Optical fiber pressure sensing for biomedical applications using frequency selective technique

Abstract

State-of-the-art optical fiber pressure sensors use displacement diaphragms and mechanical transducers to enhance pressure sensitivity, however, due to their bulkiness and large size they can’t be easily integrated inside pressure guide wire for intravital monitoring. Fiber Bragg Gratings (FBGs) due to their inherent advantages can be designed in a way that is suitable for monitoring Intracranial Pressure (ICP) and Instantaneous Wave-Free Ratio (iFR) pressure indices. The main disadvantage of FBG is that it has a low-pressure sensitivity of 3.04pm/MPa, which is insufficient for these applications and is made worse by the cross-sensitivity caused by temperature. We hereby present a two-pronged strategy to tackle this issue. The first step in improving sensitivity is to modify FBGs, and the second is to use signal processing methods to recover minor wavelength shifts. A frequency-selective detection technique can be used to measure sub-pm wavelength shifts for small modulated pressure signals. This technique was used to establish a test bench for measuring the pressure sensitivity of standard acrylate and polyimide coated FBGs as well as to confirm a linear relationship between the pressure range of interest and Bragg wavelength shift.