WO2023138496A1

WO2023138496A1 - Optical fiber, optical amplifier, and optical transmission network

Info

Publication number: WO2023138496A1
Application number: PCT/CN2023/072049
Authority: WO
Inventors: 姜恒云; 吴波; 邓宁
Original assignee: 华为技术有限公司
Priority date: 2022-01-24
Filing date: 2023-01-13
Publication date: 2023-07-27
Also published as: CN116526262A

Abstract

An optical fiber (1203, 500), an optical amplifier (1200), and an optical transmission network, used for expanding a gain spectrum width amplified according to an optical fiber signal, and realizing long-distance wide-spectrum transmission. The optical fiber (500) comprises a first doped layer (510), a second doped layer (520), and a cladding layer (530). The second doped layer (520) is located outside the first doped layer (510), the cladding layer (530) is located outside the second doped layer (520), and the second doped layer (520) and the first doped layer (510) are composed of different materials. The cladding layer (530) is used for reflecting pump light, signal light of a first wave band and signal light of a second wave band by means of an inner wall of the cladding layer (530), the first doped layer (510) is used for amplifying the signal light of the first wave band by means of energy of the pump light, and the second doped layer (520) is used for amplifying the signal light of the second wave band by means of the energy of the pump light.

Description

Optical fiber, optical amplifier and optical transmission network

This application claims the priority of the Chinese patent application filed with the State Intellectual Property Office of China on January 24, 2022, with the application number 202210081639.1 and the application title "An Optical Fiber, Optical Amplifier, and Optical Transmission Network", the entire contents of which are incorporated herein by reference.

technical field

The embodiments of the present application relate to the field of optical communications, and in particular, to an optical fiber, an optical amplifier, and an optical transmission network.

Background technique

Optical communication uses optical fiber as the transmission medium to realize the transmission of optical signals, which 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 that the optical signal passes through, resulting in waveform distortion.

In order to prevent waveform distortion in long-distance optical communication, the optical signal is amplified by an optical amplifier. Optical amplifiers include pump light sources, doped fibers, and wavelength division multiplexers. The pump light emitted by the pump light source excites the doped fiber to amplify the signal light of a specific wavelength band.

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

Contents of the invention

Embodiments of the present application provide an optical fiber, an optical amplifier, and an optical transmission network, which are used to expand the gain spectrum width of optical fiber signal amplification and realize long-distance wide-spectrum transmission.

In a first aspect, the embodiment of the present application provides an optical fiber. The optical fiber includes: a first doped layer, a second doped layer and a cladding. Wherein, the second doped layer is located outside the first doped layer. The first doped layer and the second doped layer consist of different materials. The cladding layer is outside the second doped layer. The inner wall of the cladding is used to reflect 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 to amplify the signal light in the first wavelength band by the energy of the pump light. The second doped layer is used to amplify the signal light of the second wavelength band by the energy of the pump light.

In the embodiment of the present application, two doped layers are arranged in the optical fiber, and the signal light in the corresponding wavelength band of the two doped layers is amplified by pumping light. Compared with the existing single-doped layer amplification, the optical fiber provided by the embodiment of the present application broadens the gain spectrum range of the optical fiber amplification, and the long-distance wide-spectrum transmission of signal light can be realized through the optical fiber.

In an optional implementation manner, 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 first doped layer and the second doped layer from mixing to form a transition layer. Therefore, the transition layer is prevented from absorbing the gain spectrum of the first doped layer and/or the second doped layer, which affects the optical amplification effect of the optical fiber. Optionally, the isolation layer may also be used to change the propagation path of the signal light in the first wavelength band and the second wavelength band.

In an optional implementation manner, the pump light is multimode pump light. The cladding includes an inner cladding and an outer cladding, the outer cladding being located outside the inner cladding. Wherein, 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.

Compared with a single-layer cladding layer, the structure of the inner cladding layer and the outer cladding layer in the embodiment of the present application expands the transmission radius of the pumping light, so that the pumping light can be transmitted in a multi-mode form. Therefore, the transmission power of the pump light is increased, and the amplification effect of the pump light on the signal light of the corresponding wavelength band is further increased.

In an optional implementation manner, the hosts of the first doped layer and the second doped layer are different.

In an optional implementation manner, the doping elements in the first doped layer are different from those in the second doped layer.

In an optional implementation manner, the doping elements in the first doping layer are the same as the doping elements in the second doping layer.

In an optional implementation manner, the doping elements in the first doping layer are the same as the doping elements in the second doping layer. And in the first doped layer and the second doped layer, the doping concentrations of the first doping element and the second doping element are different.

In an optional implementation manner, a set of doped layers is further included between the second doped layer and the cladding layer. The set of doped layers includes n doped layers, where n is an integer greater than or equal to 1. The n doped layers in the set of doped layers are used to amplify the signal light of n wavelength bands by the energy of the pump light. The n wavebands are n different wavebands, and the n wavebands are different from the first waveband and the second waveband.

In the embodiment of the present application, the n doped layers in the doped layer set can further amplify the signal light in n wavelength bands other than the first wavelength band and the second wavelength band, thereby further expanding the wide range of the gain spectrum of the optical fiber.

In a second aspect, the embodiment of the present application provides an optical amplifier. The optical amplifier includes optical fiber and pumping light source. Wherein, the optical fiber is the optical fiber of the first aspect. The pumping light source is used to provide pumping light.

The structure of the optical amplifier provided in the embodiment of the present application does not need to design different optical fiber amplification paths for different wavebands, and directly realizes the amplification of signal light in multiple wavebands through multi-doped optical fibers. The structure of the optical path inside the optical amplifier is simple, so the structure of the optical amplifier is simple, the required components are few, the manufacturing process is simple, and the cost is low.

In an optional implementation manner, the pumping light source includes a first pumping light source and a second pumping light source. Wherein, the first pumping light source is used to provide pumping light with a wavelength corresponding to the first doped layer, and the second pumping light source is used to provide pumping light with a wavelength corresponding to the second doped layer. Wherein, the wavelengths corresponding to the first doped layer and the second doped layer are the same or different.

It should be noted that the pump light corresponding to the wavelength of the doped layer mentioned in the embodiment of the present application refers to the wavelength corresponding to the energy ΔE absorbed by electrons in the doping element when they transition to a high energy level. It should be noted that since ΔE has a certain fluctuation range, the wavelength of the pump light may also have a certain fluctuation range, which is not limited in this application.

In a third aspect, the embodiment of the present application provides an optical transmission network. The optical transmission network includes the optical amplifier described in the second aspect.

In the optical transmission network provided by the embodiment of the present application, the amplification of multi-band signal light can be realized through a multi-doped optical fiber. Therefore, there is no need to distinguish between multiple bands in the networking, and there is no need to provide corresponding devices for multiple bands, and the network structure is simple.

In an optional implementation manner, the optical amplifier is connected to a transmission fiber and/or a wide-spectrum wavelength selective switch (wavelength selective switching, WSS).

Description of drawings

Fig. 1 is the schematic diagram of the wavelength division multiplexing network of the present application;

Fig. 2 is the structural representation of the optical amplifier of the present application;

Fig. 3 is the optical amplification schematic diagram of the optical fiber doped layer of the present application;

Fig. 4 is the structural representation of the multi-band optical amplifier of the present application;

FIG. 5 is a schematic structural diagram of an optical fiber provided in an embodiment of the present application;

Figure 6 is a schematic diagram of the gain spectrum of the optical fiber and different doped layers provided by the embodiment of the present application;

FIG. 7a is a schematic structural diagram of an optical fiber including an isolation layer provided by an embodiment of the present application;

Fig. 7b is a schematic diagram of the optical path of an optical fiber including an isolation layer provided by the embodiment of the present application;

Figure 8a is a schematic diagram of different distributions of multiple doped layers of the optical fiber provided by the embodiment of the present application;

Fig. 8b is a schematic diagram of layering in different dimensions of the three-doped layer optical fiber provided by the embodiment of the present application;

Fig. 8c is a schematic diagram of the layering of the three-doped layer optical fiber provided in the embodiment of the present application in the same dimension;

FIG. 9 is a schematic diagram of an optical path of an optical fiber including multiple claddings provided by an embodiment of the present application;

FIG. 10 is a schematic diagram of the internal optical path of the optical fiber provided by the embodiment of the present application;

Figure 11a is a schematic diagram of the refractive index of different layers of the optical fiber provided by the embodiment of the present application;

Figure 11b is a schematic diagram of the optical path of the signal light in the optical fiber provided by the embodiment of the present application;

Figure 11c is a schematic diagram of the gain spectrum in the optical fiber provided by the embodiment of the present application;

FIG. 12 is a schematic structural diagram of an optical amplifier provided in an embodiment of the present application;

Fig. 13a is a structural schematic diagram of the dotted frame part in the structure shown in Fig. 12;

Fig. 13b is another structural schematic diagram of the dotted frame part in the structure shown in Fig. 12;

FIG. 14 is a schematic structural diagram of an optical transmission network provided by an embodiment of the present application.

Detailed ways

Compared with communication methods such as cable communication and wireless communication, optical communication has the advantages of large communication capacity, small transmission loss, long relay distance, strong anti-interference ability, and reliable working performance. In order to give full play to the advantages of large communication capacity of optical communication, wavelength division multiplexing of optical signals is usually implemented through a wavelength division multiplexing (WDM) network, so as to perform signal transmission.

As shown in Figure 1, a WDM network includes an optical transmitter, an optical relay amplifier, and an optical receiver. Wherein, the optical relay amplifier is also called an optical amplifier. The optical transmitter is used to convert the input optical signal or electrical signal into signal light of a specific wavelength, and combine the signal light of different channels, and send the combined signal light to the optical receiver through the optical fiber.

Due to the influence of optical fiber loss characteristics and dispersion characteristics, after the signal light is output from the optical transmitter and transmitted through the optical fiber for a certain distance, the amplitude attenuation leads to waveform distortion, thus limiting the transmission distance of the signal light. Therefore, after the signal light passes a certain transmission distance, the attenuated signal light is amplified by the optical amplifier. The optical receiver is used to receive the amplified signal light and separate the signal light of a specific wavelength from it.

It should be noted that the WDM network described in the embodiments of the present application may be a dual-fiber unidirectional transmission WDM network or a single-fiber bidirectional transmission WDM network, which is not limited in this application. In addition to WDM networks, the optical fibers and optical amplifiers provided in the embodiments of the present application can also be applied to networks such as single-wavelength transmission networks (networks for single-wavelength signal transmission), which is not limited in this application.

The structure of the optical amplifier in the WDM network shown in FIG. 1 may be shown in FIG. 2 . In the optical amplifier, including doped fiber and pump light source. The pumping light source is used to emit pumping light. Doped fibers are used to amplify signal light of specific wavelengths under the excitation of pump light. In the optical amplifier structure shown in FIG. 2 , an isolator (located in front of the light source and behind the optical fiber), a wavelength division multiplexer (for accessing pump light), a filter, etc. may also be included, which is not limited in this application.

Wherein, the core of the doped optical fiber is doped with elements such as rare earths and metals (such as Er, Bi, Pr, Nd, Yb, Tm, Ho, Dy) with luminous properties. In the embodiments of the present application, these elements with light-emitting properties in the core are called doping elements. As shown in FIG. 3 , the electrons of the doping elements are distributed on multiple energy levels (such as E1 , E2 and E3 ), and the electrons at different energy levels have different stability. The different energy levels include the ground state energy level with low stability, the excited state energy level with high stability, and the metastable state energy level with stability in between. The pumping light provided by the pumping light source can excite the electrons on the ground state energy level (for example E1 energy level) to transition to the excited state energy level (for example E3 energy level). The electrons at the excited state energy level are unstable and will spontaneously transition to the metastable energy level (such as the E2 energy level). The process of electrons jumping from an excited state energy level to a metastable state energy level is also called a non-radiative transition.

Electrons on the metastable energy level (E2 energy level) have higher stability and can stay on this energy level for a period of time. At this time, the number of electrons on the metastable energy level (E2 energy level) is greater than the number of electrons on the ground state energy level (E1 energy level), but this inversion state Can only exist temporarily. Therefore, when the electrons on the metastable energy level (E2 energy level) are excited by the signal light, they will jump to the ground state energy level (E1 energy level) to realize the enhancement (amplification) of the signal light. The transition of electrons from a metastable state to a ground state is also known as a stimulated emission transition.

It should be noted that, in addition to the excited state energy level, the metastable state energy level and the ground state energy level shown in FIG. 3 , the dopant element may also include more energy levels. Under the doped element structure with more energy levels, the transition process of electrons at different energy levels is similar to that shown in Figure 3, and will not be repeated here.

If ΔE represents the energy difference between the excited state energy level and the ground state energy level, h represents Planck's constant, c represents the speed of light, and λ represents the wavelength of light radiated outward during the stimulated radiation transition process. Then according to the law of energy conservation, ΔE=hv=hc/λ. Wherein, λ is the wavelength of the light radiated outward during the stimulated emission transition, and is also the wavelength of the signal light that excites the stimulated emission transition. That is to say, the wavelength of the optical signal that can be amplified by the doped fiber is λ=hc/ΔE.

Since the energy difference between different energy levels has a certain fluctuation range, λ also has a certain fluctuation range. That is to say, the doped fiber realizes the amplification of the signal light with the wavelength in the band around λ=hc/ΔE.

In the embodiment of the present application, the wavelength band 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 energy level and the ground state energy level of the doping element, the gain spectral width of the doped fiber is limited (that is, the wavelength band covered by the doped fiber is limited), thus limiting the wavelength range that can be transmitted in long-distance transmission scenarios.

Currently, the applicable wavelength range in optical fiber transmission is divided into multiple bands as shown in Table 1.

Table 1 The band division of the current optical fiber

When one fiber cannot cover multiple bands, it is necessary to use a variety of doped fibers to amplify different bands respectively. Or, when one fiber cannot cover a longer wavelength band, multiple doped fibers need to be used to amplify multiple wavelength bands in the longer wavelength band respectively.

Figure 4 is a schematic structural diagram of a multi-band optical fiber amplifier. Due to the limitation of the gain bandwidth characteristics of doping elements, a single optical fiber amplifier cannot realize both C-band and L-band optical amplifiers. Therefore, WDM is used to divide the signal light into C-band signal light and L-band signal light. In the optical amplifier, the signal light in the C-band and L-band is respectively amplified through doped fibers of different amplification bands. Then combined into an amplified C+L band signal through WDM.

Optionally, the optical amplifier shown in FIG. 4 may further include doped fibers of more wavelength bands for amplifying signal light of more wavelength bands. For example, the S-band doped fiber shown by the dotted line in FIG. 4 , which is not limited in the present application.

The structure shown in Figure 4 amplifies signal light in different bands through multiple branches, resulting in a complex internal structure of the optical amplifier, complicated cooperative control between different branches, and high manufacturing difficulty and cost. Moreover, since the signal light is filtered by WDM in the optical amplifier, there is a 3-5nm guard band between signal light bands amplified by different doped fibers. The entire optical transmission network also needs to be transmitted in different bands, resulting in a complex network structure.

In order to solve the above-mentioned problems such as limited fiber gain spectrum width, complex internal structure of the optical amplifier, and complex network structure, the embodiments of the present application provide an optical fiber, an optical amplifier, and an optical transmission network. The optical fiber provided by the embodiment of the present application passes through multiple doped The hybrid layer amplifies the signal light of different bands respectively, thereby expanding the gain spectrum width of optical fiber signal amplification, and realizing long-distance wide-spectrum transmission. Thereby simplifying the structure of the optical amplifier and the optical transmission network.

As shown in FIG. 5 , the optical fiber 500 provided by the embodiment of the present application includes: a first doped layer 510 , a second doped layer 520 and a cladding layer 530 . Wherein, the first doped layer 510 and the second doped layer 520 are the core of the optical fiber 500 . And 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 layer 530 is located outside the second doped layer 520 . The inner wall of the cladding layer 530 is used to reflect the pump light and the signal light of the first wavelength band and the signal light of the second wavelength band. The first doped layer 510 is used to amplify the signal light in 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.

In the optical fiber structure shown in FIG. 5, since the first doped layer and the second doped layer are composed of different materials. Therefore, the amplification of the signal light of the first wavelength band corresponding to the first doped layer and the amplification of the signal light of the second wavelength band corresponding to the second doped layer can be realized. Compared with the existing single-layer doped layer optical fiber, the wavelength band range of the amplified signal is expanded, that is, the gain spectrum width is expanded.

It should be noted that, in the optical fiber 500 provided in the embodiment of the present application, the cladding 530 may also include coating layers such as a soft coating, a hard coating, a pre-coating layer, a buffer layer, and a secondary coating layer, which are not limited in this application.

By setting the first doped layer and the second doped layer of different materials in the same optical fiber, the respective gain effects of the first doped layer and the second doped layer can be superimposed. In FIG. 6 , the abscissa is the wavelength of the signal light, and the ordinate g(λ) is the gain of the signal light corresponding to the wavelength. Wherein, the solid line represents the gain function of different doped layers to the signal light, and the dotted line represents the gain function of the optical fiber 500 including the multiple doped layers. Then the gain function g(λ) of each doped layer (such as the first doped layer 501 and the second doped layer 502) in the optical fiber 500 represented by the solid line can be expressed as:

g(λ)=[n ₂ (g*(λ)+a(λ))-a(λ)-Bgl(λ)]dz (Formula 1)

Among them, n ₂ is the doping ion inversion rate of the doped layer, (0≤n2≤1), 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 full inversion. a(λ) is the absorption coefficient of the doped layer, and the specific calculation method is as in Formula 2 and Formula 3. Bgl(λ) is the background loss of the fiber. z is the fiber length.

g*(λ)=σ _s (λ)Γ(λ)N _A (Formula 2)

a(λ)=σ _a (λ)Γ(λ)N _A (Formula 3)

Among them, σ _s (λ) and σ _a (λ) are the emission cross-section function and absorption cross-section function of the doped layer, which are determined by the luminescence characteristics of the doping material itself and have nothing to do with the geometric structure of the fiber. Γ(λ) is the mode field overlap factor of the fiber (0≤Γ(λ)≤1, when the mode field of the signal light and the doped layer are completely coincident, it is 1). N _A is the average doping concentration of doping elements.

Among them, n _t (r) is the dopant ion distribution function of the optical fiber on the cross section, and its maximum value is n _t . i _λ (r) is the mode field distribution function on the cross section of the optical signal with incident wavelength λ.

The solid line in FIG. 6 represents the gain curves of different doped layers for signal light of different wavelengths, that is, the gain function g _A (λ) of the doped layer A and the gain function g _B (λ) of the doped layer B. The dotted line in Fig. 6 represents the gain function G(λ) of the optical fiber comprising the plurality of doped layers. For the multi-doped fiber 500 provided in the embodiment of the present application, the gain function G(λ) can be written as:

G(λ)＝g _A (λ)+g _B (λ)+… (Formula 5)

It should be noted that in FIG. 6 , the doped layer A may be the first doped layer 510 , and the doped layer B may be the second doped layer 520 . The reverse is also possible, and this application does not limit it.

In (a) of FIG. 6 , the gains of the bands between the peaks of the gain spectra of the two doped layers are superimposed on each other, which directly broadens the gain spectrum of the entire optical fiber. The signal light between and near the two peaks can be amplified by optical fiber.

In (b) of FIG. 6, there is no overlapping portion between the gain spectra of the two doped layers. However, the gain spectrum of the entire fiber includes the respective gain spectrum characteristics of the two doped layers,

In (c) of FIG. 6 , the doped layer B absorbs energy in a negative gain band and amplifies signal light in a gain band. The gain band of the doped layer A covers the negative gain band of the doped layer B, and the doped layer B can absorb the gain of the doped layer A on the negative gain band of the doped layer B. The gain spectrum of the finally obtained optical fiber is relatively flat near the negative gain band of the doped layer B, and signal light in a band near the negative gain band of the doped layer B can be amplified through the optical fiber.

In (d) of FIG. 6 , the gain spectra of the two doped layers have different shapes, and mutual superposition can increase the flatness of the gain spectrum of the entire optical fiber.

It should be noted that, in the embodiment of the present application, the structures of the first doped layer and the second doped layer are only examples of the optical fiber structure with multiple doped layers. The optical fiber may also include more doped layers, which are respectively used to amplify signal light of different wavelength bands. For example, between the second doped layer and the cladding layer, a set of doped layers may also be included. The set of doped layers includes n doped layers, where n is an integer greater than or equal to 1. The n doped layers in the set of doped layers are used to amplify the signal light of n wavelength bands by the energy of the pump light. The n wavebands are n different wavebands, and the n wavebands are different from the first waveband and the second waveband.

For the convenience of description, the structure of the optical fiber provided by the embodiment of the present application is described below with a structure of two doped layers, which does not limit the number of doped layers.

In the embodiment of the present application, the materials of the first doped layer 510 and the second doped layer 520 are different, which may specifically be manifested as differences in host, doping element, and doping concentration.

On the one hand, the matrix of different doped layers can be made different. For example, taking erbium as an example of a doping element, the first doped layer 510 and the second doped layer 520 may both be erbium-doped layers. Wherein, the matrix of the first doped layer 510 may include elements such as aluminum and germanium, and the gain spectrum of the first doped layer 510 is a first band g _a (λ) with a peak at 1530 nm. The matrix of the second doped layer 520 may include components such as phosphorus and aluminum elements. Due to the effect of phosphorus, the center of the luminous energy level of the second doped layer 520 is shifted to the long wavelength by about 5 nm, so the gain spectrum of the second doped layer 520 is the second band g _b (λ) with a peak at ˉ1535 nm. Then the gain spectrum of the optical fiber 500 corresponds to the situation (a) in FIG. 6 . Due to the superposition of the first band g _a (λ) and the second band g _b (λ), broadening of the gain spectrum of the optical fiber 500 can be achieved.

On the other hand, the doping concentrations in different doped layers may be different, that is, the concentrations of doping elements in different layers may be different. The difference in doping concentration leads to the difference in the inversion rate _n of the doping elements in different layers, which affects the shape of the gain function of different layers, that is, the shape of g _a (λ) and g _b (λ), and then can adjust the bandwidth and flatness of the gain function G(λ) of the entire fiber, as shown in (d) in Figure 6.

In an optional implementation manner, the doping concentration of the first doping layer in the optical fiber is high, and the doping concentration of the second doping layer is low. Since the signal mode field distribution in the optical fiber is such that the mode field intensity of the central part of the fiber core (i.e. the first doped layer region) is high, the concentration of doping ions in the first doped layer is high, that is, the total number of doping ions is high, which can increase the saturated output optical power of the fiber region and reduce the value of saturation gain compression. In the region of the second doped layer where the mode field intensity is relatively low, a lower doping concentration can ensure a higher ion inversion rate in this region and reduce the noise factor performance of the optical amplifier. In summary, making the doping concentration of the first doping layer higher than that of the second doping layer (the doping concentration of the inner layer is higher than that of the outer layer), can increase the saturated output optical power of the entire fiber, and can improve the low noise figure performance of the fiber amplifier.

On the other hand, the doping elements of different doped layers can be made different. Since the gain spectrum characteristic of doped fiber is mainly determined by the energy level structure of the doping element itself, the change of matrix can only slightly change its gain spectrum characteristic. for further expansion The gain spectrum bandwidth of a single fiber can be doped with different doping elements in different layers of the fiber, and the doping elements are used to correspond to the optimal luminous matrix.

For example, the doping element in the first doped layer 510 can be erbium, then the gain spectrum of the first doped layer 510 mainly covers the C band; the doping 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. Then, the gain spectrum of the optical fiber 500 is shown in (b) or (c) in FIG. 6 , which is the superposition of the C-band as the first band and the S-band as the second band.

Alternatively, the doping element in the first doped layer 510 is erbium; the doping element in the second doped layer 520 is bismuth, and the second doped layer 520 uses a Ge matrix. Then 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. Then, the gain spectrum of the optical fiber 500 is shown in (c) of FIG. 6 , which is the superposition of the C-band as the first band and the L-band and U-band as the second band.

It should be noted that the embodiments of the present application use the C-band, S-band, L-band, and U-band as examples to illustrate the amplification bands of different doped layers in the optical fiber, which does not impose constraints on the amplification bands of the optical fibers provided in the embodiments of the present application. For example, different doped layers in the optical fiber can also amplify signal light in O-band, U-band and other bands, or can also amplify signal light in some bands in C-band and L-band, which is not limited in this application.

It should be noted that the above-mentioned differences in the materials of the different doped layers may exist independently or in combination. For example, the first doped layer 510 and the second doped layer 520 may have different hosts, the same doping element, and the same doping concentration; or, the first doped layer 510 and the second doped layer 520 may have different hosts, different doping elements, and different doping concentrations, etc., which are not limited in this application.

During the preparation process of the optical fiber 500 shown in FIG. 5 , thermal beam expansion occurs at the junction of the first doped layer 510 and the second doped layer 520 due to heat (that is, dopant elements in different layers diffuse into adjacent layers to form a transition layer with a new element composition), thereby forming a transition layer between the first doped layer 510 and the second doped layer 520. Since the transition layer has elements in both the first doped layer 510 and the second doped layer 520 , the gain characteristics and refractive index values of the transition layer are different from those of the first doped layer 510 and the second doped layer 520 . The gain characteristics of the transition layer may seriously change the gain characteristics and mode field distribution of the entire optical fiber 500, thereby affecting the optical amplifier effect (gain spectrum width, gain intensity, etc.) of the entire optical fiber 500.

In order to prevent the transition layer between the first doped layer 510 and the second doped layer 520 from affecting the optical radiation effect of the entire optical fiber 500, an isolation layer 540 can be provided between the first doped layer 510 and the second doped layer 520, the specific structure is shown in FIG. 7a. In the structure shown in FIG. 7 a , the isolation layer 540 is used to isolate the first doped layer 510 and the second doped layer 520 to prevent a transition layer between the first doped layer 510 and the second doped layer 520 . Wherein, the isolation layer 520 may also be called a protection layer, which is not limited in this application.

In an optional application, different bismuth-doped fibers have different centers of gain functions in different matrices (for example: Al-SiO ₂ , P ₂ O ₅ -SiO ₂ ). The central wavelength of the gain function of the transition layer formed between two adjacent bismuth-doped layers with different substrates is different from that of the two bismuth-doped layers. The transition layer may cause absorption to the two bismuth-doped layers, thereby affecting the optical radiation effect of the entire optical fiber. Inserted into the structure of the optical fiber 500 shown in FIG. 7a of the present application, the two bismuth-doped layers are separated by the isolation layer 540 (that is, the first doped layer 510 and the second doped layer 520 are bismuth-doped layers with different matrices). Then there is no transition layer, and the gain function of the entire optical fiber 500 is the superposition of the gain functions g _A (λ) and g _B (λ) of the two bismuth-doped layers (as shown in formula 5), and the existence of the transition layer will not cause absorption of g _A (λ) and g _B (λ), which ensures the optical output effect of the corresponding wavebands of g _A (λ) and g _B (λ).

The transition layer may also change the transmission path of the signal light between the first doped layer 510 and the second doped layer 520 , thereby affecting the amplification effect of the first doped layer and/or the second doped layer on the corresponding wavelength band of the signal. Therefore, disposing the isolation layer 540 between the first doped layer 510 and the second doped layer 520 can prevent the influence of the transition layer on the amplification effect. signal light is shown in Figure 7a The optical path in the optical fiber structure is shown in FIG. 7 b . By properly setting the refractive index of the isolation layer 540 (protective layer), it is possible to ensure that the signal light is transmitted on the predetermined transmission path.

It should be noted that when the optical fiber includes more than two doped layers, every two adjacent doped layers can be separated by an isolation layer, which is not limited in this application.

As shown in Fig. 8a, in the embodiment of the present application, the distribution of different doped layers can also be a structure such as upper and lower layers or front and rear layers in addition to the structure of internal and external layers, which is not limited in this application. Similar to the inner and outer layered structure, in the optical fiber structure in which doped layers are layered up and down or front and back, the number of doped layers is not limited. Each doped layer may also be isolated by an isolation layer, which is not limited in this application.

Optionally, in the front-rear layered fiber structures shown in Figs. 8a to 8c, if the connection loss between different doped fibers is very low, two adjacent doped fibers of different wavelength bands can be connected by fusion splicing or the like.

Optionally, if the optical fiber includes three or more doped layers, different layered structures can be combined to obtain an optical fiber in which the doped layers are layered in multiple dimensions. For example, as shown in FIG. 8 b , the whole composed of the first doped layer and the second doped layer and the third doped layer have a layered structure before and after; and the structure between the first doped layer and the second doped layer is layered up and down. Alternatively, a structure of three or more doped layers can also be obtained by layering in one dimension. Taking three layers as an example, the specific layered structure is shown in Figure 8c. Wherein, the materials of the first doped layer and the third doped layer may be the same or different, which is not limited in this application.

In the optical fiber structures shown in FIG. 5 to FIG. 8c, one doping layer may include one or more doping elements, which is not limited in the present application.

In the fiber structures shown in Figures 5-8c, the cladding 530 may comprise multiple layers. As shown in FIG. 9 , the cladding 530 includes an inner cladding 531 and an outer cladding 532 . The inner wall of the inner cladding layer 531 is used to reflect signal light, and the inner wall of the outer cladding layer 532 is used to reflect pump light.

The specific optical path is shown in Figure 10. In a multi-clad fiber, the signal light is totally reflected on the inner wall of the inner cladding (without considering the rationality of leakage), so the signal light is transmitted in the core (multiple doped layers). The pump light is totally reflected on the inner wall of the outer cladding (in the rational case of not considering the leakage), so the pump light is transmitted in the inner cladding and the core. The optical fiber structure enables the pumping light to be transmitted in the form of multi-mode in the optical fiber, so the multi-mode pumping light source can be used in the optical fiber amplifier including the optical fiber structure. Compared with commonly used single-mode pump light sources, multi-mode pump light sources are cheaper and have higher output power. Therefore, the output optical power of the optical fiber amplifier is improved, and the price of the optical fiber amplifier is reduced.

Optionally, the cross section of the inner cladding can be shaped as a rectangle, a regular polygon, or an ellipse, so as to increase the intensity of the pump light transmitted in the inner cladding, improve the conversion efficiency of the pump light signal intensity to the signal light intensity, and improve the optical amplifier effect.

Also shown in Figure 10 is the optical path in a single-clad fiber. In a single-clad fiber, both pump and signal light are reflected by the inner walls of the cladding and are therefore transmitted in the core. In this structure, the transmission range of the pump light is consistent with the transmission range of the signal light, so the overlap between the pump light and the signal light is high, so that the energy conversion rate in the process of energy transfer from the pump light to the signal light is high, which can reduce energy consumption.

It should be noted that, in order to ensure that both the signal light and the pump light can be reflected by the inner wall of the cladding, the refractive index of the fiber core should be greater than the refractive index of the outermost doped layer. In FIG. 11a, two doped layers are taken as an example, 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 layer. The refractive index difference Δ2 between the second doped layer and the cladding layer needs to be large enough to ensure that both the signal light and the pump light can have a total reflection effect at their junction.

In order to ensure that the incident light can be transmitted in all the doped layers, the difference Δ1 of the refractive index between the doped layers should not be too large, so as to ensure that the incident light can be refracted at the interface of different doped layers, so that part of the light is refracted into the second doped layer, and part of the light is reflected back to the first doped layer. The specific optical path is shown in Figure 11b. By adjusting the refractive index difference Δ1 between the doped layers, it is possible to control the transmission path of the signal light incident on the fiber between the first doped layer and the second doped layer and the transmission of the signal light in different layers. The intensity of transmission, that is, the mode field distribution i _λ (r) of the multi-doped fiber on the cross section. As an example, FIG. 11c is a schematic diagram of a mode field distribution i _λ (r) of a dual-doped fiber with stepped refractive index distribution, and the darker the color in the figure, the greater the intensity of the signal light. Combining the above formulas 1 to 4, 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, 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 gain function of the fiber can be adjusted, thereby controlling the shape of the gain function of the fiber.

In the design of multi-doped fiber, it is also necessary to comprehensively consider the connection loss of multi-doped fiber and conventional single-mode fiber, that is, the matching degree of mode field diameter, the effective transmission area of the fiber, the transmission loss of the fiber, the cut-off wavelength and other factors in the design of geometric parameters of conventional fiber. Integrating the above factors and the requirements of the gain function of the fiber, optimize the design of the radii (R1, R2, R3) of different layers in the fiber and the refractive index difference (Δ1, Δ2) between different layers.

The optical fiber structure provided by the embodiment of the present application is described above, and the optical amplifier structure including the optical fiber is described next. Using the optical fiber 500 shown in FIGS. 5 to 9 as the doped optical fiber in the optical amplifier structure shown in FIG. 2 is an optical amplifier structure provided by the embodiment of the present application.

Optionally, if the wavelengths of pump light 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 for providing the wavelengths of pump light corresponding to the first doped layer 510 and the second doped layer 520 respectively.

As shown in FIG. 12 , the optical amplifier 1200 provided by the embodiment of the present application includes a first pumping light source 1201 , a second pumping light source 1202 and an optical fiber 1203 . Wherein, the optical fiber 1203 is the optical fiber 500 described in FIG. 5 to FIG. 9 . The first pumping light source 1201 is used to provide pumping light of a corresponding wavelength to the first doped layer, and the second pumping light source 1202 is used to provide pumping light of a corresponding wavelength to the second doped layer. Wherein, the wavelengths corresponding to the first doped layer and the second doped layer are the same or different. Optionally, the optical amplifier 1200 may also include a multi-port wavelength division multiplexer 1204, which is used to multiplex the signal light (wavelength λs), the pump light (wavelength λ1) corresponding to the wavelength of the first doped layer emitted by the first pump light source 1201, and the pump light (wavelength λ2) corresponding to the wavelength of the second doped layer emitted by the second pump light source 1202 and input them into the optical fiber 1203.

Optionally, the wavelengths (namely λ1 and λ2) of the pump light emitted by the first pump light source 1201 and the second pump light source 1202 may be the same or different, which is not limited in this application.

It should be noted that the pump light corresponding to the doped layer described in the embodiment of the present application refers to the wavelength corresponding to ΔE described in the embodiment of FIG. 3 . That is, the energy difference between the excited state energy level and the stable state energy level of the doping element in the doped layer. It should be noted that since ΔE has a certain fluctuation range, the wavelength of the pump light may also have a certain fluctuation range, which is not limited in this application.

Optionally, the multiplex structure of the signal light λs, the pump light λ1 and the pump light λ2 in FIG. 12 (that is, the structure in the dashed box in FIG. 12 ) can also be as shown in FIG. 13a or FIG. 13b , which is not limited in the present application. It should be noted that the structure of the optical amplifier provided in the embodiment of the present application, in addition to the forward pumping structure shown in Figure 12 to Figure 13b, may also be a backward pumping or bidirectional pumping structure, which is not limited in the present application.

The structure of the optical fiber and optical amplifier provided by the embodiment of the present application has been described above, and the structure of the optical transmission network provided by the embodiment of the present application based on the above optical fiber and optical amplifier will be described below.

Since the C-band and the L-band are currently the most commonly used bands in networking, the improvement of the network architecture in the embodiment of the present application is described by taking the C-band and the L-band as examples. Since the signal light of the current C-band and L-band cannot be amplified in the same amplifying fiber Therefore, it is necessary to divide the signal light of C-band and L-band into different amplifying fibers through filters. In addition, the filter needs to retain a 3-5nm guard band when filtering the C-band and L-band, thus causing the signal light to be transmitted in bands on the C-plane and L-plane. In Fig. 14, triangles represent optical amplifiers. As shown in Figure 14, in addition to optical amplifiers that need to perform optical amplification on the C-band and L-band sub-bands, the current network also needs to perform operations such as regulating the C-band and L-band sub-bands, resulting in a complex network structure.

However, in the optical transmission network provided in the embodiments of the present application, including the multi-doped optical fibers shown in the embodiments in FIGS. 5 to 9 , full-band amplification of the C-band and L-band can be realized. Therefore, there is no need to distinguish the C-band and the L-band in the networking, and there is no need to provide corresponding devices for the C-band and the L-band respectively, and the network structure is simple.

Since the optical transmission network provided by the embodiment of the present application can transmit broadband signal light (such as C-band+L-band), in the transmission network provided by the embodiment of the present application, the optical amplifier can be connected to the transmission fiber and/or the broadband wavelength selective switch to realize the transmission of the broadband signal light.

It should be noted that Fig. 14 uses C-band and L-band as examples for illustration. The optical transmission network provided in the embodiment of the present application may also be used to transmit optical signals of other bands, such as S-band+C-band+U-band, etc., which is not limited in the present application.

Those skilled in the art can clearly understand that for the convenience and brevity of the description, the specific working process of the above-described system, device and unit can refer to the corresponding process in the foregoing method embodiment, which will not be repeated here.

In the several embodiments provided in this application, it should be understood that the disclosed system, device and method can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. 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 implemented. In another point, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

Claims

An optical fiber, characterized in that it comprises a first doped layer, a second doped layer and a cladding, the second doped layer is located outside the first doped layer, the cladding is located outside the second doped layer, and the second doped layer and the first doped layer are composed of different materials;

The inner wall of the cladding is used to reflect 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 to amplify the signal light in the first wavelength band by the energy of the pump light;

The second doped layer is used to amplify the signal light in the second wavelength band by the energy of the pump light.
The optical fiber according to claim 1, further comprising:

An isolation layer between the first doped layer and the second doped layer.
The optical fiber according to claim 1 or 2, wherein the pumping light is multimode pumping light;

The cladding includes: an inner cladding and an outer cladding;

The inner wall of the outer cladding is used to reflect the multimode pump light;

The inner wall of the inner cladding is used to reflect the signal light.
The optical fiber according to any one of claims 1 to 3, characterized in that the hosts of the first doped layer and the second doped layer are different.
The optical fiber according to any one of claims 1 to 4, characterized in that the doping element in the first doped layer is different from the doping element in the second doped layer.
The optical fiber according to any one of claims 1 to 4, characterized in that the doping element in the first doped layer is the same as the doping element in the second doped layer.
The optical fiber according to claim 6, wherein the doping concentrations of the doping elements are different in the first doped layer and the second doped layer.
The optical fiber according to any one of claims 1 to 7, characterized in that, between the second doped layer and the cladding layer, a set of doped layers is further included, the set of doped layers includes n doped layers, and n is an integer greater than or equal to 1;

The n doped layers in the set of doped layers are used to amplify the signal light of n wavebands through the energy of the pump light, and the n wavebands are n different wavebands, and the n wavebands are different from the first waveband and the second waveband.
An optical amplifier, characterized in that it comprises:

An optical fiber, the optical fiber being the optical fiber according to any one of claims 1 to 8;

A pumping light source is used to provide the pumping light.
The optical amplifier according to claim 9, wherein the pumping light source comprises:

a first pumping light source, configured to provide pumping light of a wavelength corresponding to the first doped layer;

a second pumping light source, configured to provide pumping light of a wavelength corresponding to the second doped layer;

Wherein, the wavelengths corresponding to the first doped layer and the second doped layer are the same or different.
An optical transmission network, characterized by comprising the optical amplifier according to claim 9 or 10.
The optical transmission network according to claim 11, characterized in that, the optical amplifier is connected to a transmission fiber and/or a wide-spectrum wavelength selective switch (WSS).