OOIR: Observatory of International Research

Papers

(The median citation count of ACS Photonics is 5. The table below lists those papers that are above that threshold based on CrossRef citation counts [max. 250 papers]. The publications cover those that have been published in the past four years, i.e., from 2020-05-01 to 2024-05-01.)

Article	Citations
A Critical Review on Ultraviolet Disinfection Systems against COVID-19 Outbreak: Applicability, Validation, and Safety Considerations	283
Dielectric Resonant Metaphotonics	221
Nanophotonic Structural Colors	184
Dielectric Metasurfaces Enabling Advanced Optical Biosensors	151
Inverse Design of Photonic Crystals through Automatic Differentiation	122
High Quality Factor Toroidal Resonances in Dielectric Metasurfaces	117
Functional Porous MOF-Derived CuO Octahedra for Harmonic Soliton Molecule Pulses Generation	105
Topological Insulator Laser Using Valley-Hall Photonic Crystals	105
High-Bandwidth Green Semipolar (20–21) InGaN/GaN Micro Light-Emitting Diodes for Visible Light Communication	103
Ultra-Broadband Mode Size Converter Using On-Chip Metamaterial-Based Luneburg Lens	102
On Metalenses with Arbitrarily Wide Field of View	97
High-Harmonic Generation from Resonant Dielectric Metasurfaces Empowered by Bound States in the Continuum	92
Optical Excitations with Electron Beams: Challenges and Opportunities	86
Quantum Nanophotonics in Two-Dimensional Materials	83
Nonlinear Optics in Lead Halide Perovskites: Mechanisms and Applications	83
Tunable Mie-Resonant Dielectric Metasurfaces Based on VO₂ Phase-Transition Materials	82
Generation of Spin Defects in Hexagonal Boron Nitride	78
Large-Scale Parametrized Metasurface Design Using Adjoint Optimization	73
Perspectives on Advances in Quantum Dot Lasers and Integration with Si Photonic Integrated Circuits	70
Femtosecond Laser Writing of Spin Defects in Hexagonal Boron Nitride	68
Theoretical Challenges in Polaritonic Chemistry	67
Steering and Encoding the Polarization of the Second Harmonic in the Visible with a Monolithic LiNbO₃ Metasurface	66
Robust Freeform Metasurface Design Based on Progressively Growing Generative Networks	65
Efficient On-Chip Training of Optical Neural Networks Using Genetic Algorithm	65
Deep Convolutional Mixture Density Network for Inverse Design of Layered Photonic Structures	63

Perspective on Terahertz Applications in Bioscience and Biotechnology	63
Dual-Polarization Analog 2D Image Processing with Nonlocal Metasurfaces	63
p-GaSe/n-Ga₂O₃ van der Waals Heterostructure Photodetector at Solar-Blind Wavelengths with Ultrahigh Responsivity and Detectivity	62
Nanoparticle Trapping in a Quasi-BIC System	61
Radiative Thermal Router Based on Tunable Magnetic Weyl Semimetals	61
Optical Constants of Several Multilayer Transition Metal Dichalcogenides Measured by Spectroscopic Ellipsometry in the 300–1700 nm Range: High Index, Anisotropy, and Hyperbolicity	60
PT-Symmetric Absorber-Laser Enables Electromagnetic Sensors with Unprecedented Sensitivity	60
Elucidating the Behavior of Nanophotonic Structures through Explainable Machine Learning Algorithms	60
Efficiency of Hot-Electron Generation in Plasmonic Nanocrystals with Complex Shapes: Surface-Induced Scattering, Hot Spots, and Interband Transitions	59
Generation of Optical Skyrmions with Tunable Topological Textures	59
Empowering Metasurfaces with Inverse Design: Principles and Applications	59
Microwave Programmable Graphene Metasurface	59
Highly Responsive Flexible Photodetectors Based on MOVPE Grown Uniform Few-Layer MoS₂	59
In Situ Patterning Perovskite Quantum Dots by Direct Laser Writing Fabrication	58
Tunable Metasurface Inverse Design for 80% Switching Efficiencies and 144° Angular Deflection	58
Tunable All-Dielectric Metasurfaces for Phase-Only Modulation of Transmitted Light Based on Quasi-bound States in the Continuum	58
Scalable Nanoimprint Lithography Process for Manufacturing Visible Metasurfaces Composed of High Aspect Ratio TiO₂ Meta-Atoms	57
Ultrahigh Deep-Ultraviolet Responsivity of a β-Ga₂O₃/MgO Heterostructure-Based Phototransistor	57
Lasing at Multidimensional Topological States in a Two-Dimensional Photonic Crystal Structure	57
Prospects of Surface-Enhanced Raman Spectroscopy for Biomarker Monitoring toward Precision Medicine	56
Organic Lasers Harnessing Excited State Intramolecular Proton Transfer Process	56
Photonics for Photovoltaics: Advances and Opportunities	56
Theory of Shaping Electron Wavepackets with Light	55
On-Chip Mid-Infrared Supercontinuum Generation from 3 to 13 μm Wavelength	55
On-Chip Optical Gas Sensors Based on Group-IV Materials	55
Photonic Topological Valley-Locked Waveguides	54
Boosting Strong Coupling in a Hybrid WSe₂ Monolayer–Anapole–Plasmon System	54
Tunable Metasurface Using Thin-Film Lithium Niobate in the Telecom Regime	54
Enhanced Electro-Optic Modulation in Resonant Metasurfaces of Lithium Niobate	54
Violating Kirchhoff’s Law of Thermal Radiation in Semitransparent Structures	54
Efficient Single-Photon Detection with 7.7 ps Time Resolution for Photon-Correlation Measurements	54
Inverse Design of Lightweight Broadband Reflector for Relativistic Lightsail Propulsion	54
Nonlinear Dielectric Nanoantennas and Metasurfaces: Frequency Conversion and Wavefront Control	53
Flexible and Stretchable Photonics: The Next Stretch of Opportunities	53
Enhanced Infrared Emission by Thermally Switching the Excitation of Magnetic Polariton with Scalable Microstructured VO₂ Metasurfaces	53
Scale-, Shift-, and Rotation-Invariant Diffractive Optical Networks	53
Thermal Homeostasis Enabled by Dynamically Regulating the Passive Radiative Cooling and Solar Heating Based on a Thermochromic Hydrogel	52
Optically Tunable Mie Resonance VO₂ Nanoantennas for Metasurfaces in the Visible	52
Physics-Based Approach for a Neural Networks Enabled Design of All-Dielectric Metasurfaces	52
Microwave Space-Time-Modulated Metasurfaces	51
Multifunctional Naphthol Sulfonic Salt Incorporated in Lead-Free 2D Tin Halide Perovskite for Red Light-Emitting Diodes	51
Enhanced Nonlinear Optical Responses of Layered Epsilon-near-Zero Metamaterials at Visible Frequencies	51
Metasurface-Based Optical Liquid Crystal Cell as an Ultrathin Spatial Phase Modulator for THz Applications	51
Transition Metal Dichalcogenide Resonators for Second Harmonic Signal Enhancement	50
Phase-Resolved Detection of Ultrabroadband THz Pulses inside a Scanning Tunneling Microscope Junction	50
All van der Waals Integrated Nanophotonics with Bulk Transition Metal Dichalcogenides	50
Inverse Design of Metasurfaces Based on Coupled-Mode Theory and Adjoint Optimization	50
Temperature-Dependent Energy-Level Shifts of Spin Defects in Hexagonal Boron Nitride	50
Twist-induced control of near-field heat radiation between magnetic Weyl semimetals	49
Saturation Mechanisms in Common LED Phosphors	49

Broadband Liquid Crystal Tunable Metasurfaces in the Visible: Liquid Crystal Inhomogeneities Across the Metasurface Parameter Space	49
Single-Shot Autofocusing of Microscopy Images Using Deep Learning	49
Engineering the Luminescence and Generation of Individual Defect Emitters in Atomically Thin MoS₂	49
Deep Learning to Accelerate Scatterer-to-Field Mapping for Inverse Design of Dielectric Metasurfaces	49
Ultranarrow and Wavelength-Tunable Thermal Emission in a Hybrid Metal–Optical Tamm State Structure	48
Terahertz Scanning Tunneling Microscopy for Visualizing Ultrafast Electron Motion in Nanoscale Potential Variations	46
Deep Learning Enabled Design of Complex Transmission Matrices for Universal Optical Components	46
Ten-Port Unitary Optical Processor on a Silicon Photonic Chip	46
Hybrid Dielectric Metasurfaces for Enhancing Second-Harmonic Generation in Chemical Vapor Deposition Grown MoS₂ Monolayers	45
MXenes for Photonics	45
Nighttime Radiative Cooling for Water Harvesting from Solar Panels	45
Silicon Carbide Photonics Bridging Quantum Technology	43
Spin–Orbit-Engineered Selective Transport of Photons in Plasmonic Nanocircuits with Panda-Patterned Transporters	43
Loss-Assisted Metasurface at an Exceptional Point	42
Observation of Negative Photoconductivity in Lead-Free Cs₃Bi₂Br₉Perovskite Single Crystal	42
Edge Detection with Mie-Resonant Dielectric Metasurfaces	42
Room-Temperature Quantum Emitter in Aluminum Nitride	42
Reconfigurable Multistate Optical Systems Enabled by VO₂ Phase Transitions	42
Broadband Nonvolatile Electrically Controlled Programmable Units in Silicon Photonics	42
Bound States in the Continuum in the Visible Emerging from out-of-Plane Magnetic Dipoles	42
Reduced Lasing Thresholds in GeSn Microdisk Cavities with Defect Management of the Optically Active Region	42
A Roadmap Toward the Theory of Vibrational Polariton Chemistry	41
High-Contrast Switching of Plasmonic Structural Colors: Inorganic versus Organic Electrochromism	41
Deep Learning-Based Holographic Polarization Microscopy	41
Self-Powered Photoelectrochemical (Al,Ga)N Photodetector with an Ultrahigh Ultraviolet/Visible Reject Ratio and a Quasi-Invisible Functionality for 360° Omnidirectional Detection	40
Chiral Light–Chiral Matter Interactions: an Optical Force Perspective	40
On-Demand Generation of Entangled Photon Pairs in the Telecom C-Band with InAs Quantum Dots	40
Narrow-Linewidth Tin-Vacancy Centers in a Diamond Waveguide	40
2D MoTe₂/ReS₂ van der Waals Heterostructure for High-Performance and Linear Polarization-Sensitive Photodetector	40
CMOS-Compatible Bias-Tunable Dual-Band Detector Based on GeSn/Ge/Si Coupled Photodiodes	40
Impact of Noise and Background on Measurement Uncertainties in Luminescence Thermometry	40
Exploring the Limit of Multiplexed Near-Field Optical Trapping	39
Heterostructured Vertical Organic Transistor for High-Performance Optoelectronic Memory and Artificial Synapse	39
Imaging Properties of Large Field-of-View Quadratic Metalenses and Their Applications to Fingerprint Detection	39
Nanoscale Light Confinement: the Q’s and V’s	39
Deep Learning-Enabled Orbital Angular Momentum-Based Information Encryption Transmission	38
Resolution-Enhanced Parallel Coded Ptychography for High-Throughput Optical Imaging	38
Inverse Design of Nanophotonic Devices with Structural Integrity	38
Active Tuning of Highly Anisotropic Phonon Polaritons in Van der Waals Crystal Slabs by Gated Graphene	38
Bi₂Se₃-Functionalized Metasurfaces for Ultrafast All-Optical Switching and Efficient Modulation of Terahertz Waves	38
Integrated Hybrid VO₂–Silicon Optical Memory	38
Flexible Polymer Photonic Films with Embedded Microvoids for High-Performance Passive Daytime Radiative Cooling	37
Single-Shot Real-Time Ultrafast Imaging of Femtosecond Laser Fabrication	37
Technology and Applications of Micro-LEDs: Their Characteristics, Fabrication, Advancement, and Challenges	37
Plasmonic Mid-Infrared Filter Array-Detector Array Chemical Classifier Based on Machine Learning	37
Preparation of High Damage Threshold Device Based on Bi₂Se₃ Film and Its Application in Fiber Lasers	37
Metasurface-Dressed Two-Dimensional on-Chip Waveguide for Free-Space Light Field Manipulation	36
Virtual Critical Coupling	36
Computer-Free, All-Optical Reconstruction of Holograms Using Diffractive Networks	36
Resonance Fluorescence from Waveguide-Coupled, Strain-Localized, Two-Dimensional Quantum Emitters	36
Insights into Ultrafast Carrier Dynamics in Perovskite Thin Films and Solar Cells	36
The Role of Long-Lived Excitons in the Dynamics of Strongly Coupled Molecular Polaritons	36
Single-Handedness Chiral Optical Cavities	36
Short-Wave Infrared Confocal Fluorescence Imaging of Deep Mouse Brain with a Superconducting Nanowire Single-Photon Detector	35
Antiparity-Time Symmetry in Passive Nanophotonics	35
Integration of hBN Quantum Emitters in Monolithically Fabricated Waveguides	35
Nonlinear Optical Interactions and Relaxation in 2D Layered Transition Metal Dichalcogenides Probed by Optical and Photoacoustic Z-Scan Methods	35
Site-Specific Fabrication of Blue Quantum Emitters in Hexagonal Boron Nitride	34
3D Imaging Using Extreme Dispersion in Optical Metasurfaces	34
High-Bandwidth Extended-SWIR GeSn Photodetectors on Silicon Achieving Ultrafast Broadband Spectroscopic Response	34
Extremely Confined Acoustic Phonon Polaritons in Monolayer-hBN/Metal Heterostructures for Strong Light–Matter Interactions	34
Fundamental Radiative Processes in Near-Zero-Index Media of Various Dimensionalities	33
Low-Temperature Electron–Phonon Interaction of Quantum Emitters in Hexagonal Boron Nitride	33
Tunable Ultranarrowband Grating Filters in Thin-Film Lithium Niobate	33
Visible to Mid-Infrared Photodetection Based on Flexible 3D Graphene/Organic Hybrid Photodetector with Ultrahigh Responsivity at Ambient Conditions	33
Plasmon-Enhanced Solar-Driven Hydrogen Evolution Using Titanium Nitride Metasurface Broadband Absorbers	33
Photonic Inverse Design of On-Chip Microresonators	33
Ligand-Assisted Sulfide Surface Treatment of CsPbI₃ Perovskite Quantum Dots to Increase Photoluminescence and Recovery	33
Lithium Niobate Meta-Optics	33
Genetic-Algorithm-Aided Meta-Atom Multiplication for Improved Absorption and Coloration in Nanophotonics	33
Broadband Terahertz Silicon Membrane Metasurface Absorber	33
Metasurface Generation of Paired Accelerating and Rotating Optical Beams for Passive Ranging and Scene Reconstruction	33
Optical Gap-Surface Plasmon Metasurfaces for Spin-Controlled Surface Plasmon Excitation and Anomalous Beam Steering	33
Holographic Image Reconstruction with Phase Recovery and Autofocusing Using Recurrent Neural Networks	33
Dielectric Nonlocal Metasurfaces for Fully Solid-State Ultrathin Optical Systems	32
Identification of Microplastics Based on the Fractal Properties of Their Holographic Fingerprint	32
Robust Mode Matching between Structurally Dissimilar Optical Fiber Waveguides	32
Ultrafast Quantum-Well Photodetectors Operating at 10 μm with a Flat Frequency Response up to 70 GHz at Room Temperature	32
MEMS-Enabled On-Chip Computational Mid-Infrared Spectrometer Using Silicon Photonics	32
Detection of Single W-Centers in Silicon	32

Bright High-Purity Quantum Emitters in Aluminum Nitride Integrated Photonics	32
Bound-States-in-Continuum Hybrid Integration of 2D Platinum Diselenide on Silicon Nitride for High-Speed Photodetectors	32
Video-Speed Graphene Modulator Arrays for Terahertz Imaging Applications	32
Si Microring Resonator Crossbar Array for On-Chip Inference and Training of the Optical Neural Network	32
Gigahertz Acousto-Optic Modulation and Frequency Shifting on Etchless Lithium Niobate Integrated Platform	31
Lanthanide-Based Nanosensors: Refining Nanoparticle Responsiveness for Single Particle Imaging of Stimuli	31
Highly Efficient Plasmon Induced Hot-Electron Transfer at Ag/TiO₂ Interface	31
Asymmetric Quantum-Dot Pixelation for Color-Converted White Balance	31
Mode-Matching Enhancement of Second-Harmonic Generation with Plasmonic Nanopatch Antennas	31
Machine Learning for Integrated Quantum Photonics	31
Bright Future of Deep-Ultraviolet Photonics: Emerging UVC Chip-Scale Light-Source Technology Platforms, Benchmarking, Challenges, and Outlook for UV Disinfection	31
Terahertz-Light Induced Structural Transition and Superpermeation of Confined Monolayer Water	31
Terahertz Nanoimaging and Nanospectroscopy of Chalcogenide Phase-Change Materials	31
High Speed Simulation and Freeform Optimization of Nanophotonic Devices with Physics-Augmented Deep Learning	30
Giant Intrinsic Chirality in Curled Metasurfaces	30
Strain-Induced Trapping of Indirect Excitons in MoSe₂/WSe₂ Heterostructures	30
Optical Beam Steering Using Tunable Metasurfaces	30
Demonstration of N-Polar III-Nitride Tunnel Junction LED	30
Bright Plasmons with Cubic Nanometer Mode Volumes through Mode Hybridization	30
Third-Order Nonlinear Optical Properties and Saturation of Two-Photon Absorption in Lead-Free Double Perovskite Nanocrystals under Femtosecond Excitation	30
Anapole-Assisted Absorption Engineering in Arrays of Coupled Amorphous Gallium Phosphide Nanodisks	30
Low-Charge-Noise Nitrogen-Vacancy Centers in Diamond Created Using Laser Writing with a Solid-Immersion Lens	30
Dual Nanoresonators for Ultrasensitive Chiral Detection	30
Space and Time Modulations of Light with Metasurfaces: Recent Progress and Future Prospects	30
A Smartphone-Based Fourier Ptychographic Microscope Using the Display Screen for Illumination	29
Coherent Topological Polariton Laser	29
Chiral Bioinspired Plasmonics: A Paradigm Shift for Optical Activity and Photochemistry	29
Dynamic Display of Full-Stokes Vectorial Holography Based on Metasurfaces	29
Design Space Reparameterization Enforces Hard Geometric Constraints in Inverse-Designed Nanophotonic Devices	29
Improved Quantum Efficiency by Advanced Light Management in Nanotextured Solution-Processed Perovskite Solar Cells	29
Surface-Enhanced Circular Dichroism Spectroscopy on Periodic Dual Nanostructures	29
Line Waves in Non-Hermitian Metasurfaces	29
Spatiotemporal Helicon Wavepackets	28
Space–Time Metasurfaces for Power Combining of Waves	28
Room-Temperature Blackbody-Sensitive and Fast Infrared Photodetectors Based on 2D Tellurium/Graphene Van der Waals Heterojunction	28
Photocurrent Enhanced in UV-vis-NIR Photodetector Based on CdSe/CdTe Core/Shell Nanowire Arrays by Piezo-Phototronic Effect	28
Expanding the Photonic Palette: Exploring High Index Materials	28
Opportunities and Challenges for Large-Scale Phase-Change Material Integrated Electro-Photonics	28
Variable Repetition Rate THz Source for Ultrafast Scanning Tunneling Microscopy	28
Colloidal Superstructures with Triangular Cores: Size Effects on SERS Efficiency	28
Near Transform-Limited Quantum Dot Linewidths in a Broadband Photonic Crystal Waveguide	28
Large-Area, High-Resolution Birefringence Imaging with Polarization-Sensitive Fourier Ptychographic Microscopy	28
Optical Third-Harmonic Generation in Hexagonal Boron Nitride Thin Films	28
Strain-Tunable Single-Photon Source Based on a Circular Bragg Grating Cavity with Embedded Quantum Dots	28
A 100 Gb/s PAM4 Two-Segment Silicon Microring Resonator Modulator Using a Standard Foundry Process	27
Active Perovskite Hyperbolic Metasurface	27
Lattice Resonances Induced by Periodic Vacancies in Arrays of Nanoparticles	27
Advances and Prospects in Topological Nanoparticle Photonics	27
Zero-Dimensional PbS Quantum Dot–InGaZnO Film Heterostructure for Short-Wave Infrared Flat-Panel Imager	27
Integrated Near-Field Thermophotovoltaic Device Overcoming Blackbody Limit	27
Fractal Shaped Periodic Metal Nanostructures Atop Dielectric-Metal Substrates for SERS Applications	27
Manifold Learning for Knowledge Discovery and Intelligent Inverse Design of Photonic Nanostructures: Breaking the Geometric Complexity	26
Twist-Induced Near-Field Thermal Switch Using Nonreciprocal Surface Magnon-Polaritons	26
Dielectric Nanoantennas for Strain Engineering in Atomically Thin Two-Dimensional Semiconductors	26
Cell Cycle Stage Classification Using Phase Imaging with Computational Specificity	26
Terahertz Frequency Combs Exploiting an On-Chip, Solution-Processed, Graphene-Quantum Cascade Laser Coupled-Cavity	26
Plasmonic Superchiral Lattice Resonances in the Mid-Infrared	26
Top-Seed Solution-Based Growth of Perovskite Cs₃Bi₂I₉ Single Crystal for High Performance X-ray Detection	26
Multiobjective Statistical Learning Optimization of RGB Metalens	26
Effect of Ag Nanocube Optomechanical Modes on Plasmonic Surface Lattice Resonances	26
General Inverse Design of Layered Thin-Film Materials with Convolutional Neural Networks	26
Enhanced Plasmonic Photocatalysis through Synergistic Plasmonic–Photonic Hybridization	26
Unveiling the Symmetry Protection of Bound States in the Continuum with Terahertz Near-Field Imaging	26
Upconversion Plasmonic Lasing from an Organolead Trihalide Perovskite Nanocrystal with Low Threshold	26
Toward 3D-Printed Inverse-Designed Metaoptics	26
Photonic Crystal Waveguides for >90% Light Trapping Efficiency in Luminescent Solar Concentrators	26
Defect-Enhanced Exciton–Exciton Annihilation in Monolayer Transition Metal Dichalcogenides at High Exciton Densities	26
Relevant Length Scales in Brillouin Imaging of Biomaterials: The Interplay between Phonons Propagation and Light Focalization	25
Photonic Nanojet Mediated Backaction of Dielectric Microparticles	25
Photon Acceleration Using a Time-Varying Epsilon-near-Zero Metasurface	25
Fingerprinting the Hidden Facets of Plasmonic Nanocavities	25
Magnetic Purcell Enhancement by Magnetic Quadrupole Resonance of Dielectric Nanosphere Antenna	25
Ultracompact Fiber-to-Chip Metamaterial Edge Coupler	25
Two-Dimensional Organic-Exciton Polariton Lattice Fabricated Using Laser Patterning	25
Large-Scale Metasurfaces Based on Grayscale Nanosphere Lithography	25
Cost-Effective Live Cell Structured Illumination Microscopy with Video-Rate Imaging	25
Fast Polaron Formation and Low Carrier Mobility in Defect-Free Polyhedral CsPbBr₃ Perovskite Nanocrystals	25
Holographic Super-Resolution Metalens for Achromatic Sub-Wavelength Focusing	25
Compact Stereo Waveguide Display Based on a Unidirectional Polarization-Multiplexed Metagrating In-Coupler	25
Total Reflection-Induced Efficiency Enhancement of the Spin Hall Effect of Light	25
The Path to Enlightenment: Progress and Opportunities in High Efficiency Halide Perovskite Light-Emitting Devices	25
Enhanced Nonlinear Emission from Single Multilayered Metal–Dielectric Nanocavities Resonating in the Near-Infrared	24
A Theoretical Perspective on Molecular Polaritonics	24
Perovskite Quantum Dots Based Optical Fabry–Pérot Pressure Sensor	24
Capturing Broadband Light in a Compact Bound State in the Continuum	24
Hybrid Machine Learning for Scanning Near-Field Optical Spectroscopy	24
Distinguishing Small Molecules in Microcavity with Molecular Laser Polarization	24
Transient Tap Couplers for Wafer-Level Photonic Testing Based on Optical Phase Change Materials	24
Enhanced Single-Photon Emission from GaN Quantum Dots in Bullseye Structures	24
Label-Free Optical Analysis of Biomolecules in Solid-State Nanopores: Toward Single-Molecule Protein Sequencing	24
Nonlinear Beam Shaping with Binary Phase Modulation on Patterned WS₂ Monolayer	24
Electron–Hole Plasma Lasing Dynamics in CsPbCl_mBr_3-m Microplate Lasers	24
Refractive Uses of Layered and Two-Dimensional Materials for Integrated Photonics	24
Quasi-BIC Mode Lasing in a Quadrumer Plasmonic Lattice	24
Watt-Level Visible Continuous-Wave Upconversion Fiber Lasers toward the “Green Gap” Wavelengths of 535–553 nm	24