CC BY
19LS-I-17
Photosensitivity of composite heavily erbium-doped phosphosilicate fibers
A. Rybaltovsky1, O. Egorova2, S. Vasiliev3, S. Zhuravlev1, O. Butov4, S. Semjonov5, B. Galagan6, S. Sverchkov6, B. Denker6
1Fiber Optics Research Center of Russian Academy of Sciences, Laboratory of Optical Fibers Technology, Moscow, Russian Federation
2Natural Sciences Center at Prokhorov General Physics Institute of the Russian Academy of Scie nces, Force Fiber Optics Laboratory, Moscow, Russian Federation
3Fiber Optics Research Center of Russian Academy of Sciences, Laboratory of Fiber Optics, Moscow, Russian Federation
4Kotelnikov Institute of Radio Engineering and Electronics of Russian Academy of Sciences, Laboratory of Fiber Optic Technology, Moscow, Russian Federation 5Fiber Optics Research Center of Russian Academy of Sciences, Laboratory of Optical Fiber Technology, Moscow, Russian Federation
6Prokhorov General Physics Institute of the Russian Academy of Sciences, Laboratory of Concentrated Laser Materials, Moscow, Russian Federation
Single frequency fiber lasers are attractive for many photonic applications. Narrowband emission of this laser type is usually provided by a relatively short (10-20 mm) Fabry-Perot structure (or phase-shifted fiber Bragg grating (FBG)) created in the fiber core. Two factors have key importance for short-length laser structures: high pump absorption (emission gain) per unit length and sufficient photosensitivity of the active fiber. A novel composite heavily erbium-doped phosphosilicate (24 mol. % of phosphorus oxide, 3 mol. % of aluminium oxide and 0.39 mol. % of erbium oxide) single-mode fiber has been recently developed using a rod-in-tube technique [1]. It was shown that the fiber has good lasing properties as well as rather high photosensitivity to 193-nm radiation, which allowed achieving a stable single frequency lasing using optical pump at 980 nm [2].
In this work the photosensitivity of this composite fiber was further investigated. Particularly, dose dependencies of modulation amplitude and mean index change have been measured for both pristine and hydrogen-loaded fiber samples. Thermal stability (temperature annealing) of the induced index change has been also analyzed. It was shown that the UV-induced index gradually decreases with temperature increase, nevertheless some magnitude of induced index remains unerased until the core material melts (600-650°C).
A composite fiber with a core diameter of 5 |im (cut-off wavelength - 1.43 |im) has been used for investigation. An ArF excimer laser (Coherent COMPexPro) emitting 20-ns pulses at 193 nm (repetition rate - 10 Hz) was used for fiber side irradiation with the energy density of about 200 mJ/cm2 per pulse. Low temperature hydrogen loading of fiber samples has been performed in gas chamber (H2 pressure - 120 atm) at 90°C during 24 hours. FBGs were written via the 10-mm-long phase mask having a period of 1064 nm.
Dose dependences of UV-induced index modulation amplitude and average index change measured for both as prepared and H2-loaded fibers are shown in Fig.1. Similar to germane-silicate glass, molecular hydrogen dissolved in the phosphosilicate glass increases its photosensitivity greatly. The observed photosensitivity is enough to fabricate highly reflecting FBGs, necessary to create single-frequency laser cavities. Other results obtained in our experiments on induction and
erasure of refractive index in the core of the composite Er-doped phosphosilicate fiber will be
presented at the Conference.
100 1000 Dose, Jfcm'
Fig. 1. Dose dependences of UV-induced index components for both pristine and H2-loaded composite phosphosilicate fiber (insert: FBG spectra measured at the end of UV-irradiation).
References
[1] O.N. Egorova, S.L. Semjonov, V.V. Velmiskin, Yu.P. Yatsenko, S.E. Sverchkov, B.I. Galagan, B.I. Denker,and E.M. Dianov, "Phosphate-core silica-clad Er/Yb-doped optical fiber and cladding pumped laser", Opt. Express 22, 7632 (2014).
[2] A.A. Rybaltovsky, O.N. Egorova, S.G. Zhuravlev, S.L. Semjonov, B.I. Galagan, S.E. Sverchkov, B.I. Denker, "Distributed Bragg reflector fiber laser directly written in a composite fiber manufactured by melting phosphate glass in a silica tube", to be published in Optics Letters.
