Fig. 1. Wave vectors of incident and diffracted beams

Fig. 2. Intensity distribution produced inside the fiber core region during FBG fabrication using the phase mask technique. (a) ±1 and 0 diffraction orders; (b)±2, ±1 and 0 diffraction orders; (c)±3, ±2, ±1 and 0 diffraction orders; (d)±4, ±3, ±2, ±1 and 0 diffraction orders

Fig. 3. Spatial spectra of the interfering light field over a fiber core mode field with a diameter of 10 μm. (a) ±1 and 0 diffraction orders; (b)±2, ±1 and 0 diffraction orders; (c)±3, ±2, ±1 and 0 diffraction orders; (d)±4, ±3, ±2, ±1 and 0 diffraction orders

Fig. 4. Microscopic image of FBG in 10/130 μm fiber

Fig. 5. Phase mask interference field contrast and refractive index modulation depth in FBGs as a function of the distance between the phase mask and the fiber core

Fig. 6. Loss of FBGs with the same reflectivity as a function of refractive index modulation depth in FBGs

Fig. 7. Phase mask interference field contrast as a function of the diffraction efficiency of 0 order diffracted light

Fig. 8. Spatial spectra of the interfering light field over a fiber core mode field diameter of 10 μm considering the ±4, ±3, ±2, ±1 and 0 diffraction orders. (a) z=100-110 μm; (b) z=1000-1010 μm; (c) z=2000-2010 μm

Fig. 9. Interference distance of ±1 order diffraction lights on z axis varied with incident angle of UV light