Optical fibre and optical fibre device

A method for providing optical radiation, which method comprises:

• providing an optical fibre (10) comprising at least one first core (2) and at least one second core (12), wherein the first core (2) comprises at least one active dopant (9);
• the first core (2) and the second core (12) are separated by a first cladding (3);
• and the first cladding (3) has a first refractive index (5) which is less than a refractive index (4) of the first core (2) and less than a refractive index (14) of the second core (12);
• propagating pump radiation along the second core (12) in the form of first optical modes (101) having a first propagation constant β1;
• selecting a strength and disposition of at least one perturbation (29);
• perturbing the optical fibre (10) with the at least one perturbation (29) to couple the pump radiation from the second core (12) to second optical modes (102) having a second propagation constant β2 and which overlap the active dopant (9);
• absorbing the pump radiation with the active dopant (9);
• propagating one or more signal mode (31) along the first core (2);
• amplifying the signal modes (31) with the active dopant (9) by stimulated emission;
• and
• outputting the amplified signal modes (31) in the form of the optical radiation;
• the method being characterized in that:
• when the optical fibre (10) is configured in a straight line or with a uniform bend radius,
• the first optical modes (101) can propagate along the second core (12) but are isolated from the active dopant (9).

An optical fibre (10) comprising at least one first core (2) and at least one second core (12), wherein:

• the first core (2) comprises at least one active dopant (9);
• the first core (2) and the second core (12) are separated by a first cladding (3);
• the first cladding (3) has a first refractive index (5) which is less than a refractive index (4) of the first core (2) and less than a refractive index (14) of the second core (12);
• the optical fibre (10) being characterized in that:
• when the optical fibre (10) is configured in a straight line or with a uniform bend radius, pump radiation can propagate along the second core (12) as first optical modes (101) without being absorbed by the active dopant (9);
• and
• when the optical fibre (10) is subject to a perturbation (29), the pump radiation which is launched primarily into the first optical modes (101) can be electively coupled to second optical modes (102) which overlap and are absorbed by the active dopant (9), which active dopant (9) is able to amplify by stimulated emission one or more signal modes (31) that are guided by the first core (2).

A method for providing optical radiation, using an optical fibre comprising;

• at least one first core (2) and at least one second core (12), wherein:
• the first core (2) comprises at least one active dopant (9);
• the first core (2) and the second core (12) are separated by a first cladding (3);
• the first cladding (3) has a first refractive index (5) which is less than a refractive index (4) of the first core (2) and less than a refractive index (14) of the second core (12);
• the optical fibre (10) being characterized in that:
• when the optical fibre (10) is configured in a straight line or with a uniform bend radius, pump radiation can propagate along the second core (12) as first optical modes (101) without being absorbed by the active dopant (9);
• the method comprising:
• launching pump radiation into the first optical modes;
• and
• controlling at least one of a fractional inversion of the active dopant along the optical fibre, an optical gain characteristic of the optical fibre, and a thermal load on the optical fibre by perturbing the optical fibre along its length to electively couple the first optical modes to second optical modes (102) which overlap and are absorbed by the active dopant (9),
• which active dopant (9) is able to amplify by stimulated emission one or more signal modes (31) that are guided by the first core (2).