Laser-Machined Cascaded Micro Cavities for Simultaneous Measurement of Dual Parameters Under High Temperature

Fiber-optic cascaded micro Fabry–Perot (F-P) cavities fabricated by 157-nm laser micromachining is demonstrated for simultaneous measurement of high temperature and refractive index, or high temperature and strain, respectively. The sensor head consists of a short air extrinsic F-P cavity and an intrinsic single-mode fiber F-P cavity. These two micro cavities possess different response coefficients to temperature, strain, and refractive index, which are utilized for dual parameters measurement. Experimental results show that dual parameters measurement could have been achieved from 50
$^{\circ}{\rm C}$
to 380
$^{\circ}{\rm C}$
based on such a sensing structure.