Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-09-16
2001-11-20
Sikder, Mohammad (Department: 2872)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S018000, C385S019000, C385S020000
Reexamination Certificate
active
06320993
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to fiber optic switches that employ control signals for aligning fibers to be connected for transmission of communication signals therebetween. In particular, the present invention is directed to making a communication signal pathway over which a communication signal is transmittable in an optical switch coincident with a desired pathway between two fibers by transmitting a control signal on or off of the communication signal pathway.
BACKGROUND OF THE INVENTION
Fiber optic systems are now in common use for transmitting optical communication signals i.e., optical signals modulated to encode desired information. The optical communication signals are transmitted across a network using optical fibers that support substantial transmission capacity with compact fiber bundles. Given the ever-increasing demands for improved signal quality and bandwidth, it is anticipated that the use of fiber optic communications will continue to increase for years to come.
One of the reasons that fiber optic networks have attracted attention in recent years relates to switching advantages. Because the communication signals in fiber optic networks are optical in nature, conventional electronic switching components can be eliminated. Instead, fiber optic communications lines are connected at a switch by carefully aligning the fiber ends of the lines to be connected for direct optical linkage. Such switching has proved advantageous in that switching can be accomplished quickly without unacceptable signal degradation. However, it will be appreciated that there is a continuous desire to increase the speed of operation and reduce signal losses at switch interfaces.
One of the most persistent challenges associated with optical switches is how to quickly and accurately align the fibers that are being connected, i.e., optically interfaced for signal communication therebetween. High speed is required to minimize lag times in the network. Accuracy is required to minimize signal losses. In this regard, it will be appreciated that even slight misalignments of the fiber ends will result in a significant loss of the power of the transmitted optical signal and, potentially, of the information encoded in the signal. Moreover, switch designers are continuously endeavoring to accommodate more fibers in smaller switches. Accordingly, alignment systems remain the focus of much research.
Conventional alignment systems typically employ radiation emitting devices (REDs), such as light or infrared radiation emitting diodes (“LEDs”), lasers or VCSEL lasers for fiber identification and alignment. Fiber identification relates to identifying the fibers that are to be connected for initial targeting and manipulating the switch targeting mechanisms so that the identified fibers are in rough optical alignment. In this regard, it will be appreciated that a typical switch includes a matrix of fiber ends on a first side of the switch and another matrix of fiber ends on a second side. Depending on the switch configuration, these matrices may optically interface directly, or via a folded optical path. In either case, it is generally a function of the switch to be able to optically connect any of the fibers on the first side to any of the fibers on the second side. The fiber identification process allows this connection to be initiated. Thereafter, a fiber alignment process fine tunes the connection to maximize signal transmission or minimize signal losses.
In order to facilitate the targeting and alignment processes, one or more REDs is typically mounted in known spatial relationship to each of the fibers of each matrix, e.g., adjacent to the fiber on the matrix structure. These REDs transmit radiation across the switch interface to the opposing matrix. In addition, an optical receiver is provided in conjunction with each fiber of each matrix. For example, the receiver may be incorporated into a cladding layer of a dual core optical fiber where the central fiber is used for transmission of communication signals. The receiver receives radiation from a RED or REDs of the opposing matrix and provides the received radiation to a detector/feedback system for controlling targeting. In this manner, the REDs can first be used to signal which of the fibers are to be connected. Thereafter, alignment can be optimized by analyzing the signal transmitted from the RED(s) associated with one of the target fibers to the receiver associated with the other and vice versa.
Although such conventional targeting and alignment systems have provided acceptable speed and accuracy, they impose certain limitations in switch designs. First, the REDs and receivers incorporated into the fiber matrices may limit the design of the array or impede array miniaturization. Moreover, the detectors used in such conventional systems generally include a large active area and a correspondingly low signal-to-noise ratio. The dual core fibers used for transmitting and receiving are also very expensive and difficult for switch manufacturers to reliably stock. It would therefore be advantageous to design a fiber optic switch that reduces or eliminates the need for dual core fibers and otherwise addresses limitations of conventional targeting and alignment systems.
SUMMARY OF THE INVENTION
The present invention is directed to systems for use in configuring an optical switch such that a communication signal transmittable over a communication signal pathway from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end by configuring the switch to make the communication signal pathway coincident with the desired pathway. A feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway is generated by a control signal detector that detects a transmitted control signal. The present invention contemplates implementations of such systems employing control signals transmitted on-path with the communication signal pathway in a variety of optical switches. For example, a system employing on-path control signals may be implemented in a mirror based optical switch where the optical fiber ends are stationary and positionable mirrors direct the communication signal between selected fibers ends. Another example is an optical switch where the optical fiber ends are moveable and are pointed at one another in order to direct the communication signal between selected fiber ends. The present invention also contemplates various novel implementations of a system employing a control signal transmitted off-path of the communication signal pathway in a mirror-based optical switch.
According to one aspect of the present invention, a method for use in configuring an optical switch such that a communication signal transmittable from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end includes transmitting a control signal over at least a portion of a communication signal pathway over which the communication signal is transmittable in the optical switch. Hence, the control signal is “on-path” with the communication signal pathway. The transmitted control signal is received by a control signal detector that is maintained in a known spatial relation relative to the desired pathway. A feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway is output by the detector. The feedback signal can be utilized in configuring the switch to make the communication signal pathway coincident with the desired pathway. For example, in a mirror based switch, the feedback signal may be utilized in controlling the position of one or more positionable mirrors of the optical switch in order to make the communication signal pathway and the desired pathway coincident. In a non-mirror based switch, the feedback signal may be utilized in moving the fiber ends such that they point at one another in order make the communication signal pathway co
Astarte Fiber Networks, Inc.
Burdett James R.
Sikder Mohammad
Venable
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