A single-span broadband multi-wave amplification method and system for a multi-island scenario

Abstract

The application relates to the technical field of optical fiber communication, and provides a single-span broadband multi-wave amplification method and system for a multi-island scene. C-waveband signals and L-waveband signals in C+L ultra-wideband signals transmitted by a single-mode optical fiber are divided into two paths to obtain single-waveband signals; each single-waveband signal is coupled with pump light and transmitted to a passive double-core optical fiber through a double-core fan-in device to obtain a to-be-processed signal; each to-be-processed signal is transmitted through the passive double-core optical fiber and is amplified at an asymmetric gain optical fiber to obtain a processed signal; each processed signal is transmitted through the passive double-core optical fiber and is combined through a double-core fan-out device to enter a single-mode optical fiber to continue transmission in a metropolitan area network, so that the problems of high cost and low gain in the prior art, the nonlinear problem of C+L waveband signals in the same fiber core and the loss and complexity problems caused by frequent use of fan-in and fan-out devices in the middle section of a transmission link are solved.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to a single-span broadband multi-wave amplification method and system for multi-island scenarios. Background Technology

[0002] In recent years, with the explosive growth of network data traffic, optical fiber communication systems have developed towards ultra-high capacity and ultra-long distance transmission, placing higher demands on C+L band broadband optical amplification technology. "C+L" refers to the C-band and L-band, a combination of two low-loss bands in optical communication. By simultaneously using the C-band (Conventional band, 1530 to 1565 nanometers) and the L-band (Long-wavelength band, 1565 to 1625 nanometers), the transmission capacity of a single optical fiber can be multiplied.

[0003] In metropolitan area networks based on terrestrial optical cables, C+L ultra-broadband transmission has been deployed. Correspondingly, inter-island links also need to support C+L multi-band transmission in order to connect the C+L subnets within each island and ultimately form a metropolitan area network structure that can span across islands.

[0004] However, C+L broadband signals transmitted between multiple islands are limited by various factors such as nonlinearity, amplification performance, and energy consumption costs. Existing multi-span submarine cable solutions suffer from high costs, low gain, significant impact of fiber nonlinearity on broadband signals, and losses and complexities caused by frequent use of fan-in and fan-out devices in the transmission link, resulting in poor practicality.

[0005] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the existing multi-span submarine cable technology has high cost and low gain, and there are nonlinear problems in the transmission of C+L band signals in the same fiber core, as well as loss and complexity caused by the frequent use of fan-in and fan-out devices in the middle of the transmission link, resulting in poor practicality.

[0007] In a first aspect, a single-span broadband multi-wavelength amplification method for multi-island scenarios is provided. The method is applied to a single-span broadband multi-wavelength amplification system for multi-island scenarios. The system includes at least two passive dual-core optical fibers and at least one asymmetric gain optical fiber, with the passive dual-core optical fiber and the asymmetric gain optical fiber arranged alternately. The method includes: The C-band and L-band signals in the C+L ultra-wideband signal transmitted through single-mode fiber are split into two paths to obtain a single-band signal. Each of the single-band signals is coupled with pump light and transmitted to a passive dual-core optical fiber via a dual-core fan-in device to obtain the signal to be processed. Each of the signals to be processed is transmitted through a passive dual-core optical fiber and amplified at an asymmetric gain optical fiber to obtain the processed signal. The processed signals are transmitted via passive dual-core optical fiber and then combined in single-mode optical fiber via dual-core fan-out devices to continue transmission in the metropolitan area network.

[0008] Furthermore, the asymmetric gain fiber includes active dual-core fiber and hybrid dual-core fiber; The method further includes: The fiber is modeled by dividing it into multiple small segments, and step-by-step calculations are performed to determine the gain change under dual-core coupling, so as to obtain the amplification model of the asymmetric gain fiber. Based on the transmission requirements of the cross-island link, the pump power capability at the transmitting end, and the signal optical power reception requirements at the receiving end, the amplification model is used to determine the optimal pump optical power level, the first length of the active dual-core fiber, and the second length of the hybrid dual-core fiber. Based on the pump light power level, the first length, and the second length, an asymmetric gain fiber comprising active dual-core fiber and hybrid dual-core fiber is fabricated.

[0009] Furthermore, the modeling of the fiber by dividing it into multiple small segments and performing step-by-step calculations to determine the gain variation under dual-core coupling, in order to obtain the amplification model of the asymmetric gain fiber, includes: The entire active dual-core optical fiber is divided into multiple smaller segments; the gain calculation of each smaller segment is performed iteratively in a step-by-step calculation manner until the gain calculation of the entire active dual-core optical fiber is completed. The gain of the passive core in the hybrid dual-core fiber is set to zero, and the gain calculation, including crosstalk, is performed in the same step-by-step calculation method as that of the active dual-core fiber. Based on the gain calculation results of the active dual-core fiber and the hybrid dual-core fiber, an amplification model is established to characterize the relationship between the first length, the second length and the pump light power level.

[0010] Furthermore, the step-by-step calculation, iteratively performing the gain calculation for each small segment until the gain calculation for the entire active dual-core optical fiber is completed, includes: Obtain the gain spectrum of a single-core fiber with the same doping formulation as the active dual-core fiber, and determine the emission cross-section vector and absorption cross-section vector; calibrate the relative inversion particle number based on the pump light power and signal light power; measure the crosstalk coefficient of the active dual-core fiber, and determine the relationship between the crosstalk power ratio and the fiber position. Using a step-by-step calculation method, the pump light power attenuation and signal light power gain are calculated in each segment according to the emission cross-section vector, the absorption cross-section vector, and the relative inversion particle number. At the end of each segment, crosstalk power exchange is performed between the two fiber cores based on the crosstalk coefficient to update the pump light power and signal light power of each fiber core. The relative inversion particle number at the corresponding end position of the segment is calculated according to the pump light power and the signal light power. This process is iteratively executed until the gain calculation of the entire active dual-core fiber is completed.

[0011] Furthermore, the active dual-core optical fiber includes a first core and a second core; the hybrid dual-core optical fiber includes a third core and a fourth core. The first fiber core, the second fiber core, and the fourth fiber core are active fiber cores; the third fiber core is a passive fiber core. The first fiber core is directly fused to the third fiber core, and the second fiber core is directly fused to the fourth fiber core.

[0012] Furthermore, the step of setting the gain of the passive core in the hybrid dual-core fiber to zero and performing the gain calculation including crosstalk in the same step-by-step calculation method as the active dual-core fiber also includes: Based on the relative inversion particle number, gain, and absorption eigenvector, the power changes of the pump light and signal light are iteratively calculated to obtain the pump light power value and signal light power value of the fourth fiber core at the end of the current segment. By considering only intrinsic loss for power attenuation calculation, the pump optical power value and signal optical power value of the third fiber core at the end of the current segment are obtained; At the end of the current segment, using the pump light power value and signal light power value of the fourth fiber core, the pump light power value and signal light power value of the third fiber core, and the measured crosstalk coefficient, the power exchange amount of pump light and signal light between the third fiber core and the fourth fiber core is calculated, and the power value of each fiber core is updated. The relative inversion particle number of the fourth fiber core was calculated using the updated power value.

[0013] Furthermore, each of the signals to be processed is transmitted through a passive dual-core optical fiber and amplified at an asymmetric gain optical fiber to obtain the processed signal, which further includes: Using the fabricated asymmetric gain optical fiber, the corresponding C-band signal is amplified through the first core of the active dual-core optical fiber, the corresponding L-band signal is amplified through the second core of the active dual-core optical fiber, the corresponding L-band signal is amplified through the fourth core of the hybrid dual-core optical fiber, and the corresponding C-band signal is transmitted through the third core of the hybrid dual-core optical fiber, so as to amplify the signal at the asymmetric gain optical fiber and obtain the processed signal.

[0014] Furthermore, the processed signals are transmitted via passive dual-core optical fiber and then combined after entering single-mode optical fiber via a dual-core fan-out device, including: Each of the processed signals is transmitted through the corresponding passive dual-core optical fiber and then enters the corresponding single-mode optical fiber through the dual-core fan-out device. The signals in each single-mode fiber are coupled to the back pump light through a wavelength division multiplexer and then combined through a C / L wavelength division device to obtain the processed C+L ultrawideband signal.

[0015] Secondly, a single-span broadband multi-wavelength amplification system for multi-island scenarios is provided. This system implements the single-span broadband multi-wavelength amplification method as described in the first aspect, and includes a C+L wavelength division multiplexing unit, a dual-core fan-in device, a dual-core fan-out device, at least two passive dual-core optical fibers, and at least one asymmetric gain optical fiber; wherein: The C+L wavelength division multiplexing unit is used to split the C-band signal and L-band signal in the C+L ultra-wideband signal transmitted through single-mode fiber into two paths to obtain a single-band signal; it is also used to couple pump light to each of the single-band signals respectively. The dual-core fan-in device is used to transmit the single-band signals of each separately coupled pump light to a passive dual-core optical fiber to obtain the signal to be processed. The passive dual-core optical fiber is used to transmit each of the signals to be processed or the processed signals; The asymmetric gain fiber is used to amplify each of the signals to be processed to obtain the processed signal; The dual-core fan-out device is used to combine the processed signals and then enter the single-mode optical fiber for continued transmission in the metropolitan area network.

[0016] Furthermore, the C+L wavelength division multiplexing unit is connected to the dual-core fan-in device; The dual-core fan-in device is connected to the first section of passive dual-core optical fiber to facilitate the transmission of the signal to be processed through the first section of passive dual-core optical fiber. The first passive dual-core optical fiber is connected to the first asymmetric gain optical fiber so as to realize C+L broadband forward pump amplification through the first asymmetric gain optical fiber to obtain the intermediate signal. The first asymmetric gain fiber is connected to the second passive dual-core fiber to facilitate the transmission of the intermediate signal through the second passive dual-core fiber. The second passive dual-core fiber is connected to the second asymmetric gain fiber to enable C+L broadband back-pump amplification through the second asymmetric gain fiber to obtain the processed signal. The second asymmetric gain fiber is connected to the third passive dual-core fiber to facilitate the transmission of the processed signal through the third passive dual-core fiber. The third passive dual-core optical fiber is connected to the dual-core fan-out device so that the C-band and L-band can enter the two single-mode optical fibers respectively, and the signals can continue to be transmitted in the metropolitan area network after WDM multiplexing.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention targets island scenarios and employs a broadband system solution based on remote pumping. To avoid the Raman effect caused by excessive power in repeaterless amplification scenarios, multi-core optical fibers are used to achieve wavelength division multiplexing (WDM) transmission and amplification. Instead of WDM multiplexing, a space-division multiplexing system is used in the island transmission process. By converting WDM to space-division multiplexing, low cabling size, low device complexity, low nonlinearity, and broadband amplification suitable for multi-core systems are achieved, enabling gain-flat broadband remote pumping for multi-core systems. To overcome the shortcomings of existing space-division multiplexing schemes and avoid using too many fan-in / fan-out devices in the transmission link, thus reducing the loss and complexity caused by multiple fan-in / fan-out devices, this invention uses asymmetric gain optical fibers to amplify C-band and L-band signals separately. This dual-core remote pumping method reduces the cost of multiple fan-in / fan-out devices and also mitigates the nonlinearity problem of C-band and L-band signals transmitting in the same fiber core. In addition, the system is compatible with Raman amplification to further improve gain performance, ultimately enabling high-capacity, low-cost, and easy-to-maintain cross-island repeaterless transmission. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a single-span broadband multi-wave amplification method for multi-island scenarios provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a single-span broadband multi-wave amplification system for multi-island scenarios provided by an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating a specific example of C+L amplification and direct fusion splicing of active dual-core optical fiber and hybrid dual-core optical fiber provided by an embodiment of the present invention. Figure 4 This is a flowchart illustrating step 30 provided in an embodiment of the present invention; Figure 5 This is a flowchart illustrating step 301 provided in an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating a specific example of calculating and modeling a C+L magnification model provided in an embodiment of the present invention; Figure 7 This is a flowchart illustrating step 40 provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of a prior art nonlinear power transfer effect provided by an embodiment of the present invention; Figure 9 This is a schematic diagram illustrating the reduction of nonlinear power transfer effect according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0022] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, for example, the description may use the prefix "A" or "B" to describe the same type of nouns as two independent entities. In this case, the corresponding features defined with "A" and "B" are used only to distinguish between similar entities and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0023] In describing some embodiments, the terms "coupled," "coupled," and "connected," and their derivative expressions, may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. Similarly, the term "coupled" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the terms "connected" or "coupled" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other, such as "optical coupling," "wireless connection," etc. The embodiments disclosed herein are not necessarily limited to the scope of this invention.

[0024] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Existing multi-span submarine cable technology solutions and their disadvantages: (1) Active repeater equipment has high construction and maintenance costs. Active repeater equipment includes lumped optical amplifiers and electrical repeaters. For example, a lumped optical amplifier can be a lumped optical amplifier based on an erbium-doped fiber application amplifier (EDFA), and an electrical repeater can be an electrical repeater or regenerator that performs photoelectric-optical conversion. In multi-island scenarios, building an underwater enclosure for each repeater is extremely costly, and the placement of repeaters requires specialized vessels and deep-sea equipment. Moreover, electrical repeaters and lumped amplifiers require local power supply, so high voltage needs to be transmitted from land to repeaters hundreds of kilometers away to achieve a constant current power supply of several kilovolts, which is costly and involves a complex and difficult power supply design. In addition, once a repeater fails, the optical cable needs to be retrieved from the ocean, cut, and reconnected to a new repeater, which is impractical.

[0026] (2) The disadvantage of using the C / L fiber splitting ultra-long single span scheme is that it has a large optical cable volume, and the fan-in and fan-out devices of the space splitting ultra-long single span will introduce a large insertion loss, which is not practical; where “C / L” refers to C-band or L-band.

[0027] Specifically, in traditional ultra-long single-span cables (referring to submarine cables or terrestrial links spanning hundreds of kilometers without repeaters), a "fiber splitting" approach is typically used to simultaneously transmit C-band and L-band signals and achieve remote amplification. This "fiber splitting" approach involves deploying multiple independent optical fibers within the cable, thereby physically separating the signal light and pump light (or, separating signals of different bands) to address amplification and interference issues in ultra-long-distance transmission. The system requires a pair of optical fibers, one for signal transmission and one for pump transmission. Since C-band and L-band amplification requires different pump sources or paths, four optical fibers are often needed (i.e., two for C-band signal and pump, and two for L-band signal and pump) to form a complete Remote Gain Unit (RGU) link.

[0028] However, this approach sacrifices the physical size of the optical cable to achieve gain over ultra-long distances, resulting in a large link volume and increased deployment difficulty and cost. Specifically, to achieve bidirectional C+L transmission, a single optical cable needs to accommodate multiple independent single-mode fibers (SMFs), rather than just a pair of fibers. To overcome losses over ultra-long distances, enormous pump power is required. Existing technologies often increase the number of fibers to support high-power pumping, leading to an increase in the number of fiber units contained within the optical cable. Because the optical cable contains multiple fibers and the pump power is extremely high, the cable structure (e.g., insulation layers) needs to be designed to be thicker to accommodate the fibers in high-power scenarios, further increasing the volume.

[0029] To reduce the size of optical cables and increase capacity, Space Division Multiplexing (SDM) technology, especially Multi-Core Fiber (MCF) technology, has been introduced. This technology integrates channels that originally required multiple independent optical fibers into multiple cores within a single optical fiber. Each optical fiber contains multiple cores, which are isolated from each other. However, at both ends of the cable, fan-in / fan-out devices are needed to couple light from standard single-mode devices (such as transceivers and amplifiers) into specific cores of the multi-core fiber. These fan-in / fan-out devices require precise alignment of the single optical fiber (i.e., single-core fiber) with a specific core of the multi-core fiber. Due to the extremely small core spacing of multi-core fibers (typically on the micrometer scale), the alignment accuracy requirement is extremely high; any slight misalignment will lead to loss. Furthermore, the splice points between multi-core fibers and fan-in / fan-out devices often exhibit mode field mismatch, or due to the geometric inhomogeneities of the multi-core fiber (such as core twisting), resulting in insertion loss much higher than that of ordinary single-mode fiber splices. In addition, high-quality fan-in and fan-out circuits typically require sophisticated waveguide technology, which itself introduces inherent insertion loss.

[0030] In the ultra-long single-span scenario of multi-island scenarios in the embodiments of the present invention, the signal is extremely weak, and the additional loss introduced by fan-in and fan-out devices has a significant impact on the overall link. Therefore, it is necessary to minimize the number of fan-in and fan-out devices.

[0031] Existing broadband amplification methods for C-band and L-band (C+L) mainly include erbium-doped fiber amplifiers, Raman amplifiers, and remote pump optical amplifiers.

[0032] Erbium-doped fiber amplifiers (EDFAs) offer high gain and stable output, but they require a power supply and necessitate the use of two separate C / L erbium-doped amplifiers after C / L wave demultiplexing to achieve good gain performance. In traditional optical transmission, signal light attenuates continuously as it travels through the fiber. When the transmission distance exceeds approximately 80 to 100 kilometers, the signal weakens to the point of being unrecognizable, requiring the addition of an EDFA or other equipment. While EDFAs do not require photoelectric conversion, they are active devices with high demands on local power supply, server room environment, and regular maintenance. In the marine scenario described in this embodiment, this is extremely costly and virtually impossible to implement.

[0033] Raman amplifiers use optical fibers as the gain medium to achieve dynamic amplification, enabling amplification of any wavelength with system equivalent noise approaching zero. However, they typically have low gain, complex multi-stage pump designs, poor performance, and limited practicality.

[0034] Among them, the remote pumping-based scheme, namely the ultra-long-distance optical transmission system based on the Remote Optically Pumped Amplifier (ROPA), leaves the complex parts that require electrical power (e.g., the pump source) in the local stations at both ends, and places the simple amplification medium (e.g., erbium-doped fiber) on the line.

[0035] When using a remote pumping scheme, the pump source is located at either of the substations or landing stations at both ends, while the erbium-doped fiber (RGU in this embodiment of the invention) is placed in an optical cable hundreds of kilometers away on the seabed or in an uninhabited area, achieving structural separation. The pump light (typically 1480 nm) is emitted from the terminal station, travels hundreds of kilometers along the optical fiber, and reaches the RGU. After absorbing the pump energy, the erbium-doped fiber in the RGU undergoes population inversion. When a weak signal light (i.e., C-band or L-band signal light) passes through, it can be amplified locally, thus achieving remote power supply. This allows for a line hundreds of kilometers long without any electronic equipment requiring power supply or maintenance, consisting only of a few meters to tens of meters of special optical fiber (RGU in this embodiment of the invention).

[0036] This method eliminates physical active repeater points by using fiber optic transmission of pump light instead of building intermediate equipment rooms and adding EDFAs or other equipment. Therefore, ultra-long-distance optical transmission systems based on remote pumping have a significant advantage in reducing the number of active repeaters and are suitable for single-span broadband multi-wavelength amplification applications in multi-island scenarios.

[0037] With the widespread application of multi-core optical fibers in ultra-long-distance fiber optic links, single-core C+L amplification schemes can no longer meet the flexible amplification needs of multi-core systems. Traditional C+L amplification systems (such as EDFA or remotely pumped RGU) are designed for a single fiber core. Their effectiveness relies on all light (whether C-band, L-band, or pump light) transmitting and interacting within the same physical space (i.e., the same fiber core). However, multi-core optical fibers contain multiple independent cores. If traditional C+L equipment is used to amplify all cores in a multi-core fiber, fan-in / fan-out devices must be used at both ends of the fiber to separate the signals from each core and connect them to multiple independent C+L amplifiers. This results in an extremely bloated system, defeating the original purpose of high integration in MCF (Multi-Flash Fiber). Furthermore, in long-distance remote pumping (ROPA) systems, the pump energy comes from the end station. If the pump light (usually 1480 nm) only goes through one core, then only that core can be amplified (gained), and the signals of other cores will quickly attenuate. If the pump light is distributed to each fiber core, extremely complex fan-in and fan-out devices are required, and the distribution process itself will introduce huge insertion losses, resulting in half or even more of the energy originally used for amplification being lost in the fan-in and fan-out devices.

[0038] In summary, when employing a remote pumping scheme, to address the amplification issue of C+L multi-core optical fibers, existing technologies either use a single-core EDFA for amplification, but this results in poor amplification performance in the long-wavelength band due to gain competition. Alternatively, a fan-in / fan-out device can be inserted between the unswitched and switched optical fibers, transforming two cores of the multi-core fiber into two single-mode single-fiber fibers. The corresponding RGU also uses two discrete amplifiers, one for C-band amplification and the other for L-band amplification; however, this requires multiple fan-in / fan-out devices, leading to poor amplification performance and making it unsuitable for single-span broadband multi-wavelength amplification in multi-island scenarios.

[0039] Therefore, there is an urgent need for a new C+L broadband amplification scheme that can take into account low fiber nonlinearity, simple system structure (e.g., minimizing the use of fan-in and fan-out devices), long single-span transmission distance, and good gain, noise performance, and flexible configuration capabilities, so as to ensure high-capacity, ultra-long-distance fiber optic communication and improve the overall performance and operation and maintenance efficiency of cross-island fiber optic communication systems.

[0040] To address the problems of existing technologies, this embodiment proposes a single-span broadband multi-wavelength amplification method for multi-island scenarios. The method is applied to a single-span broadband multi-wavelength amplification system for multi-island scenarios. The system includes at least two passive dual-core optical fibers and at least one asymmetric gain optical fiber. The passive dual-core optical fibers and the asymmetric gain optical fibers are arranged alternately. The corresponding signals are transmitted and amplified alternately through multiple passive dual-core optical fibers and multiple asymmetric gain optical fibers. A specific example will be given below.

[0041] Based on this, such as Figure 1 As shown, the method includes: Step 10: Split the C-band and L-band signals in the C+L ultra-wideband signal transmitted through single-mode fiber into two paths to obtain a single-band signal.

[0042] The applicable scenario for this invention is: transmitting signals on land via a broadband single-core single-mode system, and the corresponding signals become multi-core transmissions after reaching the island.

[0043] In this scenario, existing technologies for amplification employ a wavelength division multiplexing (WDM) system on land, connecting a passive MCF (Medium-Coherence Fiber) and an active RGU (Radio Reinforced Transmission Unit). A pair of fan-in / fan-out devices needs to be inserted between the passive MCF and the active RGU, effectively converting the two fiber cores of the passive MCF into two single-mode single-fiber units, and correspondingly, the RGU also consists of two single-mode single-fiber units. However, frequent use of fan-in / fan-out devices in the transmission link leads to significant losses and increased line complexity. Furthermore, in existing technologies, if a single-core EDFA (Electronic EDFA) is used for amplification, the EDFA itself experiences gain competition, resulting in poor amplification performance in the long-wavelength band.

[0044] To solve this problem, such as Figure 2 As shown, this embodiment of the invention provides a single-span C+L multi-wave EDF amplification scheme based on dual-core optical fiber, in which C-band signals and L-band signals are transmitted and amplified separately.

[0045] Specifically, the C-band and L-band signals in the C+L ultra-wideband signal transmitted through single-mode fiber are split into two paths to obtain single-band signals of the C-band and L-band respectively.

[0046] Step 20: Each of the single-band signals is coupled with pump light and transmitted to a passive dual-core optical fiber via a dual-core fan-in device to obtain the signal to be processed.

[0047] The dual-core fan-in device includes two transmission channels, one for transmitting a single-band C-band signal and the other for transmitting a single-band L-band signal. For example... Figure 2The illustration shows a specific example of a single-span broadband multi-wavelength amplification system for multi-island scenarios according to an embodiment of the present invention. A C-band single-band signal is coupled to the pump light and transmitted through the corresponding fan-in device in the dual-core fan-in device to the core position of the first passive dual-core optical fiber used for C-band transmission, thus obtaining the C-band signal to be processed. Similarly, an L-band single-band signal is coupled to the pump light and transmitted through the corresponding fan-in device to the core position of the first passive dual-core optical fiber used for L-band transmission, thus obtaining the L-band signal to be processed. The first passive dual-core optical fiber can be... Figure 2 The first MCF-link segment from left to right in the middle, the first passive dual-core fiber used for C-band transmission, has its core position as follows: Figure 2 At the beginning of the upper core of the first MCF-link segment, the core position of the first passive dual-core fiber used for L-band transmission can be... Figure 2 The beginning of the fiber core at the bottom of the first MCF-link segment.

[0048] Step 30: Each of the signals to be processed is transmitted through a passive dual-core optical fiber and amplified at an asymmetric gain optical fiber to obtain the processed signal.

[0049] Among them, each signal to be processed refers to the signal to be processed in the C-band and the signal to be processed in the L-band.

[0050] In one embodiment, the system of this invention may include two passive dual-core optical fibers and one asymmetric gain optical fiber, with the passive dual-core optical fibers and the asymmetric gain optical fiber arranged alternately. For example, when using this architecture system, in step 20, the signal to be processed is transmitted to the first passive dual-core optical fiber, and then in step 30, the signal to be processed is transmitted through the first passive dual-core optical fiber and amplified at the asymmetric gain optical fiber to obtain a processed signal, so that in step 40 below, the processed signal is transmitted through the second passive dual-core optical fiber.

[0051] In another embodiment, such as Figure 2 As shown, the system of this embodiment may include three passive dual-core optical fibers and two asymmetric gain optical fibers, with the passive dual-core optical fibers and asymmetric gain optical fibers arranged alternately. For example, using this architecture system, in step 20, the signal to be processed is transmitted to the first passive dual-core optical fiber. Then, in step 30, the signal to be processed is transmitted through the first passive dual-core optical fiber and amplified at the first asymmetric gain optical fiber to obtain an intermediate signal. This intermediate signal is then transmitted to the second passive dual-core optical fiber and transmitted through it, and amplified again at the second asymmetric gain optical fiber to obtain a processed signal. This processed signal is then transmitted through the third passive dual-core optical fiber in step 40 below. Specifically, the C-band signal to be processed is transmitted through the first passive dual-core optical fiber (e.g., through...). Figure 2 The first MCF-link segment from left to right (the upper fiber core) transmits the signal, then transmits it to... Figure 2 The first RGU section from left to right (i.e., the upper core of the first asymmetric gain fiber) amplifies the signal to obtain the intermediate C-band signal; this intermediate signal is then amplified through the second passive dual-core fiber (e.g., through...). Figure 2 The second MCF-link segment from left to right (the upper fiber core) transmits the signal, then transmits it to... Figure 2 The second RGU section from left to right (i.e., the upper core of the second asymmetric gain fiber) amplifies the signal to obtain the processed C-band signal. The L-band signal to be processed passes through the first passive dual-core fiber (e.g., through...). Figure 2 The first MCF-link segment from left to right (the lower fiber core) transmits the signal, then transmits it to... Figure 2 The first RGU section from left to right (i.e., the lower core of the first asymmetric gain fiber) amplifies the signal to obtain the L-band intermediate signal; this intermediate signal is then amplified through the second passive dual-core fiber (e.g., through...). Figure 2 The second MCF-link segment from left to right (the lower fiber core) transmits the signal, then transmits it to... Figure 2 The second RGU section from left to right (i.e., the lower core of the second asymmetric gain fiber) is amplified to obtain the processed L-band signal.

[0052] Step 40: The processed signals are transmitted through passive dual-core optical fiber and then combined in single-mode optical fiber through a dual-core fan-out device to continue transmission in the metropolitan area network.

[0053] In this dual-core fan-out device, the two fan-out components transmit the processed C-band signal and the processed L-band signal, respectively. (The last sentence appears to be incomplete and unrelated to the preceding text.) Figure 2 In the system shown, the processed C-band signal passes through a third passive dual-core optical fiber (e.g., Figure 2 The upper fiber core of the third MCF-link segment from left to right is transmitted to the corresponding fan-out device in the dual-core fan-out device; the processed L-band signal is transmitted through this third passive dual-core fiber (e.g., Figure 2 The fiber core at the bottom of the third MCF-link segment from left to right is transmitted to the corresponding fan-out device in the dual-core fan-out device; at this time, the two are combined after entering the single-mode fiber through the dual-core fan-out device and continue to be transmitted in the metropolitan area network.

[0054] This invention targets island scenarios and employs a broadband system solution based on remote pumping. To avoid the Raman effect caused by excessive power in repeaterless amplification scenarios, multi-core optical fibers are used to achieve wavelength division multiplexing (WDM) transmission and amplification. Instead of WDM multiplexing, a space-division multiplexing system is used in the island transmission process. By converting WDM to space-division multiplexing, low cabling size, low device complexity, low nonlinearity, and broadband amplification suitable for multi-core systems are achieved, enabling gain-flat broadband remote pumping for multi-core systems. To overcome the shortcomings of existing space-division multiplexing schemes and avoid using too many fan-in / fan-out devices in the transmission link, thus reducing the loss and complexity caused by multiple fan-in / fan-out devices, this invention uses asymmetric gain optical fibers to amplify C-band and L-band signals separately. This dual-core remote pumping method reduces the cost of multiple fan-in / fan-out devices and also mitigates the nonlinearity problem of C-band and L-band signals transmitting in the same fiber core. In addition, the system is compatible with Raman amplification to further improve gain performance, ultimately enabling high-capacity, low-cost, and easy-to-maintain cross-island repeaterless transmission.

[0055] This invention also provides a single-span broadband multi-wavelength amplification system for multi-island scenarios, used to achieve ultra-long single-span transmission between islands; it includes a C+L wavelength division multiplexing unit, a dual-core fan-in device, a dual-core fan-out device, at least two sections of passive dual-core optical fiber, and at least one section of asymmetric gain optical fiber; wherein: The C+L wavelength division multiplexing unit is used to split the C-band signal and L-band signal in the C+L ultra-wideband signal transmitted in single-mode fiber into two paths to obtain a single-band signal; it is also used to couple pump light to each of the single-band signals.

[0056] The dual-core fan-in device is used to transmit the single-band signals of each separately coupled pump light to a passive dual-core optical fiber to obtain the signal to be processed.

[0057] The passive dual-core optical fiber is used to transmit the signals to be processed or the processed signals.

[0058] The asymmetric gain fiber is used to amplify each of the signals to be processed to obtain the processed signal.

[0059] The dual-core fan-out device is used to combine the processed signals and then enter the single-mode optical fiber for continued transmission in the metropolitan area network.

[0060] In one embodiment, such as Figure 2As shown, the C+L wavelength division multiplexing unit is connected to the dual-core fan-in device; the dual-core fan-in device is connected to the first passive dual-core fiber to facilitate the transmission of the signal to be processed through the first passive dual-core fiber; the first passive dual-core fiber is connected to the first asymmetric gain fiber to facilitate C+L broadband forward pump amplification to obtain the intermediate signal; the first asymmetric gain fiber is connected to the second passive dual-core fiber to facilitate the transmission of the intermediate signal through the second passive dual-core fiber. The signal is generated through a combination of two segments: a passive dual-core fiber and a passive dual-core fiber. The second passive dual-core fiber is connected to the second asymmetric gain fiber to enable C+L broadband back-pump amplification, resulting in a processed signal. The second asymmetric gain fiber is connected to the third passive dual-core fiber to transmit the processed signal. The third passive dual-core fiber is connected to the dual-core fan-out device, allowing the C-band and L-band signals to enter the two single-mode fibers respectively. After WDM multiplexing, the signals continue to be transmitted in the metropolitan area network. Here, WDM stands for Wavelength Division Multiplexer.

[0061] In a specific implementation, such as Figure 2 As shown, a multi-island single-span ultra-long-distance transmission link includes: a remote optically pumped amplifier pump (ROPA pump), an ultra-wideband metro network (UWB-Metro Networks), a wavelength division multiplexing (WDM) unit, a space division multiplexing (SDM) unit, a multi-core fiber link (MCF-link), and a remote gain unit (RGU).

[0062] In this context, the ROPA pump provides pump light to passive ROPA elements, generating gain in the fiber optic line and extending the repeaterless transmission distance of the signal. UWB-Metro refers to metropolitan area networks that use ultra-wideband technology (e.g., extending to the C+L band) to increase transmission capacity to meet the rapid growth of data traffic. WDM refers to transmitting multiple optical signals of different wavelengths in a single optical fiber; SDM refers to using multi-core fibers or multiple fibers for parallel transmission; WDM-SDM refers to the combination of these two multiplexing technologies, which together achieve a significant increase in system capacity. RGU is a passive amplification unit located in a ROPA system, containing erbium-doped fiber (EDF). The RGU is remotely excited by a pump source to amplify C-band and L-band optical signals; the following embodiment of the invention provides a new example of RGU. MCF-link refers to an optical transmission link composed of multi-core fibers (one fiber containing multiple independent cores), used to significantly increase the transmission density and capacity of a single fiber.

[0063] The following section further explains the single-span broadband multi-wave amplification method for multi-island scenarios based on the single-span broadband multi-wave amplification system for multi-island scenarios according to embodiments of the present invention: In one embodiment, such as Figure 2 As shown, the passive dual-core fiber comprises two passive cores, which can be used to transmit C-band and L-band signals to be processed, respectively. The asymmetric gain fiber also comprises two cores; a specific example will be given below and will not be elaborated upon here.

[0064] In one embodiment, such as Figure 2 As shown, in a multi-island single-span ultra-long-distance transmission link, the terrestrial metropolitan area network uses standard single-mode optical fiber to transmit C+L ultra-wideband signals.

[0065] The C+L ultrawideband signal is split into two paths by a wavelength division multiplexer, with the C-band and L-band signals separated into two paths. The two signals are first coupled to 1480 nm pump light via a 1480 nm wavelength division multiplexer, and then transmitted into a passive dual-core optical fiber (e.g., ...) through a dual-core fan-in / fan-out device. Figure 2 The first segment from left to right (MCF-link) is transmitted.

[0066] Then amplification is performed at the first asymmetric gain fiber segment. In an optional embodiment, core A (e.g., Figure 2 The “Core-A EDF (C-band)” amplifies the C-band signal, and the fiber core B (e.g., Figure 2The "Core-B EDF (L-band)" amplifies the L-band signal, achieving C+L broadband forward pump amplification. The amplified signal (including the amplified C-band signal and the amplified L-band signal) then passes through a passive dual-core optical fiber (e.g., ...). Figure 2 Transmission occurs via the second MCF-link segment from left to right, through the second asymmetric gain fiber segment (e.g., Figure 2 The amplification is performed at the second segment (RGU). Similarly, the core A of the second segment of the asymmetric gain fiber amplifies the C-band signal, and the core B amplifies the L-band signal, thereby realizing C+L broadband back-pumped amplification.

[0067] In traditional single-core C+L schemes, C and L are transmitted together in the same fiber core. High-power C-band photons transfer energy to the L-band through stimulated Raman scattering (SRS), causing an abnormal drop in C-band power and an abnormal rise in L-band power, resulting in a degraded optical signal-to-noise ratio and poor system performance. When using a single fiber for amplification, since the fiber length and design are fixed, optimizing C-band processing performance will sacrifice L-band processing performance, and vice versa.

[0068] The core of an RGU (Regional Generated Fiber Unit) is a segment of erbium-doped fiber (EDF). Erbium ions, excited by pump light, are in a state capable of amplifying signals. When signal light passes through, the erbium ions release energy, amplifying the signal. If a multi-core erbium-doped fiber is used as an RGU, and all cores are designed for the C-band, it's difficult to adapt to the high-capacity C+L broadband transmission in metropolitan area networks. If the cores are designed for both C-band and L-band, there's the problem of balancing core lengths. Typically, the optimal amplification length for L-band fiber is much greater than that for C-band fiber, making it difficult to achieve equal lengths by adjusting the doping design. However, in homogeneous multi-core fibers, core crosstalk cannot be completely avoided. This crosstalk manifests as crosstalk and competition in pump light power, and crosstalk between signals of the same wavelength leads to signal quality degradation.

[0069] Furthermore, within a single core, the C-band and L-band inherently compete with each other (the L-band amplification efficiency is typically lower than that of the C-band).

[0070] In MCF, this competitive relationship extends to the chip-to-chip relationship, forming a complex two-dimensional competition matrix that cannot be managed by traditional single-chip control logic.

[0071] This invention physically avoids the coexistence of C-band and L-band signals in the same fiber core through core-splitting transmission: In passive dual-core fibers, C-band and L-band signals can be carried separately; in asymmetric gain fibers, although only the first half of the active dual-core fiber has two active cores, the passive cores in the other half of the hybrid dual-core fiber can serve as independent transmission channels. As long as it is ensured that C-band and L-band signals are always located in different cores throughout the entire transmission path, cross-band energy transfer in SRS is essentially eliminated.

[0072] To address the problems of the prior art, embodiments of the present invention provide an RGU. Specifically, in one embodiment, as follows: Figure 3 As shown, the asymmetric gain fiber includes active dual-core fiber and hybrid dual-core fiber. In one embodiment, the RGU of this invention is an active dual-core fiber (i.e., Figure 3 "Active" and hybrid dual-core fiber (i.e., Figure 3 The "passive / active" in the text refers to direct fusion splicing; wherein, the active dual-core optical fiber includes a first core (i.e., Figure 3 In an active dual-core fiber, the upper core) and the second core (i.e., Figure 3 The hybrid dual-core fiber includes a third core (i.e., the lower core of an active dual-core fiber). Figure 3 The upper core of the hybrid dual-core fiber) and the fourth core (i.e., Figure 3 (The lower core of the hybrid dual-core fiber). The first, second, and fourth cores are active cores; the third core is a passive core. The active dual-core fiber and the hybrid dual-core fiber are directly fused, that is, the first core and the third core are directly fused, and the second core and the fourth core are directly fused. Figure 3 Passive fiber cores are shown with dashed lines, while active fiber cores are shown with solid lines.

[0073] Based on this, since the RGU of this embodiment is obtained by combining active dual-core fiber and hybrid dual-core fiber, in order to determine the length parameters of the active dual-core fiber and hybrid dual-core fiber in the RGU of this embodiment, and to determine the optimal length combination of the two to meet the needs of actual application scenarios, such as... Figure 4 As shown, the method further includes: Step 301: Model the fiber by dividing it into multiple segments and perform step-by-step calculations to determine the gain change under dual-core coupling, so as to obtain the amplification model of the asymmetric gain fiber.

[0074] like Figure 6As shown, in the modeling of this embodiment, calculations are performed separately for active dual-core fibers and hybrid dual-core fibers. For active dual-core fibers or hybrid dual-core fibers, the corresponding dual-core fibers are divided into small segments for step-by-step calculation to accurately simulate the performance of the RGU. The final product is designed based on a whole fiber section. In this embodiment, the whole dual-core fiber is divided into many small segments, and the attenuation or gain of pump and signal, crosstalk coupling, and inversion particle number are calculated iteratively in each small segment.

[0075] In one embodiment, a bi-core fiber is cut into multiple segments. Within each segment, it is assumed that: fiber parameters (e.g., doping concentration, cross-sectional data) are constant; the power variations of the pump light and signal light follow the differential equations within that segment; and intercore crosstalk occurs only at the endpoints of each segment (or is uniformly distributed within the segment). Then, starting from the beginning of the bi-core fiber, the calculation is performed segment by segment: the pump light power and signal light power at the beginning of the segment are input; the gain / attenuation differential equations within each segment are solved according to the segment length to obtain the power at the end of the corresponding segment; the crosstalk coupling formula is applied at the end of the segment to exchange the power between the two fiber cores; the inverted particle number at the end of the segment is calculated using the updated power according to the segment length; the result is used as the input for the next segment, and this process is repeated until the calculation is completed for all lengths of the corresponding bi-core fiber.

[0076] Step 302: Based on the transmission requirements of the cross-island link, the pump power capability of the transmitting end, and the signal optical power reception requirements of the receiving end, use the amplification model to determine the optimal pump optical power level, the first length of the active dual-core fiber, and the second length of the hybrid dual-core fiber.

[0077] For a hybrid dual-core optical fiber with one active core and one passive core, since the gain of the passive fiber is 0 and the loss coefficient is reduced by an order of magnitude compared to the active fiber, the gain of the passive core (i.e., the third core) can be kept constant at 0. The crosstalk gain can still be calculated using the step-by-step calculation method.

[0078] Based on the transmission requirements of cross-island links, as well as the pump power capability at the transmitting end and the signal optical power reception requirements at the receiving end, an amplification model is used to calculate the optimal pump optical power level and the lengths of active dual-core optical fibers and hybrid dual-core optical fibers, thereby realizing the amplifier design. The calculation accuracy and complexity can be adjusted by the step size.

[0079] In one embodiment, the transmission requirements of the cross-island link include, for example, the required transmission distance and allowable link loss; the pump power capability at the transmitting end includes, for example, the maximum pump optical power that can be provided; and the signal optical power reception requirements at the receiving end include, for example, the receiver sensitivity. By adjusting parameters such as the pump optical power level, the length of the active dual-core fiber, and the length of the hybrid dual-core fiber, the amplifier's performance (gain, noise figure, gain flatness) is made to meet the system requirements. This is achieved by adjusting the step size; a smaller step size results in higher calculation accuracy but also a greater computational load. Those skilled in the art can select an appropriate step size based on actual needs to achieve a balance between accuracy and efficiency.

[0080] Step 303: Fabricate an asymmetric gain fiber comprising active dual-core fiber and hybrid dual-core fiber according to the pump light power level, the first length and the second length.

[0081] First, the amplification model of the asymmetric gain fiber is determined through step 301; then, when the application is required, the amplification model is used to determine the required pump power level, the first length of the active dual-core fiber, and the second length of the hybrid dual-core fiber as needed through step 302; finally, the product is designed and manufactured accordingly.

[0082] Furthermore, to illustrate the C+L amplification model based on dual-core optical fiber in one embodiment of the present invention, as follows: Figure 5 As shown, step 301 includes: Step 3011: Divide the entire active dual-core optical fiber into multiple smaller segments; iteratively perform gain calculation for each smaller segment in a step-by-step calculation manner until the gain calculation for the entire active dual-core optical fiber is completed.

[0083] For example, such as Figure 6 As shown, the entire active dual-core optical fiber is divided into sections of length [length missing]. (i.e., multiple small segments of unit step length in the following text) Indicates the total length of the dual-core optical fiber. This indicates the number of segments into which the total length is divided equally. The calculation is performed iteratively, with each segment treated as the current segment. After the calculation is completed, the next segment is calculated until the calculation of the entire active dual-core optical fiber is completed.

[0084] In one embodiment, firstly, the gain spectrum of a single-core fiber with the same doping formulation as the active dual-core fiber is obtained, and the emission cross-section vector and absorption cross-section vector are determined; the relative inversion particle number is calibrated according to the pump light power and signal light power; the crosstalk coefficient of the active dual-core fiber is measured, and the relationship between the crosstalk power ratio and the fiber position is determined.

[0085] The phrase "having the same doping formula as the active dual-core fiber" means that the single-core fiber used for testing has the same rare earth element doping type (e.g., erbium), doping concentration, and key parameters such as numerical aperture and cutoff wavelength as the reference active dual-core fiber. The gain spectrum of a single-core fiber refers to a conventional single-core fiber sample containing only one core, fabricated from doped fibers with the same material parameters, with a length close to the length of the RGU in the active multi-core fiber.

[0086] In a dual-core optical fiber, because the two cores are physically very close, the electromagnetic field of the optical signal transmitted in one core can penetrate into the other, causing some energy to "leak" to the other core. The crosstalk coefficient of a dual-core optical fiber is a key parameter describing the degree of optical signal leakage between the two cores. To quantify the intensity of inter-core interference, it is also necessary to measure the crosstalk coefficient, thereby accurately predicting and optimizing the system's gain, noise figure, and transmission performance when establishing a dual-core erbium-doped fiber amplification model. The specific method for measuring the crosstalk coefficient is determined by those skilled in the art based on the specific application scenario.

[0087] The emission cross-section vector, absorption cross-section vector, and relative inversion particle number of the single-core fiber segment are obtained to establish the physical input and core state variables of the dual-core erbium-doped fiber amplification model.

[0088] In one specific instance, a section of fiber with the same doping as the dual-core fiber was tested. The gain spectrum of a single-core optical fiber with a length of [number] meters is as follows: ; in, The total length is Single-core optical fiber at wavelength Gain at a given point (unit: decibel, expressed as "dB"). For the first Each wavelength sampling point, The total number density of erbium ions. The number density of erbium ions in the upper energy level (i.e., the excited state). wavelength The stimulated emission cross section at that location, The number density of erbium ions in the lower energy level (i.e., the ground state) is given. wavelength The absorption cross section at that location.

[0089] Among them, unit step size At wavelength The gain at that point is: ; Launch cross-section vector and absorption cross section vector Obtained through singular value decomposition. , in, For one The matrix represents the gain spectrum measured under different experimental conditions (e.g., different pump / signal powers). To be at wavelength The first The wavelength point at the _th _th Gain spectrum of the second measurement. It is a left singular matrix. It is a singular value matrix. It is a right singular matrix.

[0090] The relative inversion particle number is expressed by the following formula relative to the pump light power. and signal optical power Calibration: ; in, , , , , and All are fitting parameters; in one embodiment, This is a constant term (bias). For the logarithmic coefficient, The weight of the signal light in the molecule, The weight of the pump light in the denominator, and These are all small constants, used to prevent the denominator from being zero or to improve the fit.

[0091] The crosstalk coefficient of a dual-core optical fiber is measured. The coupling crosstalk of the dual-core optical fiber is periodic, and the crosstalk power ratio varies with position. The change is denoted as .

[0092] Then, calculations are performed for each current segment, as shown in the following specific example: In one embodiment, the pump power attenuation and signal power gain are calculated in a step-by-step manner according to the emission cross-section vector, the absorption cross-section vector, and the relative inversion particle number in each segment. At the end of each segment, crosstalk power exchange is performed between the two fiber cores based on the crosstalk coefficient to update the pump power and signal power of each fiber core. The relative inversion particle number at the corresponding end position of the segment is calculated according to the pump power and the signal power. This process is iteratively executed until the gain calculation of the entire active dual-core fiber is completed.

[0093] The iteration refers to using the output of the currently calculated segment as the input of the next segment, repeating the operation and calculation of the previous segment until the calculation of the entire dual-core active optical fiber is completed. The updated optical power includes both pump optical power and signal optical power.

[0094] By employing step-by-step iterations and simultaneously considering the cumulative effects of gain, attenuation, and crosstalk, errors introduced by simplification are avoided. The relative inversion particle number and signal power at any position along the fiber are obtained, thus accurately predicting the final gain and noise figure for the C-band and L-band.

[0095] The gain change under dual-core coupling is calculated using a step-by-step calculation method. When performing step-by-step calculations on active dual-core fibers, core A represents the first core, and core B represents the second core, as detailed below: Among them, pump light power attenuation length The following is: , in, For in position At this location, the pump optical power in fiber core A or fiber core B, subscript Indicates pump light, To the pump wavelength Below, the length is In this fiber, the gain of core A or core B on the pump light (a negative value indicates attenuation). To convert the gain to a linear power factor.

[0096] Signal optical power gain length Later ; in, To the signal wavelength Below, the length is In this section of optical fiber, the gain of the signal light by core A or core B; For in position At the location, the first in fiber core A or fiber core B The power of each signal wavelength.

[0097] After crosstalk, fiber core A ( Figure 6 The pump power of the fiber core located at the top is: ; in, After crosstalk coupling, fiber core A is in Pump light power at the location, In order to be in Crosstalk coefficient at the location, In order to be in The core A pump power before crosstalk (i.e., after gain / attenuation but before crosstalk switching), In order to be in Pump power of fiber core B before crosstalk.

[0098] The corresponding first The optical power of each signal is: ; And B fiber core ( Figure 6 The pump power of the fiber core located below is: , in, After crosstalk coupling, fiber core B is in Pump light power at the location, In order to be in Crosstalk coefficient at the location, In order to be in Core B pump power before crosstalk (i.e., after gain / attenuation but before crosstalk switching).

[0099] The corresponding first The optical power of each signal is: .

[0100] The position can then be calculated. Number of inverted particles at: For core A, the number density of erbium ions in the upper energy level (excited state) is: , in, This represents the signal optical power of fiber core A after crosstalk. This represents the pump power of fiber core A after crosstalk.

[0101] Similarly, for core B, the number density of erbium ions in the upper energy level (excited state) is: .

[0102] The number of particles in the corresponding ground state energy level can be determined by a linear relationship. Obtain, among which Given the total number density of erbium ions, the next gain segment is calculated: ; in, In order to be in The length is In the next segment of the optical fiber, core A or core B affects the wavelength. Gain; For fiber core A or fiber core B in The number density of excited-state particles at that location For fiber core A or fiber core B in The ground-state particle number density at that point. This formula is used to update the gain for the next small segment, serving as input for iteration.

[0103] The above process is iterated until the gain calculation for the entire dual-core active fiber segment is completed. In one embodiment, at each iteration, starting from the current step size, the power after transmission is calculated using the gain coefficient; at the end of the step size, the crosstalk coefficient is applied to update the power of the two fiber cores; a new inversion particle number is calculated using an empirical formula; the gain coefficient for the next fiber segment is calculated based on the new inversion particle number; and the current step size is updated (e.g., setting the gain coefficient to the current step size). Updated to Repeat these steps until the entire fiber optic cable has been calculated.

[0104] By employing step-by-step iterations and considering the cumulative effects of gain / attenuation and crosstalk, errors introduced by simplification are avoided. The actual gain distribution is calculated: the relative inverted particle number and signal power at any position along the fiber are obtained, thus accurately predicting the final gain and noise figure in the C / L band.

[0105] Step 3012: Set the gain of the passive core in the hybrid dual-core fiber to zero and perform gain calculation including crosstalk in the same step-by-step calculation method as the active dual-core fiber.

[0106] That is, the active dual-core fiber (containing two active fiber cores) is calculated according to step 3011, such as... Figure 6 As shown, the entire hybrid dual-core fiber is first divided into multiple segments. The gain spectrum of a single-core fiber segment with the same doping formulation as the active fiber (i.e., the fourth core) in the hybrid dual-core fiber is obtained, and its emission and absorption cross-section vectors are determined. The relative inversion particle number is calibrated based on the pump power and signal power of this single-core fiber segment. The crosstalk coefficient of this hybrid dual-core fiber is measured using this passive dual-core fiber segment, and the relationship between the crosstalk power ratio and fiber position is determined. Then, each segment is iteratively calculated as the current segment, and the calculation proceeds to the next segment after completion, until the calculation of the entire active dual-core fiber segment is completed. Throughout the aforementioned process, the gain of the passive core is kept constant at zero.

[0107] For a dual-core fiber structure with only one erbium-doped core (i.e., active fiber) and the other undoped (i.e., passive fiber), a simplified model is implemented. The gain coefficient of the passive core is set to 0, but its loss coefficient (transmission loss) is much smaller than the reabsorption loss of the active core. Therefore, it only needs to be considered for the accuracy requirements of the model, and is considered at a higher model accuracy. The step-by-step calculation method for the active dual-core fiber is still used, considering the impact of crosstalk on the two cores, but the passive core does not provide amplification. It should be noted that when performing step-by-step calculations on the hybrid dual-core fiber according to the formula in the embodiment of step 3011, core A represents the third core, and core B represents the fourth core.

[0108] In one embodiment, when performing step-by-step calculations on the hybrid dual-core fiber according to step 3011, step 3012 further includes: During the calculation for each segment (i.e., in each iteration), the power changes of the pump light and signal light are iteratively calculated based on the relative inversion particle number, gain, and absorption eigenvector, yielding the pump light power value and signal light power value of the fourth fiber core at the end of the current segment. When the pump light is transmitted through the third fiber core, power attenuation is calculated considering only intrinsic loss, yielding the pump light power value and signal light power value of the third fiber core at the end of the current segment. At the end of the current segment, using the pump light power value and signal light power value of the fourth fiber core, the pump light power value and signal light power value of the third fiber core, and the measured crosstalk coefficient, the power exchange between the pump light and signal light between the third and fourth fiber cores is calculated, updating the power values ​​of each fiber core. The measured crosstalk coefficient refers to the crosstalk coefficient of the hybrid dual-core fiber as previously measured. Each fiber core refers to all fiber cores within the dual-core fiber segment (i.e., the third and fourth fiber cores), and the update must simultaneously consider the power changes of all wavelengths in both fiber cores.

[0109] The relative inversion particle number of the fourth fiber core is calculated using the updated power value. Only the fourth fiber core requires calculation of the relative inversion particle number.

[0110] Step 3013: Based on the gain calculation results of the active dual-core fiber and the hybrid dual-core fiber, establish an amplification model characterizing the relationship between the first length, the second length and the pump light power level.

[0111] By establishing an amplification model and changing the total length of amplification or transmission in the C-band and the total length of amplification or transmission in the L-band, the performance under different length combinations was simulated, and the optimal length combination of active dual-core fiber and hybrid dual-core fiber for the RGU of this embodiment of the invention was found.

[0112] In one embodiment, when using the product prepared according to the above steps, step 30 further includes: Using the fabricated asymmetric gain fiber, the corresponding C-band signal is amplified through the first core of the active dual-core fiber, the corresponding L-band signal is amplified through the second core of the active dual-core fiber, the corresponding L-band signal is amplified through the fourth core of the hybrid dual-core fiber, and the corresponding C-band signal is transmitted through the third core of the hybrid dual-core fiber, thus amplifying the signal at the asymmetric gain fiber to obtain the processed signal. Figure 3 As shown, the active dual-core fiber and the hybrid dual-core fiber are directly fused together. For example, if the first fiber is used to amplify the C-band signal, then the third fiber is used to transmit the C-band signal, and the second fiber is used to amplify the L-band signal, and the fourth fiber is used to amplify the L-band signal. During the determination of the amplification model, design, and fabrication in the above steps, since the required erbium-doped fiber length for the L-band is longer than that for the C-band, it has been determined by those skilled in the art whether the third fiber core transmits the C-band signal or the L-band signal. Therefore, in use, the fourth fiber core amplifies the L-band signal while the third fiber core transmits the C-band signal.

[0113] In one embodiment, such as Figure 7 As shown, step 40 includes: Step 401: The processed signals are transmitted through the corresponding passive dual-core optical fiber and then enter the corresponding single-mode optical fiber through the dual-core fan-out device.

[0114] Step 402: The signals in each single-mode fiber are coupled to the back pump light through a wavelength division multiplexer and then combined through a C / L wavelength division device to obtain the processed C+L ultrawideband signal.

[0115] In one embodiment, in a multi-island single-span ultra-long-distance transmission link, the amplified signal then passes through a section of passive dual-core optical fiber (e.g., Figure 2 The first segment (MCF-link) from right to left is transmitted through a dual-core fan-in / fan-out device into a single-mode fiber. After being coupled to the back pump light by a 1480 nm wavelength division multiplexer, it is then combined by a C / L wavelength division multiplexer and finally continues to propagate in the single-mode fiber of the metropolitan area network.

[0116] like Figure 8 and Figure 9 The diagram shown illustrates a set of schematic representations illustrating the reduction of nonlinear power transfer effects. Figure 8 The diagram illustrates a specific example of power transfer in a single-fiber optical fiber between C+L bands (i.e., C-band and L-band light). Figure 8 In the image, the dashed line represents the input to the single-fiber optical fiber (i.e., Figure 8 The solid line represents the power of the single-mode system in the image; the solid line represents the output power of the single-fiber optical fiber (i.e., the single-mode system in the image). Figure 8 The power of a single-mode system (e.g., in a single-mode system). Figure 9The diagram shows a specific example of power transfer in the C-band and L-band of light in a two-fiber optical fiber. Figure 9 In the diagram, the dashed line represents the input to the dual-fiber optical fiber (i.e., Figure 9 The solid line represents the power of the dual-core system in the image; the solid line represents the output power of the dual-fiber optical fiber (i.e., Figure 9 The power of the dual-core system (in the example). Figure 8 The solid line in the middle and as Figure 9 The slopes of the solid lines in the text are the same, but because Figure 9 The length of the horizontal axis occupied by the middle is shortened. Figure 9 The amplitude in is only Figure 8 Half of it. This means that by avoiding the propagation of C-band and L-band light in the same fiber core, the present invention reduces the nonlinear effect of SRS on the power transfer from C-band to L-band. The SRS effect only occurs in the C-band and L-band themselves.

[0117] The foregoing embodiments provide a single-span broadband multi-wave amplification method for multi-island scenarios. In this embodiment, another single-span broadband multi-wave amplification device for multi-island scenarios will be proposed. The single-span broadband multi-wave amplification device for multi-island scenarios includes: a processor and a memory for storing processor-executable instructions; wherein, the processor is configured to execute the single-span broadband multi-wave amplification method for multi-island scenarios described in the foregoing embodiments.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A single-span broadband multi-wave amplification method for multi-island scenarios, characterized in that, The method is applied to a single-span broadband multi-wavelength amplification system for multi-island scenarios. The system includes at least two passive dual-core optical fibers and at least one asymmetric gain optical fiber, with the passive dual-core optical fiber and the asymmetric gain optical fiber arranged alternately. The method includes: The C-band and L-band signals in the C+L ultra-wideband signal transmitted through single-mode fiber are split into two paths to obtain a single-band signal. Each of the single-band signals is coupled with pump light and transmitted to a passive dual-core optical fiber via a dual-core fan-in device to obtain the signal to be processed. Each of the signals to be processed is transmitted through a passive dual-core optical fiber and amplified at an asymmetric gain optical fiber to obtain the processed signal. The processed signals are transmitted via passive dual-core optical fiber and then combined in single-mode optical fiber via dual-core fan-out devices to continue transmission in the metropolitan area network.

2. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 1, characterized in that, The asymmetric gain fiber includes active dual-core fiber and hybrid dual-core fiber; The method further includes: The fiber is modeled by dividing it into multiple small segments, and step-by-step calculations are performed to determine the gain change under dual-core coupling, so as to obtain the amplification model of the asymmetric gain fiber. Based on the transmission requirements of the cross-island link, the pump power capability at the transmitting end, and the signal optical power reception requirements at the receiving end, the amplification model is used to determine the optimal pump optical power level, the first length of the active dual-core fiber, and the second length of the hybrid dual-core fiber. Based on the pump light power level, the first length, and the second length, an asymmetric gain fiber comprising active dual-core fiber and hybrid dual-core fiber is fabricated.

3. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 2, characterized in that, The process of modeling the fiber by dividing it into multiple segments and performing step-by-step calculations to determine the gain variation under dual-core coupling, in order to obtain the amplification model of the asymmetric gain fiber, includes: The entire active dual-core optical fiber is divided into multiple smaller segments; the gain calculation of each smaller segment is performed iteratively in a step-by-step calculation manner until the gain calculation of the entire active dual-core optical fiber is completed. The gain of the passive core in the hybrid dual-core fiber is set to zero, and the gain calculation, including crosstalk, is performed in the same step-by-step calculation method as that of the active dual-core fiber. Based on the gain calculation results of the active dual-core fiber and the hybrid dual-core fiber, an amplification model is established to characterize the relationship between the first length, the second length and the pump light power level.

4. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 3, characterized in that, The step-by-step calculation method, iteratively performing the gain calculation for each small segment until the gain calculation for the entire active dual-core optical fiber is completed, includes: Obtain the gain spectrum of a single-core fiber with the same doping formulation as the active dual-core fiber, and determine the emission cross-section vector and absorption cross-section vector; calibrate the relative inversion particle number based on the pump light power and signal light power; measure the crosstalk coefficient of the active dual-core fiber, and determine the relationship between the crosstalk power ratio and the fiber position. Using a step-by-step calculation method, the pump light power attenuation and signal light power gain are calculated in each segment according to the emission cross-section vector, the absorption cross-section vector, and the relative inversion particle number. At the end of each segment, crosstalk power exchange is performed between the two fiber cores based on the crosstalk coefficient to update the pump light power and signal light power of each fiber core. The relative inversion particle number at the corresponding end position of the segment is calculated according to the pump light power and the signal light power. This process is iteratively executed until the gain calculation of the entire active dual-core fiber is completed.

5. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 3, characterized in that, The active dual-core optical fiber includes a first core and a second core; the hybrid dual-core optical fiber includes a third core and a fourth core. The first fiber core, the second fiber core, and the fourth fiber core are active fiber cores; the third fiber core is a passive fiber core. The first fiber core is directly fused to the third fiber core, and the second fiber core is directly fused to the fourth fiber core.

6. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 5, characterized in that, The step of setting the gain of the passive core in the hybrid dual-core fiber to zero and performing gain calculation including crosstalk in the same step-by-step calculation method as the active dual-core fiber further includes: Based on the relative inversion particle number, gain, and absorption eigenvector, the power changes of the pump light and signal light are iteratively calculated to obtain the pump light power value and signal light power value of the fourth fiber core at the end of the current segment. By considering only intrinsic loss for power attenuation calculation, the pump optical power value and signal optical power value of the third fiber core at the end of the current segment are obtained; At the end of the current segment, using the pump light power value and signal light power value of the fourth fiber core, the pump light power value and signal light power value of the third fiber core, and the measured crosstalk coefficient, the power exchange amount of pump light and signal light between the third fiber core and the fourth fiber core is calculated, and the power value of each fiber core is updated. The relative inversion particle number of the fourth fiber core was calculated using the updated power value.

7. The single-span broadband multi-wave amplification method for multi-island scenarios according to claim 5, characterized in that, Each of the signals to be processed is transmitted through a passive dual-core optical fiber and amplified at an asymmetric gain optical fiber to obtain the processed signal, which further includes: Using the fabricated asymmetric gain optical fiber, the corresponding C-band signal is amplified through the first core of the active dual-core optical fiber, the corresponding L-band signal is amplified through the second core of the active dual-core optical fiber, the corresponding L-band signal is amplified through the fourth core of the hybrid dual-core optical fiber, and the corresponding C-band signal is transmitted through the third core of the hybrid dual-core optical fiber, so as to amplify the signal at the asymmetric gain optical fiber and obtain the processed signal.

8. The single-span broadband multi-wave amplification method for multi-island scenarios according to any one of claims 1-7, characterized in that, The processed signals are transmitted via passive dual-core optical fiber and then combined after passing through a dual-core fan-out device into a single-mode optical fiber. Each of the processed signals is transmitted through the corresponding passive dual-core optical fiber and then enters the corresponding single-mode optical fiber through the dual-core fan-out device. The signals in each single-mode fiber are coupled to the back pump light through a wavelength division multiplexer and then combined through a C / L wavelength division device to obtain the processed C+L ultrawideband signal.

9. A single-span broadband multi-wave amplification system for multi-island scenarios, characterized in that, The single-span broadband multi-wavelength amplification system is used to implement the single-span broadband multi-wavelength amplification method as described in any one of claims 1-8, comprising a C+L wavelength division multiplexing unit, a dual-core fan-in device, a dual-core fan-out device, at least two sections of passive dual-core optical fiber, and at least one section of asymmetric gain optical fiber; wherein: The C+L wavelength division multiplexing unit is used to split the C-band signal and L-band signal in the C+L ultra-wideband signal transmitted through single-mode fiber into two paths to obtain a single-band signal; it is also used to couple pump light to each of the single-band signals respectively. The dual-core fan-in device is used to transmit the single-band signals of each separately coupled pump light to a passive dual-core optical fiber to obtain the signal to be processed. The passive dual-core optical fiber is used to transmit each of the signals to be processed or the processed signals; The asymmetric gain fiber is used to amplify each of the signals to be processed to obtain the processed signal; The dual-core fan-out device is used to combine the processed signals and then enter the single-mode optical fiber for continued transmission in the metropolitan area network.

10. The single-span broadband multi-wavelength amplification system for multi-island scenarios according to claim 9, characterized in that, The C+L wavelength division multiplexing unit is connected to the dual-core fan-in device; The dual-core fan-in device is connected to the first section of passive dual-core optical fiber to facilitate the transmission of the signal to be processed through the first section of passive dual-core optical fiber. The first passive dual-core optical fiber is connected to the first asymmetric gain optical fiber so as to realize C+L broadband forward pump amplification through the first asymmetric gain optical fiber to obtain the intermediate signal. The first asymmetric gain fiber is connected to the second passive dual-core fiber to facilitate the transmission of the intermediate signal through the second passive dual-core fiber. The second passive dual-core fiber is connected to the second asymmetric gain fiber to enable C+L broadband back-pump amplification through the second asymmetric gain fiber to obtain the processed signal. The second asymmetric gain fiber is connected to the third passive dual-core fiber to facilitate the transmission of the processed signal through the third passive dual-core fiber. The third passive dual-core optical fiber is connected to the dual-core fan-out device so that the C-band and L-band can enter the two single-mode optical fibers respectively, and the signals can continue to be transmitted in the metropolitan area network after WDM multiplexing.

Images