LEO-to-ground optical communications using SOTA (Small Optical TrAnsponder) – Payload verification results and experiments on space quantum communications

Abstract

Free-space optical communications have held the promise of revolutionizing space communications for a long time. The benefits of increasing the bitrate while reducing the volume, mass and energy of the space terminals have attracted the attention of many researchers for a long time. In the last few years, more and more technology demonstrations have been taking place with participants from both the public and the private sector. The National Institute of Information and Communications Technology (NICT) in Japan has a long experience in this field. SOTA (Small Optical TrAnsponder) was the last NICT space lasercom mission, designed to demonstrate the potential of this technology applied to microsatellites. Since the beginning of SOTA mission in 2014, NICT regularly established communication using the Optical Ground Stations (OGS) located in the Headquarters at Koganei (Tokyo) to receive the SOTA signals, with over one hundred successful links. All the goals of the SOTA mission were fulfilled, including up to 10-Mbit/s downlinks using two different wavelengths and apertures, coarse and fine tracking of the OGS beacon, space-to-ground transmission of the on-board-camera images, experiments with different error correcting codes, interoperability with other international OGS, and experiments on quantum communications. The SOTA mission ended on November 2016, more than doubling the designed lifetime of 1-year. In this paper, the SOTA characteristics and basic operation are explained, along with the most relevant technological demonstrations.

Satellite-mediated quantum atmospheric links

“…Indeed, in this case the link length is smaller compared to the link's lengths for inclined satellites. However, in many practical cases the mechanical mount of the OGS receiver or sender telescopes prevents one to use the whole advantage of the link that can lead to the interruption of the communication process near small zenith angles of the observer [39]. In such cases the trade-off exists between the use of optimal propagation path and the duration of communication session.…”

“…As a consequence the transmitted beam shows smaller diffraction-induced broadening and small beam wandering due to refraction on turbulent atmospheric inhomogeneities. This is the reason why the majority of quantum optical experiments are being performed in downlink configuration [5,8,9,39]. Under comparable atmospheric conditions an uplink communication shows inferior performance due to the influence of atmospheric turbulence already on early stages of optical signal transmission.…”

“…The following problems must be overcome for successfully establishing a feasible quantum communication with satellites: the relative motion of the communication parties [25][26][27], the influence of gravity [28,29], the clock synchronization problem [30,31], acquisition, tracking and pointing issues with moving platforms [32][33][34], the influence of background noise [35][36][37], to name just a few. For low Earth orbiting (LEO) satellites, the communication time is limited to a few minutes [38,39] and this puts additional tight bounds on communication security. Finally, Earth's atmosphere contributes significantly to the loss budget and to the deterioration of the quantum signal due to diffraction, scattering, absorption, and atmospheric turbulence [40][41][42].…”

QKD from a microsatellite: The SOTA experience

“…The Japanese National Institute of Information and Communications Technology (NICT) developed a small space lasercom terminal called SOTA (Small Optical TrAnsponder) to be embarked on the microsatellite SOCRATES (Space Optical Communications Research Advanced Technology Satellite) [8]. SOCRATES was launched in May 2014 into a…”

Optical communication on CubeSats — Enabling the next era in space science

“…These signals were received using a photomultiplier coupled to a 25-cm ground telescope [18]. The first proper lasercom system onboard a small satellite was NICT's SOTA [19] onboard SOCRATES ( Fig. 3), which was launched in May 2014 into a ~600 km LEO orbit, and it was fully operative until November 2016.…”