A steerable-light-path optical device, comprising: a light transceiver having an external light path associated therewith, wherein the light transceiver is configured to: transmit a first light beam comprising a first discrete infrared wavelength, and receive a second light beam comprising a second discrete infrared wavelength different from the first discrete infrared wavelength, and wherein the first light beam and the second light beam are substantially parallel to each other and to the light path; and a path-steering device configured to control the direction of the light path relative to a steering axis, wherein the path-steering device comprises a first beam-deviation optical element including a first prism structure comprising a first-structure prism having a first diffraction grating on a surface thereof, wherein the steering axis passes through the first beam-deviation optical element, a second beam-deviation optical element including a second prism structure comprising a second-structure prism having a second diffraction grating on a surface thereof, wherein the steering axis passes through the second beam-deviation optical element, and a rotational drive operable to rotate at least one of the first beam-deviation optical element and the second beam-deviation optical element about the steering axis, wherein the device is configured so that the first light beam and the second light beam are substantially coincident with each other and with the light path. a light transceiver having an external light path associated therewith, wherein the light transceiver is configured to: transmit a first light beam comprising a first discrete infrared wavelength, and receive a second light beam comprising a second discrete infrared wavelength different from the first discrete infrared wavelength, and wherein the first light beam and the second light beam are substantially parallel to each other and to the light path; and transmit a first light beam comprising a first discrete infrared wavelength, and receive a second light beam comprising a second discrete infrared wavelength different from the first discrete infrared wavelength, and wherein the first light beam and the second light beam are substantially parallel to each other and to the light path; and a path-steering device configured to control the direction of the light path relative to a steering axis, wherein the path-steering device comprises a first beam-deviation optical element including a first prism structure comprising a first-structure prism having a first diffraction grating on a surface thereof, wherein the steering axis passes through the first beam-deviation optical element, a second beam-deviation optical element including a second prism structure comprising a second-structure prism having a second diffraction grating on a surface thereof, wherein the steering axis passes through the second beam-deviation optical element, and a rotational drive operable to rotate at least one of the first beam-deviation optical element and the second beam-deviation optical element about the steering axis, wherein the device is configured so that the first light beam and the second light beam are substantially coincident with each other and with the light path. a first beam-deviation optical element including a first prism structure comprising a first-structure prism having a first diffraction grating on a surface thereof, wherein the steering axis passes through the first beam-deviation optical element, a second beam-deviation optical element including a second prism structure comprising a second-structure prism having a second diffraction grating on a surface thereof, wherein the steering axis passes through the second beam-deviation optical element, and a rotational drive operable to rotate at least one of the first beam-deviation optical element and the second beam-deviation optical element about the steering axis, wherein the device is configured so that the first light beam and the second light beam are substantially coincident with each other and with the light path.