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Ultra-high quality (Q) factor resonances derived from the bound states in the continuum (BICs) have drawn much attention in optics and photonics. Especially in meta-surfaces, they can enable ultrasensitive sensors, spectral filtering, and lasers because of their enhanced light-matter interactions and rare superiority of scalability. In this paper, we propose a permittivity-asymmetric all-dielectric meta-surface, comprising high-index cuboid tetramer clusters with symmetric structural parameters and configuring periodically on a glass substrate. Simulation results offer dual-band quasi-BICs with high Q values of 4447 and 11391, respectively. Multipolar decomposition in cartesian and electromagnetic distributions are engaged to analyze the physical mechanism of dual quasi-BIC modes, which reveals that they are both governed by magnetic quadrupole (MQ) and in-plane toroidal dipole (TD). The polarization-insensitive and scalable characteristics are also investigated. Additionally, we appraise the sensing performances of the proposed structure. As an example, our work supports an uncommon route to design dual-band polarization-insensitive TD quasi-BICs resonators and facilitates their applications in optic and photonics, such as low-threshold lasers and sensing.

A basic plasmonic system, consisting of a stub metal-insulator-metal (MIM) waveguide coupled with a ring resonator, is presented to realize Fano resonance and electromagnetically induced transparency-like (EIT-like) effect, which are numerically calculated by the finite element method (FEM). Meanwhile, the formation mechanism of Fano resonance is analyzed according to numerical simulations. Besides, the coupled mode theory (CMT) and the standing wave theory are used for explaining the Fano and EIT-like resonances phenomenon. Based on this system, an inner ring cavity is connected to the ring resonator by a slot and another ring cavity is later introduced under the stub resonator in order to constitute a new coupled plasmonic resonator system, providing quadruple Fano resonances and double EIT-like responses finally. In addition, the Fano and EIT-like resonances can be independently tuned by adjusting the structural parameters, which makes the design of highly integrated photonic circuits more flexible. The main contribution of this paper is that the proposed structure has a relatively good sensitivity of 1600 nm/RIU and an ultra-high FOM value of $1.2\times 10^{6}$ as a refractive index nanosensor. Moreover, it can serve as an all-optical switch with a high on/off extinction ratio of about 43 dB. Additionally, its maximum group delay time and group index are about 1.49 ps and 221, indicating that the proposed system has a pretty good slow light effect. Therefore, the proposed structures are believed to have significant applications in high-performance nanosensors, switches, slow light devices and nonlinear areas in highly integrated plasmonic devices.

Gold nanorods (Au NRs) have attracted extensive research interest due to their unique optical properties, adjustable aspect ratio, and easy surface modification in the fields of biosensing, bioimaging, and disease diagnosis and detection. In this review, we present a comprehensive review of various methods for preparing gold nanorods including hard template method, electrochemistry method, photochemistry method, seed-mediated growth method, secondary growth method, and amorphous seed method. The unique optical properties of the gold nanorods and its applications in biomedical, detection, catalysis, and information storage will also be discussed in detail.

Both toroidal dipoles, electric dipoles and magnetic dipoles belong to one type of electromagnetic excitation. In this paper, we present an all-dielectric metasurface composed of an array of square nanoholes. It can simultaneously generate four resonance responses excited by TD, EQ and MD in the continuous near-infrared band. By introducing the in-plane symmetry breaking of the unit cell, asymmetric dielectric nanohole arrays are used to achieve two quasi-BIC resonance modes with high Q-factors excited by EQ and MD. The paper theoretically analyzes and demonstrates the relationship between structural asymmetry and the radiative Q-factor of two Fano resonances, that are governed by symmetry-protected BICs. And multipole decomposition and near-field analysis are performed to demonstrate the dominant role of various electromagnetic excitations in the four modes. The spectra response is also calculated for different incident polarization angles and medium refractive indices. The proposed metasurface is more feasible and practical compared to other complex nanostructures, which may open avenues for the development of applications such as biochemical sensing, optical switches and optical modulators, and provide a reference for the design of devices with polarization-independent properties.

In this paper, a novel plasmonic structure consisting of a metal-insulator-metal (MIM) waveguide which is separated in intermediate region coupled with a cross-shaped cavity (CSC) is proposed. Based on the finite element method (FEM), results are simulated by COMSOL Multiphysics software concluding three different Fano resonances peaks and an independent Lorentz peak. Theoretically, multimode interference coupled mode theory (MICMT) is used to calculated the formation of the peaks. Besides, by changing the parameters of the structure, the influence of different parameters on each resonance peak is studied. Based on the original CSC structure, the system is extended to five types of Fano resonance system by appending a semi annular (SA) structure. The research results show that the sensitivity of expanded structure can be up to 1478 nm/RIU, and the FOM value can be as high as 5×105, demonstrating its excellent nano-sensing performance and can be used as an efficient refractive index (RI) sensor.

A plasmonic structure, constituted by metal insulator metal waveguides and split annular cavity connected with rectangular resonator (SACRR), is proposed and investigated. Numerical simulation by the finite element method (FEM) has been done to investigate the transmittance properties of the proposed structure and four Fano resonances arise in the results. To analyze and verify the simulation results, multimode interference coupled mode theory is engaged, theoretically. In addition, the structural parameters are analyzed and discussed to design and control the proposed structure, which shows sufficient flexibility. Due to multi-Fano resonances providing multiple monitoring points and the extremely sharp asymmetry of Fano resonance, the structure can service as a high-performance multichannel refractive index nanosensor with a sensitivity of 1000 nm/RIU and maximum figure of merit of 1.358 × 105. The designed structure can surely meet extensive applications for nanoscale devices and integrated optical devices.

The integrated circuit (IC) is a subject for which researchers need practical experience, but its experiment cost is high, the risk involved is high, and it is not easy to carry out experiments on a large scale. This paper designs a three-dimensional integrated circuit virtual experiment platform based on Unity3d. The platform uses the Unity3d and 3ds Max tools to build a three-dimensional model of instruments, equipment, electronic components, and ultra cleanroom laboratory scenes in an integrated circuit experiment. In addition, it uses C# script to develop the functions and three-dimensional simulation of general virtual instruments and equipment and deploys the experimental website using the frame of the jspxcms open source website. The experimental platform arranges the three-dimensional web file WebGL file in the cloud. Students can use video and text materials to acquire basic IC knowledge at any time and conduct IC virtual experiments safely, efficiently, and without constraints. At present, the platform has been tested and used in teaching and has received high praise and recognition from students.

In this paper, a surface plasmon waveguide structure consisting of annular gap and metal-insulator-metal waveguides is proposed, and its spectral characteristics are analyzed and studied. The results show that this waveguide structure has good performance in narrowband filtering in sub-wavelength band, and the central wavelength of the transmission peak is linearly related to the angle of the annular with notch. The results are of great significance for the application of filtering structures in highly integrated photonic circuits.

Fano resonance with high Q-factor plays a pivotal role in the field of optoelectronic applications, especially refractive index sensing. However, ultra-high Q-factor for metallic metasurfaces has been a challenge due to their great ohmic losses. Herein, we propose and numerically analyze an all-dielectric hollow metasurface in the near infrared region which consists of silicon cylinders with two asymmetric rectangular hollows. A sharp Fano resonance with modulation depth close to 100% excited by quasi-bound state in continuum, whose Q-factor can reach 8428 when δ = 40 nm. With the Cartesian multipole decomposition technique, the two excited Fano resonances can be characterized by toroidal dipole response and magnetic dipole (MD) response, respectively. It is worth noting that the Q-factor of MD mode can reach 17106. Moreover, the dependence of the transmission spectra on different geometric parameters is investigated as well. Due to their narrow linewidths and strong near-field confinement, the proposed structure can be applied to a refractive index sensor, yielding a maximum sensitivity (S) of 160 nm RIU−1 and a maximum figure of merit of 575 RIU−1. It is believed that the proposed structure can offer an excellent prospect for biomedical, agriculture, and chemical sensing applications.

This paper mainly presents a nanoscale plasmonic structure, consisting of a waveguide with baffle, a semicircle connecting with four rectangular cavities, called tooth cavities. The whole evolution process of adding tooth cavity and adjusting parameters from the basic structure is also analyzed. Additionally, the position of the tooth cavity is independently adjustable, and the best sensing characteristic curve can be obtained by adjusting the positions of the middle two tooth cavities. Due to the coupling between the wide-spectrum resonance excited by the baffle in waveguide and narrow spectrum resonances emerging from the semicircular cavity connecting rectangular cavities, multi-Fano resonances arise in the simulation results. The transmission spectrum of the proposed structure indicates that 5 Fano peaks are generated in total, and the transmittance of the highest Fano peak can reach 0.88. The structure can be used as a refractive index sensor with a sensitivity of 1000 nm/RIU and figure of merit (FOM) of 38026 by avail of Fano resonance.

The cross-sensitivity of fiber Bragg grating (FBG) always leads to the complexity and instability in its engineering applications, and there are more uncertain factors that affect the center wavelength when FBG is used in fiber lasers as the tunable frequency selector. In order to obtain the stable wavelength of FBG-tuned continuous wave (CW) Er3+-doped fiber laser, we propose and demonstrate a feedback wavelength demodulation and compensation system, which consists of three interrelated parts: a wavelength tuning module controlled by a stepper motor, an all-fiber wavelength demodulation module and a single-chip-based control module. They work cooperatively in a feedback mode and achieve the stabilization of any output laser wavelength in its continuous tunable wavelength range. In the experiment, the output laser wavelength can be locked at the wanted wavelength and be compensated automatically under arbitrary manual tuning in a wide range. When the temperature varies from 10 °C to 40 °C, the laser wavelength shift is less than 0.01 nm for 150 min by real-time compensation, and the corresponding total wavelength shift of ∼0.7 nm is eliminated.

High Q factor multiple Fano resonance excitation in all-dielectric metasurfaces has become an effective mode to design high performance optical devices. This paper proposed an all-dielectric metasurface, composed of silicon cuboid etched with two semicircular holes into a unit cell and periodically arranged on a silica substrate. Numerical results show that triple high Q factor Fano resonances, corresponding to 1310 nm, 1401 nm and 1550 nm, are excited simultaneously, in its transmission spectrum. Toroidal dipole (TD) response can be identified for the resonance at 1310 nm, showing the Q value as high as 2617. By introducing a symmetry breaking, the quasi- bound states in the continuum (BIC) resonances at 1401 nm and 1550 nm are excited, which can be classified by electric quadrupole (EQ) and magnetic dipole (MD) response, respectively. Simulation results demonstrate that by adjusting the structure parameters, the designed metasurface can be tunable to meet the requirements of different applications in near infrared region. The sensing performances of the proposed structure are investigated as well, yielding the refractive index sensitivity of ~ 300 nm/RIU and maximum figure of merit (FOM) of ~ 440. Typical characteristics of the novel structure allow it to cater for the designs and applications of lasers, multiple channel nano sensors and other photonics modules in photonic integrated circuits (PIC) or optical communication devices.

Exciting multiple high Q-factor Fano resonances in all-dielectric metamaterials has become an effective means of designing high performance optical devices. In this paper, we present an all-dielectric metamaterial in the near infrared region by depositing silicon material on the silica substrate and etching two square air holes in the middle of each meta-molecule. Combining with the bound states in the continuum (BIC) theory, four sharp Fano profiles with the modulation depth nearly 100% are excited, in which the maximum Q-factor can exceed 10 4 . The toroidal dipole (TD) also characterizes our metamaterial. By verifying the square inverse law satisfied by Q-factor and combining the electromagnetic field distribution characteristics, the excitation mode of the Fano resonance is expounded. In addition, by turning the polarization direction of the incident light, the Fano resonance at λ = 1238.5 nm can be turned on or off, which performs perfect characteristics for an optical switch. Utilizing the narrow linewidth and significant near-field constraints of the Fano resonances, an optical refractive index sensor can be obtained with the sensitivity of ~ 287.5 n m / R I U and maximum figure of merit (FOM) of ~ 389 R I U - 1 . It is believed that the proposed system can further enhance the development of high-performance biosensors, nonlinear optics, and optical switches.

We present and numerically investigate a novel ultra-broadband polarization independent and incident angle insensitive absorber via simulation. It has a high average absorption of 98.74% from 300 nm to 2000 nm, and the maximum absorption reaches 99.995% within the band. This high absorption is the result of three propagating and localized surface plasmon resonance modes. The absorption stays above 90% at 45°incident angle, and above 80% at 60°. Without heavily stacked alternating materials, the design can reduce fabrication complexities. The adjustability of the structural parameters is demonstrated by designing an absorber covering 200 nm to 3000 nm with over 90% absorption. This proposed device can have promising applications in solar energy harvesting, optical imaging, and optical communications.

This paper proposes a compact plasmonic structure that is composed of a metal-insulator-metal (MIM) waveguide coupled with a groove and stub resonators, and then investigates it by utilizing the finite element method (FEM). Simulation results show that the interaction between the local discrete state caused by the stub resonator and the continuous spectrum caused by the groove resonator gives rise to one of the two Fano resonances, while the generation of the other resonance relies only on the groove. Meanwhile, the asymmetrical linear shape and the resonant wavelength can be easily tuned by changing the parameters of the structure. By adding stubs on the groove, we excited multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of 2000 nm/RIU and a figure of merit of about 3.04 × 103, which can find extensive applications for nanosensors.

Fano resonances based on circle-with-inner-core and stub structure are investigated using data derived from the finite element method and theoretically explained by the multimode interference coupled mode theory and the electric distribution in the system. The parameters of specific structure are modified to investigate the influence of different parts for this metal–insulator–metal system. Due to the high sensitivity to filled dielectric materials, the proposed structure can be applied as a refractive index sensor, whose performances are also explored. High sensitivity is gained as high as 1183.3 nm / RIU. And the figure of merit, a key parameter to describe the sensing characteristic, is achieved as 5.1115 × 104, which is better than most similar structures. Our work is significant for the sensitive refractive index nanosensor.

In this letter, based on the subwavelength metal-insulator-metal (MIM) waveguide embodying a baffle and a slotted side-coupled disk resonator (SSCDR) inserted with a metallic block is designed. The proposed structure is numerically investigated and analyzed by FEM method. Two sharp transmission peaks with high transmittance and asymmetrical line-shaped Fano resonances, originating from the interferences between the width continuum state supported by the MIM waveguide embodying a baffle and the narrow discrete state from the SSCDR, arise in its transmission spectrum. And multimode interference coupled mode theory (MICMT) is employed to analyze the proposed structure theoretically, which is consistent with the simulation results. Additionally, by adjusting the parameters of the structure, the resonant wavelengths of Fano resonances can be manipulated. Finally, the proposed structure is applied to nano-filters, refractive index (RI) sensors, temperature sensors and slow light devices, all showing high performance. It is believed that the proposed system can boost the development of highly integrated photonics and support substantial applications for nano-sensors, filters and slow light devices.

A chip-scale plasmonic band-stop filter (BSF) based on periodic staggered double-side trapezoidal resonators (PSDSTR) is proposed and investigated theoretically and numerically in this letter. A wide bandgap, derived from the interference superposition of the reflection and transmission waves from each periodic unit, is achieved. One periodic unit consists of two staggered double-side trapezoidal resonators (TSDSTR) which can be tunable by modifying the parameters of the trapezoids and the horizontal distance of two staggered trapezoids. Additionally, optimization and theoretical analysis of the periodic unit structure are also made in the letter. Based on the optimized periodic unit, a chip-scale metallic nanowaveguide embodying PSDSTR is discussed and analyzed to broaden the bandgap width and further improve filter functions. With an ultra-width bandgap and tunable characteristic, the plasmonic nanowaveguide filter presented here may find significant applications in ultrafine spectrum analysis and highly integrated photonic circuits.

In this paper, we demonstrate an all-optical quantization scheme based on slicing the supercontinuum generated in the normal dispersion region of a highly nonlinear fiber. With the proposed quantization scheme, a 3-bit all-optical quantizer is experimentally achieved. The maximum values of differential nonlinear error, integral nonlinear error, effective number of bit, and signal-to-noise ratio are 0.29 least significant bit, 0.36 least significant bit, 2.64 bit, and 15.9 dB, respectively, which further proves the effectiveness of 3-bit quantizer. Moreover, the -20 dB spectral width on the anti-Stokes side is broadened to 101 nm when the input average power is 3.8 mW, which has the potential for realizing 7-bit all-optical quantization.

We demonstrate an all-optical quantization scheme by slicing the supercontinuum (SC) generated in the normal dispersion region of a highly nonlinear fiber. The −20 dB bandwidth of the SC is broadened from 12.9 to 49.7 nm when input average power varies from 0.062 to 0.692 mW, which is used for realizing subsequent quantization. In addition, in order to evaluate the system performance, we have calculated the values of differential nonlinear error, integral nonlinear error, and effective number of bit from the experimental results as 0.471 least significant bit (LSB), 0.519 LSB, and 4.39 bit, respectively.

This paper illustrates the principle of several common distributed fiber sensing techniques, especially Brillouin optical time domain reflectometry (BOTDR) and optical time domain reflectometry (OTDR). By measuring the frequency shift of spontaneous Brillouin scattering light in fiber, BOTDR could simultaneously monitor both strain and temperature with a high spatial resolution. But the spontaneous Brillouin scattering signal is so weak that it has a high demand of the laser generator and the signal-to-noise ratio of the whole system. Therefore, the BOTDR system is usually too complex, expensive and difficult to be widely used. Unlike BOTDR, OTDR utilizes Rayleigh scattering to measure the loss of fiber. Rayleigh scattering signal is much stronger than spontaneous Brillouin scattering signal, thus OTDR system has the advantages of high sensitivity, long distance and relatively low price. These advantages make OTDR very suitable for wide application in the field of slope monitoring, especially in remote areas where the geographical environment is complex and are difficult for staff to stay. This paper designed and implemented a slope monitoring and warning system based on the technology of optical time domain reflectometry(OTDR). The test result shows that the system has high sensitivity, strong real-time and provides user friendly interface.

A model for electromagnetic multi-Gaussian Schell-model beams is introduced. An analytical expression for the cross-spectral density matrix of electromagnetic multi-Gausssian Schell-model (EMGSM) beams propagating through non-Kolmogorov turbulence is derived based on the extended Huygens-Fresnel principle. With help of this expression, the average intensity, degree of coherence (DOC) and degree of polarization (DOP) of EMGSM beams are investigated in detail. Our results show that by suitable choices of the source parameters, the distance that preserve a flat profile can be prolonged. The effects of M and exponent value α on DOC and DOP of EMGSM beams are studied in detail.

This paper proposed a plasmonic resonator system, consisting of a metal-insulator-metal structure and two stubs, and a Fano resonance arose in its transmittance, which resulted from the coupling between the two stubs. On the basis of the proposed structure, a circle and a ring cavity are separately added above the stubs to create different coupled plasmonic structures, providing triple and quadruple Fano resonances, respectively. Additionally, by adjusting the geometric parameters of the system, multiple Fano Resonances obtained can be tuned. The proposed structure can be served as a high efficient refractive index sensor, yielding a sensitivity of 2000 nm/RIU and figure of merit (FOM) of 4.05 &times, 10 4 and performing better than most of the similar structures. It is believed that the proposed structure may support substantial applications for on-chip sensors, slow light and nonlinear devices in highly integrated photonic circuits.

Based on extended Huygens–Fresnel principle, an analytical expression for beam width of partially coherent Hermite–Gaussian (PCHG) beam through non-Kolmogorov turbulence is derived. The effects of inner scale l0, outer scale L0, exponent value α, beam order m and degree of source spatial coherence on the spreading of PCHG beam through non-Kolmogorov turbulence are examined in detail. Results show that the smaller inner scale l0 and bigger outer scale L0 give rise to the bigger beam spreading of PCHG beam through non-Kolmogorov turbulence. In the far field, the beam spreading of PCHG is independent of the degree of source spatial coherence, which has potential applications in long-distance free-space optical communications.

Based on extended Huygens–Fresnel principle, an analytical expression of M2 factor for partially coherent Hermite–Gaussian (PCHG) beams through non-Kolmogorov turbulence is obtained. Our results show that M2 factor of PCHG beams depends on coherence length, beam order m, wavelength, exponent value α , outer scale L0 and inner scale l0. The impact of the exponent's variation on the M2 factor is analyzed in detail. When the propagation distance fixed, the M2 factor of PCHG beams has a maximum for alpha values lower than 11/3.

Based on extended Huygens-Fresnel principle, analytical expressions of beam width and far-field angular spreading for electromagnetic Gaussian Schell-model (EGSM) beams propagating in atmospheric turbulence are obtained. The effects of coherence and polarization on beam spreading and directionality in atmospheric turbulence are investigated in detail. A condition is obtained under which beams with different degrees of spatial coherence and polarization will generate the same far-field angular spreading in atmospheric turbulence. Our results have potential application in long-distance free space optical communications.

The FBG-ECL fabricated using the interactions of laser diodes with fiber Bragg gratings has important role in optical communications. In this paper the comparison analysis of fiber Bragg grating and it's application in FBG-ECL are described in detail. The important parameters such as the bandwidth, SMSR and optimal output power of the FBG-ECL were analyzed deeply in the paper. The influence of the two important parameters (the residual reflectivity and external cavity length) on the FBG-ECL characteristic was given.