High-quality grating spectrum shape on-line writing device and high-quality grating spectrum shape on-line writing method

Abstract

The invention provides a high-quality grating spectrum shape on-line writing device and method, and belongs to the technical field of fiber grating preparation, and the device comprises a high-power excimer laser which is used for transmitting a monopulse laser beam perpendicular to the axial direction of a bare fiber based on a preset transmission parameter; the diaphragm is used for adjusting the area of the monopulse laser beam to obtain an adjusted beam; the beam expanding lens group is used for expanding the adjusted light beam in the axial direction of the bare fiber to obtain an optimized light beam; and the phase mask plate is used for masking the optimized light beam to obtain a target light beam irradiated on the bare fiber, and the target light beam is used for grating inscribing. According to the invention, the inscribing grating is flexibly adjusted by adjusting the size of the expanded beam, so that the obtained optimized beam meets different grating inscribing requirements, and the quality of the formed grating is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber grating preparation, and in particular to a high-quality grating spectrum online writing device and method. Background Art

[0002] With the rapid development of sensor network scale and industrialization, the fiber-optic sensor network built with fiber Bragg grating as the unit has been vigorously promoted and is developing in the direction of large capacity, high precision and multiple application scenarios. For the fiber Bragg grating sensing system, the grating spectrum shape written plays a vital role in its sensing precision and accuracy. How to efficiently and batch prepare high-quality grating arrays has become a research direction for the development of new fiber-optic sensor networks.

[0003] At present, among various preparation methods of grating arrays, the drawing tower online preparation technology has the best writing efficiency and engineering application capability. It realizes the online writing of multiple Bragg gratings in continuously moving optical fibers by completing the two steps of fiber drawing and grating writing on the drawing tower simultaneously. Specifically, patent CN104635295B discloses an online fiber grating preparation system, which realizes the online preparation of large-capacity grating arrays by using phase mask single-side exposure writing technology. It has the advantages of low transmission loss and large multiplexing capacity, and has been successfully applied in various environmental monitoring systems such as temperature, strain, and vibration. With the continuous expansion of the application scale of grating array sensor networks, the requirements for the quality of the written optical fiber spectrum shape have also increased. On the one hand, in temperature, strain and other sensing systems, the written Bragg gratings are required to have high consistency and narrower bandwidth in order to accommodate more gratings in the limited light source bandwidth; on the other hand, in vibration sensing systems, the written chirped gratings are required to have a larger bandwidth and a flat reflection spectrum to adapt to complex application scenarios. The grating writing technology in the prior art only writes different types of gratings by replacing the mask plate, without considering the requirements of different types of gratings on the grating quality. That is, when the light spot is too small to meet the grating engraving requirements, it is impossible to adaptively adjust the light beam to meet the requirements of different types of gratings on the grating quality, resulting in a technical problem of low grating writing quality.

[0004] Therefore, there is an urgent need to provide a high-quality grating spectrum online writing device and method to improve the grating writing quality. Summary of the invention

[0005] In view of this, it is necessary to provide a high-quality grating spectrum online writing device and method to solve the technical problem in the prior art that when the light spot is too small to meet the grating engraving requirements, the light beam cannot be adaptively adjusted to meet the grating quality requirements of different types of gratings, resulting in low grating writing quality.

[0006] On the one hand, in order to solve the above technical problems, the present invention provides a high-quality grating spectrum online writing device, comprising: A high-power excimer laser, used for emitting a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; An aperture, used for adjusting the area of ​​the single-pulse laser beam to obtain an adjusted beam; A beam expansion lens group, used for expanding the adjustment light beam in the axial direction of the bare fiber to obtain an optimized light beam; The phase mask is used to mask the optimized light beam to obtain a target light beam irradiated onto the bare fiber, and the target light beam is used for grating writing.

[0007] In a possible implementation, the beam expander lens group includes a concave cylindrical lens and a first convex cylindrical lens sequentially arranged along a direction from the aperture to the phase mask; The concave cylindrical lens is used to expand the adjustment light beam in the axial direction of the bare fiber to obtain an expanded light beam; The first convex cylindrical lens is used to focus the expanded light beam to obtain the optimized light beam.

[0008] In a possible implementation, the beam expanding lens group further includes a second convex cylindrical lens disposed between the first convex cylindrical lens and the phase mask, and the second convex cylindrical lens is used to focus the optimized light beam in a radial direction of the bare fiber.

[0009] In a possible implementation, the center of the aperture, the focus of the concave cylindrical lens, the focus of the first convex cylindrical lens, and the focus of the second convex cylindrical lens are located on the same straight line and are perpendicular to the bare fiber.

[0010] In a possible implementation, the focal length of the first convex cylindrical lens is equal to the distance between the first convex cylindrical lens and the concave cylindrical lens, and the phase mask is located at the focus of the second convex cylindrical lens.

[0011] In a possible implementation, the single pulse energy of the high-power excimer laser is 60 mJ to 170 mJ.

[0012] In a possible implementation, the focal lengths of the concave cylindrical lens, the first convex cylindrical lens, and the second convex cylindrical lens range from 50 mm to 1000 mm.

[0013] In a possible implementation, the bare fiber moves at a uniform speed along the axial direction, and the distance between the phase mask and the bare fiber is 0.5 m to 1 m.

[0014] In a possible implementation, the bare fiber is a single-mode fiber, a multi-mode fiber, a few-mode fiber or a thin-diameter fiber, and the phase mask includes a uniform phase mask and a chirped phase mask.

[0015] On the other hand, the present invention further provides a high-quality grating spectral shape online writing method, which is applicable to the high-quality grating spectral shape online writing device described in any one of the possible implementations above, and the method comprises: Controlling the high-power excimer laser to emit a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; Adjusting the area of ​​the single-pulse laser beam based on an aperture to obtain an adjusted beam; Expanding the adjusted light beam in a width direction based on a beam expanding lens group to obtain an optimized light beam; The optimized light beam is masked based on a phase mask template to obtain a target light beam irradiated onto the bare fiber, and grating writing is performed based on the target light beam.

[0016] The beneficial effects of the present invention are as follows: the high-quality grating spectrum online writing device provided by the present invention, by setting a beam expansion lens group, expands the adjusted light beam after aperture processing in the axial direction of the bare fiber, thereby realizing flexible adjustment of the written grating by adjusting the beam expansion size, so that the obtained optimized light beam meets different grating engraving requirements and improves the quality of the formed grating.

[0017] Furthermore, the present invention does not need to replace the laser, and only needs to properly set a beam expansion lens group on the existing online writing optical path to improve the grating quality, thereby reducing the grating cost. At the same time, based on the online preparation technology of the drawing tower, the present invention can give full play to the technical advantages of online writing of the phase mask grating, and has the advantages of high grating writing efficiency and good spectral quality. The grating array formed has good engineering application capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 A schematic structural diagram of an embodiment of a high-quality grating spectrum online writing device provided by the present invention; Figure 2 A schematic structural diagram of another viewing angle embodiment of the high-quality grating spectrum online writing device provided by the present invention; Figure 3A schematic diagram of the reflection spectrum of the Bragg grating provided by the present invention before and after improvement; Figure 4 A schematic diagram of the reflection spectrum of the chirped grating before and after improvement provided by the present invention; Figure 5 A schematic flow chart of an embodiment of a method for online writing of high-quality grating spectrum provided by the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0021] It should be understood that the schematic drawings are not drawn to scale. The flowchart used in the present invention shows the operations implemented according to some embodiments of the present invention. It should be understood that the operations of the flowchart can be implemented out of order, and the steps without logical context can be reversed in order or implemented simultaneously. In addition, those skilled in the art, under the guidance of the content of the present invention, can add one or more other operations to the flowchart, and can also remove one or more operations from the flowchart. Some of the block diagrams shown in the accompanying drawings are functional entities, which do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor systems and / or microcontroller systems.

[0022] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0023] The present invention provides a high-quality grating spectrum online writing device and method, which are described below respectively.

[0024] Figure 1 This is a schematic diagram of the structure of the high-quality grating spectrum online writing device in the YOZ plane. Figure 2 FIG. 1 is a schematic diagram of the structure of a high-quality grating spectrum online writing device in the XOY plane. Figure 1 and Figure 2 As shown, the high-quality grating spectrum online writing device 10 includes: A high-power excimer laser 100, used to emit a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; The aperture 200 is used to adjust the area of ​​the single pulse laser beam to obtain an adjusted beam; The beam expansion lens group 300 is used to expand the adjustment light beam in the axial direction of the bare fiber 20 to obtain an optimized light beam; The phase mask 400 is used to mask the optimized light beam to obtain a target light beam irradiated onto the bare fiber 20, and the target light beam is used for grating writing.

[0025] The shape of the single-pulse laser beam is rectangular.

[0026] It should be noted that the bare fiber is prepared by a drawing tower and is always in a uniform motion state along the OZ axis during the grating engraving process, achieving the purpose of drawing and engraving at the same time.

[0027] Among them, the movement speed of the bare fiber is 3 m / min~100 m / min.

[0028] Specifically, the preset emission parameters include pulse energy and writing frequency.

[0029] Compared with the prior art, the high-quality grating spectrum online writing device 10 provided in the embodiment of the present invention, by setting a beam expansion lens group 300 to expand the adjusted light beam processed by the aperture 200 in the axial direction of the bare fiber, realizes flexible adjustment of the written grating by adjusting the beam expansion size, so that the obtained optimized light beam meets different grating engraving requirements and improves the quality of the formed grating.

[0030] Furthermore, the present invention does not need to replace the laser, and only needs to properly set the beam expansion lens group 300 on the existing online writing optical path to improve the grating quality and reduce the grating cost. At the same time, based on the online preparation technology of the drawing tower, the present invention can give full play to the technical advantages of the phase mask plate 400 for online writing of gratings, and has the advantages of high grating writing efficiency and good spectral quality, and the formed grating array has good engineering application capabilities.

[0031] In a specific embodiment of the present invention, the single pulse energy of the high power excimer laser 100 is 60 mJ to 170 mJ, and the size of the rectangular single pulse laser beam emitted thereby is 5 mm×5 mm to 20 mm×20 mm.

[0032] Taking the laser model COMPex 110F as an example, the output beam size is 24 mm × 10 mm, and the uniformity and coherence of the beam in the width direction are better as the fiber axial direction of the grating. After selection, its spot size is 8mm × 12mm, and the former is the fiber axial direction.

[0033] The aperture 200 is also rectangular, and the aperture 200 can block and adjust the single-pulse laser beam from four directions of the XOZ plane. The size of the adjusted beam after blocking and adjustment by the aperture 200 is 1mm×1mm~20mm×20mm.

[0034] It should be noted that the process of the aperture 200 blocking and adjusting the single-pulse laser beam is as follows: the single-pulse laser beam emitted by the high-power excimer laser 100 is tested by a beam quality analyzer to determine the spot area with good coherence and energy uniformity, and the aperture 200 retains the beam in the area with good coherence and uniformity. In other words, the beam is adjusted to be a beam with good coherence and uniformity in the single-pulse laser beam.

[0035] In some embodiments of the present invention, Figure 1 and Figure 2 As shown, the beam expander lens group 300 includes a concave cylindrical lens 310 and a first convex cylindrical lens 320 which are sequentially arranged along the direction from the aperture 200 to the phase mask 400; The concave cylindrical lens 310 is used to expand the adjustment light beam in the axial direction of the bare fiber 20 to obtain an expanded light beam; The first convex cylindrical lens 320 is used to focus the expanded light beam to obtain an optimized light beam.

[0036] It should be noted that the beam expansion effect of the concave cylindrical lens 310 can be adjusted by adjusting the distance between the concave cylindrical lens 310 and the first convex cylindrical lens 320 .

[0037] The embodiment of the present invention reduces the energy loss in the uniform spot area by sampling first and then expanding the beam.

[0038] Specifically, the concave cylindrical lens 310 is fixed on a translation stage that can move forward and backward along the OY axis direction, and the beam expansion effect is adjusted by changing the distance from the first convex cylindrical lens 320 through the movement of the translation stage.

[0039] Since the lengths of the Bragg grating and the chirped grating in the axial direction of the bare fiber may be different, different grating requirements can be met by expanding the light beam in the axial direction of the bare fiber, thereby ensuring the high quality of any prepared grating.

[0040] The light beam along the radial direction of the bare fiber only needs to be screened and confirmed by the aperture 200, and does not need to be expanded. Therefore, in some embodiments of the present invention, Figure 1 and Figure 2 As shown, the beam expander lens assembly 300 further includes a second convex cylindrical lens 330 disposed between the first convex cylindrical lens 320 and the phase mask 400 , and the second convex cylindrical lens 330 is used to focus the optimized light beam in the radial direction of the bare fiber 20 .

[0041] Specifically, the length of the written grating is greater than or equal to 15 cm. Based on this parameter, the parameters of the second convex cylindrical lens 330 and the aperture 200 can be set to ensure that the length of the written grating meets this requirement.

[0042] In a specific embodiment of the present invention, the focal lengths of the concave cylindrical lens 310, the first convex cylindrical lens 320 and the second convex cylindrical lens 330 range from 50 mm to 1000 mm.

[0043] If there is an angle change in the optical path of the laser beam, in order to ensure the consistency of the engraved grating, it is necessary to strictly control parameters such as the reflection angle of the beam, which is difficult to control and leads to poor consistency of the grating.

[0044] To solve this technical problem, in some embodiments of the present invention, the center of the aperture 200, the focus of the concave cylindrical lens 310, the focus of the first convex cylindrical lens 320 and the focus of the second convex cylindrical lens 330 are located on the same straight line and perpendicular to the bare fiber 20.

[0045] In the high-quality grating spectrum online writing device 10 in the embodiment of the present invention, the laser light path is straight and perpendicular to the bare fiber, and there is no need to use structures such as reflectors to change the light path, thereby improving the stability of the light path, thereby improving the consistency of the written grating, and further improving the grating quality.

[0046] To ensure that all light beams irradiated onto the bare fiber 20 are perpendicular to the axial direction of the bare fiber 20, in some embodiments of the present invention, the focal length of the first convex cylindrical lens 320 is equal to the distance between the first convex cylindrical lens 320 and the concave cylindrical lens 310, and the phase mask 400 is located at the focus of the second convex cylindrical lens 330.

[0047] In the embodiment of the present invention, by setting the focal length of the first convex cylindrical lens 320 to be equal to the distance between the first convex cylindrical lens 320 and the concave cylindrical lens 310, and the phase mask 400 is located at the focus of the second convex cylindrical lens 330, it can be ensured that the parallel light beam generated by the high-power excimer laser 100 is still parallel to the bare fiber 20, thereby further ensuring the quality of the written grating.

[0048] In some embodiments of the present invention, the distance between the phase mask 400 and the bare fiber 20 is 0.5 m to 1 m.

[0049] Through the above arrangement, it is possible to avoid the adverse effect on the grating quality caused by the distance between the target light beam and the bare fiber 20 being too small or too large when the target light beam reaches the bare fiber 20 from the phase mask 400, thereby further improving the quality of the written grating.

[0050] It should be noted that the bare fiber 20 is a single-mode fiber, a multi-mode fiber, a few-mode fiber or a thin-diameter fiber, and the phase mask 400 includes a uniform phase mask and a chirped phase mask.

[0051] Among them, the grating produced by the uniform phase mask is a Bragg grating, which is mostly used in temperature and strain sensing systems. The grating produced by the chirped phase mask is a chirped grating, which is mostly used in vibration sensing systems.

[0052] In order to verify the effectiveness of the high-quality grating profile online writing device proposed in the embodiment of the present invention in improving the grating quality, in a specific embodiment of the present invention, a high-quality grating profile online writing device 10 is used to prepare a Bragg grating and a chirped grating, and the performances of the Bragg grating and the chirped grating prepared by a conventional writing device are compared. Figure 2 and Figure 3 shown.

[0053] Figure 3 The comparison diagram of the Bragg gratings prepared by the embodiment of the present invention and the conventional device is shown in FIG. Figure 3 As shown, the Bragg grating length engraved without the high-quality grating spectral shape online writing device 10 in the embodiment of the present invention is 8 mm, the engraved grating center wavelength is 1550 nm, the 3dB bandwidth is 0.12 nm, and the reflectivity is -25 dB; the grating length engraved with the high-quality grating spectral shape online writing device 10 in the embodiment of the present invention is increased to 15 mm, the 3dB bandwidth is reduced to 0.06 nm, and the reflectivity is increased to -23 dB. The test results show that the embodiment of the present invention can further reduce the bandwidth of the Bragg grating under the same conditions, which is of great significance to improving the measurement accuracy of the grating center wavelength of the grating demodulation system.

[0054] Figure 4 is a comparison diagram of chirped gratings prepared using the embodiment of the present invention and a conventional device, as shown in FIG. Figure 4 As shown, the length of the chirped grating not engraved by the high-quality grating spectrum online writing device 10 in the embodiment of the present invention is 8 mm, the central wavelength of the engraved grating is 1550 nm, the 3dB bandwidth is 1.04 nm, and the reflectivity is -30 dB; the grating length of the high-quality grating spectrum online writing device 10 in the embodiment of the present invention is increased to 15 mm, the 3dB bandwidth is greatly increased to 5.4 nm, and the reflectivity is reduced to -41 dB. The test results show that the present invention can significantly increase the bandwidth of the chirped grating under the same conditions and improve the flatness of the spectrum, although it will reduce the grating reflection intensity. Considering that the detection limit of the existing grating demodulation technology is generally higher than -50 dB, the embodiment of the present invention can significantly improve the grating array in vibration sensing to resist the wavelength disturbance caused by temperature and stress changes, and provide the anti-interference and complex environment adaptability of the sensing system.

[0055] In summary, the high-quality grating spectrum online writing device 10 proposed in the embodiment of the present invention can meet different grating engraving requirements and improve the quality of the written grating.

[0056] Correspondingly, the embodiment of the present invention further provides a high-quality grating spectrum online writing method, which is applicable to the high-quality grating spectrum online writing device in any of the above embodiments, such as Figure 5 As shown, the high-quality grating spectrum online writing method includes: S501, controlling a high-power excimer laser to emit a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; S502, adjusting the area of ​​the single-pulse laser beam based on the aperture to obtain an adjusted beam; S503, expanding the adjustment light beam in the axial direction of the bare fiber based on the beam expansion lens group to obtain an optimized light beam; S504, masking the optimized light beam based on the phase mask template to obtain a target light beam irradiated onto the bare fiber, and performing grating writing based on the target light beam.

[0057] Specifically, a drawing tower system is used to keep the bare fiber in a stable, uniform motion state.

[0058] It should be noted that the high-quality grating spectrum online writing method provided in the above embodiment can realize the technical solution described in the above embodiment of the high-quality grating spectrum online writing device. The principles or specific implementation details of the above steps can be found in the corresponding contents in the above embodiment of the high-quality grating spectrum online writing device, which will not be described one by one here.

[0059] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware (such as a processor, a controller, etc.) through a computer program, and the computer program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0060] The above is a detailed introduction to a high-quality grating spectrum online writing device and method provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A high-quality grating spectrum online writing device, characterized in that: include: A high-power excimer laser, used for emitting a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; An aperture, used for adjusting the area of ​​the single-pulse laser beam to obtain an adjusted beam; A beam expansion lens group, used for expanding the adjusted light beam in the axial direction of the bare fiber to obtain an optimized light beam; The phase mask is used to mask the optimized light beam to obtain a target light beam irradiated onto the bare fiber, and the target light beam is used for grating writing.

2. The high-quality grating spectrum online writing device according to claim 1 is characterized in that: The beam expansion lens group comprises a concave cylindrical lens and a first convex cylindrical lens which are sequentially arranged along the direction from the aperture to the phase mask; The concave cylindrical lens is used to expand the adjustment light beam in the axial direction of the bare fiber to obtain an expanded light beam; The first convex cylindrical lens is used to focus the expanded light beam to obtain the optimized light beam.

3. The high-quality grating spectrum online writing device according to claim 2 is characterized in that: The beam expanding lens group further includes a second convex cylindrical lens disposed between the first convex cylindrical lens and the phase mask, and the second convex cylindrical lens is used to focus the optimized light beam in the radial direction of the bare fiber.

4. The high-quality grating spectrum online writing device according to claim 3 is characterized in that: The center of the aperture, the focus of the concave cylindrical lens, the focus of the first convex cylindrical lens and the focus of the second convex cylindrical lens are located on the same straight line and are perpendicular to the bare fiber.

5. The high-quality grating spectrum online writing device according to claim 4 is characterized in that: The focal length of the first convex cylindrical lens is equal to the distance between the first convex cylindrical lens and the concave cylindrical lens, and the phase mask is located at the focus of the second convex cylindrical lens.

6. The high-quality grating spectrum online writing device according to claim 1 is characterized in that: The single pulse energy of the high-power excimer laser is 60mJ-170mJ.

7. The high-quality grating spectrum online writing device according to claim 3 is characterized in that: The focal lengths of the concave cylindrical lens, the first convex cylindrical lens and the second convex cylindrical lens range from 50 mm to 1000 mm.

8. The high-quality grating spectrum online writing device according to claim 1 is characterized in that: The bare fiber moves at a uniform speed along the axial direction, and the distance between the phase mask and the bare fiber is 0.5m~1m.

9. The high-quality grating spectrum online writing device according to claim 1, characterized in that: The bare fiber is a single-mode fiber, a multi-mode fiber, a few-mode fiber or a thin-diameter fiber, and the phase mask template includes a uniform phase mask template and a chirped phase mask template.

10. A high-quality grating spectrum online writing method, characterized in that: The high-quality grating spectrum online writing device applicable to any one of claims 1 to 9, wherein the method comprises: Controlling the high-power excimer laser to emit a single pulse laser beam perpendicular to the axis of the bare fiber based on preset emission parameters; Adjusting the area of ​​the single-pulse laser beam based on an aperture to obtain an adjusted beam; Expanding the adjusted light beam in the axial direction of the bare fiber based on a beam expanding lens group to obtain an optimized light beam; The optimized light beam is masked based on a phase mask template to obtain a target light beam irradiated onto the bare fiber, and grating writing is performed based on the target light beam.

Images