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 (P 100) for the driving frequencies of 125 MHz and 200 MHz were found to be in agreement with the calculated P 100, 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.
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.
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 LiNbO 3 substrate has been proposed for an optical wavelength of 1.55 mm. 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 mm.
A waveguide-type acoustooptic frequency shifter (AOFS) using coplanar AO coupling due to a surface acoustic wave (SAW), that is, Bragg diffraction, in a tapered crossedchannel 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 AOFS 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.
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