Tomohiro Akiyama

Two-dimensional optical signal-processing beamformer using multilayer polymeric optical waveguide arrays

Optically controlled beamforming techniques are very effective for phased-array antenna control. We have developed a two-dimensional (2-D) Fourier transform optical signal-processing (OSP) beamformer. In the OSP beamformer, we use multilayer polymeric optical waveguide arrays to generate and control a 2-D specific phase-front and sample 2-D distributed light beams. These multilayer optical waveguide arrays consist of three layers and 13 waveguides; each layer has four, five, and four waveguides, respectively. We experimentally demonstrate 2-D beam steering in the X-band, and show the feasibility of the 2-D OSP beamformer.

Fourier Transform Optical Beamformer Employing Spatial Light Modulator

Optically controlled beam forming techniques are effective for phased-array antenna control. We have developed the Fourier transform optical beamformer (FT-OBF). The antenna radiation pattern inputted into an amplitude spatial light modulator (A-SLM) is optically Fourier transformed to a specific phase-front light beam equivalent to an antenna excitation in the FT-OBF. Optical signal processing, used the Fourier transform optics, is effective to large-scale, two-dimensional, and high-speed signal processing. To implement a flexible and finer antenna beam pattern control, we use an A-SLM as input image formation of the FT optics. And, to realize a small-size FT-OBF, we use symmetric triplet lenses with convex, concave and convex lens. The total optical system becomes below 1/5 length compared with the length using single lens. Finally, we evaluated the developed FT-OBF with the generated amplitude and phase distributions, which excitation signal of an array antenna. We measured an antenna radiation beam pattern, beam steering and beam width control, in the C-band. Measurement results agreed with theoretical calculated results. These results show the feasibility of the spatial light modulator based FT-OBF.

Beam-steering and multibeam formation of Ku-band phased array antenna using optical signal processing beam-forming network

We experimentally demonstrate two types of spatial optical signal processing beamforming networks (BFN) for array antennas at Ku-band. One is a one-dimensional beam-steering antenna and the other is a multibeam antenna.

Variable spot scanning antenna using optically controlled beam forming network

An Optically controlled beam forming network has been developed, which has capacity of steering 2 beams and exciting 64 antenna elements. Using it, beam steering and beam width control is possible in parallel.

Spatial light modulator based optically controlled beamformer for variable multiple-spot beam antenna

We propose and demonstrate an optically controlled multiple-beam phased array antenna employing spatial light modulator. Developed prototype of the optical beamformer enables control multiple-beam direction and width; we demonstrated beamforming operation at 18 GHz. Furthermore, we have performed the communication test such as the bit error ratio (BER) test, data rate of 622 Mbps and 1244 Mbps in the digital communication link. We have confirmed that this optical beamformer had no serious effect for BER performance.

Beam-steering of receiving array antenna using local signal beamformer by optical signal processing

Beam-steering of receiving array antenna using local signal beamformer by optical signal processing is demonstrated in the X-band. The arriving direction of RF beam is recognized from the location of the light in the optical signal processor.

Parallax error correction method for ASTER SWIR bands

Advanced spaceborne thermal emission and reflection radiometer (ASTER) short wave infrared radiometer (SWIR) is planned to be launched with EOS-AM1 in 1998. SWIR has six bands and the linear detector arrays of all the bands are located on the same focal plane in parallel each other. Therefore parallax occurs between the six bands data. Large parallax causes errors in multiband data processing and so it is necessary to eliminate influential parallax from observation image. For the purpose of correcting parallax, we have developed a parallax estimation method for ASTER SWIR bands. To estimate parallax, image matching method is employed. But image matching method is not always effective. Cloud or featureless area in the image misleads the image matching process into a wrong result. So to prevent such misleading and to judge the validity of the result of the image matching method, coarse digital elevation model (DEM) data of which the cell size is about 1 km is introduced.

Optically controlled phased array antenna using spatial light modulator

We proposed an optically controlled phased array antenna using a spatial light modulator for an adaptive satellite communications system. We have developed a prototype of an Optical Beam Forming Network, which enables control of 2 beams individually, and demonstrated at Ka band. We confirmed a good agreement between theoretical antenna patterns and calculated antenna patterns, which are simulated by using measured amplitude and phase distributions of the prototype.

Two dimensional optical signal processing beamformer using multi-layer polymeric optical waveguide arrays

An optical heterodyne technique is a very effective procedure for a phased array antenna to generate and control a microwave signal with a particular phase shift. We developed a two-dimensional (2-D) Fourier transform optical signal processing (OSP) beam forming network (BFN). In the OSP-BFN, we use multi-layer polymeric optical waveguide arrays to make a 2-D specific phase-front and sample 2-D distributed light beams. These multi-layer optical waveguide arrays consist of three layers and 13 waveguides (4+5+4). We experimentally demonstrated 2-D beam steering in the X-band. Experimental results confirm the feasibility of the 2-D OSP-BFN.

Influence of vibrations on Fourier transform spectrometers

Spaceborne Fourier transform spectrometers (FTSs) are one of the most promising sensors for global measurements of the atmosphere and/or the surface because of its potentialities for high spectral resolution and high accuracy. One of the difficulties for realizing a high performance FTS is how to overcome its performance degradation caused by disturbances such as mechanical vibrations and shocks. We have developed a computer-based simulator to evaluate the performance degradation. Influence of vibrations for various kinds of FTSs using different optical elements and different sampling methods are examined by evaluating spectral measurement errors quantitatively. It is shown that spectral measurement errors of FTSs is restrained by using corner cube reflectors and sampling method defined by laser interference.