Page 88 - Fiber Bragg Gratings

3.1 Methods for fiber Bragg grating fabrication 67

Figure 3.8: The photograph shows the tunable phase-mask interferometer.
The distance between the mirrors can also be altered without misaligning the
interferometer. The fiber can also be rotated around the vertical axis to allow the
inscription of slanted gratings (see Section 3.1.4).

where n s is the refractive index of the silica block at the writing UV
wavelength. Assuming that sin 0 m/2 «= 6 m/2 for small angles, the maximum
length of the grating, which may be written with a side of L g is

For fiber Bragg gratings at a wavelength of 1500 nm, the angle
B m/2 ~ 10°; the length of the silica block side is then approximately 17
times the grating length. The minimum width of the silica block W s is
equal to the grating length L g without in-line zero-order suppression.
However, if the zero order is to be physically blocked by an opaque element,