Optical cross point switch using deformable micromirror

Details Optical cross point switch using deformable micromirror Optical cross point switch using deformable micromirror

1999-01-21

2001-04-03

Ngo, Hung N. (Department: 2874)

Optical waveguides

With optical coupler

Switch

C385S018000, C385S020000

Reexamination Certificate

active

06212309

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to semiconductor devices, and in particular to a device for switching photonic signals in optical networking applications.
BACKGROUND OF THE INVENTION
Optical fibers are used to carry high speed data as optical signals. These optical signals must be switched between fibers to allow a signal routing function. There are a currently number of methods for achieving switching.
FIG. 1
shows an electromechanical arrangement, where a signal in an optical fiber A is routed to fiber B by mechanically aligning fiber A with fiber B. This arrangement is bulky and mostly suited only 1×N configurations.
An alternative solution is to use a hybrid optical switch. This arrangement is shown in FIG.
2
. Firstly, the optical signals are converted to electrical signals, which are switched in a conventional manner, and the resulting outputs of the switch matrix are converted back to optical signals. The conversion process inherently makes this type of switching unidirectional.
Semiconductor optical switches are known. Presently, these are wave guide based and rely on the change of refractive indices in the waveguides under the influence of an external electric field, current or other perturbations. The most common types are: directional coupler switches, mach-zehnder interferometers, and digital optical switches.
A directional coupler switch, as shown in
FIG. 3
, consists of two coupled semiconductor wave guides. Light is injected into one of two input waveguides. When the signal reaches a region where two waveguides are weakly coupled to one another, light can be transferred from one guide to the other by altering the index of refraction of one of the guide with respect to the other. To construct a 4×4 crosspoint switch, four of these couplers are required as shown in FIG.
4
.
A Mach-Zehnder interferometer is shown in FIG.
5
. This consists of an input waveguide and an output waveguide. Light in the input waveguide is split into two paths associated with respective electrodes. The two paths recombine at the output. Depending on the optical path difference that can be electronically controlled by impressing an electrical signal on one of the electrodes, the interference at the output Y-junction can be destructive or constructive depending on the relative phase of the two paths.
As is the case with directional couplers several of these switches must be cascaded to perform the NXN switching function.
A digital optical switch is shown in FIG.
6
. Such switches operate on the “adiabatic change” principle. A beam is split into two optically identical arms with equal intensity in each arm. By influencing electrodes associated with each arm, the effective index in one arm can be reduced sufficiently to transfer all the light in this arm to the other. These switches must also be cascaded to achieve N×N switching.
An object of the invention is to alleviate this problem.
SUMMARY OF THE INVENTION
According to the present invention there is provided a photonic switching device comprising a first set of optical waveguides, a second set of optical waveguides, first and second opposed arrays of controllable deformable micromirrors associated respectively with said first and second sets of optical waveguides, at least one of said arrays being arranged in rows and columns, and means for selectively tilting pairs of said micromirrors, one from each array, to complete an optical path from any one of said first set of optical waveguides to any selected one of said second set of optical waveguides.
Micromirrors are known per se, and are described, for example, in U.S. Pat. No. 4,698,602. They consist of numerous mirror elements suspended on a substrate by mechanically compliant torsion hinges that allow individual mirrors to be tilted under the application of a voltage to a control electrode associated with each mirror element. They are typically used in imaging applications.
In the preferred embodiment, the arrangement of deformable micromirrors comprises first and second opposed arrays of controllable deformable micromirrors arranged in rows and columns, a first set of optical waveguides associated with the rows of one of said arrays, and a second set of optical waveguides associated with the columns of the other of said arrays, whereby selected micromirrors from each of said arrays can be tilted to complete an optical path from any one of said first set of optical waveguides to a selected one of said second set of optical waveguides.
For reasons to be explained in more detail, the arrays are arranged in a non-rectangular grid, i.e. with the rows intersecting the columns at an oblique angle in a rhombic arrangement. The columns are skewed by an amount such that they are aligned with the reflected light beams. The mirrors are rotationally offset with respect to the path of the light beams by an amount which ensures that an input beam is reflected off an input mirror to an output mirror, where it is reflected in the plane of the output mirrors.
The optical waveguides are preferably coupled to fibers set in micromachined grooves on the substrate supporting the micromirrors.
The invention also provides a method of switching optical signals between a first set of optical waveguides and a second set of optical waveguides, comprising the steps of a) deploying first and second opposed arrays of controllable deformable micromirrors between said first and second set of waveguides, at least one of the arrays being arranged in rows and columns, and b) controlling pairs of said micromirrors, one from each array, to selectively complete an optical path between any one of said first set of waveguides and any selected one of said second set of waveguides.


REFERENCES:
patent: 4698602 (1987-10-01), Armitage
patent: 5345521 (1994-09-01), McDonald et al.
patent: 5960132 (1999-09-01), Lin
patent: 296-18-818 (1996-12-01), None
Toshiyoshi et al, “Electrostatic Micro Torsion Mirrors for an Optical Switch Matrix”, Journal of MicroelectromechanicalSystems, vol. 5, No. 4, pp. 231-237, Dec. 1996.

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