Optical system and method for compensating for signal loss - Patents.com

Abstract

To provide an optical system and method for compensating for signal loss.SOLUTION: An optical system includes a forward and a backward Raman pump module positioned along a transmission fiber; and a noise matrix computing module configured to: determine, for first gains of the optical signal, a first noise associated with the first gain of the forward Raman pump module; determine, for second gains of the optical signal, a second noise associated with the second gain of the backward Raman pump module; generate a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and ii) the second noise for each second gain of the backward Raman pump module; identify a span loss of the optical signal as the optical signal is transmitted along the transmission fiber; identify a combination of a particular first gain of the forward Raman pump module and a particular second gain of the backward Raman pump module.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates generally to optical communication networks, and more specifically to optical systems that compensate for signal loss. [Background technology]

[0002] Telecommunications, cable television, and data communication systems use optical networks to carry large amounts of information between remote locations at restrictively high speeds. In optical network systems, information is carried in the form of optical signals through optical fibers. Optical fibers may have thin strands of glass capable of sending signals over long distances. Optical networks often use modulation schemes to carry information in optical signals over optical fibers. Such modulation schemes may include phase shift keying (PSK), frequency shift keying (FSK), amplitude shift keying (ASK), and quadrature amplitude modulation (QAM). Optical networks may also include various optical elements such as amplifiers, dispersion compensators, multiplexer / demultiplexer fibers, wavelength selective switches (WSS), optical switches, couplers, etc., to perform various operations within the network.

[0003] Erbium-doped fiber amplifiers (EDFAs) are widely used in optical systems, but EDFAs can have internal noise characteristics that can impede longer distance (e.g., greater than 80 kilometers) optical transmission of advanced modulation formats such as 256QAM. Summary of the Invention

[0004] An innovative aspect of the subject matter described herein is an optical system for compensating for signal loss, the system comprising: a transmission fiber transmitting a WDM input optical signal; a forward Raman pump module located along the transmission fiber; a backward Raman pump module located along the transmission fiber; and a noise matrix calculation module, the noise matrix calculation module determining, for one or more first gains of the optical signal, a first noise associated with the first gain of the forward Raman pump module, and determining, for one or more second gains of the optical signal, a second noise associated with the second gain of the backward Raman pump module, generating a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and i) the second noise for each second gain of the backward Raman pump module, determining a span loss of the optical signal when the optical signal is transmitted along the transmission fiber, and the forward Raman pump module and the backward Raman pump module are configured to determine a combination of a specific first gain of the forward Raman pump module and a specific second gain of the backward Raman pump module based on a gain ratio of the forward Raman pump module and the backward Raman pump module, the forward Raman pump module and the backward Raman pump module compensate for the span loss of the optical signal based on the combination of the specific first gain of the forward Raman pump module and the specific second gain of the backward Raman pump module, and the gain ratio between the specific first gain of the forward Raman pump module and the specific second gain of the backward Raman pump module may be embodied in an optical system including a minimum cumulative noise combination of the first noise and the second noise of the optical signal based on a noise matrix.

[0005] Other embodiments of such aspects include corresponding methods, apparatus, and computer programs encoded on computer storage devices and configured to perform the operations of the methods.

[0006] These and other embodiments may each optionally include one or more of the following features: For example, the optical system further comprises an optical amplifier located along the transmission fiber and a receiver configured to receive the optical signal, and the noise matrix calculation module is further configured to determine, for one or more third gains of the optical signal, a third noise associated with the third gain of the optical amplifier, generate the noise matrix based on i) the first noise for each first gain of the forward Raman pump module, ii) the second noise for each second gain of the backward Raman pump module, and iii) the third noise for each third gain of the optical amplifier, identify a receiver sensitivity of the receiver, and identify a combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier based on the noise matrix and the receiver sensitivity, and the backward Raman pump module and the optical amplifier compensate the receiver sensitivity of the receiver based on the combination of the specific second gain of the backward Raman pump module and the specific third gain of the optical amplifier. A gain ratio between the specific second gain of the backward Raman pump module and the specific third gain of the optical amplifier comprises a minimum cumulative noise combination of the second noise and the third noise of the optical signal based on a noise matrix. The optical amplifier is an EDFA.The optical system further comprises a further transmission fiber transmitting the optical signal, a further forward Raman pump module located along the further transmission fiber, and a further backward Raman pump module located along the further transmission fiber, wherein the noise matrix calculation module determines, for one or more third gains of the optical signal, a third noise associated with the third gain of the further forward Raman pump module, and for one or more fourth gains of the optical signal, a fourth noise associated with the fourth gain of the further backward Raman pump module, and generates a noise matrix based on i) the third noise for each third gain of the further forward Raman pump module and ii) the fourth noise for each fourth gain of the further backward Raman pump module, The optical signal is further configured to determine a further span loss when transmitted, and to determine a combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module based on the noise matrix and the further span noise, wherein the further forward Raman pump module and the further backward Raman pump module compensate for the further span loss of the optical signal based on the combination of the specific third gain of the further forward Raman pump module and the specific fourth gain of the further backward Raman pump module, and a gain ratio between the specific third gain of the further forward Raman pump module and the specific fourth gain of the further backward Raman pump module includes a minimum cumulative noise combination of the third noise and the fourth noise of the optical signal based on the noise matrix.

[0007] The optical system further comprises an optical amplifier located along the further transmission fiber and a receiver configured to receive the optical signal, the noise matrix calculation module is further configured to determine a fifth noise associated with the fifth gain of the optical amplifier for one or more fifth gains of the optical signal, generate a noise matrix based on i) the third noise for each third gain of the further forward Raman pump module, ii) the fourth noise for each fourth gain of the further backward Raman pump module, and iii) the fifth noise for each fifth gain of the optical amplifier, identify a receiver sensitivity of the receiver, and identify a combination of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier based on the noise matrix and the receiver sensitivity, the further backward Raman pump module and the optical amplifier compensate for said receiver sensitivity of the receiver based on the combination of the fourth gain of the further backward Raman pump module and the fifth gain of the optical amplifier. The gain ratio between the specific fourth gain of the further backward Raman pump module and the specific fifth gain of the optical amplifier comprises a minimum cumulative noise combination of the fourth noise and the fifth noise of the optical signal based on the noise matrix. The span loss is about 20 dB. The receiver sensitivity is about 10 dB.

[0008] For a more complete understanding of the present invention and its features and advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram of selected elements of an embodiment of an optical network. [Diagram 2] 1 is a block diagram of selected elements of an embodiment of an optical system for compensating for signal loss in an optical network. [Diagram 3] 2 depicts a graph of the signal power of an optical signal as the optical signal is transmitted along a transmission fiber of an optical system. [Figure 4] 2 depicts a graph of the signal power of an optical signal as the optical signal is transmitted along a transmission fiber of an optical system. [Diagram 5]1 depicts noise matrices for a forward Raman pump module, a backward Raman pump module, and an optical amplifier of an optical system. [Figure 6] 1 is a graph illustrating noise for a forward Raman pump module and a rear Raman pump module of an optical system. [Figure 7] 1 is a graph illustrating noise for a rear Raman pump module and an optical amplifier of an optical system. [Figure 8] 1 is a flow chart for compensating for signal loss in an optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following description, details are provided as examples to aid in the discussion of the disclosed subject matter, and those skilled in the art will appreciate that the disclosed embodiments are examples and do not exhaustively cover all possible embodiments.

[0011] Throughout this disclosure, hyphenated reference numbers refer to particular instances of elements, and non-hyphenated reference numbers refer to elements generically or collectively. Thus, as an example (not shown in the drawings), device "12-1" refers to an instance of a device class, the device classes may be collectively referred to as device "12," and any one of the device classes may be collectively referred to as device "12." In the drawings and description, like numbers are intended to represent like elements.

[0012] Referring now to the drawings, Figure 1 illustrates an example embodiment of an optical network 101, which may represent an optical communication system. The optical network 101 may include one or more optical fibers 106 that carry one or more optical signals exchanged by components of the optical network 101. The network elements of the optical network 101 coupled by the fibers 106 may include one or more transmitters 102, one or more multiplexers (MUX) 104, one or more optical amplifiers 108, one or more optical add / drop multiplexers (OADMs) 110, one or more demultiplexers (DEMUX) 105, and one or more receivers 112.

[0013] The optical network 101 may comprise a point-to-point optical network with terminal nodes, a ring optical network, a mesh optical network, or any other suitable optical network or combination of optical networks. The optical network 101 may be used in a short-haul metropolitan network, a long-haul intercity network, or any other suitable network or combination of networks. The capacity of the optical network 101 may be, for example, 100 Gbit / s, 400 Gbit / s, or 1 Tbit / s. The optical fiber 106 comprises a thin strand of glass capable of communicating signals over long distances with very low loss. The optical fiber 106 may comprise any suitable type of fiber selected from a wide variety of fibers for optical transmission. The optical fiber 106 may include any suitable type of fiber, such as Single-Mode Fiber (SMF), Enhanced Large Effective Area Fiber (E-LEAF), or TrueWave® Reduced Slope (TW-RS) fiber.

[0014] Optical network 101 may include devices that transmit optical signals over optical fibers 106. Information may be transmitted and received through optical network 101 by modulation of one or more wavelengths of light to encode information in the wavelengths. In optical networking, wavelengths of light may also be referred to as channels contained in the optical signals. Each channel may carry a certain amount of information through optical network 101.

[0015] To increase the information capacity and transmission capacity of the optical network 101, multiple signals transmitted on multiple channels may be combined into a single wideband optical signal. The process of communicating information on multiple channels is called wavelength division multiplexing (WDM) in optics. Coarse wavelength division multiplexing (CWDM) refers to the multiplexing of widely spaced wavelengths with a small number of channels (typically spacing greater than 20 nm and fewer than 16 wavelengths). Dense wavelength division multiplexing (DWDM) refers to the multiplexing of closely spaced wavelengths with a large number of channels (typically spacing less than 0.8 nm and more than 40 wavelengths) into a fiber. WDM or other multi-wavelength multiplexing transmission techniques are used in optical networks to increase the aggregate bandwidth per optical fiber. Without WDM, the bandwidth in an optical network may be limited to the bit rate of just one wavelength. With more bandwidth, optical networks are able to transmit greater amounts of information. Optical network 101 may transmit the separate channels using WDM or any other suitable multi-channel multiplexing technique and may amplify the multi-channel signal.

[0016] The optical network 101 may include one or more optical transmitters (Tx) 102 that transmit optical signals at a particular wavelength or channel through the optical network 101. The transmitters 102 may include a system, apparatus, or device that converts an electrical signal to an optical signal and transmits the optical signal. For example, the transmitters 102 may each include a laser and a modulator that receives an electrical signal and modulates the information contained in the electrical signal onto a beam of light generated by the laser at a particular wavelength, and transmits the beam to carry the signal through the optical network 101.

[0017] The multiplexer 104 may be coupled to the transmitter 102 and may be a system, apparatus, or device that combines the signals transmitted by the transmitter 102, for example at each individual wavelength, into a WDM signal.

[0018] The optical amplifier 108 may amplify the multi-channeled signals within the optical network 101. The optical amplifier 108 may be located before or after a length of the fiber 106. The optical amplifier 108 may include a system, apparatus, or device that amplifies an optical signal. For example, the optical amplifier 108 may include an optical repeater that amplifies the optical signal. This amplification may be performed with optical-to-electrical or electrical-to-optical conversion. In some embodiments, the optical amplifier 108 may include an optical fiber that is doped with a rare earth element to form a doped fiber amplifying element. As the signal passes through the fiber, external energy may be applied in the form of an optical pump to excite atoms in the doped portion of the optical fiber. This increases the strength of the optical signal. As an example, the optical amplifier 108 may include an erbium-doped fiber amplifier (EDFA).

[0019] OADM 110 may be coupled to optical network 101 via fiber 106. OADM 110 comprises an add / drop module. An add / drop module may include a system, apparatus, or device that adds and drops optical signals (e.g., at individual wavelengths) from fiber 106. After passing through OADM 110, the optical signal may travel directly along fiber 106 to its destination, or the signal may be passed through one or more further OADMs 110 and optical amplifiers 108 before reaching its destination.

[0020] In one embodiment of optical network 101, OADM 110 may represent a reconfigurable OADM (ROADM) capable of adding or dropping individual or multiple wavelengths of a WDM signal. Individual or multiple wavelengths may be added or dropped in the optical domain using, for example, a wavelength selective switch (WSS) that may be included in the ROADM. A ROADM is considered 'colorless' if it can add / drop any arbitrary wavelength. A ROADM is considered 'directionless' if it can add / drop any wavelength, regardless of the direction of propagation. A ROADM is considered 'contentionless' if it can switch any competing wavelength (wavelength already occupied) to any other available wavelength.

[0021] 1, optical network 101 may also include one or more demultiplexers 105 at one or more destinations of network 101. Demultiplexer 105 may include a system, apparatus, or device that acts as a demultiplexer by splitting a single composite WDM signal into individual channels at each wavelength. For example, optical network 101 may transmit and carry a 40-channel DWDM signal. Demultiplexer 105 may split the single 40-channel DWDM signal into 40 separate signals according to the 40 different channels.

[0022] 1, optical network 101 may also include receivers 112 coupled to demultiplexer 105. Each receiver 112 may receive an optical signal transmitted at a particular wavelength or channel and may process the optical signal to obtain (e.g., demodulate) information (i.e., data) contained in the optical signal. Accordingly, network 101 may include at least one receiver 112 for each channel of the network.

[0023] Optical networks, such as the optical network 101 of FIG. 1, may use modulation techniques to carry information in optical signals over optical fibers. Such modulation schemes may include phase-shift keying (PSK), frequency-shift keying (FSK), amplitude-shift keying (ASK), and quadrature amplitude modulation (QAM), among other example modulation techniques. In PSK, the information carried by the optical signal may be conveyed by modulating the phase of a reference signal, also known as a carrier wave or simply a carrier. Information may be conveyed by modulating the phase of the signal itself using two-level or binary phase-shift keying (BPSK), four-level or quadrature phase-shift keying (QPSK), multilevel phase-shift keying (M-PSK), and differential phase-shift keying (DPSK). In QAM, the information carried by the optical signal may be conveyed by modulating both the amplitude and phase of a carrier wave. PSK may be considered a subset of QAM, in that the amplitude of the carrier wave is kept constant.

[0024] In addition, polarization division multiplexing (PDM) techniques may be capable of achieving higher bit rates for information transmission. PDM transmission involves independently modulating information onto various polarization components of an optical signal associated with a channel. In this way, each polarization component can carry a separate signal simultaneously with the other polarization components, allowing the bit rate to be increased according to the number of distinct polarization components. The polarization of an optical signal may describe the direction of vibration of the optical signal. The term "polarization" generally refers to the path followed by the tip of the electric field vector at a point in space, which is perpendicular to the direction of propagation of the optical signal.

[0025] In an optical network, such as the optical network 101 of FIG. 1, it is common to refer to a management plane, a control plane, and a transport plane (sometimes referred to as the physical layer). A central management host (not shown) may reside in the management plane and may configure and supervise the components of the control plane. The management plane includes the ultimate control over all transport plane and control plane entities (e.g., network elements). By way of example, the management plane may consist of a central processing center (e.g., a central management host) that includes one or more processing resources, data storage components, and the like. The management plane may be in electrical communication with the elements of the control plane and may also be in electrical communication with one or more network elements of the transport plane. The management plane may perform management functions for the entire system and provide coordination between the network elements, the control plane, and the transport plane. By way of example, the management plane may include an element management system (EMS) that handles one or more network elements from an element perspective, a network management system (NMS) that handles many devices from a network perspective, and an operational support system (OSS) that handles network-wide operations.

[0026] Modifications, additions, or omissions may be made to optical network 101 without departing from the scope of the present disclosure. For example, optical network 101 may include more or fewer elements than depicted in Figure 1. Also, as described above, although depicted as a point-to-point network, optical network 101 may have any suitable network topology for transmitting optical signals, such as a ring, mesh, or hierarchical network topology.

[0027] As mentioned above, the amount of information that can be transmitted over an optical network can vary depending on the number of optical channels that are encoded with information and multiplexed into one signal. Thus, an optical fiber using WDM signals can carry more information than an optical fiber carrying information on a single channel. In addition to the number of channels and polarization components carried, another factor that influences how much information can be transmitted over an optical network can be the bit rate of the transmission. The higher the bit rate, the greater the amount of information that can be transmitted. Achieving higher bit rates can be limited by the availability of high bandwidth driver and digital signal processor technologies for transmission over the optical network 101 and by increasing optical signal to noise ratio (OSNR).

[0028] Current designs of optical amplifiers may include optical phase-sensitive amplifiers (PSAs). A typical phase-sensitive optical amplifier has different stages including an idler stage that first generates an idler signal using an optical pump, and an amplifier stage that amplifies the input signal using the optical pump and the idler signal. Between the idler stage and the amplifier stage, an intermediate stage may be implemented in the phase-sensitive optical amplifier. The intermediate stage may include multiple signal processing and pump power recovery to adjust the power levels of the input signal and the idler signal. In a typical phase-sensitive optical amplifier, the optical paths of the input signal, the optical pump, and the idler signal may be separated in the intermediate stage to independently modulate the power of each signal.

[0029] 2 illustrates an optical system 200 for compensating for signal loss. The optical system 200 may include transmission fibers 202a, 202b, 202c (collectively referred to as transmission fibers 202), forward Raman pump modules 204a, 204b, 204c (collectively referred to as forward Raman pump modules 204), backward Raman pump modules 206a, 206b, 206c (collectively referred to as backward Raman pump modules 206), a transmitter 208, a receiver 210, an optical amplifier 212, and a noise matrix calculation module 213. The noise matrix calculation module 213 may be in communication with one or more of the forward Raman pump modules 204 and the backward Raman pump modules 206. The optical system 200 may include any portion or all of the optical network 101.

[0030] The transmitter 208 can transmit a wavelength division multiplexed (WDM) input optical signal 220 along the transmission fiber 202. Each of the transmission fibers 202 can be associated with a span loss. In some examples, the span loss is about 20 dB. The forward Raman pump module 204 and the backward Raman pump module 206 can compensate for the span loss of the optical signal 220 as it is transmitted along the transmission fiber 202.

[0031] FIG. 3 illustrates an example graph 300 of the signal power of the optical signal 220 as it is transmitted along the transmission fiber 202. Specifically, the X-axis represents the length of each transmission fiber 202 (e.g., 80 km range for each transmission fiber 202), and the Y-axis represents the signal power of the optical signal 220 (e.g., -1 dB to -21 dB). In the illustrated example, portion 302 corresponds to transmission fiber 202a, portion 304 corresponds to transmission fiber 202b, and portion 306 corresponds to transmission fiber 202c. FIG. 4 illustrates an example graph 400 in which, for each transmission fiber 202, the forward Raman pump module 204 amplifies the optical signal 220 for the first portion 402 (e.g., 20-30 km) of the transmission fiber 202, and the backward Raman pump module 206 amplifies the optical signal 220 for the last portion 404 (e.g., 20-30 km) of the transmission fiber 202.

[0032] Returning to FIG. 2 , each forward Raman pump module 204 and each backward Raman pump module 206 may be associated with a respective gain for the optical signal. In some examples, the respective gains of the forward Raman pump modules 204 are approximately the same, and the respective gains of the backward Raman pump modules 206 are approximately the same. In some examples, the gain of one or more of the forward Raman pump modules 204 is different from the gain of the remaining forward Raman pump modules 204, and the gain of one or more of the backward Raman pump modules 206 is different from the gain of the remaining backward Raman pump modules 206. In some examples, the forward Raman pump module 204 avoids relative intensity noise (RIN) from the pump module 204 to the optical signal 220 by providing digital signal processing (DSP) RIN mitigation on the pilot tones.

[0033] The noise matrix calculation module 213 may determine, for each forward Raman pump module 204, a noise associated with one or more gains of the optical signal 220. Similarly, the noise matrix calculation module 213 may determine, for each backward Raman pump module 206, a noise associated with one or more gains of the optical signal 220. The noise matrix calculation module 213 may generate a noise matrix based on i) the noise for each gain of the forward Raman pump module 204 and the noise for each gain of the backward Raman pump module 206.

[0034] 5 illustrates a noise matrix 500 for the forward Raman pump module 204 and the backward Raman pump module 206. The noise matrix 500 illustrates, for a particular gain (dB), the noise generated by each of the forward Raman pump module 204 and the backward Raman pump module 206 for such particular gain. The noise is expressed as a linear noise amount (×10 -9 ).

[0035] Returning to FIG. 2 , the noise matrix calculation module 213 can determine a span loss of the optical signal 220 as it is transmitted along the transmission fiber 202. The noise matrix calculation module 213 can determine a combination of gains of the forward Raman pump module 204 and the backward Raman pump module 206 based on the noise matrix 500 to compensate for the span loss. Specifically, for each transmission fiber 202, the combination of gains of the forward Raman pump module 204 and the backward Raman pump module 206 for that transmission fiber 202 compensates for the span loss of the optical signal 220 as it is transmitted down the transmission fiber 202. Furthermore, for a particular transmission fiber 202, a gain ratio between the gain of the forward Raman pump module 204 and the gain of the backward Raman pump module 206 is determined for minimum cumulative noise of the optical signal 220 based on the noise matrix 500. In other words, the gain ratio between the gain of the forward Raman pump module 204 and the gain of the backward Raman pump module 206 is determined such that accumulated noise is minimized while compensating for span losses in the optical signal 220 as the optical signal is transmitted along the transmission fiber 202.

[0036] 6 illustrates a graph 600 that represents the noise for a matrix 500 of forward and backward Raman pump modules 204 and 206, as well as the total noise (the combination of the noise of the forward and backward Raman pump modules 204 and 206). Specifically, graph 600 represents the noise for matrix 500 for each combination of gain values ​​for a particular total gain (based on the span loss of optical signal 220). For example, for a span loss of 20 dB, graph 600 represents combinations of gain values ​​of forward Raman pump module 204 (represented by axis 680) and backward Raman pump module 206 (represented by axis 682) that result in a total gain that is equal to or close to the span loss of 20 dB. That is, for the noise associated with each gain value of the forward Raman pump module 204 shown by line 602 and displayed in graph 600, the noise for the corresponding gain value of the backward Raman pump module 206 shown by line 604 and displayed in graph 600 results in a total noise shown by line 606. For example, graph 600 represents the noise of a first gain value combination of 13 dB for the forward Raman pump module 204 (shown by point 610 for corresponding value 510 in matrix 500) and 7 dB for the backward Raman pump module 206 (shown by point 612 for corresponding value 512 in matrix 500) for a total gain of 20 dB (13 dB for the forward Raman pump module 204 and 7 dB for the backward Raman pump module 206). The total noise for a first gain value combination (associated with points 610 and 612) is shown at point 613 for the noise associated with a 13 dB gain for the forward Raman pump module 204 and a 7 dB gain for the rear Raman pump module 206. For example, graph 600 shows a noise associated with a 12 dB gain for the forward Raman pump module 204 (as shown by point 620 for corresponding value 520 in matrix 500) and a 8 dB gain for the rear Raman pump module 206 (as shown by point 622 for corresponding value 522 in matrix 500) for a total gain of 20 dB (12 dB for the forward Raman pump module 204 and 8 dB for the rear Raman pump module 206).Graph 600 represents the noise for a second gain value combination with 12 dB gain for the forward Raman pump module 204 and 8 dB gain for the rear Raman pump module 206. The total noise for the second gain value combination (associated with points 620 and 622) is shown at point 623 for the noise associated with 12 dB gain for the forward Raman pump module 204 and 8 dB gain for the rear Raman pump module 206. Graph 600 represents further total noise for various gain value combinations, such as 11 dB for the forward Raman pump module 204 and 9 dB for the rear Raman pump module 206, etc.

[0037] To that end, the noise matrix calculation module 213 identifies a combination of 12 dB gain in the forward Raman pump module 204 and 8 dB gain in the backward Raman pump module 206 that minimizes the accumulated noise in the optical signal 220 (e.g., the lowest total noise as shown by line 606) based on the noise matrix 500 and the graph 600 for a span loss of 20 dB. For example, the noise associated with a 12 dB gain in the forward Raman pump module 204 is 2.39×10 -9 and the noise associated with 8 dB gain of the rear Raman pump module 206 is 2.39×10 -9 , resulting in a total noise of 4.78 × 10 -9 This is the minimum noise for 20 dB gain that compensates for the 20 dB span loss of optical signal 220 as it is transmitted along transmission fiber 202.

[0038] Additionally, the optical amplifier 212 may be associated with a gain of the optical signal 220. In some examples, the optical amplifier 212 is an erbium-doped fiber amplifier (EDFA). Returning to FIG. 3, a graph 300 represents the gain of the optical signal 220 near an end 310 of the transmission fiber 202c. Specifically, the receiver 210 may be associated with a receiver sensitivity, for example, 10 dB. At the receiver 210, the optical signal 220 may be converted to an electrical signal. The optical amplifier 212 increases the gain of the optical signal 220 to aid in such conversion. In some examples, the optical amplifier 212 is a phase-sensitive amplifier.

[0039] The noise matrix calculation module 213 can determine a noise associated with one or more gains of the optical signal 220 for the optical amplifier 212. The noise matrix calculation module 213 can generate a noise matrix based on i) the noise for each gain of the forward Raman pump module 204, ii) the noise for each gain of the backward Raman pump module 206, and iii) the noise for each gain of the optical amplifier 212. Specifically, FIG. 5 illustrates a noise matrix 500 for the forward Raman pump module 204, the backward Raman pump module 206, and the optical amplifier 212. The noise matrix 500 represents, for a particular gain (dB), the noise generated by each of the forward Raman pump module 204, the backward Raman pump module 206, and the optical amplifier 212 for such particular gain. The noise is calculated by dividing the noise matrix by a linear noise amount (×10 -9 ).

[0040] The noise matrix calculation module 213 can determine the receiver sensitivity of the receiver 210. The noise matrix calculation module 213 can determine a combination of the gain of the backward Raman pump module 206 and the gain of the optical amplifier 212 to compensate the receiver sensitivity of the receiver 210 based on the noise matrix 500. Specifically, for the transmission fiber 202c, the combination of the gain of the backward Raman pump module 206c and the gain of the optical amplifier 212 compensates the receiver sensitivity. Furthermore, for the transmission fiber 202c, the gain ratio between the gain of the backward Raman pump module 206c and the gain of the optical amplifier 212 is determined for the minimum cumulative noise of the optical signal 220 based on the noise matrix 500. In other words, the gain ratio between the gain of the backward Raman pump module 206c and the gain of the optical amplifier 212 is determined such that one or more cumulative noises of the optical signal 220 are minimized while compensating the receiver sensitivity.

[0041] For example, FIG. 7 illustrates a graph 700 that graphically represents the noise for the matrix 500 of the backward Raman pump module 206c and the optical amplifier 212, as well as the total noise (the combination of the noise of the backward Raman pump module 206 and the optical amplifier 212). Specifically, the graph 700 illustrates the noise for the matrix 500 for each combination of gain values ​​for a particular total gain (based on the span loss of the optical signal 220). As previously determined, the forward Raman pump module 204c has a gain of 12 dB (based on the span loss of the optical signal 220). Therefore, the gain of the backward Raman pump module 206c and the optical amplifier 212 is the remaining gain required based on the total gain (i.e., the total gain is the span loss of the optical signal 220 and the receiver sensitivity of the receiver 210). For example, if the span loss is 20 dB and the receiver sensitivity is 10 dB, then the total gain required for the transmission fiber 202c is 30 dB. The forward Raman pump module 204c is associated with a gain of 12 dB, and the remaining gain that needs to be provided by the backward Raman pump module 206c and the optical amplifier 212 is 18 dB.

[0042] That is, for the noise associated with each gain value of the backward Raman pump module 206 shown by line 702 and displayed in graph 700, the noise for the corresponding gain value of the optical amplifier 212 shown by line 704 and displayed in graph 700, results in a total noise shown by line 706. For example, for a total residual gain of 18 dB, graph 700 represents combinations of gain values ​​of the backward Raman pump module 206c (shown by axis 782) and gain values ​​of the optical amplifier 212 (shown by axis 782) such that the total gain is equal to or close to the total residual gain of 18 dB. For example, graph 700 represents the noise for a first gain value combination of 13 dB for the backward Raman pump module 206c (as shown by point 710 for corresponding value 550 in matrix 500) and 5 dB for the optical amplifier 212 (as shown by point 712 for corresponding value 552 in matrix 500) for a total gain of 18 dB (13 dB for the backward Raman pump module 206c and 5 dB for the optical amplifier 212). The total noise for the first gain value combination (associated with points 710 and 712) is shown at point 713 for the noise associated with the 13 dB gain for the backward Raman pump module 206c and the 5 dB gain for the optical amplifier 212. For example, graph 700 represents the noise for a second gain value combination of 12 dB for the backward Raman pump module 206c (as shown by point 720 for corresponding value 560 of matrix 500) and 6 dB for the optical amplifier 212 (as shown by point 722 for corresponding value 562 of matrix 500) for a total gain of 18 dB (12 dB for the backward Raman pump module 206c and 6 dB for the optical amplifier 212). The total noise for the second gain value combination (associated with points 720 and 722) is shown at point 723 for the noise associated with the 12 dB gain for the backward Raman pump module 206c and the 6 dB gain for the optical amplifier 212. Graph 700 represents further total noise for various gain value combinations, such as 11 dB for the backward Raman pump module 206c and 7 dB for the optical amplifier 212, etc.

[0043] To that end, the noise matrix calculation module 213 identifies a combination of 12 dB gain in the backward Raman pump module 206c and 6 dB gain in the optical amplifier 212 that minimizes the accumulated noise in the optical signal 220 (e.g., the lowest total noise as shown by line 706) based on the noise matrix 500 and the graph 700 for the remaining total gain of 18 dB. For example, the noise associated with a 12 dB gain in the backward Raman pump module 206c is 7.22×10 -9 and the noise associated with 6 dB gain of the optical amplifier 212 is 7.22×10 -9 , resulting in a total noise of 14.44 × 10 -9 This is the minimum noise for a remaining total gain of 18 dB that compensates for at least a portion of the span loss of the optical signal 220 and the receiver sensitivity of the receiver 210.

[0044] In some examples, for a transmission fiber 202a, the combination of the gains of the forward Raman pump module 204a and the backward Raman pump module 206a compensates for the span loss of the optical signal 220 along the transmission fiber 202a. Furthermore, for a transmission fiber 202a, the gain ratio between the gain of the forward Raman pump module 204a and the gain of the backward Raman pump module 206a is determined such that the accumulated noise of the optical signal 220 along the transmission fiber 202a is minimized while compensating for the span loss of the optical signal 220 when the optical signal 220 is transmitted along the transmission fiber 202a. As shown by the noise matrix 500, when the span loss is 20 dB along the transmission fiber 202a, the combination of the 12 dB gain of the forward Raman pump module 204a and the 8 dB gain of the backward Raman pump module 206a compensates for the 20 dB span loss while minimizing the accumulated noise of the optical signal 220.

[0045] For the transmission fiber 202b, the combination of the gains of the forward Raman pump module 204b and the backward Raman pump module 206b compensates for the span loss of the optical signal 220 along the transmission fiber 202b. Furthermore, for the transmission fiber 202b, the gain ratio between the gain of the forward Raman pump module 204b and the gain of the backward Raman pump module 206b is determined such that the accumulated noise of the optical signal 220 along the transmission fiber 202b is minimized while compensating for the span loss of the optical signal 220 when the optical signal 220 is transmitted along the transmission fiber 202b. As shown by the noise matrix 500, when the span loss is 20 dB along the transmission fiber 202b, the combination of the 12 dB gain of the forward Raman pump module 204b and the 8 dB gain of the backward Raman pump module 206b compensates for the 20 dB span loss while minimizing the accumulated noise of the optical signal 220.

[0046] For the transmission fiber 202c, the combination of the gains of the forward Raman pump module 204c, the backward Raman pump module 206c, and the optical amplifier 212 compensates for the span loss of the optical signal 220 along the transmission fiber 202c and the receiver sensitivity of the receiver 210. Furthermore, for the transmission fiber 202c, the gain ratio between the gain of the forward Raman pump module 204c and the gain of the backward Raman pump module 206c, and the gain ratio between the gain of the backward Raman pump module 206c and the gain of the optical amplifier 212 are determined such that the accumulated noise of the optical signal 220 along the transmission fiber 202c is minimized while compensating for the span loss of the optical signal 220 when transmitted along the transmission fiber 202c and the receiver sensitivity of the receiver 210. As shown by noise matrix 500, when the span loss is 20 dB along the transmission fiber 202c and the receiver sensitivity of the receiver 210 is 10 dB, the combination of the 12 dB gain of the forward Raman pump module 204b, the 12 dB gain of the backward Raman pump module 206b, and the 6 dB gain of the optical amplifier 212 compensates for the 20 dB span loss and the 10 dB receiver sensitivity while minimizing the accumulated noise in the optical signal 220.

[0047] 8 depicts a flowchart illustrating selected elements of an embodiment of a method 800 for compensating for signal loss. Method 800 may be performed by optical system 200. It is noted that certain operations described in method 800 may be optional or reordered in different embodiments.

[0048] A WDM input optical signal 220 is received (802). The optical signal 220 is transmitted along the transmission fiber 202 (804). The noise matrix calculation module 213 determines (806) a first noise associated with a first gain of the forward Raman pump module 204 for one or more first gains of the optical signal 220. The noise matrix calculation module 213 determines (808) a second noise associated with a second gain of the backward Raman pump module 206 for one or more second gains of the optical signal. The noise matrix calculation module 213 determines (810) a third noise associated with a third gain of the optical amplifier 212 for one or more third gains of the optical signal 220. The noise matrix calculation module 213 generates (812) a noise matrix 500 based on i) the first noise for each gain of the forward Raman pump module 204, ii) the second noise for each gain of the backward Raman pump module 206, and iii) the third noise for each gain of the optical amplifier 212. The noise matrix calculation module 213 determines (814) a span loss of the optical signal 220 when the optical signal 220 is transmitted along the transmission fiber 202. The noise matrix calculation module 213 determines (816) a combination of a specific first gain of the forward Raman pump module 204 and a specific second gain of the backward Raman pump module 206 based on the noise matrix 500 and the span loss. The forward Raman pump module 204 and the backward Raman pump module 206 compensate (818) for the span loss of the optical signal 220 based on the specific first gain and the specific second gain, respectively. In some cases, the gain ratio between the specific first gain of the forward Raman pump module 204 and the specific second gain of the backward Raman pump module 206 includes a minimum cumulative noise combination of the first noise and the second noise of the optical signal 220 based on the noise matrix 500. The noise matrix calculation module 213 determines (820) a receiver sensitivity of the receiver 210. The noise matrix calculation module 213 identifies a combination of a particular second gain of the backward Raman pump module 206 and a particular third gain of the optical amplifier 212 based on the noise matrix 500 and the receiver sensitivity (822).In some cases, the gain ratio between the specific second gain of the backward Raman pump module 206 and the specific third gain of the optical amplifier 212 comprises a minimum cumulative noise combination of the second noise and the third noise of the optical signal 220 based on the noise matrix 500. The backward Raman pump module 206 and the optical amplifier 212 compensate (824) the receiver sensitivity based on the specific second gain and the specific third gain, respectively.

[0049] The above subject matter should be considered illustrative rather than limiting, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent permitted by law, the scope of the present disclosure should be determined by the broadest permissible interpretation of the following claims and their equivalents, and should not be limited or restricted by the above detailed description.

[0050] As used herein, "or" is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Thus, as used herein, "A or B" means "A, B, or both," unless expressly indicated otherwise or indicated otherwise by context. Further, "and" means jointly and severally, unless expressly indicated otherwise or indicated otherwise by context. Thus, as used herein, "A and B" means "A and B, jointly and severally," unless expressly indicated otherwise or indicated otherwise by context.

[0051] The scope of the present disclosure includes all changes, substitutions, variations, modifications, and improvements to the example embodiments described and illustrated herein, as will be understood by those skilled in the art. The scope of the present disclosure is not limited to the example embodiments described and illustrated herein. Furthermore, although the present disclosure describes and illustrates each embodiment herein as including certain components, elements, features, functions, operations, or steps, any of the embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein, as will be understood by those skilled in the art. Furthermore, any reference in the appended claims to an apparatus or system, or an apparatus or system component, adapted, arranged, capable, configured, enabled, operable, or operating to perform a particular function includes the apparatus, system, or component, whether the particular function is activated or not, turned on or not, or unlocked or not, so long as the apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operating.

[0052] In addition to the above embodiments, the following supplementary notes are disclosed. (Appendix 1) 1. An optical system for compensating for signal loss, comprising: a transmission fiber for transmitting a WDM input optical signal; a forward Raman pump module located along the transmission fiber; a backward Raman pump module located along the transmission fiber; Noise matrix calculation module and having The noise matrix calculation module includes: determining a first noise associated with a first gain of the forward Raman pump module for one or more first gains of the optical signal; determining a second noise associated with a second gain of the backward Raman pump module for one or more second gains of the optical signal; generating a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and i) the second noise for each second gain of the rear Raman pump module; determining a span loss of the optical signal as it is transmitted along the transmission fiber; Identifying a combination of a specific first gain of the forward Raman pump module and a specific second gain of the rear Raman pump module based on the noise matrix and the span loss. It is configured as follows: the forward Raman pump module and the backward Raman pump module compensate for the span loss of the optical signal based on the combination of a specific first gain of the forward Raman pump module and a specific second gain of the backward Raman pump module; a gain ratio between a specific first gain of the forward Raman pump module and a specific second gain of the rearward Raman pump module comprises a minimum cumulative noise combination of the first noise and the second noise of the optical signal based on the noise matrix; Optical system. (Appendix 2) an optical amplifier located along the transmission fiber; a receiver configured to receive the optical signal; and The noise matrix calculation module includes: determining a third noise associated with a third gain of the optical amplifier for one or more third gains of the optical signal; generating the noise matrix based on i) the first noise for each first gain of the forward Raman pump module, ii) the second noise for each second gain of the rearward Raman pump module, and iii) the third noise for each third gain of the optical amplifier; Identifying the receiving sensitivity of the receiver; A combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier is identified based on the noise matrix and the receiver sensitivity. It is further structured as follows: the backward Raman pump module and the optical amplifier compensate the receiving sensitivity of the receiver based on the combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier. 2. The optical system of claim 1. (Appendix 3) a gain ratio between the specific second gain of the backward Raman pump module and the specific third gain of the optical amplifier comprises a minimum cumulative noise combination of the second noise and the third noise of the optical signal based on the noise matrix; 3. The optical system of claim 2. (Appendix 4) The optical amplifier is an EDFA. 4. The optical system according to claim 2 or 3. (Appendix 5) a further transmission fiber for transmitting said optical signal; a further forward Raman pump module located along said further transmission fiber; a further backward Raman pump module located along said further transmission fiber; and The noise matrix calculation module includes: determining a third noise associated with a third gain of the further forward Raman pump module for one or more third gains of the optical signal; determining a fourth noise associated with a fourth gain of the further backward Raman pump module for one or more fourth gains of the optical signal; generating the noise matrix based on i) the third noise for each third gain of the further forward Raman pump module, and ii) the fourth noise for each fourth gain of the further rear Raman pump module; determining a further span loss of the optical signal as it is transmitted along the further transmission fiber; Identifying a combination of a particular third gain of the further forward Raman pump module and a particular fourth gain of the further rear Raman pump module based on the noise matrix and the further span noise. It is further structured as follows: the further forward Raman pump module and the further backward Raman pump module compensate for the further span loss of the optical signal based on the combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module; a gain ratio between a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module comprises a minimum cumulative noise combination of the third noise and the fourth noise of the optical signal based on the noise matrix; 2. The optical system of claim 1. (Appendix 6) an optical amplifier located along said further transmission fiber; a receiver configured to receive the optical signal; and The noise matrix calculation module includes: determining a fifth noise associated with a fifth gain of the optical amplifier for one or more fifth gains of the optical signal; generating the noise matrix based on i) the third noise for each third gain of the further forward Raman pump module, ii) the fourth noise for each fourth gain of the further backward Raman pump module, and iii) the fifth noise for each fifth gain of the optical amplifier; Identifying the receiving sensitivity of the receiver; Identifying a combination of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier based on the noise matrix and the receiver sensitivity. It is further structured as follows: the further backward Raman pump module and the optical amplifier compensate the receiving sensitivity of the receiver based on the combination of a fourth gain of the further backward Raman pump module and a fifth gain of the optical amplifier. 6. The optical system of claim 5. (Appendix 7) a gain ratio between a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier comprises a minimum cumulative noise combination of the fourth noise and the fifth noise of the optical signal based on the noise matrix. 7. The optical system of claim 6. (Appendix 8) The span loss is about 20 dB. 2. The optical system of claim 1. (Appendix 9) The receiving sensitivity is about 10 dB. 3. The optical system of claim 2. (Appendix 10) 1. A method for compensating for signal loss in an optical network, comprising: receiving a WDM input optical signal; transmitting the optical signal along a transmission fiber; determining, for one or more first gains of the optical signal, a first noise associated with a first gain of a forward Raman pump module located along the transmission fiber; determining, for one or more second gains of the optical signal, a second noise associated with a second gain of a backward Raman pump module located along the transmission fiber; generating a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and i) the second noise for each second gain of the rear Raman pump module; determining a span loss of the optical signal as it is transmitted along the transmission fiber; identifying a combination of a specific first gain of the forward Raman pump module and a specific second gain of the rear Raman pump module based on the noise matrix and the span loss; compensating for the span loss of the optical signal based on the combination of a specific first gain of the forward Raman pump module and a specific second gain of the backward Raman pump module; having a gain ratio between a specific first gain of the forward Raman pump module and a specific second gain of the rearward Raman pump module comprises a minimum cumulative noise combination of the first noise and the second noise of the optical signal based on the noise matrix; method. (Appendix 11) determining, for one or more third gains of the optical signal, a third noise associated with a third gain of an optical amplifier located along the transmission fiber; generating the noise matrix based on i) the first noise for each first gain of the forward Raman pump module, ii) the second noise for each second gain of the backward Raman pump module, and iii) the third noise for each third gain of the optical amplifier; determining a receiving sensitivity of a receiver configured to receive the optical signal; determining a combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier based on the noise matrix and the receiver sensitivity; compensating the receiver sensitivity based on the combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier; Further comprising 11. The method according to claim 10. (Appendix 12) a gain ratio between the specific second gain of the backward Raman pump module and the specific third gain of the optical amplifier comprises a minimum cumulative noise combination of the second noise and the third noise of the optical signal based on the noise matrix; 12. The method according to claim 11. (Appendix 13) The optical amplifier is an EDFA. 13. The method according to claim 11 or 12. (Appendix 14) transmitting the optical signal along a further transmission fiber; determining, for one or more third gains of the optical signal, a third noise associated with a third gain of a further forward Raman pump module located along the further transmission fiber; determining, for one or more fourth gains of the optical signal, a fourth noise associated with a fourth gain of a further backward Raman pump module located along the further transmission fiber; generating the noise matrix based on i) the third noise for each third gain of the further forward Raman pump module and ii) the fourth noise for each fourth gain of the further rear Raman pump module; determining a further span loss of the optical signal as it is transmitted along the further transmission fiber; identifying a combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further rear Raman pump module based on the noise matrix and the further span noise; compensating for the further span loss of the optical signal based on the combination of a particular third gain of the further forward Raman pump module and a particular fourth gain of the further backward Raman pump module; and a gain ratio between a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module comprises a minimum cumulative noise combination of the third noise and the fourth noise of the optical signal based on the noise matrix; 11. The method according to claim 10. (Appendix 15) determining, for one or more fifth gains of said optical signal, a fifth noise associated with a fifth gain of an optical amplifier located along said further transmission fiber; generating the noise matrix based on i) the third noise for each third gain of the further forward Raman pump module, ii) the fourth noise for each fourth gain of the further backward Raman pump module, and iii) the fifth noise for each fifth gain of the optical amplifier; determining a receiving sensitivity of a receiver configured to receive the optical signal; determining a combination of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier based on the noise matrix and the receiver sensitivity; compensating the receiver sensitivity of the receiver based on the combination of a fourth gain of the further backward Raman pump module and a fifth gain of the optical amplifier; Further comprising 15. The method according to claim 14. (Appendix 16) a gain ratio between a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier comprises a minimum cumulative noise combination of the fourth noise and the fifth noise of the optical signal based on the noise matrix. 16. The method according to claim 15. (Appendix 17) The span loss is about 20 dB. 11. The method according to claim 10. (Appendix 18) The receiving sensitivity is about 10 dB. 12. The method according to claim 11. [Explanation of symbols]

[0053] 101 Optical Network 102,208 Transmitters 104 Multiplexer (MUX) 105 Demultiplexer 106 Optical Fiber 108,212 Optical Amplifier 110 Optical Add Drop Multiplexer (OADM) 112,210 Receiver 200 Optical System 202 Transmission Fiber 204 Forward Raman Pump Module 206 Rear Raman Pump Module 213 Noise Matrix Calculation Module 220 WDM input optical signal 500 Noise Matrix

Claims

1. 1. An optical system for compensating for signal loss, comprising: a transmission fiber for transmitting a WDM input optical signal; a forward Raman pump module located along the transmission fiber; a backward Raman pump module located along the transmission fiber; Noise matrix calculation module and having The noise matrix calculation module includes: determining, for each of one or more first gains that the forward Raman pump module can assume, a first noise from the forward Raman pump module to the optical signal when the forward Raman pump module has the first gain; determining, for each of one or more second gains that the backward Raman pump module can assume, a second noise from the backward Raman pump module to the optical signal when the backward Raman pump module has the second gain; generating a noise matrix in which the first gain is associated with the first noise and the second gain is associated with the second noise; determining a span loss of the optical signal as it is transmitted along the transmission fiber; Identifying a combination of a specific first gain of the forward Raman pump module and a specific second gain of the rear Raman pump module based on the noise matrix and the span loss. It is configured as follows: the forward Raman pump module and the backward Raman pump module compensate for the span loss of the optical signal based on the combination of a specific first gain of the forward Raman pump module and a specific second gain of the backward Raman pump module. Optical system.

2. A combination or gain ratio of a specific first gain of the forward Raman pump module and a specific second gain of the rearward Raman pump module is determined such that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the first noise and the second noise, is minimized.

10. The optical system of claim 1 .

3. an optical amplifier located along the transmission fiber; a receiver configured to receive the optical signal; Further comprising: The noise matrix calculation module includes: determining, for each of one or more third gains that the optical amplifier can have, a third noise from the optical amplifier to the optical signal when the optical amplifier has the third gain; generating the noise matrix in which the first gain is associated with the first noise, the second gain is associated with the second noise, and the third gain is associated with the third noise; Identifying the receiving sensitivity of the receiver; A combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier is identified based on the noise matrix and the receiving sensitivity. It is further structured as follows: the backward Raman pump module and the optical amplifier compensate the receiving sensitivity of the receiver based on the combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier.

10. The optical system of claim 1 .

4. a combination or gain ratio of the specific second gain of the rear Raman pump module and the specific third gain of the optical amplifier is determined so that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the second noise and the third noise, is minimized.

4. The optical system of claim 3.

5. The optical amplifier is an EDFA.

5. An optical system according to claim 3 or 4.

6. a further transmission fiber for transmitting said optical signal; a further forward Raman pump module located along said further transmission fiber; a further backward Raman pump module located along said further transmission fiber; Further comprising: The noise matrix calculation module includes: determining, for each of one or more third gains that the further forward Raman pump module can assume, a third noise from the further forward Raman pump module to the optical signal when the further forward Raman pump module has the third gain; determining, for each of one or more fourth gains that the further backward Raman pump module can assume, a fourth noise from the further backward Raman pump module to the optical signal when the further backward Raman pump module has the fourth gain; generating the noise matrix in which the third gain is associated with the third noise and the fourth gain is associated with the fourth noise; determining a further span loss of the optical signal as it is transmitted along the further transmission fiber; Identifying a combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further rear Raman pump module based on the noise matrix and the further span noise. It is further structured as follows: the further forward Raman pump module and the further backward Raman pump module compensate for the further span loss of the optical signal based on the combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module.

10. The optical system of claim 1 .

7. A combination or gain ratio of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further rearward Raman pump module is determined such that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the third noise and the fourth noise, is minimized.

7. The optical system of claim 6.

8. an optical amplifier located along said further transmission fiber; a receiver configured to receive the optical signal; Further comprising: The noise matrix calculation module includes: determining, for each of one or more fifth gains that the optical amplifier can have, a fifth noise from the optical amplifier to the optical signal when the optical amplifier has the fifth gain; generating the noise matrix in which the third gain is associated with the third noise, the fourth gain is associated with the fourth noise, and the fifth gain is associated with the fifth noise; Identifying the receiving sensitivity of the receiver; Identifying a combination of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier based on the noise matrix and the receiver sensitivity. It is further structured as follows: the further backward Raman pump module and the optical amplifier compensate the receiving sensitivity of the receiver based on the combination of a fourth gain of the further backward Raman pump module and a fifth gain of the optical amplifier.

8. An optical system according to claim 6 or 7.

9. a combination or gain ratio of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier is determined such that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the fourth noise and the fifth noise, is minimized.

9. The optical system of claim 8.

10. 1. A method for compensating for signal loss in an optical network, comprising: receiving a WDM input optical signal; transmitting said optical signal along a transmission fiber; determining, for each of one or more first gains possible for a forward Raman pump module located along the transmission fiber, a first noise from the forward Raman pump module to the optical signal when the forward Raman pump module has the first gain; determining, for each of one or more second gains possible for a downstream Raman pump module located along the transmission fiber, a second noise from the downstream Raman pump module to the optical signal when the downstream Raman pump module has the second gain; generating a noise matrix in which the first gain is associated with the first noise and the second gain is associated with the second noise; determining a span loss of the optical signal as it is transmitted along the transmission fiber; identifying a combination of a particular first gain of the forward Raman pump module and a particular second gain of the rear Raman pump module based on the noise matrix and the span loss; Compensating for the span loss of the optical signal based on the combination of a specific first gain of the forward Raman pump module and a specific second gain of the backward Raman pump module. method.

11. A combination or gain ratio of a specific first gain of the forward Raman pump module and a specific second gain of the rearward Raman pump module is determined so that a cumulative noise of the optical signal based on the noise matrix, which is a combination of the first noise and the second noise, is minimized. The method of claim 10. determining, for each of one or more possible third gains of an optical amplifier located along the transmission fiber, a third noise from the optical amplifier to the optical signal when the optical amplifier has the corresponding third gain; generating the noise matrix in which the first gain is associated with the first noise, the second gain is associated with the second noise, and the third gain is associated with the third noise; determining a receiving sensitivity of a receiver configured to receive the optical signal; identifying a combination of a specific second gain of the backward Raman pump module and a specific third gain of the optical amplifier based on the noise matrix and the receiver sensitivity; Compensating the receiving sensitivity of the receiver based on the combination of the specific second gain of the backward Raman pump module and the specific third gain of the optical amplifier. The method of claim 10.

13. a combination or gain ratio of the specific second gain of the rear Raman pump module and the specific third gain of the optical amplifier is determined so that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the second noise and the third noise, is minimized. The method of claim 12.

14. The optical amplifier is an EDFA.

14. The method according to claim 12 or 13.

15. transmitting said optical signal along a further transmission fiber; determining, for each of one or more third gains possible for a further forward Raman pump module located along the further transmission fiber, a third noise from the further forward Raman pump module to the optical signal when the further forward Raman pump module has the third gain; determining, for each of one or more fourth gains possible for a further backward Raman pump module located along the further transmission fiber, a fourth noise from the further backward Raman pump module to the optical signal when the further backward Raman pump module has the fourth gain; generating the noise matrix in which the third gain is associated with the third noise and the fourth gain is associated with the fourth noise; determining a further span loss of the optical signal as it is transmitted along the further transmission fiber; identifying a combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further rear Raman pump module based on the noise matrix and the further span noise; Compensating for the further span loss of the optical signal based on the combination of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further backward Raman pump module. The method of claim 10.

16. A combination or gain ratio of a specific third gain of the further forward Raman pump module and a specific fourth gain of the further rearward Raman pump module is determined such that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the third noise and the fourth noise, is minimized. The method of claim 15. determining, for each of one or more possible fifth gains of an optical amplifier located along the further transmission fiber, a fifth noise from the optical amplifier to the optical signal when the optical amplifier has the corresponding fifth gain; generating the noise matrix in which the third gain is associated with the third noise, the fourth gain is associated with the fourth noise, and the fifth gain is associated with the fifth noise; determining a receiving sensitivity of a receiver configured to receive the optical signal; identifying a combination of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier based on the noise matrix and the receiver sensitivity; Compensating the receiving sensitivity of the receiver based on the combination of a fourth gain of the further backward Raman pump module and a fifth gain of the optical amplifier.

17. The method according to claim 15 or 16.

18. a combination or gain ratio of a specific fourth gain of the further backward Raman pump module and a specific fifth gain of the optical amplifier is determined such that a cumulative noise of the optical signal based on the noise matrix, the cumulative noise being a combination of the fourth noise and the fifth noise, is minimized.

20. The method of claim 17.

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