Pr-Yb doped ZBLAN glass optically pumped with NIR shows visible
fluorescence generated by an up-conversion process. With diode
laser pumping, laser emission from a single-mode Pr-Yb doped ZBLAN
fiber has been achieved at 492, 520, 605, 635 and 717 nm.
This makes it possible to build all solid state visible fiber
lasers. Solutions for building color-switchable fiber lasers by
the aid of an external resonator or by manipulation of the
reflectivity of a dielectric mirror are discussed. Experiments
with switching between two wavelengths are presented. A fiber
laser with switchable emission from 10 mW at 492 nm to > 10 mW
at 635 nm is introduced. The laser output noise is less than 1 % rms,
the beam quality is M<sup>2</sup> < 1.3, and the spectral width is < 1 nm (FWHM). Switching between 492 nm and 520 nm is also demonstrated.
All wavelengths are generated within the same fiber resulting in
identical boresight directions for different colors, and 100 % pointing stability. Fluorescence microscopy in life sciences is a typical application for this kind of laser.