1.6-micrometer emission from Ho3+-doped fluoride glasses

We have investigated the spectroscopic properties of the 1.6-micrometer emission from the 5I(5) --> 5I(7) transition of Ho3+ ions in fluoride glasses for use in U-band fiber amplifiers. The intensity profile of the emission peaks at approximately 1660 nm, with a full width at half-maximum of approximately 60 nm. The measured lifetime and emission cross section are approximately 230 micros and approximately 5.4 x 10(-21) cm2, respectively. Frequency upconversion to the 5F(1) state occurs simultaneously with excitation of the 1.6-micrometer emission, so the shorter-wavelength side of the 5I(8) --> 5I(5) absorption spectrum is favorable for population of the 5I(5) state. Codoping with rare earths such as Tb3+, Dy3+, Eu3+, and Nd3+ decreases the lifetimes of the lower-lying 5I(6) and 5I(7) levels and as a result would be of benefit in achieving population inversion between the fluorescing level and the lower-lying levels.