Controllable processing method for ring-by-ring femtosecond laser photoetching single-crystal optical fiber cladding

Abstract

The invention provides a controllable processing method for a ring-by-ring femtosecond laser photoetching single crystal optical fiber cladding, and aims to solve the technical problems of low processing efficiency, limited processing length and the like in the prior art. The basic idea of the method is that a femtosecond laser is adopted to output annular femtosecond laser spots. On the basis, accurate control over the diameter and width of the annular light spot is achieved by moving the position of the spherical reflector in the system. And then the annular light spot is focused into the single-crystal optical fiber through a light path system and interacts with a specific local area of the single-crystal optical fiber, so that the refractive index of the area is reduced, and the inscribing of the inner cladding structure of the single-crystal optical fiber is successfully realized. According to the method, the inner cladding structure which is free of length limitation and uniform in refractive index distribution can be efficiently inscribed in the single crystal optical fiber.

Description

Technical Field

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

[0002] In the field of quartz optical fiber, the importance of fiber cladding treatment lies in that it can reduce the refractive index of the fiber cladding to meet the total reflection condition of the light beam in the fiber core area, thereby improving the optical waveguide efficiency. In conventional quartz optical fiber, through the design of preform rods and fiber drawing treatment, it is easy to prepare a silica cladding with a different refractive index from the core.

[0003] However, since the growth and preparation of single-crystal optical fiber is completely different from that of quartz optical fiber, it relies on atomic-level crystal growth technology and is difficult to achieve cladding. The single-crystal optical fiber currently available on the market is basically a cladding-free optical waveguide structure. This will lead to great transmission loss when used, and when used in sensing, there is also the problem of multi-mode interference in many modes, which affects its practical application.

[0004] In order to achieve the cladding treatment of single crystal optical fibers, there are two types of methods considered in the prior art. One is to use epitaxy, sol-gel method, liquid encapsulation and other methods to add low-refractive index heterogeneous materials to the outside of single crystal optical fibers 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 there is a thermophysical property mismatch problem in heterogeneous materials. The structural stability will be significantly lower when used at high temperatures and in large temperature ranges, 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 modify the material on the inside of the single crystal optical fiber surface to achieve cladding treatment. However, the ion implantation and high-energy particle irradiation schemes are complex processes, not only are the costs extremely high, but the uniformity of the cladding formed is also poor, and they are not of practical value.

[0005] Using femtosecond lasers to perform photolithography on single-crystal optical fibers is a feasible solution. Currently, there are many 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 in the helical area, that is, to achieve cladding near the center axis of the optical fiber. There are also femtosecond laser writing at a certain radius along the axial direction of the optical fiber to achieve multiple strip-shaped refractive index reduction areas, and to achieve wrapping at 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 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 by reciprocating near the central axis of the optical fiber, the positioning requirements for the three-dimensional electric-controlled translation stage are extremely high, and a nano-translation stage is usually required, and the cost of the required processing equipment is also extremely high;

[0008] 3. Usually, the range of high-precision three-dimensional translation stages is limited, so the length of the processed clad single-crystal optical 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 and transporting 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 reflector, a spherical reflector, an optical fiber clamping and delivering system, a plane reflector and a parabolic reflector.

[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 reflective surface I of the concave reflector.

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

[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 and feeding system is used for stretching a single crystal optical fiber, and comprises 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 clamp and the lower clamp and passes through a central hole II and a central hole III.

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

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

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

[0020] 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 located between a plane reflector and a parabolic reflector, thereby performing lithography processing inside 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] After passing through the central hole I, the light beam output by the femtosecond laser is reflected by the spherical reflector to the concave reflector, and then reflected by the reflective surface I of the concave reflector into a ring-shaped femtosecond laser beam, and then reaches the plane reflector forward;

[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 photolithography is performed inside the single crystal optical fiber, the diameter and focusing depth of the annular femtosecond laser beam are adjustable.

[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 and 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 realizing the adjustment of the diameter and focusing depth of the annular femtosecond laser beam.

[0031] Furthermore, when performing photolithography inside a 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 reflector 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 adjusting the diameter and width of the annular femtosecond laser beam 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 is used to replace the original CO2 laser in the laser heating base growth system to generate a ring-shaped femtosecond laser spot. On this basis, the diameter and width of the ring-shaped femtosecond laser spot are precisely controlled by shaping and expanding the system and moving the position of the spherical reflector in the system. The ring-shaped spot is then focused into 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 the area to decrease, thereby successfully realizing the writing of the inner cladding structure of the single crystal fiber. This method can efficiently write the inner cladding structure in a single crystal fiber.

[0039] Advantages of the present invention include:

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

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

[0042] 3. The cladding is engraved by 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 a ring-shaped femtosecond laser spot. The diameter and width of the ring-shaped spot can be adjusted by moving the position of the spherical mirror, thereby achieving flexible control of the diameter of the "core" and the 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 annular femtosecond laser beam through a horizontal displacement device to achieve cladding treatment of single-crystal optical fibers with different core diameters.

[0048] Figure 5 The three-dimensional structure of clad single crystal optical fiber and its cross-section.

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

[0050] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0051] Embodiment 1:

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

[0053] 1) Assemble the single crystal optical fiber 10 on the optical fiber clamping and transporting 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 reflector 3 , a spherical reflector 4 , an optical fiber clamping system, a plane reflector 11 and a parabolic reflector 12 .

[0055] The concave reflecting mirror 3 has a central hole I301.

[0056] After passing through the central hole I301 , the light beam output by the femtosecond laser 1 is reflected by the spherical reflector 4 to the concave reflector 3 , and then 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 .

[0057] 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.

[0058] The fiber clamping system is used to stretch the single crystal fiber 10, and includes an upper clamp 8 located above the parabolic reflector 12 and a lower clamp 9 located below the 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 II1101 and the center hole III1201.

[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 and feeding system to stretch the optical fiber 10 toward one end.

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

[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 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. 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] After passing through the central hole I301 , the light beam output by the femtosecond laser 1 is reflected by the spherical reflector 4 to the concave reflector 3 , and then 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 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 the inside of the single crystal optical fiber 10 is subjected to photolithography processing, the diameter and focusing depth of the annular femtosecond laser beam are adjustable.

[0070] 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 .

[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 the inside of the single crystal optical fiber 10 is subjected to photolithography, 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 adjusting 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 . 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] Embodiment 2:

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

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

[0083] 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 .

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

[0085] After passing through the central hole I301, the light beam outputted by the femtosecond laser 1 is reflected by the spherical reflector 4 to the concave reflector 3, and then 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;

[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 the single crystal fiber 10, and includes an upper clamp 8 located above the parabolic reflector 12 and a lower clamp 9 located below the 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 II1101 and the center hole III1201.

[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 and feeding system to stretch the optical fiber 10 toward one end.

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

[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] Embodiment 3:

[0094] A controllable processing method for a 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, and further, the process of converting a femtosecond laser beam from a ring-by-ring femtosecond laser lithography system into a ring-shaped femtosecond laser beam is as follows:

[0095] After passing through the central hole I301, the light beam outputted by the femtosecond laser 1 is reflected by the spherical reflector 4 to the concave reflector 3, and then 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;

[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 between the plane reflector 11 and the parabolic reflector 12 .

[0098] Embodiment 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 embodiments 2-3, and further, the core region 1003 and the single crystal optical fiber peripheral region 1001 are not lithographically processed.

[0100] Embodiment 5:

[0101] 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 embodiments 2-4, and further, when the inside of the single-crystal optical fiber 10 is subjected to lithography, the diameter and focusing depth of the ring-shaped femtosecond laser beam are adjustable.

[0102] 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 .

[0103] Embodiment 6:

[0104] 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 2-5, and further, the ring-by-ring femtosecond laser lithography system also includes a shaping and expanding beam 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] Embodiment 7:

[0107] 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 embodiments 2-6, and further, when the inside of the single-crystal optical fiber 10 is subjected to lithography, 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] Embodiment 8:

[0110] 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 2-7, and further, 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 adjusting 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 located at different positions ( Figure 3Left side) 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 on the right).

[0114] Embodiment 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, the ring-by-ring femtosecond laser lithography system also includes a flat mirror frame 6. The spherical reflector 4 is installed 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] Embodiment 10:

[0118] A system adopting the controllable processing method of single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography as described in any one of Examples 1-9, comprising 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 a femtosecond laser. 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 regulated, and finally a ring-shaped spot focused inside the single crystal optical fiber 10 is formed to realize the lithography of the single crystal optical fiber 10.

[0120] The concave reflecting 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 to the concave reflecting mirror 3 by the spherical reflecting mirror 4, and is reflected to form a ring-shaped femtosecond laser beam by the reflecting surface I302 of the concave reflecting mirror 3, and then reaches the plane reflecting mirror 11 forward.

[0121] 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 annular light 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 III1201 for the single crystal optical fiber 10 to pass through. In the embodiment, the spherical reflector and the hollow concave reflector are used to output the annular femtosecond laser beam, and the plane reflector 11 is tilted at 45° to change the propagation direction of the annular femtosecond laser.

[0122] The fiber clamping system is used to stretch the single crystal fiber 10, and includes an upper clamp 8 located above the parabolic reflector 12 and a lower clamp 9 located below the 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 II1101 and the center hole III1201.

[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 stretches the single crystal optical fiber 10 upward. 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 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 on the cross section of a single-crystal fiber through a parabolic reflector to form a ring-shaped spot. A single exposure can achieve refractive index modulation on the cross section of the fiber. Subsequently, the axial movement of the fiber is precisely controlled by the stretching system, and the ring-shaped spot is stretched into a cylindrical structure, thereby achieving refractive index modulation on the cylindrical surface inside the fiber. This process achieves high-efficiency, length-free and uniform single-crystal fiber cladding processing.

[0125] Embodiment 11:

[0126] The main structure of this embodiment is the same as that of embodiment 10, and further comprises a shaping beam expansion system 2 arranged in front of the femtosecond laser 1. The shaping beam expansion 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 for single crystal fiber cladding using ring-by-ring femtosecond laser lithography include:

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

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

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

[0139]

[0140] Embodiment 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. The distance between the spherical reflector 4 and the concave reflector 3 is adjusted by controlling the slider to control the diameter and width of the annular femtosecond laser beam reflected by the concave reflector 3. 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 needs of cladding treatment of single-crystal optical fibers with different core diameters.

[0142] Embodiment 13:

[0143] The main structure of this embodiment is the same as that of Embodiments 10-12, and further, the spherical reflector 4 is installed 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 through 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 surrounding of the spherical reflector 4 is an annular optical window 5 that is not coated with a coating.

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 conveying 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); After passing through the central hole I (301), the light beam output by the femtosecond laser (1) is reflected by the spherical reflector (4) to the concave reflector (3), and then 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 and conveying 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 central hole II (1101) and a central 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 and feeding 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 to the outside; 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) 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 of single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1 is 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: After passing through the central hole I (301), the light beam output by the femtosecond laser (1) is reflected by the spherical reflector (4) to the concave reflector (3), and then 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 a plane reflector (11), and then is reflected by the plane reflector (11) to a 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 of 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 of single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: When photolithography is performed inside the single crystal optical fiber (10), 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).

5. The controllable processing method of 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 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.

6. The controllable processing method of single crystal optical fiber cladding by ring-by-ring femtosecond laser lithography according to claim 1, characterized in that: When photolithography is performed inside 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 of 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 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 of 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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