Highly sensitive long-period fiber-grating-based biosensor inherently immune to temperature and strain

Abstract

For two simultaneously varying external perturbation parameters, namely, temperature and strain, we propose and theoretically demonstrate a novel, to the best of our knowledge, scheme of developing inherently insensitive biosensors based on long-period fiber gratings (LPFGs). The insensitivities have been achieved by inherently nullifying (i) temperature-induced phases of the core and cladding modes by judiciously adjusting the core dopants and their concentrations and (ii) strain-induced phase changes generated inside one LPFG with that inside the other LPFG by optimizing the grating parameters (grating period, strength, and length). The resulting biosensor has ultrahigh overall bulk refractive index sensitivity of ∼ 3 µ m / R I U for biosamples (RI varying in the range of 1.33 to 1.34 RIU) and an affinity sensitivity of ∼ 1.4 n m / n m for biomolecules ( R I ∼ 1.45 R I U ). Our study should find application in developing ultrasensitive, high-precision bio/chemical sensors that are inherently immune to environmental temperature and strain variations.