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Subcarrier Acousto Optic Modulator

IP.com Disclosure Number: IPCOM000085159D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

White, JM: AUTHOR

Abstract

The utility of a surface-wave resonator as the control element in an oscillator has been described in the literature. These devices, as shown schematically in Fig. 2, consist of an interdigital electrode structure 10 mounted on a piezoelectric substrate 20 (e.g., LiNbO(3)) between a pair of reflector gratings 11 and 12. If the piezoelectric substrate 20 on which the resonator 30 is formed also has a large electrooptic figure of merit or indirect acousto-optic figure of merit, as does LiNbO(3), and if an optical waveguide film is formed in the substrate 20, then the resonator 30 will act as a light modulator.

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Subcarrier Acousto Optic Modulator

The utility of a surface-wave resonator as the control element in an oscillator has been described in the literature. These devices, as shown schematically in Fig. 2, consist of an interdigital electrode structure 10 mounted on a piezoelectric substrate 20 (e.g., LiNbO(3)) between a pair of reflector gratings 11 and 12. If the piezoelectric substrate 20 on which the resonator 30 is formed also has a large electrooptic figure of merit or indirect acousto-optic figure of merit, as does LiNbO(3), and if an optical waveguide film is formed in the substrate 20, then the resonator 30 will act as a light modulator.

When the oscillator is operating, acoustic standing waves will be induced in the substrate material. If the Bragg condition is satisfied optically, the light intensity will be deflected (modulated) at twice the resonant frequency of the oscillator. Only a small amount of power is required to keep the high-Q circuit oscillating with large resonant voltages V(LO) and strains appearing at the transducer.

The equivalent circuit for the surface wave resonator 30 and quartz crystal resonator 40 is shown in Fig. 1. The resonator 30 operates in the UHF band and can be fabricated by simple photolithography of metal patterns on the piezoelectric surface 20. The optical waveguide can be formed by metal diffusion into the LiNbO(3).

When, as shown in Fig. 2, a signal voltage V(S) is introduced across the device in addition to the oscillating voltage, the frequency of the oscillation remains constant, and the signal effectively amplitude modulates the light.

The modulated intensity of the optical beam is given by: I = Io sin/2/ A/1/2/ V where A is a constant function of material parameters and geometric factors, and V is the voltage across the device.

In strongly piezoelectric materials such as LiNbO(3), the strain to a large ...