Cardiac signal monitoring using femtosecond laser inscribed FBGs in CYTOP optical fiber

In this study, fiber Bragg gratings (FBGs) were inscribed into cyclic transparent optical polymer (CYTOP) optical fibers using a femtosecond laser plane-by-plane (Pl-b-Pl) technique. A custom-designed integrated cardiac sensor was then developed, incorporating a 3D-printed structural enclosure and PDMS-based flexible encapsulation. This sensor enables simultaneous localization and detection of cardiac signals and was evaluated on healthy volunteers at four different body locations. Experimental results demonstrated reliable performance in monitoring both respiratory rate (RR) and heart rate (HR), with high signal stability across different positions. To further explore the advantages of CYTOP FBGs—particularly their high strain sensitivity and mechanical flexibility—this work also investigated the feasibility of detecting Seismocardiography (SCG) signals as an extended application. The findings validate the potential of femtosecond-laser-written CYTOP FBGs for non-invasive, multi-parameter cardiac monitoring and support their future use in wearable, low-interference sensing systems suitable for both clinical and non-clinical environments.