Yoshio Karasawa

Ultrahigh-speed optical-beam steering by optical phased array antenna

Presented in this paper is an introduction of a fiber-type optical phased array antenna for free- space optical communications. Optical phased array antenna is a phased array antenna operated at optical frequency. The high speed beam steering, spatial power combining, and flexible beam forming characteristics of them will drastically improve the performance of future free-space optical communication systems. The system design of a fiber-type optical phased array which can steer an optical beam in 2-dimension is reviewed. Fundamental characteristics of the integrated optical beam forming network (BFN) are shown. The wide bandwidth response up to 924 MHz of optical phase shifters, which enables high speed beam steering, is highlighted. Radiation patterns demonstrate coherent spacial power combining.

An algorithm for a DBF self-phased MRC array operated in mobile-satellite multipath channels

This paper introduces a self-phasing algorithm based on antenna diversity combining scheme designed for digital beamforming antennas to be operated in multipath channels. In reception, this algorithm allows self-beam steering toward the directions of direct and multipath signal arrivals, to recombine them because it regards the multipath signals as including desired information. In transmission, in contrast, the beam can be steered only toward the direction of a direct signal arrival. This paper discusses the performance of this algorithm as evaluated by computational simulation assuming application to a mobile satellite radio terminals environment. (Author)

High-power Nd-doped double-clad fiber amplifier at 1.06 μm

In this study, we clarify the performance of a Nd-doped fiber amplifier (NDFA) at 1.06 micrometer as a booster amplifier and a preamplifier. As a booster amplifier, we propose a Nd-doped double-clad fiber (DCF) amplifier. The DCF configuration could be the most promising technique for obtaining high output power from the NDFA, because of its potentially low amplifying threshold characteristics in an ideal four-state system, and the easy pump lightwave coupling to a broader first cladding area in the DCF. The proposed DCF is spliced with a normal single mode fiber at one end of the DCF as a signal input port, to avoid multi-mode propagation of the input signal lightwave through the first cladding area. Design parameters, such as the length and Nd concentration of the DCF, will be optimized by further study. The theoretical result predicts a 2-watt signal output power by a 10-watt pump power coupling to the DCF. For comparison, a booster amplifier employing four-LDs pump scheme is also demonstrated. As a preamplifier, we clarify the NDFAs high-sensitivity performance in giga-bit transmission. The NDFA will provide high-power, low-noise, robust, multigigabit optical transmitters and receivers for free-space laser communications systems.