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Creators/Authors contains: "Lin, Hongtao"

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  1. Abstract

    The development of compact and fieldable mid-infrared (mid-IR) spectroscopy devices represents a critical challenge for distributed sensing with applications from gas leak detection to environmental monitoring. Recent work has focused on mid-IR photonic integrated circuit (PIC) sensing platforms and waveguide-integrated mid-IR light sources and detectors based on semiconductors such as PbTe, black phosphorus and tellurene. However, material bandgaps and reliance on SiO2substrates limit operation to wavelengthsλ ≲ 4 μm. Here we overcome these challenges with a chalcogenide glass-on-CaF2PIC architecture incorporating split-gate photothermoelectric graphene photodetectors. Our design extends operation toλ = 5.2 μm with a Johnson noise-limited noise-equivalent power of 1.1 nW/Hz1/2, no fall-off in photoresponse up tof = 1 MHz, and a predicted 3-dB bandwidth off3dB > 1 GHz. This mid-IR PIC platform readily extends to longer wavelengths and opens the door to applications from distributed gas sensing and portable dual comb spectroscopy to weather-resilient free space optical communications.

     
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  2. Mid-infrared photonic integrated circuits (PICs) that combine on-chip light sources with other optical components constitute a key enabler for applications such as chemical sensing, light detection, ranging, and free-space communications. In this paper, we report the monolithic integration of interband cascade lasers emitting at 3.24 µm with passive, high-index-contrast waveguides made of chalcogenide glasses. Output from the chalcogenide waveguides exhibits pulsed peak power up to 150 mW (without roll-over), threshold current density 280 A/cm2, and slope efficiency 100 mW/A at 300 K, with a lower bound of 38% efficiency for coupling between the two waveguides. These results represent an important step toward the realization of fully integrated mid-infrared PICs.

     
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  3. 3D photonics promises to expand the reach of photonics by enabling the extension of traditional applications to nonplanar geometries and adding novel functionalities that cannot be attained with planar devices. Available material options and device geometries are, however, limited by current fabrication methods. In this work, we pioneer a method that allows for placement of integrated photonic device arrays at arbitrary predefined locations in 3D using a fabrication process that capitalizes on the buckling of a 2D pattern. We present theoretical and experimental validation of the deterministic buckling process, thus demonstrating implementation of the technique to realize what we believe to be the first fully packaged 3D integrated photonics platform. Application of the platform for mechanical strain sensing is further demonstrated.

     
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  4. The extraordinary optical properties of single-layer graphene have spurred the development of a variety of photonic components. We have previously demonstrated a scalable and versatile platform to facilitate the integration of graphene and other 2-D materials with chalcogenide glass-based planar photonics. In this paper, we detail the design criteria and optimization guidelines towards high-performance graphene-integrated thermo-optic (TO) switches based on the chalcogenide glass-on-graphene platform. Notably, absorption loss of graphene can be reduced to < 20 dB/cm when it is sandwiched inside photonic structures capitalizing on the anisotropic absorption property of graphene. We quantify energy efficiency of the TO switch, showing that the choice of cladding materials plays a critical role in improving device efficiency. Furthermore, we report a record TO switching efficiency of 10 nm/mW via judicious engineering of the overlap between optical mode and thermal profile.

     
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  5. Abstract

    On-chip spectrometers have the potential to offer dramatic size, weight, and power advantages over conventional benchtop instruments for many applications such as spectroscopic sensing, optical network performance monitoring, hyperspectral imaging, and radio-frequency spectrum analysis. Existing on-chip spectrometer designs, however, are limited in spectral channel count and signal-to-noise ratio. Here we demonstrate a transformative on-chip digital Fourier transform spectrometer that acquires high-resolution spectra via time-domain modulation of a reconfigurable Mach-Zehnder interferometer. The device, fabricated and packaged using industry-standard silicon photonics technology, claims the multiplex advantage to dramatically boost the signal-to-noise ratio and unprecedented scalability capable of addressing exponentially increasing numbers of spectral channels. We further explore and implement machine learning regularization techniques to spectrum reconstruction. Using an ‘elastic-D1’ regularized regression method that we develop, we achieved significant noise suppression for both broad (>600 GHz) and narrow (<25 GHz) spectral features, as well as spectral resolution enhancement beyond the classical Rayleigh criterion.

     
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