Optical fiber, optical fiber manufacturing method, and optical fiber amplifier

Abstract

The embodiments of the present application provide an optical fiber, an optical fiber manufacturing method, and an optical fiber amplifier, in which the ratios of erbium, aluminum, and phosphorus are adjusted during optical fiber manufacturing, so that aluminum phosphate is formed around the erbium in the manufactured optical fiber, reducing the probability of the erbium in the optical fiber transitioning to a higher energy level and suppressing the excited state absorption effect of the erbium in the optical fiber on an optical signal.

Description

[Technical Field]

[0001]

[0001] This application relates to the field of optical communications, and more particularly to optical fibers, optical fiber manufacturing methods, and optical fiber amplifiers. [Background technology]

[0002]

[0002] With the rapid development of the information age and the arrival of the big data age, there is an urgent need for a large-capacity data transmission system. Based on the existing optical fiber transmission system, how to further improve the communication capacity has become a research hotspot in the field of optical communication. Generally, communication capacity is determined by the following three aspects: 1. Increasing the transmission rate of the channel; 2. Reducing channel spacing; 3.Increasing transmission bandwidth; In the long term, increasing transmission bandwidth is the fundamental method for achieving long-distance, high-speed, and bit-error-free transmission.

[0003]

[0003] Increasing the system transmission bandwidth of the entire transmission system requires the operating range of other components to match the corresponding bandwidth. Therefore, an erbium-doped fiber (EDF) amplifier (EDFA) to be developed should have characteristics such as high gain, low noise, and wide bandwidth, and should achieve flatness and locking of the gain spectrum within a wide wavelength range. This also imposes higher performance indexes on the EDF in the EDFA.

[0004]

[0004] After extensive research, it has been found that light in the long-wavelength band (L-Band) has minimal dispersion-induced signal distortion and the lowest attenuation, and is therefore most suitable for transmission in optical fibers. However, in EDF, when an L-Band signal is input, the energy and energy level of the long band in the L-Band are 4 I 13 / 2 The difference between the energy levels 4 I 13 / 2 and energy levels 4 I 9 / 2 In this case, the erbium ion in the metastable upper energy level absorbs the long-band signal photon and then moves to the energy level 4 I 9 / 2 As a result, signals in the long band of the L-band are attenuated, and existing EDFAs cannot effectively amplify L-band optical signals. Summary of the Invention

[0005]

[0005] The present application provides an optical fiber, an optical fiber manufacturing method, and an optical fiber amplifier that can suppress the excited-state absorption effect of erbium element in the optical fiber on an optical signal.

[0006]

[0006] According to a first aspect, there is provided an optical fiber for use in an optical fiber amplifier, the optical fiber being for amplifying an optical signal, the fiber core of the optical fiber including erbium, aluminum, and phosphorus, and aluminum phosphate formed around the erbium.

[0007]

[0007] According to the optical fiber provided in the present application, aluminum phosphate is formed around erbium elements, which can reduce the clustering degree of erbium elements and reduce the probability of erbium elements transitioning to higher energy levels, thereby suppressing the excited state absorption effect of erbium elements in the optical fiber on optical signals.

[0008]

[0008] Regarding the first aspect, in some implementations of the first aspect, the mass percentage of the element erbium is 0.2% to 1%; the mass percentage of the aluminum element is between 0.5% and 20%; The mass percentage of elemental phosphorus is between 2% and 30%.

[0009]

[0009] Optionally, the mass percentage of the element erbium is 0.2% to 0.6%; the mass percentage of the aluminum element is between 6% and 11%, The mass percentage of elemental phosphorus is between 15% and 22%.

[0010]

[0010] Optionally, the mass percentage of the element erbium is 0.2% to 0.3%; the mass percentage of the aluminum element is 6% to 7%; The mass percentage of elemental phosphorus is 15% to 16%.

[0011]

[0011] The proportions of erbium, aluminum, and phosphorus elements in the optical fiber are adjusted so that the optical fiber can obtain a high gain for optical signals in the L band.

[0012]

[0012] Optionally, the mass percentage of the element erbium is 0.5% to 0.6%; the mass percentage of the aluminum element is 10% to 11%; The mass percentage of elemental phosphorus is 21% to 22%.

[0013]

[0013] The proportions of erbium, aluminum, and phosphorus elements in the optical fiber are adjusted so that the optical fiber can obtain a high gain for optical signals in the L band.

[0014]

[0014] Specifically, the amount of aluminum phosphate formed around erbium can be determined based on the aluminum and phosphorus contents in the optical fiber. When the aluminum and phosphorus contents are high, more aluminum phosphate is formed around erbium. When the aluminum and phosphorus contents are low, less aluminum phosphate is formed around erbium.

[0015]

[0015] Regarding the first aspect, in some implementations of the first aspect, the fiber core comprises the following elements: Germanium Ge, silicon Si, thulium Tm, bismuth Bi, fluorine F, cerium Ce, ytterbium Yb, zirconium Zr, neodymium Nd, and lanthanum La The mass percentage of elemental germanium is between 0.01% and 30%, and the mass percentage of elemental silicon is greater than 60%.

[0016]

[0016] Regarding the first aspect, in some implementations of the first aspect, the fiber diameter of the optical fiber is 1 μm to 20 μm, and the numerical aperture of the optical fiber is 0.01 to 1.2.

[0017] According to a second aspect, there is provided a method for manufacturing an optical fiber, the method comprising: depositing a loose layer on the inner wall of the quartz glass tube; immersing the quartz glass tube on which the loose layer is deposited in a first solution to allow elements in the first solution to permeate into the loose layer, the first solution including erbium, aluminum, and phosphorus; The concentration of erbium element is 0.1 moles per liter (mol / L) to 0.3 mol / L, The aluminum concentration is 1 mol / L to 6 mol / L. The concentration of phosphorus element is 0.5 mol / L to 4 mol / L; Sintering the quartz glass tube immersed in the first solution to dope the elements in the first solution into the quartz glass tube; and The method includes drawing a sintered quartz glass tube into an optical fiber.

[0018]

[0018] Specifically, the loose layer may be deposited on the inner wall of the quartz glass tube by using a chemical vapor deposition (CVD) method, or may be deposited on the inner wall of the quartz glass tube by using a modified chemical vapor deposition (MCVD) method, which is not limited in the present application.

[0019]

[0019] Specifically, the loose layer may be a soot layer, which is for providing a doping environment for the elements in the first solution.

[0020]

[0020] Specifically, "the first solution comprises the element erbium, the element aluminum, and the element phosphorus" may be understood as the first solution comprising erbium ions, aluminum ions, and phosphorus ions.

[0021]

[0021] According to the above-mentioned method, an appropriate amount of erbium, aluminum, and phosphorus elements can be doped into the optical fiber, and aluminum phosphate can be formed around the erbium element in the fiber core of the optical fiber, so that the clustering degree of the erbium element can be reduced and the probability of the erbium element transitioning to a higher energy level can be reduced, thereby suppressing the excited state absorption effect of the erbium element in the optical fiber on the optical signal.

[0022] Optionally, The concentration of erbium element is 0.1 moles per liter (mol / L) to 0.3 mol / L, The aluminum concentration is 3 mol / L to 6 mol / L. The concentration of elemental phosphorus is 2 mol / L to 4 mol / L.

[0023] Optionally, in the first solution: The concentration of erbium element is 0.1 mol / L to 0.2 mol / L, The aluminum concentration is 3 mol / L to 4 mol / L. The concentration of elemental phosphorus is 2 mol / L to 3 mol / L.

[0024]

[0024] By adjusting the concentration ratio of erbium, aluminum, and phosphorus in the first solution, the manufactured optical fiber can obtain a high gain for an L-band optical signal.

[0025] Optionally, in the first solution: The concentration of erbium element is 0.2 mol / L to 0.3 mol / L, The aluminum concentration is 5 mol / L to 6 mol / L. The concentration of phosphorus element is 3 mol / L to 4 mol / L.

[0026]

[0026] By adjusting the concentration ratio of erbium element, aluminum element, and phosphorus element in the first solution, the manufactured optical fiber can obtain a higher gain in the L-band.

[0027]

[0027] Regarding the second aspect, in some implementations of the second aspect, the first solution contains the following elements: Thulium Tm, Bismuth Bi, Fluorine F, Cerium Ce, Ytterbium Yb, Zirconium Zr, Neodymium Nd, and Lanthanum La The method further includes at least one of:

[0028]

[0028] Regarding the second aspect, in some implementations of the second aspect, the fiber diameter of the manufactured optical fiber is between 1 μm and 20 μm, and the numerical aperture of the manufactured optical fiber is between 0.01 and 1.2.

[0029]

[0029] Regarding the second aspect, in some implementations of the second aspect, the step of immersing the quartz glass tube on which the loose layer is deposited in the first solution includes: The method includes immersing the quartz glass tube on which the loose layer is deposited in the first solution for a period of 3 to 6 hours.

[0030] Optionally, the quartz glass tube on which the loose layer is deposited may be immersed in the first solution for 5 hours.

[0031]

[0031] Regarding the second aspect, in some implementations of the second aspect, the step of sintering the quartz glass tube immersed in the first solution includes: The method includes a step of sintering the quartz glass tube immersed in the first solution in an oxygen atmosphere, the sintering temperature being 1400 degrees Celsius (°C) to 1900 degrees Celsius (°C).

[0032] Optionally, the sintering temperature may alternatively be between 1500 degrees Celsius (°C) and 1700 degrees Celsius (°C).

[0033]

[0033] According to the aforementioned sintering process, the doped ions from the first solution can react with oxygen, and the doped ions enter the quartz glass structure due to pore collapse and vitrification.

[0034]

[0034] Regarding the second aspect, in some implementations of the second aspect, the step of sintering the quartz glass tube immersed in the first solution includes: The method includes a step of sintering the quartz glass tube immersed in the first solution in an atmosphere containing elemental phosphorus.

[0035]

[0035] Specifically, the atmosphere containing phosphorus element may be provided by POCl3, or may be provided by another phosphorus-containing material, which is not limited in the present application.

[0036]

[0036] According to a third aspect, there is provided an optical fiber amplifier, which includes an optical fiber for amplifying an optical signal, and the optical fiber may be the optical fiber provided in the first aspect and various implementation forms of the first aspect. [Brief explanation of the drawings]

[0037] [Figure 1]

[0037] Figure 1 is an energy level diagram according to the present application. [Figure 2]

[0038] FIG. 2 is a diagram relating to the manufacture of an optical fiber preform according to the present application. [Figure 3]

[0039] FIG. 3 is a diagram of the microcoordination environment in which rare earth elements are doped according to the present application. [Figure 4]

[0040] FIG. 4 is a diagram of an apparatus for gain testing of optical fibers according to the present application. [Figure 5]

[0041] FIG. 5 shows an example of the gain spectrum of an optical fiber according to the present application. [Figure 6]

[0042] FIG. 6 is a diagram of another apparatus for optical fiber gain testing in accordance with the present application. [Figure 7]

[0043] FIG. 7 shows another example of the gain spectrum of an optical fiber according to the present application. [Figure 8]

[0044] FIG. 8 shows yet another example of the gain spectrum of an optical fiber according to the present application. [Figure 9]

[0045] FIG. 9 shows an example of a system architecture diagram of an optical fiber amplifier according to the present application. DETAILED DESCRIPTION OF THE INVENTION

[0038]

[0046] The technical solutions of the present application will be described below with reference to the accompanying drawings.

[0039]

[0047] For ease of understanding, terms or concepts that may be used in the embodiments of the present application will be explained first before describing the embodiments of the present application. It should be understood that the basic concepts explained below are briefly explained by using the disclosure in the current related art as an example, and the specific names are not limited in the present application.

[0040]

[0048] 1. Bridging and non-bridging oxygen bonds

[0049] Among inorganic nonmetallic materials, the crystal structure of silicates shares common features; specifically, all silicate crystal structures have an [SiO4] tetrahedron, and the silicate structural rules are derived from this; for example, [PO4] tetrahedron, [BO4] tetrahedron, [BO4] triangle, [AlO4] tetrahedron, and [AlO4] octahedron. In the crystal structure of silicate minerals, the most basic structural unit is the Si-O complex anion. All silicate minerals belong to the tetraoxysilicates family, except for the Si4+ in the structure of thaumasite, which has a six-fold coordination structure and forms an Si-O6 coordinated octahedron, which belongs to the hexaoxysilicates family. The Si4+ in tetraoxysilicates has a four-fold coordination structure and forms an Si-O4 coordinated tetrahedron. The silicon-oxygen tetrahedra can exist isolated in the structure and be interconnected by other metal cations, i.e., by non-bridging oxygen bonds. However, the silicon-oxygen tetrahedra can alternatively be interconnected by O at the corners. 2- Silicon-oxygen tetrahedrons may be connected to each other by sharing bridging oxygens (called bridging oxygens), forming a silicon-oxygen tetrahedron framework structure in various connection forms such as groups, rings, chains, layers, and frames. The silicon-oxygen framework is connected by other metal cations. Therefore, bridging oxygen refers to an oxygen ion shared at the corner by two silicon-oxygen tetrahedra, i.e., an oxygen ion that functions as a "bridge." Conversely, an oxygen ion that is bonded to only one silicon-oxygen tetrahedron and is not shared by two tetrahedra is a non-bridging oxygen. The non-bridging oxygen indicates the degree of fracture of the silicon-oxygen network, and the unsaturated valence of the non-bridging oxygen is neutralized by a cation present outside the silicon-oxygen tetrahedron.

[0041]

[0050] 2. Excited-state absorption (ESA)

[0051] A metastable upper energy level particle is in an excited state, and one or more higher energy levels may exist above the metastable energy level. If the wavelength of the incident light is close to the energy difference between the metastable energy level and one or more higher energy levels above the metastable energy level, the metastable upper energy level particle can easily absorb the energy at the wavelength of the incident light and transition to one or more higher energy levels above the metastable energy level, resulting in attenuation of the signal emitted by stimulated radiation at the wavelength of the incident light.

[0042]

[0052] 3.Upconversion light emission

[0053] Stokes' law states that a material can only be excited by high-energy light and emit low-energy light. Specifically, after being excited by short-wavelength, high-frequency light, the material will emit long-wavelength, low-frequency light. Upconversion luminescence violates Stokes' law. Upconversion luminescence occurs when a material is excited by low-energy light and emits high-energy light. Specifically, after being excited by long-wavelength, low-frequency light, the material will emit short-wavelength, high-frequency light.

[0043]

[0054] Upconversion luminescence is a process of ESA. The principle of upconversion luminescence is that the same ion transitions from the ground state to a higher energy excited state through continuous multiphoton absorption. This is the basic process of upconversion luminescence.

[0044]

[0055] 4. Wavelength division multiplexing (WDM) technology

[0056] WDM technology is a technology in which optical carrier signals of at least two different wavelengths are collected at the transmitting end by using a multiplexer and combined into the same optical fiber of an optical line for transmission. At the receiving end, the optical carrier signals of various wavelengths are separated by using a demultiplexer, and then an optical receiver performs further processing to restore the original signals. The technology used to transmit optical signals of two or more different wavelengths on the same optical fiber is called WDM technology.

[0045]

[0057] With the rapid development of the information age and the arrival of the big data age, there is an urgent need for a high-capacity data transmission system. How to further improve the communication capacity based on the existing optical fiber transmission system has become a research hotspot in the field of optical communications. Generally, communication capacity is determined by the following three aspects: 1. Increasing the transmission rate of the channel; 2. Reducing channel spacing; 3.Increasing transmission bandwidth; In the long term, increasing transmission bandwidth is the fundamental method for achieving long-distance, high-speed, and bit-error-free transmission.

[0046]

[0058] Increasing the system transmission bandwidth of the entire transmission system requires the operating range of other components to match the corresponding bandwidth. Therefore, the erbium-doped fiber (EDF) amplifier (EDFA) to be developed should have characteristics such as high gain, low noise, and wide bandwidth, and should achieve flatness and locking of the gain spectrum within a wide wavelength range. This also imposes higher performance indexes on the EDF in the EDFA.

[0047]

[0059] After extensive research, it has been found that light in the long-wavelength band (L-band) has minimal dispersion-induced signal distortion and attenuation and is therefore most suitable for transmission over optical fiber. However, due to the amplification characteristics of the long-wavelength band (i.e., L-band), existing EDFAs cannot efficiently amplify L-band optical signals. Specifically, L-band light refers to light in the wavelength range from 1260 nm to 1625 nm. Currently, L-band amplifiers only provide coverage up to approximately 1610 nm and cannot achieve high gain for optical signals greater than 1610 nm within the L-band. Therefore, how to fully utilize the effective bandwidth of the L-band (greater than 1610 nm) is a key direction for improving communication capacity.

[0048]

[0060] Currently, erbium-doped fiber amplifiers based on tellurium-based glasses are capable of performing optical amplification in the L-band. Tellurite glasses contain two types of bonding modes, namely covalent and ionic bonding, and lone-pair electrons exist in addition to the basic structural units. Erbium-doped fiber amplifiers based on tellurium-based glasses have the following advantages: 1. In rare-earth ion-doped fibers, the rare-earth ions can occupy a wide range of lattice sites, and the crystal field strengths experienced by the rare-earth ions at different lattice sites are slightly different, which gives rise to a series of slightly varying energy distributions at a particular Stark energy level, resulting in non-uniform broadening of the absorption and emission spectra of the rare-earth ions, thereby facilitating bandwidth expansion.

[0049] 2. Tellurium-based glasses have a high refractive index (about 2.0), which is beneficial for obtaining a large stimulated emission cross section.

[0050] 3. Tellurite glasses have low phonon energy, which can reduce the radiationless relaxation rate in tellurite glasses and increase the radiative quantum efficiency, thereby facilitating the production of highly efficient lasers and amplifiers.

[0051] 4. Compared with erbium-doped fiber amplifiers based on quartz substrates, erbium-doped fiber amplifiers based on tellurite glass have higher rare-earth doping solubility, which is one to two orders of magnitude larger, which facilitates effective absorption of pump light and high gain per unit length, reduces the fiber length required to achieve a specific gain, and facilitates component miniaturization.

[0052] Theoretical analysis indicates that the L-band limit achievable with erbium-doped fiber amplifiers based on tellurite glass is 1630+ nm. Therefore, erbium-doped fiber amplifiers based on tellurite glass offer an important alternative route for achieving broad-spectrum optical amplification in the L-band. However, the composition of tellurite glass directly affects the glass's formability, thermal stability, refractive index, rare-earth ion doping concentration, and rare-earth ion spectral characteristics. Currently, the melting temperature of tellurite glass for achieving optical amplification in the L-band is approximately 600°C, and the glass softening temperature is relatively low. If the refractive index is too high, tellurite glass will suffer from significant splice or fusion losses during fiber butting or fiber fusion with passive erbium-doped fibers. The fusion loss can be greater than 0.5 dB. As a result, the performance of the optical amplifier will be significantly affected. Glass has brittle mechanical properties, and when it is drawn into optical fiber, the brittleness of glass affects the subsequent use process, making the glass unsuitable for a wide range of applications. Furthermore, many tellurate glasses produced by using the fusion method have high requirements for the high purity of raw materials, which further increases the cost of producing erbium-doped fiber based on tellurate glasses.

[0053]

[0061] In addition, semiconductor optical amplifiers (SOAs) can also perform optical amplification in the L-band. SOAs are semiconductor lasers with or without facet reflections, and their structure and operating principles are similar to those of semiconductor lasers. When a bias current is applied to the component, the current can induce population inversion in the semiconductor gain material, causing electrons to transition from the valence band to the conduction band, thereby generating spontaneous emission. When an external light field is incident, stimulated emission occurs, which generates signal gain. SOAs have the following advantages: Optical amplification in a band ranging from 1.850 nm to 1600 nm can be achieved by selecting a different gain medium semiconductor material, which may be, for example, the III-V compound semiconductor InGaAsP.

[0054] 2. Currently, SOA gains can exceed 30 dB. SOAs have simple structures and small sizes, allowing them to fully utilize existing semiconductor laser technology. They have mature manufacturing processes, low cost, long life, low power consumption, and are easy to integrate with other components. SOAs have the potential to support ultra-wideband data transmission and are expected to realize the amplification of ultra-wideband spectra covering the L++ band. However, because SOAs must be integrated into existing transmission systems, the signals amplified by the SOA must be coupled into conventional optical fibers. Currently, coupling losses are still significant, approximately 3 dB to 8 dB. When coupling SOA-amplified signals into conventional optical fibers as the first stage of an amplifier, the noise figure degrades accordingly. Because SOA gain is related to factors such as polarization state and temperature, SOA stability is poor. At high output powers, the SOA gain varies with the signal, resulting in serious nonlinear distortion problems and further degrading system performance.

[0055]

[0062] In addition, fiber Raman amplifiers (FRAs) can also perform optical amplification in the L-band. FRAs are optical amplifiers based on the stimulated Raman scattering (SRS) mechanism, and their working principle is as follows: a small portion of the power of the incident light is transferred to a Stokes wave with a lower frequency than the incident light. When a weak signal and a strong signal are simultaneously transmitted in an optical fiber, and the weak signal is sustained long enough within the Raman gain bandwidth of the pump light, the weak signal light will be amplified. FRAs have the following advantages: 1. The gain medium is ordinary optical fiber for transmission, and it has good compatibility with optical fiber systems. 2. The gain wavelength is determined by the wavelength of the pump light and is not affected by other factors. In theory, any wavelength of signal light can be amplified as long as the pump light wavelength is appropriate. 3. FRA has high gain, small crosstalk, low noise figure, and wide spectral range. Optical amplification is performed in the spectral range from 1292 nm to 1660 nm, enabling a wider gain bandwidth than EDFAs, thereby extending communication systems to the L-band limit. However, FRAs require pump lasers with particularly high power when performing amplification in the L-band. Furthermore, most FRAs use a distributed amplification structure. For long-distance transmission systems, FRAs may be used as auxiliary amplification schemes for EDFAs, and are difficult to use independently. Changing the pump power and fiber length of the FRA affects the final output gain and power flatness, limiting application scenarios.

[0056]

[0063] For ease of understanding, hereinafter, the L-band from 1600 nm to 1625 nm will be referred to as the long band, and the L-band from 1260 nm to 1600 nm will be referred to as the short band. It should be understood that the long band in this case may be considered as the band in which the ESA effect affects the lightwave gain of the L-band. Note that the dividing boundary between the long band and the short band of the L-band does not necessarily have to be 1600 nm, but may be 1610 nm or similar. For the sake of explanation, an example in which the dividing boundary between the long band and the short band is 1600 nm will be used below, but this does not constitute any limitation.

[0057]

[0064] In erbium-doped fibers, the local coordination environment of the erbium ions determines the characteristics of the emission spectrum. After absorbing pump light, the erbium ions in their ground state energy level rise to the excited state energy level 4 I 11 / 2 As shown in Figure 1, the excited state energy level 4 I 11 / 2 The lifetime of erbium ions in the ion trap is on the order of 10 microseconds (μs), and therefore erbium ions undergo radiationless relaxation to reach metastable energy levels. 4 I 13 / 2 The erbium ion undergoes non-radiative relaxation to the metastable energy level 4 I 13 / 2 After the transition to the metastable energy level, spontaneous emission occurs. 4 I 13 / 2 The lifetime of erbium ions in the L-band is approximately 10 milliseconds (ms). When an L-band signal is input, the energy of the long band of the L-band is 4 I 13 / 2 and energy levels 4 I 9 / 2 In this case, the erbium ion in the metastable upper energy level absorbs the long-band signal photon and then moves to the energy level 4 I 9 / 2 This is the ESA process of erbium ions, which attenuates the signal in the long band from the L band. A portion of the long band signal light is amplified by stimulated emission of radiation.

[0058]

[0065] Specifically, the pump light absorbed by the erbium ions at the ground state energy level may be a light wave having a wavelength of 980 nanometers (nm), although this application is not limited thereto.

[0059]

[0066] Therefore, the ESA process affects the gain and noise of the amplifier in the long band of the L-band, and is a significant limitation that limits the gain in the long band of the L-band.

[0060]

[0067] Specifically, the gain of an EDF depends primarily on the following equation:

number

[0068] In Equation 1, σ e is the radiation cross section of the EDF, and σ a is the absorption cross section of the EDF, N2(z) is the number of upper energy level particles in the EDF, N1(z) is the number of lower energy level particles in the EDF, N is the total number of particles in the EDF, and G is the gain of the EDF.

[0061]

[0069] Furthermore, σ in Equation 1 e is primarily dependent on the following equation:

number

[0070] In Equation 2, g 21 is the measured radiation coefficient of the EDF, and g ESA is the excited state absorption coefficient of the signal. The larger g ESA shows a smaller advantage over the L-band in signal gain in the long band.

[0062]

[0071] Furthermore, σ in Equation 1 a (λ) is mainly dependent on the following equation:

number

[0072] In Equation 3, h is Planck's constant, ν is the corresponding optical frequency, E0 is the zero-phonon line energy, and k B is the Boltzmann constant and T is the temperature in Kelvin.

[0063]

[0073] The ESA effect of higher energy level particles can occur when the signal light in the long band of the L band enters. Also, the inverted higher energy level particles can be in a metastable energy level. 4 I 13 / 2 The longer it remains in the L-band, the higher the probability of an ESA occurring, resulting in limited gain in the long band of the L-band.

[0064]

[0074] To solve the above-mentioned problems, the present application provides a method for fabricating an L-band erbium-doped fiber with high gain and low noise, thereby realizing a wide spectrum and high gain in the L-band.

[0065]

[0075] In this application, the doping concentration of erbium ions is significantly increased to increase the metastable energy level of EDF. 4 I 13 / 2 This shortens the lifetime of erbium ions in the ion beam, thereby reducing the ESA effect.

[0066]

[0076] The present application will be described in detail by using an example in which a modified chemical vapor deposition (MCVD) method is used to manufacture an EDF capable of realizing a broad spectrum and high gain in the L-band. However, in the present application, the method for manufacturing an EDF capable of realizing a broad spectrum and high gain in the L-band is not limited to the MCVD method.

[0067]

[0077] FIG. 2 illustrates a method for manufacturing an EDF that can achieve a wide spectrum and high gain in the L-band based on an MCVD method, the method including the following steps:

[0078] Step 1: A hollow quartz glass tube is mounted on a coaxial rotating lathe.

[0068]

[0079] Step 2: Silicon tetrachloride (SiCl4), doping gas, and oxygen (O2) are passed through the quartz glass tube, and an oxy-hydrogen torch is moved at a uniform speed along the axial direction of the quartz glass tube to heat the outer surface of the quartz glass tube.

[0069]

[0080] Specifically, SiCl4, doping gas, and O2 passed through the quartz glass tube undergo high-temperature oxidation under the heating conditions of the oxyhydrogen burner to produce particles such as silicon dioxide (SiO2), phosphorus pentoxide (P2O5), silicon oxyfluoride, and boron trioxide (B2O3). Driven by the thermophoresis effect and the gas inside the tube, the particles deposit and adhere to the inner surface of the quartz glass tube.

[0070]

[0081] When the heating temperature is between 1300°C and 1600°C, a white, opaque soot layer is formed on the inner surface of the quartz glass tube, and the formed soot layer has a length of about 150 millimeters (mm) to 400 mm.

[0071]

[0082] Specifically, the soot layer on the inner surface of the quartz glass tube primarily provides a doping environment for the ions that are doped by passing through the liquid and gas phases sequentially.

[0072]

[0083] Step 3: The quartz glass tube on which the soot layer is formed is immersed in the mixed solution 1, and the lathe is kept rotating during the immersion process, so that the doping ions in the mixed solution 1 penetrate into the soot layer by surface adsorption of the soot layer.

[0073]

[0084] Specifically, mixed solution 1 contains erbium ions, Er. 3+ , phosphorus ion P 5+ , and aluminum ions Al 3+ It is produced by dissolving specific ratios of raw materials, including: in a hydrochloric acid or alcohol solution. The process needs to be carried out in an ultra-clean environment.

[0074]

[0085] Specifically, the erbium ions Er in the mixed solution 1 3+ , phosphorus ion P 5+ , and aluminum ions Al 3+ The concentrations of 1, 2, and 3 are 0.12 moles per liter (mol / l), 2.2 mol / l, and 3.1 mol / l, respectively.

[0075]

[0086] Specifically, erbium ions, Er 3+ The raw material may be erbium oxide Er2O3, and phosphorus ions P 5+ The raw material containing P2O5 may be aluminum ions Al 3+ The raw material containing may be aluminum oxide Al2O3.

[0076]

[0087] Specifically, the rotation speed at which the lathe keeps rotating during the immersion process may be 30 r / min.

[0077]

[0088] Erbium ion Er 3+ as well as the concentration of phosphorus ions P 5+ and aluminum ion Al 3+ The concentration of erbium ions is also increased, resulting in a denser aluminum phosphate AlPO4. 3+ In this case, erbium ions, Er, 3+ The coordination environment of the erbium ion Er is shown in Figure 3. 3+ The probability of transition to higher energy levels can be reduced by the erbium ion Er 3+ However, it suppresses the absorption of the long band signal light in the L band. 3+ It is also possible to reduce the degree of clustering.

[0078]

[0089] Optionally, the mixed solution 1 may further comprise at least one of the following elements: thulium Tm, bismuth Bi, fluorine F, cerium Ce, ytterbium Yb, zirconium Zr, neodymium Nd, and lanthanum La.

[0079]

[0090] Step 4: After the quartz glass tube is immersed in the mixed solution 1, the mixed solution 1 is poured out. Then, the quartz glass tube is initially dried with nitrogen (N2).

[0080]

[0091] Specifically, the quartz glass tube may be immersed in the mixed solution 1 for 3 to 6 hours, or the quartz glass tube may be immersed in the mixed solution 1 for 5 hours.

[0081]

[0092] Step 5: Chlorine Cl is passed through the initially dried quartz glass tube, and the quartz glass tube is heated to 600-900°C to further remove residual hydroxide ions in the soot layer, thereby reducing background losses in the EDF.

[0082]

[0093] Specifically, hydroxide ions are prone to vibration absorption due to their large deformability, causing optical signal attenuation in optical fibers.

[0083]

[0094] Step 6: After further drying is complete, the quartz glass tube is heated to 1500 to 1700°C, sintering the quartz glass tube into a transparent, compact quartz glass rod. 5+ A gas containing P 5+ Improve the doping concentration of

[0084]

[0095] Specifically, P 5+ The gas containing may be phosphorus oxychloride POCl3.

[0085]

[0096] Specifically, the doping elements are fixed in the glass network to form a non-porous glass layer.

[0086]

[0097] Step 7: Using the rod-in-tube technique, the sintered fused silica rod is drawn into an optical fiber.

[0087]

[0098] Erbium, phosphorus, and aluminum doped silicate fibers can be obtained using the aforementioned process. The fiber core of the erbium, phosphorus, and aluminum doped silicate fiber contains Er2O3, Al2O3, P2O5, Ge2O3, and silicon dioxide (SiO2). Erbium ions, Er 3+ The mass percentage of phosphorus ions is 0.21%. 5+ The mass percentage of aluminum ions is 15.2%. 3+ The mass percent of germanium ions is 6.1%. 3+ The mass percentage of is 6.1%, the remainder being silicon dioxide SiO2.

[0088]

[0099] For convenience, the optical fiber produced by using the above process will be referred to as optical fiber 1 hereinafter.

[0089]

[0100] The apparatus shown in FIG. 4 is used to test the gain of an optical fiber 1 for an input optical signal.

[0090]

[0101] The apparatus shown in FIG. 4 includes an apparatus for generating seed light, a pump laser for generating pump light, an optical isolator ISO1, an optical isolator ISO2, a wavelength division multiplexer (WDM), an optical fiber 1, an optical spectrum analyzer (OSA), and the like.

[0091]

[0102] Specifically, the seed light generating device generates L-band signal light, and the pump laser generates pump light of 980 nm or 1480 nm. The L-band signal light generated by the seed light generating device passes through optical isolator ISO1, then is combined with the pump light in a WDM and enters gain amplification fiber 1. The amplified L-band signal light passes through optical isolator ISO2 and enters the test OSA.

[0092]

[0103] The setup shown in Figure 4 is used to test the obtained gain of the optical fiber 1 for an input optical signal in the L band. Figure 5 is a close-up view of the gain.

[0093]

[0104] It can be seen from FIG. 5 that by using optical fiber 1, a high gain of 18 dB can be obtained in the long band of the L band.

[0094]

[0105] Furthermore, as shown in Figure 6, a four-stage amplification system is set up based on the apparatus shown in Figure 4. Each stage of the amplification system shown in Figure 6 is connected by a gain flattening filter (GFF), which is used to flatten or smooth the uneven signal strength output by the upper stage amplification system.

[0095]

[0106] For example, as shown in Figure 7, if the strength of the L-band signal passed to the four-stage amplification system shown in Figure 6 is 10 dB, it can be seen that the gain of the L-band signal can be 30 dB to 32 dB, and the gain of fiber 1 for the L-band long band can meet the requirements for long-distance applications.

[0096]

[0107] The present application further provides another method for fabricating an L-band erbium-doped fiber with high gain and low noise, which can realize a broad spectrum and high gain in the L-band.

[0097]

[0108] Optionally, erbium ions Er in mixed solution 1 in step 3 of the manufacturing process of optical fiber 1 3+ , phosphorus ion P 5+ , and aluminum ions Al 3+ The concentrations of are adjusted to 0.21 mol / L, 3.5 mol / L, and 5.2 mol / L, respectively, and the resulting solution may be referred to as mixed solution 2. For other steps, please refer to other steps in the manufacturing process of optical fiber 1. Details will not be described again here. For convenience, the optical fiber manufactured using this process will be referred to as optical fiber 2 hereinafter.

[0098]

[0109] Optionally, the mixed solution 2 may further comprise at least one of the following elements: thulium Tm, bismuth Bi, fluorine F, cerium Ce, ytterbium Yb, zirconium Zr, neodymium Nd, and lanthanum La.

[0099]

[0110] Erbium ions Er in optical fiber 2 3+ , phosphorus ion P 5+ , and aluminum ions Al 3+ It is possible to increase the non-bridging oxygen bonds in the quartz of optical fiber 2 by increasing the concentration of erbium ions Er. 3+ It is possible to tune the doping position and micro-configuration of the metastable state energy levels 4 I 13 / 2 Erbium ions in 3+ In this way, the lifetime of the erbium ion Er for the long band of the L band can be reduced. 3+ The ESA effect is reduced.

[0100]

[0111] The optical fiber 1 in the device shown in Figure 4 is replaced by the optical fiber 2. The device shown in Figure 4 is used to test the resulting gain of the optical fiber 2 for an input optical signal in the L band. Figure 8 is a close-up view of the gain.

[0101]

[0112] It can be seen from Figure 8 that a high gain of 23 dB can be obtained in the long L-band by using optical fiber 2. Optical fiber 2 can obtain a higher gain than optical fiber 1.

[0102]

[0113] According to the steps of the aforementioned embodiment, the mass percentage of the doping element in the fiber core of the optical fiber manufactured in the present application is as follows: the mass percentage of Er2O3 is 0.2 wt% to 1%; the mass percentage of Al2O3 is 0.5 wt% to 20%; The mass percentage of P2O5 is 2 wt% to 30 wt%, the mass percentage of Ge2O3 is 0.01 wt% to 30%; The mass percentage of silicon dioxide SiO2 is greater than 60 wt%.

[0103]

[0114] The erbium ions Er in the above mixed solution 3+ , phosphorus ion P 5+ , and aluminum ions Al 3+ The concentrations of are 0.1 mol / l to 0.3 mol / l, 0.5 mol / l to 4 mol / l, and 1 mol / l to 6 mol / l, respectively.

[0104]

[0115] The fiber diameter of the optical fiber produced in this application may be between 1 μm and 20 μm, and the numerical aperture may be between 0.01 and 1.2.

[0105]

[0116] By using the optical fiber manufactured in this application, an optical fiber amplifier covering the long band of the L band can be obtained, thereby implementing high-capacity optical fiber transmission technology.

[0106]

[0117] FIG. 9 illustrates an amplifier system in which optical fiber manufactured according to the manufacturing method of the present application is used in a long-haul or metropolitan dense wavelength division multiplexing (DWDM) system.

[0107]

[0118] Optical fiber is the core of the amplifier system. The optical fiber manufactured according to the manufacturing method of the present application can realize full-coverage gain amplification in the L-band in the amplifier system shown in Figure 9. Furthermore, the above amplifier system including an optical fiber with long-band gain characteristics in the L-band is an important means for realizing large-capacity optical fiber communication transmission.

[0108]

[0119] Those skilled in the art will recognize that, in conjunction with the examples described in the embodiments disclosed herein, units and algorithm steps may be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether a function is performed by hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered to go beyond the scope of the present application. It should be understood that the disclosed systems, devices, and methods in some embodiments provided in the present application may be realized in other ways. For example, the described device embodiments are merely examples. For example, the unit division is merely a logical functional division, and other divisions may be used in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented. Furthermore, the illustrated or described mutual couplings or direct couplings or communication connections may be realized using some interfaces. The indirect coupling or communication connection between the devices or units may be realized in electronic, mechanical, or other form.

[0109]

[0120] Units described as separate parts may or may not be physically separate, and parts illustrated as units may or may not be physical units, located in one location, or distributed across multiple network units. Some or all of the units may be selected based on actual requirements to achieve the objectives of the solutions of the embodiments. Furthermore, functional units in the embodiments of the present application may be integrated into one processing unit, each unit may exist physically alone, or two or more units may be integrated into one unit. When functions are realized in the form of software functional units and sold or used as independent products, the functions may be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the present application may essentially, or a part that contributes to the current art, or a part of the technical solutions may be embodied in the form of a software product. A computer software product includes some instructions stored in a storage medium for instructing a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or part of the steps of the methods described in the embodiments of the present application. The aforementioned storage medium includes any medium capable of storing program code, such as a USB flash disk, a removable hard disk, a read-only memory, a random access memory, a magnetic disk, or an optical disk.

[0110]

[0121] The above description is merely a specific implementation form of the present application and is not intended to limit the scope of protection of the present application. Any variations or replacements that can be easily devised by those skilled in the art within the technical scope disclosed in the present application shall fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the scope of protection of the claims.

Claims

1. 1. An optical fiber for use in an optical fiber amplifier, the optical fiber being configured to amplify an optical signal; An optical fiber, wherein the fiber core of the optical fiber contains elemental erbium, elemental aluminum, and elemental phosphorus, and aluminum phosphate is formed around the elemental erbium.

2. The optical fiber according to claim 1, the mass percentage of the element erbium is between 0.2% and 1%; the mass percentage of the aluminum element is between 0.5% and 20%; The optical fiber, wherein the mass percentage of elemental phosphorus is between 2% and 30%.

3. The optical fiber according to claim 1 or 2, the mass percentage of the element erbium is between 0.2% and 0.6%, the mass percentage of the aluminum element is between 6% and 11%, The optical fiber, wherein the mass percentage of elemental phosphorus is 15% to 22%.

4. The optical fiber according to any one of claims 1 to 3, the mass percentage of the element erbium is 0.2% to 0.3%; The mass percentage of the aluminum element is 6% to 7%; The optical fiber, wherein the mass percentage of elemental phosphorus is 15% to 16%.

5. The optical fiber according to any one of claims 1 to 3, the mass percentage of the element erbium is 0.5% to 0.6%, the mass percentage of the aluminum element is 10% to 11%; The optical fiber, wherein the mass percentage of elemental phosphorus is 21% to 22%.

6. 6. The optical fiber according to claim 1, wherein the fiber core is composed of the following elements: Germanium Ge, silicon Si, thulium Tm, bismuth Bi, fluorine F, cerium Ce, ytterbium Yb, zirconium Zr, neodymium Nd, and lanthanum La and further comprising at least one of the mass percentage of elemental germanium is between 0.01% and 30%, The mass percentage of silicon element is greater than 60% in the optical fiber.

7. 7. The optical fiber according to claim 1, wherein the fiber diameter of the optical fiber is 1 μm to 20 μm, and the numerical aperture of the optical fiber is 0.01 to 1.

2.

8. 1. A method for manufacturing an optical fiber, comprising: depositing a loose layer on the inner wall of a quartz glass tube; a step of immersing the quartz glass tube on which the loose layer is deposited in a first solution to allow elements in the first solution to permeate into the loose layer, the first solution including erbium, aluminum, and phosphorus; the concentration of erbium element is 0.1 mol / L to 0.3 mol / L; the concentration of elemental aluminum is between 1 mole / liter and 6 moles / liter; the concentration of phosphorus element is 0.5 mol / L to 4 mol / L; Sintering the quartz glass tube immersed in the first solution to dope the elements in the first solution into the quartz glass tube; and drawing the sintered quartz glass tube into an optical fiber; A method comprising:

9. 9. The method of claim 8, the concentration of erbium in the first solution is 0.1 mol / L to 0.3 mol / L; the concentration of elemental aluminum is between 3 moles / liter and 6 moles / liter; The method wherein the concentration of elemental phosphorus is between 2 moles / liter and 4 moles / liter.

10. 10. The method according to claim 8 or 9, the concentration of erbium in the first solution is 0.1 mol / L to 0.2 mol / L; the concentration of aluminum element is 3 moles / liter to 4 moles / liter; The concentration of elemental phosphorus is 2 moles / liter to 3 moles / liter.

11. 10. The method according to claim 8 or 9, the concentration of erbium in the first solution is 0.2 mol / L to 0.3 mol / L; the aluminum concentration is between 5 moles / liter and 6 moles / liter; The method wherein the concentration of elemental phosphorus is 3 moles / liter to 4 moles / liter.

12. 12. The method according to any one of claims 8 to 11, wherein the first solution contains the following elements: Thulium (Tm), Bismuth (Bi), Fluorine (F), Cerium (Ce), Ytterbium (Yb), Zirconium (Zr), Neodymium (Nd), and Lanthanum (La) The method further comprising at least one of:

13. 13. The method according to any one of claims 8 to 12, wherein the optical fiber has a fiber diameter of 1 μm to 20 μm and a numerical aperture of 0.01 to 1.

2.

14. 14. The method according to claim 8, wherein the step of immersing the quartz glass tube on which the loose layer is deposited in a first solution comprises: A method comprising the step of immersing the quartz glass tube on which the loose layer is deposited in a first solution for a period of 3 to 6 hours.

15. 15. The method according to claim 8, wherein the step of sintering the quartz glass tube immersed in the first solution comprises: The method includes sintering the quartz glass tube immersed in the first solution in an oxygen atmosphere, wherein the sintering temperature is between 1400 degrees Celsius and 1900 degrees Celsius.

16. 16. The method of claim 15, wherein the step of sintering the quartz glass tube immersed in the first solution comprises: The method includes a step of sintering the quartz glass tube immersed in the first solution in an atmosphere containing elemental phosphorus.

17. An optical fiber amplifier including an optical fiber for amplifying an optical signal, said optical fiber being the optical fiber according to any one of claims 1 to 7.

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