A bent optical fiber coupler (100) that employs at least one optical fiber (10) is disclosed. The coupler includes a curved optical fiber guide channel (200) having a strong curve. The optical fiber(s) held within the optical fiber guide channel have a bend corresponding to the guide channel curve. The fiber end portions are optionally disposed within a straight fiber guide (160) at a coupler input/output end, which is preferably configured to have a standard connector geometry. Use of nanostructured fibers for the at least one optical fiber allows for strong bends having tight radii of curvature without imparting significant attenuation. Coupler assemblies that include the coupler optically coupled to at least one opto-electronic device (310) are also disclosed.