A small-mode-volume, vertical-cavity, surface-emitting laser (VCSEL). The VCSEL includes an active structure to emit light upon injection of carriers, and two reflecting structures at least one of which is a grating reflector structure. The active structure is disposed within at least one of the reflecting structures. The reflecting structures are configured as a vertical-cavity resonator of small mode-volume. An optical-bus transmitter including a plurality of small-mode-volume VCSELs, and a system including at least one optical bus and at least one optical-bus transmitter in a digital-information processor, or a data-processing center, are also provided.