Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-01-25
2001-11-27
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C385S016000, C385S018000
Reexamination Certificate
active
06323974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the protection of optical devices. More particularly, the present invention is directed to the protection of liquid crystal switches in optical networking elements.
2. Technical Background
A principal interest of communications technologies is enhancing networking ability. The primary goals behind each form of communication developed over the years were the improvement of transmission fidelity, the increase of data rates, and the increase of distance between relay stations. The speed at which light travels and its potential to address all of these concerns logically led to attempts at optical communication. Early experiments with optical communication suggested the feasibility of modulating a coherent optical carrier wave at very high frequencies, but were commercially impractical because of the installation expense and the tremendous cost of developing the necessary components. The combination of semiconductor technology, which provided the necessary light sources and photodetectors, and optical waveguide technology, however, eventually enabled the development and application of optical fiber-based systems despite these initially perceived difficulties.
In the recent rapid development of optical transmissions, networking has become commonplace and networking architectures have become increasingly complex. Most architectures now provide a large number of client network elements with the ability to both listen and transmit on optical channels within the network. Interconnected ring architectures provide even greater connectivity and complexity by bringing together client network elements of multiple rings. A relatively basic optical network will incorporate terminal multiplexers, add drop multiplexers, optical crossconnect systems, matched nodes, and interconnect nodes.
While certain networking components have been well defined, the design of many of these elements continues to undergo rapid development. Add drop multiplexers and ring interconnect nodes, for example, require optical switching ability and have only recently begun to make use of liquid crystal switches. A liquid crystal switch (LCS) is a switching device that modulates light which is already present. Such a device is presently being marketed by Corning Incorporated, the assignee of the present invention, under the name PurePath™ Wavelength Selective Switch (WSS). While LCS's provide high switching accuracy and are readily adaptable to the increasing complexity of optical networking structures, they are large and very expensive. A substantial complication associated with the use of LCS's in networking architectures is the possibility of device failure.
The use of any large and expensive component within an optical network presents questions of reliability. Essentially, when a working optical component fails, the network architecture must provide the necessary redundancy and switching to eliminate or minimize the potential for loss of communication between client network elements. Conventional approaches have placed a redundant protection LCS in series with a working LCS. There are a number of potential shortcomings, however, associated with this configuration. Such a structure, for example, requires complex coordination between the two switches and a detailed capability to sense the particular fault and its state. It is also important to note that if the defective LCS is partially switched, an effective open circuit is created and the series protection LCS cannot cure the defect. Placing an additional LCS in series also doubles insertion losses. Furthermore, this approach fails to solve the problem of loss of communication during repair of the defective LCS.
Flexibility, cost, and complexity of the protection system are also issues of concern. One-for-one redundancy therefore substantially adds to the cost of LCS systems which are already expensive. Shared protection is therefore highly desirable. Another issue associated with reliability is switching control for the protection device. For example, for a pair of four-port working LCS's it is desirable to detect failures via a mechanism other than detection of optical signal strength, because optical signal strength can be affected by a number of components throughout the network. Reliance on optical signal strength could therefore lead to unnecessary protection switching and inefficient network operation. Accordingly, it is desirable to provide a system and method for protecting optical devices which is not dependent on optical signal strength.
SUMMARY OF THE INVENTION
In accordance with the present invention, an optical device protection system provides protection for optical devices with minimal redundancy and cost. The system includes an optical switch structure for routing an optical signal around an optical device when the optical device exhibits an error condition. A protection optical device performs a desired operation on the optical signal, wherein the optical switch structure directs the optical signal through the protection optical device. In a preferred embodiment, the defective optical device is a liquid crystal switch and the protection optical device is a protection liquid crystal switch, wherein the desired operation includes a switching operation. The use of liquid crystal switches allows error conditions to be defined by an incorrect capacitance value of the defective liquid crystal switch. The protection system of the present invention can be configured to provide dedicated or shared protection to the defective liquid crystal switch.
Further in accordance with the present invention, the optical switch structure includes a control system, an input switch configuration, and an output switch configuration. The control system senses an error condition in a defective optical device, where the control system generates a control signal in response to the error condition. The input switch configuration routes the optical signal from an input path of the defective optical device to a protection optical device based on the control signal. The protection optical device is therefore able to perform a desired operation on the optical signal. The output switch configuration routes the optical signal from the protection optical device to an output path of the defective optical device based on the control signal. In a preferred embodiment the control system senses an incorrect capacitance value of a defective liquid crystal switch.
In another aspect of the invention, a method is provided for protecting a liquid crystal switch. The method includes the step of routing an optical signal around the liquid crystal switch when the liquid crystal switch exhibits an error condition. The optical signal is then directed through a protection liquid crystal switch, and a desired switching operation is performed on the optical signal.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
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Gahan David F.
Harris J. Michael
Agon Juliana
Corning Incorporated
Nguyen Chau M.
Pascal Leslie
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