Mitsuo Nohara

Far-field pattern measurement of on-board laser communication equipment by free-space laser transmission simulator

We measured far-field patterns of on-board laser communication equipment (LCE) using a free-space laser transmission simulator. The LCE was developed by Communications Research Laboratories (CRL) for basic optical communications experiments using the Japans Engineering Test Satellite-VI (ETS-VI), while the free-space simulator is being developed by ATR as an on-ground test system for laser communication terminals. Far-field patterns of an on-board laser communication terminal have measured experimentally by an on-ground test system for the first time. The LCE emitted a laser beam whose peak directive gain was 104.6 dB and whose beamwidth was 31 X 19 (mu) rad in full-width at half-maximum. It was confirmed that the transmitted beam of the LCE met the experimental requirements. Through the measurement, the free-space laser transmission simulator demonstrated its effectiveness in an on-ground measurement of the beam characteristics of a laser communication terminal.

Location and Propagation Status Sensing of Interference Signals in Cognitive Radio

In a Cognitive Radio system, it is essential to recognize and avoid sources of interference signals. This paper describes a study on a location sensing scheme for interference signals, which utilizes multibeam phased array antenna for cognitive wireless networks. This paper also elucidates its estimation accuracy of the interference location for the radio communication link using an OFDM signal such as WiMAX. Furthermore, we use the frequency spectrum of the received OFDM interference signal, to create a method that can estimate the propagation status. This spectrum can be monitored by using a software defined radio receiver.

Aspheric lens laser diode collimator design for optical intersatellite communications

A design for a laser diode collimator using aspheric lens technology was employed to achieve a 5-mm-diameter circular output beam with minimal wavefront aberration, and the minimum number of lenses of the smallest size. The presently designed collimator can achieve a wavefront aberration of better than λ/100 with a pair of aspheric anamorphic lenses, and a total length of 30 mm.

A High-power Optical Intersatellite Link Transmitter Using a Broad-area Semiconductor Amplifier

A traveling-wave-type, broad-area semiconductor amplifier has been applied to an optical intersatellite link transmitter to achieve a high power output and a good beam profile.

Aspheric lens LD collimator for an optical intersatellite link

An LD collimator was constructed, using an aspheric lens configuration for the transmitter of an optical intersatellite link. The design results show that the 5 mm diameter circular LD output beam whose rms wavefront aberration is better than (lambda) /100 is available in a two-or three-lens configuration. The first fabrication trial of the three-lens configuration achieved an rms wavefront aberration of better than (lambda) /16. This result proves that it is possible to obtain high wavefront performance, while reducing the required number of lenses when an aspheric lens configuration is adopted.

PRESENT AND FUTURE ACTIVITIES IN OPTICAL SPACE COMMUNICATIONS AT ATR

In ATR, we have been conducting research on an optical inter-satellite link(ISL), focusing on a high-power transmitter and precise optical beam control technologies, both of which play a very important role in the optical ISL systems. This paper describes current optical ISL research at ATR: development of an intensity modulatioddirect detection(IM/DD) modem, LD amplifier experiments, development of a free-space simulator for laser transmission and evaluation of pointing/tracking parameters for various orbit configurations. The evaluations show that a system in a low earth orbit(LE0) satellite tracking a target in geostationary orbit(GE0) will be simplified when a particular gimbal axis configuration is selected.

Optical ISL transmitter design that uses a high-power LD amplifier

An optical intersatellite link transmitter which uses a high-power laser diode (LD) amplifier so as to simultaneously achieve a high output power, fast frequency response, and good beam profile, is presented. Calculated results indicate that a good beam profile could be achieved with a travelling-wave type broad area LD amplifier when an input beam is focused just in front of the input facet of the LD amplifier. It is also shown that optical output power is controllable as a parameter of the injection current to the LD amplifier.