Waveguide Design Research Articles

Adiabatic guided wave optics - a toolbox of generalized design and optimization methods.

Starting from the fully vectorial coupled local-mode theory, a general design rule for adiabatic waveguide design is derived. The design rule guarantees adiabaticity and puts an upper limit on the transmission loss of any guided wave transformation. The rule is applicable to any waveguide geometry, admits multi-dimensional optimization, and accounts for radiative loss to guided and radiation modes. Moreover, the design technique is enhanced with further optimization procedures that eliminate coupling between particular pairs of modes. The utility of this toolbox of design rules and methods is illustrated through the design of a 2×2 coupler and a bilayer waveguide transition. These design procedures can be used to optimize single-mode and multimode photonic devices by varying one or more waveguide parameters.

Controlling optical return loss in production silicon photonic metamaterial fiber couplers.

A cost-efficient and low-complexity optical input/output (I/O) packaging solution is a substantial challenge for volume production of photonic integrated circuits. To address this, metamaterial fiber couplers are an attractive solution for integrated photonic devices especially for optical I/O, interfacing standard optical fibers to photonic chips. They offer the advantages of refractive index engineering to achieve better mode match as well as higher fabrication tolerances. Metamaterial waveguides, as a fundamental building block of these fiber couplers, have attracted tremendous attention in recent years. Here, we report on effective optical return loss control in Si metamaterial waveguide designs to achieve ultra-low reflection loss in CMOS-compatible silicon photonics implemented in a 300 mm production line. Low backscattering is a substantial consideration for a range of applications. Here, a return loss of better than -30dB is achieved.

Designing of strongly confined short-wave Brillouin phonons in silicon waveguide periodic lattices.

We propose a feasible waveguide design optimized for harnessing Stimulated Brillouin Scattering with long-lived phonons. The design consists of a fully suspended ridge waveguide surrounded by a 1D phononic crystal that mitigates losses to the substrate while providing the needed homogeneity for the build-up of the optomechanical interaction. The coupling factor of these structures was calculated to be GB/Qm = 0.54 (W m)-1 for intramodal backward Brillouin scattering with its fundamental TE-like mode and GB/Qm = 4.5 (W m)-1 for intramodal forward Brillouin scattering. The addition of the phononic crystal provides a 30 dB attenuation of the mechanical displacement after only five unitary cells, possibly leading to a regime where the acoustic losses are only limited by fabrication. As a result, the total Brillouin gain, which is proportional to the product of the coupling and acoustic quality factors, is nominally equal to the idealized fully suspended waveguide.

An analytical method with numerical results to be used in the design of optical slab waveguides for optical communication system applications

<p>This study develops an analytical method with numerical results for the design of optical slab waveguides for optical communication system applications. An optical slab waveguide structure made of silicon on silicon dioxide material is designed and analyzed. The effective index of the mode is studied against variations in the waveguide dimensions. Transmission and reflection coefficients are studied and compared to the wavelength and dimensions of the waveguide. Variations are sketched with the x-axis, in addition to the electric field intensity distribution and effective refractive index. Waveguide bending loss is also studied with waveguide thickness and length variations within three waveguide transmission windows of 850 nm, 1300 nm, and 1550 nm.</p>

Broadband and lossless lithium niobate valley photonic crystal waveguide [Invited

We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.

Numerical techniques of the estimation the amount of waveguides surface roughness for the THz regime

The article is devoted to the problem of the efficient design of THz waveguides devices. Extreme small sizes of THz devices such as subharmonic pumped mixers for radiometer witch waveguides are integrated in copper block covered with 3 μm gold are presented. The three numerical techniques and direct measurements in the THz regime have been used to predict the effective conductivity reduction due to protrusions. Efficient design of THz systems requires the ability to predict effective conductivity, allowing engineers to determine the amount of surface roughness for acceptable reflection losses prior to fabrication. Full-wave numerical technique to predict the field enhancement factors for both the rf electric field and the rf magnetic field on the protrusion above smooth sample in the THz regime has been mentioned. The electric field and magnetic field enhancement factors on the hemispherical protrusion should be excluded in case the protrusions size are smaller than δ/50 and δ/1.5 correspondingly (δ is skin depth). Mie-Scattering-based approach approximates a unit cell of the grating as a circular cylinder protrusion the additional loss due to the protrusion compared with a perfectly flat surface of the same material. Hammerstad–Bekkadal Model demonstrates an analytical function which depends of sheet resistance for a sample with surface roughness on the surface roughness and skin depth of the metal. Numerical calculations using this technique predict 10% power absorption due to surface features 35 nm at 400 GHz. A layout of the apparatus for direct measurements of the effective conductivity of samples with roughness features using an open quasi-optical resonator is given. The results of theoretical calculation and empirical evaluation have been compared with computer simulation software taking into consideration of the effective conductivity only due to the change in the surface geometry. The comparison empirical results and numerical calculations full-wave numerical technique are more accurate for samples that are smooth relative to the skin depth. For surface features greater than the skin depth, we found the Hammerstad and Bekkadal model to be a better. The observed methods can be used as a rapid means to estimate waveguides surface roughness in terms of power loss in the THz regime.

DESIGN OF A NOVEL MICROWAVE PLASMA SOURCE BASED ON RIDGED WAVEGUIDE

DESIGN OF A NOVEL MICROWAVE PLASMA SOURCE BASED ON RIDGED WAVEGUIDE

Design and analysis of dual dumbbell and rectangular slots SIW cavity-backed antenna at 2.45 GHz

The design and realization of a wideband substrate-integrated waveguide (SIW) cavity-backed slot antenna operating at 2.45 GHz for WLAN applications are presented. Dual dumbbell-shaped slots with rectangular slots are used to achieve increased bandwidth. The bandwidth observed is 160 MHz with the dumbbell-shaped slots. Further, it has been improved up to 9.2% by adding a rectangular slot. The wideband antenna is analyzed using ANSYS HFSS and fabricated on FR-4 substrate. The measured results of the proposed design are in good agreement with the simulation results and comparable with the reported results.

Poly(dimethylsiloxane) functionalized with complementary organic and inorganic emitters for the design of white emissive waveguides

An active white-emissive waveguide is designed by introducing in a silica microfiber a PDMS doped with a blue-green emissive 3-oxindole and a red-NIR phosphorescent molybdenum nanocluster for optoelectronic applications.

Numerical Design and Investigation of Circularly Segmented Air Holes-Assisted Hollow-Core Terahertz Waveguide as Optical Chemical Sensor

In this paper,a polarization-maintaining single-mode rectangular-shaped hollow-core waveguide with four segmented air cladding in the terahertz (THz) regime is presented for detecting various toxic industrial chemicals. A new type of injection moldable cyclic olefin copolymer, commercially named as TOPAS is used as the base fiber material for its high optical transmission and high resistance to other chemicals. The finite element method with a perfectly matched layer as the boundary condition is employed for numerical explorations. The proposed sensor exhibits ultra-high relative sensitivity of 99.73% and ultra-low effective material loss of 0.007 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 1.6 THz frequency for Toluene in y polarization. This sensor also evinces a high birefringence of 4.16×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 1.6 THz frequency. A maximum V parameter of 2.224 has been found at 2.2 THz which ensures the single-mode propagation of light. The sensor shows a very low confinement loss of 3.2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> dB/m and a high numerical aperture of 0.3574 at 1.6 THz frequency for Hydrogen Sulfide. This paper also concentrates on other important design parameters such as bending loss, mode field radius, beam divergence and effective area for serviceability of the sensor in the THz region. This sensor can be a very good candidate for various chemical detection as well as other applications in the terahertz regime.

1J1-1 Design and measurement of topological elastic waveguide based on phononic crystal

1J1-1 Design and measurement of topological elastic waveguide based on phononic crystal

Oscillator Finite-Difference Time-Domain (O-FDTD) electric field propagation model: integrated photonics and networks

The recently developed Lorentz Oscillator Model-inspired Oscillator Finite-Difference Time-Domain (O-FDTD) is one of the simplest FDTD models ever proposed, using a single field equation for electric field propagation. We demonstrate its versatility on various scales and benchmark its simulation performance against theory, conventional FDTD simulations, and experimental observations. The model’s broad applicability is demonstrated for (but not limited to) three contrasting realms: integrated photonics components on the nano- and micrometer scale, city-wide propagating radiofrequency signals reaching into the hundreds of meters scale, and for the first time, in support of 3D optical waveguide design that may play a key role in neuromorphic photonic computational devices.

Design and fabrication of GeAsSeS chalcogenide waveguides with thermal annealing* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61904091 and 61775111), Zhejiang Provincial Natural Science Foundation of China (Grant No. LR18E010002), the Natural Science Foundation of Ningbo City, China (Grant No. 2019A610065), the International Cooperation Project of Ningbo City, China (Grant No. 2017D10009), and K. C.

We reported a chalcogenide glass-based rib waveguide fabricated using photolithography and dry etching method. A commercial software (COMSOL Multiphysics) was used to optimize the waveguide structure and the distribution of the fundamental modes in the waveguide based on the complete vector finite component. We further employed thermal annealing to optimize the surface and sidewalls of the rib waveguides. It was found that the optimal annealing temperature for GeAsSeS films is 220 °C, and the roughness of the films could be significantly reduced by annealing. The zero-dispersion wavelength (ZDW) could be shifted to a short wavelength around ∼ 2.1 μm via waveguide structural optimization, which promotes supercontinuum generation with a short wavelength pump laser source. The insertion loss of the waveguides with cross-sectional areas of 4.0 μm × 3.5 μm and 6.0 μm × 3.5 μm was measured using lens fiber and the cut-back method. The propagation loss of the 220 °C annealed waveguides could be as low as 1.9 dB/cm at 1550 nm.

Design and analysis of suspended core channel waveguide made using As2Se3 glass system for mid-infrared supercontinuum generation

In this study, we propose a promising 5 mm long air-clad suspended core channel waveguide made of As2Se3 chalcogenide glass for ultra-broadband supercontinuum generation (SCG) in the mid-infrared (MIR). The linear analysis of the proposed waveguide is carried out numerically by considering the potential application of pump sources at three different wavelength regions such as 1.55, 2.8, and 3.5 µm. Among several waveguide geometries analyzed, numerical simulation for SCG at the output of an optimized structure shows that a flat supercontinuum coverage from 1.5 to 15 µm can be predicted using a pump at 3.5 µm with a moderate peak power of 2000 W. To the best of the authors’ knowledge, this would be the broadest spectra in the MIR by the suspended planar waveguide design. In addition, waveguide structural imperfection has also been discussed as it is difficult to control the waveguide dimensions during the fabrication process precisely. The effect of possible deviations along the transverse dimensions is rigorously analyzed and an imperfection among the several deviations is found which could lead to a substantial supercontinuum bandwidth reduction at the waveguide output. Finally, the degree of coherence of the obtained supercontinuum coverage is also tested and it has been achieved nearly coherent spectral outcome from the proposed suspended waveguide design.

Calculation of the normal modes of closed waveguides

The aim of the work is the development of numerical methods for solving waveguiding problems of the theory of waveguides, as well as their implementation in the form of software packages focused on a wide range of practical problems from the classical issues of microwave transmission to the design of optical waveguides and sensors. At the same time, we strive for ease of implementation of the developed methods in computer algebra systems (Maple, Sage) or in software oriented to the finite element method (FreeFem++). The work uses the representation of electromagnetic fields in a waveguide using four potentials. These potentials do not reduce the number of sought functions, but even in the case when the dielectric permittivity and magnetic permeability are described by discontinuous functions, they turn out to be quite smooth functions. A simple check of the operability of programs by calculating the normal modes of a hollow waveguide is made. It is shown that the relative error in the calculation of the first 10 normal modes does not exceed 4%. These results indicate the efficiency of the method proposed in this article.

Calculation of the normal modes of closed waveguides

The aim of the work is the development of numerical methods for solving waveguiding problems of the theory of waveguides, as well as their implementation in the form of software packages focused on a wide range of practical problems from the classical issues of microwave transmission to the design of optical waveguides and sensors. At the same time, we strive for ease of implementation of the developed methods in computer algebra systems (Maple, Sage) or in software oriented to the finite element method (FreeFem++). The work uses the representation of electromagnetic fields in a waveguide using four potentials. These potentials do not reduce the number of sought functions, but even in the case when the dielectric permittivity and magnetic permeability are described by discontinuous functions, they turn out to be quite smooth functions. A simple check of the operability of programs by calculating the normal modes of a hollow waveguide is made. It is shown that the relative error in the calculation of the first 10 normal modes does not exceed 4%. These results indicate the efficiency of the method proposed in this article.

Calculation of the normal modes of closed waveguides

The aim of the work is the development of numerical methods for solving waveguiding problems of the theory of waveguides, as well as their implementation in the form of software packages focused on a wide range of practical problems from the classical issues of microwave transmission to the design of optical waveguides and sensors. At the same time, we strive for ease of implementation of the developed methods in computer algebra systems (Maple, Sage) or in software oriented to the finite element method (FreeFem++). The work uses the representation of electromagnetic fields in a waveguide using four potentials. These potentials do not reduce the number of sought functions, but even in the case when the dielectric permittivity and magnetic permeability are described by discontinuous functions, they turn out to be quite smooth functions. A simple check of the operability of programs by calculating the normal modes of a hollow waveguide is made. It is shown that the relative error in the calculation of the first 10 normal modes does not exceed 4%. These results indicate the efficiency of the method proposed in this article.

On-Chip Detector Based on Supercontinuum Generation in Chalcogenide Waveguide

We present the design, preparation, and performance optimization of strip waveguide in chalcogenide glass (ChG) for broadband supercontinuum (SC) generation. Ternary Ge-Sb-S systems possess large band-gap, high refractive index, and strong laser damage resistance. The characterization of strip waveguide in Ge-Sb-S glass for SC source generation with 1300 nm bandwidth is experimentally demonstrated. Sensing capability of the device is validated for optical absorption of β-phenylethylamine solutions near 1551 nm in various concentrations, revealing the repeatability and consistency of the generated SC spectrum in test. The advantages of high specificity detection scheme, scalable integration and ease of miniaturization might make the device a promising platform for biochemical monitoring.

Performance Analysis of Integrated Electro-Optic Phase Modulators Based on Emerging Materials

Electro-optic modulators are utilized ubiquitously ranging from applications in data communication to photonic neural networks. While tremendous progress has been made over the years, efficient phase-shifting modulators are challenged with fundamental tradeoffs, such as voltage-length, index change-losses or energy-bandwidth, and no single solution available checks all boxes. While voltage-driven phase modulators, such as based on lithium niobate, offer low loss and high speed operation, their footprint of 10’s of cm-scale is prohibitively large, especially for density-critical applications, for example in photonic neural networks. Ignoring modulators for quantum applications, where insertion loss is critical, in this work we distinguish between current versus voltage-driven modulators. We focus on the former, since current-based schemes of emerging thin electro-optical materials have shown unity-strong index modulation suitable for heterogeneous integration into foundry waveguides. Here, we provide an in-depth ab-initio analysis of obtainable modulator performance based on heterogeneously integrating low-dimensional materials, i.e., graphene, thin films of indium tin oxide, and transition metal dichalcogenide monolayers into a plurality of optical waveguide designs atop silicon photonics. Using the fundamental modulator tradeoff of energy-bandwidth-product as a design-quality quantifier, we show that a small modal cross section, such as given by plasmonic modes, enables high-performance operation, physically realized by arguments on charge-distribution and low electrical resistance. An in-depth design understanding of phase-modulator performance, beyond doped-junctions in silicon, offers opportunities for micrometer-compact yet energy-bandwidth-ratio constrained modulators with timely opportunities to hardware-accelerate applications beyond data communication towards photonic machine intelligence, for instance; where both performance and integration-density are critical.

HIGHER RADIAL MODES OF AZIMUTHAL SURFACE WAVES ABOVE THE UPPER-HYBRID FREQUENCY IN CYLINDRICAL WAVEGUIDES PARTIALLY FILLED BY PLASMA

Azimuthal surface waves (ASWs) are known to be eigen waves of cylindrical metal waveguides partially filled by magnetoactive plasma. Zeroth radial modes were under study earlier. Their dispersion properties are known to be significantly influenced by the plasma column properties: its particle density, external axial static magnetic field, geometric dimensions, – rather than properties of the dielectric layer which separates the plasma column from the metal wall. Application of higher order ASWs in the low-frequency range was shown earlier to make it possible to get advantage of exciting ASWs with higher frequency than in the case of zeroth order ASWs without no change in the waveguide design. The present study generalises those investigation for the case of the waves above the upperhybrid frequency.