A single-pumped dual-polarization erbium-ytterbium co-doped fiber amplifier device

Abstract

The application relates to a single-pump dual-polarized erbium-ytterbium co-doped optical fiber amplification device, and belongs to the optical signal field.The device comprises a signal light source, a pump laser, a coupler, a first-stage erbium-ytterbium co-doped optical fiber, an optical isolator and a second-stage erbium-ytterbium co-doped optical fiber; the signal light source and a light source emitting port of the pump laser are flush with one end of the coupler, one end of the coupler receives the signal light source and the light source of the pump laser, the other end of the coupler is connected with the first-stage erbium-ytterbium co-doped optical fiber, and two ends of the optical isolator are respectively connected with the first-stage erbium-ytterbium co-doped optical fiber and the second-stage erbium-ytterbium co-doped optical fiber; the distance L1 between one end of the optical isolator and the first-stage erbium-ytterbium co-doped optical fiber is a preset value.The application solves the problems that the erbium-ytterbium co-doped optical fiber amplification device is affected by reverse amplified spontaneous emission and the use quantity of pump lasers is increased due to the two-stage direct connection structure.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. Background Technology

[0002] The single-pumped bipolar erbium-ytterbium co-doped fiber amplifier is an optical fiber amplification device that utilizes the stimulated emission principle of rare-earth elements in the doped fiber to amplify optical signals. The technical background of the single-pumped bipolar erbium-ytterbium fiber amplifier involves optical principles and the application of optical isolators. The main technical background is as follows:

[0003] 1. All-optical amplification technology: All-optical amplification technology uses optical amplification devices to directly compensate for the attenuation of optical signals in optical fibers, replacing the photoelectric conversion mode of traditional photoelectric regeneration repeaters. Optical amplification devices have the characteristics of small size, low cost, simple structure and excellent performance, and are therefore widely used in various optical fiber communication systems.

[0004] 2. Optical Isolators: An optical isolator is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. Light reflected back from the optical fiber can be effectively isolated by the optical isolator, improving optical wave transmission efficiency. Optical isolators mainly utilize the Faraday effect of magneto-optical crystals. The selection of optical isolators generally requires characteristics such as high isolation and low insertion loss.

[0005] 3. Erbium-Ytterbium Co-doped Fiber (EYDF): Erbium-ytterbium co-doped fiber is a doped fiber in which an appropriate amount of ytterbium ions (Yb3+) are added to erbium-doped fiber. Erbium-ytterbium co-doped fiber is a key component of erbium-ytterbium co-doped fiber amplifier devices (EYDF amplifiers). Its length, core diameter, numerical aperture, erbium ion concentration and other parameters will have a great influence on the performance of the erbium-ytterbium co-doped fiber amplifier device.

[0006] The current technology has the following drawbacks: existing erbium-ytterbium co-doped fiber amplifiers are relatively long, which generates significant reverse amplification spontaneous radiation (transmission amplification spontaneous radiation) at the input end of the amplifier. The accumulation of reverse transmission amplification spontaneous radiation directly affects the pump conversion efficiency and gain improvement of the erbium-ytterbium co-doped fiber amplifier. Cascading erbium-ytterbium co-doped fiber amplifiers can increase the output power, but it inevitably increases the system cost and complexity and reduces the system reliability. At the same time, it will add more spontaneous radiation noise, which degrades the system performance. Utility Model Content

[0007] This application provides a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier, which can solve the problem of the influence of reverse amplification spontaneous emission on the erbium-ytterbium co-doped fiber amplifier, as well as the problem that the use of a two-stage direct connection structure will increase the number of pump lasers used.

[0008] To achieve the above objectives, this application provides a single-pumped bipolar erbium-ytterbium co-doped fiber amplification device, comprising: a signal source, a pump laser, a coupler, a first-stage erbium-ytterbium co-doped fiber, an optical isolator, and a second-stage erbium-ytterbium co-doped fiber; the light source emission ports of the signal source and the pump laser are flush with one end of the coupler, one end of the coupler receives the light source of the signal source and the pump laser, and the other end is connected to the first-stage erbium-ytterbium co-doped fiber; both ends of the optical isolator are connected to the first-stage erbium-ytterbium co-doped fiber and the second-stage erbium-ytterbium co-doped fiber, respectively; the distance L1 between one end of the optical isolator and the first-stage erbium-ytterbium co-doped fiber is a preset value.

[0009] Optionally, the total length of the first-stage erbium-ytterbium co-doped fiber and the second-stage erbium-ytterbium co-doped fiber is set to 4-6 meters.

[0010] Optionally, the length ratio of the first-stage erbium-ytterbium co-doped fiber to the second-stage erbium-ytterbium co-doped fiber is 1:2 to 1:11.

[0011] Optionally, the optical isolator consists of a first polarizer, a Faraday rotator, and a second polarizer, with the two ends of the Faraday rotator connected to the first polarizer and the second polarizer, respectively.

[0012] Optionally, the transmission axis of the first polarizer is the same as the polarization direction of the positively polarized light, allowing all the positively polarized light to pass through; the second polarizer allows all positively polarized light to pass through while blocking the negatively polarized light whose polarization direction is perpendicular to the second polarizer.

[0013] Optionally, the optical isolator suppresses the reverse amplified spontaneous emission from the second-stage erbium-ytterbium co-doped fiber into the first-stage erbium-ytterbium co-doped fiber.

[0014] Optionally, the optical isolator is connected to the first-stage erbium-ytterbium co-doped fiber and the second-stage erbium-ytterbium co-doped fiber via an FC interface for easy testing and replacement.

[0015] Optionally, the inputs of the signal light source are respectively set to a preset small signal and a preset large signal, and the outputs are light waves corresponding to the small signal and light waves corresponding to the large signal.

[0016] Optionally, the coupler couples the light wave emitted by the signal source with the pump light emitted by the pump laser to obtain coupled light.

[0017] Optionally, the pump laser is used to power the first-stage erbium-ytterbium co-doped fiber.

[0018] This application achieves maximum gain for the erbium-ytterbium co-doped fiber amplification device by adjusting the distance L1 between one end of the optical isolator and the first-stage erbium-ytterbium co-doped fiber; it employs a single-pump bipolar structure, reducing the number of pump lasers used, lowering device cost and complexity, and improving device performance; it uses an optical isolator to effectively suppress back-propagation amplified spontaneous emission, improving the overall performance of the amplification device; and it uses a shorter doped fiber, resulting in less loss during fiber transmission and higher transmission efficiency. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 A structural diagram of a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier provided for this application;

[0021] Figure 2 A schematic diagram of the magneto-optical rotation effect provided in this application;

[0022] Figure 3 This is a structural diagram of the optical isolator 5 provided in this application;

[0023] Figure 4 This is a schematic diagram of the principle of optical isolator 5;

[0024] Figure 5 A graph showing the relationship between the signal gain of the erbium-ytterbium co-doped fiber amplifier provided in this application and the fiber length.

[0025] Figure 6 Simulation structural diagram of the single-pumped bipolar erbium-ytterbium co-doped fiber amplifier provided in this application;

[0026] Figure 7 The signal gain versus pump power analysis graph provided in this application;

[0027] Figure 8 The noise figure as a function of pump power is provided for the purposes of this application.

[0028] Figure 9 The following graph illustrates the relationship between signal gain and input signal power provided in this application;

[0029] Figure 10 The noise figure as a function of input signal power is provided for analysis purposes in this application.

[0030] Figure 11The graph showing the relationship between output power and input signal power provided in this application;

[0031] Figure 12 A diagram showing the influence of the position (0.5m-1m) of the optical isolator 5 provided in this application on the gain of the single-pumped bipolar erbium-ytterbium co-doped fiber amplifier.

[0032] Figure 13 The diagram shows the effect of the position (1m-2m) of the optical isolator 5 provided in this application on the gain of the single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] The specific content provided by the embodiments of this application will be described in detail below with reference to the accompanying drawings and through specific examples and application scenarios.

[0035] See Figure 1 , Figure 1 This application provides a structural diagram of a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. Figure 1 As shown, the device includes: a signal light source 1, a pump laser 2, a coupler 3, a first-stage erbium-ytterbium co-doped fiber 4, an optical isolator 5, and a second-stage erbium-ytterbium co-doped fiber 6. The entire signal light amplification process is as follows: the signal light emitted by the signal light source 1 and the pump light emitted by the pump laser 2 are coupled through the coupler 3 and simultaneously enter the first-stage erbium-ytterbium co-doped fiber 4. Then, they pass through the optical isolator 5 and enter the second-stage erbium-ytterbium co-doped fiber 6. Under the action of continuous pump light, the erbium ions Er in the erbium-ytterbium co-doped fiber are amplified. 3+ Population inversion is achieved between the ground state and metastable energy levels to amplify the signal light. The optical isolator 5 suppresses the reverse amplified spontaneous emission (transmission amplified spontaneous emission) in the second-stage erbium-ytterbium co-doped fiber 6, preventing it from entering the first-stage erbium-ytterbium co-doped fiber 4 and reducing the pump power consumption in the reverse transmission amplified spontaneous emission. The isolated optical signal is sent to the second-stage erbium-ytterbium co-doped fiber 6 to amplify the optical power, and finally the output signal is obtained.

[0036] The optical signal amplification principle of this application is as follows:

[0037] 1. Using erbium-ytterbium co-doped fiber, in an erbium-doped fiber amplifier, erbium ions Er... 3+If the ion concentration is too low, the pump light cannot be fully absorbed, resulting in a low gain for the erbium-doped fiber amplifier and ineffective amplification of the signal light; Er 3+ High ion concentrations will produce a large amount of Er. 3+ Ion pairs exhibit concentration quenching, reducing energy conversion efficiency and limiting the output power increase of erbium-doped fiber amplifiers. One of the most effective methods to address the concentration quenching problem in erbium-doped fiber amplifiers is to add an appropriate amount of Yb to the erbium-doped fiber. 3+ Ions, making an Er 3+ The ions are surrounded by multiple Yb 3+ Ions surround, thereby increasing Er 3+ The spacing between ions should be avoided in Er 3+ When the ion concentration is too high, Er 3+ When ions get too close to each other and form ion pairs, Er in erbium-doped fiber amplifiers... 3+ The doping concentration of Yb is higher than that of ordinary erbium-doped optical fibers. 3+ Ions also act as sensitizers; in erbium-doped fiber amplifiers, because an Er... 3+ The ions are surrounded by multiple Yb 3+ Surrounded by ions, in this case, only a very small number of Er 3+ Ions directly absorb the pump light and transition to higher energy levels, typically Yb. 3+ Ions first absorb the energy of the pump light and transition to a higher energy level, and then transfer the absorbed energy to the similar ground state Er through sensitization. 3+ Ions, achieving population inversion in the erbium band. 3+ Another advantage of ions is Yb 3+ Ions have a simple two-level structure, which greatly reduces cross-relaxation and ion quenching, and improves pumping efficiency.

[0038] 2. An optical isolator 5 is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. Light reflected back from the optical fiber can be effectively isolated by the optical isolator 5, improving the transmission efficiency of optical waves. The optical isolator 5 mainly utilizes the Faraday effect of magneto-optical crystals. The selection of the optical isolator 5 generally requires characteristics such as high isolation and low insertion loss. The optical isolator 5 only allows forward-propagating light to pass through and blocks reverse light. Its breaking of optical path reversibility mainly utilizes the Faraday effect of magneto-optical crystals. The Faraday effect is the basis for realizing optical isolators. Under the action of an external magnetic field, the polarization direction of linearly polarized light rotates when passing through a material that does not have optical rotation. Figure 2 As shown, this phenomenon of causing linearly polarized light to rotate is also called magneto-optical rotation. The Faraday effect indicates that polarized light propagating along the direction of a magnetic field rotates its polarization direction by an angle. The magnetic flux density is proportional to the product of the length L of the magneto-optical material and the magnetic flux density B:

[0039]

[0040] Where V represents a characteristic parameter of the magneto-optical material. The Faraday effect differs from natural optical rotation; in a given magneto-optical medium, regardless of whether light travels along or against the magnetic field direction, the orientation of the vibration plane is the same, determined only by the magnetic field direction. When the propagation direction of linearly polarized light is the same as the magnetic field direction, right-handed optical rotation occurs; when the propagation direction of linearly polarized light is opposite to the magnetic field direction, left-handed optical rotation occurs. Rotation angle. The size of the light source depends on the material length, the operating wavelength, and the magnetic flux density. In the Faraday effect, when light passes back and forth through the same magneto-optical material, it undergoes two rotations, each with the same angle. Therefore, the total angle of rotation for both round trips is twice the original rotation angle, which is... This property allows magneto-optical materials to be used to manufacture optical isolators, suppressing reverse-transmitted light and achieving the function of optical isolator 5.

[0041] The structure of optical isolator 5 is as follows Figure 3 As shown, it mainly consists of a first polarizer 101, a Faraday rotator 102, and a second polarizer 103, wherein the Faraday rotator 102 is located between the first polarizer 101 and the second polarizer 103, and the first polarizer 101 and the second polarizer 103 are 45º apart.

[0042] See Figure 4 , Figure 4 This is a schematic diagram of the optical isolator 5. When linearly polarized light is incident in the forward direction, its polarization direction is the same as the transmission axis of the first polarizer 101, and it can pass through completely. After passing through the Faraday rotator 102, its polarization direction rotates clockwise by 45°, aligning with the transmission axis of the second polarizer 103, and it can also pass through completely. Therefore, forward-incident light can propagate with low loss. For linearly polarized light incident in the reverse direction, the second polarizer 103 acts as a polarizer. Only the portion of the reverse-incident light aligned with the transmission axis of the second polarizer 103 reaches the Faraday rotator 102. After passing through the Faraday rotator 102, its polarization direction still rotates clockwise by 45° (the Faraday effect is irreversible). At this point, the polarization direction of the reverse-incident light is exactly perpendicular to the transmission axis of the first polarizer 101, becoming horizontally polarized light, thus blocked by the first polarizer 101 and unable to pass through, effectively isolating the reflected light.

[0043] During propagation, light undergoes varying degrees of reflection and scattering, forming back-transmitted light. An optical isolator 5 is inserted to suppress the adverse effects of this back-transmitted light on optical equipment and fiber optic communication systems. However, the degree of suppression of back-transmitted amplified spontaneous emission varies depending on the position of the optical isolator 5 within the gain fiber. In a suitable position, the optical isolator 5 can effectively suppress back-transmitted amplified spontaneous emission, reduce pump light consumption in this emission, and improve signal gain and noise figure. In an unsuitable position, it not only fails to suppress back-transmitted amplified spontaneous emission but may also degrade amplifier performance due to its insertion loss. Therefore, there exists an optimal position where the optical isolator 5, for a given input signal power and pump power, achieves maximum gain in the erbium-ytterbium co-doped fiber amplifier.

[0044] Figure 5 This diagram illustrates the variation of the gain of an erbium-ytterbium co-doped fiber amplifier with fiber length under different pump powers. For a given pump power, there exists an optimal fiber length that maximizes the gain of the erbium-ytterbium co-doped fiber amplifier. Furthermore, the optimal fiber length increases with increasing pump power. As shown in the figure, the gain reaches its maximum when the fiber length reaches approximately 4-6 m. However, there is no linear relationship between the two. For higher pump powers, the gain decrease is not significant within a certain fiber length after reaching the maximum gain; that is, the optimal fiber length can vary over a wider range. In the experiment, to fully utilize the pump light and improve pump efficiency without affecting the gain of the erbium-ytterbium co-doped fiber amplifier, this application sets the optimal fiber length to 6 m.

[0045] Using the amplifier and optical isolator modules in the Optisystem simulation software, the performance changes under different signal and pump powers were simulated and analyzed. Based on the simulation, the optimal fiber length for erbium-ytterbium co-doped fiber was determined to be 6m, with a 1:5 ratio of the two gain media (EYDF1 = 1m, EYDF2 = 5m) to obtain the maximum signal gain, output power, and lowest noise figure.

[0046] See Figure 6 , Figure 6 The simulation structure diagram of the single-pumped bipolar erbium-ytterbium co-doped fiber amplifier provided in this application is shown below. The parameter settings for the single-pumped bipolar erbium-ytterbium co-doped fiber amplifier in the simulation experiment are as follows:

[0047] 1. The pump source operating wavelength is set to 1064nm because it has high power conversion efficiency and low excited state absorption at this wavelength, and the pump power is set to 1000mW;

[0048] 2. The gain medium is erbium / ytterbium co-doped fiber, with a fiber length of 6m. Erbium ions (Er) 3+The concentration was 5.14 × 10⁻⁶. 25 m -3 Yb ions 3+ The concentration is 6.2 × 10⁻⁶. 26 m -3 The doping radius is 2 μm and the numerical pore size is 0.15.

[0049] 3. Optical isolator 5 has an isolation of 60dB, an insertion loss of 0.5dB, and a return loss of 60dB;

[0050] 4. The operating wavelength of the signal from coupler 3 is 1550nm, and the operating bandwidth is 130nm;

[0051] 5. Based on the optimal position of the optical isolator 5 in the erbium / ytterbium co-doped fiber, the distribution ratio of the two gain media segments, the first-stage erbium-ytterbium co-doped fiber 4 and the second-stage erbium-ytterbium co-doped fiber 6, is 1:5, i.e., EYDF1=1m and EYDF2=5m.

[0052] 6. The wavelength of signal light source 1 is set to 1550nm, and the input signal power is set to -40dBm for small signal and 0dBm for large signal.

[0053] Figure 7 This is a graph showing the relationship between signal gain and pump power. Figure 8 This is a graph showing the relationship between noise figure and pump power. The gain and noise figure characteristics of the erbium-ytterbium co-doped fiber amplifier are closely related to the pump power. Figure 7 and Figure 8 The gain and noise figure characteristics of the bipolar erbium-ytterbium co-doped fiber amplifier and the conventional single-stage erbium-ytterbium co-doped fiber amplifier under different pump powers are presented. Inserting the optical isolator 5 improves the performance of the erbium-ytterbium co-doped fiber amplifier to some extent, and the improvement in signal gain and noise figure becomes more significant with increasing pump power. At high pump power (greater than 500mW), the signal gain increases by approximately 10dB, and the noise figure decreases by approximately 1.5dB to 3dB.

[0054] Figure 9 This is a graph showing the relationship between signal gain and input signal power. Figure 10 This is a graph showing the relationship between noise figure and input signal power. Figure 11The graph shows the relationship between output power and input signal power. The amplification degree of the fiber amplifier varies with different input signal powers. Therefore, this paper uses different input signal powers to simulate and analyze the signal gain characteristics, noise figure characteristics, and output power characteristics of a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. The signal light and pump light are coupled through coupler 3 and simultaneously enter the first-stage erbium-ytterbium co-doped fiber 4, then pass through optical isolator 5 into the second-stage erbium-ytterbium co-doped fiber 6. Under the action of continuous pump light, erbium ions in the erbium-ytterbium co-doped fiber form a population inversion between the ground state and metastable energy levels, achieving amplification of the signal light. The function of optical isolator 5 is to suppress the backward amplification spontaneous emission (transmission amplification spontaneous emission) in the second-stage erbium-ytterbium co-doped fiber 6, preventing it from entering the first-stage erbium-ytterbium co-doped fiber 4, and reducing the pump power consumption in the backward transmission amplification spontaneous emission. By inserting optical isolator 5, the reverse propagation amplification spontaneous emission power of the bipolar erbium-ytterbium co-doped fiber amplifier is reduced by one to two orders of magnitude compared to that of a conventional single-stage erbium-ytterbium co-doped fiber amplifier. The same applies to the forward propagation amplification spontaneous emission power. Therefore, optical isolator 5 effectively suppresses reverse propagation amplification spontaneous emission in the erbium-ytterbium co-doped fiber amplifier, preventing its accumulation in the fiber and thus improving its performance. In the small-signal region, the performance of the erbium-ytterbium co-doped fiber amplifier is significantly improved after inserting optical isolator 5, with a gain increase of approximately 10 dB, a noise figure reduction of approximately 3 dB, and an output power increase of approximately 10 dBm.

[0055] Figure 12 The graph shows the impact of the position (0.5m-1m) of the optical isolator 5 on the gain of a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. Figure 13 This diagram illustrates the impact of the position (1m-2m) of the optical isolator 5 on the gain of a single-pumped bipolar erbium-ytterbium co-doped fiber amplifier. It shows the change in gain of the erbium-ytterbium co-doped fiber amplifier with pump power at different positions of the optical isolator 5. The position of the optical isolator 5 within the erbium / ytterbium co-doped fiber is crucial, directly affecting the degree of performance improvement of the bipolar erbium-ytterbium co-doped fiber amplifier. Different positions of the optical isolator 5 within the gain fiber result in varying degrees of suppression of backward propagation spontaneous emission (ASE). At a suitable position, the optical isolator 5 can effectively suppress backward ASE, reducing pump light consumption on the backward ASE and improving signal gain and noise figure. At an unsuitable position, it not only fails to suppress backward ASE but may also degrade the amplifier's performance due to its own insertion loss. Therefore, there exists an optimal position where the optical isolator 5, for a given input signal power and pump power, achieves the maximum gain of the erbium-ytterbium co-doped fiber amplifier.

[0056] from Figure 12It can be seen that when L1 is short, i.e., L1 is 0.5m (corresponding to a ratio of 1:11), 0.75m (corresponding to a ratio of 1:7), and 1m (corresponding to a ratio of 1:5), the optical isolator 5 is close to the input end, and the gain of the erbium-ytterbium co-doped fiber amplifier is low. As L1 increases, the optical isolator 5 moves closer to the output end, and the gain of the erbium-ytterbium co-doped fiber amplifier gradually increases. When L1 = 1m (corresponding to a ratio of 1:5) and the pump power is 600mW-2000mW, the gain of the erbium-ytterbium co-doped fiber amplifier reaches its maximum value.

[0057] from Figure 13 It can be seen that as the optical isolator 5 continues to move backward from this position, i.e., L1 is 1m (corresponding to a ratio of 1:5), 1.25m (corresponding to a ratio of 1:3.8), 1.5m (corresponding to a ratio of 1:3), 1.75m (corresponding to a ratio of 1:2.429), and 2m (corresponding to a ratio of 1:2), the gain of the erbium-ytterbium co-doped fiber amplifier gradually decreases. When L1=1m (corresponding to a ratio of 1:5) and the pump power is 600mW-2000mW, the gain of the erbium-ytterbium co-doped fiber amplifier reaches its maximum value. Therefore, L1=1m (corresponding to a ratio of 1:5) is the optimal position for the optical isolator 5. At this position, the length of the first-stage erbium-ytterbium co-doped fiber 4 (i.e., EYDF1) is 1m, and the length of the second-stage erbium-ytterbium co-doped fiber 6 (i.e., EYDF2) is 5m.

[0058] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles described in this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A single-pumped bipolar erbium-ytterbium co-doped fiber amplification device, characterized in that, include: Signal source (1), pump laser (2), coupler (3), first-stage erbium-ytterbium co-doped fiber (4), optical isolator (5), and second-stage erbium-ytterbium co-doped fiber (6); The light source emission ports of the signal light source (1) and the pump laser (2) are flush with one end of the coupler (3). One end of the coupler (3) receives the light source of the signal light source (1) and the pump laser (2), and the other end is connected to the first-stage erbium-ytterbium co-doped fiber (4). The two ends of the optical isolator (5) are connected to the first-stage erbium-ytterbium co-doped fiber (4) and the second-stage erbium-ytterbium co-doped fiber (6), respectively. The distance L1 between one end of the optical isolator (5) and the first-stage erbium-ytterbium co-doped optical fiber (4) is a preset value.

2. The apparatus according to claim 1, characterized in that, The total length of the first-stage erbium-ytterbium co-doped optical fiber (4) and the second-stage erbium-ytterbium co-doped optical fiber (6) is set to 4-6 meters.

3. The apparatus according to claim 2, characterized in that, The length distribution ratio of the first-stage erbium-ytterbium co-doped fiber (4) to the second-stage erbium-ytterbium co-doped fiber (6) is 1:2-1:

11.

4. The apparatus according to claim 1, characterized in that, The optical isolator (5) includes: a first polarizer (101), a Faraday rotator (102), and a second polarizer (103), with the two ends of the Faraday rotator (102) connected to the first polarizer (101) and the second polarizer (103) respectively.

5. The apparatus according to claim 4, wherein the transmission axis of the first polarizer (101) is the same as the polarization direction of the positively polarized light, and all the positively polarized light can pass through; the second polarizer (103) allows all positively polarized light to pass through and blocks the reversely polarized light whose polarization direction is perpendicular to the second polarizer (103).

6. The apparatus according to claim 4, characterized in that, The optical isolator (5) suppresses the reverse amplified spontaneous emission from the second-stage erbium-ytterbium co-doped fiber (6) into the first-stage erbium-ytterbium co-doped fiber (4).

7. The device according to claim 6, wherein the optical isolator (5) is connected to the first-stage erbium-ytterbium co-doped fiber (4) and the second-stage erbium-ytterbium co-doped fiber (6) via an FC interface, which facilitates testing and replacement.

8. The single-pumped bipolar erbium-ytterbium co-doped fiber amplifier according to any one of claims 1 to 7, wherein the input of the signal light source (1) is respectively set to a preset small signal and a preset large signal, and the output is a light wave corresponding to the small signal and a light wave corresponding to the large signal.

9. The apparatus according to claim 8, wherein the coupler (3) couples the light wave emitted by the signal light source (1) with the pump light emitted by the pump laser (2) to obtain coupled light.

10. The apparatus according to claim 9, wherein the pump laser (2) is used to power the first-stage erbium-ytterbium co-doped fiber (4).

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