It is well known that a germanium-doped silica fiber exhibits photosensitivity, i.e., a
permanent change in the refractive index of the core when it is exposed to light from
an appropriate laser. High photosensitivity can be achieved by increasing
concentration of germanium, codoping suitable elements which has enhanced
photosensitivity, and high pressure hydrogen loading etc.

In OptiGrating 4.2, The transverse photosensitive distribution is called the
photosensitivity profile. The photosensitivity profile for a fiber can be described as:

Optical Grating - Equation 14

where (r,φ) is the radial and azimuthal co-ordinates, Pr(r)is the radial dependent
photosensitivity (its value is between 0 and 1.0), and Pφ(φ) is the azimuthal
dependent photosensitivity (value between 0 and 1.0). The photosensitivity profile for
the slab waveguide can be described as P(y) (value between 0 and 1), where y is
the transverse coordinate of the slab waveguide.

In OptiGrating 4.2, regions define the fiber radial photosensitivity profile or slab
waveguide photosensitivity profile. Each region has its dimension (width) and
photosensitivity index profile. The default photosensitivity profile options are the same
as the default options for the index profile.