All-fiber mode filter based on multi-core fiber

Abstract

The invention discloses an all-fiber mode filter based on a multi-core fiber. The mode filter adopts an all-fiber structure of a multi-core fiber, and is an optical device for selecting or filtering light beams in a specific mode from input light beams containing different modes. The fiber core diameter, the fiber core distance and the refractive index of the multi-core optical fiber are adjusted and changed, mode filtering is achieved by finding out a proper transmission period among multiple modes, in a certain specific bandwidth, multi-mode signals can be efficiently and selectively filtered, the mode filtering function is achieved, operation is easy, and accuracy is high. The multi-core optical fiber structure provided by the invention can realize the functions of selecting a specific target mode and filtering a non-target mode, and has the characteristics of simple structure, small loss, high mode purity, stable performance and the like. The invention has wide application prospects in the fields of mode division multiplexing, optical fiber mode filters, optical fiber filters, optical fiber sensors, optical fiber lasers, optical fiber transmission systems and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication, optical filter mode and multi-core optical fiber, and specifically relates to an all-optical fiber filter mode device based on multi-core optical fiber. Background Art

[0002] In recent years, with the development and popularization of mobile communication technology and the Internet, high speed, low latency, and large bandwidth have become the mainstream indicators of the new generation of technology. With the increase in bandwidth, the capacity of the optical fiber communication system has also increased. The high-order modes in the optical fiber are orthogonal, which can greatly improve the capacity of optical fiber communication. Therefore, the transmission quality and reliability of high-order mode lasers are particularly important, which puts forward new demands on optical fiber infrastructure and gradually evolves into a competition for optical fiber basic equipment.

[0003] Mode division multiplexing (MDM) technology can increase the transmission capacity by transmitting multiple data streams in parallel on the same optical fiber by increasing the number of optical modes that can be transmitted in an optical fiber or waveguide. There are also multiple high-order mode oscillations in few-mode fiber lasers or multi-mode fiber lasers, and it is necessary to regulate the mode transmitted in the laser cavity to generate high-quality high-order mode lasers. Mode filters are used in MDM systems and few-mode / multi-mode fiber lasers to select the required target mode and filter out non-target modes, thereby improving the transmission quality and reliability of optical signals.

[0004] At present, although many filter modes have been proposed, most of them are waveguide chips or polymer and metal hybrid waveguide structures, which have complex structures and demanding manufacturing processes, which are not conducive to practical applications. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide an all-fiber mode filter based on multi-core optical fiber, which is an optical device that selects or filters out a specific mode light beam from an input light beam containing different modes; the multi-core optical fiber structure of the present invention can realize the selection of a specific target mode and the filtering function of a non-target mode, and has the characteristics of simple structure, low loss, high mode purity, stable performance, etc., and is easy to use and convenient for subsequent experimental settings to verify relevant theories and technologies. The present invention has broad application prospects in the fields of mode division multiplexing, optical fiber mode filters, optical fiber filters, optical fiber sensors, optical fiber lasers, and optical fiber transmission systems.

[0006] The present invention adopts the following technical scheme.

[0007] The present invention provides an all-fiber mode filter based on multi-core optical fiber, which adopts an all-fiber structure of multi-core optical fiber. The input in the fiber core of the multi-core optical fiber is a light beam with multiple modes, that is, the light beam has different modes of the same wavelength or the same mode of different wavelengths; by adjusting the fiber core diameter, fiber core distance and refractive index in the multi-core optical fiber, a suitable transmission period between the multiple modes is obtained, and a light beam of a specific mode is selected or filtered out from the input light beams with different modes, so as to realize mode filtering and filtering functions, wherein mode filtering refers to filtering out different modes of the same wavelength, and filtering refers to filtering out the same mode of different wavelengths.

[0008] In the present invention, the multi-core optical fiber is a dual-core optical fiber or a triple-core optical fiber; the principle of the present invention is also applicable to other multi-core optical fibers with similar structures.

[0009] In the present invention, the diameters of the cores in the multi-core optical fiber are the same or different. A larger core diameter can support more propagation modes, and a suitable diameter needs to be selected according to the expected number of modes.

[0010] In the present invention, simulation is performed by optical simulation software Rsoft to adjust the radius, core distance and refractive index of the core in the multi-core optical fiber to obtain a suitable transmission period between multiple modes, and select or filter out a specific mode of light beam from input light beams with different modes.

[0011] In the present invention, under the condition that the diameter of the fiber core, the core distance and the refractive index in the multi-core optical fiber are determined, a light beam with the same wavelength but a different mode is input from the same port of one of the cores of the multi-core optical fiber, and then the light beam is periodically transmitted in the optical fiber. By adjusting the propagation distance so that the transmitted light beam meets a certain transmission period, the target mode is output at the target port, and the non-target mode is filtered out at the remaining ports, thereby achieving the functional compatibility of filtering and filtering mode.

[0012] In the present invention, in a specific embodiment, the optical simulation software Rsoft is used for simulation. For a symmetrical dual-core optical fiber, the wavelength is set to 1550nm, the refractive index of the optical fiber cladding is 1.44, the refractive index of the core is 1.45, the core diameter d1=d2=30μm, the core distance D1 is 33μm, and the LP signal is input from the same port of Port1 or Port2. 01 LP 11 and LP 21 The three modes of light beams are then transmitted periodically in the optical fiber. By adjusting S1, a specific mode meets a certain transmission period. At this time, S1 = 118714 μm, so that the target mode LP 11 When Port 3 is selected, non-target mode LP 01 and LP 21 Filtered out at Port 4.

[0013] In the present invention, when the multi-core optical fiber is an asymmetric multi-core optical fiber, the core diameter of the optical fiber is pre-set through the principle of phase matching so that the high-order mode to be filtered out is converted into a specific mode (fundamental mode or other mode), and the propagation distance is adjusted so that the high-order mode and the specific mode meet a certain transmission period, so that the target mode is output at the target port and the non-target mode is filtered out at the remaining ports, thereby realizing the function of the filter mode.

[0014] In the present invention, in a specific embodiment, simulation is performed using optical simulation software Rsoft; in a specific embodiment, for an asymmetric three-core optical fiber, the wavelength of the optical fiber is set to 1550nm, the cladding diameter and the cladding refractive index are 1.44, the core refractive index is 1.45, the core diameter d3 = 20.3μm, d5 = 25.1μm, d4 = 36μm, the core distance D2 = 33.15μm, and D3 = 33.55μm. This asymmetric three-core optical fiber uses the phase matching principle to couple the non-target high-order mode in the middle core to the offset core, so that the target high-order mode remains in the middle core and continues to transmit forward. You can input the LP signal from Port 5. 11 LP 21 and LP 31 The three modes of light beams are then transmitted periodically in the optical fiber. Using the principle of phase matching, S2 = 25500 μm is adjusted to filter out the high-order mode LP. 11 and LP 21 Converted to a specific mode so that the higher-order mode LP 31 is retained, so that the target mode LP 31 When Port 6 is selected, non-target mode LP 11 LP 21 They are filtered out at Port 7 and Port 8 respectively, realizing the function of filter mode. This method is also applicable to filtering.

[0015] In the present invention, the multiple cores in the multi-core optical fiber may have different core distances, and the optimal core distance is the core radius + 3 μm; the range is 12 μm-50 μm.

[0016] In the present invention, both the input end and the output end of the multi-core optical fiber are few-mode optical fibers.

[0017] In the present invention, the number of modes of the light beam transmitted in the core of the multi-core optical fiber is not fixed; the number of modes is determined according to actual experimental requirements.

[0018] In the present invention, the wavelength range of the light beam input into the core of the multi-core optical fiber is between 850nm and 2μm.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The all-fiber mode filter based on multi-core optical fiber proposed in the present invention adopts an all-fiber structure, has a simple structure, generates small loss, and has high mode purity (in the embodiment, within the bandwidth of 1510nm-1580nm, the mode purity after filtering reaches 90%), and has simple packaging, stable performance, and is economical and applicable.

[0021] 2. The all-fiber mode filter based on multi-core optical fiber proposed in the present invention can select and filter out a specific mode by simply calculating the transmission period of the specific mode and changing the transmission distance, and the operation is simple.

[0022] 3. The all-fiber mode filter based on multi-core optical fiber proposed in the present invention can perform efficient selective filtering on multi-wavelength and multi-mode signals within a certain specific bandwidth, thereby achieving compatibility between the mode filter and the filtering function. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a simplified structural diagram of the all-fiber filter based on multi-core optical fiber provided by the present invention.

[0024] Figure 2 This is a plan view schematic diagram of the dual-core optical fiber provided by the present invention.

[0025] Figure 3 This is a schematic diagram of the principle of the dual-core optical fiber provided by the present invention.

[0026] Figure 4 This is a diagram of the dual-core optical fiber simulation results provided by the present invention.

[0027] Figure 5 This is a simulation result diagram of the compatibility of the dual-core optical fiber filter mode and filtering function provided by the present invention.

[0028] Figure 6 This is a spatial schematic diagram of the three-core optical fiber provided by the present invention.

[0029] Figure 7 This is a plan view of a three-core optical fiber provided by the present invention.

[0030] Figure 8 This is a schematic diagram of the principle of a three-core optical fiber provided by the present invention.

[0031] Fig. 9 This is a diagram of the simulation results of the three-core optical fiber provided by the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to describe the technical solutions in the embodiments of the present invention in more detail. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The embodiments listed here are only for the present invention, and the data such as wavelength, core diameter, core distance, refractive index, etc. are not limited to the scope provided by the present invention.

[0033] The all-fiber mode filter based on multi-core optical fiber can select or filter out a specific mode light beam from input light beams with different modes, thereby improving the effectiveness and reliability of communication information.

[0034] like Figure 1 As shown, this figure is a simplified structural diagram of the all-fiber mode filter, in which 101 represents the few-mode fiber connected to the input end, 102 represents the all-fiber mode filter, and 103 represents the few-mode fiber connected to the output end.

[0035] Specifically, the following embodiments mainly introduce mode filters based on symmetrical dual-core optical fibers and mode filters based on asymmetrical triple-core optical fibers. Symmetric dual-core optical fibers refer to optical fibers with two cores symmetrical to the center of the waveguide and with the same refractive index and core diameter. The cores of asymmetrical multi-core optical fibers are still parallel cores, but the core diameters or refractive indices are different.

[0036] Example 1

[0037] like Figure 2 and Figure 3 As shown in the figure, d1 and d2 are the diameters of the dual-core fiber cores, and D1 is the core distance. The diameters (d1 and d2) of the two cores in the dual-core fiber are the same. Since its larger core diameter can support more propagation modes, the appropriate diameter needs to be selected according to the number of modes expected in the actual application process. By calculating the periodic relationship between each mode, the transmission distance S1 is adjusted, the target mode is selected, and the non-target mode is filtered out.

[0038] Specifically, Figure 4 As shown, the wavelength is 1550nm, the core diameter is set to d1=d2=30μm, and the core distance is set to D1=33μm. Through Rsoft simulation experiments, it can be compared that when the transmission distance S1=118714μm, the mode fields of the input beam are LP 01 LP 11 and LP 21 mode, it can be observed that LP 01 and LP 21 The beams of the modes are output from the same output port, such as Figure 4 (a) and Figure 4 As shown in (c), LP 11The light beam of the mode is output from the other output port, such as Figure 4 (b) shows that LP 11 Mode selection, filter out LP in the beam 01 and LP 21 model.

[0039] like Figure 5 As shown in the figure, this is the simulation result diagram of the compatibility of dual-core optical fiber filter mode and filtering function.

[0040] Specifically, based on the realization of the filter mode function, the wavelength range is set to 1450nm-1650nm, the core diameter is set to d1=d2=30μm, and the core distance is set to D1=33μm. Through Rsoft software simulation, it can be simulated that the transmittance of LP at 1510nm-1580nm (bandwidth is 70nm) reaches more than 90%. 11 mode, making the LP outside the 1510nm-1580nm wavelength 11 mode is filtered out so that its wavelength range is within the LP 11 The mode beams are output from the same port, achieving compatibility between the filter mode and the filtering function.

[0041] Example 2

[0042] like Figure 6 As shown in FIG. 6 , this figure is a spatial schematic diagram of a three-core optical fiber, where the input end 601 is a few-mode optical fiber, the middle part 602 is an all-fiber mode filter based on an asymmetric three-core optical fiber, and the output end 603 is a few-mode optical fiber. The light beam enters the middle mode filter part from the input end few-mode optical fiber, and then filters out the non-target mode, so that the target mode is output from the few-mode optical fiber.

[0043] like Figure 7 As shown, this figure is a plan view of a three-core optical fiber, where d3, d4 and d5 are the core diameters, and D2 and D3 are the core distances.

[0044] like Figure 8 As shown in the figure, this is a schematic diagram of the principle of asymmetric three-core fiber. Input from the input end few-mode fiber containing LP 11 LP 21 and LP 31 The light beam is simulated by optical simulation software Rsoft. For the asymmetric three-core optical fiber, the wavelength of the optical fiber is set to 1550nm, the cladding diameter is 125μm, the cladding refractive index is 1.44, the core refractive index is 1.45, the core diameter is d3=20.3μm, d5=25.1μm, d4=36μm, the core distance is D2=33.15μm, and D3=33.55μm.

[0045]

[0046] In the formula, C 11 , C 22 , C 12 and C 21 They are the self-coupling coefficient and the mutual coupling coefficient. The self-coupling coefficient is too small to be ignored, and C 12 Approximately equal to C 21 Approximately equal to C, the size of the coefficient C is related to the length and thickness of the optical fiber in the coupling area; z is the propagation distance of light in the coupling area, A1 and A2 are the intensities of the light fields in the middle core and the specific eccentric core, respectively, β1 and β2 are the transmission constants of the specific high-order modes in the middle core and the propagation constants of the specific high-order modes in the specific eccentric core, respectively. For multi-core optical fibers, appropriate structural parameters are selected to achieve phase matching between the middle core and a certain eccentric core, that is, the effective refractive index of the mode is equal. The effective refractive index of the mode is related to the core diameter. Therefore, the effective refractive index of the mode can be changed by changing the core diameter. When the effective refractive index of the specific high-order mode in the two cores is equal, mode conversion and energy coupling are achieved. Among them, according to the phase matching principle, when the propagation constant β1=β2, the LP in the middle core is 11 Mode and LP 21 mode are converted to LP in the eccentric core 01 Mode and LP 11 mode, due to the difference in transmission period of different coupling processes, when S2 = 25500μm, the LP in the eccentric core 01 Mode and LP 11 mode is output at Port 7 and Port 8, while the high-order mode LP is retained. 31 Output at Port 6 can filter out the LP in the middle fiber core 11 Mode and LP 21 Mode, keep LP 31 mode, output at Port 6.

[0047] Two specific examples are used in this paper to illustrate the principle and implementation of the present invention. The above examples are only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An all-fiber filter based on multi-core optical fiber, characterized in that: It adopts an all-fiber structure of multi-core optical fiber. The input in the core of the multi-core optical fiber is a light beam with multiple modes, that is, the light beam has different modes of the same wavelength or the same mode of different wavelengths; by adjusting the core diameter, core distance and refractive index in the multi-core optical fiber, a suitable transmission period between the multiple modes is obtained, and a light beam of a specific mode is selected or filtered out from the input light beams with different modes, thereby realizing mode filtering and filtering functions. Mode filtering refers to filtering out different modes of the same wavelength, and filtering refers to filtering out the same mode of different wavelengths.

2. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The multi-core optical fiber is a dual-core optical fiber or a triple-core optical fiber with parallel cores.

3. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The diameters of the cores in the multi-core optical fiber are the same or different.

4. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The optical simulation software Rsoft is used to simulate and adjust the core diameter, core distance and refractive index of the multi-core optical fiber to obtain the appropriate transmission period between multiple modes and select or filter out a specific mode of light beam from input light beams with different modes.

5. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: When the multi-core optical fiber is a dual-core optical fiber, under the condition that the diameter of the core, the core distance and the refractive index of the dual-core optical fiber are determined, a light beam with the same wavelength but a different mode is input from the same port of one of the cores of the dual-core optical fiber, and then the light beam is periodically transmitted in the optical fiber. By adjusting the propagation distance, the target mode is output at the target port, and the non-target mode is filtered out at the remaining ports, thereby achieving functional compatibility of filtering and filtering mode.

6. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: When the multi-core optical fiber is a three-core optical fiber, the core diameter of the optical fiber is pre-set through the principle of phase matching so that the high-order mode to be filtered out is converted into a specific mode. The propagation distance is adjusted so that the high-order mode and the specific mode meet a certain transmission period, so that the target mode is output at the target port and the non-target mode is filtered out at the remaining ports, thereby realizing the function of the filter mode.

7. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The input and output ends of the multi-core optical fiber are both few-mode optical fibers.

8. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The core distance in a multi-core optical fiber is the core radius + 3 μm; its range is 12 μm-50 μm.

9. The all-fiber filter based on multi-core optical fiber according to claim 1, characterized in that: The wavelength of the light beam ranges from 850nm to 2μm.

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