CN116526262A

CN116526262A - Optical fiber, optical amplifier and optical transmission network

Info

Publication number: CN116526262A
Application number: CN202210081639.1A
Authority: CN
Inventors: 姜恒云; 吴波; 邓宁
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2022-01-24
Filing date: 2022-01-24
Publication date: 2023-08-01
Also published as: WO2023138496A1

Abstract

The embodiment of the application discloses an optical fiber, an optical amplifier and an optical transmission network, which are used for expanding the gain spectrum width of optical fiber signal amplification and realizing long-distance broad spectrum transmission. The optical fiber provided by the embodiment of the application comprises: the first doping layer, the second doping layer and the cladding layer, the second doping layer is located outside the first doping layer, the cladding layer is located outside the second doping layer, and the second doping layer and the first doping layer are composed of different materials. The cladding layer is used for reflecting the pump light, the signal light of the first wave band and the signal light of the second wave band through the inner wall of the cladding layer. The first doped layer is used for amplifying the signal light of the first wave band through the energy of the pump light. The second doped layer is used for amplifying the signal light of the second wave band through the energy of the pump light.

Description

Optical fiber, optical amplifier and optical transmission network

Technical Field

Embodiments of the present disclosure relate to the field of optical communications, and in particular, to an optical fiber, an optical amplifier, and an optical transmission network.

Background

Optical communication uses optical fibers as transmission media to realize transmission of optical signals, and is a common communication method. However, in long-distance optical transmission, the amplitude of the optical signal is attenuated due to the length of the optical fiber through which the optical signal passes, resulting in waveform distortion.

To prevent waveform distortion in long-distance optical communication, an optical signal is amplified by an optical amplifier. The optical amplifier comprises a pumping light source, a doped optical fiber, a wavelength division multiplexer and the like. The doped optical fiber is excited to amplify the signal light with a specific wave band by the pumping light emitted by the pumping light source.

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

Disclosure of Invention

The embodiment of the application provides an optical fiber, an optical amplifier and an optical transmission network, which are used for expanding the gain spectrum width of optical fiber signal amplification and realizing long-distance broad spectrum transmission.

In a first aspect, embodiments of the present application provide an optical fiber. The optical fiber includes: the first doped layer, the second doped layer and the cladding layer. Wherein the second doped layer is located outside the first doped layer. The first doped layer and the second doped layer are composed of different materials. The cladding layer is located outside the second doped layer. The inner wall of the cladding is used for reflecting the pump light, the signal light of the first wave band and the signal light of the second wave band. The first doped layer is used for amplifying the signal light of the first wave band through the energy of the pump light. The second doped layer is used for amplifying the signal light of the second wave band through the energy of the pump light.

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

In an alternative implementation, an isolation layer is further included between the first doped layer and the second doped layer. The isolation layer may be used to prevent the first doped layer from intermixing with the second doped layer to form a transition layer. Thereby preventing the transition layer from absorbing the gain spectrum of the first doped layer and/or the second doped layer and affecting the optical amplification effect of the optical fiber. Alternatively, the isolation layer may also be used to change the propagation paths of the signal light of the first and second wavelength bands.

In an alternative implementation, 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. The inner wall of the outer cladding layer is used for reflecting multimode pump light, and the inner wall of the inner cladding layer is used for reflecting signal light.

Compared with a single-layer cladding layer, the inner cladding layer and the outer cladding layer structure of the embodiment of the application enlarge the transmission radius of the pump light, so that the pump light can be transmitted in a multimode mode. Thereby increasing the transmission power of the pump light and further increasing the amplification effect of the pump light on the signal light of the corresponding wave band.

In an alternative implementation, the matrices of the first doped layer and the second doped layer are different.

In an alternative implementation, the doping element in the first doped layer and the doping element in the second doped layer are different.

In an alternative implementation, the doping element in the first doped layer is the same as the doping element in the second doped layer.

In an alternative implementation, the doping element in the first doped layer is the same as the doping element in the second doped 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 alternative implementation, between the second doped layer and the cladding layer, a set of doped layers is also included. The doped layer set comprises n doped layers, wherein n is an integer greater than or equal to 1. The n doped layers in the doped layer set are used for amplifying signal light of n wave bands through the energy of the pump light. The n wave bands are n different wave bands, and the n wave bands are different from the first wave band and the second wave band.

In the embodiment of the application, the n doped layers in the doped layer set can further amplify the signal light of n wave bands outside the first wave band and the second wave band, so that the gain spectrum wide range of the optical fiber is further enlarged.

In a second aspect, embodiments of the present application provide an optical amplifier. The optical amplifier includes an optical fiber and a pump light source. Wherein the optical fiber is the optical fiber of the first aspect. The pump light source is used for providing pump light.

According to the structure of the optical amplifier, different optical fiber amplifying light paths do not need to be designed for different wavebands, and the multi-band signal light is directly amplified through the optical fibers of the multi-doped layers. The optical path structure inside the optical amplifier is simple, so the optical amplifier has simple structure, few required devices, simple production and manufacturing process and low cost.

In an alternative implementation, the pump light source comprises a first pump light source and a second pump light source. The first pump light source is used for providing pump light with the wavelength corresponding to the first doped layer, and the second pump light source is used for providing pump light with the 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 with a wavelength corresponding to the doped layer in the embodiments of the present application refers to a wavelength corresponding to energy Δe absorbed by electrons in the doped element through 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, embodiments of the present application provide an optical transmission network. The optical transmission network comprises an optical amplifier according to the second aspect.

In the optical transmission network provided by the embodiment of the application, the multi-band signal light can be amplified through the multi-doped layer optical fiber. Therefore, a plurality of wave bands do not need to be distinguished in networking, corresponding devices are not needed to be matched with the wave bands, and the network structure is simple.

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

Drawings

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

FIG. 2 is a schematic diagram of an optical amplifier of the present application;

FIG. 3 is an optical magnification schematic of the doped layer of the optical fiber of the present application;

fig. 4 is a schematic structural diagram of a multiband optical amplifier according to the present application;

FIG. 5 is a schematic structural diagram of an optical fiber according to an embodiment of the present disclosure;

FIG. 6 is a schematic gain spectrum of an optical fiber and different doped layers according to an embodiment of the present disclosure;

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

FIG. 7b is a schematic diagram of an optical path of an optical fiber including an isolation layer according to an embodiment of the present application;

FIG. 8a is a schematic diagram illustrating different distributions of multiple doped layers of an optical fiber according to an embodiment of the present disclosure;

FIG. 8b is a schematic diagram of a tri-doped layer fiber provided in an embodiment of the present application layered in different dimensions;

FIG. 8c is a schematic diagram of a triple doped layer optical fiber according to an embodiment of the present disclosure layered in the same dimension;

FIG. 9 is a schematic diagram of an optical path of an optical fiber including multiple cladding layers according to an embodiment of the present application;

FIG. 10 is a schematic view of an internal optical path of an optical fiber according to an embodiment of the present disclosure;

FIG. 11a is a schematic view of refractive indices of different layers of an optical fiber according to an embodiment of the present disclosure;

FIG. 11b is a schematic diagram of an optical path of signal light in an optical fiber according to an embodiment of the present disclosure;

FIG. 11c is a schematic diagram of gain spectrum in an optical fiber according to an embodiment of the present disclosure;

fig. 12 is a schematic structural diagram of an optical amplifier according to an embodiment of the present disclosure;

FIG. 13a is a schematic view of a portion of the dashed box in the structure of FIG. 12;

FIG. 13b is a schematic view of another configuration of the dashed box portion of the structure of FIG. 12;

fig. 14 is a schematic structural diagram of an optical transmission network according to an embodiment of the present application.

Detailed Description

Compared with communication modes such as cable communication, wireless communication and the like, the optical communication has the advantages of large communication capacity, small transmission loss, long relay distance, strong anti-interference capability, reliable working performance and the like. In order to fully exploit the advantage of large communication capacity of optical communication, signal transmission is generally performed by realizing wavelength division multiplexing of optical signals through a wavelength division multiplexing (wavelength division multiplexing, WDM) network.

As shown in fig. 1, the WDM network includes an optical transmitter, an optical repeater amplifier, and an optical receiver. Wherein the optical relay amplifier is also referred to as an optical amplifier. The optical transmitter is used for converting an input optical signal or an electrical signal into signal light with a specific wavelength, combining the signal light of different paths, and transmitting the combined signal light to the optical receiver through an optical fiber.

After the signal light is transmitted from the optical transmitter through the optical fiber for a certain distance due to the influence of the loss characteristic, dispersion characteristic and the like of the optical fiber, the amplitude attenuation causes waveform distortion, thereby 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 for receiving the amplified signal light and separating the signal light with a specific wavelength from the amplified signal light.

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 may be a single-fiber bidirectional transmission WDM network, which is not limited in this application. In addition to WDM networks, the optical fibers and the optical amplifiers provided in the embodiments of the present application may also be applied to networks such as single-wave transmission networks (networks for single-wavelength signal transmission), which are not limited in this application.

The structure of the optical amplifier in the WDM network shown in fig. 1 can be as shown in fig. 2. In an optical amplifier, a doped fiber and a pump light source are included. The pump light source is used for emitting pump light. The doped optical fiber is used for amplifying signal light with a specific wavelength under the excitation of the pump light. In the optical amplifier structure shown in fig. 2, an isolator (located before the light source and after the optical fiber), a wavelength division multiplexer (for accessing the pump light), a filter, etc. may be further included, which is not limited in this application.

Wherein, rare earth, metal and other elements (such as Er, bi, pr, nd, yb, tm, ho, dy) with luminescence property are doped in the fiber core of the doped fiber. In the embodiments of the present application, these elements having luminescence properties in the core are referred to as doping elements. As shown in fig. 3, electrons of the doping element are distributed over multiple energy levels (e.g., E1, E2, and E3), and the stability of electrons at different energy levels is different. The different energy levels include a ground state energy level of lower stability, an excited state energy level of higher stability, and a metastable state energy level of stability therebetween. The pump light provided by the pump light source may excite electrons at the ground state energy level (e.g., E1 energy level) to transition to the excited state energy level (e.g., E3 energy level). Electrons at the excited state energy level are unstable and spontaneously transition to the metastable state energy level (e.g., E2 energy level). The process of electrons transitioning from an excited state energy level to a metastable state energy level is also known as a radiationless transition.

The stability of electrons at the metastable energy level (E2 level) is high and can stay at that energy level for a period of time. At this time, the number of electrons at the metastable state level (E2 level) is larger than the number of electrons at the ground state level (E1 level), but such an inversion state can exist only temporarily. Therefore, when electrons at the metastable energy level (E2 energy level) are excited by the signal light, the electrons transit to the ground energy level (E1 energy level), and the enhancement (amplification) of the signal light is realized. The process of electrons transitioning from a metastable state to a ground state is also known as stimulated radiative transitions.

It should be noted that the doping element may include more energy levels in addition to the excited state energy level, the metastable state energy level, and the ground state energy level shown in fig. 3. The transition process of electrons at different energy levels in the doping element structure of more energy levels is similar to that shown in fig. 3, and will not be described again here.

If Δe represents the energy difference between the excited state energy level and the ground state energy level, h represents the planck constant, c represents the speed of light, and λ represents the wavelength of light radiated outward during stimulated radiation transition. Then Δe=hv=hc/λ according to the law of conservation of energy. Where λ is the wavelength of light radiated outward during the stimulated radiative transition, and also the wavelength of signal light that stimulates the stimulated radiative transition. That is, the wavelength of the optical signal that can be amplified by the doped fiber is λ=hc/Δe.

Since the energy difference between the different energy levels has a certain fluctuation range, λ also has a certain fluctuation range. That is, the doped optical fiber achieves amplification of signal light having a wavelength in a wavelength 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 optical fiber is referred to as gain spectrum width. The energy level difference deltae between the excited state energy level and the ground state energy level of the doping element results in a limited gain spectrum width of the doped optical fiber (i.e., the band covered by the doped optical fiber is limited), thereby limiting the wavelength range that can be transmitted in a long-distance transmission scenario.

Currently, the wavelength range applicable in optical fiber transmission is divided into a plurality of bands as shown in table 1.

TABLE 1 band division of current optical fibers

Wave band	Description of the invention	Wavelength range
			0 band	Original (original) band	1260-1360nm
E band	Extension (extended) band	1360-1460nm
			S-band	Short wave (wavelength) band	1460-1530nm
C band	Conventional (con-tent) band	1530-1565nm
			L-band	Long wave (long wave) band	1565-1625nm
U-band	Ultra-long wave (ultralong wavelength) band	1625--1675nm

When one optical fiber cannot cover a plurality of wave bands, a plurality of doped optical fibers are needed to amplify different wave bands respectively. Alternatively, when one optical fiber cannot cover a longer wavelength band, it is necessary to amplify a plurality of wavelength bands in the longer wavelength band with a plurality of doped optical fibers, respectively.

Fig. 4 is a schematic structural diagram of a multiband optical fiber amplifier, in which a single optical fiber amplifier cannot realize both C-band and L-band optical amplification due to the limitation of the gain bandwidth characteristics of the doping element itself. Thus, WDM is used to separate the signal light into C-band signal light and L-band signal light. In the optical amplifier, signal light of the C wave band and the L wave band are amplified respectively through doped optical fibers of different amplifying wave bands. And then combined into amplified c+l band signals by WDM.

Optionally, the optical amplifier shown in fig. 4 may further include a doped optical fiber with more wavebands, for amplifying signal light with more wavebands. Such as the S-band doped fiber shown in dashed lines in fig. 4, as this application is not limited.

The structure shown in fig. 4 amplifies signal lights of different wavebands through a plurality of branches respectively, which results in complex structure inside the optical amplifier, complex cooperative control among different branches, and high difficulty and cost of production and manufacture. And, since the signal light is filtered by WDM in the optical amplifier, a guard band of 3-5nm exists between the signal light bands amplified by the differently doped optical fibers. The whole optical transmission network also needs to transmit in different wave bands, which results in complex network structure.

In order to solve the problems of limited optical fiber gain spectrum width, complex internal structure of an optical amplifier, complex network structure and the like, the embodiment of the application provides an optical fiber, an optical amplifier and an optical transmission network. The optical fiber provided by the embodiment of the application amplifies signal lights of different wavebands respectively through the plurality of doped layers, so that the gain spectrum width of the optical fiber signal amplification is enlarged, and long-distance broad spectrum transmission is realized. Thereby simplifying the structure of the optical amplifier and the optical transmission network.

As shown in fig. 5, an optical fiber 500 provided in an 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 cores 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. Cladding layer 530 is located outside second doped layer 520. The inner wall of the cladding 530 serves to reflect the pump light as well as the signal light of the first wavelength band and the signal light of the second wavelength band. The first doping layer 510 is for amplifying the signal light of the first wavelength band by the energy of the pump light. The second doping layer 520 is used to amplify the signal light of the second 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 wave band corresponding to the first doping layer and the amplification of the signal light of the second wave band corresponding to the second doping layer can be realized. Compared with the existing optical fiber with a single-layer doped layer, the band range of the amplified signal is enlarged, namely the gain spectrum width is enlarged.

In the optical fiber 500 provided in the embodiment of the present application, the cladding 530 may further include a soft coating layer, a hard coating layer, a pre-coating layer, a buffer layer, a secondary coating layer, and the like, which is not limited in this application.

The first doped layer and the second doped layer with different materials are arranged in the same optical fiber, and the respective gain effects of the first doped layer and the second doped layer can be overlapped. In fig. 6, the abscissa indicates the wavelength of the signal light, and the ordinate g (λ) indicates the gain of the signal light corresponding to the wavelength. Where the solid line represents the gain function of the different doped layers for signal light and the dashed line represents the gain function of the fiber 500 containing the multiple doped layers. The gain function g (λ) of each doped layer (e.g., first doped layer 501 and second doped layer 502) in 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)

Wherein n is ₂ The doping ion inversion rate of the doped layer is (0 is less than or equal to n2 is less than or equal to 1), and n2 is determined by the pump light, the signal light power and the total number of doping ions. g (λ) is the gain factor of the doped layer at full inversion. a (lambda) is the absorption coefficient of the doped layer, and is calculated by the following specific ways, such as formula 2 and formula 3.Bgl (λ) is the background loss of the fiber. z is the fiber length.

g*(λ)＝σs(λ)Γ(λ)N _A (equation 2)

a(λ)＝σ _a (λ)Γ(λ)N _A (equation 3)

Wherein sigma _s (λ)、σ _a The emission cross-section function and the absorption cross-section function of the doped layer are determined by the luminescence characteristics of the doped material itself, irrespective of the geometry of the optical fiber. And Γ (lambda) is a mode field overlap factor of the optical fiber (Γ (lambda) is less than or equal to 0 and less than or equal to 1, and 1 when the signal optical mode field is completely overlapped with the doped layer). N (N) _A Is the average doping concentration of the doping element.

Wherein n is _t (r) is the doping ion distribution function of the optical fiber in cross section, and the maximum value is n _t 。i _λ (r) is a mode field distribution function over the cross-section of the optical signal at the incident wavelength λ.

Solid line table in FIG. 6Showing gain curves of different doped layers for signal light of different wavelengths, i.e. gain function g of doped layer A _A (lambda), gain function g of doped layer B _B (lambda). The dashed line in fig. 6 represents the gain function G (λ) of the fiber comprising the plurality of doped layers. For the multi-doped layer optical fiber 500 provided by embodiments of the present application, the gain function G (λ) can be written as:

G(λ)＝g _A (λ)+g _B (lambda) + … (equation 5)

Note 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. Vice versa, the present application is not limited thereto.

In fig. 6 (a), the gains of the bands between the peaks of the gain spectra of the two doped layers are superimposed on each other, directly widening the gain spectrum of the entire fiber. Amplification of the signal light between and near the two peaks can be achieved by an optical fiber.

In fig. 6 (b), there is no overlap between the gain spectra of the two doped layers. But the gain spectrum of the entire fiber includes the respective gain spectrum characteristics of the two doped layers,

in fig. 6 (c), the 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, which may absorb the gain of doped layer a over the negative gain band of doped layer B. The gain spectrum of the finally obtained optical fiber is flatter near the negative gain band of the doped layer B, and the signal light of the band near the negative gain band of the doped layer B can be amplified through the optical fiber.

In fig. 6 (d), the gain spectra of the two doped layers have different shapes, and overlapping each other can increase the flatness of the gain spectrum of the entire optical fiber.

In the embodiment of the present application, the structures of the first doped layer and the second doped layer are merely examples of the optical fiber structure of the multi-doped layer. The optical fiber can also comprise more doped layers which are respectively used for amplifying signal lights of different wave bands. For example, a set of doped layers may also be included between the second doped layer and the cladding layer. The doped layer set comprises n doped layers, wherein n is an integer greater than or equal to 1. The n doped layers in the doped layer set are used for amplifying signal light of n wave bands through the energy of the pump light. The n wave bands are n different wave bands, and the n wave bands are different from the first wave band and the second wave band.

For the purpose of this description, the structure of the optical fiber provided in the embodiments of the present application is further described below in terms of 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, and may specifically be represented by differences in terms of a host, a doping element, a doping concentration, and the like.

In one aspect, the matrices of the different doped layers may be made different. For example, with erbium as an example of the doping element, the first doping layer 510 and the second doping layer 520 may be the same erbium-doped layer. Wherein the matrix of the first doped layer 510 may include aluminum element and germanium element, the gain spectrum of the first doped layer 510 is a first band g with 1530nm as peak _a (lambda). The matrix of the second doped layer 520 may include components such as phosphorus and aluminum, and the gain spectrum of the second doped layer 520 is a second band g with-1535 nm peak, because the light emitting level center of the second doped layer 520 shifts to a long wavelength by about 5nm due to the phosphorus _b (lambda). The gain spectrum of the optical fiber 500 corresponds to the case (a) in fig. 6. Due to the first band g _a (lambda) and a second band g _b Superposition of (lambda) can achieve broadening of the gain spectrum of the optical fiber 500.

On the other hand, the doping concentration in the different doped layers may be different, i.e. the concentration of the doping element in the different layers may be different. The difference in doping concentration results in the inversion rate n of the doping elements in the different layers ₂ Different, thereby affecting the gain function shape of the different layers, i.e. g _a (λ)、g _b The shape of (λ), and thus the bandwidth, flatness, etc. of the gain function G (λ) of the entire optical fiber can be adjusted, as shown in (d) of fig. 6.

In an alternative implementation, the doping concentration of the first doped layer in the optical fiber is high and the doping concentration of the second doped layer is low. Because the mode field of the signal in the optical fiber is distributed to be high in the mode field intensity of the central part of the fiber core (namely the first doped layer area), the concentration of the doped ions of the first doped layer is high, namely the total number of the doped ions is high, so that the saturated output optical power of the optical fiber area can be improved, and the saturated gain compression value can be reduced. And in the second doped layer region with lower mode field strength, the lower doping concentration is adopted, so that the ion inversion rate of the region can be ensured to be higher, and the noise coefficient performance of the optical amplifier is reduced. In summary, the first doped layer and the doping concentration are higher than the doping concentration of the second doped layer (the doping concentration of the inner layer is higher than the doping concentration of the outer layer), so that the saturated output optical power of the whole optical fiber can be improved, and the low noise coefficient performance of the optical fiber amplifier can be improved.

On the other hand, the doping elements of the different doping layers may be made different. Since the gain spectrum characteristics of doped fibers are mainly determined by the energy level structure of the doping element itself, the change of matrix can only slightly change the gain spectrum characteristics thereof. In order to further expand the gain spectrum bandwidth of a single optical fiber, different doping elements can be doped in different layers of the optical fiber, and a matrix with the doping elements corresponding to optimal luminescence is adopted.

For example, the doping element in the first doped layer 510 may be erbium, and 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, a low Ge host may be used, and the gain spectrum of the second doped layer 520 mainly covers the S-band. The gain spectrum of the optical fiber 500 is a superposition of the C-band as the first band and the S-band as the second band as shown in (b) or (C) of fig. 6.

Alternatively, the doping element in the first doping layer 510 is erbium; the doping element in the second doped layer 520 is bismuth, and the second doped layer 520 employs a Ge host. The gain spectrum of the first doped layer 510 covers mainly the C-band and the gain spectrum of the second doped layer 520 covers mainly the L-band and the U-band. The gain spectrum of the optical fiber 500 is a superposition of the C-band, which is the first band, and the L-band and the U-band, which are the second bands, as shown in (C) of fig. 6.

It should be noted that, in the embodiments of the present application, the C-band, S-band, L-band, and U-band are used as examples of the amplifying bands of the different doped layers in the optical fiber, and the amplifying bands of the optical fiber provided in the embodiments of the present application are not limited. For example, the different doped layers in the optical fiber may amplify signal light in a wavelength band such as a 0-band or a U-band, or may amplify signal light in a partial wavelength band such as a C-band or an L-band, which is not limited in this application.

The above-described differences in the materials of the different doped layers may exist independently or may be superimposed. For example, the first doped layer 510 and the second doped layer 520 may have different matrixes, the same doping element, and the same doping concentration; alternatively, the first doped layer 510 and the second doped layer 520 may have different matrixes, different doping elements, different doping concentrations, and the like, which is not limited in the present application.

In the process of manufacturing the optical fiber 500 shown in fig. 5, a thermal beam expansion phenomenon (i.e., the doping elements of different layers diffuse into adjacent layers to form a transition layer of new element composition) occurs at the boundary between the first doped layer 510 and the second doped layer 520 due to heat, thereby forming a transition layer between the first doped layer 510 and the second doped layer 520. Since this 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 both the first doped layer 510 and the second doped layer 520. The gain characteristics of the transition layer may severely alter the gain characteristics, mode field distribution, etc. of the entire optical fiber 500, thereby affecting the light-amplifying effect (gain spectral 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 light-emitting effect of the entire optical fiber 500, an isolation layer 540 may be disposed between the first doped layer 510 and the second doped layer 520, with a specific structure as shown in fig. 7 a. In the structure shown in fig. 7a, an isolation layer 540 is used to isolate the first doped layer 510 and the second doped layer 520 to prevent a transition layer from occurring between the first doped layer 510 and the second doped layer 520. The isolation layer 520 may also be referred to as a protection layer, which is not limited herein.

In an alternative application, different bismuth-doped optical fibers are used in different matrices (e.g.:Al-SiO ₂ ，P ₂ O ₅ -SiO ₂ ) With different gain function centers. And a transition layer is formed between two adjacent bismuth-doped layers with different matrixes, and the gain function center wavelength of the transition layer is different from the gain function center of the two bismuth-doped layers. The transition layer may absorb the two bismuth-doped layers, thereby affecting the light emission effect of the entire optical fiber. In the structure of the optical fiber 500 shown in fig. 7a of the present application, two bismuth doped layers (i.e., the first doped layer 510 and the second doped layer 520 are different bismuth doped layers as a matrix) are isolated by an isolation layer 540. No transition layer is present and the gain function of the entire fiber 500 is the gain function g of the two bismuth-doped layers _A (lambda) and g _B The superposition of (lambda) (as shown in equation 5) does not result in a pair g due to the presence of the transition layer _A (lambda) and g _B ((absorption of lambda, ensure g) _A (lambda) and g _B (lambda) the light-emitting effect of the corresponding band.

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 signal corresponding band. Therefore, the spacer layer 540 is disposed between the first doped layer 510 and the second doped layer 520, and the influence of the transition layer on the amplifying effect can be prevented. The optical path of the signal light in the optical fiber structure shown in fig. 7a is as shown in fig. 7b, and by reasonably setting the refractive index of the isolation layer 540 (protective layer), the signal light can be ensured to be transmitted on a predetermined transmission path.

It should be noted that, when the optical fiber includes more than two doped layers, each two adjacent doped layers may be isolated by an isolating layer, which is not limited in this application.

As shown in fig. 8a, in the embodiment of the present application, the distribution of the different doped layers may be, besides the structure of internal and external layering, a structure of upper and lower layers or front and rear layering, etc., which is not limited in this application. Similar to the structure of the inner and outer layering, the number of doped layers is not limited in the optical fiber structure in which the doped layers are layered up and down or layered front and back. The doped layers can also be isolated by isolating layers, which is not limited in the application.

Alternatively, in the front-back layered optical fiber structure shown in fig. 8a to 8c, if the connection loss between the differently doped optical fibers is very low, the doped optical fibers of adjacent two different bands may be connected by fusion splicing or the like.

Alternatively, if the fiber includes three or more doped layers, different layered structures may be combined to provide a fiber with doped layers layered in multiple dimensions. For example, as shown in fig. 8b, the whole body formed by the first doped layer and the second doped layer and the third doped layer are in a front-back layered structure; and the first doped layer and the second doped layer are in an upper-lower layered structure. Alternatively, a structure of three or more doped layers may be layered in one dimension. Taking three layers as an example, a specific layered structure is shown in fig. 8 c. The materials of the first doping layer and the third doping layer may be the same or different, which is not limited in the present application.

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

In the fiber structure shown in fig. 5-8 c, the cladding 530 may include 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 531 serves to reflect the signal light and the inner wall of the outer cladding 532 serves to reflect the pump light.

The specific optical path is shown in fig. 10. In the multi-clad optical fiber, the signal light is totally reflected at the inner wall of the inner cladding (without considering the rationality of leakage), and thus the signal light is transmitted in the core (the plurality of doped layers). The pump light is totally reflected at the inner wall of the outer cladding (without taking leakage rationality into account) and is therefore transmitted in the inner cladding and the core. The optical fiber structure enables the pump light to be transmitted in multimode form in the optical fiber, so that a multimode pump light source can be used in an optical fiber amplifier comprising the optical fiber structure. Compared with the common single-mode pump light source, the multi-mode pump light source is cheaper and has higher output power. Thereby, 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 layer can be rectangular, regular polygon, ellipse and other shapes, so that the intensity of the pumping light transmitted in the inner cladding layer is improved, the efficiency of converting the intensity of the pumping light signal into the intensity of the signal light is improved, and the light emission effect is improved.

The optical path in a single clad fiber is also shown in fig. 10. In a single-clad fiber, both pump light and signal light are reflected by the inner wall of the cladding, and thus both are transmitted in the core. In the structure, the transmission range of the pump light is consistent with that of the signal light, so that the coincidence ratio of the pump light and the signal light is high, the energy conversion rate in the process of transferring energy from the pump light to the signal light is high, and the energy consumption can be reduced.

In order to ensure that both the signal light and the pump light are reflected by the inner wall of the cladding, the refractive index of the core should be greater than that of the outermost doped layer. In fig. 11a, taking two doped layers 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 difference in refractive index delta 2 between the second doped layer and the cladding layer needs to be large enough to ensure that the total reflection effect occurs at the interface between the signal light and the pump light.

In order to ensure that the incident light can be transmitted in all doped layers, the difference Δ1 in refractive index between the doped layers cannot be too great, so as to ensure that the incident light can be refracted at the interface of the different doped layers, so that a part of the light is refracted into the second doped layer, and a part of the light is reflected back to the first doped layer, and a specific optical path is shown in fig. 11 b. By adjusting the refractive index difference delta 1 between the doped layers, the transmission path of the signal light incident on the optical fiber between the first doped layer and the second doped layer and the transmission intensity of the signal light in different layers can be controlled, namely the mode field distribution i of the multi-doped layer optical fiber in the cross section _λ (r). Illustratively, FIG. 11c is a mode field distribution i of a dual-doped layer optical fiber having a graded index profile _λ (r) schematic diagram, in which the darker the color is, the greater the intensity of the signal light is. By 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, and the radius R3 of the cladding layer in the optical fiber, the refractive index Δ1 of the first doped layer and the refractive index Δ2 of the second doped layer can be adjusted to adjust the overlap factor Γ (λ) in the gain function of the optical fiber, therebyWhile controlling the gain function shape of the fiber.

In the design of the multi-doped layer optical fiber, the connection loss of the multi-doped layer optical fiber and the conventional single-mode optical fiber, namely the matching degree of the mode field diameters, needs to be comprehensively considered, and the factors of geometric parameter design of the conventional optical fiber such as the effective transmission area of the optical fiber, the transmission loss of the optical fiber, the cut-off wavelength and the like are also required. In combination with the above factors and the requirements of the gain function of the optical fiber, the radii (R1, R2, R3) of the different layers in the optical fiber and the refractive index difference (Δ1, Δ2) design between the different layers are optimized.

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. The optical fiber 500 shown in fig. 5 to 9 is taken as a doped optical fiber in the optical amplifier structure shown in fig. 2, which is an optical amplifier structure provided in the embodiment of the present application.

Alternatively, 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, two pump light sources may be included in the optical amplifier to provide pump light wavelengths corresponding to the first doped layer 510 and the second doped layer 520, respectively.

As shown in fig. 12, an optical amplifier 1200 provided in the embodiment of the present application includes a first pump light source 1201, a second pump light source 1202, and an optical fiber 1203. The optical fiber 1203 is the optical fiber 500 illustrated in fig. 5 to 9. The first pump light source 1201 is configured to provide pump light with a wavelength corresponding to the first doped layer, and the second pump light source 1202 is configured to provide pump 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. Optionally, the optical amplifier 1200 may further include a multiport wavelength division multiplexer 1204, configured to combine and input 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 into the optical fiber 1203.

Alternatively, 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 may be the same or different, which is not limited in the present application.

It should be noted that, the pump light corresponding to the doped layer in the embodiment of the present application refers to a wavelength corresponding to Δe in the embodiment of fig. 3. I.e. the energy difference between the excited state energy level and the steady 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.

Alternatively, the wave combining structure of the signal light λs, the pump light λ1 and the pump light λ2 in fig. 12 (i.e., the structure in the dashed frame in fig. 12) may also be as shown in fig. 13a or fig. 13b, which is not limited in this application. Note that, the structure of the optical amplifier provided in the embodiment of the present application may be a structure of backward pumping or bidirectional pumping, besides the structure of forward pumping as shown in fig. 12 to 13b, which is not limited in this application.

The structure of the optical fiber and the optical amplifier provided in the embodiment of the present application is described above, and the structure of the optical transmission network provided in the embodiment of the present application based on the optical fiber and the optical amplifier is 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 embodiments of the present application is illustrated by using the C-band and the L-band as the examples. Since the signal light of the current C-band and L-band cannot be amplified in the same amplifying optical fiber, it is necessary to split the signal light of the C-band and L-band into different amplifying optical fibers by a filter. And the filter needs to preserve a guard band of 3-5nm for filtering the C-band and L-band, thus resulting in banded transmission of signal light in the C-plane and L-plane. In fig. 14, triangles represent optical amplifiers. As shown in fig. 14, besides the optical amplifier needs to perform optical amplification on the C-band and the L-band, the current networking needs to perform operations such as adjusting and controlling the C-band and the L-band in a matching manner, which results in complex network structure.

In the optical transmission network provided in the embodiment of the present application, including the multi-doped layer optical fiber shown in the embodiments of fig. 5 to 9, full-band amplification of the C-band and the L-band can be achieved. Therefore, the C wave band and the L wave band do not need to be distinguished in networking, corresponding devices respectively matched with the C wave band and the L wave band are not needed, and the network structure is simple.

Because the optical transmission network provided by the embodiment of the application can transmit the broad spectrum signal light (for example, C band+l band), in the inventive transmission network provided by the embodiment of the application, the optical amplifier can be connected with the transmission optical fiber and/or the broad spectrum wavelength selective switch for realizing the transmission of the broad spectrum signal light.

Note that fig. 14 illustrates examples of the C-band and L-band. The optical transmission network provided in the embodiment of the present application may also be used for transmitting optical signals in other bands, for example, S band+c band+u band, etc., which is not limited in this application.

It will be clear to those skilled in the art that, for convenience and brevity of description, specific working procedures of the above-described systems, apparatuses and units may refer to corresponding procedures in the foregoing method embodiments, which are not repeated herein.

In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods may be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative, e.g., the division of the units is merely a logical function division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices or units, which may be in electrical, mechanical or other form.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may 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 in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.

Claims

1. An optical fiber comprising a first doped layer, a second doped layer and a cladding layer, said second doped layer being located outside said first doped layer, said cladding layer being located outside said second doped layer, said second doped layer and said first doped layer being comprised of different materials;

the inner wall of the cladding is used for reflecting the pump light, the signal light of the first wave band and the signal light of the second wave band;

the first doping layer is used for amplifying the signal light of the first wave band through the energy of the pump light;

the second doping layer is used for amplifying the signal light of the second wave band through the energy of the pump light.

2. The optical fiber of claim 1, further comprising:

an isolation layer between the first doped layer and the second doped layer.

3. The optical fiber according to claim 1 or 2, wherein the pump light is multimode pump light;

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

the inner wall of the outer cladding layer is used for reflecting the multimode pump light;

the inner wall of the inner cladding is used for reflecting the signal light.

4. An optical fiber according to any of claims 1 to 3, wherein the matrices of the first and second doped layers are different.

5. The optical fiber according to any one of claims 1 to 4, wherein the doping element in the first doped layer and the doping element in the second doped layer are different.

6. The optical fiber according to any one of claims 1 to 4, wherein the doping element in the first doped layer and the doping element in the second doped layer are the same.

7. The optical fiber according to claim 6, wherein the doping concentration of the doping element is different in the first doping layer and the second doping layer.

8. The optical fiber according to any one of claims 1 to 7, further comprising a set of doped layers between the second doped layer and the cladding layer, the set of doped layers comprising n doped layers, the n being an integer greater than or equal to 1;

the n doped layers in the doped layer set are used for amplifying signal light of n wave bands through the energy of the pump light, the n wave bands are n different wave bands, and the n wave bands are different from the first wave band and the second wave band.

9. An optical amplifier, comprising:

an optical fiber, which is the optical fiber of any one of claims 1 to 8;

and the pump light source is used for providing the pump light.

10. The optical amplifier of claim 9, wherein the pump light source comprises:

the first pump light source is used for providing pump light with the corresponding wavelength of the first doped layer;

the second pump light source is used for providing pump light with the 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.

11. An optical transmission network comprising the optical amplifier of claim 9 or 10.

12. An optical transmission network according to claim 11, characterized in that the optical amplifier is connected to a transmission fiber and/or a broad spectrum wavelength selective switch WSS.