Yoshihisa Takayama

OICETS on-orbit laser communication experiments

We present the results of the on-orbit free-space laser communications between the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) and the Advanced Relay and Technology Mission (ARTEMIS) geostationary satellite. We first introduce the history of developing OICETS and add some descriptions on characteristics of OICETS, where the performance of the optical communication terminal named the Laser Utilizing Communications Equipment (LUCE) is also stated. We summarize the on-orbit investigation results of LUCEs function and finally make a report on the inter-orbit laser communication experiment carried out by ARTEMIS and OICETS.

Overview of the inter-orbit and the orbit-to-ground laser communication demonstration by OICETS

The experiment results on the inter-orbit laser communications between OICETS and a geostationary satellite and the results of two kinds of orbit-to-ground laser communications between OICETS and ground stations are summarized. The geostationary satellite for the inter-orbit demonstrations is the European Space Agencys geostationary satellite, ARTEMIS, and the ground stations for the orbit-to-ground demonstrations are of the National Institute of Information, and Communications Technology (NICT) in Japan and the German Aerospace Center (DLR), respectively. The descriptions of those experiments contain some statistically analyzed results as well as data samples measured during the demonstrations. The authors present the overview of these demonstration progresses and discuss on the results.

Results of the optical downlink experiment KIODO from OICETS satellite to optical ground station Oberpfaffenhofen (OGS-OP)

Optical LEO downlinks from the Japanese OICETS to the optical ground station built by the German Aerospace Center (DLR) near Munich have been performed. This was the first optical LEO downlink on European grounds. The ground station received a 50-Mbit/s OOK signal at 847 nm on its 40-cm Cassegrain telescope and sent two spatially displaced beacon beams towards OICETS. Five out of eight trials could be performed successfully while the other three were hindered by cloud blockage. A BER of 10-6 has been reached. The elevation angle above the horizon ranged between 2° and 45°. The Fried parameter and the scintillation were measured with instruments inside the ground station. The beacon power received by the LUCE Terminal onboard OICETS has also been recorded. This paper describes the setup of the experiment and highlights the results of the measurement trials.

Ground-to-OICETS laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei of downtown Tokyo and a low earth orbit (LEO) satellite, the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) called Kirari, were successfully performed in March and May, 2006. The optical communication demonstration experiment at the optical ground station was conducted in cooperation between the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). Ten trials over the course of two months were conducted during the test campaign. Acquisition and tracking of the satellite were successful on seven days out of the assigned test days. The tests were unsuccessful during three out of the four days when it was cloudy or rainy, but they were successful on all six of the days when partly clear skies were predominant. For the uplink, the fluctuation of the received signal power was well minimized by using multi-beam laser transmissions. The bit error ratio (BER) on the downlink was measured to be as low as 10-5. The applicability of the onboard optical terminal was demonstrated, aiming not only for geostationary earth orbit (GEO)-LEO links but also for ground-to-LEO optical links.

Tracking and pointing characteristics of OICETS optical terminal in communication demonstrations with ground stations

The tracking and pointing performance of the Laser Utilizing Communications Equipment (LUCE) equipped on the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) is presented. The operation characteristics of LUCE observed in the ground-satellite communication demonstrations are focused on. Since the angular movement of LUCEs optical antenna required in the ground-satellite trials exceeds the specification demanded in the inter-satellite communications, the marginal performance for proper tracking and pointing can be observed. During the ground-satellite communication trials, the ground stations found periodical discontinuances in the optical link. By looking at the LUCEs telemetries, the cause of the repeated breaks is revealed.

Laser beam propagation in ground-to-OICETS laser communication experiments

The first bi-directional laser communication demonstration between an optical ground station and the Optical Inter-orbit Communication Engineering Test Satellite (OICETS) was successfully conducted in March, May, and September, 2006, with an uplink of 2 Mbps and a downlink of 50 Mbps. The optical ground station, located in Koganei, Tokyo, Japan, is operated by the National Institute of Information and Communications Technology (NICT), Japan. Four laser beams were transmitted from the optical ground station to the OICETS satellite in order to reduce the optical signals intensity fluctuation due to atmospheric turbulence. The optical scintillation as a function of the number of beams and the frequency response were measured, and the uplink and downlink laser transmission results were obtained.

Observation of atmospheric influence on OICETS inter-orbit laser communication demonstrations

The experimental results of an inter-orbit laser communication performed under an atmospheric influence is presented. The demonstration was planned so that the optical link was supposed to graze the earths rim because of the satellite revolution around the earth. The trial was successfully carried out on 5th April, 2006. The measured experimental data are introduced to show the temporal behavior of the OICETSs optical terminal. The atmospheric influence on the optical link is calculated with a theoretical model to obtain a probability density of normalized intensity as a predictive value. The probability density is also estimated from the experimentally measured data. The comparison shows that the theoretical prediction well describes the experimental results.

An overview of the KODEN experiment between the OICETS satellite and the optical ground station in NICT

SummaryThe KODEN is a first in-orbit laser communication demonstration between a low earth orbit satellite called OICETS/Kirari and an optical ground station at the National Institute of Information and Communications Technology (NICT) in Koganei, Tokyo. Optical links could always be established even under atmospheric turbulence when partly clear skies were predominant in March, May, and September, 2006. The uplink and downlink bit error ratios were measured to be 10−7–10−3. This achievement is a milestone for future high-data-rate satellite communications.ZusammenfassungDas Akronym KODEN steht für die erste erfolgreiche Demonstration eines Laserkommunikationsexperiments zwischen dem Satelliten OICETS/Kirari in erdnaher Umlaufbahn (LEO) und der optischen Bodenstation des staatlichen Institutes für Information und Kommunikation (NICT) in Koganei, Tokio. Trotz atmosphärischer Turbulenzen konnte die optische Verbindung stets hergestellt werden, unter vorwiegend wolkenfreiem Himmel in den Monaten März, Mai und September 2006. Die Fehlerbitraten der beiden Kommunikationskanäle lag zwischen 10−7–10−3. Das Experiment stellt einen Meilenstein in der Entwicklung zukünftiger Satellitenkommunikationssyteme mit hohen Datenraten dar.

Efficient pump beam coupling in EDFA with two mutually pumped phase conjugate mirrors

In the bidirectional pumped Erbium Doped Fiber Amplifier (EDFA), we propose the new method with two Mutually Pumped Phase Conjugate Mirrors (MPPCMs) to couple the pump beam into the fiber. This method makes it possible to couple the pump beam into the propagation mode of the fiber without high precision adjustment by the characteristic of MPPCM. Additionally, high precision readjustment is not required when a LD, fiber or lens is exchanged due to failures. In our method, it is important to obtain high diffraction efficiency of MPPCM for high coupling efficiency between the pump beam and the fiber. Diffraction efficiency of MPPCM depends on the intensity ratio of two incident beam intensities inside the PRC. We analyze the coupling efficiency for the intensity ratio of two pump beams, and show the optimum intensity ratio of two pump beams. Then, we perform an experiment to couple the pump beam (Ar+ laser 514.5nm) to the fiber (multimode fiber of 62.5μm core diameter). In the experiment, coupling efficiency higher than 35% was confirmed. Moreover, in our method, the time to complete the coupling depends on the beam intensities in the early stage of the process. Therefore, we also propose the 4f imaging system to achieve a faster coupling at the early stage, and design the optical system to improve the time to complete the coupling in our method.

A Ulexite-based animation recording system by random reference patterns

We propose a simple, compact and high-security holographic optical memory system using Ulexite in order to produce random patterns of reference beam. 100 hologram multiplexing was achieved by multiplexing exposure, rotating Ulexite by 0.2 degrees every time with LiNbO3 crystal as a recording medium. Moreover, with this system, animation readout images can play for approximately 8 seconds by continuous rotation of Ulexite. As a natural stone, the exactly same Ulexite is very difficult to be found or replicated. Basic experimental results show that Ulexite can be used as a security key for its image-reproducibility and BER calculations.