Tsutomu Nagatsuka

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.

An Ultrasonic Pulse Compression System for Nondestructive Testing Using Complementary Series Phase Modulation

An ultrasonic pulse compression system is presented, which employs complementary series phase modulated signals as transmit signals to obtain theoretically zero range sidelobes and high efficiency. In correlation based signal processing, echoes are correlated with reference signals that have the same wave forms as the echoes. The effectiveness of this signal processing over the conventional one using transmit signals as reference signals is verified by experiments.

Highly accurate measurement of LN optical intensity modulators by small RF inputs

A highly accurate measurement method of parameters of MZ-type LN optical intensity modulators is presented. In this method, a CW optical signal is input to an optical terminal and small CW RF signal is applied to an electrode of the modulator. Then sideband levels of an output optical signal at different bias points are measured by using optical spectrum analyzer. By using 1st order sideband levels which are measured at two different bias conditions, and using a compensation method to measured levels, we can obtain accurate chirp parameter even when very small power of RF signal is applied to the modulator. In this method, the chirp parameter can be obtained in good accuracy when the input RF voltage is only 3% of the halfwave voltage.

A Pulse Compression Ultrasonic Test Instrument and Its Applications

In recent years, so called “digital ultrasonic test instruments” have been commercially available. These conventional instruments employ electrical impulse excitation of ultrasonic probes. In this configuration, waveforms of ultrasonic pulses into a test object are determined only by the characteristics of probes. This means that variation of probe characteristics causes variation of evaluated results and reproducibility of evaluation is poor. Furthermore, some of the conventional instruments do not provide enough information required for quantitative nondestructive evaluation (QNDE) about a test object, since ultrasonic echo signals are A/D converted after an envelope detector in a receiver and only information of echo height and position is obtained.

NEW SETS OF TESTING CODES PROVIDING ZERO RANGE SIDELOBES FOR ULTRASONIC PULSE COMPRESSION STRUCTIVE TESTING SYSTEMS

Abstract In conventional ultrasonic pulse compression nondestructive testing systems, complementary codes have been used for modulation of transmit signals in order to obtain zero range sidelobes. In this paper,new sets of testing codes for modulation of transmit signals are shown. The sets are composed of four or more codes and provide zero range sidelobes. In the code lengths less than fifty, the new sets exist at least in twelve different kinds of lengths, for which the conventional complementary codes do not exist. The new sets of testing codes expand the selection range of code lengths providing zero range sidelobes, and thus. arc useful for reduction of dead time in a system using a transducer for both transmission and reception. Sidelobe cancellation using the new sets is demonstrated by experiments.