Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-04-05
2004-09-28
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000
Reexamination Certificate
active
06798942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention relates generally to the field of optical switching devices for use in optical networks. In particular, embodiments of the present invention relate to a micro electromechanical magnetically controlled optical switch that is particularly useful for switching optical signals between a plurality of optical fibers.
2. The Relevant Technology
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper conductor.
Many conventional electrical networks are being upgraded to optical networks to take advantage of the increased speed and efficiency. One of the many required components of an optical network is an optical switching device. An optical switching device has the capability of switching an individual light signal between at least two different locations. Usually the optical signal is first demultiplexed or dispersed and the individual channels are switched and routed to specific locations. It is preferable to optically switch the optical signals rather than converting them to electrical signals and then switching them with conventional electrical switching techniques.
The field of optical switching has progressed rapidly in the last decade. For large bandwidth applications, it is important that the optical switches be extremely small to allow many channels to be switched in a relatively small amount of space. The newest types optical switches fit into the general category of micro-electromechanical systems (MEMS). The size of these devices is typically on the order of microns. Three narrower categories of MEMS optical switches have emerged as the most promising design configurations: piezoelectric, electrostatic and electromagnetic. All of these switches utilize micro-mirrors to switch or reflect an optical channel or signal from one location to another depending on the relative angle of the micro-mirror. Because of the small size of optical MEMS switches, it is important to design a switch that is durable, consumes little power and can generate a sufficient amount of power to rotate the mirror. Durability is important because, over the lifetime of a switch, it is quite common for dust and other debris particles to pass within the switch. Power consumption in optical switches must be minimized because optical switches are usually in operation at all times and therefore any unnecessary power consumption is a significant waste of resources. It is also important for the optical switch design to be capable of generating sufficient forces to rotate the mirror within a large range of angles.
Piezoelectric switches utilize piezoelectric materials to change shape proportionally to how much electrical voltage is applied to them. The mirror is then attached to the piezoelectric material, which can be manipulated by applying varying degrees of electrical voltage. Unfortunately, piezoelectric materials used in optical switches tend to require relatively high (100V range) voltages to produce relatively small motions, which limit the angular range the mirror is capable of achieving. Piezoelectric materials also tend to be somewhat fragile and susceptible to long term drift.
Electrostatic switches are currently the most popular form of MEMS optical switches. These switches utilize the small electrostatic force produced by a diamagnetic material when an electrical field is induced upon it. Unfortunately, electrostatic optical switches require high voltages (high by 3V CMOS standards but generally less than required to actuate piezoelectric switches) and produce relatively small forces. This means that it is difficult to design an individual electrostatic optical switch that is capable of switching between a large number of fibers. For this reason, electrostatic optical switches are typically used in large arrays. In addition, these switches tend to be fragile to foreign particulates and sensitive to moisture.
Electromagnetic switches are the last category of typical MEMS optical switches. This form of optical switch is rarely used despite the numerous advantages they possess over other types of MEMS switches. Electromagnetic optical switches tend to utilize ferromagnetic materials to rotate and manipulate the angle of the mirror. Ferromagnetic materials are easily magnetized and are capable of producing large forces. A hard ferromagnetic material has a wide hysteresis curve (B v H or Magnetic curve) and therefore has the ability to generate remnant magnetization even after an external magnetic field is turned off. For this reason, hard ferromagnetic materials are commonly used to make permanent magnets. A soft ferromagnetic material has a relatively narrow hysteresis curve and consequently is incapable of producing a magnetic force without an external magnetic field being applied across it. Electromagnetic optical switches are capable of generating large forces while consuming little power. In addition, electromagnetic optical switches are durable to particles that may otherwise interfere with the performance of other switches.
There is a need in the industry for an efficient electromagnetic MEMS optical switch that consumes low power yet is still durable in relation to other forms of optical switches.
BRIEF SUMMARY OF THE INVENTION
These and other problems in the prior art are addressed by embodiments of the present invention, which relates to a MEMS electromagnetic optical switch that generates large magnetic forces and consumes little energy.
In a preferred embodiment, the electromagnetic optical switch generally comprises a reflection member rotatably coupled to a base. The optical switching function of the device is performed by rotating the reflection member to a specified angle so as to redirect an optical signal to one of a plurality of output locations. The reflection member further comprises a substrate with a mirror coupled to one surface of the substrate and at least one substrate magnetic member connected to the opposite surface of the substrate. The mirror naturally reflects an incident optical signal in a direction mathematically related to the angle of the mirror itself with respect to normal. The substrate magnetic members are permanent ferromagnetic magnets.
In a preferred embodiment, the electromagnetic optical switch further comprises a plurality of magnetic members and a plurality of electrical assemblies. The magnetic members are preferably formed from a hard ferromagnetic material with a high saturation point and a low coercivity. The magnetic members are disposed in substantial alignment with the substrate magnetic members of the reflection member. The electrical assemblies are further comprised of a conductor, a switch and a source. The conductor is configured to apply a magnetic field across one of the plurality of magnetic members when a current is induced through the conductor. The conductor is electrically connected to the source. The switch is disposed on the electrical connection between the conductor and the source so as to control the current flow from the source to the conductor.
In one preferred embodiment, the electromagnetic optical switch is operated by magnetically rotating the reflection member so as to deflect incident optical signals to a desired output location. This is accomplished by first switching the switch to electrically connect the source to the conductor of the electrical circuit. This causes a magnetic field to be genera
Freeman William R.
Meyer Dallas
Finisar Corporation
Lee John D.
Lin Tina M
Workman Nydegger
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