Multicore optical fibers with low bend loss, low cross-talk, and large mode field diameters In some embodiments a circular multicore optical fiber includes a glass matrix; at least 3 cores arranged within the glass matrix, wherein any two cores have a core center to core center spacing of less than 29 microns; and a plurality of trench layers 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.