THERMAL COMPENSATED AND TENSED SPRING COMPACT FIBER BRAGG GRATING WAVELENGTH FILTER DEVICE

A thermal-compensated fiber Bragg grating wavelength filter comprises an outer low thermal expansion coefficient metallic tube and an inner high thermal expansion coefficient cylindrical coil spring jacketed by the outer metallic tube and pre-stressed beforehand. The thermal-induced length difference of the outer metallic tube and the inner spring generates a stress-relieving effect or stress-increasing effect on the pre-stressed high thermal expansion coefficient cylindrical coil spring, whereby to increase or decrease the refractive index and compensate for the thermal-induced wavelength shift of the fiber Bragg grating.