Compact and integrated 2-D photonic crystal super-prism filter-device for wavelength demultiplexing applications

Ultrahigh-Q optomechanical crystal cavities fabricated in a CMOS foundry

Photonic crystals use periodic structures to create frequency regions where the optical wave propagation is forbidden, which allows the creation and integration of complex optical functionalities in small footprint devices. Such strategy has also been successfully applied to confine mechanical waves and to explore their interaction with light in the so-called optomechanical cavities. Because of their challenging design, these cavities are traditionally fabricated using dedicated high-resolution electron-beam lithography tools that are inherently slow, limiting this solution to small-scale or research applications. Here we show how to overcome this problem by using a deep-UV photolithography process to fabricate optomechanical crystals in a commercial CMOS foundry. We show that a careful design of the photonic crystals can withstand the limitations of the photolithography process, producing cavities with measured intrinsic optical quality factors as high as Q_i = (1.21 ± 0.02) × 10⁶. Optomechanical crystals are also created using phononic crystals to tightly confine the GHz sound waves within the optical cavity, resulting in a measured vacuum optomechanical coupling rate of g₀ = 2π × (91 ± 4) kHz. Efficient sideband cooling and amplification are also demonstrated since these cavities are in the resolved sideband regime. Further improvements in the design and fabrication process suggest that commercial foundry-based optomechanical cavities could be used for quantum ground-state cooling.

Design methodology for compact photonic-crystal-based wavelength division multiplexers

We present an extremely compact wavelength division multiplexer design, as well as a general framework for designing and optimizing frequency selective devices embedded in photonic crystals satisfying arbitrary design constraints. Our method is based on the Dirichlet-to-Neumman simulation method and uses low rank updates to the system to efficiently scan through many device designs.

Simulation and Fabrication of Two Dimensional Nonlinear Photonic Crystals using Barium Titanate Thin Films

Photonic crystal (PhC) can potentially result in enhanced optical properties around critical points in the photonic band gap. Of interest here are enhanced nonlinear optical effects. In this study, one and two dimensional nonlinear PhC were designed and fabricated using barium titanium oxide (BTO) thin films as the active medium. Nonlinear PhC made with barium titanate thin films potentially provide integrated devices with the advantages of wide tunability and high stability. Films 500 nm thick deposited on MgO substrates were utilized. Two dimensional PhC structures were defined by focused ion beams (FIB). Before patterning, a thin metal layer was deposited on the barium titanate layers in order to improve the conductivity of the samples. After writing the patterns, cylindrical air holes were generated in the thin film layers. The PhC lattice constant and the hole radius were selected in sub-micron region in order to satisfy the requirement of wave resonance. The PhCs with sub-micron features were characterized by the atomic force microscopy (AFM), scanning electron microscopy (SEM), and near field optical microscopy (NSOM). The transmission spectra of the PhC waveguides were calculated with a continuous wide band source that covered 1 to 2 micron wavelength. Simulations of the transmission characteristics were performed using the two dimensional finite difference time domain method (FDTD).

Power splitters based on the light-intensity-dependent superprism effect

By utilizing the nonlinear Kerr effect of the background medium, power splitters based on the light-intensity-dependent superprism effect are realized in a two-stage system, where two photonic lattices are rotated to each other by 16 degrees . The nonlinear finite-difference time-domain method is applied to conducting numerical experiments. The first lattice acts as the deflecting stage, in which beams with different power densities are separated from each other spatially. The second lattice has a function of "angular amplifier" that enlarges the separation angle between two power density ranges (lower than 100 W/microm2 and higher than 300 W/microm2) to 90 degrees-like. In the first photonic band, due to the local change of refractive indices induced by the pumping power, new interfaces are formed between the pumped and nonpumped areas. The k-vector will be rotated by these interfaces until the phase velocity and group velocity have the same direction. The shape of the interface between these two stages is discussed.

Adiabatic bends in surface plasmon polariton band gap structures

Propagation and interaction of surface plasmon polaritons (SPPs) excited in the wavelength range 700-860 nm with periodic triangular arrays of gold bumps placed on gold film surfaces are investigated using a collection near-field microscope. We observe the inhibition of SPP propagation into the arrays within a certain wavelength range, i.e., the band gap (BG) effect. We demonstrate also the SPP propagation along a 30 degrees bent channel obtained by an adiabatic rotation of the periodic array of scatterers. Numerical simulations using the Lippmann-Schwinger integral equation method are presented and found in reasonable agreement with the experimental results.