On-chip symmetrically and asymmetrically transformed plasmonic Bragg grating formation loaded with a functional polymer for filtering and CO2 gas sensing applications

Abstract

Herein, two configurations of transformed plasmonic Bragg grating (p-BG) formation loaded with a functional polymer are suggested for filtering and gas sensing applications. The symmetrically transformed p-BG formation is well suited for the development of a wide bandwidth (BW) bandstop filter. Desired filter specifications such as extinction ratio, stopband region, and stopband BW can be optimized by adjusting the geometric dimensions of the device. Polyhexamethylene biguanide (PHMB) is a functional polymer that is linearly correlated to the CO2 concentration. Therefore, it is possible to employ such material for the development of CO2 sensors. The asymmetrically transformed p-BG formation is created by moving the gold nano-blocks that are periodically arranged in the MIM waveguide away from the line of symmetry. As a result, an additional narrowband MZI resonance dip appears in the transmission continuum and is obtained along with the broadband Bragg reflection. The spectral features of the suggested devices are analyzed via the finite element method (FEM). The CO2 sensitivity of the suggested device is ∼ 226 pm/ppm for the gas concentration range of 215 ppm to 434 ppm which is considerably higher than most of the formerly suggested sensor designs.