Patent ID: 9645310
Date: 2017-05-09
CPC Classifications: G02B,H01S

Claim:
1. An active double-clad fiber comprising the following four layers: a. a high refractive index core having a radius in the range of 0.3 μm to 2 μm; b. an inner annular clad layer doped with active ions surrounding the core having a radius in the range of 30 μm to 50 μm; c. an outer annular clad layer having a radius in the range of 100 μm to 200 μm surrounding the inner clad layer; and d. an annular low refractive index outer coating layer surrounding the outer clad layer; wherein: the dimensions and properties of the materials of the layers of the fiber provide discrimination of between 4 and 6 against higher modes, thereby maintaining single mode operation in laser systems; the single transverse mode guided by the core has a diameter of at least 80 μm; and the diameter of the core is 0.75% to 5% of the diameter of the large single transverse mode, thereby allowing guiding and amplification to take place mainly in the inner doped clad layer, with a large overlap between the guided mode and the inner doped clad layer.