We present an optical fiber Fabry-Perot (F-P) temperature sensor based on metal welding technology. The fiber sensor is composed of a single-mode fiber and a metal capillary that are encapsulated by metal welding technology. The relationship between the cavity length and sensitivity is analyzed theoretically. The experimental results show that the sensitivity of the fabricated sensor reaches 3.85 nm / ° C when the F-P cavity length is 171 μm. In addition, the sensitivity of the F-P temperature sensor increases as the cavity length of the F-P temperature sensor decreases. The proposed sensor fabricated by metal welding technology has the advantages of a high sensitivity, simple fabrication, simple structure, and low cost.

A method for the preparation of composites that allow the growth of ZnO nanorod structures on the full surface of porous silicon (polished surface, pore walls, and pore bottoms) is presented. The porous silicon is obtained by electrochemical etching of P-type silicon (100). The nanorods were grown in two steps: a sol–gel method and an oil bath method. The morphology of ZnO nanorods at different concentrations of the growth solution was investigated using scanning electron microscopy. X-ray diffraction confirmed the formation of ZnO hexagonal fibrous zincite structures. UV–Vis absorption spectroscopy confirmed that the composites possess good light absorption in the broad spectral region. In the wavelength range of 300 to 400 nm, the light absorption value of the porous silicon/zinc oxide (porous Si/ZnO) nanorods was increased by ~25% compared to that of the porous Si/ZnO films. The photoluminescence spectra confirmed the luminescence performance of the composites. Finally, the optical properties of the composites were further verified by simulation calculations.

Bulk-layered materials were constructed into nanowall arrays, and their optical absorption properties were investigated by the finite-difference time-domain technique. The results showed that the nanowall array exhibits excellent absorption properties in both ultraviolet and visible bands. For WS₂, MoS₂, WSe₂, MoSe₂, and MoTe₂, when the excitation wavelength increases to a certain value, the absorption begins to obviously decrease, and the corresponding excitation wavelength shows a redshift trend. However, the absorptivity of graphene nanowall arrays remains above 0.9 in the 350- to 1200-nm band. In addition, with similar structural parameters, the absorption properties of nanowall arrays are better than those of nanorod arrays. The change in the structural parameter and morphology can lead to an increase in the pore number, specific surface area, and multistage reflection and achieve optical absorption enhancement. Graphene nanowall arrays show excellent absorption properties by our experimental measurement.

Our proposed work analyzes and models the photonic crystal (PhC)-based elliptical ring resonator for detecting viral and bacterial infections. Optical sensors show extreme results as sensing devices. So, they are broadly accepted in the medical field for the rapid and effective diagnosis of diseases. Optical biosensors are designed to detect cancer, malaria, typhoid, tuberculosis, etc. The principle behind the working of optical biosensors is a shift in the peak resonance wavelength corresponding to the small changes in the refractive index values. Due to the rapid mutation and replication of viral pathogens in the human cell nucleus, there is high demand for sensors that provide accurate results for viral and bacterial diseases in seconds. Hence, optical biosensors can give results in a short amount of time with a high sensitivity. The proposed sensor achieved a high sensitivity of 881.25 nm / RIU for tuberculosis and 555.55 nm / RIU for hepatitis B. The quality factor and figure of merit is also calculated, and their values come out to be 624.37 and 346.38, respectively, in the case of typhoid and Bacillus cereus. The platform used for simulating the analytes is the finite-difference time-domain.

A compact and broadband polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a hybrid plasmonic waveguide and a ridge waveguide on lithium-niobate-on-insulator. Due to the surface plasma polariton (SPP) effect, the phase-matching condition is satisfied for transverse electric polarization, whereas the transverse magnetic polarization has a significant phase mismatch by choosing reasonable widths of both waveguides. A short ( ∼ 28 μm long) PBS is designed while the gap width is chosen to be 200 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>130 nm) for an extinction ratio of >15 dB and a large fabrication tolerance for the variation of the waveguide width (over ± 50 nm).

The plasmonic color filter with sub-wavelength nanometal structure has the advantages that the traditional organic dye color filter cannot replace because of its unique characteristics. However, most plasmonic color filters have low selectivity and weak resonance. It limits their further applications and accuracy. We introduce a plasmonic color filter with a nanoring aperture array, which can exhibit high resonance intensity by fine-tuning the size of the outer aperture and the array period. Through COMSOL Multiphysics comprehensive verification, this may be potentially useful in micro- and nanodetection, optical imaging, optical filters, and other fields.

A biosensor structure based on a ternary photonic crystal (TPC) containing a defect is designed and simulated. This proposed biosensor detects the concentration of glucose in human urine. Based on the transfer matrix method, we theoretically studied the transmission spectra through the TPC presuming blood samples with different refractive indices (RIs) infiltrated into the defect layer of the proposed structures. By varying the concentration of glucose in the urine, the RI of the urine is changed, which in turn changes the sensor’s output response; both transmission response and resonance wavelength are affected. We evaluated average sensitivity (S) for the number of periods at different values N for optimization purposes. Our results show that the biosensor has performance parameters for a period value N = 6. Indeed, a value of 1033 nm of full width at half maximum photonic bandgap can be observed with a S of 965 nm / RIU. The quality factor is 1892.542 and the figure of merit is 756.86 RIU ^{− 1}. The proposed biosensor can be a miniaturized structure with extreme sensitivity in the concentration of glucose detection models

We study the multiple plasmon-induced transparencies (PIT) in the waveguide structure based on bulk Dirac semimetal (BDS) containing multiple side-coupled T-shaped cavities. Using the finite element method, we mainly investigate the transmission spectra, the transmission phase shifts, the delay times, and the magnetic field distributions of the two T-shaped cavities waveguide structure. It is shown that their transmission characteristics strongly depend on the geometric parameters of the waveguide structure. In addition, we discuss the effect of the Fermi level of BDS and the refractive index of the medium on the transmission spectrum of the two T-shaped cavities structure. To get more PIT peaks, we try to simulate the transmission spectrum of three T-shaped cavities waveguide structure. All the results about the multiple PIT phenomena may have some possible applications in designing lenses, high-capacity storage devices, and new filters.

Metamaterial absorbers are widely used in the sensing field based on their rich resonance behaviors. So far, the applications of metamaterial absorbers in gas sensing have not been paid much attention by researchers. A single-mode narrow bandwidth THz metamaterial absorber is suggested and validated. An absorption peak is excited based on local surface polarization mode resonance and dielectric loss in the 2 to 36 THz band. In experiments, the hole array diameter R is increased, the absorption peak is increased from 0.51 to 0.66, and resonance position is moved to the high-frequency region. When the dielectric layer thickness h₂ is increased, the absorption peak is increased from 0.51 to 0.57, and resonance position is moved to the low-frequency region. Similarly, when the dielectric layer thickness h₃ is increased, the absorption peak is increased from 0.51 to 0.53, and resonance position is also moved to the low-frequency region. This metamaterial absorber exhibits the feasible for gas and liquid sensing.

Dual-symmetry breakings including permittivity asymmetry and geometry asymmetry have been studied in all dielectric split-ring metamaterials supported bound states in the continuum. For any single symmetry breaking, the proposed metamaterials can support simultaneously dual quasi-bound states in the continuum (quasi-BICs). Multipolar decomposition reveals that dual quasi-BICs induced by permittivity asymmetry are both governed by magnetic dipole and electric quadrupole, whereas dual quasi-BICs induced by geometry asymmetry are governed by magnetic dipoles. Under the combined effect of the two types of symmetry breaking, it is found that the quasi-BIC can be weaken and vanished, which is different from enhanced quasi-BIC effect induced by a single symmetry breaking. In addition, asymmetric magnetic and electric field distributions can be realized by selecting different type of symmetry breaking, providing a new way of indirectly manipulating the localized magnetic fields. We show that dual-symmetry breakings point to a unique routine to analyze the physical mechanism of quasi-BICs, which furthermore provide a useful insight into their tuning behavior.

A numerical model was used to analyze the Auger coefficient in a c-plane InGaN/GaN multiple-quantum-well laser diode (MQWLD) under hydrostatic pressure. Finite difference techniques were employed to acquire energy Eigenvalues and their corresponding Eigenfunctions of InGaN/GaN MQWLD, and the hole Eigenstates were calculated via a 6 × 6 k.p method under applied hydrostatic pressure. It was found that a change in pressure up to 10 GPa increases the carrier density in the quantum well and barriers and the effective band gap. Based on the result, the exaction binding energy decreased, the electric field rate increased up to 0.77 MV / cm, and the Auger coefficient decreased down to 2.1 × 10 ^{− 31} and 0.6 × 10 ^{− 31} cm⁶ s ^{− 1} in the MQW and barrier regions, respectively. Also, the calculations demonstrated that the hole-hole-electron (CHHS) and electron-electron-hole (CCCH) Auger coefficients had the largest contribution to the Auger coefficient. Our study provides more detailed insight into the origin of the Auger recombination rate drop under hydrostatic pressure in InGaN-based light-emitting diodes.

Multimode waveguide bends (MWBs) with very compact sizes are the key building blocks in the applications of different mode-division multiplexing (MDM) systems. To further increase the transmission capacity, the silicon MWBs for dual polarizations are of particular interest considering the very distinct mode behaviors under different polarizations in the silicon waveguides. Few silicon MWBs suitable for both polarizations have been studied. In this paper, we analyze several dual-polarization-MWBs based on different bending curve functions. These special curve-based silicon MWBs have the advantages of easy fabrication and low loss compared with other structures based on subwavelength structures, such as gratings. A comparison is made between the free-form curve (FFC), Bezier curve, and Euler curve, which are used in the bending region instead of a conventional arc. The transmission spectra of the first three TE and TM modes in the silicon multimode waveguide with a core thickness of 340 nm are investigated. The simulation results indicate that, with the premise of having the same effective radius, which is only 10 μm in this paper, the six-mode MWB based on the FFC has the optimal performances, including an extremely low loss <0.052 dB and low crosstalk below −25.97 dB for all six modes in the wide band of 1500 to 1600 nm. The MWBs based on the Bezier and Euler curve have degraded performances in terms of the loss and crosstalk. The results of this paper provide an efficient design method of the polarization insensitive silicon MWBs, which may leverage research for establishing complicated optical transmission systems that incorporate both the MDM and polarization-DM technology.

Localized surface plasmon resonance (LSPR) can enhance the optical field density around the nanostructure to improve devices’ light absorption. Aluminum nanoparticles (Al NPs) were introduced into solar-blind photodetectors with carbon dots (CDs) as a photosensitive material. It is found that by inserting Al NPs into the device, the switching ratio, responsivity, and external quantum efficiency reached 125.9, 0.511 A/W, and 2.16, respectively, which has obvious improvement compared with CDs based photodetector. The results indicate that Al NPs have an apparent optimization effect on the performance of the CDs photodetector by stimulating LSPR, which improves the photoresponse ability of CDs. It is illustrated by finite difference time-domain method that Al NPs can constraint the light field energy and successfully stimulate LSPR.

A new light-responsive arylazopyrazole (AAP) containing a polymer matrix thin film is fabricated by spin-coating different concentrations of the AAP azo dye into the polydimethylsiloxane (PDMS) polymer at 150°C. The new AAP molecular switch was also used to fabricate a solid-state PDMS-AAP waveguide by contact lithography and soft replica modeling methods in the micrometer scale. The refractive index of the spin-coated photoswitchable material can be modulated via the reversible trans-to-cis photoisomerization behavior of the AAP unit using different concentrations. When 0.01 M solution of the AAP unit was used, the refractive of the composite was 2.32 in the trans state and dropped to 1.85 in the cis state in the operating wavelength of 340 nm. At higher concentrations of 0.020 and 0.03 M, a wide refractive index tuning is achieved under the same wavelength. In 0.030 M, the refractive index was 2.65 for the trans state and 2.0 for the cis state. The results suggest that the increase in refractive index tuning is related to the concentration of the AAP unit of the composite film. Theoretically, the spectral properties of the composite film are also simulated with two methods: (1) the Maxwell equations and (2) the frequency dependent finite element, showing excellent agreement for the different propagation modes of the proposed waveguide for regulated signals of 365/525 nm wavelengths. Furthermore, the photoisomerization of the PDMS-AAP thin film is analyzed with UV–vis spectroscopy to demonstrate the isomerization responses of the AAP moiety in the solid state. In addition, preliminary photomechanical actuation properties of the composite film have been investigated. The PDMS-AAP waveguide described provides a new approach for optically tunable photonics applications in the UV–visible region.

Chiroptical effects, which include the dichroism of left and right circularly polarized light, can be observed in structures made up of nanoscale chiral elements. We introduce a holistically nondestructive tunable chiral perforated photonic crystal film. The structure exhibits a strong photon spin selection effect at a wavelength of 810 nm, resulting in a significant circular dichroism (CD) value. The origin of the chiral response is explained using linear superposition theory, and the authors also discovered a strong chirality near-field enhancement at 796 and 810 nm, which could be used in molecular chirality sensing and other fields. By adjusting related parameters, the unit structure can greatly impact the reflection spectrum of the CD value. These chiral photonic crystal films may have potential applications as polarization management devices in the future.