting on a low-index spacer backed by a metallic mirror. The guided resonance of the grating combined with the reflection from the metallic mirror leads to an all-pass filter with 2π phase shift variation and unity reflectivity across the resonance. We present simulations, fabrication and measurement of passive devices fabricated in silicon over gold using a polymer as the spacer layer. Active control at high modulation speeds can be achieved by shifting the guided resonance wavelength using carrier injection or thermo-optic effect in silicon.
We propose a broadband free-space on-chip spectrometer based on an array of integrated narrowband filters consisting of Fabry-Perot resonators formed by two high-contrast grating (HCG) based reflectors separated by a low-index thin layer with a fixed cavity thickness. Using numerical simulations, broadband tunability of resonance wavelengths was achieved only by changing the in-plane grating parameters such as period or duty cycle of HCGs while the substrate geometry was kept fixed. Experimentally, the HCG reflectors were fabricated on silicon on insulator (SOI) substrates and high reflectivity was measured, fabrication process for the proposed double HCG-based narrowband filter array was developed. The filtering function that can be spanned over a wide range of wavelengths was measured.
Simulation results for an etched air hole photonic crystal (PhC) vertical cavity surface emitting laser (VCSEL) structure
with various thicknesses of metal deposited inside the holes are presented. The higher-order modes of the structure are
more spread out than the fundamental mode, and penetrate into the metal-filled holes. Due to the lossy nature of the
metal, these higher-order modes experience a greater loss than the fundamental mode, resulting in an enhanced side
mode suppression ratio (SMSR). A figure of merit for determining which metals would have the greatest impact on the
SMSR is derived and validated using a transmission matrix method calculation. A full three-dimensional simulation of
the PhC VCSEL structure is performed using the plane wave admittance method, and SMSRs are calculated for
increasing metal thicknesses. Of the metals simulated, chromium provided the greatest SMSR enhancement with more
than a 4 dB improvement with 500 nm of metal for an operating current of 12 times threshold.