Stress tuneable phase shifts of femtosecond-laser microstructured FBG for indentation measurements of biological tissue: Experimental and theoretical investigation

摘要

An automated fs-laser machining procedure was developed to engrave circumferential grooves into the cladding of optical fibres. The grooves are positioned centrally to type I fibre Bragg gratings (FBG) and form locally micro structured FBGs. The grooves realized so far were ～30μm deep and were 48 μm to 200 μm long. These devices show the occurrence of a phase shifted spectrum when axial stress is applied. It is shown in this paper that this property can be used to achieve higher force sensitivities when compared to conventional FBGs. These devices are advantageous for the investigation of tissue by indentation-type elasticity measurements. An experimental and theoretical investigation of the dependence of the force sensitivity on the length of the structure is reported.