Composite hollow-core optical fiber applied to two-photon microscopic imaging

Abstract

The invention discloses a composite hollow-core optical fiber applied to two-photon microscopic imaging, and relates to the technical field of optical fiber communication. The optical fiber sequentially comprises a fiber core area, an inner cladding layer and an outer cladding layer from outside to inside in the radial direction of the optical fiber, an air hole assembly is installed in the outer cladding layer, and a plurality of ginkgo leaf-shaped cladding pipes are installed in the inner cladding layer. The structure of the ginkgo leaf-shaped cladding tube is adopted, a large fiber core can be reserved to the maximum extent, light leakage is effectively prevented, low loss of a base film in the light transmission process is guaranteed under the condition that the wavelength of the near-infrared band ranges from 0.8 micrometer to 1.08 micrometers, the loss is smaller than 0.001 dB / km, dispersion is quite flat and close to 0, the nonlinear effect is lower than 0.12, and the optical fiber has the advantages of being high in optical fiber transmission efficiency, good in optical fiber transmission performance and the like. And the area of a mode field is basically greater than 1000 microns < 2 >, so that the requirements of high resolution, large view field and deep tissue penetration in the field of biomedical imaging can be met.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber communication, in particular to a composite hollow-core optical fiber applied to two-photon microscopic imaging. Background Art

[0002] Two-photon microscopy is a nonlinear optical imaging technique that allows deep, high-resolution imaging in biological tissues. This technique overcomes some of the limitations of traditional single-photon imaging techniques, such as light scattering and absorption, by absorbing two photons simultaneously to excite fluorescence. However, in order to achieve large fields of view and high-resolution imaging, special optical fibers are required to transmit the excitation light, and these fibers need to have characteristics such as low loss and high laser damage threshold.

[0003] In existing optical fiber technology, traditional solid-core optical fibers have some limitations when used for two-photon microscopy within a specific wavelength range, such as 0.8 to 1.1 microns, including light scattering, absorption, and nonlinear effects. In order to overcome these limitations, researchers have developed two new types of optical fibers: hollow-core photonic bandgap fibers and hollow-core antiresonant fibers. Hollow-core photonic bandgap fibers use the photonic bandgap effect formed by a periodic microhole structure to limit the propagation of light in the air core, and have the advantages of low loss, low dispersion, low nonlinearity, and high laser damage threshold. Hollow-core antiresonant fibers are based on the antiresonance effect and achieve low-loss transmission through a specific cladding structure design. Their advantages are a wide wavelength transmission window and insensitivity to the absorption and nonlinear effects of optical fiber materials.

[0004] However, existing hollow-core photonic bandgap fibers and hollow-core antiresonant fibers still face some challenges in practical applications. In the wavelength range of 0.8 to 1.1 microns, light loss is large during transmission, which cannot meet the needs of biomedical imaging for high resolution, large field of view, and deep tissue penetration. To this end, we propose a composite hollow-core fiber for two-photon microscopy. Summary of the invention

[0005] The purpose of the present invention is to provide a composite hollow-core optical fiber for two-photon microscopy, which can maintain extremely low limiting loss in the 0.8-1.08 μm band, concentrate energy in the fiber core, improve beam quality, and ensure ultra-low loss transmission.

[0006] To achieve the above object, the present invention provides the following technical solutions: a composite hollow-core optical fiber for two-photon microscopic imaging, which includes a core region, an inner cladding and an outer cladding in sequence from the outside to the inside along the radial direction of the optical fiber, an air hole assembly is installed in the outer cladding, a plurality of ginkgo leaf-shaped cladding tubes are installed inside the inner cladding, and the plurality of ginkgo leaf-shaped cladding tubes enclose the core region; The plurality of ginkgo leaf-shaped cladding tubes are arranged in a circle around the core region as a whole, a gap is provided between two adjacent ginkgo leaf-shaped cladding tubes, and the plurality of ginkgo leaf-shaped cladding tubes are all circumscribed with the edge of the core region; The ginkgo leaf-shaped cladding tube includes a first arc, a second arc, a third arc and a fourth arc, the first arc is tangent to the core region, the second arc and the third arc are respectively connected to two ends of the first arc, and the other ends of the second arc and the third arc are fused to the inner cladding, the fourth arc is connected between the second arc and the third arc, and the bending direction is toward the outside of the core region.

[0007] Furthermore, the air hole assembly includes three air hole layers from the outside to the inside, each air hole layer is formed by a plurality of air holes arranged equidistantly along the circumference, and the spacing between adjacent air hole layers is equal.

[0008] Furthermore, the outer cladding and the ginkgo leaf-shaped cladding tube are both made of silica glass material, and the refractive index range of the silica glass material is 1.44 μm-1.46 μm.

[0009] Furthermore, the number of the ginkgo leaf-shaped cladding tubes is set to six, and the inside of the ginkgo leaf-shaped cladding tubes and the air hole assembly are both filled with air, and the refractive index of the air is smaller than the refractive index of the silica glass material.

[0010] Furthermore, the radii of the first arc, the second arc, the third arc and the fourth arc are equal, and the radius range is between 23.8 μm and 24.4 μm.

[0011] Furthermore, the included angles between the second arc, the third arc and the first arc in the ginkgo leaf-shaped cladding tube are all 60°.

[0012] Furthermore, the tube wall thickness t of the ginkgo leaf-shaped cladding tube satisfies the anti-resonance formula: Where l represents the positive integer anti-resonance order, λ represents the operating wavelength, is the effective refractive index of the air core region, is the effective refractive index of the cladding material quartz, .

[0013] Furthermore, the tube wall thickness t of the ginkgo leaf-shaped cladding tube is set in the range of 0.78 μm-0.82 μm.

[0014] Furthermore, a perfect matching layer is arranged outside the outer cladding layer, and the thickness of the perfect matching layer is 1um-5um.

[0015] The present invention has at least the following beneficial effects: In addition to ensuring that it has the characteristics of a resonant optical fiber and a hollow-core photonic bandgap optical fiber, the present invention adopts a ginkgo leaf-shaped cladding tube structure, which can retain a larger core to the greatest extent, effectively prevent light leakage, and ensure a low base film loss during light transmission under the wavelength condition of 0.8μm-1.08μm in the near-infrared band, and the loss is less than 0.001dB / km, and the dispersion is very flat and close to 0, the nonlinear effect is less than 0.12, and the mode field area is basically greater than 1000um 2 , thus meeting the needs of the biomedical imaging field for high resolution, large field of view, and deep tissue penetration.

[0016] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional schematic diagram of the overall structure of an embodiment of the present invention; Figure 2 It is a basic model diagram of the overall structure of the embodiment of the present invention; Figure 3 is a graph showing the relationship between the fundamental mode effective refractive index and the high-order mode effective refractive index as a function of wavelength in an embodiment of the present invention; Figure 4 is a graph showing the relationship between the high-order mode limiting loss and the fundamental mode limiting loss as the wavelength changes in an embodiment of the present invention; Figure 5 Graph showing the relationship between dispersion and wavelength in an embodiment of the present invention.

[0018] Figure 6 4 is a graph showing the relationship between the nonlinear coefficient and the wavelength in an embodiment of the present invention.

[0019] Figure 7 is a graph showing the relationship between the extinction ratio and the wavelength in an embodiment of the present invention; Figure 8 Schematic cross-sectional view of a ginkgo leaf-shaped cladding tube in an embodiment of the present invention.

[0020] Reference numerals: 1. Outer cladding; 2. Air hole assembly; 3. Inner cladding; 4. Ginkgo leaf-shaped cladding tube; 41. First arc; 42. Second arc; 43. Third arc; 44. Fourth arc; 5. Fiber core region. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0022] The operating wavelength of the two-photon microscopic imaging band is between 0.8μm-1.08μm, and is used to achieve low-loss transmission, dispersion flatness and low nonlinear effects within its wavelength condition range. The present invention proposes a composite hollow-core optical fiber, which combines the advantages of hollow-core photonic bandgap fiber and hollow-core antiresonant fiber. Through the bandgap photonic crystal fiber design of the outer cladding and the hollow-core antiresonant fiber design of the inner cladding, efficient light transmission in the wavelength range of 0.8 to 1.1 microns can be achieved, thereby meeting the needs of the biomedical imaging field for high resolution, large field of view and deep tissue penetration.

[0023] See also Figure 1-Figure 8 The present invention provides a technical solution: a composite hollow-core optical fiber for two-photon microscopic imaging, which includes a core region 5, an inner cladding 3 and an outer cladding 1 in sequence from outside to inside along the radial direction of the optical fiber, an air hole assembly 2 is installed in the outer cladding 1, a plurality of ginkgo leaf-shaped cladding tubes 4 are installed inside the inner cladding 3, and the plurality of ginkgo leaf-shaped cladding tubes 4 enclose the core region 5; The plurality of ginkgo leaf-shaped cladding tubes 4 are arranged in a circle around the core region 5 as a whole, a gap is provided between two adjacent ginkgo leaf-shaped cladding tubes 4, and the plurality of ginkgo leaf-shaped cladding tubes 4 are all circumscribed with the edge of the core region 5; The ginkgo leaf-shaped cladding tube 4 includes a first arc 41, a second arc 42, a third arc 43 and a fourth arc 44. The first arc 41 is tangent to the core region 5. The second arc 42 and the third arc 43 are respectively connected to the two ends of the first arc 41, and the other ends of the second arc 42 and the third arc 43 are fused to the inner cladding 3. The fourth arc 44 is connected between the second arc 42 and the third arc 43, and the bending direction is toward the outside of the core region 5.

[0024] According to the technical solution of this embodiment, the air hole assembly 2 includes three air hole layers from the outside to the inside, each air hole layer is formed by a plurality of air holes arranged equidistantly along the circumference, and the spacing between adjacent air hole layers is equal. Introducing air holes in the outer cladding 1 can allow part of the light to escape along the pores, thereby reducing the reflection loss between the core region 5 and the outer cladding 1 and improving the transmission efficiency of the optical signal.

[0025] Furthermore, in this embodiment, the three air hole layers are defined as the first air hole layer, the second air hole layer, and the third air hole layer from the inside to the outside, wherein the spacing between adjacent air holes in the first air hole layer is d1=8.6um, the spacing between adjacent air holes in the second air hole layer is d2=11.8um, the spacing between adjacent air holes in the third air hole layer is d3=3.7um, and the distance between the first air hole layer and the inner cladding 3 is d4=4.4um.

[0026] According to the technical solution of this embodiment, the outer cladding 1 and the ginkgo leaf-shaped cladding tube 4 are both made of silica glass, and the refractive index range of the glass material is 1.44μm-1.46μm. Silica glass is a high-quality optical material with good refractive index and transparency, which is very beneficial for the transmission and collection of optical signals. The refractive index range is also suitable for the production of composite optical fibers, which can ensure that the propagation speed of the optical signal inside the fiber is the same as that outside, thereby realizing high-speed and long-distance data transmission.

[0027] According to the technical solution of this embodiment, the number of ginkgo leaf-shaped cladding tubes 4 is set to five or six, and the inside of the ginkgo leaf-shaped cladding tube 4 and the air hole assembly 2 are both filled with air, and the refractive index of air is less than the refractive index of silica glass material. The installed ginkgo leaf-shaped cladding tube 4 can adjust the optical path so that the incident light is completely absorbed after multiple reflections, refractions and scattering, thereby reducing the intensity of reflected light and improving the overall extinction ratio of the optical fiber. In addition, the design of filling the inside with air and adopting an air refractive index less than that of silica glass can also improve the propagation efficiency of visible light in the optical fiber, reduce the difference between refraction and reflection, and reduce the dispersion of the optical fiber, thereby improving the transmission performance and reliability of the optical fiber.

[0028] Furthermore, the ginkgo leaf-shaped cladding tube 4 is of axially symmetrical design, and because the fourth arc 44 is connected between the second arc 42 and the third arc 43, the pressure of the ginkgo leaf-shaped cladding tube 4 in the core region 5 can be effectively dispersed. Such a design ensures the stability of the ginkgo leaf-shaped cladding tube 4 and prevents it from twisting or deformation during use.

[0029] It should be noted that the combination of the ginkgo leaf-shaped cladding tube 4 and the air hole assembly 2 not only enhances the mechanical strength of the optical fiber, but also utilizes the anti-resonance effect. By introducing the air hole assembly 2 into the ginkgo leaf-shaped cladding tube 4, the constraint of light is strengthened, especially in the band of 920nm-960nm, the restrictive loss is further reduced (to the order of 10-5dB / km).

[0030] Furthermore, the radii of the first arc 41, the second arc 42, the third arc 43 and the fourth arc 44 are equal, and the radius range is 23.8μm-24.4μm. The equal radii of the four arcs facilitate the use of the same process steps and tools for design and preparation, which can simplify the production process and reduce costs.

[0031] Furthermore, the angle between the second arc 42, the third arc 43 and the first arc 41 of the ginkgo leaf-shaped cladding tube 4 is 60°. There is neither a large gap nor a node generated by the intersection in the middle of the ginkgo leaf shape, and the connection between the arcs is tighter, which helps to reduce the stress and deformation caused by temperature changes and enhance the stability of the ginkgo leaf-shaped cladding tube 4.

[0032] Furthermore, the wall thickness range of the ginkgo leaf-shaped cladding tube 4 is set to be between 0.78 μm and 0.82 μm, and the wall thickness range satisfies the optical fiber anti-resonance formula: Where l represents the positive integer anti-resonance order, λ represents the operating wavelength, is the effective refractive index of the air core region 5, is the effective refractive index of the cladding material quartz, .

[0033] According to the technical solution of this embodiment, a perfectly matched layer is arranged on the outside of the outer cladding 1, and the thickness of the perfectly matched layer is 1um-5um. The perfectly matched layer (PML) in the optical fiber is a special dielectric layer. By truncating the boundary setting in the FDTD region, the wave impedance of the medium is completely matched with the wave impedance of the adjacent medium. This design allows the incident wave to pass through the interface without reflection and enter the PML, thereby achieving lossless transmission of energy. The introduction of PML is mainly to solve the problem of the difference between the optical fiber model in the simulation environment and the actual optical fiber environment. By installing appropriate boundary conditions, the environmental difference between the two is effectively eliminated, making the simulation results closer to the actual situation.

[0034] The realization principle of the perfect matching layer is to install a boundary condition with the same material as the cladding and matching wave impedance on the outside of the outer cladding 1 of the optical fiber, so it can be regarded as a non-reflective absorption layer. When the light beam enters the perfect matching layer, it will not be reflected back immediately, but will gradually attenuate until it is finally absorbed. This non-reflective feature makes the perfect matching layer an ideal boundary condition in simulation analysis, especially when simulating and analyzing large mode area optical fibers, the use of the perfect matching layer can significantly improve the accuracy of the simulation results.

[0035] Next, the technical solution of the present invention is further described in conjunction with specific embodiments: like Figure 1 As shown, the thickness of the perfect matching layer is 1 μm, the radius of the core region is R1, the outer arc of the ginkgo leaf-shaped cladding tube is r1, the inner arc is r2, and the radius of the air hole is r3. The ginkgo leaf-shaped cladding tube has a wall thickness t, and COMSOL Multipysics is used for simulation: The parameters are: R1=24.4μm, r1=r2=24μm, r3=10μm, t=0.8μm, such as Figure 2-Figure 7 From the fundamental mode loss, we can see that the loss of this optical fiber can even reach 10 -5 dB / km, which is much less than the 0.2dB / km of traditional single-mode optical fiber. Secondly, in the numerical calculation of extinction ratio, multiple bands have reached more than 100, which shows that the single-mode characteristics of this invention are very good. Generally, the effective mode field area of ​​single-mode optical fiber is 100um 2 However, the effective mode field of the composite hollow core fiber has reached 1000um. 2 The above shows that this type of optical fiber can support high-power transmission. Compared with general optical fibers, the nonlinear effect of composite hollow-core optical fibers is 3 to 4 orders of magnitude lower. The nonlinear coefficient close to 0 shows the characteristics of composite hollow-core optical fibers.

[0036] In summary, in addition to ensuring that it has the characteristics of resonant fiber and hollow-core photonic bandgap fiber, the structure of the ginkgo leaf-shaped cladding tube can retain a larger core to the greatest extent, effectively prevent light leakage, and ensure low base film loss during light transmission under the wavelength conditions between 0.8μm-1.08μm in the near-infrared band, and the loss is less than 0.001dB / km, and the dispersion is very flat and close to 0, the nonlinear effect is less than 0.12, and the mode field area is basically greater than 1000um 2 .

[0037] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0038] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centered element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not intended to be the only implementation method.

[0039] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0040] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

Claims

1. A composite hollow-core optical fiber for two-photon microscopy imaging, comprising, from outside to inside along the radial direction of the optical fiber, a core region (5), an inner cladding (3) and an outer cladding (1), characterized in that: An air hole assembly (2) is installed inside the outer cladding (1), a plurality of ginkgo leaf-shaped cladding tubes (4) are installed inside the inner cladding (3), and the plurality of ginkgo leaf-shaped cladding tubes (4) together form a core region (5); The plurality of ginkgo leaf-shaped cladding tubes (4) are arranged in a circle around the fiber core region (5), a gap is provided between two adjacent ginkgo leaf-shaped cladding tubes (4), and the plurality of ginkgo leaf-shaped cladding tubes (4) are all circumscribed with the edge of the fiber core region (5); The ginkgo leaf-shaped cladding tube (4) comprises a first circular arc (41), a second circular arc (42), a third circular arc (43) and a fourth circular arc (44); the first circular arc (41) is tangent to the fiber core region (5); the second circular arc (42) and the third circular arc (43) are respectively connected to two ends of the first circular arc (41); the other ends of the second circular arc (42) and the third circular arc (43) are fused to the inner cladding (3); the fourth circular arc (44) is connected between the second circular arc (42) and the third circular arc (43), and the bending direction is toward the outside of the fiber core region (5).

2. The composite hollow-core optical fiber for two-photon microscopy according to claim 1, characterized in that: The air hole assembly (2) comprises three air hole layers in sequence from the outside to the inside, each air hole layer is formed by a plurality of air holes arranged equidistantly along the circumference, and the spacing between adjacent air hole layers is equal.

3. The composite hollow-core optical fiber for two-photon microscopy according to claim 2, characterized in that: The outer cladding (1) and the ginkgo leaf-shaped cladding tube (4) are both made of silica glass material, and the refractive index of the silica glass material ranges from 1.44 μm to 1.46 μm.

4. The composite hollow-core optical fiber for two-photon microscopy according to claim 3, characterized in that: The number of the ginkgo leaf-shaped cladding tubes (4) is set to six, and the interior of the ginkgo leaf-shaped cladding tubes (4) and the air hole assembly (2) are both filled with air, and the refractive index of the air is lower than the refractive index of the silica glass material.

5. The composite hollow-core optical fiber for two-photon microscopy according to claim 4, characterized in that: The radii of the first circular arc (41), the second circular arc (42), the third circular arc (43) and the fourth circular arc (44) are equal, and the radius range is between 23.8 μm and 24.4 μm.

6. The composite hollow-core optical fiber for two-photon microscopy according to claim 5, characterized in that: The included angles between the second circular arc (42), the third circular arc (43) and the first circular arc (41) in the ginkgo leaf-shaped cladding tube (4) are all 60°.

7. The composite hollow-core optical fiber for two-photon microscopy according to claim 6, characterized in that: The tube wall thickness t of the ginkgo leaf-shaped cladding tube (4) satisfies the anti-resonance formula: Where l represents the positive integer anti-resonance order, λ represents the operating wavelength, is the effective refractive index of the air core region (5), is the effective refractive index of the cladding material quartz, .

8. The composite hollow-core optical fiber for two-photon microscopy according to claim 7, characterized in that: The tube wall thickness t of the ginkgo leaf-shaped cladding tube (4) is set in the range of 0.78 μm-0.82 μm.

9. The composite hollow-core optical fiber for two-photon microscopy according to claim 1, characterized in that: A perfect matching layer is arranged outside the outer cladding layer (1), and the thickness of the perfect matching layer is 1 um-5 um.

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