Optical waveguides – Directional optical modulation within an optical waveguide – Acousto-optic
Reexamination Certificate
2000-01-28
2001-02-27
Ngo, Hung (Department: 2874)
Optical waveguides
Directional optical modulation within an optical waveguide
Acousto-optic
C385S014000, C385S016000, C385S020000, C385S021000
Reexamination Certificate
active
06195476
ABSTRACT:
This application is a continuation of International Application No. PCT/EP98/04109, filed Jul. 3, 1998, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to acousto-optic devices, and more particularly to absorbing surface acoustic waves in acousto-optic devices.
Integrated acousto-optic devices function through the interaction of surface acoustic waves (SAWs) on a crystal surface with light traversing the crystal. An example of an acousto-optic device is shown in FIG.
1
. The device is a 2×2 tunable optic switch having optical waveguides
10
,
11
,
17
,
18
,
19
, and
20
, with two bending sections
22
a
and
22
b
along a region of optical waveguides
17
and
18
. The device also has acoustic waveguides
12
and
13
, piezoelectric transducers
14
and
15
, and polarization splitters
21
. The device is formed on the surface of a crystal
16
, such as LiNbO
3
. When electrically stimulated, transducers
14
and
15
produce SAWs that travel through acoustic waveguides
12
and
13
and interact with light passing through optical waveguides
17
and
18
.
The inventor has recognized, however, that non-ideal behavior of the SAW gives rise to parasitic effects. First, the SAW may be scattered due to inhomogeneities on the surface of the crystal. Inhomogeneities can be caused, for example, by indiffusion of dopants, surface impurities, additional surface layers, or by the borders of the substrate. The scattered SAW disturbs the acousto-optic interaction between the SAW and the light traveling through the waveguides.
The SAW can be scattered, or it can be reflected by the inhomogeneities, or by the acoustic waveguides. Scattered or reflected acoustic waves can interfere with other acoustic waves. The resulting interference pattern changes with the wavelength of the SAW resulting in wavelength dependent characteristics of the acousto-optic device.
Further, the structure that generates the SAW (e.g., piezoelectric transducers
14
and
15
of
FIG. 1
) does not necessarily generate directed waves. Rather, the waves irradiate in various directions, degrading device performance.
Other problems associated with conventional acousto-optic devices include internal reflections of the transducer that result in fluctuations of transducer efficiency with frequency. Also, waves propagating inside the substrate (“bulk-waves”) can interfere with those propagating on the surface.
Finally, In acousto-optic devices like the one shown in
FIG. 1
, a coupling between acoustic waveguides
12
and
13
may develop. If such coupling develops, the efficiency of both converters Is decreased. To function effectively, then, the waveguides
12
and
13
must be separated by a relatively large distance (typically 200 microns). This required separation limits the degree to which the devices can be integrated.
U.S. Pat. No. 6,002,349 discusses the integration of acousto-optic filters and switches. The objects of the invention are to provide an efficient acousto-optic structure on an x-cut piezoelectric substrate and to provide an acousto-optic filter and coupler that do not incur an optical frequency shift and that are polarization independent To achieve these objects, the invention includes a two-stage acousto-optic filter fabricated as an integrated circuit with an acoustic absorber between the two stages.
European Patent Application EP 0737880A1 discusses an acousto-optical waveguide device for wavelength selection. As shown in FIG.
4
. the device includes an acoustic absorbing means placed along an acoustic waveguide
41
, close to the end of optical waveguide
36
that is connected to coupler
37
to absorb the residual acoustic wave. It also includes an acoustic absorbing means placed close to the end of waveguide
34
that is connected to coupler
32
to absorb the acoustic wave generated by transducer
44
propagating in a direction opposite to the optical signals.
UK Patent Application (Publication No. GB 2,304,917) entitled “Integrated Optical Devices” discloses a tunable filter having an acoustic waveguide parallel to an optical waveguide. The application discloses two methods of controlling the power density of an advancing acoustic wave and, thus, the power transfer to the optical wave. First, the acoustic waveguide can have a varying cross-sectional area. Second, the energy of the acoustic wave can be absorbed along the length of the acoustic waveguide.
Finally, a publication entitled “Passband Engineering of Acousto-Optic Tunable Filters” by R. S. Chakravarthy et al. (1995 ECIO Proceedings, paper TuPo, Poster Session, p. 137-40) investigates solutions to the problems of interchannel crosstalk and wavelength misalignment crosstalk in acousto-optic tunable filters. The authors propose, among other things, placing an attenuating overlay symmetrically along the length of the device taking care to avoid the optical waveguides. The device structure is shown in FIGS.
4
(
a
) and
5
(
a
).
The inventor has discovered that these techniques do not solve the problems recognized by the inventor. The inventor has found a need, therefore, for an acousto-optic device that reduces the parasitic effects of surface acoustic waves.
SUMMARY OF THE INVENTION
We have found that an acoustic absorber placed at predetermined locations around the acoustic waveguides and the optical waveguides acts to reduce or eliminate the problem created by the above-described parasitic effects. An acousto-optic device according to one aspect of the present invention includes a substrate of a material capable of propagating a surface acoustic wave along a portion of the surface of the substrate, a transducer for generating the surface acoustic wave, an optical waveguide formed in the substrate, and an acoustic absorber surrounding said portion of the substrate.
An acousto-optic switch according to another aspect of the present invention includes a substrate of a material capable of propagating a surface acoustic wave along a surface of the substrate, first and second optical waveguides formed in the substrate, first and second acoustic waveguides contacting the first and second optical waveguides, respectively, each having a first end and a second end, first and second transducers for generating a surface acoustic wave in the first and second acoustic waveguides, respectively, and an acoustic absorber surrounding the first and second acoustic waveguides.
Another acousto-optic device according to yet another aspect of the present invention includes a substrate of a material capable of propagating a surface acoustic wave along a surface of the substrate, at least one optical waveguide formed in the substrate, at least one acoustic waveguide formed in the substrate, at least one transducer for generating a surface acoustic wave, and an acoustic absorber surrounding the at least one acoustic waveguide.
Another acousto-optic switch according to another aspect of the present invention includes a substrate of a material capable of propagating a surface acoustic wave along a surface of the substrate, first and second optical waveguides formed in the substrate, first and second acoustic waveguides contacting the first and second optical waveguides, respectively, each having a first end and a second end, first and second transducers for generating a surface acoustic wave in the first and second acoustic waveguides, respectively, and an acoustic absorber disposed between the first and second acoustic waveguides.
A method consistent with the present invention includes the steps of providing a substrate having an optical waveguide and an acoustic waveguide formed therein, wherein the optical waveguide and the acoustic waveguide font an acousto-optic interaction region, and absorbing scattered acoustic waves in a region surrounding the acousto-optic interaction region.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the i
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Ngo Hung
Pirelli Cavi E Sistemi S.p.A.
LandOfFree
Acousto-optic devices having an acoustic attenuator structure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acousto-optic devices having an acoustic attenuator structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acousto-optic devices having an acoustic attenuator structure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2614230