A bandgap photonic crystal fiber for supercontinuum transmission

Abstract

The present invention discloses a bandgap photonic crystal fiber for transmitting a supercontinuum, and relates to the technical field of photonic crystal fibers. The present invention includes a base material, a fiber core, and a plurality of dielectric hole units arranged in the base material and distributed along the axial direction of the optical fiber and running through the entire optical fiber, wherein the fiber core is located at the center of the base material; the dielectric hole unit includes a first dielectric hole, a dielectric hole combination structure, a second dielectric hole, and a first optical fiber lattice arranged equidistantly along the circumference of the fiber core, and the first dielectric hole is externally cut with the fiber core. The photonic crystal fiber of the present invention can achieve lower loss in the 1.55‑2μm band, has a higher nonlinear coefficient, and has better single-mode characteristics, has a simple structure, meets the conditions for generating a supercontinuum, and the overall structure of the optical fiber adopts a stable hexagonal structure, which is convenient for the entire optical fiber to have a strong bending resistance and improve its service life.

Description

Technical Field

[0001] The invention relates to the technical field of photonic crystal optical fibers, in particular to a bandgap photonic crystal optical fiber for transmitting supercontinuum spectrum. Background Art

[0002] Photonic crystal fiber is a new type of microstructured optical fiber developed on the basis of photonic crystal and optical fiber technology. This type of optical fiber consists of a core and air holes arranged around it according to certain rules. Its structural design is relatively flexible, and some structural parameters have greater adjustability. Compared with general optical fibers, photonic crystal fibers have the characteristics of non-cutoff single-mode transmission, high birefringence, high nonlinearity, low loss, novel dispersion characteristics, and controllable effective mode area. It has broad application prospects in the fields of optical fiber sensing, optical fiber communication, nonlinear optics, and lasers.

[0003] Chalcogenide glass photonic crystal fiber is a new type of photonic crystal fiber that is developed by utilizing the excellent mid-infrared transmittance and high nonlinearity of chalcogenide glass materials and through reasonable and scientific design of structure and composition materials. It uses an incident laser pulse with specific frequency and pulse characteristics to pump the chalcogenide glass photonic crystal fiber to produce a supercontinuum spectrum, and its spectrum broadening range can extend from the visible light band to the mid- and far-infrared bands. In addition, the output supercontinuum spectrum also has the advantages of high average power and good flatness.

[0004] Although the laser light sources currently used to generate mid-infrared bands have high brightness and coherence, they can only generate lasers with specific wavelengths, which greatly limits the application of mid-infrared lasers in real life. Since Alfano et al. obtained a visible light supercontinuum with a spectral broadening range of 300nm in the 1970s, research in the field of supercontinuum has developed rapidly. Currently, the nonlinear materials that generate supercontinuum mainly include bulk materials, ordinary single-mode optical fibers, and photonic crystal fibers; the laser pulses used to pump nonlinear materials to generate supercontinuum mainly include femtosecond (fs) laser pulses, picosecond (ps) laser pulses, and continuous (cw) lasers. However, the optical fibers that currently generate supercontinuum have large losses and poor bending resistance when used. For this reason, we propose a bandgap photonic crystal fiber that transmits supercontinuum. Summary of the invention

[0005] The object of the present invention is to provide a bandgap photonic crystal fiber for transmitting supercontinuum spectrum, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a bandgap photonic crystal fiber for transmitting supercontinuum, comprising a substrate material, a fiber core, and a plurality of medium hole units arranged in the substrate material and distributed along the axial direction of the fiber and running through the entire fiber, wherein the fiber core is located at the center of the substrate material;

[0007] The medium hole unit comprises a first medium hole, a medium hole combination structure, a second medium hole and a first optical fiber lattice which are arranged equidistantly along the circumference of the fiber core, the first medium hole is circumscribed with the fiber core, the medium hole combination structure is arranged outside the first medium hole and arranged equidistantly along the circumference of the fiber core, and the second medium hole is located between two adjacent medium hole combination structures and circumscribed with them;

[0008] The first optical fiber lattice is located on the extension line of the line connecting the fiber core and the center of the second medium hole.

[0009] Furthermore, the number of the dielectric hole combination structures is set to six, and the six dielectric hole combination structures are arranged at equal distances along the circumference of the fiber core.

[0010] Furthermore, the dielectric hole combination structure includes a plurality of elliptical dielectric holes, the plurality of elliptical dielectric holes are distributed in a ring shape, a second optical fiber lattice is arranged between two adjacent elliptical dielectric holes, and the second optical fiber lattice is separated from the elliptical dielectric holes.

[0011] Furthermore, the lattice constants of the first optical fiber lattice and the second optical fiber lattice are set to c, and the diameter of the second medium hole is set to 0.5c.

[0012] Furthermore, the number of the first dielectric holes is six, the six first dielectric holes are equidistantly arranged along the circumference of the fiber core, and the diameter of the first dielectric holes is set to 0.7c, 0.8c or 0.9c.

[0013] Furthermore, there are multiple elliptical medium holes, with four elliptical medium holes forming a group, and the major axis and minor axis of the elliptical medium holes are set to 0.9c and 0.5c respectively.

[0014] Furthermore, the fiber core is made of silicon dioxide, and the diameter of the fiber core is 12 μm.

[0015] Furthermore, the refractive index of the base material is greater than the refractive index of the fiber core, and a perfect matching layer is arranged on the outer surface of the base material.

[0016] Furthermore, the base material is made of arsenic sulfide, and its refractive index is expressed as follows:

[0017]

[0018] Where n is the refractive index of the optical fiber and λ is the wavelength.

[0019] Furthermore, the first medium hole and the second medium hole are both configured to be circular.

[0020] The present invention has at least the following beneficial effects:

[0021] 1. The photonic crystal fiber of the present invention can achieve lower loss in the 1.55-2 μm band, has a higher nonlinear coefficient, and has better single-mode characteristics, a simple structure, and meets the conditions for generating a supercontinuum.

[0022] 2. The overall structure of the present invention adopts a stable hexagonal structure, which makes the entire optical fiber have strong bending resistance and improves its service life.

[0023] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A cross-sectional schematic diagram of the overall structure of an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the mode field distribution of the fundamental mode of an embodiment of the present invention;

[0026] Figure 3 A schematic diagram showing the variation of limiting loss of the fundamental mode with wavelength according to an embodiment of the present invention;

[0027] Figure 4 FIG. 4 is a schematic diagram showing the variation of the nonlinear coefficient with wavelength according to an embodiment of the present invention.

[0028] Reference numerals:

[0029] 1. Base material; 2. Fiber core; 3. First dielectric hole; 4. Dielectric hole combination structure; 41. Elliptical dielectric hole; 42. Second optical fiber lattice; 5. Second dielectric hole; 6. First optical fiber lattice; 7. Perfect matching layer. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0031] See also Figure 1-Figure 4The present invention provides a technical solution: a bandgap photonic crystal fiber for transmitting supercontinuum, comprising a substrate material 1, a core 2, and a plurality of medium hole units arranged in the substrate material 1 and distributed along the axial direction of the optical fiber and running through the entire optical fiber, wherein the core 2 is located at the center of the substrate material 1;

[0032] The dielectric hole unit includes a first dielectric hole 3, a dielectric hole combination structure 4, a second dielectric hole 5 and a first optical fiber lattice 6 which are arranged equidistantly along the circumference of the fiber core 2. The first dielectric hole 3 is circumscribed with the fiber core 2. The dielectric hole combination structure 4 is arranged outside the first dielectric hole 3 and is arranged equidistantly along the circumference of the fiber core 2. The second dielectric hole 5 is located between two adjacent dielectric hole combination structures 4 and is circumscribed with them.

[0033] The first optical fiber lattice 6 is located on the extension line of the line connecting the fiber core 2 and the center of the second medium hole 5 .

[0034] The number of the dielectric hole combination structures 4 is set to six, and the six dielectric hole combination structures 4 are arranged equidistantly along the circumference of the fiber core 2 , so that the optical fiber forms a hexagonal stable structure, which facilitates more stable light transmission in the fiber core 2 .

[0035] With respect to the technical solution of this embodiment, the dielectric hole combination structure 4 includes a plurality of elliptical dielectric holes 41, and the plurality of elliptical dielectric holes 41 are distributed in a ring shape. The elliptical dielectric holes 41 arranged in a ring shape can effectively confine the incident light beam within the fiber core, thereby improving the total reflection performance. This means that under certain conditions, the optical signal can maintain high-intensity transmission for a longer time, thereby improving the signal-to-noise ratio of the system. In addition, by changing the parameters of the elliptical dielectric holes arranged in a ring shape, such as size, spacing, shape, etc., the transmission characteristics of the optical signal in the fiber can be dynamically adjusted, which makes the optical fiber system have better adaptability and adjustability, and can better meet the needs of different application scenarios.

[0036] Furthermore, a second optical fiber lattice 42 is disposed between two adjacent elliptical medium holes 41 , and the second optical fiber lattice 42 is separated from the elliptical medium holes 41 .

[0037] According to the technical solution of this embodiment, the lattice constants of the first optical fiber lattice 6 and the second optical fiber lattice 42 are set to c, and the diameter of the second medium hole 5 is set to 0.5c.

[0038] Furthermore, the number of the first dielectric holes 3 is six, and the six first dielectric holes 3 are equidistantly arranged along the circumference of the fiber core 2, and the diameter of the first dielectric holes 3 is set to 0.7c, 0.8c or 0.9c, which is not limited in this embodiment and can be selected according to actual conditions.

[0039] According to the technical solution of this embodiment, there are multiple elliptical medium holes 41, and every four elliptical medium holes 41 form a group, and the major axis and minor axis of the elliptical medium holes 41 are set to 0.9c and 0.5c respectively.

[0040] According to the technical solution of this embodiment, the fiber core 2 is mainly composed of six first medium holes 3, and the diameter of the fiber core 2 is 12 μm.

[0041] With respect to the technical solution of this embodiment, the base material 1 is made of arsenic sulfide, which can cause the band gap between the core 2 and the base material 1 to blue-shift, thereby improving the total reflection performance and transmission efficiency. It should be noted that the refractive index of the base material 1 is greater than the refractive index of the core 2. When the incident light is transmitted in the bandgap photonic crystal fiber, the incident light will experience various degrees of scattering when transmitted in media with different refractive indices.

[0042] Furthermore, the refractive index of the substrate material 1 is expressed as:

[0043]

[0044] Where n is the refractive index of the optical fiber and λ is the wavelength.

[0045] According to the technical solution of this embodiment, a perfect matching layer 7 is provided on the outer surface of the base material 1, and the thickness of the perfect matching layer 7 is set to 2 μm. The perfect matching layer 7 (PML) in the optical fiber is a special dielectric layer. By setting the boundary in the FDTD region, the wave impedance of the medium is completely matched with the wave impedance of the adjacent medium. This design allows the incident wave to pass through the interface without reflection and enter the PML, thereby achieving lossless transmission of energy. The introduction of PML is mainly to solve the problem of the difference between the optical fiber model in the simulation environment and the actual optical fiber environment. By setting appropriate boundary conditions, the environmental difference between the two is effectively eliminated, making the simulation results closer to the actual situation.

[0046] The realization principle of the perfect matching layer 7 is to set a boundary condition with the same material and matching wave impedance as the cladding outside the cladding of the optical fiber, so it can be regarded as a non-reflective absorption layer. When the light beam enters the perfect matching layer 7, it will not be reflected back immediately, but will gradually attenuate until it is finally absorbed. This non-reflective feature makes the perfect matching layer 7 an ideal boundary condition in simulation analysis, especially when simulating and analyzing large mode area optical fibers, the use of the perfect matching layer 7 can significantly improve the accuracy of the simulation results.

[0047] According to the technical solution of this embodiment, the first medium hole 3 and the second medium hole 5 are both set to be circular. The arrangement of the circular medium holes can form a uniform pore distribution inside the optical fiber, so that the light can be better reflected and transmitted inside the optical fiber. Such a design can reduce the loss of light at the edge of the optical fiber and improve the transmission efficiency of the entire optical fiber. Moreover, since the medium hole is circular, the stress distribution inside the optical fiber is also uniform, which can avoid stress concentration and thus increase the service life of the optical fiber.

[0048] like Figure 2-Figure 4 As shown in, the technical effect of the present invention is further described in combination with a specific embodiment. In this embodiment, the lattice constant c=12μm, the diameter of the second medium hole 5 (small pore) is 0.5c=6μm, the major and minor axes of the elliptical medium hole 41 are 0.9c=10.8μm and 0.5c=6μm respectively, and the diameter of the first medium hole 3 (large pore) is 0.7c=8.4μm, 0.8c=9.6μm, and 0.9c=10.8μm respectively;

[0049] Figure 2 The figure shows the mode field distribution diagram of the fundamental mode. It can be seen that the energy of the hollow-core antiresonant optical fiber prepared in the embodiment is concentrated in the core 2 region during transmission, indicating that the light is confined in the core 2 region;

[0050] Figure 3 It can be seen that the limiting loss is at a low level under the condition of incident wavelength 1.55-2.0μm, at 10 -6 dB / km, while existing fiber optic simulations are generally below 10 -3 Order of magnitude, about 3 orders of magnitude lower than existing photonic crystal fibers;

[0051] Figure 4 The nonlinear coefficient changes under the condition of incident wavelength of 1.55-2.0μm. The nonlinear coefficient is basically above 100, which is 2 orders of magnitude higher than the nonlinear coefficient of general photonic crystal fiber and also meets the conditions for transmitting supercontinuum.

[0052] In summary, the photonic crystal fiber can achieve low loss in the 1.55-2.0μm band, has a high nonlinear coefficient, and has good single-mode characteristics. It has a simple structure and meets the conditions for generating a supercontinuum. The structure uses a stable hexagonal structure, which makes the entire optical fiber have strong bending resistance.

[0053] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0054] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centered element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not intended to be the only implementation method.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0056] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

Claims

1. A bandgap photonic crystal fiber for transmitting supercontinuum, characterized in that: It comprises a base material (1), a fiber core (2), and a plurality of medium hole units arranged in the base material (1) and distributed along the axial direction of the optical fiber and penetrating the entire optical fiber, wherein the fiber core (2) is located at the center of the base material (1); The medium hole unit comprises a first medium hole (3) which is equidistantly arranged along the circumference of the fiber core (2), a medium hole combination structure (4), a second medium hole (5) and a first optical fiber lattice (6); the first medium hole (3) is tangent to the fiber core (2); the medium hole combination structure (4) is arranged outside the first medium hole (3) and equidistantly arranged along the circumference of the fiber core (2); and the second medium hole (5) is located between two adjacent medium hole combination structures (4) and is tangent to them. The first optical fiber lattice (6) is located on the extension line of the line connecting the fiber core (2) and the center of the second medium hole (5); The medium hole combination structure (4) comprises a plurality of elliptical medium holes (41), the plurality of elliptical medium holes (41) are distributed in a ring shape, a second optical fiber lattice (42) is arranged between two adjacent elliptical medium holes (41), and the second optical fiber lattice (42) is separated from the elliptical medium holes (41); The number of the dielectric hole combination structures (4) is set to six, and the six dielectric hole combination structures (4) are arranged at equal distances along the circumference of the fiber core (2); The number of the first medium holes (3) is six, and the six first medium holes (3) are arranged equidistantly along the circumference of the fiber core (2).

2. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 1, characterized in that: The lattice constants of the first optical fiber lattice (6) and the second optical fiber lattice (42) are set to c, and the diameter of the second medium hole (5) is set to 0.5c.

3. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 2, characterized in that: The diameter of the first medium hole (3) is set to 0.7c, 0.8c or 0.9c.

4. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 3, characterized in that: The number of the elliptical medium holes (41) is multiple, with four elliptical medium holes (41) forming a group, and the major axis and minor axis of the elliptical medium holes (41) are set to 0.9c and 0.5c respectively.

5. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 4, characterized in that: The fiber core (2) is made of silicon dioxide, and the diameter of the fiber core (2) is 12 μm.

6. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 5, characterized in that: The refractive index of the base material (1) is greater than the refractive index of the fiber core (2), and a perfect matching layer (7) is provided on the outer surface of the base material (1).

7. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 6, characterized in that: The base material (1) is made of arsenic sulfide, and its refractive index is expressed as follows: Where n is the refractive index of the optical fiber and λ is the wavelength.

8. A bandgap photonic crystal fiber for supercontinuum transmission according to claim 7, characterized in that: The first medium hole (3) and the second medium hole (5) are both arranged in a circular shape.

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