Vacuum sealed ultra miniature fiber-optic pressure sensor using white light interferometry

We have developed a fiber-optic Fabry-Perot interferometer pressure sensor of 125 /spl mu/m in diameter of which cavity is sealed in vacuum. White light interferometry is used to avoid noise caused by bending of the optical fiber and a fluctuation of the light source. The reflection light is measured by high-speed spectrometer. A Fabry-Perot cavity is formed at the optical fiber end. A deformation of the diaphragm induced by pressure varies the cavity length. To avoid influence of temperature change to the sensor output, the cavity is sealed in vacuum. The sensing element is bonded to the optical fiber end by soldering in vacuum. Sn layer is formed on the metal spacer of the sensing element and is bonded to the Cr/Cu/Au layer patterned at the optical fiber end. Cr half-mirror is also patterned at the core of the fiber end for making interferometer. Pressure is successfully monitored in real-time using the sensor system.