Elastic-wave monitoring device and surface-acoustic-wave device

An elastic-wave monitoring device comprising:

• an optical system arranged so that a circularly polarized light from a light source is separated into a first light beam incident to a measured object and a second light beam incident to a reference mirror by a beam splitter, a light beam from the measured object passes through a polarizing filter to a first photodetector, and a coupled light beam is generated from a reflected beam from the measured object and a reflected beam from the reference mirror by the beam splitter so that the coupled light beam is received by a second photodetector;
• a first detection unit detecting periodic fluctuation components of an output signal of the first photodetector;
• a second detection unit detecting periodic fluctuation components of an output signal of the second photodetector;
• and
• a computation unit performing computations based on outputs of the first and second detection units,
• wherein the polarizing filter is arranged to have a polarization transmission axis directed to one of directions of principal axes of an ellipse formed by intersections of an index ellipsoid of the measured object and a plane perpendicular to an incidence direction of the first light beam and passing through an origin of the index ellipsoid.

A surface-acoustic-wave device comprising:

• a piezoelectric substrate;
• and
• first and second comb-shaped electrodes each having a bus-bar portion parallel to a propagation direction of a surface acoustic wave in the substrate, and respective electrode fingers periodically formed on the piezoelectric substrate and extending in directions perpendicular to the propagation direction,
• wherein the electrode fingers of the first comb-shaped electrode and the electrode fingers of the second comb-shaped electrode are separated away from the bus-bar portion of the opposing comb-shaped electrode, the respective electrode fingers being periodically arrayed in the propagation direction of the surface-acoustic-wave, and the electrode fingers of each comb-shaped electrode are inclined at root portions thereof outwardly right and left from the bus-bar portion of the corresponding comb-shaped electrode so that the inclined portions of the electrode fingers face a direction of a leaking surface-acoustic-wave perpendicularly.

A surface-acoustic-wave device comprising:

• a piezoelectric substrate;
• an inter-digital transducer provided on the piezoelectric substrate, the inter-digital transducer including first and second comb-shaped electrodes each having a bus-bar portion parallel to a propagation direction of a surface acoustic wave in the substrate, and respective electrode fingers periodically formed on the piezoelectric substrate and extending in directions perpendicular to the propagation direction;
• and
• a pair of reflectors provided at a left edge and a right edge of the inter-digital transducer along the propagation direction,
• wherein the electrode fingers of the first comb-shaped electrode and the electrode fingers of the second comb-shaped electrode are separated away from the bus-bar portion of the opposing comb-shaped electrode, the respective electrode fingers being periodically arrayed in the propagation direction of the surface-acoustic-wave, and the electrode fingers of each comb-shaped electrode are inclined at root portions thereof outwardly right and left from the bus-bar portion of the corresponding comb-shaped electrode so that the inclined portions of the electrode fingers face a direction of a leaking surface-acoustic-wave perpendicularly.

A method of designing a surface-acoustic-wave device, comprising the steps of:

• providing an elastic-wave monitoring device to monitor a distribution of a surface-acoustic-wave in the surface-acoustic-wave device;
• and
• determining a configuration of the surface-acoustic-wave device based on the distribution of the surface-acoustic-wave monitored by the elastic-wave monitoring device,
• the elastic-wave monitoring device comprising:
• an optical system arranged so that a circularly polarized light from a light source is incident to the surface-acoustic-wave device and a light beam from the surface-acoustic-wave device passes through a polarizing filter to a photodetector;
• and
• a detection unit detecting periodic fluctuation components of an output signal of the photodetector,
• wherein the polarizing filter is arranged to have a polarization transmission axis directed to one of directions of principal axes of an ellipse formed by intersections of an index ellipsoid of the surface-acoustic-wave device and a plane perpendicular to an incidence direction of the light beam and passing through an origin of the index ellipsoid.

An elastic-wave monitoring device comprising:

• a piezoelectric substrate having a first surface where a metal electrode is formed on a piezoelectric crystal, and a second surface being ground and opposing to the first surface;
• a first polarization-analysis optical system arranged so that a light beam from a light source is incident to the second surface of the substrate when the electrode on the first surface is excited by a driving voltage, and a reflected light beam from an interface between the electrode and the piezoelectric crystal on the first surface of the substrate is received by a first photodetector;
• and
• a detection unit detecting a change of a polarization state of the reflected light beam received by the first photodetector of the first polarization-analysis optical system to monitor a distribution of an elastic wave in the substrate.

An elastic-wave monitoring method comprising the steps of:

• providing a piezoelectric substrate having a first surface where a metal electrode is formed on a piezoelectric crystal, and a second surface being ground and opposing to the first surface;
• arranging a first polarization-analysis optical system so that a light beam from a light source is incident to the second surface of the substrate when the electrode on the first surface is excited by a driving voltage, and a reflected light beam from an interface between the electrode and the piezoelectric crystal on the first surface of the substrate is received by a first photodetector;
• and
• detecting a change of a polarization state of the reflected light beam received by the first photodetector of the first polarization-analysis optical system to monitor a distribution of an elastic wave in the substrate.