TM-polarized Modes Research Articles

Sensitivity detection of imidacloprid pesticide using a metasurface sensor in THz spectrum regime

Imidacloprid (C9H10ClN5O2) pesticide is frequently used in agriculture as it effectively controls various insect pests. Accurate detection of imidacloprid concentrations is crucial for food safety and other fields. This work proposes a novel metasurface (MS) sensor with efficient sensitivity in the THz frequency regime to detect imidacloprid pesticides. The MS sensor has an electrical size of 7.17λ × 7.17λ with the smallest wavelength. The transmission coefficient remains stable for the metasurface sensor’s TE and TM polarization modes. Due to the symmetrical design, it exhibits strong electric and magnetic field enhancement with polarization insensitivity for different incident angles. The sensing capability is tested by implementing different sample analyte thicknesses of imidacloprid in the top surface of the MS sensor. Imidacloprid analyte thickness increases cause a red and blue change in the metasurface’s transmission frequency. The simulation results show that the suggested MS sensor has a refractive index (RI) sensitivity of 0.125 THz/RIU, and a Q factor of 5.262 and 4.084. This is a simple, cost-effective, sufficiently sensitive, and efficient THz MS sensor with a wide range of applications in pesticide concentration measurement, including imidacloprid.

Ultra-broadband and high extinction ratio polarization splitter based on triple-tapered directional couplers

The design and numerically investigation of a silicon polarization splitter (PS) is proposed using triple-tapered directional couplers (DCs).The proposed device consists of a triple-tapered DC, a triple-bent DC at through port, and a tapered waveguide at cross port. The coupling length of the device is 20.5 µm. At the 1550 nm wavelength, the realized PS exhibits the extinction ratio (ER) values of 35.7 dB and 37.35 dB as well as the insertion loss values of < 0.58 dB and < 0.4 dB for the TE and TM polarization modes, respectively. Furthermore, the device’s bandwidth for ER > 20 dB and ER > 25 dB are 170 nm and 136 nm, respectively.

Controlling the TE-TM splitting of topological photonic interface states by precise incident angle adjustment

Topological phases in photonic systems have garnered significant attention, often relying on precise structural design for generating non-trivial topological phases. However, this dependency on fixed structures limits their adaptability. This study systematically explores incident angle-induced topological phase transitions in a one-dimensional photonic crystal (PC). Both TE and TM polarized modes undergo topological phase transitions at the same critical transition angles. Additionally, the TM-polarized mode undergoes a unique topological phase transition at the Brewster angle. When these two kinds of transition angles coincide, even if the band structure of the TM-polarized mode undergoes an open-close-reopen process, the topological properties of the corresponding bandgap remain unchanged. Based on theoretical analysis, we design the composite PCs comprising two interfaced PCs having common bandgaps but different topological properties. By tuning the incident angle, we theoretically and experimentally achieve TE-TM splitting of topological interface states in the visible region, which may have potential applications in optical communications, optical switching, photonic integrated circuits, and so on.

Highly sensitive refractive index sensing with a dual-band optically transparent ITO-based perfect metamaterial absorber for biomedical applications

In this paper, a dual-band optically transparent square-shaped perfect metamaterial absorber operating in the frequency range from 2 to 4 terahertz (THz) is proposed. The structure consists of an indium tin oxide (ITO)-based split ring resonator (SRR) structure with additional splits and rectangular inner strips to form the top layer over the lead glass substrate. Perfect absorption is attained in the frequencies of 2.089 and 3.892 THz with absorbances of 99.99% and 99.98% in TE polarization mode, respectively. Perfect absorption is also achieved in TM polarization mode at 2.23 THz. Broadband absorption is found in TM polarization mode with full width half maximum (FWHM) of 1.1742. The proposed structure has one polarization-insensitive band in TE polarization mode. Absorbance is greater than 80% and 90% in the successive absorption peaks even at 60° and 75° of incidence, respectively. The resonance frequency is sensitive to the refractive index of the medium. As a result, the proposed metamaterial structure may be implemented as a refractive index (RI) sensor with a high sensitivity of 1109 GHz/RIU and 1954 GHz/RIU in both absorption bands for a refractive index range of 1.34 to 1.40. It's interesting to note that the refractive index of most biological samples ranges from 1.3 to 1.39. The figure of merit (FOM) of the proposed sensor can reach as high as 10 and 14 for the 1st and 2nd frequency bands. As a result, the proposed sensor has a high sensitivity and can be employed in medical applications. Potential applications of the proposed absorber include imaging, biomedical sensing, etc.

Modelling of asymmetric channel plasmonic polariton waveguides

Channel plasmonic polariton (CPP) waveguides are a promising technology for integrated photonics. They offer several advantages over other plasmonic waveguides and are well-suited for various applications. In this research, a new design of asymmetric double-trenched CPP waveguide is suggested and examined. This design consists of two silicon trenches etched into a silicon dioxide substrate layer; with a gold layer sandwiched in between. The trenches are asymmetric, with one trench being wider than the other. This asymmetry creates a spatially varying surface plasmon polariton (SPP) field, which can guide light along the waveguide. The polarization characteristics of this proposed design are analyzed over a specific wavelength range (0.7 - 1.7 µm) to evaluate the mode confinement of the light within the structure. The design performance was optimized by changing the gold layer thickness and the dimensions of the lower trench. Different scenarios are examined to observe TE and TM-polarized modes’ behavior within the groove. A 1867.119 dB/µm suppression level at 0.92 µm wavelength is achieved which offers a small-size component for compact photonic logic gates, enabling the development of next-generation photonic devices.

Polarization-insensitive silicon optic switch based on mode manipulated power splitters and phase shifters

A polarization-insensitive thermo-optic switch is proposed and demonstrated on the silicon-on-insulator platform with a 220 nm silicon core layer. The present device is based on the Mach–Zehnder interferometer structure, consisting of polarization-insensitive power splitters and polarization-insensitive phase shifters (PIPSs). The polarization-insensitive power splitter has been realized by employing an adiabatic directional coupler, which utilizes the fast adiabatic mode evolution by introducing cubic Bézier curves on outer contours, providing broadband 3-dB power splitting for TE and TM polarization modes with only 70 µm coupling length. For the novel PIPSs, the ridge waveguide with large aspect ratio, based on the mode hybridness property, could obtain the same power consumption (Pπ) for an optical switch working at TE and TM polarizations. Experimental results indicate that the measured insertion losses are less than 2 dB and the extinction ratios are larger than 15 dB over a 40 nm wavelength band (covering the C-band).

Polarization control investigation based on an integrated graphene-assisted microring cavity

In this paper, we propose and analyze an integrated polarization-selective structure of a graphene-assisted silica microring cavity to realize polarization control due to different optical distributions of whispering-gallery modes in the microring and polarization-dependent absorptions of graphene. A graphene stripe is partially side coupled with a silica microring to distinctly influence the propagations of a TE mode and TM mode in the microring. Especially, the appearance of the plasmonic mode in the groove between the graphene and the microring enhances light–matter interaction between the graphene and the TM-polarized mode, while without that for the case of TE mode propagation. By applying voltage on the graphene stripe along with its electro-optic modulation effect, the difference in the polarization extinction ratio of 20.6 dB is obtained between the cases of the polarized TM mode and TE mode in the microring. Furthermore, a second silica microring is added in this hybrid structure to couple the original microring along with a graphene stripe embedded in between finally realizing an electromagnetically induced transparency line shape because of the plasmonic coupling in both cavities with the condition of TM mode propagation, while without any line-shape change for the case of TE mode propagation. This compact hybrid structure offers a good integrated photonic platform to realize an excellent polarization-selective device.

A wideband absorber working in the L- and S-bands based on magnetic materials

In this paper, a multi-layered microwave absorber that can work in the L- and S-bands is proposed. The absorber is composed of a traditional medium and magnetic material coatings. A genetic algorithm is used to achieve rapid design of a multi-layered absorber. The absorptivity of the absorber is more than 90% in 1.13–4.36 GHz under normal incidence, i.e., 117.7% fractional bandwidth. Moreover, the total thickness is 13 mm, corresponding to 0.049λ0 at the lowest operating frequency. Meanwhile, the absorber also has good wide-angle and polarization-independent characteristics. When the incident angle increases to 40°, it still can keep stable absorption in both TE and TM polarization modes. The working mechanism of the absorber is analyzed from the perspective of equivalent complex impedance, transmission line theory, and power loss density. Finally, a sample was fabricated and measured. The experimental results agree well with numerical simulations, achieving ultra-broadband and ultra-low frequency absorption.

Compact and high-performance polarization beam splitter based on triple-waveguide coupler

Polarization beam splitter (PBS) is a fundamental component of integrated photonics to manipulate wave polarization state, and most PBS devices were designed on the popular SOI. As an alternative, a PBS may be implemented on the basis of thin-film LiNbO3-on-insulator (LNOI), a promising platform for developing various compact or ultra-compact photonic active and passive devices. However, smaller modal birefringence of the LNOI waveguide makes it not easy to implement a PBS of high-performance. Here, we propose a compact, high-performance PBS on the basis of a triple-waveguide coupler consisted of two LNOI ridge waveguides and an amorphous silicon (α-Si) nanostrip assisted waveguide. By making use of the α-Si nanostrip, the PBS works in the case that the TM polarization mode meets the phase matching condition while the TE polarization mode does not. Numerical results show that the PBS is compact with a length of only 31 μm. The device can achieve an ultra-high polarization extinction ratio (>29.4 dB) and an ultra-low insertion loss (<0.066 dB) in the operating wavelength range of 1500–1600 nm for the TE polarization mode, and a polarization extinction ratio of > 20 dB and an insertion loss of < 0.16 dB over a ∼ 60 nm bandwidth from 1527 nm to 1587 nm for the TM polarization mode. Moreover, the device has a larger feature size that facilitates fabrication. Overall, this device has the advantages of compact size, higher polarization extinction ratio, lower insertion loss, and larger feature size, which is suitable for on-chip applications.

Polarization-independent and ultra-sensitive biosensor with a one-dimensional topological photonic crystal.

Optical biosensor, which perceptively captures the variety of refractive index (RI) of the surrounding environment, has great potential applications in detecting property changes and types of analytes. However, the disequilibrium of light-matter interaction in different polarizations lead to the polarization-dependence and low sensitivity. Here, we propose a polarization-independent and ultrasensitive biosensor by introducing a one-dimensional topological photonic crystal (1D TPhC), where two N-period 1D photonic crystals (PhC1 and PhC2) with different topological invariants are designed for compressing the interaction region of the optical fields, and enhancing the interaction between the light and analyte. Since the strong light-matter interaction caused by the band-inversion is polarization-independent, the biosensor can obtain superior sensing performance both for TE and TM polarization modes. The sensitivity and Figure of Merit (FOM) of the designed biosensor are 1.5677×106 RIU-1 (1.3497 × 106 RIU-1) and 7.8387×1010 RIU-1deg-1 (4.4990×1010 RIU-1deg-1) for TM (TE) polarization mode, which performs two orders of magnitude enhancement compared with the reported biosensors. With the protection of the topological edge state, this biosensor has high tolerance to the thickness deviations and refractive index (RI) variations of the component materials, which can reduce the requirements on fabrication and working environment. It is anticipated that the proposed biosensor possesses excellent sensing performances, may have great potentials in environmental monitoring, medical detection, etc.

Light Efficiency Investigation of Ultraviolet Light-Emitting Diodes Combined With Polarized Emission and Packaging Structure

Ultraviolet light-emitting diodes (UV-LEDs) have attracted extensive applications in resin curing, medical treatment, biochemical inspection, and disinfection. However, the UV-LEDs suffer from the main bottleneck of low light efficiency, which depends on the polarized emission and packaging structure of UV-LEDs simultaneously. In this work, we investigated the light efficiency of UV-LEDs combined with polarized emission and packaging structure. Four types of UV-LEDs (UVC-A, UVC-B, UVB, and UVC) without a lens (UV-Ref.), with a flat lens (UV-FL), and with a hemispherical lens (UV-HL) were fabricated, respectively. Through investigating the light output power, far-field emission pattern, and electrical field intensity distribution of UV-LEDs, the UV-HL packaging structure displays the highest emission intensity and light output power in the whole UV band. Compared with the UVC-A-Ref. and UVC-A-FL structures, the enhancement ratios of the light output power of UVC-A-HL structure are 28.9% and 46.5%, respectively. Furthermore, the light extraction efficiency of the TM-polarized mode in the UVC-A-HL structure is enhanced by 29.6% compared with the UVC-A-Ref. structure. The results indicate that the light extraction of UV-LEDs is greatly affected by the polarized emission and packaging structure. Our work opens an efficient guidance to enhance the light efficiency of various UV-LEDs with appropriate packaging structure.

High-Sensitivity Multiband Detection Based on the Local Enhancement Effect of an Electric Field at Terahertz Frequency

The terahertz detection sensitivity interaction with other substances has received extensive attention and remains challenging due to the loss of terahertz waves. Herein, a terahertz, multiband sensor with high sensitivity based on the local enhancement effect of an electric field at terahertz frequency is proposed. The designed terahertz sensor is based on a common metamaterial sandwich absorber of electromagnetic energy that only employs an asymmetric metallic strip, which produces three resonance peaks with an absorption coefficient of greater than 95% in the 0.2-1.5 THz range and a maximum Q -factor of 46 at 1.397. Based on the principle of impedance matching, the high absorption of electromagnetic wave energy is reasonably analyzed. Furthermore, the influence of the top metal structure on the absorptivity and resonance frequency is analyzed by simulation optimization, and the optimum structural parameters are obtained. In addition, the influence of the refractive index (RI) change of the sample and dielectric layer on the resonance characteristics of the sensor is analyzed. When the thickness of the surface sample of the terahertz sensor metamaterial-based absorber is changed so that the RI changes in 1-2, the RI sensitivity increases up to 208 GHz/RIU, which can be used as an RI sensor. Furthermore, the influence of the sensor sensitivity and reflection coefficient on the thickness parameters of the sample covered by the sensor surface is analyzed, and the optimal sample thickness is 6 μm. The influence of the incident angle of the THz wave on the detection performance in the TM polarization mode is analyzed, and it is determined that the change in the incident angle in the range of 0-40 degrees has minimal influence on the resonance peak and absorption rate of multiband detection. Therefore, we suggest that our proposed sensor has considerable potential in biomedicine and trace detection applications.

Performance enhancement of an ultrafast graphene photodetector via simultaneous two-mode absorption in a hybrid plasmonic waveguide.

An ultrafast, compact, zero-biased, and complementary metal-oxide semiconductor-compatible graphene photodetector (PD) based on a silicon-on-insulator hybrid plasmonic waveguide (HPWG) is proposed. Lumerical MODE solver is employed to investigate the modal characteristics of TM-polarized modes in the HPWG composing the PD. It is shown that the input light can be completely coupled into the photonic-like and plasmonic-like fundamental TM modes at the PD section. These two modes are exploited together in the photodetection process to enhance the PD performance. A rigorous analysis is performed in order to extract the optoelectronic characteristics of the single-layer graphene (SLG) used in the proposed structure. Lumerical 3D-FDTD solver is then employed to quantify the light interaction of the two aforementioned optical modes with the SLG. With a proper design at a wavelength of 1550 nm, the PD voltage responsivity reaches 2.8 V/W, and the photocurrent responsivity is obtained as 18.5 mA/W, while the corresponding absorption length is kept below 8µm and the noise equivalent power is limited to 3.7pW/Hz. Moreover, as the PD operates under zero bias, its photoresponse is predominated by the photothermoelectric mechanism, exhibiting a bandwidth that exceeds 180 GHz while avoiding the dark current.

Omnidirectional High Reflectors Using Silica/Superconductor Fibonacci Photonic Crystal for Optical Communication Applications

Using the transfer matrix method and Fibonacci structure, an omnidirectional high reflector that covers the fiber optics wavelengths is searched. We aim to make the reflector covers the operating wavelengths of Plastic and Glass fiber optics (650, 850, 1300 and 1550nm). Firstly, an ordinary Fibonacci structure composed of TiO2 and SiO2 slabs materials was studied and for TE and TM polarization modes the reflectance spectra cover only the 850, 1300 and 1550 nm wavelengths and for a limited range of wave-angle of incidence. Secondly, the SiO2 slabs were replaced with the superconductor YBCO slabs which allows the extension of the reflectance bands to cover all fiber optics wavelengths for the entire angle of incidence interval [0-1.5 radian] and for both polarization modes. During that, the structure thickness was optimized by varying the iteration number and the optical thickness of Fibonacci sequence. Finally, the optical behavior of the reflector was tested when changing the ambient temperature.

A Bandpass Frequency Selective Surface Filter for Earth Observation Satellite and Radar Applications

In this paper, a bandpass frequency selective surface filter has been suggested for the satellite and radar applications at X band frequency regime. The study has been conducted both numerically and experimentally in a wide range frequency band between 2 GHz and 14 GHz. 2 GHz of 3 dB bandwidth between 7.3 GHz and 9.3 GHz has been obtained. The proposed structure has the polarization insensitive characteristic. It also has angular stability with the incident angle ranges from 0° to 60° with very small frequency deviations both TE and TM polarization modes. The prototype of the FSS structure is composed of 20x20 unit cells in a dimension of 18cm x 18 cm. The experimental studies have been conducted by using Agilent PNA-L vector network analyzer with two horn antennas. The bandpass filter can be effectively used in many satellite and radar systems as an antenna radome to prevent noises and to reject unwanted frequency bands

Wavelength temperature insensitivity of surface-trapped optical modes in microcavities

We address theoretically lateral localization of surface-trapped optical modes in microcavities formed at a surface of a distributed Bragg reflector (DBR). GaAs-GaAlAs materials are considered as a model system. We analyze such modes and demonstrate that thick metal bars mounted on top of the DBR form a lateral cavity strongly localizing in plane the modes which exhibit in the vertical direction an evanescent decay in the air and an oscillatory decay in the DBR. Such TM-polarized modes are strongly confined between the bars, the fraction of the optical energy of the mode located in the air reaching ∼90%. We show that the wavelength of such modes is nearly temperature-insensitive, the thermal shift can be as small as below 0.005 nm/K, which is an order-of-magnitude smaller than the typical value for vertical cavity surface emitting lasers (VCSELs). TE-polarized modes are observed only if the top layer of the DBR sequence has a thickness different from λ/4 and a cavity layer is formed at the surface. The surface-trapped modes enable near-field outcoupling to an external waveguide or to an optical fiber placed closed to the DBR surface. In DBR structures incorporating an active medium these modes can be employed for construction of microlasers as well as for resonant semiconductor optical amplifiers (SOAs) having nearly temperature-insensitive lasing/resonance wavelength. In another approach applying a reverse bias to the active medium one can realize resonant intensity modulators. Surface-trapped modes can be employed in all-dielectric DBRs enabling low loss waveguides for silicon photonics. Further applications include using such modes at interfaces between a semiconductor DBR and a dielectric medium having a lower refractive index.

Design of hybrid narrow-band plasmonic absorber based on chalcogenide phase change material in the infrared spectrum

Structures absorbing electromagnetic waves in the infrared spectral region are important optical components in key areas such as biosensors, infrared images, thermal emitters, and special attention is required for reconfigurable devices. We propose a three-dimensional metal-dielectric plasmonic absorber with a layer of PCM’s (Phase Change Materials). The phase shift effects of PCMs are numerically analyzed, and it is possible to obtain a shifting control of the resonant absorption peaks between the amorphous and crystalline states using the Lorentz–Lorenz relation. By using this empirical relation, we analyzed the peak absorption shift at intermediate phases between the amorphous and the crystalline. The geometric parameters of the structure with the PCM layer in the semi-crystalline state were adjusted to exhibit strong absorption for normal incidence. The effects of the oblique incidence on the absorption for the TM and TE polarization modes were also analyzed. Our results demonstrate that PCMs have great potential for reconfigurable nanophotonic devices.

Polarization-controlled amplified spontaneous emission in 2D semiconductors with birefringent microcavity

We report on the polarization-controlled amplification of excitonic emission in the monolayer WS2 coupled with ZnO microcavity. From polarization-resolved micro-photoluminescence spectroscopy and numerical modeling, we found that the polarization of WS2 excitonic emission can be tailored by the whispering gallery modes of the birefringent ZnO microcavity. Furthermore, the light input–light output curves exhibit the clear threshold kink and the superlinear increase in the output intensity for both the TM and TE polarization modes, indicating the polarization-dependent amplification of excitonic emission. Our results suggest an approach to realize the polarization-controlled photonic devices based on 2D materials.

High-efficiency nine-port beam splitting output enabled by a dielectric lamellar sandwiched fused-silica grating

High-efficiency multi-beams output from diffraction optical element (DOE) with equal energy in parallel is of intense interest because high-performance multiple output beams can improve transmission rate of some key optical signals. Herein, we design a novel sandwiched fused-silica diffraction grating, which can operate at the high-efficiency nine-port beam splitting output with good uniformity. By performing rigorous coupled-wave analysis (RCWA) method, grating parameters and fabrication errors are optimized and discussed for TE and TM-polarized modes. A theoretical simplified modal method (SMM) can insight into an explicit light-matter coupling mechanism in grating area. In addition, for better evaluating real performances of the grating, incident spectral bandwidth of the grating can be fully investigated based on RCWA approach and finite-element method (FEM). Thus, this work can open up a possible way for optimizing more high-performance polarization-independent or polarization-dependent higher-order-port diffraction gratings.

Ultracompact and broadband mid-infrared polarization beam splitter based on an asymmetric directional coupler consisting of GaAs–CaF[formula omitted] hybrid plasmonic waveguide and GaAs nanowire

In this paper, an asymmetric directional coupler (DC) based on a GaAs–CaF2 hybrid plasmonic waveguide (HPW) and a GaAs nanowire (NW) is designed for the mid-infrared polarization beam splitter (PBS). The mode characteristics of the GaAs–CaF2 HPW and GaAs NW-based PBS are simulated by using the finite element method (FEM). With the appropriate widths of the HPW and NW, the TE polarization mode in the HPW and NW is phase-matched, whereas the TM polarization mode is phase mismatch. Hence, the TE mode undergoes a strong coupling to the GaAs NW while the TM mode pass through the GaAs–CaF2 HPW directly. The results show that the PBS achieves the extinction ratio (ER) of 19.78 dB and insertion loss (IL) of 1.64 dB for the TE mode, ER of 7.78 dB and IL of 2.64 dB for the TM mode at the operating wavelength of 3.5 μm. The PBS based on an asymmetric DC paves the way to achieve integrated waveplates, which has potential applications in the detection and analysis of airborne molecules and the optical communication techniques with large signal transmission capacity.