Exhibit 2 

Case 6:20-cv-00484-ADA Document 1-2 Filed 06/02/20 Page 1 of 14
(12) United States Patent 

Stephens 

USOO6236487B1 

(10) Patent No.: US 6,236,487 B1 

(45) Date of Patent: May 22, 2001 

(54) OPTICAL COMMUNICATION CONTROL 

SYSTEM 

(75) Inventor: Thomas D. Stephens, Ellicott City, MD 

(US) 

(73) Assignee: Corvis Corporation, Columbia, MD 

(US) 

(*) Notice: Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.C. 154(b) by 0 days. 

(21) Appl. No.: 09/119,561 

(22) Filed: Jul. 21, 1998 

(51) Int. Cl." ................................................. H04B 10/00 

(52) U.S. Cl. .......................... 359/161; 35.9/124; 35.9/177; 

359/187 

(58) Field of Search ..................................... 359/124, 161, 

359/187, 177 

(56) References Cited 

U.S. PATENT DOCUMENTS 

4,616,898 10/1986 Hicks, Jr.. 

5,007,705 4/1991 Morey et al.. 

(List continued on next page.) 

FOREIGN PATENT DOCUMENTS 

O853396 A2 

WO 99/43107 

7/1998 (EP). 

8/1999 (WO). 

OTHER PUBLICATIONS 

Park, S.Y., et al., Feasibility Demonstration Of 10 Gbit/s 

Channel WDM Network Using Dynamic Gain-Controlled 

EDFAs, Electronics Letters, Mar. 5" 1998, vol. 34, No. 5., 

Online No. 1998O346. 

Dung, J.C., et al., Gain Flattening Of Erbium Doped Fibre 

Amplifier Using Fibre Bragg Gratings, Electronics Letters, 

Mar. 19' 1998, vol. 34, No. 6., Online No. 19980446. 

11 (OPN) 16 14 li 

Yu, A., et al., Analysis. Of Optical Gain And Noise Spectral Properties Of Erbium-Doped Fiber Amplifer Cascade, Opti 

cal Amplifiers and their Application, Aug. 3-5, 1994, 1994 

OSA Technical Digest Series, V14, pp. FB1-1-3/124-126. 

Sugaya, Y., et al., Novel Configuration For Low-Noise And 

Wide-Dynamic-Range Er-Doped Fiber Amplifiers For 

WDM Systems, Optical Amplifiers and their Application, 

Jun. 15–17, 1995, 1995 OSATechnical Digest Series, V18, 

FC3-1-4/158-161. 

Jacobovitz-Veselka, G.R., et al., Single-Stage Booster 

Amplifier With Two 980 nm Pumps Stabilized By Fiber 

Gratings, Optical Amplifiers and their Application, Jun. 

15–17, 1995, 1995 OSA Technical Digest Series, V18, pp. 

FC4-1-4/162-165. 

Primary Examiner Leslie Pascal 

ASSistant Examiner Hanh Phan 

(57) ABSTRACT 

Apparatuses and methods are disclosed for operation of 

optical transmission Systems. An optical transmission Sys 

tem of the present invention includes at least one signal varying device positioned to vary an optical Signal passing 

to an optical processing node to achieve one or more desired 

Signal characteristic in the optical Signal as it approaches or 

reach the optical processing node. A controller is provided 

and configured to control the at least one signal varying 

device in response to at least one detected characteristic of 

said optical signal as it passes to the optical processing 

nodes. The Signal varying devices are controlled 

collectively, in groups, or individually to achieve the desired 

characteristics in the optical Signal when the optical Signal arrives at the optical processing nodes. The processing nodes 

include optical transmitter in optical communication with 

optical receivers via Signal varying devices, which include 

amplifiers, attenuators, filters, and other Signal varying 

devices. The Signal varying devices are controlled to pro 

duce at desired signal characteristic, Such as minimized gain 

flatneSS Variations, or uniform Signal to noise ratio verSuS 

wavelength profiles at the receiver or an intermediate pro cessing node, Such as an add/drop port, control point, or a 

Switch. 

28 Claims, 5 Drawing Sheets 

 

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US 6,236,487 B1 

Page 2 

U.S. PATENT DOCUMENTS 5,717,510 2/1998 Ishikawa et al. .................... 359/161 

5,764,406 6/1998 Newhouse et al. . 5,050,949 9/1991 DiGiovanni et al.. 5,812,710 9/1998 Sugaya ................................... 385/27 

5,058,974 * 10/1991 Mollenauer ............................ 385/27 5,815,299 9/1998 Bayart et al.. 

5, 191586 3/1993 Huber. 5,818,629 10/1998 Kinoshita ............................. 359/341 

5,283,686 2/1994 Huber. 5,861,981 * 1/1999 Jabr ....... 359/341 

5,406,411 4/1995 Button et al.. 5,880,866 * 3/1999 Stolen ...... 359/138 

5,500,756 3/1996 Tsushima et al. ................... 359/174 5,883,736 * 3/1999 Oshima et al. . 359/341 

5.530,583 6/1996 Uno et al.. 5,898,714 * 4/1999 Morita et al. ............................ 372/6 

5,541,766 7/1996 Mizrahi et al.. 5,900,969 * 5/1999 Srivastava et al 359/341 

5,557,442 9/1996 Huber ................................... 359/179 5,903,371 * 5/1999 Arecco et al. .. ... 359/119 

5,579,143 11/1996 Huber. 5,963,361 * 10/1999 Taylor et al. ... 359/337 

5,636,301 6/1997 O'Sullivan et al.. 5,986,799 * 11/1999 Itou et al. ....... 359/337 

5,673,280 9/1997 Grubb et al. ............................. 372/3 6,038,356 * 3/2000 Kerfoot, III et al. .. 385/24 

5,675,432 10/1997 Kosaka ................................. 359/341 

5,696.615 12/1997 Alexander. * cited by examiner 

 

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U.S. Patent May 22, 2001 Sheet 1 of 5 US 6,236,487 B1 

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U.S. Patent May 22, 2001 Sheet 2 of 5 US 6,236,487 B1 

 

 

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U.S. Patent May 22, 2001 Sheet 3 of 5 US 6,236,487 B1 

Amplitude v Wavelength Amplitude v Wavelength 

2O 20 

S 15 15 

E 10 E 10 

5 5 5 

O O 

Wavelength Wavelength 

Fig. 4a Fig. 4b 

Amplitude v Wavelength Amplitude v Wavelength 

20 2O 

is 15 c is 15 

E 10 5 E 10 

O 5 5 

Wavelength O 

- Wavelength 

Amplitude v Wavelength Amplitude v Wavelength 

20 

c 15 1O 

5 

O 

Wavelength 

Wavelength 

Fig. 4e Fig. 4f 

 

 

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U.S. Patent May 22, 2001 Sheet 4 of 5 US 6,236,487 B1 

 

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U.S. Patent May 22, 2001 Sheet 5 of 5 US 6,236,487 B1 

VO (N 

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US 6,236,487 B1 

1 

OPTICAL COMMUNICATION CONTROL 

SYSTEM 

CROSS-REFERENCE TO RELATED 

APPLICATIONS 

Not Applicable 

STATEMENT REGARDING FEDERALLY 

SPONSORED RESEARCH OR DEVELOPMENT 

Not Applicable 

BACKGROUND OF THE INVENTION 

The present invention is directed generally to controlling 

the transmission of information in communication Systems. 

More particularly, the invention relates to controlling optical 

Signal characteristics during transmission in information 

network, transmission and communication Systems and con 

trollers for use therein. 

The continued development of digital technology has 

provided electronic access to vast amounts of information. 

The increased access to information has fueled an increasing desire to quickly obtain and process the information. This 

desire has, in turn, placed ever increasing demands for faster 

and higher capacity electronic information processing equipment (computers) and transmission networks and Sys 

tems linking the processing equipment (i.e., telephone lines, 

cable television (CATV) systems, local, wide and metro 

politan area networks (LAN, WAN, and MAN)). 

In response to these demands, telecommunications com 

panies have turned to optical communication Systems to 

provide Substantially larger information transmission 

capacities than corresponding electrical Systems. Early opti 

cal transmission Systems, known as Space division multiplex 

(SDM) systems, transmitted one signal in a single wave 

length per waveguide, i.e. fiber optic Strand. AS demand for 

transmission capacity further increased, multiple optical Signals were transmitted in a Single wavelength by time 

division multiplexing (TDM) the various signals in a known 

Sequence onto a signal carrier wavelength. 

The continued growth in traditional communications SyS 

tems and the emergence of the Internet as a means for 

accessing data has further accelerated the demand for higher 

Speed access to information. Telecommunications compa nies have looked to wavelength division multiplexing 

(WDM) to further increase the capacity of their existing optical systems. In WDM transmission systems, pluralities 

of distinct TDM or SDM information signals are carried 

using different optical wavelengths. The pluralities of infor 

mation carrying wavelengths are combined into a multiple 

wavelength optical Signal, which is transmitted in a single 

optical fiber. In this manner, WDM systems can increase the 

transmission capacity of existing SDM/TDM systems by a 

factor equal to the number of wavelengths used in the WDM 

System. 

Optical WDM systems were not initially deployed, in 

part, because of the cost associated with providing electrical 

Signal regeneration equipment for each wavelength through 

out the system. However, the development of the erbium 

doped fiber optical amplifier (EDFA) eliminated the need for 

electrical amplifiers and the associated costs in many 

Systems, thereby gaining WDM communication Systems 

acceptance in the marketplace. 

EDFAS can theoretically be used to amplify Signals in an 

amplification wavelength range Spanning from approxi 

mately 1500 nm and 1600 nm. However, as shown in FIG. 

15 

25 

35 

40 

45 

50 

55 

60 

65 

2 

1, EDFAS do not equally amplify each wavelength in the 

range. As a result, the relative performance of EDFAS in a 

transmission System varies depending upon the wavelengths 

used in the System. 

EDFA Variations (gain non-uniformities) can be mini 

mized by the judicious Selection of the wavelengths and 

amplifier powers used in a system. For example, WDM 

Systems currently restrict the wavelengths used in the System 

to between 1540 nm and 1560 nm, which are comparably amplified by EDFAS. AS might be expected, restricting 

System designs to only those wavelengths that are compa 

rably amplified by EDFAs severely limits the number of 

wavelengths, i.e., channels, that can be used to carry infor 

mation. 

The number of wavelengths in the system can be 

increased to Some extent, if only a Small number of ampli fiers are used in the System. Wavelengths having differing 

EDFA amplification characteristics can be used in those 

Systems, because the cumulative effect of highly amplified noise does not Swamp out lowly amplified Signals when only 

a few amplifiers are used. 

In addition, the wavelength dependence of EDFAS is also 

a function of the amplification power (gain) of the EDFA, as 

further shown in FIG. 1. Thus, the amplification power of 

each EDFA in the system generally must be restricted to 

minimize amplification variations in the System. The ampli 

fier power limitations, in turn, limit how far apart the EDFAS 

can be spaced in a System, i.e., the Span length. 

The WDM system size constraints imposed by EDFA 

wavelength variations have focused attention on providing amplifier configurations that compensate for the variations 

and provide more uniform gain for a larger band of wave 

lengths. Various EDFA configurations have been proposed in 

the literature to minimize amplifier gain variations. For 

example, see U.S. Pat. Nos. 5,406,766, 5,541,766, 5,557, 

442, 5,636,301, and 5,696,615; Sugaya et al., Optical Ampli fiers and Their Applications, Technical Digest OSA 1995 v. 

18, pp. 158-161/FC3-1; Jacobovitz-Veselka et al., Optical Amplifiers and Their Applications, Technical Digest OSA 

1995 v. 18, pp. 162–165/FC3-1; Masuda et al., OSA 1997, 

pp. 40-3/MC3-1, Park et al., Electronics Letters, Mar. 5, 

1998, Vol. 34, No. 5, Online No. 1998.0346; and, Dunget al., 

Electronics Letters, Mar. 19, 1998, V. 34, n. 6, Online No. 

19980446. 

The above referenced gain flattened EDFA configurations generally attempt to flatten the amplifier gain profile to 

within an approximately 1 dB range over a range of wave 

lengths and/or amplification powers as the Signal exits the 

EDFA. The bandwidth of the amplifier is typically defined as 

the wavelength range over which there is a 3 dB variation in 

the gain profile. The improved gain flattened amplifier 

characteristics provide Some improvement in the number of 

amplifiers, amplifier power ranges, and Span lengths before 

the Signal must be regenerated. 

While an improvement, the gain profile variations of the 

various amplifier configurations nonetheless limit the num 

ber of amplifiers that can be used in a WDM system prior to 

Signal regeneration. In order to increase the number of 

amplifiers used in these Systems, each amplifier must be 

more tightly controlled to minimize amplifier variations. A 

System in which amplifier control complexity increases with 

the number of amplifiers is clearly undesirable from both a 

System management and a cost Standpoint. 

Thus, the present Systems do not provide an effective 

method to overcome the inherent gain variation in EDFAS 

and provide for continued growth and development of 

Case 6:20-cv-00484-ADA Document 1-2 Filed 06/02/20 Page 9 of 14
US 6,236,487 B1 

3 

communication Systems. Accordingly, there is a need for 

optical System controllers that allow for increased network 

capacity and flexibility. One aspect of which is to reduce the 

limitations placed on the System by amplification compo 

nents and provide for a more flexible, longer distance 

transmission System. 

BRIEF SUMMARY OF THE INVENTION 

The apparatuses and methods of the present invention 

address the above needs and concerns for improved control 

over optical Systems. An optical transmission System of the 

present invention includes one or more optical processing 

nodes, at least one signal varying device and a controller 

configured to control Said at least one signal varying device. 

The Signal varying device is positioned to vary an optical 

Signal which includes at least one wavelength passing to the 

optical processing nodes. The controller is configured to 

control the at least one signal varying device based on at 

least one detected Signal characteristic to produce at least 

one desired Signal characteristic at the optical processing 

node. 

In an embodiment, the optical processing nodes include at 

least one optical Signal receiver and at least one optical 

Signal transmitter, and the Signal varying devices include a 

plurality of optical amplifiers. The controller is configured to 

vary the amplifier properties in response to the Signal 

characteristics, Such as Signal intensity, noise intensity, Sig 

nal to noise ratio, etc., to produce an optical Signal having 

desired characteristics at the receiver. The Signals are gen erally detected and characterized as the Signals approach or 

reach the processing nodes. The amplifiers and other Signal 

varying devices can be controlled in concert, in groups, or 

individually to vary the signal characteristics at the receiver 

or other processing nodes, Such as add and/or drop ports, Switches, splitters, combiners, and control points. 

In this manner, the Signal varying devices, namely 

amplifiers, attenuators, filters, and associated components, 

do not have to be as tightly controlled to ensure proper 

System performance. Instead, the present invention manages 

the overall variation of the Signal varying devices in the 

System to provide a control System that requires Substan 

tially less oversight of each individual Signal varying device. 

Accordingly, the present invention addresses the afore 

mentioned problems and provides apparatuses and methods 

to increase the performance and control of optical commu 

nication Systems. These advantages and others will become 

apparent from the following detailed description. 

BRIEF DESCRIPTION OF THE DRAWINGS 

Embodiments of the present invention will now be 

described, by way of example only, with reference to the 

accompanying Figures wherein like members bear like 

reference numerals and wherein: 

FIG. 1 shows typical gain flattened EDFA characteristics 

Versus wavelength for various amplification powers, 

FIGS. 2-3 are optical communication systems of the 

present invention; 

FIGS. 4(a f) show Schematic variations in optical signal intensity as the optical Signal passes through the System; 

and, 

FIGS. 5-13 are signal varying devices for use in the 

present invention. 

DETAILED DESCRIPTION OF THE 

INVENTION 

The operation of optical systems 10 of the present inven 

tion will be described generally with reference to the draw 

15 

25 

35 

40 

45 

50 

55 

60 

65 

4 

ings for the purpose of illustrating present embodiments 

only and not for purposes of limiting the Same. 

As shown in FIGS. 2 and 3, the optical system 10 includes 

optical processing nodes 11, Such as optical transmitters 12, 

connected via optical fiber 14 through at least one signal varying device 16 to other optical processing nodes 11, Such 

as optical receivers 18. A controller 20 is configured to 

detect and monitor any number of characteristics of optical Signals passing to the processing nodes. The detected char 

acteristics are used by the controller 20 to provide feedback 

control over the Signal varying devices 16 via control lines 

22. The Signal varying devices 16 are controlled to vary the 

characteristics of the optical Signals passing through the 

devices 16 to produce desired characteristics in the optical Signal as it reaches the processing nodes 11. The controller 

20 is generally configured to control the Signal characteris 

tics over an optical link, which includes the optical trans 

mission fiber 14 and at least one signal varying devices 16, 

extending between the processing nodes 11. The controller 

20 can also be used to control the Signal characteristics over 

multiple links, either Separately or collectively. 

The optical Signal passing between the processing nodes 

11 includes at least one information carrying wavelength. In 

WDM systems, the optical signal will generally include a 

plurality of information carrying wavelengths. AS used 

herein, the term “information” should be broadly construed 

to include any type of data, instructions, or signals that can 

be optically transmitted. 

Transmitters 12 used in the system 10 generally include 

one or more modulated carrier wavelength Sources or 

emitters, Such as lasers. The transmitters 12 may also include narrow band incoherent Sources Such as described in U.S. 

Pat. No. 5, 191586 issued to Huber, or other suitable 

Sources. Receivers 18 used in the system 10 can include 

direct or indirect, e.g., coherent, detection receivers as are 

known in the art. One skilled in the art will appreciate that 

the present invention generally can be used with transmitters 

12 and receivers 18 currently used in optical communication 

Systems. 

Controllers 20 are used to control the Signal varying devices 16 either collectively, in groups, or individually as 

required in the system 10. The complexity of the controller 

20 overseeing the operation of the system 10 will depend, in 

part, upon the extent of individual control exerted over the 

individual signal varying devices 16. For example, the 

control Scheme can be simplified by operating the Signal 

varying devices 16 in concert to achieve desired character 

istics in the Signal arriving at a processing node. 

The system 10 can include one or more additional pro cessing nodes 11 in the form an intermediate processing 

node 24 between the terminal processing nodes, 12 and 18, 

as shown in FIG. 3. The intermediate processing node 24 can 

be add and/or drop ports, Switches, Signal distributors and 

combiners, control points (“A” in FIG. 3), or other signal processing devices. The intermediate processing nodes may include Single wavelength or multiple wavelength proceSS 

ing nodes, Such as described in the assignee's copending 

application filed herewith entitled “Optical Communication 

System”, Docket No. NTI980717OCS U.S. Ser. No. 09/119, 

562, which is incorporated herein by reference. 

The intermediate node 24 is shown in FIG. 3 connected to 

a terminal processing node including a receiver 18 and a 

transmitter 12. The intermediate processing node 24 can also 

be connected to another intermediate processing node or to 

a terminal processing node, which may include transmitters 

and/or receivers. The control points Acan be included in the 

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US 6,236,487 B1 

S 

transmission system 10 to provide additional control over 

the wavelength characteristics in the System 10 and may also 

correspond to locations at which additional functions Such as 

gain equalization or wavelength filtering can be performed. 

In FIG. 3, a plurality of signal varying devices 16 are 

provided between the intermediate processing node 24 and 

one of the receivers 18. One skilled in the art will appreciate that any number of Signal varying devices 16 can be pro Vided between the processing nodes depending upon the 

requirements of the System. 

The interaction of the controller 20 with the signal vary 

ing devices 16 can be generally described with reference to 

FIGS. 4(a-e). FIG. 4(a) depicts an optical signal intensity profile Versus wavelength for a Signal prior to entering a 

Signal varying device 16. A flat intensity profile is shown in 

FIG. 4(a) to facilitate explanation of the controller 20. If a 

Signal varying device 16 is operated as an amplifier accord 

ing to gain curve (a) shown in FIG. 1, then the signal of FIG. 

4(a) will emerge from the signal varying device 10 having 

an intensity profile similar to that shown in FIG. 4(b). As the 

optical Signal proceeds though the fiber 14, it incurs fiber 

losses and may develop an intensity profile Similar to FIG. 

4(c) as it enters a Subsequent signal varying device 16. If a 

Subsequent Signal varying device 16 is operated as an 

amplifier having a gain profile similar to curve (b) in FIG. 

1, then the optical Signal will emerge from the Subsequent Signal varying device 16 having an intensity profile Similar 

to FIG. 4(d). 

The optical signal of FIG. 4(d) can be further propagated through the fiber 14 and additional signal varying devices 16 

incurring further fiber losses and gain profile variations. AS 

the optical signal enters a signal varying device 16 preceding 

an optical processing node, it may have a profile Similar to 

FIG. 4(e). If the signal varying device 16 preceding the 

optical processing node is operated having a gain profile 

similar to curve (c) in FIG. 1, then the optical signal will 

emerge from the preceding Signal varying device and reach 

the processing node having a Substantially uniform gain 

profile similar to that shown in FIG. 4(f). 

The control of each Signal varying device is based on the 

profile at the optical processing node (FIG. 4(f)) and not 

based on the profile at each Signal varying device along the 

link as in the prior art. While the example shown in FIGS. 

4(a-f) uses the Signal intensity and profile as the detected 

characteristics, other characteristics, Such as noise and Signal 

to noise ratio, and Statistical measures, Such maximum, 

minimum, averages, and distributions can be used to control 

the system 10. 

In one aspect, the controller 20 is used to detect and 

monitor the optical Signal as it approaches the optical 

processing node 11. In a Second aspect, the controller 20 is 

used to variably control the performance of the Signal 

varying devices 16 in the link to achieve the desired char 

acteristic at the processing node 11. The control function can 

be performed by tapping off a portion of the optical Signal 

as it approaches or reaches a processing node and detecting 

the optical Signal characteristics, Such as with an optical 

Spectrum analyzer. The detected Signal characteristics are 

compared to either absolute or relative reference 

characteristics, Such as the desired wavelength characteristic 

profiles. The comparison yields a System variance that is 

compared to a control variance. If the System variance is 

within the control variance, the controller 20 does not vary the Settings of the Signal varying devices 16 in the link. If the 

System variance is outside the control variance, the control 

ler 20 will vary the settings of the signal varying devices 16 

15 

25 

35 

40 

45 

50 

55 

60 

65 

6 

until the System variance is within the control variance. For 

example, in an embodiment in which the Signal varying device includes Raman and erbium amplifiers, the optical 

energy, i.e., pump power, Supplied to the amplifiers can be 

controlled to vary the output power of the amplifier to 

achieve the desired characteristics at the optical processing 

node. In addition, the Raman or erbium fiber Sections can 

also serve as variable attenuators in which the loSS of the 

Sections is controlled by varying the pump power Supplied 

to the Raman or erbium fiber sections. 

The controller 20 can be used to control the optical signal characteristics by varying the performance of one or more of 

the Signal varying devices 16 individually, in groups, or 

collectively. The control System complexity, Stability, and 

range of applicability will invariably depend upon the man 

ner in which the Signal varying devices 16 are operated. 

For example, consider an embodiment in which only one 

out of N Signal varying devices in a link is being controlled 

by the controller 20. The controller 20 will most likely have 

to vary the one signal varying device over a wide range to 

compensate for uncontrolled variations in the N-1 indepen dent Signal varying devices. In contrast, if all the Signal varying devices in the link are individually controlled, the 

controller 20 can vary the performance of any combination 

of Signal varying devices to produce a change in the optical 

Signal characteristics. However, the number of possible control combinations may require more complex control 

Schemes and could lead to System instability and slower 

response times. 

In contrast, when all of the Signal varying devices 16 in 

the link are controlled in concert by the controller 20, the 

link can be controlled with a leSS complex control Scheme. 

This is because the possible control combinations have been 

decreased and variations in the System can be averaged over 

all of the Signal varying devices 16 in the link. Also, the link 

Stability is improved because the Signal varying device 

performance is varied continuously along the link. AS Such, 

the probability that any given Signal varying device will 

have to be grossly adjusted will be reduced, thereby improv 

ing the response time of the link. 

Individual control over the Signal varying devices can be 

useful for facilitating initialization during manufacturing 

and installation, and resetting and fine tuning of the Signal varying devices 16 during operation. The Signal varying 

devices 16 can also be controlled in groups, to provide additional control over different types of Signal varying devices 16 deployed in the system 10. 

FIGS. 5-13 show several embodiments of signal varying devices 16 containing various components that can be 

connected to the controller 20 via control line 22 in the 

present invention. The embodiments shown in FIGS. 5-13 

are provided to facilitate the explanation of the control 

Scheme, and not to limit, the present invention. 

The Signal varying devices 16 will often include an 

amplifier 26 in one or more Stages. The amplifier 26 can 

include concentrated, or lumped, and distributed EDFAS, 

Raman amplifiers, other optical amplifiers, and combina 

tions thereof that provide fixed or variable gain. Optical 

power can be Supplied to the optical amplifiers 26 by either 

locally or remotely pumping the amplifiers 26 to Supply 

optical energy. In addition, the Signal varying devices 16 can 

incorporate various gain flattening configurations Such as 

those discussed in the background Section. While the present invention does not require that each Signal varying device 16 

operate with a uniform gain profile, amplifier configurations 

that provide improved gain profile flatness will tend to 

increase the Stability, flexibility, and Overall performance of 

the system 10. 

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US 6,236,487 B1 

7 

The Signal varying device 16 can also include other Signal varying components, Such as attenuators 28, and filters 30. 

The filters 30 can be Mach-Zehnder, Fabry-Perot or dichroic 

filters, fixed or tunable Bragg gratings, or other filters as may 

be required in system 10. The filters 30 may be used in 

combination with directional couplers and/or circulators to 

vary the signal, such as described in U.S. Pat. Nos. 5,007, 

705, 5,283,686 and 5,579,143. Signal varying devices that 

are useful in the present invention are described in the 

assignee's copending application filed here with entitled 

“Optical Signal Varying Device', Docket No. 

NTI980717OSVD, U.S. Ser. No. 09/119,556 which is incor 

porated herein by reference. 

In FIGS. 5-9, a variable attenuator 28 is provided in the 

Signal varying device 16 and connected via the control line 

22 to the controller 20. In the FIG. 5 configuration, the 

variable attenuator 28 is used to vary the optical Signal intensity after the optical Signal passes through the amplifier 

26 and filter 30. The optical signal emerging from the 

variable attenuator 28 has a signal intensity profile verSuS 

wavelength that was produced by the preceding amplifier 

26, but the wavelength intensities are reduced via the 

attenuator 28 to a level set by the controller 20. 

Also in the FIG. 5 configuration, an amplifier controller 

32 provides feedback control over the output power of the 

Signal varying device 16, typically by varying the pump 

power supplied to the devices 16 by an amplifier pump 34. 

In operation, the amplifier controller 32 is used in conjunc 

tion with the controller 20 to vary the optical power Supplied 

to the amplifier 26 as part of the overall control of the signal varying device 16. 

In the FIG. 6 configuration, the amplifier controller 32 can 

also be set, either by the controller 20 or otherwise, to 

deliver the optical Signal at a predetermined intensity as it 

exits the signal varying device 16 into the fiber 14. The 

amplifier controller 32 Set point is generally determined by 

the power necessary to overcome the loss in the fiber 14 and 

to provide a signal having a predetermined power at the next 

Signal varying device 16 or processing node 11. 

In the embodiment shown in FIG. 6, an additional ampli fier configuration 26 is provided between the attenuator 28 

and the amplifier controller 32 to provide additional flex 

ibility in controlling the optical signal characteristics. AS 

previously Stated, the amplifiers 26 shown in the drawings 

can be Single or multiple Stage EDFAS, Raman amplifiers, 

and/or other gain flattening amplifier configurations, Such as 

discussed in the background. In an embodiment, the Signal 

varying device includes distributed and concentrated Raman 

sections followed by an Erbium doped fiber section and a 

gain flattening filter. The controller 20 can be used to vary 

the pump power Supplied to the Raman and erbium Sections 

to operate the fiber Sections as variable attenuators or 

amplifiers as necessary to achieve the desired signal char 

acteristics. 

The signal varying device in FIG. 7 provides for control 

ling the intensity of the Signal using the attenuator 28 

preceding the amplifier 26. In this configuration the ampli 

fier may be preset to deliver a prescribed level of amplifi 

cation to the Signal. The attenuator 28 is operated to control 

the input power to the amplifier 26 so that the signal will exit 

the amplifier 26 and pass through the filter into the fiber at 

a predetermined intensity. 

Similarly in FIG. 8, the amplifier 26 can be operated at a 

predetermined amplification power. The attenuator 28 is 

then operated to deliver the optical signal into the fiber 14 at 

a predetermined intensity. 

15 

25 

35 

40 

45 

50 

55 

60 

65 

8 

As shown in FIGS. 9-11, the signal varying device 16 can 

be embodied Solely as attenuators, amplifiers, and filters, respectively. Each of the devices being controlled by the 

controller 20 to vary the optical Signal characteristics. In 

FIG. 12, an amplifier 26 is operated in combination with the 

filter 30 to vary the characteristics of the optical signal being 

delivered into the fiber 14. 

In Some instances, it may be desirable to couple the 

intermediate processing node 24 with the Signal varying device 16 as shown in FIG. 13. This configuration provides 

for monitoring and control the Signal characteristics imme 

diately before and after the Signal has been processed in the 

intermediate processing node 24. 

In the operation of the system 10, the controller 20 

provides for dynamic control over the Signal varying devices 

to compensate for variations in the System 10. Typical 

System variations include the number of wavelengths/ channels being used in the System, Signal processing occur 

ring at the processing nodes, environmental conditions, and 

replacement or degradation of System components. 

In the present invention, Signal varying devices 16 can be 

roughly calibrated prior to insertion into the system 10. After 

insertion into the System 10, the Signal varying devices 16 

can be dynamically adjusted to provide the amplification 

power and Signal profile characteristics required in the 

system 10. 

Unlike prior art Systems, the present invention can pro vide for increased stability as the length of the system 10 is 

increased. The increased Stability is possible because the 

System performance can be averaged over a larger number 

of Signal varying devices between optical processing nodes. 

Thus, the addition of Signal varying devices 16 to the System 10, while adding loss to the system 10, can actually provide additional System stability. 

Those of ordinary skill in the art will appreciate that numerous modifications and variations that can be made to 

Specific aspects of the present invention without departing 

from the Scope of the present invention. It is intended that 

the foregoing Specification and the following claims cover 

Such modifications and variations. 

What is claimed is: 

1. An optical transmission System comprising: 

at least one optical processing node, 

at least one signal varying device including a concentrated 

amplifier remotely positioned from Said at least one 

optical processing node to vary an optical Signal pass 

ing to Said at least one optical processing node, and, 

a controller configured to control Said at least one con 

centrated amplifier to achieve a desired signal charac 

teristic in the optical Signal when the optical Signal 

reaches Said at least one optical processing node. 

2. The optical transmission System of claim 1 wherein 

Said controller controls Said at least one signal varying 

device in response to at least one detected characteristic of 

the optical Signal proximate to Said at least one optical processing node. 

3. The optical transmission system of claim 1 wherein 

Said at least one optical processing node includes at least one 

transmitter configured to optically transmit Said optical 

Signal to at least one receiver and Said at least one signal 

varying device is controlled to achieve Said desired signal characteristics in the optical Signal when the optical Signal 

reaches Said at least one optical processing node. 

4. The optical transmission System of claim 1 wherein 

Said at least one optical processing node includes at lease 

one of transmitters, receivers, add ports, drop ports, add/ 

drop ports, Switches, control points, and combinations 

thereof. 

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US 6,236,487 B1 

5. The optical transmission system of claim 1 wherein 

Said at least one signal varying device further includes Signal varying devices Selected from the group consisting of locally 

and remotely pumped, concentrated and distributed 

amplifiers, attenuators, filters, and combinations thereof. 

6. The optical transmission System of claim 1 wherein 

Said at least one Signal varying device includes a distributed 

Raman fiber Section in Series with Said concentrated optical amplifier which includes a concentrated Raman fiber 

Section, an erbium doped fiber Section and a gain flattening filter, wherein each of said fiber sections is provided with 

optical pump energy from at least one pump Source and Said 

controller is configured to vary Said pump energy Supplied 

to each of Said fiber Sections to operate Said Sections as an 

attenuator, an amplifier, a loSSleSS fiber Section, and combi 

nations thereof. 

7. The optical transmission system of claim 6 wherein 

said distributed Raman fiber section and said erbium fiber 

Section are operated as amplifiers by Said controller, and Said 

controller is configured to operate Said concentrated Raman 

fiber Section as an attenuator, an amplifier, a lossleSS fiber 

Section, and combinations thereof. 

8. The optical transmission system of claim 1 wherein: 

Said optical Signal includes a plurality of information 

carrying wavelengths that can be characterized by detecting characteristics including Signal intensity, 

noise intensity, and Signal to noise ratio, 

Said at least one signal varying device is controlled to vary 

Said detected characteristics of Said plurality of wave 

lengths to achieve Said desired characteristic in Said 

plurality of wavelengths when said plurality of wave 

lengths reach Said at least one optical processing node. 

9. The optical transmission system of claim 8 wherein 

Said detected characteristics include maximum, minimum, 

and average values and distribution profiles. 

10. The optical transmission system of claim 1 wherein 

Said controller provides for collectively controlling each of 

Said at least one signal varying devices. 

11. The optical transmission system of claim 1 wherein 

Said controller provides for individually controlling at least 

one of Said at least one Signal varying devices. 

12. The optical transmission System of claim 1 wherein 

Said desired characteristic includes minimizing gain flatneSS 

variations between Signal wavelengths in Said optical signal having wavelength Signal intensities that are detectable by 

an optical receiver included in Said at least one optical processing node. 

13. The optical transmission system of claim 1 wherein 

Said at least one Signal varying device includes Second 

optical amplifiers Selected from the group consisting of 

erbium doped fiber amplifiers, distributed Raman amplifiers, 

concentrated Raman amplifiers, and combinations thereof. 

14. The optical transmission system of claim 1 wherein 

Said at least one signal varying device includes: 

a first and a Second optical amplifier having controllable 

output powers, 

an optical filter positioned between Said first and Said 

Second amplifiers, 

a variable attenuator further controlled by said controller 

to variably attenuate the optical Signal to achieve Said 

desired signal characteristic at Said at least one optical processing node, and, 

an amplifier controller configured to locally control the 

output power of Said first and Said Second amplifiers. 

15. The optical transmission system of claim 14 wherein 

Said variable attenuator is positioned between said amplifier 

controller and Said Second amplifier. 

15 

25 

35 

40 

45 

50 

55 

60 

65 

10 

16. The optical transmission system of claim 14 wherein 

Said amplifier controller is positioned between Said variable 

attenuator and Said Second amplifier. 

17. The optical transmission system of claim 1 wherein 

Said at least one optical processing node includes at least one 

control point configured to provide gain equalization and 

wavelength filtering. 

18. The optical transmission system of claim 1 wherein 

Said at least one signal varying device includes: 

an optical amplifier having a locally controllable output 

power; 

a variable attenuator further controlled by said controller 

to variably attenuate the optical Signal to achieve Said 

desired signal characteristic at Said at least one optical processing node, and, 

an amplifier controller configured to locally control Said 

amplifier to produce a desired output power from Said 

amplifier. 

19. The optical transmission system of claim 1 wherein, 

Said optical Signal achieves Said desired Signal characteristic 

after passing through Said at least one Signal varying device 

immediately preceding Said at least one processing node. 

20. The optical transmission system of claim 1 wherein 

Said at least one signal varying device includes: 

an optical amplifier; 

a variable attenuator further controlled by said controller 

to variably attenuate the optical Signal to achieve Said 

desired signal characteristic. 

21. The optical transmission System of claim 1 wherein: 

Said at least one signal varying device is one of a plurality of Signal varying devices including a corresponding 

plurality of concentrated amplifiers remotely posi 

tioned to vary an optical signal passing to Said at least 

One optical processing node, and, 

Said controller being configured to collectively control 

Said plurality of concentrated amplifiers to achieve Said 

desired signal characteristic when said optical Signal 

reaches Said at least one optical processing node. 

22. The optical transmission System of claim 21 wherein 

Said optical Signal includes a plurality of wavelengths and 

each of Said plurality of amplifiers is controlled to Substan 

tially minimize the gain variation in Said plurality of wave 

lengths at Said at least one optical processing node. 

23. The optical transmission system of claim 1 wherein 

Said at least one signal characteristics are detected at a 

control point remote from Said plurality of processing nodes 

and Said at least one signal varying device is controlled to 

produce an optical Signal having Said desired signal char 

acteristics at Said control point. 24. An optical transmission System comprising: 

an optical transmitter for transmitting optical Signals, 

an optical receiver optically communicating with Said 

transmitter; 

a plurality of Signal varying devices each including a 

concentrated optical amplifier positioned to vary an 

optical signal passing from Said transmitter to Said 

receiver; and, 

at least one controller configured to control Said plurality of concentrated optical amplifiers in response to at least 

one detected characteristic of the optical Signal to vary 

the optical Signal to have the at least one desired Signal 

characteristic when the optical Signal reaches Said 

receiver. 

25. The optical transmission System of claim 24 including 

at least one intermediate processing node Selected from the 

Case 6:20-cv-00484-ADA Document 1-2 Filed 06/02/20 Page 13 of 14
US 6,236,487 B1 

11 

group consisting of add ports, drop ports, Switches, 

distributors, combiners, control points, and combinations 

thereof in optical communication with Said transmitter and 

Said receiver; and, 

Said at least one controller is further configured to control 

Said plurality of Signal varying devices to achieve Said 

at least one desired signal characteristic at Said at least 

one intermediate processing node. 

26. A method of controlling an optical transmission SyS 

tem comprising: 

positioning at least one signal varying device including a 

concentrated optical amplifier remote from an optical processing node to vary an optical Signal passing to the 

optical processing node, and, 

controlling the at least one concentrated optical amplifier 

to vary the optical Signal to have at least one desired 

15 

12 

Signal characteristic when the optical Signal reaches the 

optical processing node. 

27. The method of claim 26, further comprising: detecting characteristics of the optical Signal; and, 

comparing detected characteristics of the optical Signal to 

the at least one desired characteristic, and wherein Said 

controlling includes controlling the at least one signal varying device to vary the optical Signal until the 

detected characteristics correspond to the desired char 

acteristics when the optical Signal arrives at the pro cessing nodes. 

28. The method of claim 27, wherein said controlling includes Selecting the at least one desired signal character 

istic from the group consisting of Signal-to-noise ratio, 

Signal intensity, noise intensity, and combinations thereof. 

k k k k k 

Case 6:20-cv-00484-ADA Document 1-2 Filed 06/02/20 Page 14 of 14