###### Abstract
Regarding the PSC fibers intrinsic losses, they are partially explained by the Rayleigh scattering losses, \(\alpha\), which are caused by density fluctuations of the pure or F-doped glasses constituting the fiber core and cladding respectively. These scattering losses could be described in the case of a single-component glass such as silica by the following equation [16]:  
\[\alpha=\frac{8\pi^{3}}{3\lambda^{4}}n^{8}p^{2}kT_{g}\beta_{T} \tag{1}\]  
where \(T_{g}\) is the glass fictive temperature [17], \(\beta_{T}\) the isothermal compressibility at \(T_{g}\), \(p\) the photoelastic constant, \(k\) the Boltzmann's constant, \(n\) the refractive index and \(\lambda\) the wavelength. For silica-based fibers (either PSC or F-doped), the fictive temperature \(T_{g}\) is an important parameter governing the Rayleigh losses level. This criterion is strongly influenced by the amount of impurities introduced during the manufacturing process, mainly hydroxyl groups (Si-OH) and the Cl impurities [16]. A decrease of \(T_{g}\) usually leads to a decrease of the Rayleigh losses [16] and then a fiber with reduced attenuation in the UV-visible range is achieved. The relative amounts of OH groups and Cl impurities are strongly anti-correlated for most of the preform deposition processes and can be tuned by varying the production parameters. As a consequence, several PSC optical fiber classes can be defined as: \"wet\" fibers (_high-OH content_, _low-Cl content_), \"dry\" fibers (_low-OH_, _high-Cl contents_). However, less-available _low-OH_, _low-Cl_ fibers have also been produced, mainly in Russia [18]. Depending on the PSC fiber type, the attenuation in the UV-Vis differs due to the generation of some pre-existing (with respect to the irradiation) defects, mainly during the drawing process of the preform into the fiber. These defects (nature/concentration), and then the fiber attenuation, depend on the glass impurity levels too and are usually of similar structure than some of the radiation-induced defects [19]. This is the case, for example, of the so-called drawing-induced defect (DID) that corresponds to the non-bridging oxygen hole center (NBOHC, \(\equiv\)Si-O\(\bullet\)) structure having absorption bands peaking at 6.4 eV (\(\sim\)194 nm), 4.8 eV (\(\sim\)258 nm) and 1.97 eV (\(\sim\)630 nm) [20]. It has been shown that this center is created during the drawing (or by the irradiation) through the breakage of a strained (\(\equiv\)Si-O-Si\(\equiv\))' bond, a process that also leads to the generation of a SiE' (\(\equiv\)Si\(\bullet\)) defect that absorbs at shorter wavelengths, around 5.8 eV (\(\sim\)214 nm) [21]:  
\[(\equiv\mathrm{Si-O-Si}\equiv)^{*}\xrightarrow{drawing\ or\ radiations}\equiv \mathrm{Si-O\bullet}+\ \equiv\mathrm{Si\bullet} \tag{2}\]  
DIDs are mainly observed in optical fibers presenting the lower OH amount (\"dry\" fibers) [19]. As a general rule, the \"wet\" fibers are more adapted for operation in the UV range while \"dry\" fibers are suitable for IR operation, as they do not present the strong absorption peak related to the Si-OH at around 1380 nm and the associated overtones. Depending on the application requirements, both fiber types can be selected for visible transmission. Under irradiation, these PSC fibers also exhibit different radiation responses as different point defects will contribute to the RIA levels.