Bismuth-activated Silica-core Fibres Fabricated by SPCVD K.M.Golant, A.P.Bazakutsa, O.V.Butov, Yu.K.Chamorovskij, A.V.Lanin, S.A.Nikitov Kotel’nikov Institute of Radio Engineering and Electronics of RAS, 125009, Mokhovaya 11-7, Moscow, Russia, golant@cplire.ru Abstract Al, P, Ge additives to silica separately and/or in combination are used to shape refractive index profiles of Bi-doped-silica-core fibres. Loss spectra and luminescent properties of the fibres, critical for light amplification at 1.1-1.5 microns wavelengths are discussed. Introduction Lack of proper activators for fibre lasers and amplifiers makes the important spectral band in the vicinity of 1.3 μ wavelength uncovered by this type of devices, effectively operating in the neighbouring bands in the vicinity of 1 μ (Yb 3+ ) and 1.55 μ (Er 3+ ) wavelengths. It has been recently found that addition of small amount of bismuth to core glass of silica fibres leads to the formation of defects yielding a broad band near- infrared luminescence, which can be used for lasing at wavelengths of 1.1-1.5 μ depending on core glass composition and pump wavelength (see 1 and references therein). At present, exact electron energy diagram for such defect is unclear, and gain efficiency of Bi-activated silica fibre remains rather poor as compared to that one for mentioned above popular rare earth activators. Nevertheless, in the absence of alternatives for fibre devices operating in the 1.3 μ wavelength band, improvement of gain efficiency of Bi-activated silica fibre by means of technological factors looks rather challenging. Up to the moment near-IR luminescence and lasing associated with the presence of bismuth are investigated mostly in silica fibres drawn from preforms fabricated by thermodynamically equilibrium MCVD or aerosol deposition 2 processes. More flexible approaches to the synthesis of activated silica fibres demonstrate plasma chemical deposition technologies. First application of non-equilibrium surface-plasma chemical vapour deposition (SPCVD) to the synthesis of Bi-doped silica fibre preforms with refractive index profile shaped by adding alumina to core glass demonstrated an effective fibre gain at 1.1-1.2 μ wavelengths. Gain efficiency as high as 0.2 dB/mW was obtained at a pump wavelength of 1.058 μ, fibre length being 20 m 3 . The present paper summarizes recent advances in further application of SPCVD to the fabrication of Bi-activated fibres intended for light amplification. Impact of bismuth concentration and additives to silica in the fibre core on absorption spectra and near-IR luminescence of Bi-associated defects is addressed. Absorption and luminescence in Bi-doped silica fibres drawn from SPCVD preforms In the SPCVD process layer-by-layer oxide deposition takes place on the inner surface of a substrate tube due to halides oxidation in a scanning plasma column, total gas pressure inside the tube not exceeding several Torr, tube wall temperature being about 1000 ºC 4 . In these conditions no soot is formed, but oxide molecules are immediately chemically adsorbed by amorphous layer growing on the substrate surface, thus providing a way for glass stoichiometry management by means of oxidizer partial pressure variation in the gas mixture being pumped through plasma. In our experiments vapours of anhydrous BiCl3 together with other halides mixed with oxygen and nitrous oxide are used as a starting gas mixture supplied to reaction zone of the scanning plasma column. Three types of Bi-doped fibre preforms differed by additives to silica in the core are fabricated. Typical preform specifications are listed in Table 1. Aluminum, germanium together with boron, as well as phosphorous serve as additives to shape fibre refractive index profiles. Bismuth delivery to the deposition zone is controlled in a wide range by variation of the evaporation temperature of BiCl3. Mass flow of bismuth is monitored via the intensity of a 472.2 nm Bi emission line. To do that plasma emission spectrum is continuously recorded “in situ’ during the SPCVD process. Tab. 1: Specification of Bi-doped SPCVD preforms Sample Additive to core silica Core/cladding index difference, 10 -3 #1 Al 6 #2 P 5 #3 Ge+B 12 Figure 1 demonstrates loss spectra measured in multimode fibres drawn from the SPCVD ECOC 2010, 19-23 September, 2010, Torino, Italy 978-1-4244-8535-2/10/$26.00 ©2010 IEEE P1.02