A polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber
By doping rare earth ions in the fiber core area and designing an anti-resonant cladding structure, the problems of mode field instability and poor anti-resonance effects of traditional fibers are solved, and high-power, linear polarization output and high-efficiency laser conversion are achieved.
Patent Information
- Application Number
- CN202310048073.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-01-31
- Publication Date
- 2025-04-29
- Estimated Expiration
- 2043-01-31
AI Technical Summary
The mode field of traditional core-packed optical fibers is unstable in the working state of high-power lasers, making it difficult to achieve high-power and linear polarization output. Moreover, the anti-resonance effect of the solid core anti-resonance fiber is affected by the doping of rare earth ions, and the birefringence coefficient is reduced.
A large-mode field solid-core anti-resonant active single-mode fiber is designed. By doping rare earth ions in the core area and setting capillaries and solid-core quartz rods that meet the anti-resonance conditions in the cladding area, the high birefringence coefficient and core pump structure of the large-mode field area optical fiber are realized.
It realizes high birefringence coefficient and high-efficiency pump laser conversion under large-mode field area conditions, improves laser conversion efficiency and mode stability, and is suitable for high-power fiber laser applications.
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Figure CN116165739B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of high-power optical fiber lasers, and in particular to a polarization-maintaining large-mode-field solid-core anti-resonant active single-mode optical fiber. Background Art
[0002] High-power fiber lasers have gradually become the mainstream light source in industrial processing, military defense, and basic scientific research due to their advantages such as high electro-optical conversion efficiency, good beam quality, compact structure, and easy thermal management. However, some specific application fields, such as lidar, remote sensing, and nonlinear optical frequency conversion, often require high-power lasers to have linear polarization working characteristics at the same time to improve the coherent detection signal-to-noise ratio, achieve high-precision and long-distance measurement of physical quantities, or high-efficiency wavelength conversion. Therefore, it is often necessary to use polarization-maintaining large mode field fiber to achieve high-power, linearly polarized output of fiber lasers. However, the traditional core-clad structure fiber based on the principle of total internal reflection is limited by the refractive index modulation level of the quartz fiber glass matrix, and the core mode field area is difficult to effectively increase. Taking commercial polarization-maintaining active double-clad fiber as an example, its core numerical aperture is 0.06, and the core diameter is 25-30μm, all of which are operated in a few-mode state. The mode instability effect under high-power laser working conditions seriously restricts the laser performance. In recent years, a variety of new polarization-maintaining large mode field fiber structures have been developed. Among them, photonic crystal fiber has shown advantages in large-mode field fiber applications due to its non-cutoff single-mode transmission characteristics. However, due to its complex structural design, it often has high requirements on the manufacturing process, and low-loss welding of optical fibers is difficult, which leads to great restrictions on its actual application and promotion.
[0003] As a new type of solid core microstructure fiber, solid core antiresonant fiber has a more streamlined microstructure cladding. Through reasonable cladding structure design and parameter design, it can achieve large mode area single-mode laser transmission, and the solid core fiber structure is convenient for fiber fusion and all-fiber system integration. However, the regulation of the refractive index of the glass matrix by the doping of rare earth ions in the core area leads to the failure of the antiresonance effect and the reduction of the birefringence coefficient of the large mode field fiber. These are still the key problems that need to be solved in the development of polarization-maintaining large mode field active fiber based on solid core antiresonant structure. Summary of the invention
[0004] The present invention provides a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber. The present invention obtains a large mode field area single-mode optical fiber based on an anti-resonant structure, utilizes the mode coupling characteristic to realize a high birefringence coefficient of the large mode field area optical fiber, and realizes a core pumping structure of the large mode field optical fiber by regulating the refractive index of the active core region, which is used for high-efficiency laser conversion, as described below:
[0005] A polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber, the optical fiber comprising: an active core region, a cladding region and an optical fiber protective layer;
[0006] The active core region is a rare earth ion doped region, the cladding region includes an inner cladding, an outer cladding and a passive background material region, the inner cladding is composed of a capillary having a thickness satisfying anti-resonance conditions and a first solid quartz rod inside the capillary;
[0007] The outer cladding surrounds the inner cladding and the core, and is composed of a capillary with a thickness that meets the anti-resonance condition and a second solid quartz rod inside the capillary; the inner cladding capillary includes two high-refractive-index capillaries and four low-refractive-index capillaries arranged at an angle of 180°; the first and second solid quartz rods both belong to the passive background material area.
[0008] Among them, at the signal laser wavelength, the refractive index conditions of different components inside the optical fiber are:
[0009] The refractive index of the two high-refractive-index capillaries in the inner cladding, which are arranged at an angle of 180°, is greater than the refractive index of the low-refractive-index capillaries in the inner cladding, and greater than the refractive index of the active core region;
[0010] The refractive index of the inner cladding low-refractive-index capillary is equal to the refractive index of the outer cladding capillary, and the refractive index of the active core region is equal to the refractive index of the passive background material region;
[0011] In the pump laser band, the refractive index of the active core region is greater than the refractive index of the passive background material region.
[0012] Furthermore, the components with different refractive indices inside the optical fiber are quartz-based glass materials with different compositions.
[0013] Among them, all capillaries have equal wall thickness, and the thickness meets the anti-resonance condition; all outer cladding capillaries have equal inner diameter and refractive index, and the ratio of inner diameter to core diameter is in the range of 0.6 to 0.8; the inner cladding low refractive index capillaries have equal inner diameter and refractive index, and the ratio of inner diameter to core diameter is in the range of 0.3 to 0.4; the inner cladding high refractive index capillaries have equal inner diameter and refractive index, and the ratio of inner diameter to core diameter is in the range of 0.3 to 0.5.
[0014] Furthermore, the centers of all the inner cladding capillary tubes are located on the same circumference, and the centers of all the outer cladding capillary tubes are located on the same circumference.
[0015] Wherein, the active core region is tangent to the outer walls of two high refractive index capillaries.
[0016] The beneficial effects of the technical solution provided by the present invention are:
[0017] 1. The present invention proposes a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber. Under the condition of large mode field area, it uses the anti-resonance principle to achieve low-loss transmission of the fundamental mode, and at the same time, it uses the resonance coupling effect to connect the core LP 01The y mode and the resonant modes on the two high-refractive-index capillaries at an angle of 180° on the inner cladding undergo strong mode coupling, greatly increasing the birefringence coefficient of the large-mode-area optical fiber.
[0018] 2. The present invention proposes a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber, in which different components of quartz-based glass materials are used in the active core region and the passive background material region respectively; in the target laser band, the refractive index of the active core region is the same as that of the passive background material region to meet the basic conditions of anti-resonance and realize low-loss transmission of the fundamental mode; in the pump laser band, the refractive index of the active core region is greater than that of the passive background material region to ensure that the pump laser is transmitted in the active core region by total internal reflection, thereby improving the utilization rate of the pump laser and the laser conversion efficiency;
[0019] 3. The polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber proposed in the present invention has a unique double-cladding structure, in which different high-order modes can be coupled with different cladding modes, and a high high-order mode loss can still be guaranteed when the mode field area is large, thereby realizing large mode field area single-mode transmission of the optical fiber;
[0020] 4. The polarization-maintaining large-mode-field solid-core anti-resonant active single-mode optical fiber proposed in the present invention can be prepared using a stacking-drawing method, has a simple structure, is easy to implement, and has low nonlinear effects and a high laser damage threshold, and is suitable for high-power fiber laser applications. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 It is a schematic diagram of the cross-sectional structure of a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber;
[0022] Figure 2 It is a schematic diagram of the refractive index curves of the passive background material region and the active core region doped with rare earth ions in the 0.9-1.1μm band of the polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber;
[0023] Figure 3 It is a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber LP 01 x mode, the resonant mode existing in the inner cladding on two high refractive index capillaries arranged at an angle of 180°, and the LP 01 Schematic diagram of the coupling between the y mode and the resonant mode;
[0024] Figure 4 Schematic diagram of the birefringence coefficient of the polarization-maintaining large mode field solid core anti-resonant active single-mode fiber near the 1.064μm target laser band;
[0025] Figure 5 Schematic diagram of the coupling between four high-order modes of polarization-maintaining large mode field solid core anti-resonant active single-mode fiber and different cladding modes;
[0026] Figure 6 Schematic diagram of the limiting loss of two fundamental modes and four higher-order modes of the polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber;
[0027] Figure 7 Schematic diagram of the representative transmission mode of the polarization-maintaining large mode area solid-core anti-resonant active single-mode fiber in the 0.976μm pump laser band.
[0028] In the accompanying drawings, the components represented by the reference numerals are listed as follows:
[0029] 1: Active fiber core area; 2: Passive background material area;
[0030] 3: Optical fiber protective layer; 4: Outer cladding capillary;
[0031] 5: Inner cladding capillary with high refractive index; 6: Inner cladding capillary with low refractive index. DETAILED DESCRIPTION
[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.
[0033] Example 1
[0034] A polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber, see Figure 1 The optical fiber comprises: an active core region 1, a cladding region and an optical fiber protective layer 3; the active core region 1 is a rare earth ion doped region, the cladding region comprises: an inner cladding, an outer cladding and a passive background material region 2, the inner cladding is composed of a capillary with a thickness that meets the anti-resonance condition and a solid quartz rod inside the capillary; the inner cladding capillary comprises two high refractive index capillaries 5 and a low refractive index capillary 6 that are arranged at an angle of 180°; the outer cladding surrounds the inner cladding and the core, and is composed of a capillary 4 with a thickness that meets the anti-resonance condition and a solid quartz rod inside the capillary; the solid quartz rods all belong to the passive background material region.
[0035] Furthermore, at the signal laser wavelength, the refractive index conditions of different components inside the optical fiber are: the inner cladding is arranged with two high-refractive-index capillaries at an angle of 180° > the inner cladding low-refractive-index capillary = the outer cladding capillary > the active core region = the passive background material region; at the pump laser band, the refractive index of the active core region > the refractive index of the passive background material region.
[0036] Furthermore, the components with different refractive indices inside the optical fiber are quartz-based glass materials with different compositions.
[0037] Furthermore, all capillaries have equal wall thickness, and the thickness meets the anti-resonance condition; all outer cladding capillaries have equal inner diameters and refractive indices, and the ratio of inner diameter to core diameter is in the range of 0.6 to 0.8; inner cladding low-refractive-index capillaries have equal inner diameters and refractive indices, and the ratio of inner diameter to core diameter is in the range of 0.3 to 0.4; inner cladding high-refractive-index capillaries have equal inner diameters and refractive indices, and the ratio of inner diameter to core diameter is in the range of 0.3 to 0.5.
[0038] Furthermore, the active core region 1 and the inner cladding are tangent to the outer walls of two high refractive index capillaries which are arranged at an angle of 180°.
[0039] Furthermore, the centers of all the inner cladding capillary tubes are located on the same circumference, and the centers of all the outer cladding capillary tubes are located on the same circumference.
[0040] Example 2
[0041] Figure 1 This is a schematic diagram of the cross-sectional structure of a polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber. Figure 1 In the figure, the inner diameter of the active core region 1 is d core =72.0μm, surrounded by a passive background material region 2, the outermost layer is an optical fiber protective layer 3; the inner diameter of the optical fiber outer cladding capillary 4 is d1=61.5μm; the inner diameter of the two high refractive index capillaries 5 set at an angle of 180° in the optical fiber inner cladding is d2=30.8μm, and the inner diameter of the low refractive index capillary 6 is d3=18.5μm; the thickness of all capillaries is t=0.9μm; the gap between the optical fiber outer cladding capillary 4 and the two high refractive index capillaries 5 set at an angle of 180° in the optical fiber inner cladding is T1=1μm, and the gap between the optical fiber outer cladding capillary 4 and the optical fiber inner cladding low refractive index capillary 6 is T2=6μm; the components with different refractive indices inside the optical fiber are quartz-based glass materials with different components; the active core region 1 is tangent to the outer wall of the inner cladding high refractive index capillary 5 set at an angle of 180°.
[0042] The development scheme of the polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber proposed in the embodiment of the present invention is not limited to the optical fiber structure design method and the type of solid core anti-resonant optical fiber adopted in this embodiment.
[0043] Figure 1 The polarization-maintaining large mode field solid core antiresonant active single-mode optical fiber shown has a double-cladding structural design, in which the centers of all outer cladding capillaries are located on the same circumference, and the centers of all inner cladding capillaries are located on the same circumference; the thickness of all cladding capillaries is the same; the inner diameters of all outer cladding capillaries are the same, and the inner diameters and refractive indices of the inner cladding capillaries are different.
[0044] Figure 2It is a schematic diagram of the refractive index curve of the passive background material area and the active core area of the optical fiber in the 0.9-1.1μm band. In the 1.064μm band, the refractive index conditions of different components inside the optical fiber are: active core area = passive background material area = 1.45; in the 0.976μm band, the refractive index of the active core area is greater than the refractive index of the passive background material area.
[0045] In addition, at the 1.064μm band, the refractive index conditions of different components inside the optical fiber are: two high-refractive-index capillaries in the inner cladding = 1.88; low-refractive-index capillaries in the inner cladding = capillaries in the outer cladding = 1.48; active core region = passive background material region = 1.45.
[0046] Figure 3 For polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber in the 1.064μm band LP 01 x mode, the resonant mode on the inner cladding high refractive index capillary, and the LP 01 Schematic diagram of the coupling between the y mode and the resonant mode. The antiresonant wavelength of the solid core antiresonant fiber is determined by equation (1):
[0047]
[0048] Among them, n s2 is the refractive index of the outer cladding capillary and the inner cladding low-refractive-index capillary material, n s1 is the refractive index of the material in the active core region, m is an arbitrary positive integer, and t is the capillary thickness.
[0049] According to the thickness t of the outer cladding capillary and the inner cladding low refractive index capillary in this embodiment, the working wavelength of the solid core antiresonant optical fiber can be limited to around 1.064μm to achieve low-loss transmission of the target signal laser fundamental mode. The existence of two high refractive index capillaries arranged at an angle of 180° in the inner cladding makes the core LP 01 The y mode is strongly coupled to the resonant mode on the high refractive index capillary, thereby increasing the LP 01 The y-mode confinement loss increases the birefringence coefficient of the optical fiber. 01 The effective mode area of the x-mode is greater than 3000 μm 2 .
[0050] Figure 4 Schematic diagram of the birefringence distribution of solid core antiresonant fiber near 1.064μm. Under large mode area conditions, the birefringence can still reach 10 -5 Magnitude.
[0051] Figure 5 Schematic diagram of the coupling between four high-order modes of a solid-core antiresonant optical fiber at 1.064 μm and different cladding modes.
[0052] Figure 6 This is a schematic diagram of the loss curves of the fundamental mode and high-order mode of solid-core antiresonant optical fiber near 1.064μm. Thanks to the antiresonance principle, LP 01 The x-mode limiting loss is the lowest and less than 0.1dB / m, LP 01 The y mode is coupled with the resonant mode on the inner cladding high refractive index capillary, which increases its confinement loss. Figure 5 The coupling effect shown causes the limiting loss to be greater than 10dB / m, indicating that the optical fiber can achieve single-mode operation.
[0053] Figure 7 This is a representative mode of the 0.976μm pump laser propagating in the active core region of a solid-core antiresonant fiber. Figure 2 Due to the existence of the medium refractive index difference, that is, the refractive index of the active fiber core region is greater than that of the passive background material region, the 0.976μm pump laser can be transmitted in the active fiber core region in the form of total internal reflection, thereby achieving a significant improvement in the pumping efficiency and laser conversion efficiency.
[0054] In summary, the polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber proposed in the embodiment of the present invention has a large mode field area (>3000μm 2 ) can still achieve a high-order mode transmission loss greater than 10dB / m, and has a 10 -5 The solid-core anti-resonant active single-mode optical fiber proposed in the embodiment of the present invention has the advantages of simple process, stable performance, and flexible structural design. In addition, the embodiment of the present invention realizes the total internal reflection transmission of pump light in the active core region by adjusting the refractive index of the optical fiber glass matrix, improves the pump absorption and laser conversion efficiency, and has important application value in the field of high-power optical fiber laser technology.
[0055] Unless otherwise specified, the models of the components in the embodiments of the present invention are not limited, and any device that can perform the above functions may be used.
[0056] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.
[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber, characterized in that: The optical fiber comprises: an active core region, a cladding region and an optical fiber protective layer; The active core region is a rare earth ion doped region, the cladding region includes an inner cladding, an outer cladding and a passive background material region, the inner cladding is composed of a capillary having a thickness satisfying anti-resonance conditions and a first solid quartz rod inside the capillary; The outer cladding surrounds the inner cladding and the core, and is composed of a capillary tube with a thickness that meets the anti-resonance condition and a second solid quartz rod inside the capillary tube; the inner cladding capillary tube includes two high refractive index capillaries and four low refractive index capillaries arranged at an angle of 180°; the first and second solid quartz rods both belong to the passive background material area; Among them, at the signal laser wavelength, the refractive index conditions of different components inside the optical fiber are: The refractive index of the two high-refractive-index capillaries in the inner cladding, which are arranged at an angle of 180°, is greater than the refractive index of the low-refractive-index capillaries in the inner cladding, and greater than the refractive index of the active core region; The refractive index of the inner cladding low-refractive-index capillary is equal to the refractive index of the outer cladding capillary, and the refractive index of the active core region is equal to the refractive index of the passive background material region; In the pump laser band, the refractive index of the active core region is greater than the refractive index of the passive background material region.
2. The polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber according to claim 1, characterized in that: The components with different refractive indices inside the optical fiber are silica-based glass materials with different compositions.
3. The polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber according to claim 1, characterized in that: All capillaries have the same wall thickness, and the thickness meets the anti-resonance condition; all outer cladding capillaries have the same inner diameter and refractive index, and the ratio of the inner diameter to the core diameter is in the range of 0.6 to 0.8; the inner cladding low-refractive-index capillaries have the same inner diameter and refractive index, and the ratio of the inner diameter to the core diameter is in the range of 0.3 to 0.4; the inner cladding high-refractive-index capillaries have the same inner diameter and refractive index, and the ratio of the inner diameter to the core diameter is in the range of 0.3 to 0.
5.
4. The polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber according to claim 1, characterized in that: The centers of all inner cladding capillaries are located on the same circumference, and the centers of all outer cladding capillaries are located on the same circumference.
5. The polarization-maintaining large mode field solid core anti-resonant active single-mode optical fiber according to claim 1, characterized in that: The active fiber core region is tangent to the outer walls of two high refractive index capillaries.