Multi-core optical fiber amplifier with large core-to-package ratio and gain method

Abstract

The invention discloses a multi-core optical fiber amplifier with a large core-to-cladding ratio and a gain method. The multi-core optical fiber amplifier is characterized by comprising a multi-core optical fiber formed by a plurality of independent rare earth-doped fiber cores and a cladding structure located on the outer side of the multi-core optical fiber, the cladding structure is internally provided with at least one layer of low-refractive-index isolation region which is used for remarkably compressing the effective cladding area of pumping propagation and improving the capturing efficiency of the whole pumping energy, and the ratio of the total cross sectional area of the multi-core optical fiber to the effective cladding area is not less than 0.1. The low-refractive-index isolating layer is embedded in a conventional cladding structure, so that a pump light propagation area can be effectively compressed on an optical path, the relative proportion of the fiber core in the cross section is increased, the proportion (CCAR is larger than or equal to 0.1) of the total area of the fiber core to the cladding area is remarkably increased, and therefore the pump capture efficiency is improved.

Description

Technical Field

[0001] The present invention relates to a multi-core optical fiber amplifier with a large core-to-envelope ratio, and in particular to a multi-core optical fiber amplifier with a large core-to-envelope ratio and a gain method. Background Art

[0002] With the rapid development of high-speed fiber-optic communication networks and space-division multiplexing systems, traditional single-core fiber amplifiers are increasingly unable to meet the technical requirements of modern optical networks for high channel density and high gain uniformity in terms of channel capacity and pump energy efficiency. Although multi-core fiber (MCF) structures have become an effective way to improve channel carrying capacity, how to simultaneously improve pump light utilization and gain consistency within a limited cross-section structure remains a key challenge.

[0003] Traditional multi-core fiber structures typically utilize a conventional solid cladding structure, resulting in a relatively small core-to-cladding area ratio (CCAR). This results in low pump power per core when propagating within the cladding, limiting pump efficiency. Furthermore, when cladding injection is required via side-bonded pump fibers, conventional cladding structures struggle to achieve precise and efficient local coupling, which can easily lead to pump leakage, structural damage, or coupling loss. To address this issue, a multi-core fiber amplifier with a large core-to-cladding ratio and a gain method are proposed. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and to provide a multi-core fiber amplifier with a large core-to-net ratio and a gain method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a multi-core fiber amplifier with a large core-to-cladding ratio, characterized in that it includes a multi-core fiber composed of multiple independent rare-earth-doped cores and a cladding structure located outside the multi-core fiber, wherein the cladding structure is provided with at least one low-refractive-index isolation region for significantly compressing the effective cladding area for pump propagation and improving the overall pump energy capture efficiency, and the ratio between the total cross-sectional area of ​​the multi-core fiber and the effective cladding area is not less than 0.1.

[0006] Further preferably, the low-refractive-index isolation region is an annular structure with at least one circle surrounding the outside of the multi-core optical fiber; the annular structure can be in the form of any one of an air layer, a microstructured void band or a low-refractive glass layer for reducing the cladding propagation cross section and guiding pump focusing.

[0007] More preferably, when the low-refractive-index isolation layer is the innermost air layer of the cladding, a closed glass cladding or a high-refractive-index support material having a mechanical support function is provided on the outside of the low-refractive-index isolation layer.

[0008] More preferably, the high refractive index support material is any one of zirconia-doped silica glass, phosphosilicate glass, titanium-doped silica glass or high refractive index borosilicate glass.

[0009] Further preferably, the cores in the multi-core optical fiber are arranged axially symmetrically or asymmetrically, the number of cores is not less than four, and there is optical isolation between the cores for multi-channel independent signal transmission and amplification.

[0010] Further preferably, the large core-to-cladding ratio is a ratio of the total cross-section of the fiber core to the effective optical area of ​​the cladding that is not less than 0.1, wherein the effective area of ​​the cladding is optically isolated by providing at least one annular microstructure region with a refractive index significantly lower than that of the glass cladding, and the interior of the annular microstructure region can be composed of air, an air cavity surrounded by a silica support tube, or any other low-refractive-index material, and the mechanical stability of the optical fiber is maintained by structural stress regulation and an internal tube support mechanism.

[0011] A gain method for a multi-core optical fiber amplifier with a large core-to-packet ratio, characterized by comprising the following steps: (1) Reduce the effective cladding through a low-refractive-index isolation region to enhance pump capture; (2) Opening windows or etching locally on the surface of the optical fiber cladding to expose the area for pump injection; (3) Place the pump fiber in contact with the region and inject pump light into the core gain cladding through physical coupling; (4) Realize stimulated radiation in the rare earth-doped fiber core to achieve parallel amplification of multi-channel signals.

[0012] Further preferably, the pump injection region forms a fitting surface by grinding or laser etching, the pump fiber adopts a multi-mode structure, and the injection path can be axial, transverse or inclined, with local high-efficiency injection capability.

[0013] Further preferably, the wavelength of the pump light source can be 980 nm, 1480 nm or 1550 nm, which is suitable for erbium-doped or ytterbium-doped gain mechanisms in different bands, and supports single-point or multi-point injection to improve pump uniformity.

[0014] Further preferably, the pump injection bonding section is positioned and fixed using a V-groove fixture or a nested precision fixture to provide a stable mechanical support structure, and the bonding pressure is maintained within a safe range through a constant contact pressure control system to ensure steady-state contact between the pump fiber and the multi-core fiber in the injection area, while effectively avoiding structural damage and decreased coupling efficiency caused by local bending, displacement or stress concentration of the optical fiber.

[0015] Beneficial effects of the present invention: By embedding a low-refractive-index isolation layer in a conventional cladding structure, the present invention can effectively compress the pump light propagation area in the optical path, increase the relative proportion of the core in the cross section, and significantly increase the ratio of the total core area to the cladding area (CCAR ≥ 0.1), thereby enhancing the pump capture efficiency; At the same time, combined with the local window opening or grinding process of the cladding, a directional coupling interface with controllable structure and stable path can be constructed in the pump injection area, thereby improving the system power utilization and pump control accuracy; The present invention has outstanding performance in improving the efficiency of pump light energy capture, enhancing inter-channel gain balance, and suppressing structural losses. It is suitable for optical relay amplifiers in multi-channel space-division multiplexing communication systems, balanced gain modules in high-power laser synthesis platforms, and signal enhancement nodes in multi-channel distributed optical fiber sensing systems. The overall structure has good scale integration and process compatibility, and the pumping strategy is highly flexible and adaptable, suitable for the industrial integration needs of high-performance photonic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a typical cross-sectional structure of a multi-core optical fiber amplifier of the present invention; Figure 2 This is a schematic diagram of pump bonding after the local structure window is opened in the present invention; Figure 3 is a side view schematic diagram of a cladding local stripping structure formed by grinding / etching according to the present invention; Figure 4 It is a process flow diagram of the present invention. DETAILED DESCRIPTION

[0017] The following further describes a multi-core optical fiber amplifier with a large core-to-wrapper ratio and a gain method according to the present invention with reference to the accompanying drawings.

[0018] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative position relationship, movement status, etc. between the various components in a certain specific posture as shown in the accompanying drawings. If the specific posture changes, the directional indication will also change accordingly.

[0019] In the present invention, unless otherwise specified or limited, the terms "connect," "fix," etc. should be understood broadly. For example, "fix" can refer to a fixed connection, a detachable connection, or an integral connection; it can also refer to a mechanical connection, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0020] See Figures 1-4As shown in , a multi-core fiber amplifier with a large core-to-cladding ratio is characterized by comprising a multi-core fiber composed of multiple independent rare-earth-doped cores and a cladding structure outside the multi-core fiber, wherein the cladding structure is provided with at least one low-refractive-index isolation region for significantly compressing the effective cladding area for pump propagation and improving the overall pump energy capture efficiency, and the ratio between the total cross-sectional area of ​​the multi-core fiber and the effective cladding area is not less than 0.1; In one embodiment, the low-refractive-index isolation region is an annular structure that surrounds the outside of the multi-core optical fiber in at least one circle; the annular structure can be in the form of any one of an air layer, a microstructured cavity band, or a low-refractive glass layer for reducing the cladding propagation cross-section and guiding pump focusing; the air layer can be an air annular groove, the microstructured cavity can be a nested hollow microstructure, and the low-refractive glass layer can be a low-refractive glass layer material with a refractive index significantly lower than that of the cladding matrix material, and is used to compress the pump light propagation area and increase the effective proportion of the core in the cross-section; The configuration of the isolation layer can be a continuous ring, a periodic discontinuous or a dot matrix arrangement, and its structural center can be aligned with the optical fiber axis or form an asymmetric design to adapt to different core arrangement strategies.

[0021] In one embodiment, when the low-refractive-index isolation layer is the innermost air layer of the cladding, a closed glass cladding or a high-refractive-index support material having a mechanical support function is provided on the outside of the low-refractive-index isolation layer.

[0022] In one embodiment, the high refractive index support material is any one of zirconia-doped silica glass, phosphosilicate glass, titanium-doped silicate glass, or high refractive index borosilicate glass.

[0023] In one embodiment, the cores in the multi-core optical fiber are arranged axially symmetrically or asymmetrically, with no less than four cores, and are optically isolated from each other for multi-channel independent signal transmission and amplification. The cores can be arranged in concentric circles, square arrays, or irregular compact distributions, and the cores are optically uncoupled.

[0024] In one embodiment, the large core-to-cladding ratio is a ratio of the total cross-section of the fiber core to the effective optical area of ​​the cladding that is not less than 0.1, wherein the effective area of ​​the cladding is optically isolated by providing at least one annular microstructure region having a refractive index significantly lower than that of the glass cladding. The interior of the annular microstructure region can be composed of air, an air cavity surrounded by a silica support tube, or any other low-refractive-index material, and the mechanical stability of the optical fiber is maintained through structural stress regulation and an internal tube support mechanism. To ensure structural integrity and thermomechanical stability, the low refractive index layer may be encapsulated with a thin-walled glass support tube on the outside or embedded with a composite support structure; The cross-section of the multi-core fiber in this embodiment includes eight equally spaced rare-earth-doped cores arranged in a ring. The center is a hollow cavity structure in the non-transmission zone with an aperture of approximately 50 mm, which is used to adjust the thermal distribution and mechanical stability of the core. The outer layer is a composite cladding structure, in which a circle of continuous closed low-refractive index microstructure layer is set between the core region and the outermost cladding. The low-refractive index width is set to 100 μm and the thickness is 30 μm. This air layer reduces the local effective refractive index and limits the diffusion range of the pump light, thereby achieving a core-cladding area ratio (CCAR) of approximately 0.20, which is more than 60% higher than that of traditional EDFA. The diameter of each fiber core is 6μm, the outer diameter of the cladding is about 150 μm, the total outer diameter of the optical fiber is about 250 μm, and the cladding numerical aperture NA is about 0.36, which can support the annular propagation of multi-mode pump light. The eight fiber cores are optically independent of each other, with no coupling interference, and support parallel amplification.

[0025] A gain method for a multi-core fiber amplifier with a large core-to-packaging ratio: The pump injection bonding section is positioned and fixed using a V-groove fixture or a nested precision fixture to provide a stable mechanical support structure. A constant contact pressure control system is used to maintain the bonding pressure within a safe range to ensure steady-state contact between the pump fiber and the multi-core fiber in the injection area, while effectively avoiding structural damage and reduced coupling efficiency caused by local bending, displacement or stress concentration of the fiber. The pump injection region is removed by grinding, laser etching, or chemical etching to form a bonding surface. The pump fiber adopts a multi-mode structure, and the injection path can be axial, transverse, or inclined, with local high-efficiency injection capability. The effective cladding area close to the core side is exposed to form an injection window for pump coupling. The pump fiber is preferably a high numerical aperture (NA ≥ 0.22) multimode fiber, which is fitted with the injection window through surface contact to achieve lateral or oblique injection of pump light.

[0026] Reduce the effective cladding through a low-refractive-index isolation region to enhance pump capture; A window is opened or etched locally on the surface of the optical fiber cladding. The outer cladding and air layer are ground at specific points using mechanical polishing equipment or laser etching equipment. The window length is about 3 mm, and the depth is controlled to be close to the gain cladding where the fiber core is located (that is, the fiber core body is not damaged). The pump channel for bonding and the area for pump injection are exposed. The pump fiber is bonded to the window area using a high-precision V-groove fixture. The pump fiber is a standard 62.5mm core diameter multimode fiber with a numerical aperture of 0.22. The bonding pressure is controlled within 0.3 N and the bonding angle is vertical incidence (or 5° internal deviation). This ensures that the pump light can be directly coupled into the exposed gain cladding. Part of the pump light is totally reflected in the cladding and propagates, while the remaining pump light can directly excite the erbium ions in the adjacent fiber core. The coupling zone length is controlled at the millimeter level, and the bonding process is secured with a V-groove fixture, applying constant contact pressure to suppress structural deformation and power fluctuations, ensuring pump coupling stability and repeatability. This coupling method offers excellent directional control and local power focusing, avoiding the severe pump leakage and difficult alignment problems found in conventional structures. Achieve stimulated radiation in the rare earth-doped fiber core to achieve parallel amplification of multi-channel signals; The pump light source wavelength can be 980 nm, 1480 nm or 1550 nm, suitable for erbium-doped or ytterbium-doped gain mechanisms in different bands, and supports single-point or multi-point injection to improve pump uniformity. The pump injection wavelength was 980 nm, and the laser power was 800 mW. In the experiment, eight signal lights entered the corresponding fiber cores from the input ports. Within the effective gain region with a core length of approximately 25 cm, an average gain of approximately 21.2 dB was achieved for the C-band signal (1545 nm), with a gain uniformity of ±0.6 dB. This is far superior to the parallel gain deviation (up to ±1.5 dB) of the traditional solid cladding structure. The pump light coupling efficiency was measured to be approximately 84%, simplifying the pump structure while ensuring the overall efficiency of the amplifier.

[0027] The air layer, local grinding process, and pump bonding strategy used in this embodiment can be flexibly expanded to structures with more cores. Different channel requirements can be adapted by simply adjusting the air layer diameter and arrangement. This solution has strong scalability and practical value in the fields of space-division multiplexing communications, high-power multi-beam synthesis, and distributed fiber optic sensing.

[0028] The protection scope of the present invention is not limited to the above embodiment and its variations. Conventional modifications and replacements made by those skilled in the art based on the contents of this embodiment fall within the protection scope of the present invention.

Claims

1. A multi-core fiber amplifier with a large core-to-packaging ratio, characterized by The invention comprises a multi-core optical fiber composed of multiple independent rare-earth-doped cores and a cladding structure outside the multi-core optical fiber. The cladding structure is provided with at least one low-refractive-index isolation region for significantly compressing the effective cladding area for pump propagation and improving the overall pump energy capture efficiency. The ratio between the total cross-sectional area of ​​the multi-core optical fiber and the effective cladding area is not less than 0.

1.

2. The multi-core fiber amplifier with a large core-to-packet ratio according to claim 1, wherein: The low refractive index isolation zone is an annular structure with at least one circle surrounding the outside of the multi-core optical fiber; the annular structure can be in the form of any one of an air layer, a microstructured cavity band or a low refractive glass layer for reducing the cladding propagation cross section and guiding pump focusing.

3. The multi-core fiber amplifier with a large core-to-packet ratio according to claim 2, wherein: When the low-refractive-index isolation layer is the innermost air layer of the cladding, a closed glass cladding or a high-refractive-index support material having a mechanical support function is provided on the outside.

4. The multi-core fiber amplifier with a large core-to-packet ratio according to claim 3, wherein: The high refractive index supporting material is any one of zirconia-doped silica glass, phosphosilicate glass, titanium-doped silica glass or high refractive index borosilicate glass.

5. The multi-core fiber amplifier with a large core-to-packet ratio according to claim 1, wherein: The cores in the multi-core optical fiber are arranged axially symmetrically or asymmetrically, with the number of cores being no less than four. The cores are optically isolated from each other and are used for multi-channel independent signal transmission and amplification.

6. A multi-core fiber amplifier with a large core-to-packet ratio according to any one of claims 1 to 5, characterized in that: The large core-to-cladding ratio means that the ratio of the total cross-section of the fiber core to the effective optical area of ​​the cladding is not less than 0.1, where the effective area of ​​the cladding is optically isolated by setting at least one annular microstructure area with a refractive index significantly lower than that of the glass cladding. The interior of the annular microstructure area can be composed of air, an air cavity surrounded by a silica support tube, or any other low-refractive index material, and the mechanical stability of the optical fiber is maintained through structural stress regulation and an internal tube support mechanism.

7. A gain method for a multi-core optical fiber amplifier with a large core-to-packet ratio according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Reduce the effective cladding through a low-refractive-index isolation region to enhance pump capture; (2) Opening windows or etching locally on the surface of the optical fiber cladding to expose the area for pump injection; (3) Place the pump fiber in contact with the region and inject pump light into the core gain cladding through physical coupling; (4) Realize stimulated radiation in the rare earth-doped fiber core to achieve parallel amplification of multi-channel signals.

8. The gain method of a multi-core optical fiber amplifier with a large core-to-packet ratio according to claim 7, characterized in that: The pump injection area is formed into a fitting surface by grinding or laser etching. The pump optical fiber adopts a multi-mode structure. The injection path can be axial, transverse or inclined, and has local high-efficiency injection capability.

9. The gain method of a multi-core optical fiber amplifier with a large core-to-packet ratio according to claim 7, characterized in that: The pump light source wavelength can be 980 nm, 1480 nm, or 1550 nm, suitable for erbium-doped or ytterbium-doped gain mechanisms in different bands, and supports single-point or multi-point injection to improve pump uniformity.

10. The gain method of a multi-core optical fiber amplifier with a large core-to-packet ratio according to claim 7, characterized in that: The pump injection bonding section is positioned and fixed using a V-groove fixture or a nested precision fixture to provide a stable mechanical support structure. The bonding pressure is maintained within a safe range through a constant contact pressure control system to ensure steady-state contact between the pump fiber and the multi-core fiber in the injection area, while effectively avoiding structural damage and decreased coupling efficiency caused by local bending, displacement or stress concentration of the fiber.

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