Owing to their low susceptibility to environmental interference and ease of miniaturization, grating interferometers are widely used in lithography machines and precision manufacturing. This study proposes an ellipse fitting error compensation algorithm based on biorthogonal phase-locked digital upconversion (BPDU) to address the difficulty of compensating for dynamically changing nonlinear errors in grating interferometers. The causes and characteristics of dynamic changes in nonlinear errors are analyzed from both the error source and spectrum perspectives. Based on the characteristics of these nonlinear error changes, the proposed BPDU-based ellipse fitting compensation algorithm is designed and implemented. Compared with a partitioned ellipse fitting error compensation algorithm, the proposed algorithm increases the update speed and fitting accuracy under low-speed and reciprocating conditions. Through hardware-in-the-loop simulation and experiments, the nonlinear error is reduced from 12.66 nm measured at 0.2 m/s to an average of 2.15 nm at different motion speeds, thereby improving the measurement accuracy of the grating interferometer from the 10-nm level to the nm level.

A widely tunable, narrow-linewidth dual-wavelength Ti: sapphire laser incorporating a prism pair and a Littman-grating dual self-injection cavity was demonstrated. The prism pair was inserted into the gain cavity to introduce spatial dispersion to enhance the mode selection ability, while the Littman-grating dual self-injection structure in the dispersive cavity further enabled accurate dual-wavelength frequency selection. The combination of the two effectively suppressed the gain of the non-selected longitudinal modes and realize the flexible tuning of the narrow-linewidth dual-wavelength laser, which has been effectively proved in both theoretical calculations and experiments. This made up for the shortcomings of the multimode background and tuning limitation of the typical Littman-grating self-injected Ti: sapphire laser. By independently tuning the end mirrors of the dual gain cavity and the reflectors of the dual dispersive cavity, arbitrary wavelength combination and continuously adjustable intervals of the narrow-linewidth dual-wavelength output was achieved across the 740-870 nm spectral range, maintaining a linewidth of less than 3 pm throughout the entire tuning range. When the pump power was 40.8 W, the maximum total output power of the narrow-linewidth dual-wavelength at 780 nm and 800 nm was 4.2 W, and the conversion efficiency was 10.28%.

We design a terahertz[THz]biosensor supported by quasi-bound states in the continuum[QBICs]for lung cancer cell sensing.By destroying the in-plane symmetry of the bound state in the continuum[BIC],a QBIC with a high Q-factor is obtained.The designed biosensor exhibits excellent refractive index performance with a sensitivity of 354 GHZ/RIU.Unlike traditional detection schemes that require sample drying,a microfluidic liquid sample pool is utilized to detect differ-ent concentrations of lung cancer cells.As the cell concentration increases,the resonance frequency and intensity of the measured spectrum show significant changes.The designed sensor allows non-invasive real-time detection of living lung cancer cells,providing a potentially effective tool for early diagnosis and treatment of lung cancer.

This paper conducts numerical simulations and experimental investigations on a dual-wavelength cascaded Raman laser. The output characteristics of an intracavity cascaded Raman laser, including their dependence on output coupler (OC) transmittance, repetition rate, and power density, are systematically analyzed. Key parameters such as build-up time, pulse waveform, pulse width, and output power ratio under various operating conditions are obtained. These findings provide critical guidance for controlling output characteristics like dual-wavelength power ratios, enabling adaptability to diverse application scenarios. Experiment studies focus on a 1st and 2nd-Stokes dual-wavelength cascaded Raman laser. The cascading dynamics are investigated by examining output characteristics under varying OC transmittance and repetition rates. At a fixed repetition rate, the laser performance is evaluated across different OC transmittance configurations. Under optimized conditions (T=18%@1st-Stokes wavelength, T=79%@2nd-Stokes wavelength, pump power=28.8 W), a maximum output power of 4.43 W is achieved, comprising 2.69 W at the 1st-Stokes wavelength and 1.74 W at the 2nd-Stokes wavelength, yielding an overall conversion efficiency of 15.4%. Additionally, with fixed OC transmittance (T=25%@1st-Stokes, T=80%@2nd-Stokes), the output characteristics are studied at varying repetition rates. Numerical results exhibit well agreement with experimental data, successfully validating the dual-wavelength power ratio regulation mechanism. The proposed simulation model demonstrates its capability to predict output characteristics of solid-state intracavity dual-wavelength cascaded Raman lasers through numerical computation.

Cross-domain communication between sea and air plays a vital role in cross-domain collaborative operations and the establishment of cross-domain heterogeneous marine unmanned systems.Based on the different deployment methods of cross-domain communication systems between sea and air,this work introduces direct,relay,and conversion cross-domain communication technologies.The characteristics and limitations of various cross-domain communication technologies,both domestic and international,are summarized in terms of communication rate,communication distance,and deployment flexibility.Finally,the future research direction of this field is prospected.

Mass detection plays an indispensable role in many fields like medical targeted therapy,biological cytology,and nanophysics.However,traditional mass detection faces the challenge of a complex system,expensive instruments,and long testing time.Here we report an all-fiber-optic mass sensor based on a nanofilm resonator.Using resonant frequency shifts as the readout of analyte mass,the sensor achieves the mass sensitivity of 0.920 kHz/pg with a mass resolution of 1.9 × 10-14 g,for the first-order mode in the mass range up to 372 pg at room temperature.In this work,we transfer the excitation laser and detection laser to the micro-cavity structure at the end of the optical fiber.Combined with optical fibers,the sensor can be made extremely integrated,making it more stable and collimation-free compared with traditional bulky optical setups.Its good biocompatibility and anti-electromag-netism disturbance ability also make this mass sensor potentially a beneficial tool for cell biology and basic phys-ics measurements.

Multifunctional photodetectors require the photosensitive layer to exhibit both broad spectral response and high-performance characteristics. Silicon-based photodetectors are widely applied, benefiting from high quantum efficiency and mature fabrication processes. However, the silicon bandgap of over 1 eV limits its operational range across a broad spectrum. In this study, a semimetal-controlled, silicon-based broadband photodetector is developed, in which the semimetal ZrTe3 functions as both the barrier control layer and the light absorption layer. The results demonstrate that the designed silicon photodetector achieves an ultra-broad spectral response ranging from ultraviolet to mid-infrared (355 nm to 3.35 mu m). With its high responsivity and ultrafast response time, a single-pixel imaging module and a low-concentration gas sensing module are further developed. The imaging module can capture clear contours at a sampling rate as low as 1%, highlighting its significant potential in computational optics. The gas sensing module detects CH4 with a lower detection limit of 5.35 ppm in the near-infrared and successfully demonstrates stable gas detection capabilities in the prototype.

The polarizing beam splitter (PBS) plays an important role in meeting the growing demand of communication capacity. This paper presents a novel mid-infrared broadband in-fiber PBS using dual-core photonic crystal fiber (DC-PCF) with dual aluminum wires numerically. The high refractive index substrate material As2S3 glass can facilitate the extension of the working wavelength to the mid-infrared band, and the aluminum wires provide plasmonic effect to enhance the birefringence of the proposed PCF to promote the compactness of the device. The numerical results demonstrate that the coupling length ratio of 2 can be achieved at 3.3 mu m, when the diameter of cladding holes is 1.6 mu m, the diameter of central hole is 1.2 mu m, the diameter of inner small holes is 0.7 mu m, the diameter of aluminum-filled holes is 2.0 mu m and lattice constant is 2.1 mu m. The aluminum wires have a remarkable tuning effect and the length of this PBS is only 160 mu m. Meanwhile, this PBS possesses the maximum ER of -72.1 dB and a 1020 nm-long operating bandwidth of extinction ratio greater than 20 dB, ranging from 2.92 to 3.94 mu m. Additionally, with the existing manufacturing process, the device has a high feasibility. It deserves expecting that the proposed PBS has extensive application prospects in fields such as gas sensing, medical surgery, environment monitoring, optical imaging and the new generation optical communication network.

Objective Antibiotics produced by microorganisms (such as bacteria and fungi) or through semi-synthetic and synthetic methods are a class of drugs primarily used to treat various infections caused by bacteria or fungi. The misuse and overuse of antibiotics have resulted in severe problems caused by antibiotic resistance. To ensure the effective use and management of antibiotics, one must detect their concentrations precisely. Conventional methods for detecting antibiotics require professional operational technology and complex instruments; moreover, the associated procedure is cumbersome and lengthy. Therefore, an efficient, rapid, and highly sensitive method for detecting antibiotic concentrations must be devised. Bound states in the continuum (BICs) can promote strong interactions between light and matter, which are introduced into the metasurface to achieve ultrahigh Q resonance. Combined with the advantages of terahertz technology in nondestructive testing, terahertz metasurfaces based on BICs have been widely used in biological and chemical sensing. A metasurface with BICs and a high Q-factor can significantly improve the sensitivity of a biosensor to slight environmental changes, thus providing an effective scheme for the rapid, convenient, and highly sensitive detection of antibiotics. Methods A metallic structure was designed on a 500- mu m-thick quartz substrate. The transition from BICs to quasi-BICs was achieved by introducing asymmetric parameters. The transmitted spectra for different parameters l1 were simulated using CST Studio with a time-domain solver. In the simulation, the a- and y-directions were set as periodic boundary conditions, and the z-direction was set as an open-boundary condition. BICs can be excited under both a- and y-polarization incidences. The far-field scattering power of the structure was analyzed via Cartesian multipole decomposition based on electromagnetic multipole theory. A series of samples with different parameters was prepared and verified using a terahertz time-domain spectroscopy (THz-TDS) system. Additionally, the refractive-index sensitivity of the sensor was simulated and analyzed. Different mass concentrations of penicillin G potassium salt were detected using these sensors. For measurement, 10 mu L analytes with different concentrations were pipetted onto the sensor surface and then allowed to dry. The spectra were obtained using the THz-TDS system. After each measurement, the sensor was cleaned in ultrapure water to meticulously remove the residual analyte from the sensor surface and then dried. Prior to the next measurement, the spectrum transmitted by the cleaned sensor was measured to ensure that the cleaning process did not affect the optical response. Results and Discussions When a- or y-polarized terahertz waves are incident, the simulated spectra of the metasurface with BICs under different values of l1 are as shown in Figs. 2(a) and 3(a). When l1=l=70 mu m, the spectral linewidth disappears at 1.07 THz (under a-polarized incidence) and 1.12 THz (under y-polarized incidence), thus indicating the presence of BICs with an infinite Q-factor. As l(1) increases, the spectral linewidth broadens, thus indicating a gradual increase in the radiation loss. Subsequently, the BICs transform into quasi-BICs. The resonance frequency and Q-factor of the quasi-BICs can be tuned by changing the asymmetric parameter l1. The variation in the Q-factor with the asymmetric parameters adheres to the relationship Q proportional to alpha(-2) [Figs. 2(f) and 3(e)]. For the a-polarized incidence, the excited quasi-BIC and dipole modes originate from electric quadrupole (EQ) and toroidal dipole (TD), respectively [Figs. 2(c) and (d)]. For the y-polarized incidence, the excited quasi-BIC mode is derived from electric dipole (ED) [Fig. 3(c)]. The designed sensor has a refractive index sensitivity of 210 GHz/RIU, which demonstrates its excellent sensing performance [Figs. 6(a) and (b)]. The designed sensor was used to detect different concentrations of penicillin G potassium salt, where a minimum detection mass concentration of 0.625 mg/mL is recorded [Figs. 7(a) and (b)]. The spectra transmitted by the bare and cleaned sensors after measuring different concentrations of the analyte are highly consistent [Fig. 7(d)], thus demonstrating the reusability of the device. Our design provides a rapid and effective method for the high-sensitivity detection of antibiotics. Conclusions In this study, a BIC-based metallic metasurface was designed for the detection of different antibiotic concentrations. When structural symmetry is broken, the lossless BIC transforms into a quasi-BIC with a finite Q-factor. The Q-factor of the quasi- BIC can be tuned by changing the asymmetric parameters. The results of multipole decomposition show that the quasi-BIC excited by a- and y-polarization originates from EQ and ED, respectively. A series of metasurface samples with different parameters was prepared and verified experimentally in the terahertz band. The designed sensor has a refractive-index sensitivity of 210 GHz/RIU, which renders it suitable for high-sensitivity sensing applications. Considering potassium G as an example, the sensor was used to detect different concentrations of antibiotics, and the experimental results show a minimum detection mass concentration of 0.625 mg/mL. The reusable features reduce the detection costs. The designed metasurface with BICs provides a rapid and effective method for the highly sensitive detection of antibiotic concentrations, which is expected to replace conventional detection methods in the future and exhibits potential application prospects in medical diagnosis, food safety, and environmental monitoring.

This work presents a femtosecond laser fabrication method for precision-engineered nanopillar arrays, applicable for surface-enhanced Raman scattering (SERS) substrates. The proposed method consists of two steps: (1) fabrication of nanopillar arrays using femtosecond laser-induced two-photon polymerization (TPP) technology; and (2) deposition of Ag nanoparticles on the fabricated nanopillar arrays. Nanopillar arrays of the proposed SERS substrates are optimized with geometrical parameters of diameter, height, spacing, and arrangement. A limit of detection (LOD) down to 10(-7) mol/L for Rhodamine 6G solution is achieved and the enhancement factor is estimated to be up to 2 x 10(3). The experimental results indicate that the proposed SERS substrates have potential applications in biomedical detection, food safety monitoring, and quality control.

Janus metasurfaces, characterized by propagation-direction-dependent asymmetric transmission phenomena, provide an innovative design freedom for multiplexed optical systems. However, conventional approaches to asymmetric transmission typically employ three-dimensionally stacked architectures or heterogeneous material integration, exhibiting inherent limitations in fabrication complexity and intrinsic optical loss. This work presents a vanadium dioxide (VO2-) based reconfigurable monolayer Janus metasurface enabling active asymmetric wavefront manipulation within the terahertz spectral range. Through synergistic utilization of VO2's reversible insulator-to-metal phase transition coupled with a dual-parameter modulation scheme governing incident direction, three functionally distinct optical operations are realized: an asymmetric focusing metalen, an asymmetric focusing vortex beam generator, and a Janus NOR logic gate. The proposed asymmetric wavefront modulation paradigm demonstrates advantages in fabrication cost-effectiveness and structural simplicity, thereby establishing a viable pathway toward high-efficiency, multifunctional, and chip-scale integrated photonic devices.

Next‐generation photodetectors demand multidimensional information perception, high responsivity, and low noise equivalent power across an ultra‐wide spectral range. Polarization‐sensitive photodetectors based on anisotropic low‐dimensional materials offer a promising solution, yet inherent material properties impose severe performance trade‐offs. Here, this challenge is addressed by developing an ultra‐broadband polarization photodetector with back‐to‐back Schottky barriers, fabricated via UV laser treatment of semi‐metallic ZrTe 3 . The results demonstrate that the ZrTe 3 polarization photodetector achieves ultra‐wide spectral polarized light response from UV to terahertz (355 nm–1.43 mm) with antenna‐free integration at room temperature. Notably, it exhibits a high responsivity of 0.31 A W −1 with rise/fall times of 729 ns/14.9 µs at 532 nm. One‐year‐long photoresponse tests in air demonstrate stability for ultra‐broadband ZrTe 3 polarization detector (UBPD). This work highlights the transformative potential of ZrTe 3 for future wide‐spectrum polarization‐sensitive applications.

The work demonstrates a plasmonic polarization filter using dual graphene-coated aluminum (Al) wires embedded hollow core fiber (HCF). The finite element method (FEM) is employed to analyze the in-fiber transmission characteristics. The simulation results show when the outer tube diameter d1 is 13.6 μm, inner diameter tube d2 is 8.0 μm, the Al wire diameter d3 is 3.4 μm, tube-to-tube pitch Ʌ is 16.1 μm, outer tube thickness t1 is 0.48 μm, inner tube thickness t2 is 0.52 μm and graphene layer thickness tg is 1 nm, this in-fiber filter can operate around central wavelength of 1.55 μm, where the loss difference between the two polarization directions can reach 661 times. The 10-mm-long filter exhibits a maximum extinction ratio (ER) of − 53.471 dB, and an operating bandwidth with ER < − 20 dB of 230 nm, spanning from 1.48 to 1.71 μm. Additionally, an extremely strong anti-bending capability and a good cubic polynomial relationship with R2 = 0.9532 between bend radius and ER intensity can be achieved. Finally, the fabrication feasibility and tolerance are discussed. It is believed that the proposed filter possesses excellent extinction capabilities, broad bandwidth, compact dimensions, resistance to bending, and repeatability, addressing the requirements of contemporary photonic integrated systems, overcoming the “electronic bottleneck” challenge.

A study of 355 nm laser with high pulse energy across various types of atherosclerotic lesion models is presented. The 355 nm laser pulses (10 ns) are delivered via a single fiber (600 μm diameter), and the ablation of calcified tissue, lipid tissue, and thrombus-like tissue are studied under varied laser fluence (40-70 mJ/mm2) and repetition rate (5-30 Hz). The contact and noncontact ablation processes of chicken tibia samples (calcified tissue) are compared at 60 mJ/mm2 and 30 Hz, and the size of ablation particles is in the range of 0.1-1 μm. At the same repetition rate, the advancement rate of tricalcium phosphate samples reaches 150 μm/s at 70 mJ/mm2. Calcified and lipid models demonstrate predictable increases in ablation with higher laser fluence and repetition rate. The fresh porcine blood clot samples exhibit high-quality ablation with good channel effect at 50 mJ/mm2 and 30 Hz.

Yellow light sources, emitting between 570 nm and 600 nm, are interesting for their potential in several application fields and are irreplaceable to a certain extent in certain characteristic domains. Therefore, it has been a research hotspot in the field of laser technology. A crystalline Raman yellow laser is an important approach to achieving yellow light sources. This paper focuses on an important branch of all-solid-state yellow laser, i.e. crystalline Raman yellow laser, and discusses its research progress in the past twenty years by summarizing a few classic works. The paper clarifies the implementation schemes of crystalline Raman yellow lasers for different application requirements, providing a reference for future research in this field.