Very large mode area single-mode amplifying optical fiber and fiber amplifier or laser incorporating the same

Very-A very large mode area single-mode amplifying optical fiber comprising:

• a core extending along a longitudinal axis of the optical fiber, the core being solid and doped with elements presenting at least one emission band, the core having a core diameter larger than 30 micrometers, said core being surrounded by at least one glassy cladding comprising a first cladding comprising a solid matrix made of a first glass and two stress applying parts disposed symmetrically with respect to the core, the first glass having a lower refractive index than the core, the core and the two stress applying parts being aligned along an alignment axis transverse to the longitudinal axis, the core having a numerical aperture comprised between 0.038 and 0.054,
• wherein the at least one glassy cladding comprises, on its outer periphery, two and only two flat surfaces extending parallel to the longitudinal axis and being perpendicular to the alignment axis, the two flat surfaces being disposed symmetrically with respect to the core and being joined by two rounded surfaces having a shape of an arc of a circle, and
• wherein the optical fiber is configured to be bent with a bending diameter comprised between 10 cm and 30 cm in a plane comprising the longitudinal axis of the fiber and said plane forming an angle of less than 15 degrees with the alignment axis while having bending losses for the fundamental mode less than 0.5 dB/m and bending losses equal or greater than 10 dB/m for high order modes.