Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-07-19
2003-03-18
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S019000, C359S230000, C359S224200
Reexamination Certificate
active
06535663
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the field of microelectromechanical systems and, more particularly, to microelectromechanical or micromechanical devices that actuate a moving element between operative positions to provide, for example, a switching operation.
BACKGROUND OF THE INVENTION
A microelectromechanical system (MEMS) is a micro-device that is generally manufactured using integrated circuit fabrication or other similar techniques and therefore has the potential for cost-effective, large-scale production. A MEMS device is a high precision system used to sense, control, or actuate on very small scales by combining mechanical, electrical, magnetic, thermal and/or other physical phenomena. It typically includes a tiny mechanical device element such as a sensor, mirror, valve, or gear that is embedded in or deposited on a semiconductor chip or substrate. These systems may function individually, or they may be combined in array configurations to generate effects on a larger scale. Advantageously, a MEMS device may be monolithically integrated with driving, control, and/or signal processing microelectronics to improve performance and further reduce the cost of manufacturing, packaging, and instrumenting the device. As used herein, the term microelectromechanical (MEMS) device is intended to embrace devices that are physically small and have at least one component produced using micromachining or other microfabrication techniques, and the term MEMS device includes microactuators, micromechanical devices, and micromachine devices.
Due to their considerable technological potential, the use of MEMS is currently being pursued in many different fields. In particular, high precision MEMS are receiving an increasing amount of interest in the fiber-optics field because of their capability to overcome several limitations associated with prior art technologies: see generally Motamedi et al., “Micro-opto-electro-mechanical devices and on-chip optical processing”,
Optical Engineering,
vol. 36, no. 5, p. 1282 (May 1997), the contents of which are incorporated herein by virtue of this reference.
In fiber-optic communication systems, information is transmitted as a light or laser beam along a glass or plastic wire, known as a fiber. A significant amount of electronic communication and information transfer is effected through fiber-optic lines due to their much broader bandwidth and lower susceptibility to electromagnetic interference compared to conventional copper or metal wires. For example, much of the Internet and many long distance telephone communication networks are connected with fiber-optic lines. However, fast and efficient switching between optical fibers in a fiber-optic network has been difficult to achieve. Switches are needed to route signals at the backbone and gateway levels of these networks where one network connects with another, as well as at the sub-network level where data is being transported from its origin or to its destination. In addition, in a wavelength division multiplexed (WDM) optical fiber network, many channels, each occupying a distinct wavelength of light, may share the same fiber. In a WDM network, optical add-drop multiplexers and demultiplexers are used to introduce supplementary optical channels into the main optical fiber path and/or divert optical channels from the main fiber path.
Various prior art optical switching technologies have been employed. In electrical cross connect switch technology, the optical signal is transformed into an electrical signal, a switching operation is performed with an electronic switch, and the electrical signal is then transformed back into the optical domain. However, electrical cross connects are inefficient and costly. Another prior art solution is to use an optical switch or cross-connect (OXC) capable of connecting and disconnecting optical fibers in the optical domain. Integrated optical OXC devices have been used for this purpose. These devices are constructed of a material, such as lithium niobate, generally in a planar waveguide configuration that allows switching action to take place between various input and output ports. These switching devices do not add a latency or delay to the optical data. However, integrated optical devices have several drawbacks: they are relatively expensive; their minimum size is limited by the physics of optical waveguides; their operation depends strongly on wavelength and is sensitive to polarization; and they result in considerable cross talk and signal attenuation in the fiber optic paths.
In contrast, optical switches based on emerging MEMS technology, including micromechanical or micromachined systems, boast considerable promise for overcoming many of the limitations associated with alternative prior art fiber-optic switching technologies. Optical MEMS systems, also referred to as microoptoelectromechanical systems (MOEMS), use microoptical elements that reflect, diffract, refract, collimate, absorb, attenuate, or otherwise alter or modulate the properties and/or path of a light beam or signal. These types of optical switches can be made very compact and small, typically within the micrometer to millimeter range. The insertion loss of a MOEMS switch interface is comparable to alternative technologies, and occurs mainly at the entry port of the switch where light leaves a first optical fiber and at the exit port of the switch where light re-enters a second optical fiber. These losses are due to the enlargement of the beam dimensions in free space, however, as will be appreciated by those skilled in the art, using appropriate lenses can decrease this effect. The medium of a MOEMS switch is typically air, but a vacuum, inert gas, or other suitable fluid may also be used. The transmission of light within the switch medium amounts for only a small portion of the overall attenuation. Additionally, the non-blocking medium of the switch ensures that no interference occurs when different light paths cross, enabling light beams to traverse without mutual effect, attenuation, or cross-talk: see generally, Hecht J., “Optical switching promises cure for telecommunications logjam”,
Laser Focus World,
page 69, (September 1998), the contents of which are incorporated herein by virtue of this reference. This property further enables the utilization of MOEMS switches in complex array configurations.
For example, micromachined optical switches often use small mirrors that move to perform a switching operation. By actuating the moving element between a first position in which a light beam is allowed to pass unaffected by the mirror and a second mirror position in which the moving element reflects or interferes with the light beam, the path of an input light beam can be redirected into different outputs or otherwise interfered with. The use of mirrors, in particular, is advantageous since they operate independently of wavelength when reflecting an optical beam. However, MEMS switches or valves may also use other types of moving elements such as attenuators, filters, lenses, collimators, modulators, and absorbers to perform a desired switching operation.
In general, to achieve low attenuation losses in a micromachined optical switch, a mirror or other optical element should be very smooth and of optical grade. In addition, the principle and means used to actuate the moving element of a MEMS device should be fast, simple, and provide reproducible and accurate alignment of the moving element. Furthermore, the actuator must be able to move that element by a sufficient amount to accomplish the switching task.
Several prior art MEMS optical switching devices are known,. as for example those described by Toshiyoshi et al., “Electrostatic Micro Torsion Mirrors for an Optical Switch Matrix”,
Journal of Microelectromechanical Systems,
vol. 5 no. 4, p. 231 (December 1996) and by Marxer et al., “Vertical Mirrors Fabricated by Deep Reactive Ion Etching for Fiber Optic Switching Applications”,
Journal of Microelectromechanical Systems,
vol. 6, no. 3, p. 277 (September 1997). Aksyuk
Memlink Ltd.
Palmer Phan T. H.
Pennie & Edmonds LLP
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