The inventive cover assembly (1) essentially comprises a right cover (4), a left cover (5), a lower cover (6), a lower bellows (7) and an upper bellows (8).

The waveguide further includes a first cladding portion surrounding the outer core portion and having a first cladding refractive index that is less than the outer core refractive index.

It is constituted by flat waveguide which include lower cladding layer, active layer and upper cladding layer.

The inner clad consists of a first inner clad having a refractive index (n3) smaller than that (n2) of the second core and a second inner clad having a refractive index (n4) smaller than that of the second inner clad (n3).

The refractive index of the outer cladding surrounding the inner cladding is less than that of the inner cladding.

An outer cladding (36) surrounds the inner cladding (32) and has an outer cladding refractive index less than the inner cladding refractive index.

The invention concerns a cladding-pumped optical fibre comprising: a core with optical index n1, around the core, a first cladding with index n2 less than n1, around the first cladding, a second cladding with index n3 less than n2.

The outer clad diameter is less than 100μm.

The silica clad surrounds the inner clad and has a refractive index (n¿silica?) smaller than that (n4) of the second inner clad.

The inventive cover assembly (1) essentially comprises a right cover (4), a left cover (5), a lower cover (6), a lower bellows (7) and an upper bellows (8).

The lamp comprises a lower body, a central body, and an upper duct, where the central body, and the upper duct together define at least one passage way/duct for thermal airflow.

The at least one nanopillar has a cladding.

A refractive index of the cladding being smaller than a refractive index of the nanopillar.

The (n2) of the inner cladding may also be less than the (n1) of the core and more than the (ncl) of the outer cladding.

A lower mirror (14) is placed below the sheath heater (26).