Publications

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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.

Resonant subwavelength gratings have been designed and fabricated as wavelength-specific reflectors for application as a rotary position encoder utilizing ebeam based photolithography. The first grating design used a two-dimensional layout to provide polarization insensitivity with separate layers for the grating and waveguide. The resulting devices had excellent pattern fidelity and the resonance peaks and widths closely matched the expected results. Unfortunately, the gratings were particularly angle sensitive and etch depth errors led to shifts in the center wavelength of the resonances. A second design iteration resulted in a double grating period to reduce the angle sensitivity as well as different materials and geometry; the grating and waveguide being the same layer. The inclusion of etch stop layers provided more accurate etch depths; however, the tolerance to changes in the grating duty cycle was much tighter. Results from these devices show the effects of small errors in the pattern fidelity. The fabrication process flows for both iterations of devices will be reviewed as well as the performance of the fabricated devices. A discussion of the relative merits of the various design choices provides insight into the importance of fabrication considerations during the design stage. © 2012 SPIE.

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We explore the spectral and angular selectivity of near surface normal transmission of grating modified metallic surfaces and their ultimate potential for application as narrow-band spectro-polarimetric planar filter components in the development of advanced infrared focal plane arrays. The developed photonic microstructures exhibit tailored spectral transmission characteristics in the long wavelength infrared, and can be fabricated to preferentially transmit a given linear polarization within the design band. Modification of the material and structural properties of the diffractive optical element enables sub-pixel tuning of the spectro-polarimetric response of the device allowing for intelligent engineering of planar filter components for development of advanced focal plane arrays in the long wavelength infrared. The planar nature of the developed components leaves them immune to fabrication issues that typically plague thin film interference filters used for similar applications in the infrared, namely, deposition of multiple low-stress quarter-wavelength films and modification of the film thicknesses for each pixel. The solution developed here presents the opportunity for subpixel modification of the spectral response leading to an efficient, versatile filter component suitable for direct integration with commercially available focal plane array technologies via standard fabrication techniques. We will discuss the theoretical development and analysis of the described components and compare the results to the current state-of-the-art. © 2012 SPIE.

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We describe the design of pixelated filter arrays for hyperspectral monitoring of CO2 and H2O absorption in the midwave infrared (centered at 4.25μm and 5.15μm, respectively) using resonant subwavelength gratings (RSGs), also called guided-mode resonant filters (GMRFs). For each gas, a hyperspectral filter array of very narrowband filters is designed that spans the absorption band on a single substrate. A pixelated geometry allows for direct registration of filter pixels to focal plane array (FPA) sensor pixels and for non-scanning data collection. The design process for narrowband, low-sideband reflective and transmissive filters within fabrication limitations will be discussed.