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Acoustic Surface Wave Parametric Amplifiers

IP.com Disclosure Number: IPCOM000075260D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Ash, EA: AUTHOR [+2]

Abstract

Although degenerate acoustic-wave parametric amplifiers are known in which the pumping frequency is applied electrically through the use of an electrode on a piezoelectric crystal, such devices have disadvantages. These include narrow bandwidth and instability due to backward wave oscillations. The embodiment shown in Fig. 1C overcomes these disadvantages by using an electric pump wave with a nonzero wave number k(p). Figs. 1A and 1B are omega-k diagrams of parametric interactions, which are possible when the structure of Fig. 1C is used.

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Acoustic Surface Wave Parametric Amplifiers

Although degenerate acoustic-wave parametric amplifiers are known in which the pumping frequency is applied electrically through the use of an electrode on a piezoelectric crystal, such devices have disadvantages. These include narrow bandwidth and instability due to backward wave oscillations. The embodiment shown in Fig. 1C overcomes these disadvantages by using an electric pump wave with a nonzero wave number k(p). Figs. 1A and 1B are omega-k diagrams of parametric interactions, which are possible when the structure of Fig. 1C is used.

In Fig. 1C, a piezoelectric crystal 10 has an input transducer 12 and an output transducer 13 on its top surface. Located on crystal 10 is an optically flat sapphire disk 14, on which is a conventional half-wave strip line resonator 15 having a serrated edge on one side. Voltage V(p) is applied across resonator 15 in order to develop an electrical pumpwave with a proper periodicity, which interacts with the signal acoustic wave to produce parametric amplification.

Structure 15 is spaced from crystal 10 by a distance which is small compared with the pitch. A separation of, for instance, 5 microns is suitable. The spacing is not critical and can vary between 3 and 10 microns. In principle, a higher pumping field can be obtained if a first electrode is adjacent to one side of the crystal, while an other electrode is adjacent to the other side. However, the gain may be small when that is done.

The idler wave can also be introduced electrically. A backward wave, nondegenerate parametric amplifier is shown in Fig. 2, in which the electric pump wave is established by electric field transfer to the acoustic crystal 10. Input transducer 12 produces an acoustic surface wave which propagates to output transducer 13. Interdigital electrode structure 16 provides an idler wave having a spatial periodicity in the direction of travel of the acoustic signal wave. A pair of filters 17 and 18 isolate the electrical pumping action from the wave produced by interdigital structure 16. Resistance R(i) removes power generated at the idler frequency. Filter 17 passes power at the idler frequency and stops wet at the pump frequency, while filter 18 passes power at the pump...