Shoji Kakio

Lamb-Wave-Type High Frequency Resonator

In this study, we examined Lamb wave propagation on an AT cut quartz substrate; we carried out theoretical analyses and fundamental experiments using Lamb waves. Consequently, we validated that it is operable at an approximately seven times higher frequency than that of a conventional AT cut vibrator and that it also uses an approximately two times higher frequency than that of a surface acoustic wave resonator on the same substrate, assuming that they are of the same shape. Next, we applied a resonator utilizing Lamb waves, and we measure the resonance characteristics and the reflection coefficient. Results proved that the resonance characteristics were enhanced by thickening the Al film in the reflector fabricated on the substrate surface and that the reflection coefficient per reflector is considerably large in comparison with that in the case of surface acoustic waves.

Diffraction Properties and Beam-Propagation Analysis of Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Wave

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to clarify the conditions for a higher diffraction efficiency and a lower driving power, the diffraction properties of the waveguide-type AOM were measured and simulated. First, an AOM with an AO interaction region length of 3 mm was fabricated and the diffraction efficiency of 65% was obtained. Next, the measured values of the SAW power required for 100% diffraction (P100) for the driving frequencies of 125 MHz and 200 MHz were found to be in agreement with the calculated P100, which shows that there is an optimum driving frequency. Furthermore, optical frequency domain ranging using a frequency-shifted-feedback fiber laser with the waveguide-type AOM was demonstrated. Finally, the diffraction properties of the waveguide-type AOM are simulated using a beam-propagation method (BPM) and compared with the experimental results.

Surface Acoustic Wave Properties on Proton-Exchanged 128°-Rotated Y-Cut LiNbO3

The characteristics of surface acoustic waves on proton-exchanged 128°-rotated Y-cut LiNbO3 were investigated at a frequency of 100 MHz. The changes of the phase velocity and the electromechanical coupling coefficient as a function of the proton-exchange depth were measured. From these experiments, the elastic constants and the piezoelectric constants of the proton-exchanged layer were determined. The effects of annealing on the phase velocity and the surface acoustic wave propagation loss were also measured.

Shear-Horizontal-Type Surface Acoustic Waves on Quartz with Ta2O5 Thin Film

The propagation characteristics of two modes of surface acoustic waves (SAWs) on ST quartz with a tantalum pentoxide (Ta2O5) thin film are investigated theoretically and experimentally. One is the pure shear-horizontal (SH)-type SAW and the other is the Love-wave-type SAW converted from the leaky SAW (LSAW). For these SAWs, stronger energy trapping effects on the surface can be expected by loading the substrate with the Ta2O5 thin film, because this film has a relatively high density. In fact, the film thickness of the Ta2O5 film required to obtain the minimum insertion loss and the maximum K2 for the SH-type SAW on ST-90°X quartz is around 0.01 λ, which is approximately one-fourth of that reported for silicon dioxide film. Furthermore, the attenuation of the LSAW on ST-33°X quartz was reduced by loading with the Ta2O5 film because the LSAW becomes the Love-wave-type SAW without attenuation.

Characteristics of reflection of resonators using Lamb wave on AT-cut quartz

Lamb waves propagating on an AT-cut quartz substrate were studied. In this study, we propose a high-frequency resonator using a Lamb wave. A Lamb wave is excited on an extremely thin AT-cut quartz substrate which thickness is comparable to the wavelength of an elastic wave propagating on a substrate. This Lamb wave propagates at a higher phase velocity mode than surface acoustic waves. This realizes an RF resonator operable in a high frequency range in which a conventional quartz resonator hardly operates. A theoretical analysis of the reflection coefficient of a Lamb wave with a grating reflector was conducted. The analysis results and experimental results are compared and discussed in this study. A reflection coefficient which is 10 to 20 times higher than that for a Rayleigh-type surface acoustic wave is obtained.

An Integrated Acoustooptic Frequency Shifter Driven by Surface Acoustic Wave for 1.55 µm Optical Wavelength

An integrated acoustooptic frequency shifter in a crossed-channel waveguide is demonstrated at an optical wavelength of 1.55 ?m. A novel tapered device was designed to make the acoustooptic interaction region longer and thus the driving surface acoustic wave (SAW) power lower, and the device was fabricated by the proton-exchange method and post-annealing in a 128? rotated Y-cut LiNbO3 substrate. At SAW power of 1.4 W, a 40% diffraction efficiency and a bandwidth of 5 MHz centered at 196 MHz were obtained. The frequency shift of Bragg diffracted light was confirmed in an optical heterodyne experiment.

Improvement of Diffraction Properties in Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Wave

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to improve the diffraction properties of the waveguide-type AOM, the dependences of the diffraction properties on the relative position of the SAW beam for the diffraction region were simulated using a beam-propagation method (BPM) and measured. By decreasing SAW beam width, although the input voltage needed to obtain the maximum diffraction efficiency increased, diffraction efficiency improved to 84% from the previous value of 65%. Furthermore, to obtain a lower driving voltage, the utilization of a unidirectional transducer was investigated for the AO interaction on a planar optical waveguide at an optical wavelength of 0.633 µm.

Resonators Using a Lamb Wave on AT-Cut Quartz

We applied a plate mode wave (Lamb wave) to a high-frequency resonator. A Lamb wave in an acoustic bulk mode is excited faster than a surface acoustic wave in an extremely thin quartz substrate. The thickness of the substrate is comparable to the wavelength of the Lamb wave. This fact enables the fabrication of a high-frequency resonator that is operable at a high-frequency range, which cannot be achieved using a conventional quartz oscillator. In this manuscript, we present a discussion and comparison of an analytical procedure with experimental results.

Monolithically Integrated Tandem Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Waves

A waveguide-type acoustooptic modulator (AOM) using coplanar AO coupling due to a surface acoustic wave (SAW), that is, Bragg diffraction, in a tapered crossed-channel proton-exchanged (PE) optical waveguide on a 128°-rotated Y-cut LiNbO3 substrate for an optical wavelength of 1.55 µm has been proposed. In this study, a monolithically integrated tandem waveguide-type AOM driven by SAW was designed and fabricated. The structure considered was a 2×4 optical switch, in which the input ports of two second 1×2 switches were connected to the two output ports of the first 2×2 switch on the same substrate. An interdigital transducer (IDT) with a period length of 32 µm and an overlap length of 2 mm was fabricated in the first and second stages of the AO interaction region. Diffraction efficiency was measured at a driving frequency of approximately 120 MHz. A diffraction efficiency of approximately 90% was obtained for each stage. When both stages were driven at the same frequency, a peak diffraction efficiency of 63% was obtained. Furthermore, the optical frequency shifts for the sum of two driving frequencies and the difference frequency ranging from DC to 5 MHz were observed.

Propagation Characteristics of Leaky Surface Acoustic Wave on Proton-Exchanged 36.DEG. Y-X LiTaO3.

The propagation characteristics of leaky surface acoustic waves (LSAWs) on proton-exchanged 36°-rotated Y-cut LiTaO 3 were investigated experimentally. The dependence of the insertion loss between transducer pairs on the proton-exchange depth and the number of finger pairs of the transducer were measured at a frequency of 210 MHz. The insertion loss of the LSAW for the free surface case was improved considerably by the proton exchange because bulk wave radiation from the transducer was suppressed. The challge of the amplitude of the mechanical displacement perpendicular to the surface was also measured using a laser probe method.