Electrical and Electronic Engineering - Research Publications
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ItemNanostructured Fishnet Silicon Photodetector Pixels as a Fully-Contained Microspectrometer Chip(IEEE, 2018)We experimentally demonstrate a microspectrometer comprising twenty silicon photodetector pixels, whose responsivities are engineered via nanostructured fishnet patterns. We computationally reconstruct the spectrum of light that illuminates the chip from the measured pixel photocurrents.
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ItemHigh-resolution mid-infrared spectral reconstruction using a subwavelength coaxial aperture array(OSA & IEEE, 2019-01-01)We demonstrate mid-infrared computational spectroscopy using an array of coaxial aperture filters. We experimentally determine material transmission spectra using an algorithm whose inputs are the transmission spectra and the power transmitted through each filter.
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ItemNanostructured all-Silicon Photodetector Pixels with Tailored Responsivity Spectra(SPIE-INT SOC OPTICAL ENGINEERING, 2019)We experimentally demonstrate nanostructured silicon photodetectors which consist of subwavelength arrays of verticallyoriented waveguides etched into a P-I-N photodiode. Our device combines both spectral-filtering and photocurrentgeneration in one all-Si structure. We show that absorption and responsivity spectra of these nanophotonic devices can be tuned by appropriate geometric design.
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ItemVertically stacked silicon nanowire photodetectors for spectral reconstruction(OSA & IEEE, 2019-01-01)We experimentally demonstrate the use of vertically stacked silicon nanowire photodetectors for computational spectral reconstruction at visible wavelengths. The method is based on the photodetectors having tailored responsivity spectra, achieved by standard nanofabrication processes.
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ItemVertical waveguide arrays as wavelength selective nanostructured silicon photodetector pixels(OSA, 2019)We experimentally demonstrate a nanostructured silicon photodetector that consists of subwavelength arrays of vertical waveguides. Our device combines spectral-filtering and photocurrent-generation. We show that absorption and responsivity spectra can be tuned by appropriate design.
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ItemExperimental demonstration of infrared spectral reconstruction using plasmonic metasurfaces(OPTICAL SOC AMER, 2018-09-15)We computationally reconstruct short- to long-wave infrared spectra using an array of plasmonic metasurface filters. We illuminate the filter array with an unknown spectrum and measure the optical power transmitted through each filter with an infrared microscope to emulate a filter-detector array system. We then use the recursive least squares method to determine the unknown spectrum. We demonstrate our method with light from a blackbody. We also demonstrate it with spectra generated by passing the light from the blackbody through various materials. Our approach is a step towards miniaturized spectrometers spanning the short- to long-wave infrared based on filter-detector arrays.
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ItemSilicon microspectrometer chip based on nanostructured fishnet photodetectors with tailored responsivities and machine learning(Optical Society of America, 2019-09-20)The realization of on-chip microspectrometers would allow spectroscopy and colorimetry measurement systems to be readily incorporated into platforms for which size and weight are critical, such as consumer grade electronics, smartphones, and unmanned aerial vehicles. This would allow them to find use in diverse fields such as interior design, agriculture, and in machine vision applications. All spectrometers require a detector or detector array and optical elements for spectral discrimination. A single device that combines both detection and spectral discrimination functions therefore represents an ultimate limit of miniaturization. Motivated by this, we here experimentally demonstrate a novel nanostructured silicon-based photodetector design whose responsivity can be tailored by an appropriate choice of geometric parameters. We utilize a unique doping profile with two vertically stacked, back-to-back photodiode regions, which allows us to double the number of detectors in a given on-chip footprint. By patterning the top photosensitive regions of each device with two sets of interleaved vertical slab waveguide arrays of varied width and period, we define the absorption spectra (and thus responsivity spectra) of both the upper and lower photodiode regions. We then use twenty such “fishnet pixels” to form a microspectrometer chip and demonstrate the reconstruction of four test spectra using a two-stage supervised machine-learning-based reconstruction algorithm.
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ItemMid- to long-wave infrared computational spectroscopy using a subwavelength coaxial aperture array(Nature Publishing Group, 2019-09-19)Miniaturized spectrometers are advantageous for many applications and can be achieved by what we term the filter-array detector-array (FADA) approach. In this method, each element of an optical filter array filters the light that is transmitted to the matching element of a photodetector array. By providing the outputs of the photodetector array and the filter transmission functions to a reconstruction algorithm, the spectrum of the light illuminating the FADA device can be estimated. Here, we experimentally demonstrate an array of 101 band-pass transmission filters that span the mid- to long-wave infrared (6.2 to 14.2 μm). Each filter comprises a sub-wavelength array of coaxial apertures in a gold film. As a proof-of-principle demonstration of the FADA approach, we use a Fourier transform infrared (FTIR) microscope to record the optical power transmitted through each filter. We provide this information, along with the transmission spectra of the filters, to a recursive least squares (RLS) algorithm that estimates the incident spectrum. We reconstruct the spectrum of the infrared light source of our FTIR and the transmission spectra of three polymer-type materials: polyethylene, cellophane and polyvinyl chloride. Reconstructed spectra are in very good agreement with those obtained via direct measurement by our FTIR system.