CN117369046B - Hollow anti-resonance optical fiber with flat mid-infrared dispersion - Google Patents

Abstract

The invention discloses a hollow anti-resonance optical fiber with flat mid-infrared dispersion, which belongs to the technical field of optical fiber communication and comprises a fiber core area and a cladding area, wherein the cladding comprises an inner cladding and an outer cladding; the outer cladding region is tubular and is composed of silicon dioxide, and the inner cladding region and the air fiber core region are covered by the outer cladding region; the inner cladding is of a double-layer structure, the inner layer is a circular medium tube, the outer layer is formed by nesting a first type elliptical medium tube and a second type elliptical medium tube, the circular medium tube and the first type elliptical medium tube are circumscribed and welded with surfaces, and the first type elliptical medium tube and the second type elliptical medium tube are tangent and welded with surfaces inside and outside each other. The hollow anti-resonance optical fiber provided by the invention has low restrictive loss in a large wavelength range in a wave band of 2-4 mu m, large mode field area, near zero flat dispersion, good single-mode characteristic at a position of 3 mu m, simple structure and capability of meeting the requirements of optical communication and optical fiber sensing.

Description

A mid-infrared dispersion flat hollow-core anti-resonance fiber

Technical field

The invention relates to the technical field of optical fiber communication, and in particular to a hollow-core anti-resonant optical fiber with flat mid-infrared dispersion.

Background technique

The mid-infrared band generally refers to the band with a wavelength ranging from 2 to 20 μm. The light in this band is widely used in many fields such as medical treatment, sensing, and communications due to some special properties. However, due to In the mid-infrared band, lattice vibration will cause multi-phonon absorption, causing traditional quartz optical fibers to face huge absorption losses when transmitting the mid-infrared band, forcing researchers to develop new materials and new structures of optical fibers to cope with the mid-infrared. Band transmission problems.

Compared with solid-core optical fiber, hollow-core optical fiber guides light in the hollow core and has the advantages of low material absorption, dispersion and nonlinearity, and high damage threshold. Therefore, hollow core optical fiber has application potential in high-power pulse transmission. In high-power pulse transmission, it is very important to maintain large mode fields and single-mode transmission. Therefore, achieving large mode field and single-mode transmission simultaneously is a key challenge for high-power pulse transmission in hollow-core fibers. Hollow-core optical fibers mainly include photonic bandgap optical fibers and hollow-core anti-resonant fibers (HC-ARF). Due to the structural characteristics of hollow-core photonic bandgap fibers, it is difficult to achieve large mode fields. Hollow core anti-resonant fiber (HC-ARF) has attracted the research interest of scientific researchers in recent years due to its advantages such as wide transmission bandwidth and flexible design.

At present, most of the research on hollow-core anti-resonant optical fiber is at the communication wavelength of 1.55um, and there are few performance studies involving the mid-infrared band, especially around 3um. In patent documents in recent years, the performance of limiting loss, mode field area, and dispersion in the 3um band needs to be improved. Moreover, the existing common single-layer structure has fewer adjustable aspects, and the adjustability of the structure is slightly worse.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention proposes a hollow-core anti-resonant optical fiber with flat mid-infrared dispersion, which can simultaneously achieve single-mode guidance, low loss, large mode field and flat dispersion near the 3 μm band.

The object of the present invention can be achieved through the following technical solutions:

A hollow-core anti-resonant optical fiber with flat mid-infrared dispersion, including: an outer cladding, an inner cladding and an air core area in order from the outside to the inside; the inner cladding is evenly distributed with anti-resonance units in a circumferential manner; the air core The area is surrounded by a number of anti-resonance units;

The anti-resonance unit includes a first type of dielectric tube, a second type of dielectric tube and a third type of dielectric tube; the third type of dielectric tube and the first type of dielectric tube are circumscribed and welded; the second type of dielectric tube It is located inside the first type of medium pipe; the first type of medium pipe and the second type of medium pipe are incised and welded on their surfaces.

In some embodiments, the first type of medium tube, the second type of medium tube and the third type of medium tube have the same thickness, satisfying:

;

Among them, t is the thickness, λ is the designed working wavelength, Represents the refractive index of the cladding tube material,/> Represents the refractive index of air, m is a positive integer.

In some embodiments, the number of anti-resonance units is 4 to 8.

In some embodiments, the cross-sections of the first type of medium tube and the second type of medium tube are elliptical; the cross-section of the third type of medium tube is circular.

In some embodiments, the ratio of the major axis to the minor axis of the first type of medium tube is 1~3; the ratio of the long axis to the short axis of the second type of medium tube/> is 1~7.

In some embodiments, the diameter of the third type of medium tube is 20~40 μm; the long axis of the first type of medium tube is 50~70 μm, and the short axis is 30~50 μm; the long axis of the second type of medium tube is It is 18~38μm, and the short axis is 6~26μm.

In some embodiments, the outer cladding, the first type of dielectric tube, the second type of dielectric tube and the third type of dielectric tube are made of at least one of sulfide, fluoride, diamond and indium selenide.

In some embodiments, the inside of the outer cladding, the inside of the first type of dielectric tube, the inside of the second type of dielectric tube, the inside of the third type of dielectric tube and the air core area are provided with a medium; the medium is Gas, vacuum or liquid; the medium has a refractive index of 1.

In some embodiments, the diameter of the air core region is 50~70 μm.

Beneficial effects of the present invention:

Compared with the existing common single-layer structure, the present invention has good structural adjustability. It can not only adjust the radius of the circular third medium tube, but also adjust the long axis and short axis of the two types of elliptical medium tubes so that the Hollow core anti-resonance fiber has low limiting loss in the mid-infrared band over a wide wavelength range of 2~4μm, 1500 The above large mode field area, near-zero flat dispersion and good single-mode characteristics at 3μm, and simple structure meet the needs of optical communications and fiber optic sensing.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is a schematic structural diagram of the hollow-core anti-resonant fiber with flat mid-infrared dispersion of the present invention.

Figure 2 is an enlarged view of partial details of the double-layer structure of the hollow-core anti-resonant optical fiber of the present invention;

Figure 3 is a diagram of the mode field distribution and its height expression of the fundamental mode according to the embodiment of the present invention;

Figure 4 High-order mode according to the embodiment of the present invention The mode field distribution diagram;

Figure 5 is a schematic diagram of the limiting loss of the fundamental mode and higher-order mode as a function of wavelength according to the embodiment of the present invention;

Figure 6 is a schematic diagram of the change of high-order mode extinction ratio with wavelength according to the embodiment of the present invention;

Figure 7 is a schematic diagram of the variation of dispersion with wavelength according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of the mode field area changing with wavelength according to the embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

In the description of this specification, reference to the terms "one embodiment," "example," "specific example," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one aspect of the invention. in an embodiment or example. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

A hollow-core anti-resonant optical fiber with flat mid-infrared dispersion, including: an outer cladding, an inner cladding and an air core area in order from the outside to the inside; the inner cladding is evenly distributed with anti-resonance units in a circumferential manner; the air core The area is surrounded by a number of anti-resonance units;

The anti-resonance unit includes a first type of dielectric tube, a second type of dielectric tube and a third type of dielectric tube; the third type of dielectric tube and the first type of dielectric tube are circumscribed and welded; the second type of dielectric tube It is located inside the first type of medium pipe; the first type of medium pipe and the second type of medium pipe are incised and welded on their surfaces.

In some embodiments, the first type of medium tube, the second type of medium tube and the third type of medium tube have the same thickness, satisfying:

;

Among them, t is the thickness, λ is the designed working wavelength, Represents the refractive index of the cladding tube material,/> Represents the refractive index of air, m is a positive integer.

Parameters such as wall thickness of hollow-core anti-resonant optical fibers need to meet anti-resonance conditions. As long as the anti-resonance conditions are met, the reflection of the glass wall is maximum and the transmission is minimum, and most of the light is reflected back into the fiber core to form an optical waveguide. According to the principle of anti-resonant reflection, the nested structure can further effectively reduce the leakage loss of the optical fiber due to the addition of additional anti-resonant glass wall layers. Therefore, the present invention designs a double-layer nested structure to increase the number of anti-resonant glass wall layers. Moreover, replacing circular capillaries with elliptical capillaries can effectively improve the single-mode characteristics of HC-ARF. Therefore, an elliptical nested structure is designed based on the advantages of the above graphics and structures.

In some embodiments, the number of anti-resonance units is 4 to 8.

In some embodiments, the cross-sections of the first type of medium tube and the second type of medium tube are elliptical; the cross-section of the third type of medium tube is circular.

In some embodiments, the diameter of the third type of medium tube is 20~40 μm; the ratio of the long axis to the short axis of the first type of medium tube is 1~3; the ratio of the long axis to the short axis of the second type of medium tube/> is 1~7.

In some embodiments, the diameter of the air core region is 50~70 μm.

In some embodiments, the outer cladding, the first type of dielectric tube, the second type of dielectric tube and the third type of dielectric tube are made of materials including but not limited to sulfide, fluoride, diamond, and indium selenide.

In some embodiments, the inside of the outer cladding, the inside of the first type of dielectric tube, the inside of the second type of dielectric tube, the inside of the third type of dielectric tube and the air core area are provided with a medium; the medium is Gas, vacuum or liquid; the medium has a refractive index of 1.

Example: As shown in Figures 1 and 2, a schematic structural diagram of a hollow-core anti-resonant optical fiber with flat mid-infrared dispersion and an enlarged view of local details of the double-layer structure are shown.

In Figure 1, from the inside to the outside, they are the air core area 1 of the optical fiber, the circular third dielectric tube 2, the oval first type dielectric tube 3, the oval second type dielectric tube 4 and the outer casing of quartz glass. Layer 5. Among them, the circular third dielectric tube 2, the oval first type dielectric tube 3 and the oval second type dielectric tube 4 have the same thickness, t=0.8 μm, and the core radius R=30 μm. The number of the circular third medium tube 2, the oval first type medium tube 3 and the oval second type medium tube 4 is 4 to 8.

Figure 2 is an enlarged view of partial details of the double-layer structure. In the figure, the circular third medium pipe and the oval first type medium pipe are tangent to each other and have welded surfaces. The oval first type medium pipe and the oval second type medium pipe are tangent to each other inside and outside and have welded surfaces. , and the center of the circular third medium tube and the centers of the two types of elliptical medium tubes are collinear. Among them, the circular third medium tube r=15μm, the ratio of the long axis to the short axis of the first type medium tube is 1~3; the ratio of the long axis to the short axis of the second type of medium tube/> is 1~7.

The present invention uses the finite element simulation software COMSOL Multiphysics to conduct simulation tests on this embodiment. The finite element method is used and combined with the perfect matching layer boundary absorption conditions to perform theoretical calculations to obtain the mode field distribution diagram, limiting loss, mode field area and corresponding wavelength. Moreover, the second-order derivation of the real part of the effective refractive index of the fundamental mode with respect to the wavelength cannot be directly performed in COMSOL Multiphysics, so the dispersion needs to be calculated through the MATLAB program.

From the mode field distribution diagram of the fundamental mode in Figure 3, it can be seen that the energy of the hollow-core anti-resonant optical fiber prepared in the embodiment is concentrated in the core area during transmission, indicating that the light is trapped in the core area.

FIG. 5 is a schematic diagram showing how the limiting loss of the fundamental mode and the higher-order mode changes with wavelength according to the embodiment of the present invention. As can be seen from Figure 3, the measured loss of this embodiment under the condition of incident wavelength 2~4μm is at a low level, of which 3μm is about 0.0156dB/km, while the existing optical fiber simulation is generally 10 ^-1 Order of magnitude, about 1 order of magnitude lower than existing photonic crystal fibers.

Figure 6 is a schematic diagram of the change of high-order mode extinction ratio with wavelength according to an embodiment of the present invention; the high-order mode extinction ratio is defined as the minimum higher-order mode loss (Minimum higher-order mode loss, Min HOM loss) and fundamental mode loss (Fundamental mode) in the optical fiber loss, FM loss) ratio. The greater the value of the high-order mode extinction ratio, the faster the energy of the high-order mode in the fiber core attenuates compared to the energy of the fundamental mode in the fiber core per unit length. This can effectively filter out unnecessary high-order modes and ensure the high purity of the fundamental mode of the fiber. When the light wavelength is 3 μm, the high-order mode extinction ratio reaches a maximum of more than 500. However, the high-order mode extinction ratio does not reach such a high extinction ratio under other wavelength conditions. Therefore, the designed working conditions of the optical fiber are mainly at the wavelength of 3μm. Therefore, the single-mode characteristics of optical fiber are excellent under working conditions.

Figure 7 is a schematic diagram of the variation of dispersion with wavelength according to an embodiment of the present invention; optical fiber dispersion will cause the optical signal to spread out due to different propagation speeds when the optical signal is transmitted in the optical fiber, which will affect the quality of optical fiber transmission data. From the dispersion diagram You can see the dispersion of the optical fiber at the corresponding wavelength. The closer the dispersion is to zero, the higher the fiber transmission quality. In terms of dispersion, the hollow-core anti-resonant fiber with flat mid-infrared dispersion still follows the typical anti-resonant fiber rules. The dispersion is flat in a wide wavelength range of 2.5~4μm, and the group velocity dispersion values are within ±5ps/(km∙nm). .

Figure 8 is a schematic diagram of the mode field area changing with wavelength according to an embodiment of the present invention; in high-power laser transmission, if the fiber has a small mode field area, it will produce very high nonlinear effects and even damage the fiber. Therefore, fibers with larger mode field areas will be used in a wider range. It can be seen from the figure that the changing trend of the mode field area of the optical fiber decreases with the change of wavelength. When the optical wavelength is 2~4 μm, the mode field area is 1500 As mentioned above, an optical fiber with this mode field area size can theoretically transmit high-power laser.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have other aspects. Various changes and modifications are possible, which fall within the scope of the claimed invention.

Claims (3)

1. A hollow-core antiresonant fiber with flat mid-infrared dispersion, comprising: the outer cladding, the inner cladding and the air fiber core area are sequentially arranged from outside to inside; anti-resonance units are uniformly distributed on the circumference of the inner cladding; the air fiber core area is formed by enclosing a plurality of anti-resonance units;

the antiresonance unit comprises a first type medium pipe, a second type medium pipe and a third type medium pipe; the third type medium pipe and the first type medium pipe are circumscribed and welded; the second type medium pipe is arranged in the first type medium pipe; the first type medium pipe and the second type medium pipe are inscribed and welded on the surfaces; the number of the anti-resonance units is 4-8;

the thicknesses of the first type medium pipe, the second type medium pipe and the third type medium pipe are the same, and the requirements are satisfied:

；

wherein t is the thickness, lambda is the designed working wavelength,indicating the refractive index of the cladding tube material +.>Represents the refractive index of air, m is a positive integer;

the cross sections of the first type medium pipe and the second type medium pipe are elliptical; the cross section of the third medium pipe is round; the ratio of the long axis to the short axis of the first-class medium pipe1-3; the ratio of the major axis to the minor axis of the second type medium tube>1-7;

the diameter of the third medium pipe is 20-40 mu m; the long axis of the first type of medium pipe is 50-70 mu m, and the short axis of the first type of medium pipe is 30-50 mu m; the long axis of the second type medium tube is 18-38 mu m, and the short axis is 6-26 mu m; the diameter of the air fiber core region is 50-70 mu m.

2. The hollow-core antiresonant fiber of claim 1, wherein the outer cladding, the first type of dielectric tube, the second type of dielectric tube, and the third type of dielectric tube are at least one of sulfide, fluoride, diamond, and indium selenide.

3. The mid-infrared dispersion flattened hollow-core antiresonant fiber according to claim 1, wherein the medium is disposed inside the outer cladding, inside the first type of medium tube, inside the second type of medium tube, inside the third type of medium tube, and in the air core region; the medium is gas, vacuum or liquid; the refractive index of the medium is 1.