Controllable processing method for photoetching single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask plate

Abstract

The invention provides a controllable processing method for a photoetching single crystal optical fiber multi-ring cladding based on femtosecond laser and a multi-ring mask plate. The technical bottlenecks that in the prior art, the processing efficiency is low, the processing length is limited, and the structural precision is insufficient are effectively solved. The core of the method is that high-energy ultrashort pulse laser generated by a femtosecond laser is combined with a spatial light modulation technology of a programmable multi-ring mask plate to generate multi-layer femtosecond laser spots in specific annular distribution. Micron-scale focusing of multi-ring femtosecond laser beams can be achieved through a precisely-designed optical system, and precise spatial selective refractive index modulation is achieved on the cross section of the single-crystal optical fiber. Compared with a single-crystal optical fiber with a single-multi-ring annular cladding structure, the multi-ring annular cladding structure can further enhance the suppression capability of the multi-ring annular cladding structure on a high-order mode, realizes flexible regulation and control of a light wave transmission mode field, effectively reduces the influence of a multi-mode interference problem in the single-crystal optical fiber on the signal quality, and improves the signal quality. The stability of signal transmission and the quality of sensing signals are improved, and the application requirements of different scenes are met.

Description

Technical Field

[0001] The present invention relates to the processing of multi-ring annular claddings inside single-crystal optical fibers, and belongs to the technical field of optical fiber sensors. Background Art

[0002] Single-crystal optical fiber is a "quasi-one-dimensional" functional crystal material, possessing both the excellent physical and chemical properties of bulk crystals and the unique advantages of large aspect ratio and large specific surface area of optical fibers. It is the preferred material for optical transmission and sensing in extreme environments. However, different from the preparation process of quartz optical fibers, single-crystal optical fibers are usually prepared by the guiding mode method, the micro-pulling method or the laser-heated pedestal growth method in a way of melting or pulling bulk crystals. Therefore, single-crystal optical fibers belong to step-index optical fibers with air as the annular cladding. This atomic-level growth method makes it difficult to precisely control the surface quality of single-crystal optical fibers, resulting in large scattering losses during the transmission of optical signals. When single-crystal optical fibers are applied in extreme environments, surface damage caused by factors such as high temperature and radiation will exacerbate this scattering loss and reduce the transmission quality of optical signals. In addition, single-crystal optical fibers have a relatively large diameter, and there is a large refractive index difference between the core and air, resulting in a relatively large numerical aperture of single-crystal optical fibers and supporting a large number of propagation modes in the optical fiber. Although multi-mode propagation endows single-crystal optical fibers with high sensitivity in physical quantity sensing, inter-modal interference effects will occur between numerous modes, greatly reducing the fringe contrast of sensing signals. The combined effect of the above factors limits the sensing performance of single-crystal optical fibers in practical applications.

[0003] In order to reduce the influence of surface defects and damage on the transmission quality of optical signals, reduce the interference of inter-modal interference on the quality of sensing signals, and improve the sensing performance of single-crystal optical fibers in extreme environments, the use of annular cladding treatment is an effective and reliable technical means. In the field of quartz optical fibers, by designing a preform and through fiber drawing treatment, it is convenient to prepare a silica annular cladding with a refractive index different from that of the core.

[0004] However, due to the completely different growth and preparation of single-crystal optical fibers from quartz optical fibers, relying on atomic-level crystal growth technology, it is difficult to achieve annular cladding.

[0005] In the prior art, methods such as epitaxy method, sol method, and liquid encapsulation are used to add low-refractive-index heterogeneous materials outside single-crystal optical fibers to achieve total reflection conditions. The disadvantage of this technology is that the heterogeneous material annular cladding will peel off and fall off under high-temperature environments. There is also an ion implantation modification scheme to modify the material inside the surface of single-crystal optical fibers to achieve annular cladding treatment. The disadvantage of this technology is that it is difficult to control the uniformity of the annular cladding. Summary of the Invention

[0006] The object of the present invention is to provide a controllable processing method for lithographic single-crystal optical fiber multi-ring claddings based on femtosecond laser and multi-ring mask plates, including the following steps:

[0007] 1) Assemble the single-crystal optical fiber on the fiber feeding system of the femtosecond laser lithography system.

[0008] The femtosecond laser lithography system includes a femtosecond laser, a concave mirror, a spherical mirror, a multi-ring mask plate, a fiber feeding system, a plane mirror, and a parabolic mirror.

[0009] The concave mirror has a central hole I;

[0010] After the beam output by the femtosecond laser passes through the central hole I, it is reflected by the spherical mirror and then reflected by the reflecting surface I of the concave mirror to form an annular femtosecond laser beam, which reaches the multi-ring mask plate forward.

[0011] Due to the occlusion of the mask, after the above-mentioned annular beam passes through the multi-ring mask plate, several layers of annular multi-ring femtosecond laser beams are formed.

[0012] The multi-ring mask plate is located on one side of the spherical mirror. The main body of the multi-ring mask plate is a transparent plate, and its plate surface has an opaque mask. The areas not covered by the mask form several light-transmitting annular windows. The number of the annular windows is the same as the number of layers of the multi-ring annular cladding to be formed in the single-crystal optical fiber to be processed.

[0013] The beam forms a multi-ring femtosecond laser beam after passing through the multi-ring mask plate and reaches the plane mirror. The plane mirror is inclined, and its center has a central hole II for the single-crystal optical fiber to pass through. The multi-ring femtosecond laser beam is reflected by the plane mirror to the parabolic mirror above. The center of the parabolic mirror has a central hole III for the single-crystal optical fiber to pass through.

[0014] The fiber feeding system is used to stretch the single-crystal optical fiber, and includes an upper clamp above the parabolic mirror and a lower clamp below the plane mirror. The single-crystal optical fiber is clamped between the upper clamp and the lower clamp and passes through the central hole II and the central hole III.

[0015] The multi-ring femtosecond laser beam reflected by the parabolic mirror is focused inside the single-crystal optical fiber between the plane mirror and the parabolic mirror.

[0016] 2) Start the fiber feeding system and stretch the single-crystal optical fiber towards one end.

[0017] During the stretching process, the femtosecond laser outputs a femtosecond laser beam.

[0018] The femtosecond laser beam is converted into a multi-ring femtosecond laser beam by the femtosecond laser lithography system and focused inside the single-crystal optical fiber between the plane mirror and the parabolic mirror, thereby performing lithography processing on the inside of the single-crystal optical fiber.

[0019] The processed single-crystal optical fiber includes a core that is not lithographed and is located in the innermost layer, and n layers of multi-ring annular claddings and n layers of optical fiber regions that are not lithographed, which are alternately distributed;

[0020] Among them, the core is in contact with the multi-ring annular cladding and not in contact with the optical fiber regions that are not lithographed; the multi-ring annular cladding is obtained by lithography;

[0021] The outermost layer of the processed single-crystal optical fiber is an optical fiber region that is not lithographed.

[0022] Furthermore, the multi-ring mask plate has an opaque mask on its surface. On the surface of the multi-ring mask plate, regions not covered by the opaque mask form a plurality of light-transmitting annular windows.

[0023] Furthermore, the number of layers of the multi-ring annular cladding is greater than or equal to 2.

[0024] Furthermore, the process of converting the femtosecond laser beam into a multi-ring femtosecond laser beam by the ring-by-ring femtosecond laser lithography system is as follows:

[0025] After the beam output by the femtosecond laser passes through the central hole I, it is reflected by the spherical mirror, and then reflected by the reflecting surface I of the concave mirror to form an annular femtosecond laser beam, which reaches the multi-ring mask plate forward;

[0026] The multi-ring mask plate divides the annular beam into a multi-ring femtosecond laser beam with multiple layers of rings and transmits it to the plane mirror.

[0027] The multi-ring femtosecond laser beam is reflected by the plane mirror to the parabolic mirror above.

[0028] The parabolic mirror reflects the multi-ring femtosecond laser beam so that the multi-ring femtosecond laser beam is focused inside the single-crystal optical fiber between the plane mirror and the parabolic mirror.

[0029] Furthermore, when performing lithography on the inside of the single-crystal optical fiber, the diameter and focusing depth of the annular femtosecond laser beam are adjustable.

[0030] The diameter and focusing depth of the annular femtosecond laser beam are achieved by adjusting the divergence angle of the femtosecond laser beam output by the femtosecond laser.

[0031] Furthermore, the ring-by-ring femtosecond laser lithography system further includes a shaping and beam expanding system.

[0032] The shaping and beam expanding system is arranged in front of the femtosecond laser and is used to regulate the divergence angle of the femtosecond laser beam output by the femtosecond laser, thereby realizing the regulation of the diameter and focusing depth of the annular femtosecond laser beam.

[0033] Furthermore, the ring-by-ring femtosecond laser lithography system further includes a flat mirror frame. The spherical mirror is installed at the center of the mirror frame.

[0034] The spectacle frame has an annular optical window. After the annular light beam reflected by the concave mirror passes through the optical window, it is transmitted to the plane mirror.

[0035] Furthermore, the spectacle frame is mounted on the support base.

[0036] The multi-ring mask plate is mounted on the support base through a bracket.

[0037] It should be noted that the present invention introduces a multi-ring mask plate to generate a femtosecond laser spot with a specific annular distribution. After being focused by a precisely designed optical path, it accurately acts on the cross-section of the single-crystal optical fiber, and the multi-ring modulation of the refractive index inside the single-crystal optical fiber can be completed through single exposure, successfully constructing a multi-ring annular cladding structure. Compared with the single-crystal optical fiber with a single / multi-ring annular cladding structure, the multi-ring annular cladding structure can further enhance the suppression ability of the multi-ring annular cladding structure for high-order modes, effectively reduce the influence of multi-mode interference problems in the single-crystal optical fiber on the signal quality, and improve the stability of signal transmission and the quality of sensing signals.

[0038] The advantages of the present invention include:

[0039] 1. The multi-ring annular cladding inscribed in the single-crystal optical fiber is a periodic structure in the radial direction. On the basis of forming the multi-ring annular cladding, the oscillation of high-order modes can be further suppressed, and the influence of inter-modal interference on the transmission signal quality can be reduced;

[0040] 2. By introducing a multi-ring mask plate into the optical path, high-efficiency photolithography of the multi-ring annular cladding structure of the single-crystal optical fiber is realized;

[0041] 3. Based on the spatial light modulation technology of the programmable multi-ring mask plate, multi-ring femtosecond laser spots with an annular distribution can be flexibly generated, realizing spatial selective refractive index regulation of the micro-structured cladding inside the single-crystal optical fiber, and supporting high-precision photolithography of diversified micro-structured claddings. Description of the Drawings

[0042] Figure 1 It is a structural diagram of a multi-ring annular cladding system for femtosecond laser lithography of a single-crystal optical fiber ring by ring.

[0043] Figure 2 It is a schematic diagram of a multi-ring annular cladding structure formed by focusing and lithography of a four-ring femtosecond laser beam in a single-crystal optical fiber.

[0044] Figure 3 It is a multi-ring mask plate for generating a multi-ring femtosecond laser beam in the system.

[0045] Figure 4 It is a programmable multi-ring mask plate design and the corresponding multi-ring annular cladding structure of the single-crystal optical fiber.

[0046] Figure 5 It is a three-dimensional structure diagram of a four-ring multi-ring annular cladding single-crystal optical fiber.

[0047] In the figure: femtosecond laser (1), integer beam expander system (2), concave mirror (3), central hole I (301), reflecting surface I (302), spherical mirror (4), optical window (5), mirror frame (6), multi-ring mask plate (7), annular window (701), opaque mask (702), upper fixture (8), lower fixture (9), optical fiber (10), un-lithographed core of single-crystal optical fiber (1003), n layers of alternately distributed multi-ring annular cladding (1002), n layers of un-lithographed optical fiber regions (1001); plane mirror (11), central hole II (1101), reflecting surface II (1102), parabolic mirror (12), central hole III (1201), reflecting surface III (1202), support base (13). Specific implementation mode

[0048] The present invention will be further described below in conjunction with embodiments, but it should not be understood that the above-mentioned subject matter scope of the present invention is limited to the following embodiments. Without departing from the above technical idea of the present invention, various substitutions and changes made according to common general knowledge and conventional means in the art should be included within the protection scope of the present invention.

[0049] Embodiment 1:

[0050] See Figures 1 to 5 , a controllable processing method for lithographing multi-ring cladding of single-crystal optical fiber based on femtosecond laser and multi-ring mask plate, comprising the following steps:

[0051] 1) Assemble the single-crystal optical fiber 10 on the optical fiber clamping and feeding system of the femtosecond laser lithography system.

[0052] The femtosecond laser lithography system includes a femtosecond laser 1, a concave mirror 3, a spherical mirror 4, a multi-ring mask plate 7, an optical fiber clamping and feeding system, a plane mirror 11, and a parabolic mirror 12.

[0053] The concave mirror 3 has a central hole I 301;

[0054] After the beam output by the femtosecond laser 1 passes through the central hole I 301, it is reflected by the spherical mirror 4, and then reflected by the reflecting surface I 302 of the concave mirror 3 to form an annular femtosecond laser beam, which reaches the multi-ring mask plate 7 forward;

[0055] Due to the shielding of the mask, after the above-mentioned annular beam passes through the multi-ring mask plate 7, several layers of annular multi-ring femtosecond laser beams are formed.

[0056] The multi-ring mask plate 7 is located on one side of the spherical mirror 4, that is, on the side of the spherical mirror 4 away from the concave mirror 3. The main body of the multi-ring mask plate 7 is made of a transparent plate, and its plate surface has an opaque mask 702. The areas not covered by the mask 702 form a number of light-transmitting ring-shaped windows 701. The number of the ring-shaped windows 701 is the same as the number of layers of the multi-ring cladding to be formed in the single-crystal optical fiber to be processed.

[0057] The light beam forms a multi-ring femtosecond laser beam after passing through the multi-ring mask plate 7 and reaches the plane mirror 11. The plane mirror 11 is inclined, and its center has a central hole II1101 for the single-crystal optical fiber 10 to pass through. The multi-ring femtosecond laser beam is reflected by the plane mirror 11 to the parabolic mirror 12 above. The center of the parabolic mirror 12 has a central hole III1201 for the single-crystal optical fiber 10 to pass through.

[0058] The optical fiber feeding and clamping system is used to stretch the single-crystal optical fiber 10, and includes an upper clamp 8 above the parabolic mirror 12 and a lower clamp 9 below the plane mirror 11. The single-crystal optical fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the central hole II1101 and the central hole III1201.

[0059] The multi-ring femtosecond laser beam reflected by the parabolic mirror 12 is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12.

[0060] 2) Start the optical fiber feeding and clamping system to stretch the single-crystal optical fiber 10 towards one end.

[0061] During the stretching process, the femtosecond laser 1 outputs a femtosecond laser beam.

[0062] The femtosecond laser beam is converted into a multi-ring femtosecond laser beam by the femtosecond laser lithography system and is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12, so as to perform lithography processing on the inside of the single-crystal optical fiber 10.

[0063] The processed single-crystal optical fiber 10 includes an un-lithographed core 1003 located in the innermost layer, and n layers of multi-ring claddings 1002 and n layers of un-lithographed optical fiber regions 1001 that are alternately distributed;

[0064] Among them, the core 1003 is in contact with the multi-ring cladding 1002 and not in contact with the un-lithographed optical fiber region 1001; the multi-ring cladding 1002 is obtained by lithography;

[0065] The outermost layer of the processed single-crystal optical fiber 10 is an un-lithographed optical fiber region 1001.

[0066] The multi-ring mask plate 7 has an opaque mask 702 on its surface. On the surface of the multi-ring mask plate 7, the areas not covered by the opaque mask 702 form a plurality of light-transmitting annular windows 701.

[0067] The number of layers of the multi-ring annular cladding 1002 is greater than or equal to 2.

[0068] The process of converting the femtosecond laser beam into a multi-ring femtosecond laser beam by the femtosecond laser lithography system is as follows:

[0069] After the beam output by the femtosecond laser 1 passes through the central hole I301, it is reflected by the spherical mirror 4, and then reflected by the reflecting surface I302 of the concave mirror 3 to form an annular femtosecond laser beam, which reaches the multi-ring mask plate 7 forward;

[0070] The multi-ring mask plate 7 separates the annular beam into a multi-ring femtosecond laser beam with multiple layers of rings and transmits it to the plane mirror 11.

[0071] The multi-ring femtosecond laser beam is reflected by the plane mirror 11 to the parabolic mirror 12 above.

[0072] The parabolic mirror 12 reflects the multi-ring femtosecond laser beam so that the multi-ring femtosecond laser beam is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12.

[0073] When performing lithography processing inside the single-crystal optical fiber 10, the diameter and focusing depth of the annular femtosecond laser beam are adjustable.

[0074] The diameter and focusing depth of the annular femtosecond laser beam are achieved by adjusting the divergence angle of the femtosecond laser beam output by the femtosecond laser 1.

[0075] The ring-by-ring femtosecond laser lithography system further includes a shaping and beam expanding system 2.

[0076] The shaping and beam expanding system 2 is arranged in front of the femtosecond laser 1 and is used to control the divergence angle of the femtosecond laser beam output by the femtosecond laser 1, thereby realizing the control of the diameter and focusing depth of the annular femtosecond laser beam.

[0077] The ring-by-ring femtosecond laser lithography system further includes a flat mirror frame 6. The spherical mirror 4 is installed at the center of the mirror frame 6.

[0078] The mirror frame 6 has an annular optical window 5. The annular beam reflected by the concave mirror 3 passes through the optical window 5 and then is transmitted to the plane mirror 11.

[0079] The mirror frame 6 is installed on the support base 13.

[0080] The multi-ring mask plate 7 is installed on the support base 13 through a bracket.

[0081] Embodiment 2:

[0082] A controllable processing method for a multi-ring cladding of a single-crystal optical fiber by femtosecond laser and multi-ring mask plate, comprising the following steps:

[0083] 1) Assemble the single-crystal optical fiber 10 on the fiber feeding system of the femtosecond laser lithography system.

[0084] The femtosecond laser lithography system includes a femtosecond laser 1, a concave mirror 3, a spherical mirror 4, a multi-ring mask plate 7, a fiber feeding system, a plane mirror 11, and a parabolic mirror 12.

[0085] The concave mirror 3 has a central hole I301;

[0086] After the beam output by the femtosecond laser 1 passes through the central hole I301, it is reflected by the spherical mirror 4, and then reflected by the reflecting surface I302 of the concave mirror 3 to form an annular femtosecond laser beam, which reaches the multi-ring mask plate 7 forward.

[0087] Due to the occlusion of the mask, the above-mentioned annular beam forms several layers of annular multi-ring femtosecond laser beams after passing through the multi-ring mask plate 7.

[0088] The multi-ring mask plate 7 is located on one side of the mirror frame 6 where the spherical mirror 4 is installed. The main body of the multi-ring mask plate 7 is a transparent plate, and its plate surface has an opaque mask 702. The areas not covered by the mask 702 form several light-transmitting annular windows 701. The number of the annular windows 701 is the same as the number of layers of the multi-ring annular cladding to be formed in the single-crystal optical fiber to be processed.

[0089] The beam forms a multi-ring femtosecond laser beam after passing through the multi-ring mask plate 7 and reaches the plane mirror 11. The plane mirror 11 is inclined, and its center has a central hole II1101 for the single-crystal optical fiber 10 to pass through. The multi-ring femtosecond laser beam is reflected by the plane mirror 11 to the parabolic mirror 12 above. The center of the parabolic mirror 12 has a central hole III1201 for the single-crystal optical fiber 10 to pass through.

[0090] The fiber feeding system is used to stretch the single-crystal optical fiber 10, and includes an upper clamp 8 above the parabolic mirror 12 and a lower clamp 9 below the plane mirror 11. The single-crystal optical fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the central hole II1101 and the central hole III1201.

[0091] The multi-ring femtosecond laser beam reflected by the parabolic mirror 12 is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12.

[0092] 2) Start the fiber feeding system and stretch the single-crystal optical fiber 10 towards one end.

[0093] During the stretching process, the femtosecond laser 1 outputs a femtosecond laser beam outward.

[0094] The femtosecond laser beam is converted into a multi-ring femtosecond laser beam by the femtosecond laser lithography system and focused inside the single-crystal optical fiber 10 located between the plane mirror 11 and the parabolic mirror 12, thereby performing lithography processing inside the single-crystal optical fiber 10.

[0095] The processed single-crystal optical fiber 10 includes an un-lithographed core 1003 located in the innermost layer, and n layers of multi-ring claddings 1002 and n layers of un-lithographed optical fiber regions 1001 that are alternately distributed;

[0096] Among them, the core 1003 is in contact with the multi-ring cladding 1002 and not in contact with the un-lithographed optical fiber region 1001; the multi-ring cladding 1002 is obtained by lithography;

[0097] The outermost layer of the processed single-crystal optical fiber 10 is the un-lithographed optical fiber region 1001.

[0098] Example 3:

[0099] A controllable processing method for lithographing a multi-ring cladding of a single-crystal optical fiber based on femtosecond laser and a multi-ring mask plate, the technical content is the same as that of Example 2. Further, the multi-ring mask plate 7 has an opaque mask 702 on its plate surface. On the plate surface of the multi-ring mask plate 7, regions not covered by the opaque mask 702 form a plurality of light-transmitting annular windows 701.

[0100] The multi-ring mask plate has a decisive influence on the periodic distribution of the multi-ring cladding structure after lithography. When using a multi-ring mask plate with an equal-period distribution, due to the optical path difference between different annular light spots, the periodic distribution of the finally formed multi-ring cladding structure will be uneven (as shown in Figure 3 (a)). However, the multi-ring mask plate has advantages such as flexible design, simple processing, and low cost. In order to improve the optical performance of the multi-ring cladding structure, by designing a multi-ring mask plate with a radially chirped distribution (as shown in Figure 3 (b)), introducing non-linear periodic modulation, the focusing deviation of different annular light spots in the lithography process can be compensated, so as to obtain a periodically multi-ring cladding structure with a uniform distribution after lithography.

[0101] Example 4:

[0102] A controllable processing method for lithographing a multi-ring cladding of a single-crystal optical fiber based on femtosecond laser and a multi-ring mask plate, the technical content is the same as any one of Examples 2-3. Further, the number of layers of the multi-ring cladding 1002 is greater than or equal to 2.

[0103] Example 5:

[0104] A controllable processing method for the multi-ring cladding of a single-crystal optical fiber by lithography based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Embodiments 2-4. Further, the process of converting the femtosecond laser beam into a multi-ring femtosecond laser beam by the femtosecond laser lithography system is as follows:

[0105] After the beam output by the femtosecond laser 1 passes through the central hole I301, it is reflected by the spherical mirror 4, and then reflected by the reflecting surface I302 of the concave mirror 3 to form an annular femtosecond laser beam, which reaches the multi-ring mask plate 7 forward.

[0106] The multi-ring mask plate 7 divides the annular beam into a multi-ring femtosecond laser beam with multiple layers of rings and transmits it to the plane mirror 11.

[0107] The multi-ring femtosecond laser beam is reflected by the plane mirror 11 to the parabolic mirror 12 above.

[0108] The parabolic mirror 12 reflects the multi-ring femtosecond laser beam so that the multi-ring femtosecond laser beam is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12.

[0109] Embodiment 6:

[0110] A controllable processing method for the multi-ring cladding of a single-crystal optical fiber by lithography based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Embodiments 2-5. Further, when performing lithography processing inside the single-crystal optical fiber 10, the diameter and focusing depth of the annular femtosecond laser beam are adjustable.

[0111] The diameter and focusing depth of the annular femtosecond laser beam are realized by adjusting the divergence angle of the femtosecond laser beam output by the femtosecond laser 1.

[0112] Embodiment 7:

[0113] A controllable processing method for the multi-ring cladding of a single-crystal optical fiber by lithography based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Embodiments 2-6. Further, the ring-by-ring femtosecond laser lithography system further includes a shaping and beam expanding system 2.

[0114] The shaping and beam expanding system 2 is arranged in front of the femtosecond laser 1 and is used to regulate the divergence angle of the femtosecond laser beam output by the femtosecond laser 1, thereby realizing the regulation of the diameter and focusing depth of the annular femtosecond laser beam.

[0115] Embodiment 8:

[0116] A controllable processing method for the multi-ring cladding of a single-crystal optical fiber by lithography based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Embodiments 2-7. Further, the ring-by-ring femtosecond laser lithography system further includes a flat mirror frame 6. The spherical mirror 4 is installed at the center of the mirror frame 6.

[0117] The spectacle frame 6 has an annular optical window 5. After the annular light beam reflected by the concave mirror 3 passes through the optical window 5, it is transmitted to the plane mirror 11.

[0118] Example 9:

[0119] A controllable processing method for lithographic single-crystal fiber multi-ring cladding based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Examples 2-8. Further, the spectacle frame 6 is mounted on the support base 13.

[0120] The multi-ring mask plate 7 is mounted on the support base 13 through a bracket.

[0121] Example 10:

[0122] A controllable processing method for lithographic single-crystal fiber multi-ring cladding based on femtosecond laser and multi-ring mask plate, the technical content is the same as any one of Examples 2-9. Further, the structural design of the multi-ring mask plate has high flexibility and can be customized and optimized according to different application requirements of the single-crystal fiber multi-ring annular cladding. By drawing on the design concept of microstructured optical fiber, the multi-ring mask plate can realize complex and diverse multi-ring annular cladding structures, such as ring arrays arranged periodically, quasi-periodically or aperiodically. This flexibility stems from the wide adjustability of the mask plate design parameters, including key geometric parameters such as ring spacing, ring width, ring height, and radial distribution function. Based on computational methods such as strict finite element, the light field distribution pattern can be precisely controlled to meet the requirements of different application scenarios.

[0123] Example 11:

[0124] A system applying the controllable processing method for lithographic single-crystal fiber multi-ring annular cladding based on femtosecond laser and multi-ring mask plate, including a femtosecond laser 1, a concave mirror 3, a spherical mirror 4, a multi-ring mask plate 5, a fiber feeding system, a plane mirror 11, and a parabolic mirror 12.

[0125] See Figure 1 . The femtosecond laser is used to generate femtosecond laser. The light beam generated by the femtosecond laser 1 is converted into an annular light beam by the processing system. By adjusting the distance between the concave mirror 3 and the spherical mirror 4, the diameter parameter of the annular light beam is regulated, and finally an annular light focused inside the single-crystal fiber 10 is formed to realize the lithography of the single-crystal fiber 10.

[0126] The concave mirror 3 has a central hole I301. After the light beam output by the femtosecond laser 1 passes through the central hole I301, it is reflected by the spherical mirror 4 and then reflected by the reflecting surface I302 of the concave mirror 3 to form an annular femtosecond laser beam, which reaches the multi-ring mask plate 7 forward;

[0127] The main body of the multi-ring mask 7 is made of a transparent plate, and its plate surface has an opaque mask 702. The areas not covered by the mask 702 form a number of light-transmitting annular windows 701. The number of the annular windows 701 is the same as the number of layers of the multi-ring annular cladding to be formed in the single-crystal optical fiber to be processed. In the embodiment, a spherical mirror and a hollow concave mirror are used to generate an annular light beam, and the plane mirror 11 is inclined at 45° to change the propagation direction of the annular femtosecond laser beam, that is, to reflect the horizontal light beam into a vertical light beam.

[0128] The optical fiber clamping and feeding system is used to stretch the single-crystal optical fiber 10, and includes an upper clamp 8 above the parabolic mirror 12 and a lower clamp 9 below the plane mirror 11. The single-crystal optical fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the central hole II 1101 and the central hole III 1201.

[0129] The annular multi-ring laser beam reflected by the parabolic mirror 12 is focused inside the single-crystal optical fiber 10 between the plane mirror 11 and the parabolic mirror 12. In the embodiment, the optical fiber clamping and feeding system stretches the single-crystal optical fiber 10 upward or downward. Since the multi-layer annular light is focused inside the single-crystal optical fiber 10, photolithography can be performed on the focused part inside the single-crystal optical fiber 10 to form Figure 3 the multiple multi-ring annular claddings 1002 as shown. The inside of the innermost annular multi-ring annular cladding 1002 is the fiber core 1003; between the annular multi-ring annular claddings 1002 and outside the outermost annular multi-ring annular cladding 1002 is the outer optical fiber 1001.

[0130] Embodiment 12:

[0131] The main structure of this embodiment is the same as that of Embodiment 11. Further, it further includes a shaping and beam expanding system 2 arranged in front of the femtosecond laser 1. The shaping and beam expanding system 2 is used to regulate the divergence angle of the femtosecond laser beam output by the femtosecond laser 1, so as to realize precise regulation of the diameter and focusing depth of the annular femtosecond laser beam.

[0132] In the present invention, typical single-crystal optical fibers include:

[0133] 1. Single-crystal sapphire (Al2O3) optical fiber

[0134] 2. Single-crystal lutetium oxide (Lu2O3) optical fiber

[0135] 3. Single-crystal yttrium aluminum garnet (Y3Al5O 12 ) optical fiber

[0136] 4. Single-crystal lithium niobate (LiNbO3) optical fiber

[0137] 5. Single-crystal yttrium oxide (Y2O3) optical fiber

[0138] 6. Single-crystal tantalum pentoxide (Ta2O5) optical fiber

[0139] 7. Single-crystal lithium tantalate (LiTaO3) optical fiber

[0140] The control parameters for lithography of the multi-ring annular cladding of single-crystal optical fibers mainly include:

[0141] The central wavelength, pulse energy, and repetition frequency of the femtosecond laser.

[0142] In the embodiment, the following parameters can be adopted:

[0143] Relevant parameters for femtosecond laser lithography of the multi-ring annular cladding of single-crystal optical fibers

[0144]

[0145] Example 13:

[0146] The main structure of this embodiment is the same as that of Example 11 or 12. Further, the spherical mirror 4 is installed at the center of the mirror frame and has an annular optical window 5. The annular light beam reflected by the concave mirror 3 passes through the optical window 5. In the embodiment, the multi-ring mask plate is fixed on the horizontal base through a bracket. The matrix of the multi-ring mask plate 7 is made of a transparent material, and a periodically distributed opaque coating is applied to its surface part, so that the light beam passing through the multi-ring mask plate 7 is a periodically multi-ring femtosecond laser beam.

Claims

1. A controllable processing method for multi-ring cladding of single-crystal optical fiber based on femtosecond laser and multi-ring mask, characterized in that: The following steps are involved: 1) assembling the optical fiber (10) on the optical fiber clamping and transporting system of the femtosecond laser lithography system; The femtosecond laser lithography system comprises a femtosecond laser (1), a concave reflector (3), a spherical reflector (4), a multi-ring mask plate (7), an optical fiber clamping system, a plane reflector (11), and a parabolic reflector (12); The concave reflecting mirror (3) has a central hole I (301); The light beam output by the femtosecond laser (1) passes through the central hole I (301), is reflected by the spherical reflector (4), and is then reflected by the reflective surface I (302) of the concave reflector (3) to form a ring-shaped femtosecond laser beam, which then reaches the multi-ring mask plate (7); Due to the shielding of the mask, the annular light beam passes through the multi-ring mask plate (7) to form a plurality of layers of annular multi-ring femtosecond laser beams; The multi-ring mask plate (7) is located on one side of the spherical reflector (4); the main part of the multi-ring mask plate (7) is a transparent plate, and the plate surface has an opaque mask (702); the area not covered by the mask (702) forms a plurality of light-transmitting annular windows (701); the number of the annular windows (701) is the same as the number of layers of the multi-ring annular cladding required to be formed in the single crystal optical fiber to be processed; After passing through the multi-ring mask plate (7), the light beam forms a multi-ring femtosecond laser beam and reaches a plane reflector (11); the plane reflector (11) is tilted and has a center hole II (1101) at its center for the optical fiber (10) to pass through; the multi-ring femtosecond laser beam is reflected by the plane reflector (11) to the parabolic reflector (12) above; the center of the parabolic reflector (12) has a center hole III (1201) for the optical fiber (10) to pass through; The optical fiber clamping and delivery system is used for stretching an optical fiber (10), and comprises an upper clamp (8) located above a parabolic reflector (12) and a lower clamp (9) located below a plane reflector (11); the optical fiber (10) is clamped between the upper clamp (8) and the lower clamp (9), and passes through a center hole II (1101) and a center hole III (1201); The multi-ring femtosecond laser beam reflected by the parabolic reflector (12) is focused inside the optical fiber (10) between the plane reflector (11) and the parabolic reflector (12). 2) starting the optical fiber clamping and feeding system to stretch the optical fiber (10) toward one end; During the stretching process, the femtosecond laser (1) outputs a femtosecond laser beam to the outside; A femtosecond laser beam is converted into a multi-ring femtosecond laser beam by a femtosecond laser lithography system and focused inside an optical fiber (10) between a plane reflector (11) and a parabolic reflector (12), thereby performing a lithography process on the inside of the optical fiber (10); The processed optical fiber (10) comprises an innermost fiber core (1003) which has not been photolithographically processed, and n layers of multi-ring annular cladding (1002) and n layers of fiber regions (1001) which have not been photolithographically processed and are alternately distributed; The fiber core (1003) is in contact with the multi-ring annular cladding (1002) and is not in contact with the optical fiber region (1001) that has not been photolithographically processed; the multi-ring annular cladding (1002) is obtained by photolithography; The outermost layer of the processed optical fiber (10) is an optical fiber region (1001) that has not been photolithographically processed.

2. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: The multi-ring mask plate (7) has an opaque mask (702) on its surface; and a plurality of light-transmitting annular windows (701) are formed in the area not covered by the opaque mask (702) on the multi-ring mask plate (7).

3. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: The number of layers of the multi-ring annular cladding (1002) is greater than or equal to 2.

4. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: The process of converting a femtosecond laser beam from a femtosecond laser lithography system into a multi-ring femtosecond laser beam is as follows: The light beam output by the femtosecond laser (1) passes through the central hole I (301), is reflected by the spherical reflector (4), and is then reflected by the reflective surface I (302) of the concave reflector (3) to form a ring-shaped femtosecond laser beam, which then reaches the multi-ring mask plate (7); The multi-ring mask plate (7) separates the ring-shaped light beam into multi-ring femtosecond laser beams having multiple layers of rings, and transmits the beams to the plane reflector (11); The multi-ring femtosecond laser beam is reflected by the plane reflector (11) to the parabolic reflector (12) above; The parabolic reflector (12) reflects the multi-ring femtosecond laser beam so that the multi-ring femtosecond laser beam is focused inside the optical fiber (10) between the plane reflector (11) and the parabolic reflector (12).

5. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: When the inside of the optical fiber (10) is subjected to photolithography, the diameter and focusing depth of the annular femtosecond laser beam are adjustable; The diameter and focusing depth of the annular femtosecond laser beam are achieved by adjusting the divergence angle of the femtosecond laser beam output by the femtosecond laser (1).

6. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: The ring-by-ring femtosecond laser lithography system further comprises a beam shaping and expansion system (2); The shaping and beam expansion system (2) is arranged in front of the femtosecond laser (1) and is used to adjust the divergence angle of the femtosecond laser beam output by the femtosecond laser (1), thereby achieving the adjustment of the diameter and focusing depth of the annular femtosecond laser beam.

7. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 1, characterized in that: The ring-by-ring femtosecond laser lithography system further comprises a flat mirror frame (6); the spherical reflector (4) is mounted at the center of the mirror frame (6); The mirror frame (6) has an annular optical window (5); the annular light beam reflected by the concave reflector (3) passes through the optical window (5) and is then transmitted to the plane reflector (11).

8. The controllable processing method for lithography of single crystal optical fiber multi-ring cladding based on femtosecond laser and multi-ring mask according to claim 7, characterized in that: The mirror frame (6) is mounted on a support seat (13); The multi-ring mask plate (7) is mounted on a support seat (13) via a bracket.

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