Optical Fibre And Optical Fibre Device

An optical fibre device comprising a splice between a first optical fibre and a second optical fibre, wherein the splice has a loss less than 0.5 dB, and the first optical fibre has a first refractive index profile that can be changed by heating to a second refractive index profile, the optical fibre comprising at least one core, a cladding, at least one first dopant for providing the first refractive index profile, at least one concealed dopant, and at least one mobile dopant, the core having a refractive index that is greater than a refractive index of the cladding, and the optical fibre being characterized in that:

• one of the concealed dopant and the mobile dopant has a negative molar refractivity and the other one has a positive molar refractivity;
• the mobile dopant is present in a concentration to balance the change in the first refractive index profile induced by the concealed dopant;
• the concealed dopant is present in a concentration that if not balanced by the mobile dopant would change the first refractive index profile;
• the mobile dopant has a diffusion constant greater than a diffusion constant of the concealed dopant so that heating of the optical fibre causes the mobile dopant to diffuse more quickly than the concealed dopant, thereby allowing the concealed dopant and the mobile dopant to change the first refractive index profile of the optical fibre to the second refractive index profile and so change an optical guidance property of the optical fibre such that the optical fibre can be used in different optical devices having different requirements;
• wherein the concentration of the first dopant has a maximum value, and
• the concentration of the concealed dopant is more than the maximum value.

A method for changing a first refractive index profile in an optical fibre to a second refractive index profile, the method comprising:

• providing an optical fibre comprising at least one core, a cladding, at least one first dopant for providing the first refractive index profile, at least one concealed dopant, and at least one mobile dopant, the core having a refractive index that is greater than a refractive index of the cladding, and the optical fibre being characterized in that:
• i. one of the concealed dopant and the mobile dopant has a negative molar refractivity and the other one has a positive molar refractivity;
• ii. the mobile dopant is present in a concentration to balance the change in the first refractive index profile induced by the concealed dopant;
• iii. the concealed dopant is present in a concentration that if not balanced by the mobile dopant would change the first refractive index profile;
• iv. the mobile dopant has a diffusion constant greater than a diffusion constant of the concealed dopant;
• and
• heating the optical fibre to cause the mobile dopant to diffuse more quickly than the concealed dopant, thereby
• allowing the concealed dopant and the mobile dopant to change the first refractive index profile of the optical fibre to the second refractive index profile and so change the optical guidance properties of the optical fibre such that the optical fibre can be used in different optical devices having different requirements
• wherein the concentration of the first dopant has a maximum value, and
• the concentration of the concealed dopant is more than the maximum value.