Tolerant low-loss three-lens coupling system for 1.48-μm unstable-cavity lasers

Abstract

A 1.48-tm unstable-cavity laser is coupled into a single-mode fiber using three microlenses. Reproducible coupling of very high power is demonstrated with different types of lenses (piano-convex or bi-convex, with different apertures). Over 550mW in single-mode fiber were reproducibly reached ; to our knowledge, it is the highest power coupled into a single-mode fiber from a singlesemiconductor Laser at this wavelength. Tolerance measurements on all of the coupling elements of a three-lens system are reported for the first time ; an unexpected very large tolerance on the axial displacement of the second lens was measured. Results and interpretation with the aid of Gaussian and aberration simulations are also presented. Finally, we report on the first realization of a module with 46% chip to fiber coupling efficiency.