Adjustable attenuator based on anti-resonance hollow-core optical fiber and preparation method thereof

Abstract

The invention belongs to the technical field of optical fiber communication, and particularly relates to an adjustable attenuator based on an anti-resonance hollow-core optical fiber and a preparation method of the adjustable attenuator. The adjustable attenuator is composed of an outer cladding, a capillary layer, a fiber core and a gap filling area. The outer cladding is used for improving the mechanical reliability of the optical fiber; the capillary tube layer is used as an anti-resonance layer and is uniformly distributed and attached to the inner surface of the outer cladding layer, and is annularly distributed along the circumferential direction of the outer cladding layer to form a fiber core area in a surrounding manner; the capillary layer, the fiber core and the inner surface of the outer cladding jointly define a gap filling area. The functional material is introduced into the gap filling area, on the basis that the transmission characteristic is not obviously influenced, the filling material is utilized to generate thermal expansion along with the change of the external environment, the adjustment of the attenuation coefficient of an optical signal is realized, and the performance of the optical fiber is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and in particular relates to an adjustable attenuator based on antiresonant hollow-core optical fiber and a preparation method thereof. Background Art

[0002] With the rapid development of optical communication systems, data throughput has surpassed the terabit per second mark, placing higher demands on the precise control and regulation of optical signals. Attenuators, as key components in optical communication systems, dynamically adjust optical signal strength to ensure the signal maintains the appropriate power level during transmission, thereby preventing system performance degradation caused by excessive or insufficient signals. Currently, mechanical variable attenuators, widely used both domestically and internationally, dominate the market with their low insertion loss and high precision. However, they also suffer from significant limitations such as bulk and high cost. Consequently, all-fiber variable attenuators based on liquid crystals, thermo-optical effects, or acousto-optic effects have become a research hotspot due to their compact design and strong integration capabilities. Hollow-core optical fibers, in particular, are widely used in the development of various sensor devices due to their ultra-low nonlinearity, extremely low transmission delay, and strong anti-interference capabilities.

[0003] Currently available hollow-core fiber attenuators include liquid crystal hollow-core fiber variable attenuators, thermo-optic hollow-core fiber variable attenuators, thermal-effect variable optical attenuators, and electrically tunable variable optical attenuators. Liquid crystal hollow-core fiber variable attenuators achieve electric-field-based adjustable optical switching by filling the core and cladding air holes of a hollow-core photonic crystal fiber with nematic liquid crystals. Their attenuation range exceeds 30dB, but they suffer from issues such as temperature sensitivity, high insertion loss, and complex liquid crystal filling. Thermo-optic variable optical attenuators achieve 60dB attenuation by filling the hollow-core fiber with a high-refractive-index liquid and heating the liquid. However, they suffer from disadvantages such as a limited temperature range, complex systems, and complex dynamic response. Thermal-effect variable attenuators achieve a high extinction ratio of 50dB through the air liquefaction and evaporation effects of a hollow-core photonic crystal fiber in a liquid nitrogen environment. However, they suffer from slow response speed, environmental dependence, and a limited control range. While these aforementioned fiber optic attenuators can attenuate optical signals, they often suffer from complex structures, high costs, narrow dynamic adjustment ranges, limited applicability, low attenuation accuracy, high fill loss, and poor performance stability. Furthermore, hollow-core fiber attenuators based on antiresonance mechanisms have yet to be reported. Therefore, designing an antiresonant hollow-core fiber variable attenuator that overcomes these shortcomings is of great significance. Summary of the Invention

[0004] The present invention addresses the technical difficulties of existing adjustable attenuators such as high insertion loss, small dynamic adjustment range, and complex preparation, and proposes an adjustable attenuator based on antiresonant hollow-core optical fiber and a preparation method thereof.

[0005] The tunable attenuator based on an anti-resonant hollow fiber provided by the present invention has a structure including: an outer cladding, a capillary layer, a gap filling region, and a core; the capillary layer is uniformly attached to the inner surface of the outer cladding as an anti-resonant layer and is distributed in a ring shape along its circumferential direction, surrounding and forming a core region; the capillary layer, the core, and the inner surface of the outer cladding jointly define a gap filling region; a functional material is introduced into the gap filling region.

[0006] Further:

[0007] The functional material is selected from PDMS, ultraviolet curable glue, hydrogel, etc.;

[0008] The thickness of the gap filling region is 17.9 - 25.4 μm;

[0009] The length of the gap filling region is 0.5 - 510 cm;

[0010] The thickness and length of the gap filling region are adjusted according to the core diameter and spacing of the anti-resonant hollow fiber used, so as to form an attenuation with low filling loss and high tunable range.

[0011] The core diameter is 30 - 50 μm;

[0012] The number of capillaries in the capillary layer is 4 - 10;

[0013] The thickness of the capillary is 0.2 - 1 μm;

[0014] The diameter of the outer cladding is 100 - 120 μm;

[0015] In the capillary layer, a smaller-diameter capillary is nested within a single capillary.

[0016] The preparation method of the above tunable attenuator based on an anti-resonant hollow fiber specifically includes the following steps:

[0017] (1) After cleaning the anti-resonant hollow fiber with anhydrous ethanol, cut the end face of the anti-resonant hollow fiber flat;

[0018] (2) Perform arc discharge / carbon dioxide laser heating on the cut fiber end face, so that the capillary layer of the anti-resonant hollow fiber collapses, and only the core of the fiber remains open;

[0019] (3) Uniformly configure the functional material to be filled;

[0020] (4) Immerse the fiber with only the core open after melting and collapsing in step (2) into the functional material in step (3);

[0021] (5) Due to the fluidity of the material, under capillary action, the material slowly fills into the gap;

[0022] (6) Cure the material (high temperature or normal temperature or ultraviolet lamp) in the gap filling region, and an adjustable attenuator based on the anti-resonant hollow fiber can be obtained.

[0023] The adjustable attenuator prepared by the present invention can be used in the field of signal modulation in the field of optical fiber communication systems.

[0024] Beneficial effects of the present invention: The adjustable attenuator designed by the present invention realizes the regulation of optical transmission through the expansion / shrinkage performance of the material filled in the gap filling region of the anti-resonant hollow fiber, so as to achieve the purpose of controlling the optical attenuation amount; on the basis of not significantly affecting the transmission characteristics of the optical fiber, the present invention significantly reduces the filling loss of the optical fiber attenuator and greatly improves the performance of the optical fiber. The present invention solves the problem of large filling loss when the existing optical fiber attenuator adjusts the attenuation range, and provides an ideal working device with a simple structure and low insertion loss for the application of optical fiber sensing technology. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of an anti-resonant hollow fiber provided by an embodiment of the present invention.

[0026] Figure 2 It is a restricted loss curve graph of different filling gap filling region thicknesses at a wavelength of 1.55 μm in an embodiment of the present invention. The inset is a fiber fundamental mode transmission mode field graph of the present invention at filling thicknesses of 18, 23, 25.4, and 26.8 μm in the gap filling region.

[0027] Figure 3 It is an energy ratio curve of an embodiment of the present invention.

[0028] Figure 4 It is a schematic diagram of the end face of an optical fiber filled with an anti-resonant hollow fiber under a microscope (1) provided by an embodiment of the present invention.

[0029] Figure 5 It is a schematic diagram of the end face of an optical fiber filled with an anti-resonant hollow fiber under a microscope (2) provided by an embodiment of the present invention.

[0030] Reference numerals in the figure: 1 is an outer cladding, 2 is a first micro-capillary, 3 is a second micro-capillary, 4 is a core, and 5 is a gap filling region. Detailed Embodiments

[0031] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0032] See the appendix Figure 1The nested anti-resonant hollow-core optical fiber in [description], the outermost outer cladding 1, the outer cladding defines the outer surface of the inner unenclosed cladding; the first micro-capillary 2 is attached to the inner surface of the outer cladding 1, along the circumferential direction of the inner surface of the outer cladding, the first micro-capillary is in a uniform circumferential direction and surrounds to form a core region; the second micro-capillary 3 is nested in the first capillary 2; the inner surfaces of adjacent first micro-capillaries, the core and the outer cladding jointly define a gap filling region 5, and a functional material is filled in the gap filling region.

[0033] Preferably, the core diameter is about 25.5 μm, the diameter of the first micro-capillary is 24.5 μm, the diameter of the second micro-capillary is 14.1 μm, the capillary thickness is 1.2 μm, and the filled material is polydimethylsiloxane (PDMS). As Figure 2 Shown are the simulation results of the confinement loss for filling different thicknesses of the gap filling region at a wavelength of 1.55 μm. As the thickness of the filling material in the gap filling region increases, the confinement loss gradually increases. When the filling thickness is 18 μm, the loss is 0.006 dB / cm; when the filling thickness is 23 μm, the loss is 0.83 dB / cm; when the filling thickness is 25.4 μm, the confinement loss is 6.57 dB / cm; when the filling thickness is 26.8 μm, the loss is 30.06 dB / cm, and the transmission loss increases by 3 orders of magnitude compared to filling a thickness of 18 μm; the inset shows the fiber fundamental mode transmission field patterns of the present invention at gap filling region filling thicknesses of 18, 23, 25.4, and 26.8 μm.

[0034] As Figure 3 Shown, at a wavelength of 1550 nm, when the thickness of the gap filling region of the anti-resonant hollow-core optical fiber is 18 - 23 μm, the core energy ratio of the anti-resonant hollow-core optical fiber can reach 99.7%; when the filling thickness of the gap filling region is 23 - 25.4 μm, the core energy ratio of the anti-resonant hollow-core optical fiber reaches 99%. Within the transmission window, as the thickness of the material in the gap filling region increases, the core energy ratio gradually decreases.

[0035] In this embodiment, due to the liquid tension of PDMS, the end face structure after introducing the material into the gap filling region of the anti-resonant hollow-core optical fiber is as Figure 4 shown. The thickness of the gap filling region is 20.6 μm, and the length of the gap filling region is 30 cm, such that the filling loss is as low as 2.7 dB. By applying different temperatures to the material introduced into the fiber gap region, fine regulation of light transmission can be achieved. When heating causes the thickness of the gap filling region to expand to 23 μm, the attenuation can reach 22.07 dB.

[0036] In this embodiment, due to the liquid tension of PDMS, the end face structure after introducing the material into the gap filling region of the anti-resonant hollow-core optical fiber is as Figure 5As shown, the thickness of the gap filling region is 24.4 um, and the length of the gap filling region is 0.8 cm, so that the filling loss is as low as 2.56 dB. By applying different temperatures to the material introduced into the fiber gap region, fine control of optical transmission can be achieved. When the temperature is increased and the thickness of the gap filling region expands to 26.8 um, the attenuation can reach 21.44 dB.

[0037] The preparation method of the above tunable optical attenuator based on anti-resonant hollow-core fiber specifically includes:

[0038] (1) After cleaning the anti-resonant hollow-core fiber with absolute ethanol, cut the end face of the anti-resonant hollow-core fiber flat.

[0039] (2) Perform arc discharge / carbon dioxide laser heating on the cut fiber end face to collapse the capillary layer of the anti-resonant hollow-core fiber, leaving only the core of the fiber open.

[0040] (3) Configure the PDMS to be filled evenly.

[0041] (4) Immerse the fiber with only the core open after melting and collapsing in step (2) into the PDMS in step (3).

[0042] (5) Due to the fluidity of the material, under capillary action, the material slowly fills into the gap.

[0043] (6) Cure the material in the gap filling region at high temperature to obtain a tunable optical attenuator based on anti-resonant hollow-core fiber.

[0044] By designing a tunable optical attenuator of anti-resonant hollow-core fiber, without affecting the optical transmission characteristics of the fiber, the polarization-dependent loss and insertion loss are significantly reduced, and the dynamic range of the tunable optical attenuator is improved.

[0045] According to the characteristics that the material filled in the gap filling region of the anti-resonant hollow-core fiber expands / contracts with the change of the external environment, the attenuation coefficient of the optical attenuator can be changed. Finally, the above specific implementation can be locally adjusted by those skilled in the art in different ways without departing from the principles and purposes of the present invention, and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An adjustable attenuator based on an anti-resonant hollow fiber, characterized in that, Comprising: An outer cladding, a capillary layer, an interstitial filling region, and a core; The capillary layer is uniformly arranged and attached to the inner surface of the outer cladding as an anti-resonant layer, and is distributed in a ring shape along its circumferential direction, surrounding and forming a core region; the inner surfaces of the capillary layer, the core, and the outer cladding jointly define an interstitial filling region; a functional material is introduced into the interstitial filling region.

2. The adjustable attenuator according to claim 1, characterized in that, The functional material is selected from PDMS, ultraviolet curable glue, and hydrogel.

3. The adjustable attenuator according to claim 1, wherein The thickness of the interstitial filling region is 17.9 - 25.4 um; the length of the interstitial filling region is 0.5 - 510 cm; the thickness and length of the interstitial filling region are adjusted according to the core diameter and pitch of the anti-resonant hollow fiber used, so as to form an attenuation with low filling loss and a high adjustable range.

4. The adjustable attenuator according to claim 1, wherein: The core diameter is 30 - 50 μm; The number of capillaries in the capillary layer is 4 - 10; The thickness of the capillary is 0.2 - 1 μm; The outer cladding diameter is 100 - 120 μm.

5. The adjustable attenuator according to claim 1, characterized in that, A smaller-diameter capillary is nested in a single capillary in the capillary layer.

6. The adjustable attenuator according to claim 1, wherein The materials of the outer cladding and the capillary layer are silica.

7. The preparation method of the adjustable attenuator according to any one of claims 1-6, characterized in that, The specific steps are as follows: (1) After cleaning the anti-resonant hollow fiber with absolute ethanol, cut the end face of the anti-resonant hollow fiber flat; (2) Perform arc discharge / carbon dioxide laser heating on the cut flat fiber end face, so that the capillary layer of the anti-resonant hollow fiber collapses, and only the core of the fiber remains open; (3) Uniformly configure the functional material to be filled; (4) Immerse the fiber with only the core open after melting and collapsing in step (2) into the functional material in step (3); (5) Due to the fluidity of the material, under capillary action, the material slowly fills into the gap; (6) Cure the material in the interstitial filling region to obtain an adjustable attenuator based on the anti-resonant hollow fiber.

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