Optical communications in space is the most significant application of modern optical transmission
technology. This paper outlines optical communications in space and its history. Also described are
current expectations and subjects for future development.
In this paper, the research and development results and trends in the field of satellite-to-ground laser
communication technology are described. Furthermore, the development challenges related to laser
propagation through the atmosphere will be discussed in relation to the planned experiments and current
studies carried out by NICT during the current development project, HICALI.
Adaptive optics in astronomy has opened a new era especially for a ground-based 8 to 10 m telescopes.
The effect of atmospheric turbulence is no longer restriction to achieve a diffraction limited spatial
resolution for large telescopes. Stellar image size has been improved by a factor of more than 10.
Further, laser guide star adaptive optics expands the possibility to observe the sky area, where no bright
star can be found as a reference source of measuring a wavefront. This article introduces a basic concept
of laser guide star adaptive optics, laser system and a system components to create a laser beacon, hybrid
control system of laser guide star adaptive optics with tip-tilt and focus natural guide stars, laser safety
operation to protect aircrafts and satellites, as well as to avoid a contamination to the adjacent telescopes.
We present preliminary study on optical phased array technology aiming free-space optical
communication for optical feeder link of High Throughput Satellite in the future. The propagation of
non-Gaussian beams produced with optical phased array has been estimated less affected by atmospheric
turbulence than a single Gaussian beam. 2-elements optical phased array has also demonstrated both
beam pointing control and 5.6 Gbps free-space optical communication.
Application developments are in an early phase for the space transmission of laser energy. The recent
development of drone systems has been remarkable, and a power beaming system for drones is a
promising technology. The atmospheric phenomena, which inhibit the optical energy transmission, are
thermal blooming and atmospheric turbulence. In this article, we describe the influence of these
phenomena on the transmitted wavefront of the laser beam and our research progress on wavefront
We describe procedures to estimate the atmospheric fluctuations based on optical intensity measurements
to use such methods for the free-space laser transmission toward moving objects. Focusing on some
indices of atmospheric characteristics, the relations are indicated between the indices and the
requirements in the system specifications. We introduce approaches to assess the atmospheric
fluctuations and issues for laser transmission to moving objects.
We propose the substitution of a transmission-type holographic optical element (HOE) for a finepointing
mechanism (FPM) in equipment that receives free-space optical communications. According to
the concept, we experimentally evaluated the potential of our proposed HOE, which was fabricated. We
investigated the dependence of the fiber coupling efficiency of the diffracted light intensity as a function
of the incident angle of the HOE’s reference beam.