Integrated photonics design, fabrication, and characterization tools

Integrated photonics provides access to a wide range of geometries and materials systems in which light-matter interactions can be harnessed to realize physically useful functions for applications in areas such as quantum information science, metrology, and sensing.  At its core, such device-level development involves design and numerical simulation, nanofabrication, and optical characterization.  Independent of the application space, our projects tend to have some common ingredients that are briefly summarized here.

For design, we generally use commerical software packages for simulating electromagnetic structures via the finite-difference time-domain and finite-element methods, though other techniques are used when appropriate for specific types of structures (e.g., photonic bandgap materials, gratings, metamaterials, etc).  For electromechanics, we use a commerical finite-element method solver and pair it with our optics simulations when appropriate.  As needed, we write customized codes for studying the physics of specific systems (e.g., nonlinear resonators, cavity-quantum dot systems), where the results of detailed electromangetic simulations typically enter as parameters within the governing equations that describe the physics of the light-matter interaction. 

For nanofabrication, we primarily work in the Si3N4/SiO2/Si and the GaAs/AlGaAs systems, as well as their heterogeneous integration.  We typically perform top-down fabrication based on high-resolution lithography (usually e-beam) and plasma dry etching, though we are also interested in pick-and-place and transfer printing approaches as means to combine disparate materials platforms together.  Our fabrication is currently done at the NIST Center for Nanoscale Science and Technology facility, and we make extensive use of the Nanolithography Toolbox in our work.  Recently, we have started using high-resolution 3D printing in the UMD Research Prototyping Lab as a means to create free-form optical structures that can be combined with planar chip-integrated geometries. 

On the characterization side, our setups range from fairly standardized (e.g., coupling to photonic chips via lensed fibers in a room-temperature ambient environment) to more customized (coupling to photonic chips in a closed-cycle cryostat with fiber, free-space, and microwave access simultaneously). The problem of coupling light on and off chip is central to interrogation and utilization of nanophotonic devices, and we use a variety of approaches based on far-field and evanescent coupling techniques.  In some cases, these approaches require detailed input from design and fabrication.  Our experiments make use of a variety of laser sources (external cavity tunable diode lasers and continuous wave and mode-locked Ti:sapphire lasers) and a number of spectrometers for resolving optical signals at wavelengths from the visible to the short-infrared and at optical fluxes down to the single-photon level.  We have closed-cycle cryostats for interrogating devices in a 4 K environment and for hosting superconducting single photon detectors in a 1 K environment, and a number of standard pieces of microwave electronics (signal generators, RF spectrum and vector network analyzers, oscilloscopes, etc).