An optical fiber, optical amplifier and optical transmission network

Abstract

This application discloses an optical fiber, an optical amplifier, and an optical transmission network for expanding the gain spectral width of optical fiber signal amplification and achieving long-distance broadband transmission. The optical fiber provided in this application includes: a first doped layer, a second doped layer, and a cladding. The second doped layer is located outside the first doped layer, and the cladding is located outside the second doped layer. The second and first doped layers are composed of different materials. The cladding is used to reflect pump light, as well as first-band and second-band signal light, through its inner wall. The first doped layer is used to amplify the first-band signal light using the energy of the pump light. The second doped layer is used to amplify the second-band signal light using the energy of the pump light.

Description

Technical Field

[0001] This application relates to the field of optical communication, and more particularly to an optical fiber, an optical amplifier, and an optical transmission network. Background Technology

[0002] Optical communication uses optical fiber as the transmission medium to transmit optical signals, and it is a commonly used communication method. However, in long-distance optical transmission, the amplitude of the optical signal is attenuated due to the long optical fiber it travels through, resulting in waveform distortion.

[0003] To prevent waveform distortion in long-distance optical communication, optical signals are amplified using optical amplifiers. An optical amplifier includes a pump source, doped optical fiber, and a wavelength division multiplexer. Pump light emitted from the pump source excites the doped optical fiber to amplify signal light in a specific wavelength band.

[0004] However, optical amplifiers can only amplify signal light in a specific band corresponding to the doped fiber, and cannot amplify signal light outside the band range, which limits the wavelength range that can be transmitted in long-distance transmission scenarios. Summary of the Invention

[0005] This application provides an optical fiber, an optical amplifier, and an optical transmission network to expand the gain spectral width of optical fiber signal amplification and achieve long-distance broadband transmission.

[0006] In a first aspect, embodiments of this application provide an optical fiber. The optical fiber includes a first doped layer, a second doped layer, and a cladding. The second doped layer is located outside the first doped layer. The first and second doped layers are composed of different materials. The cladding is located outside the second doped layer. The inner wall of the cladding is used to reflect pump light, as well as signal light of a first and second wavelength band. The first doped layer is used to amplify the signal light of the first wavelength band using the energy of the pump light. The second doped layer is used to amplify the signal light of the second wavelength band using the energy of the pump light.

[0007] In this embodiment, two doped layers are disposed in the optical fiber, and pump light is used to amplify the signal light in the corresponding wavelength bands of the two doped layers. Compared with existing single-doped-layer amplification, the optical fiber provided in this embodiment broadens the gain spectrum range of optical fiber amplification, enabling long-distance broadband transmission of signal light.

[0008] In one alternative implementation, an isolation layer is further included between the first doped layer and the second doped layer. The isolation layer can be used to prevent the formation of a transition layer due to mixing between the first and second doped layers. This prevents the transition layer from absorbing the gain spectrum of the first and / or second doped layers, thus affecting the optical amplification effect of the fiber. Optionally, the isolation layer can also be used to change the propagation path of the signal light in the first and second wavebands.

[0009] In one alternative implementation, the pump light is a multimode pump light. The cladding includes an inner cladding and an outer cladding, with the outer cladding located outside the inner cladding. The inner wall of the outer cladding is used to reflect the multimode pump light, and the inner wall of the inner cladding is used to reflect the signal light.

[0010] Compared to a single-layer cladding, the inner and outer cladding structures of this embodiment expand the transmission radius of the pump light, enabling it to transmit in multimode. This increases the transmission power of the pump light, thereby enhancing its amplification effect on the signal light in the corresponding wavelength band.

[0011] In one alternative implementation, the substrates of the first doped layer and the second doped layer are different.

[0012] In one alternative implementation, the dopant elements in the first doped layer and the dopant elements in the second doped layer are different.

[0013] In one alternative implementation, the doping elements in the first doped layer and the doping elements in the second doped layer are the same.

[0014] In one alternative implementation, the dopant elements in the first doped layer and the second doped layer are the same. Furthermore, the doping concentrations of the first and second doped elements differ between the first and second doped layers.

[0015] In one alternative implementation, a set of doped layers is further included between the second doped layer and the cladding layer. This set of doped layers includes n doped layers, where n is an integer greater than or equal to 1. These n doped layers are used to amplify signal light across n wavelength bands using the energy of the pump light. These n wavelength bands are n distinct bands, and are different from both the first and second wavelength bands.

[0016] In the embodiments of this application, the n doped layers in the doped layer set can further amplify the signal light in n bands other than the first and second bands, thereby further expanding the gain spectral width range of the optical fiber.

[0017] Secondly, embodiments of this application provide an optical amplifier. The optical amplifier includes an optical fiber and a pump light source. The optical fiber is the same as that described in the first aspect. The pump light source is used to provide pump light.

[0018] The optical amplifier structure provided in this application does not require designing different optical fiber amplification paths for different wavelength bands; it directly amplifies multi-band signal light through multi-doped optical fibers. The internal optical path structure of the optical amplifier is simple, resulting in a simple structure, fewer required components, and simple and low-cost manufacturing processes.

[0019] In one optional implementation, the pump light source includes a first pump light source and a second pump light source. The first pump light source provides pump light at a wavelength corresponding to the first doped layer, and the second pump light source provides pump light at a wavelength corresponding to the second doped layer. The wavelengths corresponding to the first and second doped layers may be the same or different.

[0020] It should be noted that the pump light corresponding to the wavelength of the doped layer described in the embodiments of this application refers to the wavelength corresponding to the energy ΔE absorbed by the electron in the dopant element when it transitions to a higher energy level. It should also be noted that since ΔE has a certain fluctuation range, the wavelength of the pump light can also have a certain fluctuation range, which is not limited in this application.

[0021] Thirdly, embodiments of this application provide an optical transmission network. This optical transmission network includes the optical amplifier described in the second aspect.

[0022] In the optical transmission network provided in this application embodiment, multi-band signal light amplification can be achieved through multi-doped optical fibers. Therefore, it is not necessary to distinguish between multiple bands in the network configuration, nor is it necessary to provide corresponding devices for each band, resulting in a simple network structure.

[0023] In one alternative implementation, the optical amplifier is connected to a transmission fiber and / or a broadband wavelength selective switching (WSS). Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the wavelength division multiplexing network of this application;

[0025] Figure 2 This is a schematic diagram of the structure of the optical amplifier in this application;

[0026] Figure 3 This is a schematic diagram of the optical amplification principle of the optical fiber doped layer in this application;

[0027] Figure 4 This is a schematic diagram of the structure of the multi-band optical amplifier of this application;

[0028] Figure 5 This is a schematic diagram of the structure of the optical fiber provided in the embodiments of this application;

[0029] Figure 6 This is a schematic diagram of the gain spectrum of an optical fiber with different doped layers provided in the embodiments of this application;

[0030] Figure 7a This is a schematic diagram of the structure of an optical fiber including an isolation layer, provided in an embodiment of this application.

[0031] Figure 7bA schematic diagram of the optical path of an optical fiber including an isolation layer is provided for an embodiment of this application;

[0032] Figure 8a A schematic diagram illustrating the different distributions of multiple doped layers in an optical fiber provided in an embodiment of this application;

[0033] Figure 8b A schematic diagram illustrating the layering of a three-doped fiber in different dimensions, as provided in an embodiment of this application;

[0034] Figure 8c A schematic diagram showing the three-doped fiber layered in the same dimension as provided in the embodiments of this application;

[0035] Figure 9 A schematic diagram of the optical path of an optical fiber including multiple cladding layers is provided for embodiments of this application;

[0036] Figure 10 This is a schematic diagram of the internal optical path of the optical fiber provided in the embodiments of this application;

[0037] Figure 11a A schematic diagram of the refractive index of different layers of an optical fiber provided in an embodiment of this application;

[0038] Figure 11b This is a schematic diagram of the optical path of the signal light in the optical fiber provided in the embodiments of this application;

[0039] Figure 11c This is a schematic diagram of the gain spectrum in an optical fiber provided in an embodiment of this application;

[0040] Figure 12 This is a schematic diagram of the structure of an optical amplifier provided in an embodiment of this application;

[0041] Figure 13a for Figure 12 A schematic diagram of one structure of the dashed box portion shown;

[0042] Figure 13b for Figure 12 Another structural diagram of the dashed box portion shown;

[0043] Figure 14 This is a schematic diagram of the structure of an optical transmission network provided in an embodiment of this application. Detailed Implementation

[0044] Compared to cable communication and wireless communication, optical communication has advantages such as large communication capacity, low transmission loss, long relay distance, strong anti-interference ability, and reliable operation. To fully utilize the advantage of large communication capacity in optical communication, wavelength division multiplexing (WDM) networks are typically used to perform wavelength division multiplexing of optical signals for signal transmission.

[0045] like Figure 1 As shown, a WDM network includes an optical transmitter, an optical repeater amplifier, and an optical receiver. The optical repeater amplifier is also called an optical amplifier. The optical transmitter converts the input optical or electrical signal into a signal light of a specific wavelength, combines signal light from different paths, and transmits the combined signal light to the optical receiver via optical fiber.

[0046] Due to the loss and dispersion characteristics of optical fibers, the signal light attenuates in amplitude after traveling a certain distance from the optical transmitter through the fiber, causing waveform distortion and thus limiting the transmission distance. Therefore, after the signal light has traveled a certain distance, it is amplified by an optical amplifier. An optical receiver is used to receive the amplified signal light and separate the signal light of a specific wavelength.

[0047] It should be noted that the WDM network described in the embodiments of this application can be a dual-fiber unidirectional transmission WDM network or a single-fiber bidirectional transmission WDM network, and this application does not limit it in this regard. In addition to WDM networks, the optical fiber and optical amplifier provided in the embodiments of this application can also be applied to networks such as single-wavelength transmission networks (networks for single-wavelength signal transmission), and this application does not limit them in this regard.

[0048] Figure 1 The structure of the optical amplifier in the WDM network shown can be as follows: Figure 2 As shown. An optical amplifier includes a doped fiber and a pump source. The pump source emits pump light. The doped fiber amplifies a signal light of a specific wavelength under the excitation of the pump light. Figure 2 The optical amplifier structure shown may also include an isolator (located before the light source and after the optical fiber), a wavelength division multiplexer (for accessing the pump light), a filter, etc., but this application does not limit this.

[0049] In this type of optical fiber, the core is doped with rare earth elements, metals, and other elements with luminescent properties (such as Er, Bi, Pr, Nd, Yb, Tm, Ho, and Dy). In the embodiments of this application, these luminescent elements in the core are referred to as dopant elements. Figure 3 As shown, electrons in a doped element are distributed across multiple energy levels (e.g., E1, E2, and E3), with varying stability at different levels. These energy levels include the less stable ground state, the more stable excited state, and metastable levels with stability between the two. Pump light from a pump source can excite electrons at the ground state (e.g., E1) to transition to an excited state (e.g., E3). Electrons at the excited state are unstable and will spontaneously transition to a metastable level (e.g., E2). This transition from an excited state to a metastable state is also known as a nonradiative transition.

[0050] Electrons in the metastable energy level (E2 level) are highly stable and can remain at this level for a period of time. At this point, the number of electrons in the metastable energy level (E2 level) is greater than the number of electrons in the ground state energy level (E1 level), but this inversion state is only temporary. Therefore, when an electron in the metastable energy level (E2 level) is excited by signal light, it will transition to the ground state energy level (E1 level), thus amplifying the signal light. The process of an electron transitioning from a metastable state to the ground state is also called stimulated emission transition.

[0051] It should be noted that, in addition to Figure 3 The diagram shows excited state, metastable state, and ground state energy levels; doped elements can include even more energy levels. In doped element structures with more energy levels, the electron transition processes at different energy levels are... Figure 3 The process shown is similar and will not be repeated here.

[0052] If ΔE represents the energy difference between the excited state and the ground state, h represents Planck's constant, c represents the speed of light, and λ represents the wavelength of the light emitted during stimulated emission, then according to the law of conservation of energy, ΔE = hv = hc / λ. Here, λ is the wavelength of the light emitted during stimulated emission, and also the wavelength of the signal light that induced the stimulated emission. In other words, the wavelength of the optical signal that can be amplified by a doped optical fiber is λ = hc / ΔE.

[0053] Since the energy difference between different energy levels has a certain fluctuation range, λ also has a certain fluctuation range. In other words, doped optical fibers amplify signal light with wavelengths in the band near λ = hc / ΔE.

[0054] In this embodiment, the wavelength range of the signal light that can be amplified in the doped fiber is called the gain spectral width. Limited by the energy level difference ΔE between the excited state and ground state of the dopant element, the gain spectral width of the doped fiber is finite (i.e., the wavelength range covered by the doped fiber is limited), thus restricting the range of wavelengths that can be transmitted in long-distance transmission scenarios.

[0055] Currently, the wavelength range that can be used in optical fiber transmission is divided into multiple bands as shown in Table 1.

[0056] Table 1 Current optical fiber band division

[0057] band describe wavelength range 0 band Original band 1260-1360nm E-band Extended bands 1360-1460nm S-band shortwave band 1460-1530nm C-band Conventional band 1530-1565nm L-band Long wavelength band 1565-1625nm U-band Ultralong wavelength band 1625-1675nm

[0058] When one type of optical fiber cannot cover multiple wavelength bands, multiple doped optical fibers are needed to amplify different wavelength bands separately. Alternatively, when one type of optical fiber cannot cover a long wavelength band, multiple doped optical fibers are needed to amplify multiple wavelength bands within that long wavelength band separately.

[0059] Figure 4 This is a schematic diagram of a multi-band fiber optic amplifier. Due to the limitations of the gain-bandwidth characteristics of the doping elements themselves, a single fiber optic amplifier cannot achieve both C-band and L-band optical amplification. Therefore, WDM is used to split the signal light into C-band and L-band signal light. In the optical amplifier, the C-band and L-band signal light are amplified separately through doped fibers of different amplification bands. Then, WDM is used to combine them into an amplified C+L band signal.

[0060] Optionally, Figure 4 The optical amplifier shown can also include doped optical fibers with more wavelengths to amplify signal light across even more wavelengths. For example... Figure 4 The S-band doped fiber shown by the dashed line is not limited in this application.

[0061] Figure 4 The structure shown amplifies signal light in different wavelength bands through multiple branches, resulting in a complex internal structure of the optical amplifier, complex coordination and control between different branches, and high manufacturing difficulty and cost. Furthermore, because the optical amplifier uses WDM to filter the signal light, a 3-5nm guard band exists between the amplified signal light bands of different doped fibers. The entire optical transmission network also needs to transmit in different wavelength bands, leading to a complex network structure.

[0062] To address the aforementioned issues of limited gain bandwidth in optical fibers, complex internal structures of optical amplifiers, and complex network structures, this application provides an optical fiber, an optical amplifier, and an optical transmission network. The optical fiber provided in this application amplifies signal light in different wavelength bands through multiple doped layers, thereby expanding the gain bandwidth of the amplified optical fiber signal and achieving long-distance broadband transmission. This simplifies the structure of the optical amplifier and the optical transmission network.

[0063] like Figure 5 As shown, the optical fiber 500 provided in this embodiment includes: a first doped layer 510, a second doped layer 520, and a cladding 530. The first doped layer 510 and the second doped layer 520 form the core of the optical fiber 500. The second doped layer 520 and the first doped layer 510 are composed of different materials. The second doped layer 520 is located outside the first doped layer 510. The cladding 530 is located outside the second doped layer 520. The inner wall of the cladding 530 is used to reflect pump light and signal light of the first and second wavelength bands. The first doped layer 510 is used to amplify the signal light of the first wavelength band by the energy of the pump light. The second doped layer 520 is used to amplify the signal light of the second wavelength band by the energy of the pump light.

[0064] exist Figure 5In the fiber structure shown, because the first and second doped layers are composed of different materials, it is possible to amplify the signal light in the first band corresponding to the first doped layer and the signal light in the second band corresponding to the second doped layer. Compared to existing single-layer doped fibers, this expands the bandwidth of the amplified signal, i.e., it increases the gain spectral width.

[0065] It should be noted that, in the optical fiber 500 provided in the embodiments of this application, in addition to the cladding 530, there may also be coating layers such as soft coating layer, hard coating layer, pre-coating layer, buffer layer, and secondary coating layer, and this application does not limit this.

[0066] By placing a first doped layer and a second doped layer made of different materials in the same optical fiber, the gain effects of the first doped layer and the second doped layer can be superimposed. Figure 6 In the diagram, the horizontal axis represents the wavelength of the signal light, and the vertical axis g(λ) represents the gain of the signal light at the corresponding wavelength. The solid line represents the gain function of different doping layers on the signal light, and the dashed line represents the gain function of the optical fiber 500 containing these multiple doping layers. Therefore, the gain function g(λ) of each doping layer (e.g., the first doping layer 501 and the second doping layer 502) in the optical fiber 500, represented by the solid line, can be expressed as:

[0067] g(λ)=[n2(g*(λ)+a(λ))-a(λ)-Bgl(λ)]dz (Formula 1)

[0068] Where n2 is the dopant ion inversion rate of the doped layer (0≤n2≤1), and n2 is determined by the pump light, signal light power, and the total number of dopant ions. g*(λ) is the gain coefficient of the doped layer under total inversion. a(λ) is the absorption coefficient of the doped layer, calculated using formulas 2 and 3. Bgl(λ) is the background loss of the optical fiber. z is the length of the optical fiber.

[0069] g*(λ)=σs(λ)Γ(λ)N A (Formula 2)

[0070] a(λ)=σ a (λ)Γ(λ)N A (Formula 3)

[0071] Where, σ s (λ), σ a Γ(λ) represents the emission and absorption cross-section functions of the doped layer, determined by the luminescence properties of the doped material itself and independent of the fiber's geometry. Γ(λ) is the mode field overlap factor of the fiber (0 ≤ Γ(λ) ≤ 1, 1 when the signal light mode field completely overlaps with the doped layer). A The average doping concentration of the doped element.

[0072]

[0073] Where, n t (r) is the doped ion distribution function on the cross-section of the optical fiber, and its maximum value is n. t i λ (r) is the mode field distribution function of the incident light signal with wavelength λ on the cross section.

[0074] Figure 6 The solid line in the graph represents the gain curves of different doped layers for signal light of different wavelengths, that is, the gain function g of doped layer A. A (λ), the gain function g of the doped layer B B (λ). Figure 6 The dashed line in the figure represents the gain function G(λ) of the optical fiber containing the multiple doped layers. For the multi-doped optical fiber 500 provided in this embodiment, the gain function G(λ) can be written as:

[0075] G(λ)=g A (λ)+g B (λ)+… (Formula 5)

[0076] It should be noted that, in Figure 6 The intermediate doped layer A can be the first doped layer 510, and the doped layer B can be the second doped layer 520. Conversely, they can also be different, and this application does not limit them in this regard.

[0077] exist Figure 6 In (a), the gains of the bands between the peaks of the gain spectra of the two doped layers superimpose, directly broadening the gain spectrum of the entire optical fiber. Signal light between and near the two peaks can be amplified using optical fiber.

[0078] exist Figure 6 In (b), there is no overlap between the gain spectra of the two doped layers. However, the gain spectrum of the entire optical fiber includes the gain spectrum characteristics of both doped layers.

[0079] exist Figure 6 In (c), doped layer B absorbs energy in the negative gain band and amplifies the signal light in the gain band. The gain band of doped layer A covers the negative gain band of doped layer B, and doped layer B can absorb the gain of doped layer A in the negative gain band of doped layer B. The resulting fiber's gain spectrum is relatively flat near the negative gain band of doped layer B, allowing for amplification of signal light in the band near the negative gain band of doped layer B.

[0080] exist Figure 6 In (d), the gain spectra of the two doped layers have different shapes, and their superposition can increase the flatness of the gain spectrum of the entire optical fiber.

[0081] It should be noted that the structures of the first and second doped layers in this embodiment are merely examples of multi-doped fiber structures. The fiber may also include more doped layers, each used to amplify signal light in different wavelength bands. For example, a set of doped layers may be included between the second doped layer and the cladding. This set of doped layers includes n doped layers, where n is an integer greater than or equal to 1. These n doped layers amplify signal light in n wavelength bands using the energy of the pump light. These n wavelength bands are n distinct wavelength bands, and these n wavelength bands are different from both the first and second wavelength bands.

[0082] For ease of description, the optical fiber structure provided in the embodiments of this application will still be described below with a structure of two doped layers, which does not limit the number of doped layers.

[0083] In the embodiments of this application, the materials of the first doped layer 510 and the second doped layer 520 are different, specifically in terms of different matrix, doping elements and doping concentration.

[0084] On the one hand, different doping layers can have different matrices. For example, using erbium as the doping element, the first doped layer 510 and the second doped layer 520 can both be erbium-doped layers. The matrix of the first doped layer 510 can include components such as aluminum and germanium, and the gain spectrum of the first doped layer 510 is a first-band g with a peak at 1530 nm. a (λ). The matrix of the second doped layer 520 may include components such as phosphorus and aluminum. Due to the effect of phosphorus, the center of the luminescent energy level of the second doped layer 520 is shifted to a longer wavelength by about 5 nm. Therefore, the gain spectrum of the second doped layer 520 is a second-band g with a peak at ~1535 nm. b (λ). Then the gain spectrum of fiber 500 corresponds to... Figure 6 Case (a) in the text. Due to the first band g a (λ) and the second band g b The superposition of (λ) can broaden the gain spectrum of fiber 500.

[0085] On the other hand, the doping concentration can be different in different doped layers, meaning the concentration of doped elements can vary between different layers. This difference in doping concentration leads to different inversion rates (n²) of the doped elements in different layers, thus affecting the shape of the gain function (g) of each layer. a (λ), g b The shape of (λ) can be used to adjust the bandwidth and flatness of the entire fiber's gain function G(λ), such as... Figure 6 As shown in (d) in the figure.

[0086] In one alternative implementation, the first doped layer in the optical fiber has a high doping concentration, while the second doped layer has a low doping concentration. Since the signal mode field distribution in the optical fiber is characterized by high mode field intensity in the core center (i.e., the first doped layer region), a high concentration of dopant ions in the first doped layer (i.e., a high total number of dopant ions) can increase the saturated output optical power in this region and reduce the saturation gain compression. Conversely, in the second doped layer region, where the mode field intensity is lower, a lower doping concentration ensures a higher ion inversion rate, reducing the noise figure performance of the optical amplifier. In summary, making the first doped layer have a higher doping concentration than the second doped layer (with the inner layer having a higher doping concentration than the outer layer) can increase the overall saturated output optical power of the optical fiber and improve the low noise figure performance of the fiber amplifier.

[0087] On the other hand, different doping elements can be used in different doping layers. Since the gain spectrum characteristics of doped optical fibers are mainly determined by the energy level structure of the doping elements themselves, changes in the matrix can only slightly alter its gain spectrum characteristics. To further extend the gain spectrum bandwidth of a single optical fiber, different doping elements can be incorporated into different layers of the fiber, using a matrix that corresponds to the optimal emission of the doping elements.

[0088] For example, if the dopant element in the first doped layer 510 is erbium, then the gain spectrum of the first doped layer 510 mainly covers the C-band; if the dopant element in the second doped layer 520 is bismuth, and a low-Ge matrix can be used, then the gain spectrum of the second doped layer 520 mainly covers the S-band. The gain spectrum of optical fiber 500 is then as follows: Figure 6 As shown in (b) or (c), it is the superposition of the C band as the first band and the S band as the second band.

[0089] Alternatively, the dopant element in the first doped layer 510 is erbium; the dopant element in the second doped layer 520 is bismuth, and the second doped layer 520 uses a Ge matrix. In this case, the gain spectrum of the first doped layer 510 mainly covers the C-band, and the gain spectrum of the second doped layer 520 mainly covers the L-band and U-band. The gain spectrum of fiber 500 would then be as follows: Figure 6 As shown in (c), this is the superposition of the C band as the first band and the L band and U band as the second band.

[0090] It should be noted that the embodiments of this application use C-band, S-band, L-band, and U-band as examples to illustrate the amplification bands of different doped layers in optical fibers, and do not impose any constraints on the amplification bands of the optical fibers provided in the embodiments of this application. For example, different doped layers in optical fibers can also amplify signal light in bands such as O-band and U-band, or they can also amplify signal light in some bands of C-band and L-band, etc., and this application does not limit this.

[0091] It should be noted that the differences in the materials of the different doped layers described above can exist independently or in combination. For example, the first doped layer 510 and the second doped layer 520 can have different matrices, the same doping elements, and the same doping concentration; or, the first doped layer 510 and the second doped layer 520 can have different matrices, different doping elements, and different doping concentrations, etc., which are not limited in this application.

[0092] exist Figure 5 During the fabrication of the optical fiber 500 shown, thermal expansion occurs at the interface between the first doped layer 510 and the second doped layer 520 due to heating (i.e., doping elements from different layers diffuse into adjacent layers, forming a transition layer with a new elemental composition), thus forming a transition layer between the first doped layer 510 and the second doped layer 520. Because this transition layer contains elements from both the first doped layer 510 and the second doped layer 520, its gain characteristics and refractive index differ from both the first doped layer 510 and the second doped layer 520. The gain characteristics of this transition layer can significantly alter the overall gain characteristics and mode field distribution of the optical fiber 500, thereby affecting the overall optical amplification performance (gain bandwidth, gain intensity, etc.) of the optical fiber 500.

[0093] To prevent the transition layer between the first doped layer 510 and the second doped layer 520 from affecting the overall optical amplification performance of the optical fiber 500, an isolation layer 540 can be provided between the first doped layer 510 and the second doped layer 520, as shown in the specific structure. Figure 7a As shown. In Figure 7a In the structure shown, the isolation layer 540 is used to isolate the first doped layer 510 and the second doped layer 520 to prevent the formation of a transition layer between the first doped layer 510 and the second doped layer 520. The isolation layer 520 can also be referred to as a protective layer, and this application does not limit it to that term.

[0094] In one alternative application, different bismuth-doped fibers have different gain function centers in different matrices (e.g., Al-SiO2, P2O5-SiO2). The transition layer formed between two adjacent bismuth-doped layers in different matrices has a gain function center wavelength different from that of both bismuth-doped layers. This transition layer may cause absorption by the two bismuth-doped layers, thus affecting the overall optical amplification performance of the fiber. (Adapted into this application) Figure 7a The optical fiber 500 shown has two bismuth-doped layers (i.e., the first doped layer 510 and the second doped layer 520 are bismuth-doped layers with different matrices) isolated by an isolation layer 540. Therefore, there is no transition layer, and the gain function of the entire optical fiber 500 is the gain function g of the two bismuth-doped layers. A (λ) and g B The superposition of (λ) (as shown in Equation 5) will not cause any impact on g due to the presence of the transition layer. A(λ) and g B ((λ absorption ensures g) A (λ) and g B (λ) corresponds to the optical amplification effect of the band.

[0095] The transition layer may also alter the transmission path of signal light between the first doped layer 510 and the second doped layer 520, thereby affecting the amplification effect of the first and / or second doped layers on the corresponding waveband of the signal. Therefore, providing an isolation layer 540 between the first doped layer 510 and the second doped layer 520 can prevent the transition layer from affecting the amplification effect. Figure 7a The optical path in the fiber optic structure shown is as follows Figure 7b As shown, by properly setting the refractive index of the isolation layer 540 (protective layer), it can be ensured that the signal light is transmitted along the predetermined transmission path.

[0096] It should be noted that when an optical fiber contains more than two doped layers, each pair of adjacent doped layers can be isolated by an isolation layer, and this application does not limit this.

[0097] like Figure 8a As shown in the embodiments of this application, the distribution of different doped layers can be in the form of inner and outer layering, or in a top-bottom layering or front-and-back layering structure, etc., and this application does not limit this. Similar to the inner and outer layering structure, in the fiber structure with top-bottom or front-and-back layering of doped layers, the number of doped layers is not limited. Each doped layer can also be isolated by an isolation layer, and this application does not limit this.

[0098] Optionally, in Figures 8a to 8c In the layered fiber structure shown, if the connection loss between different doped fibers is very low, adjacent doped fibers of different wavelengths can be connected by means of fusion splicing or other methods.

[0099] Optionally, if the optical fiber includes three or more doped layers, different layered structures can be combined to obtain an optical fiber with doped layers layered in multiple dimensions. For example, Figure 8b As shown, the first and second doped layers together form a layered structure with the third doped layer in between; furthermore, the first and second doped layers are layered vertically. Alternatively, a structure with three or more doped layers can be obtained by layering in one dimension. Taking three layers as an example, the specific layered structure is as follows: Figure 8c As shown. The materials of the first doped layer and the third doped layer can be the same or different; this application does not impose any limitations on this.

[0100] exist Figures 5 to 8c In the optical fiber structure shown, a doped layer may include one or more doping elements, which is not limited in this application.

[0101] exist Figures 5 to 8c In the fiber optic structure shown, the cladding 530 may include multiple layers. For example... Figure 9 As shown, the cladding 530 includes an inner cladding 531 and an outer cladding 532. The inner wall of the inner cladding 531 is used to reflect signal light, and the inner wall of the outer cladding 532 is used to reflect pump light.

[0102] The specific optical path is as follows: Figure 10 As shown, in multi-clad optical fibers, the signal light undergoes total internal reflection at the inner wall of the inner cladding (ignoring leakage), thus propagating in the core (multiple doped layers). The pump light undergoes total internal reflection at the inner wall of the outer cladding (ignoring leakage), thus propagating in both the inner cladding and the core. This fiber structure allows the pump light to propagate in multimode within the fiber, enabling the use of multimode pump sources in fiber amplifiers incorporating this structure. Compared to commonly used single-mode pump sources, multimode pump sources are cheaper and have higher output power. This results in increased output optical power and reduced price of the fiber amplifier.

[0103] Optionally, the cross-section of the inner cladding can be rectangular, regular polygonal, elliptical, or other shapes, thereby increasing the intensity of pump light transmission within the inner cladding, improving the efficiency of pump light signal intensity conversion to signal light intensity, and enhancing the optical amplification effect.

[0104] Figure 10 The paper also illustrates the optical path in a single-clad fiber. In a single-clad fiber, both the pump light and the signal light are reflected by the inner wall of the cladding, and therefore both propagate within the fiber core. In this structure, the transmission range of the pump light coincides with that of the signal light, resulting in a high degree of overlap between the two. This leads to a high energy conversion rate during the energy transfer from the pump light to the signal light, thus reducing energy consumption.

[0105] It should be noted that, in order to ensure that both signal light and pump light can be reflected by the inner cladding wall, the refractive index of the fiber core should be greater than that of the outermost doped layer. Figure 11a In this example, taking two doped layers, R1 is the radius of the first doped layer, R2 is the radius of the second doped layer, and R3 is the radius of the cladding. The refractive index difference Δ2 between the second doped layer and the cladding needs to be sufficiently large to ensure that both the signal light and the pump light undergo total internal reflection at their interface.

[0106] To ensure that incident light can propagate through all doped layers, the refractive index difference Δ1 between the doped layers cannot be too large. This ensures that the incident light is refracted at the interface between different doped layers, so that part of the light is refracted into the second doped layer and part is reflected back to the first doped layer. The specific optical path is as follows: Figure 11bAs shown. By adjusting the refractive index difference Δ1 between the doped layers, the path of the signal light incident on the fiber between the first and second doped layers, as well as the intensity of the signal light propagating in different layers, can be controlled, i.e., the mode field distribution i on the cross-section of the multi-doped fiber. λ (r). For example, Figure 11c A mode field distribution i for a double-doped fiber with a stepped refractive index distribution λ (r) Schematic diagram, where darker colors indicate greater signal light intensity. Combining Equations 1 to 4 above, it can be seen that by adjusting the radius R1 of the first doped layer, the radius R2 of the second doped layer, the radius R3 of the cladding layer, the refractive index Δ1 of the first doped layer, and the refractive index Δ2 of the second doped layer in the optical fiber, the overlap factor Γ(λ) in the optical fiber gain function can be adjusted, thereby controlling the shape of the optical fiber gain function.

[0107] In the design of multi-doped optical fibers, it is also necessary to comprehensively consider the connection loss between the multi-doped fiber and conventional single-mode fiber, i.e., the mode field diameter matching degree, as well as the geometric parameters of conventional optical fibers such as the effective transmission area, transmission loss, and cutoff wavelength. Taking into account the above factors and the gain function requirements of the fiber, the radii (R1, R2, R3) of different layers and the refractive index differences (Δ1, Δ2) between different layers in the fiber are optimized.

[0108] The fiber optic structure provided in the embodiments of this application has been described above. Next, the optical amplifier structure including this fiber optic cable will be described. Figures 5 to 9 The fiber optic cable 500 shown is used as Figure 2 The doped fiber in the optical amplifier structure shown is an optical amplifier structure provided in the embodiments of this application.

[0109] Optionally, if the pump light wavelengths corresponding to the first doped layer 510 and the second doped layer 520 in the optical fiber 500 are different, the optical amplifier may include two pump light sources, which are used to provide the pump light wavelengths corresponding to the first doped layer 510 and the second doped layer 520, respectively.

[0110] like Figure 12 As shown, the optical amplifier 1200 provided in this embodiment includes a first pump light source 1201, a second pump light source 1202, and an optical fiber 1203. The optical fiber 1203 is... Figures 5 to 9The optical fiber 500 includes a first pump light source 1201 providing pump light at a wavelength corresponding to the first doped layer, and a second pump light source 1202 providing pump light at a wavelength corresponding to the second doped layer. The wavelengths corresponding to the first and second doped layers may be the same or different. Optionally, the optical amplifier 1200 may further include a multi-port wavelength division multiplexer 1204 for combining the signal light (wavelength λs), the pump light at a wavelength corresponding to the first doped layer emitted by the first pump light source 1201 (wavelength λ1), and the pump light at a wavelength corresponding to the second doped layer emitted by the second pump light source 1202 (wavelength λ2) and inputting them into the optical fiber 1203.

[0111] Optionally, the wavelengths (i.e., λ1 and λ2) of the pump light emitted by the first pump light source 1201 and the second pump light source 1202 can be the same or different, and this application does not limit this.

[0112] The optical amplifier structure provided in this application does not require designing different optical fiber amplification paths for different wavelength bands; it directly amplifies multi-band signal light through multi-doped optical fibers. The internal optical path structure of the optical amplifier is simple, resulting in a simple structure, fewer required components, and simple and low-cost manufacturing processes.

[0113] It should be noted that the pump light corresponding to the doped layer described in the embodiments of this application refers to... Figure 3 The wavelength corresponding to ΔE mentioned in the embodiments is the energy difference between the excited state energy level and the stable state energy level of the dopant element in the doped layer. It should be noted that since ΔE has a certain fluctuation range, the wavelength of the pump light can also have a certain fluctuation range, which is not limited in this application.

[0114] Optionally, Figure 12 The combined wave structure of the signal light λs, pump light λ1, and pump light λ2 (i.e. Figure 12 The structure within the dashed box can also be as follows: Figure 13a or Figure 13b As shown, this application does not limit the scope of the invention. It should be noted that the structure of the optical amplifier provided in the embodiments of this application, in addition to the following... Figures 12 to 13b The forward pumping structure shown can also be a backward pumping or bidirectional pumping structure, and this application does not limit it.

[0115] The structure of the optical fiber and optical amplifier provided in the embodiments of this application has been described above. The structure of the optical transmission network provided in the embodiments of this application based on the above-described optical fiber and optical amplifier is described below.

[0116] Since C-band and L-band are currently the most commonly used bands in network deployment, this application's embodiments are used as examples to illustrate the improvements to the network architecture. Because C-band and L-band signals cannot be amplified in the same amplifying fiber, filters are needed to separate the C-band and L-band signals into different amplifying fibers. Furthermore, the filters need to retain a 3-5nm guard band when filtering C-band and L-band signals, resulting in segmented transmission of the signal light in the C-plane and L-plane. Figure 14 In the diagram, the triangle represents an optical amplifier. For example... Figure 14 As shown, in addition to the optical amplifier needing to perform optical amplification for C-band and L-band bands separately, the current network also requires corresponding operations such as adjustment of C-band and L-band bands, resulting in a complex network structure.

[0117] In the optical transmission network provided in this application embodiment, including Figures 5 to 9 The multi-doped fiber shown in the embodiment can achieve full-band amplification in both C-band and L-band. Therefore, it is not necessary to distinguish between C-band and L-band in the network, nor is it necessary to provide corresponding devices for C-band and L-band separately, resulting in a simple network structure.

[0118] Since the optical transmission network provided in this application embodiment can transmit broadband signal light (e.g., C-band + L-band), the optical amplifier in the optical transmission network provided in this application embodiment can be connected to the transmission optical fiber and / or broadband wavelength selection switch to realize the transmission of broadband signal light.

[0119] It is worth noting that, Figure 14 The C-band and L-band are used as examples for illustration. The optical transmission network provided in this application can also be used to transmit optical signals in other bands, such as S-band + C-band + U-band, etc., and this application does not limit it in this way.

[0120] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0121] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0122] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0123] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

Claims

1. An optical fiber, characterized by, The optical fiber comprises a first doped layer, a second doped layer and a cladding layer, the second doped layer is located outside the first doped layer, the cladding layer is located outside the second doped layer, the second doped layer and the first doped layer are composed of different materials, and the first doped layer and the second doped layer are cores of the optical fiber. An inner wall of the cladding layer is used for reflecting the pump light and the signal light of the first waveband and the signal light of the second waveband. The first doped layer is used for amplifying the signal light of the first waveband by the energy of the pump light. The second doped layer is used for amplifying the signal light of the second waveband by the energy of the pump light.

2. The optical fiber of claim 1, wherein, Further comprising: An isolation layer located between the first doped layer and the second doped layer.

3. The optical fiber according to claim 1 or 2, characterized in that, The pump light is multimode pump light. The cladding layer comprises an inner cladding layer and an outer cladding layer. An inner wall of the outer cladding layer is used for reflecting the multimode pump light. An inner wall of the inner cladding layer is used for reflecting the signal light.

4. The optical fiber according to any one of claims 1 to 2, characterized in that, The matrix of the first doped layer and the second doped layer is different.

5. The optical fiber of any of claims 1-2, wherein, The doping elements in the first doped layer and the doping elements in the second doped layer are different.

6. The optical fiber of any of claims 1-2, wherein, The doping elements in the first doped layer and the doping elements in the second doped layer are the same.

7. The optical fiber of claim 6, wherein, In the first doped layer and the second doped layer, the doping concentrations of the doping elements are different.

8. The optical fiber of any of claims 1-2, wherein, Further comprising a doped layer set between the second doped layer and the cladding layer, the doped layer set comprising n doped layers, n being an integer greater than or equal to 1; The n doped layers in the doped layer set are used for amplifying n wavebands of signal light by the energy of the pump light, the n wavebands being n different wavebands, and the n wavebands being different from the first waveband and the second waveband.

9. The optical fiber of any of claims 1-2, wherein, The distribution of the first doped layer and the second doped layer in the optical fiber comprises at least one of the following: an inner-outer layered structure, an up-down layered structure, and a front-back layered structure.

10. The optical fiber of any of claims 1-2, wherein, The optical fiber further comprises a third doped layer; The whole of the first doped layer and the second doped layer is in a front-back layered structure with the third doped layer, and the first doped layer and the second doped layer are in an up-down layered structure.

11. An optical amplifier, characterized by comprising: The optical fiber comprises: The optical fiber is the optical fiber according to any one of claims 1 to 10; The pump light source is used for providing the pump light.

12. The optical amplifier of claim 11, wherein, The pump light source comprises: A first pump light source is used for providing pump light of a wavelength corresponding to the first doped layer; A second pump light source is used for providing pump light of a wavelength corresponding to the second doped layer; The wavelengths corresponding to the first doped layer and the second doped layer are the same or different.

13. An optical transport network, characterized by, The optical amplifier comprises the optical amplifier according to claim 11 or 12.

14. An optical transport network as recited in claim 13, wherein, The optical amplifier is connected with a transmission optical fiber and / or a wide-spectrum wavelength selective switch (WSS). The optical amplifier is connected with a transmission optical fiber and / or a wide-spectrum wavelength selective switch (WSS).

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