A nearly two-octave wide coherent mid-infrared supercontinuum is demonstrated in a dispersion-engineered step-index indium fluoride fiber pumped near 2 µm. The pump source is an all-fiber femtosecond laser with 100 fs pulse width, 570 mW average power and 50 MHz repetition rate. The supercontinuum spectrum spans from 1.25 µm to 4.6 µm. Numerical modelling of the supercontinuum spectra show good agreement with the measurements. The coherence of the supercontinuum is calculated using a numerical model and shows a high degree of coherence across the generated bandwidth allowing it to be used for frequency comb applications.
Fluoride glasses are the only materials that transmit light in a continuous fashion from ultraviolet up to 8 μm in the midinfrared region, and can be drawn into high quality optical fibers. In fact fluoride glass fiber technology is the second most mature, beside silica based fiber technology. Fluoride glasses have experienced extraordinary development for more than 25 years. This development was motivated in the beginning by their outstanding optical properties, especially the minimum theoretical attenuation which is 0.01 dB/km between 2 and 3 μm. High quality optical fibers are now commercially available, with attenuation ranging from 5 to 30 dB/km, and mechanical strength ranging from 50 to 100 kpsi depending on fiber diameter.. The fluoride glass transmission window is from 0.25 μm to 8 μm without any absorption peaks, while the resulting fiber transmission window can be from 0.3 μm to 4.5 μm for standard fiber and from 0.3 μm to 6 μm for the extended window fiber. In this paper we will present mechanical and optical properties of current fluoride glasses and fibers, as well as high power transmission results.
A fiber laser using a thulium-doped ZBLAN gain medium was used to generate laser radiation simultaneously at 1461, 1505 and 1874 nm, with > 5 mW output power at each of the wavelengths. The laser was used to quantify the near-infrared absorption of liquid water in acetone. Additionally, near-infrared spectra were recorded using a broad band source and were interpreted using parallel factor (PARAFAC) analysis to rationalize the concentration-dependent peak shifts.
The availability of high quality optical fibers with transmission window, larger than that of silica fiber, extends the use of optical fibers and open new application fields. There is increasing demand of optical fiber with transmission over 2 microns, where silica is opaque, for applications as diverse as sensing, fiber lasers and amplifiers, defense (IRCM), spectroscopy… No materials can fulfill all applications needs. Engineers have to make some compromise when choosing the right materials for the right application. Heavy metal fluoride glass is one of these materials. The glass, under bulk form, has a wide transmission window from 0.3 up to 8 microns, without any absorption peaks. Heavy metal fluoride glass fibers are drawn using the preform technique, the same technique used for silica fiber. This technique has proven to allow good control of fiber dimensions and geometry. Fluoride glass fibers with different exotics shapes have already been obtained, such as D-shaped, square, of centered fiber, multi cladding fibers and microstructured fibers…. As far as active fibers are concerned, heavy metal fluoride glasses have low phonon energy and can contain high concentration of active ions, rare-earth elements. Therefore, new laser lines have been already demonstrated using fluoride glass fibers. Fiber lasers with output power exceeding 10 w have been obtained by different groups. This paper will present the latest development of fluoride glass fiber technology, including fibers optical and mechanical properties, fiber lasers and power handling.
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