In this paper, the energy band structure and topological surface state of type Ⅱ Dirac semimetal PtTe2 are calculated based on first-principle calculation. A layered PtTe2 is prepared by the mechanical lift-off approach, and a metal-PtTe2-metal field effect transistor is fabricated based on micro-nano processing. The photocurrent response of a field-effect transistor device based on type Ⅱ Dirac semimetal PtTe2 in terahertz region is studied. The device has an obvious photoresponse to terahertz, with a responsivity of 3.85 A/W and an equivalent noise power of about 4.81 pW·Hz-1/2. It shows a wide range of application prospects in low-energy bands, especially terahertz bands.

Terahertz wave is an important band for 6G communication in the future and has become a hot issue studied in the optics and electronics fields. However, the terahertz source, especially the integrated terahertz source based on micro-nano optics, gets a lot of attention. In this paper, a broadband terahertz radiation source is proposed, and it is based on the plasmonic resonant characteristics of the nano-antenna array. Using Maxwell's equation and a hydrodynamic equation of the metal plasma, this paper studies the terahertz time-domain wave generation from the nano-antenna array excited by a pulsed laser. The results show that the polarization of the generated terahertz radiation is perpendicular to the polarization of the incident light, and the terahertz emission bandwidth is closely related to the pulse width of the exciting laser. A nano-antenna array is designable and easy to integrate, and thus it is expected to be better applied in integrated terahertz source devices. This paper will provide a theoretical basis for the design of terahertz source based on surface plasmonics in the future.

A high-precision time transfer method based on fiber frequency transfer is proposed to achieve higher stability of time transfer. On the premise of ensuring the uncertainty of time transfer, the proposed method can achieve the fiber time transfer with high stability and good uncertainty considering the high stability of fiber frequency transfer. On the basis of the fiber time and frequency transfer, the highly stable 1PPS (one pulse per second) time signal is regenerated using the frequency signal transmitted from the fiber frequency transfer system. Then, the regenerated 1PPS time signal tracks the 1PPS time signal transmitted by the fiber time transfer system, which renders the regenerated 1PPS time signal good stability and uncertainty simultaneously. The time transfer data measured by fiber links are used to conduct simulation experiments to verify the feasibility of the proposed method. The results indicate that under the proposed method, the fiber time transfer stability reaches 0.5 ps@1 s and 0.09 ps@104 s. The experiment device for the fiber time and frequency transfer is employed to perform a test on a fiber link of 500 km, and the result demonstrates that the high-precision time transfer can be achieved by the proposed method, with the stability of 2.5 ps@1 s and 0.9 ps@105 s, and the uncertainty of 6.4 ps.

A radio-over-fiber (RoF) system combines the advantages of fiber and wireless communication,has the characteristics of large bandwidth, low loss, and flexible mobility,and has broad development prospects in the future beyond 5G/6G communication networks. In this paper, we have realized the effective transmission of polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) signals with a transmission rate more than 100 Gbit/s in the RoF system based on commercial optical transport network (OTN) real-time processing. Specifically, we respectively demonstrate the transmission of PDM-QPSK signals with a frequency of 22 GHz and a transmission rate of 125.52 Gbit/s in 20 km+25 km two-span fiber and PDM-QPSK signals in 20 km+25 km two-span fiber and 1 cm wireless links with a frequency of 60 GHz and a transmission rate of 125.52 Gbit/s. The results show that if soft-decision forward-error-correction (SD-FEC) coding with a 15% overhead is enabled, error-free transmission can be realized. In addition, we propose a new method for polarization modulation by an integrated dual-polarization Mach-Zehnder modulator (DP-MZM) in the real-time processing. The RoF system reduces system complexity, which has great application value in future mobile data communication networks.

The adjustability of differential mode gain for few-mode erbium-doped fiber amplifiers (FM-EDFAs) can be used for mode gain equalization and compensation for link mode-dependent loss, which can significantly improve the networking flexibility of mode division multiplexing systems. A few-mode optical fiber device integrating the isolator and the wavelength division multiplexer (FM-IWDM) is produced to build all-fiber FM-EDFAs. Two optical amplifying experiments using the codirectional and bidirectional pumps with a center wavelength of 1480 nm are carried out, and the maximum adjustable differential mode gain of 2.6 dB and 4.8 dB can be achieved by adjusting the pump power ratio under the pump total power of 200 mW.

For the cross-sea optical communication system, the power efficiency problem caused by the power supply structure between shores is the main factor that limits its capacity. Multiple single-mode fiber (M-SMF) multiplexing is the main solution to improve the capacity of communication submarine cables at present. However, the maximum deployed fiber count in a submarine cable is usually limited up to 32 due to the considerations of cable mechanics and deployment engineering. As a consequence, high-density spatial division multiplexing is expected to show its advantages in the field of submarine cable communication. The power efficiency formula based on multi-core fiber (MCF) submarine cable is deduced theoretically, the power efficiency characteristics of MCF submarine cable and M-SMF submarine cable are compared, and the effects of marginal parameters such as insertion loss of multi-core coupler and inter-core crosstalk on the overall power efficiency of the system are analyzed. The results show that the optimal number of trans-Atlantic 4-core fiber and trans-Pacific 4-core fiber is 86 and 14 respectively, and the optimal number of trans-Atlantic 7-core fiber and trans-Pacific 7-core fiber is 50 and 8 respectively. When fiber count is limited to 32, the power efficiency of 4-core fiber can be improved by 2.50 times and 1.13 times compared with M-SMF submarine cable in trans-Atlantic and trans-Pacific scenarios, and that of 7-core fiber can be improved by 3.20 times and 1.13 times compared with M-SMF submarine cable in trans-Atlantic and trans-Pacific scenarios.

A test system is designed for evaluating the characteristics of single-spectrum radiant energy-electricity energy conversion of thermophotovoltaic cells. A band-pass filter and a secondary concentrator with a straight funnel are used to achieve single-spectrum and directional radiation transmission between the xenon lamp and the thermophotovoltaic cells with adjustable energy flux density. Based on Monte-Carlo ray tracing method, the spectral radiation transmission model of the xenon lamp-thermophotovoltaic test system is constructed. The distribution characteristics of radiant energy flux on the cell surface are analyzed, and the effects of opening size and height of the secondary concentrator are discussed. Meanwhile, the current-voltage curve, output power, and thermoelectric conversion efficiency of GaSb cell under single-spectrum and high energy flux radiation are theoretically calculated. The results show that the introduction of a secondary concentrator can effectively improve the thermoelectric conversion performance of the thermophotovoltaic cells. The radiant energy on the cell surface increases by 105.3%, with the uniformity reaching 95%, and the output power of the cell increases by 109.1%.

According to the measurement requirements of the gas-liquid two-phase flow parameters in thermal design and modeling of a nuclear reactor, a laser-imaging-based method for measuring the characteristics of bubble groups is investigated. Specifically, a planar laser is used to illuminate the two-phase flow outside the transparent model core to form a transverse detection cross-section, and the forward light scattering images of the bubble groups in this cross-section are obtained by high-speed photography. Then, the images are processed with a roundness classification method and an optimized graph segmentation algorithm of the fast radial symmetry transform to effectively reduce the area calculation errors introduced by the overlapping bubble images. Finally, the vertical velocity of the bubbles is calculated on the basis of the "fault contour-velocity-morphology" constraint of bubbles. Thus, the proposed method achieves the measurement of the instantaneous cross-sectional void fraction, the imaging of the mean value of cross-sectional void fraction, the three-dimensional morphology reconstruction of bubbles, and the calculation of average particle size distribution.

A rapid formwork position and pose measurement method based on computer vision techniques, such as three-dimensional reconstruction and image recognition, is proposed to address the time-consuming, labor-intensive, and inefficient problems of traditional position and pose measurement methods for segment girder formworks in precast girder yards. Experiments are conducted inside and outside the laboratory to investigate the influences of common factors at the engineering site on measurement accuracy, and the shooting conditions for obtaining high measurement accuracy are summarized. On this basis, the feasibility and applicability of the proposed method are verified through experiments at actual precast girder yards. The results show that the proposed method can measure the position and pose of segment girder formworks quickly, easily, and inexpensively in addition to meeting accuracy requirements.

Reliability is an important index to assess the validity of an optical instrument, which is directly related to the practicability of the equipment. Therefore, it is very important to study the reliability of the Mueller imaging polarimeter in pathological diagnosis for its clinical application. In this paper, the Mueller imaging polarimeter which is developed independently by our laboratory is used to diagnose 155 cases of skin tissue sections, including melanoma, pigmented nevus, and normal skin. The depolarization, retardance, and diattenuation can be obtained after the polarimetry. By analyzing receiver operating characteristic (ROC) curves, we find that the diagnostic reliability of depolarization, retardance, and diattenuation of normal and melanoma skin tissue sections is 100%, 100%, and 90%, respectively. The diagnostic reliability of depolarization, retardance, and diattenuation of normal and pigmented nevus skin tissue sections is 99%, 88%, and 75%, respectively. The diagnostic reliability of depolarization, retardance, and diattenuation of pigmented nevus and melanoma is 96%, 97%, and 78%, respectively. The reliability and validity of our homemade Mueller imaging polarimeter have been demonstrated in diagnosing skin sections and the instrument is expected to be a potential tool to assist doctors in pathological diagnosis.

The traditional low-coherence vertical scanning method has low measurement efficiency when measuring the three-dimensional surface topography of steps or groove-like microstructures with a height of tens or hundreds of microns. For this reason, a fast vertical scanning topography measurement method based on spectral distribution characteristics is proposed, and this method includes twice vertical scanning processes. An evaluation function to describe the fringe contrast of a single interferogram is established, the approximate position of the upper and lower surfaces of the test object is located by coarse scanning, and the upper and lower coarse scanning images are connected to calculate the image acquisition areas of the fine scanning that cover the coherent areas on the upper and lower surfaces of the test object. The fine scanning is not performed in other areas, but its displacement is recorded. With the fine scanning interferogram of π/2 scanning phase shift, the three-dimensional surface topography of the test object is restored. The scanning step length of the coarse scanning is calculated based on the low-coherence spectral distribution, and the step length of the fine scanning is one-eighth of the center wavelength. Experiments on the step with a height of 7.805 μm and the groove with a depth of 200.99 μm show that the proposed method reduces the acquisition time by 48.2% and 55.2% respectively, compared with the traditional vertical scanning method.

A three-dimensional vertical surface measurement method based on phase-shifting and focal-switching method is proposed. When the projector scans the depth information of the measured object, the three-frame fringe patterns in the three-step phase-shifting method will be projected to the surface of the measured object as a continuous loop, and the corresponding fringe patterns are collected synchronously by the camera. When calculating the modulation distribution of the fringe pattern for each focal length value of the projector, the modulation distribution at the focal length position is approximately calculated by using the three-frame fringe patterns of the focal length position and its adjacent position before and after the focal length value, and the three-dimensional shape of the measured object is reconstructed according to the relationship between the maximum modulation value and the depth information. Experimental results show that the amount of fringe projection and data collection of the proposed method is only one third of that of the the traditional three-step phase-shifting method, but the measurement accuracy is almost the same as that of the traditional three-step phase-shifting method. In the depth range of 1100 μm, the average root-mean-square error for the inclined plane with different poses can reach 4.98 μm by using phase-shifting and focal-switching method.

To improve the quality of Doppler signal and signal processing accuracy, a set of homodyne laser vibration measurement system based on pupil-plane interferometry and wavelet transform is proposed and implemented. In this system, pupil-plane interferometry is introduced into the laser Doppler vibrometry, which overcomes the phenomenon that the detection spot drifts relative to the detector caused by the complex vibration of the measured object in optical path for vibration measurement based on image-plane interferometry, and suppresses the modulation of Doppler signal caused by this kind of drift. In the session of vibration information extraction, the instantaneous frequency of signal is extracted by wavelet ridge extraction algorithm, and then the vibration velocity is calculated. With a standard shaker as the vibration source and a magnetoelectric velocity sensor as the reference, the performance of the designed system is verified through the experiments of measuring the velocity and the vibration. Experimental results show that the measurement of the velocity of a vibrating object by the designed system is consistent with the magnetoelectric velocity sensor, and the relative errors of different simple harmonic vibration parameters measured by the designed system are all within 1.5%.

The uncooled thermal infrared imaging spectrometer with small size, low cost, and long life has great potential for detecting high-temperature targets, but its severe internal noise will reduce the detection sensitivity. The main noise of uncooled thermal infrared imaging spectrometer includes the detector noise, the noise caused by the stray light from the surface of the opto-mechanical component, stray light noise generated by the non-working order of the grating, and the background radiation noise of the opto-mechanical component. The noise equivalent temperature difference (NETD) formula containing the above noise is derived. Taking the Offner thermal infrared imaging spectrometer as an example, the relationship among NETD, the F number of the system, and the optical properties of the inner surface of mechanical components is analyzed. Then, the ability of opto-mechanical surface polishing to suppress the internal background radiation noise of the spectrometer is studied. Finally, the linear relationship between pixels is used to remove the remaining noise, so that the detection signal is basically consistent with the target signal.

It is difficult to obtain effective bonding defects characteristics from the main echo of terahertz pulse when the defect thickness is too small, because the terahertz time-domain pulse carrying the defect information overlaps with the reflection pulse from the substrate. To this end, a terahertz propagation model based on transfer matrix method is established. The model is used to numerically analyze the propagation characteristics of terahertz pulse in the bonding defects of thin coating. Combined with the terahertz time-domain simulation results of coating bonding defects, a method for identifying coating bonding defects based on multiple echo features is proposed, and the skewness characteristic of defect signal is used to construct terahertz image. The 10- and 15-μm-thick bonding defects preset in 50- and 80-μm-thick coatings are identified successfully with an average recognition accuracy of 95.2%.

In this paper, a novel photonic digital-to-analog converter (PDAC) based on phase-change materials (PCMs) and electro-optic tuning microring resonators (MRs) is proposed, and the arbitrary waveform generation is realized. The PDAC uses MR array to process the optical signals of different wavelengths at the same time and integrates programmable phase-change materials into the optical waveguide to complete the power control of the optical signal and the power compensation of the electro-optic tuning MR, thereby realizing high-precision conversion of digital signals into analog signals. A 4-bit PDAC structure is simulated with 25 GSa/s input data rate using the Ansys Lumerical simulation platform. The proposed PDAC can achieve an effective number of bits of 3.63 bit, and the maximum integral nonlinearity (INL) and maximum differential nonlinearity (DNL) are 0.88BLSB (BLSB represents least significant bit) and 0.35BLSB, respectively. In addition, the proposed PDAC can realize the generation of square wave, sawtooth wave, triangular wave, and sine wave with small error compared to idea waveforms. Simulation proves that the proposed structure will be used in digital-to-analog converters and arbitrary waveform generators with high speed and low conversion error.

Surface plasmon-photon hybrid waveguides have been widely used in micro-nano photonics due to their strong enhancement effect in the local field and relatively long transmission distance. Based on the finite element method, the enhancement of resonance energy transfer (RET) between two two-level atoms in a hybrid waveguide with different sizes is studied systematically. The hybrid waveguide is composed of a metal surface plasmon waveguide and a rectangular medium waveguide, with a low refractive index gap between them. The waveguide mode is solved by the two-dimensional (2D) finite element method to obtain the approximate photon dyadic Green's function in the waveguide, and it is compared with the strict three-dimensional (3D) finite element solution. The comparison results prove that for the single mode, the photon dyadic Green's function constructed by the waveguide mode agrees well with the strict solution. In addition, compared with the 3D finite element method, the 2D finite element method needs much fewer computation resources. With the help of the 2D finite element method, the size required for the single mode transmission at 1550 nm and its effect on the RET enhancement are systematically studied. It is found that a narrower waveguide is accompanied by a higher medium waveguide needed for the single mode transmission. As the waveguide widens, for a higher medium waveguide, its transmission distance increases, and the RET enhancement factor decreases. While for a lower medium waveguide, its transmission distance firstly increases and then decreases, and the RET enhancement factor declines sharply. As the height of the medium waveguide increases, the transmission distance decreases sharply at first and then increases slowly, while the RET enhancement factor increases sharply at first and then changes slowly. Furthermore, the small low refractive index gap is followed by a short transmission distance and a large RET enhancement factor.

Considering the fast motion, illumination variation, and scale transform of tracking targets in actual scenarios, a triplet network based on a dynamic feature attention (DFA) model for object tracking is proposed to solve these problems. Specifically, on the basis of the SiamRPN++ tracking framework, an online update triplet network with dynamic template branches is designed to strengthen the semantic information of extracted features and improve the matching similarity between template features and search features. A sample generation method for the triplet network training is developed to change the allocation of negative samples and improve the balance of positive and negative training samples. Moreover, a DFA model, where the historical dynamic features of the templates are enhanced through equivalent self-attention and mutual attention operation, is designed to achieve the adaptive refinement of template features. Meanwhile, the channel attention score is used to control the weight distribution of the search feature maps, and the response of the score maps is improved. Compared with the state-of-the-art algorithms such as SiamRPN++ and SiamBAN, the proposed algorithm has achieved the highest success rate (71.0%) and the best robustness (0.122) on the OTB100 and VOT2018 datasets that contain scenes with motion blur, illumination variation, and similar background interference. This algorithm also can meet the requirement of real-time target tracking.

Metamaterial absorbers are widely used in various fields due to their ability to achieve "perfect" absorption close to 100% at a specific wavelength. Metamaterials with saturable absorption properties can be used to control laser pulses, but the studies on the optical properties of metamaterials are mainly focused on infrared or terahertz bands, and there are few studies in visible bands. Based on the traditional three-layer structure model of the metamaterial absorber and the phase change characteristics of the vanadium dioxide which has the temperature-dependent electromagnetic parameters, a visible range metamaterial saturable absorber is designed. The absorptivity of this kind of absorber will be saturated with the increase of the temperature caused by the incident electromagnetic wave, and finally it will convert to a highly reflective state, which is similar to that of a semiconductor saturable absorber mirror. The numerical simulation of the structure shows that the average saturation depth is 16% in the wavelength range of 405-650 nm.

The propagation and interaction properties of Airy-Gaussian beams in saturable nonlinear medium under fractional effect are investigated numerically by means of split-step Fourier transform method. It is shown that for the propagation of a single Airy-Gaussian beam, variation in the evolution structure of the light field is determined by the fractional Lévy index and the saturable nonlinear strength parameter. The breathing soliton can be formed when the light field evolves under the action of focusing nonlinearity, and the characteristic parameters of the soliton, such as the peak intensity and width, can be controlled by adjusting the Lévy index, the saturable nonlinear strength parameter, the incident light field distribution factor and the light field attenuation coefficient. For the interaction of double Airy-Gaussian beams, two in-phase Airy-Gaussian beams attract each other to generate a single breathing soliton, and two out-of-phase Airy-Gaussian beams repel each other to form a breathing soliton pair. The magnitude of the force between the two beams and the peak intensity of the soliton or soliton pair can be manipulated by adjusting the initial beam interval, Lévy index, the saturable nonlinear strength parameter and the incident light field distribution factor.

In order to solve the problems of low energy utilization, large lens size, and non-uniform illumination of existing lighting systems with the extended light source, according to the non-imaging optical marginal ray principle, this paper proposes a double freeform surface design method suitable for the extended light source and utilizes the angle difference formed by the refraction of the left and right marginal rays of the extended light source through the lens to control the illuminance distribution in the target plane. According to the design parameters, this paper calculates discrete points in the internal and external freeform surfaces, fits the contour curves of the internal and external freeform surfaces, and obtains a rotationally symmetric double freeform surface lens. In the case that the ratio of lens height to light source diameter is only 2, the paper adopts this method to design a double freeform surface lens with high energy utilization and high uniformity after numerical calculation and optical simulation. The energy utilization of the near-field double freeform optical system is 99.52%, and the illuminance uniformity is 95.81%; the energy utilization of the far-field double freeform optical system is 99.12%, and the illuminance uniformity is 93.45%. The research results show that the proposed method will guide the design of lighting systems with extended light sources.

A novel dish concentrator formed by a rotating array of curved mirror units with same size is proposed, and the mirrors in the array can be either parabolic or spherical. This concentrator has the advantages of simple manufacturing, low cost, and readiness for compact arrangement owing to the obstruction-free state between mirror units. Taking a concentrator with the typical aperture (width is D=10 m) as an example, the influences of mirror width d and dimensionless parameters on the optical performance of the concentrator in detail are analyzed by the ray tracing method. The dimensionless parameters include the ratio of the concentrator's focal length f1=R1/2 to its width D (i.e., f1/D), the ratio of the parabolic mirror's focal length fm to the radius R1 of the rotating array (i.e., fm/R1), and the ratio of the spherical mirror's radius Rm to R1 (i.e., Rm/R1). The results demonstrate the application value of the new concentrator in concentrating thermal systems (high concentration ratio requirement) and concentrating photovoltaic systems (high flux uniformity requirement), and provide a basis for its design. The following observations can be made from the results. The plane receiver in the novel dish concentrator should be located at a reasonable position below z=f1 to minimize the focal spot. Interception width of the focused spot reaches the minimum value at fm/R1=0.6 when parabolic mirrors are used, whereas it usually reaches its minimum value at Rm/R1=1.0 when the mirrors utilized are spherical. The variation laws of the average local concentration ratio and the peak concentration ratio with the concentrator's geometric parameters are opposite to those of interception width. When parabolic mirrors are used, the average local concentration ratio and the peak concentration ratio can be as high as 2846.8 and 7107.0 respectively, whereas the corresponding interception width is only 88.3 mm. In the case of spherical mirrors, they can reach 3000.0 and 7800.0 respectively, while the corresponding interception width is as small as 87.5 mm. Therefore, the proposed concentrator is readily applicable to high-temperature concentrating thermal systems. When reasonable geometric parameters are chosen for the concentrator, it can always obtain a square focal spot with a highly uniform flux distribution, and its average local concentration ratio can reach 420, indicating that it also works well in high-power concentrating photovoltaic systems.

A bandpass filter is proposed in this paper by utilizing the high-order mode of spoof surface plasmon polaritons (SSPPs). The adopted SSPPs unit cell is a Yagi-like antenna structure, which can effectively reduce the asymptotic frequency of the SSPPs. In addition, the asymptotic frequency of the mode 1 and the intersection frequency with the light line in free space can be manipulated by adjusting the geometric parameters of the SSPPs unit cell. Compared with the fundamental mode with low-pass characteristics, the mode 1 has inherent band-pass response and does not require an additional gradient transition structure for excitation. In order to verify the feasibility of proposed high-order mode based bandpass filter, a topology is fabricated and measured by the vector network analyzer. The measured results show that the insertion loss is less than 1 dB from the frequency range of 6 GHz to 9.9 GHz, and the in-band return loss is better than 10 dB, which is in agreement with the simulated ones.

Resonant metasurfaces with a high Q factor have received widespread attention in nanophotonics due to their significant enhancement effect in local electromagnetic fields. On the basis of the unique electromagnetic properties of all-dielectric materials, an all-dielectric nanohole array metasurface with a symmetry-broken square lattice is proposed in this paper. The in-plane symmetry of the square lattice unit cell is broken to excite multiple Fano resonances with a high Q factor in the near-infrared region. Under the excitation of plane waves at a normal incidence, the proposed metasurface can realize the double degenerate Fano resonance independent of polarization and the triple nondegenerate Fano resonance dependent on polarization, and the latter has a higher Q factor and stronger electromagnetic locality. The numerical simulation is performed to investigate the influence of lattice-perturbed parameters on the properties of the triple nondegenerate Fano resonance. The results reveal that the Q factor and the local electric field intensity of the triple nondegenerate Fano resonance are controlled by lattice-perturbed parameters. Through the optimization of lattice-perturbed parameters, the Q factor of the triple nondegenerate Fano resonance can be simultaneously up to 1.8×104, 2.7×104, and 1.9×104, and their local electric field intensity can be simultaneously up to 2×104, 3×104, and 1.5×104.

A method of fabricating surface-enhanced Raman scattering (SERS) substrate by one-step exposure of mixed electron beam resists is reported. Stable and scattered nanospheres were produced by mixing immiscible hydrogen silsesquioxane (HSQ) and polymethyl methacrylate (PMMA) electron beam resists in equal quantity, followed by electron beam exposure with an appropriate dosage of 2000 μC/cm2 and development. Thin Au film was then deposited using electron beam evaporation to form SERS substrates with superior Raman enhancement effects. The size distribution of the microspheres with the relative standard deviation of 7.56% is uniform, and the gaps between rough Au layers and the nanospheres could provide abundant SERS "hot spots". The SERS substrates thus fabricated showed superior performance for different targets. A SERS enhancement factor of 5.8×106 and detection limit of 1.06×10-8 mol/L for 4-mercaptophenylboronic acid (4-MPBA), and the detection limits of 7.08×10-9 mol/L for rhodamine 6G (R6G) and 7.94×10-10 mol/L for melamine in water were achieved. For melamine, a wide detection range (1.0×10-9-1.0×10-5 mol/L) with a good linearity (R2=0.952) was achieved. The pronounced performance of detecting melamine makes the SERS substrates very overwhelming among the ones reported. The facile and repeatable approach of preparing high-performance SERS substrates by exposing the mixture of different resists proposed here is undoubtedly favorable for the exploration of novel SERS substrates and their fabrication.

The reduction in the display chip size of micro light emitting diode (Micro-LED) exerts a sidewall effect and consequently results in a decreased forward light extraction efficiency (LEE). The display chip structure of Micro-LED with high LEE still needs to be further studied. For this reason, an optimized model of GaN-based Micro-LED with high LEE is explored by leveraging the finite-difference time-domain method from a simulation perspective. Specifically, the initial laminated structure of GaN-based Micro-LED with vertical sidewalls is constructed, and the influence of the sidewall effect on LEE is analyzed quantitatively. Then, the impact of the position change of multiple-quantum-well active layer in Micro-LED on the light output effect is investigated, and Micro-LED structure models with different inclined sidewall angles are analyzed. The influence of the bottom reflective material on LEE is discussed, and the parameters of the preliminarily optimized GaN-based Micro-LED model are obtained. Finally, LEE is further improved by designing a top transmission grating, and the effects of period, height, and duty cycle on LEE are examined. The results show that the overall LEE of the optimized GaN-based Micro-LED is 2.42 times higher than that of the initial structure.

A high-sensitivity through-hole cantilever beam vibration sensor based on dispersion-turning-point (DTP) optical microfiber coupler (OMC) is studied. First, the axial strain and vibration characteristics of OMCs, and the spectral characteristics of OMCs under the loading of axial strain are theoretically analyzed. Then, OMCs with different diameters are prepared by the melting taper method, and the axial strain experiments are carried out. Experimental results show that the axial sensitivity of the OMC is as high as -35 pm/με when the diameter of the OMC is 1.6 μm and DTP is near 1500 nm, which is about 3.5 times of that of the normal OMC. Finally, the OMC with high axial-strain sensitivity is fixed on a through-hole cantilever beam to construct a high-sensitivity vibration sensor, which is used to detect the vibration signal. Results show that the frequency detection range of the sensor is 30-2800 Hz, the response reaches the highest value at the first-order vibration frequency (52 Hz), and the acceleration sensitivity of the sensor is as high as 85 mV/(m·s-2) with good linearity under the micro-vibration (0-0.6g) at the flat response area (~40 Hz).

Rydberg atoms have extremely large polarizability and transition dipole moments, allowing for non-destructive and traceable precise measurement or communications over ultra-broadband electromagnetic signals by the Autler-Townes splitting effect in the resonance region and the alternating current Stark (AC Stark) shift effect in the off-resonance region. In a cesium vapor cell at room temperature, by varying the coupling laser wavelength, three energy levels 70S1/2, 42D5/2, and 30D5/2 are selected to measure the spatial electric field strength of electromagnetic signals in the far-off-resonance region (2 GHz) and the resonance region (9.953 GHz and 29.54 GHz), respectively. On this basis, the attenuation factors caused by environment scattering and vapor cell perturbations are calculated. Meanwhile, the potential of Rydberg atoms for communication applications in the broadband frequency range is demonstrated by experiments on the variation of the signal-to-noise ratios (SNRs) of electromagnetic signals with different modulation frequencies under amplitude modulation and frequency modulation in the far-off-resonance region (2 GHz), near-off-resonance region (9.5 GHz), and the resonance region (29.54 GHz). Furthermore, for the amplitude modulation signal with a modulation frequency of 10 kHz, the demodulated signal SNR is investigated in the ultra-broadband frequency range of 100 kHz-40 GHz. The experimental results reveal that Rydberg atoms can break the operational bandwidth limit of conventional electronic sensors, and have the ability of electric field sensing and communications in the ultra-broadband continuous spectrum range.

A method of displacement reaction between metals based on ultraviolet (UV) induction is employed to prepare a substrate of a silver/foam nickel composite structure, which is then used as the surface-enhanced Raman scattering (SERS) substrate. The simulation software COMSOL Multiphysics is utilized to calculate the electromagnetic field distributions and the theoretical enhancement factors for substrates composed of silver nanoparticles with diameters of 43 nm, 53 nm, and 63 nm,respectively. The maximum electric field intensities obtained are 43.76 V/m, 55.16 V/m, and 87.25 V/m, respectively, and the corresponding enhancement factors (EFs) are 3.67×106, 9.26×106, and 5.80×107,respectively. Raman tests show that the measurement effect of the prepared substrate of the silver/foam nickel composite structure is optimal when the concentration of the reaction solution is 1.5 mol·L-1 and the displacement time is 120 min. The detection limit of the substrate on rhodamine 6G (R6G) is as low as 10-12 mol·L-1 and the EF calculated reaches 2.47×109. R6G with a concentration of 10-7 mol·L-1 is used as the probe molecule of Raman uniformity tests on the substrate of the silver/foam nickel composite structure. The relative standard deviation (RSD) values corresponding to the characteristic peaks at 613 cm-1 and 1364 cm-1 in the Raman shift spectrum are 14.5% and 13.6%, respectively, which indicates that the substrate enjoys favorable uniformity.