Uncoupled-core multicore optical fiber with reduced cross talk

An uncoupled-core multicore optical fiber comprising:

• at least two core portions, each core portion comprising:
• a core having a radius r1 and a relative refractive index Δ1 relative to pure silica, the core being doped with at least one of sodium, potassium, and rubidium;
• and
• a depressed-index cladding having a radius r2 and a relative refractive index Δ2 relative to pure silica such that Δ2<Δ1, the depressed-index cladding surrounding and directly contacting the core, a volume V2 of the depressed-index cladding being about 5.0% Δ-micron2 to about 37.0% Δ-micron2;
• and
• a common cladding having a radius r3 and a relative refractive index Δ3 relative to pure silica such that Δ2<Δ3<Δ1, the common cladding surrounding and directly contacting the depressed-index cladding,
• wherein:
• a cable cutoff wavelength of each core portion is about 1530 nm or less,
• an effective area of each core portion is about 100 micron2 to about 135 micron2 at a wavelength of 1550 nm,
• each core portion comprises an attenuation at a wavelength of 1550 nm of about 0.165 dB/km or less,
• a center-to-center spacing between centerlines of adjacent core portions is about 48 microns to about 60 microns,
• co-propagating cross talk between the at least two core portions is about −40 dB or less per 100 km of optical fiber for a bend diameter of 140 mm, and
• counter-propagating cross talk between the at least two core portions is about −45 dB or less per 100 km of optical fiber.