@article{zhao_zhou_li_moon_cassidy_harankahage_hu_savoy_gu_zamkov_et al._2024, title={Green Light from Red-Emitting Nanocrystals: Broadband, Low-Threshold Lasing from Colloidal Quantum Shells in Optical Nanocavities}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.4c02346}, abstractNote={Spherical semiconductor nanoplatelets, known as quantum shells (QSs), have captured significant interest for their strong suppression of Auger recombination, which leads to long multiexciton lifetimes and wide optical gain bandwidth. Yet, the realization of benefits associated with the multiexciton lasing regime using a suitably designed photonic cavity remains elusive. Here, we demonstrate broadly tunable lasing from close-packed films of CdS/CdSe/CdS QSs deposited over nanopillar arrays on Si substrates. Wide spectral tuning of the stimulated emission in QSs with a fixed bandgap value was achieved by engaging single exciton (λX ∼ 634 nm), biexciton (λBX ∼ 627 nm), and multiple exciton (λMX ∼ 615-565 nm) transitions. The ensemble-averaged gain threshold of <N> ∼ 2.6 electron-hole pairs per QS particle and the low photonic cavity fluence threshold of ∼4 μJ/cm2 were attributed to Auger suppression. The tuning of the lasing emission closely aligns with our model predictions achieved by varying the array period while preserving mode confinement and quality (Q) factors. These results mark a notable step toward the development of colloidal nanocrystal lasers.}, journal={ACS NANO}, author={Zhao, Kehui and Zhou, Xiaohe and Li, Xi and Moon, Jiyoung and Cassidy, James and Harankahage, Dulanjan and Hu, Zhongjian and Savoy, Steve M. and Gu, Qing and Zamkov, Mikhail and et al.}, year={2024}, month={Apr} }
 @article{li_ghaffari_abbas_gu_2024, title={Plasmon near-field coupling and universal scaling behavior in shifted-core coaxial nano-cavity pair}, volume={32}, ISSN={["1094-4087"]}, DOI={10.1364/OE.516604}, abstractNote={We computationally and analytically investigate the plasmon near-field coupling phenomenon and the associated universal scaling behavior in a pair of coupled shifted-core coaxial nano-cavities. Each nano-cavity is composed of an InGaAsP gain medium sandwiched between a silver (Ag) core and an Ag shell. The evanescent coupling between the cavities lifts the degeneracy of the cut-off free transverse electromagnetic (TEM) like mode. The mode splitting of the supermodes is intensified by shifting the metal core position, which induces symmetry breaking. This coupling phenomenon is explained with spring-capacitor analogy and circuit analysis. The numerical simulation results reveal an exponential decay in the fractional plasmon wavelength relative to the ratio of gap distance and core shifting distance, which aligns with the plasmon ruler equation. In addition, by shifting the Ag cores in both cavities toward the center of the coupled structure, the electromagnetic field becomes strongly localized in nanoscale regions (hotspots) in the gain medium between the cavities, thus achieving extreme plasmonic nanofocusing. Utilizing this nanofocusing effect, we propose a refractive index sensor by placing a fluidic channel between the two cavities in close vicinity to the hotspots and reaching the highest sensitivity of ∼700nm/RIU.}, number={8}, journal={OPTICS EXPRESS}, author={Li, Xi and Ghaffari, Abbas and Abbas, Farhat and Gu, Qing}, year={2024}, month={Apr}, pages={14770–14779} }
 @article{li_gu_2024, title={Topological hyperbolic metamaterials}, ISSN={["2192-8614"]}, DOI={10.1515/nanoph-2023-0768}, abstractNote={Abstract}, journal={NANOPHOTONICS}, author={Li, Zhitong and Gu, Qing}, year={2024}, month={Feb} }
 @article{lin_li_luo_gharajeh_moon_hou_zhang_gu_2023, title={Edge-Mode Lasing from A non-Hermitian Topological Bulk}, ISSN={["2374-0140"]}, DOI={10.1109/IPC57732.2023.10360714}, abstractNote={We demonstrate single-mode topological lasing from a 1D array of coupled micro-ring resonators with a well-defined non-Hermitian topological bulk. Our 1D array is equivalent to a 2D non-Hermitian Chen insulator.}, journal={2023 IEEE PHOTONICS CONFERENCE, IPC}, author={Lin, Dayang and Li, Zhitong and Luo, Xi-Wang and Gharajeh, Abouzar and Moon, Jiyoung and Hou, Junpeng and Zhang, Chuanwei and Gu, Qing}, year={2023} }
 @article{li_biswas_zhou_brigner_friedman_gu_2023, title={Experimental demonstration of online learning in deep photonic neural networks}, ISSN={["2374-0140"]}, DOI={10.1109/IPC57732.2023.10360778}, abstractNote={We demonstrate supervised and unsupervised online learning of a deep photonic neural network. While the present system employs a fiber-optics setup with variable optical attenuators as synapses and software neurons, it can be adapted to chip-scale implementations with optical neurons and synapses.}, journal={2023 IEEE PHOTONICS CONFERENCE, IPC}, author={Li, Xi and Biswas, Disha and Zhou, Peng and Brigner, Wesley H. and Friedman, Joseph S. and Gu, Qing}, year={2023} }
 @article{moon_mehta_gundogdu_so_gu_2023, title={Metal-Halide Perovskite Lasers: Cavity Formation and Emission Characteristics}, volume={7}, ISSN={["1521-4095"]}, DOI={10.1002/adma.202211284}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Moon, Jiyoung and Mehta, Yash and Gundogdu, Kenan and So, Franky and Gu, Qing}, year={2023}, month={Jul} }
 @article{li_luo_gu_2023, title={Topological on-chip lasers}, volume={8}, ISSN={["2378-0967"]}, DOI={10.1063/5.0150421}, abstractNote={A miniature on-chip laser is an essential component of photonic integrated circuits for a plethora of applications, including optical communication and quantum information processing. However, the contradicting requirements of small footprint, robustness, single-mode operation, and high output power have led to a multi-decade search for the optimal on-chip laser design. During this search, topological phases of matter—conceived initially in electronic materials in condensed matter physics—were successfully extended to photonics and applied to miniature laser designs. Benefiting from the topological protection, a topological edge mode laser can emit more efficiently and more robustly than one emitting from a trivial bulk mode. In addition, single-mode operation over a large range of excitation energies can be achieved by strategically manipulating topological modes in a laser cavity. In this Perspective, we discuss the recent progress of topological on-chip lasers and an outlook on future research directions.}, number={7}, journal={APL PHOTONICS}, author={Li, Zhitong and Luo, Xi-Wang and Gu, Qing}, year={2023}, month={Jul} }
 @article{sheikhlari_nikfarjam_abbasalipour_gharajeh_gu_pourkamali_2022, title={An Electrothermally Actuated Bulk Mode UHF Silicon Resonator}, DOI={10.1109/IC-MAM55200.2022.9855307}, abstractNote={This work presents fabrication and characterization of a bulk-mode thermally actuated silicon resonator with piezoresistive readout. Bulk-modes enable achieving operating frequencies in the UHF range and above without the need to shrink the resonator dimensions deep into the nanoscale. While having the potential to unlock new possibilities, thermal-piezoresistive transduction of bulk resonance modes is associated with challenges that have prevented its demonstration so far. In this work, a dual-block crystalline silicon resonator with 1st bulk mode resonance frequency of 488 MHz has been fabricated and successfully operated utilizing a 200nm × 1μm beam as its electromechanical transducer. Quality factor of 2800 and active motional resistance as low as −150Ω (motional conductance of −6.68 mA/V) has been measured for the fabricated resonator.}, journal={2022 IEEE MTT-S INTERNATIONAL CONFERENCE ON MICROWAVE ACOUSTICS AND MECHANICS (IC-MAM)}, author={Sheikhlari, Sepehr and Nikfarjam, Hamed and Abbasalipour, Amin and Gharajeh, Abouzar and Gu, Qing and Pourkamali, Siavash}, year={2022}, pages={110–113} }
 @article{lin_liu_haroldson_moon_li_zakhidov_hu_gu_2022, title={High-Performance Directly Patterned Nanograting Perovskite Photodetector with Interdigitated Electrodes}, ISSN={["2195-1071"]}, DOI={10.1002/adom.202201516}, abstractNote={Abstract}, journal={ADVANCED OPTICAL MATERIALS}, author={Lin, Dayang and Liu, Jinbo and Haroldson, Ross and Moon, Jiyoung and Li, Zhitong and Zakhidov, Anvar and Hu, Wenchuang and Gu, Qing}, year={2022}, month={Oct} }
 @article{liu_haroldson_verkhogliadov_lin_gu_zakhidov_hu_young_2022, title={Introduction of a Reset MOSFET to Mitigate the Influence of Ionic Movement in Perovskite MOSFET Photodetector Measurements}, ISSN={["1071-9032"]}, DOI={10.1109/ICMTS50340.2022.9898238}, abstractNote={A Reset MOSFET is added to a perovskite MOSFET-based photodetector to serve as a current source to mitigate the influence of ionic movement on the performance of the photodetector. With the added MOSFET, the hysteresis is significantly reduced, and the dark current is controllable. The on/off ratio resumes to 106 and an ultrasensitive responsivity (over 80, 000 A/W) is achieved under only 13 nW/cm2 red (665 nm) light intensity.}, journal={2022 IEEE 34TH INTERNATIONAL CONFERENCE ON MICROELECTRONIC TEST STRUCTURES (ICMTS)}, author={Liu, Jinbo and Haroldson, Ross and Verkhogliadov, Grigorii and Lin, Dayang and Gu, Qing and Zakhidov, Anvar A. and Hu, Wenchuang and Young, Chadwin D.}, year={2022}, pages={174–177} }
 @article{abbas_daunis_pandey_clark_lascola_dikmelik_robbins_hodges_roodenko_gu_2022, title={Near-Field Thermal Profiling and 3D Anisotropic Thermal Analysis of Quantum Cascade Lasers}, ISSN={["1862-6319"]}, DOI={10.1002/pssa.202200453}, abstractNote={The development of a scanning near‐field optical microscopy (SNOM) method with high temperature and spatial resolution to probe the thermal behavior of quantum cascade lasers (QCLs) is reported. Specifically, thermal profiling of InGaAs/InAlAs/InP buried heterostructure (BH) mounted epi‐layer side down QCLs is performed. The findings are verified by 3D anisotropic thermal analysis of QCLs with anisotropic thermal conductivities in the superlattice active region. Good agreement is observed between the simulated and the measured time constants. Within this design, various realistic device configurations, such as overhanging the laser chip on the submount and placing different dielectric coatings on the front facet, are considered. Analytical studies of the steady‐state thermal performance of QCL arrays compared to an isolated QCL are demonstrated for high‐power requirements with minimal thermal damage and future application in spectroscopic devices.}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Abbas, Farhat and Daunis, Trey and Pandey, Binay J. and Clark, Kevin and Lascola, Kevin and Dikmelik, Yamac and Robbins, Dennis and Hodges, Kimari L. and Roodenko, Katy and Gu, Qing}, year={2022}, month={Dec} }
 @article{moon_alahbakhshi_gharajeh_li_haroldson_kwon_hawkins_kim_hu_zhang_et al._2022, title={Quasi-CW Lasing from Directly Patterned and Encapsulated Perovskite Cavity at 260 K}, volume={9}, ISSN={["2330-4022"]}, DOI={10.1021/acsphotonics.2c00071}, abstractNote={Metal halide perovskites have emerged as promising gain materials for on-chip lasers in photonic integrated circuits. For these to become commercially relevant as economical on-chip light sources, a clear onset of quasi-continuous wave (quasi-CW) and, eventually, continuous wave (CW) lasing at room temperature or Peltier-cooling accessible temperatures from directly patterned perovskite cavities is a critical milestone that must be achieved. Herein, through directly patterning with nanoimprint lithography and encapsulation of the cavity with a thin layer of polycarbonate (PC), quasi-CW lasing from CH3NH3PbBr3 (MAPbBr3) is demonstrated up to 260 K. The PC layer is also shown to effectively encapsulate the surface defects of MAPbBr3 and protect devices from environmental hazards. Through the combined analysis of the crystal quality, degradation process during optical pumping, defect encapsulation, and laser performance, room temperature CW lasing from directly patterned perovskite cavities should be within reach.}, number={6}, journal={ACS PHOTONICS}, author={Moon, Jiyoung and Alahbakhshi, Masoud and Gharajeh, Abouzar and Li, Quanwei and Haroldson, Ross and Kwon, Sunah and Hawkins, Roberta and Kim, Moon J. and Hu, Walter and Zhang, Xiang and et al.}, year={2022}, month={Jun}, pages={1984–1991} }