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Title: Enhanced axial confinement in a monolithically integrated self-rolled-up SiN x vertical microring photonic coupler

Abstract

We report an efficient method to introduce enhanced axial confinement in the self-rolled-up SiN x vertical microtube coupler by depositing a thin layer of high refractive index material strip within the coupling section and effectively forming a vertical microring. Three times wider mode spacing is observed in such a vertical microring coupler monolithically integrated with a silicon nitride ridge waveguide as compared to the one without such axial confinement. More importantly, single mode operation within the telecomm C-band and S-band is achieved. The self-rolled-up microtube has been demonstrated to be a versatile device platform, which has found application in a number of areas including nanophotonics,1–7 microelectronics,8 chemical and biological sensing,9–11 and intelligent synthetic neural circuits.12 Because the microtube is a three dimensional (3D) structure readily fabricated using two dimensional processing technology, it may serve naturally as a component in 3D-integrated devices. We had previously demonstrated a vertical microtube coupler (VμTC) monolithically integrated with planar ridge waveguides in silicon photonic platform to achieve 3D photonic coupling and observed greatly enhanced coupling between the microtube and the underlying ridge waveguide.1,13 A similar result was reported independently by another research group shortly thereafter.2 One limitation of the VμTC used in previous experiments ismore » that it supports many modes within the telecommunication C-band because of poor axial confinement. For example, we found multiple resonant coupling peaks, which is not desirable for wavelength division multiplexing (WDM) switches. In order to increase the mode spacing of this 3D photonic coupler and to achieve single mode operation within the C-band, we propose efficient axial confinement in the microtube to suppress the higher order modes. Axial confinement in self-rolled-up microtubes had been studied both theoretically and experimentally by a couple of research groups.14–17 In all these previous cases, the axial confinement was introduced by a specially designed geometrical shape of a section of the microtube. After being rolled up, the microtube wall will have different thicknesses at different axial locations. The different wall thicknesses result in a slightly varying effective refractive index of the supported whispering gallery modes (WGMs) along the axial direction of the microtube. When a parabolic shape is used, the effective index of the WGM at the center of the parabola will be the highest and decrease adiabatically along both sides. However, the refractive index change due to different wall thicknesses is very small; hence, the axial confinement is rather weak. Here in this paper, we present our experimental endeavor to incorporate a different axial confinement scheme in the monolithically integrated vertical microtube (VμT) to form a vertical microring (VμR) resonator and demonstrate 3 times wider mode spacing than the microtube based vertical photonic coupler and the potential to achieve a higher Q-factor.« less

Authors:
 [1];  [1];  [1]; ORCiD logo [1]
  1. Univ. of Illinois, Urbana, IL (United States). Dept. of Electrical and Computer Engineering, Micro and Nanotechnology Lab.
Publication Date:
Research Org.:
Univ. of Illinois, Urbana, IL (United States). Dept. of Electrical and Computer Engineering, Micro and Nanotechnology Lab.
Sponsoring Org.:
USDOE
OSTI Identifier:
1468930
Alternate Identifier(s):
OSTI ID: 1324485
Grant/Contract Number:  
FG02-07ER46471
Resource Type:
Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 109; Journal Issue: 11; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; 36 MATERIALS SCIENCE

Citation Formats

Yu, Xin, Goddard, Lynford L., Li, Xiuling, and Chen, Xiaogang. Enhanced axial confinement in a monolithically integrated self-rolled-up SiNx vertical microring photonic coupler. United States: N. p., 2016. Web. doi:10.1063/1.4962901.
Yu, Xin, Goddard, Lynford L., Li, Xiuling, & Chen, Xiaogang. Enhanced axial confinement in a monolithically integrated self-rolled-up SiNx vertical microring photonic coupler. United States. doi:10.1063/1.4962901.
Yu, Xin, Goddard, Lynford L., Li, Xiuling, and Chen, Xiaogang. Wed . "Enhanced axial confinement in a monolithically integrated self-rolled-up SiNx vertical microring photonic coupler". United States. doi:10.1063/1.4962901. https://www.osti.gov/servlets/purl/1468930.
@article{osti_1468930,
title = {Enhanced axial confinement in a monolithically integrated self-rolled-up SiNx vertical microring photonic coupler},
author = {Yu, Xin and Goddard, Lynford L. and Li, Xiuling and Chen, Xiaogang},
abstractNote = {We report an efficient method to introduce enhanced axial confinement in the self-rolled-up SiNx vertical microtube coupler by depositing a thin layer of high refractive index material strip within the coupling section and effectively forming a vertical microring. Three times wider mode spacing is observed in such a vertical microring coupler monolithically integrated with a silicon nitride ridge waveguide as compared to the one without such axial confinement. More importantly, single mode operation within the telecomm C-band and S-band is achieved. The self-rolled-up microtube has been demonstrated to be a versatile device platform, which has found application in a number of areas including nanophotonics,1–7 microelectronics,8 chemical and biological sensing,9–11 and intelligent synthetic neural circuits.12 Because the microtube is a three dimensional (3D) structure readily fabricated using two dimensional processing technology, it may serve naturally as a component in 3D-integrated devices. We had previously demonstrated a vertical microtube coupler (VμTC) monolithically integrated with planar ridge waveguides in silicon photonic platform to achieve 3D photonic coupling and observed greatly enhanced coupling between the microtube and the underlying ridge waveguide.1,13 A similar result was reported independently by another research group shortly thereafter.2 One limitation of the VμTC used in previous experiments is that it supports many modes within the telecommunication C-band because of poor axial confinement. For example, we found multiple resonant coupling peaks, which is not desirable for wavelength division multiplexing (WDM) switches. In order to increase the mode spacing of this 3D photonic coupler and to achieve single mode operation within the C-band, we propose efficient axial confinement in the microtube to suppress the higher order modes. Axial confinement in self-rolled-up microtubes had been studied both theoretically and experimentally by a couple of research groups.14–17 In all these previous cases, the axial confinement was introduced by a specially designed geometrical shape of a section of the microtube. After being rolled up, the microtube wall will have different thicknesses at different axial locations. The different wall thicknesses result in a slightly varying effective refractive index of the supported whispering gallery modes (WGMs) along the axial direction of the microtube. When a parabolic shape is used, the effective index of the WGM at the center of the parabola will be the highest and decrease adiabatically along both sides. However, the refractive index change due to different wall thicknesses is very small; hence, the axial confinement is rather weak. Here in this paper, we present our experimental endeavor to incorporate a different axial confinement scheme in the monolithically integrated vertical microtube (VμT) to form a vertical microring (VμR) resonator and demonstrate 3 times wider mode spacing than the microtube based vertical photonic coupler and the potential to achieve a higher Q-factor.},
doi = {10.1063/1.4962901},
journal = {Applied Physics Letters},
number = 11,
volume = 109,
place = {United States},
year = {2016},
month = {9}
}

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