This paper presents a selective review of planar guided-wave acoustooptics, including some of the most recent results. The emphasis is on those aspects which relate to wide-band multichannel optical communications and real-time signal processing. First to be discussed are the analytical and numerical techniques required for the treatment of a Bragg modulator which uses a single aperture SAW transducer. The frequency responses generated for Y -cut LiNbO_3 waveguides using a digital computer serve as the basic data for the design of such a basic modulator. Next the key device parameters relevant to modulation and signal processing are discussed. The design parameters and procedures for wide-band Bragg modulators and deflectors are then established. Finally, some potential applications of such wide-band modulators and deflectors in optical communications and RF signal processing together with the best measured performance figures are described.

Guided-wave acoustooptic Bragg modulators for wide-band integrated optic communications and signal processing (Invited Paper)

Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c11=19.0, c12=11.0, c13=9.0, c33=19.6, c44=3.9, and c66=4.0 in units of 1011 dyn/cm2. The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p11, p13, p44, and p66=1.8, 2.3, 0.50, and 0.38, respectively, relative to p12.

Brillouin scattering study of ZnO

Studies of ZnO films which have been performed at Tohoku University are summarized to describe the important role of ZnO films in their application to surface acoustooptic devices on nonpiezoelectric substrates. The ZnO film has been confirmed experimentally as one of the most suitable materials for SAW transducers which can generate surface acoustic waves with power enough to attain the maximum diffraction efficiency in surface acoustooptic devices on nonpiezoelectric substrates in VHF and higher frequencies. It has also been confirmed to be useful as an optical waveguide which is suitable for use as the interaction medium in surface acoustooptic devices.

ZnO films for surface acoustooptic devices on nonpiezoelectric substrates

[78] L. B. Lambert, “Wide-Band, Instantaneous Spectrum  An[81] D. L. Hecht, “Acousto-Optic Nonlinearities in Multi-Frequency alyzers Em loying  Delay-Line  Light  Modulators,” IRE Inf . Acousto-Optic  Diffraction,” Tnt’l.  Quantum Electron  Conf., Conv. Rec., fit. 6, Vol. 10, Mar. 1962, pp. 69-78. [79] R. W. Damon, W. T. Maloney, and D. H. McMahon, “Ink:; [82] A. J. DeMaria and G. E. Danielson, “Internal Laser Modulation San Francisco, June 1974.

II. Acoustooptic Interactions Between Guided Optical Waves and Acoustic Surface Waves

Acoustooptic Bragg deflectors (ABDs) with high diffraction efficiencies were fabricated using ZnO thin films deposited on sapphire, glass, and Si substrates by an RF magnetron sputtering system. Optical waveguide losses of the ZnO films were about 0.5 dBcm/sup -1/. Diffraction efficiencies of 95 and 98% for the TE/sub 0/ mode beam (at 632.8 nm) were accomplished by acoustic powers of 90 mW in a ZnO film on glass and 80 mW in a ZnO film on Si, respectively. The diffraction efficiencies of the ABD using a ZnO film on sapphire with interdigital transducers of different Q values and with the surface-acoustic-wave propagating along and perpendicular to the c-axis of the ZnO film were also determined. >

Low-loss ZnO optical waveguides for SAW-AO applications

The thickness dependence of the efficiency of the Bragg diffraction between the same optical modes (TE0→TE0, TM0→TM0) by acoustic surface waves in ZnO−film optical waveguides is investigated at an acoustic frequency of 130 MHz and a film thickness from 0.6 to 8.0 μm. It is observed that the efficiencies for both the TE0 and the TM0 modes vary more than 2 orders of magnitude with the film thickness.

Thickness dependence of acousto−optic diffraction efficiency in ZnO−film optical waveguides

A strain‐controlling film to change acoustic strain distributions in the interaction region between acoustic surface waves and optical guided waves is introduced to improve the Bragg‐diffraction efficiency in surface‐acoustic‐optic devices. An improvement of about 2 orders of magnitude has been achieved in the efficiency of TM0‐TM0 diffraction at an acoustic frequency of 130 MHz in a 2.0‐μm ZnO‐film optical waveguide with a strain‐controlling film of a 1.5‐μm‐thick fused‐quartz film, as predicted by the theory.

Improvement of diffraction efficiency in surface-acoustic-optic devices by means of multilayered structure

Thickness Dependence of the Diffraction Efficiency of Optical Guided Waves by Acoustic Surface Waves

The absolute signs of the photoelastic constants of a ZnO crystal were measured by the Biegelsen method. All of them were determined to be negative.

N. Chubachi

Papers

Thickness dependence of acousto−optic diffraction efficiency in ZnO−film optical waveguides

Improvement of diffraction efficiency in surface-acoustic-optic devices by means of multilayered structure

Thickness Dependence of the Diffraction Efficiency of Optical Guided Waves by Acoustic Surface Waves

Absolute signs of photoelastic constants of ZnO

Mode Conversion Between TE and TM Modes of Optical Guided Waves by Love Waves in the Structure of LiNbO 3 Epitaxial Film on Al 2 O 3 Substrate