Multicore optical fiber

A circular multicore optical fiber, comprising:

• a glass matrix having a front endface, a back endface, a length, a refractive index n20, and a central axis;
• at least 3 cores arranged within the glass matrix, each core having a center positioned along at least one diameter of the glass matrix and wherein any two adjacent cores have a core center to core center spacing of less than 29 microns, wherein the cores are positioned generally parallel to the central axis between the front and back endfaces and having respective refractive indices n50, wherein n50>n20, wherein each core and the glass matrix define a waveguide;
• and
• a plurality of trench layers, wherein each trench layer is positioned between a corresponding core and the glass matrix, each trench layer having an outer radius of less than or equal to 14 microns and a trench volume of greater than 50% Δ micron2;
• wherein the optical fiber has a mode field diameter of greater than about 8.2 microns at 1310 nm, and
• wherein the optical fiber has an outer diameter of less than about 130 microns.