A dual-core erbium-doped optical fiber for simultaneous C-band and L-band amplification

Abstract

This invention discloses a dual-core erbium-doped optical fiber for simultaneous amplification of C-band and L-band signals, relating to the field of erbium-doped optical fiber technology. The fiber includes a first core, a second core, and an outer cladding. The erbium doping concentration of the first core, used for C-band amplification, differs from that of the second core, used for L-band amplification. The outer cladding surrounds the first and second cores. The first and second cores constitute a single-mode dual-core optical fiber structure. This invention achieves amplification of C-band and L-band signal light within the same erbium-doped optical fiber by using first and second cores with different erbium doping concentrations.

Description

Technical Field

[0001] This invention relates to the field of erbium-doped fiber technology, and more specifically, to a dual-core erbium-doped fiber for simultaneous amplification in the C-band and L-band. Background Technology

[0002] Erbium-doped fiber (EDFA) is a type of silica fiber incorporating a small amount of the rare-earth element erbium ions. It is a core component of EDFAs and lasers, and is an indispensable part of long-distance optical communication systems. An EDFA mainly consists of a section of erbium-doped fiber and a pump source. Under the influence of the pump source, the erbium-doped fiber generates stimulated emission, and the emitted light changes with the input optical signal, effectively amplifying the input signal.

[0003] To improve the capacity of optical fiber communication, the gain bandwidth of EDFA has been extended from the traditional C-band to the C+L-band. However, existing erbium-doped fiber technology cannot achieve C+L-band optical signal amplification in a single erbium-doped fiber. The realization of C+L-band EDFA requires combining C-band EDFA and L-band EDFA in parallel or series structures, resulting in a complex and difficult-to-integrate structure for the entire EDFA. Therefore, improvements and innovations are urgently needed in the design and fabrication of erbium-doped fibers.

[0004] In 2004, Yi Bin Lu et al. reported an ultra-wideband gain-flattened fiber amplifier composed of a C-band EDFA and an L-band EDFA connected in parallel. The gain medium was erbium-doped fiber with a dual-core structure, but only one core was erbium-doped, providing optical amplification, while the other core only guided light to achieve two-beam interference, thus flattening the gain spectrum. Therefore, amplification of both the C-band and L-band still requires different erbium-doped cores.

[0005] The prior art discloses a gain-equalized few-mode erbium-doped fiber, which comprises, from the inside out, a core (1), an inner cladding (2), and an outer cladding (3). The core (1) is a silicon dioxide layer with different erbium doping concentrations, comprising a circular core layer (1-1) located in the central region of the core (1), and a first annular core layer (1-2) and a second annular core layer (1-3) sequentially surrounding the circular core layer (1-1); wherein the circular core layer (1-1) and the first annular core layer... The erbium doping concentrations of (1-2) and the second annular core layer (1-3) are a1, a2 and a3 respectively, which satisfy the relationship: a2 < a1, a2 < a3; the refractive indices of the circular core layer (1-1), the first annular core layer (1-2) and the second annular core layer (1-3) are n1, n2 and n3 respectively, which satisfy the relationship: n2 > n3 > n1; however, the shortcomings of the prior art are that the optical signals of the C-band and L-band need to be amplified in different erbium-doped fibers, which makes the structure of the erbium-doped fiber amplifier complex and difficult to integrate. Summary of the Invention

[0006] To address the problem that existing technologies require C-band and L-band optical signals to be amplified in different erbium-doped fibers, resulting in complex erbium-doped fiber amplifier structures that are difficult to integrate, a dual-core erbium-doped fiber for simultaneous amplification of C-band and L-band signals is proposed. By using a first core and a second core with different concentrations, C-band and L-band signal light can be amplified in a single erbium-doped fiber.

[0007] The technical solution of the present invention is as follows:

[0008] A dual-core erbium-doped optical fiber for simultaneous C-band and L-band amplification includes a first core, a second core, and an outer cladding; the erbium doping concentration of the first core for C-band amplification is different from that of the second core for L-band amplification; the outer cladding wraps around the first and second cores; the first and second cores constitute a single-mode dual-core optical fiber structure.

[0009] Working principle of the invention:

[0010] When C-band or L-band signal light is coupled into the corresponding fiber core, the ground-state erbium ions are excited to a high-energy state under the action of pump light, causing a population inversion and thus generating stimulated emission, thereby realizing optical amplification in the C-band and L-band.

[0011] Preferably, the first fiber core provides a first gain for the C-band signal light; the second fiber core provides a second gain for the L-band signal light; and the gain difference between the first gain and the second gain is less than 5dB.

[0012] Preferably, both the first and second fiber cores are made of quartz material doped with rare earth erbium ions.

[0013] Preferably, the outer cladding layer is made of silica material.

[0014] Preferably, the erbium doping concentration of the first core for amplifying the C band is above 300 ppm, and the erbium doping concentration of the second core for amplifying the L band is above 1000 ppm.

[0015] Furthermore, the concentration ratio of the erbium doping concentration of the first core to that of the second core is 0.3 - 2.

[0016] Preferably, the core diameters of the first core and the second core are 3 - 10 μm.

[0017] Furthermore, the refractive index distributions of the first core and the second core are step - type distributions; the refractive index coefficient is related to the refractive index distribution of the core; the sizes and refractive indices of the first core and the second core are designed to meet the single - mode light - guiding requirements of the C + L band.

[0018] Furthermore, the core - to - core distance between the first core and the second core > 30 μm. By imposing conditions on the core - to - core distance, cross - talk between cores of signal light is avoided, and the energy distribution between the two cores is not affected.

[0019] Furthermore, the relationship between the linear coupling coefficient and the core - to - core distance between the first core and the second core is as follows:

[0020]

[0021] In the formula, C is the linear coupling coefficient, d NA is the numerical aperture of the optical fiber, n1 is the refractive index of the core, r is the radius of the core, d is the core - to - core distance between the first core and the second core, U, W, V are fiber normalized parameters and satisfy U 2 +W 2 =V 2 and W = 1.1428V - 0.996 and 1.5 < V < 2.4; K0, K1 are the second - kind modified Bessel functions.

[0022] Advantages of the present invention:

[0023] 1. By different erbium doping concentrations of the first core and the second core, simultaneous amplification of optical signals in the C band and the L band is achieved, and the same gain is obtained.

[0024] 2. By the single - mode dual - core optical fiber structure and imposing conditions on the core - to - core distance, cross - talk between cores of signal light is avoided, and the energy distribution between the two cores is not affected.

[0025] 3. By designing the dimensions and refractive index of the first and second fiber cores, the requirements for single-mode light guiding in the C+L band are met. Attached Figure Description

[0026] Figure 1 This is a structural diagram of a dual-core erbium-doped optical fiber used for simultaneous amplification in both C-band and L-band.

[0027] Figure 2 This is a cross-sectional view of a dual-core erbium-doped optical fiber used for simultaneous amplification in both C-band and L-band. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] like Figure 1 , Figure 2 As shown, a dual-core erbium-doped optical fiber for simultaneous C-band and L-band amplification includes a first core 2, a second core 3, and an outer cladding 1. The erbium doping concentration of the first core 2, used for C-band amplification, is different from that of the second core 3, used for L-band amplification. The outer cladding 1 wraps around the first core 2 and the second core 3. The first core 2 and the second core 3 constitute a single-mode dual-core optical fiber structure.

[0031] Working principle of the invention:

[0032] When C-band or L-band signal light is coupled into the corresponding fiber core, the ground-state erbium ions are excited to a high-energy state under the action of pump light, causing a population inversion and thus generating stimulated emission, thereby realizing optical amplification in the C-band and L-band.

[0033] Erbium-doped fiber is used as the gain medium. When signal light and pump light are coupled and incident into a dual-core erbium-doped fiber, the energy carried by the incident light, due to absorption by the medium, excites electrons in the medium to higher energy levels. This process is called population inversion. Through relaxation, electrons transition from higher energy levels to the ground state, releasing energy and emitting more photons, thus achieving optical amplification.

[0034] In this embodiment, the first fiber core provides a first gain for the C-band signal light; the second fiber core provides a second gain for the L-band signal light; and the gain difference between the first gain and the second gain is less than 5dB.

[0035] Factors affecting gain include pumping method, pumping power, erbium fiber length, erbium doping concentration, and structural differences; a change in any one of these factors will affect the gain level.

[0036] In this embodiment, both the first core 2 and the second core 3 are made of quartz material doped with rare earth erbium ions.

[0037] In this embodiment, the outer cladding 1 is made of silica material. The chemical properties of silica are stable, making the double-core erbium-doped fiber have good stability.

[0038] In this embodiment, the erbium doping concentration of the first core 2 for amplifying the C band is above 300 ppm, and the erbium doping concentration of the second core 3 for amplifying the L band is above 1000 ppm. By the different erbium doping concentrations of the first core 2 and the second core 3, simultaneous amplification of the C band and the L band is achieved.

[0039] More specifically, the concentration ratio of the erbium doping concentration of the first core 2 to that of the second core 3 is 0.3 - 2.

[0040] In this embodiment, the core diameters of the first core 2 and the second core 3 are 3 - 10 μm.

[0041] More specifically, the refractive index distributions of the first core 2 and the second core 3 are step-type distributions; the refractive index coefficient is related to the refractive index distribution of the core; the sizes and refractive indices of the first core 2 and the second core 3 are designed to meet the single-mode light guiding requirements of the C + L bands.

[0042] In this embodiment, the core pitch between the first core 2 and the second core 3 > 30 μm, aiming to prevent coupling between the first core 2 and the second core 3; through the conditional constraint on the core pitch, core-to-core crosstalk of the signal light is avoided, and the energy distribution between the first core 2 and the second core 3 is prevented from being affected.

[0043] More specifically, the relationship between the linear coupling coefficient and the core pitch between the first core 2 and the second core 3 is as follows:

[0044]

[0045] In the formula, C is the linear coupling coefficient, d NA is the numerical aperture of the fiber, n1 is the refractive index of the core, r is the core radius, d is the core pitch between the first core 2 and the second core 3, U, W, V are fiber normalized parameters and satisfy U 2 +W 2 =V 2 and W = 1.1428V - 0.996 and 1.5 < V < 2.4; K0, K1 are the second-kind modified Bessel functions;

[0046] Embodiment 2

[0047] A dual-core erbium-doped optical fiber for simultaneous C-band and L-band amplification includes a first core 2, a second core 3, and an outer cladding 1. The erbium doping concentration of the first core 2 for C-band amplification is different from that of the second core 3 for L-band amplification. The outer cladding 1 wraps around the first core 2 and the second core 3. The first core 2 and the second core 3 constitute a single-mode dual-core optical fiber structure.

[0048] In this embodiment, the first fiber core provides a first gain for the C-band signal light; the second fiber core provides a second gain for the L-band signal light; and the gain difference between the first gain and the second gain is less than 5dB.

[0049] In this embodiment, both the first fiber core 2 and the second fiber core 3 are made of quartz material doped with rare earth erbium ions.

[0050] In this embodiment, the outer cladding layer 1 is made of silicon dioxide. Silicon dioxide has stable chemical properties, which makes the dual-core erbium-doped optical fiber have good stability.

[0051] In this embodiment, when the dual-core erbium-doped fiber amplifies the signal light, it is not necessary to convert the signal light into an electrical signal, which reduces the energy loss in the energy conversion process and allows the light to interact fully with the erbium ions.

[0052] In this embodiment, the erbium doping concentration of the first fiber core 2 used for amplifying the C-band is 500 ppm, and the erbium doping concentration of the second fiber core 3 used for amplifying the L-band is 1362 ppm. By using the different erbium doping concentrations of the first fiber core 2 and the second fiber core 3, simultaneous amplification of the C-band and L-band can be achieved.

[0053] More specifically, the erbium doping concentration ratio of the first fiber core 2 to the erbium doping concentration of the second fiber core 3 is 0.3 to 2. In this embodiment, the concentration ratio is 0.367.

[0054] In this embodiment, the diameter of the first fiber core 2 and the second fiber core 3 is 9 μm, and the diameter of the outer cladding 1 is 125 μm.

[0055] More specifically, the refractive index distribution of the first fiber core 2 and the second fiber core 3 is a step-type distribution; the refractive index coefficient is related to the refractive index distribution of the fiber core; the size and refractive index design of the first fiber core 2 and the second fiber core 3 meet the requirements of single-mode light guiding in the C+L band.

[0056] In this embodiment, the spacing between the first fiber core 2 and the second fiber core 3 is >30μm, in order to prevent coupling between the first fiber core 2 and the second fiber core 3; by constraining the spacing between the cores, crosstalk between the signal light is avoided, and the energy distribution between the first fiber core 2 and the second fiber core 3 is not affected.

[0057] More specifically, the relationship between the linear coupling coefficient and the core pitch of the first core 2 and the second core 3 is as follows:

[0058]

[0059] In the formula, d NA is the numerical aperture of the optical fiber, n1 is the refractive index of the core, r is the radius of the core, d is the core pitch between the first core 2 and the second core 3, U, W, and V are the normalized parameters of the optical fiber and satisfy U 2 +W 2 =V 2 and W = 1.1428V - 0.996 and 1.5 < V < 2.4; K0 and K1 are the second-kind modified Bessel functions.

[0060] Example 3

[0061] Based on the dual-core erbium-doped optical fiber for simultaneous amplification in the C band and the L band described in Example 2, it includes a first core 2, a second core 3, and an outer cladding 1; the erbium doping concentration of the first core 2 for amplifying the C band is different from that of the second core 3 for amplifying the L band; the outer cladding 1 is wrapped around the outer layers of the first core 2 and the second core 3; the first core 2 and the second core 3 form a single-mode dual-core optical fiber structure.

[0062] In this embodiment, the first core provides the first gain for the signal light in the C band; the second core provides the second gain for the signal light in the L band; the gain difference between the first gain and the second gain is less than 3 dB.

[0063] In this embodiment, both the first core 2 and the second core 3 are made of quartz material doped with rare-earth erbium ions.

[0064] In this embodiment, the outer cladding 1 is made of silica material, and the chemical properties of silica are stable, making the dual-core erbium-doped optical fiber have good stability.

[0065] In this embodiment, the erbium doping concentration of the first core 2 for amplifying the C band is 600 ppm, and the erbium doping concentration of the second core 3 for amplifying the L band is 1635 ppm. By the different erbium doping concentrations of the first core 2 and the second core 3, the simultaneous amplification in the C band and the L band is achieved.

[0066] More specifically, the concentration ratio of the erbium doping concentration of the first core 2 to that of the second core 3 is 0.367.

[0067] In this embodiment, the core diameters diameters of the first core 2 and the second core 3 has a diameter of 10 μm, and the outer cladding 1 has a diameter of 125 μm.

[0068] More specifically, the refractive index distributions of the first core 2 and the second core 3 are step-type distributions; the refractive index coefficient is related to the refractive index distribution of the core; the sizes and refractive indices of the first core 2 and the second core 3 are designed to meet the single-mode light guiding requirements in the C+L band.

[0069] In this embodiment, the core pitch between the first core 2 and the second core 3 is >30 μm, aiming to prevent coupling between the first core 2 and the second core 3; by imposing a conditional constraint on the core pitch, crosstalk between cores of the signal light is avoided, and the energy distribution between the first core 2 and the second core 3 is prevented from being affected.

[0070] More specifically, the relationship between the linear coupling coefficient and the core pitch between the first core 2 and the second core 3 is as follows:

[0071]

[0072] In the formula, d NA is the numerical aperture of the optical fiber, n1 is the refractive index of the core, r is the radius of the core, d is the core pitch between the first core 2 and the second core 3, U, W, V are the normalized parameters of the optical fiber and satisfy U 2 +W 2 =V 2 and W = 1.1428V - 0.996 and 1.5 < V < 2.4; K0, K1 are the second-kind modified Bessel functions;

[0073] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A dual-core Erbium-doped fiber for simultaneous amplification in C-band and L-band, characterized in that, The application relates to a single-mode dual-core optical fiber, which comprises a first core (2), a second core (3) and an outer cladding (1); the doping concentration of the first core (2) for amplifying C-band is different from the doping concentration of the second core (3) for amplifying L-band; the outer cladding (1) is wrapped on the outer layer of the first core (2) and the second core (3); the first core (2) and the second core (3) form a single-mode dual-core optical fiber structure. The first core (2) provides a first gain for C-band signal light; the second core (3) provides a second gain for L-band signal light; the gain difference between the first gain and the second gain is less than 5dB; the doping concentration of the first core (2) for amplifying C-band is more than 300ppm, and the doping concentration of the second core (3) for amplifying L-band is more than 1000ppm; the concentration ratio of the doping concentration of the first core (2) and the doping concentration of the second core (3) ranges from 0.3 to 2; the core spacing of the first core (2) and the second core (3) is larger than 30mu m.

2. The dual-core Erbium-doped fiber for simultaneous amplification of C-band and L-band according to claim 1, wherein, The first core (2) and the second core (3) are made of quartz material doped with rare earth erbium ions.

3. The dual-core Erbium-doped fiber for simultaneous amplification of C-band and L-band according to claim 1, wherein, The outer cladding (1) is made of silica material.

4. The dual-core Erbium-doped fiber for simultaneous amplification of C-band and L-band according to claim 1, wherein, The core diameter of the first core (2) and the second core (3) is 3-10mu m.

5. The dual-core Erbium-doped fiber for simultaneous amplification of C-band and L-band according to claim 1, wherein, The refractive index distribution of the first core (2) and the second core (3) is step distribution.

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