Self-compensating gold-encapsulated tilted fiber Bragg grating for peak tracking based biosensing applications

• Published in: Journal of optics (New Delhi) 2024-07, Vol.53 (3), p.2005-2019
• Main Authors: Prathap, P. B., Saara, K.
• Format: Article
• Language: English
• Subjects: Lasers; Optical Devices; Optics; Photonics; Physics; Physics and Astronomy; Research Article
• ISSN: 0972-8821; 0974-6900
• DOI: 10.1007/s12596-023-01369-6

Fiber Bragg Grating sensors are playing decisive role in clinical decisions, where its ability to show chemical-inertness, small in size and high-sensitivity makes it superior over the electric-sensors for both in vivo as well as ex vivo examinations. In the recent years, different FBG sensors are proposed for biosensing task(s); yet, ensuring high-resolution, accurate and high-sensitive sensing under complex operating environment remains challenge. The fiber Bragg grating coating or grating-encapsulation(s) by using metals or polymers enables better spectral efficiency; yet, inappropriate coating and allied grating might cause varied spectral-responses or reflectivity, causing multiple peaks over response. Demodulating such ambiguous spectral responses might be difficult and can cause false positive result. Its severity can be more frequent over biosensing involving viscous analytes-antibody or aqueous (test)-solutions. The local conditions like viscosity-strain and temperature caused noises too give rise to the different peaks over fiber Bragg grating spectra response that might impose wrong clinical diagnosis decisions. With such inference, this research proposes a robust self-compensating gold-encapsulated tilted fiber Bragg grating structure for peak-tracking-based biosensing. It involves two sequential phases, where initially a gold-encapsulated tilted fiber Bragg grating is designed with grating’s tilt angle of 9°. Simulating the sensor, the spectral responses are obtained for the different Bragg wavelengths, which are subsequently processed for cross-correlation-based matched filtering for peak identification to make clinical decisions. Toward self-compensation, cross-correlation was performed between the reference spectra and the measured fiber Bragg grating responses. Employing Mexican-Hat wavelet response as the reference signal and measured spectra, zero-crossing points and correlation-vectors were obtained signifying the peak locations. Thus, retaining the correlation vectors with higher peak intensity over the Bragg wavelength, the target peak for the tilted fiber Bragg grating was tracked. Simulation results confirmed that the proposed tilted fiber Bragg grating with self-compensation ability can achieve 0.9 nm/refractive index unit sensitivity while suppressing noise elements and false-peaks caused due to local artefacts like viscosity, strain, temperature, etc. Such abilities make the proposed gold-encapsulated sensor suitable for both bio