High-power upconversion fibre lasers for the visible wavelength range

For projection and display applications integrated red, green and blue lasers are required. While blue and red diode lasers are becoming widely available, there is no such technology for green wavelengths. Therefore frequency conversion schemes have to be used. Besides second harmonic generation, upconversion provides a simple way to convert infrared photons into the visible, making use of the highly efficient infrared laser diodes. In this article, upconversion lasers based on Er³⁺ -doped ZBLAN-glass are re-investigated (Whitley et al., 1991). Special focus is laid to the achievable efficiency, to the temperature sensitivity of the process and to the scaling of the output power towards the watt-level.