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FDTD investigation of adiabatic optical coupling between Silicon nitride and Germanium-based optical structures for energy-efficient photonic integration
(2023-01-01)
Khongpetch, Natdanai
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Chaisakul, Papichaya
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Traiwattanapong, Worawat
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Chiangga, Surasak
;
Limsuwan, Pichet
This paper aims to investigate the potential of a direct integration between Si3N4 waveguides and Germanium(Ge)-based structures, which are considered two of the most promising silicon(Si)-compatible materials for passive and active functions for Si-based energy-efficient photonics, respectively. This paper focuses on investigating the vertical coupling scheme between these materials employing a tapered structure of the Ge-based layer using 2D FDE and 3D FDTD simulations, to match the optical mode from a passive Si3N4 waveguide to the Ge-based layer and vice versa. The expected optical coupling performance will be reported, and its dependence on the unavoidable fabrication variation in the coupling region will be also investigated. Additionally, the coupling performance of the vertical coupling approach compared to the previous investigation between a Si waveguide and a Ge layer will be addressed.
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FDTD Investigation of Efficient and Robust Integration Between Si3N4and Ge-Rich GeSi for Waveguide-Integrated Electro-Absorption Optical Modulators
(2023-01-01)
Khongpetch, Natdanai
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Traiwattanapong, Worawat
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Chiangga, Surasak
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Limsuwan, Pichet
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Chaisakul, Papichaya
Si3N4 photonic integrated circuits have gain significant and rapid interest in different photonic applications thanks to its superior passive performance. Nevertheless, optical integration between Si3N4 and Ge-based optical components remains critically challenging especially for optical modulation. In this paper, via 3D-FDTD calculations we investigate the optical integration between Si3N4 and Ge-based waveguides using vertical coupling configuration employing amorphous Si (α-Si) as an optical bridge showing efficient and robust coupling efficiency, which can be maintained according to the tolerant analysis with respect to the variations in optical wavelengths and critical parameters of the coupling structure. In addition, with respect to the recent theoretically-optimized SOI waveguide-integrated and also laterally-coupled Si3N4 waveguide-integrated Ge-based optical modulators, we found that the studied coupling structure could be employed to enable a low-voltage Si3N4 waveguide-integrated Ge-based optical modulator with a competitive extinction ratio/insertion loss performance, increasing the prospect of Si3N4-based photonic integrated circuits for low-energy optical interconnects.
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An FDTD Investigation of Compact and Low-Voltage Waveguide-Integrated Plasmonic Ge/SiGe Multiple Quantum Wells Photodetectors
(2022-10-01)
Srikam, Saranisorn
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Traiwattanapong, Worawat
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Limsuwan, Pichet
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Chaisakul, Papichaya
We report on 3-D FDTD simulation of waveguide-integrated plasmonic Ge/SiGe MQWs photodetectors. Despite several significant works on Ge/SiGe MQW optical modulators, Ge/SiGe MQW photodetectors still show improvable performance, limiting the potential to employ them for both optical modulation and detection. In this paper, we investigate the use of plasmonic concept to enhance electromagnetic field confinement inside the Ge/SiGe MQWs absorbing region with a view to having a compact and low-voltage waveguide-integrated Ge/SiGe MQWs photodetectors. Optical responsivities in term of applied electric fields, device dimensions of width and length, optical bandwidth, fabrication misalignment, and number of QWs periods are taken into account. The investigation shows that using plasmonic enhancement, a waveguide-integrated Ge/SiGe MQWs photodetector that is as short as 5 μm could be obtained with comparable responsivity and bias voltage values to some of the state-of-the-art bulk Ge-based devices, increasing the potential usage of Ge/SiGe MQWs for both optical modulation and detection in low-energy optical interconnects.
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Investigation on optical integration between LED Mid-IR light sources and Si-based waveguides for sensing applications
(2022-01-07)
Jaturaphagorn, Pawaphat
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Chaisakul, Papichaya
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Chattham, Nattaporn
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Limsuwan, Pichet
Research on mid-IR silicon-based waveguides has recently received strong interest. Particularly, this paper focuses on one of the critical issues in micron-scale photonic integrated circuits, which is to efficiently couple a mid-IR LED (light emitting diode) light source to an external micron-scale waveguide. The optical coupling scheme is crucial for the exploitation of LED light sources in waveguide-based spectroscopic sensing applications. This paper reports optical coupling scheme between an LED mid-IR light source and a silicon rich silicon nitride (SiN) waveguide that could enable the use of LED-based light sources. Finally, the detection limit of the investigated device for carbon dioxide gas detection is calculated.
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Optimization of end-fire coupling between an LED mid-IR light source and SiNx optical waveguides for spectroscopic sensing
(2021-12-01)
Jaturaphagorn, Pawaphat
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Chattham, Nattaporn
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Limsuwan, Pichet
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Chaisakul, Papichaya
We design and optimize an optical coupling structure between a superluminescent light emitting diodes (SLED) and SiN<inf>x</inf> waveguides for the optical sensing, in which an efficient coupling between these waveguides is challenging due to significant cross-sectional difference. From FDTD investigation, we identify the coupling scheme that is suitable to directly couple light from a SLED into a relatively-thin SiN<inf>x</inf> waveguide suitable for optical sensing based on the evanescent field absorption. The coupling structure is systematically investigated and optimized in terms of refractive indices, coupler's geometrical parameters, and fabrication variations with corresponding detection performance. The coupling scheme could be instrumental in enabling the use of SLED technology in Si-based photonic integrated circuits for sensing applications.
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Design and simulation investigation of si3n4 photonics circuits for wideband on-chip optical gas sensing around 2 µm optical wavelength
(2021-04-01)
Koompai, Natnicha
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Chaisakul, Papichaya
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Limsuwan, Pichet
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Roux, Xavier Le
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Vivien, Laurent
We theoretically explore the potential of Si<inf>3</inf>N<inf>4</inf> on SiO<inf>2</inf> waveguide platform toward a wideband spectroscopic detection around the optical wavelength of 2 µm. The design of Si<inf>3</inf>N<inf>4</inf> on SiO<inf>2</inf> waveguide architectures consisting of a Si<inf>3</inf>N<inf>4</inf> slot waveguide for a wideband on-chip spectroscopic sensing around 2 µm, and a Si<inf>3</inf>N<inf>4</inf> multi-mode interferometer (MMI)-based coupler for light coupling from classical strip waveguide into the identified Si<inf>3</inf>N<inf>4</inf> slot waveguides over a wide spectral range are investigated. We found that a Si<inf>3</inf>N<inf>4</inf> on SiO<inf>2</inf> slot waveguide structure can be designed for using as optical interaction part over a spectral range of interest, and the MMI structure can be used to enable broadband optical coupling from a strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing. Reasons for the operating spectral range of the system are discussed.

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