|Publication number||USRE41610 E1|
|Application number||US 11/150,606|
|Publication date||Aug 31, 2010|
|Filing date||Jun 10, 2005|
|Priority date||Dec 14, 2001|
|Also published as||US6577788, WO2003052507A1|
|Publication number||11150606, 150606, US RE41610 E1, US RE41610E1, US-E1-RE41610, USRE41610 E1, USRE41610E1|
|Inventors||Michael H. Eiselt, Mark Shtaif|
|Original Assignee||Eiselt Michael H, Mark Shtaif|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Classifications (19), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to an equalization system, and more particularly, to a system for use in an optical network to correct for unequal gain of power in the channels of the optical signal.
The transmission, routing and dissemination of information has occurred over computer networks for many years via standard electronic communication lines. These communication lines are effective, but place limits on the amount of information being transmitted and the speed of the transmission. With the advent of light-wave technology, a large amount of information is capable of being transmitted, routed and disseminated across great distances at a high transmission rate over fiber optic communication lines.
When information is transmitted over fiber optic communication lines, impairments of the pulse of light carrying the information can occur, including pulse broadening (dispersion) and attenuation (energy loss). In-line amplifiers spaced throughout the fiber optic communication system boosts the power of each channel of the optical signal to assist in the compensation of the energy lost during transmission. The in-line amplifiers boost each channel of the optical signal with the same amount of power. However, as different wave lengths of light are used over the different channels of the fiber optic communication system, the amount of energy lost per channel is not consistent. As the in-line amplifier boosts the energy across all channels of the optical signal transmitted over the fiber optic communication system, the power gain of any specific channel may fail to meet or exceed the desired power gain. Further, energy loss caused by polarization dependent loss (PDL) lead to further nonuniform power gain over the multiple channels of the optical signal transmitted over the fiber optic communication system.
As the optical signal is transmitted across the fiber optic communication system, the gain differences on a channel-by-channel basis accumulate. These gain differences can cause distortions of the optical signal shape and therefore lead to performance degradation. Current systems allow for the optical signals' power deviations to accumulate before they are compensated by the gain equalizer after analysis by the optical spectrum analyzer (“OSA”). Inherent in these systems is a process which allows a large amount of gain differences to accumulate prior to equalization. Prior to the gain equalization of the channels of the optical signal, the optical signal performance beings to degrade and thus the overall performance of the fiber optic communications system is degraded.
To compensate for gain differences in the multiple channels of the optical signal, gain equalizers are provided, spaced periodically, throughout the fiber optic communication lines (FIG. 1). the gain equalizers equalize the power at the in-line amplifiers on a channel-by-channel basis throughout the optical signal. To determine the amount of gain on a channel-b-channel basis, an optical spectrum analyzer is co-located with the gain equalizer. The Optical measures the power level associated with each channel of the optical signal and compares this power level with the desired power level for each channel and provides this information to the gain equalizer which is co-located with the Optical spectrum analyzer at an in-line amplifier within the fiber optic communication system. The gain equalizer then equalizes the power of each channel based upon the analysis performed by the Optical spectrum analyzer at this in-line amplifier location. As can be seen in
A power equalization system and method for use in an optical transmission system are provided. The power equalization system includes an optical line including at least one transmission channel and a management line. The transmission system further includes a plurality of amplifiers, a plurality of Optical spectrum analyzers and a plurality of equalizers. The plurality of amplifiers are coupled to the optical line, spaced periodically throughout the optical transmission system. As information is sent through the optical transmission system, the plurality of amplifiers boost the power of each channel of the optical signal. A plurality of Optical spectrum analyzers are also coupled to the optical lien and are spaced periodically throughout the optical transmission system and are co-located with a first portion of the amplifiers coupled to the optical line. A plurality of equalizers are also coupled to the optical line and are spaced periodically throughout the optical transmission system and equalize the power on each channel of the optical line. The plurality of equalizers are co-located with a second portion of the plurality of amplifiers and at least one of the plurality of Optical spectrum analyzers is not co-located with one of the plurality of equalizers. Thus, as the optical information is transmitted over the optical transmission system, the Optical spectrum analyzers provide analysis data via the management line to the non co-located equalizers for use by the equalizers in equalizing the power of the channels of the optical line at that point. The analysis data generated by the Optical spectrum analyzer identifies the analysis data at the point of the Optical spectrum analyzer which is not co-located with the equalizer.
A better understanding of the invention can be obtained from the following detailed description of one exemplary embodiments as considered in conjunction with the following drawings in which:
In the descriptions which follows, like parts are marked throughout the specification and drawings with the same numerals, respectively. The drawing figures are not necessarily drawn to scale and certain figures may be shown in exaggerated or generalized form in the interest of clarity and conciseness.
In an optical transmission sytem, the optical signal is transmitted over an optical line. In certain optical transmission systems, including dense wavelength division multiplexed systems (DWDM systems), the optical signal that is transmitted includes multiple channels where each channel of the optical signal is transmitted at a different wavelength. As originally transmitted, the optical signal does not contain enough energy to complete a long haul or ultra long haul transmission therefore, the optical signal must be amplified periodically throughout the optical line. The amplifiers are used to replace energy loss due to attenuation with an equal amount of replacement energy per wavelength (or per channel) in the optical signal. There are multiple wavelengths or channels in each optical signal transmitted over the optical transmission system. In one disclosed embodiment, forty wavelengths are capable of being transmitted through one optical signal. As the amount of power attenuation varies among the channels of the optical signal, some channels experience an excessive amount of gain caused by the amplifier, some experience the correct amount of gain and some experience too little gain. These gain differences experienced by different channels of the optical signal are accumulated and are caused by the wavelength profile of the amplifiers or by effects such as polarization dependent loss (PDL) in the various components located in the optical system. The losses per wavelength are not perfectly flat. The number of energy lost between any two points along the optical network will typically remain nearly constant if the lost power is caused by the amplification of the amplifiers. A random gain deviation can be experienced intermittently and is typically not consistent.
In a conventional optical networks 100, as can be seen in
The optical signal 101 is typically comprised of twenty to forty channels. Each channel of the optical signal 101 is a separate wavelength of the optical signal. The optical signal 101 is typically transmitted in wavelengths between 1530 and 1610 nm. As the optical signal 101 is transmitted from the terminal 102 over the optical network 100, the optical signal 101 begins to experience attenuation or power loss. therefore, an in-line amplifier 106 is provided at fixed intervals to boost the power of the optical signal 101.
The in-line amplifier 106 boosts the power of the optical signal 101 according to a predetermined value or according to a value that can be adjusted during operation. The In-line amplifier 106 boosts the power of the optical signal 101 across every channel, applying the same power boost to every channel regardless of the channels current power level. Therefore, as gain differences are experienced in the multiple channels of the optical signal 101, these gain differences are accumulated through the amplification of the optical signal 101 from the In-line amplifiers 106. As the optical signal 101 is transmitted from In-line amplifier 106a to In-line amplifier 106b, the optical signal 101 experiences attenuation and again must be amplified.
However, prior to amplification at In-line amplifier 106b, an optical spectrum analyzer 108a evaluates each channel of the optical signal 101 to determine its current power deviation from the expected value. The optical signal analyzer 108a then transmits this power or gain deviation information to a dynamic gain equalizer 110a which then adjusts the optical signal 101 on a channel-by-channel basis to optimize the power in each channel. Thus, any differences in gain accumulated through the transmission of the optical signal 101 because of random gain or through amplification by the In-line amplifiers 106 are corrected based upon the evaluation of the Optical spectrum analyzer 108a and implemented by the Dynamic gain equalizer 110a.
The process repeats as the optical signal 101 is transmitted through In-line ampolfiers 106c, 106d, 106e, 106f and 106g. The optical signal 101 is analyzed by the optical spectrum analyzers 108b and 108c once the signal reaches In-line amplifiers 106d. The optical spectrum analyzer 108b and 108c identify any gain differences on a channel-by-channel basis of the optical signal 101 before transmitting these gain differences to the dynamic gain equalizers 110b and 110c. The dynamic gain equalizers 110b and 110c then correct for gain differences accumulated, regardless if the gain differences are caused by the In-line amplifiers 106 or through polarization dependent loss.
The number of In-line amplifiers 106 is determined based upon the distance the conventional optical network 100 must cover. Thus, whether the conventional optical network 100 is a long haul or ultra long haul optical network, the frequency in quantity of In-line amplifiers 106 must be determined. Further, the fiber characteristics, the characteristics of the amplifiers, and characteristics of the power necessary for the optical signal 101 determine the quantity of amplifiers 106 needed throughout the conventional optical network 100 and also determine the quantity of analyzers 108 and equalizers 110 necessary in the conventional optical network 100. Therefore, the optical spectrum analyzer 108 and the dynamic gain equalizers 110 may only repeat every nth In-line amplifier 106 where n will be determined based upon the characteristics described above. In the example shown in
One constant of the conventional optical network 100 is that the Optical spectrum analyzer 108 and the dynamic gain equalizer 110 are co-located at the same in-line amplifier 106. Therefore, the analysis and equalization of the optical signal 101 occurs at one specific point in the optical network and is typically located at an in-line amplifier 106 site.
As the gain increases on any channel of the optical signal 101, the integrity of the signal is reduced. Therefore, the greater the area defined by the triangle formed by lines 200, 204 and 206 the greater than accumulated gain 202 and the greater the distortion of the optical signal 101. The graph of
Referring now to
Referring now to
After a predetermined distance, an in-line amplifier 404 is connected to the optical line 410. The repeating predetermined distance of the in-line amplifier 404 is determined as discussed previously. In one embodiment of the invention, erbium-doped fiber amplifiers are implemented as the in-line amplifiers 404, however, a wide range of amplifiers can be implemented without detracting from the spirit of the invention. Once the optical signal 403 travels across this predetermined distance, the In-line amplifier 404a boosts the power of each channel of the optical signal 403. In one embodiment, at start up of the optical network 401, the in-line amplifier 404 do not initially boost the optical signal 403 as the optical signal 403 is transmitted along the optical network 401 as no prior analysis of the optical signal 403 has been completed. An optical spectrum analysis 406 located within the optical system 401 analyzes the optical signal 403 to determine the amount of energy loss experienced by the optical signal 403 through transmission over the optical network 401. The optical spectrum analyzer 406 then transmits this analysis data to the in-line amplifiers 440 and commands the in-line amplifiers 404 to boost the channels of the optical signal 403 by an amount necessary to maintain a constant power level of the optical signal 403 across the optical network 401. This fine turning of the optical network 401 occurs when the optical network is initially initiated, however, the optical spectrum analyzer 406 continuously monitors the strength of the optical signal 403 and can periodically direct a modification to the amounts of power boosted by a specific In-line amplifier 404 during continuous use of the optical network 401 to correct this gain tilt. In another exemplary embodiment the in-line amplifiers' 404 output power is monitored by each in-line amplifier. This self-monitoring allows for the average power out of each in-line amplifier 404 to remain approximately constant. As an additional step to the self-monitoring, a measurement at the Optical spectrum analyzer 406 determines the need for fine turning of the in-line amplifiers 404 output power/average gain of the in-line amplifier 404.
When the optical signal 403 has its power boosted by the In-line amplifier 404a, each channel of the optical signal 403 has the power boosted with a consistent amount from the In-line amplifier 404a. In one disclosed embodiment there are forty channels present in the optical signal 403. All forty channels of the optical signal 403 are boosted by the same power level from the In-line amplifier 404a. As was disclosed with
The optical spectrum analyzer 406 also determines the power boost to correct gain tilt propagated by the In-line amplifiers 404 by averaging the power level of all channels and then applying a boost so that the average level of all channels equal the pre-determined power level of the optical signal 403 and further determines the accumulated gain or loss on a channel-by-channel basis of the power level as compared to the pre-determined optimal power level. The optical spectrum analyzer 406 transmits the power boost data to the in-line amplifiers 404 over line 414 via an optical supervising channel 412. Once the Optical spectrum analyzer 406a determines the amount of gain differential for each channel of the optical signal 403, the optical signal analyzer 406a transmits these gain differentials to the dynamic gain equalizer 408 over line 418 via an optical supervising channel 412. The optical supervising channel 412 is a management channel and supervisory information is transmitted via this ethernet channel at 100 megabits to 1 gigabit. The rates of transmission of information over the optical supervising channel 412 may vary without detracting from the spirit and scope of the invention. In another embodiment, the management or supervisory channel can be implemented as a public telephone network or Internet line without detracting from the spirit of the invention. The transmission of management or supervisory information over the management or supervisory channel does not require the use of fiber and is not necessarily one of the wavelength channels of the optical line 410. In one disclosed embodiment, the management and supervisory channel are implemented as the optical supervising channel 412 which transmits management supervisory information optically to the devices connected within the optical network 401. The Optical spectrum analyzer 406a transmits the gain differential of each channel of the optical signal 403 to the dynamic gain equalizer 408a which is co-located with in-line amplifier 404a. The dynamic gain equalizer 408a receives the gain differentials transmitted by the Optical spectrum analyzer 406a through the optical supervising channel 412 over communication line 416. The dynamic gain equalizer 408a and the Optical spectrum analyzer 406a are not co-located with the same in-line amplifier 404. The dynamic gain equalizer 408a is located at a point between Optical spectrum analyzers 406 or between the transmitting terminal 400 and the first Optical spectrum analyzer 406a. Therefore, the dynamic gain equalizer 408a corrects the optical signal 403 at the first In-line amplifier 404a based upon the signal deviation present at the Optical spectrum analyzer 406a located at In-line amplifier 404b. This methodology is repeated for dynamic gain equalizers 408b, 408c and optical spectrum analyzers 406b and 406c. Thus, the optical signal 403 is modified at in-line amplifier 404c by the dynamic gain equalizer 408b based upon information transmitted to the dynamic gain equalizer 408b by the optical spectrum analyzer 408b based upon information transmitted to the dynamic gain equalizer 408b by the optical spectrum analyzer 406b located with in-line amplifier 404d. The dynamic gain equalizer 408c modifies the optical signal 403 at in-line amplifier 404e based upon data transmitted from the optical spectrum analyzer 408c located with in-line amplifier 404f. Therefore, the dynamic gain equalizer 408 correct the optical signal 403 at one subset of in-line amplifier 404 based upon the signal deviation analyzed at the optical spectrum analyzer 406 located at a second subset of in-line amplifiers 404.
In one embodiment, the dynamic gain equalizer 408 and the Optical spectrum analyzer 406 are spaced evenly throughout the optical network 401. The dynamic gain equalizer 408 are placed approximately in the center between two adjacent. Optical spectrum analyzers 406. The dynamic gain equalizer 408 closed to the transmitting terminal 400 is placed approximately in the center between the transmitting terminal 400 and the first Optical spectrum analyzer 406a. A wide variety of alignment schemes can be implemented without detracting from the spirit of the invention as long as at least one dynamic gain equalizer is not co-located with one Optical spectrum analyzer. In one embodiment, the control of the optical supervisory channel 412 is implemented through the use of a token which is transmitted to each device throughout the optical network 401. For example, when the Optical spectrum analyzer 406a has the token, that Optical spectrum analyzer 406a controls the gain tuning of the optical network 401 and can then transit amplification and gain differential information to the in-line amplifiers 404a and 404b and the dynamic gain equalizers 408a. Once this information has been transmitted and the in-line amplifiers 404a and 404b and the Dynamic gain equalizer 408a adjust the power appropriately, the Optical spectrum analyzer 406a sends the token downstream of the optical spectrum network 401, allowing another deice to transit the optical supervisory channel 412. The Optical spectrum analyzers 406a, in one embodiment, are in communication with the in-line amplifiers 404 and dynamic gain equalizers 408 which are located prior to the Optical spectrum analyzer 406. Thus, each Optical spectrum analyzer 406 maintains communication with the dynamic gain equalizer 408 and the in-line amplifiers 404 that are immediately preceding it and are not in communication with any other Optical spectrum analyzers 406. However, optional communication and control schemes are available and can be implemented without departing from the spirit of the invention.
Referring now to
It should be noted that during start-up procedures, the integrity of the optical signal 403 is not maintained until a series of adjustments are performed on the optical signal 430. Therefore, there will be a period of time upon the start-up of the transmission of the optical network 401 in which the data transmitted over the optical signal 403 will be invalid. However, once the integrity of the optical signal 403 is established, then the process described above continues to modify the amount of gain equalization necessary over time.
A benefit of the present invention occurs because the pre-emphasis of the gain equalization ensures that the average power over the n spans, where n equals the number of in-line amplifiers 404 for each channel of the dense wavelength division multiplexed system, is the expected or optimal power level. Further, the effects of random wavelength losses, as well as time varying polarization dependent losses are reduced by a factor of 2 by compared to the conventional approach. This improvement allows for twice as large component tolerances or with the same component parameters induces only half the penalty on the system margin. This improvement is demonstrated by the area formed by triangles outlined by lines 600, 608 and the distance ½× which define area 606. Area 606 plus area 604 (a negative value) are approximately zero. The system distortion from the fixed gain deviation has been nearly eliminated. Thus, when compared to area 202 of the prior art, a large benefit is realized. As the accumulated gain remain closer to zero (−2 dBs to 2 dBs) without straying as far as −4 dBs to 4 dBs in the conventional systems, the overall integrity of the optical signal 403 is increased.
The foregoing disclosure and description of the invention are illustrative and explanatory thereof of various changes to the size, shape, materials, components and order may be made without departing from the spirit of the invention.
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|U.S. Classification||385/24, 359/885, 359/337|
|International Classification||H04B10/293, H04B10/077, H04B10/079, H04B10/2507, H04J14/02, G02B6/28|
|Cooperative Classification||H04J14/0221, H04B10/2935, H04B10/07955, H04B10/077, H04B10/25073|
|European Classification||H04B10/25073, H04B10/07955, H04B10/2935, H04B10/077, H04J14/02B|
|Aug 25, 2005||AS||Assignment|
Owner name: DOWLING CONSULTING, INC., FLORIDA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CELION NETWORKS, INC.;REEL/FRAME:016446/0411
Effective date: 20050629
Owner name: PIVOTAL DECISIONS LLC, NEVADA
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Effective date: 20050629
|Sep 22, 2010||FPAY||Fee payment|
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|Sep 29, 2015||AS||Assignment|
Owner name: XYLON LLC, NEVADA
Free format text: MERGER;ASSIGNOR:PIVOTAL DECISIONS LLC;REEL/FRAME:036718/0302
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