A metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission

Abstract

The present invention discloses a metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission. The metamaterial photonic crystal fiber includes a core (1) and a cladding (2). The cladding has five layers of air holes, including an innermost circular structure air hole (3), a second-layer circular structure air hole (4), third and fourth-layer circular structure air holes (5), and an outermost circular structure air hole (6). The core is a solid region located at the center of the optical fiber body. The air holes in the cladding are arranged in a hexagonal radial pattern around the outer circumference of the core, forming a two-dimensional photonic crystal structure in the cross-section of the photonic crystal fiber. The dielectric constant changes periodically at the wavelength scale, enabling the light wave propagating therein to have a band structure. By only changing the parameters of the five layers of circular structure air holes in the cladding, the performance of the cladding can be adjusted like that of a single material, thereby realizing the functions of smooth dispersion, adjustable dispersion compensation, and reduced confinement loss in a broadband range.

Description

Technical Field

[0001] The present invention belongs to the technical field of metamaterial photonic crystal fibers, and particularly relates to a metamaterial photonic crystal fiber that realizes effective transmission with broadband dispersion compensation. Background Art

[0002] Compared with traditional solid-state lasers, high-power fiber lasers have the advantages of high conversion efficiency, good beam quality, and convenient heat dissipation, and are one of the hottest research topics in the international laser technology field. In recent years, with the continuous increase in the output power of a single fiber, the application prospects of high-power fiber lasers are more promising, and they have been rapidly applied in the fields of optical communication, material processing and treatment, medicine, printing, etc., showing a trend of gradually replacing existing traditional high-power lasers.

[0003] The concept of photonic crystals was initially proposed from the perspective of controlling spontaneous emission of light. E. Yablonovitch pointed out in 1987 that if dielectric materials with different dielectric constants are composed into a periodic structure, for example, low-refractive-index materials are periodically introduced at certain positions in a material with a higher refractive index, light waves are affected by the periodic potential field of the medium and have energy bands, similar to the energy band gaps of electrons in a crystal. Since the coupling between photons and atoms is related to the density of the initial and final states of the atoms, if the band gap of the electromagnetic wave overlaps with the band edge of the electron energy band, then the radiative recombination of electrons and holes will be strongly suppressed due to the decrease in the density of states; theoretically, the loss of the dielectric structure is extremely low, and this suppression will be more thorough than that of a metal waveguide.

[0004] In the traditional hollow-core photonic crystal fiber structure, dielectric air holes and a substrate are periodically distributed in the cross-section. By changing the size of the air holes, the mutual positional relationship, and the refractive index between the air holes and the substrate, the transmission performance of the fiber can be improved. However, the photonic crystal bandgap is not very clear. Therefore, the transmission mode and effective refractive index of this kind of fiber are not ideal. Moreover, during the transmission in the hollow-core fiber, if the confinement effect of the cladding structure on the guided mode is not obvious enough, lateral leakage will occur, and the confinement effect of the hollow-core structure fiber on the mode is not obvious; in high-power laser systems, both the broadening fiber and the grating will introduce positive dispersion into the system, and this dispersion will accumulate continuously, resulting in the deterioration of the amplified pulse quality. Based on the above background, the present invention proposes a photonic crystal fiber with broadband dispersion compensation and effective transmission, realizing a metamaterial photonic crystal fiber that can achieve adjustable dispersion compensation in a specific band, smooth dispersion in some other bands, has a shiftable zero-dispersion point, and reduces the confinement loss. Other researchers have also proposed the photonic crystal fiber structure with sandwich air holes, but it does not have the characteristic of smooth dispersion in the target band; different from previous work, we designed three sizes of air holes. Experimental data show that the innermost air holes have an important influence on modulating the dispersion coefficient, and the data results are one order of magnitude or more better than previous structures. Summary of the Invention

[0005] Technical Problem: The present invention is proposed to solve the above problems, aiming to provide a metamaterial photonic crystal fiber with broadband dispersion compensation and effective transmission, realizing a metamaterial photonic crystal fiber that can achieve adjustable dispersion compensation in a specific band, smooth dispersion in some other bands, has a shiftable zero-dispersion point, and reduces the confinement loss.

[0006] Technical solution: The present invention discloses a metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission. The metamaterial photonic crystal fiber includes a core and a cladding. The cladding has five layers of air holes, including an innermost circular structure air hole, a second-layer circular structure air hole, third and fourth-layer circular structure air holes, and an outermost circular structure air hole. The core is a solid region located at the center of the fiber body. The air holes in the cladding are arranged in a hexagonal radial pattern around the outer circumference of the core, forming a two-dimensional photonic crystal structure in the cross-section of the photonic crystal fiber. The aperture D2 of the second-layer circular structure air hole is equal to the aperture D4 of the outermost circular structure air hole. The aperture D1 of the innermost circular structure air hole is smaller than the aperture D2 of the second-layer circular structure air hole. The apertures D3 of the third and fourth-layer circular structure air holes are equal and smaller than the aperture D1 of the innermost circular structure air hole. The dielectric constant in the cladding varies periodically on the wavelength scale, and the radial spacing L of each layer of circular structure air holes is of the same order as the incident light wavelength, so that the light wave propagating in the cladding has a band structure. By simply changing the size parameters of each layer of circular structure air holes in the cladding, the performance of a single material can be adjusted for the cladding, achieving smooth dispersion, adjustable dispersion compensation, and reduced confinement loss over a wide band.

[0007] The axes of the innermost circular structure air hole, the second-layer circular structure air hole, the third and fourth-layer circular structure air holes, and the outermost circular structure air hole in the cladding are arranged parallel to the axis of the photonic crystal fiber. The cross-sectional distribution structure of the innermost circular structure air hole, the second-layer circular structure air hole, the third and fourth-layer circular structure air holes, and the outermost circular structure air hole in the photonic crystal fiber is a hexagonal sandwich circular structure air hole structure. Each layer of circular structure air holes is symmetrically arranged around the center of the core and is radially arranged.

[0008] The innermost circular structure air hole of the cladding structure uses 6 circular structure air holes, and the aperture of each circular structure air hole is D1. The central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the innermost circular structure air hole and the center of the core are all equal.

[0009] The second-layer circular structure air hole of the cladding structure uses 12 circular structure air holes, and the aperture of each circular structure air hole is D2, and the aperture D2 is larger than the aperture D1. The central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the second-layer circular structure air hole and the center of the core are all equal.

[0010] The third and fourth-layer circular structure air holes of the cladding structure use 24 and 36 circular structure air holes respectively. The aperture of each circular structure air hole is D3, and the aperture D3 is smaller than the aperture D1. The apertures of the third and fourth-layer circular structure air holes are equal. The central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the third and fourth-layer circular structure air holes and the center of the core are all equal.

[0011] The outermost circular structure air holes of the cladding structure adopt 24 circular structure air holes, and the aperture of each circular structure air hole is D4, and the aperture D4 is equal to the aperture D2; the central angles formed by the connecting lines of the centers of every two adjacent circular structure air holes in the outermost circular structure air holes and the center of the fiber core are equal.

[0012] The fiber core material is a solid silica glass material.

[0013] The cladding background material is a solid silica glass material.

[0014] The aperture D1 of the innermost circular structure air hole is 600 - 690 nm; the aperture D2 of the second-layer circular structure air hole is equal to the aperture D4 of the outermost circular structure air hole, that is, D2 = D4 = 660 - 760 nm; the aperture D3 of the third and fourth-layer circular structure air holes is 360 - 440 nm; the radial spacing L of the air holes of each layer of circular structure is 910 - 1200 nm.

[0015] The number of layers of the outermost circular structure air holes is 1 - 3 layers, and the number of the three layers of air holes is 24, 36, and 48 from the inside to the outside in sequence.

[0016] Advantages: Compared with the prior art, the advantages of the present invention are as follows: Due to the different light guiding mechanisms, it does not need to guide light through the confinement of the photonic bandgap, so the accuracy requirements for the cladding structure are not high, which is very beneficial for production. Moreover, the optical fiber of the present invention has an adjustable single-material structure, and has great advantages in manufacturing processes and costs. Compared with the prior art, a similar sandwich structure can only achieve large negative dispersion compensation within the relevant wavelength band, and only when the incident wavelength is 1.55 μm, there is a large negative dispersion coefficient value of -440.837 ps / nm / km; the gradient air hole structure only shows the function of controlling dispersion in a longer wavelength band, and the dispersion coefficient value within the wavelength range of 3.8 - 5 μm is ±1.2 ps / nm / km; the present invention shows smooth dispersion within the long wavelength band of 600 - 2,000 nm, and the dispersion in a specific wavelength band can be controlled within ±0.5 ps / nm / km by adjusting the air hole size, having great advantages. Another prior art is a common photonic crystal fiber with the same air hole aperture size, arranged in a triangular lattice uniformly in a background material of silica, and the dispersion coefficient value is -8 to +3 ps / nm / km when the incident wavelength is 8.5 - 1.55 μm. The optical fiber of the present invention has very good single-mode characteristics within the range of the incident wavelength of 600 - 2,000 nm. The difference between the core electric field mode integral of the fundamental mode and other high-order modes and the integral of the entire optical fiber electric field mode always remains at three orders of magnitude or more; the effective mode area of the optical fiber shows a trend of first decreasing and then increasing with the incident wavelength; within the wavelength band of 600 - 2,000 nm of the incident wavelength, the dispersion coefficient of the optical fiber of the present invention is relatively smooth, and a zero-dispersion point appears at about 1,150 nm of the incident wavelength; as the diameter D1 of the air hole in the innermost circular structure increases, the zero-dispersion point becomes smaller and moves to the left in the optical fiber dispersion coefficient distribution diagram, and adjustment can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic cross-sectional structure diagram of the optical fiber of the present invention;

[0018] In the figure: there are core 1, cladding 2, air hole 3 in the innermost circular structure, air hole 4 in the second-layer circular structure, air holes 5 in the third and fourth-layer circular structures, and air hole 6 in the outermost circular structure.

[0019] Figure 2 is an optical fiber mode analysis diagram of Embodiment 1 of the present invention;

[0020] Figure 3 is a distribution diagram of the ratio of the core electric field mode integral of different modes to the integral of the entire optical fiber electric field mode of Embodiment 1 of the present invention;

[0021] Figure 4 is an optical fiber dispersion coefficient distribution diagram of Embodiment 1 of the present invention;

[0022] Figure 5Dispersion coefficient distribution diagram of a photonic crystal fiber when the incident wavelength range is 850 - 1200 nm under different structural parameters of the present invention;

[0023] Figure 6 Schematic structural diagram of Comparative Example 1, where PML is the perfectly matched layer, AH is the air hole, Si is the background material silicon, d1 is the diameter of the outer air hole, d2 is the diameter of the inner air hole, and Λ is the spacing between the air holes;

[0024] Figure 7 Schematic structural diagram of Comparative Example 2, where d1 is the diameter of the outermost air hole, Λ1 is the spacing between the outermost air holes, d2 is the diameter of the second - layer air hole, Λ2 is the spacing between the second - layer air holes, d3 is the diameter of the innermost air hole, and Λ3 is the spacing between the innermost air holes;

[0025] Figure 8 Schematic structural diagram of Comparative Example 3. Detailed implementation manners

[0026] Example 1:

[0027] A broadband dispersion - compensating and effectively - transmitting metamaterial photonic crystal fiber of the present invention includes a core 1 and a cladding 2. The cladding 2 includes an innermost - layer circular - structure air hole 3, a second - layer circular - structure air hole 4, third - and fourth - layer circular - structure air holes 5, and an outermost - layer circular - structure air hole 6. The core 1 is a solid region located at the center of the fiber body. The cladding 2 is regularly arranged in a regular - hexagon around the outer circumference of the core 1, forming a two - dimensional photonic crystal in the cross - section. The dielectric constant changes periodically at the wavelength scale, enabling the light wave propagating therein to have a band structure. By only changing the parameters of the five - layer circular - structure air holes in the cladding 2, the performance of a single material can be adjusted for the cladding, thereby realizing the functions of adjustable dispersion compensation, movable zero - dispersion point, and reduced confinement loss in a wide band.

[0028] The background material of the cladding 2 is selected as silica glass material due to its excellent light transmittance, and its refractive index is 1.45. The core 1 is located at the exact center of the background material, and the diameter of the core 1 is 5.307 μm.

[0029] The diameter of the fiber is 10.613 μm. The innermost - layer circular - structure air hole 3 of the cladding uses 6 small - circular - structure air holes with a pore diameter of 600 nm;

[0030] The second - layer circular - structure air hole 4 uses 12 large - circular - structure air holes with a pore diameter of 660 nm;

[0031] The third layer uses 24 small - circular - structure air holes with a pore diameter of 388.2 nm;

[0032] The fourth layer uses 36 large - circular - structure air holes. The pore diameter is 388.2 nm;

[0033] The outermost circular structure air holes 6 adopt 36 large circular structure air holes with a pore diameter of 660 nm;

[0034] For the innermost circular structure air holes 3, the central angle formed by the connection lines between the centers of every two adjacent circular structure air holes and the center of the fiber core 1 is 60°; for the second-layer circular structure air holes 4, the central angle formed by the connection lines between the centers of every two adjacent circular structure air holes and the center of the fiber core 1 is 30°; for the third and fourth-layer circular structure air holes 5, for the third layer, the central angle formed by the connection lines between the centers of every two adjacent circular structure air holes and the center of the fiber core 1 is 15°, and for the fourth layer, the central angle formed by the connection lines between the centers of every two adjacent circular structure air holes and the center of the fiber core 1 is 10°; for the fifth layer, i.e., the outermost circular structure air holes 6, the central angle formed by the connection lines between the centers of two adjacent circular structure air holes and the center of the fiber core 1 is 10°.

[0035] Examples 2 to 10: The methods and steps adopted are the same as those in Example 1, and the specific structural parameters are shown in Table 1.

[0036] Table 1 Comparison Table of Implementation Schemes

[0037]

[0038]

[0039] After calculation, for the above structural parameters, very good single-mode characteristics exist in the range of the incident wavelength from 600 to 2000 nm; the difference between the core electric field mode integral of the fundamental mode and that of other high-order modes and the integral of the entire optical fiber electric field mode always remains at 3 orders of magnitude or more; the effective mode area of the optical fiber first decreases and then increases with the incident wavelength; the dispersion coefficient of this structure is relatively smooth in the wavelength band of 600 to 2000 nm for the incident wavelength, and a zero-dispersion point appears at about 1150 nm for the incident wavelength; as D1 increases, the zero-dispersion point becomes smaller and shifts to the left in the optical fiber dispersion coefficient distribution diagram, and adjustment can be achieved (see the simulation results in the appendix Figure 5 ).

[0040] Comparative Example 1: A sandwich air hole structure photonic crystal fiber with two air hole aperture sizes, and the background material is silica; by adjusting the aperture sizes of the fourth and fifth layer air holes, a relatively large negative dispersion coefficient value of -440.837 ps / nm / km is obtained at the incident wavelength of 1.55 μm. As Figure 6 shown.

[0041] Comparative Example 2: A gradient air-hole aperture photonic crystal fiber with a sulfide as the background material; when d1 = 0.4 μm, d2 = 0.16 μm, d3 = 0.04 μm, Λ1 = 0.88 μm, Λ2 = 0.8 μm, and Λ3 = 0.5 μm, three zero-dispersion wavelengths are obtained, which are 4 μm, 4.62 μm, and 5.9 μm respectively; and the dispersion coefficient value in the wavelength range of 3.8 - 5 μm is ±1.2 ps / nm / km. As Figure 7 shown.

[0042] Comparative Example 3: A common photonic crystal fiber with the same air-hole aperture size, arranged in a triangular lattice uniformly in a silica background material; when the incident wavelength is 8.5 - 1.55 μm, the dispersion coefficient value is -8 to +3 ps / nm / km. As Figure 8 shown. Analysis of simulation results:

[0043] Comparative Example 1 can obtain a relatively large negative dispersion coefficient when modulating dispersion, and can be used as a dispersion compensation fiber when connected to a standard single-mode fiber; the present invention can maintain the good characteristic of smooth dispersion in a relatively long wavelength band of optical communication propagation, and has the potential to replace the structure of the standard single-mode fiber connected to the dispersion compensation fiber in the optical communication system.

[0044] Comparative Example 2 is applied in the wavelength range of 3.8 - 5 μm and does not have the characteristic of smooth dispersion in a shorter wavelength band; the present invention well supplements the function of achieving smooth dispersion in a shorter wavelength band.

[0045] Comparative Example 3 is a common photonic crystal fiber, and the dispersion coefficient value is not smooth when the incident wavelength is 8.5 - 1.55 μm; the present invention can control the dispersion coefficient value within ±0.5 ps / nm / km by adjusting the sizes of different air holes in the cladding, which has been greatly improved compared with the common photonic crystal fiber.

[0046] Those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on these technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A broadband dispersion-compensated and effectively transmissive metamaterial photonic crystal fiber, characterized in that, The metamaterial photonic crystal fiber includes a core (1) and a cladding (2). The cladding (2) has five layers of air holes, including an innermost circular structure air hole (3), a second-layer circular structure air hole (4), third and fourth-layer circular structure air holes (5), and an outermost circular structure air hole (6); the core (1) is a solid region located at the center of the fiber body, and the air holes in the cladding (2) are arranged in a hexagonal radial pattern around the outer circumference of the core (1), forming a two-dimensional photonic crystal structure in the cross-section of the photonic crystal fiber; the aperture D2 of the second-layer circular structure air hole (4) is equal to the aperture D4 of the outermost circular structure air hole (6); the aperture D1 of the innermost circular structure air hole (3) is smaller than the aperture D2 of the second-layer circular structure air hole (4). The apertures D3 of the third and fourth-layer circular structure air holes (5) are equal and smaller than the aperture D1 of the innermost circular structure air hole (3); the dielectric constant in the cladding (2) changes periodically on the wavelength scale, and the radial spacing L of each layer of circular structure air holes is of the same order as the incident light wavelength, so that the light wave propagating in the cladding (2) has a band structure; by only changing the size parameters of each layer of circular structure air holes in the cladding (2), the performance of a single material can be adjusted for the cladding, and smooth dispersion in a wide band, adjustable dispersion compensation, and reduced confinement loss can be obtained.

2. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1, characterized in that The axes of the innermost circular structure air hole (3), the second-layer circular structure air hole (4), the third and fourth-layer circular structure air holes (5), and the outermost circular structure air hole (6) in the cladding (2) are arranged parallel to the axis of the photonic crystal fiber. The cross-sectional distribution structure of the innermost circular structure air hole (3), the second-layer circular structure air hole (4), the third and fourth-layer circular structure air holes (5), and the outermost circular structure air hole (6) in the photonic crystal fiber is a hexagonal sandwich circular structure air hole structure, and each layer of circular structure air holes is symmetrically arranged around the center of the core (1) and is arranged radially.

3. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1 or 2, characterized in that, The innermost circular structure air hole (3) of the cladding (2) structure uses 6 circular structure air holes, and the aperture of each circular structure air hole is D1; the central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the innermost circular structure air hole (3) and the center of the core (1) are all equal.

4. A metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission, characterized in that, The second-layer circular structure air hole (4) of the cladding (2) structure uses 12 circular structure air holes, and the aperture of each circular structure air hole is D2, and the aperture D2 is larger than the aperture D1; the central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the second-layer circular structure air hole (4) and the center of the core (1) are all equal.

5. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1 or 2, characterized in that, The third and fourth-layer circular structure air holes (5) of the cladding (2) structure use 24 and 36 circular structure air holes respectively, and the aperture of each circular structure air hole is D3, and the aperture D3 is smaller than the aperture D1; the apertures of the third and fourth-layer circular structure air holes are equal, and the central angles formed by the connection lines of the centers of every two adjacent circular structure air holes in the third and fourth-layer circular structure air holes (5) and the center of the core (1) are all equal.

6. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1 or 2, characterized in that, The outermost circular structure air holes (6) of the cladding (2) structure adopt 24 circular structure air holes, and the aperture of each circular structure air hole is D4, and the aperture D4 is equal to the aperture D2; the central angles formed by the connecting lines of the centers of every two adjacent circular structure air holes in the outermost circular structure air holes (6) and the center of the fiber core (1) are all equal.

7. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1 or 2, characterized in that The material of the fiber core (1) is a silica glass solid material.

8. The metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission according to claim 1 or 2, characterized in that, The background material of the cladding (2) is a silica glass solid material.

9. The broadband dispersion compensation effective transmission metamaterial photonic crystal fiber according to claim 1, characterized in that, The aperture D1 of the innermost circular structure air holes (3) is 600 - 690 nm; the aperture D2 of the second-layer circular structure air holes (4) is equal to the aperture D4 of the outermost circular structure air holes (6), that is, D2 = D4 = 660 - 760 nm; the aperture D3 of the third and fourth-layer circular structure air holes (5) is 360 - 440 nm; the radial spacing L of the air holes of each layer of circular structure is 910 - 1200 nm.

10. A metamaterial photonic crystal fiber for effective broadband dispersion compensation transmission, characterized in that, The number of layers of the outermost circular structure air holes (6) is 1 - 3 layers, and the number of the three layers of air holes from the inside to the outside is 24, 36, and 48 in sequence.

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