Phosphate glasses for fiber laser applications

There is a technological and industrial need for compact and intense sources in particular for those operating in pulsed mode operation. These types of sources are required for micromachining and marking applications using 1 um wavelength sources and also for lidar applications at eye-safe wavelengths in the 1.5 micron wavelength region. Phosphate glasses are particularly well suited for developing such devices. As rare earth ion hosts, they allow for achieving doping concentrations up to 1021 ions/cm3 without clustering and photordarkening. Their high phonon energy is also well suited for efficient emissions from Nd3+ and Yb3+ at 1 micron and the 1.5 micron emission from Er3+, using standard pumping schemes either at 808 nm or 980 nm. Thanks to this efficiency together with their outstanding thermo-mechanical properties, phosphate glasses can sustain high beam intensity. We present and discuss the development of rare earth doped phosphate glasses and fibers for laser and optical amplification applications operating in the 1 micron and 1.5 wavelength regions. Three host glass compositions have been designed for fabricating double clad structured fibers where the core glass composition was doped either with Nd3+, Yb3+ or Yb3+/Er3+ according to the operation wavelength foreseen. Single mode fibers with losses of 3.5 dB/m have been developed allowing for basic implementation of fiber lasers and optical amplifiers.