Optical: systems and elements – Optical modulator
Reexamination Certificate
1999-09-27
2001-08-14
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
C359S290000, C359S291000, C359S245000, C359S871000, C385S140000, C310S306000
Reexamination Certificate
active
06275320
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microelectromechanical optical attenuator structures, and more particularly to variably controlled, microelectromechanically actuated, optical attenuators and methods of fabricating such structures.
BACKGROUND OF THE INVENTION
Advances in thin film technology have enabled the development of sophisticated integrated circuits. This advanced semiconductor technology has also been leveraged to create MEMS (Micro Electro Mechanical System) structures. MEMS structures are typically capable of motion or applying force. Many different varieties of MEMS devices have been created, including microsensors, microgears, micromotors, and other microengineered devices. These MEMS devices can be employed in a variety of applications including hydraulic applications in which pumps and valves are used and optical applications that include MEMS light valves and shutters. Currently, MEMS devices are being developed for a wide variety of applications because they provide the advantages of low cost, high reliability and extremely small size.
Design freedom afforded to engineers of MEMS devices has led to the development of various techniques and structures for providing the force necessary to cause the desired motion within microstructures. For example, microcantilevers have been used to apply rotational mechanical force to rotate micromachined springs and gears. Electromagnetic fields have been used to drive micromotors. Piezoelectric forces have also successfully been used to controllably move micromachined structures. Controlled thermal expansion of actuators or other MEMS components has been used to create forces for driving microdevices. One such device is found in U.S. Pat. No. 5,475,318 entitled “Microprobe” issued Dec. 12, 1995 in the name of inventors Marcus et al., which leverages thermal expansion to move a microdevice. A micro cantilever is constructed from materials having different thermal coefficients of expansion. When heated, the bimorph layers arch differently, causing the micro cantilever to move accordingly. A similar mechanism is used to activate a micromachined thermal switch as described in U.S. Pat. No. 5,463,233 entitled “Micromachined Thermal Switch” issued Oct. 31, 1995 in the name of inventor Norling.
In addition, U.S. Pat. No. 5,909,078 entitled “Thermal Arched Beam Microelectromechanical Actuators” which issued Jun. 1, 1999 in the name of inventors Wood, et al., describes thermal actuators having a pair of arched beams extending between a pair of supports disposed on a microelectronic substrate. By passing current through the arched beams, the arched beams will expand so as to further arch. The thermal actuator of the Wood patent can also include an actuator member that connects a plurality of arched beams and serves to push against a workpiece.
The need exists to develop MEMS actuated variable optical attenuators that will benefit from the low cost fabrication, high reliability and size advantage that are characteristic of similar MEMS structures. Of particular importance in optical attenuation is the need to fabricate devices that are variable over a full optical power range and benefit from low insertion loss. By providing a device capable of attenuating optical power across a much larger dynamic power range, it would be possible to attenuate beams that have a much wider optical beam and/or an unfocussed beam at the point of attenuation. Additionally, a MEMS actuated variable optical attenuator would provide for finer and more precise control over the optical attenuation allowing for the transmitted optical power to be dynamically altered as required by the specific application. It is also desirable to devise a MEMS actuated variable optical attenuator that would benefit from less power consumption. To date, however, MEMS activated variable optical attenuators are not available, at least not commercially, even though such MEMS variable optical attenuators will likely be instrumental in future light wave communication systems and optoelectronic systems.
SUMMARY OF THE INVENTION
The present invention provides for improved MEMS variable optical attenuator devices. Further, a method for using and a method for making the MEMS variable optical attenuators according to the present invention are provided.
A MEMS variable optical attenuator according to the present invention comprises a microelectronic substrate, a microelectronic actuator disposed on the substrate and an optical shutter disposed on the substrate. The optical shutter is actuated by the microelectronic actuator and is adapted to be held at various attenuation positions, each position blocking a different percentage of optical power. In attenuating optical signals in such a fashion, the variable optical attenuator of the present invention is capable of attenuating an optical beam across a full optical power range. Additionally, the variable optical attenuator of the present invention may comprise an electrostatic clamping element operably connected to the optical shutter. The clamping element provides for the optical shutter to be electrostatically clamped at a desired attenuation position with very low standby power being applied to the MEMS actuator. In one embodiment of the invention, the MEMS actuator comprises a thermal arched beam actuator.
In one embodiment of the MEMS variable optical attenuator according to the present invention, the MEMS actuator and the optical shutter lie in-plane with the substrate and attenuate an optical beam that is generally perpendicular to the substrate and passes through an opening in the substrate. In another embodiment of the present invention, the MEMS actuator and the optical shutter of the MEMS variable optical attenuator lie in-plane with the substrate and attenuate an optical beam that is generally parallel to the substrate.
Alternatively, another embodiment of the present invention provides for the MEMS actuator to lie in-plane with the substrate and the optical shutter to lie in a plane generally perpendicular to the substrate and attenuate an optical beam that is generally parallel to the surface of the substrate. In addition, the present invention may provide for the MEMS actuator and optical shutter to lie in plane with the substrate with the optical shutter being extended beyond the edge of the substrate upon activation thereof so as to attenuate optical beams lying in planes outside the periphery of the substrate.
In another embodiment of the present invention, the variable optical attenuator may comprise an array of MEMS actuators configured so as to provide the optical shutter with greater displacement distances. MEMS actuators configured in an array benefit from increases in force or distance. In this manner, the optical shutter is capable of attenuating optical beams having wider cross-sections or unfocussed optical beams. Additionally, variable optical attenuators can also have multiple MEMS actuators configured so as to actuate a central hub that provides force to levers operably connected to optical shutters. Such a rotary hub arrangement utilizes mechanical advantages to provide increased actuation displacements and greater attenuation range. Alternatively, the present invention may comprise more than one optical shutter actuated from more than one MEMS actuator in which the optical shutters converge at the optical beam to provide attenuation. In such an arrangement, the shutters may be shaped so as to allow for an operative seal to form amongst the adjoining optical shutters.
In yet another embodiment of the present invention, the variable optical attenuator may comprise a microelectronic substrate having a generally planar surface and a thermal bimorph cantilever structure comprised of at least two materials having different coefficients of thermal expansions. A portion of the thermal bimorph is affixed to the substrate and another portion is released from the substrate so that when thermal activation is applied to the bimorph structure the bimorph moves in a direction consistent with the materi
Dhuler Vijayakumar R.
Hill Edward A.
Mahadevan Ramaswamy
Walters Mark David
Wood Robert L.
Ben Loha
JDS Uniphase Inc.
Myers Bigel & Sibley & Sajovec
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