Patent ID: 7983312

Claim:
A laser gain medium comprising: an active core having a high aspect ratio cross-section with a fast-axis dimension and a slow-axis dimension; first means for forming reflective boundaries at fast-axis boundaries of said core; edge sections arranged at each slow-axis boundary of said active core, said edge sections comprising mode index matching material arranged in contact with and covering edge portions of said active core and edge portions of said first means only at each slow axis boundary; an outer cladding portion arranged to surround the first means, the edge sections, and the active core, wherein a thickness of said active core is chosen to control a fast-axis mode profile and a number of fast-axis modes propagating in said active core, wherein said thickness of said active core is adapted to support one or more modes in said fast-axis direction; and means for stripping any higher-order modes out of said active core, and wherein said mode index matching material has a refractive index different from an active core index so that anti-guiding is provided at slow-axis boundaries of said active core, said mode index matching material being disposed only along the edge portions of said active core and the edge portions of said first means at each slow axis boundary.