Multi-channel tunable filter and preparation method thereof

Abstract

The invention provides a multi-channel tunable filter and a preparation method thereof, and relates to the technical field of photonic devices. The multi-channel tunable filter comprises a section of input multi-core optical fiber, a section of output multi-core optical fiber and a section of microstructure optical fiber, the microstructure optical fiber is welded between the input multi-core optical fiber and the output multi-core optical fiber; at least two isolated micropore channels are arranged in the microstructure optical fiber in a penetrating mode in the axial direction of the microstructure optical fiber. The fiber core of the input multi-core optical fiber and the fiber core of the output multi-core optical fiber are correspondingly collimated with the micropore channel of the microstructure optical fiber respectively; wherein the at least two micropore channels are respectively filled with functional liquids with different optical characteristics; each micropore channel filled with the functional liquid and the collimated fiber cores at the two ends of the micropore channel jointly form a Fabry-Perot filtering cavity with the independent filtering characteristic. On the basis, the problem that a device capable of realizing multiple independent filtering channels in a single optical fiber is lacked in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photonic devices, in particular to a multi-channel tunable filter and a preparation method thereof. BACKGROUND

[0002] With the explosive growth of fiber communication capacity demand, wavelength division multiplexing technology is developing towards higher channel density, which puts forward higher requirements for tunable optical filters as key passive devices in optical fiber systems; tunable filters are responsible for dynamic wavelength selection, routing and monitoring in dense wavelength channels, and their performance directly determines the flexibility, reconfigurability and management efficiency of optical networks. At present, the technical solutions for realizing tunable filtering function mostly have limitations in practical application, specifically:

[0003] Solution one is a filter based on fiber Bragg grating (FBG), which has good compatibility with fiber systems, but usually relies on stress or temperature for tuning, with limited tuning range and response speed. Solution two is a filter based on bulk optics or micro-electro-mechanical system (MEMS), such as a MEMS fiber wavelength tunable filter and forming method provided in the patent with publication number CN115373081A; although this filter can achieve a larger tuning range, it has problems such as difficulty in miniaturization, introduction of large loss when coupled with the fiber system, complex mechanical structure, weak resistance to vibration and environmental changes, etc. More importantly, these traditional technical solutions are difficult to realize parallel and independent operation of multiple channels on a single device; if a multi-channel system is to be built, multiple discrete filters need to be combined, which greatly increases the volume, cost, complexity and potential failure points of the system.

[0004] For the above problems, the present application applicant believes that it is feasible to fill functional liquid (such as liquid crystal, refractive index matching liquid) in the axial micro-holes of special optical fibers (such as edge-hole optical fibers, photonic crystal optical fibers), use the fiber end face and the liquid to form a Fabry-Perot (F-P) filter cavity, and then change the optical properties (such as refractive index) of the liquid to realize the tuning of the filtering wavelength; but the related research in the prior art is mostly limited to filling a single type of liquid in a single micro-hole of a single-core optical fiber, so only single-channel filtering and tuning operation can be realized, which cannot meet the demand of multi-channel parallel processing.

[0005] Therefore, the technical problem of multi-channel tunable filter in the field is that there is no device scheme with high structural integration and capable of realizing multiple independent filtering channels in a single optical fiber. In addition, to integrate multiple independent F-P cavities on a single optical fiber substrate, multiple liquids with different optical properties must be filled in multiple microchannels that are close to each other (with a spacing of only tens of microns) and have a diameter of only microns. However, when multiple liquid filling is performed at such a small scale by using conventional liquid filling methods such as microinjection or pressure pumping, the operation is extremely cumbersome and has a low success rate, and thus cannot meet the requirements of repeatability and large-scale production. SUMMARY

[0006] The present application aims to provide a multi-channel tunable filter and a preparation method thereof, so as to solve the problems mentioned in the background that there is no device capable of realizing multiple independent filtering channels in a single optical fiber. In addition, there is also a lack of an efficient and reliable filter preparation method capable of realizing accurate filling of heterogeneous liquids in a microchannel array.

[0007] The present application is implemented by using the following technical solutions: A multi-channel tunable filter comprises an input interface, an output interface, and a filtering unit arranged between the input interface and the output interface. The input interface comprises a section of input multi-core optical fiber, the output interface comprises a section of output multi-core optical fiber, and the filtering unit comprises a section of microstructured optical fiber. The microstructured optical fiber is fused between the input multi-core optical fiber and the output multi-core optical fiber. At least two mutually isolated micro-hole channels are arranged in the microstructured optical fiber along the axial direction. The cores of the input multi-core optical fiber and the cores of the output multi-core optical fiber are respectively aligned with the micro-hole channels of the microstructured optical fiber. At least two micro-hole channels are respectively filled with functional liquids with different optical properties. Each micro-hole channel filled with a functional liquid and the cores aligned at both ends thereof jointly form a Fabry-Perot filtering cavity with independent filtering characteristics.

[0008] In the present application, a sandwich structure comprising a multi-core optical fiber, a microstructured optical fiber filled with heterogeneous liquids, and a multi-core optical fiber is proposed, and multiple parallel and physically isolated optical resonant cavities are ingeniously constructed in a single device. Since the functional liquids filled in each cavity have different optical properties, the resonant wavelengths are also different, thereby directly realizing multi-channel filtering and tuning functions at the hardware level, breaking through the limitations of single-channel filtering and tuning in the prior art, and achieving a high spatial integration.

[0009] Further, when the number of micro-hole channels of the micro-structured fiber is odd, all the micro-hole channels are arranged in a layout mode in which one micro-hole channel is located at the center and the rest of the micro-hole channels are arranged in a ring array around the center in a center-symmetrical manner; the cores of the input multi-core fiber and the cores of the output multi-core fiber are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing in the input multi-core fiber and the output multi-core fiber matches the micro-hole channel spacing in the micro-structured fiber; when the number of micro-hole channels of the micro-structured fiber is even, all the micro-hole channels are arranged in a layout mode in which the ring array is arranged in a center-symmetrical manner; the cores of the input multi-core fiber and the cores of the output multi-core fiber are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing in the input multi-core fiber and the output multi-core fiber matches the micro-hole channel spacing in the micro-structured fiber.

[0010] In the above scheme, the ring array arrangement can form a uniform structure to facilitate precise geometric matching between the micro-hole channels and the cores, which is a prerequisite for achieving low-loss, low-crosstalk fusion and ensuring accurate optical path butt joint; thus, it can be ensured that the light emitted from the input cores can be efficiently coupled into the corresponding micro-hole channels and then coupled to the output cores, which is the geometric basis for constructing multiple independent optical paths.

[0011] Further, the input multi-core fiber and the output multi-core fiber are both seven-core fibers, and the micro-structured fiber is a seven-hole fiber with seven micro-hole channels; the seven micro-hole channels are respectively filled with seven functional liquids with different optical properties.

[0012] In the above scheme, the seven-core / seven-hole structure is an optimized design that takes into account both high integration and low channel crosstalk, which is consistent with the development trend of current wavelength division multiplexing technology and has good application prospects and standardization potential.

[0013] Further, the core spacing and the micro-hole channel spacing are 38-45 μm.

[0014] In the above scheme, by designing a pitch of 38-45 μm, a good balance between ensuring low inter-channel optical crosstalk and achieving high-density integration can be achieved, and meanwhile, efficient and low-loss coupling with fan-in / fan-out modules (used to connect the tunable filter with external optical devices) can be facilitated, thereby providing convenience for system-level applications of the device. In actual applications, if the pitch is too small, the light field mode coupling between adjacent core / micro-hole channels will be significantly enhanced, thereby causing the inter-channel optical crosstalk to deteriorate sharply; if the pitch is too large, the spatial integration density of the device will be reduced, and meanwhile, the device can be mismatched with the interface of a standard commercial fan-in / fan-out module, thereby introducing additional alignment loss and engineering complexity. In addition, the diameters of the micro-hole channels and the core can also be set to 8-10 μm. Such a diameter design can accommodate sufficient functional liquid, and ensure sufficient interaction length between light and liquid, so as to achieve effective tuning effect; meanwhile, the diameter is small enough to ensure high mechanical strength and structural stability during fusion splicing.

[0015] Further, the functional liquid is a refractive index matching liquid, and different refractive index matching liquids with different refractive indexes are filled in different micro-hole channels; or the functional liquid comprises a combination of the refractive index matching liquid and one or more of liquid crystal, temperature-sensitive polymer or fluorescent dye, and different liquids in the combination are filled in different micro-hole channels.

[0016] In the above scheme, by filling the refractive index matching liquids with different refractive indexes, different initial filtering wavelengths can be set for the micro-hole channels, thereby realizing multi-channel tunable filtering; on this basis, by increasing different types of functional liquids, the filter can be further endowed with rich functions to expand the application scenarios of the device, such as filling liquid crystal to realize electrical tuning (quickly changing the refractive index of liquid crystal by applying voltage), filling temperature-sensitive polymer to realize temperature sensing (monitoring wavelength drift) and temperature-controlled tuning (actively controlling temperature), and filling fluorescent dye to be used for fluorescence detection (the dye emits fluorescence when pumped by specific wavelength excitation light). For example, in actual applications, for a seven-hole optical fiber having seven micro-hole channels, three different refractive index matching liquids with different refractive indexes can be filled in three of the micro-hole channels to constitute three fixed-wavelength filtering channels; two different liquid crystals can be filled in two of the micro-hole channels and micro-electrodes can be integrated to constitute two independently electrically tunable filtering channels; temperature-sensitive polymer can be filled in one of the micro-hole channels to constitute a temperature sensing and tuning channel; and fluorescent dye can be filled in one of the micro-hole channels to constitute a biological / chemical fluorescence detection channel.

[0017] A preparation method of a multi-channel tunable filter, for preparing the multi-channel tunable filter described above, comprising the following steps: Step one: material preparation; providing two sections of multicore optical fiber and one section of microstructured optical fiber; Step two: selective filling; The microstructured optical fiber is executed at least twice filling cycle, each filling cycle includes: Selective blocking: at one end of the microstructured optical fiber, a target micro-hole channel is selected, and the openings of the remaining non-target micro-hole channels are temporarily blocked; Liquid filling: the other end of the microstructured optical fiber is immersed in a functional liquid, the functional liquid is filled into the target micro-hole channel by capillary action, and the gas in the target micro-hole channel is discharged from the opening at one end of the microstructured optical fiber; Sealing treatment: sealing material is applied to both ends of the target micro-hole channel and solidified to seal the functional liquid filled inside; Wherein, the optical properties of the functional liquid used in at least two filling cycles are different; Step three: fusion forming; The microstructured optical fiber treated in step two is fused between two segments of multicore optical fiber, and the cores of the two segments of multicore optical fiber are aligned with the micro-hole channels of the microstructured optical fiber.

[0018] In the present application, a selective filling processing method is proposed, through the iterative cycle of selective blocking, liquid filling and sealing treatment, the self-filling of the functional liquid in each micro-hole channel can be realized by capillary action; compared with the prior art, the present method only needs to perform blocking operation in the filling process, without the need to adopt microscopic injection or pressure pumping and other methods which are difficult to control precision and have low success rate. In summary, the present systematic method decomposes a complex multivariate process problem into a series of simple, controllable and independent steps, and further makes the preparation of the multi-channel tunable filter become streamlined, reliable and repeatable.

[0019] Further, the specific way of selective blocking is: An elastic mold with a microstructure array is adopted, and the elastic mold is pressed on one end of the microstructure optical fiber, the microstructure array on the elastic mold is matched with the array of the micro-hole channels, so that the target micro-hole channel is communicated with the atmosphere and the non-target micro-hole channels are physically isolated and blocked. Further, the overall surface area of the surface of the elastic mold in contact with the one end of the microstructure optical fiber is greater than the cross-sectional area of the one end of the microstructure optical fiber; the microstructure array on the elastic mold is a plurality of micro-grooves corresponding to the array of the micro-hole channels, the openings of the plurality of micro-grooves are located on the surface of the elastic mold in contact with the one end of the microstructure optical fiber, and each micro-groove is communicated with an air outlet hole. Further, during selective blocking, the elastic mold is placed on the one end of the microstructure optical fiber, and by alignment operation and offset operation, a certain micro-groove on the elastic mold is aligned with the target micro-hole channel, and the remaining micro-grooves are misaligned with the remaining non-target micro-hole channels, that is, the remaining non-target micro-hole channels are covered and blocked by the mold entity part between the micro-grooves on the elastic mold.

[0020] In the above scheme, the elastic mold is adopted, and the tight and non-damaging sealing can be formed by using the elasticity of the material, which effectively improves the operation efficiency and reliability compared with the manual blocking mode of each hole. Among them, the micro-grooves and air outlet holes on the elastic mold provide conditions for capillary action; when the self-filling of the functional liquid is realized by using the capillary action, one end of the micro-hole channel needs to be in contact with the liquid, and the other end needs to be communicated with the atmosphere; when the opening of one end of a certain micro-hole channel is communicated with the air outlet hole through the micro-groove aligned therewith, the condition of being communicated with the atmosphere is realized, and then the other end of the micro-hole channel is kept in contact with the corresponding functional liquid for a period of time, so that the functional liquid can be automatically sucked into the micro-hole channel by using the capillary action. In the preparation method, the filling of different micro-hole channels can be realized by alignment operation and offset operation of the elastic mold, which is simple to use and has high success rate.

[0021] Further, the specific way of the sealing treatment is: The ultraviolet curing glue is spotted at the openings of the two ends of the target micro-hole channel, and the ultraviolet curing glue is cured by ultraviolet light irradiation.

[0022] The beneficial effects realized by the present application are: A multi-channel tunable filter is provided, which comprises a multi-core optical fiber, a microstructure optical fiber filled with heterogeneous materials, and a sandwich structure of the multi-core optical fiber. The independent filter channels can be integrated on a single optical fiber, and the independent access and tuning of different wavelength channels can be realized by external optical path switching, and the channels do not interfere with each other. Compared with the prior art which is limited to a single-channel structure, the present application can meet the demand of multi-channel parallel processing, improve the space utilization, and meet the development trend of miniaturization and integration of optical devices.

[0023] The application provides a preparation method of a multi-channel tunable filter, by setting an iterative cycle of selective plugging, liquid filling and sealing treatment, self-filling of functional liquid in each micro-hole channel can be realized by using capillary action; compared with the existing micro-injection or pressure pumping mode which is difficult to control precision and has low success rate, the application has simple operation, high success rate, and makes the preparation of the multi-channel tunable filter become flowable, reliable and repeatable. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a structural composition schematic diagram of the multi-channel tunable filter described in the embodiment of the application; Figure 2 is a structural schematic diagram of the micro-structured optical fiber described in the embodiment of the application; Figure 3 is a filter principle schematic diagram of the multi-channel tunable filter described in the embodiment of the application; Figure 4 is a structural schematic diagram of the elastic mold described in the embodiment of the application; Figure 5 is a structural composition schematic diagram of the optical fiber amplifier system described in the embodiment of the application; In the figure: 1, pump source; 2, wavelength division multiplexer; 3, gain optical fiber; 4, isolator; 5, fan-in fan-out module; 6, multi-channel tunable filter; 61, input multi-core optical fiber; 62, output multi-core optical fiber; 63, micro-structured optical fiber; 7, coupler; 8, optical spectrum analyzer; 9, micro-groove; 10, air outlet through hole. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application.

[0026] Embodiment 1 The first aspect of the embodiment provides a multi-channel tunable filter, which is suitable for dense wavelength division multiplexing system, reconfigurable optical add-drop multiplexer, multi-wavelength sensing demodulation and spectral analysis and the like. Please refer to Figures 1 to 3 The multi-channel tunable filter 6 includes an input interface, an output interface and a filter unit arranged between the input interface and the output interface, specifically: The input interface includes an input multi-core optical fiber 61, the output interface includes an output multi-core optical fiber 62, and the filter unit includes a micro-structured optical fiber 63, and the micro-structured optical fiber 63 is fused between the input multi-core optical fiber 61 and the output multi-core optical fiber 62. Wherein: Inside the microstructure fiber 63, at least two micro-hole channels are arranged along the axial direction; the cores of the input multi-core fiber 61 and the cores of the output multi-core fiber 62 are respectively collimated with the micro-hole channels of the microstructure fiber 63. Different functional liquids are filled in the at least two micro-hole channels respectively; each micro-hole channel filled with the functional liquid and the cores collimated at both ends of the micro-hole channel form a Fabry-Perot filtering cavity with independent filtering characteristics.

[0027] When the number of the micro-hole channels of the microstructure fiber 63 is odd, the micro-hole channels are arranged in a layout mode in which one micro-hole channel is located at the center and the remaining micro-hole channels are arranged in a circular array around the center micro-hole channel in a center-symmetrical manner; the cores of the input multi-core fiber 61 and the cores of the output multi-core fiber 62 are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing of the input multi-core fiber 61 and the output multi-core fiber 62 matches the micro-hole channel spacing of the microstructure fiber 63. When the number of the micro-hole channels of the microstructure fiber 63 is even, all the micro-hole channels are arranged in a layout mode in which the micro-hole channels are arranged in a circular array in a center-symmetrical manner; the cores of the input multi-core fiber 61 and the cores of the output multi-core fiber 62 are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing of the input multi-core fiber 61 and the output multi-core fiber 62 matches the micro-hole channel spacing of the microstructure fiber 63.

[0028] The core spacing and the micro-hole channel spacing are 38-45 μm, and the micro-hole channel diameter and the core diameter are 8-10 μm.

[0029] The functional liquid is an index matching liquid, and index matching liquids with different refractive indexes are filled in different micro-hole channels respectively; or the functional liquid includes a combination of the index matching liquid and one or more of liquid crystal, temperature-sensitive polymer or fluorescent dye, and different liquids in the combination are filled in different micro-hole channels respectively.

[0030] In this embodiment, specifically: The microstructure fiber 63 is a seven-hole fiber with seven micro-hole channels, such as a seven-hole edge-hole fiber. The microstructure fiber 63 has seven micro-hole channels arranged along the axial direction inside, one of which is located at the center and the other six are arranged in a circular array around the center micro-hole channel in a center-symmetrical manner; the length of the microstructure fiber 63 is about 500 μm and the outer diameter is 125 μm, wherein the diameter of a single micro-hole channel is 9 μm and the micro-hole channel spacing is about 42 μm. Seven kinds of functional liquids with different optical characteristics are filled in the seven micro-hole channels respectively, and in this embodiment, seven index matching liquids with different refractive indexes are used, for example, carbon tetrachloride (refractive index n≈1.460), ethanol (refractive index n≈1.361) and five glycerol aqueous solutions with different concentrations (refractive index n is continuously adjustable between 1.333 and 1.474).

[0031] The input multi-core optical fiber 61 and the output multi-core optical fiber 62 are both seven-core optical fibers. The inner part of the seven-core optical fiber contains seven independent cores, which are arranged in the same way as the microchannel array in the microstructure optical fiber 63, i.e., one central core and six annularly arranged cores; the diameter of a single core and the core spacing are both corresponding to the microchannel, i.e., about 9 μm and 42 μm, respectively; in addition, the length and the outer diameter of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 are also set to be consistent with the microchannel, i.e., 500 μm and 125 μm, respectively.

[0032] The working principle of the above multi-channel tunable filter 6 is based on Fabry-Perot interference, specifically: When a broadband light is introduced into a certain specific core of the input multi-core optical fiber 61, the optical signal will propagate along the core to the first fusion surface of the microstructure optical fiber 63 (i.e., the fusion surface between the input multi-core optical fiber 61 and the microstructure optical fiber 63); at this interface, due to the difference in refractive index between the core (mostly quartz glass) and the functional liquid filled in the microchannel, part of the light will be reflected, and the other part will be transmitted into the corresponding microchannel. The transmitted light propagates in the microchannel filled with functional liquid, and when it reaches the second fusion surface (i.e., the fusion surface between the microstructure optical fiber 63 and the output multi-core optical fiber 62), it will again undergo partial reflection and partial transmission, and the transmitted part of the light will enter the corresponding core of the output multi-core optical fiber 62 and be finally output.

[0033] The light beams reflected back and forth between the two fusion surfaces will undergo multi-beam interference, and only the light waves that satisfy the resonance condition can be effectively transmitted. The transmission spectrum peak (i.e., the transmission wavelength) satisfies the resonance condition: 2nL = mλ (m = 1, 2, 3...), where n is the refractive index of the functional liquid, L is the length of the Fabry-Perot filter cavity (i.e., the microchannel), and m is an integer (interference order). Since the seven microchannels in this embodiment are filled with seven different refractive index (n1, n2...n7) functional liquids, the seven independently formed Fabry-Perot filter cavities correspond to seven different initial central transmission wavelengths (λ1, λ2...λ7). In application, the user selects a core of the input multi-core optical fiber 61 to couple the input light, which is equivalent to selecting to activate the Fabry-Perot filter cavity corresponding to the core, thereby realizing independent selection of the seven preset wavelength channels. In addition, if the filled functional liquid is a tunable material such as liquid crystal, the value of the refractive index n can be changed by applying an external field (such as an electric field), thereby realizing dynamic tuning of the filter wavelength of the corresponding microchannel.

[0034] The above multi-channel tunable filter 6 can be applied in a fiber amplifier system, please refer to Figure 5The system comprises a pump source 1, a wavelength division multiplexer 2, a gain optical fiber 3 (using an erbium-doped optical fiber), a multi-channel tunable filter 6, a fan-in fan-out module 5, a coupler 7, an isolator 4 and an optical spectrum analyzer 8. The fan-in fan-out module 5 can be of the MCFIFOM type, which functions to guide the signal from a single optical fiber into a specified core of the input multi-core optical fiber 61, and then the signal can pass through the multi-channel tunable filter 6. The selected specific wavelength of light is output from the corresponding core of the output multi-core optical fiber 62, and then re-enters the fan-in fan-out module 5 and is output to a single-mode optical fiber. By switching the input / output ports of the fan-in fan-out module 5, the transmission spectrum of multiple channels can be tested sequentially.

[0035] The second aspect of the embodiment provides a preparation method of a multi-channel tunable filter, which is used to prepare the multi-channel tunable filter 6 described above, and comprises the following steps: Step one: material preparation; including optical fiber material preparation and elastic mold preparation. Specifically: Optical fiber material preparation: provide two sections of multi-core optical fiber with seven cores and a section of microstructured optical fiber 63 with seven micro-hole channels, and the related parameters (fiber length, etc., but since the end of the microstructured optical fiber 63 needs to be cut off during the preparation process, the length at this time should be greater than 500 μm required finally) meet the above requirements; for the two sections of multi-core optical fiber and the section of microstructured optical fiber 63, the coating layers at both ends are stripped with an optical fiber stripping pliers, and then the end faces are cleaned with alcohol and dust-free paper, and high-pressure gas is blown to ensure smooth channels.

[0036] Elastic mold preparation: first, a master mold with seven micro-pillars is made on a silicon wafer through photolithography and deep etching process; the layout of the micro-pillar array is consistent with the layout of the micro-hole channels in the microstructured optical fiber 63 (i.e. one central pillar and six annularly arranged pillars); the diameter of each pillar is 9.2±0.1 μm (slightly larger than the diameter of the micro-hole channel to form a slightly larger micro-groove 9), the height is 5-10 μm, and the pitch is 42 μm; the silicon wafer is preferably circular, and the diameter is much larger than the outer diameter of the microstructured optical fiber 63, for example, it can be 200 μm.

[0037] Then, the polydimethylsiloxane (PDMS) prepolymer is mixed with the curing agent at a mass ratio of 10:1, and is placed in a vacuum drying box to remove bubbles; then, the degassed PDMS mixture is poured onto the master mold with the micro-pillar array, and after curing in an 80°C oven for 1 hour, it is peeled off; after curing, the elastic mold is peeled off from the master mold, and a microstructure array with seven micro-grooves 9 is obtained, which is consistent with the array layout of the micro-hole channels in the microstructured optical fiber 63, and the diameter of the elastic mold is much larger than the outer diameter of the microstructured optical fiber 63. Finally, the elastic mold is placed on a rubber pad and perforated using a special perforator; please refer toFigure 4 Specifically, at a corresponding position on the elastic mold surface opposite to the opening of each micro-groove 9, a hole is punched, which needs to penetrate through the solid part of the elastic mold to realize the communication between the hole and the micro-groove 9, that is, the gas outlet through-hole 10.

[0038] Step two: selective filling; seven filling cycles (the number of cycles corresponds to the number of micro-pore channels) are performed on the above microstructured optical fiber 63, each filling including selective plugging, liquid filling and sealing treatment. Specifically: Selective plugging: first, with the aid of an optical microscope, the microstructured optical fiber 63 is fixed on a three-axis manual micro-displacement stage, and the prepared elastic mold is fixed on another micro-adjustment holder; wherein the A end face (i.e. one of the end faces, hereinafter referred to as the A end for convenience of description) of the microstructured optical fiber 63 is placed in the field of view of the microscope and imaged clearly.

[0039] Then, the elastic mold is slowly moved close to the A end face of the above microstructured optical fiber 63, and the elastic mold is aligned, offset (for example, first align the seven micro-grooves 9 and the seven micro-pore channels, then slightly rotate the elastic mold with the target micro-pore channel as the positioning point, so that the target micro-pore channel and the corresponding micro-groove 9 remain in correspondence, and the other non-target micro-pore channels are misaligned with the corresponding micro-grooves 9) and lightly pressed under the microscope field of view, so that the elastic mold is lightly pressed on the microstructured optical fiber 63, and the target micro-pore channel in the selected microstructured optical fiber 63 is aligned with the corresponding micro-groove 9 in the elastic mold, while the remaining six non-target micro-pore channels in the microstructured optical fiber 63 are misaligned with the remaining micro-grooves 9, that is, the remaining six non-target micro-pore channels are covered and plugged by the solid part of the elastic mold between the micro-grooves 9. Thus, the target micro-pore channel is connected to the atmosphere, and the non-target micro-pore channels are temporarily physically isolated and plugged; wherein the flexible and self-adhesive properties of the PDMS material allow for damage-free and tight contact with the end face of the microstructured optical fiber 63.

[0040] Liquid filling: slowly immerse the B end (i.e. the other end face) of the microstructured optical fiber 63 vertically into a liquid tank containing a functional liquid, and control the immersion depth to be about 5 μm; under capillary action, the following will occur: For the target micro-pore channel, the B end is in contact with the liquid, and the A end is connected to the atmosphere through the micro-groove 9; therefore, under the action of capillary force, the liquid will be easily absorbed from the B end and advance along the channel, while the air in the channel will be discharged from the opening of the A end, until the liquid fills the entire channel.

[0041] For the non-target micro-pore channel, the B end is also in contact with the liquid, but the A end is plugged by the solid part of the elastic mold; therefore, the internal gas cannot be discharged and forms an air block, so capillary action cannot occur and the liquid cannot enter.

[0042] Wherein, the PDMS material itself has a certain van der Waals force, so when the elastic mold and the clean microstructure optical fiber 63 surface contact, will produce weak but effective adhesion; in the absence of external disturbance, this self-adhesion is sufficient to maintain the position relationship between the elastic mold and the microstructure optical fiber 63 in a short time of liquid filling process. On this basis, in order to further enhance the stability of the alignment in the liquid filling process, a slight positive pressure can be applied between the elastic mold and the microstructure optical fiber 63 end face to keep close and position fixed. Specifically, the microstructure optical fiber 63 and the elastic mold can be fixed on two opposite high-precision micro-displacement tables, after alignment, the two are contacted and about 2-5 μm overpressure is applied by Z-axis fine adjustment; thus, using the elasticity and self-adhesion of the PDMS material, and the continuous pressure, a stable and reliable temporary sealing can be achieved, which is sufficient to resist environmental micro-vibration and force disturbance in the capillary process.

[0043] Sealing process: after confirming the filling of the target micro-pore channel by microscope, the microstructure optical fiber 63 is quickly removed from the liquid tank, and the UV curing glue is quickly spotted and cured at the B end opening of the target micro-pore channel, completing the first sealing; then, the A end of the microstructure optical fiber 63 is separated from the elastic mold in the vertical direction for a distance, so as to spot and cure the UV glue at the A end opening of the target micro-pore channel, thereby completing the double-end sealing and firmly packaging the liquid in the target micro-pore channel.

[0044] After the above steps complete the filling and double-end sealing of one micro-pore channel, the elastic mold is re-approached to the A end of the microstructure optical fiber 63, and the next micro-pore channel becomes the target micro-pore channel through the alignment operation and the offset operation, and then different functional liquids are used for filling, and after filling, sealing is also performed. According to the above logic, the selective plugging, liquid filling and sealing process are repeatedly performed until the seven micro-pore channels are independently filled and sealed.

[0045] Step three: fusion forming. Specifically: After all the micro-pore channels are filled and sealed, a high-precision optical fiber cutting knife is used to cut off the part of the microstructure optical fiber 63 with elastic mold plugging residues and uneven UV glue at both ends, so as to obtain a microstructure optical fiber 63 with a length of about 500 μm, clean end faces at both ends and internal heterogeneous filling. Finally, the two ends of the microstructure optical fiber 63 are respectively high-precision rotationally aligned and fused with the input multi-core optical fiber 61 and the output multi-core optical fiber 62 to make a complete seven-channel tunable filter.

[0046] It should be particularly pointed out that the parts not described in detail or expanded in the above scheme are all prior art, do not belong to the improvement of the prior art by the present application, and do not belong to the protection scope of the technical scheme of the present application, therefore, this paper will not be described. Of course, the above content is only the preferred embodiment of the present application, and cannot be considered as limiting the scope of the embodiment of the present application. The present application is also not limited to the above examples, and the equivalent changes and improvements made by those skilled in the art within the essential scope of the present application should also belong to the patent coverage scope of the present application.

Claims

1. A multi-channel tunable filter, comprising an input interface, an output interface, and a filter unit arranged between the input interface and the output interface, characterized in that: the input interface comprises a section of input multi-core optical fiber (61), the output interface comprises a section of output multi-core optical fiber (62), and the filter unit comprises a section of micro-structured optical fiber (63); the micro-structured optical fiber (63) is fused between the input multi-core optical fiber (61) and the output multi-core optical fiber (62); inside the micro-structured optical fiber (63), at least two mutually isolated micro-hole channels are arranged along the axial direction thereof; the cores of the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are respectively collimated with the micro-hole channels of the micro-structured optical fiber (63); wherein, the at least two micro-hole channels are respectively filled with functional liquids with different optical properties; each micro-hole channel filled with a functional liquid, together with the cores collimated at both ends thereof, forms a Fabry-Perot filter cavity with independent filtering characteristics. 2.The multi-channel tunable filter according to claim 1, characterized in that: when the number of micro-hole channels of the micro-structured optical fiber (63) is odd, all the micro-hole channels are arranged in a layout mode in which one micro-hole channel is located at the center and the remaining micro-hole channels are arranged in a ring array in a center-symmetrical manner around the center; the cores of the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing in the input multi-core optical fiber (61) and the output multi-core optical fiber (62) matches the micro-hole channel spacing in the micro-structured optical fiber (63); when the number of micro-hole channels of the micro-structured optical fiber (63) is even, all the micro-hole channels are arranged in a layout mode in which a ring array is arranged in a center-symmetrical manner; the cores of the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are arranged in a layout mode corresponding to the micro-hole channels, and the core spacing in the input multi-core optical fiber (61) and the output multi-core optical fiber (62) matches the micro-hole channel spacing in the micro-structured optical fiber (63). 3.The multi-channel tunable filter according to claim 2, characterized in that: the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are both seven-core optical fibers, and the micro-structured optical fiber (63) is a seven-hole optical fiber with seven micro-hole channels; the seven micro-hole channels are respectively filled with seven kinds of functional liquids with different optical properties. 4.The multi-channel tunable filter according to claim 2, characterized in that: the core spacing and the micro-hole channel spacing are 38-45μm. 5.The multi-channel tunable filter according to claim 1, characterized in that: the functional liquid is an index matching liquid, and different index matching liquids with different refractive indexes are respectively filled in different micro-hole channels; or the functional liquid comprises a combination of an index matching liquid and one or more of liquid crystal, temperature-sensitive polymer, or fluorescent dye, and different liquids in the combination are respectively filled in different micro-hole channels. ​ ​ ​ ​ ​ ​ ​ ​ ​ 6. A method for producing a multichannel tunable filter, for producing a multichannel tunable filter according to any one of claims 1 to 5, characterized in that Includes the following steps: Step 1: Material preparation; Two multi-core optical fibers and one microstructure optical fiber are provided (63); Step 2: Selective Fill; At least two filling cycles are performed on the microstructured optical fiber (63), each filling cycle comprising: Selective blocking: At one end of the microstructured optical fiber (63), a target micropore channel is selected, and the openings of the other non-target micropore channels are temporarily blocked. Liquid filling: The other end of the microstructured optical fiber (63) is immersed in a functional liquid, and the functional liquid is filled into the target micropore channel by capillary action, and the gas in the target micropore channel is discharged from the opening located at one end of the microstructured optical fiber (63). Sealing process: Apply sealing material to both ends of the target microporous channel and cure it to seal the functional liquid inside. In at least two of the filling cycles, the optical properties of the functional liquids used are different; Step 3: Welding and forming; The microstructured optical fiber (63) after step two is fused between two multi-core optical fibers, and the cores of the two multi-core optical fibers are aligned with the micro-pore channels of the microstructured optical fiber (63).

7. The method for fabricating a multi-channel tunable filter according to claim 6, characterized in that: The specific method of selective blocking is as follows: An elastic mold with a microstructure array is used to press the elastic mold against one end of the microstructure optical fiber (63). The elastic mold is configured such that the microstructure array on it matches the array of micropore channels, so as to realize the communication between the target micropore channel and the atmosphere and the physical isolation and sealing of non-target micropore channels.

8. The method for fabricating a multi-channel tunable filter according to claim 7, characterized in that: The overall surface area of ​​the surface on the elastic mold that contacts one end of the microstructure optical fiber (63) is greater than the cross-sectional area of ​​one end of the microstructure optical fiber (63); the microstructure array on the elastic mold consists of a plurality of microgrooves (9) distributed corresponding to the micropore channel array, the openings of the plurality of microgrooves (9) are located on the surface on which the elastic mold contacts one end of the microstructure optical fiber (63), and each microgroove (9) is connected to an air outlet (10).

9. The method for fabricating a multi-channel tunable filter according to claim 8, characterized in that: During selective blocking, the elastic mold is placed at one end of the microstructure optical fiber (63). Through alignment and offset operations, a certain micro-groove (9) on the elastic mold is aligned with the target micro-hole channel, and the remaining micro-grooves (9) are misaligned with the remaining non-target micro-hole channels. That is, the remaining non-target micro-hole channels are all covered and blocked by the mold body part between the micro-grooves (9) on the elastic mold.

10. The method for fabricating a multi-channel tunable filter according to claim 6, characterized in that: The specific method of the sealing process is as follows: UV-curable adhesive is applied to the openings at both ends of the target microporous channel and cured by UV light irradiation.

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