Miniature fiber optic pressure sensor for medical applications

Presents a theoretical description, fabrication and experimental investigation of miniature optical fiber pressure sensor for invasive measurement of blood pressure. Sensor measures only 125 μm in diameter. The essential element is thin polymer diaphragm that is positioned inside a hollow end of the optical fiber. The cavity at the fiber end is made by wet etching in diluted HF acid. Thus the Fabry-Perot interferometer is formed between the inner fiber-cavity interface and the diaphragm. Deflection of the diaphragm and so pressure magnitude is determined by reading the reflectance spectrum of the sensing Fabry-Perot interferometer using broadband illumination. The configuration of Fabry-Perot interferometer at the optical fiber end makes sensor immune from bending of optical fiber and optical power fluctuations of light source. We deployed sensor prototype from 125 μm-diameter optical fiber. It is optimized for human blood pressure range, namely from 0 to 40 kPa (0 to 300 mmHg) with 1 mmHg resolution. Our fabrication technique offers simple and low-cost disposable medical pressure sensor production.