Optical channel regulator and method
An optical channel regulator (46) is provided. The optical channel regulator (46) includes a tapped optical coupler (60) receiving an optical line carrying an optical signal. The tapped optical coupler (60) provides substantially all of the optical signal as an output. An electrically variable optical attenuator (64) receives the output of the tapped optical coupler (60) and attenuates the optical signal responsive to a feedback control signal. A second tapped optical coupler (66) receives an output of the attenuator (64). The second coupler (66) provides substantially all of the received optical signal as an output and provides a remaining portion of the optical signal as a tapped output. An optical detector (68) then receives the tapped output and provides an output signal representing the optical signal. A comparator (70) receives the output signal of the optical detector (68) and a reference signal. The comparator (70) compares the output signal and the reference signal and provides the feedback control signal to the attenuator (64) responsive to the comparison. As part of a multi-channel communication system, the regulator is used to adjust the levels of each channel for automatically maintaining channel balance and equalization.
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This application claims priority under 35 U.S.C. 119(e) to Provisional Application No. 60/060,526 filed Sep. 30, 1997.
TECHNICAL FIELD OF THE INVENTIONThis invention relates in general to optical communication systems, and more particularly to an optical channel regulator and method.
BACKGROUND OF THE INVENTIONIn multiple channel wavelength division multiplexed (WDM) communication systems, optical amplifiers are used to boost signal powers to provide for longer transmission spans. When using optical amplifiers in such systems, it is important to balance the channels at the input to the amplifiers to assure that the available amplifier output power is shared equally among the channels. If the channels are not balanced across each amplifier input, the weaker signals reduce the transmission span distance.
Another problem faced is that optical amplifiers used in multiple channel wavelength division multiplexed communication systems often do not have uniform gain across all of the optical channels. This creates some channel imbalance. In other systems where optical amplifiers are used as repeaters, the cascade of the amplifiers results in signal inequalities even when they are well balanced at the head end.
Other problems relate to the configuration of a bi-directional line amplifier (BDLA) which uses a single amplifier. The receive signals from each direction needs to be balanced to assure proper gain and power sharing in the amplifier. Further, significant power level imbalances between channels at the end of a cascade of amplifiers may require attenuation of the strong channels to keep the signal level to the receiver at an acceptable level.
One conventional solution to balancing of channels has been to insert manually selected fixed attenuators or manually adjusted variable attenuators in each channel path before multiplexing them together. However, the selection or the adjustment of the attenuators requires manual measurement of each optical channel, since the source transmitter power level for each channel varies and is not precisely known beforehand. Furthermore, when the source transmit power changes, due to aging or module replacement, the attenuator adjustment process has to be repeated.
SUMMARY OF THE INVENTIONThe present invention provides an optical channel regulator method that substantially eliminates or reduces disadvantages and problems associated with previously developed optical channel regulation schemes.
More specifically, the present invention provides a method for regulating an optical channel. The optical channel regulator includes an electrically variable optical attenuator receiving an optical signal. The attenuator attenuates the optical signal responsive to a feedback control signal and yields an attenuated optical signal. A tapped optical coupler receives the attenuated optical signal of the attenuator and provides substantially all of the attenuated optical signal as an output. The tapped optical coupler also provides a remaining portion of the attenuated optical signal as a tapped output. An optical detector receives the tapped output and provides an electrical signal representing the attenuated optical signal. A comparator receives the electrical signal of the optical detector and a reference signal. Finally, the comparator compares the electrical signal to the reference signal and provides a feedback control signal to the attenuator.
The present invention provides an important technical advantage by eliminating the need for manual measurement and selection of fixed attenuators required for balancing the channels.
The present invention provides another technical advantage by solving the problem of balancing the power levels at bi-directional line amplifiers using a single amplifier.
Additional technical advantages should be readily apparent from the drawings, description, and claims.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:
Preferred embodiments of the present invention are illustrated in the FIGURES, like numerals being used to refer to like and corresponding parts of the various drawings.
The optical channel regulator of the present invention electronically performs a power level measurement for each channel of a wavelength division multiplexed communication system. The optical channel regulator of the present invention also electronically varies the path attenuation to bring all optical channels into balance before being combined in a multiplexer and before being amplified. If the balance changes at a later time, the control system automatically readjusts to maintain the balance.
More specifically, the present invention provides a method for regulating an optical channel. The optical channel regulator includes an electrically variable optical attenuator receiving an optical signal. The attenuator attenuates the optical signal responsive to a feedback control signal and yields an attenuated optical signal. A tapped optical coupler receives the attenuated optical signal of the attenuator and provides substantially all of the attenuated optical signal as an output. The tapped optical coupler also provides a remaining portion of the attenuated optical signal as a tapped output. An optical detector receives the tapped output and provides an electrical signal representing the attenuated optical signal. A comparator receives the electrical signal of the optical detector and a reference signal. Finally, the comparator compares the electrical signal to the reference signal and provides a feedback control signal to the attenuator.
Optical amplifier 24 provides an output to an optical demultiplexer 26 that recovers the plurality of optical signals and provides each optical signal to one of a plurality of fixed attenuators 28. The attenuators 28 are also manually selected or adjusted, and provide fixed attenuation of the optical signal. Each attenuator 28 is connected to a receive channel 30 of terminal equipment 32.
Fixed attenuators 16 and 28 operate to balance the optical channels, but are manually selected and installed or manually adjusted variable attenuators. The selection or adjustment of attenuators 16 and 28 involves manual measurement of each optical channel since the source transmitter power level for each channel varies, and is not precisely known beforehand.
Furthermore, when the source transmit power changes, due to aging or module replacement, the attenuator selection or adjustment process needs to be repeated. Thus, there is little flexibility when line conditions change.
According to the present invention, optical regulators 46 and 50 electronically perform a power level measurement for each channel and electronically vary the path attenuation to bring the optical channels into balance before being combined in optical combiner 18 and after being separated by optical demultiplexer 26. The input from microprocessor controllers 48 or 52 provide a level against which to compare the level of the respective channel. If the balance changes at a later time, system 40 can thus automatically readjust to maintain the balance.
According to the present invention, optical regulator 46 taps the optical line and compares the signal with a controlled power level. The controlled power level is provided by a microprocessor controller, for example, as shown in FIG. 2. The microprocessor controller receives the input monitor level from optical detector 62 and the output monitor level from output detector 68. The microprocessor controller then processes those inputs according to executed program code and generates the microprocessor controlled power level used as a reference by comparator 70. Based upon the comparison, feedback may be provided to electrically vary optical attenuator 64 to regulate the power level of the optical signal. It should be noted that optimum balance often can be best determined at the received end of the systems. This may mean that the channels at the transmit end are deliberately unequal. It also should be noted that often the optimum balance at the receive end may be determined by signal-to-noise ratio rather than power level.
On the opposite side of the transmission line, a multiplexer 98 provides signals to and receives signals from amplifiers 100. Incoming signals are provided to a demultiplexer 102 to separate the multiplexed signals. Outgoing signals are provided to a combiner 103 by optical regulators 104, as shown. Optical regulators 104 are connected as shown to terminal equipment 106 that provides receive channels 108 and transmit channels 110. It should be understood that microprocessor control of optical regulators 88 and 104, although not shown, is similar to that shown in FIG. 2.
Although the present invention has been described in detail, it should be understood that various substitutions, changes and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.
Claims
1. An optical channel regulator, comprising:
- an electrically variable optical attenuator receiving an optical signal, the attenuator operating to attenuate the optical signal responsive to a feedback control signal and to provide an attenuated optical signal;
- a tapped optical coupler receiving the attenuated optical signal of the attenuator, the optical coupler operating to provide substantially all of the attenuated optical signal as an output and to provide a remaining portion of the attenuated optical signal as a tapped output;
- an optical detector receiving the tapped output and providing an electrical signal representing the attenuated optical signal; and
- a comparator receiving the electrical signal of the optical detector and a reference signal, the comparator operating to compare the electrical signal, the reference signal, and responsive to the comparison to provide the feedback control signal to the attenuator.
2. The optical channel regulator of claim 1 further comprising:
- a second tapped optical coupler receiving an input optical signal, the second tapped optical coupler providing substantially all of the input optical signal as the optical signal received by the electrically variable optical attenuator and providing a remaining portion of the input optical signal as a tapped output; and
- a second optical detector receiving the tapped output from the second tapped optical coupler and providing an electrical signal representing the input optical signal.
3. An optical regulator assembly comprising:
- a plurality of optical channel regulators, each optical channel regulator comprising: an electrically variable optical attenuator; a tapped optical coupler; an optical detector; and a comparator; and
- a microprocessor, operable to: receive the electrical signal representing the attenuated optical signal from each of the plurality of optical channel regulators; generate a plurality of reference signals responsive to the electrical signals; and provide a reference signal to the comparator in each of the plurality of optical channel regulators.
4. The optical channel regulator of claim 3, wherein each optical channel regulator further comprises:
- a second tapped optical coupler receiving an input optical signal, the second tapped optical coupler providing substantially all of the input optical signal as the optical signal received by the electrically variable optical attenuator and providing a remaining portion of the input optical signal as a tapped output; and
- a second optical detector receiving the tapped output from the second tapped optical coupler and providing an electrical signal representing the input optical signal.
5. An optical channel regulator assembly comprising:
- a plurality of optical channel regulators, each optical channel regulator comprising: an electrically variable optical attenuator; a tapped optical coupler; an optical detector; and a comparator; and
- a microprocessor, operable to: receive the electrical signal representing the input optical signal from each of the plurality of optical channel regulators; generate a plurality of reference signals responsive to the electrical signals; and provide a reference signal to the comparator in each of the plurality of optical channel regulators.
6. The optical channel regulator of claim 5, wherein each optical channel regulator further comprises:
- a second tapped optical coupler receiving an input optical signal, the second tapped optical coupler providing substantially all of the input optical signal as the optical signal received by the electrically variable optical attenuator and providing a remaining portion of the input optical signal as a tapped output; and
- a second optical detector receiving the tapped output from the second tapped optical coupler and providing an electrical signal representing the input optical signal.
7. A multiple channel wavelength division multiplexed communication system comprising:
- a plurality of transmission channels;
- a plurality of optical regulators operable to receive a plurality of optical signals from said plurality of transmission channels, each optical regulator comprising: an electrically variable optical attenuator; a tapped optical coupler; an optical detector; and a comparator;
- a first microprocessor, operable to: receive an electrical signal representing the attenuated optical signal from each of the plurality of optical regulators; generate a plurality of reference signals responsive to the electrical signals; and provide a reference signal to the comparator in each of the plurality of optical regulators;
- an optical combiner operable to receive a plurality of said attenuated signals;
- a first optical amplifier operable to receive an output signal from said optical combiner;
- a second optical amplifier operable to receive an output signal from said first optical amplifier;
- a third optical amplifier operable to receive an output signal from said second optical amplifier;
- an optical demultiplexer operable to receive an output signal from said third optical amplifier and recover said plurality of optical signals;
- a plurality of optical regulators operable to receive a plurality of optical signals from said optical demultiplexer, each optical regulator comprising: an electrically variable optical attenuator; a tapped optical coupler; an optical detector; and a comparator;
- a second microprocessor, operable to: receive the electrical signal representing the input optical signal from each of the plurality of optical regulators; generate a plurality of reference signals responsive to the electrical signals; and provide a reference signal to the comparator in each of the plurality of optical regulators; and
- a plurality of receive channels operable to receive a plurality of optical signals from said plurality of optical regulators.
8. The optical channel regulator of claim 7, wherein each optical channel regulator further comprises:
- a second tapped-optical coupler receiving an input optical signal, the second tapped optical coupler providing substantially all of the input optical signal as the optical signal received by the electrically variable optical attenuator and providing a remaining portion of the input optical signal as a tapped output; and
- a second optical detector receiving the tapped output from the second tapped optical coupler and providing an electrical signal representing the input optical signal.
5392154 | February 21, 1995 | Chang et al. |
5557439 | September 17, 1996 | Alexander et al. |
5812710 | September 22, 1998 | Sugaya |
5815299 | September 29, 1998 | Bayart et al. |
5900983 | May 4, 1999 | Ford et al. |
5963291 | October 5, 1999 | Wu et al. |
5970201 | October 19, 1999 | Anthony et al. |
5974216 | October 26, 1999 | Nakaya |
6031647 | February 29, 2000 | Roberts |
6157475 | December 5, 2000 | Dugan et al. |
0637148 | July 1994 | EP |
0762677 | August 1997 | EP |
2294170 | July 1995 | GB |
Type: Grant
Filed: Mar 16, 2004
Date of Patent: Nov 7, 2006
Assignee: Alcatel (Paris)
Inventors: J. Michael Dugan (Richardson, TX), Kenneth Y. Maxham (Richardson, TX)
Primary Examiner: Leslie Pascal
Attorney: Jessica W. Smith
Application Number: 10/802,118
International Classification: H04J 14/02 (20060101); H04B 10/18 (20060101);