Tolerant low-loss three-lens coupling system for 1.48-mu m unstable-cavitylasers

A 1.48-mu m unstable-cavity laser is coupled into single-mode fiber using t hree microlenses, Reproducible coupling of very high power is demonstrated with different types of lenses (plano-convex or biconvex, with different ap ertures). Over 550 mW in single-made fiber (SMF) were reproducibly reached; to our knowledge? it is the highest power coupled into an SMF from a singl e semiconductor laser at this wavelength, Tolerance measurements on all of the coupling elements of a three-lens system are reported for the first tim e; an unexpected very large tolerance on the axial displacement of the seco nd lens was measured. Results and interpretation with the aid of Gaussian a nd aberration simulations are also presented.