Amplifying optical fibers

An amplifying optical fiber comprising:

• a common cladding comprising a radius defining a glass portion of the amplifying optical fiber and having a relative refractive index delta4;
• and
• a plurality of waveguides extending through the common cladding, each waveguide of the plurality of waveguides comprising a core region, an inner cladding region encircling and directly contacting the core region, and a depressed cladding region encircling and directly contacting the inner cladding region, wherein:
• the core region of each waveguide comprises from greater than or equal to about 500 ppm and less than or equal to about 10,000 ppm Er2O3 and a core maximum relative refractive index delta1max;
• the inner cladding region of each waveguide comprises an inner cladding relative refractive deltaΔ2;
• the depressed cladding region of each waveguide comprises a minimum depressed relative refractive index A3min and a trench volume VT greater than or equal to 10% μm2 and less than or equal to 60% μm2;
• Δ1max>Δ2>Δ3min and Δ4>3min;
• and
• an inter-waveguide crosstalk between each waveguide of the plurality of waveguides and a nearest neighbor of each waveguide is less than or equal to −30 dB as measured for a 50 m length of the amplifying optical fiber comprising a bend radius of less than or equal to 70 mm operating at a wavelength of 1550 nm;
• wherein the core region of each waveguide comprises greater than or equal to 1 wt.% and less than or equal to 20 wt.% Al2O3.