Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-04-26
2004-07-13
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Switch
C385S012000, C385S013000
Reexamination Certificate
active
06763160
ABSTRACT:
RELATED APPLICATIONS
The present application is related to U.S. patent application ENTITLED “ABSOLUTE POSITION MOIRÉ TYPE ENCODER FOR USE IN A CONTROL SYSTEM”, filed Apr. 24, 2001 by Michel G. Laberge, Thomas W. Steiner and Valentin Karasyuk.
FIELD OF THE INVENTION
The invention disclosed herein relates generally to the field of optical switching. Specifically, the invention relates to alignment control systems for implementing the optical signal connection between fibers in optical cross-connect switches.
BACKGROUND OF THE INVENTION
Fiber optic systems are now in common use for transmitting optical communication signals, which are optical signals modulated to encode desired information. Such optical communication signals may be modulated with data, voice or video signals, and are typically transmitted across optical networks using optical fibers that support substantial transmission capacity. Given the continually escalating demand for improved signal quality and bandwidth, it is anticipated that the use of, and demand for, fiber optic communication will continue to increase.
One of the reasons that fiber optic networks have recently attracted attention relates to new methods of switching in the optical domain without having to convert the optical communication signals into conventional electronic signals for switching purposes. In this manner, conventional electronic switching components can be eliminated and higher bandwidth optical switches can be implemented in their place. Fiber optic communication lines may be switched by simply aligning the opposing ends of the fibers to be connected for direct optical linkage. Optical switching is advantageous when compared to conversion of optical communication signals to electrical signals for electrical switching, because optical switches can achieve higher bandwidth than comparable electronic switches. Consequently, network application having minimum bandwidth requirements can be achieved at overall lower costs by employing optical rather than electronic switching. It will be appreciated, however, that increasing switching speed and reducing signal degradation across the switch remains a continual desire.
Optical cross-connect switches may be understood to include a first array of fibers on one “side” of the switch and a second array of fibers on the second “side” of the switch. It will be appreciated after reading the disclosure below, that the first and second “sides” of a switch relate to optical signal transmission pathways and not to a spatial arrangement.
The control of optical switches involves alignment of the two fibers to be optically connected. Typically, external network information is received, identifying two optical fibers (one from either “side” of the switch) that are to be optically connected across a switch interface in order to permit transmission of communication signals there-between. Alignment control involves identifying the first side fiber and the fiber on the second side that are to be optically interconnected, aligning and configuring an optical connection between the two fibers and fine tuning the optical connection between the identified fibers to optimise signal transmission.
Some older prior art optical cross-connect switches employ “one-sided” control systems for targeting and alignment. That is, the control system for aligning a particular transmitting fiber to a particular receiving fiber is resident on one “side” of the switch. Such alignment control systems attempt to control the trajectory of the communication signal based on known device geometry and pre-calibrated target positions. One example of such a system is U.S. Pat. No. 5,206,497 (referred to herein as the '497 patent), which controls the alignment of the transmitting fiber on the transmission “side” of the switch. The '497 patent discloses a fiber that transmits an optical communication signal to one of a plurality of receiving fibers on the other side of the switch. A small fraction of the power in the communication signal is split off from the main component of the beam using a beam splitting device. This split-off component of the beam, referred to as the monitor component, is directed towards a charge coupled device (CCD) optical detector. The CCD detector determines the position of the monitor component of the beam on the surface of the CCD detector and feeds this information back to the alignment control system. Using feedback information from the CCD detector, the alignment control system operates actuators, which effect the desired trajectory of the transmitting fiber. During calibration which takes place prior to use, a predetermined target position is identified, so that each receiving fiber is associated with a known target position on the CCD detector. In this manner, the alignment control system achieves the desired communication signal trajectory by directing the monitor component of the communication signal to impinge on the surface of the CCD detector at the desired target position.
A major drawback with the control system of the '497 patent is the requirement of a CCD sensor for each transmission fiber. CCD sensors are relatively expensive and increase the cost of the overall switch. An additional disadvantage of the '497 invention is the space required to split each communication signal to an independent CCD sensor, which prohibits miniaturization of the switch. Another limitation of the '497 patent is the dependence of the control system on the presence of the communication signal. When the system is “unlit” (i.e. no optical communication signal is being transmitted from one side of the switch to the other) it can not be controlled. The requirement for the presence of a communication signal prior to effecting control becomes a problem if it is desired to insert the switch in a communications network prior to use and then use the switch only when additional network capacity is required. The necessity of having the communication signal on during control is also problematic, because a signal may be inadvertently inserted into the wrong receiving fiber during a switching operation. Additional drawbacks with the '497 patent include: a limitation on insertion efficiency across the switch interface, because of a need to split off some of the transmitted power to form the monitor component of the beam for the control system, and a critical dependence on the geometry of the device.
Another drawback, common to all “one-sided control” switches (like that of the '497 patent) is that the numerical aperture (NA) of the receiving fibers prevents the implementation of very large switches. Recently, larger switches have been developed by having controllable fibers on both “sides” of the switch. That is, control of the communication signal trajectory is implemented on the transmission side of the switch and control of the angle at which the signal is inserted into the receiving fiber is controlled at the reception side of the switch. In this manner, the limited NA of the receiving fibers can be overcome.
An example of a “two-sided control” switch is U.S. Pat. No. 6,005,998 (referred to herein as '998), which comprises two arrays of light beam collimators arranged on either side of the switch. The control system comprises two motors, which each have an associated encoder to track their positions. The motors are used to effect a particular angle of a collimating lens. On the transmission side of the switch, the angle of the collimating lens is adjusted such that the beam of the transmission fiber is collimated and steered on both the x and y axes to a pre-calibrated target position on the other side of the switch. On the receiving side of the switch, two additional motors control the angle of a similar collimator lens. The angle of the collimator lens permits reception of the communication signal from the pre-calibrated target position and insertion of the communication signal into the receiving fiber at an appropriate angle, helping to overcome the limited NA of the receiving fibers.
A major d
Karasyuk Valentin
Laberge Michel
Steiner Thomas W.
Creo SRL
Font Frank G.
Kianni Kevin
Oyen Wiggs Green & Mutala
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