Planar Waveguide Array Research Articles

Fiber spectrum analyzer based on planar waveguide array aligned to a camera without lens

We propose and experimentally demonstrate a fiber spectrum analyzer based on a planar waveguide chip butt-coupled with an input fiber and aligned to a standard camera without any free-space optical elements. The chip consists of a single-mode waveguide to connect with the fiber, a beam broadening area, and a waveguide array in which the lengths of the waveguides are designed for both wavelength separation and beam focusing. The facet of the chip is diced open so that the outputs of the array form a near-field emitter. The far field are calculated by the Rayleigh-Sommerfeld diffraction integral. We show that the chip can provide a focal depth on the millimeter scale, allowing relaxed alignment to the camera without any fine-positioning stage. Two devices with 120 and 220 waveguides are fabricated on the polymer waveguide platform. The measured spectral width are 0.63 nm and 0.42 nm, respectively. This simple and practical approach may lead to the development of a spectrum analyzer for fiber that is easily mountable to any commercial camera, thereby avoiding the complication for customized detectors as well as electronic circuits afterwards.

Single-Layer Planar Waveguide Array Antenna With High Antenna Efficiency

This letter proposes a 60 GHz planar waveguide array antenna with high antenna efficiency, low cost, and low processing difficulty. The array integrates the radiating elements and the hollow <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -plane waveguide feed network in a single-layer structure in a simple way. To demonstrate the idea, a 16×16 prototype was designed, fabricated, and measured. The measured 10 dB impedance bandwidth (|S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ −10 dB) is 16.4% with the antenna efficiency being 89.1% at 61.5 GHz. To the best of our knowledge, it has the highest antenna efficiency and the lowest processing difficulty among similar waveguide arrays.

Ka-band planar slotted waveguide array based on groove gap waveguide technology with a glide-symmetric holey metasurface

The design of a planar slot array in groove gap waveguide technology implemented by glide-symmetric holes as Electromagnetic Band Gap structure is here presented. Despite the advantages of using holes instead of pins in terms of manufacturing simplicity and cost,the larger size of the holes compared to pins needs to be considered when designing slot arrays without grating lobes. A 1 to 4 corporate feed network is designed using this technology as well. Corrugations are included to further reduce the grating lobes. Experimental results support the viability of the proposed concept for designing glide-symmetric planar arrays of any size.

Endless single-polarization single-mode photonic-crystal planar waveguide arrays with ultra-large mode area and ultra-low transmission loss

In this paper, single-polarization single-mode (SPSM) optical waveguides of ultra-broad bandwidth and very large mode areas are proposed and analyzed based on photonic crystal planar waveguides (PCPWs) and arrays with advanced elliptic features. The multi-unit PCPW arrays have been found particularly effective in achieving ultra-broadband operation with substantially expanded modal areas, as an optimized five-unit PCPW array offers an unprecedentedly broad SPSM spectrum of 4310 nm (from 0.11 to 4.42 μm). In addition, near-zero transmission loss conditions have also been identified for PCPW arrays at various resonant wavelengths. Such very-large-mode-area (VLMA), ultra-broadband, SPSM optical waveguides with “lossless” transmission conditions are highly desirable for basic waveguide research as well as related application fields.

Semidiscrete Vortex Solitons

A possibility of creation of stable optical solitons combining one continuous and one discrete coordinates, with embedded vorticity, in an array of planar waveguides with intrinsic cubic–quintic (CQ) nonlinearity is demonstrated. The same system may be realized in terms of the spatiotemporal light propagation in an array of tunnel‐coupled optical fibers with the CQ nonlinearity. In contrast with zero‐vorticity states, semidiscrete vortex solitons do not exist without the quintic term in the nonlinearity. Two types of the solitons, viz., intersite‐centered (IC) and onsite‐centered (OC) ones, with even and odd numbers N of actually excited sites in the discrete direction, are identified. The modes carrying the embedded vorticity and 2 are considered. In accordance with their symmetry, the vortex solitons of the OC type exhibit an intrinsic core, whereas the IC solitons with small N may have a coreless structure. Facilitating their creation in the experiment, the modes reported in the present work may be much more compact states than their counterparts considered in other systems, and they feature strong anisotropy. They can be set in motion in the discrete direction, provided that the coupling constant exceeds a certain minimum value. Collisions between moving vortex solitons are also considered.

A coplanar‐waveguide‐fed planar integrated cavity backed slotted antenna array using TE 33 mode

This short communication presents a substrate integrated waveguide planar cavity slotted antenna array. The proposed antenna array, excited in its TE33 higher mode, incorporates a grounded coplanar-waveguide (CPW) CPW-feeding excitation mechanism. The electromagnetic energy is coupled to the air through 3 × 3 slot array etched on top metallic layer. The proposed antenna operates in the X-band for the frequency range around the 10 to 11 GHz with resonances at 10.4 and 10.8 GHz frequencies. The proposed antenna array was fabricated and tested. Experimental results show good impedance matching with enhanced radiation characteristics, in terms of peak gain, cross-polarization level, and low back-radiation. The proposed antenna has the advantages of low-footprints, lightweight, high gain, low-cost, and ease of integration with other electronic circuits. With these characteristics, the proposed antenna array can find its applications in compact wireless digital transceivers.

Circular Optical Arrays Using Waveguide Fed 45° Angled Mirrors

An array of optical waveguide fed 45° metal-coated mirrors are proposed and validated by simulation, for generating optical scalar and vector vortices. Subwavelength element-to-element spacings are achieved, which is not possible in traditional grating-based phased arrays. This vortex source can be superior over other methods like phase masks which are not planar process integrable with lasers and phase modulators. A simple plane wave reflection model is used to analyze the mirror and the results are matched with reasonable tolerance against simulation results. The spin and orbital angular momentum charges are directly calculated from the field values for quantifying the performance. Four- and eight-element arrays are studied. The matching of prediction with simulation has been good for linear, azimuthal and radial polarization. Good angular momentum conversion efficiencies are obtained for up to orbital angular momentum charges ${l}$ = ±2. Important aspects of generating vortices with circular polarization are brought out. Directional beams with >10 dB gains are achieved. This is the first report in which a planar dielectric optical waveguide array with subwavelength spacing has achieved good angular momentum control for linearly, azimuthally, radially and circularly polarized beams, in the same geometry.

Surface Micro-Reflector Array for Augmented Reality Display

Geometric optical waveguide display can significantly miniaturize the augmented reality eyeglasses, but suffers from the ghost image. In this paper, a method using surface micro-reflector array is proposed, which can dramatically suppress the ghost image. The transmission and expansion of the light bearing image are completed by using planar waveguide and micro-reflector array embedded in the surface layer of waveguide. The image quality is improved by using the dual channel to eliminate ghost image. The imaging process of optical system is modeled and simulated. The surface micro-reflector array waveguide element of 3 mm thickness is prepared for verification. The whole optical system has the advantages of simple structure, easy preparation and high structural strength. The display field of view is shown to be 25° × 25°, and the size of the full field of view area is 15 mm with even light distribution. What's more, the uniformity of imaging intensity is better than 20%, and the image is clear without ghost image, which can effectively realize the fusion of the virtual image and the real environment. Thus, the efficiency of augmented reality is greatly improved, and the danger of human eye safety is effectively avoided.

Waveguide-Imprinted Slim Polymer Films: Beam Steering Coatings for Solar Cells

We report that transparent polymer coatings imprinted with tilted planar waveguides significantly reduce optical loss caused by the scattering of incident light by front metal contacts of solar cells. A periodic array of planar waveguides oriented at specific angles with respect to the film’s surface normal efficiently captures and steers incident light away from contacts and, in this way, suppresses scattering. These beam steering films are fabricated in a single, room temperature step by self-trapped incandescent beams. The beams inscribe multimode planar waveguides oriented at angles ranging from 0° to 2.7° inphotopolymerizable epoxide resin. We characterized the microstructural and optical properties of the films and demonstrated their ability to deflect incident white light, comparable to sunlight, by as much as 180 μm. Solar cells coated with beam steering films showed significant enhancements in external quantum efficiency (EQE) of up to 4.42% relative to unstructured films. This first demonstration of waveguide-based deflection of light from metal contacts represents a facile, inexpensive, low energy approach to EQE enhancement, which can be integrated without disrupting well-established solar cell manufacturing technologies.

Synthesis and analysis of a planar waveguide array with two-dimensional frequency scanning focused in the Fresnel zone

A 2D array of radiators with raster frequency scanning focused in the Fresnel zone is presented. The problem of determining the radiator positions for field focusing at a finite distance from the array plane is solved. An approximate matrix model of the array antenna describing its properties as a microwave multiport and allowing determination of the distribution of radiation sources in the array aperture is proposed. The problem of improvement of the array matching in scanning ranges is considered. An approximate model describing radiation from the array is built. This model is used for determining the position and shape of the scanning surface and the field distribution inside the focal spot as well as for the analysis of the dynamics of the field maximum in the frequency scanning sector.

Electromagnetic Performance Analysis of Graded Dielectric Inhomogeneous Streamlined Airborne Radome

Streamlined nosecone radomes for airborne applications have to cater to high-end electromagnetic (EM) performance requirements of fire control radar antenna system. In this regard, the EM performance analysis of an ogival radome based on novel graded dielectric inhomogeneous wall structure is presented. The radome wall considered here consists of seven dielectric layers cascaded in such a way that the middle layer has maximum dielectric parameters (dielectric constant and electric loss tangent) and on either side, dielectric parameters of the layers decrease in a graded (or stepwise) manner. Further, the outer surface of the radome wall is coated with an antistatic and antierosion radome paint. The EM performance parameters of the radome enclosing an X-band slotted waveguide planar array antenna (center frequency: 10 GHz; bandwidth: 1 GHz) are computed based on 3-D ray tracing in conjunction with aperture integration method. The study shows that the proposed graded dielectric inhomogeneous streamlined radome is an excellent choice for airborne applications as compared to airborne radomes based on conventional constant thickness radome designs and variable thickness radome (VTR) designs. Further, it circumvents the constraints on fabrication that occur in streamlined VTR designs.

The study of the amplitudes of the fields excited linear grating horn irradiators

The problem of scattering from a linear grating of horns can be solved only with approximate methods because known mathematical methods allow to obtain solutions only for simple mathematical models for example for the endless arrays of planar waveguides. Other sources include experimental characteristics of the amplitudes of the fields excited in apertures and the fields scattered by such grating, however, the theoretical calculations are not given. The problem determining of the amplitudes of the field excited by horn radiators, for arbitrary incidence of the plane electromagnetic wave is solved in references. However, the applicability of this solution for the linear grating of the horn irradiators (waveguides) is investigated, which in turn hinders the development of antenna arrays with reduced scattered field. Thus, there is the problem of developing methods for the investigation of electromagnetic fields amplitudes excited in aperture of n-th radiator grating when incident to flat electromagnetic wave, properly polarized in the plane of incidence from an arbitrarily specified sources. The methodology of the study of the electromagnetic fields amplitudes, which are excited in n-th radiator linear grating aperture when the incidence of the plane electromagnetic wave polarized normal to the plane of incidence from an arbitrarily specified sources. It is found that under these conditions, aperture will be excited only with the waves of magnetic type – $A^{H\perp}_{+0m_y}$. The amplitude of the waves excited by n-th emitter is virtually identical to the amplitude of the central even with the distance between them. The results can be used to study more complex rectangular antenna arrays consisting of the n-th number of linear.

Synthesis and analysis of a frequency-scanned planar waveguide array focused in the Fresnel zone

A 2D array of radiators excited by the modes of a planar array of parallel waveguides and focused in the Fresnel zone is considered. The problem of determining the positions of array radiators for focusing the field at a finite distance from the array aperture is solved for the cases of plane and cylindrical fronts of the initial distribution of the phases of waveguide modes. A phenomenological model of the slotted-waveguide array is used to determine the position of the focal line, the aberration of the scattering spot, and the frequency scanning sector.

Tunable beam steering enabled by graphene metamaterials.

We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.

Scalar coupled mode theory and variational analysis for planar SOI waveguide arrays: a detailed comparison

We present a detailed analytical comparison of two extensively used theories to study the coupled optical waveguide arrays. Various formulations of the scalar Coupled Mode Theory and the Ritz Galerkin variational analysis have been applied to 1-D SOI coupled waveguide arrays to study the TE modes of the structure having identical and non-identical waveguides. Equivalence between scalar Ritz Galerkin variational formulation and the coupled mode theory without any approximations is shown. Comparisons of various modal characteristics obtained from the different coupled mode and variational formulations have been shown along with the exact results obtained from the solution of the scalar wave equation. For the 1-D SOI array under consideration the non-identical waveguide configuration leads to stronger coupling which results in non-orthogonal supermodes using two of the coupled mode formulations. The excellent agreement with exact results and the much lower computational time compared to numerical techniques, make these analytical methods a preferred choice for the simulation of coupled waveguide arrays.

Design Equations for Cylindrically Conformal Arrays of Longitudinal Slots

The Elliott’s procedure for the design of planar waveguide arrays of longitudinal slots has been extended to the cylindrical conformal case. The presented procedure has been devised to deal with the most general case of a cylindrical conformal substrate integrated waveguide (SIW) longitudinal slot array with a dielectric cover. Both external and internal mutual coupling have been accurately and effectively taken into account. The results of the synthesis procedure have been validated using both Ansys HFSS simulations and experimental results, showing a good agreement with the design specifications.

Electromagnetic Bloch-like oscillations in planar quasiperiodic metal-dielectric waveguide arrays

We investigate the spatial Bloch-like oscillations in planar double-period silver waveguide arrays. Three types of oscillation modes are obtained in the sixth-generation double-period structure at different incident position, namely positive oscillation mode, negative oscillation mode and breathing-wave–like oscillation mode. The period of the three types of oscillation modes increases when the incident wavelength is redshifted, while the period of the up-oscillation and down-oscillation of the breathing-wave–like oscillation mode decreases and increases, respectively, in the gradient sixth-generation double-period system.

Graded dielectric inhomogeneous streamlined radome for airborne applications

A graded dielectric inhomogeneous nosecone radome design with superior electromagnetic (EM) performance characteristics for airborne applications is presented. The radome wall is designed in such a way that the middle layer has the maximum dielectric parameters (dielectric constant and electric loss tangent). On either side of the middle layer, the dielectric parameters of the constituent layers decrease in a graded (or step-wise) manner. This wall configuration facilitates better impedance matching as required for radome applications. The computation of the EM performance parameters of a tangent ogive nosecone radome based on the above-mentioned wall configuration, enclosing an X-band slotted waveguide planar array antenna, is carried out using ‘geometric optics’ based three-dimensional ray tracing along with the ‘aperture integration’ method. EM performance analysis shows that the proposed graded inhomogeneous dielectric radome design is a better choice for streamlined airborne radomes compared with the ‘variable thickness radome’ (VTR) designs based on monolithic half-wave and multilayered radome wall configurations. Furthermore, it excludes the constraints on fabrication that generally occur in the case of streamlined airborne VTRs.

TEMPERATURE-DEPENDENT ELECTROMAGNETIC PERFORMANCE PREDICTIONS OF A HYPERSONIC STREAMLINED RADOME

Nosecone radomes of hypersonic flight vehicles show degradation of electromagnetic (EM) performance characteristics due to variations in the dielectric parameters (dielectric constant and electric loss tangent) of the radome wall resulting from heating due to extreme aerodynamic drag. It is indicated that the EM performance predictions based on conventional monolithic half-wave wall based on average dielectric parameters corresponding to temperature ranges in hypersonic conditions may not be accurate. This necessitates the radome wall under hypersonic conditions to be modeled as an inhomogeneous dielectric structure for accurate EM performance predictions. In the present work, the hypersonic radome is considered as an inhomogeneous dielectric radome such that the cross-section of the radome wall in each EM window region is considered as an inhomogeneous planar layer (IPL) model with stacked layers of varying dielectric parameters. The material considered is RBSN Ceralloy 147-010F (an alloy of silicon nitride), which has excellent thermal shock resistance, dielectric and mechanical properties required for hypersonic radome applications. The EM modeling of a section of the radome wall in hypersonic conditions (i.e., IPL structure) is based on Equivalent Transmission Line Method. A comparative study of basic EM performance parameters of the radome wall (power transmission, power reflection, and insertion phase delay) for both the IPL model and conventional monolithic half-wave model are carried out over a range of incidence angles corresponding to the antenna scan ranges in each EM window region of the radome. Further the study is extended to compute the EM performance parameters of an actual tangent ogive nosecone radome (made of RBSN Ceralloy 147-010F) enclosing an X-band slotted waveguide planar array antenna, in a hypersonic environment. The antenna-radome interaction studies are based on 3-D Ray tracing in conjunction with Aperture Integration Method .I t is observed that the EM performance analysis based on conventional monolithic radome wall design cannot accurately predict the radome performance parameters in actual operating conditions during hypersonic flight operations. The current work establishes the efficacy of Inhomogeneous Dielectric Radome model for better EM performance predictions of streamlined airborne radomes in hypersonic environments.

Microsecond optical switching of five channels by KTN electro‐optic deflector

A 1 × 5 optical switch with a switching speed of microseconds is demonstrated. Switching between different channels in a planar lightwave circuit waveguide array was controlled using an electro-optic beam deflector. A single crystal of potassium tantalate niobate (KTa 1− x Nbx O3, KTN) was used as a deflector to realise this operation. A switching speed of 8.1 μs was demonstrated for the switching of two adjacent channels.