Shinichi Wakana

Backside observation technique for SAW distribution under electrodes

A modified SAW distribution observation technique, which employs the polarization detection method, has been developed. A probe light was projected from the backside of the substrate to detect the SAW under the electrodes. The observed results proved that the origin of the leakage SAW is the penetration from the IDT (inter digital transducer) to the electrodes, and busbars transmit the wave as waveguides.

Novel optical observation technique for shear horizontal wave in SAW resonators on 42/spl deg/YX-cut lithium tantalate

We developed a new optical technique for observing the shear horizontal component of surface acoustic waves. The technique detects the change in polarization of the probe light caused by the photoelastic effect. We measured the distribution in and around a resonator on rotated Y-cut LiTaO/sub 3/, and occurrence and propagation of leakage was observed.

Magnetic near-field measurements over LSI package pins by fiber-edge magnetooptic probe

To establish a method for investigating hidden radiation sources and their mechanisms in a printed circuit board, we performed preliminary measurements of one-dimensional magnetic near-field distribution over pins of a large-scale integrated circuit (LSI) package by means of an optical method: the fiber-edge magnetooptic (FEMO) probing technique. The FEMO probe consists of fiber optics and a magnetooptic crystal glued at a fiber edge. Its planar spatial resolution is approximately 100 /spl mu/m. It was found that a magnetic field generated from each LSI pin could be distinguished and some radiation was generated from ground and power supply lines. We compared the measured results with corresponding radiated electric field strength that was separately measured. The frequency of interest was the tenth harmonic of the output signal. We observed a strong correlation between those two experimental results, which suggests the effectiveness of our proposed method for near-field investigation. One of the beneficial features of the FEMO probe is its small probe head, due to which one can perform detailed near-field evaluations in a microscopic region. Furthermore, we tried to specify a major electromagnetic interference source by additional measurements of near-field distributions and frequency dependence of magnetooptic signals. It was suggested that the short-through current flowing in the power-supply system of the input/output circuits caused high-level radiated emission.

Novel high-spatial resolution probe for electric near-field measurement

A new probe with a micro-hole chip has been developed for measurement of near-field electrical radiation from printed circuit boards. The chip is fixed onto a semi-rigid cable probe facet and the radiated electric field is coupled with the surface of its inner conductor through an aperture with a diameter of 100 µm. Using a 50-µm-wide microstrip line for the device under test, we obtained a distance of 100 µm where the probe output decreases by 6 dB at a measurement height of 50 µm. This distance is in good agreement with our simulation results based on FDTD analysis. With a rectangular aperture of having a 50 µm width, we obtained a 72 µm distance at a 25 µm height. In addition, we confirmed that both the S21 characteristics of the measured line and the frequency characteristics of the probe can be dramatically improved by covering the outside of the probe with magnetic film.

Wide bandwidth scanning Kerr microscope based on optical sampling technique using externally triggerable pulse laser diode

We have developed a wide bandwidth scanning Kerr microscope to diagnose HDD heads using an optical sampling technique. By using an externally triggerable pulse diode laser source, the temporal response and frequency dependence of the magnetization behavior can be easily evaluated. The developed system has 5 GHz of the measurement bandwidth and 0.3 μm of the spatial resolution.

Observation of waves propagating within a substrate

We developed a technique for observing the distribution of acoustic waves based on polarization detection. This technique enabled visualization of wave distributions in an LiTaO/sub 3/ substrate at various depths. Significant differences of the distribution in the substrate were observed at different frequencies. At the resonant frequency, the waves were distributed near the surface of the resonator. In contrast, a non-negligible amount of the acoustic wave was detected in a deeper area (4/spl lambda/) above the anti-resonant frequency. This improved technique enables us to observe the behavior of acoustic waves both on the surface and in the substrate.

Direct core monitoring technique for passive optical alignment between multichannel silicon waveguide and single-mode fiber array

We propose a passive optical alignment method between multichannel silicon waveguides with spot size converters and a single-mode fiber array. In this method, highly accurate positional and angular alignment is realized by a novel monitoring technique of the waveguide and the fiber in one field of view. We achieve a simultaneous accurate multichannel coupling using a developed assembly system.

High-speed terahertz spectroscopic imaging using noncollinear electro-optic sampling and a multistep mirror

We propose a method for high-speed terahertz spectroscopic imaging that is based on electro-optic sampling with a noncollinear geometry of the THz beam and probe laser beam and has a multistep mirror in the path of the probe beam. We made an imaging system that operates in the over 2.0-THz range and enables the sample region corresponding to a (28 × 28)-pixel area on the sensor to be imaged with a spatial resolution of 1.07 mm and a frequency resolution of 0.079 THz. We also show how the proposed method might be extended for faster THz spectroscopic imaging.

Optical delay tester

The authors have developed an optical delay tester based on electro-optic sampling, and designed a prototype to test the timing of high-speed IC chips. The device puts an electro-optic crystal in contact with the terminals to be tested and measures the voltage waveform applied to the crystal. Measurement precision is 100 mV or better and timing precision measurement is 50 ps.

Terahertz spectroscopic imaging using noncollinear electro-optic sampling and a multistep mirror without shifting the object

We previously developed a high-speed terahertz spectroscopic imaging method based on electro-optic sampling with a noncollinear geometry of the THz beam and probe laser beam and using a multistep mirror in the path of the probe beam. We set the incident probe laser into MAST at a 45° angle, to prevent interference between adjacent beams. However, this produced beam vignetting, so imaging had to be performed twice, between sample movements, and this increased the imaging time accordingly. Thus, we improved the probe-laser imaging system after reflecting from the MAST to correct for the effects of diffraction. This prevents interference from adjacent beams and allows the angle of incidence on the MAST to be set to 0°, enabling the entire sample surface to be imaged in one measurement. As a result, we are able to perform measurements in 40 seconds, half the time of the previous method, and obtain a 28x28-pixel spectral image with spatial resolution of 1.07 mm. To verify the imaging performance, we also measured test samples, showing that the shape and thickness of items inside an opaque plastic case can be distinguished using amplitude and phase images, and metallic foreign objects can be detected. We also evaluated the method and were able to show the validity of the spectral imaging results by distinguishing the transmission or blocking of arbitrary frequency components.