Variable optical fiber Bragg filter arrangement

A variable light filtering arrangement comprising

• at least one optical fiber section including a waveguiding core;
• at least one permanent Bragg grating region in said optical fiber section, including a plurality of grating elements constituted by periodic refractive index variations of a predetermined initial periodicity and cumulatively redirecting, of the light launched into said core for guided propagation therein, that having an axial wavelength within a narrow band around a central wavelength that is determined by the periodicity and refractive index variations of said grating elements;
• and
• means for so applying at least to said grating region of said optical fiber section an external influence that is representative of a parameter other than structural strain as to modify at least one of the periodicity and refractive index variations of said grating region with an attendant change in said central wavelength within a predetermined wavelength range to an extent indicative of the magnitude of said parameter.