Abstract

The ability to operate fibre lasers above the temperature limits traditionally set by degradation of fluoropolymer outer coatings opens up a number of interesting possibilities, such as increased operating wavelength range, reduced weight requirements of cooling systems and even the possibility of negating the effects of photodarkening [1] and stimulated Brillouin scattering (SBS) [2]. Typical fluoropolymers used in the low refractive index coating of a double clad fibre laser tend to degrade at temperatures above 80 – 100°C. Operation of a fibre laser over a much broader temperature range can be achieved by utilising an all-glass fibre design with a low refractive index fluorine-doped glass cladding. This design has a number of interesting effects on both laser spectroscopy and glass properties. For quasi-three-level gain media the increased operating temperature tends to shift the operating wavelength towards longer values due to the increased signal reabsorption at shorter wavelengths. Operating at higher temperatures also has the potentially detrimental effect of reducing the effective upper state lifetime [3]. The removal of the temperature sensitive fluoropolymer cladding could allow simplified designs for cooling of the fibre laser. For example, platforms with tight space and energy requirements, or where a large number of lasers are required, could benefit from the cooling efficiency and weight savings to be gained from removing the need for maintaining <80°C operating temperatures. This approach may even enable passive cooling schemes to be adopted.

© 2015 IEEE