Acousto-optical switch for fiber optic lines

Details Acousto-optical switch for fiber optic lines Acousto-optical switch for fiber optic lines

2001-02-22

2003-03-25

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

Directional optical modulation within an optical waveguide

Acousto-optic

C385S016000, C385S022000

Reexamination Certificate

active

06539132

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to switches for fiber optic lines. More particularly, it relates to an optical switch for coupling a single fiber optic line to a plurality of fiber optic lines or for coupling a plurality of fiber optic lines to a single fiber optic line.
BACKGROUND OF THE INVENTION
Increasingly, fiber optic communication lines are used in place of, or in conjunction with, electrical communication systems. Fiber optic lines are advantageously unaffected by ambient electromagnetic fields, can provide faster communication lines and can carry a broader bandwidth than electrical lines.
Fiber optic cables are often organized in bundles which include a large number of individual optic fibers, each of which may be coupled to a separate device. In order for each device to communicate with a remote device that is accessible only through a single optic trunk fiber, it is necessary to provide an optical switch which couples the device's specific optic fiber with the the trunk fiber. It is desirable that such an optical switch be capable of switching rapidly so that different devices may be sequentially connected to the trunk fiber with minimal switching delays.
U.S. Pat. No. 5,757,990 describes an optical switch that allows an input optical signal to be switched between two optical outputs. The switch includes an optically active substrate which is responsive to electrical signals to control its refractive index. When an electric signal is applied in a positive direction, the refractive index of the substrate is altered to direct the input optical signal to one of the optic outputs. When the electric signal is applied in a negative direction, the refractive index is inversely altered to direct the input optical signal to the other output. Such an optical switch may be constructed to have a switching time on the order of 10 &mgr;S, and possibly even less. However, this device provides only two optical outputs, and therefore is not suitable use in connecting a trunk optic fiber with a large number of local optic fibers.
U.S. Pat. No. 4,491,384 discloses an optical switch that can switch an input optical signal between a number of optic outputs. The device has a piezoelectric substrate with a waveguide layer. A pair of interdigital transducers (IDTs) are formed on the waveguide layer. Each of the IDTs can selectively produce surface acoustic waves (SAWs) on the piezoelectric substrate. An input optical signal received by the waveguide layer may be refracted by one or both of the surface acoustic waves, allowing the input optical signal to be directed to one of three optical outputs. By adding additional IDTs, the number of optical outputs may be increased. However, because this device uses a thin surface layer to deflect the input optical signal, it cannot practically be used to couple the optical input signal with a large number optic outputs. Furthermore, the efficiency of this device is limited, particularly where a large number of IDTs is used to provide additional optical outputs, since this will, in general, increase the number of times the input optical signal must be deflected to reach some of the optical outputs.
U.S. Pat. No. 5,621,829 to Ford discloses a device and method for selectively connecting an input optic fiber in a fiber bundles to at a selected output optic fiber in a fiber bundle. The device includes a collimator which directs an optical signal from the input fiber onto a scan mechanism. The scan mechanism reflects the optical signal back through the collimator onto the output fiber. The scan mechanism described comprises a mirror that may be moved by a mechanical system to reflect the optical signal into the output fiber. The scan mechanism and collimator together act as an optical switch. Although this switching device can couple the input fiber to a large number of output fibers in the fiber bundle, the device has a relatively long switching delay. The delay is required to reposition the mirror when the optical signal is to be reflected onto a different output fiber in the fiber bundle. Typically, these devices have a switching time on the order of 1 millisecond or more. Although the patent states that the scan mechanism may also be a liquid crystal or electro-optical device, no explanation is given as to how these devices might be implemented.
Accordingly, there is a need for an optical switch which can be used to couple a first optic fiber with a second optic fiber selected from a fiber bundle and which can switch between different fibers in the fiber bundle with a relatively short propogation delay. It is preferable if the optical switch is operative in both directions to allow signals emitted from either the first or second optic fiber to be received by other optic fiber. Further, it is preferable if the switch has a relatively high efficiency so that a large proportion of light incident on the switch is transmitted by the switch.
SUMMARY OF THE INVENTION
This invention provides an acousto-optical switch for coupling a first optic fiber to a second optic fiber. The second optic fiber may be one of many optic fibers in a fiber bundle. The switch includes a controller which generates two frequency modulated electrical control signals. Each control signal is received by a piezoelectric transducer which generates a three dimensional acoustic wave in a corresponding optically active element coupled to the piezoelectric transducer, thereby changing the diffraction angle of the optically active element. The piezoelectric transducers and optically active elements are arranged so that their respective diffraction angles are generally at right angles to one another. An optical signal emitted by the first optic fiber is passes through the optically active elements in turn and is deflected in two dimensions. The frequencies of the acoustic waves are selected such that the optical signal is deflected into the second optic fiber.
In a first aspect, the present invention provides an optical switching apparatus for coupling a first optic fiber with a second optic fiber, said switch comprising: a controller for producing a first electric signal and a second electric signal; first and second optically active elements, each of said optically active elements having a diffraction angle; first and second piezoelectric transducers coupled to said controller for receiving said first and second electric signals, said first piezoelectric transducer being coupled to said first optically active element and being responsive to said first electric signal to produce a first acoustic wave in said first optically active element, said second piezoelectric transducer being coupled to said second optically active element and being responsive to said second electric signal to produce a second acoustic wave in said second optically active element, wherein the diffraction angle of said first optically active element corresponds to said first acoustic wave, and wherein the diffraction angle of said second optically active element corresponds to said second acoustic wave, and wherein an optical signal emitted from said first optic fiber is deflected by said first and second optically active elements into said second optic fiber.
In a second aspect, the present invention provides an optical switch for coupling a first optic fiber with a second optic fiber, said switch comprising: a controller for producing an electric signal; a piezoelectric transducer for receiving said electric signal and providing an acoustic signal corresponding to said electric signal; an optically active element responsive to said acoustic signal for controlling the diffraction angle of said optically active element, wherein said controller generates a signal to control the diffraction angle of said optically active element such that an optical signal emitted from said first fiber passes through said optically active element and is deflected into said second optic fiber.
In a third aspect, the present invention provides a method for directing an optical signal emitted from a first optic fiber in

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