CN110361813B - Double-core terahertz optical fiber coupler - Google Patents
Double-core terahertz optical fiber coupler Download PDFInfo
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- CN110361813B CN110361813B CN201910759385.2A CN201910759385A CN110361813B CN 110361813 B CN110361813 B CN 110361813B CN 201910759385 A CN201910759385 A CN 201910759385A CN 110361813 B CN110361813 B CN 110361813B
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 18
- 239000000835 fiber Substances 0.000 claims abstract description 34
- 238000005253 cladding Methods 0.000 claims abstract description 5
- 230000008878 coupling Effects 0.000 abstract description 30
- 238000010168 coupling process Methods 0.000 abstract description 30
- 238000005859 coupling reaction Methods 0.000 abstract description 30
- 230000010287 polarization Effects 0.000 abstract description 12
- 238000010521 absorption reaction Methods 0.000 abstract description 8
- 239000000463 material Substances 0.000 abstract description 7
- 238000009826 distribution Methods 0.000 abstract description 5
- 230000005540 biological transmission Effects 0.000 description 11
- 230000005684 electric field Effects 0.000 description 4
- 239000004038 photonic crystal Substances 0.000 description 3
- 238000004891 communication Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
- G02B6/2793—Controlling polarisation dependent loss, e.g. polarisation insensitivity, reducing the change in polarisation degree of the output light even if the input polarisation state fluctuates
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Abstract
The invention discloses a double-core terahertz optical fiber coupler, wherein two parallel first rectangular dielectric layers are intersected with two parallel second rectangular dielectric layers, two dielectric cylinders are respectively hung at the intersection points of the left side and the right side of the first rectangular dielectric layers and the second rectangular dielectric layers to form two fiber cores of an optical fiber, and the first rectangular dielectric layers, the second rectangular dielectric layers, a dielectric circular tube and air holes are cladding layers of the fiber cores to form a total internal reflection structure. The invention effectively reduces the material absorption loss, the fiber core size is far smaller than the operating wavelength, and the energy of the fiber core conduction mode can be mostly distributed in the air, thereby reducing the material absorption loss. The distribution of the core mode fields can be adjusted by changing the included angles of the two rectangular dielectric layers, so that the coupling lengths of the x-polarization mode and the y-polarization mode are the same, and the polarization-independent low-loss double-core terahertz optical fiber coupler is obtained.
Description
Technical Field
The invention relates to the field of optical fiber communication, in particular to a double-core terahertz optical fiber coupler.
Background
Terahertz (Terahertz, THz) generally refers to electromagnetic waves with frequencies in the range of 0.1-10 THz, the band of which lies between the microwaves and the infrared in the electromagnetic spectrum. THz radiation has potential for use in many fields, such as communications, sensing, imaging, spectroscopy and medicine. In the near infrared band, directional coupling devices based on micro-structured optical fibers have been widely studied, and theoretically, these directional coupling device structures can be applied to the THz band, that is, equal proportion of increase in the optical fiber size can realize application of the coupler structure operating in the near infrared band to THz coupling, for example, the operating wavelength of the coupler is 1.55 μm, the parameters of the coupler structure are expanded to 300/1.55 times, and the directional coupling with the wavelength of 300 μm can be realized, but unfortunately, the length of the coupler is also expanded to 300/1.55 times. Therefore, the length of such a coupler is long, and excessive device transmission loss is caused in the THz band. Ming-Yang Chen et al [Ming-Yang Chen, et al., "Design and analysis of a low-loss terahertz directional coupler based on three-core photonic crystal fibre configuration," J. Phys. D: Appl. Phys,2011, 44: 405104] propose a directional coupler based on solid photonic crystal fibers, which can only reduce the transmission loss by shortening the length of the coupler, because the core conduction mode is mainly transmitted in the material and has a large absorption loss. A. Dupuis et al [A. Dupuis, et al., "Fabrication and THz loss measurements of porous subwavelength fibers using a directional coupler method," Opt. Express,2009, 17, 8012] propose a sub-wavelength fiber based directional coupler that is susceptible to external environmental interference during optical transmission. K. Nielsen et al [K. Nielsen, H. K. Rasmussen, P. U. Jepsen, and O. Bang, "Broadband terahertz fiber directional coupler," Opt. Lett., 35, 2879~2881 (2010)] theories studied a THz dual-core photonic crystal fiber coupler with a low-doped core, which utilized the low-doped core to shorten the coupler length, at a center wavelength of 1.4 THz, the coupling length was 20 cm.
The above couplers ignore the influence of different coupling lengths of an x-polarization mode and a y-polarization mode, and the coupling quality is limited by the different coupling lengths of the x-polarization mode and the y-polarization mode.
Disclosure of Invention
In order to overcome the defects, the invention provides a double-core terahertz (THz) optical fiber coupler, which has low loss, short length and no external interference and polarization in the optical transmission process.
The invention achieves the above object by the following technical scheme. A dual-core terahertz optical fiber coupler is characterized in that two parallel first rectangular dielectric layers are intersected with two parallel second rectangular dielectric layers, an included angle between each first rectangular dielectric layer and the horizontal direction is theta, and an included angle between each second rectangular dielectric layer and the horizontal direction is pi-theta; the two medium cylinders are respectively hung at the intersection points of the left side and the right side of the first rectangular medium layer and the second rectangular medium layer to form two fiber cores of the optical fiber; the outer ends of the first rectangular dielectric layer and the second rectangular dielectric layer are connected with the inner wall of the dielectric circular tube; the first rectangular dielectric layer, the second rectangular dielectric layer and the medium circular tube form air holes in gaps, and the first rectangular dielectric layer, the second rectangular dielectric layer, the medium circular tube and the air holes are cladding layers of fiber cores to form a total internal reflection structure.
Further, the included angle θ between the first rectangular dielectric layer and the horizontal direction satisfies: 0< θ <45 o.
Further, the widths t of the first rectangular dielectric layer and the second rectangular dielectric layer are: t is less than or equal to 100 mu m.
Further, the diameter of the section of the medium cylinder is d, and the conditions are satisfied: d/lambda <2/3.
The diameter of the fiber core is far smaller than the operating wavelength, and the energy of the fiber core mould can be distributed in the air holes adjacent to the fiber core, so that the material absorption loss is effectively reduced. The coupling length of the x-polarization mode can be equal to the coupling length of the y-polarization mode by adjusting the included angle between the first rectangular dielectric layer and the horizontal direction. When the fiber is equal to the coupling length of the x-polarization mode (i.e., the coupling length of the y-polarization mode), both polarization modes of the fiber are simultaneously coupled from the input core to the output core, enabling polarization independent coupling. The length of the coupler is the coupling length of the two polarization modes. When the coupler length is short, the transmission loss of the core die is extremely small. In addition, the fiber core conduction mode is effectively limited around the fiber core by the fiber cladding, the coupling performance of the coupler is not affected by the change of the surrounding environment, and the device is convenient to operate.
Drawings
FIG. 1 is a schematic diagram of a dual-core fiber THz coupler of the invention;
FIG. 2 is a graph of the x-and y-polarization mode coupling length as a function of θ for the embodiment of FIG. 1;
FIG. 3 is a graph showing the field strength distribution of the x-polarization coupled supermode electric field of the embodiment of FIG. 1;
FIG. 4 is a graph of the field strength distribution of the x-polarized odd supermode electric field of the embodiment of FIG. 1;
FIG. 5 is a graph of the field strength distribution of the y-polarization coupled supermode electric field of the embodiment of FIG. 1;
FIG. 6 is a graph of the field strength distribution of the y-polarized odd supermode electric field of the embodiment of FIG. 1;
FIG. 7 is a graph of normalized power of the x-polarization mode versus transmission distance for the embodiment of FIG. 1;
FIG. 8 is a graph of normalized power of the y-polarization mode versus transmission distance for the embodiment of FIG. 1;
in the figure: 1-a first rectangular dielectric layer, 2-a second rectangular dielectric layer, 3-a dielectric cylinder, 4-a dielectric circular tube and 5-an air hole.
Detailed Description
The invention is further described below with reference to the drawings and examples. FIG. 1 shows a schematic cross-sectional view of a dual-core optical fiber THz coupler of the invention, wherein two parallel first rectangular dielectric layers 1 are intersected with two parallel second rectangular dielectric layers 2, the included angle between the first rectangular dielectric layers 1 and the horizontal direction is theta, and the included angle between the second rectangular dielectric layers 2 and the horizontal direction is pi-theta; the two medium cylinders 3 are respectively hung at the intersection points of the left side and the right side of the first rectangular medium layer 1 and the second rectangular medium layer 2 to form two fiber cores of the optical fiber; the outer ends of the first rectangular dielectric layer 1 and the second rectangular dielectric layer 2 are connected with the inner wall of the dielectric circular tube 4; the gaps among the first rectangular dielectric layer 1, the second rectangular dielectric layer 2 and the circular dielectric tube 4 form an air hole 5, and the first rectangular dielectric layer 1, the second rectangular dielectric layer 2, the circular dielectric tube 4 and the air hole 5 are cladding layers of fiber cores to form a total internal reflection structure.
As shown in FIG. 1, the thicknesses of the first rectangular dielectric layer 1 and the second rectangular dielectric layer 2 are t, the inner diameter of the dielectric circular tube 4 is D, the distance between the two dielectric cylinders 3 is D 1, the diameter of the section of the dielectric cylinder 3 is D, the included angle between the first rectangular dielectric layer 1 and the horizontal direction x is theta, and the included angle between the second rectangular dielectric layer 2 and the horizontal direction x is pi-theta.
The principle of the invention is to adjust the angle theta to enable the fiber core to have double refraction characteristics so as to control the coupling length of two polarization modes. Under a specific theta value, the coupling lengths of the two polarization modes are equal, so that the length of the coupler is equal to one coupling length of the polarization modes, and a coupler with a shorter length can be realized; in addition, the fiber core dimension is smaller than the operation wavelength, so that a large amount of fiber core mode energy can be distributed in the air holes, the material absorption loss is reduced, and the THz fiber coupler with low transmission loss can be realized by combining the fiber core dimension and the operation wavelength.
The absorption loss of the core mode increases with the rectangular dielectric layer width t, so that the rectangular dielectric layer width t is required to be less than or equal to 100 μm.
The invention can realize that the coupling length of two polarization modes is equal, and the angle value of the angle value satisfies: 0< θ <45 o, another angle value satisfies: 45 o<θ<90o, in order to obtain a small coupling length, it is here required that θ satisfies: 0< θ <45 o.
The coupler operates in the THz band and requires a core dimension less than the operating wavelength so that more of the fundamental mode energy of the core can be distributed in the air holes around the core, where the medium cylinder cross-section diameter d is required to satisfy: d/lambda <2/3.
Examples:
The structure of the dual-core THz optical fiber coupler is shown in fig. 1, the refractive index n air =1.0 of air, the refractive index n=1.5258 of matrix material of the optical fiber, the thickness t of the first rectangular dielectric layer 1 and the second rectangular dielectric layer 2 is 30 μm, the distance between two dielectric cylinders 3 is D 1 =300 μm, and the diameter of the section of each dielectric cylinder 3 is d=140 μm. The coupling length of the x-and y-polarization modes as a function of θ at a frequency of 1THz is shown in FIG. 2. It can be seen from the figure that the coupling length curves of the two polarization modes have two intersections, where the coupling lengths of the two polarization modes are equal, and the corresponding values of θ are 30.5 o and 53.2 o, respectively. Obviously, θ=30.5 o is smaller than the coupling length corresponding to θ=53.2 o, so here it is required that θ satisfies: 0< θ <45 o.
Fig. 3,4,5 and 6 show the field strength profiles of the x-polarization odd, x-polarization coupled, y-polarization odd and y-polarization coupled supermodes, respectively, for θ=30.5 o. As can be seen from the figure, the mode energy is distributed in the air holes around the fiber core in a larger part, so that the material absorption loss can be reduced, and in order to meet the low material absorption loss, the diameter d of the section of the medium cylinder 3 is required to meet the following conditions: d/lambda <2/3, the rectangular dielectric layer width t is less than or equal to 100 mu m.
Fig. 7 and 8 show the normalized power curves of the x-and y-polarization modes, respectively, as a function of transmission distance, and it can be seen from the figures that the coupling lengths of the two polarization modes are equal, and are both 0.421cm. Since the coupling length is short and part of energy is distributed in the air hole, the transmission loss of the coupling device is small, and the calculated coupling transmission loss of the x-polarization mode and the y-polarization mode is 0.30dB and 0.27dB respectively.
The drawings described above are only illustrative and are not intended to limit the scope of the present invention. It should be understood that this example is merely illustrative of the invention and is not intended to limit the scope of the invention in any way.
Claims (4)
1. The double-core terahertz optical fiber coupler is characterized in that two parallel first rectangular dielectric layers are intersected with two parallel second rectangular dielectric layers, the included angle between the first rectangular dielectric layers and the horizontal direction is theta, and the included angle between the second rectangular dielectric layers and the horizontal direction is pi-theta; the two medium cylinders are respectively hung at the intersection points of the left side and the right side of the first rectangular medium layer and the second rectangular medium layer to form two fiber cores of the optical fiber; the outer ends of the first rectangular dielectric layer and the second rectangular dielectric layer are connected with the inner wall of the dielectric circular tube; the first rectangular dielectric layer, the second rectangular dielectric layer and the medium circular tube form air holes in gaps, and the first rectangular dielectric layer, the second rectangular dielectric layer, the medium circular tube and the air holes are cladding layers of fiber cores to form a total internal reflection structure.
2. The dual-core terahertz fiber coupler according to claim 1, wherein an included angle θ between the first rectangular dielectric layer and the horizontal direction satisfies: 0< θ <45 o.
3. The dual-core terahertz fiber coupler according to claim 1, wherein the widths t of the first and second rectangular dielectric layers are each: t is less than or equal to 100 mu m.
4. The dual-core terahertz fiber coupler according to claim 1, wherein the medium cylinder cross-section diameter is d, satisfying: d/lambda <2/3.
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| CN201910759385.2A CN110361813B (en) | 2019-08-16 | 2019-08-16 | Double-core terahertz optical fiber coupler |
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| CN201910759385.2A CN110361813B (en) | 2019-08-16 | 2019-08-16 | Double-core terahertz optical fiber coupler |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103645535A (en) * | 2013-12-11 | 2014-03-19 | 江苏大学 | High double-refraction terahertz optical fiber |
| WO2015180850A1 (en) * | 2014-05-28 | 2015-12-03 | Spinner Gmbh | Flexible, bendable and twistable terahertz waveguide |
| CN107643561A (en) * | 2017-11-07 | 2018-01-30 | 江西师范大学 | A kind of low-loss terahertz polarization beam splitter |
| CN210166532U (en) * | 2019-08-16 | 2020-03-20 | 江西师范大学 | Double-core terahertz optical fiber coupler |
-
2019
- 2019-08-16 CN CN201910759385.2A patent/CN110361813B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103645535A (en) * | 2013-12-11 | 2014-03-19 | 江苏大学 | High double-refraction terahertz optical fiber |
| WO2015180850A1 (en) * | 2014-05-28 | 2015-12-03 | Spinner Gmbh | Flexible, bendable and twistable terahertz waveguide |
| CN106463810A (en) * | 2014-05-28 | 2017-02-22 | 斯宾纳有限公司 | Flexible, bendable and twistable terahertz waveguide |
| CN107643561A (en) * | 2017-11-07 | 2018-01-30 | 江西师范大学 | A kind of low-loss terahertz polarization beam splitter |
| CN210166532U (en) * | 2019-08-16 | 2020-03-20 | 江西师范大学 | Double-core terahertz optical fiber coupler |
Non-Patent Citations (3)
| Title |
|---|
| A low transmission loss THz polarization splitter based on dual-core optical fiber;Yuan-Feng Zhu et al.;Photonics and Nanostructures – Fundamentals and Applications;20160811;1-5 * |
| Low loss and polarization-insensitive coupling length for a terahertz fiber directional coupler with symmetric dual-suspended core structure;Yuan-Feng Zhu et al.;Optics Communications;20201001;1-6 * |
| 太赫兹双空芯光纤定向耦合器;姜子伟;白晋军;侯宇;王湘晖;常胜江;;物理学报;20130123(第02期);524-527 * |
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