TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Fiber: The central core region comprises germanium at a concentration of 0.1-4 (preferably 0.5-3.5) wt.% taken at any given radius. The concentration of germanium in the central core region is constant or varies parabolically over the radial distance and decreases within the central core region of 0 to ra, and remains constant over the inner cladding region. The concentration of fluorine increases as the radial distance increases from the central axis 0 to the outer circumference of the central core region having ra, preferably the concentration of fluorine at ra is 0.005-7 (preferably 1-5) wt.% at radius ra. The concentration of fluorine in the central core region varies parabolically over the radial distance and increases within the central core region of 0 to ra and remains constant over the inner cladding region. The inner cladding region comprises germanium at a concentration of 0.1-4 (preferably 0.5-3, especially 1-1.6) wt.% taken at a given radius. In the fiber, attenuation at 850 nm is less than 2.3 (preferably less than 2.1, especially less than 2) dB/km, and/or attenuation at 1310 nm is less than 0.6 (preferably less than 0.5, especially less than 0.4) dB/km, and less than 0.5 db at 850 nm and at 1300 nm for 100 turns around a cylinder of 75 mm diameter. The Numerical Aperture (NA) of the core is 0.200 plus minus 0.015, where the core radius (ra) is 25 plus minus 2.5 mu m. The inner cladding comprises at least one trench, where the trench preferably has a width of 2-33 (preferably 2-8)% of the core radius (ra), and/or the trench has depth Delta nt with respect to the inner cladding of -5x 10-3 to -1x 10-3, and/or the trench is located between the core radius (ra) and the outer radius (ric). The fiber (F1) further comprises an outer cladding surrounding the inner cladding, where the outer cladding has a higher refractive index than the inner cladding region and is silica doped with at least one dopant (preferably germanium and/or fluorine), where the outer cladding is pure silica, preferably the outer cladding comprises deposited glass layer, optionally fluorine and/or germanium doped and preferably the deposited glass layer is obtained by an inside plasma deposition process. The outer radius (ric) of the inner cladding region (ric) is Y1-62.5 (preferably 40-50) mu m, where Y1 is greater than or equal to ra+5 mu m. EXAMPLE - No suitable example given.