Browsing by Author "Gan, Xuetao"
Now showing 1 - 11 of 11
Results Per Page
Sort Options
Item All-optically controlled slow and fast lights in graphene-coated tilted fiber Bragg grating(IOP PUBLISHING LTD, 2019-01-01) Wang, Yadong; Jiang, Biqiang; Das, Susobhan; Zhao, Qiang; Gan, Xuetao; Zhao, Jianlin; Department of Electronics and Nanoengineering; Northwestern Polytechnical University; China Aerospace Science and Technology CorporationWe demonstrate all-optically controlled slow and fast lights in tilted fiber Bragg grating (TFBG) with a graphene film. By employing graphene's efficient photothermal effect, the global resonances in TFBG are shifted with slopes of 1.1 and 1.01 pm mW-1 for cladding and core modes, respectively. This enables changes of group delay and thus supports tunable fast and slow lights from -156 to 20 ps in cladding modes and up to 400 ps in core modes. Our demonstration with an all-in-fiber scheme possesses advantages, such as low-cost manufacture, simple and compact configuration, and multi-wavelength operation.Item Chip-integrated van der Waals PN heterojunction photodetector with low dark current and high responsivity(Springer Nature, 2022-04-20) Tian, Ruijuan; Gan, Xuetao; Li, Chen; Chen, Xiaoqing; Hu, Siqi; Gu, Linpeng; Van Thourhout, Dries; Castellanos-Gomez, Andres; Sun, Zhipei; Zhao, Jianlin; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Northwestern Polytechnical University; Ghent University; Instituto de Ciencia de Materiales de MadridTwo-dimensional materials are attractive for constructing high-performance photonic chip-integrated photodetectors because of their remarkable electronic and optical properties and dangling-bond-free surfaces. However, the reported chip-integrated two-dimensional material photodetectors were mainly implemented with the configuration of metal-semiconductor-metal, suffering from high dark currents and low responsivities at high operation speed. Here, we report a van der Waals PN heterojunction photodetector, composed of p-type black phosphorous and n-type molybdenum telluride, integrated on a silicon nitride waveguide. The built-in electric field of the PN heterojunction significantly suppresses the dark current and improves the responsivity. Under a bias of 1 V pointing from n-type molybdenum telluride to p-type black phosphorous, the dark current is lower than 7 nA, which is more than two orders of magnitude lower than those reported in other waveguide-integrated black phosphorus photodetectors. An intrinsic responsivity up to 577 mA W-1 is obtained. Remarkably, the van der Waals PN heterojunction is tunable by the electrostatic doping to further engineer its rectification and improve the photodetection, enabling an increased responsivity of 709 mA W-1. Besides, the heterojunction photodetector exhibits a response bandwidth of similar to 1.0 GHz and a uniform photodetection over a wide spectral range, as experimentally measured from 1500 to 1630 nm. The demonstrated chip-integrated van der Waals PN heterojunction photodetector with low dark current, high responsivity and fast response has great potentials to develop high-performance on-chip photodetectors for various photonic integrated circuits based on silicon, lithium niobate, polymer, etc.Item Difference frequency generation in monolayer MoS2(ROYAL SOC CHEMISTRY, 2020-10-14) Wang, Yadong; Ghotbi, Masood; Das, Susobhan; Dai, Yunyun; Li, Shisheng; Hu, Xuerong; Gan, Xuetao; Zhao, Jianlin; Sun, Zhipei; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; University of Kurdistan; National Institute for Materials Science; Northwestern Polytechnical UniversityDifference frequency generation has long been employed for numerous applications, such as coherent light generation, sensing and imaging. Here, we demonstrate difference frequency generation down to atomic thickness in monolayer molybdenum disulfide. By mixing femtosecond optical pulses at wavelength of 406 nm with tunable pulses in the spectral range of 1300-1520 nm, we generate tunable pulses across the spectral range of 550-590 nm with frequency conversion efficiency up to ∼2 × 10-4. The second-order nonlinear optical susceptibility of monolayer molybdenum disulfide, χ(2)eff, is calculated as ∼1.8 × 10-8 m V-1, comparable to the previous results demonstrated with second harmonic generation. Such a highly efficient down-conversion nonlinear optical process in two-dimensional layered materials may open new ways to their nonlinear optical applications, such as coherent light generation and amplification.Item Giant All-Optical Modulation of Second-Harmonic Generation Mediated by Dark Excitons(ACS Publications, 2021-08-18) Wang, Yadong; Das, Susobhan; Iyikanat, Fadil; Dai, Yunyun; Li, Shisheng; Guo, Xiangdong; Yang, Xiaoxia; Cheng, Jinluo; Hu, Xuerong; Ghotbi, Masood; Ye, Fangwei; Lipsanen, Harri; Wu, Shiwei; Hasan, Tawfique; Gan, Xuetao; Liu, Kaihui; Sun, Dong; Dai, Qing; García De Abajo, F. Javier; Zhao, Jianlin; Sun, Zhipei; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Harri Lipsanen Group; Barcelona Institute of Science and Technology; National Institute for Materials Science; National Center for Nanoscience and Technology Beijing; Changchun Institute of Optics Fine Mechanics and Physics; University of Kurdistan; Shanghai Jiao Tong University; Fudan University; University of Cambridge; Northwestern Polytechnical University; Peking UniversityAll-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics.Item Graphene Actively Mode-Locked Lasers(2018-07) Bogusławski, Jakub; Wang, Yadong; Xue, Hui; Yang, Xiaoxia; Mao, Dong; Gan, Xuetao; Ren, Zhaoyu; Zhao, Jianlin; Dai, Qing; Soboń, Grzegorz; Sotor, Jarosław; Sun, Zhipei; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; National Center for Nanoscience and Technology Beijing; Northwestern Polytechnical University; Northwest University; Wroclaw University of Science and TechnologyActively mode-locked lasers offer varying degrees of flexibility for a wider range of applications than their passively modulated counterparts, due to their capability for electrically controlled ultrahigh repetition rate operation. Graphene based electrooptic modulators with unique advantages of broad operation bandwidth and ultrafast speed are suitable for light modulation in various optoelectronic applications. Here, an actively mode-locked laser with a graphene based electrooptic modulator is reported for the first time. The active mode-locking technique combined together with the intracavity nonlinear pulse shortening effect allows the generation of transform-limited 1.44 ps pulses with pulse energy of 844 pJ. The electrically controlled repetition rate of generated pulses, a key performance advantage of active mode-locking, is also demonstrated. These results provide a practical and effective approach for actively mode-locked lasers with broad operation bandwidth and compact footprint, which contributes a new way for applications of two-dimensional (2D) layered materials in ultrafast lasers.Item Low‐Power Continuous‐Wave Second Harmonic Generation in Semiconductor Nanowires(2018-10) Yuan, Qingchen; Fang, Liang; Yang, He; Gan, Xuetao; Khayrudinov, Vladislav; Lipsanen, Harri; Sun, Zhipei; Zhao, Jianlin; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Harri Lipsanen Group; Zhipei Sun Group; Northwestern Polytechnical UniversitySemiconductor nanowires (NWs) are promising for realizing various on‐chip nonlinear optical devices, due to their nanoscale lateral confinement and strong light–matter interaction. However, high‐intensity pulsed pump lasers are typically needed to exploit their optical nonlinearity because light couples poorly with nanometric‐size wires. Here, microwatts continuous‐wave light pumped second harmonic generation (SHG) in AlGaAs NWs is demonstrated by integrating them with silicon planar photonic crystal cavities. Light–NW coupling is enhanced effectively by the extremely localized cavity mode at the subwavelength scale. Strong SHG is obtained even with a continuous‐wave laser excitation with a pump power down to urn:x-wiley:18638880:media:lpor201800126:lpor201800126-math-0001W, and the cavity‐enhancement factor is estimated around 150. Additionally, in the integrated device, the NW's SHG is more than two orders of magnitude stronger than third harmonic generations in the silicon slab, though the NW only couples with less than 1% of the cavity mode. This significantly reduced power requirement of NW's nonlinear frequency conversion would promote NW‐based building blocks for nonlinear optics, especially in chip‐integrated coherent light sources, entangled photon pairs and signal processing devices.Item Mode couplings of a semiconductor nanowire scanning across a photonic crystal nanocavity(Science Press, 2019-06-10) Yuan, Qingchen; Fang, Liang; Zhao, Qiang; Wang, Yadong; Mao, Bo; Khayrudinov, Vladislav; Lipsanen, Harri; Sun, Zhipei; Zhao, Jianlin; Gan, Xuetao; Department of Electronics and Nanoengineering; Department of Applied Physics; Harri Lipsanen Group; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Northwestern Polytechnical University; China Aerospace Science and Technology CorporationThe position-dependent mode couplings between a semiconductor nanowire (NW) and a planar photonic crystal (PPC) nanocavity are studied. By scanning anNWacross a PPC nanocavity along the hexagonal lattice's Γ -M and M - K directions, the variations of resonant wavelengths, quality factors, and mode volumes in both fundamental and second-order resonant modes are calculated, implying optimal configurations for strong mode-NW couplings and light-NW interactions. For the fundamental (second-order) resonant mode, scanning anNWalong theM- K (Γ - M) direction is preferred, which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously. The simulation results are confirmed experimentally with good agreements.Item A MoSe2/WSe2 Heterojunction-Based Photodetector at Telecommunication Wavelengths(2018-11-21) Xue, Hui; Wang, Yadong; Dai, Yunyun; Kim, Wonjae; Jussila, Henri; Qi, Mei; Susoma, Jannatul; Ren, Zhaoyu; Dai, Qing; Zhao, Jianlin; Halonen, Kari; Lipsanen, Harri; Wang, Xiaomu; Gan, Xuetao; Sun, Zhipei; Department of Electronics and Nanoengineering; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Kari Halonen Group; Harri Lipsanen Group; Zhipei Sun Group; Northwest University; National Center for Nanoscience and Technology Beijing; Northwestern Polytechnical University; Nanjing University; VTT Technical Research Centre of Finlandvan der Waals (vdW) heterojunctions enable arbitrary combinations of different layered semiconductors with unique band structures, offering distinctive band engineering for photonic and optoelectronic devices with new functionalities and superior performance. Here, an interlayer photoresponse of a few-layer MoSe2/WSe2 vdW heterojunction is reported. With proper electrical gating and bias, the heterojunction exhibits high-sensitivity photodetection with the operation wavelength extended up to the telecommunication band (i.e. 1550 nm). The photoresponsivity and normalized photocurrent-to-dark current ratio reach up to 127 mA W−1 and 1.9 × 104 mW−1, respectively. The results not only provide a promising solution to realize high-performance vdW telecommunication band photodetectors, but also pave the way for using sub-bandgap engineering of two-dimensional layered materials for photonic and optoelectronic applications.Item Nanowire-assisted microcavity in a photonic crystal waveguide and the enabled high-efficiency optical frequency conversions(OPTICAL SOC AMER, 2020-10-22) Gu, Linpeng; Fang, Liang; Yuan, Qingchen; Gan, Xuetao; Hao, Yang; Zhang, Xutao; Li, Juntao; Fang, Hanlin; Khayrudinov, Vladislav; Lipsanen, Harri; Sun, Zhipei; Zhao, Jianlin; Department of Electronics and Nanoengineering; Harri Lipsanen Group; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Northwestern Polytechnical University; Sun Yat-sen UniversityWe report an indium phosphide nanowire (NW)-induced cavity in a silicon planar photonic crystal (PPC) waveguide to improve the light–NW coupling. The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide, which gives rise to a microcavity located on the NW section. Resonant modes with 푄 factors exceeding 103 are obtained. Leveraging on the high density of the electric field in the microcavity, the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion. Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts, showing a cavity-enhancement factor of 112. The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions, but also provides a compact platform to construct NW-based on-chip active devices.Item Strong Second Harmonic Generation from Bilayer Graphene with Symmetry Breaking by Redox-Governed Charge Doping(AMERICAN CHEMICAL SOCIETY, 2022-05-24) Zhang, Mingwen; Han, Nannan; Wang, Jing; Zhang, Zhihong; Liu, Kaihui; Sun, Zhipei; Zhao, Jianlin; Gan, Xuetao; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Northwestern Polytechnical University; Peking UniversityMissing second-order nonlinearity in centrosymmetric graphene overshadows its intriguing optical attribute. Here, we report redox-governed charge doping could effectively break the centrosymmetry of bilayer graphene (BLG), enabling a strong second harmonic generation (SHG) with a strength close to that of the well-known monolayer MoS2. Verified from control experiments with in situ electrical current annealing and electrically gate-controlled SHG, the required centrosymmetry breaking of the emerging SHG arises from the charge-doping on the bottom layer of BLG by the oxygen/water redox couple. Our results not only reveal that charge doping is an effective way to break the inversion symmetry of BLG despite its strong interlayer coupling but also indicate that SHG spectroscopy is a valid technique to probe molecular doping on two-dimensional materials.Item Waveguide-Integrated MoTe2p- i- n Homojunction Photodetector(AMERICAN CHEMICAL SOCIETY, 2022-12-27) Li, Chen; Tian, Ruijuan; Chen, Xiaoqing; Gu, Linpeng; Luo, Zhengdong; Zhang, Qiao; Yi, Ruixuan; Li, Zhiwen; Jiang, Biqiang; Liu, Yan; Castellanos-Gomez, Andres; Chua, Soo Jin; Wang, Xiaomu; Sun, Zhipei; Zhao, Jianlin; Gan, Xuetao; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Northwestern Polytechnical University; Xidian University; Instituto de Ciencia de Materiales de Madrid; National University of Singapore; Nanjing UniversityTwo-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe2p-i-n homojunction fabricated directly on a silicon photonic crystal (PC) waveguide, which enables on-chip photodetection with ultralow dark current, high responsivity, and fast response speed. The adopted silicon PC waveguide is electrically split into two individual back gates to selectively dope the top regions of the MoTe2 channel in p- or n-types. High-quality reconfigurable MoTe2 (p-i-n, n-i-p, n-i-n, p-i-p) homojunctions are realized successfully, presenting rectification behaviors with ideality factors approaching 1.0 and ultralow dark currents less than 90 pA. Waveguide-assisted MoTe2 absorption promises a sensitive photodetection in the telecommunication O-band from 1260 to 1340 nm, though it is close to MoTe2's absorption band-edge. A competitive photoresponsivity of 0.4 A/W is realized with a light on/off current ratio exceeding 104 and a record-high normalized photocurrent-to-dark-current ratio of 106 mW-1. The ultrasmall capacitance of p-i-n homojunction and high carrier mobility of MoTe2 promise a high dynamic response bandwidth close to 34.0 GHz. The proposed device geometry has the advantages of employing a silicon PC waveguide as the back gates to build a 2D material p-i-n homojunction directly and simultaneously to enhance light-2D material interaction. It provides a potential pathway to develop 2D material-based photodetectors, laser diodes, and electro-optic modulators on silicon photonic chips.
