Optical fibre filter

Process for the production of an optical filter, characterized by the fact of:

• providing an optical fibre that is dual-mode in a wavelength band comprised between 1500 nm and 1650 and has a core and a cladding, said cladding comprising a radially inner region adjacent to the core, said radially inner region having a composition such as to obtain a variation in refractive index equal to at least 5·10−4 following thermal stressing, and
• applying an electric arc to a first and a second portions of said optical fibre in such a way as to stress the cladding of said optical fibre thermally in an asymmetrical manner.

Method for filtering an optical signal, said optical signal being transmitted in a waveguide in the fundamental mode LP01, the method comprising the steps of:

• transmitting said signal through a first waveguide region having, in cross section, an asymmetrical refractive index profile, so as to transfer power from the fundamental mode LP01 to the asymmetrical mode LP11;
• conveying said fundamental mode LP01 and said asymmetrical mode LP11 over a predefined distance so as to produce a relative phase shift depending on said distance and the wavelength;
• transmitting said fundamental mode LP01 and said asymmetrical mode LP11 through a second waveguide region having, in cross section, an asymmetrical refractive index profile, so as to couple power between the fundamental mode LP01 and the asymmetrical mode LP11.