Abstract: A high birefringence photonic crystal fiber(HiBi-PCF) loop mirror structure was proposed with a reflective independent probe， in which the thermo-optic effect of ethanol was used to modulate linearly photonic crystal fiber birefringence. The Sagnac interference optical path difference was changed by the birefringence variations， resulting in the linearly changes of spectral intensity in a certain temperature region. Based on the above principle， high sensitive temperature measurement could be implemented. The structure improves the shortcoming of the traditional ring inner structure affected by external disturbance， and makes it possible to build a distributed sensing system in practical application. The experimental results showed that the refractive index of ethanol changes versus the measured temperature linearly with the sensitivity of 4.45e-4/℃. The birefringence change rule of ethanol-filled HiBi-PCF with temperature was also indicated with the sensitivity of 0.015625/℃. In addition， the change rule of output light intensity with temperature between 20~40℃ was tested with the sensitivity of 0.0031mW/℃. The formation mechanism of interference spectrum was demonstrated by using the Jones matrix theory， with the interference spectrum equation obtained.

Key words: fiber loop mirror, optical fiber sensor, temperature sensor, HiBi-PCF(high birefringence photonic crystal fibers), ethanol