Fiber optic Fabry-Perot pressure sensor based on lensed fiber and polymeric diaphragm

A novel optical fiber-based Fabry-Perot pressure sensor fabricated with a lensed fiber and a polymeric diaphragm is proposed for application in the medical field. The lensed fiber was constructed at the tip of a single mode fiber, for use with a deformable flexible polymeric diaphragm. The sensor can reduce the loss of optical power of the back-reflected light, and the flexible diaphragm can increase deformation sensitivity. The lensed fiber was fabricated from a coreless silica fiber attached to a single mode fiber by splicing using a fusion splicing method, and arc discharge. The polymeric diaphragm consists of layered PDMS, parylene and gold mirror. The intermediate parylene layer is helpful to prevent cracking of the mirror when the diaphragm is deformed by external pressure. The polymeric diaphragm was fabricated by MEMS processing including spin-coating, vaporization, and sputtering. The deformation of the polymeric diaphragm was evaluated through numerical simulation. The change in cavity length between the lensed fiber and the polymeric diaphragm with external pressure was estimated using the interference generated from two reflected lights. Experimental results showed that the proposed pressure sensor has a sensitivity of 1.41 μm/kPa over a pressure range from 0 kPa to 4 kPa with good linearity, and its minimum detection resolution is less than 0.03 kPa. The proposed sensor could be used for reliable low-pressure measurement, especially in medical applications.