ACOUSTO-OPTIC DEFLECTOR COMPRISING MULTIPLE ELECTRO-ACOUSTIC TRANSDUCERS

Abstract

The invention relates to an acousto-optic deflector comprising a bulk of acousto-optic medium and acoustic wave generator coupled to the bulk, characterised by that the acoustic wave generator comprises at least two different electro-acoustic transducers for generating acoustic waves in the bulk.

Claims

1. Acousto-optic deflector comprising a bulk of acousto-optic medium and acoustic wave generator coupled to the bulk, characterised by that the acoustic wave generator comprises at least two different electro-acoustic transducers for generating acoustic waves in the bulk.

2. Acousto-optic deflector according to claim 1, characterised by that each transducer comprises a first electrode coupled to the bulk, a second electrode, and a piezoelectric plate interposed between the first and second electrodes.

3. Acousto-optic deflector according to claim 2, characterised by that the at least two transducers comprise different piezoelectric plates, which differ in thickness and/or crystal orientation.

4. Acousto-optic deflector according to claim 2, characterised by that the first electrode of at least two of the transducers is common.

5. Acousto-optic deflector according to claim 2, characterised by that the second electrodes have contact means that are connectable to an electric driving signal source over an electric switch.

6. Acousto-optic deflector according to claim 5, characterised by that the electric switch is a radio-frequency switch, preferably having a switching time of less than 10 nsec.

7. Acousto-optic deflector according to claim 1, characterised by that the acoustic wave generator comprises at least: a first transducer having a first acoustic frequency working range, and a second transducer having a second acoustic frequency working range.

8. Acousto-optic deflector according to claim 7, characterised by that the first transducer's acoustic frequency working range is optimised for laser beams of a first range of central optical wavelengths to be deflected when passing through the bulk, and the second transducer's acoustic frequency working range is optimised for laser beams of a second range of central optical wavelengths to be deflected when passing through the bulk.

9. Acousto-optic deflector according to claim 1, characterised by that the acoustic wave generator comprises at least: a first transducer generating a first acoustic polarisation mode, and a second transducer generating a second acoustic polarisation mode.

10. Acousto-optic deflector according to claim 1, characterised by that the at least two transducers are mounted on the same side of the bulk.

Description

[0014] Further details of the invention will be apparent from the accompanying figures and exemplary embodiments.

[0015] FIG. 1 is the theoretical diffraction efficiency curve of a prior art acousto-optic deflector, as a function of frequency for different optical wavelengths.

[0016] FIG. 2 is a schematic cross sectional view of a preferred embodiment of an acousto-optic deflector according to the invention.

[0017] FIG. 2 schematically illustrates a preferred embodiment of an acousto-optic deflector 10 in accordance with the present invention. The deflector 10 comprises a bulk 12 of acousto-optic medium and an acoustic wave generator 14 coupled to the bulk 12. According to the depicted embodiment the acoustic wave generator 14 comprises two different, a first and a second electro-acoustic transducer 16, 18 for generating acoustic waves in the bulk 12 in order to deflect a laser beam propagating through the bulk 12. The first and the second transducers 16, 18 are different in that they work in different acoustic frequency ranges (i.e. they have different acoustic frequency working ranges) and/or they generate acoustic waves of different acoustic polarisation mode, whereby the acousto-optic deflector 10 is optimised for laser beams of different central optical wavelength and/or of different polarisation when operating with the first or the second transducer 16, 18. It should be appreciated that the acoustic wave generator 14 may comprise more than two transducers 16, 18 in which case each transducer 16, 18 may have a different acoustic frequency working range and/or different acoustic polarisation mode.

[0018] The possibility to generate different acoustic modes propagating in the same direction has also its practical importance, since modes with different polarization propagate with different velocity thus allowing scanning with different speeds over different angle ranges. In a typical arrangement the slowest acoustic mode provides the highest scanning angle range and highest optical throughput, whereas the faster modes provide 5-10 times faster scanning over a limited scanning range. Both functions can be useful during imaging most preferably the slow scanning providing larger image and during functional measurement the faster scanning capable to capture dynamic biological processes.

[0019] The two transducer 16, 18 preferably comprise a common first electrode 20 (as shown in FIG. 2), which is coupled to the bulk 12. This renders the manufacture of the acoustic wave generator 14 more simple and economic, however, the transducers 16, 18 may have separate first electrodes 20 that are coupled to the bulk 12, moreover such transducers 16, 18 may be coupled to different sides of the bulk 12.

[0020] The two transducers 16, 18 further comprise separate second electrodes 22, 24 preferably being provided with contact means 22a, 24a that are connectable to an electric driving signal source over an electric switch 26. The electric signal source is preferably a control system 27 providing the drive signals for the acoustic wave generator 14 and the electric switch 26 as well. The electric switch 26 may be a fast radio-frequency switch, preferably having a switching time of less than 50 nsec, more preferably of less than 10 nsec.

[0021] Each transducer 16, 18 further comprises a piezoelectric plate 28, 30 interposed between the common (or separate) first electrode 20 and the second electrodes 22, 24. The transducers 16, 18 may comprise further layers such as acoustic matching layers and/or bonding layers (not shown). The piezoelectric plates 28, 30 are preferably made of piezoelectric crystals that transform electric signals into acoustic waves by changing their static dimension in response to an external electric field.

[0022] The different acoustic frequency working range of the transducers 16, 18 may be achieved by providing transducers 16, 18 of different thickness, e.g. the piezoelectric plates 28, 30 and/or the acoustic matching layers may have different thicknesses. Alternatively, if the first and second transducers 16, 18 differ in acoustic polarisation mode this may be achieved by providing piezoelectric plates 28, 30 of different crystal orientation.

[0023] Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.