Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-05-12
2002-08-06
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S033000, C385S047000, C385S052000, C359S199200, C359S199200
Reexamination Certificate
active
06430332
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to optical switching and more particularly to non-electrical switching of laser communication signals.
BACKGROUND OF THE INVENTION
In recent years optical fibers have come into wide spread use in a wide variety of applications in which optical signals are transmitted along such fibers and are switched from one fiber to another by means of an optical switch. Conventional optical switches generally include fiber positioning means, alignment signal emitter means and interconnected computer control means. A fiber positioning means is provided near the end of each fiber to selectively point the end of a given fiber in one fiber group toward the end of a given fiber in another fiber group for switched optical transmission therebetween. An alignment signal emitter means is provided near an end of and in predetermined spaced relationship to the end of each fiber to emit an alignment signal for receipt and use in controlling the fiber positioning means when aligning the ends of selected fibers in the fiber groups for switched optical transmission therebetween, for example as shown in U.S. Pat. Nos. 4,512,036 and 5,177,348. This approach requires considerable complexity and duplication of alignment means for each alignable fiber. It would be very desirable to reduce this complexity and duplication and to increase speed of switching, reliability, as well as to reduce cost in implementation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical switch that overcomes the limitations of the above noted prior art. Another object of the inventions is to provide an optical switching unit which is relatively low in cost, has high speed and is reliable in operation. Briefly in accordance of the invention, an improved optical light transmission switch employs a microelectromechanical (hereinafter MEM) movable mirror assembly with associated electromagnet coils mounted in a package and preferably including control LED's with both drive and LED signals being supplied through a wiring harness. The following described preferred embodiments relate to a hermetic package using inorganic materials in order to provide extended life, however, units can be made which include organic materials for other shorter life applications.
The package comprises an LED lead frame of suitable material such as ceramic, which mounts LED's used by the control system to aim the movable mirror as well as circuitry to electrically connect the LED's to their package terminations. As will be discussed below, the LED's provide signals for controlling the position of the movable mirror so that any two mirrors in an array can be positioned to reflect a alight beam precisely at each other so that the light beam is focused entirely on the reflective surface of the mirrors and in that way no energy of the beam is lost in the reflection process of the switched connection. The LED's are die and wire bonded to the lead frame using conventional techniques. The LED's are located so that lines drawn through diagnonal pairs would pass through a selected location on the lead frame which is referenced the movable mirror. A mirror assembly, described below, is attached to the lead frame so that the center of the mirror portion coincides with the selected location on the lead frame in order to accurately locate the mirror relative to one another for proper control of mirror movement. The mirror assembly and lead frame are mounted in a header of suitable material, such as ceramic which, along with driving means and a wiring harness, are in turn mounted on a bracket. The package is received in a housing in which an optical fiber is received and in which another mirror is disposed in alignment with the fiber for reflecting an optical signal from the fiber to the movable mirror.
MEM micromirrors are presently used to build digital micromirror display (DMD) devices where the mirrors rotate about a single axis by an electrostatic drive. The mirror of the present invention provides two axes of motion and is preferably driven magnetically. The micromirror is preferably made from a single piece of crystal material such as silicon and has three portions connected by two sets of hinges. An inner portion forms the mirror. One of the hinge pairs, one hinge on each of two opposite sides of the mirror portion, ties the mirror portion and the middle gimbals portion, which surrounds the mirror portion. This allows the mirror portion to rotate about the gimbals portion, providing the first axis of rotation. The second set of hinges ties the gimbals portion and the frame portion, one hinge on each of two opposite sides on a line disposed, 90 degrees relative to a line drawn through the first set of hinges. This allows the gimbals portion, which carries the mirror, to rotate about the frame portion, providing a second axis of rotation.
Two pair magnets, one for each axis of rotation, are used to move the mirror portion and are mounted on one face of the single piece to form a mirror assembly. The first pair of magnets are attached by suitable means to the mirror portion of the mirror assembly, one on each of two opposite sides of a line, 90 degrees relative to a line through the mirror/gimbals portions set of hinges. When magnetically stimulated, the mirror portion rotates about the mirror/gimbals portions set of hinges, providing the first axis of motion. The second pair of magnets are suitably attached to the gimbals portion of the mirror assembly, one on each of two opposite sides of a line, 90 degrees relative to a line drawn through the gimbals/frame portions set of hinges. When magnetically stimulated, the mirror and gimbals portions rotate about the second set of axis, to providing the second axis of rotation.
According to a feature of the invention, an additional magnet is provided at each magnet location, with the poles in opposing relationship to each other and disposed on the opposite face of mirror assembly to balance the weight of the magnets relative to the hinge centerlines of the mirror assembly, eliminating undesirable oscillations under external shock or other conditions.
According to a modified embodiment, a single magnet can be utilized located in the center of the mirror portion, on the face opposing the surface serving as the mirror.
According to another feature of the invention, motion stops, disposed in a plane described by the two axes of rotation, are added to the mirror assembly at each hinge location to limit motion and thereby prevent failure of the hinge. Tabs are preferably formed in the plane described by the two axes of rotation, extending from the mirror portion to the gimbals portion and from the gimbals portion to the frame portion, to prevent rotation during initial manufacture. Sometime prior to final assembly, laser or other suitable cutting means severs the tabs, preferably perpendicular to each respective axis of the hinges, to allow free rotation.
In order to obtain extended operation without degradation, the mirror assembly is preferably hermetically assembled into a cavity in the package to lock out moisture and allow the provision of a benign atmosphere for micromirror operation. The cavity can be filled with selected gases to provide improved heat transfer and, if desired, exclude oxygen or other gases that would adversely affect the micromirror over time. The hermetic package comprises the header in which the cavity is formed and which includes sealed pins for electrical LED connection pins. A peripheral seal surface on the header extending around the cavity is coated with indium or suitable non-organic seal materials, for later attachment of a window over the cavity. The use of indium allows the seal to be made at room temperature to avoid seal temperature induced stresses and window distortions. Indium or other non-organic attach materials are used exclusively to assembly all items within the body cavity of the hermetic package, avoiding any unwanted long term organic out gassing or other similar problem
Krozier David A.
Laor Herzel
Plouffe Leo A.
Fiber, LLC
Marsh & Fischmann & Breyfogle LLP
Pak Sung
Sanghavi Hemang
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