Research on supercontinuum sources on silicon has made significant progress in the past few decades.However,conventional approaches to broaden the spectral bandwidth often rely on complex and critical dispersion engin...Research on supercontinuum sources on silicon has made significant progress in the past few decades.However,conventional approaches to broaden the spectral bandwidth often rely on complex and critical dispersion engineering by optimizing the core thickness or introducing the cladding with special materials and structures.We propose and demonstrate supercontinuum generation using long-periodgrating(LPG)waveguides on silicon with a C-band pump.The LPG waveguide is introduced for quasi-phase matching,and the generated supercontinuum spectrum is improved greatly with grating-induced dispersive waves.In addition,the demonstrated LPG waveguide shows a low propagation loss comparable with regular silicon photonic waveguides without gratings.In experiments,when using a 1550-nm 75-fs pulse pump with a pulse energy of 200 pJ,the supercontinuum spectrum generated with the present LPG waveguide shows an ultrabroad extent from 1150 to 2300 nm,which is much wider by 200 nm than that achieved by dispersionengineered uniform silicon photonic waveguides on the same chip.This provides a promising option for on-chip broadband light source for silicon photonic systems.展开更多
A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etchin...A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etching depth.Thinning of the p-side waveguide layer makes the light field bias to the n-side cladding layer.By coordinating the confinement effect of the cladding layer,the light confinement factor on the p-side is regulated.On the other hand,the introduction of a mode expansion layer facilitates the expansion of the mode profile on the p side cladding layer.Both these factors contribute positively to reducing the grating etching depth.Compared to the reported epitaxial structures of symmetric waveguides,the new structure significantly reduces the etching depth of the grating while ensuring adequate reflection intensity and maintaining resonance.Moreover,to improve the output performance of the device,the new epitaxial structure has been optimized.Based on the traditional epitaxial structure,an energy release layer and an electron blocking layer are added to improve the electronic recombination efficiency.This improved structure has an output performance comparable to that of a symmetric waveguide,despite being able to have a smaller gain area.展开更多
Aiming at the requirement for high-precision tilt monitoring in the field of structural health monitoring(SHM),this paper proposes a sensitivity-enhanced tilt sensor based on a femtosecond fiber Bragg grating(FBG).Fir...Aiming at the requirement for high-precision tilt monitoring in the field of structural health monitoring(SHM),this paper proposes a sensitivity-enhanced tilt sensor based on a femtosecond fiber Bragg grating(FBG).Firstly,structural design of the tilt sensor was conducted based on static mechanics principles.By positioning the FBG away from the beam’s neutral axis,linear strain enhancement in the FBG was achieved,thereby improving sensor sensitivity.The relationship between FBG strain,applied force,and the offset distance from the neutral axis was established,determining the optimal distance corresponding to maximum strain.Based on this optimization scheme,a prototype of the tilt sensor was designed,fabricated,and experimentally tested.Experimental results show that the FBG offset distance yielding maximum sensitivity is 4.4 mm.Within a tilt angle range of−30°to 30°,the sensor achieved a sensitivity of 129.95 pm/°and a linearity of 0.9997.Compared to conventional FBG-based tilt sensors,both sensitivity and linearity were significantly improved.Furthermore,the sensor demonstrated excellent repeatability(error<0.94%),creep resistance(error<0.30%),and temperature stability(error<0.90%).These results demonstrate the sensor’s excellent potential for SHM applications.The sensor has been successfully deployed in an underground pipeline project,conducting long-term monitoring of tilt and deformation in the steel support structures,further proving its value for engineering safety monitoring.展开更多
Long-period fiber gratings have the advantages of small size,corrosion resistance,anti-electro-magnetic interference,and high sensitivity,making them widely used in biomedicine,the power industry,and aerospace.This pa...Long-period fiber gratings have the advantages of small size,corrosion resistance,anti-electro-magnetic interference,and high sensitivity,making them widely used in biomedicine,the power industry,and aerospace.This paper develops a long-period fiber grating sensor based on periodic microchannels.First,a series of linear structures were etched in the cladding of a single-mode fiber by femtosecond laser microma-chining.Then,the laser-modified region was selectively eroded by selective chemical etching to obtain the periodic microchannel structure.Finally,the channels were filled with polydimethylsiloxane(PDMS)to im-prove the spectral quality.The experimental results show that the sensor has good sensitivity in the measure-ment of various parameters such as temperature,stress,refractive index(RI),and bending.It has a temperat-ure sensitivity of−55.19 pm/℃,a strain sensitivity of−3.19 pm/με,a maximum refractive index sensitivity of 540.28 nm/RIU,and a bending sensitivity of 2.65 dB/m^(-1).All of the measurement parameters show good lin-ear responses.The sensor has strong application prospects in the field of precision measurement and sensing.展开更多
There is limited amount of research on surface plasmon resonance(SPR)sensors with self-referencing capabilities which are based on dielectric gratings.In the short-wavelength range,a metal grating sensor is capable of...There is limited amount of research on surface plasmon resonance(SPR)sensors with self-referencing capabilities which are based on dielectric gratings.In the short-wavelength range,a metal grating sensor is capable of simultaneously measuring liquid refractive index under proposed temperature.A fabricated gold grating is placed on one side of a thin gold film for refractive index measurement,while the other with polydimethylsiloxane(PDMS)is deposited on the other side for temperature measurement.We use finite element analysis to research its sensing characteristics.Due to the high refractive index sensitivity of SPR sensors and thermo-optic coefficient of PDMS,we discovered the maximum spectral sensitivity of the sensor is 564 nm/RIU and-50 pm/℃when the liquid refractive index ranges from 1.30 to 1.40 with temperature ranging from 0℃ to 100℃.Numerical results indicate that there may not be mutual interference between two channels for measuring refractive index and temperature,which reduces the complexity of sensor measurements.展开更多
We proposed and demonstrated the ultra-compact 1310/1550 nm wavelength multiplexer/demultiplexer assisted by subwavelength grating(SWG)using particle swarm optimization(PSO)algorithm in silicon-on-insulator(SOI)platfo...We proposed and demonstrated the ultra-compact 1310/1550 nm wavelength multiplexer/demultiplexer assisted by subwavelength grating(SWG)using particle swarm optimization(PSO)algorithm in silicon-on-insulator(SOI)platform.Through the self-imaging effect of multimode interference(MMI)coupler,the demultiplexing function for 1310 nm and 1550 nm wavelengths is implemented.After that,three parallel SWG-based slots are inserted into the MMI section so that the effective refractive index of the modes can be engineered and thus the beat length can be adjusted.Importantly,these three SWG slots significantly reduce the length of the device,which is much shorter than the length of traditional MMI-based wavelength demultiplexers.Ultimately,by using the PSO algorithm,the equivalent refractive index and width of the SWG in a certain range are optimized to achieve the best performance of the wavelength demultiplexer.It has been verified that the device footprint is only 2×30.68μm^(2),and 1 dB bandwidths of larger than 120 nm are acquired at 1310 nm and 1550 nm wavelengths.Meanwhile,the transmitted spectrum shows that the insertion loss(IL)values are below 0.47 dB at both wavelengths when the extinction ratio(ER)values are above 12.65 dB.This inverse design approach has been proved to be efficient in increasing bandwidth and reducing device length.展开更多
Metal micro-nano grating has received much attention due to its ability to provide high-efficiency light absorption.However,the current research scales of these metal gratings are focused on subwavelengths,and little ...Metal micro-nano grating has received much attention due to its ability to provide high-efficiency light absorption.However,the current research scales of these metal gratings are focused on subwavelengths,and little attention has been paid to the absorption properties of metal gratings at other scales.We investigate the absorption properties of metal gratings based on surface plasmon resonance(SPR)across the scales from superwavelength to subwavelength.Under grazing incidence,we observe continuous strong absorption phenomena from superwavelength to subwavelength Al triangle-groove gratings(TGGs).Perfect absorption is realized at the subwavelength scale,whereas the maximum absorption at all other scales exceeds 74%.The electric field distribution gives the mechanism of the strong absorption phenomenon attributed to SPR on the surface of Al TGGs at different scales.In particular,subwavelength Al TGGs have perfectly symmetric absorption properties for different blaze angles,and the symmetry is gradually broken as the grating period’s scale increases.Furthermore,taking Al gratings with varying groove shapes for example,we extend the equivalence rule of grating grooves to subwavelength from near-wavelength and explain the symmetric absorption properties in Al TGGs.We unify the research of metal grating absorbers outside the subwavelength scale to a certain extent,and these findings also open new perspectives for the design of metal gratings in the future.展开更多
With the advantage of high light intensity due to low scatting, structural colors generated by metallic diffraction nanograting structures, used as a type of diffractive optical element, have shown great potential for...With the advantage of high light intensity due to low scatting, structural colors generated by metallic diffraction nanograting structures, used as a type of diffractive optical element, have shown great potential for application in industrial and scientific research fields such as optical anti-counterfeiting and sensors. Within the visible light wavelength range, the diffraction performance is highly dependent on the height and shape consistencies of the nanograting. However, there is still room for the improvement in the flexible control over structure formation through mechanical nanomachining within this scale. The novelty of this paper lies in proposing a machining strategy for nanograting structures with variable heights through precise regulation of the revolving trajectory using tip-based nano down-milling. It explores how different geometric features of trajectories impact the amount of material deformed into a grating and its distribution shape, referred to as undeformed grating area. By analyzing the forming mechanisms of nanogratings under various trajectories with finite element simulation, the desired undeformed grating area is successfully achieved, which is mainly extruded by the tip flank face to form the right facet of the grating, resulting in a small deformation degree and a high deformation efficiency. Three distinct types of revolving trajectories are filtered out according to five quantitative evaluation indicators for machining performance, namely material plastic deformation, grating profile consistency, grating height consistency, machining forces, and area transforming height, and then are compared in processing nanogratings with different heights. It is obtained that only by regulating the vertical vibration amplitude of the revolving trajectory, the semicircle trajectory with the optimal geometric features has the ability to machine high-quality nanograting structures with a continuous height variation of up to 220 nm in a spacing of 400 nm.展开更多
A compact and highly sensitive gas pressure and temperature sensor based on Fabry-Pérot interferometer(FPI)and fiber Bragg grating(FBG)is proposed and demonstrated experimentally in this paper.The theoretical mod...A compact and highly sensitive gas pressure and temperature sensor based on Fabry-Pérot interferometer(FPI)and fiber Bragg grating(FBG)is proposed and demonstrated experimentally in this paper.The theoretical model for pressure and temperature sensing is established.Building on this foundation,a novel micro silicon cavity sensor structure sensitive to pressure is devised downstream of an FBG.The concept of separate measurement and the mechanisms enhancing pressure sensitivity are meticulously analyzed,and the corresponding samples are fabricated.The experimental results indicate that the pressure sensitivity of the sensor is-747.849 nm/MPa in 0—100 k Pa and its linearity is 99.7%and it maintains good stability in 150 min.The sensor offers the advantages of compact size,robust construction,easy fabrication,and high sensitivity,making it potentially valuable for micro-pressure application.展开更多
To enhance the quality factor and sensitivity of refractive index sensors,a feedback waveguide slot grating micro-ring resonator was proposed.An air-hole grating structure was introduced based on the slot micro-ring,u...To enhance the quality factor and sensitivity of refractive index sensors,a feedback waveguide slot grating micro-ring resonator was proposed.An air-hole grating structure was introduced based on the slot micro-ring,utilizing the reflection of the grating to achieve the electromagnetic-like induced transparency effect at different wavelengths.The high slope characteristics of the EIT-like effect enabled a higher quality factor and sensitivity.The transmission principle of the structure was analyzed using the transmission matrix method,and the transmission spectrum and mode field distribution were simulated using the finite-difference time-domain(FDTD)method,and the device structure parameters were adjusted for optimization.Simulation results show that the proposed structure achieves an EIT-like effect with a quality factor of 59267.5.In the analysis of refractive index sensing characteristics,the structure exhibits a sensitivity of 408.57 nm/RIU and a detection limit of 6.23×10^(-5) RIU.Therefore,the proposed structure achieved both a high quality factor and refractive index sensitivity,demonstrating excellent sensing performance for applications in environmental monitoring,biomedical fields,and other areas with broad market potential.展开更多
Metasurfaces composed of two-dimensional nanopillar arrays can manipulate light fields in desirable ways and exhibit the unique advantage of beam steering.Here,we experimentally demonstrate a metasurface-based wide-an...Metasurfaces composed of two-dimensional nanopillar arrays can manipulate light fields in desirable ways and exhibit the unique advantage of beam steering.Here,we experimentally demonstrate a metasurface-based wide-angle broadband all-dielectric blazed grating with an extreme incident angle of up to 80°,which is achieved by optimizing the wide-angle phase shifts and transmissivities of the unit cells.It exhibits a maximum diffraction efficiency of 72%and a high average efficiency of 64%over a wide range of incident angles from−80° to 45° at 1.55μm.Moreover,the proposed grating has a broad bandwidth of 200 nm(1.45-1.65μm),and average efficiencies of more than 50%can be achieved experimentally over the same incidence angles.Our results may pave the way for the creation of novel and efficient flat optical devices for wavefront control.展开更多
Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term ...Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term axle counting system monitoring.Design/methodology/approach–Wheel–rail mechanical behavior was simulated via finite element analysis(FEA)to determine optimal sensor placement.A clip-on composite sensor was subsequently engineered.Stress transduction efficacy was validated through FEA quantification of stress responses at the axle counter location.Findings–The proposed FBG axle counter integrates temperature compensation and anti-detachment monitoring as well as advantages such as simplified installation with minimal maintenance and sustained operational reliability.It effectively transmits stress,yielding a measured strain of 39μe under static loading conditions without sensitivity-enhancing elements.Originality/value–This study performs FEA of wheel-rail stress distribution and engineers the dual-slot composite sensor,FEAwas conducted to quantify the stress magnitude at the axle sensor position of the dual-slot composite sensor.Additionally,FEA was performed on sensors with different structural configurations,including adjustments to the axle sensor position,number of slots and axle position.The results confirmed that the designed composite sensor exhibits superior stress transfer characteristics.展开更多
We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW...We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.展开更多
In response to the shortcomings of the common encoders in the industry,of which the photoelectric encoders have a poor anti-interference ability in harsh industrial environments with water,oil,dust,or strong vibration...In response to the shortcomings of the common encoders in the industry,of which the photoelectric encoders have a poor anti-interference ability in harsh industrial environments with water,oil,dust,or strong vibrations and the magnetic encoders are too sensitive to magnetic field density,this paper designs a new differential encoder based on the grating eddy-current measurement principle,abbreviated as differential grating eddy-current encoder(DGECE).The grating eddy-current of DGECE consists of a circular array of trapezoidal reflection conductors and 16 trapezoidal coils with a special structure to form a differential relationship,which are respectively located on the code plate and the readout plate designed by a printed circuit board.The differential structure of DGECE corrects the common mode interference and the amplitude distortion due to the assembly to some extent,possesses a certain anti-interference capability,and greatly simplifies the regularization algorithm of the original data.By means of the corresponding readout circuit and demodulation algorithm,the DGECE can convert the periodic impedance variation of 16 coils into an angular output within the 360°cycle.Due to its simple manufacturing process and certain interference immunity,DGECE is easy to be integrated and mass-produced as well as applicable in the industrial spindles,especially in robot joints.This paper presents the measurement principle,implementation methods,and results of the experiment of the DGECE.The experimental results show that the accuracy of the DGECE can reach 0.237%and the measurement standard deviation can reach±0.14°within360°cycle.展开更多
A multi-wavelength and transversely mode-switchable fiber laser based on a ring-core fiber Bragg grating(RCFBG) is proposed. Two RCFBGs with high and low reflectivity are inscribed using a femtosecond laser and the ph...A multi-wavelength and transversely mode-switchable fiber laser based on a ring-core fiber Bragg grating(RCFBG) is proposed. Two RCFBGs with high and low reflectivity are inscribed using a femtosecond laser and the phase mask scanning technique, serving as the mirrors in an all-fiber laser linear resonator. Leveraging the polarization dependence of the RCFBG through side exposure, we can readily achieve switchable single-wavelength, dual-wavelength, or triple-wavelength laser outputs by adjusting the polarization controller(PC) inside the resonator. Additionally, three distinct modes, namely, cylindrical vector beam(CVB), fundamental and mixed modes, are successfully obtained in single-wavelength laser operation.Azimuthally or radially polarized lasers can be realized by tuning two PCs inside and outside the resonator while operating in CVB mode. This innovative multi-wavelength and transversely mode-switchable fiber laser based on RCFBGs holds significant potential for applications in wavelength division multiplexing and mode division multiplexing systems.展开更多
In x-ray dark-field imaging using dual phase grating interferometer,multi-contrast signals are extracted from a set of acquired phase-stepping data by using the least-squares fitting algorithm.The extracted mean inten...In x-ray dark-field imaging using dual phase grating interferometer,multi-contrast signals are extracted from a set of acquired phase-stepping data by using the least-squares fitting algorithm.The extracted mean intensity,amplitude and visibility signals may be intrinsically biased.However,it is still unclear how large these biases are and how the data acquisition parameters influence the biases in the extracted signals.This work set out to address these questions.Analytical expressions of the biases of the extracted signals were theoretically derived by using a second-order Taylor series expansion.Extensive numerical simulations were performed to validate the theoretical results.It is illustrated that while the estimated mean intensity signal is always unbiased,the estimated amplitude and visibility signals are both positively biased.While the biases of the estimated amplitude signals are proportional to the inverse of the total number of phase steps,the biases of the estimated visibility signals are inversely proportional to the product of the total number of phase steps and the mean number of photons counted per phase step.Meanwhile,it is demonstrated that the dependence of the biases on the mean visibility is quite different from that of Talbot-Lau interferometer due to the difference in the intensity model.We expect that these results can be useful for data acquisition optimizations and interpretation of x-ray dark-field images.展开更多
We present a compact cold atom platform where an optical grating chip and planar coil chip are placed inside a compact vacuum chamber to create a magneto-optical trap.This approach significantly reduces the system vol...We present a compact cold atom platform where an optical grating chip and planar coil chip are placed inside a compact vacuum chamber to create a magneto-optical trap.This approach significantly reduces the system volume to about 20×20×20 cm^(3) compared to conventional vacuum systems and offers greater flexibility in accessing the trapped atoms.We demonstrate the trapping of 3×10^(5) cold rubidium atoms at a temperature of 100μK in a vacuum pressure below 10^(−7) mbar.The simplified optical geometry,low power consumption,and high degree of integration make this a promising platform for portable and versatile cold-atom devices in quantum sensing,timing,and information processing.展开更多
The actively heated fiber-optic(AHFO)technology has emerged as a frontier and hotspot in soil water content measurement,offering advantages such as easy installation,large-scale distributed measurement capability,and ...The actively heated fiber-optic(AHFO)technology has emerged as a frontier and hotspot in soil water content measurement,offering advantages such as easy installation,large-scale distributed measurement capability,and resistance to electromagnetic interference.However,current AHFO water content sensors fail to simultaneously achieve high precision,applicability for deep soil,and automated real-time monitoring,thereby limiting their development and application.Therefore,this study introduces a novel actively heated fiber Bragg grating(AH-FBG)cable.Laboratory tests were conducted to assess the heating uniformity of the AH-FBG cable and to establish the temperature characteristic value(T_(t))-soil water content(θ)calibration formula for water content measurement.Subsequently,AH-FBG cables were deployed for in situ soil water content monitoring in a test pit on the Loess Plateau.Through two-year monitoring data verified the accuracy of the AH-FBG cable and elucidated the spatiotemporal distribution of in situ loess water content.Laboratory results demonstrated superior heating uniformity of AHFBG cable,with a T_(t) standard deviation of approximately 0.3℃.In the field,the AH-FBG cable exhibited excellent performance in soil water content measurement,achieving a high accuracy of 0.023 cm^(3)/cm^(3).Further analysis revealed that the θ fluctuation predominantly occurred within a 10 m depth from the soil surface,with an overall upward trend over the two-year monitoring period;the response of shallow θ to precipitation was significant but exhibited increasing hysteresis with depth;frequent precipitation significantly enhanced water infiltration depth.This study provides technical guidance for highprecision,quasi-distributed,automated and real-time water content measurement of deep soil.展开更多
The phenomenon of photothermally induced transparency(PTIT)arises from the nonlinear behavior of an optical cavity,resulting from the heating of mirrors.By introducing a coupling field in the form of a standing wave,P...The phenomenon of photothermally induced transparency(PTIT)arises from the nonlinear behavior of an optical cavity,resulting from the heating of mirrors.By introducing a coupling field in the form of a standing wave,PTIT can be transitioned into photothermally induced grating(PTIG).A two-dimensional(2D)diffraction pattern is achieved through the adjustment of key parameters such as coupling strength and effective detuning.Notably,we observe first,second,and third-order intensity distributions,with the ability to transfer probe energy predominantly to the third order by fine-tuning the coupling strength.The intensity distribution is characterized by(±m,±n),where m,n=1,2,3.This proposed 2D grating system offers a novel platform for manipulating PTIG,presenting unique possibilities for enhanced functionality and control.展开更多
We experimentally investigate the effective working regions of a planar-integrated magneto-optical trap(MOT).By scanning a blocking point in the incident laser beam,we identify four effective working regions of the la...We experimentally investigate the effective working regions of a planar-integrated magneto-optical trap(MOT).By scanning a blocking point in the incident laser beam,we identify four effective working regions of the laser beam contributing to MOT:a central region corresponding to the downward incident beam and three regions associated with the upward diffracted beams.The latter three regions are the effective regions of the grating chip.It is demonstrated that only three3.5 mm radius grating regions can produce a MOT that is capable of trapping 105atoms with a temperature below 150μK,retaining over 60%of atoms compared to a complete grating chip.This finding suggests that more than 60%of the grating chip area can be saved for other on-chip components,such as metasurfaces and nanophotonic devices,without significantly compromising MOT performance,paving the way for more compact and versatile atom–photon interfaces.展开更多
基金supported by the UK’s Engineering and Physical Sciences Research Council(Grant Nos.EP/V000624/1,EP/X03495X/1,EP/X041166/1,and EP/T02643X/1)the Royal Society(Grant No.RG\R2\232531).
文摘Research on supercontinuum sources on silicon has made significant progress in the past few decades.However,conventional approaches to broaden the spectral bandwidth often rely on complex and critical dispersion engineering by optimizing the core thickness or introducing the cladding with special materials and structures.We propose and demonstrate supercontinuum generation using long-periodgrating(LPG)waveguides on silicon with a C-band pump.The LPG waveguide is introduced for quasi-phase matching,and the generated supercontinuum spectrum is improved greatly with grating-induced dispersive waves.In addition,the demonstrated LPG waveguide shows a low propagation loss comparable with regular silicon photonic waveguides without gratings.In experiments,when using a 1550-nm 75-fs pulse pump with a pulse energy of 200 pJ,the supercontinuum spectrum generated with the present LPG waveguide shows an ultrabroad extent from 1150 to 2300 nm,which is much wider by 200 nm than that achieved by dispersionengineered uniform silicon photonic waveguides on the same chip.This provides a promising option for on-chip broadband light source for silicon photonic systems.
文摘A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etching depth.Thinning of the p-side waveguide layer makes the light field bias to the n-side cladding layer.By coordinating the confinement effect of the cladding layer,the light confinement factor on the p-side is regulated.On the other hand,the introduction of a mode expansion layer facilitates the expansion of the mode profile on the p side cladding layer.Both these factors contribute positively to reducing the grating etching depth.Compared to the reported epitaxial structures of symmetric waveguides,the new structure significantly reduces the etching depth of the grating while ensuring adequate reflection intensity and maintaining resonance.Moreover,to improve the output performance of the device,the new epitaxial structure has been optimized.Based on the traditional epitaxial structure,an energy release layer and an electron blocking layer are added to improve the electronic recombination efficiency.This improved structure has an output performance comparable to that of a symmetric waveguide,despite being able to have a smaller gain area.
文摘Aiming at the requirement for high-precision tilt monitoring in the field of structural health monitoring(SHM),this paper proposes a sensitivity-enhanced tilt sensor based on a femtosecond fiber Bragg grating(FBG).Firstly,structural design of the tilt sensor was conducted based on static mechanics principles.By positioning the FBG away from the beam’s neutral axis,linear strain enhancement in the FBG was achieved,thereby improving sensor sensitivity.The relationship between FBG strain,applied force,and the offset distance from the neutral axis was established,determining the optimal distance corresponding to maximum strain.Based on this optimization scheme,a prototype of the tilt sensor was designed,fabricated,and experimentally tested.Experimental results show that the FBG offset distance yielding maximum sensitivity is 4.4 mm.Within a tilt angle range of−30°to 30°,the sensor achieved a sensitivity of 129.95 pm/°and a linearity of 0.9997.Compared to conventional FBG-based tilt sensors,both sensitivity and linearity were significantly improved.Furthermore,the sensor demonstrated excellent repeatability(error<0.94%),creep resistance(error<0.30%),and temperature stability(error<0.90%).These results demonstrate the sensor’s excellent potential for SHM applications.The sensor has been successfully deployed in an underground pipeline project,conducting long-term monitoring of tilt and deformation in the steel support structures,further proving its value for engineering safety monitoring.
文摘Long-period fiber gratings have the advantages of small size,corrosion resistance,anti-electro-magnetic interference,and high sensitivity,making them widely used in biomedicine,the power industry,and aerospace.This paper develops a long-period fiber grating sensor based on periodic microchannels.First,a series of linear structures were etched in the cladding of a single-mode fiber by femtosecond laser microma-chining.Then,the laser-modified region was selectively eroded by selective chemical etching to obtain the periodic microchannel structure.Finally,the channels were filled with polydimethylsiloxane(PDMS)to im-prove the spectral quality.The experimental results show that the sensor has good sensitivity in the measure-ment of various parameters such as temperature,stress,refractive index(RI),and bending.It has a temperat-ure sensitivity of−55.19 pm/℃,a strain sensitivity of−3.19 pm/με,a maximum refractive index sensitivity of 540.28 nm/RIU,and a bending sensitivity of 2.65 dB/m^(-1).All of the measurement parameters show good lin-ear responses.The sensor has strong application prospects in the field of precision measurement and sensing.
基金supported by the National Natural Science Foundation of China(No.52276094)the Education Project of Hunan Provincial Department(Nos.20B602 and 22C0112)+2 种基金the Industry University Education Cooperation Project(No.230803117185211)the Research Project on Teaching Reform in Ordinary Undergraduate Universities in Hunan Province(No.202401000142)the Natural Science Foundation of Hunan Province(No.2020JJ4935)。
文摘There is limited amount of research on surface plasmon resonance(SPR)sensors with self-referencing capabilities which are based on dielectric gratings.In the short-wavelength range,a metal grating sensor is capable of simultaneously measuring liquid refractive index under proposed temperature.A fabricated gold grating is placed on one side of a thin gold film for refractive index measurement,while the other with polydimethylsiloxane(PDMS)is deposited on the other side for temperature measurement.We use finite element analysis to research its sensing characteristics.Due to the high refractive index sensitivity of SPR sensors and thermo-optic coefficient of PDMS,we discovered the maximum spectral sensitivity of the sensor is 564 nm/RIU and-50 pm/℃when the liquid refractive index ranges from 1.30 to 1.40 with temperature ranging from 0℃ to 100℃.Numerical results indicate that there may not be mutual interference between two channels for measuring refractive index and temperature,which reduces the complexity of sensor measurements.
基金supported by the National Natural Science Foundation of China(No.61505160)the Innovation Capability Support Program of Shaanxi(No.2018KJXX-042)+2 种基金the Natural Science Basic Research Program of Shaanxi(No.2019JM-084)the State Key Laboratory of Transient Optics and Photonics(No.SKLST202108)the Graduate Innovation and Practical Ability Training Project of Xi’an Shiyou University(No.YCS22213190)。
文摘We proposed and demonstrated the ultra-compact 1310/1550 nm wavelength multiplexer/demultiplexer assisted by subwavelength grating(SWG)using particle swarm optimization(PSO)algorithm in silicon-on-insulator(SOI)platform.Through the self-imaging effect of multimode interference(MMI)coupler,the demultiplexing function for 1310 nm and 1550 nm wavelengths is implemented.After that,three parallel SWG-based slots are inserted into the MMI section so that the effective refractive index of the modes can be engineered and thus the beat length can be adjusted.Importantly,these three SWG slots significantly reduce the length of the device,which is much shorter than the length of traditional MMI-based wavelength demultiplexers.Ultimately,by using the PSO algorithm,the equivalent refractive index and width of the SWG in a certain range are optimized to achieve the best performance of the wavelength demultiplexer.It has been verified that the device footprint is only 2×30.68μm^(2),and 1 dB bandwidths of larger than 120 nm are acquired at 1310 nm and 1550 nm wavelengths.Meanwhile,the transmitted spectrum shows that the insertion loss(IL)values are below 0.47 dB at both wavelengths when the extinction ratio(ER)values are above 12.65 dB.This inverse design approach has been proved to be efficient in increasing bandwidth and reducing device length.
基金upported by the Guangdong Provincial Pearl River Talents Program(Grant No.2019ZT08Z779)the National Natural Science Foundation of China(Grant Nos.U21A20509 and 62205124).
文摘Metal micro-nano grating has received much attention due to its ability to provide high-efficiency light absorption.However,the current research scales of these metal gratings are focused on subwavelengths,and little attention has been paid to the absorption properties of metal gratings at other scales.We investigate the absorption properties of metal gratings based on surface plasmon resonance(SPR)across the scales from superwavelength to subwavelength.Under grazing incidence,we observe continuous strong absorption phenomena from superwavelength to subwavelength Al triangle-groove gratings(TGGs).Perfect absorption is realized at the subwavelength scale,whereas the maximum absorption at all other scales exceeds 74%.The electric field distribution gives the mechanism of the strong absorption phenomenon attributed to SPR on the surface of Al TGGs at different scales.In particular,subwavelength Al TGGs have perfectly symmetric absorption properties for different blaze angles,and the symmetry is gradually broken as the grating period’s scale increases.Furthermore,taking Al gratings with varying groove shapes for example,we extend the equivalence rule of grating grooves to subwavelength from near-wavelength and explain the symmetric absorption properties in Al TGGs.We unify the research of metal grating absorbers outside the subwavelength scale to a certain extent,and these findings also open new perspectives for the design of metal gratings in the future.
基金financial supports from the National Natural Science Foundation of China(52105434)China Postdoctoral Science Foundation(2022M710642).
文摘With the advantage of high light intensity due to low scatting, structural colors generated by metallic diffraction nanograting structures, used as a type of diffractive optical element, have shown great potential for application in industrial and scientific research fields such as optical anti-counterfeiting and sensors. Within the visible light wavelength range, the diffraction performance is highly dependent on the height and shape consistencies of the nanograting. However, there is still room for the improvement in the flexible control over structure formation through mechanical nanomachining within this scale. The novelty of this paper lies in proposing a machining strategy for nanograting structures with variable heights through precise regulation of the revolving trajectory using tip-based nano down-milling. It explores how different geometric features of trajectories impact the amount of material deformed into a grating and its distribution shape, referred to as undeformed grating area. By analyzing the forming mechanisms of nanogratings under various trajectories with finite element simulation, the desired undeformed grating area is successfully achieved, which is mainly extruded by the tip flank face to form the right facet of the grating, resulting in a small deformation degree and a high deformation efficiency. Three distinct types of revolving trajectories are filtered out according to five quantitative evaluation indicators for machining performance, namely material plastic deformation, grating profile consistency, grating height consistency, machining forces, and area transforming height, and then are compared in processing nanogratings with different heights. It is obtained that only by regulating the vertical vibration amplitude of the revolving trajectory, the semicircle trajectory with the optimal geometric features has the ability to machine high-quality nanograting structures with a continuous height variation of up to 220 nm in a spacing of 400 nm.
基金supported in part by the National Natural Science Foundation of China(Nos.61735014 and 61927812)the Shaanxi Provincial Education Department(No.18JS093)+2 种基金the Natural Science Basic Research Program of Shaanxi Province(No.2024JC-YBMS-530)the Operation Fund of Logging Key Laboratory of Group Company(No.2021DQ0107-11)the Graduate Student Innovation Fund of Xi’an Shiyou University(No.YCS23213193)。
文摘A compact and highly sensitive gas pressure and temperature sensor based on Fabry-Pérot interferometer(FPI)and fiber Bragg grating(FBG)is proposed and demonstrated experimentally in this paper.The theoretical model for pressure and temperature sensing is established.Building on this foundation,a novel micro silicon cavity sensor structure sensitive to pressure is devised downstream of an FBG.The concept of separate measurement and the mechanisms enhancing pressure sensitivity are meticulously analyzed,and the corresponding samples are fabricated.The experimental results indicate that the pressure sensitivity of the sensor is-747.849 nm/MPa in 0—100 k Pa and its linearity is 99.7%and it maintains good stability in 150 min.The sensor offers the advantages of compact size,robust construction,easy fabrication,and high sensitivity,making it potentially valuable for micro-pressure application.
基金supported by Natural Science Foundation of Gansu Province(NO.21JR7RA289)。
文摘To enhance the quality factor and sensitivity of refractive index sensors,a feedback waveguide slot grating micro-ring resonator was proposed.An air-hole grating structure was introduced based on the slot micro-ring,utilizing the reflection of the grating to achieve the electromagnetic-like induced transparency effect at different wavelengths.The high slope characteristics of the EIT-like effect enabled a higher quality factor and sensitivity.The transmission principle of the structure was analyzed using the transmission matrix method,and the transmission spectrum and mode field distribution were simulated using the finite-difference time-domain(FDTD)method,and the device structure parameters were adjusted for optimization.Simulation results show that the proposed structure achieves an EIT-like effect with a quality factor of 59267.5.In the analysis of refractive index sensing characteristics,the structure exhibits a sensitivity of 408.57 nm/RIU and a detection limit of 6.23×10^(-5) RIU.Therefore,the proposed structure achieved both a high quality factor and refractive index sensitivity,demonstrating excellent sensing performance for applications in environmental monitoring,biomedical fields,and other areas with broad market potential.
基金support by the Advanced Integrated Optoelectronics Facility at Tianjin University
文摘Metasurfaces composed of two-dimensional nanopillar arrays can manipulate light fields in desirable ways and exhibit the unique advantage of beam steering.Here,we experimentally demonstrate a metasurface-based wide-angle broadband all-dielectric blazed grating with an extreme incident angle of up to 80°,which is achieved by optimizing the wide-angle phase shifts and transmissivities of the unit cells.It exhibits a maximum diffraction efficiency of 72%and a high average efficiency of 64%over a wide range of incident angles from−80° to 45° at 1.55μm.Moreover,the proposed grating has a broad bandwidth of 200 nm(1.45-1.65μm),and average efficiencies of more than 50%can be achieved experimentally over the same incidence angles.Our results may pave the way for the creation of novel and efficient flat optical devices for wavefront control.
文摘Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term axle counting system monitoring.Design/methodology/approach–Wheel–rail mechanical behavior was simulated via finite element analysis(FEA)to determine optimal sensor placement.A clip-on composite sensor was subsequently engineered.Stress transduction efficacy was validated through FEA quantification of stress responses at the axle counter location.Findings–The proposed FBG axle counter integrates temperature compensation and anti-detachment monitoring as well as advantages such as simplified installation with minimal maintenance and sustained operational reliability.It effectively transmits stress,yielding a measured strain of 39μe under static loading conditions without sensitivity-enhancing elements.Originality/value–This study performs FEA of wheel-rail stress distribution and engineers the dual-slot composite sensor,FEAwas conducted to quantify the stress magnitude at the axle sensor position of the dual-slot composite sensor.Additionally,FEA was performed on sensors with different structural configurations,including adjustments to the axle sensor position,number of slots and axle position.The results confirmed that the designed composite sensor exhibits superior stress transfer characteristics.
基金supported by the National Natural Science Foundation of China(Grant No.12105210)the Knowledge Innovation Program of Wuhan-Basi Research(Grant No.2023010201010149)。
文摘We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.
基金the Biomedical Science and Technology Support Special Project of Shanghai Science and Technology Committee(No.20S31908300)。
文摘In response to the shortcomings of the common encoders in the industry,of which the photoelectric encoders have a poor anti-interference ability in harsh industrial environments with water,oil,dust,or strong vibrations and the magnetic encoders are too sensitive to magnetic field density,this paper designs a new differential encoder based on the grating eddy-current measurement principle,abbreviated as differential grating eddy-current encoder(DGECE).The grating eddy-current of DGECE consists of a circular array of trapezoidal reflection conductors and 16 trapezoidal coils with a special structure to form a differential relationship,which are respectively located on the code plate and the readout plate designed by a printed circuit board.The differential structure of DGECE corrects the common mode interference and the amplitude distortion due to the assembly to some extent,possesses a certain anti-interference capability,and greatly simplifies the regularization algorithm of the original data.By means of the corresponding readout circuit and demodulation algorithm,the DGECE can convert the periodic impedance variation of 16 coils into an angular output within the 360°cycle.Due to its simple manufacturing process and certain interference immunity,DGECE is easy to be integrated and mass-produced as well as applicable in the industrial spindles,especially in robot joints.This paper presents the measurement principle,implementation methods,and results of the experiment of the DGECE.The experimental results show that the accuracy of the DGECE can reach 0.237%and the measurement standard deviation can reach±0.14°within360°cycle.
基金Project supported by the National Natural Science Foundation of China (Grant No. 62075182)the National Key Research and Development Program of China (Grant No. 2022YFB3207502)。
文摘A multi-wavelength and transversely mode-switchable fiber laser based on a ring-core fiber Bragg grating(RCFBG) is proposed. Two RCFBGs with high and low reflectivity are inscribed using a femtosecond laser and the phase mask scanning technique, serving as the mirrors in an all-fiber laser linear resonator. Leveraging the polarization dependence of the RCFBG through side exposure, we can readily achieve switchable single-wavelength, dual-wavelength, or triple-wavelength laser outputs by adjusting the polarization controller(PC) inside the resonator. Additionally, three distinct modes, namely, cylindrical vector beam(CVB), fundamental and mixed modes, are successfully obtained in single-wavelength laser operation.Azimuthally or radially polarized lasers can be realized by tuning two PCs inside and outside the resonator while operating in CVB mode. This innovative multi-wavelength and transversely mode-switchable fiber laser based on RCFBGs holds significant potential for applications in wavelength division multiplexing and mode division multiplexing systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1532113,11475170,11905041)Anhui Provincial Natural Science Foundation(Grant No.2208085MA18)Fundamental Research Funds for the Central Universities(Grant No.JZ2022HGTB0244)。
文摘In x-ray dark-field imaging using dual phase grating interferometer,multi-contrast signals are extracted from a set of acquired phase-stepping data by using the least-squares fitting algorithm.The extracted mean intensity,amplitude and visibility signals may be intrinsically biased.However,it is still unclear how large these biases are and how the data acquisition parameters influence the biases in the extracted signals.This work set out to address these questions.Analytical expressions of the biases of the extracted signals were theoretically derived by using a second-order Taylor series expansion.Extensive numerical simulations were performed to validate the theoretical results.It is illustrated that while the estimated mean intensity signal is always unbiased,the estimated amplitude and visibility signals are both positively biased.While the biases of the estimated amplitude signals are proportional to the inverse of the total number of phase steps,the biases of the estimated visibility signals are inversely proportional to the product of the total number of phase steps and the mean number of photons counted per phase step.Meanwhile,it is demonstrated that the dependence of the biases on the mean visibility is quite different from that of Talbot-Lau interferometer due to the difference in the intensity model.We expect that these results can be useful for data acquisition optimizations and interpretation of x-ray dark-field images.
基金supported by the National Key R&D Program(Grant Nos.2021YFA1402004 and 2021YFF0603701)the National Natural Science Foundation of China(Grant Nos.12134014,U21A20433,U21A6006,and 92265108)+1 种基金the Fundamental Research Funds for the Central Universitiesthe University of Science and Technology of China(USTC)Research Funds of the Double First-Class Initiative。
文摘We present a compact cold atom platform where an optical grating chip and planar coil chip are placed inside a compact vacuum chamber to create a magneto-optical trap.This approach significantly reduces the system volume to about 20×20×20 cm^(3) compared to conventional vacuum systems and offers greater flexibility in accessing the trapped atoms.We demonstrate the trapping of 3×10^(5) cold rubidium atoms at a temperature of 100μK in a vacuum pressure below 10^(−7) mbar.The simplified optical geometry,low power consumption,and high degree of integration make this a promising platform for portable and versatile cold-atom devices in quantum sensing,timing,and information processing.
基金supported by the National Natural Science Foundation of China(Grant Nos.42307189 and 42030701)the China Postdoctoral Science Foundation(Grant No.2023M740974).
文摘The actively heated fiber-optic(AHFO)technology has emerged as a frontier and hotspot in soil water content measurement,offering advantages such as easy installation,large-scale distributed measurement capability,and resistance to electromagnetic interference.However,current AHFO water content sensors fail to simultaneously achieve high precision,applicability for deep soil,and automated real-time monitoring,thereby limiting their development and application.Therefore,this study introduces a novel actively heated fiber Bragg grating(AH-FBG)cable.Laboratory tests were conducted to assess the heating uniformity of the AH-FBG cable and to establish the temperature characteristic value(T_(t))-soil water content(θ)calibration formula for water content measurement.Subsequently,AH-FBG cables were deployed for in situ soil water content monitoring in a test pit on the Loess Plateau.Through two-year monitoring data verified the accuracy of the AH-FBG cable and elucidated the spatiotemporal distribution of in situ loess water content.Laboratory results demonstrated superior heating uniformity of AHFBG cable,with a T_(t) standard deviation of approximately 0.3℃.In the field,the AH-FBG cable exhibited excellent performance in soil water content measurement,achieving a high accuracy of 0.023 cm^(3)/cm^(3).Further analysis revealed that the θ fluctuation predominantly occurred within a 10 m depth from the soil surface,with an overall upward trend over the two-year monitoring period;the response of shallow θ to precipitation was significant but exhibited increasing hysteresis with depth;frequent precipitation significantly enhanced water infiltration depth.This study provides technical guidance for highprecision,quasi-distributed,automated and real-time water content measurement of deep soil.
文摘The phenomenon of photothermally induced transparency(PTIT)arises from the nonlinear behavior of an optical cavity,resulting from the heating of mirrors.By introducing a coupling field in the form of a standing wave,PTIT can be transitioned into photothermally induced grating(PTIG).A two-dimensional(2D)diffraction pattern is achieved through the adjustment of key parameters such as coupling strength and effective detuning.Notably,we observe first,second,and third-order intensity distributions,with the ability to transfer probe energy predominantly to the third order by fine-tuning the coupling strength.The intensity distribution is characterized by(±m,±n),where m,n=1,2,3.This proposed 2D grating system offers a novel platform for manipulating PTIG,presenting unique possibilities for enhanced functionality and control.
基金Project supported by the National Key R&D Program of China(Grant Nos.2021YFA1402004 and 2021YFF0603701)the National Natural Science Foundation of China(Grant Nos.12134014,U21A20433,U21A6006,and 92265108)+1 种基金supported by the Fundamental Research Funds for the Central UniversitiesUSTC Research Funds of the Double First-Class Initiative。
文摘We experimentally investigate the effective working regions of a planar-integrated magneto-optical trap(MOT).By scanning a blocking point in the incident laser beam,we identify four effective working regions of the laser beam contributing to MOT:a central region corresponding to the downward incident beam and three regions associated with the upward diffracted beams.The latter three regions are the effective regions of the grating chip.It is demonstrated that only three3.5 mm radius grating regions can produce a MOT that is capable of trapping 105atoms with a temperature below 150μK,retaining over 60%of atoms compared to a complete grating chip.This finding suggests that more than 60%of the grating chip area can be saved for other on-chip components,such as metasurfaces and nanophotonic devices,without significantly compromising MOT performance,paving the way for more compact and versatile atom–photon interfaces.
