Heterogeneous photonic crystal fibers for visible and near-infrared wavelengths

Abstract

The present invention discloses heterogeneous photonic crystal fibers in visible light and near-infrared bands, and relates to the field of optical fiber communication technology. The present invention includes an outer cladding, a left middle layer, a right middle layer, a left core region and a right core region, and a first air hole matrix is ​​arranged inside the outer cladding. The present invention expands the working bandwidth of a single photonic crystal fiber. For the right core region working at a shorter wavelength, its optimal working bandwidth range covers the complete visible light band, which can meet the transmission requirements of optical fibers for high-energy bands. For the left core region working at a longer wavelength, its optimal working bandwidth covers the near-infrared band, including the most commonly used 1.55μm wavelength in communication-related services. This working bandwidth can well meet the needs of communication services, the transmission of near-infrared band optical signals that are safe for human eyes, and the research requirements of nonlinear optics in the near-infrared band.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber communication, in particular to heterogeneous photonic crystal optical fibers in visible light and near infrared bands. Background Art

[0002] Photonic crystal fiber is a microstructured optical fiber based on silica glass. Photonic crystal fiber has a unique structure. Its cladding is composed of periodically arranged air holes, and the core is composed of quartz or air holes, so that light can be effectively transmitted in the core. Due to its flexible structural design and excellent optical properties, such as non-cutoff single-mode transmission, high birefringence, high nonlinearity, low loss, controllable dispersion characteristics and effective mode area, photonic crystal fiber has attracted widespread attention in recent years. The flexibility of its structural design enables photonic crystal fiber to be optimized according to different needs, which makes it widely used in high-energy optical signal transmission, optical fiber communication and near-infrared band research for human eye safety.

[0003] For complex optical signals that are non-uniformly distributed on the cross section, the modulation and transmission process sometimes requires differentiated processing in different directions. High-birefringence photonic crystal fiber is a type of optical fiber with different optical properties in different directions. Due to its high birefringence characteristics, it can independently process optical signals in different directions, thereby achieving highly controlled optical signal transmission and modulation. This characteristic gives high-birefringence photonic crystal fiber a significant advantage in processing and transmitting complex optical signals.

[0004] Multi-core photonic crystal fiber forms multiple cores by introducing multiple defect states in the photonic crystal, and each core can maintain single-mode transmission. The structural mechanism of multi-core photonic crystal fiber is similar to that of single-core photonic crystal fiber. A theoretical equivalent cladding structure is formed on the optical fiber quartz substrate by multiple circles of air holes, and the quartz state is maintained in the central core area to form a multi-core structure composed of multiple cores and outer circle air holes. However, existing multi-core photonic crystal fibers mostly use inter-core mode coupling to transmit optical signals of the same wavelength in multiple cores, and are mostly used in the field of optical fiber splitters. Therefore, existing multi-core photonic crystal fibers do not have the characteristics of expanding the working bandwidth of a single optical fiber. Its multiple cores cannot work independently at different bandwidths, and their functions are relatively single. Summary of the invention

[0005] The purpose of the present invention is to provide heterogeneous photonic crystal fibers in the visible light and near-infrared bands, which are used to solve the problem that multiple fiber cores cannot work independently at different bandwidths and have relatively single functions.

[0006] To achieve the above object, the present invention provides the following technical solution: a heterogeneous photonic crystal fiber in the visible light and near-infrared bands, comprising an outer cladding, a left middle layer, a right middle layer, a left core region and a right core region, wherein a first air hole matrix is ​​arranged inside the outer cladding, the left middle layer and the right middle layer are both arranged inside the first air hole matrix, and first elliptical air holes are arranged inside the outer cladding on both upper and lower sides of the first air hole matrix for filling the gaps;

[0007] The left middle layer includes a second elliptical air hole, a third elliptical air hole and a first circular air hole, and the left core region is surrounded by the second elliptical air hole, the third elliptical air hole and the first circular air hole. The second elliptical air hole is arranged at the top and bottom of the left middle layer, the third elliptical air hole is arranged between the second elliptical air hole and the left core region, and the first circular air hole is arranged on both sides of the left middle layer and close to the first air hole matrix;

[0008] The right middle layer includes a fourth elliptical air hole, a second air hole matrix, a fifth elliptical air hole, a sixth elliptical air hole and a seventh elliptical air hole. The right core region is located inside the second air hole matrix and is surrounded by the sixth elliptical air hole and the seventh elliptical air hole. The fourth elliptical air hole is arranged at the four corners of the second air hole matrix to fill the gaps. The fifth elliptical air hole is located on the upper and lower sides of the right core region, and the sixth elliptical air hole is located between the right core region and the fifth elliptical air hole. The seventh elliptical air hole is located on both sides of the right core region.

[0009] Furthermore, a perfect matching layer is arranged on the outer side of the outer cladding.

[0010] Further, the first air hole matrix is ​​composed of a plurality of elliptical air holes, and the first air hole matrix is ​​configured as a hexagonal shape as a whole;

[0011] The elliptical pores arranged in the first air hole matrix have a center distance of 0.7 μm between two adjacent pores in the horizontal direction and a center distance of 1 μm between two adjacent rows of pores in the vertical direction. The major axis range of the elliptical pores is 0.8 μm-1 μm, and the minor axis range is 0.5 μm-0.7 μm.

[0012] Furthermore, the working bandwidth of the left core region is 1.55 μm-2.5 μm, and the working bandwidth of the right core region is 0.45 μm-1 μm.

[0013] Furthermore, the outer cladding, the left middle layer, the right middle layer, the left core region and the right core region are all made of silica material, and the refractive index ranges from 1.40 to 1.45.

[0014] Further, the first elliptical air hole, the first air hole matrix, the second elliptical air hole, the first circular air hole, the second air hole matrix, the fourth elliptical air hole, the fifth elliptical air hole, the sixth elliptical air hole 9 and the seventh elliptical air hole are all filled with air having a refractive index of 1.0;

[0015] The third elliptical pore is filled with anhydrous ethanol having a refractive index of 1.33-1.36.

[0016] Furthermore, the number of the second elliptical pores is set to four, the number of the fifth elliptical pores is set to two, and the major axes of the second elliptical pores and the fifth elliptical pores are both 1.2 μm-1.4 μm, and the minor axes are both 0.5 μm-0.8 μm.

[0017] Further, the number of the third elliptical pore, the sixth elliptical pore and the seventh elliptical pore is set to two, and the major axis of the third elliptical pore, the sixth elliptical pore and the seventh elliptical pore is set to 1.8 μm-2.2 μm, and the minor axis is set to 0.6 μm-1.0 μm;

[0018] There are four fourth elliptical pores, and the major axes of the four fourth elliptical pores are all 1.2 μm, and the minor axes are all 0.35 μm;

[0019] The number of the first elliptical pores is two, and the major axes of the two first elliptical pores are both 8 μm, and the minor axes are both 2 μm.

[0020] Furthermore, the second air hole matrix is ​​formed by a plurality of circular air hole arrays, the overall shape of the second air hole matrix is ​​a hexagon, the fifth elliptical pore, the sixth elliptical pore and the seventh elliptical pore are all located inside the second air hole matrix, and the radius range of the circular pores of the second air hole matrix and the first circular pores are both set to 0.2μm-0.4μm.

[0021] Furthermore, the center point of the left core region is taken as the origin, the direction of the line connecting the center points of the left core region and the right core region is the x-axis direction, and the direction perpendicular to the x-axis direction is set as the y-axis direction. The left middle layer and the right middle layer are both arranged in a mirror-symmetrical manner with the x-axis as the symmetry axis;

[0022] The center distance between the two third elliptical air holes symmetrically arranged in the left core area is 2.8 μm, and the center distance between the elliptical air holes in the first air hole matrix on both sides of the left core area is 2.1 μm;

[0023] The center distance between the two sixth elliptical air holes symmetrically arranged in the upper and lower parts of the right core region is 1.5 μm, and the center distance between the two seventh elliptical air holes on both sides of the right core region is 3 μm.

[0024] The present invention has at least the following beneficial effects:

[0025] 1. The two cores of the heterogeneous dual-core photonic crystal fiber designed in the present invention can work in different bands respectively, and avoid mutual interference through the horizontal hole structure design, while the multi-core photonic crystal fiber of traditional technology can only transmit optical signals of the same wavelength at the same time.

[0026] 2. The technical solution of the present invention expands the working bandwidth of a single photonic crystal fiber. For the right core region working at a shorter wavelength in the present invention, the optimal working bandwidth is 0.45μm to 1μm, and this bandwidth range covers the complete visible light band, which can meet the transmission requirements of optical fiber for high-energy bands; for the left core region working at a longer wavelength, the optimal working bandwidth is 1.55μm to 2.5μm, and this bandwidth range mainly covers the near-infrared band, including the 1.55μm wavelength most commonly used in communication-related services. This working bandwidth can well meet the needs of communication services, the transmission of near-infrared band optical signals that are safe for human eyes, and the research needs of nonlinear optics in the near-infrared band.

[0027] 3. The two fiber cores in the present invention can work completely independently at their respective optimal working bandwidths without generating coupling and crosstalk, and the two fiber cores have good single-mode characteristics at all working bandwidths, which can perfectly meet relevant business requirements.

[0028] 4. The two fiber cores in the present invention have excellent high birefringence characteristics in the entire working bandwidth, and their high birefringence coefficient is 1 to 2 orders of magnitude higher than that of ordinary photonic crystal fibers, thereby having excellent performance that surpasses existing optical fibers in long-distance transmission and short-distance high-precision optical signal transmission, and can meet the needs of relevant practitioners for more precise regulation of optical signals.

[0029] 5. The two fiber cores of the present invention have extremely low non-restrictive losses in all working bandwidths, and their values ​​can fully meet the loss values ​​required by the industry standards widely used internationally.

[0030] 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

[0031] Figure 1 It is a cross-sectional schematic diagram of the overall structure of the present invention;

[0032] Figure 2 It is a schematic diagram of the electric field mode distribution in the y-polarization state when the right core region of the present invention works at a wavelength of 0.45 μm;

[0033] Figure 3 It is a schematic diagram of the electric field mode distribution in the y-polarization state when the left core region of the present invention works at a wavelength of 1.55 μm;

[0034] Figure 4It is a schematic diagram of the distribution of the electric field mode of the y-polarization state in the X direction when the right core region of the present invention works at a wavelength of 0.45 μm;

[0035] Figure 5 It is a schematic diagram of the distribution of the electric field mode of the y-polarization state in the X direction when the left core region of the present invention works at a wavelength of 2.5 μm;

[0036] Figure 6 Schematic diagram of the variation of the birefringence coefficient of the right core region with wavelength in the present invention;

[0037] Figure 7 Schematic diagram of the birefringence coefficient of the left core region of the present invention varying with wavelength;

[0038] Figure 8 It is a schematic diagram of the variation of the limiting loss of the right core region with the wavelength of the present invention;

[0039] Fig. 9 It is a schematic diagram of the variation of the limiting loss of the left core region with the wavelength of the present invention;

[0040] Fig.10 It is a schematic diagram of the variation of the effective mode field area of ​​the right core region with the wavelength of the present invention;

[0041] Fig.11 It is a schematic diagram of the variation of the effective mode field area of ​​the left core region with the wavelength of the present invention.

[0042] Reference numerals:

[0043] 1. Outer cladding; 2. First air hole matrix; 3. Second elliptical air hole; 4. Third elliptical air hole; 5. First circular air hole; 6. Left core region; 7. Fourth elliptical air hole; 8. Fifth elliptical air hole; 9. Sixth elliptical air hole; 10. Seventh elliptical air hole; 11. Second air hole matrix; 12. Right core region; 13. First elliptical air hole; 14. Perfect matching layer. DETAILED DESCRIPTION

[0044] 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.

[0045] The present invention proposes heterogeneous photonic crystal fibers for visible light and near-infrared bands. By innovatively introducing two different structural defects into the photonic crystal, the two cores of the dual-core photonic crystal fiber can work in different bands while avoiding mode coupling and crosstalk. At the same time, through the design and adjustment of the photonic crystal structure, the two cores of the heterogeneous dual-core photonic crystal fiber can have very low restrictive loss and high birefringence at their own working wavelengths. The fiber design is multifunctional, simple in structure and easy to implement, while achieving full coverage of commonly used bands from visible light to near-infrared, and can be applied to the fields of high-energy transmission of light, optical communication, nonlinear optical research, and near-infrared band research for human eye safety.

[0046] See also Figure 1-Figure 11 The present invention provides a technical solution: a heterogeneous photonic crystal fiber in the visible light and near-infrared bands, comprising an outer cladding 1, a left middle layer, a right middle layer, a left core region 6 and a right core region 12, a first air hole matrix 2 is arranged inside the outer cladding 1, the left middle layer and the right middle layer are both arranged inside the first air hole matrix 2, and first elliptical air holes 13 are arranged inside the outer cladding 1 on both upper and lower sides of the first air hole matrix 2 to fill the gaps;

[0047] The left middle layer includes a second elliptical air hole 3, a third elliptical air hole 4 and a first circular air hole 5, and the left core region 6 is surrounded by the second elliptical air hole 3, the third elliptical air hole 4 and the first circular air hole 5. The second elliptical air hole 3 is arranged at the top and bottom of the left middle layer, the third elliptical air hole 4 is arranged between the second elliptical air hole 3 and the left core region 6, and the first circular air hole 5 is arranged on both sides of the left middle layer and close to the first air hole matrix 2;

[0048] The right middle layer includes a fourth elliptical air hole 7, a second air hole matrix 11, a fifth elliptical air hole 8, a sixth elliptical air hole 9 and a seventh elliptical air hole 10. The right core region 12 is located inside the second air hole matrix 11 and is surrounded by the sixth elliptical air hole 9 and the seventh elliptical air hole 10. The fourth elliptical air hole 7 is arranged at the four corners of the second air hole matrix 11 to fill the gaps. The fifth elliptical air hole 8 is located on the upper and lower sides of the right core region 12, and the sixth elliptical air hole 9 is located between the right core region 12 and the fifth elliptical air hole 8. The seventh elliptical air hole 10 is located on the left and right sides of the right core region 12.

[0049] According to the technical solution of this embodiment, the center point of the left core area 6 is taken as the origin, the direction of the line connecting the center points of the left core area 6 and the right core area 12 is the x-axis direction, and the y-axis direction is perpendicular to the x-axis direction. The overall structure of the optical fiber takes the x-axis as the axis of symmetry and is mirror-symmetrical, and the left middle layer and the right middle layer also take the x-axis as the axis of symmetry and are arranged in a mirror-symmetrical manner.

[0050] According to the technical solution of this embodiment, the radius of the outer cladding 1 is set to 10 μm, and a perfect matching layer 14 is provided on the outside of the outer cladding 1. The perfect matching layer 14 is formed by setting a special dielectric layer at the truncation boundary of the calculation area, and setting the wave impedance of the dielectric layer to completely match the wave impedance of the adjacent dielectric, so that the incident wave can pass through the interface without reflection and enter the perfect matching layer 14, thereby avoiding the influence of the reflected wave on the calculation result.

[0051] Furthermore, the outer cladding 1, the left middle layer, the right middle layer, the left core region 6 and the right core region 12 are all made of silica, and the refractive index range can be set to 1.40-1.45. For the technical solution of this embodiment, the refractive index is set to 1.44. Since the band gap of silica is located near the core, the transmission direction of photons can be effectively limited, and the total reflection performance of the photonic crystal fiber can be improved. In addition, due to the band gap structure of silica, photons cannot directly transition from the core to the surrounding medium, reducing the scattering and absorption loss of the optical signal between the core and the cladding, thereby reducing the overall loss and improving its transmission performance.

[0052] Further, the first elliptical air hole 13, the first air hole matrix 2, the second elliptical air hole 3, the first circular air hole 5, the second air hole matrix 11, the fourth elliptical air hole 7, the fifth elliptical air hole 8, the sixth elliptical air hole 9 and the seventh elliptical air hole 10 are all filled with air with a refractive index of 1.0. In this case, the refractive index of air is relatively small, and the binding effect on light is weak, which is conducive to the transmission of photons inside the fiber core;

[0053] The third elliptical air hole 4 is filled with anhydrous ethanol with a refractive index of 1.33-1.36. The refractive index of anhydrous ethanol is between that of air and silica, and has a moderate light binding effect, which can not only ensure the transmission of photons inside the fiber core, but also introduce a material with a refractive index different from that of silica into the band gap to increase the high birefringence coefficient.

[0054] According to the technical solution of this embodiment, the first air hole matrix 2 is composed of a plurality of elliptical air holes, and the first air hole matrix 2 is configured as a hexagonal shape as a whole. Such a design can effectively control the propagation direction and mode of light, while ensuring that the number of band gaps of the core and the intermediate layer in each direction is roughly the same as much as possible;

[0055] The elliptical air holes arranged in the first air hole matrix 2 have a center distance of 0.7 μm between two adjacent air holes in the horizontal direction and a center distance of 1 μm between two adjacent rows of air holes in the vertical direction, which can effectively reduce the coupling between the air holes, avoid energy loss during light transmission, and improve the transmission efficiency of the optical fiber. The major axis range of the elliptical air holes is 0.8 μm-1 μm, and the minor axis range is 0.5 μm-0.7 μm. Using an appropriate air hole size can make the light produce obvious reflection between the air holes, enhance the total reflection effect, and improve the transmission efficiency.

[0056] Furthermore, the number of the second elliptical holes 3 is set to four, and the number of the fifth elliptical holes 8 is set to two. The second elliptical holes 3 and the fifth elliptical holes 8 are arranged in a mirror-symmetrical manner with the x-axis as the symmetry axis, and the long axes of the second elliptical holes 3 and the fifth elliptical holes 8 are both 1.2μm-1.4μm, and the short axes are both 0.5μm-0.8μm, which is convenient for further optimizing the transmission path of photons, reducing the distortion and attenuation of optical signals, and enhancing the stability of the system.

[0057] Furthermore, the number of the third elliptical holes 4, the sixth elliptical holes 9 and the seventh elliptical holes 10 is set to two, and the major axes of the third elliptical holes 4, the sixth elliptical holes 9 and the seventh elliptical holes 10 are set to 1.8μm-2.2μm, and the minor axes are set to 0.6μm-1.0μm; the number of the fourth elliptical holes 7 is four, and the major axes of the four fourth elliptical holes 7 are all 1.2μm, and the minor axes are all 0.35μm; the number of the first elliptical holes 13 is two, and the major axes of the two first elliptical holes 13 are both 8μm, and the minor axes are both 2μm. This structure can effectively reduce the restrictive loss of the optical fiber, so as to facilitate the stable transmission of light in the fiber core.

[0058] According to the technical solution of this embodiment, the second air hole matrix 11 is formed by a plurality of circular hole arrays, and the overall shape of the second air hole matrix 11 is a hexagon. The fifth elliptical hole 8, the sixth elliptical hole 9 and the seventh elliptical hole 10 are all located inside the second air hole matrix 11, and the radius range of the circular holes of the second air hole matrix 11 and the first circular holes 5 are both set to 0.2μm-0.4μm. The second air hole matrix 11 is designed to be a hexagonal shape, so that more light can be controlled within the second air hole matrix 11, especially placing the fifth to seventh elliptical holes inside the second air hole matrix 11, so that more light can be confined inside it, thereby expanding the band gap control range of the air matrix, and making the band gap distribution more flexible, which is conducive to the transmission of optical signals in a specific band or wavelength range, and adapting to more application scenarios.

[0059] According to the technical solution of this embodiment, the distance between the center points of the left core region 6 and the right core region 12 in the horizontal direction is set to 8.75 μm, the working bandwidth of the left core region 6 is 1.55 μm-2.5 μm, the working bandwidth of the right core region 12 is 0.45 μm-1 μm, the center distance between the two third elliptical air holes 4 symmetrically arranged in the left core region 6 is 2.8 μm, and the center distance between the elliptical air holes in the first air hole matrix 2 on both sides of the left core region 6 is 2.1 μm;

[0060] The center distance between the two sixth elliptical air holes 9 symmetrically arranged in the right core area 12 is 1.5μm, and the center distance between the two seventh elliptical air holes 10 on both sides of the right core area 12 is 3μm. This core structure design and the refractive index design of the air holes around the core are to effectively improve the birefringence coefficient of the optical fiber.

[0061] according to Figure 2 and Figure 3 As shown, the present invention uses finite element simulation software COMSOL Multiphysics to simulate and test this embodiment and uses the finite element method combined with the perfect matching layer boundary absorption condition to perform theoretical calculations to obtain two-dimensional and three-dimensional graphs of the electric field mode distribution of the two cores. The data in the subsequent graphs are also obtained by this method.

[0062] See also Figure 4 as well as Figure 5 It can be found that when one of the cores of the dual-core optical fiber of the present invention is in working state, the electric field strength at the other core is close to 0. The simulation data shows that its value is less than 10 -7 V / m, so it can be considered that the two cores of the dual-core optical fiber of the present invention can work independently without interfering with each other and without coupling. Due to space limitations, only images of each core working in its respective shortest and longest wavelength bands are shown here.

[0063] The formula for calculating the birefringence coefficient is B = | - |, from which we can calculate Figure 6 , Figure 7 ,in represents the effective refractive index in the Y polarization direction, Represents the effective refractive index in the X-polarization direction.

[0064] See also Figure 6 as well as Figure 7 It can be found that the birefringence coefficients of the two cores of the dual-core optical fiber of the present invention are generally higher than 0.01, among which the birefringence coefficient of the right core region 12 at 1 μm reaches a maximum value of 0.02; it is generally believed that the birefringence coefficient of the optical fiber is higher than 10 -4It can be called a high-birefringence optical fiber, which shows that the two fiber cores of the present invention both have good high-birefringence characteristics and can achieve different control effects of optical signals in different directions.

[0065] The size of the restrictive loss directly affects the transmission distance of light in the optical fiber, so the restrictive loss is an important evaluation parameter of photonic crystal fiber. Studies have shown that more cladding air hole layers can result in lower restrictive loss.

[0066] The limiting loss is calculated as:

[0067]

[0068] in, To limit the loss, is the imaginary part of the effective refractive index, is the wavelength.

[0069] After unit conversion, the data unit is dB / km.

[0070] See also Figure 8 as well as Fig. 9 It can be found that the maximum value of the limiting loss of the four fundamental modes of the dual-core photonic crystal fiber of the present invention, including the two polarization directions of the two cores X and Y, is on the order of 10 -3 , where the right core operates at a wavelength of 0.9 μm, its limiting loss can reach a minimum of 10 -11 The results show that the limiting loss of the dual-core photonic crystal fiber of the present invention is 1 to 2 orders of magnitude lower than that of existing photonic crystal fibers in most bands, and even at the point of maximum loss, it is lower than the maximum loss value specified by international standards.

[0071] The effective mode field area is an important parameter for evaluating and selecting optical fibers. The mode field in the optical fiber is distributed in the core and cladding, so the mode field area of ​​the optical fiber is not equal to the core area. The Petermann II method is used to calculate the effective mode field area. The calculation formula for the effective mode field area is:

[0072]

[0073] In the formula, is the effective mode field area, and E is the electric field intensity.

[0074] See also Fig.10 as well as Fig.11 It can be seen that the two fiber cores of the present invention have available effective mode field area and single-mode characteristics in the entire working bandwidth.

[0075] In summary, the technical solution of this embodiment expands the working bandwidth of a single photonic crystal fiber. For the right core region 12 working at a shorter wavelength, the optimal working bandwidth is 0.45μm to 1μm, and this bandwidth range covers the complete visible light band, which can meet the transmission requirements of optical fibers for high-energy bands. For the left core region 6 working at a longer wavelength, the optimal working bandwidth is 1.55μm to 2.5μm, and this bandwidth range mainly covers the near-infrared band, including the 1.55μm wavelength most commonly used in communication-related services. This working bandwidth can well meet the needs of communication services, the transmission of near-infrared band optical signals that are safe for the human eye, and the research needs of nonlinear optics in the near-infrared band.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 heterogeneous photonic crystal fiber for visible light and near infrared bands, comprising an outer cladding (1), a left middle layer, a right middle layer, a left core region (6) and a right core region (12), characterized in that: A first air hole matrix (2) is arranged inside the outer cladding (1), the left middle layer and the right middle layer are both arranged inside the first air hole matrix (2), and first elliptical air holes (13) are arranged inside the outer cladding (1) on both upper and lower sides of the first air hole matrix (2) for filling the gaps; The left middle layer comprises a second elliptical air hole (3), a third elliptical air hole (4) and a first circular air hole (5); the left core region (6) is formed by the second elliptical air hole (3), the third elliptical air hole (4) and the first circular air hole (5); the second elliptical air hole (3) is arranged at the top and bottom of the left middle layer; the third elliptical air hole (4) is arranged between the second elliptical air hole (3) and the left core region (6); and the first circular air hole (5) is arranged on both sides of the left middle layer and close to the first air hole matrix (2); The right middle layer comprises a fourth elliptical air hole (7), a second air hole matrix (11), a fifth elliptical air hole (8), a sixth elliptical air hole (9) and a seventh elliptical air hole (10); the right core region (12) is located inside the second air hole matrix (11) and is surrounded by the sixth elliptical air hole (9) and the seventh elliptical air hole (10); the fourth elliptical air hole (7) is arranged at the four corners of the second air hole matrix (11) to fill the gap; the fifth elliptical air hole (8) is located at the upper and lower sides of the right core region (12); the sixth elliptical air hole (9) is located between the right core region (12) and the fifth elliptical air hole (8); and the seventh elliptical air hole (10) is located at both sides of the right core region (12).

2. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 1, characterized in that: A perfect matching layer (14) is provided on the outer side of the outer cladding (1).

3. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 2, characterized in that: The first air hole matrix (2) is composed of a plurality of elliptical air holes, and the first air hole matrix (2) is configured as a hexagonal shape as a whole; The elliptical pores arranged in the first air pore matrix (2) have a center distance of 0.7 μm between two adjacent pores in the horizontal direction, a center distance of 1 μm between two adjacent rows of pores in the vertical direction, and a major axis range of 0.8 μm-1 μm and a minor axis range of 0.5 μm-0.7 μm.

4. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 2, characterized in that: The working bandwidth of the left fiber core region (6) is 1.55 μm-2.5 μm, and the working bandwidth of the right fiber core region (12) is 0.45 μm-1 μm.

5. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 4, characterized in that: The outer cladding (1), the left middle layer, the right middle layer, the left core region (6) and the right core region (12) are all made of silicon dioxide, and the refractive index ranges from 1.40 to 1.

45.

6. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 5, characterized in that: The first elliptical air hole (13), the first air hole matrix (2), the second elliptical air hole (3), the first circular air hole (5), the second air hole matrix (11), the fourth elliptical air hole (7), the fifth elliptical air hole (8), the sixth elliptical air hole (9) and the seventh elliptical air hole (10) are all filled with air having a refractive index of 1.0; The third elliptical air hole (4) is filled with anhydrous ethanol having a refractive index of 1.33-1.

36.

7. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 6, characterized in that: The number of the second elliptical pores (3) is set to four, the number of the fifth elliptical pores (8) is set to two, and the major axes of the second elliptical pores (3) and the fifth elliptical pores (8) are both 1.2 μm-1.4 μm, and the minor axes are both 0.5 μm-0.8 μm.

8. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 6, characterized in that: The number of the third elliptical pore (4), the sixth elliptical pore (9) and the seventh elliptical pore (10) is set to two, and the major axis of the third elliptical pore (4), the sixth elliptical pore (9) and the seventh elliptical pore (10) is set to 1.8 μm-2.2 μm, and the minor axis is set to 0.6 μm-1.0 μm; The number of the fourth elliptical pores (7) is four, and the major axes of the four fourth elliptical pores (7) are all 1.2 μm, and the minor axes are all 0.35 μm; The number of the first elliptical pores (13) is two, and the major axes of the two first elliptical pores (13) are both 8 μm, and the minor axes are both 2 μm.

9. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 8, characterized in that: The second air hole matrix (11) is formed by a plurality of circular air hole arrays. The overall shape of the second air hole matrix (11) is a hexagon. The fifth elliptical air hole (8), the sixth elliptical air hole (9) and the seventh elliptical air hole (10) are all located inside the second air hole matrix (11). The radius range of the circular air holes in the second air hole matrix (11) and the first circular air holes (5) is set to be 0.2 μm-0.4 μm.

10. The heterogeneous photonic crystal fiber in the visible light and near infrared bands according to claim 9, characterized in that: The center point of the left fiber core region (6) is taken as the origin, the direction of the line connecting the center points of the left fiber core region (6) and the right fiber core region (12) is the x-axis direction, and the direction perpendicular to the x-axis direction is set as the y-axis direction. The left middle layer and the right middle layer are both arranged in a mirror-symmetrical manner with the x-axis as the symmetry axis; The center distance between the two third elliptical air holes (4) symmetrically arranged in the left fiber core region (6) is 2.8 μm, and the center distance between the elliptical air holes in the first air hole matrix (2) on both sides of the left fiber core region (6) is 2.1 μm; The center distance between the two sixth elliptical air holes (9) symmetrically arranged in the upper and lower parts of the right fiber core region (12) is 1.5 μm, and the center distance between the two seventh elliptical air holes (10) on both sides of the right fiber core region (12) is 3 μm.

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