Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure
In this paper, we report a compact wavelength-flattened directional coupler (WFDC) based chemical sensor featuring an incorporated subwavelength grating (SWG) structure for the mid-infrared (MIR). By incorporating a SWG structure into directional coupler (DC), the dispersion in DC can be engineered...
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| Format: | Article |
| Language: | English |
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MDPI AG
2018-11-01
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| Series: | Nanomaterials |
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| Online Access: | https://www.mdpi.com/2079-4991/8/11/893 |
| _version_ | 1831674181036539904 |
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| author | Bowei Dong Ting Hu Xianshu Luo Yuhua Chang Xin Guo Hong Wang Dim-Lee Kwong Guo-Qiang Lo Chengkuo Lee |
| author_facet | Bowei Dong Ting Hu Xianshu Luo Yuhua Chang Xin Guo Hong Wang Dim-Lee Kwong Guo-Qiang Lo Chengkuo Lee |
| author_sort | Bowei Dong |
| collection | DOAJ |
| description | In this paper, we report a compact wavelength-flattened directional coupler (WFDC) based chemical sensor featuring an incorporated subwavelength grating (SWG) structure for the mid-infrared (MIR). By incorporating a SWG structure into directional coupler (DC), the dispersion in DC can be engineered to allow broadband operation which is advantageous to extract spectroscopic information for MIR sensing analysis. Meanwhile, the Bragg reflection introduced by the SWG structure produces a sharp trough at the Bragg wavelength. This sharp trough is sensitive to the surrounding refractive index (RI) change caused by the existence of analytes. Therefore, high sensitivity can be achieved in a small footprint. Around fivefold enhancement in the operation bandwidth compared to conventional DC is achieved for 100% coupling efficiency in a 40 µm long WFDC experimentally. Detection of dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>) in ethanol (C<sub>2</sub>H<sub>5</sub>OH) is investigated in a SWG-based WFDC sensor 136.8 µm long. Sensing performance is studied by 3D finite-difference time domain (FDTD) simulation while sensitivity is derived by computation. Both RI sensing and absorption sensing are examined. RI sensing reveals a sensitivity of −0.47% self-normalized transmitted power change per percentage of CH<sub>2</sub>Cl<sub>2</sub> concentration while 0.12% change in the normalized total integrated output power is realized in the absorption sensing. As the first demonstration of the DC based sensor in the MIR, our device has the potential for tertiary mixture sensing by utilizing both changes in the real and imaginary part of RI. It can also be used as a broadband building block for MIR application such as spectroscopic sensing system. |
| first_indexed | 2024-12-20T03:40:44Z |
| format | Article |
| id | doaj.art-988c1830fbfa44fe9da79207bed588a5 |
| institution | Directory Open Access Journal |
| issn | 2079-4991 |
| language | English |
| last_indexed | 2024-12-20T03:40:44Z |
| publishDate | 2018-11-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Nanomaterials |
| spelling | doaj.art-988c1830fbfa44fe9da79207bed588a52022-12-21T19:54:46ZengMDPI AGNanomaterials2079-49912018-11-0181189310.3390/nano8110893nano8110893Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating StructureBowei Dong0Ting Hu1Xianshu Luo2Yuhua Chang3Xin Guo4Hong Wang5Dim-Lee Kwong6Guo-Qiang Lo7Chengkuo Lee8Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, SingaporeInstitute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore 138634, SingaporeInstitute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore 138634, SingaporeDepartment of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, SingaporeSchool of Electrical & Electronic Engineering, Nanyang Technological University, Singapore 639798, SingaporeSchool of Electrical & Electronic Engineering, Nanyang Technological University, Singapore 639798, SingaporeInstitute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore 138634, SingaporeInstitute of Microelectronics, Agency for Science, Technology and Research (A*STAR), Singapore 138634, SingaporeDepartment of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, SingaporeIn this paper, we report a compact wavelength-flattened directional coupler (WFDC) based chemical sensor featuring an incorporated subwavelength grating (SWG) structure for the mid-infrared (MIR). By incorporating a SWG structure into directional coupler (DC), the dispersion in DC can be engineered to allow broadband operation which is advantageous to extract spectroscopic information for MIR sensing analysis. Meanwhile, the Bragg reflection introduced by the SWG structure produces a sharp trough at the Bragg wavelength. This sharp trough is sensitive to the surrounding refractive index (RI) change caused by the existence of analytes. Therefore, high sensitivity can be achieved in a small footprint. Around fivefold enhancement in the operation bandwidth compared to conventional DC is achieved for 100% coupling efficiency in a 40 µm long WFDC experimentally. Detection of dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>) in ethanol (C<sub>2</sub>H<sub>5</sub>OH) is investigated in a SWG-based WFDC sensor 136.8 µm long. Sensing performance is studied by 3D finite-difference time domain (FDTD) simulation while sensitivity is derived by computation. Both RI sensing and absorption sensing are examined. RI sensing reveals a sensitivity of −0.47% self-normalized transmitted power change per percentage of CH<sub>2</sub>Cl<sub>2</sub> concentration while 0.12% change in the normalized total integrated output power is realized in the absorption sensing. As the first demonstration of the DC based sensor in the MIR, our device has the potential for tertiary mixture sensing by utilizing both changes in the real and imaginary part of RI. It can also be used as a broadband building block for MIR application such as spectroscopic sensing system.https://www.mdpi.com/2079-4991/8/11/893nanophotonicsphotonics sensorsmid-infraredwaveguide couplersubwavelength grating |
| spellingShingle | Bowei Dong Ting Hu Xianshu Luo Yuhua Chang Xin Guo Hong Wang Dim-Lee Kwong Guo-Qiang Lo Chengkuo Lee Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure Nanomaterials nanophotonics photonics sensors mid-infrared waveguide coupler subwavelength grating |
| title | Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure |
| title_full | Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure |
| title_fullStr | Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure |
| title_full_unstemmed | Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure |
| title_short | Wavelength-Flattened Directional Coupler Based Mid-Infrared Chemical Sensor Using Bragg Wavelength in Subwavelength Grating Structure |
| title_sort | wavelength flattened directional coupler based mid infrared chemical sensor using bragg wavelength in subwavelength grating structure |
| topic | nanophotonics photonics sensors mid-infrared waveguide coupler subwavelength grating |
| url | https://www.mdpi.com/2079-4991/8/11/893 |
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