Yasumasa Hisada

Trade-off between IM-DD and coherent system in high-data-rate optical interorbit links

Trade-off between Intensity Modulation Direct Detection (IM- DD) and coherent system oriented to the inter-orbit lightwave communication link is performed. Improvement in sensitivity of IM-DD system adopting high power optical fiber booster/pre- amplifiers is discussed preciously. In this paper, IM-DD system with booster/pre-amplifier and five kinds of coherent system (ASK-heterodyne, FSK-heterodyne, PSK-heterodyne, DPSK- heterodyne, and PSK-homodyne) are compared for high-data rate communication. Numerical analysis shows the superior characteristics of coherent communication system in low BER transmission under severe ASE noise.

Double-clad Nd-doped fiber amplifiers for transmitter of interorbit communications

Since Nd-doped fiber amplifiers could be used as power amplifiers for high data rate optical inter-orbit communications, we have fabricated and studied a square shaped double clad Nd-doped fiber for the 1.06 micrometers amplifier characteristics. The output signal power is not saturated up to 1 watt level using the single frequency broad linewidth signal source. It is, however, saturated at a few hundred milliwatts by a stimulated Brillouin scattering effect using narrow linewidth non-modulated linewidth signal source. The maximum output power of 1.17 Watts is obtained with extraction efficiency of 37 percent from absorbed pump power. The net gain is estimated more than 25dB.

High-power optical amplifier for optical interorbit communications

The laser transmitter systems have been our latest and largest topic in optical inter-orbit communications (OIC). We believe that laser subsystem using erbium doped fiber amplifier (EDFA) or neodymium doped fiber amplifier (NDFA) are eminently suitable for high power and wide bandwidth transmitters. Thus, we have been testing commercial EDFA and have obtained good results. In addition, results of FFP measurement of transmitted laser power from single mode silica fiber are also discussed. It is also feasible to apply transmitter subsystems using EDFA or NDFA to future OIC systems, but there are some optical features that have to be considered when designing OIC equipment.

Present and future of optical intersatellite communication research at the National Space Development Agency of Japan (NASDA)

We report our research results of system trial fabrication and tests as the first step of Optical Intersatellite Communication research. Second, the results of the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) feasibility study are reported. Last, we describe the draft results of a conceptual study of a future optical communications system that will be needed as space infrastructure.

Fine pointing mechanism using multi-layered piezo-electric actuator for optical ISL system

A new type of the fine pointing mechanism (FPM) was examined as part of the optical ISL studies conducted by NASDA. Compact piezo-electric mirror deflecting mechanism (MDM) , having a very high resolution (less than 3 irad) was fabricated, and the performance of the MDM was evaluated aiming for application in the ISL optical FPM. The fundamental performance of the fine pointing assembly (FPA) in optical ISL with the multi-layered piezo—electric MDM was confirmed sufficient for optical ISL having pointing error by disturbance (± 0.75 irad) and pointing angle (± 720 Mrad). It was confirmed that the examined FPM is suitable for the fine pointing of optical ISL, by combining appropriately designed optics and coarse pointing assembly (CPA) , through a preliminary system design.

INVESTIGATION ON ENCODING MODULATION EQUIPMENT FOR HIGH SPEED DATA TRANSMISSION

Transmission data are increasing because of larger satellites and higher performances of mission equipment, so QPSK will not be effective in near future. It is possible to transmit higher speed data if satellite antenna and transmission power are larger or earth station receiving performance is better, but there are limitations to these improvements. So, it is necessary to adopt encoding modulation techniques. Applicability of encoding modulation system to satellite communication links is examined in case of high speed data transmission. As the result, trellis-coded 8PSK and trellis-coded 16QAM with Reed-Solomon encoding are applicable in Earth observing satellite communication link and geostationary communication link Corrective actions on the communication line fault are investigated and it was found that low speed data transmission mode was effective in prevention of the line fault. Performances of above two coded modulation techniques are calculated by simulation under non-linear transmission way. It was found that they are better than that of non-encoding QPSK Configurations and specifications of two equipment whose data rate are about 300 Mbps are investigated. We decide to manufacture Nyquist low-pass filters in digital circuits, and it is shown that they can be realized using high speed RAM.

Trial manufacturing results and characteristics of InGaAs-quadrant detectors (QD) as a fine pointing sensor

We would like to report our research and development on InGaAs-QD as a part of our research on optical inter-orbit communication technology. Optical transmitter subsystems using Erbium doped fiber amplifier (EDFA, wavelength 1550nm) and Neodymium doped fiber amplifier (NDFA, wavelength 1060nm) have been candidate subsystems of future optical-IOC system. However, present fine pointing sensors, such as Si- QD and Si-CCD, have little sensitivity at 1060nm, and no sensitivity at wavelengths longer than 1100nm. There is a need for a fine pointing sensor that has a high sensitivity at 1060nm and 1550 nm. Thus, we tried to manufacture InGaAs- pin-QD, adding optical surface separation processes into conventional production processes of commercially available InGaAs-pin-PD. InGaAs-QD with high sensitivity and low dark current was produced. Our analysis shows that these devices are suitable as a fine pointing sensor of optical-IOC systems using EDFA or NDFA as a transmitter subsystem.

Laser transmitter systems for high-data-rate optical interorbit communications

We would like to report present status of our research on future optical inter-orbit communications. First, we will discuss the key subsystem, that is high power laser transmitter subsystem, making comparison among EDFA, Nd:YAG laser, NDFA and MOPA-LD. Second, we will describe the results of our study that optical downlink would be required in future, mentioning its bottle neck technologies and transmittance laser subsystem. Finally, we will raise a question on a space interoperability, which will be the next item of consideration among concerning entities organization.