A mode division multiplexer based on a five-core photonic crystal fiber

Abstract

This invention discloses a mode-division multiplexer (MDD) based on a five-core photonic crystal fiber. The MMDD includes a substrate and an air-hole layer region disposed on the substrate. The air-hole layer region is composed of a plurality of air holes arranged in a pattern, and is divided into a core region and a cladding region, with the cladding region enclosing the core region. The core includes a main core region, a first side core region, a second side core region, a third side core region, and a fourth side core region. The main core region is located at the center of the substrate, and the first, second, third, and fourth side core regions surround the main core region. The cladding region surrounds the main core region. This invention modulates the incident light in the side core regions into coupled light in the main core region, thereby increasing the operating bandwidth of the MMDD and reducing insertion loss, while effectively shortening the device length. This makes the MMDD suitable for miniaturized and integrated optical fiber communication systems and MMDD systems.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to a mode division multiplexer based on a five-core photonic crystal fiber. Background Technology

[0002] In recent years, technologies such as cloud computing, big data, the Internet of Things, autonomous driving, and telemedicine have rapidly emerged. Their data transmission is via the Internet. To improve the capacity and transmission speed of photonic networks, researchers have successively proposed various optical multiplexing techniques (such as wavelength division multiplexing, time division multiplexing, and polarization multiplexing), higher-order modulation, and coding, greatly improving the total transmission capacity and spectral efficiency of a single optical fiber. However, with technological advancements, Internet data traffic has grown exponentially year by year. The capacity and transmission speed of traditional single-mode fiber cannot meet the demands of Internet transmission, and further increasing the capacity of traditional single-mode fiber is extremely difficult. Therefore, to improve the capacity and transmission speed of current photonic networks, it is inevitable that researchers will explore new multimode multiplexing methods. The concept of mode division multiplexing was first proposed by S. Berdague and P. Facq. They used spatial filtering technology to transmit two different modes of light in a traditional graded-index multimode fiber, with each mode having the same bandwidth as when transmitted alone in a single-mode fiber. This also reduces the nonlinear effects generated when transmitting information in multimode fiber. Mode division multiplexing (MDM) technology refers to the technique of allowing multiple orthogonal modes with different paths and mode field distributions, carrying different information, to propagate together in the same multimode optical waveguide. The core of MDM technology is the mode divider, whose performance, such as the number of modes multiplexed, bandwidth, and insertion loss, determines the performance of the MDM system. Based on different geometric structures, existing mode dividers are mainly classified into free-space optical path type, multimode interferometer (MMI) type, asymmetry directional coupler (ADC) type, asymmetric Y-junction type, "photonic lantern" type, and photonic crystal fiber (PCF) type. PCF, also known as microstructured fiber, contains air holes of varying wavelengths arranged in its cladding or core. These air holes extend throughout the entire length of the fiber, confining light waves to the low-refractive-index core region. By adjusting the structure, size, and arrangement of these air holes, many light-guiding characteristics not found in traditional fibers can be achieved, such as large mode area, high nonlinearity, endless single-mode operation, high birefringence, and ultra-flat dispersion, offering significant design flexibility. Therefore, mode divider multiplexers based on PCF effectively reduce device size and greatly increase the number of modes multiplexed. Furthermore, these multiplexers possess wide operating bandwidth and low insertion loss, making them commonly used in applications and experiments.Chen MY, Zhou J. Mode converter based on mode coupling in an asymmetric dual-core photonic crystal fiber[J]. Journal of Optics A-pure and Applied Optics, 2008, 10(1334): 1-5. A mode converter based on mode coupling in an asymmetric dual-core photonic crystal fiber was proposed. By introducing two adjacent defects in the photonic crystal fiber to form two cores of different sizes, LP coupling can be achieved in a 12.7 mm long fiber. 01 and LP 02 The mode was obtained with 1 dB insertion loss at a center wavelength of 1.55 μm; DJ Richardson, JMFini, LENelson. Space-division multiplexing in optical fibres[J]. Nature Photonics, 2013, 7(5) proposed that MDM is to maintain the fiber transmission capacity along Moore's Law and designed a three-mode spatial mode division multiplexer. This mode division multiplexer is large in size and difficult to connect with subsequent long-distance fiber mode multiplexing waveguides. At the same time, this mode division multiplexer is difficult to use in miniaturized and integrated mode division multiplexing systems; Zhang YJ, Wang Y, Cai SY, Lan MY, Yu S, Gu W Y. Modeconverter based on dual-core all-solid photonic bandgap fiber[J].PhotonicsResearch,2015,3(220):1-3 A mode divider based on three-core all-solid-state photonic crystal fiber (AS-PBGF) is proposed. This device realizes simultaneous conversion and multiplexing of LP01 to LP02 and LP11 modes, but its operating bandwidth is relatively narrow; Yu YY,Sun B.Ultra-Wide-Bandwidth Tunable Magnetic Fluid-Filled Hybrid Connected Dual-Core Photonic Crystal Fiber Mode Converter[J].Crystals,2018,8(95):3-5 A tunable magnetic fluid-filled hybrid photonic crystal fiber mode divider is proposed. This converter can convert the LP11 mode in the refractive index guide core into the LP11 mode in the photonic bandgap guide core. 01The device achieves insertion loss of -0.457dB and -0.222dB in the wavelength range of 1.33μm-1.85μm, respectively. However, due to the complex fabrication process and high manufacturing cost, it is not suitable for industrial production. Cardona JAM, Cardona NDG, Valencia EG, Trujillo P T. Mode Converter Device Based on Photonic Crystal Fiber with a Thermo-Responsive Liquid Crystal Core[J]. Photonics, 2019, 7(1): 1-6. A tunable mode divider based on asymmetric dual-core photonic crystal fiber was proposed. Liquid crystal material was added to the air hole between the two cores. The thermo-optical tunable characteristics of the liquid crystal material between the two cores were used to control the operating wavelength of the mode converter. The device achieved LP in the bandwidth of 1.28μm-1.32μm. 01 With LP 11 The conversion and multiplexing of two modes, but the operating bandwidth of the device is relatively narrow; Wang Xiao-Kai, Li Jian-She, Li Shu-Guang, Guo Ying, Wang Lu-Yao, Li Zeng-Hui, Zhao Yuan-Yuan, Ding Yu-Xin. Design and research of a broadband mode-division multiplexer based on three-core photonic crystal fiber[J]. Acta Physica Sinica, 2022, 71(04) proposed a three-core mode-division multiplexer based on photonic crystal. The device realizes the side-core LP by adding doped rods to the left and right side cores. 01 Motion-oriented center core LP 21 Model and LP 31 The device features mode switching and multiplexing, a length of 4.9 mm, an insertion loss of 0.543 dB, and a bandwidth of 140 nm. However, this design requires the introduction of doped rods with different effective refractive indices, making it complex and extremely limited in terms of the number of multiplexed modes and operating bandwidth, thus failing to meet practical application requirements.

[0003] In summary, with the deepening development of mobile Internet in various vertical application fields, the transmission capacity of optical fiber communication systems in backbone networks is also increasing. However, existing mode divider multiplexers have long device lengths and narrow operating bandwidths, making them unsuitable for miniaturized and integrated modern optical fiber communication systems and mode divider multiplexing systems. There is an urgent need to develop a mode divider multiplexer with larger operating bandwidth, smaller size, and lower insertion loss. Summary of the Invention

[0004] This invention provides a mode divider multiplexer based on a five-core photonic crystal fiber. By setting multiple fiber cores, the operating bandwidth of the mode divider multiplexer is increased and the length of the device is shortened.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A mode divider based on a five-core photonic crystal fiber, the mode divider comprising a substrate and an air hole layer region, the air hole layer region being disposed on the substrate;

[0007] The air hole layer region is composed of a plurality of air holes arranged in a manner. The air hole layer is divided into a core region and a cladding region, and the cladding region encloses the core region.

[0008] The fiber core includes a main core region, a first side core region, a second side core region, a third side core region, and a fourth side core region;

[0009] The main core region is located at the center of the substrate, and the first side core region, the second side core region, the third side core region, and the fourth side core region surround the main core region.

[0010] Furthermore, the main core area is a circular area composed of one seventh air hole, one eighth air hole, one ninth air hole, one tenth air hole, and several first air holes;

[0011] The first side core region is a regular hexagonal region composed of several second air holes and one seventh air hole;

[0012] The second side core region is a regular hexagonal region composed of several third air holes and one eighth air hole;

[0013] The third side core region is a regular hexagonal region composed of several fourth air holes and one ninth air hole;

[0014] The fourth side core region is a regular hexagonal region composed of several fifth air holes and one tenth air hole.

[0015] Furthermore, the center distance Λ1 between two adjacent air holes in the main core region, the second side core region, the third side core region, and the fourth side core region is 4.975-5.025 μm, and the center distance Λ2 between two adjacent air holes in the first side core region is 5.97-6.03 μm.

[0016] Furthermore, the first air hole, the second air hole, the third air hole, the fourth air hole, the fifth air hole, the sixth air hole, the seventh air hole, the eighth air hole, the ninth air hole, and the tenth air hole are circular;

[0017] The diameter of the fifth air hole is r5 = 1.95~1.97μm;

[0018] The diameter of the fourth air hole is r4 = 1.67~1.69 μm;

[0019] The diameter of the sixth air hole is r6 = 1.243~1.257 μm;

[0020] The diameter of the third air hole is r3 = 0.945~0.955μm;

[0021] The diameter of the second air hole is r2 = 0.646~0.654 μm;

[0022] The diameter of the tenth air hole is r 10 =0.527~0.533μm;

[0023] The diameter of the first air hole is r1 = 0.4975~0.5025 μm;

[0024] The diameter of the eighth air hole is r8 = 0.477~0.483 μm;

[0025] The diameter of the ninth air hole is r9 = 0.447~0.453μm;

[0026] The diameter of the seventh air hole is r7 = 0.368~0.372μm.

[0027] Furthermore, the cladding region is composed of a plurality of sixth air holes, which surround the fiber core region, and the center-to-center distance between two adjacent sixth air holes is Λ1 = 4.975~5.025μm.

[0028] Furthermore, the air hole layer region is provided with 6 layers of air holes, which are, from the inside out, the first layer of air holes, the second layer of air holes, the third layer of air holes, the fourth layer of air holes, the fifth layer of air holes and the sixth layer of air holes;

[0029] The first layer of air holes is arranged in a circle by a seventh air hole, a first air hole, an eighth air hole, a first air hole, a ninth air hole, a first air hole, a tenth air hole, and a first air hole in sequence;

[0030] The second layer of air holes is composed of a second air hole, a third air hole, a sixth air hole, a fourth air hole, a fifth air hole, and a sixth air hole arranged in sequence to form a regular hexagon;

[0031] The third layer of air holes includes a second air hole, a sixth air hole, a third air hole, a sixth air hole, a fourth air hole, a sixth air hole, a fifth air hole, and a sixth air hole arranged in sequence to form a regular hexagon;

[0032] The fourth layer of air holes is composed of a regular hexagon formed by six sixth air holes;

[0033] The fifth layer of air holes is composed of a regular hexagon formed by a sixth air hole;

[0034] The sixth layer of air holes is composed of a regular hexagon formed by a series of sixth air holes.

[0035] Furthermore, the substrate is made of silicon dioxide.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. This invention is a five-core photonic crystal mode divider (MDD) based on coupled modes. A main core region, a first side core region, a second side core region, a third side core region, and a fourth side core region, along with a cladding, are disposed on a substrate. Incident light from the side core regions is modulated into coupled light within the main core region, thereby expanding the operating bandwidth of the device to 1.33μm–1.95μm. This increases the operating bandwidth of the MMD and reduces insertion loss while effectively shortening the device length, making the MMD suitable for miniaturized and integrated optical fiber communication systems and MMD systems.

[0038] 2. This invention utilizes the flexibility of photonic crystal fiber design. By adjusting the radius and spacing of the air hole cladding in the main core region, the first side core region, the second side core region, the third side core region, and the fourth side core region, the LP in the side core region can be controlled during transmission. 01 The module is converted into a specific higher-order module in the core.

[0039] 3. This invention fully leverages the flexible design characteristics of photonic crystal fibers. By setting a structure with six layers of air holes, it achieves efficient multiplexing of five modes, enabling the mode divider to have ultra-large bandwidth and low insertion loss. The device length is only 1.84mm, which facilitates the fusion splicing and combination of the mode divider with existing optical fiber communication systems. It is more suitable for miniaturized and integrated modern optical fiber communication systems and mode divider systems. At the same time, within a certain length deviation range, the overall variation of the device is within a reasonable range, making it suitable for factory production. Attached Figure Description

[0040] Figure 1 A schematic diagram of the cross-sectional structure of an ultra-wide bandwidth low-loss mode divider based on a five-core photonic crystal fiber provided for this invention;

[0041] Figure 2 For a mode divider based on a five-core photonic crystal fiber, the main core region LP 01 The model field diagram;

[0042] Figure 3 For a mode divider based on a five-core photonic crystal fiber, the main core region LP 11 The model field diagram;

[0043] Figure 4 For a mode divider based on a five-core photonic crystal fiber, the main core region LP 21 The model field diagram;

[0044] Figure 5 For a mode divider based on a five-core photonic crystal fiber, the main core region LP 31 The model field diagram;

[0045] Figure 6 For a mode divider based on a five-core photonic crystal fiber, the main core region LP 12 The model field diagram;

[0046] Figure 7 This is a graph showing the relationship between the effective refractive index in the main core region and the effective refractive index difference between two adjacent modes in a mode divider based on a five-core photonic crystal fiber, as a function of the input light wavelength.

[0047] Figure 8 In a mode divider based on a five-core photonic crystal fiber, the LP in the first side core region is... 01 Graph showing the relationship between the effective refractive index of the model and the radius of the first air hole;

[0048] Figure 9 In a mode divider based on a five-core photonic crystal fiber, the LP in the first side core region is... 01 Graph showing the relationship between the effective refractive index of the mode and the radius of the seventh air hole;

[0049] Figure 10 In a mode divider based on a five-core photonic crystal fiber, the LP in the first side core region is... 01 A graph showing the relationship between the effective refractive index of the model and the distance between two adjacent air holes in the first side core region;

[0050] Figure 11 In a mode divider based on a five-core photonic crystal fiber, the LP in the first side core region is... 01 LP in the mold and core area 11 Graph showing the relationship between the effective refractive index difference of the modes and the wavelength of the input light;

[0051] Figure 12 In a mode divider based on a five-core photonic crystal fiber, the second side core region LP 01 Graph showing the relationship between the effective refractive index of the model and the radius of the second air hole;

[0052] Figure 13 In a mode divider based on a five-core photonic crystal fiber, the second side core region LP 01 Graph showing the relationship between the effective refractive index of the mode and the radius of the eighth air hole;

[0053] Figure 14 In a mode divider based on a five-core photonic crystal fiber, the second side core region LP 01 A graph showing the relationship between the effective refractive index of the mode and the distance between two adjacent air holes in the second side core region;

[0054] Figure 15 In a mode divider based on a five-core photonic crystal fiber, the second side core region LP 01 With the LP in the main core area 21 Graph showing the relationship between the effective refractive index difference of the modes and the wavelength of the input light;

[0055] Figure 16 In a mode divider based on a five-core photonic crystal fiber, the LP in the third side core region is... 01 Graph showing the relationship between the effective refractive index of the model and the radius of the third air hole;

[0056] Figure 17 In a mode divider based on a five-core photonic crystal fiber, the LP in the third side core region is... 01 Graph showing the relationship between the effective refractive index of the mode and the radius of the ninth air hole;

[0057] Figure 18 In a mode divider based on a five-core photonic crystal fiber, the LP in the third side core region is... 01 A graph showing the relationship between the effective refractive index of the mode and the distance between two adjacent air holes in the third side core region;

[0058] Figure 19 In a mode divider based on a five-core photonic crystal fiber, the LP in the third side core region is... 01 With the LP in the main core area 31 Graph showing the relationship between the effective refractive index difference of the modes and the wavelength of the input light;

[0059] Figure 20 In a mode divider based on a five-core photonic crystal fiber, the LP in the fourth side core region is... 01 Graph showing the relationship between the effective refractive index of the mode and the radius of the fourth air hole;

[0060] Figure 21 In a mode divider based on a five-core photonic crystal fiber, the LP in the fourth side core region is... 01 Graph showing the relationship between the effective refractive index of the mode and the radius of the tenth air hole;

[0061] Figure 22 In a mode divider based on a five-core photonic crystal fiber, the LP in the fourth side core region is... 01 Graph showing the relationship between the effective refractive index of the mode and the air hole spacing in the fourth side core region;

[0062] Figure 23 In a mode divider based on a five-core photonic crystal fiber, the LP in the fourth side core region is... 01 LP in the mold and core area 12 Graph showing the relationship between the effective refractive index difference of the modes and the wavelength of the input light;

[0063] Figure 24 For a mode divider based on a five-core photonic crystal fiber, LP 11 LP 21 LP 31 LP 12 Figure showing the variation of coupling efficiency from the side core to the main core region in four modes with device length;

[0064] Figure 25 For a mode divider based on a five-core photonic crystal fiber, LP 11 LP 21 LP 31 LP 12 The coupling efficiency of the mode varies with wavelength at a device length of 1840 μm;

[0065] Figure 26 For a mode divider based on a five-core photonic crystal fiber, LP 11 LP 21 Simultaneously transmitted mode field diagrams;

[0066] Figure 27For a mode divider based on a five-core photonic crystal fiber, LP 31 LP 12 Simultaneously transmitted mode field diagrams;

[0067] Figure 28 This is a graph showing the coupling efficiency as a function of input light wavelength when the size of a mode divider based on a five-core photonic crystal fiber changes by +0.5%.

[0068] Figure 29 This is a graph showing the coupling efficiency of a mode divider based on a five-core photonic crystal fiber as a function of the input light wavelength when the size change is -0.5%.

[0069] In the diagram: 1. First air hole; 2. Second air hole; 3. Third air hole; 4. Fourth air hole; 5. Fifth air hole; 6. Sixth air hole; 7. Seventh air hole; 8. Eighth air hole; 9. Ninth air hole; 10. Tenth air hole. Detailed Implementation

[0070] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0071] This invention discloses a mode divider multiplexer based on a five-core photonic crystal fiber, the cross-sectional structure of which is as follows: Figure 1 As shown, it includes a substrate and an air-pore layer region; the air-pore layer region is disposed on the substrate;

[0072] The air pore layer region is composed of a number of air pores arranged in a row. The air pore layer region is divided into a core region and a cladding region. Both the cladding region and the core region are set on the substrate, and the cladding region wraps around the core region.

[0073] The fiber core region includes the main core region, the first side core region, the second side core region, the third side core region, and the fourth side core region.

[0074] The main core region is located at the center of the substrate. The first side core region, the second side core region, the third side core region, and the fourth side core region surround the main core region. The cladding region surrounds the main core region, the first side core region, the second side core region, the third side core region, and the fourth side core region, and encloses the aforementioned regions.

[0075] Specifically, the main core region is composed of an inner seventh air hole 7, an eighth air hole 8, a ninth air hole 9, a tenth air hole 10, and several first air holes 1; the first side core region is composed of several second air holes 2 and an eighth air hole 7; the second side core region is composed of several third air holes 3 and an eighth air hole 8; the third side core region is composed of several fourth air holes 4 and a ninth air hole 9; and the fourth side core region is composed of several fifth air holes 5 and a tenth air hole 10. The main core region is circular, and the first, second, third, and fourth side core regions are hexagonal. Those skilled in the art can select, according to their needs, the number of first air holes 1 in the main core region, the number of second air holes 2 in the first side core region, the number of third air holes 3 in the second side core region, the number of fourth air holes 4 in the third side core region, and the number of fifth air holes 5 in the fourth side core region. In the implementation of this application, eight first air holes 1 are set in the main core region, forming a circular region with other air holes. The seventh air hole region 7 and the eighth air hole 8 in the main core region are separated by one first air hole 1, the eighth air hole 8 and the ninth air hole 9 are separated by three first air holes 1, the ninth air hole 9 and the tenth air hole 10 are separated by one first air hole 1, and the tenth air hole 10 and the seventh air hole region 7 are separated by three first air holes 1. A circle is formed according to this arrangement.

[0076] Five second air holes 2 are arranged in the first side core region, forming a regular hexagonal structure with the seventh air hole 7; five third air holes are arranged in the second side core region, forming a regular hexagonal structure with the eighth air hole 8; five fourth air holes 4 are arranged in the third side core region, forming a regular hexagonal structure with the ninth air hole 9; and five fifth air holes 5 are arranged in the fourth side core region, forming a regular hexagonal structure with the tenth air hole 10. Meanwhile, the center distance Λ1 between two adjacent air holes in the main core region, the second side core region, the third side core region, and the fourth side core region is 4.975-5.025 μm, and the center distance Λ2 between two adjacent air holes in the first side core region is 5.97-6.03 μm.

[0077] This invention leverages the flexibility of photonic crystal fiber design by incorporating five fiber cores—a main core region, a first side core region, a second side core region, a third side core region, and a fourth side core region—on a substrate to support localized optical transmission. The side core regions modulate the coupled light from the main core region, thus transmitting the fundamental mode LP from the side core regions. 01 This corresponds to efficient coupling to the main core region, forming a higher-order mode, namely the fundamental mode LP of the first peripheral core region. 01 High-order mode LP is efficiently coupled into the core region. 11 Second side core region fundamental mode LP 01High-order mode LP is efficiently coupled into the core region. 21 Third side core region fundamental mode LP 01 High-order mode LP is efficiently coupled into the core region. 31 Fourth side core region fundamental mode LP 01 High-order mode LP is efficiently coupled into the core region. 12 The main core area transmits its own fundamental mode LP. 01 Therefore, the device has LP. 01 LP 11 LP 21 LP 31 LP 12 By multiplexing five modes, the operating bandwidth of this device is expanded to 1.33μm to 1.95μm. While increasing the operating bandwidth of the mode divider and reducing insertion loss, the device length is effectively shortened, making the device easier to fusion and combine with existing optical fiber communication systems. It is more suitable for miniaturized and integrated modern optical fiber communication systems and mode divider systems.

[0078] In a further specific implementation process, the first air hole 1, the second air hole 2, the third air hole 3, the fourth air hole 4, the fifth air hole 5, the sixth air hole 6, the seventh air hole 7, the eighth air hole 8, the ninth air hole 9, and the tenth air hole 10 are all circular; at the same time, the diameter of the fifth air hole 5, the fourth air hole 4, the sixth air hole 6, the third air hole 3, the second air hole 2, the tenth air hole 10, the first air hole 1, the eighth air hole 8, the ninth air hole 9, and the seventh air hole 7 decreases sequentially.

[0079] Specifically, the diameter of the fifth air hole 5 is r5 = 1.95–1.97 μm; the diameter of the fourth air hole 4 is r4 = 1.67–1.69 μm; the diameter of the sixth air hole 6 is r6 = 1.243–1.257 μm; the diameter of the third air hole 3 is r3 = 0.945–0.955 μm; the diameter of the second air hole 2 is r2 = 0.646–0.654 μm; and the diameter of the tenth air hole 10 is r 10 =0.527~0.533μm; the diameter of the first air hole 1 is r1=0.4975~0.5025μm; the diameter of the eighth air hole 8 is r8=0.477~0.483μm; the diameter of the ninth air hole 9 is r9=0.447~0.453μm; the diameter of the seventh air hole 7 is r7=0.368~0.372μm.

[0080] In a more detailed implementation, the air holes in the air hole layer area are arranged in 6 layers, from the inside out: the first layer of air holes, the second layer of air holes, the third layer of air holes, the fourth layer of air holes, the fifth layer of air holes, and the sixth layer of air holes.

[0081] The first layer of air holes includes one seventh air hole 7, one eighth air hole 8, one ninth air hole 9, one tenth air hole 10, and eight first air holes 1. The arrangement of these air holes is the same as that of the main core area.

[0082] The second layer of air holes includes two second air holes 2, two third air holes 3, two fourth air holes 4, two fifth air holes 5, and six sixth air holes 6. The air holes are arranged in the order of two second air holes 2, two third air holes 3, three sixth air holes 6, two fourth air holes 4, two fifth air holes 5, and three sixth air holes 6, forming a regular hexagon that surrounds the first layer of air holes.

[0083] The third layer of air holes includes 3 second air holes 2, 3 third air holes 3, 3 fourth air holes 4, 3 fifth air holes 5 and 12 sixth air holes 6. The above air holes are arranged in a regular hexagon that encloses the second layer of air holes, with 3 second air holes 2, 1 sixth air hole 6, 3 third air holes 3, 5 sixth air holes 6, 3 fourth air holes 4, 1 sixth air hole 6, 3 fifth air holes 5 and 5 sixth air holes 6.

[0084] The fourth layer of air holes consists of 26 sixth air holes, each forming a regular hexagon that encloses the third layer of air holes;

[0085] The fifth layer of air holes includes 34 sixth air holes, forming a regular hexagon that encloses the fourth layer of air holes;

[0086] The sixth layer of air holes consists of 42 sixth air holes arranged in a regular hexagon that encloses the fourth layer of air holes;

[0087] Among them, the center distance between two adjacent air holes in the fourth, fifth and sixth layers of air holes is Λ1 = 4.975~5.025μm.

[0088] The substrate can be selected by those skilled in the art according to actual needs. In the implementation of this application, silicon dioxide is used as the substrate material.

[0089] Example 1

[0090] A mode divider based on a five-core photonic crystal fiber, the mode divider including a substrate and an air hole layer region; the air hole layer region is disposed on the upper surface of the substrate;

[0091] The air pore layer region consists of a number of air pores arranged in 6 layers. These 6 layers of air pores are arranged from the inside out as the first layer of air pores, the second layer of air pores, the third layer of air pores, the fourth layer of air pores, the fifth layer of air pores, and the sixth layer of air pores, forming a regular hexagonal region, with the innermost layer of the region being a circular region.

[0092] The 6-layer air hole area can be divided into a core area and a cladding area. Both the cladding area and the core area are set on the substrate, and the cladding area wraps around the core area.

[0093] The core region includes the main core region, the first side core region, the second side core region, the third side core region, and the fourth side core region;

[0094] The main core area is a circular area consisting of one seventh air hole 7, one eighth air hole 8, one ninth air hole 9, one tenth air hole 10 and eight first air holes 1, and is located at the center of the substrate;

[0095] The first side core region is a regular hexagonal region composed of 5 second air holes 2 and 1 seventh air hole 7, located on the upper left side of the main core region, and the center distance between two adjacent air holes is Λ1 = 5μm;

[0096] The second side core region is a regular hexagonal region composed of 5 third air holes 3 and 1 eighth air hole 8, located on the lower left side of the main core region, and the center distance between two adjacent air holes is Λ2 = 6μm;

[0097] The third side core region is a regular hexagonal region composed of 5 fourth air holes 4 and 1 ninth air hole 9, located on the lower right side of the main core region, and the center distance between two adjacent air holes is Λ2 = 6μm;

[0098] The fourth side core region is a regular hexagonal region composed of five fifth air holes 5 and one tenth air hole 10, located on the upper right side of the main core region, and the center distance between two adjacent air holes is Λ2 = 6μm;

[0099] The first, second, third, and fourth side core regions surround the main core region.

[0100] Among them, the diameters of the fifth air hole 5, the fourth air hole 4, the sixth air hole 6, the third air hole 3, the second air hole 2, the tenth air hole 10, the first air hole 1, the eighth air hole 8, the ninth air hole 9, and the seventh air hole 7 decrease sequentially.

[0101] That is, the diameter of the fifth air hole 5 is r5 = 1.96 μm; the diameter of the fourth air hole 4 is r4 = 1.68 μm; the diameter of the sixth air hole 6 is r6 = 1.25 μm; the diameter of the third air hole 3 is r3 = 0.95 μm; the diameter of the second air hole 2 is r2 = 0.5 μm; and the diameter of the tenth air hole 10 is r 10=0.53μm; the diameter of the first air hole 1 is r1 = 0.5μm; the diameter of the eighth air hole 8 is r8 = 0.48μm; the diameter of the ninth air hole 9 is r9 = 0.45μm; the diameter of the seventh air hole 7 is r7 = 0.37μm.

[0102] Figures 2-6 These are the main core region multiplexing modes LP of the present invention. 01 LP 11 LP 21 LP 31 LP 12 The mode field diagram shows the width of the mode field on the x-axis and the height on the y-axis. As can be seen from the diagram, the mode fields of these five modes are clear, and the optical energy is well suppressed within the fiber core, allowing for efficient transmission. Compared to traditional mode dividers (MDDs), this increases the number of multiplexed modes, resulting in better suppression of inter-mode crosstalk, which improves the mode extinction ratio and thus achieves stable transmission.

[0103] See Figure 7 The figure shows the variation of the effective refractive index and the difference in effective refractive index between adjacent modes in a mode-division multiplexer across the five modes as a function of wavelength. In a mode-division multiplexing system, the effective refractive index difference Δ between different modes... neff When the value is greater than 0.001, transmission can occur within the same few-mode fiber without interference. Figure 7 It can be understood that in the wavelength range of 1.3μm-1.8μm, LP 01 LP 11 LP 21 LP 31 LP 12 The difference Δ in the effective refractive index of these five modes neff Δ is satisfied near the center wavelength of 1.55 μm. neff >0.001, and Δ neff The extinction ratio increases with the operating wavelength, indicating that intermode crosstalk is well suppressed, which is beneficial to improving the mode extinction ratio, thereby achieving stable transmission and increasing the transmission rate.

[0104] See 8- Figure 10 LP in the first side core region 01 The effective refractive index coefficient of the mode decreases with the increase of the radius r2 of the second air hole 2, decreases slowly with the increase of the radius r7 of the seventh air hole 7 at the connection between the first side core region and the main core, and increases significantly with the increase of the distance Λ2 between the two adjacent centers in the first side core region; and when the radius r2 of the second air hole 2 is 0.65 μm, the radius r7 of the seventh air hole 7 is 0.37 μm, and the distance Λ2 between the two adjacent centers in the first side core region is 6 μm, the first side core region LP 01The effective refractive index of the mode and the core region LP 11 The effective refractive index may have a high matching degree at different center wavelengths, which can improve the coupling efficiency of the device.

[0105] Figure 11 In the first side core region of this invention, LP 01 LP in the mold and core area 11 The graph shows the relationship between the effective refractive index difference of the modes and the wavelength of the input light. Within a wide wavelength range, the LP value in the first side-core region... 01 The effective refractive index coefficient of the mode gradually decreases with increasing wavelength, LP 01 The effective refractive index coefficient of the mode and the core region LP 11 The difference in effective refractive index coefficients also gradually decreases, with the maximum value of the effective refractive index difference being 1.3 × 10⁻⁶ in the input wavelength range of 1.3 μm–2 μm. -4 The minimum difference between the effective refractive index and the actual refractive index is 0.8 × 10⁻⁶. -4 That is, the effective refractive index difference is low throughout the entire wavelength range, resulting in a high phase matching degree.

[0106] See Figures 12-14 In the second side core region of this invention, LP 01 The effective refractive index coefficient of the mode decreases with the increase of the radius r3 of the third air hole 3, decreases slowly with the increase of the radius r8 of the eighth air hole 8 at the connection between the second side core region and the main core, and increases significantly with the increase of the distance Λ2 between the two adjacent centers in the second side core region; and when the radius r3 of the third air hole 3 is 0.95μm, the radius r8 of the eighth air hole 8 is 0.48μm, and the distance Λ2 between the two adjacent centers in the second side core region is 6μm, the second side core region LP 01 The effective refractive index of the mode and the core region LP 11 The effective refractive index has a high degree of matching at different center wavelengths, which improves the coupling efficiency of the device.

[0107] Figure 15 In the second side core region of this invention, LP 01 LP in the mold and core area 21 The graph shows the relationship between the effective refractive index difference of the modes and the wavelength of the input light. As can be seen from the graph, within the wavelength range of 1.3 μm to 2 μm, the LP value in the second side-core region... 01 LP in the mold and core area 21 The effective refractive index difference is generally very low, thus satisfying the phase matching condition.

[0108] See Figures 16-18 In the third side core region of this invention, LP 01The effective refractive index coefficient of the mode decreases with the increase of the radius r4 of the fourth air hole 4, decreases slowly with the increase of the radius r9 of the ninth air hole 9 at the connection between the third side core region and the main core, and increases significantly with the increase of the distance Λ2 between the two adjacent centers in the third side core region; and when the radius r4 of the fourth air hole 4 is 1.68 μm, the radius r9 of the ninth air hole 9 is 0.45 μm, and the distance Λ2 between the two adjacent centers in the third side core region is 6 μm, the LP of the third side core region... 01 The effective refractive index of the mode and the core region LP 11 The effective refractive index has a high degree of matching at different center wavelengths, which improves the coupling efficiency of the device.

[0109] Figure 19 In the third side core region of this invention, LP 01 LP in the mold and core area 21 The graph shows the relationship between the effective refractive index difference of the modes and the wavelength of the input light. As can be seen from the graph, within the wavelength range of 1.3 μm to 2 μm, the LP value in the third side-core region... 01 LP in the mold and core area 21 The effective refractive index difference is generally very low, thus satisfying the phase matching condition.

[0110] See Figures 20-22 In the fourth side core region of this invention, LP 01 The effective refractive index coefficient of the mode decreases with the increase of the radius r5 of the fifth air hole 5, and decreases with the increase of the radius r of the tenth air hole 10 at the connection between the fourth side core region and the main core. 10 The radius of the fifth air hole 5 decreases slowly as the radius increases, and increases significantly as the distance Λ2 between two adjacent centers in the fourth side core region increases; and the radius r5 of the fifth air hole 5 is 1.96μm, while the radius r of the tenth air hole 10 is... 10 When the center distance Λ2 between two adjacent circles in the fourth peripheral core region is 6 μm and the diameter is 0.053 μm, the fourth peripheral core region LP 01 The effective refractive index of the mode and the core region LP 11 The effective refractive index has a high degree of matching at different center wavelengths, which improves the coupling efficiency of the device.

[0111] Figure 23 In the fourth side core region of this invention, LP 01 LP in the mold and core area 21 The graph shows the relationship between the effective refractive index difference of the modes and the wavelength of the input light. It can be seen from the graph that in the wavelength range of 1.3 μm to 2 μm, the LP value in the fourth side-core region... 01 LP in the mold and core area 21 The effective refractive index difference is generally very low, thus satisfying the phase matching condition.

[0112] Figure 24When the center wavelength of the input incident light wave is 1.55 μm, the LP of this invention... 11 LP 21 LP 31 LP 12 The graph shows the coupling efficiency of the four modes from the first, second, third, and fourth side core regions to the main core region as a function of device length. It can be seen from the graph that the coupling efficiency reaches its highest value when the device length is 1840 μm, which means that the coupling efficiency of the input light incident wave can be met when the device length is 1840 μm. Figure 26 This is the LP of the present invention. 11 LP 21 LP 31 LP 12 The graph shows the coupling efficiency of the mode as a function of wavelength at a device length of 1840 μm, and in LP... 11 The content in the model was 99.3%, and in LP 21 The percentage in the model was 94.6%, and in LP... 31 The rate was 96.3% in the model, and in LP 12 The normalized coupling efficiency of the device is 93.5%, which results in a high normalized coupling efficiency.

[0113] from Figure 25 It can be understood that LP in this invention 11 LP 21 LP 31 LP 12 The conversion efficiency of these four modes first increases and then decreases with the increase of the input light wavelength, and all have a conversion efficiency of more than 80% in the wavelength range of 1.33-1.95μm.

[0114] The coupling efficiency (coupling efficiency η is defined as the ratio of the light energy in the input side core to the light energy of the corresponding higher-order mode in the output main core) of each main core region and side core region in the fiber core region of the device is calculated by the following expression (1);

[0115]

[0116] In the formula, P in P is the total energy input to the incident side core. out This refers to the total energy output from the main core at the output end.

[0117] The normalized coupling efficiency η0 of the device is calculated from the coupling efficiency of the main core region, the coupling efficiency of the first side core region, the coupling efficiency of the second side core region, the coupling efficiency of the third side core region, and the coupling efficiency of the fourth side core region using expression (2):

[0118]

[0119] In the formula, η1 represents the coupling efficiency of the main core region, η2 represents the coupling efficiency of the first side core region, η3 represents the coupling efficiency of the second side core region, η4 represents the coupling efficiency of the third side core region, and η5 represents the coupling efficiency of the fourth side core region.

[0120] The insertion loss of the main core region, the first side core region, the second side core region, the third side core region, and the fourth side core region in the device is calculated using expression (3):

[0121] The insertion loss IL is defined as ten times the logarithm of the ratio of input energy to output energy.

[0122]

[0123] In the formula, P in P is the total energy input to the incident side core. out This refers to the total energy output from the main core at the output end.

[0124] The normalized insertion loss IL0 of the device is calculated using expression (4):

[0125]

[0126] In the formula, IL1 represents the insertion loss of the main core region, IL2 represents the insertion loss of the first side core region, IL3 represents the insertion loss of the second side core region, IL4 represents the insertion loss of the third side core region, and IL5 represents the insertion loss of the fourth side core region.

[0127] The coupling length L of the device C The coupling length L is defined as the transmission distance required for optical energy to be completely transferred from the lateral core to the main core. C The result is obtained by calculation using expression (5):

[0128]

[0129] In the formula, β represents the propagation constant, λ represents the incident light wavelength, f represents the incident light frequency, n represents the mode refractive index, c represents the speed of light in vacuum, and the subscripts e and o represent the even mode and odd mode of the mode, respectively.

[0130] LP input in the main core region of the device 01 The mode does not undergo a coupling conversion process, resulting in almost no loss during transmission, thus achieving 100% coupling efficiency and 0dB insertion loss; at a center wavelength of 1.55μm, LP 11 The coupling efficiency is 99.3%, and the insertion loss is 0.03 dB; LP 21 The coupling efficiency is 94.6%, and the insertion loss is 0.24 dB; LP 31The coupling efficiency is 96.3%, and the insertion loss is 0.16 dB; LP 12 The coupling efficiency is 93.5%, and the insertion loss is 0.29 dB.

[0131] From the above expressions (1)-(5), it can be calculated that the overall normalized coupling efficiency of the present invention is 96.7% at the incident light center wavelength of 1.55μm, the normalized insertion loss is 0.15dB, and the device operating bandwidth is 1.33μm-1.95μm.

[0132] Figure 26 This invention is in LP 11 LP 21 Mode field diagram of simultaneous mode transmission; Figure 27 This invention is in LP 31 LP 12 The mode field diagram transmitted simultaneously; by Figure 26 and Figure 27 It is understood that the more red the color in the diagram, the closer the energy intensity is to 1, and the closer the color is to blue, the closer the energy intensity is to 0. That is, the light input into the first, second, third, and fourth side core regions can be efficiently coupled to the main core region for simultaneous transmission after propagating a certain distance.

[0133] Figure 28 This is a graph showing the change in coupling efficiency with input light wavelength when the device size changes by +0.5%. Figure 29 This is a graph showing the coupling efficiency as a function of the input light wavelength when the device size changes by -0.5%. Figure 28 and Figure 29 It can be seen that when the air hole size increases by +0.5%, the device operating bandwidth is 1.38μm-1.87μm; when the air hole size increases by -0.5%, the device operating bandwidth is 1.4μm-1.87μm. The overall changes are within a reasonable range and can be applied to industrial production.

[0134] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0135] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A mode divider multiplexer based on a five-core photonic crystal fiber, characterized in that, The module multiplexer includes a substrate and an air hole layer region, wherein the air hole layer region is disposed on the substrate; The air hole layer region is composed of a plurality of air holes arranged in a manner. The air hole layer is divided into a core region and a cladding region, and the cladding region encloses the core region. The fiber core includes a main core region, a first side core region, a second side core region, a third side core region, and a fourth side core region; The main core region is located at the center of the substrate, and the first side core region, the second side core region, the third side core region and the fourth side core region surround the main core region, and the cladding surrounds the main core region. The main core region is a circular region composed of a seventh air hole (7), an eighth air hole (8), a ninth air hole (9), a tenth air hole (10) and a number of first air holes (1) within the cladding layer; The first side core region is a regular hexagonal region composed of a plurality of second air holes (2) and a seventh air hole (7) within the cladding layer; The second side core region is a regular hexagonal region composed of several third air holes (3) and one eighth air hole (8) within the cladding layer; The third side core region is a regular hexagonal region composed of several fourth air holes (4) and one ninth air hole (9) within the cladding layer; The fourth side core region is a regular hexagonal region composed of several fifth air holes (5) and one tenth air hole (10) within the cladding layer; The cladding region is composed of a plurality of sixth air holes, the sixth air holes (6) surround the core region, and the center-to-center distance between two adjacent sixth air holes (6) is Λ1 = 4.975~5.025μm; The first air hole (1), the second air hole (2), the third air hole (3), the fourth air hole (4), the fifth air hole (5), the sixth air hole (6), the seventh air hole (7), the eighth air hole (8), the ninth air hole (9), and the tenth air hole (10) are circular; The diameter of the fifth air hole (5) is r5 = 1.95~1.97 μm; The diameter of the fourth air hole (4) is r4 = 1.67~1.69 μm; The diameter of the sixth air hole (6) is r6 = 1.243~1.257 μm; The diameter of the third air hole (3) is r3 = 0.945~0.955μm; The diameter of the second air hole (2) is r2 = 0.646~0.654 μm; The diameter of the tenth air hole (10) is r 10 =0.527~0.533μm; The diameter of the first air hole (1) is r1 = 0.4975~0.5025 μm; The diameter of the eighth air hole (8) is r8 = 0.477~0.483 μm; The diameter of the ninth air hole (9) is r9 = 0.447~0.453 μm; The diameter of the seventh air hole (7) is r7 = 0.368~0.372 μm.

2. A mode divider based on a five-core photonic crystal fiber according to claim 1, characterized in that, The center distance Λ1 between two adjacent air holes in the main core region, the second side core region, the third side core region, and the fourth side core region is 4.975-5.025 μm, and the center distance Λ2 between two adjacent air holes in the first side core region is 5.97-6.03 μm.

3. A mode divider multiplexer based on a five-core photonic crystal fiber according to claim 1, characterized in that, The air hole layer area is provided with 6 layers of air holes, which are, from the inside out, the first layer of air holes, the second layer of air holes, the third layer of air holes, the fourth layer of air holes, the fifth layer of air holes and the sixth layer of air holes; The first layer of air holes is formed in a circle by the sequence of 1 seventh air hole (7), 1 first air hole (1), 1 eighth air hole (8), 3 first air holes (1), 1 ninth air hole (9), 1 first air hole (1), 1 tenth air hole (10) and 3 first air holes (1); The second layer of air holes is composed of a regular hexagon formed by two second air holes (2), two third air holes (3), three sixth air holes (6), two fourth air holes (4), two fifth air holes (5), and three sixth air holes (6) in sequence; The third layer of air holes includes three second air holes (2), one sixth air hole (6), three third air holes (3), five sixth air holes (6), three fourth air holes (4), one sixth air hole (6), three fifth air holes (5), and five sixth air holes (6) arranged in a regular hexagon. The fourth layer of air holes is composed of 26 sixth air holes (6) forming a regular hexagon; The fifth layer of air holes is composed of 34 sixth air holes (6) forming a regular hexagon; The sixth layer of air holes consists of 42 sixth air holes (6) forming a regular hexagon.

4. A mode divider multiplexer based on a five-core photonic crystal fiber according to claim 1, characterized in that, The substrate is made of silicon dioxide.

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