Juliet Gopinath · University of Colorado Boulder · PhdFit
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Juliet Gopinath
· Professor • Alfred T. and Betty E. Look Endowed ProfessorVerified
University of Colorado Boulder · Electrical, Computer & Energy Engineering
Juliet Gopinath is the Alfred T. and Betty E. Look Endowed Professor in the Department of Electrical, Computer & Energy Engineering at the University of Colorado Boulder. Her research focuses on photonics and quantum engineering. She is associated with the College of Engineering and Applied Science and is involved in various initiatives and programs related to engineering education, research, and workforce development. Her contact information includes her email at Juliet.Gopinath@colorado.edu and her office located in ECEE 1B43.
A packaged electrowetting-based element with tunable lens and prism capability is demonstrated. Laser micromachining is used to pattern individually addressable electrodes on a sloped wall glass substrate, and the working liquids are sealed in the device using commercially available epoxies. The device operates in lens and prism modes with focal length tunability, diverging from −14 mm to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\infty$</tex> and converging from +14 mm to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\infty$</tex>, while providing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 4.5^{\circ}$</tex> beam steering capability.
Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact, source of indistinguishable pairs of polarization entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves $(99.11 \pm 0.01) \%$ polarization entanglement visibility, $(96.3 \pm 0.6) \%$ successive-photon Hong-Ou-Mandel interference visibility, $(68.0 \pm 0.1$) \% heralded efficiency as detected, and $(88.6 \pm 0.2) \%$ interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.
Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact, source of indistinguishable pairs of polarization entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves $(99.11 \pm 0.01) \%$ polarization entanglement visibility, $(96.3 \pm 0.6) \%$ successive-photon Hong-Ou-Mandel interference visibility, $(68.0 \pm 0.1$) \% heralded efficiency as detected, and $(88.6 \pm 0.2) \%$ interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.
High-quality factor microresonators are an attractive platform for the study of nonlinear photonics, with diverse applications in communications, sensing, and quantum metrology. The characterization of loss mechanisms and nonlinear properties in a microresonator is a necessity for the development of photonic integrated circuits. Here, we demonstrate a high-quality chalcogenide (Ge23Sb7S70) micro-racetrack resonator utilizing Euler curves. The racetrack geometry is studied to minimize loss at both the straight–curved waveguide junction and through the waveguide curve. The material absorption, intrinsic quality factor, and nonlinear index are extracted by a comprehensive model fit to laser wavelength resonance scans. The micro-racetrack resonator possesses a waveguide propagation loss of 8.5 dB/m, an intrinsic quality factor of 4.5 × 106, and nonlinear index of 1.28 × 10–18 m2/W, in a waveguide cross section less than 1 μm2. Our results yield state-of-the-art nonlinear microresonators and establish Ge23Sb7S70 as a low-loss PIC platform.
Optical gyroscopes based on the Sagnac effect have been widely used for inertial navigation in aircraft, submarines, satellites, and unmanned robotics. With the rapid progress in the field of ultrahigh-quality whispering gallery mode and ring resonators in recent years, these devices offer the promise of a compact alternative to ring laser gyroscopes and fiber optic gyroscopes. Yet, the successful commercialization of a microresonator gyroscope has been hindered by the scaling of the Sagnac effect with resonator area. While several techniques have been proposed to enhance the Sagnac effect in microresonators, these enhancements also amplify the thermal noise in the microresonator. Here, we present an approach to measuring the Sagnac signal in chip-scale devices that overcomes this fundamental noise limitation to achieve unprecedented performance in a 200 μm optical resonator—the smallest reported to date. Our proof-of-concept design shows a 104 enhancement of the Sagnac signal while simultaneously suppressing thermal noise by 27 dB and environmental contributions to noise by 22 dB. We believe this approach offers a pathway to compact integrated photonic gyroscopes that reach the sensitivity required for inertial navigation.
Recent advances in stimulated emission depletion (STED) microscopy have resulted in breakthroughs in biological imaging. Such advances include three-dimensional (3D) imaging, aberration correction to enhance resolution at depth in tissue, reduction in photobleaching, and label-free STED-inspired alternatives, enabling in vivo applications. In this perspective, we first summarize the basic principles of stimulated emission depletion microscopy and its major challenges. Next, we discuss techniques to reduce photobleaching, 3D imaging with STED, deep tissue imaging with STED, fiber-coupled STED, live animal imaging, and label-free imaging with super-resolution. Finally, we summarize and provide perspectives for future research.
Dispersion engineering in chalcogenide integrated photonics is crucial for nonlinear optical applications. We have developed a thermal-reflow-assisted fabrication method that creates Ge<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sub>Sb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub>S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> reflowed wedge resonators with supreme surface roughness and quality factors exceeding 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup>. Our simulations show the ability to engineer the dispersion of their whispering-gallery modes to overcome large material dispersion in near-infrared wavelength and achieve anomalous dispersion. We have successfully fabricated the designed tightly confined reflow bump geometry and experimentally demonstrate an engineered flat anomalous dispersion of the supported TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> optical mode.
High-quality factor microresonators are an attractive platform for the study of nonlinear photonics, with diverse applications in communications, sensing, and quantum metrology. The characterization of loss mechanisms and nonlinear properties in a microresonator is a necessity for the development of photonic integrated circuits. Here, we demonstrate a high-quality chalcogenide ($Ge_{23}Sb_{7}S_{70}$) micro-racetrack resonator utilizing Euler curves. The racetrack geometry is studied to minimize loss at both the straight-curved waveguide junction and through the waveguide curve. The material absorption, intrinsic quality factor, and nonlinear index are extracted by a comprehensive model fit to laser wavelength resonance scans. The micro-racetrack resonator possesses an absorption loss of $0.43 dB/m$, an intrinsic quality factor of $4.5 \times 10^6$, and nonlinear index of $1.28 \times 10^{-18} m^2/W$, in a waveguide cross-section less than $1 μm^2$. Our results yield state-of-the-art nonlinear microresonators and establish $Ge_{23}Sb_{7}S_{70}$ as a low-loss PIC platform.
We present a numerical and experimental investigation into the dynamics of two-dimensional electrowetting prism scanners. These scanners are an attractive option as they are transmissive, miniaturizable, nonmechanical and consume little power. We characterize the resonant frequencies of an electrowetting tunable prism for one-dimensional beam steering and find close agreement between simulation and experiment. The resonance frequencies are shown to produce an inherent standing wave resonance mode on the liquid-liquid interface that proves beneficial for linear performance. We extend our results to analyze two-dimensional raster scanning performance by driving the device on- and off-resonance modes. To validate the improvement in performance, we integrate the electrowetting prism into a two-photon laser scanning microscope as an optical scanner for fluorescence imaging.
Optical gyroscopes based on the Sagnac effect have been widely used for inertial navigation in aircrafts, submarines, satellites and unmanned robotics. With the rapid progress in the field of ultrahigh-quality whispering gallery mode and ring resonators in recent years, these devices offer the promise of a compact alternative to ring-laser gyroscopes (RLGs) and fiber-optic gyroscopes (FOGs). Yet, successful commercialization of a microresonator gyroscope has been hindered by the scaling of the Sagnac effect with resonator area. While several techniques have been proposed to enhance the Sagnac effect in microresonators, these enhancements also amplify the thermal noise in the microresonator. Here, we present a novel approach to measuring the Sagnac signal in chip-scale devices that overcomes this fundamental noise limitation to achieve unprecedented performance in a 200 μm optical resonator - the smallest reported to date. Our proof-of-concept design shows a 10^4 enhancement of the Sagnac signal while simultaneously suppressing thermal noise by 27 dB and environmental contributions to noise by 22 dB. We believe this approach offers a pathway for integrated photonic gyroscopes with sensitivities that match or exceed RLGs and FOGs.
