Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to t...Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to the static metasurfaces and metadevices,where the functionalities cannot be actively tuned in situ post-fabrication.Due to the in-trinsic advantage of active tunability by external stimulus,graphene has been successively demonstrated as a favorable candidate to empower metasurfaces with remarkably dynamic tunability,and their recent advances are propelling the EM wave manipulations to a new height:from static to dynamic.Here,we review the recent progress on dynamic metasur-faces and metadevices enabled by graphene with the focus on electrically-controlled dynamic manipulation of the EM waves covering the mid-infrared,terahertz,and microwave regimes.The fundamentals of graphene,including basic ma-terial properties and plasmons,are first discussed.Then,graphene-empowered dynamic metasurfaces and met-adevices are divided into two categories,i.e.,metasurfaces with building blocks of structured graphene and hybrid metasurfaces integrated with graphene,and their recent advances in dynamic spectrum manipulation,wavefront shap-ing,polarization control,and frequency conversion in near/far fields and global/local ways are elaborated.In the end,we summarize the progress,outline the remaining challenges,and prospect the potential future developments.展开更多
The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protect...The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum(BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.展开更多
Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum comm...Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.展开更多
Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonst...Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.展开更多
We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, re...We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, revealing that cylindrical metal waveguides only support TM01 and HEm1 surface modes. During propagation on the metal tip, the gratingcoupled SPPs are converted to HE31, HE21, HE11 and TM01 successively, and these modes are sequentially cut off except TM01. The TM01 mode further propagates with drastically increasing effective mode index and is converted to localized surface plasmons （LSPs） at the tip apex, which is responsible for plasmonic nanofocusing. The gapmode plasmons can be excited with the focusing TM01 mode by approaching a metal substrate to the tip apex, resulting in further enhanced electric field and reduced size of the plasmonic focus.展开更多
We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating(TFBG)for enhanced refractive index sensing.The TFBG is UV-inscribed in series in ordinary single-mode fiber(SMF)and reduced-diameter SM...We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating(TFBG)for enhanced refractive index sensing.The TFBG is UV-inscribed in series in ordinary single-mode fiber(SMF)and reduced-diameter SMF with the same tilt angle,and then excites two sets of superposed spectral combs of cladding modes.The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF,enabling an enlarged range and a higher accuracy of refractive index measurement.The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.展开更多
Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures.Here,we rep...Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures.Here,we report an in-fiber photoelec-tric device by wrapping a few-layer graphene and bonding a pair of electrodes onto a tilted fiber Bragg grating(TFBG)for photoelectric and electric-induced thermo-optic conversions.The transmitted spectrum from this device consists of a dense comb of narrowband resonances that provides an observable window to sense the photocurrent and the electrical injection in the graphene layer.The device has a wavelength-sensitive photoresponse with responsivity up to 11.4 A/W,allowing the spectrum analysis by real-time monitoring of photocurrent evolution.Based on the thermal-optic effect of electrical injection,the graphene layer is energized to produce a global red-shift of the transmission spectrum of the TF-BG,with a high sensitivity approaching 2.167×10^(4)nm/A^(2).The in-fiber photoelectric device,therefore as a powerful tool,could be widely available as off-the-shelf product for photodetection,spectrometer and current sensor.展开更多
Recently,physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications.Therein,topological light fields,...Recently,physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications.Therein,topological light fields,because of their unique opportunity of combining experimental and analytical studies,are attracting more interest.Here,based on the Pancharatnam-Berry(PB)phase,we report the creation of Hopf linked and Trefoil knotted optical vortices by using phaseonly encoded liquid crystal(LC)holographic plates.Utilizing scanning measurement and the digital holographic interference method,we accurately locate the vortex singularities and map these topological nodal lines in three-dimensions.Compared with the common methods realized by the spatial light modulator(SLM),the phase-only LC plate is more efficient.Meanwhile,the smaller pixel size of the LC element reduces the imperfection induced by optical misalignment and pixellation.Moreover,we analyze the influence of the incident beam size on the topological configuration.展开更多
The conversion-efficiency for second-harmonic(SH)in optical fibers is significantly limited by extremely weak second-order nonlinearity of fused silica,and pulse pump lasers with high peak power are widely employed.He...The conversion-efficiency for second-harmonic(SH)in optical fibers is significantly limited by extremely weak second-order nonlinearity of fused silica,and pulse pump lasers with high peak power are widely employed.Here,we propose a simple strategy to efficiently realize the broadband and continuous wave(CW)pumped SH,by transferring a crystalline GaSe coating onto a microfiber with phase-matching diameter.In the experiment,high efficiency up to 0.08%W-1mm-1 is reached for a C-band pump laser.The high enough efficiency not only guarantees SH at a single frequency pumped by a CW laser,but also multi-frequencies mixing supported by three CW light sources.Moreover,broadband SH spectrum is also achieved under the pump of a superluminescent light-emitting diode source with a 79.3 nm bandwidth.The proposed scheme provides a beneficial method to the enhancement of various nonlinear parameter processes,development of quasi-monochromatic or broadband CW light sources at new wavelength regions.展开更多
Phase unwrapping is an indispensable step for many optical imaging and metrology techniques.The rapid development of deep learning has brought ideas to phase unwrapping.In the past four years,various phase dataset gen...Phase unwrapping is an indispensable step for many optical imaging and metrology techniques.The rapid development of deep learning has brought ideas to phase unwrapping.In the past four years,various phase dataset generation methods and deep-learning-involved spatial phase unwrapping methods have emerged quickly.However,these methods were proposed and analyzed individually,using different strategies,neural networks,and datasets,and applied to different scenarios.It is thus necessary to do a detailed comparison of these deep-learning-involved methods and the traditional methods in the same context.We first divide the phase dataset generation methods into random matrix enlargement,Gauss matrix superposition,and Zernike polynomials superposition,and then divide the deep-learning-involved phase unwrapping methods into deep-learning-performed regression,deep-learning-performed wrap count,and deep-learningassisted denoising.For the phase dataset generation methods,the richness of the datasets and the generalization capabilities of the trained networks are compared in detail.In addition,the deep-learning-involved methods are analyzed and compared with the traditional methods in ideal,noisy,discontinuous,and aliasing cases.Finally,we give suggestions on the best methods for different situations and propose the potential development direction for the dataset generation method,neural network structure,generalization ability enhancement,and neural network training strategy for the deep-learning-involved spatial phase unwrapping methods.展开更多
We demonstrate a reconfigurable black phosphorus electrical field transistor,which is van der Waals heterostructured with few-layer graphene and hexagonal boron nitride flakes.Varied homojunctions could be realized by...We demonstrate a reconfigurable black phosphorus electrical field transistor,which is van der Waals heterostructured with few-layer graphene and hexagonal boron nitride flakes.Varied homojunctions could be realized by controlling both source–drain and top-gate voltages.With the spatially resolved scanning photocurrent microscopy technique,photovoltaic photocurrents originated from the band-bending regions are observed,confirming nine different configurations for each set of fixed voltages.In addition,as a phototransistor,high responsivity(～800 mA/W)and fast response speed(～230μs)are obtained from the device.The reconfigurable van der Waals heterostructured transistors may offer a promising structure towards electrically tunable black phosphorus-based optoelectronic devices.展开更多
Emerging as a family of waves,Janus waves are known to have“real”and“virtual”components under inversion of the propagation direction.Although tremendous interest has been evoked in vortex beams featuring spiral wa...Emerging as a family of waves,Janus waves are known to have“real”and“virtual”components under inversion of the propagation direction.Although tremendous interest has been evoked in vortex beams featuring spiral wavefronts,little research has been devoted to the vortex beam embedded Janus waves,i.e.,Janus vortex beams.We propose a liquid crystal(LC)Pancharatnam–Berry(PB)phase element to demonstrate the realization of the Janus vortex beams and the modulation of the associated orbit angular momentum(OAM)and spin angular momentum(SAM).The generated Janus vortex beams show opposite OAM and SAM states at two distinct foci,revealing a spin-orbit interaction during propagation enabled by the LC PB phase element,which may play special roles in applications such as optical encryption and decryption.Other merits like reconfigurability and flexible switching between Janus vortex beams and autofocusing or autodefocusing vortex beams additionally increase the degree of freedom of manipulating vortex beams.This work provides a platform for tailoring complex structured light and may enrich the applications of vortex beams in classical and quantum optics.展开更多
Phase recovery(PR)refers to calculating the phase of the light field from its intensity measurements.As exemplified from quantitative phase imaging and coherent diffraction imaging to adaptive optics,PR is essential f...Phase recovery(PR)refers to calculating the phase of the light field from its intensity measurements.As exemplified from quantitative phase imaging and coherent diffraction imaging to adaptive optics,PR is essential for reconstructing the refractive index distribution or topography of an object and correcting the aberration of an imaging system.In recent years,deep learning(DL),often implemented through deep neural networks,has provided unprecedented support for computational imaging,leading to more efficient solutions for various PR problems.In this review,we first briefly introduce conventional methods for PR.Then,we review how DL provides support for PR from the following three stages,namely,pre-processing,in-processing,and post-processing.We also review how DL is used in phase image processing.Finally,we summarize the work in DL for PR and provide an outlook on how to better use DL to improve the reliability and efficiency of PR.Furthermore,we present a live-updating resource(https://github.com/kqwang/phase-recovery)for readers to learn more about PR.展开更多
Check dams have been widely constructed in the Chinese Loess Plateau and has played an important role in controlling soil loss during last 70 years.However,the large-scale and automatic mapping of the check dams and t...Check dams have been widely constructed in the Chinese Loess Plateau and has played an important role in controlling soil loss during last 70 years.However,the large-scale and automatic mapping of the check dams and the resulting silted fields are lacking.In this study,we present a novel methodological framework to extract silted fields and to estimate the location of the check dams at a pixel level in the Wuding River catchment by remote sensing and ensemble learning models.The random under-sampling method and 23 features were used to train and validate three ensemble learning models,namely Random Forest,Extreme Gradient Boosting and EasyEnsemble,based on a large number of samples.The established optimal model was then applied to the whole study area to map check dams and silted fields.Our results indicate that the imbalance ratio of the samples has a significant impact on the performance of the models.Validation of the results on the testing set show that the F1-score of silted fields of three models is higher than 0.75 at the pixel level.Finally,we produced a map of silted fields and check dams at 10 m-spatial resolution by the optimal model with an accuracy of ca.90%at the object level.The proposed framework can be used for the large-scale and high-precision mapping of check dams and silted fields,which is of great significance for the monitoring and management of the dynamics of check dams and the quantitative evaluation of their eco-environmental benefits.展开更多
We demonstrate an intracavity self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating(PI-FBG), fabricated by a femtosecond laser with a point-by-point parallel inscription ...We demonstrate an intracavity self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating(PI-FBG), fabricated by a femtosecond laser with a point-by-point parallel inscription method. The multi-color Q-switched pulses can be always self-synchronized when the group delay differences between neighboring spectra range from-3.4 to 3.4 ps.The starting and evolution dynamics indicate that the saturable absorption effect of the carbon nanotube plays a dual role: synchronously triggering the startup of the pulse at successive colors by active Q-switching and spontaneously compensating to some extent the temporal walk-off of the multi-color pulses through the cross saturable absorption modulation. This work unveils the intracavity self-synchronization mechanism of the multi-color Q-switched pulses and also demonstrates the potential of PI-FBGs for the customizable generation of the synchronized multi-color pulse in a single cavity.展开更多
The suppression of polarization cross talk in lead zirconate titanate phase modulators as a key error source has been challenging for open-loop fiber optic gyroscopes(FOGs).We developed a polarization-diversity optica...The suppression of polarization cross talk in lead zirconate titanate phase modulators as a key error source has been challenging for open-loop fiber optic gyroscopes(FOGs).We developed a polarization-diversity optical frequency domain reflectometry(OFDR)to measure the distributed modulation polarization error in the modulator.The error contributes 8×10^(−6) rad to FOG’s bias instability.Using a UV-fabricated in-fiberλ/4 wave plate and polarization-mode converter with fiber taper technology,the modulation error has been suppressed by 15 dB in assembled FOGs.This approach reduced error with temperature from 25°/h to 0.7°/h,meeting the requirements of control-level gyroscopes with bias errors less than 1°/h.展开更多
The miniaturization of spectrometers has received much attention in recent years.The rapid development of metasurfaces has provided a new avenue for creating more compact and lightweight spectrometers.However,most met...The miniaturization of spectrometers has received much attention in recent years.The rapid development of metasurfaces has provided a new avenue for creating more compact and lightweight spectrometers.However,most metasurface-based spectrometers operate in the visible light region,with much less research on near-infrared wavelengths.This is possibly caused by the lack of effective metasurface filters for the near-infrared light.We design and fabricate a polarizationinsensitive amorphous silicon metasurface that exhibits unique transmission spectra in parts of the visible and nearinfrared wavelengths.By passing the light to be measured through a metasurface filter array and measuring the transmitted power,we achieve the precise reconstruction of unknown spectra in the visible and near-infrared range(450-950 nm)using an algorithm matched to the filter model.Our approach is a step towards miniaturized spectrometers within the visible-to-near-infrared range based on metasurface filter arrays.展开更多
Optical cavities play crucial roles in enhanced light-matter interaction,light control,and optical communications,but their dimensions are limited by the material property and operating wavelength.Ultrathin planar cav...Optical cavities play crucial roles in enhanced light-matter interaction,light control,and optical communications,but their dimensions are limited by the material property and operating wavelength.Ultrathin planar cavities are urgently in demand for large-area and integrated optical devices.However,extremely reducing the planar cavity dimension is a critical challenge,especially at telecommunication wavelengths.Herein,we demonstrate a type of ultrathin cavities based on large-area grown Bi_(2)Te_(3)topological insulator(TI)nanofilms,which present distinct optical resonance in the near-infrared region.The result shows that the Bi_(2)Te_(3)TI material presents ultrahigh refractive indices of>6 at telecommunication wavelengths.The cavity thickness can approach 1/20 of the resonance wavelength,superior to those of planar cavities based on conventional Si and Ge high refractive index materials.Moreover,we observed an analog of the electromagnetically induced transparency(EIT)effect at telecommunication wavelengths by depositing the cavity on a photonic crystal.The EIT-like behavior is derived from the destructive interference coupling between the nanocavity resonance and Tamm plasmons.The spectral response depends on the nanocavity thickness,whose adjustment enables the generation of obvious Fano resonance.The experiments agree well with the simulations.This work will open a new door for ultrathin cavities and applications of TI materials in light control and devices.展开更多
Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the tele...Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the telecom band.Here,we report on-substrate vertical emitting lasing from ordered InGaAs/InP multi-quantum well core–shell nanowire array epitaxially grown on InP substrate by selective area epitaxy.To reduce optical loss and tailor the cavity mode,a new nanowire facet engineering approach has been developed to achieve controlled quantum well nanowire dimensions with uniform morphology and high crystal quality.Owing to the strong quantum confinement effect of InGaAs quantum wells and the successful formation of a vertical Fabry–Pérot cavity between the top nanowire facet and bottom nanowire/SiO_(2) mask interface,stimulated emissions of the EH11a/b mode from single vertical nanowires from an on-substrate nanowire array have been demonstrated with a lasing threshold of~28.2μJ cm^(−2) per pulse and a high characteristic temperature of~128 K.By fine-tuning the In composition of the quantum wells,room temperature,single-mode lasing is achieved in the vertical direction across a broad near-infrared spectral range,spanning from 940 nm to the telecommunication O and C bands.Our research indicates that through a carefully designed facet engineering strategy,highly ordered,uniform nanowire arrays with precise dimension control can be achieved to simultaneously deliver thousands of nanolasers with multiple wavelengths on the same substrate,paving a promising and scalable pathway towards future advanced optoelectronic and photonic systems.展开更多
Surface plasmon resonance microscopy(SPRM)has been massively applied for near-field optical measurement,sensing,and imaging because of its high detection sensitivity,nondestructive,noninvasive,wide-field,and label-fre...Surface plasmon resonance microscopy(SPRM)has been massively applied for near-field optical measurement,sensing,and imaging because of its high detection sensitivity,nondestructive,noninvasive,wide-field,and label-free imaging capabilities.However,the transverse propagation characteristic of the surface plasmon wave generated during surface plasmon resonance(SPR)leads to notable“tail”patterns in the SPR image,which severely deteriorates the image quality.Here,we propose an incidence angle scanning method in SPRM to obtain a resonance angle image with exceptional contrast that significantly mitigates the adverse effects of“tail”patterns.The resonance angle image provides the complete morphology of the analyzed samples and enables two-dimensional quantification,which is incapable in conventional SPRM.The effectiveness of the method was experimentally verified using photoresist square samples with different sizes and two-dimensional materials with various geometric shapes.The edges of samples were fully reconstructed and a maximum fivefold increase in the image contrast has been achieved.Our method offers a convenient way to enhance the SPRM imaging capabilities with low cost and stable performance,which greatly expands the applications of SPRM in label-free detection,imaging,and quantification.展开更多
基金supported by the National Key R&D Program of China (2017YFA0303800)the National Natural Science Foundation of China (61805277, 11634010, 91950207, 11974283, 11774290)+1 种基金the Fundamental Research Funds for the Central Universities (3102017AX009, 3102019PY002, 3102019JC008)the Natural Science Basic Research Program of Shaanxi (2019JQ-447, 2020JM-130)
文摘Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to the static metasurfaces and metadevices,where the functionalities cannot be actively tuned in situ post-fabrication.Due to the in-trinsic advantage of active tunability by external stimulus,graphene has been successively demonstrated as a favorable candidate to empower metasurfaces with remarkably dynamic tunability,and their recent advances are propelling the EM wave manipulations to a new height:from static to dynamic.Here,we review the recent progress on dynamic metasur-faces and metadevices enabled by graphene with the focus on electrically-controlled dynamic manipulation of the EM waves covering the mid-infrared,terahertz,and microwave regimes.The fundamentals of graphene,including basic ma-terial properties and plasmons,are first discussed.Then,graphene-empowered dynamic metasurfaces and met-adevices are divided into two categories,i.e.,metasurfaces with building blocks of structured graphene and hybrid metasurfaces integrated with graphene,and their recent advances in dynamic spectrum manipulation,wavefront shap-ing,polarization control,and frequency conversion in near/far fields and global/local ways are elaborated.In the end,we summarize the progress,outline the remaining challenges,and prospect the potential future developments.
基金support from the National Key Research and Development Project (Grant No. 2018YFB2200500, 2018YFB2202800)National Natural Science Foundation of China (Grant No. 61534004, 91964202, 61874081, 61851406, 91950119, and 61905196)。
文摘The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum(BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11634010,11774289,61675168,and 61377035)the National Key Research and Development Program of China(Grant No.2017YFA0303800)+1 种基金Joint Fund of the National Natural Science Foundation Committee of China Academy of Engineering Physics(Grant No.U1630125)the Fundamental Research Funds for the Central Universities,China(Grant No.3102018zy036)
文摘Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0303800)the National Natural Science Foundation of China(Grant Nos.11634010,61675168,91850118,11774289,and 11804277)+1 种基金the Fundamental Research Funds for the Central Universities,China(Grant No.3102019JC008)the Basic Research Plan of Natural Science in Shaanxi Province,China(Grant Nos.2018JM1057 and 2019JM-583).
文摘Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.
基金This work was financially supported by the National Natural Science Foundation of China （NSFC） （61675169, 61377055 and 11634010）, the National Key R＆D Program of China （2017YFA0303800）, and the Fundamental Research Funds for the Central Universities （3102017zy021, 3102017HQZZ 022）.
文摘We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, revealing that cylindrical metal waveguides only support TM01 and HEm1 surface modes. During propagation on the metal tip, the gratingcoupled SPPs are converted to HE31, HE21, HE11 and TM01 successively, and these modes are sequentially cut off except TM01. The TM01 mode further propagates with drastically increasing effective mode index and is converted to localized surface plasmons （LSPs） at the tip apex, which is responsible for plasmonic nanofocusing. The gapmode plasmons can be excited with the focusing TM01 mode by approaching a metal substrate to the tip apex, resulting in further enhanced electric field and reduced size of the plasmonic focus.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61775182 and 61505165)Marie Sktodowska-Curie Individual Fellowships in the European Union’s Horizon 2020 Research and Innovation Programme(Grant No.660648)
文摘We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating(TFBG)for enhanced refractive index sensing.The TFBG is UV-inscribed in series in ordinary single-mode fiber(SMF)and reduced-diameter SMF with the same tilt angle,and then excites two sets of superposed spectral combs of cladding modes.The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF,enabling an enlarged range and a higher accuracy of refractive index measurement.The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.
基金We are grateful for financial supports from National Natural Science Foundation of China(Grant No.61975166)Key Research and Development Program(Grant No.2022YFA1404800).
文摘Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures.Here,we report an in-fiber photoelec-tric device by wrapping a few-layer graphene and bonding a pair of electrodes onto a tilted fiber Bragg grating(TFBG)for photoelectric and electric-induced thermo-optic conversions.The transmitted spectrum from this device consists of a dense comb of narrowband resonances that provides an observable window to sense the photocurrent and the electrical injection in the graphene layer.The device has a wavelength-sensitive photoresponse with responsivity up to 11.4 A/W,allowing the spectrum analysis by real-time monitoring of photocurrent evolution.Based on the thermal-optic effect of electrical injection,the graphene layer is energized to produce a global red-shift of the transmission spectrum of the TF-BG,with a high sensitivity approaching 2.167×10^(4)nm/A^(2).The in-fiber photoelectric device,therefore as a powerful tool,could be widely available as off-the-shelf product for photodetection,spectrometer and current sensor.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11634010,91850118,11774289,61675168,and 11804277)the National Key Research and Development Program of China(Grant No.2017YFA0303800)+1 种基金the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics(Grant No.U1630125)the Fundamental Research Funds for the Central Universities,China(Grant Nos.3102018zy036,3102019JC008,and 310201911cx022)。
文摘Recently,physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications.Therein,topological light fields,because of their unique opportunity of combining experimental and analytical studies,are attracting more interest.Here,based on the Pancharatnam-Berry(PB)phase,we report the creation of Hopf linked and Trefoil knotted optical vortices by using phaseonly encoded liquid crystal(LC)holographic plates.Utilizing scanning measurement and the digital holographic interference method,we accurately locate the vortex singularities and map these topological nodal lines in three-dimensions.Compared with the common methods realized by the spatial light modulator(SLM),the phase-only LC plate is more efficient.Meanwhile,the smaller pixel size of the LC element reduces the imperfection induced by optical misalignment and pixellation.Moreover,we analyze the influence of the incident beam size on the topological configuration.
基金supports from National Natural Science Foundation of China(No.61975166,11634010)Key Research and Development Program(No.2017YFA0303800).
文摘The conversion-efficiency for second-harmonic(SH)in optical fibers is significantly limited by extremely weak second-order nonlinearity of fused silica,and pulse pump lasers with high peak power are widely employed.Here,we propose a simple strategy to efficiently realize the broadband and continuous wave(CW)pumped SH,by transferring a crystalline GaSe coating onto a microfiber with phase-matching diameter.In the experiment,high efficiency up to 0.08%W-1mm-1 is reached for a C-band pump laser.The high enough efficiency not only guarantees SH at a single frequency pumped by a CW laser,but also multi-frequencies mixing supported by three CW light sources.Moreover,broadband SH spectrum is also achieved under the pump of a superluminescent light-emitting diode source with a 79.3 nm bandwidth.The proposed scheme provides a beneficial method to the enhancement of various nonlinear parameter processes,development of quasi-monochromatic or broadband CW light sources at new wavelength regions.
基金National Natural Science Foundation of China(61927810,62075183)NSAF Joint Fund(U1730137)Fundamental Research Funds for the Central Universities(3102019ghxm018).
文摘Phase unwrapping is an indispensable step for many optical imaging and metrology techniques.The rapid development of deep learning has brought ideas to phase unwrapping.In the past four years,various phase dataset generation methods and deep-learning-involved spatial phase unwrapping methods have emerged quickly.However,these methods were proposed and analyzed individually,using different strategies,neural networks,and datasets,and applied to different scenarios.It is thus necessary to do a detailed comparison of these deep-learning-involved methods and the traditional methods in the same context.We first divide the phase dataset generation methods into random matrix enlargement,Gauss matrix superposition,and Zernike polynomials superposition,and then divide the deep-learning-involved phase unwrapping methods into deep-learning-performed regression,deep-learning-performed wrap count,and deep-learningassisted denoising.For the phase dataset generation methods,the richness of the datasets and the generalization capabilities of the trained networks are compared in detail.In addition,the deep-learning-involved methods are analyzed and compared with the traditional methods in ideal,noisy,discontinuous,and aliasing cases.Finally,we give suggestions on the best methods for different situations and propose the potential development direction for the dataset generation method,neural network structure,generalization ability enhancement,and neural network training strategy for the deep-learning-involved spatial phase unwrapping methods.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0307200 and 2017YFA0303800)the National Natural Science Foundations of China(Grant Nos.61522507 and 61775183)+1 种基金the Key Research and Development Program in Shaanxi Province of China(Grant No.2017KJXX-12)the Fundamental Research Funds for the Central Universities(Grant Nos.3102017jc01001 and 3102018jcc034)
文摘We demonstrate a reconfigurable black phosphorus electrical field transistor,which is van der Waals heterostructured with few-layer graphene and hexagonal boron nitride flakes.Varied homojunctions could be realized by controlling both source–drain and top-gate voltages.With the spatially resolved scanning photocurrent microscopy technique,photovoltaic photocurrents originated from the band-bending regions are observed,confirming nine different configurations for each set of fixed voltages.In addition,as a phototransistor,high responsivity(～800 mA/W)and fast response speed(～230μs)are obtained from the device.The reconfigurable van der Waals heterostructured transistors may offer a promising structure towards electrically tunable black phosphorus-based optoelectronic devices.
基金supported by the National Natural Science Foundation of China(NSFC)(12074313,12074312,12174309,and 62175200)National Key R&D Program of China(2017YFA0303800)Fundamental Research Funds for the Central Universities(3102019JC008).
文摘Emerging as a family of waves,Janus waves are known to have“real”and“virtual”components under inversion of the propagation direction.Although tremendous interest has been evoked in vortex beams featuring spiral wavefronts,little research has been devoted to the vortex beam embedded Janus waves,i.e.,Janus vortex beams.We propose a liquid crystal(LC)Pancharatnam–Berry(PB)phase element to demonstrate the realization of the Janus vortex beams and the modulation of the associated orbit angular momentum(OAM)and spin angular momentum(SAM).The generated Janus vortex beams show opposite OAM and SAM states at two distinct foci,revealing a spin-orbit interaction during propagation enabled by the LC PB phase element,which may play special roles in applications such as optical encryption and decryption.Other merits like reconfigurability and flexible switching between Janus vortex beams and autofocusing or autodefocusing vortex beams additionally increase the degree of freedom of manipulating vortex beams.This work provides a platform for tailoring complex structured light and may enrich the applications of vortex beams in classical and quantum optics.
基金The work was supported in part by the National Natural Science Foundation of China(61927810)the Research Grants Council of Hong Kong(GRF 17201620,GRF 17200321,RIF R7003-21)the Hong Kong Innovation and Technology Fund(ITS/148/20).We thank Yi Zhang and Heng Du in CUHK for proofreading.
文摘Phase recovery(PR)refers to calculating the phase of the light field from its intensity measurements.As exemplified from quantitative phase imaging and coherent diffraction imaging to adaptive optics,PR is essential for reconstructing the refractive index distribution or topography of an object and correcting the aberration of an imaging system.In recent years,deep learning(DL),often implemented through deep neural networks,has provided unprecedented support for computational imaging,leading to more efficient solutions for various PR problems.In this review,we first briefly introduce conventional methods for PR.Then,we review how DL provides support for PR from the following three stages,namely,pre-processing,in-processing,and post-processing.We also review how DL is used in phase image processing.Finally,we summarize the work in DL for PR and provide an outlook on how to better use DL to improve the reliability and efficiency of PR.Furthermore,we present a live-updating resource(https://github.com/kqwang/phase-recovery)for readers to learn more about PR.
基金supported by the National Natural Science Foundation of China(No.41907048)The Fundamental Research Funds for the Central Universities,CHD(No.300102260206)The Shannxi Academy of Forestry(No.SXLK2023-02-15).
文摘Check dams have been widely constructed in the Chinese Loess Plateau and has played an important role in controlling soil loss during last 70 years.However,the large-scale and automatic mapping of the check dams and the resulting silted fields are lacking.In this study,we present a novel methodological framework to extract silted fields and to estimate the location of the check dams at a pixel level in the Wuding River catchment by remote sensing and ensemble learning models.The random under-sampling method and 23 features were used to train and validate three ensemble learning models,namely Random Forest,Extreme Gradient Boosting and EasyEnsemble,based on a large number of samples.The established optimal model was then applied to the whole study area to map check dams and silted fields.Our results indicate that the imbalance ratio of the samples has a significant impact on the performance of the models.Validation of the results on the testing set show that the F1-score of silted fields of three models is higher than 0.75 at the pixel level.Finally,we produced a map of silted fields and check dams at 10 m-spatial resolution by the optimal model with an accuracy of ca.90%at the object level.The proposed framework can be used for the large-scale and high-precision mapping of check dams and silted fields,which is of great significance for the monitoring and management of the dynamics of check dams and the quantitative evaluation of their eco-environmental benefits.
基金supported by the National Natural Science Foundation of China (No.12274344)the Natural Science Basic Research Program of Shaanxi (No.2023-JC-YB-563)the Guangdong Basic and Applied Basic Research Foundation (No.2023A1515011517)。
文摘We demonstrate an intracavity self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating(PI-FBG), fabricated by a femtosecond laser with a point-by-point parallel inscription method. The multi-color Q-switched pulses can be always self-synchronized when the group delay differences between neighboring spectra range from-3.4 to 3.4 ps.The starting and evolution dynamics indicate that the saturable absorption effect of the carbon nanotube plays a dual role: synchronously triggering the startup of the pulse at successive colors by active Q-switching and spontaneously compensating to some extent the temporal walk-off of the multi-color pulses through the cross saturable absorption modulation. This work unveils the intracavity self-synchronization mechanism of the multi-color Q-switched pulses and also demonstrates the potential of PI-FBGs for the customizable generation of the synchronized multi-color pulse in a single cavity.
基金supported by the National Natural Science Foundation of China(Nos.61975166,62322510,and 62375223).
文摘The suppression of polarization cross talk in lead zirconate titanate phase modulators as a key error source has been challenging for open-loop fiber optic gyroscopes(FOGs).We developed a polarization-diversity optical frequency domain reflectometry(OFDR)to measure the distributed modulation polarization error in the modulator.The error contributes 8×10^(−6) rad to FOG’s bias instability.Using a UV-fabricated in-fiberλ/4 wave plate and polarization-mode converter with fiber taper technology,the modulation error has been suppressed by 15 dB in assembled FOGs.This approach reduced error with temperature from 25°/h to 0.7°/h,meeting the requirements of control-level gyroscopes with bias errors less than 1°/h.
基金supported by the National Natural Science Foundation of China(No.62175200)the National Key Research and Development Program of China(No.2022YFA1404800).
文摘The miniaturization of spectrometers has received much attention in recent years.The rapid development of metasurfaces has provided a new avenue for creating more compact and lightweight spectrometers.However,most metasurface-based spectrometers operate in the visible light region,with much less research on near-infrared wavelengths.This is possibly caused by the lack of effective metasurface filters for the near-infrared light.We design and fabricate a polarizationinsensitive amorphous silicon metasurface that exhibits unique transmission spectra in parts of the visible and nearinfrared wavelengths.By passing the light to be measured through a metasurface filter array and measuring the transmitted power,we achieve the precise reconstruction of unknown spectra in the visible and near-infrared range(450-950 nm)using an algorithm matched to the filter model.Our approach is a step towards miniaturized spectrometers within the visible-to-near-infrared range based on metasurface filter arrays.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1404800)the National Natural Science Foundation of China(Grant Nos.11974283,61705186,and 11774290)+2 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2020JM-13)the“Double First-Class”Construction Fund Project(Grant No.0206022GH0202)the Fundamental Research Funds for the Central Universities(Grant No.D5000220175)
文摘Optical cavities play crucial roles in enhanced light-matter interaction,light control,and optical communications,but their dimensions are limited by the material property and operating wavelength.Ultrathin planar cavities are urgently in demand for large-area and integrated optical devices.However,extremely reducing the planar cavity dimension is a critical challenge,especially at telecommunication wavelengths.Herein,we demonstrate a type of ultrathin cavities based on large-area grown Bi_(2)Te_(3)topological insulator(TI)nanofilms,which present distinct optical resonance in the near-infrared region.The result shows that the Bi_(2)Te_(3)TI material presents ultrahigh refractive indices of>6 at telecommunication wavelengths.The cavity thickness can approach 1/20 of the resonance wavelength,superior to those of planar cavities based on conventional Si and Ge high refractive index materials.Moreover,we observed an analog of the electromagnetically induced transparency(EIT)effect at telecommunication wavelengths by depositing the cavity on a photonic crystal.The EIT-like behavior is derived from the destructive interference coupling between the nanocavity resonance and Tamm plasmons.The spectral response depends on the nanocavity thickness,whose adjustment enables the generation of obvious Fano resonance.The experiments agree well with the simulations.This work will open a new door for ultrathin cavities and applications of TI materials in light control and devices.
基金supported by the Key Research and Development Program(2022YFA1404800)the National Natural Science Foundation of China(62375226,62375225,12374359,62105267)+1 种基金the Fundamental Research Funds for the Central Universities(23GH02023)the Analytical&Testing Center of Northwestern Polytechnical University and the Australian Research Council.The Australian National Fabrication Facility ACT Node is acknowledged for access to the epitaxial growth facilities.
文摘Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the telecom band.Here,we report on-substrate vertical emitting lasing from ordered InGaAs/InP multi-quantum well core–shell nanowire array epitaxially grown on InP substrate by selective area epitaxy.To reduce optical loss and tailor the cavity mode,a new nanowire facet engineering approach has been developed to achieve controlled quantum well nanowire dimensions with uniform morphology and high crystal quality.Owing to the strong quantum confinement effect of InGaAs quantum wells and the successful formation of a vertical Fabry–Pérot cavity between the top nanowire facet and bottom nanowire/SiO_(2) mask interface,stimulated emissions of the EH11a/b mode from single vertical nanowires from an on-substrate nanowire array have been demonstrated with a lasing threshold of~28.2μJ cm^(−2) per pulse and a high characteristic temperature of~128 K.By fine-tuning the In composition of the quantum wells,room temperature,single-mode lasing is achieved in the vertical direction across a broad near-infrared spectral range,spanning from 940 nm to the telecommunication O and C bands.Our research indicates that through a carefully designed facet engineering strategy,highly ordered,uniform nanowire arrays with precise dimension control can be achieved to simultaneously deliver thousands of nanolasers with multiple wavelengths on the same substrate,paving a promising and scalable pathway towards future advanced optoelectronic and photonic systems.
基金National Natural Science Foundation of China(61927810,62275219).
文摘Surface plasmon resonance microscopy(SPRM)has been massively applied for near-field optical measurement,sensing,and imaging because of its high detection sensitivity,nondestructive,noninvasive,wide-field,and label-free imaging capabilities.However,the transverse propagation characteristic of the surface plasmon wave generated during surface plasmon resonance(SPR)leads to notable“tail”patterns in the SPR image,which severely deteriorates the image quality.Here,we propose an incidence angle scanning method in SPRM to obtain a resonance angle image with exceptional contrast that significantly mitigates the adverse effects of“tail”patterns.The resonance angle image provides the complete morphology of the analyzed samples and enables two-dimensional quantification,which is incapable in conventional SPRM.The effectiveness of the method was experimentally verified using photoresist square samples with different sizes and two-dimensional materials with various geometric shapes.The edges of samples were fully reconstructed and a maximum fivefold increase in the image contrast has been achieved.Our method offers a convenient way to enhance the SPRM imaging capabilities with low cost and stable performance,which greatly expands the applications of SPRM in label-free detection,imaging,and quantification.
