The spectroscopic analysis of the frequency distribution of the amplification of optical radiation due to the Raman effect (Raman gain profile) in single-mode fibers based on silica glass has been carried out in the region of Stokes frequency shifts from 0 to 1400 cm −1 . The Raman gain profiles are determined from the experimental spectra of spontaneous scattering for widespread fibers, namely for pure SiO2, GeO2, P2O5, and TiO2 doped fibers. The analytic expressions of the Raman gain profiles are given. They are obtained, by using the Gaussian decomposition by means of 11-12 modes, and the experimental profile is approximated with an accuracy of not less than 0.3%. The decomposition results are analyzed in terms of the fundamental oscillatory dynamics of molecular nanocomplexes in amorphous glass, as well as in the application aspect of the modeling of photonics devices. Examples of the proposed method applications are presented for the analysis of noise parameters of the fiber Raman amplifiers and for the generation bandwidth in fiber Raman lasers. K e y w o r d s: optical amplification, Raman gain, fiber Raman lasers, fiber Raman amplifiers.

The properties of TiO2-doped fiber are considered as optoelectronic material in our work. The advantages of such fiber have been studied with the aim of its application to active medium in Raman fiber lasers. The comparison of spontaneous Raman spectra and corresponding gain profiles in TiO2-doped and GeO2-doped fiber is presented. Raman gain profiles were obtained over a broad spectral range of Stokes shifted frequencies up to 1400 cm-1(42 THz). The spectral decomposition using multimode Gaussian components has been performed for both Raman gain profiles. High accuracy analytic form of Raman gain profile of TiO2-doped fiber is obtained using 12 components. The pump power of Raman gain threshold is introduced as the function of wavelength within the telecommunication windows for both fiber types. Our spectroscopic analysis allows presenting the numerical results on lasing bandwidth and Raman gain threshold inTiO2-doped single-mode fiber. It has been shown that the lasing bandwidth in TiO2-doped fiber may be almost twice wider than the lasing bandwidth in standard GeO2-doped fiber.

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We analyze Raman lasing bandwidth for TiO 2 -doped single-mode fibre as a function of pumping power, following from modelling of the gain profile, and compare it with that typical for an etalon Raman (GeO 2 -doped) fibre. The both Raman gain profiles are quantified using the spontaneous Raman cross-sections derived with an original spectroscopic method. Extremely high accuracy of the multimode Gaussian decomposition is obtained for the Raman gain profiles. As a result, the Raman gain profiles can be presented in analytical form. A threshold spectral Raman profile is introduced and the lasing bands in the both single-mode fibres are simulated numerically. We discuss also the advantages of TiO 2 -doped fibres as the active media for fibre Raman lasing and compare their characteristics with those of the other fibre types.