Expanded beam (EB) connector includes a fiber holder having an alignment channel that is configured to receive an optical fiber. The alignment channel has a channel opening and extends from the channel opening to a channel end face. The EB connector also includes an optical substrate having a three-dimensional (3D) waveguide that includes a waveguide core and a cladding. The optical substrate includes the channel end face. The waveguide core extends lengthwise between first and second coupling faces of the waveguide core. The first coupling face is at least a portion of the channel end face. The first coupling face is configured to optically couple to the optical fiber disposed within the alignment channel. The second coupling face defines an exterior of the optical substrate. The waveguide core is shaped to change a mode field diameter and a numerical aperture of light propagating between the first and second coupling faces.