A bidirectional optical communication system employing one or more spans of hollow-core optical fiber. In at least some embodiments, the hollow-core optical fiber can be used to simultaneously transmit, in opposite directions, optical data signals having substantially the same carrier wavelength. In such embodiments, the spectral efficiency of the bidirectional optical communication system can advantageously be about two times higher than the spectral efficiency of a comparable conventional optical communication system employing only solid-core optical fibers. In some embodiments, the bidirectional optical communication system may have a solid-core optical fiber end-connected between two spans of hollow-core optical fiber. In some embodiments, the bidirectional optical communication system may use a hollow-core optical fiber for transmission of different WDM optical data signals in opposite directions.