Composite Waveguide Research Articles

Wave energy localization near the rough surfaces of piezoelectric waveguide. Near-surface inhomogeneities as a resonator or filter

Propagation of high-frequency electro-elastic normal wave signal in a composite waveguide is investigated. The roughnesses on a two surfaces of the piezoelectric waveguide are filled with an ideal conductor and ideal dielectric respectively. The both of the influence of surface roughness and the influence non-homogeneity of materials near the surfaces on the process of high frequency electro-elastic normal wave signal propagation, is discussed. The behaviors the frequency characteristics of wave in the composite waveguide at the propagation of normal wave signals numerically are investigated. The problem by the method of virtual cross sections and input of Magneto Elastic Layered System (MELS) hypotheses is solved. It is shown that in a case of not filled roughness of the piezoelectric layer surfaces, only two short wave modes are arise. The filling of the surface roughness with a dielectric or a conductor respectively, leads to the appearance of up to four such wave modes, depending at the wave signal length. The dispersion dependencies for all possible characteristic modes of shear electroelastic waves are given. It is shown that in a case of the propagation of slow waves, on certain wave lengths the silence frequency zones are arise.

Sound transmission induced by tunable asymmetry coupling vibrations in a composite waveguide

We report a sound impedance matching induced by asymmetry coupling vibrations. To achieve the vibration, acoustic waveguides with two different winding branch pipes are designed. In the acoustic device, the coupling effects of the two different winding branch pipes generate resonant vibrations, which constructs an impedance matching layer and produces a sound transmission with a wide band at lower frequencies. Importantly, multi-mode vibration can be adjusted by adding water. Consequently, the asymmetry winding branch pipes realize multi-mode vibrations that have the potential for use in sound control in broad frequencies.

Распространение поверхностных волн вдоль границы фоторефрактивного кристалла с нелинейным дефокусирующим покрытием

A composite waveguide structure, which is a crystal with a diffusion mechanism for the formation of a nonlinear photorefractive response, the surface of which is coated with a non-linear Kerr defocusing type, is considered. It is shown that there exist TM polarized nonlinear surface waves of two types, which differ in the range of existence and the profile of field decay. The propagation modes of nonlinear surface waves are determined in which the field intensity can be maximum or minimum near the surface or at the boundary of the coated crystal.

Nonlinear surface waves propagating along the composite waveguide consisting of self-focusing slab between defocusing media separated by interfaces with nonlinear response

The model of the composite symmetric waveguide consisting of self-focusing slab between defocusing nonlinear media separated by interfaces characterized by own nonlinearity response is proposed. Two new types of nonlinear surface waves propagating along it with anti-phase amplitude oscillations at interface planes are found. The frequencies of the nonlinear surface waves existing near the interfaces with the nonlinear response only are calculated analytically. The conditions of the surface wave existence are found. The frequencies and localization distances of the surface waves in dependence on nonlinearity waveguide parameters, slab width and interface characteristics are analyzed.

Miniaturised quadrature hybrid coupler using composite planar transmission lines

In this Letter, a novel miniaturisation technique for a 3-dB quadrature hybrid coupler is described. The revolutionary structure is composed of folded microstrip lines and folded coplanar waveguides that are printed on the top- and bottom-surfaces of a dielectric substrate, respectively. The two different planar lines are connected by copper vias to form the double-path composite microstrip-coplanar waveguide (CMCPW) line. To demonstrate the effectiveness of the technique, a simple yet miniaturised hybrid coupler is devised by introducing folded S-shaped CMCPW-lines, wherein their lengths are gradually changed to address the design goals. The simulated and measured results of the proposed coupler validate its good performance metrics in the amplitude responses of power splitting, return- and insertion-loss. Moreover, its isolation and quadrature phase between outputs have been examined. A very small footprint size of 0.0667 λ 0 × 0.0667 λ 0 at 0.5 GHz has been realised.

Record Purcell factors in ultracompact hybrid plasmonic ring resonators.

For integrated optical devices and traveling-wave resonators, realistic use of the superior wave-matter interaction offered by plasmonics is impeded by ohmic loss, which increases rapidly with mode volume reduction. In this work, we report composite hybrid plasmonic waveguides (CHPWs) that are not only capable of guiding subwavelength optical mode with long-range propagation but also unrestricted by stringent requirements in structural, material, or modal symmetry. In these asymmetric CHPWs, the versatility afforded by coupling dissimilar plasmonic modes provides improved fabrication tolerance and more degrees of device design optimization. Experimental realization of CHPWs demonstrates propagation loss and mode area of 0.03 dB/μm and 0.002 μm2, corresponding to the smallest combination among long-range plasmonic structures reported to date. CHPW ring resonators with 2.5-μm radius were realized with record Purcell factor compared with existing plasmonic and dielectric resonators of similar radii.

Acoustic waves splitter employing orbital angular momentum

A sound splitter using the orbital angular momentum (OAM) of acoustic vortices is proposed and experimentally demonstrated. We show that a helical waveguide with a periodic array of shunted tubes can be used to achieve different transmission spectra for the acoustic vortices with opposite OAM topological charges due to their different Bragg scattering type bandgaps. By symmetry, the transmission spectra will reverse if the handedness of the helical waveguides is changed. Therefore, two such composite waveguides with opposite handedness can be combined to separate the OAM-dependent flow of sound. Our study of the acoustic vortex splitter may provide a route for demultiplexing in acoustic OAM-based communication.

Tunable composite waveguide based on piezoelectric phononic crystal

The acoustic artificial structures with tunable parameters have attracted much research interest in these days. In this paper, we present a tunable composite waveguide based on the piezoelectric phononic crystal shunted by an inductor circuit. A pass band based on local resonance will emerge in the complete band gap through modulating the shunted inductor circuit. This local-resonant pass band can be used to realize a waveguide. Both the work frequency and the shape of this waveguide can be tuned simultaneously by modulating the inductance and the space distribution of the external inductor circuit. For the excellent tunable ability, the proposed tunable composite waveguide could be useful in elastic wave sensors and frequency filters.

Detection of diethyl chlorophosphate using a composite optical waveguide sensor

A highly sensitive composite optical waveguide sensor was developed for diethyl chlorophosphate vapor detection.

Mode Composite Coplanar Waveguide

In this paper, a mode composite coplanar waveguide (MCCPW) is proposed and studied. The MCCPW can be regarded as a combination of a quasi-coplanar waveguide and a substrate integrated waveguide (SIW). In this composite structure, the center conductor of the quasi-coplanar waveguide serves as the SIW supporting TE10 mode, while the TEM mode operates in the quasi-coplanar waveguide part. The characteristics and design method of the MCCPW are analyzed and illustrated in this work. The MCCPW is fabricated together with two transition structures to demonstrate its integration capability further with other planar circuits. The MCCPW is a single layer structure, and it has the advantages of joint structure and mode composition, which make it a possible solution for multifunction and multiband application systems. The measured and the simulated results agree well with each other, and good transition performances are achieved.

On-chip optical trapping of extracellular vesicles using box-shaped composite SiO2-Si3N4 waveguides.

The application of on-chip optical trapping and Raman spectroscopy using a dual-waveguide trap has so far been limited to relatively big synthetic and biological particles (e.g., polystyrene beads and blood cells). Here, from simulations, we present the capabilities of dual-waveguide traps built from composite SiO2-Si3N4 waveguides for optical trapping of extracellular vesicles (EVs). EVs, tiny cell-derived particles of size in the range 30-1000 nm, strongly attract attention as potential biomarkers for cancer. EVs are hard to trap, because of their smallness and low index contract w.r.t. water. This poses a challenge for on-chip trapping. From finite-difference time-domain simulations we obtain the narrow beam emitted from the waveguide facet into water, for λ = 785 nm. For a pair of such beams, in a counter-propagating geometry and for facet separations of 5, 10 and 15 µm, we derive the inter-facet optical field, which has a characteristic interference pattern with hot spots for trapping, and calculate the optical force exerted on EVs of size in the range 50-1000 nm, as a function of EV position. We use two refractive index models for the EV optical properties. Integration of the force curves leads to the trapping potentials, which are well-shaped in the transverse and oscillatory in the longitudinal direction. By applying Ashkin's criterion, the conditions for stable trapping are established, the central result of this work. Very small EVs can be stably trapped with the traps by applying a power also suitable for Raman spectroscopy, down to a smallest EV diameter of 115 nm. We thus argue that this dual-waveguide trap is a promising lab-on-a-chip device with clinical relevance for diagnosis of cancer.

Half-Mode Composite Waveguide

In this paper, a guided-wave structure, the half-mode composite waveguide (HMCW) is proposed and presented. Similar to the conventional mode composite wave- guide (MCW), the HMCW also has an inner and outer waveguides, each working in its half-mode operation, respectively. In the HMCW structure, the signal propagates in the inner waveguide with quasi- $\text{TE}_{0.5-0}$ mode and along the outer waveguide with the quasi-TEM mode. The HMCW’s half-mode operation principle, impedance, loss, and propagation characteristics including higher order modes are analyzed. Compared to its full-size counterpart, the HMCW only occupies half the space, when operating within the same frequency band. Simulation results show that the transmission loss of the HMCW is comparable to that of the full-size MCW. Thus, it is also suitable for both low- and high-frequency design and applications. To measure and integrate the HMCW with other planar circuits, a joint feeding network for the HMCW is also proposed. Its circuit prototype is fabricated on three layers of substrate using a multilayer substrate integration technique. This joint feeding network can simultaneously excite the inner and outer waveguides, respectively, in an independent manner. In measurements, both the inner and outer waveguides are transitioned to microtrip lines, and a good matching is achieved from 4.4 to 11.2 GHz with a relative bandwidth of 87.2% for the outer waveguide at low frequency and from 18.6 to 32.6 GHz with a relative bandwidth of 54.7% for the inner waveguide at high frequency, respectively.

Peculiarities in the Formation of X-Ray Fluxes by Waveguide–Resonators of Different Construction

The phenomenon of total external reflection (TER) of quasi-monochromatic X-ray radiation fluxes on a material interface and the effect of waveguide–resonator propagation of these fluxes in nanosize extended slit clearance, as well as a device operating on the basis of this effect—a planar X-ray waveguide–resonator—are briefly described. Experimental data on the formation of an X-ray flux by a composite X-ray waveguide–resonator are presented, and a model describing the decrease in the angular divergence of the formed flux without a decrease in the integral intensity is proposed. The model is based on the conception of partial angular tunneling of the radiation flux in the gap between two consequently mounted and mutually adjusted waveguide–resonators; the tunneling is implemented due to the interaction between interference fields of standing X-ray waves excited by the radiation transported by the slit clearance of these waveguide–resonators.

Composite layer based plasmon waveguide resonance for label-free biosensing with high figure of merit

A plasmon waveguide resonance (PWR) sensing structure was presented based on composite waveguide layer in this article. This composite layer based PWR (CLPWR) could provide stronger evanescent electric field and sharper resonance curve than surface plasmon resonance (SPR). Owing to these, the CLPWR sensor could provide up to 20 times higher resolution than the conventional SPR technology under ideal conditions. The vacuum coating techniques and optimal optical arrangements were developed for the realization of CLPWR sensor, and the residual analysis was introduced to quantify the effect of experimental system noise on measurement accuracy. In the label free biosensing experiment, it was demonstrated that the CLPWR sensor could provide more accurate measurement results than conventional SPR sensor for label free biomolecular interaction analysis in complex media.

Ultra-Broadband All-Optical Graphene Modulator

In this letter, a monolayer graphene-clad microfiber device is designed to achieve ultra-broadband all-optical modulation. Based on the broadband advantage of graphene, we sufficiently discussed the priority absorption characteristic of graphene and continuous wave light saturated absorption characteristic of composite waveguide. Furthermore, superior to previous related publications which the wavelength of pump light is limited, we pioneered and verified that various wavelength light can be used as pump light to achieve all-optical modulation in the designed device. In our experiment, supercontinuum light with spectrum range (0.48 μm-1.7 μm) is modulated by the conventional low-power continuous wave laser diode (808 nm) with pump power under 50 mW. Experimental results for the all-optical modulator achieve modulation depths of ~5.7 dB (1310 nm), -6.8 dB (1550 nm), and ~7.3 dB (1610 nm), modulation efficiency of ~0.11 dBmW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (1310 nm), ~0.14 dBmW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (1550 nm), and ~0.15 dBmW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (1610 nm), respectively, crossing the O, C, and L bands. The modulation bandwidth reaches 970 nm which is obviously 20 times higher than the modulation bandwidth ~50 nm reported in related publications. This alloptical modulator based on graphene microfiber provides an easy and efficient way to modulate the ultra-broadband light with very low pump power.

Tunable terahertz wave difference frequency generation in a graphene/AlGaAs surface plasmon waveguide

Graphene-based surface plasmon waveguides (SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation (DFG) under near-infrared pumps. The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs/AlOx structure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs/AlOx waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.

Efficient third-harmonic generation in composite aluminum nitride/silicon nitride microrings

Aluminum nitride and silicon nitride have recently emerged as important nonlinear optical materials in integrated photonics for their quadratic and cubic optical nonlinearity, respectively. A composite aluminum nitride and silicon nitride waveguide structure, if realized, will simultaneously allow highly efficient second- and third-harmonic generation on the same chip platform and therefore assists 2f-3f self-referenced frequency combs. On-chip third-harmonic generation, being a higher-order nonlinear optics effect, is more demanding than second-harmonic generation due to the large frequency difference between the fundamental- and third-harmonic frequencies, which implies a large change of refractive indices and more stringent requirements on phase matching. In this work we demonstrate high-efficiency third-harmonic generation in a high-Q composite aluminum nitride/silicon nitride ring cavity. By carefully engineering the microring resonator geometry of the bilayer structure to optimize the quality factor, mode volume, and modal overlap of the optical fields, we report a maximum conversion efficiency of 180% W−2, corresponding to an absolute conversion efficiency of 0.16%. This composite photonic chip design provides a solution for efficient frequency conversion over a large wavelength span, broadband comb generation, and self-referenced frequency combs.

Образование и распространение упругих (sh) сдвиговых волн в сетчатом композитном волноводе

Образование и распространение упругих (sh) сдвиговых волн в сетчатом композитном волноводе

Graphene-based broadband all-optical spatial modulator

In this paper, the all-optical spatial modulation of monolayer graphene-coated microfiber is proposed. Graphene is used as a saturable absorber wrapped on the microfiber produced by heating the carbon dioxide laser. When the signal light travels along the microfiber, part of the light will pass along the surface of the microfiber in the form of an evanescent field, and it will be absorbed by the graphene. Simultaneously we shoot the 808 nm pump light into the micro-nanofiber wrapped by the graphene vertically from the space. According to graphene characteristic of preferential absorption, the absorption of the signal light is controlled by the pump light, thus the broadband all-optical space modulation is realized. In a conventional graphene microfiber all-optical modulator, signal light and pump light are generally input into a microfiber via a coupler. However, the mode of operation of pump light and graphene in all-optical spatial modulation are different from those of the traditional modulation, the pump light works on the graphene outside the microfiber, which realizes the separation of the pump light and the signal light. The output signal does not need to be optically filtered for the pump light to obtain the modulated signal. The output signal light of the spatial all-optical modulator has the characteristics of “clean”. We also verify this in experiment. In addition, the pump light is vertically incident from space, the effect of the graphene length on the modulation is not considered and the modulation time is only related to the relaxation time of graphene, which is helpful in improving the response time. Modulation experiments include static spectral modulation and dynamic frequency modulation. In the static spectral modulation, the broad spectrum signal has a maximum modulation depth of 6 dB at 1095 nm when the pump power is 569 mW. The relationship among pump power, wavelength and modulation depth is also analyzed. The higher the pump power, the higher the modulation depth will be; with the same pump power, the modulation depth of long wave length is higher than that of short wave. In the dynamic modulation experiment with the modulation bandwidth~50 nm and the modulation rate~1.5 kHz, the influence of pump light and signal light on output dynamic signal are studied, the feasibility of all-optical space modulation based on graphene is verified experimentally. The composite waveguide of all-optical spatial modulator opens the door to micro-nano ultrafast signal, processing in a more flexible and efficient way.

Invisibility Cloaking Scheme by Evanescent Fields Distortion on Composite Plasmonic Waveguides with Si Nano-Spacer

A new, composite plasmonic waveguide based electromagnetic cloaking scheme is proposed with Si nano-spacer. Here we show, that the scattering fields of an object located on the cloak do not interact with the evanescent field, resulting in object’s invisibility. Finite difference time domain (FDTD) numerical calculations were performed to extract the modal distributions and surface intensities on a composite plasmonic waveguide with a metasurface overlayer. Spatially varying effective permittivity was analytically calculated using transformation optics. Cloaking was demonstrated for a cylindrical object with diameter of 70% from the waveguide width on a high index ridge waveguide structure with silicon nitride guiding layer on silica substrate. Our results open the door to new integrated photonic devices, harnessing from evanescent fields distortion on composite plasmonic waveguides and dielectric nano-spacers for the variety of applications from on-chip optical devices to all-optical processing.