Working Wavelength Research Articles

A Broadband Planar Spiral Antenna Design for Electromagnetic Signal Monitoring

In order to meet the wide-band full-space radio monitoring task, the design of a circular-polarized planar dual-arm composite spiral antenna is presented in this paper. The antenna operation covers the L-band and S-band frequencies ranging from 200 MHz to 6 GHz (relative bandwidth is 187.1%). The equiangular spiral is applied to the beginning of the Archimedean spiral, which reduces the input impedance of the antenna, thereby reducing the length of the cross-section of the feed balun and realizing the miniaturization of antenna. The antenna is designed to be simple in structure and small in size. The diameter of the radiating surface and the length of the section are only 1/5 and 1/50 of the working wavelength. The simulated and measured results show that the antenna has a very good impedance matching (standing wave ratio of less than 2.5), and the antenna has good symmetry, and has good circular polarization and wideband characteristics. Finally, the antenna is applied with an USRP (universal software radio peripheral) to carry out the electromagnetic signal monitoring experiment outdoors. The results show that the designed antenna can receive electromagnetic signals in the 200 MHz - 6 GHz band and can be used for full-space radio monitoring.

AlGaN-based UV-C distributed Bragg reflector with a λ-cavity designed for an external cavity structure electron-beam-pumped VCSEL

The external cavity structure electron-beam-pumped (EB-pumped) vertical cavity surface emitting laser (VCSEL) has an important demand for the distributed Bragg reflector (DBR) with an emission window at the working wavelength called λ-cavity. Herein, AlGaN-based UV-C band DBRs with λ-cavities around 280 nm are designed and investigated in detail, which have almost no been reported so far. The DBRs based on alternate stacked Al0.47Ga0.53N/AlN bilayers are in-situ grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Through a comprehensive protocol of structure optimization by theoretical simulation, epitaxial growth and in-depth characterization and analysis, a high-performance UV-C band DBR with a λ-cavity around 280 nm is successfully fabricated. The DBR presents a reflectivity as high as 81.3% at the λ-cavity, a maximum reflectivity of 89.8% at 282 nm and a stopband with a full-width at half-maximum (FWHM) of 24.7 nm, laying a foundation for developing the external cavity structure EB-pumped AlGaN-based UV-C VCSELs emerging as a promising alternative to the electrically pumped AlGaN-based UV-C lasers.

Ultrawideband, Wide-Angle Scanning Array With Compact, Single-Layer Feeding Network

This article presents a single-polarization and ultrawideband tightly coupled dipole array (TCDA) with a compact, single-layer feeding network, and a superstrate layer for wide-angle scanning. The feeding network based on a microstrip-to-slotline structure can significantly reduce the size and complexity of the array. The superstrate layer consists of two frequency selective surfaces (FSSs), which can efficiently increase the scanning angle. The single-polarization TCDA has a bandwidth of 5.13:1 (0.75–3.85 GHz) with the simulated active VSWR $16\times16$ elements is only $0.12\lambda $ at the largest working wavelength. The measured results of a subset of the array are consistent with the simulated.

High Performance Polarization Beam Splitter Based on Cascaded Directional Couplers Assisted by Effectively Anisotropic Structures

A high performance polarization beam splitter (PBS) based on cascaded directional couplers (DCs) assisted by effectively anisotropic structures is proposed. The sub-wavelength grating (SWG) structures between the two coupled waveguides act as anisotropic metamaterial cladding to block/enhance light coupling for transverse electric (TE)/magnetic (TM) polarization. Cascading the DCs designed at different central wavelengths can improve the extinction ratio (ER) within the desired bandwidth or broaden the working wavelength bandwidth for TM polarization. Three design examples show the excellent performance of PBS with ER of >35 dB, 20 dB or 14 dB and loss of 20dB of the PBS based on the cascaded DCs increases by ∼11 times when compared with a single DC.

Broadband multi-wavelength optical sensing based on photothermal effect of 2D MXene films

Abstract Two-dimensional (2D) materials were widely used in sensing owing to the tunable physical or chemical properties. For years, optical sensing attracted a massive amount of attention on account of high accuracy, high security, non-invasive measurement, and strong anti-interference ability. Among the various optical sensing schemes, multi-wavelength optical sensing (MWOS) is an important branch and widely adopted in optical image, spectroscopy, or bio/chemical research. However, no spectral selectivity, limited working wavelength range, or intrinsic instability makes conventional 2D materials unsuitable for MWOS. A new class of 2D materials, known as MXene, exhibits outstanding electronic, optical, and thermal properties, leading to new applications in optical sensing. In this paper, we propose an integrated photothermal optical sensor (PHOS) using Ti3C2Tx MXene films. Thanks to the inherent spectral dependence of Ti3C2Tx MXene over a broadband range, the proposed PHOS can respond to different wavelengths from visible to short-wavelength infrared. Because of the efficient photothermal conversion, the PHOS has a control efficiency up to 0.19 π · mW−1 · mm−1 under 980-nm laser pumping and shows a higher control efficiency under red light (690 nm) irradiation. The measured response time of the proposed PHOS is 23.4 μs. This paper brings MXene into chip-integrated optical sensing fields for the first time and shows the potential applications.

Mathematical model experimental verification for non-invasive method of glucose concentration in blood determination

The mathematical model of the device which provides performance of the non-invasive measurements of glucose concentration in blood has been created. The model includes composition and solution of the system (or the set of systems) of linear equations in which the concentrations of different absorbing components are variables. This model has some problems from the point of view of the equation system solution convergence, and it was necessary to perform some experiments for the model verification. The present paper is devoted to the experiments performance methods and results for the mentioned mathematical model verification. The study allowed us to determine the working wavelengths in the spectral ranges that are optimal for measuring the concentration of glucose in the blood, and to establish the correlation of the measured and calculated values according to the developed mathematical model.

Dynamic regulation of nonlocal effect and nonlocal degree in gyromagnetic metamaterials with an applied magnetic field.

We report dynamic regulation of nonlocal degree, nonlocal effects and spatial dispersion characteristics for transverse electric (TE) waves in periodic layered gyromagnetic metamaterials (PLGMs) by an applied magnetic field. A nonlocal effective permeability tensor, relying on both frequency and wave vector, is derived by expanding the accurate dispersion relation obtained by the transfer-matrix method (TMM) to high-order terms. The numerical results indicate that the degree of nonlocality of electromagnetic response in such PLGMs is closely dependent on the ratio between the period of PLGMs and the working wavelength. There are giant spatial nonlocality and strong spatial dispersion near the center or boundary of the first Brillouin zone, which leads two or three propagating modes to appear in these regions for a fixed frequency. Interestingly, the degree of nonlocality, nonlocal effects and spatial dispersion properties in such PLGMs can be manipulated dynamically by an applied static magnetic field. In addition, it is possible that a quasi-straight isofrequency contour occurs in the case of linear response. These properties make the PLGMs become excellent candidates for designing photonic devices in information communication, storage, nondiffraction transmission, and so on.

Design and optimization of microstructure optical fiber sensor based on bimetal plasmon mode interaction**Project supported by the National Natural Science Foundation of China (Grant Nos. 61575066, 61527822, and 61735005), the Natural Science Foundation of Guangdong Province, China (Grant No. 2017A030313333), the Science and Technology Program of Guangzhou City, China (Grant No. 201707010133), the Science and Technology Planning Project of Guangdong

A surface plasmon resonance (SPR) sensor with two orthogonal open loops based on microstructured optical fibers (MOFs) is introduced. The interaction between core mode and surface plasmon polariton (SPP) mode produced by two different metal films is studied. Full vector finite element method is used to analyze the coupling and sensing characteristics. The results show that there are three loss peaks near the Au/Ag film, and multi-peak calibration is achieved. Because of the positive and negative sensitivity of the amplitude, the sensor has strong anti-interference capability when the external environment changes. The sensor can detect the refractive index between 1.37 and 1.40, and the working wavelength is between 1600 nm and 2400 nm. Because the sensor has some excellent characteristics, it can be used in biochemical sensing, environmental detection, and other related fields.

Gaseous discharge plasma switching in oversized interference microwave switches

The first results of the study of gaseous discharge plasma switching in oversized interference switches of X-band active resonant microwave compressors are presented. The switching occured in a mixture of argon and air at atmospheric pressure in the mode of spontaneous breakdown. The breakdown was initiated by a sizable conductive discontinuity represented by a section of thin copper conductor of different lengths not exceeding the working wave length. The section was introduced inside the gaseous discharge quartz tube into the switching arm of the switch through the below cut off circular waveguide. The tube formed the discharge gap in the arm and was located coaxially in the circular waveguide. The tube was located at the antinode area of the electric field standing wave parallel to lines of electric force. The threshold nature of effective switching was proved. The switching efficiency as a function of the conductor length is obtained. The model of the switch was proposed and analyzed by the scattering matrix method within single-wave approximation. The calculation results were in substantial agreement with the experimental data. The operation of two oversized switches in a cascade circuit was studied. It is shown, that in switching circuits of these type formed by one or several oversized H-tees, the switching identical to processes in a conventional switch based on a single-wave H-tee is possible.

Fabrication and Study of a Concave Crystal Mirror for the KORTES Project

A method for fabrication of a concave spherical mirror made of crystalline quartz is proposed and X-ray optical properties of the mirror are studied. The radius of curvature is 1630 mm. The shape of the mirror surface is studied using an interferometer with a diffraction reference wave. In the entire processing region, the maximum deviation from the nearest sphere is about 0.2 μm and the rms is 34 nm, so that high quality of imaging is provided with an angular error of about 2″ (angular seconds). Reflection coefficient (about 7%) and lower bound limit of spectral selectivity (λ/δλ ≈ 1775) are determined in the vicinity of a wavelength of λ = 0.834 nm, which is close to the working wavelengths of the MgXII doublet (λ = 0.8418 and 0.8423 nm). Position of the Bragg peak and spectral selectivity remain unchanged upon bending of the crystal mirror within measurement accuracy.

AND logic device based on chiral surface plasmon polaritons in Y-shape nanowire

An optical AND logic device based on chiral surface plasmon polaritons (SPPs) is theoretically proposed. The AND logic device is made up of five Y-shape nanowires with two input ports and one output port. Chiral SPPs excited at the end of input ports propagate along the nanowire. By adding two gold blocks on one side of the AND logic device, the chirality of the device is amplified. By modifying parameters, we find suitable parameters to design the structure with a large chirality at the working wavelength. By setting the threshold, we achieve the AND logic devices. Our structure may provide a significant component in signal transmission and processing devices.

The method of multicomponent determination of herbicides of various chemical classes in water

In the work there are considered results of the development of the multicomponent method of measurement of concentration of herbicides of various chemical nature under their joint presence in the water. There was justified the optimality of application of HPLC-DAD (the working wavelength of 240 nm) for the determination of levels of 10 active ingredients of herbicides of class of sulfonylurea (metsulfuron-methyl, nikosulfuron, sulfometuron-methyl, thifensulfuron-methyl, triflusulfuron-methyl), imidazolinone (imazapyr, imazethapyr), 2,6-Bis[(4,6-dimethoxy-2- pyrimidinyl)oxy]benzoic acid (bispyribac acid), triazol-pyrimidines (Penoxsulam), a benzoylpyrazole compound (Topramenzone). For the concentrating and cleaning of samples of water there were used cartridges for solid-phase extraction of Oasis HLB - the macro porous copolymer made on the basis of the balanced ratio of 2 monomers - lipophilic divinylbenzene and hydrophilic N-vinylpirrolidone. The range of the detected concentrations in water was volatile between 0.0005 and 0.005 mg/L, values of standard deviation vary in the range of 1.8-3.9%. Chlorine-containing acidic herbicides were analyzed by the method of GC-ECD and GC-MS (IE) after preliminary converting of compounds into flying derivatives with the use of diazomethane. Satisfactory extraction of substances from a water sample may be achieved by classical extraction in the system “liquid-liquid” with the application of Methyl tert-butyl ester. For cleaning of the derivatized sample there were used cartridges for solid-phase extraction on the basis of silica gel. The range of the determination of 9 active ingredients referring to classes of phenoxy-acetic acid (2,4- D, MCPA), pyridinecarboxylic (aminopyiralid, picloram, clopyralid), benzoic acids (dicamba), benzothiadiazinone (bentazone), biphenyl ester (acifluorfen) and a chloroacetamide (acetochlor) - 0.0001-0.001 mg/L, SD values vary in the range of 1.8-33%.

Time-division-multiplexed observation bandwidth for ultrafast parametric spectro-temporal analyzer.

Parametric spectro-temporal analyzer (PASTA) has been demonstrated as a powerful tool for ultrafast spectrum measurement with superior frame rate and resolution. Compared with other time-stretch-based counterparts, the temporal focusing mechanism enlarges the initial condition and enables the observation of arbitrary waveform, especially the emission spectrum. However, due to the limited conversion bandwidth of the parametric mixing-based time-lens, the observation bandwidth of PASTA is constrained within the C (conventional) band, which hinders its practical applications. To overcome this constraint, both stokes and anti-stokes conversions of the parametric mixing process are leveraged, and the concept of time division multiplexing (TDM) is introduced to ensure their separability. Therefore, the TDM-based PASTA system successfully demultiplexes the C band and L (long) band spectra in two adjacent temporal frames. It is capable of reconstructing the wavelength-to-time sequence for arbitrary waveform over a record 58-nm observation bandwidth, which can be further improved by optimizing the filters and amplifiers. Meanwhile, both of these two bands achieve 20-pm resolution, 10-MHz frame rate, and -30-dBm sensitivity. Moreover, this TDM concept can also be applied to other parametric mixing-based temporal imaging systems to enlarge the working wavelength band, such as temporal magnification.

A generalized model for space-coiling resonators

An ultra-thin absorber with a coiling chamber can realize a total sound absorption in an extremely low frequency. This can be regarded as the extreme case of a resonator with an extended partition. A coiled partition extends into a cavity, paving an elongated path and hence tuning the control band into lower frequency. To theoretically investigate the performance evolution during this process, a theoretical model is proposed in this paper, which is then validated by numerical simulations as well as experiments. In fact, this theory links the space-coiling resonator to the conventional Helmholtz resonator and the quarter-wavelength tube, which are two extreme cases representing no partition and full partition, respectively. It turns out that, by extending the partition, the working wavelength can reach approximately 26 times the side length of the original cavity, revealing the effective capability of low frequency control via a small unit.

Realization of broadband negative refraction in visible range using vertically stacked hyperbolic metamaterials.

Negative refraction has generated much interest recently with its unprecedented optical phenomenon. However, a broadband negative refraction has been challenging because they mainly involve optical resonances. This paper reports the realization of broadband negative refraction in the visible spectrum by using vertically-stacked metal-dielectric multilayer structures. Such structure exploits the characteristics of the constituent metal and dielectric materials, and does not require resonance to achieve negative refraction. Broadband negative refraction (wavelength 270–1300 nm) is numerically demonstrated. Compared to conventional horizontally-stacked multilayer structures, the vertically-stacked multilayer structure has a broader range of working wavelength in the visible range, with higher transmittance. We also report a variety of material combinations with broad working wavelength. The broadband negative refraction metamaterial provides an effective way to manipulate light and may have applications in super-resolution imaging, and invisibility cloaks.

Conical Double-Core Structure LPmn Mode Converter

In this work, a LPmn mode converter is proposed based on a tapered double-core structure. With opposite changes of the two cores in radius dimension, matching the effective refractive index between the fundamental mode (LP01) in one core and one desired high-order mode in the other core is obtained, and the fundamental mode power is gradually converted to the high-order mode. The simulation results show that the mode conversion of LP01 to any high-order mode of LP11, LP21, LP31, LP12, LP41, LP22, LP32, LP42 and LP23 modes can be obtained with a conversion efficiency of ∼99%, ∼96%, ∼92%, ∼93%, ∼82%, ∼92%, ∼84%, ∼85% and ∼81% at the working wavelength of 1550 nm, respectively, and also conversion bandwidth (>80% conversion efficiency) is 265, 125, 130, 130, 100, 35 and 30 nm, respectively. Compared to the previously reported works, the proposed mode converter structure is more universal to support any of higher-order mode conversions with wider bandwidth.

Broadband and Ultrathin Metamaterial Absorber Fabricated on a Flexible Substrate in the Long-Term Evolution Band

In the low-frequency regime, we demonstrated an efficient broadband metamaterial absorber (MA) by integrating an active low-conductivity ground plate into the common sandwiched structure. The energy of every electromagnetic (EM) wave radiated from the ultrahigh frequency to the long-term evolution band is trapped inside an ultrathin/flexible MA, which has a thickness of only λ/1362 at the lowest working wavelength. This performance of proposed MA in the defined band is also predicted through a simplified equivalent-circuit model and the simulation. Correspondingly, our MA absorbs over 90% in the wide band from 0.2 GHz to 3.6 GHz (fractional bandwidth of 179.0%). In particular, this MA also exhibits the stable features of omni-directionality (incident angle up to 40°) and polarization independence of the EM waves. Our innovation offers a different approach to realize the potential wearable smart meta-devices by using these ultrathin broadband MAs.

Optical radiation forces of focused Gaussian beams on the three-layered microgel particles with near-infrared responses

Optical manipulation of three-layered microgel particles with near-infrared responses is important for drug delivery and release in vivo. In this work, we investigate the optical radiation force (ORF) on a three-layered SiO2–Au–pNIPAM particle in a focused Gaussian beam (FGB) based on Mie scattering theory. As the radius of inner SiO2 core increases to 43 nm, the dipole plasmon resonance of the SiO2–Au–pNIPAM particle moves to ~ 800 nm. In the vicinity of this wavelength, the ORF of the FGB on the SiO2–Au–pNIPAM is always positive due to the strong scattering. As the working wavelength is larger than ~ 1100 nm, the gradient force on the particle becomes stronger than the scattering force, and thus the negative ORF is realized. We focus on negative ORF on the SiO2–Au–pNIPAM, and find that the beam waist radius, the outer gel shell, and the embedding medium all influence the ORF on the SiO2–Au–pNIPAM particle. The present work may be helpful for manipulating three-layered microgel particles, with the negative ORF being particularly important for particle trapping.

Inverse synthetic aperture ladar autofocus imaging algorithm for micro-vibrating satellites based on two prominent points.

As an important imaging method for long-range satellite targets, inverse synthetic aperture ladar (ISAL) has the characteristics of high-resolution imaging and competitive detectability. Since the working wavelength of the ISAL is comparable to the micro-vibrations generated by mechanical moving components of satellites, which will cause image defocusing, motion compensation is of great significance. In this paper, an autofocus algorithm is proposed for estimating and compensating the phase error relating to both translational and rotational micro-vibrations. Comparing with non-parametric algorithms like phase gradient autofocus and parametric algorithms like contrast-based autofocus and entropy-based autofocus, the proposed one, which is based on two prominent points, is especially effective for the rotational phase error oscillating numbers of cycles. Simulations and experiments are conducted to validate the feasibility of the proposed algorithm.

Ultra-low-cost fabrication of polymer-based microfluidic devices with diode laser ablation.

In this work, a diode laser ablation approach was used for the fabrication of PMMA-based microfluidic devices. Compared with the conventional CO2 or femtosecond laser fabrication method, the proposed laser ablation method based on diode laser significantly lowered the cost in the fabrication of polymer-based microfluidic devices with comparable resolution and surface quality. PMMA substrate was used for the laser ablation process, due to the transparency of PMMA in the diode laser's working wavelength, a layer of Kraft tape was applied on the surface of PMMA for the absorption of laser energy, and microchannels were then achieved on the surface of PMMA with the proposed low-cost diode laser system. The comparison between the proposed method and the CO2 laser ablation method was also conducted in this study. The profile of the fabricated microchannels was carefully characterized, several microfluidic devices were also fabricated for the demonstration of the proposed fabrication method using a diode laser.