Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-01-20
2001-06-26
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S018000, C385S019000
Reexamination Certificate
active
06253001
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to optical switches and more particularly to optical cross-connected switches having micromirrors that are individually manipulated.
BACKGROUND ART
Continuing innovations in the field of fiberoptic technology have contributed to the increasing number of applications of optical fibers in various technologies. With the increased utilization of optical fibers, there is a need for efficient optical devices that assist in the transmission and the switching of optical signals. At present, there is a need for optical switches that direct light signals from an input optical fiber to any one of several output optical fibers, without converting the optical signal to an electrical signal.
The coupling of optical fibers by a switch may be executed using various methods. One method of interest involves employing a micromirror that is placed in the optical path of an input fiber to reflect optical signals from the input fiber to one of alternative output fibers. The input and output fibers can be either uni-directional or bidirectional fibers. In the simplest implementation of the mirror method, the input fiber is aligned with one of two output optical fibers, such that when the mirror is not placed in the optical path between the two fibers, the aligned fibers are in a communicating state. However, when the mirror is placed between the two aligned fibers, the mirror steers (i.e., reflects) optical signals from the input fiber to a second output fiber. The positioning of the mirror relative to the path of the input fiber can be accomplished by using an apparatus that mechanically moves the mirror. There are number of proposals to using micromachining technology to make optical signals. In general, the proposals fall into two categories: in-plane free-space switches and in-plane guided wave switches. Free-space optical switches are limited by the expansion of optical beams as they propagate through free space. For planar approaches, the optical path length scales linearly with the number of input fibers. Switches larger than 30×30 require large mirrors and beam diameters on the order of 1 millimeter (mm). For these planar approaches, the number (N) of input fibers scales linearly with the beam waist and the size of the optical components. Thus, the overall switch size grows as N
2
. It is estimated that a 100×100 switch would require an area of 1 m
2
, which would be a very large switch. Moreover, constraints such as optical alignment, mirror size, and actuator cost are likely to limit the switch to much smaller sizes. One planar approach claims that the optical switch can be designed so that it scales with the optical path difference, rather than the overall optical path. If this is possible, it would certainly allow larger switches. However, the optical path difference also scales linearly with the number of input fibers for a planar approach, so the switch grows very large as it is scaled to large fiber counts.
For guided wave approaches, beam expansion is not a problem. However, loss at each cross point and the difficulty of fabricating large guided wave devices are likely to limit the number of input fibers in such switches.
For both approaches, constraints such as loss, optical component size, and cost tend to increase with the number of fibers. There is a need for an optical cross connect switch which scales better with the number of input and output fibers. Some free-space optical systems can achieve better scaling. These systems make use of the fact that it is possible to use optical steering around in two directions to increase the optical fiber count. Recently, optical switches that use such mirrors have been announced. The systems use piezoelectric elements or magnetically or electrostatically actuated micromirrors. The actuation method for these approaches is often imprecise. To achieve a variable switch, it is typically necessary to use a very high level of optical feedback.
What is needed is a micromachine that enables steering of optical signals from at least one input to a number of alternative outputs, where the arrangement of the outputs is not limited to a linear configuration. What is further needed is a method of fabricating and arranging arrays of the micromachines such that the switching is accurate and repeatable.
SUMMARY OF THE INVENTION
In one embodiment of an optical switch, a micromachine for steering optical signals includes utilizing electrostatic forces to manipulate a dual-axis micromirror. The micromirror is supported adjacent to a substrate to enable movement of the micromirror relative to the substrate. A first surface electrostatic arrangement is configured to generate electrostatic forces for rotating the micromirror about a first axis. Similarly, a second surface electrostatic arrangement is configured to generate electrostatic forces for rotating the micromirror about a second axis. The two electrostatic arrangements may be used to drive a single mover that controls the positioning of the micromirror, or may be used to drive separate movers.
Preferably, an array of micromirrors is formed on a substrate. In one application, the micromirrors are formed separately from the electrostatically driven movers. For example, a micromirror substrate may be formed to include an array of micromirrors in a side-by-side relationship, with the micromirrors being supported to allow rotation about perpendicular first and second axes. The micromirror substrate may then be attached to a mover substrate on which the movers are incorporated, such that the micromirrors are generally parallel to the paths of the movers. Each micromirror may be connected to a projection that extends toward the mover substrate and that is controlled by at least one of the movers. In this embodiment, the movers manipulate the projections in a manner similar to manipulation of joysticks.
In another embodiment, the micromirrors and movers are integrated onto a single substrate. Each micromirror may be supported on the substrate by means of a frame. A first mover is driven by electrostatic forces to manipulate the position of the frame, thereby rotating the micromirror about one axis. A second electrostatically driven mover may be connected to the micromirror to rotate the micromirror about the second axis. However, there may be embodiments in which a single mover is used to control rotations about both axes. For example, the mover may be electrostatically driven in two perpendicular directions.
Each surface electrostatic arrangement includes at least two sets of electrodes. For a particular surface electrostatic arrangement, a first set of drive electrodes may be formed along a surface of a mover, while a second set of drive electrodes is formed along a surface of the substrate. The lengths of the electrodes are perpendicular to the direction of travel by the mover. The drive electrodes are electrically coupled to one or more voltage sources that are used to provide an adjustable pattern of voltages to at least one of the sets of drive electrodes. The change in the electrostatic force that results from variations in the voltage patterns causes movement of the mover. As an example, the first set of drive electrodes may be electrically connected to a voltage source that provides a fixed pattern of voltages, while the second set is electrically connected to a microcontroller that is configured to selectively apply different voltages to the individual drive electrodes. The reconfiguration of the applied voltage pattern modifies the electrostatic forces between the substrate and the mover, thereby laterally displacing the mover.
Each surface electrostatic arrangement preferably includes levitator electrodes on the same surfaces as the drive electrodes. Unlike the drive electrodes, the levitator electrodes are positioned with the length of the electrodes parallel to the direction of travel by the mover. An acceptable fixed voltage pattern along the levitator electrodes is one that alternates between high and low voltages. Repulsive electrostat
Agilent Technologie,s Inc.
Palmer Phan T. H.
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