eff 24(5), 50265038 (2016). This attenuation is due to the divergence of the light exiting the NW LED (as shown in Figure 2c), which is not guided but coupled to free space modes at rather large angles. In Lumerical FDTD solver, two-dimensional simulation of plane waves of p-polarization enters the optical system at surface plasmon angle. 1(right). 3. The platform consists of a NW LED, waveguide and NW photodetector; (b) Front-view cross-section schematic illustration with refractive indices for materials used in the simulations given; (c) The fundamental mode and three higher order modes of a hexagonal GaN NW with a diameter of 1 m for the wavelength of 400 nm. To calculate the effective index n Google Scholar. These potential applications have motivated extensive research on NW integrated platforms [2830]. (right) The same plot showing the result from a standard 2D FDTD approximation and 3D FDTD. (left) Transmission into the fundamental mode at the through port obtained from a varFDTD simulation and a 3D FDTD simulation. sharing sensitive information, make sure youre on a federal Lumerical MODE Solutions variational FDTD (varFDTD) solver efficiently simulates the propagation of optical radiation in a wide array of guided structures, from ridge waveguide-based systems to more complex geometries such as photonic crystals. The 2023 R1 release brings a new modernized GUI to Ansys Lumerical FDTD. Optics Letters 20(2), 291299 (2016). 11 AM EDT / 4 PM GMT / 8:30 PM IST. As shown in Figure 4b, the leakage caused by the multimode nature at the waveguidedetector coupling is mostly reduced thanks to the lateral confinement of the waveguide with a reduced width. (left) Waveguide dispersion can be seen in the vertical slab mode profile (shown as a function of the vertical dimension z and wavelength). Ansys Insight: Why my simulation result is different from published paper or experiment? The maximum CE achieved at the central wavelength of 1550nm, as a function of the etch-depth, for each of the two SOI platforms is reported in Fig. In reality, precise positioning of this peak is achieved through thermal tuning. Left: Contour plot of the peak CE at =1550nm of the linearly apodized GC realized in 260nm SOI platform, as a function of etch depth and of the linear apodization factor R. Right: maximum CE at the central wavelength of 1550nm for the linearly apodized GC based on 220nm SOI (red plot) and 260nm (blue plot). (right) Spectrum showing the pump, signal and converted light. To illustrate an example of the simulation results, we plot in Fig. If we define the grating fill-factor F as the ratio between the length of the un-etched section L One of the measured CE curves as a function of wavelength is shown in Fig. 5(left). For this reason different parameters (such as etch-depth or the grating period) are generally considered as fixed, thus allowing to reduce the computation time but, simultaneously, limiting the explored solutions-range. (right) The generated effective materials contain both waveguide dispersion from the slab waveguide geometry as well as material dispersion from silicon. FDTD is a simulator within Lumerical's DEVICE Multiphysics Simulation Suite, the world's first multiphysics suite purpose-built for photonics designers. Perfectly matched layers were used as the boundaries to truncate computational regions. Recently, an integrated photonic platform consisting of an InGaN/GaN NW LED and a pn NW photodiode interconnected with a SiNx waveguide was demonstrated [30]. A coupling efficiency above 59% is calculated for a wide range of widths between 1.3 and 1.6 m. With the varFDTD solver, it is trivial to accurately determine the broadband transmission into multiple modes of a wide taper. But so is the human ingenuity to fight it. Modeling and simulation of evanescent coupling to Si eff 1 . Once the 2D effective materials are generated, one can proceed with a 2D FDTD simulation using Lumericals optimized computation engine, which allows for parallel computation on multi-core processors and multi-node high performance computing systems. As a result, a coupling yield of the entire system (i.e., from the LED to the detector) of only 8.7% is achieved, which is not sufficient for the previously discussed applications. air In the optimization, calculations without the spin-on-glass layer are also performed. Coupling length (FDTD, INTERCONNECT): Length of racetrack straight section, zero for circular rings. From battery reliability, product design review to accelerated life testing our experts can solve your challenges. the contents by NLM or the National Institutes of Health. In this example, we use the Inverse Design Toolbox (lumopt) to optimize a 3D SOI grating coupler. Directionality results are shown, as a function of etch depth e, in Fig. The flexible material plugins are constructed via an open framework that allows end-users to develop their own models, tailored to their unique needs, in native C/C++/FORTRAN as dynamically linked library plugins. It can be seen that by using a SOI platform with a thicker Si layer it is possible to obtain a higher CE, as already reported in other works20, and that deep etching levels (110nm and 160nm for the 220nm and 260nm SOI platforms, respectively) are required to obtain the maximum CE. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. A. Babichev acknowledges the support of the President of the Russian Federation grant (grant no. A graphical representation of the difference between our linear apodization scheme and the standard approach based on fixed , is given in Fig. To investigate this aspect, we performed 2D-FDTD simulations of the apodized GC, inserting a 100nm wide trench in the Si waveguide, at a distance of 500 m from the end of the grating section. The electric field of the Gaussian beam was polarized along the \(\hat{{\rm{x}}}\) direction with reference to Fig. and X.C. We performed measurements on several different structures, from four different chips, obtaining an average CE of 1.1dB, and a maximum CE of 0.9dB. The highest CE experimentally measured was 0.9dB, which currently represents the best result ever obtained without the use of embedded back-reflectors. The varFDTD solver combined with theflexible material pluginsavailable within MODE Solutions is capable of simulating wave propagation over long distances efficiently, while still being able to accurately capture the interplay between the linear and nonlinear effects. 1(left)), to properly accommodate the Gaussian mode of the fiber, and 14.847 m long. They make use of different approaches, such as the use of either poly-Silicon over-layers12,13 or back-reflectors embedded in the substrate, e.g. Were here to answer your questions and look forward to speaking with you. The arrows in the left panel indicate the maximum directionality achievable in each structure. This is followed by examining the relevant parameters affecting the light coupling efficiency to a silicon waveguide of input dimensions of 220 750 nm. The 2D computational area was set to be 33.4 m wide and 5.8 m high, while the refractive index of both Silicon and SiO2 were calculated following the data reported by Palik: as a consequence the refractive indices at the design wavelength of 1550nm are \({n}_{Si}\)=3.48 and \({n}_{Si{O}_{2}}\)=1.44. One exploratory approach for visible photonics consists of the monolithic integration of InGaN emitters/detectors with GaN-based waveguides [79]. Anyway, this is applicable to the cylindrical waveguide structure. Error: addfdtd is not a valid function or a variable name, Using a license file on a new license server, Ansys Insight: Transmission results greater than one, Finding your Ansys (or Lumerical) account number. CAS The length of the NW LED and the detector is 10 m, and the waveguide between them is 31 m long. Lumerical's 2.5D FDTD Propagation Method The SiNx waveguide shows efficient vertical and horizontal confinement of the propagating light. Following the experimental realization of [30], an encapsulating spin-on-glass layer partially covering the NW is considered (used as a mechanical support for the contacts). There are several alternative methods for simulating wave propagation over large distances: the well-known Beam Propagation Method (BPM) relies on a slowly varying envelope assumption and can simulate large structures quickly. Lumerical simulation tutorial: Coupling Efficiency to a Waveguide An official website of the United States government. (a) Coupling efficiency from the LED to the waveguide (black squares) and from the LED to the detector (red circles) as a function of the waveguide width calculated with a step of 0.1 m. FDTDs CAD environment and parameterizable simulation objects allow for rapid model iterations for 2D and 3D models. The FDTD reference manual provides detailed descriptions of product features. After reviewing the settings, close the Edit window and run the optimization. It is important to highlight that Eq. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Professora Popova 5, 197376 Saint Petersburg, Russia. is the effective refractive index of the radiative unit, as shown in Fig. Considering Silicon-on-Insulator (SOI) technology, the strong refractive index difference between Si and SiO2 allows the implementation of very small, single mode waveguide structures9. Cloud and HPC Capability. Optics Express Considering the computational capability, the minimum mesh step is fixed at 0.25 nm for both 2D and 3D simulations, giving an accuracy sufficient for this study. The results demonstrate that for a SiO2 thickness larger than 300 nm, the absorption of the Si substrate becomes negligible due to total internal reflection at the GaN/SiO2 interface and the transmission of the waveguide is independent of this thickness. A member of our Ansys sales team will contact you shortly. The spin-on-glass SiOx was assumed to have a refractive index of n (SiOx) = 1.557. National Library of Medicine Google Scholar. and n High-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible Silicon-On-Insulator platform. O Time: September 21, 2023. Figure 1. Unfortunately, the value producing the highest CE (F We carried out specific simulations in order to ensure that the interaction between the non-ideal taper and the grating would not lead to an unexpected spectral redistribution of the transmission efficiency. The length of each tooth (L government site. To increase the coupling yield, the waveguide width should be adjusted to couple light strongly also in the lateral direction. The integrated design environment provides scripting capability, advanced post-processing, and optimization routines. For every grating configuration, the offset of the fiber mode from the starting point of the grating was also optimized. Ansys is committed to setting today's students up for success, by providing free simulation engineering software to students. There are currently two approaches for collapsing the geometry with the varFDTD solver: In both cases, the key assumption is that there is negligible coupling between the different slab modes supported by the vertical waveguide structure. The same procedure used for the design of the apodized GC based on the 260nm SOI platform, was also applied to the 220nm SOI grating, achieving a maximum CE of 70% (1.6dB) when e=110nm and R=0.0275 m1. An optical micrograph of the fabricated apodized GC is shown in Fig. A High-Efficiency Nonuniform Grating Coupler Realized With 248-nm Optical Lithography. E realized on-chip optical coupling between an LED and a photoconductive detector both based on GaN NWs [29]. https://doi.org/10.1038/s41598-017-16505-z, DOI: https://doi.org/10.1038/s41598-017-16505-z. air Right: 2D-FDTD simulation of the optimum grating transmission, when a 100nm wide hole is inserted in the Si waveguide at a distance of 500 m from the end of the grating section, at different etching percentage. The finite-difference time-domain (FDTD) technique is one of the most versatile and accurate methods for simulating light propagation in nanoscale components. where The optimization should complete in ten to twenty minutes. Considering a beam coupling from the SOI waveguide to a fiber, a low grating directionality (65%) means that a large percentage of the optical power incident on the GC is diffracted towards the substrate (35%) instead of being sent towards the fiber. However, when applied to three-dimensional structures, FDTD is highly computationally intensive, making it difficult to treat large integrated optical components efficiently. 3D CAD Environment and parameterizable simulation objects allow for rapid model iterations. 1Centre de Nanosciences et de Nanotechnologies (C2N), UMR9001 CNRS, University Paris-Sud, University Paris-Saclay, 91405 Orsay, France, 2ITMO University, Kronverkskiy Prospekt 49, 197101 St. Petersburg, Russia. The optical losses due to the LEDwaveguide and waveguidephotodetector coupling were reduced by removing the spin-on-glass encapsulation layer and reducing the SiNx waveguide width. Ding, Y., Peucheret, C., Ou, H. & Yvind, K. Fully etched apodized grating coupler on the SOI platform with 0.58 dB CE. Automatically discover optimal designs and geometries for a targeted design goal. Xanadu builds X8 quantum computing chip with unprecedented low-loss performance while significantly accelerating their design schedule. 25(9), 97619767 (2017). Today, infrared (IR) photonic integrated circuits (PICs) represent a well-established technology with numerous applications in optical telecommunications [14].
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