Publications

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Surface acoustic wave (SAW) devices are used as sensing elements in the best performing portable chemical detectors. The SAW device, with a selectively absorbing chemical coating, serves as a mass sensor which preferentially responds to various chemical exposures. To obtain the highest performance, a number of criteria must be optimized, including SAW microwave insertion loss, impedance matching, electrode design configuration, RF shielding, chemically absorbent coating area, electronic measurement approach, and microfluidic packaging. A properly optimized system can be sensitive to chemical exposures the parts-per-trillion range. We report on a design optimization approach consisting of multiple comparison experiments made with competing designs. © 2012 IEEE.

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We design and fabricate arrays of diffractive optical elements (DOEs) to realize neutral atom micro-traps for quantum computing. We initialize a single atom at each site of an array of optical tweezer traps for a customized spatial configuration. Each optical trapping volume is tailored to ensure only one or zero trapped atoms. Specifically designed DOEs can define an arbitrary optical trap array for initialization and improve collection efficiency in readout by introducing high-numerical aperture, low-profile optical elements into the vacuum environment. We will discuss design and fabrication details of ultra-fast collection DOEs integrated monolithically and coaxially with tailored DOEs that establish an optical array of micro-traps through far-field propagation. DOEs, as mode converters, modify the lateral field at the front focal plane of an optical assembly and transform it to the desired field pattern at the back focal plane of the optical assembly. We manipulate the light employing coherent or incoherent addition with judicious placement of phase and amplitude at the lens plane. This is realized through a series of patterning, etching, and depositing material on the lens substrate. The trap diameter, when this far-field propagation approach is employed, goes as 2.44λF/#, where the F/# is the focal length divided by the diameter of the lens aperture. The 8-level collection lens elements in this presentation are, to our knowledge, the fastest diffractive elements realized; ranging from F/1 down to F/0.025. © 2012 SPIE.

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We demonstrate the effects of integrating a nanoantenna to a midwave infrared (MWIR) focal plane array (FPA). We model an antenna-coupled photodetector with a nanoantenna fabricated in close proximity to the active material of a photodetector. This proximity allows us to take advantage of the concentrated plasmonic fields of the nanoantenna. The role of the nanoantenna is to convert free-space plane waves into surface plasmons bound to a patterned metal surface. These plasmonic fields are concentrated in a small volume near the metal surface. Field concentration allows for a thinner layer of absorbing material to be used in the photodetector design and promises improvements in cutoff wavelength and dark current (higher operating temperature). While the nanoantenna concept may be applied to any active photodetector material, we chose to integrate the nanoantenna with an InAsSb photodiode. The geometry of the nanoantenna-coupled detector is optimized to give maximal carrier generation in the active region of the photodiode, and fabrication processes must be altered to accommodate the nanoantenna structure. The intensity profiles and the carrier generation rates in the photodetector active layers are determined by finite element method simulations, and iteration between optical nanoantenna simulation and detector modeling is used to optimize the device structure. © 2012 SPIE.

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Membrane projection lithography is extended from a single layer fabrication technique to a multilayer process, adding polymeric backfill and planarization after each layer is completed. Unaligned contact lithography is used as a rapid prototyping tool to aid in process development, patterning resist membranes in seconds without requiring long e-beam write times. The fabricated multilayer structures show good resistance to solvent attack from subsequent process steps and demonstrate in-plane and out of plane multilayer metallic inclusions in a dielectric host, which is a critical step in the path to develop bulklike metamaterials at optical frequencies.

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Interaction between metamaterial elements and intersubband transitions in GaAs/AlGaAs quantum wells is observed in the mid-infrared. Transmission measurements were performed through metamaterial arrays, each having a different resonance frequency. © 2011 OSA.

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A tandem interferometer system measuring the absolute phase and amplitude of planar split-ring resonators fabricated on a BaF2 substrate with a designed resonance at 10.5 μm is presented. © 2010 Optical Society of America.

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We present a photonic integrated circuit (PIC) composed of two strongly coupled lasers. This PIC utilizes the dynamics of mutual injection locking to increase the relaxation resonance frequency from 3 GHz to beyond 30 GHz.

We present the bandwidth enhancement of an EAM monolithically integrated with two mutually injection-locked lasers. An improvement in the modulation efficiency and bandwidth are shown with mutual injection locking.

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