Method for impressing gratings within fiber optics

A method of impressing at least one grating into at least one predetermined region of a core of an optical fiber which further includes a cladding surrounding the core and is centered on a longitudinal axis, comprising the steps of

• making the core of a material of a material whose index of refraction can be permanently changed by exposing such material to light of a predetermined intensity at a wavelength in a predetermined range of the spectrum;
• and
• simultaneously exposing the core through the cladding to two light beams propagating at respective different angles of incidence relative to the longitudinal axis of the optical fiber toward and through the cladding into the predetermined region of the core to form an interference pattern of longitudinally varying intensity propagating transversely through the core and forming permanent periodic refractive index perturbations in the material of the predetermined region of the core in dependence on the intensity of the interference pattern.