Ultra-broadband emission in Er3+/Tm3+/Ho3+ triply-doped germanate glass and double-clad optical fiber

Abstract

In this paper 1400 nm–2200 nm broadband emission under 808 nm and 976 nm laser diodes excitation in germanate glasses co-doped with (0.35–0.7) Er2O3/(0.35–0.7) Tm2O3/(0–0.15) Ho2O3 (mol%) are presented. Flattened luminescence profiles were achieved as a result of RE content optimization in glasses co-doped with 0.35Er2O3/0.7Tm2O3/0.15Ho2O3, (λexc = 808 nm) and 0.7Er2O3/0.35Tm2O3/0.07Ho2O3, (λexc= 976 nm). The second, glass characterized by the widest emission range, has been used for the fabrication of double-clad optical fiber with 15 µm/250 µm (core/outer cladding) diameters. The optimization of broadband spectrum in glass and optical fiber was performed as the result of the superposition of 1550 nm (Er3+: 4I13/2 → 4I15/2), 1800 nm (Tm3+: 3F4 → 3H6), and 2000 nm (Ho3+:5I7 → 5I8) emission bands. The influence of optical fiber length and pump wavelength on near-infrared amplified spontaneous emission (ASE) features have been determined. As a result, the broadest bandwidth of ASE (415 nm - 3 dB and 731 nm – 10 dB) was obtained in 5 m length optical fiber under 808 nm pumping. It is significantly broader than in silica and tellurite fibers, which showed the advantage of RE triply-doped germanate optical fiber.