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The spontaneous emission coupling factor β is studied for fiber-coupled microspheres with a thin gain layer of phosphorus codoped sol-gel erbium silica-aluminum glass. From the input-output characteristics of the lasing, β=0.039 is estimated for a sample with a gain layer on the sphere surface. β is estimated to increase to 0.19 when an additional silica glass thin layer is overcoated to improve the overlap between the gain layer and the optical mode of the lasing inside the sphere. [ABSTRACT FROM AUTHOR]

Lasing of a taper-microsphere system with a gain layer of submicrometer thickness is demonstrated. For the gain layer, an Er3+-doped P2O5–Al2O3–SiO2 thin film with a thickness of 200 nm was fabricated using the sol-gel method on a silica microsphere. The demonstration of single-mode lasing with the thin gain layer suggests the improved dispersion of Er ions in the P codoped gain layer. [ABSTRACT FROM AUTHOR]