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    FDTD analysis of optical integration between SiGe waveguides and Ge-rich SiGe heterostructures on graded buffer for quantum-confined Stark effect optical modulators
    (2026-02-01)
    Khongpetch, N.
    ;
    Limsuwan, P.
    ;
    Tangsangiumvisai, N.
    ;
    Chaisakul, P.
    Ge-rich SiGe heterostructures with superior crystal and photonic quality have been enabled via a thick linear graded SiGe buffer platform on Si. Nevertheless, due to a very low refractive index contrast between the Ge-rich SiGe heterostructures and the graded buffer, it is challenging to have efficient optical integration with other photonic components. In this paper, a coupling scheme based on a top adiabatic coupling between Ge-rich SiGe heterostructures on graded buffer and a SiGe waveguide in SiO<inf>2</inf> cladding is proposed to address a low-loss coupling of the Ge-rich SiGe heterostructures with a high-index-contrast waveguide structure. 3D-FDTD simulations demonstrate that efficient optical coupling between the top SiGe waveguide (high-index-contrast platform) and Ge-rich SiGe heterostructures on a thick graded buffer (low-index-contrast platform) can be adiabatically achieved with practical fabrication tolerance. In addition, the proposed coupling structure can be potentially applied with Ge/SiGe MQWs, enabling SiGe waveguide integrated Ge/SiGe MQWs optical modulator with a viable integrated extinction ratio and insertion loss performance.
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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
    ;
    Traiwattanapong, Worawat
    ;
    Chiangga, Surasak
    ;
    Limsuwan, Pichet
    ;
    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
    ;
    Traiwattanapong, Worawat
    ;
    Limsuwan, Pichet
    ;
    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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    Dispersion characteristics of terahertz transverse electric mode in a smooth-wall cylindrical waveguide with a degenerate plasma layer
    (2020-05-01)
    Asadiamiri, F.
    ;
    Nejati, M.
    ;
    Chaudhary, K.
    ;
    Baboli, M.
    ;
    Ali, J.
    The propagation of transverse electric mode in a cylindrical metallic smooth-wall waveguide contains a dielectric rod and a cold collisionless unmagnetized degenerate plasma layer is analytically investigated in the terahertz frequency region. The dispersion relations of fast and slow waves for this mode are derived and solved numerically. The effects of geometrical and physical parameters such as dielectric, plasma and metal radii, and dielectric permittivity on the dispersion characteristics of terahertz transverse electric mode and its frequency spectrum are studied. It is shown that the decrease of dielectric permittivity and metal radius, and the increase of degenerate plasma radius leads to higher frequency fast waves. It is also indicated that an increase in the dielectric radius results in a decrease in the frequency of fast waves. In addition, it is found that by reducing the dielectric rod radius and with increasing metal radius, the frequency is increased in the slow waves. Finally, it is shown that the increase in dielectric permittivity causes a decrease in the frequency of both fast and slow waves.
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    Analysis of effective numerical aperture in 2-D photonic crystal waveguide
    (2014-01-01)
    Chantakit, T.
    ;
    Kamoldilok, S.
    ;
    Srinuanjan, K.
    ;
    Yupapin, P. P.
    The effective numerical aperture calculation in two-dimensional Photonic crystal waveguide has been proposed. In this paper we present the analysis of ray optics refracted inside nano rods and at the boundaries between rods, which separates rod gap is much smaller than the incident wavelength assumed to reflect on the region. In operation, the resolving numerical aperture was compared with the finite difference time domain method via OptiFDTD software. Although numerical aperture mentioned above was found to be extremely close to fiber optics, a transmission passes though compartments of the rods are observed due to significant estimation of transmission and reflection of electric field. The compared simulation results will be discussed. By the aforementioned is that in the near future we will modify wave equation in periodic media of waveguide structures reached to the transverse electric equation of beam propagation in the two-dimensional Photonic crystal waveguide analysed. © (2014) Trans Tech Publications, Switzerland.