Eye safe emission in Tm3+/Ho3+ and Yb3+/Tm3+ co-doped optical fibers fabricated using MCVD-CDS system

The RE-co-doped silica optical fibers emitting in the eye-safe spectral range are still attractive for new applications like LIDAR, pollution monitoring, navigation, and free-space optical communication. High gain and beam quality of fiber sources based on large mode area (LMA) active fibers can be fabricated by the well-known Modified Chemical Vapor Deposition (MCVD) technology improved by the chelate doping system. Considering silica matrix, the most interesting co-dopants in the region above 1400 nm are thulium and holmium. In the paper Tm3+/Ho3+ and Yb3+/Tm3+ co-doped silica optical fibers (refractive index and rare earth distribution profile, luminescence) are presented. Their respective emission spectra has been measured over the range 1550-2150 nm for Tm3+/Ho3+ (exc. at 796 nm) and 1600-2100 nm for Yb3+/Tm3+ (exc. at 976 nm). A wide luminescent spectrum has been recorded from RE co-doping of silica glass during the MCVD process and we were able to achieve the appropriate and uniform concentration for getting the conditions of energy transfer. The fabrication and characterization of Tm3+/Ho3+ and Yb3+/Tm3+ co-doped optical fibres are presented. The analysis of luminescence spectrum changes vs. fibre length has shown that there is Amplified Spontaneous Emission (ASE) at 1960 nm in Yb3+/Tm3+ co-doped optical fibre. The possibilities of obtaining novel constructions of RE co-doped optical fibers for eye-safe emission region will be also shown.