Exhibit 3 

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USOO6344922B1 

(12) United States Patent (10) Patent No.: US 6,344,922 B1 

Grubb et al. (45) Date of Patent: Feb. 5, 2002 

(54) OPTICAL SIGNAL VARYING DEVICES WO 98/42088 * 9/1998 

WO WO 98/42088 9/1998 

(75) Inventors: Stephen G. Grubb; Raymond Zanoni; 

Thomas D. Stephens; Deepak 

Boggavarapu, all of Columbia; 

Ruxiang Jin, Ellicott City, all of 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.: 09/253,819 

(22) Filed: Feb. 19, 1999 

Related U.S. Application Data 

(63) Continuation-in-part of application No. 09/119,556, filed on 

Jul. 21, 1998, now Pat. No. 6,115,174. 

(51) Int. Cl. .................................................. H01S 3/00 

(52) U.S. Cl. ................... 359/334; 359/134; 35.9/341.31 

(58) Field of Search ................................. 359/118, 124, 

359/134, 160,337,341, 334, 341.31 

(56) References Cited 

U.S. PATENT DOCUMENTS 

4,315,666 A 2/1982 Hicks, Jr. 

4,342.499 A 8/1982 Hicks, Jr. 

4,401,364 A 8/1983 Mochizuki 

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

4,699.452 A * 10/1987 Mollenauer et al. ........ 359/334 

4,728,170 A 3/1988 Robertson 

(List continued on next page.) 

FOREIGN PATENT DOCUMENTS 

EP O 734 105 A2 9/1996 

EP O7341.05 * 9/1996 

JP 72O2306 A 8/1995 

JP 7-2O2306 * 8/1995 

OTHER PUBLICATIONS 

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

Channel WDM Network Using Dynamic Gain-Controlled 

EDFAs, Electronics Letters, 5 Mar. 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, 

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

Masuda, H., et al., Ultra-Wideband Optical Amplification 

With a 3-Db Bandwidth Of 67 nm Using a Partially Gain 

Flattened Erbium-Doped Fiber Amplifier and Raman 

Amplification, Optical Amplifiers and their Application, 

Aug. 3-5, 1994, 1997 OSA Technical Digest Series, V20, 

pp. MC3–1-4/4.0–3. 

(List continued on next page.) 

Primary Examiner Nelson Moskowitz 

(57) ABSTRACT 

Optical Systems of the present invention include a plurality 

of optical processing nodes in optical communication via at 

least one signal varying device. The Signal varying devices 

includes an optical fiber Suitable for facilitating Raman 

Scattering/gain in a Signal Wavelength range and a pump 

energy Source for providing pump energy in a plurality of 

pump wavelengths. The pump Source provides Sufficient 

pump energy in each pump wavelength to Stimulate Raman 

Scattering/gain in the optical fiber within the Signal wave 

length range. The pump wavelengths are Selected Such that 

the combined Raman gain resulting from the pump energy Supplied by each pump wavelength produces a desired 

Signal variation profile in the Signal wavelength range. In 

addition, the pump energy Supplied by at least one of the 

pump wavelengths can be varied to produce a controlled 

Signal intensity variation profile over the Signal wavelength 

range in the optical fiber. 

33 Claims, 11 Drawing Sheets 

 

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Page 2 

U.S. PATENT DOCUMENTS 

4,805,977 A * 2/1989 Tamura et al. .............. 359/334 

4.881,790 A 11/1989 Mollenauer 

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

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

5,095,519 A 3/1992 Dorsey 

5,191,628 A * 3/1993 Byron ........................ 359/134 

5,228,105. A 7/1993 Glista .......................... 385/89 

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

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

5,557.442 A 9/1996 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 

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

5,696.615 A 12/1997 Alexander 

5,883,736 A 3/1999 Oshima et al. ............. 359/341 

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

5,963,361 A 10/1999 Taylor et al. ............... 359/337 

5.999.548 A 12/1999 Mori et al. ................... 372/22 

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. ............... 359/241 

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

OTHER PUBLICATIONS 

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, 

pp. 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. 

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

OFC 98 Technical Digest pp. 20–21. 

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

For Long-Haul Transmission, OFC 98 Technical Digest pp. 

30-31. 

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. 32–33. 

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

fier, OFC 98 Technical Digest pp. 33–34. 

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 400 km 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, 25" Jun. 1998, vol. 34, 

No. 13, Online No. 1998.0935. 

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

Gain Control Function, Proceedings of the 1995 IEICE 

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

Institute of Technology b-1067, p. 513. 

Stentz, Andrew, et al., Analog-Grade Power Raman Ring Amplifier at 1.3 um, OSA Trends in Optics and Photonics, 

vol. 5, Optical Amplifiers and Their Applications. From the 

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

USA, Jul 13, 1996. 

Aida, 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. 

Zou et al., IEEE Photonics Technology Letters, v8, n1, pp. 

139–141 (1/96). 

Grubb, OFC 98 Technical Digest Series, v2, (abstract only). 

Masuda et al., Electronics letters, vol. 341 #13, pp. 1-2, Jun. 

25, 1998.* 

Stentz et al, DAS Trends in Optics and Photonics, vol. 5, pp. 

350-368, Jul 13, 1996.* 

Wen et al, IEEE Photonics Tech. Letters, #4, pp. 189-192, 

Feb. 1992. 

Masuda et al., Electronics Letters, vol. 341 #13, pp. 2, Jun. 

25, 1998.* 

* cited by examiner 

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1 

OPTICAL SIGNAL WARYING DEVICES 

CROSS-REFERENCE TO RELATED 

APPLICATIONS 

This application is a continuation in part of commonly 

assigned U.S. Ser. No. 09/119,556 filed Jul. 21, 1998 entitled 

“Optical Signal Varying Devices”, now U.S. Pat. No. 6,115, 

111 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 Signal varying devices that provide for controllably varying 

optical Signal characteristics. More particularly, the inven 

tion relates to optical amplifiers and attenuators that have 

controllable gain, loSS and transparent intensity variation 

profiles for use in optical communication Systems. 

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, driven demand for faster and higher capacity electronic information processing equipment 

(computers) and transmission networks and Systems linking the processing equipment (telephone lines, cable television 

(CATV) systems, local, wide and metropolitan area net 

works (LAN, WAN, and MAN)). 

In response to this demand, telecommunications compa 

nies have turned to optical communication Systems to pro 

vide Substantially larger information bandwidth transmis 

Sion capacities than traditional electrical communication 

Systems. Early optical transmission Systems, known as Space 

division multiplex (SDM) systems, transmitted one infor 

mation signal using a Single wavelength in Separate 

waveguides, i.e. fiber optic Strand. Time division multiplex ing (TDM) multiple information signals onto a single wave 

length in a known Sequence that can be separated upon 

receipt has further increased the transmission capacity of 

optical Systems. 

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 

capacity communications networks. Telecommunications 

companies have looked to wavelength division multiplexing 

(WDM) to further increase the capacity of their existing 

Systems. 

In WDM transmission systems, pluralities of distinct 

TDM or SDM information signals are carried using elec 

tromagnetic waves having different wavelengths in the opti 

cal spectrum, i.e., far-UV to far-infrared. The pluralities of 

information carrying wavelengths are combined into a mul 

tiple wavelength optical signal, which is transmitted in a 

Single waveguide. 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 high cost of electrical Signal regeneration/amplification equipment required to compen 

Sate for Signal attenuation for each optical wavelength throughout the system. However, the development of the 

erbium doped fiber optical amplifier (EDFA) eliminated the 

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65 

2 

need for, and the associated costs of, electrical Signal regeneration/amplification equipment to compensate for Sig 

nal attenuation in many systems. Thus, WDM systems 

became a cost effective means to increase optical network capacity. 

Erbium doped fiber amplifiers (“EDFAs”) can theoreti 

cally be used to amplify signals in an amplification wave 

length range Spanning from approximately 1500 nm and 

1600 nm. However, EDFAs do not equally amplify each 

optical Signal wavelength within the range. The differences 

in amplification can result in attenuation of Some signals 

and/or signal loSS or distortion because of highly amplified 

noise. Thus, the performance of EDFAS in a transmission 

System varies depending upon the number of wavelengths 

and the wavelengths used in the System. 

Judicious Selection of the wavelengths and amplifier 

powers used in a System can minimize EDFA Variations 

(gain non-uniformities). For example, many WDM systems currently restrict the wavelengths used in the System to 

between 1540 nm and 1560 nm, a range in which EDFAS 

comparably amplify optical Signals. AS might be expected, 

restricting System designs to only those wavelengths that are 

comparably amplified by EDFAS severely limits the number 

of wavelengths and the information transmission capacity of 

WDM systems. 

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. A broader range of wavelengths 

can be used with a less Stringent requirement for uniform 

amplification, because cumulative amplifier variations will 

generally not Swamp out lowly amplified signals over a 

Small number of amplifiers. 

In addition to the wavelength dependence, EDFA perfor 

mance is also a function of the amplification power Supplied 

to the EDFA. Thus, EDFAS generally must be operated with 

a limited power range to minimize amplification variations 

in the System. The amplifier power limitations, in turn, 

increase the number of amplifiers in a System by limiting the 

allowable distance between EDFAS, i.e., the Span length. 

In discussing the Signal intensity variation of EDFAS and 

other devices, the uniformity of gain or loSS profiles over a 

wavelength range is generally referred to as the flatness of 

the profile. A perfectly flat profile is a gain, loSS, or trans 

parency profile that has a constant value over the wavelength 

range of interest. 

WDM system constraints imposed by EDFA wavelength 

variations have focused attention on providing EDFA con 

figurations that compensate for the variations and provide 

more uniform gain for a larger band of wavelengths and over 

a greater power range. Various EDFA configurations have 

been proposed to minimize amplifier gain variations. For 

example, see U.S. Pat. Nos. 5,406,411, 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; Park et al., Electronics 

Letters, Mar. 5, 1998, Vol. 34, No. 5, Online No. 1998.0346; 

and, Dung et al., Electronics Letters, Mar. 19, 1998, V. 34, 

n. 6, Online No. 19980446. 

Other amplifier configurations have used EDFAS in com 

bination with a Raman amplifier to Statically vary the gain 

profile of an EDFA. For example, see Masuda et al., OSA 

1997, pp. 40-3/MC3-1, Masuda et al., Electronics Letters, 

v34, n.13, Online No. 19980935 (Jun. 25, 1998), and U.S. 

Pat. No. 5,083,874 issued to Aida et al. It has also been 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 15 of 22
US 6,344,922 B1 

3 

proposed to eliminate EDFAS and use amplifier configura tions that employ only Raman amplifiers. However, the 

all-Raman configurations to date have not greatly improved 

the amplifiers gain flatneSS profile and may still require gain 

equalization to flatten the gain profile as discussed by 

Rottwitt et al., “A 92 nm Bandwidth Raman Amplifier”, 

OFC 98, p. 72/CAT-1. 

The above referenced gain flattened configurations are 

generally Statically configured to have a wavelength range 

defined by a 3 dB variation (~ a factor of 2) in the gain profile and having a t1 dB variation between wavelengths. The gain flattened amplifiers provide Some improvement 

over conventional EDFAS in the number of amplifiers, amplifier power ranges, and Span lengths before the Signal 

must be regenerated. The gain flattened optical amplifiers 

nonetheless introduce exceSS amplifier noise and gain non 

uniformities that limit the number of optical amplifiers that 

can be used in a WDM System prior to Signal regeneration. 

Gain flattening in optical amplifier configurations is gen 

erally performed using filters and/or attenuators to decrease 

the Signal intensity of the wavelengths to a specified value. 

For example, in many embodiments, the optical Signals are 

amplified to an intensity higher than the amplifier output 

value and the filters and attenuators are used to flatten the 

gain profile by decreasing the optical signal intensity. These 

methods tend to increase the noise in the Signal with a 

corresponding decrease in the output power of the device. 

Optical filters and attenuators are often included as Sepa 

rate optical devices in the System, but may also be allfiber 

devices, Such as Bragg grating filters and all-fiber 

attenuators, included in the transmission fiber. For example, 

see U.S. Pat. Nos. 4,728,170, 5,095,519, 5,633,974, 5,651, 

085, and 5,694,512. The filters and attenuators can be 

variable or fixed depending upon the configuration. The 

amplifier, filters, and attenuators are Statically configured to 

flatten the gain profile. 

AS the demand for transmission capacity continues to 

grow, there is an increasing need for Systems that Span 

longer distances and provide a greater number of informa 

tion carrying wavelengths/channels. However, it has proven 

difficult to balance the non-linear gain of EDFA configura tions with Selective wavelength filtering and attenuation to 

provide gain flattened amplifier configurations that meet this 

need. 

Accordingly, there is a need for optical amplifiers and 

attenuator particularly, and Signal varying devices generally, 

that provide increased control over the Spectral intensity profile of optical signal in the optical Systems. The improved 

Signal varying devices will provide for higher capacity, more 

Versatile, longer distance communication Systems. 

BRIEF SUMMARY OF THE INVENTION 

The apparatuses and methods of the present invention 

address the above difficulties with prior art optical devices 

and Systems. An optical System of the present invention 

includes a plurality of optical processing nodes in optical 

communication via at least one Signal varying device. The 

Signal varying devices includes an optical fiber Suitable for 

facilitating Raman Scattering/gain in a signal wavelength 

range and a pump energy Source for providing pump energy 

in a plurality of pump wavelengths. The pump Source 

provides Sufficient pump energy in each pump wavelength to 

Stimulate Raman Scattering/gain in the optical fiber within 

the Signal wavelength range. 

The Signal varying device can be embodied as a distrib 

uted device that employs a portion or all of an optical 

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40 

45 

50 

55 

60 

65 

4 

transmission fiber extending between two optical nodes, 

Such as between an optical transmitter and an optical 

receiver. The Signal varying device can also be embodied as 

a lumped or concentrated device that is placed in the optical 

transmission fiber at discrete locations between the optical 

nodes. 

The pump wavelengths are Selected Such that the com 

bined Raman gain resulting from the pump energy Supplied 

by each pump wavelength produces a desired Signal varia 

tion profile in the Signal wavelength range. In addition, the 

pump energy Supplied by at least one of the pump wave 

lengths can be dynamically varied to produce a controlled 

Signal intensity variation profile over the Signal wavelength 

range in the optical fiber. In an embodiment, four pump 

wavelengths spaced in 10-30 nm intervals can be used to 

provide intensity gain and flatness control to over 30 nm to 

within 0.2 dB. 

Also in an embodiment, erbium doped fiber is included in 

the Signal varying device to provide a multiple Stage Signal 

varying device. The erbium doped fiber and the multiple 

wavelength controlled Raman portion of the Signal varying 

device can be operated in conjunction to impart a desired 

intensity profile to the optical Signal. 

The design and length of the optical fiber used in con 

junction with the pump Source can be tailored to provide flexibility in operation of the System. For example, a 

concentrated, or lumped, high gain signal varying device can 

be provided using a Small core fiber, Such as dispersion 

compensated or dispersion shifted fiber. The lumped device 

further provides for a greater range over which the Signal 

varying device can be used as an attenuator because of its 

higher localized loSS. 

Multistage concentrated and/or distributed Raman Signal varying devices can also be employed to further tailor the 

profile using either Separate or common pump Sources. For 

example, a first concentrated Raman Stage can employ Small 

core fiber to provide for efficient Raman amplification of the 

Signal wavelengths. A Second concentrated Raman Stage can 

employ a larger core fiber to further amplify the Signal 

power, while lessening the extent of non-linear interactions 

amongst the Signal wavelengths that may occur in a single 

Stage with Smaller core fibers. The Second concentrated 

Raman Stage can also employ fiber having low loSS in the 

1400-1520 nm range to allow for more efficient Raman 

pumping of the multiple Stages using a common Source. In 

addition, the first and Second Raman Stages can use fibers 

that have different chromatic dispersion characteristics to 

further reduce the extent of non-linear interaction between 

the Signal wavelengths. 

Distributed Signal varying devices can be provided by 

employing the optical transmission fiber spanning between 

the optical nodes to control the Signal variation profile 

occurring in the transmission fiber. Also, different optical fiber types, including doped fibers, can be used in various 

portions to replace existing transmission fiber to provide for 

different distributed Signal varying profiles. The concen 

trated and distributed Raman Signal varying devices can be 

used alone or in combination to Statically or dynamically impart desired Signal varying profile characteristics to the 

System. 

In an embodiment, a distributed Raman amplifier can be 

employed with one or more first pump Sources propagating 

pump energy in the transmission fiber to amplify counter 

propagating Signal wavelengths to provide a first signal 

varying profile. A concentrated Raman Signal varying device 

can be placed in Series with the distributed Raman amplifier 

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US 6,344,922 B1 

S 

employing one or more Second pump Sources to provide a 

Second signal varying profile. The first and Second Signal varying profiles acting to produce a desired overall signal varying profile. Additionally, an EDFA can be employed to 

contribute a third signal varying profile to the overall signal varying profile. 

A distributed Raman amplifier can also be used to provide 

pump energy to one or more remotely located concentrated 

or distributed Raman amplifiers and/or doped amplifying 

fibers. For example, the pump Sources can be Selected to 

produce a first signal varying profile in the distributed 

Raman amplifier and a Second Signal varying profile in the 

remotely located erbium doped fiber. The pump power 

and/or the wavelength of the pump energy Sources can be 

varied to control to individual and overall Signal varying profiles. Pump energy can also be Supplied to remotely 

located Signal varying devices using one or more Separate 

fibers. Such fibers can be pure SiO2 to minimize loss and 

nonlinear conversion of the pump light. 

Additional gain and gain profile control in Raman ampli fier Stages can be produced by including one or more pumps 

at lower Raman wavelengths that Serve to provide additional 

pump energy to the higher Raman pump wavelengths. The 

pump Source can employ numerous configurations to 

decrease the extent of interference, i.e., cross-talk, that 

occurs between the Raman pump wavelengths, as well as the 

Signal wavelength. 

Thus, the devices and methods of the present invention 

provide for control of the Signal intensity over a range of 

wavelengths in optical transmission Systems. Accordingly, 

the present invention addresses the aforementioned prob 

lems and provides signal varying devices, methods, and 

optical Systems that provide increased control over optical 

Signal characteristics in the System. 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: 

FIGS. 1-2 shows optical communication systems of the 

present invention; 

FIGS. 3-5 show signal varying devices of the present 

invention; 

FIGS. 6-7 show remote pumping embodiments of the 

present invention; 

FIG. 8 shows exemplary overall, distributed Raman, and 

remote erbium gain profiles using remote pumping embodi 

ments of the present invention; 

FIGS. 9-10 show alternative pump combining configu 

rations of the present invention; 

FIGS. 11(a&b) show (a) Raman gain profiles over a 30 

nm range as a function of gain and (b) various Raman gain profiles, and, 

FIGS. 12-13 show Raman gain profiles over 35 and 100 

nm, respectively, based on a Summation of experimental data using Single pump wavelength signal varying devices. 

DETAILED DESCRIPTION OF THE 

INVENTION 

The optical systems 10 of the present invention will be 

described generally with reference to the drawings for the 

15 

25 

35 

40 

45 

50 

55 

60 

65 

6 

purpose of illustrating present embodiments only and not for 

purposes of limiting the same. 

FIG. 1 shows an optical System 10 including a signal varying device 12 optically connecting two optical process 

ing nodes 14 to form an optical link 15. As shown in FIG. 

2, the optical processing nodes 14 generally include at least 

one transmitter 16 for transmitting optical Signals in at least 

one information carrying wavelength, or channel, or at least 

one optical Signal receiver 18 for receiving the optical Signals. 

AS is known in the art, the transmitter 16 includes at least 

one optical Source or emitter, Such as lasers, incoherent 

Sources, or other Sources to provide one or more optical 

carriers at fixed or tunable wavelengths. The information to 

be transmitted in the system 10 can be used to directly 

modulate the Source or externally modulate the optical carrier, or can be upconverted onto an optical wavelength 

other than the optical carrier wavelength. 

Likewise, the receiver 18 can employ direct or indirect, 

e.g. coherent, detection equipment, Such as photodiodes and 

wavelength Selective devices as are known in the art, to 

receive and perform an opto-electronic conversion of the 

Signal. Similarly, the optical receiver 18 can detect a fixed or 

tunable wavelength depending upon the requirements of the 

system 10. The optical processing nodes 14 may further 

include add and/or drop ports 20, Switches 22, Signal dis 

tributors 24 and combiners 26, or other signal processing 

devices as are further known in the art. 

The optical system 10 may include a plurality of optical 

linkS 15 interconnected via the optical processing nodes 14 

and/or Signal varying devices 12. The optical processing 

nodes 14 can Serve as terminals in the optical System 10 or 

may be disposed intermediately along optical transmission 

fiber 28 interconnecting the nodes 14 and devices 12. 

AS shown in FIG. 2, the Signal varying device 12 includes 

a Raman gain Section of transmission fiber 30 in optical 

communication with the processing nodes 14, which is 

Supplied with pump energy by a pump energy Source 32. The 

Signal varying device 12 can be embodied as a distributed 

device in which the Raman gain transmission fiber 30 

includes a Substantial portion or all of the optical transmis 

Sion fiber 28 extending between nodes 14, Such as a optical 

transmitter 16 and optical receiver 18, and/or devices 12. 

The Signal varying device 12 can also be embodied as a 

lumped, or concentrated, device that is placed in the optical 

transmission fiber 28 at discrete locations between the 

optical nodes 14. 

One skilled in the art will appreciate that concentrated 

devices 12 of the present invention can be produced in a 

manner analogous to prior art EDFA construction. For 

example, the concentrated devices 12 are constructed by winding optical fiber of Sufficient length to provide the 

desired signal variation range, Such as amplification, within 

a discrete device around a spool to control the Size of the 

devices 12. 

As shown in FIG. 3, a controller 34 can be included in the 

device 12 and configured to dynamically control the pump 

energy Supplied via one or more of the pump wavelengths. 

Dynamic control of the pump energy allows for the perfor 

mance of the device 12 to be varied as Signal transmission 

changes occur, either upstream and/or downstream of the 

device 12. Thus, the dynamic control provides the ability to 

continually or periodically modify the operation of the 

devices 12 in response to communication System/ 

environmental variations that inevitably occur with time. 

The devices 12 allow the signal varying profiles to be 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 17 of 22
US 6,344,922 B1 

7 

controlled both on-line or off-line, Such as during installation, maintenance, grooming, etc. 

In one aspect of the invention, the pump Source 32 is 

configured to combine arbitrarily Spaced pump wavelengths 

as shown in FIG.3. Grating stabilized lasers 32 can be used 

to provide pump wavelengths that are combined in pairs 

using fused DWDM couplers 36. The paired pump wave 

lengths can be further combined with arbitrarily Spaced 

pump wavelengths using a dichroic filter 38. Alternatively, 

polarization combiners 39 can be used to combine two pump wavelengths having orthogonal polarizations, which can be 

further combined with other wavelengths using the dichroic 

filter 38. The use of polarization combiners 39 provides additional control over the pump energy polarization and the 

resulting pump energy conversion in the Raman amplifiers. 

The combination of fused couplers 36, dichroic filter 38, 

and polarization combiners 39 in the present invention 

provides increased flexibility in wavelength combining and 

amplfier gain profile control. It will be appreciated that 

additional wavelengths can be added by cascading the lasers 

and wavelength combining arrangements. 

The pump energy is introduced into the optical transmis 

Sion fiber 28 using combiners 26, Such as wavelength division multiplexers. Other wavelength Selective or nonse 

lective couplers, circulator, reflectors, and other combining 

device known in the art can be used to introduce the pump 

energy. 

In the present invention, the Raman gain optical fiber 30 

can be selected to facilitate Raman Scattering/gain over a 

range of transmission signal wavelengths that include opti 

cal signal wavelengths 2-0, when the fiber 30 is Stimu 

lated using pump energy provided in a pump wavelength 

range. Most Silica-based fiber, including most transmission 

fibers, facilitate Raman gain in a wide range of wavelengths, 

thus, additional fiber 30 included in the device 12 is gener ally Selected to complement any existing fiber as will be 

further discussed. With proper pump wavelength Selection, 

it is expected that Raman gain can be provided across the 

optical fiber transparent transmission wavelength range, 

which currently ranges from approximately 1240 to 1650 nm for silica based fiber. 

For example, in the transmission signal wavelength range 

of 1520 nm to 1620 nm, the corresponding pump wave 

length range is approximately 1420 nm to 1520 nm. 

Likewise, in the transmission signal wavelength range of 

1250 nm to 1350 nm, the corresponding pump wavelength 

range is 1150 nm to 1250 nm. Thus, more than one signal wavelength range can be transmitted in the optical System 

10. The signal wavelength ranges can be interleaved with the 

pump wavelengths to provide a multiple Signal wavelength 

range System as Stated above. It is also expected that changes in the optical fiber transmission signal wavelength range can 

be accommodated by the present invention by proper Selec 

tion of pump wavelengths. 

Devices 12 having different Signal variation profiles and 

employing different pump wavelengths can be used in 

combination within the system 10. The optical fiber 30 used 

in the Signal varying device 12 can be the same as the 

transmission fiber 28 in the system 10 or another type of 

optical fiber having different properties. The length and type 

of fiber deployed in the system 10 can be tailored to provide flexibility in the operation of the system. 

For example, the extent of Raman Scattering in the fiber 

is partly dependent upon the size of the optical fiber core. In 

addition, the loSS in the fiber increases as the size of the core 

decreases. Thus, a concentrated, or lumped, high gain/loss 

15 

25 

35 

40 

45 

50 

55 

60 

65 

8 

Signal varying device can be provided using a Small core 

fiber. Also, Some fiber core composition, Such as cores with 

increased germania concentrations, can provide for wider 

Raman gain variation profiles. In addition, fibers can be 

chosen to impart other characteristics, i.e., chromatic 

dispersion, to the optical Signals that may differ from those 

of the transmission fiber. 

In at least one embodiment, a Small core dispersion compensating fiber (“DCF"), such as is manufactured by 

Lucent Technologies or Sumitomo Electric Company, is 

used as the Raman gain fiber in a concentrated Signal varying device 12. The DCF concentrated device 12 pro vides for a greater range over which the Signal varying 

device can be used as an attenuator, an amplifier, or a 

transparent link, because of the high attenuation/high gain 

properties of the DCF. Conversely, standard single mode 

transmission fiber can used to provide a distributed lower 

gain signal varying device 12 to provide control over a 

Smaller intensity variation (gain/loss) range. 

Non-linear intensity profiles can be also provided using 

the device 12. The device 12 can include inherently nonlin 

ear or nonlinearly operated components, Such as one or more 

doped fiber amplifiers, etc., to produce a net linear intensity 

profiles or different non-linear profiles. For example, an 

erbium doped fiber 40 can be included in the transmission 

fiber and optically pumped using wavelengths, 21-), Supplied by one or more erbium pump Sources 42i. The 

erbium doped fiber 40 can be embodied as a distributed or 

concentrated portion in combination with the Raman Section 

of the Signal varying device to provide a multiple stage 

signal varying device 12, as shown in FIGS. 4 and 5. It will 

be appreciated that various EDFA configurations, Such as 

those discussed in the Background, can be used in embodi 

ments incorporating erbium doped fiber. 

Devices 12 having multiple concentrated/lumped Raman 

Stages can be introduced into the transmission fiber 28 to 

further tailor the Signal varying profile. For example, a first 

concentrated Raman fiber Stage 12 can employ a Small core 

fiber, such as DCF, to provide for efficient Raman amplifi cation of the Signal wavelengths. A Second concentrated 

Raman fiber Stage 12 can employ a larger core fiber to 

provide additional Signal amplification, while lessening the 

extent of non-linear interactions compared to Smaller core 

fibers. The Second concentrated Raman Stage can also 

employ fiber having low loss in the 1420-1510 nm range, 

such as AllWave fiber sold by Lucent Technologies. The use 

of low loSS fiber provides increased pumping efficiency, So 

that both Stages can be more effectively pumped using a 

common Raman pump Source. Alternatively, the pump 

Source 32 can be configured to provide different Raman 

pump wavelengths to pump the first and Second Stages. 

In addition, the first and Second Raman Stages can use 

fibers that have different chromatic dispersion characteris 

tics. The change in fiber dispersion characteristics will tend 

to reduce the extent of non-linear interaction that occurs 

between the highly amplified signal wavelengths. 

Other optical components including gain profile varying 

components can be included in the devices 12. AS shown in 

FIG. 5(b), wavelength selective reflectors 44, such as Bragg gratings, can be included to reflect exceSS pump energy back 

into optical fiber 30 or erbium sections 40. Gain flattening 

filters 46 can also be included to impart a fixed or variable 

gain profile on the optical Signal. Optical isolators 48 are 

provided to eliminate discrete reflections from the gain flattening filter 46. Also, the device 12 can be provisioned to 

allow the local controller 34 to transmit and receive Super 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 18 of 22
US 6,344,922 B1 

Visory and/or monitoring, i.e., Service, information from a 

network manager 50 via optical wavelength 2 as shown in 

FIG. 5(b). 

Also, it will be further appreciated that the devices 12 can 

be divided into multiple Stages, i.e., pre- and post-amplifier 

Stages. Signal processing, Such as adding/dropping or 

Switching channels, etc., and/or controlling accumulated 

noise and/or gain profile variations can be performed 

between the Stages as is known in the art. 

The pump energy Source 32 provides pump energy to the 

fiber 30 in a plurality of pump wavelengths, 2-0, within 

the pump wavelength range. The pump energy can be 

supplied to the fiber 30 counter-directionally and/or codi 

rectionally with the optical Signal wavelengths 2-0, being 

transmitted in the System 10. Counter-propagating the first 

Stokes order Raman wavelengths relative to the Signal 

wavelengths generally lessens Signal degradation due to 

interference, i.e., cross-talk, between the pump energy and 

the optical Signal. Also, the pump energy Supplied via each 

pump wavelength can be controlled to compensate for any 

Self-pumping that might occur between the pump wave 

lengths. It is also desirable to Select pump wavelengths. So 

that the pump energy Supplied by each pump wavelength is 

relatively uniform, i.e., within t10% of the average pump 

energy per pump Wavelength. 

In addition, the pump Source 32 can Supply the pump 

energy at one or more points along the fiber 30 as shown in 

FIG. 5(a). In at least one embodiment, pump energy is 

Separately Supplied to each Stage of the device 12 from a 

point on the fiber 30 and counter-directionally to the optical Signals being transmitted. 

The pump Source 32 can be any Source of pump energy 

that is Sufficient to induce Raman gain in the transmission 

wavelength ranges of the System 10. Typically, the pump 

Source 32 will include one or more pump lasers of the type 

known in the art, and may also include other coherent and 

incoherent broad and narrow band Sources. The number of 

lasers and other pump energy Sources used in the pump Source 32 depends upon the transmission wavelength 

ranges over which the Signal varying device 12 will be 

operated. 

The pump wavelengths used in erbium fiber Stages of the 

devices 12 can be Selected to provide pump energy in the 

980 nm range for only erbium gain or in the 1480 nm range 

for both Raman and erbium gain. One will appreciate that 

pump wavelengths in the 980 nm range may be used to 

provide Raman gain by pumping Successive Stokes orders in 

the device 12, as discussed within. 

The pump Sources 32 may be locally or remotely located 

from the signal varying device, such as shown in FIGS. 6 

and 7. The Signal varying devices 12 can be configured Such 

that the residual pump energy from a distributed Raman 

amplifier is Supplied to pump one or more concentrated or 

distributed Raman and/or doped fiber Signal varying devices 

12. For example, Sections of the transmission fiber are 

replaced with corresponding Sections of doped fiber and/or 

different types fiber to provide distributed Signal varying 

devices 12. In these configurations, residual pump energy 

from the distributed Raman amplifier can be used to pump 

and control the Signal variation profiles of the remotely 

distributed devices 12. 

FIG. 8 shows a plot of the signal variation profiles using 

the transmission fiber 28 to form a distributed Raman 

15 

25 

35 

40 

45 

50 

55 

60 

65 

10 

amplifier, which provides pump energy to a remotely located 

section of erbium fiber 40 spliced into the transmission fiber 

28. Curve A shows the remote erbium gain profile. Curves 

B and C show the target and acheived Raman gain profile. 

Curve D shows the overall gain profile for the erbium and 

the Raman gain Section. AS can be seen, the pump wave 

lengths and energy provided by the pump Source 32 can be 

Selected to provide complementary non-linear gain profiles 

in the transmission fiber 28 and the erbium fiber 40. The 

resulting overall profile is Substantially uniform. AS would 

be expected the overall profile can be varied to provide other 

profiles as may be desired. For example, the gain profile can 

be tilted to offset higher bending losses at longer wave 

lengths. 

AS Shown in FIG. 6, a portion of the optical Signal, 

including the Signal wavelengths, can be tapped off the 

transmission fiber 28 for analysis. Characteristics of the 

Signal wavelengths can be determined using an analyzer 43, 

Such as an optical Spectrum analyzer and a tunable receiver 

18 and bit error rate test device. The signal characteristics 

can used by the controller 34 to vary pump energy Supplied 

by pump sources 32-32" to maintain a desired profile/ 

System performance. The variation in pump energy will 

change the overall signal varying profile by varying profiles 

of both the remote signal varying device 12 and the distrib 

uted Raman amplifier Supplying the remote devices 12. 

In addition, one or more wavelength Selective reflectors 

44 can be disposed proximate to the remote Signal varying 

device 12. Thus, exceSS pump energy can be reflected to 

provide additional gain in the distributed Raman Section 

and/or the remote signal varying devices depending upon the 

position of the reflectors 44. 

As further shown in FIG. 7, additional gain and gain profile control in Raman amplifier Stages and remotely pumped doped fiber Stages can be produced by including 

one or more pumps at higher Stokes order Raman wave 

lengths to amplify lower Stokes order Raman pump wave 

lengths. In Raman amplifiers, the pump energy attenuates 

with distance traveled in the fiber reaching a level at which 

very little Raman amplification of the Signal wavelengths 

occurs. However, pump energy at higher Stokes order 

Raman wavelengths (1320–1420 nm, etc.) can be introduced 

into the fiber to amplify the lower Stokes order Raman 

wavelengths (1420-1520 nm, etc.), which, in turn, will 

amplify the signal wavelengths (1520–1620 nm, etc.). If 

co-propagating Raman wavelengths are Staggered by at least 

every other Raman wavelength and adjacent Stokes orders 

are counter-propagated, cross-talk between the wavelengths 

should not greatly affect the Signal wavelength. 

An exemplary Raman wavelength pump arrangement is 

shown in FIG. 7. Pump lasers 32, Supply Raman wave 

lengths in the Stokes orders (2i-1) counter-propagating to 

the Signal wavelength range and Raman wavelengths in the 

Stokes orders 2i co-propagating with the Signal wavelengths 

for values of i from 1 to an arbitrary value. For a signal 

wavelength in the 1520 to 1620 nm range, the first and 

second Raman wavelength ranges would be 1420-1520 nm 

and 1320-1420 nm, respectively, which corresponds to i=1. 

In Some embodiments, information can be transmitted on 

a wavelength in one direction, while providing pump energy 

in the same wavelength in the other direction. For example, 

in newer fibers that have lower loss in the 1400 nm range, 

information could be transmitted in one direction at 1450 nm. 

and pump energy Supplied for Raman gain in the 1550 range 

in the other direction. When allocating the same wavelength 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 19 of 22
US 6,344,922 B1 

11 

for use in both directions, consideration must be given to 

potential Signal degradation due to Rayleighback-Scattering. 

The pump wavelengths in the various Stokes orders are 

Selected Such that the combined Raman gain resulting from 

the pump energy Supplied by each pump wavelength pro 

duces a desired Raman gain Signal variation profile in the 

Signal transmission wavelength ranges. The Raman gain 

Signal variation profile can be uniform or nonuniform, linear 

or nonlinear depending upon a particular application of the 

device 12. In wide band optical Systems, i.e., Signal wave 

length range >30 nm, the Signal varying profile of the 

devices 12 can be used to compensate for loSS Variation of 

the Signal wavelengths, Such as bending loSS Variations, etc. 

The number of pump wavelengths and the wavelength spacing used in the device 12 can be varied to provide 

Raman gain over a range of wavelengths. The pump wavelengths, 2-), pn?are generally Selected to provide Sufficient overlap of the Raman gain profiles to provide 

control over the Raman gain at one or more wavelengths in 

the transmission Signal wavelength range. 

In addition, the pump energy Supplied by at least one of 

the pump wavelengths can be controllably varied to change 

the Signal variation profile over the wavelength range in the 

optical fiber. Also, the total pump energy Supplied via all the 

pump wavelengths can be held constant or varied 

accordingly, while varying the pump energy provided by the 

individual pump wavelengths. One skilled in the art will 

appreciate that the choice of wavelength can be made to 

tailor the Signal varying characteristics of the device 12 to a 

particular System configuration. 

Typically, the pump wavelengths, 21-), are Selected So 

that overall signal variation profile will be substantially 

uniform over the range of wavelengths. One skilled in the art 

will appreciate that decreasing the Spacing intervals of the 

pump wavelengths can provide increased control over the 

uniformity of the intensity profile. For example, pump 

energy could be Supplied in narrow spectral ranges to 

maximize the gain in the Signal wavelengths will minimiz 

ing the gain of the noise wavelength between the Signals. 

However, the increased uniformity and control must be 

balanced with the increased cost of using additional wave 

lengths in the device 12 and allowable total power require 

ments. Conversely, a broadband optical Source can be 

employed to provide pump energy over a broad Spectral 

range of wavelengths, thereby minimizing the required 

number of pumps. 

When a plurality of pump wavelengths are used, it is 

generally necessary to employ cascaded combining arrange 

ment. AS the number of cascaded combining arrangements 

is increased or the range of wavelengths is varied, it may become necessary to employ other arrangements to reduce 

the loSS associated with combining the pump energy. Such 

alternatives can include prism 52 and lens 54 combiners or 

circulator 56/grating 44 multiplexers, Such as shown in 

FIGS. 9 and 10. FIGS. 9(a&b) show the use of a single prism 52 to combine a plurality of pump wavelengths. The plu 

rality of pump wavelengths are focused using either one or 

more lenses 54 at appropriate angles into the prism 52, 

which combines the plurality of pump wavelengths into a 

single beam that is output into optical fiber 30 in the device 

12 or the transmission fiber 28. The difference in the angles 

of incidence is determined based on the refractive indices of 

the prism for each wavelength. 

The difference in the refractive indices for each wave 

length can be used to calculate the angle of incidence on the 

prism for each wavelength. The index of refraction in the 

prism is calculated as: 

5 

15 

25 

35 

40 

45 

50 

55 

60 

65 

where C=22L/180, 0 is the refraction angle, ) is the pump wavelength, and A-E are prism constants. 

For example, a AgGaSea prism (A-E=3.9362, 2.9113, 

0.1507, 1.7954, 1600) can be used to combine two pump wavelengths at 1480 and 1470, respectively. The pump 

wavelengths are transmitted into the prism at angles which 

differ by approximately 0.136 degrees to produce a com 

bined signal exiting the prism 52. One skilled in the art will 

appreciate that combining prisms 52 may also be cascaded 

Similar to couplers and other multiplexing devices to com 

bine additional pump Sources. 

Circulator 56 and grating 44, shown in FIG. 10, are 

typically more expensive than coupler arrangements. 

However, as the number of pump Sources 32, is increased, 

the circulator/grating devices can reduce the loSS associated 

with pump combining. The circulators 56 can be provided with a plurality of ports and corresponding gratings to 

combine the pump wavelengths. One or more circulators 50 

can also be cascaded to provide for more efficient combining of the pump wavelengths. 

The configuration shown in FIG. 3 was used to further 

demonstrate the advantages of the present invention. In one 

example, four pump wavelengths, 1450, 1460, 1485, and 

1495 nm, were combined using two 10 nm DWDM couplers 

and a dichroic filter, which allows the unevenly Spaced 

wavelengths to be effectively combined. The combined 

pump wavelengths were Supplied to DCF to provide Raman 

gain in the transmission signal wavelength range of 1555 to 

1585 nm. 

AS shown in FIG. 11(a), Substantially flat Raman gain Signal variation profiles (t0.16 dB) can be produced over a 

30 nm range for gains ranging from 1 to 8 dB. In addition, 

the relative power of the pump wavelengths Supplied to the 

device 12 can be varied to produce non-linear profiles that 

generally increase or decrease across the Signal wavelength 

range, as shown in FIG. 11(b). Experimental gain profiles were determined for a number 

of additional pump wavelengths. Based on the experimental 

results, Raman Signal varying device Simulations were per 

formed over 35 nm wide (1530–1565 nm) and 100 nm wide 

(1530–1630 nm) signal wavelength ranges. The predicted 

performance of +0.12 dB and +0.342 dB over the 35 nm and 

100 nm wavelength ranges, as shown in FIGS. 12 (curve a) 

and 13, respectively, indicates that the Signal varying 

devices of the present invention can be used over a wide 

range of wavelengths to accommodate numerous channels. 

FIG. 12 (curves band c) also shows examples of linear and 

non-linear profiles that can be produced by varying the 

relative power at the various pump wavelengths. It is also 

expected that the number of pumpS and the pump wave 

length spacing can be further varied to provide a range of 

Signal variation profiles over wide and narrow wavelength 

rangeS. 

The Signal varying devices 12 of the present invention can 

be operated in one, two, or three of the Signal varying modes, 

amplification, attenuation, and lossleSS. By controlling the 

pump power, one signal varying device can be continuously 

transitioned between the three modes of operation. In 

addition, the intensity gain/loSS profile can be adjusted in 

each Signal varying device 12 to dynamically control the 

characteristics of the optical Signals exiting the Signal vary 

ing device 12. It is also possible to operate the Signal varying 

device 12 in more than one mode at the same time. For 

example, the Signal varying device 12 can be operated as an 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 20 of 22
US 6,344,922 B1 

13 

amplifier over part of the Signal wavelength range and as an 

attenuator and/or a lossleSS link over the remaining part of 

the Signal wavelength range. The multiple mode operation of 

the Signal varying device 12 can be used to compensate for 

optical Signals that enter the Signal varying device 12 with 

a non-linear intensity profile. 

Different Signal varying devices 12 can be included in the 

system 10 that are operated with different pump wavelengths 

and powers to provide a cumulative Signal variation profiles differing from the Signal variation profiles of each device 12. 

For example, the pump wavelengths used in different 

devices 12 can be varied to compensate for individual device 

Signal variation profile nonuniformities and provide a cumu 

lative signal variation profile that is Substantially more 

uniform than the individual device profiles. Devices 12 of the present invention provide flexibility in 

the control of the optical system 10, because the power level, 

i.e. amplification and/or attenuation level, can be varied 

without changing the Signal varying profile. Control of the 

individual devices can be performed as is known in the art. 

Alternatively, the devices 12 along the transmission fiber 28 

can be controlled as one or more groups to provide addi 

tional stability in the system 10. An example of such an 

optical control Systems is disclosed in commonly assigned 

U.S. patent Application Ser. No. 09/119,561, which is incor 

porated herein by reference. 

Unlike prior art Systems, the present invention does not 

require that a number of non-linear devices be coordinated 

and controlled to provide linear intensity variation (gain/ loSS) profiles. Instead, the present invention provides an 

optical System incorporating a continuous transition Signal 

varying device that provides increased control over the 

characteristics of optical Signals being transmitted in the 

System. 

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 Signal varying device comprising: 

an optical fiber for transmitting optical signals in at least 

one signal wavelength range and facilitating Raman 

gain in the at least one signal wavelength range, and, 

a first pump Source configured to provide pump energy to 

Said optical fiber in a first Set of Raman wavelengths including a plurality of pump wavelengths having 

Sufficient pump energy to controllably produce Raman 

gain and Signal variation profiles over the at least one 

Signal wavelength range and a Second pump Source 

configured to provide pump energy in at least a Second 

Set of Raman wavelengths to provide Raman gain in the 

first Set of Raman wavelengths in Said optical fiber, 

wherein the pump energy is adjusted to provide Raman 

amplification, attenuation, and lossleSS transmission 

within the Signal wavelength range. 

2. The device of claim 1 wherein said first pump source 

is configured to vary at least one of the pump energy carried 

by at least one of Said pump wavelengths and at least one of 

the pump wavelengths to control the Signal variation pro 

files. 

3. The device of claim 1 wherein said first and second 

pump Source includes pump wavelengths Selected to provide 

a Substantially uniform Signal variation profile over the 

Signal Wavelength range. 

4. The device of claim 1 wherein said optical fiber 

includes at least one doped optical fiber Section ranges 

15 

25 

35 

40 

45 

50 

55 

60 

65 

14 

remotely located from Said first pump Source and Suitable for 

amplifying optical signals in at least one Signal wavelength; 

and, 

Said first pump Source is configured to Supply pump 

energy in pump wavelengths to provide Raman gain in 

Said optical fiber and optically amplify optical Signals 

in said doped fiber. 

5. The device in claim 4 wherein said first pump source 

includes pump wavelengths Selected to provide an adjust 

able overall gain profile over the at least one signal wave 

length range. 

6. The device in claim 4 wherein said optical fiber 

includes at least a portion of transmission fiber in an optical transmission System. 

7. The device in claim 4 wherein said first pump source 

includes pump wavelengths Selected to provide a Substan 

tially uniform Overall gain profile over the Signal wavelength 

range. 

8. The device in claim 4 wherein said first pump source 

includes pump wavelengths Selected to provide different 

Raman and doped fiber gain profiles over the at least one Signal Wavelength range. 

9. The device of claim 4 wherein said doped fiber includes 

at least one erbium doped fiber. 

10. The device of claim 9 wherein said first pump source 

is controllable to provide a Raman gain profile that Substan 

tially compensates for gain non-uniformities introduced by Said at least one erbium doped fiber. 

11. The device of claim 4 further comprising at least one 

wavelength Selective reflector positioned to reflect a portion of the pump energy from at least one pump wavelength back 

toward Said first pump Source. 

12. The device of claim 11 wherein said at least one 

wavelength Selective reflectors includes at least one fiber 

Bragg grating positioned to reflect the portion of the at least 

one pump wavelength before reaching Said doped fiber. 

13. The device of claim 10 wherein said first pump source 

is configured to Supply pump energy in at least one wave 

length that is not absorbed by said doped fiber and to provide 

Raman gain in Said optical fiber. 

14. The device of claim 1 wherein said first pump source 

is remotely located from said optical fiber and delivers the 

pump energy to Said optical fiber via a separate pump path. 

15. The device of claim 1 wherein said optical fiber 

includes first and second Raman fiber, said first Raman fiber 

having different Raman gain characteristics than Said Second 

optical fiber; and, 

Said first pump Source is configured to provide pump 

energy in Raman wavelengths to Said first and Second 

Raman fibers. 

16. The device of claim 1 wherein said first Raman fiber 

includes optical fibers having a Smaller core than Said 

Second Raman fiber. 

17. The device of claim 16 wherein said first pump source 

is configured to provide a common Source of pump energy 

to Said first and Second Raman fibers. 

18. The device of claim 17 wherein said second Raman 

fiber provides for low loss in the 1420 to 1510 nm range and 

pump energy is transmitted through Said Second Raman fiber 

to said first Raman fiber. 

19. The device of claim 16 wherein said first pump source 

is configured to provide different Raman pump wavelengths 

to said first Raman fiber and said second Raman fiber. 

20. The device of claim 1 wherein said second set of 

Raman wavelengths is counter-propagated in Said optical 

fiber relative to the first set of Raman wavelengths. 

21. The device of claim 1 wherein said pump source 

includes a third Set of Raman wavelengths to provide Raman 

gain to the Second Set of Raman wavelengths. 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 21 of 22
US 6,344,922 B1 

15 

22. The device of claim 1 wherein a portion of said optical fiber provides for distributed Raman gain and another por 

tion of Said optical fiber provides for concentrated Raman 

gain. 

23. The device of claim 22 further comprising a gain flattening filter positioned to impart a Signal variation profile 

over at least a portion of at least one signal wavelength 

range. 

24. The device of claim 1 wherein said first pump wavelengths are Selected to provide a cumulative signal variation profile over the Signal wavelength range having a 

variation of <+1 dB. 

25. The device of claim 1 wherein the signal wavelength 

range includes at least a portion of 1240 nm to 1650 nm. 

26. The device of claim 1 wherein said optical fiber is 

Suitable for transmitting a plurality of Signal wavelength 

ranges; and, 

at least one of Said first and Second pump Sources is 

configured to provide a plurality of pump wavelength 

interleaved with the plurality of Signal wavelength 

ranges and having Sufficient pump energy to produce 

Raman gain in a plurality of Signal varying profiles in 

the plurality of Signal wavelength ranges. 

27. The device of claim 1 including a controller config 

ured to control the pump energy Supplied by at least one of 

Said first pump wavelengths to produce an adjustable Signal 

variation profile over the wavelength range in Said optical 

fiber. 

28. The device of claim 1 wherein said first pump source 

includes pump wavelengths Selected to control the overall 

gain profile over the Signal wavelength range and each pump 

wavelength provides pump energy within ten percent of the 

average pump energy Supplied by the pump wavelengths. 

29. An optical transmission System comprising: 

a plurality of optical processing nodes optically connected 

to pass optical signals between Said processing nodes, 

and, 

at least one signal varying device positioned to vary the 

optical Signals passing between Said processing nodes, 

wherein Said Signal varying device includes an optical fiber Suitable for transmitting optical Signals in at least 

one signal wavelength range and facilitating Raman 

gain in the at least one signal wavelength range; 

a first pump Source configured to provide pump energy to 

Said optical fiber in a first Set of Raman wavelengths including a plurality of pump wavelengths having 

Sufficient pump energy to controllably produce Raman 

gain and a plurality of Signal variation profiles over the 

at least one signal wavelength range and a Second pump 

Source configured to provide pump energy in at least a 

Second Set of Raman wavelengths to provide Raman 

gain in the first Set of Raman wavelengths in Said 

optical fiber, wherein the pump energy is adjusted to 

provide Raman amplification, attenuation, and lossleSS 

transmission within the Signal wavelength range. 

15 

25 

35 

40 

45 

50 

16 

30. The system of claim 29 wherein: 

Said at least one signal varying device is disposed along 

optical transmission fiber interconnecting Said plurality 

of optical nodes, 

Said optical fiber includes: 

a distributed Raman fiber including at least a portion of 

Said optical transmission fiber, 

a concentrated Raman fiber having a Smaller core than 

Said transmission fiber, and 

an erbium doped fiber; and, 

Said first pump Source includes 

a first Raman pump Source configured to transmit pump 

energy counter-directionally to the optical Signals 

and produce Raman gain and a first Raman Signal 

varying profile in Said distributed Raman fiber, 

a Second Raman pump Source configured to transmit 

pump energy counter-directionally to the optical 

Signals and Raman gain and a Second Raman Signal 

varying profile in Said concentrated Raman fiber, and 

a erbium pump Source configured to provide optical 

gain and an erbium Signal varying profile in Said 

erbium doped fiber. 

31. The system of claim 29 wherein said first pump 

Sources are configured to provide pump energy to Said fiber 

in a direction counter-propagating to the optical signal. 

32. A computerized method of controlling Signal variation 

in an optical fiber comprising: 

providing an optical fiber Suitable for transmitting optical 

Signals in at least one Signal wavelength range and 

facilitating Raman gain in the at least one signal wavelength range; 

coupling a first pump Source to the fiber to provide pump 

energy in a first Set of Raman wavelengths including a 

plurality of pump wavelengths having Sufficient pump 

energy to produce Raman gain in the optical Signal 

according to a signal variation profile in the Signal 

wavelength range and a Second pump Source config 

ured to provide pump energy in at least a Second Set of 

Raman wavelengths to provide Raman gain in the first 

Set of Raman wavelengths in Said optical fiber; 

monitoring characteristics of the optical Signals in a signal wavelength range passing through the optical fiber; 

and, 

controlling the pump energy Supplied by the at least one 

of the first and Second pump Sources in at least one of 

the pump wavelengths to vary the Signal variation 

profile and Raman gain to provide Raman 

amplification, attenuation, and lossleSS transmission 

Over the Signal wavelength range in the optical fiber. 

33. The device of claim 1, wherein said second pump 

Source is positioned remotely from Said first pump Source. 

k k k k k 

Case 6:20-cv-00484-ADA Document 1-3 Filed 06/02/20 Page 22 of 22