An optical fiber, comprising: a plurality of individual cores (41a-e) surrounded by a respective depressed inner cladding extending through a common outer cladding, wherein each individual core (41a-e) supports at least one local transverse spatial mode carrying a respective data signal, wherein the individual cores (41a-e) and surrounding cladding are structured to support propagation of plurality of desired signal-carrying modes, while suppressing undesired modes, thereby supporting the propagation of one or more spatially multiplexed signals, wherein the individual cores (41a-e) and surrounding cladding are configured such that undesired modes have respective effective indices that are less than the cladding index so as to result in leaky modes that dissipate into the surrounding cladding, and such that the index spacing between the desired mode having the lowest effective index and the leaky mode with the highest effective index is large so as to reduce coupling therebetween, wherein the core-to-core spacing is configured to maintain an acceptably low level of mode-coupling between cores (41a-e) characterised in that each individual core (41a-e) has an outer radius of 7.375 μm, a relative percentage index difference Δ=0.0024, and an alpha parameter α=25; wherein each of the individual core (41a-e) is surrounded by a respective depressed inner cladding region having an inner radius of 7.375 μm, a width of 10.5 μm, an outer radius of 17.875 μm, and a Δ=-0.0050, and wherein the common outer cladding has a Δ=0. a plurality of individual cores (41a-e) surrounded by a respective depressed inner cladding extending through a common outer cladding, wherein each individual core (41a-e) supports at least one local transverse spatial mode carrying a respective data signal, wherein the individual cores (41a-e) and surrounding cladding are structured to support propagation of plurality of desired signal-carrying modes, while suppressing undesired modes, thereby supporting the propagation of one or more spatially multiplexed signals, wherein the individual cores (41a-e) and surrounding cladding are configured such that undesired modes have respective effective indices that are less than the cladding index so as to result in leaky modes that dissipate into the surrounding cladding, and such that the index spacing between the desired mode having the lowest effective index and the leaky mode with the highest effective index is large so as to reduce coupling therebetween, that undesired modes have respective effective indices that are less than the cladding index so as to result in leaky modes that dissipate into the surrounding cladding, and such that the index spacing between the desired mode having the lowest effective index and the leaky mode with the highest effective index is large so as to reduce coupling therebetween, wherein the core-to-core spacing is configured to maintain an acceptably low level of mode-coupling between cores (41a-e) characterised in that each individual core (41a-e) has an outer radius of 7.375 μm, a relative percentage index difference Δ=0.0024, and an alpha parameter α=25; wherein each of the individual core (41a-e) is surrounded by a respective depressed inner cladding region having an inner radius of 7.375 μm, a width of 10.5 μm, an outer radius of 17.875 μm, and a Δ=-0.0050, and wherein the common outer cladding has a Δ=0.