Waveguide Arrangement Research Articles

Microwave assistance effect for rock breaking of TBM disc cutter using the coupled method of continuum and grain-based model

Microwave-assisted rock breaking technique can significantly weaken the strength and the stiffness of hard rock, and can consequently enhance TBM efficiency as well as relieve wear of disc cutters. Understanding the mechanism of microwave-assisted rock breaking requires knowledge of the intersection and connectivity properties of freshly formed fractures below the cutter and the fracture network resulting from microwave-induced damage. In this study, a numerical approach, coupled with the grain-based model (GBM) and continuum based microwave electromagnetic analysis, for simulating the microwave-treated granite is proposed firstly. Subsequently, the numerical experiment of TBM cutter penetration is conducted with the consideration of five levels of microwave power irradiation as well as two waveguide arrangements. The temperature field and fracture behavior are analyzed to investigate the thermal damage of the granite after the treatment of the microwave. Furthermore, the reduction of peak normal force and variation of average coordination number are examined to evaluate the impact of waveguide position on the effectiveness of microwave-assisted rock breaking. The simulation results indicate that the suitable power of microwave irradiation (≥ 30 kW) can promote the rise of granite temperature directly below the waveguide, further resulting in an increase in the quantity of microcracks and noticeable damage to the rock block. When the microwave power exceeds 30 kW, the peak normal force and average coordination number progressively start to decline for the case of a waveguide port facing the centerline of a single cutter. In the case of waveguide facing the gap between double cutters, the decreasing trend of the peak normal force is similar to that under the condition of single cutter, but the starting threshold has been raised to 45 kW. When the microwave power is below 60 kW, the average coordination does not change significantly. After comparing the improvement effects of microwave-assisted rock breaking under the two waveguide arrangements, a preferred condition of the microwave for breaking is determined. The waveguide port facing the centerline of a single cutter, and the microwave power of 30 ∼ 60 kW can lead a success in a satisfactory effect in term of the reduction rate of peak normal force and average coordination number.

Plasmonic sensor for rapid detection of water adulteration in honey and quantitative measurement of lactose concentration in solution

In this article, a novel surface plasmon polariton-based plasmonic refractive index sensor is proposed and numerically investigated. It consists of a structure of an octagonal cavity resonator inside a square disk along with silver nanodots and two slits which are coupled to a straight metal–insulator–metal (MIM) waveguide arrangement. The finite element method (FEM) has been employed to perform a numerical analysis of the proposed structure in the near-IR (Infrared) and mid-IR spectrum. The sensor detects changes in refractive index in terms of changes in resonant wavelength which can be measured using an optical spectrum analyzer. The recorded maximum sensitivity is 2527.6 nm per refractive index unit (RIU) with a sensing resolution of 3.956×10−7 RIU. The proposed sensor has been further numerically analyzed, and its ability to measure the quality of honey samples and detect lactose concentration in a solution has been verified.

SCIENTIFIC AND TECHNICAL BASIS FOR THE DEVELOPMENT OF INSTALLATIONS WITH MICROWAVE POWER SUPPLY FOR PROCESSING RAW MATERIALS AT AGRICULTURAL ENTERPRISES

The developed methodology of designing installations with microwave power supply for heat treatment of raw materials of agricultural enterprises is described. The scientific problem is the low energy efficiency of installations designed for heat treatment of raw materials with steam-water mixture, convective heat supply, the absence of continuous-flow installations for farms that ensure the preservation of consumer properties of the heat-treated product at reduced operating costs. (Research purpose) The research purpose is developing the scientific and technical foundations of installations with microwave power supply for processing raw materials at agricultural enterprises. (Materials and methods) Carried out three-dimensional modeling of the structural design of the installations in the Compass 20 program, determined the electrodynamic parameters of the “generator-resonator” system in the CST Microwave Studio program. (Results and discussion) Resonators of different structural designs have been developed for different types of raw materials, in which electromagnetic safety is ensured by forbidden waveguides, decelerating systems in the form of a chain of connected resonators, comb, cylindrical spiral, rod ring, counter pins. In resonators with curved surfaces, several magnetrons of the same frequency or operating at close frequencies with dissectors were used to change the frequency of the generator and increase the number of types of vibrations, and mixing, transporting mechanisms that allow maintaining the well of the technological process less than 0.5 and observing the dimensions of the raw materials in accordance with the depth of penetration of the wave. It was found that when using several magnetrons, the concentration of the electromagnetic field energy in the resonator volume and the reduction of radiation losses are achieved using ceramic reflectors. The values of the intrinsic Q-values of the resonators were determined to evaluate the thermal efficiency coefficient. (Conclusions) Using the examples of an animal colostrum defroster, instant milk pasteurizer and a three-section hop dryer with air-cooled magnetrons, the implementation of the scientific and technical fundamentals of designing microwave equipment for processing raw materials of agricultural enterprises was shown. It was revealed that they provide ways to achieve a continuous mode of operation of the equipment in compliance with electromagnetic safety without a shielding housing by implementing metal-dielectric resonators with decelerating systems and ceramic reflectors with an optimal arrangement of waveguides with air-cooled magnetrons on the curved surfaces of the resonators.

Branching High‐Order Exceptional Points in Non‐Hermitian Optical Systems

AbstractExceptional points are complex‐valued spectral singularities that lead to a host of intriguing features such as loss‐induced transparency—a counterintuitive process in which an increase in the system's overall loss can lead to enhanced transmission. In general, the associated enhancements scale with the order of the exceptional points. Consequently, it is of great interest to devise new strategies to implement realistic devices capable of exhibiting high‐order exceptional points. Here, it is shown that high‐order ‐photon exceptional points can be generated by exciting non‐Hermitian waveguide arrangements with coherent light states. Using photon‐number resolving detectors it then becomes possible to observe ‐photon enhanced loss‐induced transparency in the quantum realm. Further, it is analytically shown that the number‐resolved dynamics occurring in the same nonconservative waveguide arrays will exhibit eigenspectral ramifications having several exceptional points associated to different sets of eigenmodes and dissipation rates.

Preparation of Cerium Oxide via Microwave Heating: Research on Effect of Temperature Field on Particles

Micro–nano cerium oxide particles with regular morphology and good dispersity have been widely used in polishing and other industrial fields. Microwave heating is an effective, controllable and green heating technology. The Venturi reactor used for microwave heating developed by our team was the core equipment utilized to study the effects of pyrolysis conditions on the purity and microstructure of cerium oxide particles. The experiments were carried out and the products were characterized using XRD, SEM and EDS. Microwave heating, fluid flow and chemical reaction were coupled using numerical simulation, the effects of microwave power, reactor location and waveguide arrangement on temperature fields were investigated. The results showed that with the microwave power increasing, the degree of crystallinity and purity of cerium oxide improved. The morphology gradually became sphere-like. Varied reactor locations and waveguide arrangements changed the gradient and dispersity of temperature fields. Bulk particles and agglomeration could be avoided, and cerium oxide particles with average size of 80 nm were produced when the reactor was located in the center of the cavity. Vertical arrangement of waveguides had the advantages of higher temperature value, gentle gradient and better dispersity.

Realization of low-cross-talk half-wavelength pitch waveguide array on a silicon-on-insulator platform.

Realizing a densely packed waveguide antenna array is of great importance in light detection and ranging (LIDAR), owing to its suppressed grating lobes. In this work, a low-cross-talk half-wavelength pitch silicon waveguide array is proposed and experimentally demonstrated. It has a periodic arrangement of silicon strip nanophotonic waveguides, between which deep-subwavelength silicon strips are placed. Our experimental results show that this array's cross talk suppression is nearly 20 dB and has a bandwidth covering a wavelength range from 1500 nm to 1560 nm. Our realization of a half-wavelength pitch waveguide array may offer a promising platform for studying integrated optical phased arrays for solid-state LIDAR with a very low grating lobe and thus potentially a large field of view.

Nonvolatile Plasmonics Based on Optically Reprogrammable Phase Change Materials

Here, a new platform for a realization of novel nonvolatile optical switching devices was proposed that takes an advantage of high field confinement provided by plasmonics and multi-state programming capabilities of chalcogenide phase change materials. A high reduction in the overall energy consumption consists of a high field enhancement provided by plasmonic that allow to lower the switching energies and implementation of phase change materials that allow to operate under a zero-static power consumption. A combination of plasmonics and phase change materials provide additionally an essential improvement in terms of a switching time, attenuation contrast and possibility to perform a phase shift with the wide bandgap phase change materials. In most of the all-optical switching photonic devices, a switching mechanism is realized optically through heating of phase change materials. Here, two stage heating process is proposed that is based on the absorption of light by phase change materials itself, and a heat transfer from the metal stripe under an absorption of light by a metal. Thus, compared to any other previously presented optical switches, even a wide bandgap phase change materials that show zero absorption of light can be implemented in the proposed structure. The proposed plasmonic waveguide arrangement is extremely sensitive to any changes of the phase change material properties, thus, even a minor change of temperature provides an essential change in the transmitted light.

Symmetry-protected non-Abelian geometric phases in optical waveguides with nonorthogonal modes

The generation of non-Abelian geometric phases from a system of evanescently coupled waveguides is extended towards the framework of nonorthogonal coupled-mode theory. Here, we study an experimentally feasible tripod arrangement of waveguides that contain dark states from which a nontrivial U(2)-mixing can be obtained by means of an adiabatic parameter variation. We investigate the influence of higher-order contributions beyond nearest-neighbour coupling as well as self-coupling on the stability of a U(3)-phase generated from an optical tetrapod setup. Our results indicate that, despite the mode nonorthogonality, the symmetry of dark states protects the geometric evolution of light from distortion.

Fiber-integrated hollow-core light cage for gas spectroscopy

Interfacing integrated on-chip waveguides with spectroscopic approaches represents one research direction within current photonics aiming at reducing geometric footprints and increasing device densities. Particularly relevant is to connect chip-integrated waveguides with established fiber-based circuitry, opening up the possibility for a new class of devices within the field of integrated photonics. Here, one attractive waveguide is the on-chip light cage, confining and guiding light in a low-index core through the anti-resonance effect. This waveguide, implemented via 3D nanoprinting and reaching nearly 100% overlap of mode and material of interest, uniquely provides side-wise access to the core region through the open spaces between the cage strands, drastically reducing gas diffusion times. Here, we extend the capabilities of the light cage concept by interfacing light cages and optical fibers, reaching a fully fiber-integrated on-chip waveguide arrangement with its spectroscopic capabilities demonstrated here on the example of tunable diode laser absorption spectroscopy of ammonia. Controlling and optimizing the fiber circuitry integration have been achieved via automatic alignment in etched v-grooves on silicon chips. This successful device integration via 3D nanoprinting highlights the fiber-interfaced light cage to be an attractive waveguide platform for a multitude of spectroscopy-related fields, including bio-analytics, lab-on-chip photonic sensing, chemistry, and quantum metrology.

Spin wave modulation by topographical perturbation in Y3Fe5O12 thin films

We present a comparison of the spin wave propagation in Au/Y3Fe5O12 and Pt/Y3Fe5O12 bilayers. Microwave technique with a co-planner waveguide arrangement was used to excite and detect the spin wave. We observed a suppression in the propagating spin wave intensity when a metal stripe is placed on the surface of Y3Fe5O12 in the spin wave propagation path due to the spin pumping from Y3Fe5O12 to nonmagnetic metal stripe. However, a significant difference in the suppression property was observed with the Au and Pt electrode layers, which cannot be explained by the enhancement of the damping constant induced by spin pumping alone. The significant suppression of the spin wave propagation in the Au/Y3Fe5O12 bilayer system is attributed to the spin backflow and two magnon scattering.

Design of a slab waveguide using a graded index profile and a left hand material

In the present paper, we consider a pulse propagation in a slab waveguide structure having three layers. The guiding layer is assumed to have a linearly graded-index profile. Maxwell's equations are solved in the three layers and both electric and magnetic fields are written in terms of the asymmetry measure (a), the generalized frequency (V) and the generalized guide index (b). The dispersion properties are investigated for three waveguide arrangements: the first one has a left-handed material (LHM) cladding, the second one has a LHM substrate layer and the third has both surroundings as LHMs. The results show the proposed waveguide exhibits normal dispersion property in which b increases as V increases.

Integrated Nonlinear Waveguide Optics for High-Efficiency and Wideband-Tunable Generation of THz Radiation

On the basis of nonlinear downconversion, we propose how folded waveguide structures can be utilized as highly efficient, compact, and tunable sources of THz radiation. A folded waveguide arrangement allows us to exploit long-range efficient light–matter interaction at a compact geometrical footprint. Nonlinear THz generation in these systems is analytically modeled with results well supported by numerical simulations. For a practical device, based on the silicon photonics platform in combination with nonlinear organic materials, we show that the emitted THz radiation has a monochromatic continuous wave power on the order of tens of microwatts. The required optical input power is only 100 milliwatts. The THz emission frequency can be in situ tuned to any desired frequency in the 1–10 THz spectral range without spectral gaps. This unique property makes such integrated THz sources suitable for applications in THz spectroscopy and THz imaging.

5-way radial power combiner at W-band by stacked waveguide micromachining

This work presents a 5-way radial power combiner using the very low loss TE01 circular waveguide mode with a performance in the state of art for W-band. The accomplished design shows excellent characteristics: the experimental prototype has a return loss better than 20 dB, with a balance for the amplitudes of (±0.4 dB) and (±3.5o) for the phases, in a 12.8% fractional bandwidth (12 GHz centered at 94 GHz). In order to obtain these specifications, required for instance in plasma diagnosis systems or in power amplifiers, a meticulous step-by-step procedure is developed for both, the design and the challenging manufacture at W-band by stacked waveguide micromachining. The first step involves the design of a mode transducer, from the TE10 mode in the rectangular waveguide to the low-loss TE01 mode in the circular waveguide, with very high purity. In the second step, a 5-way radial power divider is designed. These designs, in order to be successful, have incorporated all the constrains for the manufacturing at W-band, using an E-plane stacked waveguide arrangement for low losses. The power combiner, made up by the transducer and the divider, has been manufactured with great accuracy using a very challenging assembly process, providing experimental results in very good agreement with the theoretical results.

Slot Waveguide Enhanced Bloch Surface Waves

The paper presents a novel concept for the on-chip integration of a multilayer platform sustaining Bloch surface waves further enhanced by the so-called slot waveguide effect. Through simulations, we demonstrate that a carefully designed polymer waveguide arrangement coated with a subwavelength dielectric multilayer can be efficiently used to first excite a Bloch surface wave at the surface of the multilayer and second to enhance this wave and allow longer propagation of the surface mode by constructive superimposition of two evanescent tails inside a narrow gap.

Review of optical fibre probes for enhanced Raman sensing

Raman scattering is a photon‐molecular interaction based on the kinetic modes of an analyte. It offers unique fingerprint‐type signals that allow molecular identification. A serious challenge frequently encountered in Raman measurements arises from the requirements of fast, real‐time remote sensing, fluorescence suppression, ultra‐micro concentration detection, small sample volumes and label‐free biological specimens. This review focuses on fibre‐optic probes for Raman spectroscopy, especially for enhanced sampling applications. It aims at providing an overview over contemporary technology and recent excellent researches, and helps identifying future developments necessary to bring the emerging technology to instrument manufacturers and end users. After a short introduction to surface‐enhanced Raman scattering technology, professional algorithms for design optimization of the fibre Raman probe will be discussed and general design considerations presented. Subsequently, various common geometries employed for enhanced Raman sampling are enumerated based on the types of waveguide fibres: multi‐fibre optodes, long‐pathlength capillary, microstructured photonic crystal fibre and other waveguide arrangements. Additionally, the relevant detection parameters are reviewed, such as target analyte, limit of detection, waveguide media and detection principle. The review also includes a brief summary of the advantages and limitations of various fibre Raman probes. Finally, the future work is discussed which will promote the reliability and the applicability of fibre enhanced Raman sensors. Copyright © 2017 John Wiley & Sons, Ltd.

Nonlinear imaging in photonic lattices.

We show that nonlinear imaging is possible in periodic waveguide configurations, provided that we use two different segments of nonlinear media with opposite signs of the Kerr nonlinearity with, in general, no other restriction about their magnitudes. The second medium is used to implement effective "reverse propagation." A main ingredient in achieving nonlinear imaging is the control of the sign and the amplitude of the coupling coefficient. We numerically test our results in one- and two-dimensional square arrangements of waveguides.

Design and characterization of MEMS optical devices using slot-ring resonator for low-voltage operation

To realize MEMS optical devices with low-voltage operation of less than 1 V, we have proposed a slot-ring resonator with a beam structure. The performance of the proposed device is investigated. From the simulation, a more than 10 dB extinction ratio is estimated at a low voltage of 0.5 V, when the slot waveguide width is 250 nm and the slot width is 50 nm. We succeeded in the fabrication of the proposed device structure, and improvement of the quality factor (from 6400 to 14000) is achieved by changing the lithography process. The modulating operation is confirmed but the extinction ratio is lower than the simulated value. There are several considerable reasons for this low extinction ratio, such as non-optimal carrier concentration in slot waveguides and nonparallel arrangement of slot waveguides and so on. Optimizing the fabrication processes will solve this, and the expected high performance will be achieved.

Novel Mach–Zehnder Interferometer Waveguide Design as a Light Delivery System for Heat-Assisted Magnetic Recording

We propose a light delivery system to the near-field transducer (NFT) of a heat-assisted magnetic recording (HAMR) head using a Mach–Zehnder interferometer (MZI) waveguide arrangement with a transverse electric (TE) mode coupled to the planar waveguide from a single mode fiber. The proposed design offers great flexibility in the coupling of light to the NFT in order to match the desired radiation pattern of the antenna and thus to optimize the energy transfer. Furthermore, it allows excitation of particular surface plasmon (SP) resonances of the transducer (quadrupole or higher) by controlling the coupling angle and the phase of the two beams of light. The optimum phase shift between the TE waveguide modes incident on the NFT can be achieved either statically by making one of the MZI arms longer/shorter compared with the other one, or dynamically by changing the mode effective index of the MZI waveguide arm through electro-optic or thermo-optic modulation. In addition, the proposed MZI waveguide arrangement enables easier coupling from a laser with coupling losses from laser to MZI waveguide being below 3 dB and the design enables an arrangement of the NFT placed either on the top of the waveguide at the termination side of the MZI or between the rib and the ridge at the maximum of the electric field of the waveguide, which maximizes the SP resonance enhancement of the NFT. Another advantage is that the magnetic-write pole, in our design, can be easily integrated on the same chip, preferably above the center of the MZI, between the two arms of the interferometer and away from the propagating mode, thus avoiding blocking of the light path.

Realization and Performance of an All-Polymer Optical Planar Deformation Sensor

Novel concepts for a planar optical deformation measurement promise broad application potential in fields such as structural health monitoring, process control, or life sciences. In this paper, we present a new approach to optical displacement and tilt sensing in thin polymer foils. We report on the design, simulation, realization, and characterization of an all-polymer planar strain and tilt sensor based on simple optical principles. The sensor relies on the evaluation of the coupling efficiency between two arrays of emitting and receiving waveguides. As a proof-of-concept, we show that the developed waveguide arrangement and readout algorithm allow monitoring a combination of both displacement/strain and tilt with the same sensor system at once. The performance and sensitivity achieved are in good agreement with simulations, and can pave the way for the future integrated 2-D measurement of larger deformations.

Diffraction grating polarization beam splitter using nano optical slits

In this work a polarization sensitive diffraction grating is proposed that has an effective density of lines being different according to the polarization of the input. This results in diffracting different polarizations at separate angles. The structure of the proposed diffraction grating consists of an arrangement of nanoscale waveguides in a metal slab. The structure is simulated using the finite difference time domain technique. The diffraction pattern from the structure is calculated using an integral expression for the free space propagation after the diffraction grating. A first order diffraction at an angle of 10.3° with an extinction ratio of 22.8 dB was obtained for one polarization and an angle of 15.7° with an extinction ratio of 23.4 dB was obtained for the second polarization.