Erbium-doped optical fiber and method for manufacturing an erbium-doped optical fiber

Abstract

The application discloses an erbium-doped optical fiber. The erbium-doped optical fiber can be applied to the fields of amplifiers, optical communication and rare earth-doped optical fiber preparation. The core of the erbium-doped optical fiber comprises a first layer and a second layer from inside to outside. The first layer comprises the center of the core. The second layer is annular, and the outer ring of the annular ring is the outer ring of the core. The average erbium ion doping concentration of the first layer is higher than that of the second layer. In the application, by reducing the erbium ion doping concentration of the second layer, the ASE can be reduced, the noise figure of the erbium-doped optical fiber is reduced, and the communication quality is improved.

Description

Technical Field

[0001] This application relates to the fields of amplifiers, optical communications, and rare-earth-doped optical fiber fabrication, and particularly to erbium-doped optical fibers and methods for fabricating erbium-doped optical fibers. Background Technology

[0002] In optical communication systems, erbium-doped fiber amplifiers (EDFAs) are used to amplify signal light, thereby increasing its transmission distance. Specifically, an EDFA consists of a pump source, an optical coupler, and erbium-doped fiber. The pump source generates pump light. The optical coupler couples the signal light and pump light into the erbium-doped fiber. Within the erbium-doped fiber, the pump light serves as the excitation source for the signal light, amplifying it.

[0003] Erbium-doped fiber, under the influence of an excitation source, generates amplified spontaneous emission (ASE). ASE increases the noise figure of erbium-doped fiber, affecting communication quality. Summary of the Invention

[0004] This application provides an erbium-doped optical fiber and a method for fabricating erbium-doped optical fiber. In this application, by reducing the erbium ion doping concentration in the second layer, the ester-like structure (ASE) can be reduced, thereby lowering the noise figure of the erbium-doped optical fiber and improving communication quality.

[0005] This application provides an erbium-doped optical fiber. The core of the erbium-doped optical fiber comprises a first layer and a second layer from the inside out. The first layer includes the center of the core. The second layer is a ring, and the outer ring of the ring is the outer ring of the core. The average erbium ion doping concentration of the first layer is higher than that of the second layer.

[0006] In this application, by reducing the erbium ion doping concentration in the second layer, the ASE (associated ester) can be reduced, thereby lowering the noise figure of the erbium-doped fiber and improving communication quality. At this point, the average erbium ion doping concentration in the first layer is higher than that in the second layer.

[0007] In one alternative embodiment of the first aspect, erbium-doped fiber is used in the L-band. The L-band erbium-doped fiber has a higher erbium ion concentration compared to C-band erbium-doped fiber. Therefore, the erbium-doped fiber of this application can further reduce noise in the system and improve communication quality.

[0008] In one alternative embodiment of the first aspect, the average erbium ion doping concentration of the first layer is more than M percent higher than the average erbium ion doping concentration of the second layer, where M is greater than or equal to 30. When the erbium ion distribution in the fiber core is uniform, using a 0 dBm signal light as the input signal for the L-band erbium-doped fiber, the noise figure of the erbium-doped fiber is generally greater than 6.0 dB, for example, 6.3 dB. By limiting M to be greater than or equal to 30, the noise figure of the erbium-doped fiber can be effectively reduced; for example, the noise figure of the erbium-doped fiber can be reduced to below 5.5 dB.

[0009] In one alternative embodiment of the first aspect, the value of M is between 30 and 75.6. Increasing the ratio of the average erbium ion concentration in the first and second layers reduces the gain of the erbium-doped fiber for the signal light. This application specifies that the value of M is less than 75.6, which allows for a reduction in the noise figure of the erbium-doped fiber with minimal loss of gain.

[0010] In one alternative embodiment of the first aspect, the cross-sectional area of ​​the first layer is less than N percent of the cross-sectional area of ​​the fiber core, where N is less than or equal to 50. However, when the area of ​​the first layer is too large, the effect on reducing the noise figure is limited. By limiting N to less than or equal to 50, the noise figure of erbium-doped fiber can be effectively reduced; for example, the noise figure of erbium-doped fiber can reach below 5.5 dB.

[0011] In one alternative embodiment of the first aspect, the value of N is between 20 and 50. This means that continuously reducing the area of ​​the first layer decreases the gain of the erbium-doped fiber for the signal light. This application specifies that reducing the area of ​​the first layer by more than or equal to 20% can reduce the noise figure of the erbium-doped fiber with minimal loss of gain.

[0012] In one alternative embodiment of the first aspect, the average erbium ion doping concentration of the first layer is between 2742 parts per million (ppm) and 2966 ppm. The average erbium ion doping concentration of the second layer is between 1560 ppm and 2280 ppm. When the average erbium ion doping concentration in the fiber core is too high, more ASE (associated ester) will be generated in the fiber core, thereby increasing the noise figure of the erbium-doped fiber. When the average erbium ion doping concentration in the fiber core is too low, the gain of the erbium-doped fiber will decrease. This application, by limiting the average erbium ion doping concentration in the fiber core, can reduce the noise figure of the erbium-doped fiber with minimal reduction in gain.

[0013] In one alternative embodiment of the first aspect, the first layer comprises K sublayers, where K is an integer greater than 1. The second layer comprises P sublayers, where P is an integer greater than 0. Along the center of the fiber core, from the inside out, the erbium ion doping concentration of the K and P sublayers gradually decreases. The light intensity distribution in the fiber core follows a Gaussian distribution. The closer the erbium ion distribution in the fiber core is to a Gaussian distribution, the more effectively the noise figure of the optical fiber can be reduced. This application divides the fiber core into K+P sublayers. Along the center of the fiber core, from the inside out, the erbium ion doping concentration of the K+P sublayers gradually decreases, thereby making the erbium ion distribution in the fiber core close to a Gaussian distribution. Therefore, this application can more effectively reduce the noise figure of erbium-doped optical fibers.

[0014] In one alternative embodiment of the first aspect, K and P are both 2. K sublayers include a first sublayer and a second sublayer. P sublayers include a third sublayer and a fourth sublayer. The more sublayers in the fiber core, the closer the erbium ion distribution in the fiber core is to a Gaussian distribution. However, the more sublayers in the fiber core, the higher the processing cost of the fiber core. This application limits the number of layers in the fiber core to 4, which can reduce the noise figure of the erbium-doped fiber while minimizing processing costs.

[0015] In one alternative embodiment of the first aspect, the erbium ion doping concentration of the first sublayer ranges from 2687 ppm to 3087 ppm. The erbium ion doping concentration of the second sublayer ranges from 2006 ppm to 2406 ppm. The erbium ion doping concentration of the third sublayer ranges from 1028 ppm to 1428 ppm. The erbium ion doping concentration of the fourth sublayer ranges from 301 ppm to 701 ppm. When the erbium ion concentration of the fiber core meets the above conditions, the noise figure of the erbium-doped fiber can be effectively reduced; for example, the noise figure of the erbium-doped fiber can reach below 5.5 dB.

[0016] In one alternative of the first aspect, the erbium ion doping concentration at the core center is between 1500 ppm and 4000 ppm.

[0017] In one alternative approach of the first aspect, the erbium ion doping concentration of the fiber core satisfies the following relationship: Where A is the erbium ion doping concentration at the center of the fiber core. C(r) is the erbium ion doping concentration at the target point. r is the distance of the target point from the center of the fiber core, and β is a negative correction factor.

[0018] In one alternative of the first aspect, the radius of the fiber core is between 0.01 micrometers and 0.3 micrometers.

[0019] In one alternative of the first aspect, the erbium-doped fiber comprises, from the inside out, a core and a cladding.

[0020] A second aspect of this application provides a method for preparing erbium-doped optical fiber. The method for preparing erbium-doped optical fiber includes the following steps:

[0021] A loose layer is deposited inside the base tube, and the loose layer is then immersed in an erbium ion solution.

[0022] The porous layer is removed from the erbium ion solution, dried, and vitrified to obtain a glass rod.

[0023] Repeat the two steps described above Z times, gradually increasing the concentration of the erbium ion solution each time, where Z is an integer greater than 1.

[0024] The glass rod is sintered into a solid glass rod. The solid glass rod is then fabricated into an erbium-doped optical fiber.

[0025] In one alternative embodiment of the second aspect, Z is 4. The more sublayers in the fiber core, the closer the erbium ion distribution in the fiber core is to a Gaussian distribution. However, the more sublayers in the fiber core, the higher the processing cost of the fiber core. This application limits the number of layers in the fiber core to 4, which can reduce the noise figure of erbium-doped fiber while minimizing processing costs.

[0026] In one alternative embodiment of the second aspect, the concentrations of the erbium ion solutions in the Zth iteration are Y1, Y2, Y3, and Y4 mol / L, respectively. The difference between Y2 and Y1 is between 0.001 mol / L and 0.004 mol / L. The difference between Y3 and Y2 is between 0.004 mol / L and 0.01 mol / L. The difference between Y4 and Y3 is between 0.01 mol / L and 0.016 mol / L.

[0027] A third aspect of this application provides an erbium-doped fiber amplifier (EDFA). The EDFA includes a pump source, an optical coupler, and the erbium-doped fiber described in the first aspect or any optional embodiment thereof. The pump source generates pump light. The optical coupler receives the signal light and the pump light, coupling them into the erbium-doped fiber. The erbium-doped fiber amplifies the signal light under the action of the pump light.

[0028] This application provides a fourth aspect of an optical communication system. The optical communication system includes a transmitter, a receiver, and the EDFA described in the third aspect above. The transmitter transmits signal light to the receiver via an optical fiber. The optical fiber is connected to the EDFA; the EDFA generates pump light and amplifies the signal light based on the pump light. The receiver receives the amplified signal light. Attached Figure Description

[0029] Figure 1 This is a schematic diagram showing the distribution of erbium ions in the fiber core.

[0030] Figure 2This is the first schematic diagram of the distribution of erbium ions in the fiber core provided in this application;

[0031] Figure 3 This is a first structural schematic diagram of the fiber core provided in this application;

[0032] Figure 4 This is a second structural schematic diagram of the fiber core provided in this application;

[0033] Figure 5 This is a third structural schematic diagram of the fiber core provided in this application;

[0034] Figure 6 This is a fourth structural schematic diagram of the fiber core provided in this application;

[0035] Figure 7 This is the first structural schematic diagram of the optical communication system provided in this application;

[0036] Figure 8 This is a schematic diagram showing the noise figure distribution of erbium-doped fiber at different wavelengths.

[0037] Figure 9 This is the first schematic diagram showing the noise figure distribution of the erbium-doped optical fiber provided in this application;

[0038] Figure 10 This is a second schematic diagram showing the noise figure distribution of the erbium-doped optical fiber provided in this application;

[0039] Figure 11 This is a second schematic diagram of the distribution of erbium ions in the fiber core provided in this application;

[0040] Figure 12 This is a schematic diagram of the erbium-doped optical fiber provided in this application during the fabrication process.

[0041] Figure 13 This is a schematic diagram of the structure of the EDFA provided in this application;

[0042] Figure 14 This is a second structural schematic diagram of the optical communication system provided in this application. Detailed Implementation

[0043] This application provides an erbium-doped optical fiber and a method for fabricating erbium-doped optical fiber. In this application, by reducing the erbium ion doping concentration in the second layer, the ASE (associated ester) can be reduced, thereby reducing the noise figure of the erbium-doped optical fiber and improving communication quality. It should be understood that the terms "first," "second," etc., used in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or order. Furthermore, for the sake of brevity and clarity, reference numerals and / or letters are repeated in several figures of this application. This repetition does not indicate a strict limiting relationship between the various embodiments and / or configurations.

[0044] The erbium-doped fiber in this application is used in the field of optical communication. In optical communication, the erbium-doped fiber in an amplifier is used to amplify signal light under the action of an excitation source. The signal light propagates in the core of the erbium-doped fiber. When the distribution of erbium ions in the core is uniform, the amplifier will generate a relatively large noise figure. Specifically, Figure 1 This is a schematic diagram showing the distribution of erbium ions in the fiber core. (Example:) Figure 1 As shown, the horizontal axis represents the position of the fiber core, with units of micrometers (μm). Figure 1 In the diagram, the center of the fiber core is located at coordinate 0. The radius of the fiber core is 2.5 micrometers, and the diameter is 5 micrometers. The vertical axis represents the erbium ion doping concentration of the fiber core, in ppm. Erbium ions are uniformly distributed in the fiber core. Therefore, concentration 101 is a straight line. It should be understood that in actual processing, the processing technology cannot guarantee that the concentration is the same at every point in the fiber core. Therefore, concentration 101 can also be a fluctuating curve.

[0045] Under the influence of an excitation source, erbium ions in the fiber core transition from the ground state to an upper energy level. When signal light is injected into the fiber core, the intensity of the signal light is mainly distributed in the inner layer of the core. The upper-level erbium ions in the inner layer undergo stimulated emission, thereby amplifying the signal light. In the outer layer of the core, the upper-level erbium ions cannot obtain enough signal light for stimulated emission and spontaneously transition from the excited state to the ground state, generating an ASE (excited emission state). ASE is the main source of noise in amplifiers or erbium-doped fibers. Specifically, the following is the formula for calculating the noise figure NF.

[0046]

[0047] Among them, P ASE Let ν be the noise power of the amplifier or erbium-doped fiber, generated by the ASE. h is Planck's constant. v is the signal light frequency. B is the spectrometer detection linewidth. G is the amplifier gain. With the amplifier gain constant, NF is related to the amplifier's P... ASE Strongly correlated. Specifically, P ASE The larger the value, the larger the NF; P ASE The smaller the value, the smaller the noise factor (NF). Therefore, when a large amount of ASE (associated ester) is generated in the outer layer of the fiber core, erbium-doped fiber will produce a large noise figure.

[0048] Therefore, this application provides an erbium-doped optical fiber. In the core of the erbium-doped fiber, the erbium ion doping concentration in the outer layer is reduced, thereby reducing the esterification (ASE) and lowering the noise figure of the erbium-doped fiber. In this case, the average erbium ion doping concentration in the inner core is higher than that in the outer core. For example, Figure 2 This is the first schematic diagram of the distribution of erbium ions in the fiber core provided in this application. Figure 2 As shown, the average erbium ion doping concentration in the inner layer of the fiber core is concentration 201. The average erbium ion doping concentration in the outer layer of the fiber core is concentration 202. Concentration 202 is less than concentration 201. It should be understood that in actual processing, the processing technology cannot guarantee that the concentration at every point in the fiber core is the same. Therefore, concentration 201 and concentration 202 can also be a fluctuating curve. Similarly, in the following description, "the erbium ion doping concentration in the first sublayer is the same" means "the erbium ion doping concentration in the first sublayer is approximately the same".

[0049] The average erbium ion doping concentration of the fiber core in this application has been described above. The structure of the fiber core in this application will be described below. Figure 3 This is the first structural schematic diagram of the fiber core provided in this application. (See attached diagram.) Figure 3 As shown, the fiber core includes a first layer 301 and a second layer 302. The first layer 301 is also called the inner layer, and the second layer 302 is also called the outer layer. The first layer 301 can be circular. The first layer 301 includes the center of the fiber core. The second layer is annular. The outer ring of the annular ring is the outer ring of the fiber core. The average erbium ion doping concentration of the first layer 301 is higher than that of the second layer 302.

[0050] It should be understood that when the fiber core includes two sublayers, the boundary line between the first layer 301 and the second layer 302 and the boundary line between the two sublayers may or may not overlap.

[0051] When two boundary lines overlap, there is a sudden change in the erbium ion doping concentration at the boundary line. Specifically, for example... Figure 3 As shown, the two sublayers include a first sublayer and a second sublayer. The first sublayer 301 is the first sublayer, and the second sublayer 302 is the second sublayer. The erbium ion doping concentration is the same in the first sublayer. The erbium ion doping concentration is the same in the second sublayer. However, because the erbium ion doping concentration in the first sublayer is greater than that in the second sublayer, there is a sudden change in the erbium ion doping concentration at the boundary.

[0052] When the two boundary lines do not overlap, there is a sudden change in the erbium ion doping concentration at the boundary line between the two sublayers. There is no sudden change in the erbium ion doping concentration at the boundary line between the first layer 301 and the second layer 302. Specifically, Figure 4 This is a second structural schematic diagram of the fiber core provided in this application. (See attached diagram.) Figure 4As shown, the fiber core includes a first boundary line 401 and a second boundary line 402. The first boundary line 401 divides the fiber core into a first sublayer and a second sublayer. Within the first boundary line 401, the erbium ion doping concentration in the first sublayer is the same. Outside the second boundary line 401, the erbium ion doping concentration in the second sublayer is the same. The erbium ion doping concentration in the first sublayer is higher than that in the second sublayer. Therefore, there is a sudden change in erbium ion doping concentration at the first boundary line 401. The second boundary line 402 divides the fiber core into a first layer and a second layer. The first layer is within the second boundary line 402, and the second layer is outside the second boundary line 402. The average erbium ion doping concentration in the first layer is higher than that in the second layer. However, since the erbium ion doping concentration is the same within the first sublayer, and the second boundary line 402 is located within the first sublayer, there is no sudden change in erbium ion doping concentration at the second boundary line 402.

[0053] In other embodiments, all layer boundaries and sublayer boundaries in the fiber core overlap. A layer boundary is the boundary between "layers", and a sublayer boundary is the boundary between "sublayers".

[0054] In the attached figures, solid lines represent boundaries or dividing lines where erbium ion doping concentration abruptly changes, with the areas on either side of the solid line belonging to different "sublayers." For a definition of "sublayer," please refer to the description of sublayers in the subsequent section on erbium-doped fiber fabrication methods. Dashed lines represent different "layers" on either side.

[0055] Figure 5 This is a third structural schematic diagram of the fiber core provided in this application. (See attached diagram.) Figure 5 As shown, the fiber core includes a first layer 301 and a second layer 302. The first layer 301 includes the center of the fiber core. The outer ring of the second layer 302 is the outer ring of the fiber core. The average erbium ion doping concentration of the first layer 301 is higher than that of the second layer 302.

[0056] In other embodiments, the fiber core further includes other layers between the first and second layers. For example, such as... Figure 5 As shown, the fiber core also includes a third layer 501. The third layer 501 is located between the first layer 301 and the second layer 302. The average erbium ion doping concentration of the third layer 501 is lower than that of the first layer 301, and the average erbium ion doping concentration of the second layer 302 is lower than that of the third layer 501.

[0057] It should be understood that in the fiber core of this application, a "layer" may include one or more "sublayers". For example, the first layer includes K sublayers, where K is an integer greater than 0. In one instance, K is an integer greater than 1. The second layer includes P sublayers, where P is an integer greater than 0. The light intensity distribution in the fiber core follows a Gaussian distribution. The closer the erbium ion distribution in the fiber core is to a Gaussian distribution, the more effectively the noise figure of the erbium-doped fiber can be reduced. Therefore, this application can limit the erbium ion doping concentration to gradually decrease from the center of the fiber core outwards in the K+P sublayers, so that the erbium ion distribution in the fiber core is close to a Gaussian distribution.

[0058] The more sublayers in the fiber core, the closer the erbium ion distribution in the core will be to a Gaussian distribution. However, the more sublayers in the core, the higher the processing cost. This application limits K and P to 2 to reduce the noise figure of erbium-doped fiber while minimizing processing costs. In this case, K sublayers include the first and second sublayers, and P sublayers include the third and fourth sublayers. Specifically, Figure 6 This is a fourth structural schematic diagram of the fiber core provided in this application. (See attached diagram.) Figure 6 As shown, the fiber core includes a first sublayer 601, a second sublayer 602, a third sublayer 603, and a fourth sublayer 604. The first sublayer 601 and the second sublayer 602 belong to the first layer. The third sublayer 603 and the fourth sublayer 604 belong to the second layer. Along the center of the fiber core, from the inside out, the erbium ion doping concentration of the first sublayer 601, the second sublayer 602, the third sublayer 603, and the fourth sublayer 604 gradually decreases.

[0059] In other embodiments, the erbium-doped fiber of this application is used in the L-band. Specifically, the gain coefficient of the signal light in the erbium-doped fiber is relatively low. Therefore, to improve the gain of the erbium-doped fiber amplifier, it is necessary to increase the erbium ion doping concentration of the erbium-doped fiber. For example, when the erbium-doped fiber is used in the C-band, the erbium ion doping concentration is typically 300 ppm to 500 ppm. When the erbium-doped fiber is used in the L-band, the erbium ion doping concentration typically needs to be greater than 1500 ppm. After increasing the erbium ion doping concentration of the erbium-doped fiber, the outer layer of the erbium-doped fiber has more erbium ions. More erbium ions generate a larger ASE (associated ester), which in turn generates a larger noise figure. For example, the noise figure of the erbium-doped fiber amplifier in the C-band is typically less than 5 dB. The noise figure of the erbium-doped fiber amplifier in the L-band is typically greater than 6 dB. Therefore, in the L-band, it is even more necessary to reduce the erbium ion doping concentration in the outer layer of the erbium-doped fiber to reduce the noise figure.

[0060] As described above, when the erbium ions in the fiber core are uniformly distributed, the amplifier will generate a large noise figure. The following description uses a specific experimental scenario. Figure 7This is the first structural schematic diagram of the optical communication system provided in this application. Figure 7 As shown, the optical communication system includes optical amplifiers 701, 705, and 709, and an optical spectrum analyzer (OSA) 713. Optical amplifier 701 includes a pump source 704, a wavelength division multiplexing (WDM) 703, and erbium-doped fiber 702. Pump source 704 generates pump light. WDM 703 couples the signal light and pump light into erbium-doped fiber 702. In erbium-doped fiber 702, the pump light serves as the excitation source for the signal light, amplifying it. Similarly, optical amplifier 705 includes a pump source 708, a wavelength division multiplexing (WDM) 707, and erbium-doped fiber 706. Optical amplifier 709 includes a pump source 712, a wavelength division multiplexing (WDM) 711, and erbium-doped fiber 710. Figure 7 In the optical communication system, three-stage amplification of the signal light is implemented. The OSA 713 is used to measure the noise figure of the signal light after three-stage amplification. When the erbium ions in erbium-doped fiber 702, erbium-doped fiber 706, and erbium-doped fiber 710 are uniformly distributed, the noise figure of the amplifier is measured using a 0 dBm L-band signal light as the input signal. The noise figure of the amplifier can also be referred to as the noise figure of the erbium-doped fiber. Figure 8 This is a schematic diagram showing the noise figure distribution of erbium-doped fiber at different wavelengths. (Example:) Figure 8 As shown, the horizontal axis represents wavelength in nanometers (nm), and the vertical axis represents noise figure in dB. Within the 1575nm to 1618nm range, the amplifier's maximum noise figure is 6.6dB, and the average noise figure is approximately 6.3dB.

[0061] use Figure 7 The noise figure of the erbium-doped fiber amplifier in this application is measured in an optical communication system. A schematic diagram of the erbium-doped fiber structure is shown below. Figure 3 As shown.

[0062] In Experiment 1, the area of ​​the first layer 301 accounts for 50% of the fiber core area. The average erbium ion doping concentration of the first layer 301 is 2742 ppm. The average erbium ion doping concentration of the second layer 302 is 1560 ppm. The average erbium ion doping concentration of the first layer 301 is 75.6% higher than that of the second layer 302. Figure 9 This is the first schematic diagram showing the noise figure distribution of the erbium-doped fiber provided in this application. Figure 9 As shown, in the range of 1575nm to 1618nm, the maximum noise figure of the erbium-doped fiber amplifier is 5.2dB, and the average noise figure is less than 5dB.

[0063] In Experiment 2, the area of ​​the first layer 301 accounts for 20% of the fiber core area. The average erbium ion doping concentration of the first layer 301 is 2966 ppm. The average erbium ion doping concentration of the second layer 302 is 2280 ppm. The average erbium ion doping concentration of the first layer 301 is 30% higher than that of the second layer 302. Figure 10 This is a second schematic diagram showing the noise figure distribution of the erbium-doped optical fiber provided in this application. (See attached diagram.) Figure 10 As shown, in the range of 1575nm to 1618nm, the maximum noise figure of the erbium-doped fiber amplifier is 5.4dB, and the average noise figure is less than 5.2dB.

[0064] The average erbium ion doping concentration of the first layer is defined to be more than M percent higher than that of the second layer. Experiments show that when M is between 30 and 75.6 percent, the average noise figure of the erbium-doped fiber amplifier is less than 5.5 dB. The cross-sectional area of ​​the first layer is defined to be less than N percent of the cross-sectional area of ​​the fiber core. Experiments show that when N is between 20 and 50 percent, the average noise figure of the erbium-doped fiber amplifier is less than 5.5 dB. Furthermore, experiments show that when the average erbium ion doping concentration of the first layer is between 2742 ppm and 2966 ppm, and the average erbium ion doping concentration of the second layer is between 1560 ppm and 2280 ppm, the average noise figure of the erbium-doped fiber amplifier is less than 5.5 dB.

[0065] When using Figure 6 When measuring the noise figure of an erbium-doped fiber amplifier in the fiber core, similar results can be obtained. Figure 9 The experimental results are as follows. At this point, the area of ​​the first sublayer 601 accounts for 19% of the core area, and the erbium ion doping concentration of the first sublayer 601 is 2887 ppm. The area of ​​the second sublayer 602 accounts for 26% of the core area, and the erbium ion doping concentration of the second sublayer 602 is 2206 ppm. The area of ​​the third sublayer 603 accounts for 27% of the core area, and the erbium ion doping concentration of the third sublayer 603 is 1228 ppm. The area of ​​the fourth sublayer 604 accounts for 28% of the core area, and the erbium ion doping concentration of the fourth sublayer 604 is 501 ppm. Since there may be errors during the core processing, the error is defined as ±200 ppm. At this point, the erbium ion doping concentration of the first sublayer 601 ranges from 2687 ppm to 3087 ppm. The erbium ion doping concentration of the second sublayer 602 ranges from 2006 ppm to 2406 ppm. The erbium ion doping concentration of the third sublayer 603 ranges from 1028 ppm to 1428 ppm. The erbium ion doping concentration of the fourth sublayer 604 ranges from 301 ppm to 701 ppm.

[0066] In other embodiments, the distribution of erbium ions in the fiber core is Gaussian by increasing the number of neutron layers in the core. Specifically, the erbium ion doping concentration in the fiber core satisfies the following relationship.

[0067]

[0068] Where A is the erbium ion doping concentration at the center of the fiber core. A ranges from 1500 ppm to 4000 ppm. C(r) is the erbium ion doping concentration at the target point. r is the distance from the target point to the center of the fiber core. r is less than or equal to R. R is the radius of the fiber core. R ranges from 0.01 μm to 0.3 μm. β is a correction factor for negative values. Specifically, Figure 11 This is a second schematic diagram showing the distribution of erbium ions in the fiber core as provided in this application. Figure 11 As shown, when R equals 2.5, A equals 3000, and β equals -0.5, the distribution of erbium ions in the fiber core approaches a Gaussian distribution.

[0069] The erbium-doped optical fiber of this application has been described above. The method for preparing the erbium-doped optical fiber of this application is described below. The method for preparing the erbium-doped optical fiber includes the following steps.

[0070] In step one, a loose layer is deposited inside the base tube, and the loose layer is immersed in an erbium ion solution.

[0071] First, the base tube undergoes pretreatment to preheat it and effectively eliminate impurities and air bubbles from its inner wall. Then, raw materials are introduced into the base tube through an MCVD (Metal-Concentrated Vapor Deposition) device. Under the heating conditions of a hydrogen-oxygen torch, the raw materials undergo a chemical reaction, generating fine particles such as silica, phosphorus pentoxide, silicon oxyfluoride, and boron trioxide. Driven by the thermophoretic effect and the gas inside the tube, these fine particles deposit and adhere to the inner surface of the base tube. At lower heating temperatures (e.g., 1300℃~1500℃), a white, opaque, porous layer is formed, with a length between 150mm and 300mm.

[0072] In a cleanroom environment, rare earth co-doped raw materials are dissolved in an alcohol or hydrochloric acid solution in a specific ratio to obtain a mixed solution. This mixed solution contains erbium ions (Er³⁺), phosphorus ions (P⁵⁺), aluminum ions (Al³⁺), and lanthanum ions (La³⁺). Therefore, the mixed solution is also called an erbium ion solution. The resulting porous material is then immersed in the prepared mixed solution. During immersion, the base tube can be placed in a rotary lathe and rotated at 30 rpm. Through surface adsorption, the rare earth co-doped ions penetrate into the porous layer.

[0073] In step two, the porous layer is removed from the erbium ion solution, dried, and vitrified to obtain a glass rod.

[0074] After soaking for 2 hours, the erbium ion solution is poured out. The base tube is then subjected to preliminary nitrogen drying. To reduce the background loss of the erbium-doped fiber, the pre-dried base tube is passed through chlorine gas and heated to 800-1000°C to further remove residual hydroxyl ions in the porous layer. After drying, the porous layer is heated to 1500°C and sintered into a transparent and dense glass rod. A gas containing P5+ is then introduced for gas-phase compensation to increase the P5+ doping concentration. The dopant element is finally fixed into the glass rod, forming a non-porous glass layer.

[0075] Repeat steps one and two Z times, gradually increasing the concentration of the erbium ion solution each time, where Z is an integer greater than 1.

[0076] In step three, the glass rod is sintered into a solid glass rod.

[0077] At high temperatures, the vitrified glass rod is sintered into a solid glass rod; this process is also known as collapse.

[0078] In step four, the solid glass rod is fabricated into erbium-doped fiber. The solid glass rod is then drawn thinner into erbium-doped fiber.

[0079] In the method for preparing erbium-doped optical fiber in this application, Z is an integer greater than 0. The following description uses Z=2 as an example to illustrate the method for preparing erbium-doped optical fiber in this application. Figure 12 This is a schematic diagram of the structure of the erbium-doped optical fiber provided in this application during its fabrication process. Figure 12 As shown, firstly, in step one, a base tube is provided, and a porous body 1 is deposited inside the base tube. The porous body 1 is then immersed in an erbium ion solution 1. Next, in step two, the porous body 1 is dried and vitrified to obtain a glass rod 1. Then, steps one and two are repeated. Specifically, a porous body 2 is deposited inside the glass rod 1. The porous body 2 is immersed in an erbium ion solution 2. The concentration of the erbium ion solution 2 is greater than that of the erbium ion solution 1. The porous body 2 is dried and vitrified to obtain a glass rod 2. Finally, in step three, the glass rod 2 is collapsed to obtain a solid glass rod. In step four, the solid glass rod is fabricated into an erbium-doped optical fiber.

[0080] In the doped optical fiber obtained by the method described in this application, the number of sublayers in the fiber core is equal to Z. For example, when Z is 2, steps one and two are performed a total of 2 times in the fabrication method. During the fabrication process, two loose layers are deposited. These two loose layers correspond to the two sublayers of the fiber core. For example, when Z is 4, steps one and two are performed a total of 4 times in the fabrication method. During the fabrication process, four loose layers are deposited. These four loose layers correspond to the four sublayers of the fiber core.

[0081] When Z equals 4, four loose layers are deposited during the preparation process. These four loose layers are then immersed in erbium ion solutions of different concentrations. The concentrations of the erbium ion solutions for the four immersions are Y1, Y2, Y3, and Y4 mol / L, respectively. The difference between Y2 and Y1 is between 0.001 mol / L and 0.004 mol / L. The difference between Y3 and Y2 is between 0.004 mol / L and 0.01 mol / L. The difference between Y4 and Y3 is between 0.01 mol / L and 0.016 mol / L. By gradually increasing the concentration of the erbium ion solution each time, the average erbium ion doping concentration of the outer layer of the fiber core can be made lower than that of the inner layer.

[0082] The preparation method of erbium-doped optical fiber in this application has been described above. The EDFA provided in this application is described below. Figure 13 This is a schematic diagram of the structure of the EDFA provided in this application. Figure 13 As shown, EDFA 1301 includes a pump source 1304, an optical coupler 1303, and an erbium-doped fiber 1302. The optical coupler 1303 can be a WDM (Wave Diode Matrix). The pump source 1304 generates pump light. The optical coupler 1303 receives the signal light and the pump light, coupling them into the erbium-doped fiber 1302. The erbium-doped fiber 1302 amplifies the signal light under the influence of the pump light. For a description of the erbium-doped fiber, please refer to the foregoing description of the fabrication method of the erbium-doped fiber and erbium-doped optical drive.

[0083] The EDFA in this application has been described above, and the optical communication system provided in this application will be described below. Figure 14 This is a second structural schematic diagram of the optical communication system provided in this application. (See diagram below.) Figure 14 As shown, the optical communication system includes a transmitter 1401, a receiver 1403, and an EDFA 1402. The transmitter 1401 transmits signal light to the receiver 1403 via an optical fiber. The optical fiber is connected to the EDFA 1402. The EDFA 1402 generates pump light and amplifies the signal light based on the pump light. The receiver 1403 receives the amplified signal light. A description of the EDFA 1402 can be found in the previously described description of the EDFA 1301.

[0084] In other embodiments, multiple EDFAs 1402 may be connected in series between the transmitter 1401 and the receiver 1403. The multiple EDFAs 1402 are used to amplify the signal light multiple times.

[0085] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. An erbium-doped optical fiber, characterized in that, The erbium-doped fiber core comprises a first layer and a second layer from the inside out. The first layer includes the center of the fiber core, and the second layer is a ring, the outer ring of which is the outer ring of the fiber core. The average erbium ion doping concentration of the first layer is higher than that of the second layer. The average erbium ion doping concentration of the first layer is more than M percent higher than that of the second layer, where M is greater than or equal to 30 percent. The value of M is between 30 and 75.6 percent.

2. The erbium-doped optical fiber according to claim 1, characterized in that, The erbium-doped fiber is used in the L-band.

3. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The average erbium ion doping concentration of the first layer is between 2742 ppm and 2966 ppm, and the average erbium ion doping concentration of the second layer is between 1560 ppm and 2280 ppm.

4. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The cross-sectional area of ​​the first layer is less than N percent of the cross-sectional area of ​​the fiber core, where N is less than or equal to 50%.

5. The erbium-doped optical fiber according to claim 4, characterized in that, The value of N is between 20 and 50.

6. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The first layer includes K sub-layers, where K is an integer greater than 1, and the second layer includes P sub-layers, where P is an integer greater than 0. Along the center of the fiber core, from the inside out, the erbium ion doping concentration of the K sublayers and the P sublayers gradually decreases.

7. The erbium-doped optical fiber according to claim 6, characterized in that, K and P are 2. The K sublayers include a first sublayer and a second sublayer. The P sublayers include a third sublayer and a fourth sublayer. The erbium ion doping concentration of the first sublayer ranges from 2687 ppm to 3087 ppm. The erbium ion doping concentration of the second sublayer ranges from 2006 ppm to 2406 ppm. The erbium ion doping concentration of the third sublayer ranges from 1028 ppm to 1428 ppm. The erbium ion doping concentration of the fourth sublayer ranges from 301 ppm to 701 ppm.

8. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The erbium ion doping concentration at the core of the fiber is between 1500 ppm and 4000 ppm.

9. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The erbium ion doping concentration of the fiber core satisfies the following relationship: Where A is the erbium ion doping concentration at the center of the fiber core. Let r be the erbium ion doping concentration at the target point, and r be the distance from the target point to the center of the fiber core. The correction factor is negative.

10. The erbium-doped optical fiber according to any one of claims 1 to 2, characterized in that, The erbium-doped optical fiber comprises, from the inside out, the core and the cladding.

11. An erbium-doped fiber amplifier, characterized in that, include: The pump source, the optical coupler, and the erbium-doped optical fiber as described in any one of claims 1 to 10; The pump light source is used to generate pump light; The optical coupler is used to receive the signal light and the pump light, and to couple the signal light and the pump light into the erbium-doped fiber; The erbium-doped fiber is used to amplify the signal light under the action of the pump light.

12. An optical communication system, characterized in that, include: The transmitting end, the receiving end, and the erbium-doped fiber amplifier (EDFA) as described in claim 11; The transmitting end is used to transmit signal light to the receiving end via optical fiber; The optical fiber is connected to the EDFA; The EDFA is used to generate pump light, and the signal light is amplified based on the pump light; The receiving end is used to receive the amplified signal light.

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