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Sensors 2015, 15(10), 25868-25881; doi:10.3390/s151025868

Optimization of High-Q Coupled Nanobeam Cavity for Label-Free Sensing

1
Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan
2
Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan
3
Research Centre for Applied Sciences, Academia Sinica, Taipei 115, Taiwan
4
Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
5
Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan
6
Department of Photonics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
*
Authors to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 18 August 2015 / Revised: 29 September 2015 / Accepted: 9 October 2015 / Published: 13 October 2015
(This article belongs to the Section Physical Sensors)
View Full-Text   |   Download PDF [1498 KB, uploaded 13 October 2015]   |  

Abstract

We numerically and experimentally investigated the lateral coupling between photonic crystal (PhC) nanobeam (NB) cavities, pursuing high sensitivity and figure of merit (FOM) label-free biosensor. We numerically carried out 3D finite-difference time-domain (3D-FDTD) and the finite element method (FEM) simulations. We showed that when two PhC NB cavities separated by a small gap are evanescently coupled, the variation in the gap width significantly changes the coupling efficiency between the two coupled NB cavities and the resulting resonant frequencies split. Experimentally, we fabricated laterally-coupled PhC NB cavities using (InGaAsP) layer on the InP substrate. For sensing, we showed that the laterally coupled PhC NB cavities sensor exhibits higher sensitivity than the single PhC NB cavity. The higher sensitivity of laterally coupled PhC NB cavities is due to the strong evanescent coupling between nearby PhC NB cavities, which depends on the gap width and it is attributed to the large confinement of the electromagnetic field in the gap (air or liquid). As a result of the lateral coupling, both even (symmetric) and odd (asymmetric) modes exist. We show that even modes are more sensitive than odd modes. In addition, higher-order modes exhibit higher sensitivity. Hence, we characterized and examined the fabricated PhC NB cavity as a label-free biosensor, and it exhibits high figure of merit due to its high Q-factor. This illustrates a potentially useful method for optical sensing at nanoscale. View Full-Text
Keywords: Photonic crystals (PhCs); nanobeam (NB) cavity; finite-difference time-domain (FDTD); label-free sensing Photonic crystals (PhCs); nanobeam (NB) cavity; finite-difference time-domain (FDTD); label-free sensing
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Yaseen, M.T.; Yang, Y.-C.; Shih, M.-H.; Chang, Y.-C. Optimization of High-Q Coupled Nanobeam Cavity for Label-Free Sensing. Sensors 2015, 15, 25868-25881.

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