Dispersion flattened photonic crystal fiber for oam mode transmission

Abstract

The utility model discloses a kind of dispersion flat photonic crystal fibers for OAM mode transmission, comprising: concentric and from the center of dispersion flat photonic crystal fiber to outside sequentially arranged first air hole layer, annular light transmission channel and cladding, wherein: the first air hole layer is the regular hexagon structure that is by multiple first circular air hole arrangement composition, and the central position is equipped with a first circular air hole;The cladding includes: second air hole layer and third air hole layer, second air hole layer is the circular ring structure that is by first circular air hole and second circular air hole alternate arrangement composition;Third air hole layer is the circular ring structure that is by one regular hexagon structure unit composition;Regular hexagon structure unit includes 7 second circular air hole, and the central position is equipped with a first circular air hole.The arrangement of air hole array in the dispersion flat photonic crystal fiber of the utility model guarantees the effective transmission of optical fiber, improves mode quality, and is beneficial to long-distance transmission of optical fiber.

Description

Technical Field

[0001] This utility model relates to the field of optical fiber technology, specifically to a dispersion-flat photonic crystal fiber for OAM mode transmission. Background Technology

[0002] Vortex beams, as a special type of optical field carrying orbital angular momentum (OAM), offer a novel dimension of multiplexing for optical communication due to their spiral phase wavefront and annular intensity distribution characteristics. Theoretically, the OAM states of vortex beams possess infinite orthogonality, which can greatly enhance channel capacity and show broad application prospects in fields such as optical tweezers, quantum entanglement, and nonlinear optics.

[0003] However, the practical application of vortex light faces two major challenges: first, high-order vortex beams are prone to mode decomposition during transmission; and second, traditional optical devices are difficult to integrate on-chip. Early methods for generating vortex light relied on bulky discrete optical components such as spiral phase plates and spatial light modulators. While these methods could generate and detect low-order vortex beams, they could not meet the requirements for on-chip integration. Furthermore, during fiber optic transmission, as the mode order increases, the effective refractive index of the mode gradually approaches the cladding refractive index, causing electric field energy to leak into the cladding, increasing the transmission loss of the fiber and thus preventing high-quality transmission. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a dispersion-flat photonic crystal fiber (PCF) for OAM mode transmission. Taking into account the actual production difficulties and costs of PCF, this PCF employs a design that avoids elemental doping and non-circular air holes, achieving long-distance, high-capacity, and accurate OAM mode transmission.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] A dispersion-flat photonic crystal fiber for OAM mode transmission includes a first air hole layer, an annular light transmission channel, and a cladding arranged concentrically outward from the center of the dispersion-flat photonic crystal fiber, wherein:

[0007] The first air hole layer is a regular hexagonal structure composed of multiple first circular air holes arranged in a circle, with a first circular air hole at its center. The diameter of the first circular air hole is [missing information]. The center-to-center distance between any two adjacent first circular air holes in the first air hole layer is ; , ≥ ;

[0008] The cladding layer comprises: a second air-porous layer and a third air-porous layer, wherein:

[0009] The second air-hole layer is a ring structure composed of alternating first and second circular air holes, the diameter of which is [missing information]. , > ;

[0010] The third air pore layer is composed of A ring structure composed of regular hexagonal structural units; each regular hexagonal structural unit includes 7 second circular air holes, with a first circular air hole at its center;

[0011] In a regular hexagonal structural unit, there is one and only one second circular air hole that is closest to the second circular air hole layer.

[0012] In the above technical solution, , .

[0013] In the above technical solution, the distance between the center of the dispersion-flattened photonic crystal fiber and the center of any one of the first circular air holes in the second air hole layer is... The distance between the center of any second circular air hole in the second air hole layer and the center of the second circular air hole layer is , , , .

[0014] In the above technical solution, the center-to-center distance between any two adjacent second circular air holes in the regular hexagonal structural unit is... , ≥ , .

[0015] In the above technical solution, the center-to-center distance between the center of the dispersion-flattened photonic crystal fiber and the center of any regular hexagonal structural unit is... , .

[0016] In the above technical solution, the outer diameter of the dispersion-flattened photonic crystal fiber is , .

[0017] In the above technical solution, the second air-hole layer of the cladding has 18 first circular air holes and 18 second circular air holes; in the second air-hole layer of the cladding, .

[0018] In the above technical solution, the substrate of the dispersion-flat photonic crystal fiber is quartz glass.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The dispersion-flat photonic crystal fiber of this invention does not undergo element doping and uses non-circular air holes, which reduces the difficulty of the manufacturing process, reduces the number of production steps, and effectively controls the production cost.

[0021] 2. The reasonable air hole array arrangement design in the dispersion-flat photonic crystal fiber of this invention not only ensures effective transmission, but also significantly improves mode quality. It has the advantages of low confinement loss, near-zero flat dispersion, large effective mode field area, and is conducive to long-distance transmission of optical fibers.

[0022] 3. The selection of air hole size and number of air hole layers in the dispersion-flat photonic crystal fiber of this invention increases the material refractive index difference between the core and cladding, thereby increasing the number of modes for high-quality transmission in the dispersion-flat photonic crystal fiber. Attached Figure Description

[0023] Figure 1 This is a simplified structural diagram of the dispersion-flattened photonic crystal fiber of this invention;

[0024] Figure 2 The simulation results are shown in the 11th-order mode of the embodiments of this utility model.

[0025] Figure 3 The simulation results are shown in the 10th-order mode in the embodiments of this utility model.

[0026] Figure 4 The simulation results are shown in the 9th order mode in the embodiments of this utility model;

[0027] Figure 5 This refers to the difference in effective refractive index between different order modes in the embodiments of this utility model;

[0028] Figure 6 These are dispersion curves under different order modes in embodiments of this utility model;

[0029] Figure 7 These are mode quality curves under different orders in embodiments of this utility model. Detailed Implementation

[0030] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings and embodiments.

[0031] Example

[0032] like Figure 1 As shown, a dispersion-flat photonic crystal fiber for OAM mode transmission includes: a first air-hole layer, an annular light transmission channel, and a cladding, arranged concentrically outward from the center of the dispersion-flat photonic crystal fiber. Wherein:

[0033] The first air hole layer is a regular hexagonal structure composed of multiple first circular air holes arranged in a circle, with a first circular air hole at its center. The diameter of the first circular air hole is [missing information]. The center of the first air-hole layer is located at the center of the dispersion-flat photonic crystal fiber; the center-to-center distance between any two adjacent first circular air holes in the first air-hole layer is... Center distance ≥ .

[0034] The annular light transmission channel is wrapped around the outside of the first air hole layer, and the center of the annular light transmission channel is located at the center of the dispersion-flat photonic crystal fiber.

[0035] The cladding layer comprises: a second air-porous layer and a third air-porous layer, wherein:

[0036] The second air-hole layer is a ring structure composed of alternating first and second circular air holes, the diameter of which is [missing information]. The center of the second air-hole layer is located at the center of the dispersion-flattened photonic crystal fiber; the second air-hole layer is located outside the annular light transmission channel; the center-to-center distance between the center of the dispersion-flattened photonic crystal fiber and the center of any one of the first circular air holes in the second air-hole layer is... The center-to-center distance between the center of the dispersion-flattened photonic crystal fiber and the center of any second circular air hole in the second air hole layer is... ;

[0037] The third air pore layer is composed of A ring structure composed of regular hexagonal structural units, with a third air hole layer located outside the second air hole layer, the center of which is located at the center of the dispersion-flattened photonic crystal fiber; each regular hexagonal structural unit includes seven second circular air holes, with a first circular air hole at its center, and the center-to-center distance between any two adjacent second circular air holes in the regular hexagonal structural unit is [missing information]. , ≥ ;

[0038] The distance between the center of the dispersion-flat photonic crystal fiber and the center of any regular hexagonal structural unit is: In a regular hexagonal structural unit, there is one and only one second circular air hole that is closest to the second circular air hole in the second air hole layer.

[0039] Both the first and second circular air holes penetrate the interior of the dispersion-flattened photonic crystal fiber along its extension direction. The outer diameter of the dispersion-flattened photonic crystal fiber is... ,

[0040] The dispersion-flat photonic crystal fiber of this invention is made of quartz glass except for the air holes.

[0041] In this embodiment, , , , , , , , In the second air-pore layer of the cladding, there are 18 first circular air pores and 18 second circular air pores. .

[0042] The first and second circular air holes are used to increase the difference in refractive index between the core (ring light transmission channel) and the cladding (outside the ring light transmission channel). The larger the number and radius of the air holes, the greater the difference in refractive index in the dispersion-flat photonic crystal fiber, the more high-quality transmission modes the dispersion-flat photonic crystal fiber has, and the more stable it is.

[0043] Simulation experiments were conducted on the dispersion-flattened photonic crystal fiber in this embodiment:

[0044] Simulation results under different order modes are as follows Figures 2-4 As shown in the simulation results, the mode field distribution in a dispersion-flat photonic crystal fiber is mainly concentrated within the ring core (ring-shaped optical transmission channel). Even higher-order modes can be confined within the ring core (ring-shaped optical transmission channel), achieving high-quality transmission. Figure 2 The simulation results are for the 11th-order mode. Figure 3 The simulation results are for the 10th order mode. Figure 4 The simulation results are for the 9th order mode.

[0045] The effective refractive index of the dispersion-flat photonic crystal fiber of this invention in different order modes, such as Figure 5 As shown, according to Figure 5 It can be seen that the difference in effective refractive index between different order modes is greater than 10. -4 Therefore, the dispersion-flat photonic crystal fiber of this invention reduces the difficulty of separating and identifying different modes, and provides a guarantee for OAM mode transmission and application. Figure 5 In the graph, the horizontal axis represents wavelength, and the vertical axis represents the difference in effective refractive index. The difference in effective refractive index is relatively large between the near orders of each curve.

[0046] The dispersion curves of the dispersion-flat photonic crystal fiber of this invention in different order modes are as follows: Figure 6 As shown, according to Figure 6It can be seen that the different order modes of the dispersion-flat photonic crystal fiber of this invention are present in common communication bands (1.4~1.6). All of them remained at very low numerical levels. Figure 6 Some of the dispersion curves in the mode achieve near-zero dispersion flatness, which effectively prevents signal distortion during transmission, providing favorable conditions for long-distance signal transmission. Figure 6 In the figure, the horizontal axis represents wavelength and the vertical axis represents dispersion coefficient.

[0047] The mode quality curves of the dispersion-flat photonic crystal fiber of this invention at different orders are shown below. Figure 7 As shown, according to Figure 7 It can be seen that the dispersion-flat photonic crystal fiber of this invention can maintain a mode quality value of over 0.99 in different order modes, which provides a guarantee for long-distance transmission and mode resolution in OAM mode. Figure 7 In the figure, the horizontal axis represents wavelength, and the vertical axis represents mode quality.

[0048] During optical fiber transmission, electric field energy is mainly concentrated in the core of the dispersion-flat photonic crystal fiber (PCF). As the mode order increases, the effective refractive index of the mode becomes increasingly close to the refractive index of the cladding. At this point, the confinement of the mode by the core gradually weakens, causing electric field energy to gradually leak into the cladding, ultimately preventing high-quality mode transmission. This invention addresses this issue by adding air holes to the cladding, thereby reducing the refractive index of the cladding material. This is equivalent to doping silica with air, without significantly increasing transmission loss.

[0049] In this embodiment, , , , , , , , , , , .

[0050] Five different implementation examples were set up based on the range of values ​​for the above geometric parameters. The geometric parameters of Examples 1 to 5 are shown in Table 1. The performance parameters of Examples 1 to 5 were obtained from simulation experiments and are shown in Table 2.

[0051] Table 1

[0052] Example 1 6 4 125 6 41 40 5 54 Example 2 6.5 4.5 135 6.5 41.5 40.5 5.5 55 Example 3 7 5 140 7 42 41 6 55 Example 4 7.5 5.5 145 8 42.5 41.5 6.5 55.5 Example 5 8 6 150 9 43 42 7 56

[0053] Table 2

[0054] Fiber optic parameters Example 1 Example 2 Example 3 Example 4 Example 5 Dispersion (min) 1.3443 1.22748 1.6107 1.1789 1.1516 Model purity (max) 99.6% 99.7% 99.5% 99.7% 99.3% Effective modulus area (max) 1267.8 1307.3 1219.5 1353.6 1204.1 Nonlinear coefficient (min) 0.06 0.06 0.06 0.07 0.06 Limit losses (centralized) <![CDATA[10 -12 ]]> <![CDATA[10 -12 ]]> <![CDATA[10 -12 ]]> <![CDATA[10 -12 ]]> <![CDATA[10 -12 ]]>

[0055] As shown in Tables 1 and 2, by adjusting the geometric parameters of the dispersion-flat photonic crystal fiber of this invention, different fiber parameters of the dispersion-flat photonic crystal fiber can be achieved as needed.

[0056] This invention relates to a dispersion-flat photonic crystal fiber (PCF), which forms a unique microstructure by periodically arranging air holes or doped regions in a quartz substrate. Its flexible design parameters allow for effective control of the optical field modes. The size and arrangement of the air holes in the PCF have a crucial impact on the fiber's performance. The multiple layers of air holes in the cladding of the PCF increase the effective refractive index difference between the core and cladding, thereby enhancing mode confinement and supporting high-purity, low-loss OAM mode transmission.

Claims

1. A dispersion-flattened photonic crystal fiber for OAM mode transmission, comprising a first air-hole layer, an annular light transmission channel, and a cladding arranged concentrically outward from the center of the dispersion-flattened photonic crystal fiber, characterized in that: The first air hole layer is a regular hexagonal structure composed of multiple first circular air holes arranged in a circle, with a first circular air hole at its center. The diameter of the first circular air hole is [missing information]. The center-to-center distance between any two adjacent first circular air holes in the first air hole layer is ; , ≥ ; The cladding layer comprises: a second air-porous layer and a third air-porous layer, wherein: The second air-hole layer is a ring structure composed of alternating first and second circular air holes, the diameter of which is [missing information]. , > ; The third air pore layer is composed of A ring structure composed of regular hexagonal structural units; each regular hexagonal structural unit includes 7 second circular air holes, with a first circular air hole at its center; In a regular hexagonal structural unit, there is one and only one second circular air hole that is closest to the second circular air hole layer.

2. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: ， 。 3. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: The distance between the center of the dispersion-flattened photonic crystal fiber and the center of any first circular air hole in the second air hole layer is... The distance between the center of any second circular air hole in the second air hole layer and the center of the second circular air hole layer is , , , .

4. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: The distance between the centers of any two adjacent second circular air holes in the hexagonal structural unit is , ≥ , .

5. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: The distance between the center of the dispersion-flat photonic crystal fiber and the center of any hexagonal structural unit is: , .

6. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: The outer diameter of the dispersion-flattened photonic crystal fiber is , .

7. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: In the second air-pore layer of the cladding, there are 18 first circular air pores and 18 second circular air pores; in the second air-pore layer of the cladding, .

8. The dispersion-flattened photonic crystal fiber for OAM mode transmission according to claim 1, characterized in that: The substrate of the dispersion-flat photonic crystal fiber is quartz glass.

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