Multi-channel tunable filter and method of making the same

Abstract

The application provides a kind of multi-channel tunable filter and its preparation method, it is related to photon device technical field.The multi-channel tunable filter includes a section of input multicore optical fiber, a section of output multicore optical fiber and a section of microstructure optical fiber;The microstructure optical fiber is fused between the input multicore optical fiber and the output multicore optical fiber;At least two mutually isolated micro-hole channels are provided along the axial direction in the microstructure optical fiber;The cores of the input multicore optical fiber and the output multicore optical fiber are respectively collimated with the micro-hole channels of the microstructure optical fiber;Wherein, the at least two micro-hole channels are respectively filled with functional liquids with different optical properties;Each micro-hole channel filled with functional liquid and the cores collimated at both ends thereof jointly constitute a Fabry-Perot filtering cavity with independent filtering characteristics.Based on this, the application solves the problem that there is no device capable of realizing multiple independent filtering channels in a single optical fiber in the prior art.

Description

Technical Field

[0001] This invention relates to the field of photonic device technology, specifically to a multi-channel tunable filter and its fabrication method. Background Technology

[0002] With the explosive growth in demand for fiber optic communication capacity, wavelength division multiplexing (WDM) technology is continuously evolving towards higher channel densities. This places higher demands on tunable optical filters, which are key passive components in fiber optic 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. Currently, most technical solutions for implementing tunable filtering functions have limitations in practical applications, specifically:

[0003] Option 1 involves filters based on fiber Bragg gratings (FBGs). While these filters offer good compatibility with fiber optic systems, they typically rely on stress or temperature for tuning, resulting in limited tuning range and response speed. Option 2 involves filters based on bulk optics or microelectromechanical systems (MEMS), such as the MEMS fiber wavelength-tunable filter and its fabrication method disclosed in patent CN115373081A. Although such filters can achieve a wider tuning range, they suffer from limitations in miniaturization, significant losses introduced when coupled to fiber optic systems, complex mechanical structures, and weak resistance to vibration and environmental changes. More importantly, these traditional solutions struggle to achieve parallel, independent operation of multiple channels on a single device. Constructing a multi-channel system requires combining multiple discrete filters, which significantly increases the system's size, cost, complexity, and potential failure points.

[0004] Regarding the above-mentioned problems, the applicant of this invention, through practice and research, believes that it is feasible to fill the axial micro-holes of special optical fibers (such as edge-hole optical fibers and photonic crystal fibers) with functional liquids (such as liquid crystals and refractive index matching liquids), and use the fiber end face and the liquid to form a Fabry-Perot (FP) filter cavity, and then achieve the tuning of the filter wavelength by changing the optical properties (such as refractive index) of the liquid. However, most of the relevant research in the prior art is limited to filling a single type of liquid in a single micro-hole of a single-core optical fiber, so it can only realize single-channel filtering and tuning operations, and cannot meet the needs of multi-channel parallel processing.

[0005] Therefore, the current technical challenge in this field for multi-channel tunable filters is the lack of a highly integrated device solution capable of realizing multiple independent filtering channels within a single optical fiber. Furthermore, integrating multiple independent FP cavities on a single optical fiber substrate requires filling multiple microchannels, each close to each other (spaced only tens of micrometers apart) and with diameters on the order of micrometers, with various liquids possessing different optical properties. However, conventional liquid filling methods, such as microinjection or pressure pumping, are extremely cumbersome and have low success rates when performing multi-liquid filling at such a small scale, thus failing to meet the requirements for repeatability and large-scale production. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-channel tunable filter and its fabrication method, in order to solve the following problems mentioned in the background art: In the prior art, there is a lack of devices capable of realizing multiple independent filtering channels within a single optical fiber. Furthermore, there is a lack of an efficient and reliable filter fabrication method capable of accurately filling heterogeneous liquids in microchannel arrays.

[0007] This invention is achieved using the following technical solution:

[0008] A multi-channel tunable filter includes an input interface, an output interface, and a filtering unit disposed between the input interface and the output interface. The input interface includes a section of input multi-core optical fiber, the output interface includes a section of output multi-core optical fiber, and the filtering unit includes 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 micropore channels are disposed axially through the microstructured optical fiber. The cores of the input multi-core optical fiber and the cores of the output multi-core optical fiber are respectively collimated to the micropore channels of the microstructured optical fiber. Each of the at least two micropore channels is filled with a functional liquid with different optical properties. Each micropore channel filled with the functional liquid, together with its collimated cores at both ends, constitutes a Fabry-Perot filter cavity with independent filtering characteristics.

[0009] This invention proposes a sandwich structure comprising multi-core optical fiber, heterogeneously filled microstructure optical fiber, and multi-core optical fiber, thereby ingeniously constructing multiple parallel and physically isolated optical resonant cavities within a single device. Since the optical properties of the functional liquid filling each cavity are different, their resonant wavelengths are also different, thus 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 extremely high spatial integration.

[0010] Furthermore, when the number of micro-channels in the microstructured optical fiber is odd, all micro-channels are arranged in a circular array with one micro-channel at the center and the remaining micro-channels arranged symmetrically around the central micro-channel. The cores of the input multi-core optical fiber and the output multi-core optical fiber are arranged in a layout corresponding to the micro-channels, and the spacing between the cores of the input and output multi-core optical fibers matches the spacing between the micro-channels in the microstructured optical fiber. When the number of micro-channels in the microstructured optical fiber is even, all micro-channels are arranged in a circular array with central symmetry. The cores of the input and output multi-core optical fibers are arranged in a layout corresponding to the micro-channels, and the spacing between the cores of the input and output multi-core optical fibers matches the spacing between the micro-channels in the microstructured optical fiber.

[0011] In the above scheme, a uniform structure can be formed by arranging the ring array, so as to achieve precise geometric matching between the micro-channel and the fiber core. This matching is a prerequisite for achieving low-loss, low-crosstalk fusion splicing and ensuring accurate optical path docking. Thus, it can be ensured that the light energy emitted from the input fiber core is efficiently coupled into the corresponding micro-channel and then coupled to the output fiber core again, which is the geometric basis for constructing multiple independent optical paths.

[0012] Furthermore, both the input multi-core optical fiber and the output multi-core optical fiber are seven-core optical fibers, and the microstructure optical fiber is a seven-hole optical fiber with seven micro-channels; the seven micro-channels are respectively filled with seven functional liquids with different optical properties.

[0013] In the above scheme, the seven-core / seven-hole structure is an optimized design that balances high integration and low channel crosstalk. It is in line with the current development trend of wavelength division multiplexing technology and has good application prospects and standardization potential.

[0014] Furthermore, the spacing between the fiber cores and the spacing between the micropore channels are 38~45μm.

[0015] In the above scheme, a spacing design of 38~45μm achieves a good balance between ensuring low inter-channel optical crosstalk and realizing high-density integration. It also facilitates efficient and low-loss coupling with fan-in / fan-out modules (used to connect tunable filters to external optical devices), providing convenience for system-level applications. In practical applications, if the spacing is too small, the optical field mode coupling between adjacent fiber cores / micro-channels will be significantly enhanced, leading to a sharp deterioration in inter-channel optical crosstalk. If the spacing is too large, the spatial integration density of the device will decrease, and it may cause interface mismatch with standard commercial fan-in / fan-out modules, introducing additional alignment losses and engineering complexity. Alternatively, the diameter of the micro-channels and fiber cores can be set to 8~10μm. This diameter design can accommodate sufficient functional liquid, ensuring adequate interaction length between light and liquid for effective tuning; at the same time, it is small enough to ensure high mechanical strength and structural stability during welding.

[0016] Furthermore, the functional liquid is a refractive index matching liquid, with refractive index matching liquids of different refractive indices filling different microporous channels; or, the functional liquid includes a combination of a refractive index matching liquid and one or more of liquid crystal, thermosensitive polymer or fluorescent dye, with different liquids in the combination filling different microporous channels.

[0017] In the above scheme, by filling with refractive index matching liquids with different refractive indices, different initial filtering wavelengths can be set for each micropore channel, thereby achieving multi-channel tunable filtering. Based on this, by adding different types of functional liquids, the filter can be further endowed with rich functionality to expand the application scenarios of the device. For example, filling with liquid crystal can achieve electrical tuning (rapidly changing the refractive index of the liquid crystal by applying voltage), filling with thermosensitive polymer can achieve temperature sensing (by monitoring wavelength drift) and temperature-controlled tuning (by actively controlling temperature), and filling with fluorescent dye can be used for fluorescence detection (the dye emits fluorescence when pump light (excitation light) of a specific wavelength is incident). For example, in practical applications, for a seven-hole optical fiber with seven micropore channels, three micropore channels can be filled with three different refractive index matching liquids to form three fixed-wavelength filtering channels; two micropore channels can be filled with two different liquid crystals and integrated with microelectrodes to form two independently electrically tunable filtering channels; one micropore channel can be filled with a thermosensitive polymer to form a temperature sensing and tuning channel; and one micropore channel can be filled with a fluorescent dye to form a biological / chemical fluorescence detection channel.

[0018] A method for fabricating a multi-channel tunable filter, used to fabricate the multi-channel tunable filter described above, includes the following steps:

[0019] Step 1: Material preparation;

[0020] It provides two segments of multi-core optical fiber and one segment of microstructured optical fiber;

[0021] Step 2: Selective Fill;

[0022] At least two filling cycles are performed on the microstructured optical fiber, each filling cycle comprising:

[0023] Selective blocking: At one end of the microstructured optical fiber, a target micropore channel is selected, and the openings of the other non-target micropore channels are temporarily blocked.

[0024] Liquid filling: The other end of the microstructured optical fiber 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.

[0025] Sealing process: Apply sealing material to both ends of the target microporous channel and cure it to seal the functional liquid inside.

[0026] In at least two of the filling cycles, the optical properties of the functional liquids used are different;

[0027] Step 3: Welding and forming;

[0028] The microstructured optical fiber processed in step two is fused between two multi-core optical fibers, ensuring that the cores of the two multi-core optical fibers are aligned with the micropore channels of the microstructured optical fiber.

[0029] This invention proposes a selective filling process. Through an iterative cycle of selective plugging, liquid filling, and sealing, capillary action can be used to gradually achieve self-filling of the functional liquid within each micropore channel. Compared to existing technologies, this method only requires a plugging operation during the filling process, eliminating the need for methods like microinjection or pressure pumping, which are difficult to control and have low success rates. In summary, this systematic approach decomposes a complex, multivariate process problem into a series of simple, controllable, and independent steps, thereby making the fabrication of multi-channel tunable filters more streamlined, reliable, and repeatable.

[0030] Furthermore, the specific method of selective blocking is as follows:

[0031] An elastic mold with a microstructure array is used, pressed against one end of a microstructured optical fiber. The elastic mold is configured such that its microstructure array matches the array of micropore channels, enabling communication between the target micropore channel and the atmosphere, and physically isolating and blocking non-target micropore channels. Further, the overall surface area of ​​the surface of the elastic mold in contact with one end of the microstructured optical fiber is greater than the cross-sectional area of ​​one end of the microstructured optical fiber. The microstructure array on the elastic mold consists of several microgrooves corresponding to the micropore channel array, with the openings of these microgrooves located on the surface in contact with the microstructured optical fiber. Each microgroove communicates with an air outlet. Further, during selective blocking, the elastic mold is placed at one end of the microstructured optical fiber. Through alignment and offset operations, a certain microgroove on the elastic mold is aligned with the target micropore channel, while the remaining microgrooves are misaligned with the remaining non-target micropore channels. That is, the remaining non-target micropore channels are all covered and blocked by the mold body portion between the microgrooves on the elastic mold.

[0032] In the above scheme, an elastic mold is used, which utilizes the elasticity of the material to form a tight and undamaged seal. Compared with the manual sealing method of one hole at a time, this effectively improves operational efficiency and reliability. The microgrooves and vent holes on the elastic mold provide conditions for capillary action. When using capillary action to achieve self-filling of the functional liquid, one end of the micropore channel needs to be in contact with the liquid, and the other end needs to be open to the atmosphere. When one end of a micropore channel opens through the aligned microgrooves and connects to the vent hole, the condition for opening to the atmosphere is achieved. Then, by keeping the other end of the micropore channel in contact with the corresponding functional liquid for a period of time, the functional liquid can be automatically drawn into the micropore channel by capillary action. In this preparation method, different micropore channels can be filled by aligning and offsetting the elastic mold, making it simple to use and with a high success rate.

[0033] Furthermore, the specific method of the sealing process is as follows:

[0034] UV-curable adhesive is applied to the openings at both ends of the target microporous channel and cured by UV light irradiation.

[0035] The beneficial effects achieved by this invention are:

[0036] This invention provides a multi-channel tunable filter. By setting up a sandwich structure including multi-core optical fiber, heterogeneous filled microstructure optical fiber, and multi-core optical fiber, multiple independent filtering channels can be integrated on a single optical fiber. This allows for independent access and tuning of different wavelength channels through external optical path switching, and the operation of each channel does not interfere with each other. Compared with the prior art which is limited to a single-channel structure, this invention can meet the needs of multi-channel parallel processing, improve space utilization, and conform to the development trend of miniaturization and integration of optical devices.

[0037] This invention provides a method for fabricating a multi-channel tunable filter. By setting an iterative cycle of selective blocking, liquid filling, and sealing treatment, the self-filling of functional liquid in each micropore channel can be gradually achieved by utilizing capillary action. Compared with existing methods such as microinjection or pressure pumping, which are difficult to control in terms of precision and have low success rates, this invention is simple to operate and has a high success rate, making the fabrication of multi-channel tunable filters more streamlined, reliable, and repeatable. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structural composition of the multi-channel tunable filter described in an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the microstructure optical fiber described in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the filtering principle of the multi-channel tunable filter described in an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the structure of the elastic mold described in an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram of the structural composition of the fiber optic amplifier system described in an embodiment of the present invention;

[0043] In the diagram: 1. Pump source; 2. Wavelength division multiplexer; 3. Gain fiber; 4. Isolator; 5. Fan-in / fan-out module; 6. Multi-channel tunable filter; 61. Input multi-core fiber; 62. Output multi-core fiber; 63. Microstructure fiber; 7. Coupler; 8. Spectrometer; 9. Microgroove; 10. Exhaust vent. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0045] Example 1

[0046] The first aspect of this embodiment provides a multi-channel tunable filter, suitable for dense wavelength division multiplexing systems, reconfigurable optical add-drop multiplexers, multi-wavelength sensing demodulation, and spectral analysis. Please refer to... Figures 1 to 3 The multi-channel tunable filter 6 includes an input interface, an output interface, and a filtering unit located between the input interface and the output interface, specifically:

[0047] The input interface includes an input multi-core optical fiber 61, the output interface includes an output multi-core optical fiber 62, and the filtering unit includes a microstructured optical fiber 63, which is fused between the input multi-core optical fiber 61 and the output multi-core optical fiber 62. Wherein:

[0048] Inside the microstructured optical fiber 63, at least two mutually isolated micropore channels are arranged along its axial direction; the cores of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 are collimated to the micropore channels of the microstructured optical fiber 63. Each of the at least two micropore channels is filled with a functional liquid with different optical properties; each micropore channel filled with the functional liquid, together with the collimated cores at both ends, constitutes a Fabry-Perot filter cavity with independent filtering characteristics.

[0049] When the number of micro-channels in the microstructured optical fiber 63 is odd, the micro-channels are arranged in a circular array with one micro-channel at the center and the remaining micro-channels arranged symmetrically around the central micro-channel. The cores of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 are arranged in a layout corresponding to the micro-channels, and the spacing between the cores of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 matches the spacing between the micro-channels in the microstructured optical fiber 63. When the number of micro-channels in the microstructured optical fiber 63 is even, all micro-channels are arranged in a circular array with central symmetry. The cores of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 are arranged in a layout corresponding to the micro-channels, and the spacing between the cores of the input multi-core optical fiber 61 and the output multi-core optical fiber 62 matches the spacing between the micro-channels in the microstructured optical fiber 63.

[0050] The core spacing and micropore channel spacing are 38~45μm, and the micropore channel diameter and core diameter are 8~10μm.

[0051] The functional liquid is a refractive index matching liquid, with refractive index matching liquids of different refractive indices filling different microporous channels; or, the functional liquid includes a combination of a refractive index matching liquid and one or more of liquid crystals, thermosensitive polymers or fluorescent dyes, with different liquids in the combination filling different microporous channels.

[0052] Specifically in this embodiment:

[0053] The microstructured optical fiber 63 is a seven-hole optical fiber with seven micro-channels, such as a seven-hole edge-hole optical fiber. The microstructured optical fiber 63 has seven axially penetrating micro-channels internally, with one micro-channel located at the center and the other six arranged in a circular array, symmetrically arranged around the central micro-channel. The microstructured optical fiber 63 has a length of approximately 500 μm and an outer diameter of 125 μm, with each micro-channel having a diameter of 9 μm and a spacing of approximately 42 μm. The seven micro-channels are filled with seven functional liquids with different optical properties. In this embodiment, these are specifically seven refractive index matching liquids with different refractive indices, such as carbon tetrachloride (refractive index n≈1.460), ethanol (refractive index n≈1.361), and five different concentrations of glycerol aqueous solutions (refractive index n is continuously adjustable between 1.333 and 1.474).

[0054] Both the input multi-core fiber 61 and the output multi-core fiber 62 are seven-core fibers. Each seven-core fiber contains seven independent cores arranged in a manner consistent with the micro-aperture channel array in the microstructure fiber 63, namely, one central core and six ring-shaped cores. The diameter and spacing of each core correspond to the micro-aperture channels, approximately 9 μm and 42 μm, respectively. Furthermore, the length and outer diameter of the input multi-core fiber 61 and the output multi-core fiber 62 are also set to match the micro-aperture channels, specifically 500 μm and 125 μm, respectively.

[0055] The operating principle of the aforementioned multi-channel tunable filter 6 is based on Fabry-Perot interferometry, specifically:

[0056] When a broadband beam of light is guided into a specific core of the input multi-core fiber 61, the optical signal propagates along that core to the first fusion splice of the microstructure fiber 63 (i.e., the fusion splice between the input multi-core fiber 61 and the microstructure fiber 63). At this interface, due to the refractive index difference between the fiber core (mostly quartz glass) and the functional liquid filling the micropore channel, part of the light is reflected, while the other part is transmitted into the corresponding micropore channel. The transmitted light propagates in the micropore channel filled with functional liquid, and when it reaches the second fusion splice (i.e., the fusion splice between the microstructure fiber 63 and the output multi-core fiber 62), it undergoes partial reflection and partial transmission again. The transmitted portion of the light enters the corresponding core of the output multi-core fiber 62 and is finally output.

[0057] A beam of light reflecting back and forth between two fused surfaces will undergo multi-beam interference. Only light waves that meet the resonance condition can be effectively transmitted. The peak value of the transmission spectrum (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 micro-channel), and m is an integer (interference order). Since the seven micro-channels in this embodiment are filled with seven different functional liquids with different refractive indices (n1, n2...n7), the seven independently formed Fabry-Perot filter cavities correspond to seven different initial center transmission wavelengths (λ1, λ2...λ7). In application, by selecting to couple the input light to a certain core of the input multi-core optical fiber 61, the user is equivalent to selecting and activating the Fabry-Perot filter cavity corresponding to that core, thereby achieving 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 achieving dynamic tuning of the filtering wavelength of the corresponding micro-channel.

[0058] The aforementioned multi-channel tunable filter 6 can be applied to fiber optic amplifier systems; please refer to [reference needed]. Figure 5 The system includes a pump source 1, a wavelength division multiplexer 2, a gain fiber 3 (using erbium-doped fiber), a multi-channel tunable filter 6, a fan-in / fan-out module 5, a coupler 7, an isolator 4, and a spectrometer 8. The fan-in / fan-out module 5, which can be an MCFIFOM model, guides the signal from a single fiber into a designated core of the input multi-core fiber 61. The signal then passes through the multi-channel tunable filter 6, and the selected wavelength of light exits from the corresponding core of the output multi-core fiber 62 before re-entering the fan-in / fan-out module 5 and converging into the single-mode fiber. By switching the input / output ports of the fan-in / fan-out module 5, the transmission spectra of multiple channels can be tested sequentially.

[0059] The second aspect of this embodiment provides a method for fabricating a multi-channel tunable filter, used to fabricate the multi-channel tunable filter 6 described above, comprising the following steps:

[0060] Step 1: Material Preparation; including optical fiber material preparation and flexible mold preparation. Specifically:

[0061] Optical fiber material preparation: Provide two sections of multi-core optical fibers with seven cores each and one section of microstructured optical fiber 63 with seven micro-channels. The relevant parameters (optical 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 the final required 500μm) meet the above requirements. For the two sections of multi-core optical fibers and the section of microstructured optical fiber 63, the coating layer at both ends is removed with optical fiber strippers. Then, the end faces are cleaned with alcohol and lint-free paper and blown with high-pressure gas to ensure that the channels are unobstructed.

[0062] Preparation of the elastic mold: First, a master mold with seven micro-protrusions is fabricated on a silicon wafer using photolithography and deep etching processes; the layout of this micro-protrusion array is consistent with the layout of the micro-hole channels in the microstructured optical fiber 63 (i.e., one central protrusion and six protrusions arranged in a ring); the diameter of each protrusion is 9.2±0.1μm (slightly larger than the diameter of the micro-hole channel to form a slightly larger micro-groove 9), the height is 5-10μm, and the spacing is 42μm; the silicon wafer is preferably circular, with a diameter much larger than the outer diameter of the microstructured optical fiber 63, for example, it can be 200μm.

[0063] Then, the polydimethylsiloxane (PDMS) prepolymer and curing agent were thoroughly mixed at a mass ratio of 10:1, and the mixture was placed in a vacuum drying oven to remove air bubbles. Subsequently, the degassed PDMS mixture was poured onto the master mold with the micro-protrusion array, cured in an oven at 80°C for 1 hour, and then peeled off. After curing, the elastic mold was peeled off from the master mold to obtain an elastic mold with a microstructure array consisting of seven microgrooves 9. The array layout of the seven microgrooves 9 is consistent with the array layout of the micropore 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 was placed on a rubber pad and perforated using a special punch. Please refer to [reference needed]. Figure 4 Specifically, holes are drilled at corresponding positions on the surface of the elastic mold opposite to the opening of each micro-groove 9. The holes need to penetrate the solid part of the elastic mold to achieve communication between the holes and the micro-groove 9. These holes are the air vent holes 10.

[0064] Step Two: Selective Filling; Seven filling cycles are performed on the microstructured optical fiber 63 (the number of cycles corresponds to the number of micropore channels), each filling cycle including selective plugging, liquid filling, and sealing treatment. Specifically:

[0065] Selective blocking: 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 fine-tuning holder; wherein, the A end face of the microstructured optical fiber 63 (i.e., one of the end faces, referred to as A end for ease of description) is placed under the microscope field of view to make it clearly imaged.

[0066] Then, the elastic mold is slowly brought close to the A end face of the microstructured optical fiber 63. Under a microscope, the elastic mold is aligned, offset (for example, the seven microgrooves 9 and the seven micropore channels are aligned first, and then the elastic mold is slightly rotated with the target micropore channel as the positioning point so that the correspondence between the target micropore channel and the corresponding microgrooves 9 remains unchanged, while the other non-target micropore channels are misaligned with the corresponding microgrooves 9) and lightly pressed, so that the elastic mold is lightly pressed on the microstructured optical fiber 63, and the target micropore channel in the selected microstructured optical fiber 63 is aligned with the corresponding microgroove 9 in the elastic mold, while the other six non-target micropore channels in the microstructured optical fiber 63 are misaligned with the other microgrooves 9, that is, the other six non-target micropore channels are all covered and blocked by the mold body part between the microgrooves 9 on the elastic mold. This achieves the connection between the target micropore channel and the atmosphere, as well as the temporary physical isolation and sealing of non-target micropore channels; among them, by utilizing the flexibility and self-adhesion of PDMS material, a non-damaging and tight contact can be achieved with the end face of the microstructure optical fiber 63.

[0067] Liquid filling: The B end (i.e., the other end face) of the microstructured optical fiber 63 is slowly and vertically immersed into a liquid tank containing a functional liquid, with the immersion depth controlled to be approximately 5 μm; under capillary action, the following will occur:

[0068] For the target microporous channel, its B end is in contact with the liquid, and its A end is connected to the atmosphere through the microgroove 9; therefore, under the action of capillary force, the liquid will be smoothly drawn in from the B end and move along the channel, while the air in the channel will be discharged from the opening at the A end until the liquid fills the entire channel.

[0069] For non-target microporous channels, end B is also in contact with the liquid, but end A is blocked by the solid part of the elastic mold; therefore, the internal gas cannot be discharged and forms an air resistance, so capillary action cannot take place, and the liquid cannot enter.

[0070] PDMS material itself possesses van der Waals forces, resulting in a weak but effective adhesive force when the elastic mold contacts the clean surface of the microstructured optical fiber 63. Under normal conditions, this self-adhesion is sufficient to maintain the positional relationship between the elastic mold and the microstructured optical fiber 63 during short-term liquid filling. To further enhance alignment stability during liquid filling, a continuous, slight positive pressure can be applied between the elastic mold and the end face of the microstructured optical fiber 63 to maintain a tight fit and fixed position. Specifically, the microstructured optical fiber 63 and the elastic mold can be fixed on two opposing high-precision micro-displacement stages. After alignment, Z-axis fine-tuning brings them into contact, and an overpressure of approximately 2-5 μm is applied. Thus, utilizing the elasticity and self-adhesion of PDMS material, along with this continuous pressure, a stable and reliable temporary seal can be achieved, sufficient to resist environmental micro-vibrations and force disturbances during capillary action.

[0071] Sealing process: After confirming the target microporous channel is filled using a microscope, the microstructured optical fiber 63 is quickly removed from the liquid tank, and UV-curable adhesive is rapidly applied to the B-end opening of the target microporous channel and then UV-cured to complete the first sealing. Subsequently, the A-end of the microstructured optical fiber 63 is separated from the elastic mold by a certain distance in the vertical direction so that UV adhesive can also be applied to the A-end opening of the target microporous channel and cured, thereby completing the double-end sealing and firmly encapsulating the liquid inside the target microporous channel.

[0072] After completing the filling and double-end sealing of one micropore channel through the above steps, the elastic mold is brought back close to the A end of the microstructured optical fiber 63. Alignment and offset operations are then performed to make the next micropore channel the target micropore channel. Different functional liquids are then used for filling, followed by sealing. This selective plugging, liquid filling, and sealing process is repeated according to the above logic until all seven micropore channels are independently filled and sealed.

[0073] Step 3: Welding and forming. Specifically:

[0074] After all micropore channels are filled and sealed, a high-precision fiber cleaver is used to remove the portions of the microstructured fiber 63 with residual elastic mold sealing and uneven UV adhesive at both ends, resulting in a microstructured fiber 63 with a length of approximately 500 μm, clean end faces, and heterogeneous internal filling. Finally, the two ends of this microstructured fiber 63 are precisely rotated, aligned, and fused with the input multi-core fiber 61 and the output multi-core fiber 62, respectively, to fabricate a complete seven-channel tunable filter.

[0075] It should be noted that the parts not described in detail or in elaboration in the above solutions are all prior art and do not constitute improvements made by this invention to existing technology, nor are they within the protection scope of this invention's technical solutions. Therefore, they will not be elaborated upon further in this document. Of course, the above content is merely a preferred embodiment of this invention and should not be considered as limiting the scope of the embodiments of this invention. This invention is also not limited to the above examples; equivalent changes and improvements made by those skilled in the art within the substantial scope of this invention should all fall within the patent coverage of this invention.

Claims

1. A multi-channel tunable filter, comprising an input interface, an output interface, and a filtering unit disposed between the input interface and the output interface, characterized in that: The input interface includes an input multi-core optical fiber (61), the output interface includes an output multi-core optical fiber (62), and the filtering unit includes a microstructure optical fiber (63); the microstructure optical fiber (63) is fused between the input multi-core optical fiber (61) and the output multi-core optical fiber (62). Inside the microstructure optical fiber (63), at least two mutually isolated micro-pore channels are provided along its axial direction; the core of the input multi-core optical fiber (61) and the core of the output multi-core optical fiber (62) are respectively aligned with the micro-pore channels of the microstructure optical fiber (63); Among them, at least two of the micropore channels are filled with functional liquids with different optical properties; each micropore channel filled with functional liquids together with the collimated fiber cores at both ends constitutes a Fabry-Perot filter cavity with independent filtering characteristics. When the number of micro-channels in the microstructured optical fiber (63) is odd, all micro-channels are arranged in a circular array with one micro-channel at the center and the remaining micro-channels arranged symmetrically around the center micro-channel. The cores of the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are arranged in a layout corresponding to the micro-channels, and the spacing between the cores in the input multi-core optical fiber (61) and the output multi-core optical fiber (62) matches the spacing between the micro-channels in the microstructured optical fiber (63). The input multi-core fiber (61) and the output multi-core fiber (62) are both seven-core fibers, and the microstructure fiber (63) is a seven-hole fiber with seven micro-channels. The fiber core spacing and the micropore channel spacing are 38~45μm; The functional liquid is a refractive index matching liquid, and refractive index matching liquids with different refractive indices are filled in different microporous channels respectively; Alternatively, the functional liquid may include a combination of one or more of a refractive index matching liquid and a liquid crystal, a thermosensitive polymer, or a fluorescent dye, with different liquids in the combination filling different microporous channels.

2. The multi-channel tunable filter according to claim 1, characterized in that: When the number of micro-channels in the microstructured optical fiber (63) is even, all micro-channels are arranged in a centrally symmetrical ring array. The cores of the input multi-core optical fiber (61) and the output multi-core optical fiber (62) are arranged in a layout corresponding to the micro-channels, and the spacing between the cores in the input multi-core optical fiber (61) and the output multi-core optical fiber (62) matches the spacing between the micro-channels in the microstructured optical fiber (63).

3. The multi-channel tunable filter according to claim 2, characterized in that: The seven micropore channels are each filled with a different functional liquid with different optical properties.

4. A method for fabricating a multi-channel tunable filter, used to fabricate the multi-channel tunable filter according to any one of claims 1-3, 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).

5. The method for fabricating a multi-channel tunable filter according to claim 4, 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.

6. The method for fabricating a multi-channel tunable filter according to claim 5, 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).

7. The method for fabricating a multi-channel tunable filter according to claim 6, 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.

8. The method for fabricating a multi-channel tunable filter according to claim 4, 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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