Power-Referenced Optical Fiber Refractometer Based on a Hybrid Fiber Grating

An in-fiber structure for power-referenced refractometry based on a hybrid fiber grating is proposed and demonstrated experimentally. The hybrid fiber grating is formed by superimposing a short fiber Bragg grating (FBG) on the rear part of a much longer tilted-FBG (TFBG) so that it can work in the reflection mode. The reflected optical power from the hybrid fiber grating can be changed with the variation of the surrounding refractive index. Experimental results show that maximum sensitivity of 228.24 dB/R.I.U. has been achieved within the refractive index range of 1.33-1.46, and the measurement is nearly insensitive to temperature.