The control of polarization,an essential property of light,is of broad scientific and technological interest.Polarizers are indispensable optical elements for direct polarization generation.However,arbitrary polarizat...The control of polarization,an essential property of light,is of broad scientific and technological interest.Polarizers are indispensable optical elements for direct polarization generation.However,arbitrary polarization generation,except that of common linear and circular polarization,relies heavily on bulky optical components such as cascading linear polarizers and waveplates.Here,we present an effective strategy for designing all-in-one full Poincare sphere polarizers based on perfect arbitrary polarization conversion dichroism and implement it in a monolayer all-dielectric metasurface.This strategy allows preferential transmission and conversion of one polarization state located at an arbitrary position on the Poincare sphere to its handedness-flipped state while completely blocking its orthogonal state.In contrast to previous methods that were limited to only linear or circular polarization,our method manifests perfect dichroism of nearly 100%in theory and greater than 90%experimentally for arbitrary polarization states.By leveraging this attractive dichroism,our demonstration of the generation of polarization beams located at an arbitrary position on a Poincare sphere directly from unpolarized light can substantially extend the scope of meta-optics and dramatically promote state-of-the-art nanophotonic devices.展开更多
We report the development of a head-mounted photoacoustic fiberscope for cerebral imaging in a freely behaving mouse.The 4.5-gram imaging probe has a 9-µm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wi...We report the development of a head-mounted photoacoustic fiberscope for cerebral imaging in a freely behaving mouse.The 4.5-gram imaging probe has a 9-µm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area.The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution,showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state.For example,when subjected to high-concentration CO_(2) respiration,enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state.Comparative studies exhibit significantly weakened compensation capabilities in obese rodents.This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity,disorders and their treatments.展开更多
Photoacoustic imag ing(PAI)is a nonin vasive biomedical imag ing tech no logy capable of multiscale imag ing of biological samples from orga ns dow n to cells.Multiscale PAI requires differe nt ultraso und tra nsducer...Photoacoustic imag ing(PAI)is a nonin vasive biomedical imag ing tech no logy capable of multiscale imag ing of biological samples from orga ns dow n to cells.Multiscale PAI requires differe nt ultraso und tra nsducers that are flat or focused because the current widely-used piezoelectric transducers are rigid and lack the flexibility to tune their spatial ultrasound responses.Inspired by the rapidly-developing flexible photonics,we exploited the inherent flexibility and low-loss features of optical fibers to develop a flexible fiber-laser ultrasound sensor(FUS)for multiscale PAI.By simply bending the fiber laser from straight to curved geometry,the spatial ultraso und resp onse of the FUS can be tuned for both wide-view optical-resolution photoacoustic microscopy at optical diffraction-limited depth(~1 mm)and photoacoustic computed tomography at optical dissipation-limited depth of several centimeters.A radio-frequency demodulation was employed to get the readout of the beat frequency variation of two orthogonal polarization modes in the FUS output,which ensures low-noise and stable ultrasound detection.Compared to traditional piezoelectrical transducers with fixed ultrasound responses once manufactured,the flexible FUS provides the freedom to design multiscale PAI modalities including wearable microscope,intravascular endoscopy,and portable tomography system,which is attractive to fundamental biologic-al/medical studies and clinical applications.展开更多
Interaction of acoustic waves and microbubbles occurs in numerous biomedical applications including ultrasound imaging,drug delivery,lithotripsy treatment,and cell manipulation,wherein the acoustically driven microbub...Interaction of acoustic waves and microbubbles occurs in numerous biomedical applications including ultrasound imaging,drug delivery,lithotripsy treatment,and cell manipulation,wherein the acoustically driven microbub-blcs routincly act as active microscale oscillators or actuators.In contrast,microbubbles were utilized here as passive reccivers to detect broadband ultrasound waves in aqueous environments.The microbubble was photo-thermally generated on a microstructured optical fiber(MOF)tip,forming a flexible Fabry-Perot cavity whose gas-water interface was sensitive to ultrasound waves.The MOF severed as both a low-loss waveguide and a compact light condenser,allowing high-efficiency generation and stabilization of ultrasmall microbubbles.Integrated with all-fiber interferometry,a 10 um diameter microbubble exhibited a low noise-cquivalcnt pressur elevei of^3.4 mPa/Hz^1/2 and a broad bandwidth of^0.8 MHz,capable of detecting weak ultrasounds emittedfrom red blood cells irradiated by pulsed laser light.With advantages of high sensitivity,compact size,and low cost,the microbubble-based ultrasound sensor has great potential in biomedical imaging and sensing applications.展开更多
Obtaining detailed insight into the photocatalytic performance of heterogeneous photocatalytic materials,is important for evaluating material properties as well as guiding material design.However,capture of the detail...Obtaining detailed insight into the photocatalytic performance of heterogeneous photocatalytic materials,is important for evaluating material properties as well as guiding material design.However,capture of the detailed matter changes on a photocatalyst surface in real time,and in situ during photocatalysis remains challenging.This work reports a promising optical microfiber sensor integrating a photocatalytic reaction monolayer on an optical microfiber surface to monitor reaction kinetics using Cu_(2)O-based heterogeneous photocatalysts,as an example.The evanescent field of microfiber is used to track the photocatalytic process in real time,through the interaction with the catalytic layer,by monitoring the surface refractive index changes caused by adsorption and degradation.Since the catalytic layer is less than 1µm thick,the typical high-power light source can be replaced by low-power light irradiation.This method successfully reveals that relative to the pristine Cu_(2)O microspheres,the photocatalytic activity is enhanced by the incorporation of Ti_(3)C_(2)T_(x) MXene into Cu_(2)O,whereas incorporation of CdS into Cu_(2)O suppresses the activity.Compared with the existing methods used for photocatalysis evalu-ation,this optical microfiber can be directly employed in real matrices to track local photocatalytic performance.It can also provide details about the different adsorption/degradation kinetics of photocatalysts.It is suitable for most photocatalytic processes and is not limited to pollutants with characteristic UV–visible absorption spectra.This study provides important inspiration for the future development of in situ,real-time reaction assessment.展开更多
Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of ma...Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing.The discovery of all-optical magnetization reversal in GdFeCo with the help of 100fs laser pulses has further aroused intense interest in this compelling problem.Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching,the latter remains virtually unknown.Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27 Fe63.87 C09.T3.Varying the intensities of the shots and the shotto-shot separation,we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits.It is shown that although magnetic writing launched by the first shot is completed after 100 ps,a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps.Using two shots partially overlapping in space and minimally separated by 300 ps,we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.展开更多
We propose and demonstrate a dual-wavelength single-longitudinal-mode(SLM) fiber laser with switchable wavelength spacing based on a graphene saturable absorber(GSA) and a Wave Shaper. By virtue of the excellent satur...We propose and demonstrate a dual-wavelength single-longitudinal-mode(SLM) fiber laser with switchable wavelength spacing based on a graphene saturable absorber(GSA) and a Wave Shaper. By virtue of the excellent saturable absorption ability of graphene, the linewidths of the lasing wavelengths can be effectively reduced and eventually SLM operation can be obtained. The linewidths of both wavelengths are measured to be narrower than 7.3 kHz. The obtained results suggest that the graphene would be a good candidate nonlinear optical material for applications in related photonic fields, such as SLM oscillation generation for microwave generation and optical sensing.展开更多
Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and com...Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients.The implementation is complicated.In this paper,we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity.By controlling the polarization states of light in the single spatial unit,the localized eigenfrequencies,gain,loss,and coupling coefficients of two polarimetric loops can be tuned,leading to PT symmetry breaking.As a demonstration,a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.展开更多
Auto-regressive （AR） spectral estimation technology is proposed to analyze the Brillouin scattering spectrum in Brillouin optical time-domain refelectometry. It shows that AR based method can reliably estimate the B...Auto-regressive （AR） spectral estimation technology is proposed to analyze the Brillouin scattering spectrum in Brillouin optical time-domain refelectometry. It shows that AR based method can reliably estimate the Brillouin frequency shift with an accuracy much better than fast Fourier transform （FFT） based methods provided the data length is not too short. It enables about 3 times improvement over FFT at a moderate spatial resolution.展开更多
A dual-frequency distributed Bragg reflector （DBR） fiber laser based sensor is demonstrated for low-frequency vibration measurement through the Doppler effect. The response of the proposed sensor is quite linear and...A dual-frequency distributed Bragg reflector （DBR） fiber laser based sensor is demonstrated for low-frequency vibration measurement through the Doppler effect. The response of the proposed sensor is quite linear and is much higher than that of a conventional accelerometer. The proposed sensor can work down to 1 Hz with high sensitivity. Therefore, the proposed sensor is very efficient in low-frequency vibration measurement.展开更多
A wavelength-swept fiber laser is proposed and successfully demonstrated based on a bidirectional used linear chirped fiber Bragg grating(LC-FBG). The wavelength-swept operation principle is based on intracavity pulse...A wavelength-swept fiber laser is proposed and successfully demonstrated based on a bidirectional used linear chirped fiber Bragg grating(LC-FBG). The wavelength-swept operation principle is based on intracavity pulse stretching and compression. The LC-FBG can introduce equivalent positive and negative dispersion simultaneously, which enables a perfect dispersion matching to obtain wide-bandwidth mode-locking. Experimental results demonstrate a wavelength-swept fiber laser that exhibits a sweep rate of about 5.4 MHz over a 2.1 nm range at a center wavelength of 1550 nm. It has the advantages of simple configuration and perfect dispersion matching in the laser cavity.展开更多
A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin.The alternating c...A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin.The alternating current generates Ampere force in a magnetic field,which changes the birefringence of the fiber laser and hence tunes the frequency of the beat signal after photodetection.The magnetic flux density can then be detected by measuring the frequency change of the beat signal.The sensitivity of the sensor can be tuned with a maximum response of 35.21 kHz/kGs demonstrated.Moreover,the sensor shows good immunity to environment interference.展开更多
Immunosensor is a powerful tool in healthcare and clinic,food and drug industry,and environmental protection.Label-free fiber-optic immunosensors have shown a myriad of advantages,such as high sensitivity,anti-electro...Immunosensor is a powerful tool in healthcare and clinic,food and drug industry,and environmental protection.Label-free fiber-optic immunosensors have shown a myriad of advantages,such as high sensitivity,anti-electromagnetic interference,and afield measurement via the fiber network.However,the fiber-optic based sensor may bear the temperature cross-talk,especially under the warming condition for bio-activating the immune molecules.In this study,we proposed a highly birefringent microfiber Bragg grating for immunosensing with the temperature-compensation.The birefringent microfiber was drawn from the elliptical cladding multimode fiber that was ablated by the CO2 laser.The considerably large energy overlap region offered by the original multimode fiber favored the efficient inscription of FBG with high reflectivity.The dual reso-nances derived by the orthogonal polarization states presented similar temperature responsivities but significantly different ambient refractive index sensitivities,allowing the temperature-compensational RI sensing.The human immunoglobulin G(IgG)molecules were anchored on the surface of the microfiber grating probe by the covalent functionalization technique to enable the specific detection of the anti-IgG molecule.The proposed method promises a high-efficiency and low-cost design for the microfiber Bragg grating-based biosensor without being subjected to the temperature cross-sensitivity.展开更多
In this study,a virtual-point concept was introduced into fiber-laser photoacoustic tomography to improve the elevational image resolution.The flexible fiber laser was bent into an arc shape to conform to the ultrasou...In this study,a virtual-point concept was introduced into fiber-laser photoacoustic tomography to improve the elevational image resolution.The flexible fiber laser was bent into an arc shape to conform to the ultrasound wavefront,which formed an ultrasound focus at the center of the arc.The synthetic aperture focusing technique was utilized to reconstruct the images;as a result,the elevational resolution particularly within the out-of-focus region was considerably improved compared to the resolution of an image retrieved by multiplexing the PA time-resolved signals with sound velocity.The all-optical fiber-laser photoacoustic tomography system with a high spatial resolution has potential for various applications,including biomedical research and preclinical/clinical diagnosis.展开更多
We demonstrate a compact and high-resolution dual-polarization fiber laser accelerometer. A spring-mass like scheme is constructed by fixing a 10-gram proof mass on the laser cavity to transduce applied vibration into...We demonstrate a compact and high-resolution dual-polarization fiber laser accelerometer. A spring-mass like scheme is constructed by fixing a 10-gram proof mass on the laser cavity to transduce applied vibration into beat-frequency change. The loading is located at the intensity maximum of intracavity light to maximize the optical response. The detection limit reaches 107 ng/Hz1/2 at 200 Hz. The working bandwidth ranges from 60 Hz to 600 Hz.展开更多
We report on fiber Bragg gratings in all-solid photonie bandgap fiber that was composed of a triangular array of high-index Ge-doped rods in pure silica background with fluorine-doped index-depressed layer surrounding...We report on fiber Bragg gratings in all-solid photonie bandgap fiber that was composed of a triangular array of high-index Ge-doped rods in pure silica background with fluorine-doped index-depressed layer surrounding the Ge-doped rod. Fiber Bragg gratings were photowritten with 193 nm ArF excimer laser and characterized for their response to strain, temperature, bending, and torsion. These gratings couple light from the forward core mode to not only backward core mode but also backward rod modes. This results in multiple resonance peaks in the reflection spectrum. All resonance wavelengths exhibited the same temperature and strain response with coefficient similar to that of Bragg gratings in standard single-mode fiber. The strength of the resonance peaks corresponding to the backward rod modes showed high sensitivity to bending and torsion.展开更多
基金supported by the National Key R&D Program of China(2018YFB1107200)the National Natural Science Foundation of China(NSFC)(Grants 62075084,61522504,61420106014,11734012,and 11574218)+3 种基金the Guangdong Provincial Innovation and Entrepreneurship Project(Grant 2016ZT06D081)the Guangdong Basic and Applied Basic Research Foundation(2020A1515010615)the Fundamental Research Funds for the Central Universities(21620415)the China Scholarship Council(201906785011).
文摘The control of polarization,an essential property of light,is of broad scientific and technological interest.Polarizers are indispensable optical elements for direct polarization generation.However,arbitrary polarization generation,except that of common linear and circular polarization,relies heavily on bulky optical components such as cascading linear polarizers and waveplates.Here,we present an effective strategy for designing all-in-one full Poincare sphere polarizers based on perfect arbitrary polarization conversion dichroism and implement it in a monolayer all-dielectric metasurface.This strategy allows preferential transmission and conversion of one polarization state located at an arbitrary position on the Poincare sphere to its handedness-flipped state while completely blocking its orthogonal state.In contrast to previous methods that were limited to only linear or circular polarization,our method manifests perfect dichroism of nearly 100%in theory and greater than 90%experimentally for arbitrary polarization states.By leveraging this attractive dichroism,our demonstration of the generation of polarization beams located at an arbitrary position on a Poincare sphere directly from unpolarized light can substantially extend the scope of meta-optics and dramatically promote state-of-the-art nanophotonic devices.
基金support from the National Natural Science Foundation of China(62275104 and 62322506)L.J.acknowledges the financial support from the National Natural Science Foundation of China(62122031)+1 种基金B.-O.G.acknowledges the financial support from the National Natural Science Foundation of China(62135006 and 61860206002)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(2019BT02X105).
文摘We report the development of a head-mounted photoacoustic fiberscope for cerebral imaging in a freely behaving mouse.The 4.5-gram imaging probe has a 9-µm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area.The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution,showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state.For example,when subjected to high-concentration CO_(2) respiration,enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state.Comparative studies exhibit significantly weakened compensation capabilities in obese rodents.This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity,disorders and their treatments.
基金This work was supported by the National Natural Science Foundation of China(61775083,61705082,61805102,and 61860206002)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(2019BT02X105)Guangzhou Science and Technology Plan(201904020032).
文摘Photoacoustic imag ing(PAI)is a nonin vasive biomedical imag ing tech no logy capable of multiscale imag ing of biological samples from orga ns dow n to cells.Multiscale PAI requires differe nt ultraso und tra nsducers that are flat or focused because the current widely-used piezoelectric transducers are rigid and lack the flexibility to tune their spatial ultrasound responses.Inspired by the rapidly-developing flexible photonics,we exploited the inherent flexibility and low-loss features of optical fibers to develop a flexible fiber-laser ultrasound sensor(FUS)for multiscale PAI.By simply bending the fiber laser from straight to curved geometry,the spatial ultraso und resp onse of the FUS can be tuned for both wide-view optical-resolution photoacoustic microscopy at optical diffraction-limited depth(~1 mm)and photoacoustic computed tomography at optical dissipation-limited depth of several centimeters.A radio-frequency demodulation was employed to get the readout of the beat frequency variation of two orthogonal polarization modes in the FUS output,which ensures low-noise and stable ultrasound detection.Compared to traditional piezoelectrical transducers with fixed ultrasound responses once manufactured,the flexible FUS provides the freedom to design multiscale PAI modalities including wearable microscope,intravascular endoscopy,and portable tomography system,which is attractive to fundamental biologic-al/medical studies and clinical applications.
基金Guangzhou Scicnce and Technology Plan Project(201904020032)The Local Innowative and Research leams Project of Guangdong Pearl River Talents Program(2019BT02X105)+3 种基金National Natural Science Foundation of China(61705082,U1701268)Natural Science Foundation of Guangdong Province(2017A030313361,2018030310587)Fundlamental Research Funds for the Central Universiies(21617304)Province High-Level Talents Introduction Plan(2017GCO10420).
文摘Interaction of acoustic waves and microbubbles occurs in numerous biomedical applications including ultrasound imaging,drug delivery,lithotripsy treatment,and cell manipulation,wherein the acoustically driven microbub-blcs routincly act as active microscale oscillators or actuators.In contrast,microbubbles were utilized here as passive reccivers to detect broadband ultrasound waves in aqueous environments.The microbubble was photo-thermally generated on a microstructured optical fiber(MOF)tip,forming a flexible Fabry-Perot cavity whose gas-water interface was sensitive to ultrasound waves.The MOF severed as both a low-loss waveguide and a compact light condenser,allowing high-efficiency generation and stabilization of ultrasmall microbubbles.Integrated with all-fiber interferometry,a 10 um diameter microbubble exhibited a low noise-cquivalcnt pressur elevei of^3.4 mPa/Hz^1/2 and a broad bandwidth of^0.8 MHz,capable of detecting weak ultrasounds emittedfrom red blood cells irradiated by pulsed laser light.With advantages of high sensitivity,compact size,and low cost,the microbubble-based ultrasound sensor has great potential in biomedical imaging and sensing applications.
基金Funding National Natural Science Foundation of China,51773084,Yunyun Huang,U1701268,Bai-Ou Guan,Natural Science Foundation of Guangdong Province,2019A1515011278,Yunyun Huang,Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program,2019BT02X105,Bai-Ou Guan,Special Funds for the Cultivation of Guangdong College Students'Scientific and Technological Innovation,pdjh2020a0061,Jiaxuan Liang,Undergraduate Innovation and Entrepreneurship Program,202010559050,Jiaxin Wan.
文摘Obtaining detailed insight into the photocatalytic performance of heterogeneous photocatalytic materials,is important for evaluating material properties as well as guiding material design.However,capture of the detailed matter changes on a photocatalyst surface in real time,and in situ during photocatalysis remains challenging.This work reports a promising optical microfiber sensor integrating a photocatalytic reaction monolayer on an optical microfiber surface to monitor reaction kinetics using Cu_(2)O-based heterogeneous photocatalysts,as an example.The evanescent field of microfiber is used to track the photocatalytic process in real time,through the interaction with the catalytic layer,by monitoring the surface refractive index changes caused by adsorption and degradation.Since the catalytic layer is less than 1µm thick,the typical high-power light source can be replaced by low-power light irradiation.This method successfully reveals that relative to the pristine Cu_(2)O microspheres,the photocatalytic activity is enhanced by the incorporation of Ti_(3)C_(2)T_(x) MXene into Cu_(2)O,whereas incorporation of CdS into Cu_(2)O suppresses the activity.Compared with the existing methods used for photocatalysis evalu-ation,this optical microfiber can be directly employed in real matrices to track local photocatalytic performance.It can also provide details about the different adsorption/degradation kinetics of photocatalysts.It is suitable for most photocatalytic processes and is not limited to pollutants with characteristic UV–visible absorption spectra.This study provides important inspiration for the future development of in situ,real-time reaction assessment.
基金We are grateful to Dr.Dmytro V.Afanasiev,Tonnie Toonen,Dr.Bowen Jiang,and Dr.Sergey Semin for their professional technical support This research is financially supported by the National Key R&D Program of China(2018YFB1107200)Ministry of Science and Technology of the Peopled Republic of China(MOST)(Grant numbers 2016丫FA0300802 and 2018YFE0109200)+6 种基金National Natural Science Foundation of China(NSFC)(61975066 and 11604123)Guangdong Basic and Applied Basic Research Foundation(2019A1515010864)Fundamental Research Funds for the Central Universities(21620413)Guangdong Provincial Innovation and Entrepreneurship Project(Grant 2016ZT06D081)Grant-in-Aid for Scientific Research on Innovative Area,Nano Spin Conversion Science1(Grant number 26103005)‘Nano Spin Conversion Science'(Grant number 26103004)European Research Council ERC,Grant agreement number 339813(Exchange),and Netherlands Organization for Scientific Research(NWO).
文摘Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing.The discovery of all-optical magnetization reversal in GdFeCo with the help of 100fs laser pulses has further aroused intense interest in this compelling problem.Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching,the latter remains virtually unknown.Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27 Fe63.87 C09.T3.Varying the intensities of the shots and the shotto-shot separation,we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits.It is shown that although magnetic writing launched by the first shot is completed after 100 ps,a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps.Using two shots partially overlapping in space and minimally separated by 300 ps,we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.
基金supported by the National Natural Science Foundation of China (No. 61475065)
文摘We propose and demonstrate a dual-wavelength single-longitudinal-mode(SLM) fiber laser with switchable wavelength spacing based on a graphene saturable absorber(GSA) and a Wave Shaper. By virtue of the excellent saturable absorption ability of graphene, the linewidths of the lasing wavelengths can be effectively reduced and eventually SLM operation can be obtained. The linewidths of both wavelengths are measured to be narrower than 7.3 kHz. The obtained results suggest that the graphene would be a good candidate nonlinear optical material for applications in related photonic fields, such as SLM oscillation generation for microwave generation and optical sensing.
基金supported by the National Natural Science Foundation of China(61860206002,61905095,61805103).
文摘Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients.The implementation is complicated.In this paper,we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity.By controlling the polarization states of light in the single spatial unit,the localized eigenfrequencies,gain,loss,and coupling coefficients of two polarimetric loops can be tuned,leading to PT symmetry breaking.As a demonstration,a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 11474133 and 61235005） and Science and Technology Program of Guangzhou （No. 201707010338）.
文摘Auto-regressive （AR） spectral estimation technology is proposed to analyze the Brillouin scattering spectrum in Brillouin optical time-domain refelectometry. It shows that AR based method can reliably estimate the Brillouin frequency shift with an accuracy much better than fast Fourier transform （FFT） based methods provided the data length is not too short. It enables about 3 times improvement over FFT at a moderate spatial resolution.
基金Acknowledgment This work was supported by the National Natural Science Foundation of China （Grant Nos. 11474133 and 61235005）, Natural Science Foundation of Guangdong Province of China （No. 2014A030310419）, and the Guangzhou Key Collaborative Innovation Foundation of China （No.
文摘A dual-frequency distributed Bragg reflector （DBR） fiber laser based sensor is demonstrated for low-frequency vibration measurement through the Doppler effect. The response of the proposed sensor is quite linear and is much higher than that of a conventional accelerometer. The proposed sensor can work down to 1 Hz with high sensitivity. Therefore, the proposed sensor is very efficient in low-frequency vibration measurement.
基金National Natural Science Foundation of China(NSFC)(61475065)Natural Science Foundation of Guangdong Province(2015A030313322)
文摘A wavelength-swept fiber laser is proposed and successfully demonstrated based on a bidirectional used linear chirped fiber Bragg grating(LC-FBG). The wavelength-swept operation principle is based on intracavity pulse stretching and compression. The LC-FBG can introduce equivalent positive and negative dispersion simultaneously, which enables a perfect dispersion matching to obtain wide-bandwidth mode-locking. Experimental results demonstrate a wavelength-swept fiber laser that exhibits a sweep rate of about 5.4 MHz over a 2.1 nm range at a center wavelength of 1550 nm. It has the advantages of simple configuration and perfect dispersion matching in the laser cavity.
基金supported in part by the National Natural Science Foundation of China(NSFC)(Grant Nos.61875246 and 61675091)the Science and Technology Plan of Guangzhou(Grant No.201707010338).
文摘A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin.The alternating current generates Ampere force in a magnetic field,which changes the birefringence of the fiber laser and hence tunes the frequency of the beat signal after photodetection.The magnetic flux density can then be detected by measuring the frequency change of the beat signal.The sensitivity of the sensor can be tuned with a maximum response of 35.21 kHz/kGs demonstrated.Moreover,the sensor shows good immunity to environment interference.
基金supported by National Natural Science Foundation of China(61775082,U1701268,61405074,61805106)Guangdong Natural Science Foundation(2015A030313324,2018A030313677)+2 种基金the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(2019BT02X105)Youth Top-notch Scientific and Technological Innovation Talent of Guangdong Special Support Plan(2019TQ05X136)the Fundamental Research Funds for the Central Universities.
文摘Immunosensor is a powerful tool in healthcare and clinic,food and drug industry,and environmental protection.Label-free fiber-optic immunosensors have shown a myriad of advantages,such as high sensitivity,anti-electromagnetic interference,and afield measurement via the fiber network.However,the fiber-optic based sensor may bear the temperature cross-talk,especially under the warming condition for bio-activating the immune molecules.In this study,we proposed a highly birefringent microfiber Bragg grating for immunosensing with the temperature-compensation.The birefringent microfiber was drawn from the elliptical cladding multimode fiber that was ablated by the CO2 laser.The considerably large energy overlap region offered by the original multimode fiber favored the efficient inscription of FBG with high reflectivity.The dual reso-nances derived by the orthogonal polarization states presented similar temperature responsivities but significantly different ambient refractive index sensitivities,allowing the temperature-compensational RI sensing.The human immunoglobulin G(IgG)molecules were anchored on the surface of the microfiber grating probe by the covalent functionalization technique to enable the specific detection of the anti-IgG molecule.The proposed method promises a high-efficiency and low-cost design for the microfiber Bragg grating-based biosensor without being subjected to the temperature cross-sensitivity.
基金This research was supported by the National Natural Science Foundation of China(NSFC)(61705082,U1701268)Natural Science Foundation of Guangdong Province(2018030310587)+1 种基金Fundamental Research Funds for the Central Universities(21617304)Guangdong Province High-Level Talents Introduction Plan(2017GC010420).
文摘In this study,a virtual-point concept was introduced into fiber-laser photoacoustic tomography to improve the elevational image resolution.The flexible fiber laser was bent into an arc shape to conform to the ultrasound wavefront,which formed an ultrasound focus at the center of the arc.The synthetic aperture focusing technique was utilized to reconstruct the images;as a result,the elevational resolution particularly within the out-of-focus region was considerably improved compared to the resolution of an image retrieved by multiplexing the PA time-resolved signals with sound velocity.The all-optical fiber-laser photoacoustic tomography system with a high spatial resolution has potential for various applications,including biomedical research and preclinical/clinical diagnosis.
基金This work is supported by the National Natural Science Foundation of China （Nos. 61235005 and 11474133）, Guangdong Natural Science Foundation （No. $2013030013302）, and the Planned Science ＆ Technology Project of Guangzhou （Nos. 2012J510028 and 2014J2200003）. L. Jin is supported by the Department of Education, Guangdong Province （No. Yq2013021） and by Open Fund of the Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques （South China University of Technology）.
文摘We demonstrate a compact and high-resolution dual-polarization fiber laser accelerometer. A spring-mass like scheme is constructed by fixing a 10-gram proof mass on the laser cavity to transduce applied vibration into beat-frequency change. The loading is located at the intensity maximum of intracavity light to maximize the optical response. The detection limit reaches 107 ng/Hz1/2 at 200 Hz. The working bandwidth ranges from 60 Hz to 600 Hz.
基金supported by the Key Project of National Natural Science Foundation of China under Grant No. 60736039.
文摘We report on fiber Bragg gratings in all-solid photonie bandgap fiber that was composed of a triangular array of high-index Ge-doped rods in pure silica background with fluorine-doped index-depressed layer surrounding the Ge-doped rod. Fiber Bragg gratings were photowritten with 193 nm ArF excimer laser and characterized for their response to strain, temperature, bending, and torsion. These gratings couple light from the forward core mode to not only backward core mode but also backward rod modes. This results in multiple resonance peaks in the reflection spectrum. All resonance wavelengths exhibited the same temperature and strain response with coefficient similar to that of Bragg gratings in standard single-mode fiber. The strength of the resonance peaks corresponding to the backward rod modes showed high sensitivity to bending and torsion.
