Low refractive index resonate waveguide grating with high sensitivity in sensing refractive index change in environment
Ko-Tang Chen1*, Yu-Sheng Ye1, Jian Hung Lin1, Chu-Chian Liu2, Shiao-Wei Kuo2, Hung Chi Kan1, Chia Chen Hsu1
1Department of Physics, National Chung Cheng University, Ming Hsiung, Chia Yi, 62102, Taiwan
2Department of Materials and Optoelectronics Science, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan
* presenting author:陳可唐, email:asd6939937510@gmail.com
In this work, we employed the nano-imprint technique to fabricate a low refractive index (n =1.22) one-dimensional resonant waveguide grating (RWG) structure based on PEO-PCL triblock copolymer. It produces sharp reflection and transmission anomalies that signature the guided mode resonance (GMR), whose peak-wavelength can be tuned by changing refractive index of the medium contacted with the top surface of the RWG. From both theoretical simulation and experimental measurement, we show that the low refractive index RWG can provide higher sensitivity in sensing the change of refractive index of the environment, compared to a traditional used high refractive index (n =1.58) SU8 RWG. Its peak-wavelength shift induced by per unit-index change is two times of that of the high refractive index SU8 RWG. The main reason is that the low refractive index RWG can result in stronger localized electric field on the top surface of the structure when GMR condition is satisfied.

Keywords: Sensitivity, Low refractive index, Resonant waveguide grating, Guided mode resonance