Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-06-09
2001-05-22
Negash, Kinfe-Michael (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06236481
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical signal communications networks, and more particularly to providing loss equalization or adjustments for optical signals transmitted through the network.
BACKGROUND OF THE INVENTION
Fiber optic systems are now commonly used 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 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.
Between the switches, various lengths of fiber optic line carry the optical signals. The lengths of fiber optic line are connected together using splices or connectors. The lengths of fiber optic line may also include cascaded chains of optical amplifiers which act to amplify the signals in order to maintain signal strength.
In order to increase the amount of information being transmitted across a fiber optic telecommunications network, wavelength division multiplexing (WDM) has been employed. In a WDM system, each individual fiber carries signals at a number of different wavelengths. At a predetermined point in the system, the optical signal is demultiplexed and the individual signals are transmitted to unique destinations.
SUMMARY OF THE INVENTION
The inventor has recognized that when optical signals are transmitted through an optical communications network, loss may be introduced into the signals at different points in the network. The amount of loss may vary for each optical path. This variation in signal level may be unacceptable in some networks. In a WDM network, for example, the signal level entering an optical amplifier should be equal for all wavelengths, otherwise the stronger wavelength will be amplified more than the weaker wavelength. The inventor has further recognized that loss equalization for the optical signals may be performed within the optical switch itself.
The present invention describes an apparatus and method for equalizing or adjusting the loss which may be introduced due to network functions such as signal routing, amplification, as well as transmission along spliced fiber optic lines. In an optical signal communications network, an M×N switch may receive a plurality of optical signals over communications lines from a remote source. Within the switch, the signals are routed to the appropriate output lines. Different amounts of loss may be introduced depending on the optical path taken by a signal through the optical switch. In order to determined the losses along each optical path, readings may be taken at the input and output of each optical path through the switch to measure the strength of the optical signal at these two points. A comparison of these measurements may then be made to determine the losses occurring along each path.
In one aspect of the invention, the optical switch may include a number of devices for routing incoming signals to the appropriate outgoing optical line. These devices may be manipulated such that strength of signal transmitted along the various paths through the optical switch may be varied. When the losses through the switch are identified, the various devices may be employed to equalize the strengths of the optical signals.
In another aspect of the invention, each path in the optical switch may include a movable optical device such as an optical lens, prism, fiber or mirror for directing the optical signal. Translation or rotation of this optical device may be performed through use of a servo motor. Through measurements made of the incoming and outgoing signals along the incoming and outgoing lines, a determination may be made as to which routing path through the optical switch introduces the greatest loss. Once this path is identified, the appropriate servos may be employed to manipulate the optical devices such that the optical signal strength measured over the output lines are equalized. In another aspect of the invention, once the path with the maximum loss is identified, the adjustments made to the other paths introduce sufficient loss to equalize the signal strength across all the output lines.
In another aspect of the invention, the optical switch may comprise multiple cross points positioned to direct the incoming optical signals to the appropriate output lines. Measurements may be made of the optical signal magnitudes at the exit and entrance to the optical switch. Through these measurements the loss through the various optical paths may be determined. Once this determination is made, the appropriate cross points may be manipulated in order to equalize the magnitude of the optical signals exiting from the optical switch. In another aspect of the invention, the path over which the maximum loss occurs may be determined. Based on this determination, adjustments may be made to the appropriate crosspoints to introduce sufficient loss in the other paths to equalize the signal strength across all the output lines.
In another aspect of the invention, the optical switch may include a number of 1×N couplers connected to the incoming optical signal lines. Each coupler splits the incoming signal into N identical signals. The N identical signals are each routed to N×1 couplers connected to each of the outgoing lines. Between the couplers are positioned on/off optical amplifiers which are either turned on or off depending the desired routing scheme through the optical switch. The optical amplifiers which are in the on mode, may direct the optical signals to the desired output line. Measurements may be taken at the entry and exit of the optical switch in order to measure signal losses which occur over the different paths. These measured losses may then be employed to adjust the gain of the amplifiers to equalize the strength of the optical signals.
The strength of the signal entering and exiting the optical switch may be measured in an number of different ways. In one aspect of the invention, tap sensors may be positioned proximate to the signal lines at the input and output areas of the optical switch. Readings from these sensors may then be compared to determine the loss along a particular path through the switch.
Within the network, losses in the optical lines may occur at other places than the optical switches. For example, losses may be introduced at splices or connectors which connect communications lines together. Yet another source of variation may be the optical amplifiers positioned along the communication lines to maintain signal strength. In a system which employs WDM, these amplifier may provide different gain for different wave-lengths transmitted along the communications lines.
In another aspect of the invention, the optical signal strength may be measured at the source of the optical signals, i.e., the optical transmitter, and measured at the destination of the optical signal (i.e., optical receiver). Once the two measurements are made, they may be compared in order to determine losses which occur along a particular path through the network. Once this information is determined, it may be used with regards to the optical switch to equalize the optical signals through manipulation of the routing mechanisms contained therein.
Equalization of signals may be performed in a number of different ways. Before the system goes into normal operation, test signals may be tra
Astarte Fiber Networks, Inc.
Burdett James R.
Negash Kinfe-Michael
Venable
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