A laser filter based on ultra-narrow linewidth phase-shift grating and a manufacturing method thereof

Abstract

The present invention relates to a laser filter based on an ultra-narrow linewidth phase-shift grating and a manufacturing method thereof; the manufacturing method comprises pre-processing an optical fiber, grinding one end of the optical fiber to obtain an optical fiber lens; metallizing the rear end of the optical fiber lens on the optical fiber; writing an ultra-narrow linewidth phase-shift grating on the tail end of the optical fiber in S2; compensating and packaging the ultra-narrow linewidth phase-shift grating into a first compensation packaging part and a second compensation packaging part, wherein the thermal expansion coefficient of the first compensation packaging part is greater than that of the second compensation packaging part; connecting the above-treated optical fiber to a laser chip, and coupling and welding the metallized optical fiber position to the laser chip through welding coating. The present invention is simple to operate, can realize ultra-narrow linewidth of laser sub-beams, and is easy to realize high integration of filter devices and laser chips. By performing temperature-drift-free packaging on the grating area, the wavelength does not drift with temperature changes, and the maximum wavelength drift can reach 0.03nm when the temperature difference is 100°C, thereby realizing the stabilization of the laser output wavelength.

Description

Technical Field

[0001] This invention relates to the field of laser filter technology, and in particular to a laser filter based on an ultra-narrow linewidth phase-shifting grating and its fabrication method. Background Technology

[0002] Fiber lasers possess outstanding advantages such as high efficiency, small size, good beam quality, stable and reliable operation, and strong environmental adaptability. They have broad application prospects in fields such as communications, industrial processing, medicine, and national defense, and are one of the important directions in laser research. With the development of double-clad large-mode-field fibers, the improvement of semiconductor pumping performance, and the rapid advancement of fiber integration technology, the output power of fiber lasers has been rapidly increased.

[0003] Currently, an effective solution for further increasing the output power of fiber lasers is beam combining, mainly including coherent combining and spectral combining. Beam combining places demands on the laser sub-beams, generally requiring them to possess narrow linewidth and high-power beam quality characteristics. As laser output power increases, the wavelength of the grating used for filtering also shifts with increasing temperature; specifically, a 1nm shift occurs for every 100°C increase in temperature, thus affecting the stability of the laser's output wavelength. Furthermore, the fabrication of ultra-narrow linewidth phase-shifting gratings for current laser sub-beams is quite complex, resulting in poor system integration. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for fabricating a laser filter based on an ultra-narrow linewidth phase-shifting grating, comprising the following steps:

[0005] S1: Pre-process the selected optical fiber by grinding one end of the optical fiber to obtain an optical fiber lens;

[0006] S2: Metallize the back end of the fiber optic lens on the fiber optic cable;

[0007] S3: Write an ultra-narrow linewidth phase-shift grating at the end of the optical fiber in S2;

[0008] S4: The ultra-narrow linewidth phase-shifting grating is compensated and encapsulated. A first compensation encapsulation part and a second compensation encapsulation part are arranged side by side on the outside of the ultra-narrow linewidth phase-shifting grating. The thermal expansion coefficient of the first compensation encapsulation part is greater than that of the second compensation encapsulation part.

[0009] S5: Connect the optical fiber obtained in S4 to the laser chip, and couple the metallized optical fiber to the laser chip using a welding coating.

[0010] Furthermore, in step S4, the first compensation encapsulation part is encapsulated with aluminum material, and the second compensation encapsulation part is encapsulated with borosilicate glass.

[0011] Furthermore, in step S3, the method for writing the ultra-narrow linewidth phase-shifting grating is as follows:

[0012] A writing platform is constructed, including a laser and a reflector, a cylindrical mirror, and a phase mask arranged sequentially along the optical path, with the optical fiber positioned in front of the phase mask;

[0013] The reflector is connected to a motion control platform that drives its movement, and a piezoelectric ceramic that drives its movement is connected below the phase mask. The motion control platform and the piezoelectric ceramic are connected to a control system.

[0014] Furthermore, the distance between the cylindrical mirror and the phase mask is equal to the focal length of the cylindrical mirror.

[0015] Furthermore, the ultra-narrow linewidth phase-shift grating has a linewidth of 30MHz to 1000MHz and a reflectivity greater than 10dB.

[0016] Furthermore, in step S1, the fiber optic lens is conical or wedge-shaped, with a wedge angle of 10–150° and a radius of curvature of 3–20 μm. ， Off-axis <2°.

[0017] Furthermore, in step S2, the thickness of the film layer at the optical fiber metallization treatment is 1 to 10 μm.

[0018] Furthermore, the optical fiber includes a core, a cladding, and a coating layer, wherein the cladding covers the outside of the core, and the coating layer is disposed on the outside of the cladding.

[0019] Furthermore, in step S5, the welding coating is AuSn20, the welding temperature is 290℃, and the welding time is less than 10 seconds.

[0020] On the other hand, the present invention also provides a laser filter based on an ultra-narrow linewidth phase-shifting grating, which is a laser filter fabricated using the method described above for fabricating a laser filter based on an ultra-narrow linewidth phase-shifting grating.

[0021] By employing the above technical solutions, this invention has the following advantages compared to existing technologies:

[0022] 1) The method for fabricating a laser filter based on an ultra-narrow linewidth phase-shifting grating provided by the present invention is simple to operate, can realize ultra-narrow linewidth of laser sub-beams, and can easily achieve high integration of filter devices and laser chips. By encapsulating the grating area without temperature drift, the wavelength does not drift with temperature changes, and the maximum wavelength drift can reach 0.03nm with a temperature difference of 100℃, thereby stabilizing the laser output wavelength.

[0023] 2) The laser filter based on an ultra-narrow linewidth phase-shift grating provided by the present invention has a simple structure, is easy to assemble, and can achieve ultra-narrow linewidth, stabilization, compact integration, and intelligence, while also having a low cost. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the fabrication process of the laser filter based on an ultra-narrow linewidth phase-shifting grating according to the present invention.

[0025] Figure 2 This is a schematic diagram of the laser filter based on an ultra-narrow linewidth phase-shifting grating according to the present invention;

[0026] Figure 3 This is a schematic diagram of the fiber optic lens in this invention;

[0027] Figure 4 This is a schematic diagram of the structure of the ultra-narrow linewidth phase-shifting grating in this invention;

[0028] Figure 5 This is a schematic diagram of the writing platform in this invention;

[0029] Figure 6 This is a test spectrum of the ultra-narrow linewidth laser filter in an embodiment of the present invention;

[0030] Figure 7 This is a test spectrum of wavelength variation with temperature before and after packaging of the ultra-narrow linewidth phase-shift grating in an embodiment of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the accompanying drawings, the dimensions and relative dimensions of certain parts may be enlarged for clarity.

[0032] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connection" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] In the description of this invention, terms such as "upper," "lower," "left," "right," "front," and "rear," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] Furthermore, in the description of this invention, the terms "first" and "second" are used only for descriptive purposes.

[0035] This invention provides a method for fabricating a laser filter based on an ultra-narrow linewidth phase-shifting grating, comprising the following steps:

[0036] S1: Pre-process the selected optical fiber by grinding one end of the optical fiber to obtain an optical fiber lens;

[0037] S2: Metallize the back end of the fiber optic lens on the fiber optic cable;

[0038] S3: Write an ultra-narrow linewidth phase-shift grating at the end of the optical fiber in S2;

[0039] S4: The ultra-narrow linewidth phase-shifting grating is compensated and encapsulated. A first compensation encapsulation part and a second compensation encapsulation part are arranged side by side on the outside of the ultra-narrow linewidth phase-shifting grating. The thermal expansion coefficient of the first compensation encapsulation part is greater than that of the second compensation encapsulation part.

[0040] S5: Connect the optical fiber obtained in S4 to the laser chip, and couple the metallized optical fiber to the laser chip using a welding coating.

[0041] As per the instruction manual Figure 2 As shown, the laser filter fabricated by the above method includes a laser chip 1 and an optical fiber 5. Specifically, the laser chip 1 has a wavelength of 980nm, but other wavelengths are also possible, including but not limited to 980nm. It features standard 14-pin and 8-pin butterfly-shaped metallized hermetically sealed design, a cooler, and a monitoring photodetector. One end of the fiber optic lens 2 of the optical fiber 5 is coupled to the laser chip 1. The rear end of the fiber optic lens 2 is provided with a fiber metallized region 3. The tail end of the optical fiber 5 is provided with an ultra-narrow linewidth phase-shifting grating 4, and the grating is encapsulated.

[0042] In an optimized implementation, the optical fiber 5 is a single-mode optical fiber or a double-clad optical fiber. In this embodiment, the optical fiber is a double-clad optical fiber. The optical fiber 5 includes a core 51, a cladding 52, and a coating layer 53. The cladding 52 covers the outside of the core 51, and the coating layer 53 is disposed on the outside of the cladding 52. The core 51 is made of silicon dioxide or other doped materials and has a diameter of 6-15 μm. The cladding 52 is made of silicon dioxide or other doped materials and has a diameter of 40-400 μm. The coating layer 53 is an organic polymer such as acrylate and has a diameter of 80-500 μm.

[0043] Optimized implementation methods, as shown in the appendix to the instruction manual. Figure 3 As shown, in step S1, the fiber optic lens 2 is conical or wedge-shaped. The shape and size of the fiber optic lens 2 are determined according to the light spot output by the laser chip 1. The fiber optic lens 2 can also be other shapes. When the fiber optic lens 2 is conical or wedge-shaped, its wedge angle is 10 to 150° and its radius of curvature is 3 to 20 μm. ， Off-axis <2°.

[0044] In the optimized implementation, in step S2, the rear end of the fiber optic lens 2 is metallized. The length of the fiber optic metallization region 3 can be set according to actual needs. The coating material is a metal material such as gold or zinc. The film thickness at the fiber optic metallization treatment is 1-10 μm, and the tensile strength is >10N. The fiber optic metallization position is coupled and welded to the laser chip 1 to assemble a laser filter, so that the fiber optic lens 2 is placed inside the laser chip 1 and coupled to the laser chip 1.

[0045] In the optimized implementation method, the method for writing the ultra-narrow linewidth phase-shifting grating in step S3 is as follows:

[0046] a. As per the instruction manual Figure 5 As shown, a grating writing platform system is constructed, with a laser 6 and a reflector 8, a cylindrical mirror 9, and a phase mask 10 arranged sequentially along the optical path. The optical fiber is arranged in front of the phase mask 10, and the area of ​​the optical fiber to be written is placed at the corresponding position of the phase mask 10. A piezoelectric ceramic 11 is arranged below the phase mask 10.

[0047] b. Start the laser 6 and output the laser beam 7. The laser beam 7 passes through the reflector 8 and is focused by the cylindrical mirror 9. The reflector 8 is set on the motion control platform that can drive its movement. The position of the reflector 8 can be adjusted so that the laser beam 7 passes through the cylindrical mirror 9. The control system 12 is connected to the motion control platform and the piezoelectric ceramic, and adjusts the motion control platform and the piezoelectric ceramic to move independently of each other.

[0048] c. The laser beam focused by the cylindrical mirror illuminates the phase mask. The distance between the cylindrical mirror and the phase mask is the focal length of the cylindrical mirror, so that the focal point of the cylindrical mirror can fall on the optical fiber to write the grating. The focal length of the cylindrical mirror is 15-40cm.

[0049] d. Place the optical fiber to be exposed at a small distance in front of the phase mask 10. Specifically, place the optical fiber to be etched 0.5 mm in front of the phase mask 10.

[0050] e. A moving laser beam scans and exposes the optical fiber, controlling the reflector to move according to a motion function equation.

[0051] y=1*(0.54-0.46*cos(2.0*pi*i / n-1.25))+0.0736*cos(2.0*pi*i / n);

[0052] Where pi is π, i = 1, 2, 3...n, and n is the number of runs;

[0053] g. During the exposure process, based on the predetermined phase shift magnitude and position, the program controls the tiny and precise movement of the piezoelectric ceramic to achieve the appearance of an ultra-narrow communication window for the phase shift grating. By controlling the tiny and precise movement of the piezoelectric ceramic through the program, a sudden perturbation is generated, which in turn creates a tiny slit in the originally uniformly changing refractive index. An ultra-narrow communication window will then appear in the reflection peak, thus realizing the writing of an ultra-narrow linewidth phase shift grating.

[0054] The above method can be used to obtain ultra-narrow linewidth phase-shift gratings with linewidths of 30MHz to 1000MHz, reflectivity greater than 10dB, and center wavelengths of 980nm, 1550nm, or other bands.

[0055] The refractive index of a phase-shifted grating changes abruptly at a certain position, making the refractive index change discontinuous. This characteristic gives it advantages such as high-quality wavelength selectivity and insensitivity to polarization. When a signal passes through a fiber Bragg grating, a reflection peak with a certain bandwidth is formed at its resonant wavelength, thereby identifying the signal. When a phase shift is introduced, a narrow slit appears in the reflection peak at the resonant wavelength.

[0056] When the optical fiber is not subjected to stress, and the ambient temperature changes by ΔT, the change in the emitted wavelength at the center of the grating is given by Δλ = (a + £)ΔT, where Δλ is the wavelength change, λ is the center wavelength of the grating, a is the thermal expansion coefficient of the optical fiber, £ is the thermo-optic coefficient of the optical fiber, and ΔT is the change in ambient temperature. To avoid wavelength drift due to temperature changes, the ultra-narrow linewidth phase-shifting grating 4 is encapsulated without drift, as detailed in the attached manual. Figure 4As shown, a first compensation encapsulation part 43 and a second compensation encapsulation part 44 are encapsulated side by side on the outside of the grating. The first compensation encapsulation part 43 is encapsulated with aluminum, and the second compensation encapsulation part 44 is encapsulated with borosilicate glass. The coefficient of thermal expansion of aluminum is greater than that of borosilicate glass. 41 is the grating region position, and 42 is the periodic phase shift offset, which is 0-2π. When the temperature rises, both the first compensation encapsulation part and the second compensation encapsulation part expand, which reduces the distance between the fixed points at both ends of the grating, thereby reducing the strain on the grating. This causes the emission wavelength of the grating to drift towards the short-wave direction, which cancels out the drift of the reflection wavelength of the grating towards the long-wave direction caused by the temperature rise.

[0057] The manufacturing method of the present invention will be further illustrated with specific embodiments.

[0058] Step 1: Select Corning HI1060 optical fiber with a cladding diameter of 125±0.5μm and a coating diameter of 245±10μm;

[0059] Step 2: Take a 1000mm long optical fiber, remove 40mm of the coating from the initial end, and wipe it clean with alcohol;

[0060] Step 3: Grind the fiber end face on a polishing machine to obtain a fiber lens. The fiber lens is wedge-shaped with an angle of 60°, a radius of curvature of 10μm, and an off-axis of ≤1.5°.

[0061] Step 4: Gold plating is performed 10mm from the right end of the fiber optic lens, with a plating thickness of 3μm and a tensile strength >10N;

[0062] Step 5: At 500mm from the right end of the metallized lens fiber, an ultra-narrow linewidth phase-shifted fiber grating is inscribed with a center wavelength of 974nm, a linewidth of 120MHz, a reflectivity of 24dB, and a periodic phase shift of 0.5π.

[0063] Step 6: Encapsulate the grating area with temperature drift-free components using custom aluminum and high borosilicate structural parts;

[0064] Step 7: Couple and weld the fiber metallization position to the pump laser chip. The welding temperature is 290℃, the welding time is <10 seconds, and the welding material is AuSn20. The wavelength of the laser chip is 980nm. The standard 14-pin and 8-pin butterfly-shaped metallization is gas-sealed.

[0065] Turn on the pump laser; the output laser wavelength linewidth is as shown in the attached manual. Figure 6 As shown, the wavelength changes with temperature as the temperature rises. The test results are as shown in the attached instruction manual. Figure 7 As shown, it can be seen that after encapsulating the ultra-narrow linewidth phase-shift grating, the wavelength does not drift with temperature changes.

[0066] Those skilled in the art will understand that the present invention can be implemented in many other specific forms without departing from the spirit and scope of the invention. Although embodiments of the invention have been described, it should be understood that the invention is not limited to these embodiments, and those skilled in the art can make changes and modifications within the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating, characterized in that: The following steps are involved: S1: pre-processing the selected optical fiber, grinding one end of the optical fiber to obtain an optical fiber lens; S2: performing metallization processing on the rear end of the optical fiber lens on the optical fiber; S3: Write an ultra-narrow linewidth phase-shift grating on the tail end of the optical fiber in S2; S4: performing compensation packaging on the ultra-narrow linewidth phase-shift grating, wherein a first compensation packaging part and a second compensation packaging part are arranged side by side outside the ultra-narrow linewidth phase-shift grating, and the thermal expansion coefficient of the first compensation packaging part is greater than the thermal expansion coefficient of the second compensation packaging part; S5: Connect the optical fiber obtained in S4 to the laser chip, and couple and weld the metallized optical fiber position to the laser chip using welding paint.

2. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: In the step S4, the first compensation packaging part is packaged with aluminum, and the second compensation packaging part is packaged with high borosilicate glass.

3. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: In step S3, the writing method of the ultra-narrow linewidth phase-shift grating is: Building a writing platform, including a laser and a reflector, a cylindrical mirror, and a phase mask plate arranged in sequence along the optical path, wherein the optical fiber is arranged in front of the phase mask plate; The reflector is connected to a motion control platform for driving its movement, the phase mask is connected below a piezoelectric ceramic for driving its movement, and the motion control platform and the piezoelectric ceramic are connected to a control system.

4. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 3, characterized in that: The distance between the cylindrical mirror and the phase mask is equal to the focal length of the cylindrical mirror.

5. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: The line width of the ultra-narrow line width phase shift grating is 30 MHz to 1000 MHz, and the reflectivity is greater than 10 dB.

6. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: In step S1, the optical fiber lens is conical or wedge-shaped, the wedge angle of the optical fiber lens is 10 to 150°, and the radius of curvature is 3 to 20 μm. ， Off-axis <2°.

7. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: In the step S2, the thickness of the film layer at the optical fiber metallization treatment site is 1-10 μm.

8. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: The optical fiber comprises a core, a cladding and a coating layer, wherein the cladding is coated on the outside of the core, and the coating layer is arranged on the outside of the cladding.

9. The method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating according to claim 1, characterized in that: In step S5, the welding coating is AuSn20, the welding temperature is 290° C., and the welding time is less than 10 seconds.

10. A laser filter based on an ultra-narrow linewidth phase-shift grating, characterized in that: A laser filter manufactured by the method for manufacturing a laser filter based on an ultra-narrow linewidth phase-shift grating as described in any one of claims 1-9.

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