A controllable processing method for ring-by-ring femtosecond laser inscription of a single crystal fiber cladding

Abstract

The application provides a controllable processing method for ring-by-ring femtosecond laser marking of a single crystal fiber cladding, and aims to solve the technical problems of low processing efficiency and limited processing length in the prior art. The basic idea of the method is to use a femtosecond laser to output a ring-shaped femtosecond laser spot. On this basis, the diameter and width of the ring-shaped spot are precisely controlled by moving the position of the spherical mirror in the system. The ring-shaped spot is then focused inside the single crystal fiber through the optical path system, interacts with a specific local area of the single crystal fiber, reduces the refractive index of the area, and successfully realizes the writing of the cladding structure in the single crystal fiber. The method can efficiently write the inner cladding structure with no length limit and uniform refractive index distribution in the single crystal fiber.

Description

Technical Field

[0001] The invention relates to a femtosecond laser lithography single crystal optical fiber cladding structure, belonging to the technical field of optical fiber sensors. Background Art

[0002] In the field of silica optical fiber, the importance of fiber cladding treatment lies in its ability to reduce the refractive index of the fiber cladding, thereby meeting the conditions for total internal reflection of the light beam in the fiber core region, thereby improving optical waveguide efficiency. In conventional silica optical fiber, through preform design and fiber drawing, it is easy to prepare a silica cladding with a refractive index different from that of the fiber core.

[0003] However, because the growth and preparation of single-crystal optical fibers differ significantly from that of quartz optical fibers, relying on atomic-level crystal growth techniques, cladding is difficult to achieve. Currently available single-crystal optical fibers are essentially cladding-free waveguide structures. This results in significant transmission losses during use and, in sensing applications, faces the problem of multimode interference, hindering practical application.

[0004] In order to achieve cladding treatment of single crystal optical fibers, there are two types of methods considered in the existing technology. One is to use epitaxy, sol-gel method, and liquid encapsulation methods to add low-refractive index heterogeneous materials to the outside of the single crystal optical fiber to achieve total reflection conditions. However, due to the use of heterogeneous materials, this method usually has lower temperature resistance than single crystal optical fiber materials, and heterogeneous materials have thermophysical property mismatch problems. The structural stability when used at high temperatures and large temperature ranges will be significantly lower, which loses the technical advantages of single crystal optical fibers. The second is to use ion implantation, high-energy particle irradiation, and femtosecond laser modification schemes to perform material modification on the inner surface of the single crystal optical fiber to achieve cladding treatment. However, the ion implantation and high-energy particle irradiation schemes are complex processes, not only extremely costly, but also the uniformity of the cladding formed is poor, and has no practical value.

[0005] Using femtosecond lasers to perform photolithography on single-crystal optical fibers is a feasible solution. Currently, there are multiple solutions for single-crystal optical fiber cladding based on femtosecond lasers, such as performing helical femtosecond laser lithography in optical fibers to reduce the refractive index of the helical region, that is, to achieve cladding near the center axis of the optical fiber. There is also femtosecond laser writing at a certain radius along the optical fiber axis to achieve multiple strip-shaped refractive index reduction areas, and to achieve wrapping of the center axis near the center of the optical fiber, which can also achieve cladding. However, these reported femtosecond laser cladding methods are all based on point-by-point lithography, and there are obvious technical problems, including:

[0006] 1. To achieve cylindrical surface processing near the optical fiber axis, the efficiency is extremely low by relying on point-by-point, line-by-line, and then surface-by-surface processing methods.

[0007] 2. Since point-by-point lithography is achieved through reciprocating motion near the optical fiber's central axis, the positioning requirements for the 3D electronic translation stage are extremely high, usually requiring the use of a nano-translation stage, and the required processing equipment is also extremely expensive;

[0008] 3. Usually, the range of high-precision three-dimensional translation stages is limited, so the length of the processed clad single crystal fiber is very limited. Summary of the Invention

[0009] The object of the present invention is to provide a controllable processing method for ring-by-ring femtosecond laser lithography of a single-crystal optical fiber cladding, comprising the following steps:

[0010] 1) Assemble the single crystal optical fiber on the optical fiber clamping system of the ring-by-ring femtosecond laser lithography system.

[0011] The ring-by-ring femtosecond laser lithography system comprises a femtosecond laser, a concave reflecting mirror, a spherical reflecting mirror, an optical fiber clamping system, a plane reflecting mirror and a parabolic reflecting mirror.

[0012] The concave reflector has a central hole I.

[0013] The light beam output by the femtosecond laser passes through the central hole I and is reflected by the spherical reflector to the reflecting surface I of the concave reflector.

[0014] The light beam output by the femtosecond laser passes through the central hole I, is reflected by the spherical reflector to the concave reflector, and is reflected by the reflective surface I of the concave reflector into a ring-shaped femtosecond laser beam, which then reaches the plane reflector.

[0015] The plane reflector is tilted and has a center hole II at its center for the single crystal optical fiber to pass through. The parabolic reflector has a center hole III at its center for the single crystal optical fiber to pass through.

[0016] The fiber clamping system is used to pull a single-crystal optical fiber and includes an upper clamp located above a parabolic reflector and a lower clamp located below a plane reflector. The single-crystal optical fiber is clamped between the upper and lower clamps and passes through center holes II and III.

[0017] The annular femtosecond laser beam reflected by the parabolic mirror is focused inside the single crystal optical fiber between the plane mirror and the parabolic mirror.

[0018] 2) Start the fiber clamping system and stretch the fiber toward one end.

[0019] During the stretching process, the femtosecond laser outputs a femtosecond laser beam outward.

[0020] The femtosecond laser beam is converted into a ring-shaped femtosecond laser beam by a ring-by-ring femtosecond laser lithography system, and then focused inside a single crystal optical fiber located between a plane mirror and a parabolic mirror, thereby performing lithography processing on the inside of the single crystal optical fiber.

[0021] The processed single crystal optical fiber includes, from the inside to the outside, a core region that has not been photolithographically processed, a cladding, and a peripheral region of the single crystal optical fiber.

[0022] Furthermore, the process of converting the femtosecond laser beam from the ring-by-ring femtosecond laser lithography system into a ring-shaped femtosecond laser beam is as follows:

[0023] The light beam output by the femtosecond laser passes through the central hole I, is reflected by the spherical reflector to the concave reflector, and is reflected by the reflective surface I of the concave reflector into a ring-shaped femtosecond laser beam, which then reaches the plane reflector.

[0024] The annular femtosecond laser beam is transmitted to a plane mirror and then reflected by the plane mirror to the parabolic mirror above.

[0025] The parabolic reflector reflects the annular femtosecond laser beam, so that the annular femtosecond laser beam is focused inside the single crystal optical fiber located between the plane reflector and the parabolic reflector.

[0026] Furthermore, the core region and the peripheral region of the single crystal optical fiber are not photolithographically processed.

[0027] Furthermore, when performing photolithography processing inside the single crystal optical fiber, the diameter and focusing depth of the annular femtosecond laser beam can be adjusted.

[0028] 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.

[0029] Furthermore, the ring-by-ring femtosecond laser lithography system also includes a shaping and beam expansion system.

[0030] The shaping beam expansion system is arranged in front of the femtosecond laser and is used to adjust the divergence angle of the femtosecond laser beam output by the femtosecond laser, thereby achieving the adjustment of the diameter and focusing depth of the annular femtosecond laser beam.

[0031] Furthermore, when performing photolithography processing inside the single crystal optical fiber, the diameter and width of the annular femtosecond laser beam can be adjusted.

[0032] The diameter and width of the annular femtosecond laser beam are achieved by adjusting the distance between the spherical reflector and the concave reflector.

[0033] Furthermore, the ring-by-ring femtosecond laser lithography system also includes a horizontal displacement control system.

[0034] The spherical mirror is mounted on a slider on the horizontal displacement control system.

[0035] The distance between the spherical reflector and the concave reflector is adjusted by controlling the slider, thereby regulating the diameter and width of the annular femtosecond laser beam after being reflected by the concave reflector.

[0036] Furthermore, the ring-by-ring femtosecond laser lithography system further comprises a flat mirror frame, and the spherical reflector is installed at the center of the mirror frame.

[0037] The mirror frame has an annular optical window. The annular light beam reflected by the concave reflector passes through the optical window and is then transmitted to the plane reflector.

[0038] It is worth noting that a femtosecond laser was used to replace the original CO2 laser in the laser-heated pedestal growth system to generate a ring-shaped femtosecond laser spot. On this basis, the diameter and width of the ring-shaped femtosecond laser spot were precisely controlled by the position of the spherical reflector in the shaping and expansion system and the movement system. The ring-shaped spot was then focused into the interior of the single-crystal fiber through the optical path system, interacting with a specific local area of ​​the single-crystal fiber, causing the refractive index of this area to decrease, thereby successfully achieving the inscription of the inner cladding structure of the single-crystal fiber. This method can efficiently inscribe the inner cladding structure in a single-crystal fiber.

[0039] Advantages of the present invention include:

[0040] 1. Use annular spot to lithographically process the cladding structure to improve writing efficiency;

[0041] 2. Use high-precision fiber stretching system to control the movement of single crystal fiber to meet the writing requirements of fiber cladding of any single crystal length;

[0042] 3. The cladding is inscribed with a circular femtosecond laser spot with uniform energy distribution to improve the uniformity of the cladding refractive index distribution;

[0043] 4. A spherical mirror and a concave mirror are used to output an annular femtosecond laser spot. The diameter and width of the annular spot can be adjusted by moving the position of the spherical mirror, thereby achieving flexible control of the core diameter and cladding thickness of the single crystal optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the structural diagram of the ring-by-ring femtosecond laser lithography system.

[0045] Figure 2 Schematic diagram of the focusing and cladding of a circular femtosecond laser beam inside a single crystal fiber.

[0046] Figure 3 Schematic diagram of the principle of changing the diameter and width of the annular femtosecond laser beam by adjusting the shaping beam expansion system.

[0047] Figure 4 Schematic diagram of the principle of controlling the diameter of a circular femtosecond laser beam through a horizontal displacement device to achieve cladding treatment of single-crystal fibers with different core diameters.

[0048] Figure 5 The three-dimensional structure and cross-sectional diagram of the clad single crystal optical fiber.

[0049] In the figure: femtosecond laser (1), shaping beam expander system (2), concave mirror (3), central hole I (301), reflecting surface I (302), spherical mirror (4), optical window (5), mirror holder (6), horizontal displacement control system (7), upper clamp (8), lower clamp (9), single crystal fiber (10), single crystal fiber peripheral area (1001), cladding (1002), core area (1003), plane mirror (11), central hole II (1101), reflecting surface II (1102), parabolic mirror (12), central hole III (1201), reflecting surface III (1202). DETAILED DESCRIPTION

[0050] The application will be further described in conjunction with the examples below, but should not be understood as limiting the above-mentioned subject matter of the application to the following examples. Various substitutions and modifications can be made according to ordinary technical knowledge and conventional means without departing from the above-mentioned technical idea of the application, and all such substitutions and modifications shall be included in the protection scope of the application.

[0051] Example 1

[0052] Reference Figures 1 to 5 A controllable processing method for ring-by-ring femtosecond laser lithography of single crystal fiber cladding, comprising the following steps:

[0053] 1) Assemble the single crystal fiber 10 on the fiber clamping and feeding system of the ring-by-ring femtosecond laser lithography system.

[0054] The ring-by-ring femtosecond laser lithography system comprises a femtosecond laser 1, a concave mirror 3, a spherical mirror 4, a fiber clamping and feeding system, a plane mirror 11 and a parabolic mirror 12.

[0055] The concave mirror 3 has a central hole I 301.

[0056] After the light beam output by the femtosecond laser 1 passes through the central hole I 301, it is reflected by the spherical mirror 4 to the concave mirror 3, and is reflected by the reflecting surface I 302 of the concave mirror 3 into a ring-shaped femtosecond laser beam, which reaches the plane mirror 11.

[0057] The plane mirror 11 is arranged obliquely, and has a central hole II 1101 through which the single crystal fiber 10 passes. The parabolic mirror 12 has a central hole III 1201 through which the single crystal fiber 10 passes.

[0058] The fiber clamping system is used to stretch a single crystal fiber 10 and includes an upper clamp 8 located above a parabolic reflector 12 and a lower clamp 9 located below a plane reflector 11. The single crystal fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the center hole II 1101 and the center hole III 1201.

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

[0060] 2) Start the optical fiber clamping system to stretch the optical fiber 10 toward 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 ring-shaped femtosecond laser beam by the ring-by-ring femtosecond laser lithography system, and then focused inside the single crystal optical fiber 10 between the plane reflector 11 and the parabolic reflector 12 , thereby performing lithography processing on the inside of the single crystal optical fiber 10 .

[0063] The processed single crystal optical fiber 10 comprises, from the inside to the outside, a core region 1003 that has not been photolithographically processed, a cladding 1002, and a single crystal optical fiber peripheral region 1001. The cladding 1002 is an annular cladding.

[0064] The process of converting the femtosecond laser beam from the ring-by-ring femtosecond laser lithography system into a ring-shaped femtosecond laser beam is as follows:

[0065] The light beam output by the femtosecond laser 1 passes through the central hole I301, is reflected by the spherical reflector 4 to the concave reflector 3, is reflected by the reflective surface I302 of the concave reflector 3 to form a ring-shaped femtosecond laser beam, and then reaches the plane reflector 11.

[0066] The annular femtosecond laser beam is transmitted to the plane mirror 11 and then reflected by the plane mirror 11 to the parabolic mirror 12 above.

[0067] The parabolic reflector 12 reflects the annular femtosecond laser beam, so that the annular femtosecond laser beam is focused inside the single crystal optical fiber 10 located between the plane reflector 11 and the parabolic reflector 12 .

[0068] The core region 1003 and the peripheral region 1001 of the single crystal optical fiber are not photolithographically processed.

[0069] When performing photolithography processing on the interior of the single crystal optical fiber 10 , the diameter and focus depth of the annular femtosecond laser beam are adjustable.

[0070] The diameter and focus 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 .

[0071] The ring-by-ring femtosecond laser lithography system further includes a beam shaping and expansion system 2 .

[0072] 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.

[0073] When performing photolithography processing on the interior of the single crystal optical fiber 10 , the diameter and width of the annular femtosecond laser beam are adjustable.

[0074] The diameter and width of the annular femtosecond laser beam are achieved by adjusting the distance between the spherical reflecting mirror 4 and the concave reflecting mirror 3 .

[0075] The ring-by-ring femtosecond laser lithography system further includes a horizontal displacement control system 7 .

[0076] The spherical reflector 4 is mounted on a slider on the horizontal displacement control system 7 .

[0077] The distance between the spherical reflector 4 and the concave reflector 3 is adjusted by controlling the slider, thereby regulating the diameter and width of the annular femtosecond laser beam reflected by the concave reflector 3 .

[0078] The ring-by-ring femtosecond laser lithography system further comprises a flat mirror frame 6 , wherein the spherical reflector 4 is mounted at the center of the mirror frame 6 .

[0079] 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.

[0080] Example 2:

[0081] A controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography comprises the following steps:

[0082] 1) Assemble the single crystal optical fiber 10 on the optical fiber clamping system of the ring-by-ring femtosecond laser lithography system.

[0083] The ring-by-ring femtosecond laser lithography system includes a femtosecond laser 1 , a concave reflector 3 , a spherical reflector 4 , an optical fiber clamping system, a plane reflector 11 and a parabolic reflector 12 .

[0084] The concave reflecting mirror 3 has a central hole I301.

[0085] The light beam output by the femtosecond laser 1 passes through the central hole I301, is reflected by the spherical reflector 4 to the concave reflector 3, is reflected by the reflective surface I302 of the concave reflector 3 into a ring-shaped femtosecond laser beam, and then reaches the plane reflector 11;

[0086] The plane reflector 11 is tilted and has a center hole II1101 at its center for the single crystal optical fiber 10 to pass through. The parabolic reflector 12 has a center hole III1201 at its center for the single crystal optical fiber 10 to pass through.

[0087] The fiber clamping system is used to stretch a single crystal fiber 10 and includes an upper clamp 8 located above a parabolic reflector 12 and a lower clamp 9 located below a plane reflector 11. The single crystal fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the center hole II 1101 and the center hole III 1201.

[0088] The annular femtosecond laser beam reflected by the parabolic reflector 12 is focused inside the single crystal optical fiber 10 between the plane reflector 11 and the parabolic reflector 12 .

[0089] 2) Start the optical fiber clamping system to stretch the optical fiber 10 toward one end.

[0090] During the stretching process, the femtosecond laser 1 outputs a femtosecond laser beam.

[0091] The femtosecond laser beam is converted into a ring-shaped femtosecond laser beam by the ring-by-ring femtosecond laser lithography system, and then focused inside the single crystal optical fiber 10 between the plane reflector 11 and the parabolic reflector 12 , thereby performing lithography processing on the inside of the single crystal optical fiber 10 .

[0092] The processed single crystal optical fiber 10 includes, from the inside to the outside, a core region 1003 that has not been photolithographically processed, a cladding 1002 , and a single crystal optical fiber peripheral region 1001 .

[0093] Example 3:

[0094] A controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography, the technical content of which is the same as that of Example 2, further, the process of converting the femtosecond laser beam from the ring-by-ring femtosecond laser lithography system into a ring-shaped femtosecond laser beam is as follows:

[0095] The light beam output by the femtosecond laser 1 passes through the central hole I301, is reflected by the spherical reflector 4 to the concave reflector 3, is reflected by the reflective surface I302 of the concave reflector 3 into a ring-shaped femtosecond laser beam, and then reaches the plane reflector 11;

[0096] The annular femtosecond laser beam is transmitted to the plane mirror 11 and then reflected by the plane mirror 11 to the parabolic mirror 12 above.

[0097] The parabolic reflector 12 reflects the annular femtosecond laser beam, so that the annular femtosecond laser beam is focused inside the single crystal optical fiber 10 located between the plane reflector 11 and the parabolic reflector 12 .

[0098] Example 4:

[0099] A controllable processing method for ring-by-ring femtosecond laser lithography of a single crystal optical fiber cladding, the technical content of which is the same as any one of Examples 2-3, further, the core region 1003 and the single crystal optical fiber peripheral region 1001 are not lithographically processed.

[0100] Example 5:

[0101] A controllable processing method for ring-by-ring femtosecond laser lithography of a single-crystal optical fiber cladding has the same technical content as any one of embodiments 2-4. Furthermore, when performing lithography processing on the interior of the single-crystal optical fiber 10, the diameter and focusing depth of the ring-shaped femtosecond laser beam are adjustable.

[0102] The diameter and focus 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 .

[0103] Example 6:

[0104] A controllable processing method for the cladding of a single crystal optical fiber by ring-by-ring femtosecond laser lithography, the technical content of which is the same as any one of Examples 2-5. Furthermore, the ring-by-ring femtosecond laser lithography system also includes a shaping and beam expansion system 2.

[0105] 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.

[0106] Example 7:

[0107] A controllable processing method for ring-by-ring femtosecond laser lithography of a single-crystal optical fiber cladding has the same technical content as any one of embodiments 2-6. Furthermore, when performing lithography processing on the interior of the single-crystal optical fiber 10, the diameter and width of the ring-shaped femtosecond laser beam are adjustable.

[0108] The diameter and width of the annular femtosecond laser beam are achieved by adjusting the distance between the spherical reflecting mirror 4 and the concave reflecting mirror 3 .

[0109] Example 8:

[0110] A controllable processing method for the cladding of a single crystal optical fiber by ring-by-ring femtosecond laser lithography, the technical content of which is the same as any one of Examples 2-7. Furthermore, the ring-by-ring femtosecond laser lithography system also includes a horizontal displacement control system 7.

[0111] The spherical reflector 4 is mounted on a slider on the horizontal displacement control system 7 .

[0112] The distance between the spherical reflector 4 and the concave reflector 3 is adjusted by controlling the slider, thereby regulating the diameter and width of the annular femtosecond laser beam reflected by the concave reflector 3 .

[0113] like Figure 3 As shown, the spherical reflector is positioned differently ( Figure 3Left) results in different diameters and widths of the annular femtosecond laser beam ( Figure 3 middle), which results in different lithography effects of the annular grating in the core cross section ( Figure 3 right).

[0114] Example 9:

[0115] A controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography, the technical content of which is the same as any one of embodiments 2-8, further comprising a flat mirror frame 6. The spherical reflector 4 is mounted at the center of the mirror frame 6.

[0116] 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.

[0117] Example 10:

[0118] A system adopting the controllable processing method of ring-by-ring femtosecond laser lithography single crystal optical fiber cladding as described in any one of Examples 1-9 comprises a femtosecond laser 1, a concave reflector 3, a spherical reflector 4, an optical fiber clamping system, a plane reflector 11, and a parabolic reflector 12.

[0119] See also Figure 1 The femtosecond laser is used to output femtosecond laser light. The femtosecond laser beam output by the femtosecond laser 1 is converted into a ring-shaped femtosecond laser spot by the ring-shaped femtosecond laser lithography system. By adjusting the shaping and expansion system and the distance between the concave reflector 3 and the spherical reflector 4, the diameter and width of the ring-shaped femtosecond laser beam are controlled, and finally a ring-shaped spot focused inside the single crystal optical fiber 10 is formed, thereby achieving lithography of the single crystal optical fiber 10.

[0120] The concave reflecting mirror 3 has a central hole I301. The light beam output by the femtosecond laser 1 passes through the central hole I301, is reflected by the spherical reflecting mirror 4 to the concave reflecting mirror 3, and is reflected by the reflecting surface I302 of the concave reflecting mirror 3 to form a ring-shaped femtosecond laser beam, and then reaches the plane reflecting mirror 11.

[0121] The plane reflector 11 is tilted and has a central hole II1101 at its center for the single-crystal optical fiber 10 to pass through. The annular light beam is reflected by the plane reflector 11 to the parabolic reflector 12 above. The parabolic reflector 12 has a central hole III1201 at its center for the single-crystal optical fiber 10 to pass through. In this embodiment, a spherical reflector and a hollow concave reflector are used to output the annular femtosecond laser beam. The plane reflector 11 is tilted at 45 degrees to change the propagation direction of the annular femtosecond laser.

[0122] The fiber clamping system is used to stretch a single crystal fiber 10 and includes an upper clamp 8 located above a parabolic reflector 12 and a lower clamp 9 located below a plane reflector 11. The single crystal fiber 10 is clamped between the upper clamp 8 and the lower clamp 9 and passes through the center hole II 1101 and the center hole III 1201.

[0123] The annular femtosecond laser beam reflected by the parabolic reflector 12 is focused inside the single crystal optical fiber 10 between the plane reflector 11 and the parabolic reflector 12. In the embodiment, the optical fiber clamping system pulls the single crystal optical fiber 10 upwards. Since the annular light spot is focused inside the single crystal optical fiber 10, photolithography can be performed on the focused area inside the single crystal optical fiber 10 to form a circular spot. Figure 2 The annular cladding 1002 shown has a core region 1003 inside and an optical fiber peripheral region 1001 outside. The core 1003 and the outer optical fiber 1001 are not photolithographically processed, forming a cladding structure inside the optical fiber.

[0124] See also Figure 2 The system diffuses the femtosecond laser spot into a ring-shaped femtosecond laser beam and focuses it onto the cross section of a single-crystal fiber using a parabolic reflector, forming a circular ring spot. A single exposure can achieve refractive index modulation on the fiber cross section. Subsequently, the stretching system precisely controls the axial movement of the fiber, stretching the circular ring spot into a cylindrical structure, thereby achieving refractive index modulation on the cylindrical surface inside the fiber. This process achieves highly efficient, length-unlimited, and uniform single-crystal fiber cladding.

[0125] Example 11:

[0126] The main structure of this embodiment is the same as that of embodiment 10, and further includes a shaping and expanding beam system 2 disposed in front of the femtosecond laser 1. The shaping and expanding beam system 2 is used to adjust the divergence angle of the femtosecond laser beam output by the femtosecond laser 1, thereby achieving precise control of the diameter and focusing depth of the annular femtosecond laser beam.

[0127] In the present invention, the single crystal optical fiber comprises:

[0128] 1. Single crystal sapphire (Al2O3) optical fiber

[0129] 2. Single crystal lutetium oxide (Lu2O3) optical fiber

[0130] 3. Single crystal yttrium aluminum garnet (Y3Al5O 12 )optical fiber

[0131] 4. Single crystal lithium niobate (LiNbO3) optical fiber

[0132] 5. Single crystal yttrium oxide (Y2O3) optical fiber

[0133] 6. Single crystal tantalum oxide (Ta2O5) optical fiber

[0134] 7. Single crystal lithium tantalate (LiTaO3) optical fiber

[0135] The main parameters of single crystal fiber cladding using ring-by-ring femtosecond laser lithography include:

[0136] The central wavelength, pulse energy and repetition rate of femtosecond laser.

[0137] In an embodiment, the following parameters may be used:

[0138] Parameters of single-crystal optical fiber cladding by ring-by-ring femtosecond laser lithography

[0139]

[0140] Example 12:

[0141] The main structure of this embodiment is the same as that of embodiment 10 or 11, and further includes a horizontal displacement control system 7. The spherical reflector 4 is mounted on a slider on the horizontal displacement control system 7. By controlling the slider to adjust the distance between the spherical reflector 4 and the concave reflector 3, the diameter and width of the annular femtosecond laser beam reflected by the concave reflector 3 can be controlled. Figure 3 As shown, by adjusting the distance between the spherical mirror and the concave reflector through a high-precision horizontal displacement device, the diameter and width of the annular femtosecond laser beam can be precisely controlled to meet the requirements of cladding treatment of single-crystal optical fibers with different core diameters.

[0142] Example 13:

[0143] The main structure of this embodiment is the same as that of Embodiments 10-12. Furthermore, 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 femtosecond laser beam reflected by the concave reflector 3 passes through the optical window 5. In the embodiment, the mirror frame 6 is in the shape of a flat plate, and its lower end is fixed to the horizontal displacement control system 7 by a bracket 9. The base of the flat plate is made of a transparent material, and its surface is partially coated with an opaque coating, that is, the rear of the spherical reflector 4 is an opaque coating, and the spherical reflector 4 is surrounded by an uncoated annular optical window 5.

Claims

1. A controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography, characterized in that: The following steps are involved: 1) assembling the single crystal optical fiber (10) on the optical fiber clamping and transporting system of the ring-by-ring femtosecond laser lithography system; The ring-by-ring femtosecond laser lithography system comprises a femtosecond laser (1), a concave reflector (3), a spherical reflector (4), 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) to the concave reflector (3), is reflected by the reflective surface I (302) of the concave reflector (3) to form a ring-shaped femtosecond laser beam, and then reaches the plane reflector (11). The plane reflector (11) is tilted and has a center hole II (1101) at its center for the single crystal optical fiber (10) to pass through; the parabolic reflector (12) has a center hole III (1201) at its center for the single crystal optical fiber (10) to pass through; The optical fiber clamping system is used for stretching a single crystal 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 single crystal 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 annular femtosecond laser beam reflected by the parabolic reflector (12) is focused inside the single crystal optical fiber (10) between the plane reflector (11) and the parabolic reflector (12); 2) starting the optical fiber clamping system to stretch the single crystal optical fiber (10) toward one end; During the stretching process, the femtosecond laser (1) outputs a femtosecond laser beam outward; A femtosecond laser beam is converted into a ring-shaped femtosecond laser beam by a ring-by-ring femtosecond laser lithography system, and then focused inside a single crystal optical fiber (10) located between a plane reflector (11) and a parabolic reflector (12), thereby performing a photolithography process on the inside of the single crystal optical fiber (10); The processed single crystal optical fiber (10) comprises, from the inside to the outside, a core region (1003) that has not been photoetched, a cladding (1002), and a single crystal optical fiber peripheral region (1001).

2. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: The process of converting the femtosecond laser beam from the ring-by-ring femtosecond laser lithography system into a ring-shaped 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) to the concave reflector (3), is reflected by the reflective surface I (302) of the concave reflector (3) to form a ring-shaped femtosecond laser beam, and then reaches the plane reflector (11). The annular femtosecond laser beam is transmitted to the plane reflector (11), and then reflected by the plane reflector (11) to the parabolic reflector (12) above; The parabolic reflector (12) reflects the annular femtosecond laser beam, so that the annular femtosecond laser beam is focused inside the single crystal optical fiber (10) located between the plane reflector (11) and the parabolic reflector (12).

3. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: The core region (1003) and the peripheral region (1001) of the single crystal optical fiber are not photolithographically processed.

4. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: When photolithography is performed on the interior of the single crystal optical fiber (10), the diameter and focus 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).

5. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 4, characterized in that: The ring-by-ring femtosecond laser lithography system further includes 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 focus depth of the annular femtosecond laser beam.

6. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: When performing photolithography processing on the interior of the single crystal optical fiber (10), the diameter and width of the annular femtosecond laser beam are adjustable; The diameter and width of the annular femtosecond laser beam are achieved by adjusting the distance between the spherical reflector (4) and the concave reflector (3).

7. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: The ring-by-ring femtosecond laser lithography system further includes a horizontal displacement control system (7); The spherical reflector (4) is mounted on a slider on a horizontal displacement control system (7); The distance between the spherical reflector (4) and the concave reflector (3) is adjusted by controlling the slider, thereby regulating the diameter and width of the annular femtosecond laser beam reflected by the concave reflector (3).

8. The controllable processing method for single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography 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).

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