A multimode erbium-doped fiber amplifier module with mode equalization
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JINAN UNIVERSITY
- Filing Date
- 2023-06-20
- Publication Date
- 2026-06-02
Smart Images
Figure CN116742454B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical device technology, and more specifically, to a mode-equalized multimode erbium-doped fiber amplifier module. Background Technology
[0002] With the development of internet technology, new services such as high-definition television and mobile multimedia are constantly emerging, leading to an exponential increase in the demand for information transmission bandwidth. Traditional single-mode optical fiber, limited by the nonlinear Shannon limit, has a transmission capacity capped at 100 Tbit / s. Therefore, we need to research new technologies to further improve the transmission capacity of optical networks. Over the past few decades, submarine networks have evolved alongside terrestrial submarine networks. While these two network categories share similarities (e.g., the need to cover ultra-long distances and transmit large amounts of data), some important differences determine their distinct evolutionary paths. Spatial demultiplexing multiplexing (SDM) holds promise as the ultimate solution to address future capacity demands and overcome these two network challenges.
[0003] Mode division multiplexing (MDD) technology utilizes the orthogonality between modes in optical fiber to treat each mode as an independent channel signal. In mode multiplexing systems, modes are introduced as a new dimensional resource, which helps to significantly improve the communication capacity of optical networks. Currently, the transmission loss of MMD-multiplexed optical fibers has been reduced to 0.2 dB / km. However, when the transmission distance reaches hundreds or thousands of kilometers, the signal power cannot continue to be transmitted due to attenuation. Therefore, in order to transmit the optical signal carrying information further, amplifiers must be used during optical signal transmission. Signal amplification is one of the most important key parameters in telecommunications networks.
[0004] In submarine networks, the number of power stations and the amount of electricity are limited. Distances are around thousands of kilometers, therefore amplification plays a crucial role in signal transmission. There has been significant progress in the evolution of submarine amplifiers, from the first generation (TAT-1 electrical repeaters using only electrical components) to the fifth generation 32FP mega-class optical amplifiers (repeaters), which are almost ready for service. Currently, there are two main types of submarine amplifiers for seabed operations. The first type is named the Remote Optical Pump Amplifier (ROPA). ROPAs can effectively amplify optical signals, increase transmission distance and cable system capacity, and compensate for optical signal loss. This type of amplifier can support signal amplification in different bands (C-band, etc.). It has up to 32 pairs of optical fibers, which is currently the limitation of commercial systems. Finally, it features a pressure-resistant, corrosion-resistant, high-strength hull and is capable of supporting operations at great depths.
[0005] EDFAs contain optical modules for transmitting signal and pump light and isolating reverse signal light. However, EDFAs are still limited by expensive and complex optical modules, as well as the complex fiber fusion splicing process required to combine multiple optical modules. Therefore, there is a need for EDFAs with simplified structures and smaller optical modules. EDFA modules are characterized by high integration, small size, and ease of maintenance, making them suitable for integration into submarine cables for signal amplification in submarine networks.
[0006] Another crucial parameter in telecommunications networks is mode gain equalization in EDFA (Differential Mode Gain). Differential mode gain (DMG) can cause system outages. It is well known that DMG strongly depends on the overlap between signal mode strength, pump mode strength, and rare-earth dopant distribution. Therefore, it can be addressed by adjusting the pump mode settings or erbium doping distribution within the fiber core pump. However, with the increase in multiplexing spatial modes, pump mode settings and erbium doping distribution become exceptionally complex.
[0007] Another method to achieve mode gain equalization is to use a cladding pump configuration. In this case, the pump intensity in the core is almost uniform, and the DMG is determined only by the overlap of the signal mode intensity and the erbium doping distribution. For erbium-doped step-index double-clad fibers, only a portion of the optical signal mode electric field within the core can interact with and be amplified by erbium ions, resulting in a higher intensity distribution of lower-order modes in the core compared to higher-order modes. However, by employing a suitable erbium doping distribution, it is possible to achieve a higher gain for higher-order modes under cladding pumping and a higher gain for lower-order modes under core pumping, thereby achieving low differential mode gain. Summary of the Invention
[0008] To address the aforementioned issues, this invention proposes a mode-equalized multimode erbium-doped fiber amplifier module. This module features a small size, simple structure, easy debugging, and full compatibility with fiber optic transmission links, reducing manufacturing complexity. Furthermore, it allows for the control of the power ratio between cladding pump and core pump under simultaneous cladding and core pumping, thereby achieving low differential mode gain. This makes it suitable for relay amplification in submarine communication transmissions.
[0009] To achieve the above technical objectives, the present invention provides a mode-equalized multimode erbium-doped fiber amplifier module, comprising: an optical multiplexing isolator, a pump source, a ring-core erbium-doped fiber, and a wavelength division multiplexer;
[0010] The optical multiplexing isolator is used to isolate the reverse signal and couple the pump light to the output. The optical multiplexing isolator is a device integrated by the pump fiber and the self-made submarine cable optical fiber. Isolation is achieved by the Faraday crystal in the middle, and the embedded dichroic mirror realizes the multiplexing of the signal light and the pump light. The input end of the optical multiplexing isolator receives the pump light through the pump fiber, and the signal fiber receives the signal light transmitted in the submarine optical cable. The signal fiber at the output end is fused with the erbium-doped ring fiber to perform core pumping.
[0011] The pump light source is used to output pump light;
[0012] The ring-core erbium-doped fiber is used for signal amplification;
[0013] The output of the wavelength division multiplexer is fused to the ring-core mode erbium-doped fiber to perform cladding pumping on the erbium-doped fiber, thereby controlling the gain difference between different modes.
[0014] Preferably, the core of the erbium-doped fiber comprises, from the inside out, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer. The first layer is circular, the second layer is a first ring, the third layer is a second ring, the fourth layer is a third ring, and the fifth layer is a fourth ring. The refractive index of the second layer is greater than that of the first layer and also greater than that of the third layer. The refractive index of the first layer is greater than that of the third layer. The refractive index of the fourth layer is the smallest. The refractive index of the fifth layer is equal to that of the third layer. The erbium doping distribution is two-layer erbium doping, and the erbium ion doping concentration of the second layer is less than that of the first layer.
[0015] Preferably, the ring-core erbium-doped fiber adopts a ring-core structure and ring doping. Under the cladding pumping action, the erbium doping distribution achieves a higher gain in higher-order modes than in lower-order modes, and under the core pumping action, the lower-order mode gain is greater than the higher-order mode gain, thereby achieving low differential mode gain.
[0016] Preferably, the refractive index structure of the ring-core erbium-doped fiber is the same as that of the submarine cable fiber.
[0017] Preferably, the optical multiplexing isolator uses an embedded dichroic mirror to couple the signal light and pump light for output, and at the same time, the addition of an isolation crystal prevents the signal from being coupled in reverse.
[0018] Preferably, the wavelength division multiplexer is combined with the optical multiplexing isolator to achieve the effect of gain control between high-order and low-order signals, thereby controlling the gain difference between low-mode signals.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: the ring-core erbium-doped fiber amplifier module has the advantages of small size, simple structure, easy debugging, and full compatibility with fiber optic transmission links. Secondly, the optical multiplexing isolator used in this structure supports the combination of signal light and pump light for fiber core pumping, while the wavelength division multiplexer performs cladding pumping through side pumping. Since the ring-core erbium-doped fiber adopts a ring doping distribution, the manufacturing process difficulty can be further reduced. At the same time, it can achieve low differential mode gain by controlling the power ratio of cladding pumping and fiber core pumping under the simultaneous action of cladding pumping and fiber core pumping. It is suitable for relay amplification in submarine communication transmission. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.
[0021] Figure 1 This is a schematic diagram of a ring-core erbium-doped fiber amplifier module for submarine transmission according to the present invention.
[0022] Figure 2 This is a schematic diagram of the optical multiplexing isolator structure in this invention;
[0023] Figure 3 This is a schematic diagram of the communication system structure in this invention;
[0024] Figure 4 This is a schematic diagram of a ring-core erbium-doped optical fiber structure for submarine transmission according to the present invention.
[0025] Figure 5 This is a gain curve diagram under the action of fiber core pump in this invention;
[0026] Figure 6 This is a gain curve diagram under cladding pumping in this invention;
[0027] Figure 7 This is a gain curve diagram of the combined action of core pumping and cladding pumping in this invention. Detailed Implementation
[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0029] This invention provides a mode-equalized multimode erbium-doped fiber amplifier module, comprising: an optical multiplexing isolator, a pump source, a ring-core erbium-doped fiber, and a wavelength division multiplexer;
[0030] The optical multiplexing isolator is used to isolate the reverse signal and couple the pump light to the output. The optical multiplexing isolator is a device integrated by the pump fiber and the self-made submarine cable optical fiber. Isolation is achieved by the Faraday crystal in the middle, and the embedded dichroic mirror realizes the multiplexing of the signal light and the pump light. The input end of the optical multiplexing isolator receives the pump light through the pump fiber, and the signal fiber receives the signal light transmitted in the submarine optical cable. The signal fiber at the output end is fused with the erbium-doped ring fiber to perform core pumping.
[0031] The pump light source is used to output pump light;
[0032] The ring-core erbium-doped fiber is used for signal amplification;
[0033] The output of the wavelength division multiplexer is fused to the ring-core mode erbium-doped fiber to perform cladding pumping on the erbium-doped fiber, thereby controlling the gain difference between different modes.
[0034] Furthermore, the core of the ring-core erbium-doped fiber comprises, from the inside out, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer. The first layer is circular, the second layer is a first ring, the third layer is a second ring, the fourth layer is a third ring, and the fifth layer is a fourth ring. The refractive index of the second layer is greater than that of the first layer and also greater than that of the third layer. The refractive index of the first layer is greater than that of the third layer. The refractive index of the fourth layer is the smallest. The refractive index of the fifth layer is equal to that of the third layer. The erbium doping distribution is two-layer erbium doping, and the erbium ion doping concentration of the second layer is less than that of the first layer.
[0035] Furthermore, the ring-core erbium-doped fiber adopts a ring-core structure and ring doping. Under the cladding pumping action, the erbium doping distribution achieves a higher gain in higher-order modes than in lower-order modes, and under the core pumping action, the lower-order mode gain is greater than the higher-order mode gain, thereby achieving low differential mode gain.
[0036] Furthermore, the refractive index structure of the ring-core erbium-doped fiber is the same as that of the submarine cable fiber.
[0037] Furthermore, the optical multiplexing isolator uses an embedded dichroic mirror to couple the signal light and pump light for output, and at the same time, the addition of an isolation crystal prevents the signal from being coupled in reverse.
[0038] Furthermore, the wavelength division multiplexer, combined with the aforementioned optical multiplexing isolator, achieves the effect of gain control for high-order and low-order signals, thereby controlling the gain difference between low-mode signals.
[0039] Embodiments of the present invention provide a structure for an all-fiber loop-core erbium-doped fiber amplifier module with a simplified structure and reduced size, the basic structure of which is as follows: Figure 1 As shown, in a long-distance mode-division multiplexing (MDD) transmission system, after the MMD-division multiplexed signal is transmitted through submarine optical fiber, it cannot continue to transmit due to signal loss during transmission within the fiber. Therefore, it needs to be amplified by an erbium-doped fiber amplifier. In the erbium-doped fiber amplifier, the pump light and signal light are first multiplexed and injected into the erbium-doped fiber through an optical multiplexing isolator. The structure of the optical multiplexing isolator is shown below. Figure 2 As shown, the optical multiplexing isolator uses an embedded dichroic mirror to couple the mode-division multiplexed signal light and pump light to the output. This structure uses a Faraday rotator to prevent the signal light from returning. This structure is mode-insensitive, thus it can be extended to support the number of modes in submarine fiber optic cables. At the output of the optical multiplexing isolator, the signal light and pump light are combined and then injected into the erbium-doped fiber. The amplified mode-division multiplexed signal then enters the next segment of the submarine fiber optic cable for continued transmission. It should be noted that the input and output ends of the devices used in this invention are all fiber-coupled. The refractive index structure of the erbium-doped fiber is the same as that of the submarine fiber. Therefore, in mode-division multiplexing signal transmission, they can be connected by fiber coupling to achieve an all-fiber structure and integration.
[0040] Meanwhile, since the amplifier's gain differs between different modes during signal transmission, it can degrade the performance of the communication system. This invention provides a mode-equalized multimode erbium-doped fiber amplifier module structure. Core pumping and cladding pumping are implemented using an optical multiplexing isolator and a wavelength division multiplexer, respectively. Combining cladding pumping with core pumping allows for gain difference control. When the gain of higher-order signals is low, the cladding pump power can be increased to compensate for the gain of higher-order signals. Similarly, when the gain of lower-order signals is low, the core pump power can be increased to compensate for the gain of lower-order signals. By adjusting the power ratio of core pumping and cladding pumping, the differential mode gain is effectively reduced.
[0041] The key points of this plan include:
[0042] (1) All-fiber structure
[0043] Existing technical solutions utilize discrete optical components, requiring adjustment frames to collimate the optical path. Whether for pump light mode conversion or coupling the pump light and signal light into the erbium-doped fiber, this type of structure suffers from drawbacks such as large size, difficulty in adjustment, and poor compatibility with fiber optic links. In contrast, the optical multiplexing isolator proposed in this invention replaces optical components, ensuring that the input and output ends of all devices used in the erbium-doped fiber amplifier are fiber-coupled. In practical engineering, this allows the entire optical path structure to be housed in a small module, simplifying the optical path using the optical multiplexing isolator. Furthermore, the simplified optical path facilitates implementation in practical applications. Figure 3 As shown, the erbium-doped fiber amplifier of this invention is placed in a communication system to realize the function of a repeater amplifier. For example, the eight wavelength signals emitted by the transmitter can be modulated with 32G-QPSK (32G-Quadrature Phase Shift Keying). The emitted signals are transmitted through a 25KM submarine fiber optic cable. During the transmission process, losses will occur. Since this invention is an all-fiber structure, the input end of the erbium-doped amplifier can be fused to it to realize the function of repeater amplification.
[0044] (2) Ring-core erbium-doped fiber
[0045] Different light modes propagating in erbium-doped fiber have different intensity distributions. Therefore, amplification using conventional erbium-doped fiber typically yields different gains. To maintain transmission quality across all modes, it is necessary to reduce the differential gain (DMG) in the EDFA. To enable the EDFA to support simultaneous amplification of multiple modes and reduce differential mode gain, one approach is to use a ring-shaped erbium-doped fiber design in the EDFA, such as... Figure 4The diagram shows the structure of the erbium-doped fiber in this scheme. The core of the erbium-doped fiber comprises, from the inside out, five layers: a first layer, a second layer, a third layer, a fourth layer, and a fifth layer. The first layer is circular with a radius of r1. The second layer is a first ring, where the difference between r3 and r1 is the ring width w1. The third layer is a second ring, where the difference between r4 and r3 is the ring width w2. The fourth layer is a third ring, where the difference between r5 and r4 is the ring width w3. The fifth layer is a fourth ring, where the difference between r4 and r3 is the ring width w4. The refractive index n1 of the second layer is greater than the refractive index n2 of the first layer and greater than the refractive index n3 of the third layer. The refractive index n2 of the first layer is greater than the refractive index n3 of the third layer. The refractive index n4 of the fourth layer is the smallest. The refractive index of the fifth layer is the same as that of the third layer, both being n3. Studies have shown that crosstalk between signal light modes decreases as the effective refractive index difference between modes increases. When the first, second, third, fourth, and fifth layers meet the aforementioned refractive index requirements, mode crosstalk within the transmission fiber can be effectively reduced, achieving weak coupling between modes. The refractive index structure of erbium-doped fiber is the same as that of submarine cable fiber, with a two-layer erbium doping distribution. The erbium ion doping concentration nt1 in the second layer is lower than that in the first layer.
[0046] (3) Ring doping distribution
[0047] like Figure 1 This erbium-doped fiber employs a ring-shaped doping distribution, where the erbium ion doping concentration nt1 in the second layer is lower than the erbium ion doping concentration nt2 in the first layer, i.e., ring doping. Under this doping distribution, such as Figure 5 Under the action of core pumping, the gain of the low-order mode is greater than the gain of the high-order mode. For example... Figure 6 Under cladding pumping, the gain of higher-order modes is greater than that of lower-order modes. By adjusting the power ratio of cladding pumping and core pumping, it is possible to achieve... Figure 7 The low differential mode gain is shown. As the number of multiplexed spatial modes increases, achieving gain balance and reducing DMG requires complex pump mode configurations and erbium doping distributions. However, using a ring-shaped doping distribution can reduce manufacturing difficulty and achieve gain balance.
[0048] (4) Optical multiplexing isolator
[0049] In existing erbium-doped amplifiers, the pump and signal beams are mostly multiplexed using optical lenses, resulting in significant size and insertion loss. To address this, this invention proposes using an embedded dichroic mirror to couple the signal and pump beams for output. Furthermore, by adding an isolating crystal, the isolator and multiplexer are combined into one, greatly reducing the amplifier's size. This scheme uses optical fibers with the same refractive index at both the input and output ends, resulting in an even smaller size and high practicality.
[0050] (5) Wavelength division multiplexer
[0051] The input of the wavelength division multiplexer is connected to the transmission fiber and the pump source, respectively. The output of the few-mode wavelength division multiplexer is connected to the erbium-doped ring core fiber. The wavelength division multiplexer is used to couple the signal to be amplified in the few-mode transmission fiber with the pump light side and then inject it into the erbium-doped ring core fiber for cladding pump amplification.
[0052] The ring-core erbium-doped fiber amplifier module described in this invention has the advantages of small size, simple structure, easy debugging, and full compatibility with fiber optic transmission links. Secondly, the optical multiplexing isolator used in this structure supports the combination of signal light and pump light for fiber core pumping, while the wavelength division multiplexer performs cladding pumping through side pumping. Since the ring-core erbium-doped fiber adopts a ring doping distribution, the manufacturing process difficulty can be further reduced. At the same time, it can achieve low differential mode gain by controlling the power ratio of cladding pumping and fiber core pumping under the simultaneous action of cladding pumping and fiber core pumping. It is suitable for relay amplification in submarine communication transmission.
[0053] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention should be determined by the claims.
[0054] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In addition, the terms "first", "second", "third", etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0055] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. All should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A mode-equalized multimode erbium-doped fiber amplifier module, characterized in that, include: Optical multiplexing isolator, pump source, erbium-doped ring fiber, wavelength division multiplexer; The optical multiplexing isolator is used to isolate the reverse signal and couple the pump light to the output. The optical multiplexing isolator is a device integrated by the pump fiber and the self-made submarine cable optical fiber. Isolation is achieved by the Faraday crystal in the middle, and the embedded dichroic mirror realizes the multiplexing of the signal light and the pump light. The input end of the optical multiplexing isolator receives the pump light through the pump fiber, and the signal fiber receives the signal light transmitted in the submarine cable optical fiber. The signal fiber at the output end is fused with the erbium-doped ring fiber to perform core pumping. The pump light source is used to output pump light; The ring-core erbium-doped fiber is used for signal amplification; The output of the wavelength division multiplexer is fused to the erbium-doped fiber in the ring core, and is used to side-couple the pump light into the cladding of the erbium-doped fiber to perform cladding pumping on the erbium-doped fiber in the ring core, thereby controlling the gain difference between different modes. The core of the erbium-doped fiber consists of a first layer, a second layer, a third layer, a fourth layer, and a fifth layer from the inside out. The first layer is circular, the second layer is a first ring, the third layer is a second ring, the fourth layer is a third ring, and the fifth layer is a fourth ring. The refractive index of the second layer is greater than that of the first layer and also greater than that of the third layer. The refractive index of the first layer is greater than that of the third layer. The refractive index of the fourth layer is the smallest. The refractive index of the fifth layer is equal to that of the third layer. The refractive index structure of the erbium-doped fiber is the same as that of the submarine cable fiber. The erbium doping distribution is two-layer erbium doping, and the erbium ion doping concentration of the second layer is less than that of the first layer. The ring-core erbium-doped fiber adopts a ring-core structure and ring doping. Its erbium doping distribution achieves a higher gain in higher-order modes than in lower-order modes under cladding pumping, and a higher gain in lower-order modes than in higher-order modes under core pumping, thereby achieving low differential mode gain. The wavelength division multiplexer, combined with the aforementioned optical multiplexing isolator, achieves the effect of gain control between high-order and low-order signals, thereby controlling the gain difference between low-mode signals.
2. The mode-equalized multimode erbium-doped fiber amplifier module according to claim 1, characterized in that, The optical multiplexing isolator uses an embedded dichroic mirror to couple the signal light and pump light for output, and at the same time, the addition of a Faraday crystal prevents the signal from being coupled in reverse.