FBG based novel sensor design for low vacuum measurement with high sensitivity

This article demonstrates use of a fiber Bragg grating (FBG) sensor for in situ monitoring of vacuum process with high sensitivity. The sensor head consists of a commercial syringe barrel with plunger, metal spring, pressure chamber, FBG and safeguarding outer tube. The sensor is configured by firmly fixing the FBG between the plunger and the rigid support provided to the safeguarding tube. Under vacuum process the metal spring facilitates the FBG to get strained in axial direction which results in shift of Bragg wavelength of FBG. The Bragg wavelength shift of FBG is found to be linear with respect to vacuum pressure with a linear coefficient of 0.9988. Pressure sensitivity of the sensor is found to be 27 pm/cm Hg. The sensor design is simple, low-cost and has the advantage of all fiber optic sensors.