Uncoupled multicore optical fiber

A method of bidirectional transmission over a multicore optical fiber, wherein the multicore optical fiber comprises a first plurality of core portions and a second plurality of core portions disposed within a common cladding having a refractive index ΔCC and an outer diameter DCC greater than or equal to 120 μm and less than or equal to 130 μm, the method comprising:

• transmitting a first optical signal over at least one core portion of the first plurality of core portions in a first direction, wherein the at least one core portion of the first plurality of core portions comprises:
• a core region comprising an alkali dopant and having a relative refractive index Δ1,1 relative to pure silica;
• and
• a trench region encircling the core region, the trench region comprising a relative refractive index Δ1,3 relative to pure silica, wherein the common cladding directly contacts the trench region, and wherein Δ1,1>ΔCC>Δ1,3;
• and
• transmitting a second optical signal over at least one core portion of the second plurality of core portions in a second direction opposite the first direction, wherein the at least one core portion of the second plurality of core portions comprises:
• a core region comprising an alkali dopant and having a relative refractive index Δ2,1 relative to pure silica;
• and
• a trench region encircling the core region, the trench region comprising a relative refractive index Δ2,3 relative to pure silica, wherein the common cladding directly contacts the trench region, and wherein Δ2,1>ΔCC>Δ2,3;
• wherein a counter-propagating crosstalk at 1550 nm between two adjacent core portions of the first plurality of core portions and the second plurality of core portions is less than or equal to −40 dB per 100 km of the uncoupled multicore optical fiber.