The Development of a High Power, Broadly Tunable 3 µm Fibre Laser for the Measurement of Optical Fibre Loss

Abstract

Mid-Infrared Photonics has attracted growing interest in recent years due to the presence of many strong characteristic vibrational transitions that are highly resonance with the low-energy photons of the mid-infrared. As such, a plethora of potential applications stand to benefit from the availability of well-understood and robust sources within this wavelength region including spectroscopy, medicine and defence. The region surrounding 3 µm, corresponding to the antisymmetric stretching vibration of O-H as well as a region of high atmospheric transparency, is of particular interest. However, this spectral region is not yet accessible via readily available devices. As such, the development of well understood, versatile, laser sources at 3 µm remains an area of great scientific interest. In this work, a Ho3+, Pr3+ co-doped fluoride fibre laser is presented that produces an output power of 7.2 W generated at a slope efficiency of 29 %. The excitation source was a power scalable Yb3+-pumped 1.150 µm Raman fibre laser which emitted up to 50 W. The emission linewidth of the system was <0.14 nm and the wavelength of the system was observed to tune between 2.825 µm and 2.975 µm, overlapping with the O-H absorption region of many midinfrared transparent glasses. The system then finds use as a tool for the accurate measurement of the background scattering loss and the degree of water incorporation in the rare earth doped core of a range of commercially available double clad ZBLAN fibres. Furthermore, the spectral location of the O-H absorption feature was observed to be dependent on glass composition shifting from 2.872 µm in undoped ZBLAN to 2.896 µm upon co-doping with Ho3+, Pr3+. Additionally, the chalcogenide glass, As2S3, was observed to have an O-H peak location of 2.911 µm.