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The study of optical topological insulators (PTIs) has revealed intriguing optical properties that diversify the ways in which light can be manipulated, offering significant potential for a wide range of applications. This paper presents a machine learning (ML)-based approach for the reverse design of optical PTIs. Using finite element methods, the paper addresses the challenge of computing the band structure of a dual-band model, enabling the construction of a dataset suitable for ML training. With the goal of maximizing dual-band bandgaps, the study employs the random forest algorithm to predict target parameters and further designs topological edge states. Leveraging these boundary state patterns, two different optical PTI beam splitters are devised, and their transmission coefficients and losses are computed. The results demonstrate that optical devices designed using topological boundary states exhibit enhanced stability and robustness. This approach offers a reliable solution for applications in fields such as optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

Metasurfaces have gained a considerable amount of interest in the past decade for their capabilities to manipulate electromagnetic (EM) waves in different manners. They have offered multiple functionalities in terms of wave control depending on the given application. In terms of wave control, particularly EM beam splitting, it can be challenging compared to the given literature review, to achieve a wide number of beam-splitting reflections and coverage for multiple incident angles simultaneously. In this paper, we focus on the design of a metasurface based on the methodology of high periodicity supercell design (5.76 λ) and impedance modulation to achieve a various number of beam-splitting angles, while maintaining the same coverage at multiple incident angles for millimeter-wave (mm-Wave) frequencies. Following the generalized phase law of reflection alongside proper optimization of the surface impedance, the proposed reflective anomalous beam splitter (RABS) metasurface is designed to be polarization independent, and high reflection efficiency is achieved with a wave beam split into 11 different directions while operating for multiple incident angles simultaneously, making it a promising candidate to overcome challenges for various mm-Wave communication applications, especially in expanding 5G coverage in non-line of sight regions at a 28 GHz frequency band. The performance of the RABS metasurface is evaluated using both full-wave simulations and experimental measurements, which demonstrate its effectiveness in achieving 11 efficient reflective anomalous beams with a reflection efficiency of up to 96.65% and 97.36% in TE and TM modes at 28 GHz. [ABSTRACT FROM AUTHOR]

In recent years, handheld and portable terahertz instruments have been in rapid development for various applications ranging from non-destructive testing to biomedical imaging and sensing. For instance, we have deployed our Portable Handheld Spectral Reflection (PHASR) Scanners for in vivo full-spectroscopic imaging of skin burns in large animal models in operating room settings. In this paper, we debut the polarimetric version of the PHASR Scanner, and describe a generalized calibration technique to map the spatial and spectral dependence of the Jones matrix of an imaging scanner across its field of view. Our design is based on placement of two orthogonal photoconductive antenna (PCA) detectors separated by a polarizing beam splitter in the PHASR Scanner housing. We show that as few as three independent measurements of a well-characterized polarimetric calibration target are sufficient to determine the polarization state of the incident beam at the sample location, as well as to extract the Jones propagation matrix from the sample location to the detectors. We have tested the accuracy of our scanner by validating polarimetric measurements obtained from a birefringent crystal rotated to various angles, as compared to the theoretically predicted response of the sample. This new version of our PHASR scanner can be used for high-speed imaging and investigation of heterogeneity of polarization-sensitive samples in the field. [ABSTRACT FROM AUTHOR]

This paper presents a polarizing beam splitter (PBS) based on a hexagonal lattice silver-filled photonic crystal fiber (PCF) with two silver wires, which possesses advantages such as a short splitting length, high extinction ratio (ER), and an ultra-wide bandwidth in commonly used communication bands. Utilizing the full-vector finite element method (FV-FEM), thorough investigations were conducted on lasers within the wavelength range of 1.1 to 1.9 μm. The PBS demonstrates a working bandwidth of 725 nm (1.14 to 1.865 μm) under an ultra-short splitting length of 55.3 μm, with an ER exceeding 20 dB, covering all bands of O + E + S + C + L + U optical communication, and achieving a maximum ER of 74.65 dB, where the surface plasmon resonance (SPR) effect of silver metal plays a significant role. It not only features an ultra-short splitting length and an ultra-wide splitting bandwidth but also exhibits excellent manufacturing tolerances and anti-interference capabilities. This polarizing beam splitter represents a promising candidate in communication and may find various applications in optical communication. [ABSTRACT FROM AUTHOR]

This paper presents a novel pentagonal structure dual-core photonic crystal fiber polarizing beam splitter (PS-DC-PCF PBS) filled with a nematic liquid crystal (NLC) in the central hole. Unlike previous designs with symmetric arrangements, the upper and lower halves of the structure have different air hole arrangements. The upper half consists of air holes arranged in a regular quadrilateral pattern, while the lower half features a regular hexagonal arrangement of air holes. By filling the central hole with birefringent liquid crystal, the birefringence of the structure is enhanced, reducing the coupling lengths along the x polarization and y polarization directions. The polarization properties, coupling characteristics, and the influence of different structural parameters on the extinction ratio of the polarizing beam splitter are analyzed using the full-vector finite element method. Simulation results demonstrate that the designed PS-DC-PCF PBS achieves a maximum extinction ratio (ER) of 72.94 dB with a splitting length of only 61.9 μm and a wide operating bandwidth of 423 nm (1.324–1.747 μm), covering most of the O, E, S, C, L, and U communication bands. It exhibits not only ultra-short splitting lengths and ultra-wide splitting bandwidth but also good manufacturing tolerances and anti-interference capabilities. The designed PS-DC-PCF PBS could provide crucial device support for future all-optical communication systems and has potential applications in fiber optic communication or fiber laser systems. [ABSTRACT FROM AUTHOR]

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (CMC SiC f /SiC) has the advantages of high temperature resistance, corrosion resistance, high strength, low density, and oxidation resistance. It is a high-performance advanced material in aerospace, energy and other fields. However, due to its high hardness, brittleness and anisotropy of fiber structure, the research on application-oriented high-quality processing technology has become a hot issue. In this paper, a new process of rotational thirteen-beam coupling nanosecond laser processing of CMC-SiC f /SiC was studied. The rotational thirteen-beam coupling ablation experiments were carried out on CMC-SiC f /SiC workpiece. A laser beam is divided into thirteen beams and rotated around the beam center by using a beam splitter element. The morphology, structure and composition of ablation holes at different speeds were observed and analyzed by laser confocal microscope, scanning electron microscope, and X-ray energy dispersive spectrometer. It is found that the characteristics of rotational beam coupling have a significant effect on the laser ablation morphologies. The results show that the ablation region of CMC-SiC f /SiC is elliptical due to the fast heat transfer of fibers. The energy density distribution of the waist section of the Gaussian like beam after beam coupling is similar to the "W" shape, and the central energy is lower than the surrounding energy, and the ablation holes also show a similar "W" shape. With the increase of rotational speed, the hole depth first decreased and then increased, the hole diameter and roundness first increased and then decreased, and the hole section was "W" shaped. The ablation area can be divided into five parts: the white granular SiO 2 solid coverage area, the recast layer, the lower recast layer, the molten layer, and the heat affected zone. The rotational characteristics will make the reaction intensity of the whole ablation area more uniform in the circumferential direction. The formation mechanism and element distribution of each part were explored. The research work in this paper will provide a new technical way for the high-performance application of CMC-SiC f /SiC. [ABSTRACT FROM AUTHOR]

Quasi-continuous-phase metasurfaces overcome the side effects imposed by high-order diffraction on imaging and can impart optical parameters such as amplitude, phase, polarization, and frequency to incident light at sub-wavelength scales with high efficiency. Structured-light three-dimensional (3D) imaging is a hot topic in the field of 3D imaging because of its advantages of low computation cost, high imaging accuracy, fast imaging speed, and cost-effectiveness. Structured-light 3D imaging requires uniform diffractive optical elements (DOEs), which could be realized by quasi-continuous-phase metasurfaces. In this paper, we design a quasi-continuous-phase metasurface beam splitter through a vector iterative Fourier transform algorithm and utilize this device to realize structured-light 3D imaging of a target object with subsequent target reconstruction. A structured-light 3D imaging system is then experimentally implemented by combining the fabricated quasi-continuous-phase metasurface illuminated by the vertical-cavity surface-emitting laser and a binocular recognition system, which eventually provides a new technological path for the 3D imaging field. [ABSTRACT FROM AUTHOR]

Impedance theory has become a favorite method for metasurface design as it allows perfect control of wave properties. However, its functionality is strongly limited by the condition of strict continuity of normal power flow. In this paper, it is shown that acoustic impedance theory can be generalized under the integral equivalence principle without imposing the continuity of power flow. Equivalent non-local power flow transmission is instead realized through local design of metasurface unit cells that are characterized by a passive, asymmetric impedance matrix. Based on this strategy, a beam splitter loosely respecting local power flow is designed and demonstrated experimentally. It is concluded that arbitrary wave fields can be connected through arbitrarily shaped boundaries, i.e. transformed into one another. Generalized impedance metasurface theory is expected to extend the possible design of metasurfaces and the manipulation of acoustic waves. Impedance theory grants insight to design metasurfaces for controlling acoustic fields, but such theory imposes great limitation on boundary conditions. The authors propose a generalized acoustic impedance theory connecting arbitrarily conservative acoustic fields, and design a beam splitter as an example of power flow processing. [ABSTRACT FROM AUTHOR]

In this paper, the thermo-optical performance using novel cooling strategy improvements for a hybrid photovoltaic/parabolic dish concentrator with a conical thermal receiver using a beam splitter filter (PV/PDC-CTR-BSF) is investigated. The study's main goal is to improve the cooling effectiveness of the serpentine-shaped cooling duct by investigating the effect of the cross-section shape and positioning of the cooling duct under the PV panel. Typical cooling pipes have either a rectangular or circular cross-section and are usually attached to the back sheet of the PV panel using off-the-shelf adhesives that have very low thermal conductivity. With the advent of 3D printing technology, the back sheets could be 3D-printed with integral cooling ducts of different cross-sections at different locations and orientations within the back sheet that allow for increased heat transfer from the back sheet and thus improve PV/PDC-CTR-BSF's thermos-optical performance. For this purpose, the study investigates and compares the thermal performance of four different cooling duct cross-sections that include: rectangular, semi-circular, semi-elliptical and triangular. For each of the cooling duct cross-sections, several positions and orientations, which include flush below the back sheet layer and embedded inside the back sheet but positioned at the bottom, middle and top of the back sheet, are examined. Numerical simulations using the commercial software ANSYS FLUENT(R2019) are performed to assess the performance of the cooling ducts and, in turn, the thermo-optical performance of the PV/PDC-CTR-BSF system. The semi-elliptical cross-section duct embedded in the middle of the back sheet was found to yield the best cooling performance since its rate of heat removal from the PV back sheet was found to be the highest. [ABSTRACT FROM AUTHOR]

In this paper a procedure to design transmissive metasurfaces based on graphene-metal hybrid layers is developed and employed to design a multi-functional reconfigurable structure. Due to the inclusion of graphene, with tunable conductivity, different applications are achieved without any physical changes in the structure and by just varying the chemical potential of graphene through an electrostatic bias voltage. The designed structure consists of four identical layers to provide 360° phase-shift range with acceptable amplitude and full control of the transmitted wave front. By imposing an appropriate phase gradient profile on the supercell, several applications like beam steering, lens with arbitrary focal length and beam splitter with arbitrary angles are achieved. Simulation results of near field distributions as well as far field patterns vindicate the effectiveness of the proposed design procedure. The designed structure is promising for applications in the 6G wireless communication networks, nano-photonic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we present a distal-scanning common path probe for optical coherence tomography (OCT) equipped with a hollow ultrasonic motor and a simple and specially designed beam-splitter. This novel probe proves to be able to effectively circumvent polarization and dispersion mismatch caused by fiber motion and is more robust to a variety of interfering factors during the imaging process, experimentally compared to a conventional noncommon path probe. Furthermore, our design counteracts the attenuation of backscattering with depth and the fall-off of the signal, resulting in a more balanced signal range and greater imaging depth. Spectral-domain OCT imaging of phantom and biological tissue is also demonstrated with a sensitivity of ∼ 1 0 0 dB and a lateral resolution of ∼ 3 μ m. This low-cost probe offers simplified system configuration and excellent robustness, and is therefore particularly suitable for clinical diagnosis as one-off medical apparatus. [ABSTRACT FROM AUTHOR]

In this paper, unlike many researches that focus on beam splitters based on gratings with symmetrical structures, an asymmetric grating with double-groove structure is proposed. Based on the double-groove grating, multi-port beam splitters including dual-port, three-port, and four-port, under normal incidence working at terahertz frequency are designed for both transverse-electric and transverse-magnetic polarizations. Rigorous couple-wave analysis and simulated annealing algorithm are employed to get the optimal parameters of the grating and accelerate the computing process. For the purpose of understanding the phenomenon of the beam incident, the finite element method is also applied to get the simulation result. It is proven that the proposed beam splitters all present great efficiency and uniformity on the energy distribution. High manufacturing tolerance of the beam splitters is also analyzed, which allows for greater flexibility in the fabrication process. Compared with beam splitters based on single-groove grating, multi-port beam splitters based on double grooves show great performance and universality. [ABSTRACT FROM AUTHOR]

To improve the accuracy of infrared radiation characteristics measurement in the aviation field, an infrared Fourier transform imaging spectrometer based on a double-swing solid angle reflector was designed. This imaging spectrometer operates in the 3–5 μm wavelength range and has a field of view of 1.7° × 1.7°. This article presents a comprehensive analysis of the system's stray light and also studies the impact of external stray light on the imaging quality, along with the influence of internal stray light on the interference effects and the spectral resolution. It also present the design of a hood that suppresses the point source transmittance of the external stray light down to the order of 10−4. Based on this, we propose a method that incorporates the introduction of wedge and inclination angles. Additionally, a numerical range is provided for the addition of these angles on the beam splitter mirror and compensation plate. This ensures the effective suppression of any internal stray light. This study fills the gap in the knowledge about Fourier transform imaging spectrometers operating in the mid-infrared band for aviation applications, and proposes a suppression method suitable for interference systems, which is also suitable for Fourier transform imaging spectrometers based on other types of interferometers. This study broadens the application field of Fourier transform imaging spectrometers in stray light, and has great significance to promote the development of Fourier transform imaging spectrometer. [ABSTRACT FROM AUTHOR]

Many devices based on silicon and other photonic integrated circuit platforms exhibit significant polarization dependence. Polarization beam splitter (PBS) is a device that split optical signals into transverse electric (TE) and transverse magnetic (TM) modes. Among various PBSs, asymmetric directional couplers are widely used due to their fine performance, but their working bandwidth is limited due to wavelength changes that can lead to deviations in effective refractive index and coupling strength. We propose a PBS, which uses metamaterial anisotropy to replace structural asymmetry and break the bandwidth bottleneck. It achieves good performance in the wavelength range of 258 nm, where the extinction ratio of the TM polarization is greater than 24 dB and that of the TE polarization is greater than 26 dB. It covers the E, S, C, L, and U bands, and the coupling area is as small as 7.25×2.625 μm, with a total device footprint of 15.65×6.125 μm. [ABSTRACT FROM AUTHOR]

In this paper, a triple-layer grating beam splitter with three-port output is designed. Through the combination of rigorous coupled-wave analysis (RCWA) and simulated annealing algorithms (SAA), the calculation and optimization of each parameter of the grating is carried out to make the diffraction efficiency of the grating meet the conditions. At the incident wavelength of 800 nm, the diffraction efficiencies of 0th order and ±1st order under TE polarization are 31.6% and 31.4%, respectively. The diffraction efficiencies of 0th order and ±1st order under TM polarization are 32.7% and 32.5%, respectively. It can be seen that not only the total diffraction efficiency under TE polarization and TM polarization exceeds 90%, but also the uniformity of diffraction efficiency at each order exceeds 99%. Finally, the influence of grating parameters and incident wave characteristics on diffraction efficiency is discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a bidirectional trifunctional splitter with a bilayer ridge structure for polarization-selective and polarization-insensitive outputs at the wavelength of 1550 nm. The configuration can realize a four-port output for both polarizations and TE-two/TM-three output. In the upper part of the bidirectional trifunctional splitter, for TE polarization, two outputs exhibit diffraction efficiencies greater than 49%, while for TM polarization, three outputs exhibit diffraction efficiencies greater than 32%. Furthermore, for the lower part of this beam splitter, under both TE and TM polarization, the diffraction efficiencies of four outputs exceed 24%. Compared to the previous beam splitter, the bidirectional trifunctional splitter exhibits superior uniformity and is capable of simultaneously achieving polarization-selective and polarization-insensitive outputs. Furthermore, the configuration is theoretically resistant to the geometric dimensions, which greatly reduces the difficulty of fabrication. This work exhibits a novel approach to the design of energy-splitting devices and optical communication systems with multiple outputs. • Novel bidirectional trifunctional splitter with a bilayer ridge on two sided microstructure. • Implementing four-port output either for two polarizations simultaneously or TE-two/TM-three output. • Exhibiting superior uniformity or achieving polarization-selective and polarization-insensitive outputs. [ABSTRACT FROM AUTHOR]

For the polarization multiplexing requirements in all-optical networks, this work presents a compact all-fiber polarization beam splitter (PBS) based on dual-core photonic crystal fiber (PCF) and an elliptical gold layer. Numerical analysis using the finite element method (FEM) demonstrates that the mode modulation effect of the central gold layer effectively reduces the dimensions of the proposed PBS. By determining reasonable structural parameters of the proposed PCF, the coupling length ratio (CLR) between X- and Y-polarized super-modes can approach 2, achieving a minimal device length of 0.122 mm. The PBS exhibits a maximum extinction ratio (ER) of − 65 dB at 1.55 μm, with an operating bandwidth spanning 100 nm (1.5–1.6 μm) and a stable insertion loss (IL) of ~ 1.5 dB at 1.55 μm. Furthermore, the manufacture feasibility and performance verification scheme are also investigated. It is widely anticipated that the designed PBS will play a crucial role in the ongoing development process of miniaturization and integration of photonic devices. [ABSTRACT FROM AUTHOR]

The Goos–Hänchen (GH) shift and the spin polarization are theoretically investigated under the anti-parallel double δ -magnetic-barrier nanostructure model by applying a bias using Airy's function formalism and transfer-matrix technique, which is an improvement on previous calculation. The results show the magnitude and sign of GH shift and spin polarization can be easily changed by modulating the applied bias. The closer the applied bias to the critical value is, the more intensive GH shift and spin polarization will be. Furthermore, two critical values come through modulating the strength of magnetic fields, and an intensive GH shift and a spin polarization also exist near each critical value. These findings can provide a practical approach to designing and fabricating spin beam filters or splitters modulated by applied bias. [ABSTRACT FROM AUTHOR]

Compact and high efficiency microdisplays are essential for lightweight augmented reality (AR) glasses to ensure longtime wearing comfort. Liquid-crystal-on-silicon (LCoS) is a promising candidate because of its high-resolution density, high brightness, and low cost. However, its bulky illumination system with a polarizing beam splitter (PBS) cube remains an urgent issue to be overcome. To reduce the volume of the LCoS illumination system, here, we propose a compact structure with four thin PBS cuboids. Through simulations, the optical efficiency of 36.7% for an unpolarized input light can be achieved while maintaining reasonably good spatial uniformity. Such a novel design is expected to have a significant impact on future compact and lightweight AR glasses. [ABSTRACT FROM AUTHOR]

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of new miniaturized optical devices and integrated optical circuits. We propose and investigate in detail a novel physical concept of a highly miniaturized (up to two working wavelengths) planar optical resonant splitter/coupler with a switching element comprising a photonic molecule (PM) pair dispersing input optical fluxes in multiple directions with a tailored power ratio. The structural design of the proposed splitter is based on a silicon-on-insulator (SOI) platform and composed of high-quality resonators in the form of electromagnetically coupled submicron-sized microcylinders. The control on the power division ratio and the selection of optical beam directions is realized by tuning the photonic splitter structure to the corresponding resonance of the PM supermode. Compared to known analogs, the proposed design is easy and cheap in fabrication. Because of its tiny dimensions, it is suitable for integration into a "System-on-a-chip" platform and can dynamically change the beam power division ratio by input wave-phase manipulation. [ABSTRACT FROM AUTHOR]

The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) has been researched in both fiber and atmospheric channels. However, the wavelength attack may also pose a threat to the case of ocean turbulent channels, which are vital for the secure communication of both ocean sensor networks and submarines. In this work, we propose two wavelength attack schemes on underwater discrete modulated (DM) CV-QKD protocol, which is effective for the case with and without local oscillator (LO) intensity monitor, respectively. In terms of the transmittance properties of the fused biconical taper (FBT) BS, two sets of wavelengths are determined for Eve's pulse manipulation, which are all located in the so-called blue–green band. The derived successful criterion shows that both attack schemes can control the estimated excess noise of Alice and Bob close to zero by selecting the corresponding condition parameters based on channel transmittance. Additionally, our numerical analysis shows that Eve can steal more bits when the wavelength attack controls the value of the estimated excess noise closer to zero. [ABSTRACT FROM AUTHOR]

To reduce the polarization sensitivity, a T-type grating with the material SiO2 is proposed on a reflective layer made of aluminum material. Based on structural parameters derived from rigorous coupled-wave analysis and simulated annealing, the described reflection beam splitter enables a nine-port separation under normal incidence. In addition, it demonstrates exceptional and uniform diffraction efficiency. For transverse electric polarization, the diffraction efficiencies of 0th, ±1st, ±2nd, ±3rd, and ±4th are 10.02%, 11.70%, 10.85%, 11.00%, and 10.03%, respectively. For transverse magnetic polarization, the diffraction efficiencies of 0th, ±1st, ±2nd, ±3rd, and ±4th are 12.54%, 10.13%, 9.51%, 10.46%, and 11.89%, respectively. The finite element technique is used to verify the diffraction efficiency values. In addition, a thorough analysis of the fabrication tolerance, wavelength bandwidth, and electromagnetic field dispersion is conducted. The outcome shows that the suggested grating structure has outstanding uniformity and efficiency, and these studies greatly enhance our knowledge of and progress toward the creation of the nine-port beam splitter. Consequently, there is a lot of room for the implementation of the suggested grating in multi-channel optical communication systems. [ABSTRACT FROM AUTHOR]

• A concise all-fiber hydrostatic pressure sensor is proposed. • High hydrostatic pressure sensitivity of −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa is obtained. • Ultra-low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ proves our sensor more competitive in harsh environment applications. With the rapid development of physical ocean observation, high-performance pressure sensor integrated with stable mechanical strength, sufficient pressure sensitivity as well as negligible temperature crosstalk is highly desirable but still lack of research. This paper proposes an all-fiber optical sensor based on a Mach-Zehnder interferometer (MZI) for hydrostatic pressure measurement, utilizing a multi-mode fiber (MMF)-single-hole-dual-core fiber (SHDCF)-MMF structure. The MMF sections act as a beam splitter and coupler to enhance the Mach-Zehnder interference. The SHDCF serves as the pressure-sensing section. Under the action of the enclosed air hole in SHDCF, hydraulic variations cause changes in the structural parameters of the fiber, especially the refractive index change caused by the elasto-optical effect, which leads to the shift of the interference dips. The experimental results prove that the SHDCF-based MZI sensor has a higher hydrostatic pressure sensitivity than other hole-less silica fiber-based sensors. The max pressure sensitivity is −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa with good linearity and reliability. Moreover, the low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ also proves our sensor more competitive in harsh environment applications. [ABSTRACT FROM AUTHOR]

• We synthesized dielectric material particles by copolymerizing (-)-MnMA and MMA with benzoyl peroxide (BPO). Combining with the co-extrusion method, the dielectric chiral fiber is drawn by several meters for the first time, which has a more simplified fiber fabrication process and higher fiber drawing speed with good continuity and consistency comparing with structural chiral fiber. • Some important optical performances of dielectric chiral fiber (DCF) were tested. The results of optical activity of dielectric materials, optical power loss, circular polarization maintaining characteristic demonstrated that DCF can be used as a novel concept circular polarization maintaining fiber. Besides, the measurement of refractive index data fills in a gap in refractive index of DCF, which can not only supply the basis of analyzing the distribution of optical field and modes for transmission, but also designing DCF with different optical characteristics according to the requirements in different applications. • We designed a dual-core photonic crystal fiber with optimized parameters as a beam splitter which can separate different polarization states of light. The polarized beam split effect demonstrated that there is a potential of DCF for polarization division multiplexing in theory. Compared with linearly polarized light, circularly polarized light can hardly cause the cross coupling effect during transmission. Therefore, it is important to study chiral fibers for optical fiber communication and optical fiber sensing. However, the requirements in structural chiral fiber fabrication raise its cost. In the paper, we demonstrated the entire fiber fabrication method of dielectric chiral fiber. This is the first fabrication of long dielectric chiral fiber. We also measured key optical properties of the chiral material. The value of fabricating dielectric chiral fiber is demonstrated by its physical implementation and good performance in circular polarization maintaining characteristic. The fiber fabrication method is expected to provide a solution for low cost. Moreover, the dielectric chiral fiber supplies the potential application of dielectric chiral fiber for optical fiber communication and optical fiber sensing. [ABSTRACT FROM AUTHOR]

• Polarization converter based on niobium nitride realizes dynamical cross-polarized amplitude by temperature modulation. • The purity of the output cross-polarized amplitude is considered, with PCRs greater than 80% at different temperatures. • Introduction of the niobium nitride facilitates integration in highly sensitive cryogenic systems. In this paper, we innovatively employ superconducting material niobium nitride (NbN) into the polarization converter, designing a C-shape split resonant ring (SRR) polarization converter that works in the frequency range from 0.21 THz to 0.39 THz with a relative bandwidth of 60 % and the polarization conversion ratio (PCR) is more than 90 % in the superconducting state. The employment of NbN also brings dynamic modulation characteristic of cross-polarized amplitude. The cross-polarized amplitude reaches the maximum of −1 dB at 4.5 K, and decreases to the minimum of −10 dB at 16 K. Meanwhile, focusing on the output purity of cross-polarized amplitude at different temperatures, PCRs are more than 80 % in the frequency range of 0.25 to 0.33 THz. The characteristic is validated in the form of composite beam splitters. The simulation results show that the beam intensity controlled by NbN module decreases with the increase of temperature, achieving a switch in the number of beams. Variation trend is in a good agreement with the decreasing trend of cross-polarized amplitude of the polarization converter. This structure probably provides a new idea for the design of dynamically tuned polarization converter and expands the application of NbN which is beneficial for integration in low-temperature systems. [ABSTRACT FROM AUTHOR]

In this paper, a reflective trapezoidal dual-functional beam splitter grating is proposed, which performs two independent functions at 1550 nm. For TE polarization, the grating can achieve a uniform three-port output with efficiencies of 32.85%, 32.89%, and 32.75% for 0th, -1st, and -2nd orders respectively. For TM polarization, the grating can achieve a highly-efficient single-channel output of order -2nd with an efficiency of 93.27%. HfO 2 is chosen as the material of grating ridge layer, the structural parameters of the grating are studied by using rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SAA), and the results are verified by using finite element method (FEM). In addition, the influence of structure and incident error on grating efficiency was also analyzed, the results indicate that the grating has good incident bandwidth and manufacturing tolerance with excellent performance. • Trapezoidal dual-functional splitter with two reflective independent functions. • For TE polarization, a uniform three-port with efficiencies of 32.85%, 32.89%, and 32.75% for 0th, -1st, and -2nd orders. • For TM polarization, a highly-efficient single-channel output of order -2nd with an efficiency of 93.27%. [ABSTRACT FROM AUTHOR]

We present in this paper an all-fiber Optical Coherence Tomography OCT system in the time domain by employing a Sagnac fiber loop. The optical fiber version of TD-OCT uses directional couplers to construct a Michelson interferometer instead of a beam splitter which is used in the bulk optics version. Instead of implementing the optical delay by an external movable mirror, we present a new configuration that employs a Sagnac interferometer. Avoiding the use of an external movable mirror, eliminates the problems of alignment to couple back the optical signal into the fiber after being delayed by the external mirror. Moreover, this all-fiber system has the advantage of being compact and having large values of optical path difference. [ABSTRACT FROM AUTHOR]

Combustible gas concentration detection faces challenges of increasing accuracy, and sensitivity, as well as high reliability in harsh using environments. The special design of the optical path structure of the sensitive element provides an opportunity to improve combustible gas concentration detection. In this study, the optical path structure of the sensitive element was newly designed based on the Pyramidal beam splitter matrix. The infrared light source was modulated by multi-frequency point signal superimposed modulation technology. At the same time, concentration detection results and confidence levels were calculated using the 4-channel combustible gas concentration detection algorithm based on spectral refinement. Through experiment, it is found that the sensor enables full-range measurement of CH4, at the lower explosive limit (LEL, CH4 LEL of 5%), the reliability level is 0.01 parts-per-million (PPM), and the sensor sensitivity is up to 0.5PPM. The sensor is still capable of achieving PPM-level detections, under extreme conditions in which the sensor's optical window is covered by 2/3, and humidity is 85% or dust concentration is 100mg/m3. Those improve the sensitivity, robustness, reliability, and accuracy of the sensor. [ABSTRACT FROM AUTHOR]

Mass-deployable implementations for quantum communication require compact, reliable, and low-cost hardware solutions for photon generation, control and analysis. We present a fiber-pigtailed hybrid photonic circuit comprising nonlinear waveguides for photon-pair generation and a polymer interposer reaching 68 dB of pump suppression and photon separation based on a polarizing beam splitter with > 25 dB polarization extinction ratio. The optical stability of the hybrid assembly enhances the quality of the entanglement, and the efficient background suppression and photon routing further reduce accidental coincidences. We thus achieve a 96 - 8 + 3 % concurrence and a 96 - 5 + 2 % fidelity to a Bell state. The generated telecom-wavelength, time-bin entangled photon pairs are ideally suited for distributing Bell pairs over fiber networks with low dispersion. [ABSTRACT FROM AUTHOR]

Nanofluids containing metal nanoparticles have promising application prospects in the spectral beam splitters (SBSs) of photovoltaic/thermal (PV/T) setups on the merits of the tunable spectral absorption characteristic and relatively low price. While the existing nanofluid-based SBSs show some difficulties in large-scale industrial applications, such as their poor stability, sophisticated manufacturing process, etc. In this paper, a cheap and stable hybrid nanofluid containing antimony tin oxide (ATO) and cupric oxide (CuO) nanoparticles has proven to be a good candidate for SBSs. ATO has high absorption in the infrared region while CuO shows strong absorption for ultraviolet and visible light, so ATO and CuO nanoparticles have complementary optical properties and the spectral absorption of ATO-CuO hybrid nanofluids is expected to be effectively regulated by adjusting nanoparticles' composition. Meanwhile, the increase in nanoparticle concentration can enhance the light absorption ability of hybrid nanofluids in the full spectrum. The hybrid nanofluid SBS with a 5:5 ATO:CuO mass ratio and 200 ppm concentration proves to perform best and the merit function is as high as 1.679 (worth factor is 3), which is highly competitive among the metal-based nanofluid SBSs from literature. • A hybrid nanofluid containing ATO and CuO nanoparticles was prepared for the use as SBS in PV/T systems. • The dependence of hybrid nanofluids' optical properties on ATO:CuO mass ratio and total concentration is analyzed. • The influence of ATO:CuO mass ratio and total concentration on the PV/T performance of nanofluid SBSs is investigated. • A high MF value of 1.679 for ATO-CuO hybrid nanofluid SBS is found with 5:5 mass ratio and 200 ppm concentration. [ABSTRACT FROM AUTHOR]

• The error tolerance characteristics of different PPIC structures are compared. • An effective strategy to compensate the 3 dB beam splitter error is proposed. • A deep learning task of the MNIST handwritten digit classification is carried out. • The recognition accuracy can be significantly improved with this method. Programmable photonic integrated circuits (PPICs) can realize linear optical unitary transformation between arbitrary multi-port input and multi-port output for optical computing and signal processing. With the scale increase of PPICs, the accumulation of manufacturing errors will lead to overall performance deviations. A symmetrical Mach-Zehnder interferometer (MZI) circuit with a shorter optical path and lower propagation loss has been proposed recently to replace the traditional asymmetrical MZI circuit. However, no systematic research on the error compensation of symmetrical MZI circuits has been reported yet. In this paper, the error tolerance characteristics of symmetrical MZI circuits and asymmetrical MZI circuits are analyzed and compared in detail. An effective strategy to compensate the 3 dB beam splitter error of a symmetrical MZI circuit is proposed. A deep learning task of the Modified National Institute of Standards and Technology (MNIST) handwritten digit dataset classification was carried out with two hidden layers, which are implemented by rectangular symmetrical MZI circuit structures. The recognition accuracy can be significantly improved with this error compensation method. [ABSTRACT FROM AUTHOR]

• A novel I-shaped stack configuration is proposed to function as the multi-port splitter and the bi-functional polarization-selective splitter. • For the multi-port splitter, the efficiency of each order can be greater than 48%, 32%, 24%, and 19% for dual- to five-port output, respectively. • For the bi-functional splitter, the I-shaped stack configuration can work as TE three-port/TM dual-port or TE five-port/TM four-port splitter. In this paper, a high-efficiency beam splitter based on an I-shaped stack configuration under normal incidence is proposed, which can function as a multi-functional polarization-independent and a bi-functional polarization-selective beam splitter at the wavelength of 1550 nm. The rigorous coupled-wave analysis and a simulated annealing algorithm are used in the process of calculating and optimizing. When the grating functions as a polarization-independent beam splitter, the diffraction efficiency of each main diffraction order can be greater than 48%, 32%, 24%, and 19% of dual- to five-port output for transverse electric (TE) and transverse magnetic (TM) polarizations respectively. When the grating is employed as a polarization-selective beam splitter, the total efficiencies exceed 95% for TE and TM polarizations as well. Furthermore, this research applies a simplified modal method to reveal the energy distribution inside the grating. Compared to previously reported beam splitters, the proposed grating structure has higher efficiency and uniformity, making it well-suited to the various output mode requirements of large-scale optical communication systems. [ABSTRACT FROM AUTHOR]

Metasurface, with its powerful and flexible terahertz(THz) wave manipulation capability, has become a key component of beamforming and imaging systems in the THz band. However, its practical application is limited by fixed properties and propagation mode on a single metasurface. In this paper, we propose a coding metasurface with tunable characteristics and bidirectional working modes. The complete 2π phase compensation can be realized by rotating the InSb unit according to the Pancharatnam-Berry phase concept, and eight meta-atoms are selected to regulate the wavefront of terahertz waves using phase compensation. By increasing the temperature of the InSb from 290 K to 370 K, the working frequency permits wideband coverage from 1.7 to 4.5 THz. As the temperature reaches 341.15 K, which is required for vanadium dioxide's(VO 2) phase transition, the metasurface's propagation direction mode will switch from transmission to reflection. The proposed metasurface can perform beam deflecting, splitting, and focusing functions when VO 2 is in a dielectric state. Meanwhile, beam deflecting, splitting, and radar scattering surface (RCS) reduction can also be achieved when VO 2 is in a metallic state. Furthermore, a near-field image of the letter P is presented as verification. Numerous potential applications for the reconfigurable metasurfaces include polarization beam splitters, imaging, and terahertz switching. • Multi-function. The metalens achieves focusing and RCS attenuation. • Multi-mode. Every metasurface operates in both reflecting and transmissive modes. • Broadband. Metasurface makes advantage of InSb to broaden the operational range. [ABSTRACT FROM AUTHOR]

• The length of the designed PBS based on DNDHC-NCF is 1.38 cm, which solves the technical problems of long length of traditional PBS. • The operation bandwidth is 320 nm, covering S + C + L + U bands. • Is of great significance in promoting the application and development of DNDHC-NCF. In this paper, a polarization beam splitter（PBS） based on double nested dual-core negative-curvature fiber (DNHC-NCF) is designed. Two hollow cores are constructed by eight double nested cladding tubes arranged at certain angles. The influences of structural parameters on the performances of the DNHC-NCF PBS have been studied by using the finite element method (FEM). According to the simulation results, the structure of the proposed DNHC-NCF PBS is optimized. The final results indicate that the length of the proposed DNHC-NCF PBS is 1.38 cm and the extinction ratio (ER) is less than −20 dB in the wavelength range of 1.48–1.80 µm (320 nm, covers S + C + L + U bands). Besides, the higher order mode extinction ratio (HOMER) in the wavelength range of 1.3–1.71 µm is greater than 100, showing good single-mode characteristic as well. It is believed that the proposed double nested dual-core negative curvature fiber polarization beam splitter will have important applications in the fields of optical communication system. [ABSTRACT FROM AUTHOR]

Static Fourier transform spectrometers are devices that can be realized as monolithic and compact assemblies. In the "grating-based" monolithic version, they are usually realized gluing together a beam-splitter with two reflective diffraction gratings using spacers as connecting elements. In this work we present the development and test of an alternative form of this kind of instrument in which the dispersive elements are Littrow's prisms and are glued to the splitting element, forming in this way a robust and filled structure with no air gaps. The device can work in the visible/near infrared spectral region with a resolution power that varies across the spectral range due to the dispersion of the used glasses. The absence of hollow regions inside the monolithic block makes the device extremely robust and protects the optical surfaces inside the interferometer from possible contaminations. The device can be easily miniaturized, as it does not require spacers or structural elements other than just the optical parts. The tested instrument works in the 470–850 nm wavelength range with a variable resolution between 3000 and 300. [ABSTRACT FROM AUTHOR]