Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-11-16
2004-01-20
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S017000, C359S223100, C359S224200
Reexamination Certificate
active
06681063
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device used for directing optical signals throughout a fiber optic network. Specifically, the present invention provides a key component for the implementation of all-optical communication networks.
The growing demand for increased data rate transmission throughout communication networks has recently created tremendous interest in the field of fiber optic telecommunication. With the deployment of fiber optic cables and the use of dense wave division multiplexing (DWDM), optical data transmission has allowed much greater transmission rates in comparison to its electrical counterpart. Fiber optic cables, each carrying multiple wavelengths of light, are replacing metallic cables. Each wavelength of light denotes a data channel in similar fashion to the multiplexed frequencies that denote television channels traveling through an electrical coaxial cable. Transmission of each optical signal begins with a wavelength-tuned light source at the entrance of the fiber optic cable. Each data channel or wavelength requires a light source emitting at the appropriate wavelength. The optical signals then travel throughout the network and are eventually delivered to the proper destination.
For each data stream to reach its destination, several different components located at junctions throughout the optical network are required. At these junctions, the components must perform tasks such as adding and dropping data from the optical stream, multiplexing and de-multiplexing of the data into and out of the fiber carrier, and switching and routing each data signal between optical fibers to reach its intended destination. In current fiber optic networks, many of these tasks are performed by opto-electronic components such that incoming photonic signals are converted to electrical signals before being manipulated at these junctions. For example, as an optical data stream arrives at a switching node to be switched onto another fiber, each optical signal is first converted into an electrical signal, which is then transmitted through an electrical circuit. The signals are then directed throughout the electrical circuit to the entrance of the appropriate fiber. The electrical signals must then be converted back to their optical forms before being passed along to the targeted fiber. The optical signals continue to travel throughout the optical network, transforming between optical and electrical states until the intended destination is reached.
As the demand for bandwidth increases, more opto-electronic components will be necessary to handle the increased data traffic. Additionally, existing opto-electronic interfaces currently being used cannot be utilized as advances in optical transmission are achieved. Therefore, as light sources develop and more wavelengths are transmitted along a fiber, existing opto-electronic components will need to be replaced. Furthermore, as more opto-electronic devices are deployed, more electrical power is consumed. The added cost of power consumption and the cost and time needed for device replacement has created a demand for alternative methods of photonic signal direction throughout fiber optic networks. The inherent non-scalability of existing opto-electronic interfaces presents a bottleneck in the progression of next-generation telecommnunications.
One proposed remedy is the use of optical devices that maintain the transmitting signals in the optical domain while switching and cross connecting from fiber to fiber such that no opto-electronic conversions are required. A method currently being market tested and also being proposed in the present invention is the use of micromirror arrays to reflect light from a fiber entering the junction to a targeted fiber for continuation of the signal to its appropriate destination. Through the use of micro-electromechanical systems (MEMS) techniques, micromirror arrays containing individually movable mirrors can be accurately manufactured.
Current MEMS micro-mirror arrays developed and being tested for fiber optic switching are actuated via either electrostatic or electromagnetic forces. The most common method of actuation in MEMS-based devices is currently electrostatic actuation. Such devices typically take the form of air-gap capacitors comprising a movable top electrode, a fixed bottom electrode, and air as the dielectric between the electrodes. Electrostatic forces between the electrodes causes motion in the freely movable top electrode. One limitation of electrostatic devices is the air-gap thickness, which dictates the range of motion for the top electrode. Furthermore, as the air gap increases, greater voltage is required for actuation. Since it is an air gap the problem of stiction arises where the top mirror can be stuck to the bottom electrode, hence making the device useless. This problem known as “stiction” is common to these types of devices. This can occur even during the fabrication process which results in lowered yields.
Electromagnetic MEMS-based devices utilize magnetic materials co-deposited onto the device along with coils external to the device for magnetic field generation. Such devices present a solution to the air-gap restrictions of electrostatic devices, although low voltage operation is still a challenge. Furthermore, the added need for external coils creates a larger device profile.
Therefore, there is still a demand for small form factor, low voltage operating optical switches for enabling all-optical networking. Such a device is a piezoelectrically actuated micromirror. An applied voltage across a piezoelectric material, such as quartz, barium titanate, and lead zirconium titanate, deforms the material proportionally to the voltage being applied. This deformation can be used as an actuating mechanism. Piezoelectric materials are widely used in applications where precise actuation is required such as atomic force microscopy and linear micro-positioning for electron beam lithography. Until recently, most applications have used bulk piezoelectric ceramics that required high voltage for operation. To take advantage of the precise positioning of piezoelectric actuation in MEMS devices, thin film piezoelectric materials have been developed utilizing deposition techniques such as sol-gel, metal organic chemical vapor deposition (MOCVD), and sputtering. With the use of thin film piezoelectric materials, much lower operating voltages can be utilized in comparison to bulk piezoelectric materials.
In contrast with the following prior art, the present invention uses a coplanar arrangement of extremely thin, very low voltage operated cantilevered actuators and mirrors such that one or more actuators are located on each side of each mirror enabling highly precise multi-axial motion of each mirror, often in push-pull mode.
Examples of MEMS micro-actuators utilizing piezoelectric elements can be found outlined by Furuhata and Hirano, U.S. Pat. Nos. 5,351,412, 5,489,812, and 5,709,802 and by Motamedi et al. in U.S. Pat. No. 5,903,380. The inventions proposed by Furuhata and Hirano incorporate a laminated structure formed by bonding metalized piezoelectric elements to the MEMS fabricated structure. A shortcoming of this device and method is the process of bonding a piezoelectric element to another substrate. The said method must utilize piezoelectric elements that can be adequately handled and positioned, this implies a larger operating voltage than the use of a deposited thin piezoelectric film which can be on the order of several microns thick or less. Furthermore, the efficiency of actuation is dependent upon the placement accuracy and bonding efficacy between the piezoelectric element and the MEMS structure. These shortcomings are resolved in the present invention by utilizing thin film deposition techniques and accurate photolithography. Motamedi at al. outline in their invention a low voltage optical resonator comprising sputtered zinc oxide (ZnO) as the piezoelectric material and claim operating voltages of 2 volts AC. Piezoelectric materials such as
Hughes Gareth A.
Kane Jonathan S.
Computer Optics Inc
Doan Jennifer
Lee John D.
Nathans Robert
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