Piezoelectric tunable filter

Details Piezoelectric tunable filter Piezoelectric tunable filter

2002-09-03

2004-09-28

Healy, Brian (Department: 2874)

Optical waveguides

Temporal optical modulation within an optical waveguide

C385S007000, C385S008000, C385S002000, C385S014000, C385S037000, C385S129000, C385S130000

Reexamination Certificate

active

06798929

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to tunable filters used in telecommunications applications such as Dense Wavelength Division Multiplexing (DWDM), and more particularly to piezoelectric tunable filters.
2. Description of the Prior Art
DWDM is an essential technology to meet the growing need for increased communications system capacity. Current DWDM technology requires at least one filter for one DWDM channel. Each channel includes one filter, one multi-fiber collimator and one single-fiber collimator. Therefore, the more channels there are, the more filters are required. Thus conventional DWDM systems are very expensive and bulky. In addition, mechanical and optical reliability is limited due to there being a great many three-port devices in the system.
A tunable filter can be provided to resolve the above-mentioned problems. The tunable filter can selectively add or drop particular wavelength channels from a multi-wavelength network. Tuning mechanisms used include thermo-optic, electro-optic, and piezoelectric mechanisms.
Arrayed Waveguide Grating (AWG) technology is based on a thermo-optic mechanism. However, AWG systems are not directly tunable, and have high loss and slow tuning speed.
A Mach-Zehnder Interferometer typically uses electro-optic actuation. However, manufacturing of such interferometer is very complicated because four reflecting surfaces thereof need to be parallel.
A piezoelectric tunable Fabry-Perot filter is described in J. Stone and L. W. Stulz, “Pigtailed High-Finesse Tunable Fibre Fabry-Perot Interferometers With Large, Medium and Small Free Spectral Ranges” Elect. Lett., Vol. 23, pp. 781-783 (Jul. 16, 1987). This article describes three Fabry-Perot filter prototypes and their test results. All three designs use standard lead zirconate titanate (PZT) piezoelectric components for tuning. These filters yielded finesse values up to 200. Furthermore, an insertion loss as low as 1.5 dB is observed for lower finesse values. These mechanically tunable filters have excellent wavelength selectivity and low insertion loss. Since they are mechanically tuned, however, they can only attain tuning speeds in the order of milliseconds.
A tunable optical filter is disclosed in U.S. Pat. No. 5,062,684, the disclosure of which is incorporated herein by reference. Referring to
FIG. 3
, a tunable optical filter
20
comprises two spaced ferrules
24
that are aligned along a common axis
28
and symmetrically oppose each other. Each ferrule
24
has an inmost end face
34
, and a wafer
30
attached by adhesive material
31
to the end face
34
. The wafer
30
has an inmost end face
38
. A mirror
40
comprising alternating layers of material, at least one of which is a dielectric material, is embedded between the end face
34
and the wafer
30
. An optical fiber
29
is disposed in a passageway
26
that is defined through the ferrule
24
and the wafer
30
along the axis
28
. The two ferrules
24
are mounted in a support
42
. The support
42
allows the ferrules
24
to be movable with respect to each other in directions along the axis
28
. The movement may be accomplished by use of a piezoelectric transducer system
44
. By applying a voltage across the transducer system
44
, a distance between the opposing ends faces
38
of the wafers
30
can be changed. The higher the applied voltage, the greater the distance between the end faces
38
. However, when the distance is changed, it is difficult to maintain accurate alignment between the optical fibers
29
. This often causes high insertion loss.
Hence, a fast tunable filter that overcomes the above-mentioned problems is desired.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a tunable filter which can tune a wavelength of a desired channel and which has the capability to manage multiple wavelengths for different channels.
In order to achieve the above object, a piezoelectric tunable filter of the present invention comprises a thin film waveguide, a ring made of piezoelectric material surrounding the thin film waveguide, and an actuator surrounding the ring. The actuator generates acoustic waves that apply an external radial force on the ring. Because the ring has piezoelectric properties, a periodic, high frequency piezoelectric signal can be generated by the action of the acoustic wave. The piezoelectric signal can be input to the thin film waveguide, and produce lattice vibration of the thin film waveguide. The lattice vibration can generate a fluctuating pattern of refractive index in the thin film waveguide due to the modulating effect of the piezoelectric signal. That is, a predetermined radial force on the ring produces a desired vibration of the thin films of the thin film waveguide. Such vibration of the thin films of the thin film waveguide produces a desired refractive index in each thin film. An optical thickness of each thin film of the thin film waveguide is changed accordingly. Thus, a desired optical wavelength equal to the combined optical thickness of two optically adjacent high refractive index thin films or two optically adjacent low refractive index thin films of the thin film waveguide can be selected to pass through the thin film waveguide.
Other objects, novel features and advantages of the present invention will be more readily understood from the following detailed description of a specific embodiment thereof when read in conjunction with the accompanying drawings, in which:


REFERENCES:
patent: 5062684 (1991-11-01), Clayton et al.
patent: 6363089 (2002-03-01), Fernald et al.
patent: 6507693 (2003-01-01), Maron et al.
patent: 6535665 (2003-03-01), Kim et al.
patent: 6597711 (2003-07-01), Fernald et al.
patent: 6650810 (2003-11-01), Lieberman et al.

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