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Leaky Wave Couplers for Guided Elastic Wave and Guided Optical Wave Devices

IP.com Disclosure Number: IPCOM000077220D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Ash, EA: AUTHOR [+3]

Abstract

Coupling from a first waveguide into a second one or into any device utilizing transmitted waves, is effected by means of a limited length coupling region having a different phase-velocity characteristic than that of waveguides adjacent to it. Waves tend toward regions where phase velocity is low. Guided optical wave velocity is inversely related to the refractive index of the medium. A coupling region causes waves travelling in a guide to leak out of it. Then, these waves-encounter a transducer or a second waveguide and are coupled into it. Material for the coupling region with electroacoustic or electrooptic effect can be used to electronically control its phase-velocity characteristic, thus permitting switchable couplers.

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Leaky Wave Couplers for Guided Elastic Wave and Guided Optical Wave Devices

Coupling from a first waveguide into a second one or into any device utilizing transmitted waves, is effected by means of a limited length coupling region having a different phase-velocity characteristic than that of waveguides adjacent to it. Waves tend toward regions where phase velocity is low. Guided optical wave velocity is inversely related to the refractive index of the medium. A coupling region causes waves travelling in a guide to leak out of it. Then, these waves-encounter a transducer or a second waveguide and are coupled into it. Material for the coupling region with electroacoustic or electrooptic effect can be used to electronically control its phase-velocity characteristic, thus permitting switchable couplers.

Input transducer 3 in embodiment A generates waves guided along surface 4 (arrow) of bulk material 2. Presence of surface layer 1 causes waves travelling in the x direction to leak into bulk material 2 at an angle omega, where omega = cos (Vb/Vs), Vb being the shear velocity of material 2 and Vs the surface-wave velocity as determined by surface layer 1. The The surface-wave velocity is increased by surface layer 1, thus causing the waves to leak into bulk material 2 as indicated by the arrows. Transducer 5, functioning as an output means, converts the bulk elastic waves into electrical signals.

For elastic waves, device A for instance is constructed using glass as bulk material 2, chromium as surface layer 1 and lithium niobate as input and output transducers 3 and 5, respectively.

Diagram B shows wave amplitude versus distance along surface layer 1.

A surface layer 1 of sufficient length results in total coupling of surface waves into bulk material 2. A coupling length x from ten to one hundred wavelengths avoids reflections due to impedance mismatch.

Embodiment C shows a surface-to-surface coupler, Bulk material 11 has opposing surfaces 12 and 13 on which surface layers 14 and 1...