WO2022001436A1 - Appareil d'inscription de réseau de fibres et procédé d'inscription de réseau de fibres - Google Patents

Appareil d'inscription de réseau de fibres et procédé d'inscription de réseau de fibres Download PDF

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Publication number
WO2022001436A1
WO2022001436A1 PCT/CN2021/094389 CN2021094389W WO2022001436A1 WO 2022001436 A1 WO2022001436 A1 WO 2022001436A1 CN 2021094389 W CN2021094389 W CN 2021094389W WO 2022001436 A1 WO2022001436 A1 WO 2022001436A1
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light sheet
light
optical fiber
fiber
generator
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PCT/CN2021/094389
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English (en)
Chinese (zh)
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张�林
贺梦霞
杨志群
王序涛
郭睿
周锐
郭强
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华为技术有限公司
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating

Definitions

  • the present application relates to the field of optical devices, and more particularly, to a fiber grating writing device and a fiber grating writing method.
  • Fiber grating is a passive optical device.
  • fiber grating has been widely studied and applied in the field of fiber optic communication and fiber optic sensing.
  • the resonant wavelength of fiber grating is sensitive to changes in external environment such as temperature, strain, refractive index, concentration, etc., and has the advantages of small size, low splice loss, full compatibility with optical fibers, and implantable smart materials.
  • the fiber grating is usually sensitive to the resonant wavelength of the optical signal to reflect or transmit light in a specific wavelength range, so as to realize a series of functions such as optical filtering and optical signal up/down site processing. .
  • the new space division multiplexing optical fiber communication system is expected to greatly increase the transmission and switching capacity.
  • the fiber grating can not only realize the traditional optical filtering function, but also use the phase matching principle to couple and convert the energy of the optical signal of different fiber modes, so it is expected to play an extremely important role in the new optical fiber communication system. effect. Therefore, fiber gratings have also received special attention in the above-mentioned space division multiplexing transmission technology field in recent years.
  • Common fiber gratings can be divided into short-period ( ⁇ 1 ⁇ m) fiber gratings and long-period ( ⁇ >1 ⁇ m) fiber gratings according to the characteristics of the period length.
  • the basic principle of making fiber gratings is to introduce an axial refractive index change in the fiber core through a specific writing method to make it periodically modulated.
  • the common writing methods mainly include mask-based UV exposure method and online point-by-point writing method based on carbon dioxide (CO2) laser.
  • the ultraviolet exposure method requires the use of an ultraviolet light source, and at the same time, the optical fiber core to be written is required to be a photosensitive material, and these requirements will increase the cost.
  • the online point-by-point writing method can avoid the above-mentioned cost problem and has greater flexibility, and the cross-section and length of the fiber grating can be arbitrarily designed and fabricated. With the realization of precise displacement control by various precision mobile platforms, the online point-by-point writing method for writing the long-period fiber grating is being used more and more.
  • the above-mentioned mainstream fiber grating writing schemes have higher writing costs and lower writing efficiency.
  • the present application provides a fiber grating writing device and a fiber grating writing method, which have higher stability and flexibility, and can greatly improve the writing efficiency.
  • a fiber grating writing device comprising at least one set of laser system and light sheet generation system, and a displacement stage, wherein the laser system is used for emitting light for writing; the light sheet generation system is used for passing the light To form a light sheet, the light sheet is a sheet-like light field, the thickness direction of the light sheet is along the axis of the optical fiber, and the plane formed by the width direction and the length direction of the light sheet is parallel to the radial cross section of the optical fiber; the displacement stage is used to load and Periodically move the fiber to expose the fiber to the light sheet to complete the grating writing of the fiber.
  • the fiber grating writing device of the first aspect includes a laser system, a light sheet generation system and a displacement stage. By forming a light sheet in space to expose the optical fiber periodically moving on the displacement stage, the writing of the fiber grating can be realized, and the writing can be greatly improved. efficient.
  • the optical sheet generation system realizes the writing of single-core or multi-core fiber gratings by changing the phase wavefront of the incident light, so that the light forms a non-diffraction slender beam at a preset position in space, that is, a sheet-like light field. , which can effectively improve the writing speed and writing accuracy, and at the same time, the stability and flexibility of the fiber grating writing device are also higher.
  • the light used for writing emitted by the laser system can be a laser or other types of light, such as incoherent light sources such as light emitting diode (LED) light sources, broad-spectrum light sources, and superradiant diodes.
  • the laser system of the present application may be a CO2 laser, or may be another type of laser capable of generating light for writing, such as an ultraviolet laser, etc., which is not limited in this application.
  • the fiber grating writing device may further include a control module for controlling the laser system to emit light, or controlling the light sheet generating system to form a light sheet, or controlling the stage to periodically move the optical fiber.
  • the control module can be used to control the incident power of the laser system, so as to control and change the energy of the light sheet to achieve efficient writing.
  • the control module may be used to control the light sheet generation system or components in the light sheet generation system to move appropriately to obtain a light sheet of the proper size in the proper position.
  • the control module can be used to control the movement of the displacement stage, so that the optical fiber loaded on the mobile stage can be properly translated, rotated or rolled, etc., so as to obtain a better writing effect.
  • the apparatus may comprise at least two sets of laser systems and light sheet generation systems, the at least two sets of laser systems and light sheet generation systems being arranged to uniformly surround the radial cross-section of the optical fiber.
  • multiple laser systems and optical sheet generation systems are placed in different directions in the plane surrounding the radial cross-section of the optical fiber to write the optical fiber at the same time, which can ensure that the radial cross-section of the optical fiber is irradiated with uniform energy, and can Improve writing efficiency and performance.
  • the device further includes a beam splitter and a reflection element, and the light sheet formed by the light sheet generation system is divided into multiple beams by the beam splitter and then reflected to the optical fiber by the reflection element.
  • a beam splitter is placed behind the laser system and the light sheet generator, and is reflected by the reflective element into multiple light sheets to write on the optical fiber at the same time, so as to ensure uniform energy irradiated on the radial cross-section of the optical fiber, which can improve the Writing efficiency and performance.
  • the light sheet generation system includes at least one light sheet generator, the light sheet generator is based on a metasurface structure, the metasurface structure includes a plurality of units, each unit includes a substrate and a micro/nano The light emitted by the laser system is incident on the substrate and then undergoes phase modulation of the micro-nano structure to form a light sheet.
  • using the metasurface structure to generate light sheets is simple, efficient, and easy to implement and control.
  • the material of the micro-nano structure may include at least one of silicon, silicon nitride, germanium, titanium dioxide, quartz glass, gold, silver, copper, liquid crystal, indium tin oxide or lithium niobate.
  • the light sheet generating system may include at least one light sheet generator, and the light sheet generator is a conical light sheet generator or a triangular prism light sheet generator.
  • the conical light sheet generator can irradiate multiple fiber cores on one path at a time, and the writing effect on the multi-core optical fiber whose cores are linearly arranged is better.
  • the triangular prism-shaped light sheet generator can generate a flat beam, and has good writing effect on the linearly arranged multi-core optical fiber and the non-linearly arranged multi-core optical fiber.
  • the light sheet generating system includes at least one light sheet generator, and the light sheet generator may be diffractive optical elements (diffractive optical elements, DOE).
  • the DOE does not need to accumulate the optical path difference through the thickness of the device, and the thickness is relatively thin, which is beneficial to the miniaturization of the fiber grating writing device.
  • the material of the light sheet generator includes at least one of silicon, silicon nitride, germanium, titanium dioxide, quartz glass, liquid crystal, indium tin oxide or lithium niobate.
  • the light sheet generation system includes at least three light sheet generators, and the at least three light sheet generators are arranged in series in cascade, including a movable first light sheet generator, The second light sheet generator with a fixed position and the third light sheet generator with a fixed position, the light is incident from the bottom surface of the first light sheet generator, and is incident on the second light sheet generator after passing through the first light sheet generator.
  • the bottom surface of the second light sheet generator is disposed opposite to the bottom surface of the third light sheet generator, so that light exits from the second light sheet generator in parallel and enters the third light sheet generator in parallel.
  • This possible implementation can arbitrarily adjust the position and size of the optical fiber irradiated by the light sheet, so that the fiber grating writing device can be adapted to a single-core optical fiber or a multi-core optical fiber, thereby realizing flexible writing.
  • the light sheet generating system includes at least two light sheet generators, the at least two light sheet generators are cascaded in parallel, and each light sheet generator forms an independent light sheet .
  • This possible implementation manner can realize the writing of multiple fiber grating periods at a time, so the writing efficiency can be greatly improved.
  • the fiber grating writing device may further include an inverted telescope system located behind the light sheet generating system on the optical path.
  • the inverted telescope system may include a first lens and a second lens, the right focus of the first lens being coincident with the left focus of the second lens.
  • the optical fibers may be single-mode optical fibers, few-mode optical fibers, multi-mode optical fibers, super-mode optical fibers, or multi-core few-mode optical fibers.
  • the refractive index distribution of the core region of the optical fiber after grating writing can be a step-type distribution, a multi-step-type distribution, a gradient-type distribution or a groove-type gradient-type distribution.
  • the optical fiber grating writing device of the present application is applicable to the refractive index distribution and core arrangement of various optical fiber core regions, and can achieve efficient writing.
  • a fiber grating writing method is performed by a fiber grating writing device, the device includes at least one group of a laser system, a light sheet generation system, and a displacement stage, and the method includes: controlling the laser system to emit light for writing; Pass the light through the light sheet generation system and form a light sheet.
  • the light sheet is a sheet-like light field.
  • the thickness direction of the light sheet is along the axis of the optical fiber.
  • the plane formed by the width direction and the length direction of the light sheet is parallel to the radial cross section of the optical fiber. ; Control the stage to move the fiber periodically, so that the fiber is exposed under the light sheet to complete the grating writing of the fiber.
  • a computer-readable medium for storing a computer program comprising instructions for performing the method of the second aspect.
  • FIG. 1 is a schematic diagram of fiber grating writing by ultraviolet exposure method.
  • FIG. 2 is a schematic diagram of fiber grating writing by an online point-by-point writing method.
  • FIG. 3 is a schematic diagram of fiber grating writing by CO2 laser multi-directional writing method.
  • FIG. 4 is a schematic structural diagram of a fiber grating writing device according to an embodiment of the present application.
  • FIG. 5 is a schematic flowchart of a method for writing a fiber grating according to an embodiment of the present application.
  • FIG. 6 is a schematic diagram of the refractive index profile of the core region.
  • FIG. 7 is a schematic diagram of various core arrangements of a multi-core optical fiber.
  • Figure 8 is a schematic diagram of a radial cross-section of an element of a fiber grating inscription package surrounding an optical fiber.
  • FIG. 9 is a partially enlarged schematic diagram of the optical sheet generator based on the metasurface structure of the present application for writing fiber gratings.
  • FIG. 10 is a schematic diagram of a metasurface structure according to an embodiment of the present application.
  • FIG. 11 is a schematic diagram of one unit of a metasurface structure according to an embodiment of the present application.
  • FIG. 12 is a schematic diagram of the principle of light propagation with ordinary surface structures and light propagation with metasurface structures.
  • Figure 13 is a schematic diagram of the phases that the metasurface structure needs to satisfy.
  • FIG. 14 is a schematic diagram of light energy distribution of a light sheet formed by light passing through a metasurface structure in an embodiment of the present application.
  • FIG. 15 is a schematic diagram of writing a fiber grating by generating a light sheet by a conical light sheet generator according to an embodiment of the present application.
  • FIG. 16 is a schematic diagram of writing a fiber grating by generating a light sheet by a triangular prism-shaped light sheet generator according to an embodiment of the present application.
  • FIG. 17 is a side view of the triangular prism-shaped light sheet generator corresponding to FIG. 16 .
  • FIG. 18 is a schematic diagram of the formation method of the cone-shaped light sheet generator and the triangular prism-shaped light sheet generator.
  • FIG. 19 is a schematic diagram of design parameters of a conical light sheet generator according to an embodiment of the present application.
  • FIG. 20 is a schematic structural diagram of a diffractive optical element (diffractive optical elements, DOE) according to an embodiment of the present application.
  • DOE diffractive optical elements
  • Figure 21 is a schematic diagram of a light sheet generation system comprising at least three light sheet generators arranged in series cascade.
  • Figure 22 is a schematic diagram of a light sheet generation system comprising at least two light sheet generators arranged in parallel cascade.
  • 23 is a schematic diagram of a combined design of a light sheet generation system and an inverted telescope system according to an embodiment of the present application.
  • the mask-based UV exposure method the CO2 laser-based online point-by-point writing method and the CO2 laser multi-directional writing method are briefly explained.
  • the ultraviolet exposure method uses an ultraviolet (ultra-violet, UV) light source and a specific exposure device to make two beams of ultraviolet light form periodic coherent fringes (coherent light); the core of the optical fiber to be written is made of photosensitive material; when the external coherent light is incident on When the fiber core is connected, its material properties change, resulting in periodic changes in the refractive index of the fiber core, thereby forming a fiber grating.
  • FIG. 1 is a schematic diagram of fiber grating writing by ultraviolet exposure method. As shown in Figure 1, incident ultraviolet (UV) light passes through a periodic phase mask (PM).
  • UV ultraviolet
  • PM periodic phase mask
  • the two beams of UV light interfere with each other on the fiber to form interference fringes for fiber grating writing.
  • the UV mirror can be rotated as shown in the figure. By adjusting the rotation of the two UV mirrors, the angle of the reflection of the two beams of UV light can be adjusted, thereby changing the spatial position of the interference light and other writing parameters.
  • the UV exposure method has some disadvantages, for example, it requires the core material of the optical fiber to be a photosensitive material, the processing process requires a mask, the writing is not flexible and expensive, and the thermal stability is poor.
  • the wavelength of UV light is short, and it is easy to diffract in the multi-core fiber, resulting in the weakening of the light intensity, which is not conducive to the writing of the multi-core fiber grating.
  • FIG. 2 is a schematic diagram of fiber grating writing by an online point-by-point writing method.
  • the writing device of the online point-by-point writing method is composed of a computer, a CO2 laser, a lens and a displacement stage.
  • the CO2 laser is controlled by the computer to turn on, and the light emitted by the CO2 laser is focused by the lens during the propagation process, forming a light spot in space, and the light spot is irradiated on the core of the optical fiber on the displacement stage. Since heat is generated when the laser is irradiated, the refractive index of the core of the optical fiber can be changed based on the thermal effect.
  • the optical fiber placed on the stage is controlled by the stage to move (for example, moving at a constant speed), so as to realize online writing and period control of the fiber grating.
  • the on-line point-by-point writing method uses the method of focusing the laser to write. Due to the limitation of the spot size, only one core of the fiber can be written at the same time. For multi-core optical fibers, this method cannot realize multi-core writing at the same time, and the writing efficiency of fiber grating is low.
  • FIG. 3 is a schematic diagram of fiber grating writing by CO2 laser multi-directional writing method.
  • the writing device of the CO2 laser multidirectional writing method is composed of a CO2 laser (CO2laser), a cylindrical lens (for example, a zinc selenide cylindrical lens, ZnSe cylindrical lens) and a reflector.
  • CO2 laser CO2laser
  • cylindrical lens for example, a zinc selenide cylindrical lens, ZnSe cylindrical lens
  • the light emitted by the CO2 laser is focused by a cylindrical lens, and then reflected to different parts of the fiber to be written after passing through a reflective element that is symmetrical up and down. Due to the thermal effect, the refractive index of the core of the optical fiber is changed, and the writing of the fiber grating is completed.
  • the fiber can be irradiated with laser light in all directions (the left, upper right and lower right of the fiber), so the received light is relatively uniform, which can improve the writing quality of the fiber grating.
  • the fiber In order to ensure that all directions of the fiber can be irradiated by the laser, the fiber needs to be placed in a relatively precise position. When the optical fiber is too close or too far from the reflective element, part of the light reflected by the reflective element cannot illuminate the surface of the optical fiber, which will reduce the writing effect. By appropriately increasing the width of the incident light, the position requirements of the optical fiber can be relaxed accordingly, but the energy of the incident light will also be wasted.
  • the CO2 laser multi-directional writing method is currently mainly used for writing on traditional single-core fibers. If it is used in a new type of multi-core fiber, when writing the core arranged in the center of the multi-core fiber, it may have an inevitable impact on other surrounding cores, resulting in the output fiber grating completely unable to achieve the expected function.
  • the above-mentioned writing schemes are mainly for traditional single-mode single-core fibers.
  • the above-mentioned writing schemes all have the problem of low efficiency. .
  • high cost and poor performance are also problems that need to be solved urgently.
  • the present application proposes a brand-new writing method based on optical sheets, which can be considered as an improved on-line point-by-point writing method.
  • FIG. 4 is a schematic structural diagram of a fiber grating writing device 400 according to an embodiment of the present application. As shown in FIG. 4 , the fiber grating writing device 400 includes at least one group of laser systems 410 and light sheet generation systems 420 , and a displacement stage 430 .
  • the laser system 410 is used to emit light for writing; the light sheet generation system 420 is used to pass the light to form a light sheet, the light sheet is a sheet-like light field, the thickness direction of the light sheet is along the axis of the optical fiber, and the width of the light sheet is The plane formed by the direction and the length direction is parallel to the radial cross section of the optical fiber; the displacement stage 430 is used to load and periodically move the optical fiber to expose the optical fiber under the light sheet to complete the grating writing of the optical fiber.
  • the light used for writing emitted by the laser system can be a laser or other types of light, such as incoherent light sources such as light emitting diode (LED) light sources, broad-spectrum light sources, and superradiant diodes.
  • LED light emitting diode
  • the fiber grating writing device includes a laser system, a light sheet generation system and a displacement stage. By forming a light sheet in space to expose the periodically moving optical fiber on the displacement stage, the writing of the fiber grating can be realized, and the writing can be greatly improved. efficient.
  • the optical sheet generation system of the present application realizes the generation of single-core or multi-core fiber gratings by changing the phase wavefront of the incident light, so that the light forms a non-diffraction slender beam at a preset position in space, that is, a sheet-like light field.
  • Writing can effectively improve the writing speed and writing accuracy, and at the same time, the stability and flexibility of the fiber grating writing device are also higher.
  • the laser system of the present application may be a CO2 laser, or may be other types of lasers capable of generating light for writing, such as an ultraviolet laser, etc., which is not limited in the present application.
  • the fiber grating writing device 400 may further include a control module 440 for controlling the laser system 410 to emit light, or controlling the light sheet generating system 420 to form a light sheet, or controlling the stage 430 to periodically move the optical fiber .
  • the control module 440 can be used to control the incident power of the laser system 410, so as to control and change the energy of the light sheet to achieve efficient writing.
  • the control module 440 can be used to control the light sheet generation system 420 or components in the light sheet generation system 420 to move appropriately to obtain a light sheet of the proper size in the proper position.
  • the control module 440 can be used to control the movement of the stage 430, so that the fiber loaded on the stage can be properly translated (translation along the axis of the fiber or up/down/left/in a plane parallel to the radial cross-section of the fiber). right/oblique translation, etc.), rotation or scrolling, etc., to get a better engraving effect.
  • the stage 430 can move the optical fiber according to a specific period (for example, a typical period is 100 nm ⁇ 1000 ⁇ m, and a typical step distance of the stage can be 1 ⁇ m, for example.
  • Fig. 5 is a schematic flow chart of a method 500 for writing a fiber grating according to an embodiment of the present application.
  • the fiber grating writing method 500 is performed by a fiber grating writing apparatus, which includes at least one set of a laser system and a light sheet generation system, and a translation stage.
  • the fiber grating writing method 500 may include: S510, controlling the laser system to emit light for writing; S520, making the light pass through the light sheet generating system to form a light sheet, the light sheet is a sheet-like light field, and the thickness direction of the light sheet is along the length of the optical fiber.
  • the plane formed by the width direction and the length direction of the light sheet is parallel to the radial cross section of the optical fiber; S530, control the displacement stage to move the optical fiber periodically, so that the optical fiber is exposed under the light sheet to complete the grating writing of the optical fiber.
  • the above writing operation of the fiber grating can be performed at the same time as the optical fiber is drawn, and can also be performed after the optical fiber is drawn and before the coating.
  • the light emitted by the laser system passes through the light sheet generation system to form a sheet-like beam, the beam passes through the optical fiber, exposes for a certain period of time, continues to move and exposes the next point, and repeats until the writing of the entire fiber grating is completed.
  • the refractive index distribution of the core region of the optical fiber after the fiber grating is written may be a step-type distribution, a multi-step-type distribution, a gradient-type distribution, or a groove-type gradient-type distribution.
  • FIG. 6 is a schematic diagram of the refractive index profile of the core region.
  • the fiber grating writing device and method of the present application can be applied to single-core fibers, such as single-mode fibers (with a core diameter of about 9 ⁇ m), few-mode fibers (with a core diameter of about 10-50 ⁇ m), Multimode fiber (core diameter greater than 50 ⁇ m) or supermode fiber with larger diameter.
  • the fiber grating writing device of the present application can also be applied to multi-core optical fibers, such as multi-core few-mode optical fibers (the diameter of the core region can reach several hundreds of microns).
  • FIG. 7 is a schematic diagram of various core arrangements of a multi-core optical fiber.
  • the fiber grating writing device and method of the present application can be applied to the case of the refractive index distribution of the core region shown in FIG. 6 and the arrangement of the fiber core shown in FIG. 7 . It is worth noting that FIG. 6 and FIG. 7 show only some examples of fiber design. For the refractive index distribution and core arrangement of other fiber core regions, the fiber grating writing device and method proposed in this application are also applicable. , and can achieve efficient writing.
  • light sheets can be generated in different directions around the radial cross-section of the optical fiber, and the optical fiber can be written at the same time, which can ensure that the radial cross-section of the optical fiber is irradiated with uniform energy, and can improve the writing efficiency and performance.
  • the fiber grating writing apparatus may include at least two sets of laser systems and light sheet generation systems arranged to uniformly surround the radial cross-section of the optical fiber.
  • a in FIG. 8 is a schematic diagram of a radial cross-section of three sets of laser systems and light sheet generation systems uniformly surrounding the fiber. Placing multiple laser systems (such as CO2 lasers) and light sheet generation systems in different directions in the plane surrounding the radial cross-section of the optical fiber to write on the optical fiber at the same time can ensure that the radial cross-section of the optical fiber is irradiated with uniform energy, which can improve writing Efficiency and performance.
  • the optical fiber grating writing device may further include a beam splitter and a reflection element, and the light sheet formed by the light sheet generating system is divided into multiple beams by the beam splitter and then reflected to the optical fiber by the reflection element.
  • a fiber grating writing device may include a set of laser systems and light sheet generation systems, several beam splitters and several reflective elements. After passing through the beam splitter and the reflective element, the positions of the light sheets are uniformly arranged in the radial cross section of the surrounding optical fiber.
  • B in Figure 8 is a schematic diagram of a radial cross-section of a set of laser systems and light sheet generation systems, beam splitters, and reflective elements surrounding the fiber.
  • a one-to-three beam splitter is placed behind the laser system and the light sheet generator, and multiple light sheets, such as three light sheets, are reflected from two reflective elements (eg, adjustable mirrors), reflective element 1 and reflective element 2.
  • the chip writes the optical fiber to ensure that the radial cross-section of the optical fiber is irradiated with uniform energy, which can improve the writing efficiency and performance. It should be understood that the number of the above-mentioned light sheets is only an example and not a limitation.
  • the refractive index change rate of the core region required to write a fiber grating on a single-mode fiber using a CO2 laser generally does not exceed the order of 10-3.
  • the required refractive index change rate will be lower, generally much less than the order of 10-3.
  • the radial cross-sectional area of the new fiber is also larger than that of the single-mode fiber (such as the radial diameter of the 19-core 6-mode fiber).
  • the cross-sectional area is about 100 times the radial cross-sectional area of a single-mode fiber), and the laser energy acting on a unit radial cross-section may be reduced accordingly.
  • the fiber grating writing device and method of the present application can provide the required refractive index change rate of the fiber core.
  • the specific design can achieve the required amount of refractive index change by appropriately increasing the axial stress of the fiber and the writing time, combined with the increase in the power of the laser system.
  • the China Academy of Launch Vehicle Technology has installed a 1kW CO2 laser marking machine.
  • a light sheet generation system may include at least one light sheet generator based on a metasurface structure, the metasurface structure may include a plurality of units, each unit including a substrate and a micro/nano The light emitted by the laser system is incident on the substrate and then undergoes phase modulation of the micro-nano structure to form a light sheet.
  • FIG. 9 is a partially enlarged schematic diagram of the optical sheet generator based on the metasurface structure of the present application for writing fiber gratings.
  • the light emitted by the laser system is incident from the substrate of the metasurface structure, and forms a sheet-like light field (light sheet) through the phase control of the micro-nano structures on the metasurface substrate.
  • the formed light sheet is in the y-z plane, the x direction is defined as the thickness of the light sheet, the y direction is defined as the width of the light sheet, and the z direction is defined as the length of the light sheet.
  • the optical fiber is placed in the x-y plane, which is orthogonal to the position of the light sheet, and the writing of the fiber grating is carried out.
  • FIG. 10 is a schematic diagram of a metasurface structure according to an embodiment of the present application.
  • the metasurface structure is a two-dimensional structure that can arbitrarily control the wavefront of the beam.
  • a two-dimensional structure is called a two-dimensional structure because of its small and uniform size in the height direction, so people usually think of it as a planar structure.
  • the metasurface structure may include a plurality of units, and each unit includes two parts, a substrate and a micro/nano structure placed on the substrate. Multiple units are closely arranged to form metasurface structures.
  • FIG. 11 is a schematic diagram of one unit of a metasurface structure according to an embodiment of the present application.
  • the micro-nano structure is also called sub-wavelength structure.
  • the so-called sub-wavelength means that each dimension of the structure is smaller than the wavelength of the incident light.
  • subwavelength means dimensions in the micrometer or nanometer scale.
  • the substrate plays a supporting role, and the material of the substrate can be selected from a material that does not absorb the wavelength of the working laser.
  • the micro-nano structure can be a columnar or column-like structure.
  • the micro-nano structure can be used but not limited to various structures such as cubic column, cylinder, elliptical column, layer, strip, cross, letter, etc.
  • the aforementioned structures of the structures may be the same or different.
  • Micro-nano structures are often made of high-refractive-index materials, such as but not limited to dielectric materials such as silicon (Si), silicon nitride (SiN), germanium (Ge), titanium dioxide (TiO2), quartz glass (SiO2), gold ( Au), silver (Ag), copper (Cu) and other noble metals, and at least one of liquid crystal, indium tin oxide (ITO), lithium niobate and other tunable materials.
  • dielectric materials such as silicon (Si), silicon nitride (SiN), germanium (Ge), titanium dioxide (TiO2), quartz glass (SiO2), gold ( Au), silver (Ag), copper (Cu) and other noble metals
  • ITO indium tin oxide
  • lithium niobate lithium niobate and other tunable materials.
  • FIG. 12 is a schematic diagram of the principle of light propagation with ordinary surface structures and light propagation with metasurface structures.
  • a in FIG. 12 is a schematic diagram of the principle of light propagation of ordinary surface structure; B, C and D are schematic schematic diagrams of the principle of light propagation of metasurface structure.
  • the parallel lines (or curves) in the figure represent the wavefront, the arrows represent the direction of the wave vector, and the direction of the wave vector and the wavefront are perpendicular to each other. in the air.
  • the surface in A in Figure 12 is a common surface structure, which can be understood as a parallel flat plate formed by a medium such as glass or water. According to the principle of optical propagation, light incident on a vertical surface will exit the vertical surface.
  • the metasurface structure when the selected size of the micro-nano structure enables the wavefront to be transformed into a spherical surface, the metasurface structure can form a metasurface lens to realize the focusing function of the lens.
  • the wavefront that the light sheet generator needs to form is two columns of symmetrical inclined planes. As shown in D of FIG. 12 , when the selected micro-nano structure size makes the wavefront two-column symmetrical inclined planes, the light can form a light sheet through the metasurface structure, which can be used for the fiber grating writing proposed in this application. in the device.
  • Figure 13 is a schematic diagram of the phases that the metasurface structure needs to satisfy.
  • the metasurface structure needs to satisfy the phase shown in Figure 13; and the structure can be repeatedly arranged in the y-direction to form a light sheet.
  • DA represents the thickness of the formed light sheet, which is along the x direction, the light sheet extends in the y direction, and ⁇ represents the angle between the wavefront and the normal.
  • the metasurface structure can be regarded as a plane structure, it can be designed using the following formula (1):
  • D represents the aperture of the metasurface structure
  • ⁇ represents the inclination angle of the wavefront, that is, the angle between the wavefront and the normal direction of the substrate of the metasurface structure
  • ⁇ represents the wavelength of the light generated by the laser system, where 10.6 ⁇ m will be described as an example.
  • a suitable micro-nano structure can be selected to design the light sheet generator, wherein the structure shown in FIG. 11 can be used as a unit here.
  • the thickness DA of the optical sheet should be smaller than the period of the fiber grating (for example, the period of the long-period fiber grating is about 100-1000 ⁇ m), for example, a critical value can be taken, that is, the thickness DA of the optical sheet is 100 ⁇ m.
  • the calculation can obtain that the inclination angle ⁇ of the beam wavefront is 4.642 degrees.
  • the aperture D of the metasurface structure and the diffraction-free transmission distance of the light sheet (the usable distance of the light sheet in the z-axis direction) Z max can also be obtained based on formula (1).
  • the metasurface structure is symmetrical about the origin in the x-direction, and on the same side of the origin, the micro-nano structures are periodically arranged. Therefore, as long as the design of one period group (for example, the first period group on the left) is completed, a complete design in the x-direction can be obtained by repeated arrangement and symmetry, and a complete device can be obtained by repeated arrangement in the y-direction.
  • the optimal size of each unit can be designed to be smaller than the vacuum wavelength ⁇ 0 . Therefore, the height of the micro-nano structure is usually in the range of 0.3 ⁇ 0 to 2 ⁇ 0 . If the micro-nano structure is too high, a higher aspect ratio (the ratio of the height to the width of the micro-nano structure) is required, which is unfavorable for processing; if the micro-nano structure is too short, it is difficult to cover a large phase range, and it is difficult to meet the design requirements.
  • D can take any size, usually in the order of millimeters (mm), and ⁇ can take any angle (preferably, 10-80 degrees can be selected).
  • the use of this metasurface structure can generate beam lengths within the mm order and spot radii close to the diffraction limit.
  • the period of the micro-nano structure should be about 130 ⁇ m, that is, a phase change of 2 ⁇ is introduced every 130 ⁇ m.
  • the 130 ⁇ m can be divided into 26 units, and the period of each unit is 5 ⁇ m, and the phase change introduced by it should satisfy the curve shown in FIG. 13 .
  • the substrate of the metasurface structure and the material of the micro-nano structure can be selected as BaF2 and Ge respectively, and other materials suitable for this wavelength can also be selected but are not limited to, such as Si.
  • the thickness of the substrate can be 500 ⁇ m, and the bottom surface can be a square with a length of 5 ⁇ m; the micro-nano structure placed on the substrate can be a cuboid with a square bottom surface, the height is 1 ⁇ m, and the bottom surface is square.
  • the length of the side can be selected differently according to different phase requirements.
  • phase introduced by the 26 units and the side lengths of the square bottom surface of the micro-nano structure meet the requirements shown in Table 1 below.
  • p represents the phase introduced by the micro-nano structure, the unit is degree;
  • l represents the side length of the bottom square of the micro-nano structure, the unit is ⁇ m.
  • Table 1 The side length of the bottom square of 26 micro-nano structures in one cycle and the phase introduced by the unit
  • FIG. 14 is a schematic diagram of light energy distribution of a light sheet formed by light passing through a metasurface structure in an embodiment of the present application.
  • the light energy distribution in the x-z plane which is a cross-section showing the thickness of the formed optical sheet, is shown by A in FIG. 14 .
  • B in FIG. 14 is the light energy distribution along the z-axis direction in all y-directions of A in FIG. 14 at the midpoint of the x-direction, which represents the width section of the light sheet along the y-direction.
  • the optical fiber formed by this scheme is used, and the optical fiber is placed in the high-brightness area of the light sheet on the x-y plane, which is placed orthogonally to the optical sheet, and the fiber grating is written.
  • 2V2/m2 is taken as the writing threshold
  • the thickness of the optical sheet is smaller than the writing period, and the side lobes will not adversely affect the writing process.
  • the width of the optical sheet is greater than 250 ⁇ m, which meets the requirements for writing fiber gratings, and can achieve efficient writing.
  • the incident power of the laser system can be adjusted to change the energy of the optical sheet to achieve efficient writing.
  • the light sheet generating system includes at least one light sheet generator, and the light sheet generator is a conical light sheet generator or a triangular prism light sheet generator.
  • the material of the light sheet generator may include at least one of silicon, silicon nitride, germanium, titanium dioxide, quartz glass, liquid crystal, indium tin oxide or lithium niobate, which is not limited in this application.
  • FIG. 15 is a schematic diagram of writing a fiber grating by generating a light sheet by a conical light sheet generator according to an embodiment of the present application.
  • a conical light sheet generator can generate an elongated light beam, which can also be considered a light sheet.
  • the plane of the light sheet is in the yz plane, and the x direction is perpendicular to the light sheet.
  • the light sheet in the x direction reflects its thickness.
  • the light spot of the light sheet in the y direction is small, that is, the light sheet is narrow in the y direction, and can be illuminated at one time. Multiple cores in one path.
  • the conical light sheet generator has a better writing effect on multi-core fibers with linearly arranged cores.
  • FIG. 16 is a schematic diagram of writing a fiber grating by generating a light sheet by a triangular prism-shaped light sheet generator according to an embodiment of the present application.
  • a triangular prism-shaped light sheet generator can be used to generate a flat beam.
  • the plane of the flat beam is in the yz plane, the x direction is perpendicular to the light sheet, and the light sheet in the x direction reflects its thickness, In this way, the cores at different positions can be irradiated at one time, and the writing efficiency will be greatly improved.
  • the triangular prism-shaped light sheet generator has good writing effect on the linearly arranged multi-core optical fiber and the non-linearly arranged multi-core optical fiber.
  • the power consumption of the triangular prism light sheet generator is slightly larger than that of the conical light sheet generator.
  • FIG. 17 is a side view of the triangular prism-shaped light sheet generator corresponding to FIG. 16 . Since the generated light sheet extends in the y direction in FIG. 17 , it is indicated by an ellipsis in FIG. 17 , DA is the thickness of the formed light sheet, W is the width of the light sheet, and Zmax is the non-diffraction transmission distance of the formed light sheet.
  • FIG. 18 is a schematic diagram of the formation method of the cone-shaped light sheet generator and the triangular prism-shaped light sheet generator.
  • the cross-sectional shapes of the light sheet generators used in FIGS. 15 and 16 are all triangular. The difference is that the conical light sheet generator in Figure 15 is obtained by rotating the cross-sectional triangle along the axis, while the triangular prism light sheet generator in Figure 16 is obtained by extending the cross-sectional triangle along the y direction, as shown in Figure 18 A and B shown separately.
  • the light beams obtained by the conical light sheet generator and the triangular prism light sheet generator are all axisymmetric light sheets.
  • the diffraction-free transmission distance Z max and the spot size D A generated by it can be expressed by the following formula 2 respectively.
  • FIG. 19 is a schematic diagram of design parameters of a conical light sheet generator according to an embodiment of the present application.
  • the shaded part represents the conical light sheet generator
  • D represents the aperture size of the conical light sheet generator.
  • the above formula is derived when the light fills the entire aperture. Therefore, D can also be considered as the diameter of the incident light
  • n represents the material refractive index of the conical light sheet generator
  • ⁇ represents the base angle (in radians) of the conical light sheet generator
  • Z max represents the Bessel spot
  • the length of that is, the "diffraction-free transmission distance"
  • D A represents the thickness of the light sheet (spot)
  • ⁇ represents the wavelength of the heat radiated light.
  • the wavelength of 10.6 ⁇ m is used as an example for description.
  • one irradiation can cover all the fiber cores, and the non-diffraction transmission distance Z max of the optical sheet is required to be greater than the cladding diameter of the fiber to be written.
  • the empirical parameters of general multi-core fibers are For example, it can be taken as 250 ⁇ m.
  • the width W of the incident light should also be larger than the cladding diameter (250 ⁇ m), and the light sheet diameter D A should be smaller than the period of the fiber grating.
  • the material of the cone-shaped light sheet generator can be selected as quartz glass, and the refractive index is 1.53.
  • the diameter of the cone-shaped light sheet generator should be 250 ⁇ m, and the bottom angle should be selected At this time, the width of the optical sheet is 250 ⁇ m, the non-diffraction transmission distance is 751 ⁇ m, and the minimum radius of the optical sheet is about 10 ⁇ m.
  • the optical sheet can completely cover all the core sections and realize efficient and accurate writing.
  • the light sheet generation system includes at least one light sheet generator, which is a diffractive optical element (DOE).
  • DOE diffractive optical element
  • the material of the light sheet generator may include at least one of silicon, silicon nitride, germanium, titanium dioxide, quartz glass, liquid crystal, indium tin oxide or lithium niobate, which is not limited in this application.
  • FIG. 20 is a schematic structural diagram of a DOE according to an embodiment of the present application.
  • DOE employs photolithographic techniques to provide full phase control of transmitted light.
  • the DOE is composed of two symmetrical parts, which form a light sheet by diffracting the incident light to a fixed angle and constructively interfering at preset positions in space.
  • DOE does not need to accumulate optical path difference through the thickness of the device, and the thickness is thinner, which is conducive to the miniaturization of the fiber grating writing device.
  • the DOE acts as a light sheet generator, light is incident from above or below the DOE as shown in Figure 20.
  • the light sheet generation system may include at least three light sheet generators, and the at least three light sheet generators are arranged in series in cascade, including a movable first light sheet generator, a fixed position The second light sheet generator and the fixed third light sheet generator, the light is incident from the bottom surface of the first light sheet generator, and then incident on the non-bottom surface of the second light sheet generator after passing through the first light sheet generator, The bottom surface of the second light sheet generator is disposed opposite to the bottom surface of the third light sheet generator, so that light exits from the second light sheet generator in parallel and enters the third light sheet generator in parallel.
  • the light sheet generating system of the present application may also include more combinations of light sheet generators with opposite bottom surfaces, similar to the second light sheet generator and the third light sheet generator, so that the optical fiber irradiated by the light sheet can be adjusted arbitrarily. location and size.
  • Figure 21 is a schematic diagram of a light sheet generation system comprising at least three light sheet generators arranged in series cascade.
  • the first three light sheet generators are taken as examples to illustrate the working principle of the light sheet generation system.
  • Three light sheet generators are cascaded in series, the first light sheet generator can be moved, and light is incident from its bottom surface.
  • the bottom surfaces of the second and third light sheet generators are opposite to the bottom surfaces to ensure that light can be parallel emitted from the second light sheet generator and parallel to the third light sheet generator, and the positions of the second and third light sheet generators are fixed. Later, if more light sheet generators are set, the propagation process repeats the foregoing process.
  • the optical sheet generation system can make the fiber grating writing device adapt to single-core optical fiber or multi-core optical fiber, so as to realize flexible writing.
  • the bottom surface of the light sheet generator can be understood as the side of the light sheet generator that receives incident light.
  • it can be the substrate side of the metasurface structure.
  • it may be the upper side or the lower side of the DOE shown in FIG. 20 .
  • the light sheet generation system may include at least two light sheet generators, the at least two light sheet generators are cascaded in parallel, and each light sheet generator forms an independent light sheet.
  • Figure 22 is a schematic diagram of a light sheet generation system comprising at least two light sheet generators arranged in parallel cascade.
  • the light sheet generation system uses multiple light sheet generators that can simultaneously generate multiple light sheets periodically arranged along the fiber axis, that is, along the x-direction, ie, multiple light sheet generators that generate a single light sheet
  • the devices are cascaded in parallel.
  • the shaded area represents multiple light sheet generators, which can be cascaded in parallel to form multiple independently distributed light sheets.
  • the light sheet represents its thickness in the x-direction, and extends the width W in the y-direction.
  • the fiber grating writing device may further include an inverted telescope system located behind the light sheet generation system in the optical path.
  • FIG. 23 is a schematic diagram of a combined design of a light sheet generation system and an inverted telescope system according to an embodiment of the present application.
  • the length of the sheet of light (diffraction-free transmission distance) Z max and the average thickness of the light sheet and the light sheet generator corner size is related to the smaller base angle, the greater the Z max, DA The larger it is, it is unfavorable for FBG writing. Therefore, some embodiments of the present application propose a solution as shown in FIG. 23 , in which an inverted telephoto system is added after the light sheet generation system, and the non-diffraction transmission distance Z max and the thickness of the light sheet can be adjusted arbitrarily.
  • the inverted telescope system may include a first lens and a second lens, the right focus of the first lens being coincident with the left focus of the second lens.
  • the inverted telescope system can be composed of two lenses, which can use conventional lenses or metasurface-based metalens.
  • the focal length of the first lens is f1
  • the focal length of the second lens is f2
  • the right focus of the first lens is coincident with the left focus of the second lens.
  • formula (1) can be transformed into formula (3) in the following form.
  • the inverted telescope system may also have other structures, which are not limited in this application.
  • the present application also provides a computer-readable medium for storing a computer program, the computer program including instructions for executing the foregoing grating optical fiber writing method.
  • the disclosed system, apparatus and method may be implemented in other manners.
  • the apparatus embodiments described above are only illustrative.
  • the division of the units is only a logical function division. In actual implementation, there may be other division methods.
  • multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not implemented.
  • the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of devices or units, and may be in electrical, mechanical or other forms.
  • the units described as separate components may or may not be physically separated, and components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment.
  • each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit.
  • the functions, if implemented in the form of software functional units and sold or used as independent products, may be stored in a computer-readable storage medium.
  • the technical solution of the present application can be embodied in the form of a software product in essence, or the part that contributes to the prior art or the part of the technical solution.
  • the computer software product is stored in a storage medium, including Several instructions are used to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application.
  • the aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), magnetic disk or optical disk and other media that can store program codes .

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  • General Physics & Mathematics (AREA)
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  • Manufacturing & Machinery (AREA)
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Abstract

Appareil d'inscription de réseau de fibres (400) et procédé d'inscription de réseau de fibres. L'appareil d'inscription de réseau de fibres (400) comprend au moins un ensemble d'un système laser (410) et d'un système de génération de feuille de lumière (420), et un étage de translation (430). Le système laser (410) est utilisé pour émettre de la lumière aux fins d'une inscription ; le système de génération de feuille de lumière (420) est utilisé pour permettre à la lumière de passer afin de former une feuille de lumière ; la feuille de lumière est un champ lumineux de type feuille ; le sens de l'épaisseur de la feuille de lumière est dans la direction axiale d'une fibre optique ; un plan formé par le sens de la largeur et le sens de la longueur de la feuille de lumière est parallèle à une section transversale radiale de la fibre optique ; et l'étage de translation (430) est utilisé pour charger et périodiquement déplacer la fibre optique, de telle sorte que la fibre optique est exposée sous la feuille de lumière pour exécuter l'inscription de réseau de la fibre optique. Au moyen de l'appareil d'inscription de réseau de fibres (400), une feuille de lumière est formée dans l'espace pour exposer une fibre optique qui se déplace périodiquement sur l'étage de translation (430), de telle sorte que l'inscription d'un réseau de fibres peut être exécutée, et l'efficacité d'inscription peut être considérablement améliorée.
PCT/CN2021/094389 2020-06-30 2021-05-18 Appareil d'inscription de réseau de fibres et procédé d'inscription de réseau de fibres WO2022001436A1 (fr)

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