Exhibit 4 

Case 6:20-cv-00484-ADA Document 1-4 Filed 06/02/20 Page 1 of 16
USOO6356383B1 

(12) United States Patent (10) Patent No.: US 6,356,383 B1 

Cornwell, Jr. et al. (45) Date of Patent: Mar. 12, 2002 

(54) OPTICAL TRANSMISSION SYSTEMS EP O853396 A2 7/1998 

INCLUDING OPTICAL AMPLIFERS JP O72O2306 A 8/1995 

APPARATUSES AND METHODS WO WO 98/42088 9/1998 

(75) Inventors: Donald M. Cornwell, Jr., Silver OTHER PUBLICATIONS 

Spring; John J. Veselka, Jr., Park, S.Y., et al., Feasibility Demonstration of 10 Gbit/s 

Clarksville; Stephen G. Grubb; Channel WDM Network Using Dynamic Gain-Controlled 

Thomas D. Stephens, both of EDFAS, Electronics Letters, Mar. 5, 1998, vol. 34, No. 5., 

Columbia; Ruxiang Jin, Ellicott City; Online No. 1998O346. 

Alistair J. Price, Columbia; Michael Dung, J.C., et al., Gain Flattening of Erbium Doped Fibre 

C. Antone, Ellicott City, all of MD Amplifier Using Fibre Bragg Gratings, Electronics Letters, 

(US) Mar. 19, 1998, vol. 34, No. 6. Online No. 19980446. 

Yu, A., et al., Analysis of Optical Gain and Noise Spectral (73) Assignee: Corvis Corporation, Columbia, MD Properties of Erbium-Doped Fiber Amplifier Cascade, Opti 

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

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

(*) Notice: Subject to any disclaimer, the term of this Masuda, H., et al., Ultra-Wideband Optical Amplification 

patent is extended or adjusted under 35 with a 3-dB Bandwidth of 67 nm Using a Partially Gain 

U.S.C. 154(b) by 0 days. Flattened Erbium-Doped Fiber Amplifier and Raman 

Amplification, Optical Amplifiers and their Application, 

(21) Appl. No.: 09/540,708 Aug. 3-5, 1994, 1997 OSA Technical Digest Series, V20, 

pp. MC3–1-4/4.0–3. (22) Filed: Mar. 31, 2000 Sugaya, Y., et al., Novel Configuration for Low-Noise and 

O O Wide-Dynamic-Range Er-Doped Fiber Amplifiers for 

Related U.S. Application Data WDM Systems, Optical Amplifiers and their Application 

(6) Psional application No. 60127.665, filed on Apr 2, 0, is 7,365,1650SXTERIDE SEVIS. 

pp. FC3–1–4/158-161. (51) Int. Cl. .................................................. H01S 3/00 

(52) U.S. Cl. ................................... 359/334; 359/341.33 (List continued on next page.) 

(58) Field of Search ................................. 359/334, 124, Primary Examiner Mark Hellner 

359/341.33: 385/24 (57) ABSTRACT 

(56) References Cited Optical Systems of the present invention include amplifiers 

U.S. PATENT DOCUMENTS configured to achieve maximum signal channel in a Span 

4,315,666 A 2/1982 Hicks, Jr. downstream of the transmitter and amplifier Site and tO 

4,342.499 A 8/1982 Hicks, Jr. decrease the interaction between the wavelengths at high 4.401.364 A 8/1983 Mochizuki Signal channel powers. In addition, the System can include 

2 - - -a- various types of optical fiber positioned in the network to 

(List continued on next page.) provide for increased signal channel powers and higher gain 

FOREIGN PATENT DOCUMENTS efficiencies in the System. 

EP O 734 105 A2 9/1996 20 Claims, 6 Drawing Sheets 

 

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US 6,356,383 B1 

Page 2 

U.S. PATENT DOCUMENTS 

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

4,699.452 A 10/1987 Mollenauer et al. 

4,728,170 A 3/1988 Robertson 

4.881,790 A 11/1989 Mollenauer 

5,039,199 A 8/1991 Mollenaur et al. 

5,050949 A 9/1991 DiGiovanni 

5,083,874. A 1/1992 Aida et al. 

5,095,519 A 3/1992 Dorsey 

5, 191586 A 3/1993 Huber 

5,191,628 A 3/1993 Byron 

5,228,105. A 7/1993 Glista 

5,283,686 A 2/1994 Huber 

5,406,411 A 4/1995 Button et al. 

5,500,756 A 3/1996 Tsushima et al. 

5.530,583 A 6/1996 Uno et al. 

5,541,766. A 7/1996 Mizrahi et al. 

5,557.442 A 9/1996 Huber 

5,579,143 A 11/1996 Huber 

5,633,974. A 5/1997 Chia 

5,636,301 A 6/1997 O'Sullivan et al. 

5,651,085. A 7/1997 Chia 

5,675.432 A 10/1997 Kosaka 

5,694,512 A 12/1997 Gonthier et al. 

5,696.615 A 12/1997 Alexander 

5,717,510 A 2/1998 Ishikawa et al. 

5,764,406 A 6/1998 Newhouse et al. 

5,812,710 A 9/1998 Sugaya 

5,815,299 A 9/1998 Bayart et al. 

5,861981. A 1/1999 Jabr 

5,880,866 A 3/1999 Stolen 

5,883,736 A 3/1999 Oshima et al. 

5,900,969 A 5/1999 Srivastava et al. 

5,903,371 A 5/1999 Arecco et al. 

5,920,423. A 7/1999 Grubb et al. 

5,963,361 A 10/1999 Taylor et al. 

5.999,548. A 12/1999 Mori et al. 

6,031,646 A 2/2000 Sniadower 

6,055,092 A 4/2000 Sugaya et al. 

6,057.959 A 5/2000 Taylor et al. 

6,081,366 A 6/2000 Kidorf et al. 

6,122.298 A 9/2000 Kerfoot, III et al. 

6,163,636 A 12/2000 Stentz et al. .................. 385/24 

6,181,464 B1 1/2001 Kidorf et al. ............... 359/334 

OTHER PUBLICATIONS 

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. 

Hansen, P.B., et al., LOSS Compensation in Dispersion Compensation Fiber Modules by Raman Amplification, 

OFC'98 Technical Digest pp. 20-1. 

Rottwitt, K., et al., Detailed Analysis of Raman Amplifiers 

for Long-Haul Transmission, OFC'98 Technical Digest pp. 

30-1. 

Chernikov, S.V., et al., 10 Gbit/s Error-Free Transmission of 

2-ps Pulses Over a 45-km Span Using Distributed Raman 

Amplification at 1300 nm, OFC'98 Technical Digest p. 31. 

Kawai, S. et al., Ultrawide 75 nm 3-dB Gain-Band Optical Amplifier Utilizing Erbium-Doped Fluoride Fiber and 

Raman Fiber, OFC'98 Technical Digest pp. 32-3. 

Dianov, E.M., et al., Highly Efficient 1.3 um Raman Ampli 

fier, OFC'98 Technical Digest pp. 33–4. 

Rottwitt, K., et al., A 92 nm Bandwidth Raman Amplifier, 

OFC 98, Post-Deadline Paper PD6–1–4. 

Srivastava, A. K., et al., 1 Tb/s Transmission of 100 WDM 

10 Gb/s Channels over 400km Of TrueWave Fiber, OFC 98, 

Post-Deadline Paper PD10-1-4. 

Masuda, H., et al., Ultra-Wideband Hybrid Amplifier Com 

prising Distributed Raman Amplifier and Erbium-Doped 

Fiber Amplifier, Electronics Letters, Jun. 25, 1998, vol. 34, 

No. 13, Online No. 1998.0935. 

Takano, K., et al., An Optical Pre-Amplifier with Automatic 

Gain Control Function, Proccedings of the 1995 IEICE 

General Conference, Mar. 27-30, 1995, Fukuoka, Fukuoka 

Institute of Technology b-1067, p. 513. 

Zou et al., Compensation of Raman Scattering and EDFA's 

Nonuniform Gain in Ultra-Long-Distance WDM Links, 

IEEE Photonics Technology Letters, vol. 8, No. 1, Jan. 1996, 

pp. 139-141. 

Stentz, A., et al., OSA Trends in Optics and Photonics, vol. 

5, Optical Amplifiers and Their Applications. From the 

Topical Meeting, pp. 350-368, Published: Washington, DC, 

USA, 1996. 

Wen, Senfar, et al., IEEE Phontonics Technology Letters, 

Feb. 1992, vol. 4, No. 2, New York, US, pp. 189-192, IEEE 

Log No.: 9105789. 

Aide, K., et al., Long-Span Repeaterless IM/DD Optical 

Transmission Experiment over 300 KM using Optical 

Amplifies, ICC 91, vol. 3, pp. 1228-1232, 1991, Published: 

New York, NY, USA. 

Grubb, S. G., Raman Amplifiers for Broadband Communi 

cations, OFC 98, OSATechnical Digest Series vol. 2, 1998, 

abstract. 

* cited by examiner 

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1 

OPTICAL TRANSMISSION SYSTEMS 

INCLUDING OPTICAL AMPLIFERS 

APPARATUSES AND METHODS 

CROSS-REFERENCE TO RELATED 

APPLICATIONS 

This application is a continuation-in-part (“CIP”) of com 

monly assigned U.S. Provisional Application No. 60/127, 

665 filed Apr. 2, 1999, which is incorporated herein by 

reference. 

STATEMENT REGARDING FEDERALLY 

SPONSORED RESEARCH OR DEVELOPMENT 

Not Applicable 

BACKGROUND OF THE INVENTION 

The present invention is directed generally to optical transmission Systems. More particularly, the invention 

relates to amplifying optical Signals in optical transmission 

Systems and controlling nonlinear interactions between Sig 

nal channels, as well as the amplifier Spacing in the optical 

Systems. 

Optical communication Systems transmit information by generating and Sending optical signals corresponding to the 

information through optical transmission media. Informa 

tion transported by the optical Systems can include audio, 

Video, data, or any other information format. The optical 

Systems can be used in long distance and local telephone, 

cable television, LAN, WAN, and MAN systems, as well as 

other communication Systems. 

Information can be transmitted optically using a broad 

range of frequencies/wavelengths at high data rates and 

relatively low cost, which are desirable attributes for high capacity, transmission Systems. Also, multiple optical wave 

lengths that are combined using wavelength division mul 

tiplexing (“WDM”) techniques into one optical signal that 

can be transmitted through one optical fiber, which further 

increases the data carrying capacity of optical Systems. AS 

Such, optical fiber transmission Systems have emerged as a 

cost-effective alternative to electrical Systems for providing high capacity, communication Systems. 

However, optical transmission Systems are not free from 

attenuation and various forms of degradation that limit the 

performance of the Systems. For example, optical fiber is not 

a perfect transmitter of electromagnetic radiation in the 

optical Spectrum. Thus, the intensity of an optical signal will 

attenuate as it travels through the fiber, due to Scattering 

from fiber material imperfections and other degradation 

mechanisms. In addition, optical noise, from Signal 

attenuation, chromatic dispersion, nonlinear interactions, 

and other Sources, will accumulate and propagate in the fiber 

along with the Signal further degrading the quality of the 

Signal. Furthermore, optical Systems generally are not oper 

ated in the identical manner, which requires that interfaces 

be provided to interconnect different optical Systems. 

It is therefore necessary to regenerate optical signals 

being transmitted through the optical System to overcome 

the three primary limitations on optical transport, namely: 1) 

optical signal attenuation, 2) optical noise accumulation, and 

3) optical System interconnectivity. The regeneration of 

optical Signals can be performed either optically or electri 

cally. 

The development of optical amplifiers greatly reduced the 

cost of optical systems, and WDM systems in particular, by essentially eliminating the need to electrically regenerate 

15 

25 

35 

40 

45 

50 

55 

60 

65 

2 

Signal merely to overcome signal attenuation. While the 

development of optical amplifierS has greatly reduced the 

equipment costs associated with amplifiers in optical 

Systems, there remain Substantial operational costs. Real 

estate and building acquisition and maintenance costs asso 

ciated with optical amplifiers can be a sizable portion of the 

optical System operational costs, which Suggests maximiz 

ing the distance between optical amplifiers in an optical 

System. However, maximizing the distance between ampli fiers can reduce the maximum distance that optical signals 

can be transmitted before having to be regenerated to 

overcome accumulated optical noise. 

Additional cost Savings in the System can be achieved by increasing the transmission capacity of existing optical fiber 

compared to installing additional fiber in the System. 

Therefore, it is desirable to increase the information bit 

transmission rate in the fiber and the number of wavelengths 

used to carry information to increase the information car 

rying capacity of the fiber. However, increasing the bit rate 

of each channel generally requires the channel spacing to be 

increased. Furthermore, increasing the bit rate and/or the 

number of channels often requires that the transmission 

distance to be decreased, which increases the System cost. 

The ability to increase the capacity of the System is 

limited by the optical Signal degradations that occur in the 

System. Optical Signal degradation occurs via numerous 

mechanisms during transmission in optical fiber. The pri 

mary mechanisms are chromatic dispersion and various 

nonlinear interactions, Such as four wave mixing. The deg radation caused by these mechanisms increases proportion 

ally as either the bit transmission rate or the number of the 

channels within a wavelength range is increased. 

Generally, information carrying Signal wavelengths, or 

Signal channels, are launched into the optical fiber at a 

maximum signal channel power. The Signal channel power 

decreases as it travels through the fiber until it reaches a 

minimum signal power, at which time it must be amplified 

to prevent degradation of the Signal. Thus, for a given 

channel Spacing, the maximum signal launch power, mini 

mum Signal power, and the attenuation of the fiber establish 

the maximum amplifier spacing in the System. 

The maximum Signal launch power is limited to powers 

below which nonlinear interactions do not cause unaccept able Signal degradation. The Spacing of the channels as well 

as other factors, Such as the Signal channel polarization, 

affect the maximum signal launch power. Safety concerns 

may further limit the total power that can be launched into 

the fiber. The minimum Signal power is determined based on 

the minimum acceptable Signal to noise ratio required to 

reliably transmit information through the System. 

The development of optical fiber technology has resulted 

in fiber having very low attenuation levels (0.25 dB/km) 

compared to older fiber designs (>0.30 dB/km) in the 

wavelength range around 1550 nm. The lower loss fiber 

allows amplifiers to be separated by greater distances for 

Signal transmitted at a given power level and/or lower power Signals to be transmitted over greater amplifier spacings. 

The different optical fibers used in systems introduce 

different amounts of chromatic dispersion as a function of 

optical wavelength. Chromatic dispersion in Standard Single 

mode, Silica-based, optical transmission fiber, Such as SMF 

28, generally varies as a function of wavelength. Average 

dispersion values in Standard Silica-based fiber are approxi 

mately -17 pS/km/nm in the 1550 nm low loss optical 

transmission window, whereas the wavelength at which Zero 

dispersion occurs (the “Zero dispersion wavelength') is 

typically around 1300 nm. 

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US 6,356,383 B1 

3 

In optical transmission Systems employing Standard trans 

mission fiber, chromatic dispersion can Severely degrade the 

optical Signal quality and thereby limit the maximum trans 

mission distance. Numerous methods have been developed 

to effectively counteract dispersion in the standard fiber. For 

example, dispersion compensating (“DC) fibers have been 

developed that have high dispersion rates, on the order of 

10 pm/km/nm, that are opposite in sign from transmission 

fiber. The DC fibers can be inserted into the transmission 

fiber at various locations to maintain the absolute dispersion in the System to within a desired range. 

New transmission fibers have been designed to minimize 

the chromatic dispersion in the 1550 nm window. The new 

fiber types, generally referred to as low dispersion (“LD') 

fiber, have much lower dispersion than standard fiber in the 

range +5 pm/km/nm for non-zero dispersion shifted (“NZ 

DS”) fiber, such as Truewave, LEAF, and LS, and even 

lower for Zero dispersion shifted (“DS”) fibers. The LD 

fiberS facilitate the optical Signal transmission over Substan 

tially longer distances before Substantial signal degradation 

occurs as a result of chromatic dispersion. In addition, DC 

fiberS also have been developed to compensate for disper 

Sion in LD fibers. 

However, a problem with LD fiber arises from the inter 

relation of chromatic dispersion and nonlinear interactions. 

High rates of dispersion tend to decrease nonlinear interac 

tions between closely spaced wavelengths, because the 

relative velocity of the channels, or “walk-off, decreases 

the interaction time between the channels. In LD fiber there 

is much less walk-off between adjacent closely spaced 

channels resulting in longer interaction time between 

channels, which increases the nonlinear interaction and 

resulting degradation of the signal channels. 

Nonlinear interactions in LD fiber can be decreased in the 

System by increasing the Spacing between adjacent channels 

or decreasing the Signal channel power. However, increasing 

the channel spacing generally reduces the total number of 

channels in the System. Likewise, decreasing the Signal channel power generally requires a corresponding decrease 

in the amplifier Spacing and the transmission distance 

between electrical regeneration sites. 

The limitations imposed by nonlinear interactions become 

increasing problematic for LD fibers at relatively low trans 

mission capacities and Short distances. The current methods 

of reducing the nonlinear interactions in LD fiber greatly decreases the optical System capacity and performance com 

pared to equivalent Systems employing Standard fiber. 

The capacity limitation resulting from non-linear interac 

tions is not limited to LD fiber, but also plagues Standard 

fiber, transmission Systems. This limitation will require increased capital and operating expenditures to expand optical communication System capacity. Accordingly, there 

is an extremely pressing need to overcome the fiber limita 

tions in current optical Systems to allow continued growth in 

communication Systems and communications based tech 

nology. 

BRIEF SUMMARY OF THE INVENTION 

The present invention addresses the need for optical transmission Systems, apparatuses, and methods having increased flexibility and reliability. Optical systems of the 

present invention include amplifiers and methods configured 

to provide increased control over optical signals being 

transmitted in the Systems. 

In various embodiments, the optical System and amplifiers 

are configured to achieve maximum signal channel power in 

15 

25 

35 

40 

45 

50 

55 

60 

65 

4 

a span downstream of the transmitter and amplifier Sites and 

to decrease the interaction between the wavelengths at high Signal channel powers. In addition, the System can include 

various types of optical fiber positioned in the network to 

provide for increased signal channel powers and higher gain 

efficiencies in the System. 

In various embodiments, fiber Bragg gratings and other 

devices are used to control the optical noise in the optical 

energy Supply by optical Sources, Such as Semiconductor 

laser diodes, to provide for lower noise pump Sources. The 

lower noise pump Sources can be used to Supply optical 

energy for amplification to various optical amplifiers, Such 

as Raman and erbium/rare earth doped fiber amplifiers and 

to control the noise figure of the amplifier. 

In addition, the System can include composite gain flat 

tening filters that are used to modify the gain profile pro 

duced over a plurality of optical amplifiers. The composite gain flattening filter provides flexibility in the operation of 

the individual amplifiers, which can be dynamically con 

trolled to accommodate changes in the System and to the 

optimize the performance of the composite filter. 

Accordingly, the present invention addresses the afore 

mentioned concerns by providing optical Systems 

apparatuses, and methods having increased performance and 

reliability. These advantages and others will become appar 

ent 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 drawings for the purpose of illustrating 

present embodiments only and not for purposes of limiting 

the same, wherein like members bear like reference numer 

als and: 

FIGS. 1-2 show optical communication systems of the 

present invention; 

FIGS. 3(a&b) show signal power versus distance curves 

in the present invention; 

FIGS. 4-5 show optical amplifier embodiments of the 

present invention; and, 

FIGS. 6-7 show Raman gain profiles. 

DESCRIPTION OF THE INVENTION 

FIG. 1 shows an embodiment of an optical system 10, in 

which an optical energy pump Source 12 is deployed 

between two optical nodes 14. The optical system 10 can be 

controlled by a network management System 16 and pump 

Sources 12 configured to operate in one or more Serially 

connected point to point links (FIG. 1) or in multi 

dimensional networks (FIG. 2). The network management 

System 16 can communicate with the various nodes and 

elements in the optical Systems 10 via wide area, data 

communication networks external to the System 10 and/or 

Supervisory optical channels within the system 10. 

The optical nodes 14 can be interconnected optically via 

guided and unguided transmission media, which is typically optical fiber waveguide 18. Optical amplifiers 20 typically 

will be provided along optical links 15 of sufficient length 

where amplification will be required to overcome optical 

Signal attenuation or proximate other components to over 

come component losses in the System 10. 

One or more transmitters 22 can be included in the nodes 

14 and configured to transmit information via the optical Signals in one or more information carrying Signal 

wavelengths, or Signal channels, 2. Similarly, one or more 

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US 6,356,383 B1 

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optical receiverS 24 can be provided in various nodes 14, 

each configured to receive one or more signal channels 2. 

from the fiber 18. 

The optical processing nodes 14 may also include other 

optical components, Such as one or more add/drop devices 

26 and optical and electrical Switches/routerS/cross-connects 

28 interconnecting the transmitters 22 and receivers 24. For 

example, broadcast and/or wavelength reusable, add/drop 

devices, and optical and electrical/digital croSS connect 

Switches and routers can be configured via the network 

management System 22 in Various topologies, i.e., rings, 

mesh, etc. to provide a desired network connectivity. 

The transmitters 22 used in the system 10 will generally 

include a narrow bandwidth laser optical Source that pro vides an optical carrier. The transmitterS 22 also can include 

other coherent narrow or broadband Sources, Such as Sliced 

Spectrum Sources, as well as Suitable incoherent optical 

Sources, Such light emitting diodes and fiber lasers, as 

appropriate. Information can be imparted to the optical carrier either by directly modulating the optical Source or by 

externally modulating the optical carrier emitted by the 

Source. Alternatively, the information can be imparted to an 

electrical carrier that can be upconverted using the optical carrier onto an optical wavelength to produce the optical Signal. Similarly, the optical receiver 24 used in the present 

invention can include various detection techniques, Such 

coherent detection, optical filtering and direct detection, and 

combinations thereof. Employing tunable transmitters 22 

and receiverS 24 in the optical nodes 14 in a network, Such 

as in FIG. 2, can provide additional versatility in the System 

10. 

The transmitterS 22 and receiverS 24 can be also con 

nected to interfacial devices 30, Such as electrical and optical 

cross-connect Switches, IP routers, etc., to provide interface 

flexibility within, and at the periphery of, the optical System 

10. The interfacial devices 30 can be configured to receive, 

convert, and provide information in one or more various 

protocols, encoding Schemes, and bit rates to the transmitters 

22, and perform the converse function for the receivers 24. 

The interfacial devices 30 also can be used to provide protection Switching in various nodes 14 depending upon the 

configuration. 

Generally Speaking, N transmitters 22 can be used to 

transmit M different signal wavelengths to J different receiv 

erS 24. In various embodiments, one or more of the trans 

mitters 22 and/or receiverS 24 can be wavelength tunable to 

provide wavelength allocation flexibility in the optical SyS 

tem 10. In addition, the system 10 can also be configured to 

carry uni- and bi-directional traffic. 

Optical combiners 32 can be used to combine the multiple Signal channels of into WDM optical Signals, as well as 

multiple pump wavelengths for transmission in the fiber 

18. Likewise, optical distributors 34 can be provided to 

distribute the optical signal to the receivers 24, and optical signal and pump wavelengths 2 to multiple paths. The 

optical combiners 32 and distributors 34 can include various 

multi-port devices, Such as wavelength Selective and non 

Selective (“passive’), fiber and free space devices, as well as 

polarization Sensitive devices. The multi-port devices can 

various devices, Such as circulators, passive, WDM, and 

polarization couplers/splitters, dichroic devices, prisms, dif 

fraction gratings, arrayed Waveguides, etc. 

The multi-port devices can be used alone or in various 

combinations along with various tunable or fixed wave 

length filters in the optical combiners 32 and distributors 34. 

The filters can include various transmissive or reflective, 

15 

25 

35 

40 

45 

50 

55 

60 

65 

6 

narrow or broadband filters, Such as Bragg gratings, Mach 

Zehnder, Fabry-Perot and dichroic filters, etc. Furthermore, 

the combiners 32 and distributors 34 can include one or 

more Stages incorporating various multi-port device and 

filter combinations to multiplex, consolidate, demultiplex, 

multicast, and/or broadcast Signal channels 2 and pump wavelengths) in the optical systems 10. 

In various embodiments, the optical systems 10 include 

transmitters 22 that are configured to launch the optical 

Signals below the nonlinear limits for the maximum signal launch power. Likewise, optical amplifiers 20 are configured 

Such that the optical signals are not amplified to the maxi 

mum signal power at discrete amplifier Sites. Instead, the 

optical signals are amplified during transmission in the fiber 

18 Such that the maximum Signal channel power in the link 

15 is achieved downstream from nodes and amplifier sites 

using distributed amplification. 

Amplification of the optical Signals to maximum power 

during transmission generally is performed using Stimulated 

Raman Scattering of optical energy co-propagating with the 

signal channels. The optical fiber 18 or other transmission 

media generally will be a Silica-based waveguide or other 

material compositions that produces Raman Scattering of 

optical energy in the material resulting in Raman amplifi 

cation of the signal channels ). However, various embodi 

ments can include doped transmission fiber or fiber designed for use with other amplification techniques to provide for 

distributed amplification in the transmission fiber. 

By moving the location of the maximum channel power 

downstream of the transmitters 22 and the amplifiers 20, the 

physical distance between the optical amplifiers 20 actually 

can be increased, while the effective amplifier spacing is 

decreased. FIGS. 3(a&b) depicts optical signal power varia 

tions during transmission through the fiber 18 as a function 

of distance. The curve in FIG.3(a) depicts the variations in 

the Signal channel powers that are amplified by co-propagating Raman amplification after being launched 

into the fiber 18 and at discrete amplifier sites 1 and 2. The 

distance designated as T in FIG. 3(a) shows the maximum 

amplifier Spacing achievable by maximizing the Signal 

launch power. This can be contrasted to the amplifier Spac ing of the present invention as shown by the spacing 

between the launch point 0 and amplifier sites 1 and 2. 

FIG.3(b) is similar to FIG.3(a), except additional ampli fication is provided via counter-pumped distributed ampli 

fication and/or concentrated amplification at the amplifier Site. As shown in FIG. 3(b), both co- and counter-pumping 

the fiber 18 can further increase the distance between the 

launch point and the first amplifier and the amplifier before 

the next node 14. 

Curve 1 in FIG. 3(b) depicts the signal power assuming distributed Raman gain resulting from both co-pumping and 

counter-pumping the transmission fiber 18 using an ampli 

fier configuration similar to that shown in FIG. 4. The skilled 

artisan will appreciate that each pump Source 12 shown in 

the drawings can be configured to include various numbers 

of pumps and combinations of pump wavelengths. 

Similarly, curve 2 in FIG. 3(b) shows the effect of 

including a concentrated, or lumped, amplifier Stage 36 at 

each amplifier site, such as shown in FIG. 5, which includes 

two concentrated amplifiers 36 for exemplary purposes. The 

optical amplifier 20 can include one or more Serial and/or 

parallel amplifier Stages, which may include combinations 

of one or more, distributed and concentrated amplifier Stages. The optical amplifiers 12 may also include remotely 

pumped doped fiber or Raman amplifying fiberS 36 having 

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US 6,356,383 B1 

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different amplification and transmission characteristics, e.g., dispersion, etc., than the transmission fiber 14. The remotely 

pumped amplifying fiber 36 can be pumped with exceSS 

pump power Supplied to provide Raman gain in the trans 

mission fiber 14 or via a separate fiber. In addition, the 

optical amplifiers 20 can include lumped fiber amplifier 

Stages operated in deep Saturation using pump power being 

Supplied to other stages. 

Other optical Signal varying devices, Such attenuators, 

filters, isolators, and equalizers can be deployed before, 

between, and after various Stages of the amplifier 12 to 

decrease the effective loSS associated with the devices. 

Similarly, Signal processing devices, Such as add/drop 

devices, routers, etc. can be included proximate the various amplifier Stages. 

Contrary to traditional optical Systems, if the amplifier 

spacing is to be increased in various embodiments of the 

present invention, the Signal launch power will be decreased. 

Likewise, the Signal power emerging from the optical ampli 

fier Sites also will be decreased. The Signal launch power is 

lowered to extend the distance from the transmitter 22 and 

amplifier 20 at which the signal channels will achieve 

maximum power. The cumulative slope of the Raman gain 

and fiber attenuation versus distance will determine the 

location at which the maximum signal channel power will be 

achieved downstream of the nodes 14 and amplifiers 20. 

The nonlinear interaction limit on Signal power and the 

minimum power level required to provide a signal to noise 

ratio to allow detection with an acceptable bit error rate 

define a transmission window for fiber. Employing various 

coding techniques, Such as forward error correction “FEC', 

can expand the transmission window by enabling a finite 

number of transmission errors to be corrected following 

transmission. The number of transmission errors that can be 

corrected depends upon the particular coding Schemes used. 

Therefore, the Systems 10 can tolerate increased signal degradation resulting higher levels of nonlinear interactions 

and lower Signal to noise ratioS. 

Pump Sources 12 generally include one or more optical 

Sources, or pumps, configured to introduce optical energy, or 

pump power, in one or more pump wavelength 2 bands 

into the fiber 18 to produce Raman gain in the optical Signal 

wavelengths, or channels, 2. The optical Sources are typi 

cally Semiconductor laser diodes, the emission bandwidth 

and power of which is tailored to the specific system. Other 

narrow or broadband, coherent and incoherent Sources, Such 

as optical noise Sources, fiber lasers, light emitting diodes, 

etc. that can provide Sufficient optical energy also can be 

used in the system 10. 

As shown in FIG. 6, the introduction of pump power in 

one wavelength/frequency band can produce Raman ampli 

fication of optical Signal channels in another wavelength/ 

frequency band. In fact, the pump wavelengths) can be 

Selected and the pump Source 12 operated to allow for 

dynamic control over the amplification, or gain, profile of 

the Signal channels being amplified. Exemplary optical 

amplifiers 20 providing for dynamic control are described in 

U.S. patent application Ser. Nos. 09/119,556 and 09/253, 

819, which are incorporated herein by reference. 

AS described in the incorporated references, the pump 

Source 12 within the amplifiers 20 can be configured to 

operate in concert with other optical amplifiers 20 in the 

System 10. For example, the optical amplifiers can include 

pump Sources 12 to provide for distributed and/or concen 

trated amplification using counter-pumping and/or 

co-pumping. 

15 

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65 

8 

In various embodiments, the fiber spans extending between the nodes 14 and amplifier 20 are co-pumped using 

a first set of one or more pump wavelengths), and are 

counter-pumped using a Second Set of one or more pump 

wavelengths 22. The first and second sets of pump wave 

lengths 21, and 22, are selected to minimize the gain variation acroSS the Signal wavelength range as described in 

the incorporated references. 

The gain profile of the distributed amplification can be 

controlled in various embodiments by varying the pump 

power delivered in each of the pump wavelengths counter 

pumping of a Span of fiber between amplifier locations. 

While the gain profile can be controlled, the noise figure of 

the amplifier 20 will tend to be higher for signal channels at 

Shorter wavelengths that are amplified correspondingly by 

the shorter pump wavelengths. AS Such, the Signal to noise 

ratio of the Signal channels tends to degrade more rapidly at 

the shorter wavelength signal channels, thereby limiting the 

overall transmission distance of the Signal channels. 

In one aspect of the present invention, it was found that 

Selectively co-pumping the span in addition to counter 

pumping the fiber span can be used to vary the noise figure of the amplifier 20. The co-pumping thereby provides a 

means to control the noise figure profile over the Signal wavelength range, in addition to the gain profile. In these 

embodiments, co-pumping with optical energy in the shorter 

pump wavelengths can be used to lower the noise figure for 

Shorter wavelength channels relative to longer wavelength 

Signal channels, while tending to lower the effective noise 

figure of amplifier for the entire Signal channel range. 

In exemplary embodiments, the counter-pumped, Second 

set of pump wavelengths), can be equally or unequally distributed across an entire pump wavelength range. 

Whereas, the first set of pump wavelengths may not 

cover the entire pump wavelength range, but may be limited 

to one or more co-pump wavelengths in the shorter wave 

length end of the range to control the noise figure. The 

co-pumped wavelengths , also can be used to provide Some level of Raman amplification to the shorter Signal channel wavelengths and to the longer pump wavelengths 

used to counter-pump the Signal channels. For example, 

pump wavelengths ranging from approximately 1410–1490 

nm can be used to counter-pump transmission fiber 18 to 

provide distributed Raman amplification of Signal channels 

) in the 1520–1570 nm wavelength range. One or more 

pump wavelengths in the 1410–1430 range can be used to 

co-pump the transmission fiber to control the amplifier noise 

figure for the Signal channels. Similarly, other Signal channel 

ranges, such as 1520–1630 nm, 1300-1310, etc. can be used 

to transmit Signals depending upon the attenuation of the 

particular fiber 18 in the system 10. It will be appreciated 

that more than one wavelength ranges can be used to 

transmit signal channels, each of which can be amplified using Raman amplification Supplied with pump power in a 

corresponding wavelength range. 

The selection of pump wavelengths used in the system 10 

will depend upon the Signal channel wavelengths and the 

type of fiber being used in the system 10 and the various 

nonlinear interactions between the wavelengths. For 

example, Single frequency pumps can used to control non 

linear interactions between the pump and Signal wavelengths 

and the location and intensity of mixing products in the 

System 10. In the present invention, low speed dithering 

below the Signal bit rate, e.g., <1 MHz, of the pump 

frequency can be used to minimize Stimulated Brillouin 

scattering (“SBS”) interactions and avoid non-linear 

interactions, Such as four wave mixing. High Speed dithering 

Case 6:20-cv-00484-ADA Document 1-4 Filed 06/02/20 Page 13 of 16
US 6,356,383 B1 

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Significantly above the channel bit rate, e.g., 5x, can also be 

employed, if it is only necessary to minimize SBS as in the 

prior art. 

While controlling the pump power supplied by the various 

pump Sources 12 provides increased flexibility in controlling 

the gain profile of the amplifier 20, the discrete nature of the 

Raman gain associated with each pump wavelength can 

introduce Some variations into the gain profile. The gain variations can accumulate, when amplifiers 20 including discrete pump wavelengths) are cascaded in the system 10. 

In the present invention, a composite gain flattening filter 

38 in combination with a plurality of Raman amplifiers to 

collectively equalize gain variations from a desired gain 

profile, as shown in FIGS. 7a-7b. The composite Raman 

filter can be matched to and configured to control the gain profile based on the composite pump wavelengths) of a 

plurality of Raman amplifiers. Unlike gain flattening filters 

of the prior art, the present invention does not attempt to 

perform gain filtering at each amplifier. Instead, gain flat 

tening filters 38 of the present invention are designed based 

on a composite gain variation profile from a plurality of 

optical amplifiers 20, thereby reducing the extent and pre 

cision of the filtering required to control the gain profile. In 

addition, the composite gain flatten filters 38 allow for the 

gain in the individual amplifiers 20 to be varied without 

affecting the performance of the filter 20, because the 

composite gain of the amplifiers 20 is being filtered. AS Such, 

the performance of the filters 38 in present invention does 

not require each amplifier 20 to be operated in a fixed mode 

to ensure proper control of the gain profile, as in the prior art. 

In addition, the composite gain filtering does not require 

the precision of individual amplifier filtering, because there 

are fewer devices used in the System which reduces the 

accumulation of errors. This provides additional flexibility in the design of the filters 38. In fact, the gain profile of the 

amplifiers 20 being filtered can be varied to accommodate 

variations in the gain flattening profile of the filter 38. 

Periodic gain flattening also allows the amplifier 20 to be 

operated dynamically to adjust for changes in the System 

performance without being limited to maintaining a specific 

gain shape at each amplifier 20. For example, if a laser diode 

fails in one of the amplifiers, it may be necessary to vary the 

gain profiles in the other amplifiers to compensate for the 

failed amplifier. Thus, each of the amplifiers in an amplifier 

chain being gain flattened by the filter 38 can be operated to 

provide a different gain profile than during normal operation, 

but the composite gain profile at the filter 38 could be 

maintained. AS Such, it is possible to compensate for System 

changes and maintain System performance through the use 

of a composite Raman gain flattening filter 38. 

A limitation of co-pumped Raman amplification is that 

when the Signal channels are launched near maximum 

power, the pump wavelengths and the Signal wavelengths 

can cause interference with each other, which is referred to 

as croSStalk interference. In Saturated amplifiers, the Signal channels can cause a pattern dependent depletion of the 

optical energy in the pump wavelengths, which can then be 

transferred to other signals. Crosstalk occurs in co-pumping 

Scenarios to a greater extent because the walk-off between 

pump wavelengths and Signal channels is limited to the 

dispersion rate in the fiber. Whereas, in counter-pumped 

Raman amplifiers, pump depletion generally is averaged, 

because of the rate at which the pump wavelengths counter 

propagate relative to the Signal channels. 

However, if the Signal channel powers are reduced 

Sufficiently, the co-pumped Raman amplifier can transition 

15 

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60 

65 

10 

to unsaturated regime where croSStalk is Substantially reduced. In this regime, co-pumped Raman amplifiers can be 

used to provide additional gain in the fiber span. The walkoff 

between Signal channels and the pump wavelengths also is 

affected by the dispersion difference between standard and 

LD fibers. The dispersion profile in LD fibers are controlled 

by waveguide design and not material dispersion as in 

Standard fiber. Thus, the dispersion difference between pump and Signals can be greater in Some LD fibers than in Standard 

fiber. 

In co-pumped Raman amplifiers, intensity noise in the 

pump Sources 12 can be transferred from the pump wave 

lengths onto the Signal channels more readily than when 

counter-pumped. Therefore, it generally is desirable to use 

pump Sources 12 that have low noise characteristics, Such as 

Single frequency diodes. Also, the pump Sources 12 can 

generally be constructed using fiber Bragg gratings in polar 

ization maintaining ("PM") fiber pigtails on diode lasers as 

discussed in the incorporated applications to control the 

emission wavelength range. 

In one aspect of the present invention, the positioning of 

the Bragg grating relative to the optical Source, e.g. laser 

diode, can be used to control the noise Spectra of the emitted 

optical energy. It is generally desirable to position the Bragg 

grating in the PM pigtail, Such that relative intensity noise 

generated by relaxation oscillations of the external cavity are 

at Sufficiently high frequencies that the noise will not be 

imprinted on the Signal channels. For example, positioning 

the Bragg grating or other external cavity device close to the 

output facet of the cavity can reduce the noise. In addition, 

the output facet of the laser cavity can be provided with an 

anti-reflective (“AR”) coating and/or angled to Suppress relative intensity noise due to competition between external 

cavity modes and the internal lasing modes of the laser. 

Generally, it is desirable to minimize the relative intensity 

noise associated with the pumps, for example, less than 

-130 dB/Hz, to minimize the imprinting of noise onto the 

Signal channels. 

In addition, fiber Bragg gratings or other bandwidth 

controlling devices can be used to control the emission 

wavelength range of the optical Sources, So the pump power 

can be efficiently combined through the pass band of WDM 

couplers and other WDM pass band devices. In the present invention, the pump Source 12 in the amplifier 20 includes 

WDM couplers having pass bands outside the pump wave 

length range required to provide Raman amplification to the 

Signal channels being used in the System 10. For example, 

fused tapered WDM couplers can be cascaded to span the 

desired pump wavelength range. Fiber Bragg gratings can be 

used to control the emission Spectra of the optical Sources to 

be within the pass bands of the couplers. These embodi 

ments can provide for a Scalable, non-Service interrupting expansion of the Signal channel capacity of the System 10. 

Pump wavelengths can be added to the pump Source 12 in 

the unused pass bands to expand the amplification range of 

the amplifier 20 and the available signal channel wavelength 

range during operation. 

Additionally, the Raman gain achieved in the Span is 

dependent upon the relative polarization of the Signal chan 

nels and the pump wavelengths. Polarization dependent gain 

can by reduced or eliminated by depolarizing the pump light. Linearly polarized output from these pumps can be coupled 

to polarization maintaining ("PM") fiber with its electric 

field vector polarized at 45 degrees to a polarization axis of 

the PM fiber to depolarize the output. Some higher power applications require multiple pumps to be multiplexed 

together, such as embodiments shown in FIG. 5. This can be 

Case 6:20-cv-00484-ADA Document 1-4 Filed 06/02/20 Page 14 of 16
US 6,356,383 B1 

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done using a polarization beam splitter/combiner (“PBC) 

24 to combine the pump wavelengths. PM fiber can be 

placed after the polarization combiner 24 to depolarize the 

light from both pumps. When the same pump wavelengths 

are combined using a PBC the combined power is effectively depolarized. However, in the absence of a depolarizer fol 

lowing the PBC, the failure of one of the two optical sources 

will result in a linearly polarized output from the PBC. 

The launched signal channel power and relative maxi 

mum signal channel powers at the transmitters 22 and 

amplifiers 20 can be tailored to accommodate variations in 

the nonlinear interaction limits acroSS the wavelength range. 

For example, in LD fibers, the dispersion profile and non 

linear interaction profile Strongly varies acroSS the Signal 

channel band. Therefore, the Signal channels can be 

launched having varying channel powers, which can be 

compensated by varying the Raman amplification of the 

channels accordingly. The net gain acroSS one complete Span 

between amplifiers can be made to be flat, but the nonlinear 

penalties can be minimized, by varying the relative signal 

channel powerS along the Span. 

AS discussed in the incorporated applications, additional 

amplification may be possible by co-pumping the fiber Span 

with pump wavelengths in the 1320-1410 nm range to 

amplify the counter-pump wavelengths in the 1410–1490 

nm range. AS also discussed, a doped Section of fiber, i.e., erbium, can be spliced into the Span at an appropriate 

location, which will be pumped by remnant pump energy 

and provide additional amplification. However, the inclusion 

of a doped fiber could limit the Signal channel wavelength 

range. 

The maximum signal channel launch power in LD fibers 

is Substantially lower than in Standard fiber. AS Such, it is 

necessary to achieve increased levels of Raman gain to 

achieve LD fiber System performance that is comparable to 

the performance of Standard fiber Systems. An advantage of 

LD fiberS is that the Raman croSS Section is generally Smaller 

than Standard fiber; therefore, higher Raman gains are 

achievable for the same pump power in LD fibers. The 

improved Raman gain performance tends to offset to Some 

extent the lower launch powers. Also, because the LD fiber 

was designed to have very low dispersion, it can reduce the 

number of dispersion compensating components and fibers 

required in the System. 

It may be desirable to combine fiber types along a Span 

between nodes and/or amplifiers to obtain the benefits 

asSociated with each fiber type. For example, Standard fiber 

or higher dispersion fiber could be deployed as the trans 

mission fiber 18 in regions of the system in which the signal 

channel power is high. Such regions include the transmis 

sion fiber 18 following transmitters 22 and amplifiers 20 in 

the system 10. The use of high dispersion fiber in high power 

regions allows for higher maximum signal channel powers. 

Analogously, LD fiber would be particularly useful in 

regions where the Signal channel power is low. For example, 

LD fiber can be placed before amplifiers and receivers in the 

System, where the Signal power is low. The inclusion of LD 

fiber regions would Substantially decrease the Overall dis 

persion in the System, which could Substantially reduce or 

eliminate the need for DC components and fibers. 

Additionally, the higher Raman gain achievable in LD fiber 

would enable more efficient pump utilization and distributed 

amplifier performance. 

In application, a first Section extending from the trans 

mitters 22 and output of the amplifiers 20 could be a larger 

core fiber, Such as SMF-28-like standard transmission fiber, 

15 

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60 

65 

12 

that allows for higher signal powers than in smaller LD fiber. 

Second section of Smaller core fibers, Such as the LD fiber, 

can be used in lower Signal power regions, Such as before 

receivers 24 and amplifiers 20, where the smaller core fiber 

can provide increased Raman gain efficiencies. Other fibers can be interleaved between the first and second fiber sections 

as may be appropriate to achieve various objectives in the 

Systems. 

The benefits associated with other fiber types could also 

be leveraged by appropriately positioning of fiber in the 

transmission path. Hybrid fiber types could be most cost 

effectively deployed at the time a new fiber path is installed, 

particularly in festooned and underSea Systems. In existing 

Systems, retrofitting one or more different fibers into an 

existing fiber plant may not be a cost effective proposition. 

However, in fiber paths that contain multiple fiber types, it 

may be possible to interleave the existing fibers, for example 

at junction boxes, to produce a hybrid fiber having increased 

performance. 

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. A method of amplifying optical Signals comprising: 

transmitting optical Signals in a transmission media con 

figured to transmit and provide Raman amplification of 

the optical Signals, 

counter-propagating optical energy in the transmission 

media in a first pump wavelength range to produce 

Raman amplification of the optical signals, wherein the 

Raman amplification has a corresponding noise figure profile over an optical Signal wavelength range, and, 

co-propagating optical energy with the optical signals in 

a Second pump wavelength range to vary the noise 

figure profile of the Raman amplification produced by 

Said counter-propagating optical energy Over at least a 

portion of the optical signal wavelength range; 

Wherein Said co-propagating includes co-propagating optical energy in the Second pump wavelength range 

that overlaps with shorter wavelengths in the first 

wavelength range. 

2. The method of claim 1, wherein: 

Said transmitting includes transmitting optical Signals in a 

signal wavelength range from 1530-1570 nm, 

Said counter-propagating includes counter-propagating 

optical energy in the first pump wavelength range from 

1410 to 1480 nm, and, 

Said co-propagating includes co-propagating optical 

energy in the Second pump wavelength range from 

1410 to 1430 nm. 

3. The method of claim 1, further comprising: 

imparting information onto a plurality of Signal channels, 

determining a nonlinear interaction limit for the Signal 

channels in the transmission media; 

controlling the Signal channel launch power to produce a 

level of nonlinear interaction below the nonlinear inter 

action limit when the Signal channels are combined into 

the optical Signals as a WDM optical signal; 

combining the Signal channels into a WDM optical Signal; 

Said transmitting including launching the WDM optical 

Signal into the transmission media; and, 

Said co-propagating including co-propagating optical 

energy with the Signal channels in the transmission 

Case 6:20-cv-00484-ADA Document 1-4 Filed 06/02/20 Page 15 of 16
US 6,356,383 B1 

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media to amplify the Signal channels and achieve a 

maximum signal channel power below the nonlinear 

interaction limit at a point in the transmission media 

downstream from where the WDM optical signal was 

launched. 

4. The method of claim 3, wherein: 

Said controlling includes controlling the Signal channel 

launch power to vary inversely with the distance to 

over which the Signal channels are to be transmitted; 

and, 

Said co-propagating includes co-propagating optical 

energy at a power that varies directly with the distance 

over which the Signal channels are to be transmitted. 

5. The method of claim 3, wherein said method includes counter-propagating optical energy to provide Raman gain 

in the Signal channels in the transmission media. 

6. The method of claim 3, wherein: 

Said imparting includes imparting the information onto 

signal channels in the 1520–1630 nm wavelength 

range, and, 

Said co-propagating includes co-propagating optical 

energy in the 1400-1520 nm wavelength range to 

provide Raman gain to the Signal channels. 

7. The method of claim 3, further comprising: 

providing at least one pump Source configured to Supply 

the optical energy in one or more pump wavelengths 

having a low relative intensity noise. 

8. The method of claim 7, further comprising counter 

propagating the optical energy from at least one of the pump 

Sources relative to the optical Signals to provide Raman 

amplification of the optical Signals. 

9. The method of claim 7, wherein said providing includes 

providing the at least one pump Source including a laser 

having a Bragg grating positioned to relative to the laser to 

form an external cavity to control relative intensity noise of 

the optical energy. 

10. The method of claim 9, wherein said providing includes providing the laser with an output facet that 

includes at least one of an anti-reflective coating and an 

angled output facet. 

11. An optical System comprising: 

at least two optical nodes configured to transmit and 

receive optical signals between Said nodes via a trans 

mission media configured to provide Raman amplifi cation of the optical Signals, 

a counter-pump Source configured to counter-propagate 

optical energy in the transmission media in a first pump wavelength range to produce Raman amplification of 

the optical signals, wherein the Raman amplification 

has a corresponding noise figure profile over an optical Signal Wavelength range; 

a co-pump Source configured to co-propagate optical 

energy with the optical Signals in a Second pump 

wavelength range to vary the noise figure profile of the 

Raman amplification produced by Said counter 

propagating optical energy over at least a portion of the 

optical Signal Wavelength range; 

a plurality of optical amplifiers disposed between said 

optical nodes and configured to optically amplify the 

optical signals passing between said nodes, wherein 

Said optical amplifiers include pump Sources config 

ured to provide optical energy in a pump wavelength 

range to produce Raman amplification of the optical 

Signals, and, 

again flattening filter configured to filter a composite gain profile produced by Said plurality of optical amplifiers 

and impart a desired gain profile to the optical Signals. 

15 

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55 

60 

65 

14 

12. The system of claim 11, wherein: 

Said plurality of optical amplifiers includes a plurality of 

different pump Sources providing different amounts of 

optical energy in pump wavelengths within the pump 

Wavelength range; and, 

Said Raman gain flattening filter is configured to filter the 

composite gain profile produced by the pump wave 

lengths. 

13. The system of claim 11, wherein said plurality of 

optical amplifiers includes at least one of distributed and 

concentrated Raman amplifiers. 

14. The system of claim 11, wherein: 

at least one of Said processing nodes is configured to 

launch optical Signals into Said transmission media at a 

power below a nonlinear interaction limit of Said trans 

mission media; 

at least one pump Source positioned to co-propagate 

optical energy with the optical Signals in Said transmis 

Sion media to amplify the Signal channels and achieve 

a maximum signal channel power below the nonlinear 

interaction limit at a point in the transmission media 

downstream from Said first processing node. 

15. The system of claim 14, wherein: 

Said System includes at least one optical amplifier con 

figured to amplify the Signal channels passing through 

Said amplifier; 

Said at least one pump Source includes at least one pump included with Said optical amplifier and configured to 

co-propagate optical energy with the optical Signals to 

amplify the Signal channels and achieve a maximum 

Signal channel power below the nonlinear interaction 

limit at a point in Said transmission media downstream 

from Said optical amplifier. 

16. The system of claim 15, wherein said optical amplifier 

includes pump Sources configured to introduce optical 

energy co-propagating and counter-propagating with the 

Signal channels in Said transmission media to amplify the 

Signal channels. 

17. The system of claim 14, wherein said system includes 

launching signal channels in the 1520–1630 nm transmis 

Sion range, and, 

Said at least one pump Source provides optical energy in 

the 1400-1520 nm wavelength range to amplify the 

Signal channels via Stimulated Raman Scattering. 

18. The system of claim 14, wherein said transmission 

media includes optical fiber. 

19. The system of claim 14, wherein said transmission 

media includes at least first and Second fiber Sections, 

wherein 

Said first fiber Section has a first core diameter and is 

disposed between the node transmitting optical Signals 

and the Second fiber Section, and, 

Said Second fiber Section has a Second core diameter that 

is less than the first core diameter and is disposed between the node receiving optical Signals and the first 

fiber section. 

20. The system of claim 19, further comprising at least 

one optical amplifier disposed between Said at least two 

optical nodes and configured to amplify optical signals 

passing from one of the Second fiber Sections to one of the 

first fiber sections. 

Case 6:20-cv-00484-ADA Document 1-4 Filed 06/02/20 Page 16 of 16