Miniature fiber-optic sensor for simultaneous measurement of pressure and refractive index

This Letter presents a fiber-optic sensor created at the tip of an optical fiber for simultaneous measurements of pressure and refractive index. The sensor diameter does not exceed the standard fiber diameter and is shorter than 300 μm. Measurement resolutions of 0.2 mbar and 2×10(-5)  RIU were demonstrated experimentally by using spectral interrogation and Fourier-transform-based measurement algorithms (interrogation system bandwidth corresponded to 1 Hz). A micromachining process based on selective chemical etching of specially designed phosphorus-doped fibers, and a sequence of splice and cleave steps were used to fabricate the sensor.