A mid-infrared band single-polarization single-mode optical fiber

Abstract

The present invention relates to the field of optical fiber technology, and specifically provides a mid-infrared band single-polarization single-mode optical fiber. The optical fiber comprises: a sheath tube, which is cylindrical with openings at both ends; two glass tubes arranged in the sheath tube, and the two glass tubes are tangent to each other in the sheath tube. When the single-polarization single-mode optical fiber disclosed in the present invention is in use, the tangent point of the two glass tubes and the air nearby form an equivalent fiber core, and the remaining sheath tube portion and the air portion form an equivalent cladding to achieve mode field confinement. The optical fiber disclosed in the present invention has low limiting loss only for the Y polarization fundamental mode. Other modes cannot be effectively transmitted in this optical fiber due to their extremely large limiting loss. It has the characteristics of single mode and single polarization. Compared with the existing technology, the present invention avoids the complex geometric structure of photonic crystal optical fiber and the material doping process required for traditional optical fiber to control the refractive index. It has the advantages of simple structure, convenient drawing, wide working bandwidth, etc.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and in particular to a mid-infrared band single-polarization single-mode optical fiber. Background Art

[0002] Single-polarization single-mode fiber supports transmission in only one polarization fundamental mode, completely eliminating polarization mode dispersion and polarization coupling effects in the fiber, effectively ensuring the linear polarization characteristics of the transmitted beam. Using single-polarization single-mode fiber for beam transmission offers significant advantages in applications requiring extremely high beam polarization stability.

[0003] Traditional optical fibers rely on doping processes and the introduction of stress to manipulate the refractive index profile to achieve single-polarization, single-mode performance. In contrast, photonic crystal fibers can introduce high birefringence through structural design, making the effective refractive index of the fundamental mode in a certain polarization direction lower than the effective refractive index of the fundamental mode filling the cladding space, thereby suppressing the polarization fundamental mode in that direction. Alternatively, the fundamental mode in a certain polarization direction can be coupled with the cladding mode, causing the fundamental mode energy in that polarization direction to leak into the cladding and rapidly attenuate.

[0004] Although photonic crystal fibers do not require doping or the introduction of stress, achieving high birefringence typically requires the introduction of elliptical air holes or complex arrays of small circular holes. For example, Chinese patent publication number "CN204241719U" discloses a single-polarization, single-mode photonic crystal fiber that achieves single-mode, single-polarization fiber through a microhole structure. However, this structure increases the difficulty of fiber drawing and places extremely high demands on the fiber drawing process. Therefore, this application proposes a single-polarization, single-mode fiber. Summary of the Invention

[0005] The purpose of the present invention is to provide a mid-infrared band single-polarization single-mode optical fiber to solve the problems of complex manufacturing process and great difficulty in drawing the current single-polarization single-mode optical fiber.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A single-polarization single-mode optical fiber, comprising:

[0008] A sheath tube, the sheath tube being cylindrical with openings at both ends;

[0009] Two glass round tubes are arranged in the sheath tube, and the two glass round tubes are circumscribed to each other in the sheath tube.

[0010] Furthermore, the intersection point of the two glass tubes is located at the geometric center of the sheath tube.

[0011] Preferably, the two glass tubes and the sheath tube are both made of arsenic triselenide sulfide glass.

[0012] Preferably, the outer diameter of the glass tube is 14 microns.

[0013] Preferably, the thickness of the glass tube is 1.4 microns.

[0014] Preferably, the thickness of the sheath tube is greater than 10 microns.

[0015] Preferably, the sheath tube is a round tube, and the two glass round tubes are inscribed in the sheath tube.

[0016] In summary, the present invention has the following beneficial effects compared with the prior art:

[0017] When the mid-infrared band single-polarization single-mode optical fiber disclosed in the present invention is in use, the tangent point of the two glass tubes and the nearby air form an equivalent fiber core, and the remaining sheath tube part and the air part form an equivalent cladding to achieve mode field confinement. The optical fiber disclosed in the present invention has low restriction loss only for the Y polarization fundamental mode. Other modes cannot be effectively transmitted in this optical fiber due to the extremely large restriction loss. It has the characteristics of single mode and single polarization. Compared with the existing technology, the present invention avoids the complex geometric structure of photonic crystal fiber on the one hand, and avoids the material doping process required for traditional optical fiber to control the refractive index on the other hand. It has the advantages of simple structure, convenient drawing, and wide working bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of a cross section of a mid-infrared band single-polarization single-mode optical fiber disclosed in an embodiment of the present invention.

[0019] Figure 2 for Figure 1 The Y-polarization fundamental mode electric field intensity distribution diagram of the publicly disclosed mid-infrared band single-polarization single-mode optical fiber at a light wavelength of 6μm.

[0020] Figure 3 for Figure 1 The electric field intensity distribution diagram of the X-polarization fundamental mode of the disclosed mid-infrared band single-polarization single-mode optical fiber at a light wavelength of 6μm.

[0021] Figure 4 for Figure 1 The electric field intensity distribution diagram of the high-order mode with the lowest loss of the disclosed mid-infrared band single-polarization single-mode optical fiber at a light wavelength of 6μm.

[0022] Figure 5 for Figure 1 Schematic diagram of the Y-polarization fundamental mode-limited loss and the lowest-loss higher-order mode-limited loss corresponding to the disclosed mid-infrared band single-polarization single-mode optical fiber in the 3μm to 10μm band.

[0023] Reference numerals: 1, sheath tube; 2, glass round tube. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part 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 ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] At present, the research on single-polarization single-mode optical fiber is divided into two directions. One is to achieve single-polarization single-mode performance by regulating the refractive index distribution through doping process and introduction of stress. The other direction is to structurally design the photonic crystal fiber to make it have high birefringence. At present, the structural design of photonic crystal fiber generally realizes the single-mode and single-polarization characteristics of the optical fiber through a microporous structure. However, this method is difficult to manufacture and has high requirements on the optical fiber drawing process.

[0026] In the structural design of optical fibers, considering the actual optical fiber drawing process level, the complexity of the optical fiber structure should be reduced as much as possible to facilitate production and drawing. Therefore, this application proposes a structure of a single-polarization single-mode optical fiber in the mid-infrared band, as shown below:

[0027] like Figure 1 As shown, one embodiment of the present invention provides a mid-infrared band single-polarization single-mode optical fiber, the optical fiber comprising:

[0028] The sheath tube 1 is cylindrical with openings at both ends;

[0029] Two glass tubes 2 are arranged in the sheath tube 1, and the two glass tubes 2 are circumscribed with each other in the sheath tube 1;

[0030] In this embodiment, two glass tubes 2 are disposed within the sheath tube 1, and the two glass tubes 2 are circumscribed. The inner and outer diameters of the two glass tubes 2 are the same. During optical propagation, light propagates from the tangent point of the two glass tubes 2 and the nearby air. During light propagation, the material of the glass tubes 2 at the tangent point and the nearby air region constitute an equivalent fiber core, and the light propagates along the equivalent optical fiber. The remaining material of the glass tubes 2 and the air region form an equivalent cladding, achieving mode field confinement during light propagation.

[0031] The single-polarization single-mode optical fiber disclosed in the embodiment of the present invention achieves mode field confinement through the air within the two glass tubes 2 and the air within the glass tube 2 and the sheath tube 1. Compared with the porous photonic crystal fiber, it has the advantage of a simple structure, thereby reducing the requirements for the optical fiber drawing process during optical fiber drawing.

[0032] As a preferred implementation in this embodiment, the intersection point of the two glass tubes 2 is located at the geometric center of the sheath tube;

[0033] Specifically, when the sheath tube 1 is a round tube, Figure 1 As shown, when the optical fiber is cut, the intersection of the two glass tubes 2 is located at the center of the sheath tube 1. At this time, the light propagates along the intersection of the glass tubes 2 and the surrounding air area. This arrangement facilitates the connection of the optical structure.

[0034] It should be noted that the tangent point of the two glass tubes 2 may not be located at the geometric center of the sheath tube 1, and the outer diameters of the two glass tubes 2 may be different. However, there will be a problem of different limiting losses, and a better single polarization effect cannot be achieved. In order to achieve a better effect, in this embodiment, the two glass tubes 2 have the same shape, and the tangent point of the two glass tubes 2 is located at the geometric center of the sheath tube 1.

[0035] As a further preferred embodiment of this embodiment, the two glass tubes and the sheath tube are both made of arsenic triselenide chalcogenide glass;

[0036] In this embodiment, the transmission wavelength range of arsenic triselenide is wider, and it can better transmit the mid-infrared band light beam;

[0037] As a preferred implementation in this embodiment, Figure 1 As shown, the sheath tube 1 is a round tube, and the two glass round tubes 2 are inscribed in the sheath tube; in this embodiment, the sheath tube 1 plays the role of fixing the two glass round tubes 2;

[0038] When drawing the optical fiber, the optical fiber of the embodiment of the present invention is drawn using the holey optical fiber drawing method;

[0039] It should be noted that the sheath tube 1 and the glass tube 2 may not be tangent to each other, and other materials, such as a skeleton layer or a protective layer, may be filled between the sheath tube 1 and the glass tube 2. In this embodiment, the materials are not limited to the skeleton layer or the cladding.

[0040] As a preferred implementation in this embodiment, the outer diameter of the glass tube 2 is 14 microns, the thickness of the glass tube 2 is 1.4 microns, and the thickness of the sheath tube 1 is greater than 10 microns;

[0041] like Figure 2 、 Figure 3 and Figure 4 As shown, in this embodiment, the outer diameter of the glass tube 2 is 14 microns, the thickness of the glass tube 2 is 1.4 microns, and the thickness of the sheath tube 1 is greater than 10 microns. The tangent point of the two glass tubes 2 is located at the junction center of the sheath tube 1. When the wavelength of the mid-infrared light is 6 μm, full vector finite element calculation is performed on the optical fiber;

[0042] The Y-polarization fundamental mode electric field intensity distribution is as follows Figure 2As shown in the figure, the electric field energy is concentrated in the area near the geometric center of the optical fiber on the two glass tubes. The simulation calculation shows that the real part of the effective refractive index of the mode field is 2.532, and the limiting loss is 1.47×10 - 6 dB / m;

[0043] The X-polarization fundamental mode electric field intensity distribution is as follows Figure 3 As shown in the figure, the electric field energy is concentrated in the air region between the two glass tubes. At the same time, the X-polarized fundamental mode couples with the glass tube's own mode, causing the X-polarized fundamental mode to leak out of the sheath tube, resulting in a significant confinement loss. Simulation calculations show that the real part of the mode field effective refractive index is 2.333, and the confinement loss is as high as 45821 dB / m.

[0044] The electric field intensity distribution of the high-order mode with the lowest loss is as follows Figure 4 As shown in the figure, it can be seen that due to the large mode field area, the mode field distribution is close to the sheath tube, so it is also easy to leak out of the sheath tube, causing a large limiting loss. From the simulation calculation, it can be seen that the real part of the mode field effective refractive index is 2.407, and the limiting loss reaches 1551dB / m;

[0045] Therefore, by Figures 2 to 4 It can be seen that this fiber has low confinement loss only for the Y-polarization fundamental mode. Other modes cannot be effectively transmitted in this fiber due to their large confinement loss. Therefore, it has the characteristics of single-polarization single-mode.

[0046] The above verified the working characteristics of this fiber at a wavelength of 6μm. In order to verify the working bandwidth of the single-polarization single-mode characteristics of this fiber, the limiting loss values of the Y-polarization fundamental mode and the highest-order mode with the lowest loss were simulated and calculated in the 3μm to 10μm band. The results are shown in the figure. Figure 5 As shown in the figure, the confinement loss of the Y-polarization fundamental mode increases monotonically with the increase of wavelength. In the range of 3μm to 7.7μm, the confinement loss is less than 1×10 -4 dB / m. At 10μm, the limiting loss is the largest, with a value of 8.63×10 -3 dB / m.

[0047] The limiting loss of the high-order mode with the lowest loss basically increases with the increase of wavelength, but there is a peak near the wavelength of 4μm. This is caused by the coupling of the high-order mode with the thin-walled tube mode at this time. The limiting loss of the high-order mode with the lowest loss exceeds 1000dB / m in the 3μm to 10μm band. The limiting loss of the X-polarization fundamental mode is much greater than that of the high-order mode. Therefore, in the 3μm to 10μm band, only the Y-polarization fundamental mode has a low limiting loss. Other modes cannot be effectively transmitted in this optical fiber due to their extremely large limiting losses. Therefore, in the 3μm to 10μm band, this optical fiber has the characteristics of single polarization and single mode.

[0048] In summary, the mid-infrared band single-mode single-polarization optical fiber disclosed in the present invention avoids the complex geometric structure of photonic crystal fiber on the one hand, and avoids the material doping process required for traditional optical fiber to control the refractive index on the other hand. It has the advantages of simple structure, convenient drawing, and wide operating bandwidth.

[0049] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A mid-infrared band single-polarization single-mode optical fiber, characterized in that: The optical fiber comprises: A sheath tube, the sheath tube being cylindrical with openings at both ends; Two glass round tubes are arranged in the sheath tube, and the two glass round tubes are circumscribed to each other in the sheath tube; the sheath tube is a round tube, and the two glass round tubes are inscribed in the sheath tube.

2. The mid-infrared band single-polarization single-mode optical fiber according to claim 1, characterized in that: The tangent point of the two glass tubes is located at the geometric center of the sheath tube.

3. The mid-infrared band single-polarization single-mode optical fiber according to claim 1, characterized in that: The two glass tubes and the sheath tube are both made of arsenic triselenide sulfide glass.

4. The mid-infrared band single-polarization single-mode optical fiber according to claim 1 or 2, characterized in that: The outer diameter of the glass tube is 14 microns.

5. The mid-infrared band single-polarization single-mode optical fiber according to claim 4, characterized in that: The thickness of the glass tube is 1.4 microns.

6. The mid-infrared band single-polarization single-mode optical fiber according to claim 1 or 2, characterized in that: The thickness of the sheath tube is greater than 10 microns.

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