WO2022001436A1 - Fiber grating inscribing apparatus and fiber grating inscribing method - Google Patents
Fiber grating inscribing apparatus and fiber grating inscribing method Download PDFInfo
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- 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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- 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
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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
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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Abstract
A fiber grating inscribing apparatus (400) and a fiber grating inscribing method. The fiber grating inscribing apparatus (400) comprises at least one set of a laser system (410) and a light sheet generation system (420), and a translation stage (430). The laser system (410) is used for emitting light for inscribing; the light sheet generation system (420) is used for allowing light to pass to form a light sheet; the light sheet is a sheet-like light field; the thickness direction of the light sheet is in the axial direction of an optical fiber; a plane formed by the width direction and length direction of the light sheet is parallel to a radial cross section of the optical fiber; and the translation stage (430) is used for loading and periodically moving the optical fiber, such that the optical fiber is exposed under the light sheet to complete the grating inscribing of the optical fiber. By means of the fiber grating inscribing apparatus (400), a light sheet is formed in the space to expose an optical fiber that periodically moves on the translation stage (430), such that the inscribing of a fiber grating can be realized, and the inscribing efficiency can be greatly improved.
Description
本申请要求于2020年6月30日提交中国国家知识产权局、申请号为202010608570.4、申请名称为“光纤光栅刻写装置和光纤光栅刻写方法”的中国专利申请的优先权,其全部内容通过引用结合在本申请中。This application claims the priority of the Chinese patent application filed on June 30, 2020, with the application number 202010608570.4 and the application name "Fiber grating writing device and fiber grating writing method", the entire contents of which are incorporated by reference in this application.
本申请涉及光学器件领域,更具体地,涉及一种光纤光栅刻写装置和光纤光栅刻写方法。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.
光纤光栅是一种无源光学器件,近年来光纤光栅在光纤通信和光纤传感领域得到了广泛地研究和应用。光纤光栅的谐振波长对温度、应变、折射率、浓度等外界环境变化敏感,且具有体积小、熔接损耗低、全兼容于光纤、能植入智能材料等优点。在传统的单模光纤通信系统中,通常利用光纤光栅对光信号谐振波长敏感的特点,将特定波长范围的光进行反射或透射,从而实现光学滤波、光信号上/下站点处理等一系列功能。随着近年来多芯、少模和多芯少模等新型光纤技术的迅猛发展,相较于传统的光纤通信系统,新型的空分复用光纤通信系统有望大幅提升传输和交换的容量。光纤光栅在新型光纤通信系统中既可以实现传统的光学滤波功能,又能够利用相位匹配原理针对不同光纤模式的光信号进行能量的耦合和转换,因而其有望在新型光纤通信系统中起到极为关键的作用。因此,近年来光纤光栅在上述空分复用传输技术领域也受到了格外关注。Fiber grating is a passive optical device. In recent years, 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. In the traditional single-mode fiber communication system, 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. . With the rapid development of new optical fiber technologies such as multi-core, few-mode, and multi-core-few-mode in recent years, compared with the traditional optical fiber communication system, the new space division multiplexing optical fiber communication system is expected to greatly increase the transmission and switching capacity. In the new optical fiber communication system, 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.
常见的光纤光栅按照周期长度的特征通常可以分为短周期(Λ<1μm)光纤光栅和长周期(Λ>1μm)光纤光栅。制作光纤光栅的基本原理是通过特定的刻写方法在光纤纤芯引入轴向的折射率变化,使其发生周期性调制。对于长周期光纤光栅,常见的刻写方法主要有基于掩膜的紫外曝光法和基于二氧化碳(CO2)激光器的在线逐点写入法等。其中,紫外曝光法需要使用紫外光源,同时要求被刻写的光纤纤芯为光敏材料,这些要求会带来成本的增加。在线逐点写入法能够避免上述成本问题且具有较大的灵活性,对光纤光栅的截面和长度可以进行任意设计制作。随着当前各种精密移动平台对精准的位移控制的实现,在线逐点写入法刻写该长周期光纤光栅正在越来越多地被采用。上述主流的光纤光栅刻写方案刻写成本较高、刻写效率较低。Common fiber gratings can be divided into short-period (Λ<1 μm) fiber gratings and long-period (Λ>1 μm) 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. For long-period fiber gratings, the common writing methods mainly include mask-based UV exposure method and online point-by-point writing method based on carbon dioxide (CO2) laser. Among them, 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.
发明内容SUMMARY OF THE INVENTION
本申请提供一种光纤光栅刻写装置和光纤光栅刻写方法,稳定性及灵活性更高,且能够大幅提升刻写效率。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.
第一方面,提供了一种光纤光栅刻写装置,包括至少一组激光系统和光片生成系统,以及位移台,其中,激光系统用于发出用于刻写的光;光片生成系统用于使光通过以形成光片,光片为片状光场,光片的厚度方向沿光纤的轴向,光片的宽度方向和长度方向形成的平面与光纤的径向横截面平行;位移台用于装载并周期性移动光纤,使光纤曝光在光片下以完成光纤的光栅刻写。In a first aspect, a fiber grating writing device is provided, 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.
第一方面的光纤光栅刻写装置,包括激光系统、光片生成系统和位移台,通过在空间形 成光片对位移台上周期性移动的光纤进行曝光,可以实现光纤光栅的刻写,能够大幅提升刻写效率。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.
其中,光片生成系统通过改变入射光的相位波前,使光在空间的预设位置形成无衍射的细长的光束,即片状光场,来实现单芯或者多芯的光纤光栅的刻写,可以有效提升刻写速度和刻写精准度,同时光纤光栅刻写装置的稳定性及灵活性也更高。Among them, 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.
应理解,激光系统发出的用于刻写的光可以为激光,也可以为其他类型的光,例如发光二极管(light emitting diode,LED)光源、宽谱光源、超辐射二极管等非相干光源。本申请的激光系统可以是CO2激光器,也可以是能够产生用于刻写的光的其他类型的激光器,例如紫外激光器等,本申请对此不做限定。It should be understood that 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.
在第一方面的一种可能的实现方式中,光纤光栅刻写装置还可以包括控制模块,用于控制激光系统发出光,或控制光片生成系统形成光片,或控制位移台周期性移动光纤。控制模块可以用来控制激光系统的入射功率,从而控制改变光片的能量而实现高效刻写。控制模块可以用来控制光片生成系统或光片生成系统中的部件进行适当的移动,以在适当位置获得大小合适的光片。控制模块可以用来控制位移台的移动,使装载在移动台上的光纤适当的平移、转动或滚动等,来获得更好的刻写效果。In a possible implementation manner of the first aspect, 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.
在第一方面的一种可能的实现方式中,装置可以包括至少两组激光系统和光片生成系统,至少两组激光系统和光片生成系统被设置为均匀环绕光纤的径向横截面。本可能的实现方式中,在环绕光纤的径向横截面所在平面内不同方向放置多台激光系统和光片生成系统同时对光纤进行刻写,可以保证光纤径向横截面上被照射均匀的能量,能够提升刻写效率与性能。In a possible implementation of the first aspect, 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. In this possible implementation, 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.
在第一方面的一种可能的实现方式中,装置还包括分束器和反射元件,经光片生成系统形成的光片被分束器分为多束后被反射元件反射到光纤上。本可能的实现方式中,在激光系统和光片生成器后放置分束器,经反射元件反射成多个光片同时对光纤进行刻写,保证光纤径向横截面上被照射均匀的能量,能够提升刻写效率与性能。In a possible implementation manner of the first aspect, 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. In this possible implementation, 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.
在第一方面的一种可能的实现方式中,光片生成系统包括至少一个光片生成器,光片生成器基于超表面结构,超表面结构包括多个单元,每个单元包括基底和微纳结构,激光系统发出的光由基底入射后经过微纳结构的相位调控形成光片。本可能的实现方式中,利用超表面结构生成光片简单高效易于实现和控制。In a possible implementation manner of the first aspect, 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. In this possible implementation, using the metasurface structure to generate light sheets is simple, efficient, and easy to implement and control.
其中,微纳结构的材料可以包括硅、氮化硅、锗、二氧化钛、石英玻璃、金、银、铜、液晶、氧化铟锡或铌酸锂中的至少一种。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.
在第一方面的一种可能的实现方式中,光片生成系统可以包括至少一个光片生成器,光片生成器为圆锥状光片生成器或三棱柱状光片生成器。本可能的实现方式中,圆锥状光片生成器一次可以照射一条路径上的多条纤芯,对纤芯线性排列的多芯光纤的刻写效果较好。三棱柱状光片生成器可以产生一个平面状的光束,对纤芯线性排列的多芯光纤和非线性排列的多芯光纤的刻写效果均较好。In a possible implementation manner of the first aspect, 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. In this possible implementation manner, 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.
在第一方面的一种可能的实现方式中,光片生成系统包括至少一个光片生成器,光片生成器可以为衍射光学元件(diffractive optical elements,DOE)。本可能的实现方式中,DOE无需通过器件厚度积累光程差,厚度较薄,有利于光纤光栅刻写装置的小型化。In a possible implementation manner of the first aspect, 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). In this possible implementation manner, 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.
其中,光片生成器的材料包括硅、氮化硅、锗、二氧化钛、石英玻璃、液晶、氧化铟锡或铌酸锂中的至少一种。Wherein, 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.
在第一方面的一种可能的实现方式中,光片生成系统包括至少三个光片生成器,至少三个光片生成器串行级联设置,包括可移动的第一光片生成器、位置固定的第二光片生成器和 位置固定的第三光片生成器,光从第一光片生成器的底面入射,经第一光片生成器后入射到第二光片生成器的非底面上,第二光片生成器的底面与第三光片生成器的底面相对设置,使得光从第二光片生成器平行出射并平行入射第三光片生成器。本可能的实现方式可以任意调整光纤被光片照射的位置和大小,使得光纤光栅刻写装置能够适应于单芯光纤或多芯光纤,从而实现灵活刻写。In a possible implementation manner of the first aspect, 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. On the bottom surface, 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.
在第一方面的一种可能的实现方式中,光片生成系统包括至少两个光片生成器,至少两个光片生成器并行级联设置,每个光片生成器形成一个独立的光片。本可能的实现方式可以实现单次刻写多个光纤光栅周期,因此能大大能提高刻写效率。In a possible implementation manner of the first aspect, 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.
在第一方面的一种可能的实现方式中,光纤光栅刻写装置还可以包括在光路上位于光片生成系统之后的倒置望远镜系统。倒置望远镜系统可以包括第一透镜和第二透镜,第一透镜的右焦点与第二透镜的左焦点重合。本可能的实现方式可以任意调整光纤被光片照射的位置和大小,对于纤芯折射率变化的精确控制具有有益价值。In a possible implementation manner of the first aspect, 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. This possible implementation can arbitrarily adjust the position and size of the optical fiber irradiated by the light sheet, which has beneficial value for the precise control of the refractive index change of the fiber core.
应理解,光纤可以为单模光纤、少模光纤、多模光纤、超模光纤或多芯少模光纤。光栅刻写后光纤的纤芯区域的折射率分布可以为阶跃型分布、多阶跃型分布、渐变型分布或槽式渐变型分布。本申请的光纤光栅刻写装置对于各种光纤纤芯区域的折射率分布和纤芯排布情况均适用,并可以实现高效刻写。It should be understood that 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.
第二方面,提供了一种光纤光栅刻写方法,方法由光纤光栅刻写装置执行,装置包括至少一组激光系统和光片生成系统,以及位移台,方法包括:控制激光系统发出用于刻写的光;使光通过光片生成系统并形成光片,光片为片状光场,光片的厚度方向沿光纤的轴向,光片的宽度方向和长度方向形成的平面与光纤的径向横截面平行;控制位移台周期性移动光纤,使光纤曝光在光片下以完成光纤的光栅刻写。In a second aspect, a fiber grating writing method is provided, the 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.
第三方面,提供了一种计算机可读介质,用于存储计算机程序,该计算机程序包括用于执行第二方面的方法的指令。In a third aspect, a computer-readable medium is provided for storing a computer program comprising instructions for performing the method of the second aspect.
图1是通过紫外曝光法进行光纤光栅刻写的示意图。FIG. 1 is a schematic diagram of fiber grating writing by ultraviolet exposure method.
图2是通过在线逐点写入法进行光纤光栅刻写的示意图。FIG. 2 is a schematic diagram of fiber grating writing by an online point-by-point writing method.
图3是通过CO2激光器多方向刻写法进行光纤光栅刻写的示意图。FIG. 3 is a schematic diagram of fiber grating writing by CO2 laser multi-directional writing method.
图4是本申请的一个实施例的光纤光栅刻写装置的示意性结构图。FIG. 4 is a schematic structural diagram of a fiber grating writing device according to an embodiment of the present application.
图5是本申请的一个实施例的光纤光栅刻写方法的示意性流程图。FIG. 5 is a schematic flowchart of a method for writing a fiber grating according to an embodiment of the present application.
图6是纤芯区域的折射率分布的示意图。FIG. 6 is a schematic diagram of the refractive index profile of the core region.
图7是多芯光纤的各种纤芯排布情况的示意图。FIG. 7 is a schematic diagram of various core arrangements of a multi-core optical fiber.
图8是光纤光栅刻写装的元件环绕光纤的径向横截面的示意图。Figure 8 is a schematic diagram of a radial cross-section of an element of a fiber grating inscription package surrounding an optical fiber.
图9是本申请的基于超表面结构的光片生成器进行光纤光栅刻写的局部放大示意图。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.
图10是本申请的一个实施例的超表面结构的示意图。FIG. 10 is a schematic diagram of a metasurface structure according to an embodiment of the present application.
图11是本申请的一个实施例的超表面结构的一个单元的示意图。FIG. 11 is a schematic diagram of one unit of a metasurface structure according to an embodiment of the present application.
图12是普通表面结构光传播和超表面结构光传播的原理示意图。FIG. 12 is a schematic diagram of the principle of light propagation with ordinary surface structures and light propagation with metasurface structures.
图13是超表面结构需要满足的相位的示意图。Figure 13 is a schematic diagram of the phases that the metasurface structure needs to satisfy.
图14是本申请的一个实施例中光通过超表面结构形成的光片的光能分布的示意图。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.
图15是本申请的一个实施例的通过圆锥状光片生成器产生光片来刻写光纤光栅的示意图。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.
图16是本申请的一个实施例的通过三棱柱状光片生成器产生光片来刻写光纤光栅的示意图。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.
图17是对应于图16的三棱柱状光片生成器的侧视图。FIG. 17 is a side view of the triangular prism-shaped light sheet generator corresponding to FIG. 16 .
图18是圆锥状光片生成器和三棱柱状光片生成器的形成方式示意图。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.
图19是本申请的一个实施例的圆锥状光片生成器的设计参数示意图。FIG. 19 is a schematic diagram of design parameters of a conical light sheet generator according to an embodiment of the present application.
图20是本申请的一个实施例的衍射光学元件(diffractive optical elements,DOE)的结构示意图。FIG. 20 is a schematic structural diagram of a diffractive optical element (diffractive optical elements, DOE) according to an embodiment of the present application.
图21是光片生成系统包括串行级联设置的至少三个光片生成器的示意图。Figure 21 is a schematic diagram of a light sheet generation system comprising at least three light sheet generators arranged in series cascade.
图22是光片生成系统包括并行级联设置的至少两个光片生成器的示意图。Figure 22 is a schematic diagram of a light sheet generation system comprising at least two light sheet generators arranged in parallel cascade.
图23是本申请的一个实施例的光片生成系统与倒置望远镜系统的组合设计的示意图。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.
下面将结合附图,对本申请中的技术方案进行描述。The technical solutions in the present application will be described below with reference to the accompanying drawings.
为了便于理解光纤光栅刻写技术,首先对基于掩膜的紫外曝光法、基于CO2激光器的在线逐点写入法和CO2激光器多方向刻写法进行简单的说明。In order to facilitate the understanding of the fiber grating writing technology, 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.
紫外曝光法通过紫外(ultra-violet,UV)光源和特定的曝光装置,使两束紫外光形成周期性相干条纹(相干光);待刻写光纤的纤芯采用光敏材料;当外部相干光入射到纤芯时,其材料性质发生改变,造成纤芯的折射率发生周期性的变化,从而形成光纤光栅。图1是通过紫外曝光法进行光纤光栅刻写的示意图。如图1所示,入射的紫外(UV)光通过周期性相位掩膜(phase mask,PM)。PM将入射的UV光衍射到相同级次的正负两个角度上(m=1和m=-1),然后入射到两面紫外反射镜(UV mirror)上,经过反射照射到光纤上并在光线上形成一片光纤光栅刻写区域。两束UV光在光纤上相互叠加发生干涉,形成干涉条纹进行光纤光栅刻写。UV反射镜可以进行如图所示的旋转,通过调节两面UV反射镜的旋转可以调整两束UV光反射的角度,从而改变干涉光的空间位置和其他刻写参数。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). The PM diffracts the incident UV light to positive and negative angles of the same order (m=1 and m=-1), then incident on the two-sided UV mirrors (UV mirrors), and irradiates the optical fiber after reflection A fiber grating writing area is formed on the light. 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.
紫外曝光法具有一些缺点,例如,其要求光纤的纤芯材料为光敏材料,加工过程需要掩膜板,刻写不够灵活且价格昂贵,热稳定性差等。此外,UV光的波长较短,容易在多芯光纤中发生衍射,导致光强度减弱,不利于多芯光纤光栅的刻写。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. In addition, 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.
图2是通过在线逐点写入法进行光纤光栅刻写的示意图。如图2所示,在线逐点写入法的刻写装置由计算机、CO2激光器、透镜和位移台等组成。通过计算机控制CO2激光器开启,CO2激光器发出的光在传播过程中由透镜进行聚焦,在空间上形成光斑,光斑照射在位移台上的光纤的纤芯上。由于激光照射时会产生热,基于热效应作用可使光纤的纤芯的折射率发生改变。同时,置于位移台上的光纤由位移台控制进行移动(例如以恒定速度移动),从而实现光纤光栅的在线刻写和周期控制。FIG. 2 is a schematic diagram of fiber grating writing by an online point-by-point writing method. As shown in Figure 2, 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. At the same time, 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.
在线逐点写入法采用将激光聚焦的方式进行刻写,由于光斑尺寸的限制,同一时刻只能对光纤的一个纤芯进行刻写。对多芯光纤而言,此方式不能同时实现多芯的刻写,光纤光栅的刻写效率较低。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.
图3是通过CO2激光器多方向刻写法进行光纤光栅刻写的示意图。CO2激光器多方向刻写法的刻写装置由CO2激光器(CO2laser)、柱透镜(例如,硒化锌柱透镜,ZnSe cylindrical lens)和反射元件(reflector)构成。如图3所示,CO2激光器发出的光经过柱透镜聚焦,再经过一个上下对称的反射元件后被反射至待刻写的光纤(fiber)的不同部位。由于热效应,致使光纤的纤芯的折射率发生改变,完成光纤光栅的刻写。由图3所示可知,光纤各个方向 (光纤的左方、右上方与右下方)都能够受到激光照射,因此受照相对均匀,可以提高光纤光栅的刻写质量。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. As shown in Figure 3, 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. As shown in Figure 3, 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.
为了保证光纤的各个方向都能够受到激光照射,光纤需要置于比较精准的位置上。当光纤距离反射元件太近或太远时,部分光经反射元件反射回来照射不到光纤表面,会使刻写效果下降。通过适当地增加入射光的宽度,可以对光纤的位置要求有相应地放宽,但也会浪费入射光的能量。另外,CO2激光器多方向刻写法目前主要用于传统的单芯光纤的刻写。如果将其用于新型多芯光纤,在刻写排布在多芯光纤中心位置处的纤芯时,可能对周围其他纤芯产生不可避免的影响,致使输出的光纤光栅完全无法实现预期功能。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. In addition, 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.
上述刻写方案主要是针对传统的单模单芯光纤的,对于多芯光纤、少模光纤、多芯少模光纤等极具未来应用前景的新型光纤而言,上述刻写方案均存在着效率低问题。此外成本高、性能差也是亟需解决的问题。The above-mentioned writing schemes are mainly for traditional single-mode single-core fibers. For new optical fibers with great future application prospects, such as multi-core fibers, few-mode fibers, and multi-core few-mode fibers, the above-mentioned writing schemes all have the problem of low efficiency. . In addition, high cost and poor performance are also problems that need to be solved urgently.
基于上述问题,本申请提出一种全新的基于光片的刻写方法,其可以认为是一种改进的在线逐点写入法。Based on the above problems, 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.
本申请提供了一种光纤光栅刻写装置。图4是本申请的一个实施例的光纤光栅刻写装置400的示意性结构图。如图4所示,光纤光栅刻写装置400包括至少一组激光系统410和光片生成系统420,以及位移台430。激光系统410用于发出用于刻写的光;光片生成系统420用于使光通过以形成光片,光片为片状光场,光片的厚度方向沿光纤的轴向,光片的宽度方向和长度方向形成的平面与光纤的径向横截面平行;位移台430用于装载并周期性移动光纤,使光纤曝光在光片下以完成光纤的光栅刻写。The present application provides a fiber grating writing device. 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.
应理解,激光系统发出的用于刻写的光可以为激光,也可以为其他类型的光,例如发光二极管(light emitting diode,LED)光源、宽谱光源、超辐射二极管等非相干光源。It should be understood that 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.
本申请提供的光纤光栅刻写装置,包括激光系统、光片生成系统和位移台,通过在空间形成光片对位移台上周期性移动的光纤进行曝光,可以实现光纤光栅的刻写,能够大幅提升刻写效率。The fiber grating writing device provided by the present application 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.
本申请的光片生成系统通过改变入射光的相位波前,使光在空间的预设位置形成无衍射的细长的光束,即片状光场,来实现单芯或者多芯的光纤光栅的刻写,可以有效提升刻写速度和刻写精准度,同时光纤光栅刻写装置的稳定性及灵活性也更高。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.
应理解,本申请的激光系统可以是CO2激光器,也可以是能够产生用于刻写的光的其他类型的激光器,例如紫外激光器等,本申请对此不做限定。It should be understood that 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.
在本申请的一些实施例中,光纤光栅刻写装置400还可以包括控制模块440,用于控制激光系统410发出光,或控制光片生成系统420形成光片,或控制位移台430周期性移动光纤。In some embodiments of 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 .
控制模块440可以用来控制激光系统410的入射功率,从而控制改变光片的能量而实现高效刻写。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.
控制模块440可以用来控制光片生成系统420或光片生成系统420中的部件进行适当的移动,以在适当位置获得大小合适的光片。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.
控制模块440可以用来控制位移台430的移动,使装载在移动台上的光纤适当的平移(沿光纤的轴向平移或在与光纤的径向横截面平行的平面内上/下/左/右/斜向平移等)、转动或滚动等,来获得更好的刻写效果。位移台430可以按照特定的周期(例如,典型周期为100nm~1000μm移动光纤,位移台典型的步进距离例如可以为1μm。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 μm, and a typical step distance of the stage can be 1 μm, for example.
基于上述光纤光栅刻写装置,本申请还提供了一种光纤光栅刻写方法。图5是本申请的 一个实施例的光纤光栅刻写方法500的示意性流程图。光纤光栅刻写方法500由光纤光栅刻写装置执行,该装置包括至少一组激光系统和光片生成系统,以及位移台。光纤光栅刻写方法500可以包括:S510,控制激光系统发出用于刻写的光;S520,使光通过光片生成系统并形成光片,光片为片状光场,光片的厚度方向沿光纤的轴向,光片的宽度方向和长度方向形成的平面与光纤的径向横截面平行;S530,控制位移台周期性移动光纤,使光纤曝光在光片下以完成光纤的光栅刻写。Based on the above fiber grating writing device, the present application also provides a fiber grating writing method. 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. In the axial direction, 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.
应理解,以上光纤光栅的刻写操作可在光纤拉制的同时进行,也可在光纤拉制完成之后、涂敷之前进行。It should be understood that 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.
在本申请的一些实施例中,由激光系统发出的光经过光片生成系统形成片状的光束,光束穿过光纤,曝光一定时间,继续移动曝光下一点,不断重复,直到整个光纤光栅刻写完成。In some embodiments of the present application, 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. .
在本申请的一些实施例中,光纤光栅刻写后光纤的纤芯区域的折射率分布可以为阶跃型分布、多阶跃型分布、渐变型分布或槽式渐变型分布。图6是纤芯区域的折射率分布的示意图。在本申请的一些实施例中,本申请的光纤光栅刻写装置和方法可以应用于单芯光纤,例如单模光纤(芯区直径约9μm)、少模光纤(芯区直径约10~50μm)、多模光纤(芯区直径大于50μm)或直径较大的超模光纤。本申请的光纤光栅刻写装置也可以应用于多芯光纤,例如多芯少模光纤(芯区直径可达到数百微米)。图7是多芯光纤的各种纤芯排布情况的示意图。本申请的光纤光栅刻写装置和方法可以适用于图6所示的纤芯区域的折射率分布和图7所示的纤芯排布的情况。值得注意的是,图6和图7示出的仅是部分光纤设计的示例,对于其他光纤纤芯区域的折射率分布和纤芯排布情况,本申请提出的光纤光栅刻写装置和方法同样适用,并可以实现高效刻写。In some embodiments of the present application, 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. In some embodiments of the present application, 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 μm), few-mode fibers (with a core diameter of about 10-50 μm), Multimode fiber (core diameter greater than 50μm) 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.
在本申请的一些实施例中,可以在环绕光纤径向横截面的不同方向上生成光片,同时对光纤进行刻写,可以保证光纤径向横截面上被照射均匀的能量,能够提升刻写效率与性能。In some embodiments of the present application, 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.
在一些实施例中,光纤光栅刻写装置可以包括至少两组激光系统和光片生成系统,该至少两组激光系统和光片生成系统被设置为均匀环绕光纤的径向横截面。图8中的A是三组激光系统和光片生成系统均匀环绕光纤的径向横截面的示意图。在环绕光纤的径向横截面所在平面内不同方向放置多台激光系统(例如CO2激光器)和光片生成系统同时对光纤进行刻写,可以保证光纤径向横截面上被照射均匀的能量,能够提升刻写效率与性能。In some embodiments, 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.
在另一些实施例中,光纤光栅刻写装置还可以包括分束器和反射元件,经光片生成系统形成的光片被分束器分为多束后被反射元件反射到光纤上。换句话说,光纤光栅刻写装置可以包括一组激光系统和光片生成系统、若干分束器和若干反射元件。经过分束器和反射元件后的环绕光纤的径向横截面内各光片位置均匀排列。图8中的B是一组激光系统和光片生成系统、分束器、反射元件环绕光纤的径向横截面的示意图。在激光系统和光片生成器后放置一分三的分束器,经两个反射元件(例如可以是可调节反射镜),反射元件1和反射元件2反射出多个光片,例如三个光片同时对光纤进行刻写,保证光纤径向横截面上被照射均匀的能量,能够提升刻写效率与性能。应理解,上述光片的个数仅是举例而非限定。In other embodiments, 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. In other words, 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. At the same time, 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.
根据一般经验,使用CO2激光器在单模光纤上刻写光纤光栅所需的芯区折射率变化率一般不超过10-3量级。对于多芯少模光纤的光纤光栅的刻写,所需的折射率变化率会更低,一般远小于10-3量级。但是随着新型光纤径(例如多芯少模光纤)的纤芯数和模式数的增加,新型光纤的径向横截面积也相比单模光纤增大(例如19芯6模光纤的径向横截面积约为单模光纤的径向横截面积100倍左右),作用于单位径向横截面上的激光能量可能会相应降低,因此需要从影响芯区折射率变化量的主要因素,例如光纤类型、光纤轴向应力大小、激光系统 的功率、刻写时间等方面入手,确保本申请的光纤光栅刻写装置和方法能够提供光纤的纤芯所需要的折射率变化率。具体设计可以通过适当增加光纤轴向应力和刻写时间,结合激光系统功率的提升,来达到所需的折射率变化量。根据现有数据,目前中国运载火箭技术研究院已装配1kW的CO2激光打标机。According to general experience, 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. For the writing of the fiber grating of the multi-core few-mode fiber, the required refractive index change rate will be lower, generally much less than the order of 10-3. However, with the increase of the number of cores and modes of the new fiber diameter (such as multi-core few-mode fiber), 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. Starting from the fiber type, the axial stress of the fiber, the power of the laser system, and the writing time, it is ensured that 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. According to the existing data, the China Academy of Launch Vehicle Technology has installed a 1kW CO2 laser marking machine.
下面以几个具体的实施例来说明本申请的光纤光栅刻写装置和方法。The fiber grating writing device and method of the present application will be described below with several specific embodiments.
在本申请的一些实施例中,光片生成系统可以包括至少一个光片生成器,该光片生成器基于超表面结构,该超表面结构可以包括多个单元,每个单元包括基底和微纳结构,激光系统发出的光由基底入射后经过微纳结构的相位调控形成光片。In some embodiments of the present application, 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.
用于光纤光栅刻写的光片生成器可由基于超表面结构的波束形成器实现。图9是本申请的基于超表面结构的光片生成器进行光纤光栅刻写的局部放大示意图。如图9所示,激光系统发出的光从超表面结构的基底入射,经超表面基底上微纳结构的相位调控作用,形成一个片状光场(光片)。形成的光片处于y-z平面,x方向定义为光片的厚度,y方向定义为光片的宽度,z方向定义为光片的长度。将光纤置于x-y平面,与光片的位置正交,进行光纤光栅的刻写。Optical sheet generators for fiber grating writing can be realized by beamformers based on metasurface structures. 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. As shown in Fig. 9, 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.
图10是本申请的一个实施例的超表面结构的示意图。如图10所示,超表面结构是一种可以任意调控光束波前的二维结构。之所以称之为二维结构,是由于其高度方向的尺寸较小且一致,因此人们通常将其视为平面结构。FIG. 10 is a schematic diagram of a metasurface structure according to an embodiment of the present application. As shown in Figure 10, 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.
在本申请的一些实施例中,超表面结构可以包括多个单元,每个单元又包括两部分,基底和放置在基底上的微纳结构。多个单元紧密排列可以形成超表面结构。图11是本申请的一个实施例的超表面结构的一个单元的示意图。In some embodiments of the present application, 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.
微纳结构又称为亚波长结构,所谓亚波长,是指结构的各个尺寸均小于入射光的波长。对于光波段,亚波长意味着尺寸在微米或纳米尺度。其中,基底起到承托作用,基底的材料可以选取对于工作激光的波长无吸收的材料。微纳结构可以为柱状或类柱状结构,例如微纳结构可以使用但不限于立方柱、圆柱、椭圆柱、层状、条状、十字架型、字母型等各种结构,各单元中的微纳结构的上述结构可以相同或不同。微纳结构常选用高折射率材料,例如可以使用但不限于如硅(Si)、氮化硅(SiN)、锗(Ge)、二氧化钛(TiO2)、石英玻璃(SiO2)等电介质材料,金(Au)、银(Ag)、铜(Cu)等贵金属,以及液晶、氧化铟锡(ITO)、铌酸锂等可调谐材料中的至少一种。激光系统发出的光入射到超表面结构时,不同位置处放置的不同的微纳结构,即不同位置处放置的微纳结构的参数不同,经过微纳结构的光场响应也会不同,相位和幅度被调制,在原始波阵面上叠加附加相位使得波阵面发生改变,当波阵面满足光片生成器对应相位分布时即可生成光片。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. For wavelengths of 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. For example, 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. When the light emitted by the laser system is incident on the metasurface structure, different micro-nano structures placed at different positions, that is, the parameters of the micro-nano structures placed at different positions are different, and the optical field response through the micro-nano structure will also be different, and the phase and The amplitude is modulated, and an additional phase is superimposed on the original wavefront to change the wavefront. When the wavefront satisfies the phase distribution corresponding to the light sheet generator, the light sheet can be generated.
图12是普通表面结构光传播和超表面结构光传播的原理示意图。其中,图12中的A是普通表面结构光传播的原理示意图;B、C和D是超表面结构光传播的原理示意图。图中平行线(或曲线)代表波阵面,箭头代表波矢方向,波矢方向与波阵面互相垂直,光从空气中入射至表面(普通表面或超表面)后经表面后又出射到空气中。FIG. 12 is a schematic diagram of the principle of light propagation with ordinary surface structures and light propagation with metasurface structures. Among them, 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.
图12的A中的表面为普通表面结构,可以理解为玻璃或水等介质形成的平行平板,根据光学传播原理,垂直表面入射的光将垂直表面出射。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.
图12的B中的光入射到超表面结构时,不同位置处放置不同的微纳结构可引入相位突变,在原始波阵面上叠加附加相位使波阵面发生改变。When the light in B of Figure 12 is incident on the metasurface structure, placing different micro-nano structures at different positions can introduce a sudden phase change, and superimpose additional phases on the original wavefront to change the wavefront.
如图12的C所示,当所选择的微纳结构尺寸使得波阵面可以转化为球面时,该超表面结构就可以形成一个超表面透镜,实现透镜的聚焦功能。As shown in C of Figure 12, 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.
光片生成器需要形成的波阵面为两列对称的倾斜平面。如图12的D所示,当所选择的微纳结构尺寸使得波阵面为两列对称的倾斜平面时,光通过该超表面结构就可以形成光片,可以用于本申请提出的光纤光栅刻写装置中。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.
图13是超表面结构需要满足的相位的示意图。在x方向上,超表面结构需要满足如图13所示的相位;并将该结构在y方向上重复排列,即可形成光片。图12中DA表示形成光片的厚度,其沿着x方向,光片在y方向延展,θ表示波前与法线的夹角。Figure 13 is a schematic diagram of the phases that the metasurface structure needs to satisfy. In the x-direction, 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. In FIG. 12 , DA represents the thickness of the formed light sheet, which is along the x direction, the light sheet extends in the y direction, and θ represents the angle between the wavefront and the normal.
由于超表面结构可视为平面结构,因此可以使用如下公式(1)进行设计:Since the metasurface structure can be regarded as a plane structure, it can be designed using the following formula (1):
其中,D表示超表面结构的口径,θ表示波阵面的倾角,即指波前与超表面结构基底的法线方向之间的夹角,λ表示激光系统生成的光的波长,此处以10.6μm为例进行说明。Among them, D represents the aperture of the metasurface structure, θ 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, λ represents the wavelength of the light generated by the laser system, where 10.6 μm will be described as an example.
根据光片的波前相位轮廓,可以挑选合适的微纳结构,来设计光片生成器,其中这里可使用图11所示的结构作为单元。根据公式(1),为保证正常刻写,光片的厚度DA应该小于光纤光栅的周期(例如长周期光纤光栅的周期约为100-1000μm),例如可以取临界值,即光片的厚度DA为100μm。此时计算可以得到光束波阵面的倾角θ为4.642度。超表面结构的口径D和光片的无衍射传输距离(光片在z轴方向的可用距离)Z
max也可以基于公式(1)得到。根据图12的D和图13分析可知,超表面结构在x方向上关于原点对称,而在原点的同一侧,是微纳结构周期性排布形成的。因此只要完成一个周期组(例如左侧第一个周期组)的设计,通过重复排列和对称即可得到完整的x方向上的设计,在y方向上重复排列即可得到完整器件。
According to the wavefront phase profile of the light sheet, 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. According to formula (1), in order to ensure normal writing, 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 μm), for example, a critical value can be taken, that is, the thickness DA of the optical sheet is 100μm. At this time, the calculation can obtain that the inclination angle θ 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). According to the analysis of D of Fig. 12 and Fig. 13, 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.
在超表面结构的设计中,各单元的尺寸最优可以设计为小于真空波长λ
0。因此,微纳结构的高度可取范围通常在0.3λ
0~2λ
0。微纳结构过高需要较高的深宽比(微纳结构的高度与宽度的比值),对于加工不利;微纳结构过矮难以实现覆盖较大的相位范围,难以实现设计需求。根据公式(1),D可以取任意大小,通常可取到毫米(mm)量级,θ也可以取任意的角度(优选地,可以选取10-80度)。因此理论上,利用该超表面结构可以产生mm量级以内的光束长度以及接近衍射极限的光斑半径。若要满足波阵面的倾角θ为4.642度,微纳结构的周期应约为130μm,即每130μm引入2π的相位变化。在一个具体的例子中,可将这130μm划分为26个单元,每个单元周期为5μm,其引入的相位变化应满足图13所示的曲线。
In the design of the metasurface structure, the optimal size of each unit can be designed to be smaller than the vacuum wavelength λ 0 . Therefore, the height of the micro-nano structure is usually in the range of 0.3λ 0 to 2λ 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. According to formula (1), D can take any size, usually in the order of millimeters (mm), and θ can take any angle (preferably, 10-80 degrees can be selected). Therefore, theoretically, the use of this metasurface structure can generate beam lengths within the mm order and spot radii close to the diffraction limit. To satisfy the inclination angle θ of the wavefront of 4.642 degrees, the period of the micro-nano structure should be about 130 μm, that is, a phase change of 2π is introduced every 130 μm. In a specific example, the 130 μm can be divided into 26 units, and the period of each unit is 5 μm, and the phase change introduced by it should satisfy the curve shown in FIG. 13 .
在一个具体的例子中对于10.6μm的光的波长,超表面结构的基底和微纳结构材料可以分别选为BaF2和Ge,也可选用其他适用于该波长的材料但不限于,例如Si。在该例子中,对于一个单元而言,基底的厚度可以为500μm、底面可以为长度是5μm的正方形;放置在基底上的微纳结构可以是底面为正方形的长方体,高度均为1μm、底面正方形的边长根据不同的相位需求有不同选择。在该例子中,这26个单元引入的相位及微纳结构的底面正方形的边长大小满足下表1所示。其中,p代表微纳结构引入的相位,单位为度;l代表微纳结构的底面正方形的边长,单位为μm。In a specific example, for the wavelength of 10.6 μm light, 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. In this example, for a unit, the thickness of the substrate can be 500 μm, and the bottom surface can be a square with a length of 5 μm; the micro-nano structure placed on the substrate can be a cuboid with a square bottom surface, the height is 1 μm, and the bottom surface is square. The length of the side can be selected differently according to different phase requirements. In this example, the 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. Among them, 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 μm.
表1一个周期中26个微纳结构的底面正方形的边长和单元引入的相位Table 1 The side length of the bottom square of 26 micro-nano structures in one cycle and the phase introduced by the unit
pp | -40-40 | -53.8-53.8 | -67.7-67.7 | -81.5-81.5 | -95.4-95.4 | -109.2-109.2 | -123.1-123.1 | -136.9-136.9 | -150.8-150.8 | -164.6-164.6 |
ll | 1.41.4 | 1.5071.507 | 1.5651.565 | 1.6131.613 | 1.6441.644 | 1.6751.675 | 1.7051.705 | 1.7261.726 | 1.7461.746 | 1.7641.764 |
pp | -178.5-178.5 | 167.7167.7 | 153.8153.8 | 140140 | 126.2126.2 | 112.31112.31 | 98.4698.46 | 84.6184.61 | 70.7770.77 | 56.9256.92 |
ll | 1.7821.782 | 1.81.8 | 1.8191.819 | 1.8391.839 | 1.861.86 | 1.881.88 | 1.91.9 | 1.9351.935 | 1.971.97 | 2.012.01 |
pp | 43.0743.07 | 29.2329.23 | 15.3815.38 | 1.541.54 | -12.3-12.3 | -26.16-26.16 | ||||
ll | 2.0692.069 | 2.1442.144 | 2.2462.246 | 2.3742.374 | 2.5152.515 | 2.65432.6543 |
根据上述具体的例子中超表面结构的尺寸建模可以得到光能分布的结果。图14是本申请的一个实施例中光通过超表面结构形成的光片的光能分布的示意图。图14中A所示表示所形成的光片的厚度的截面即x-z平面的光能分布。图14中B为图14中A在x方向中点处在所有y方向上沿z轴方向的光能分布,其表示光片沿着y方向的宽度截面。图14中C为图14中A在x=0μm位置沿着z方向的光能分布。由图14中C可知光片约在500-1500μm的范围内光强均保持在2V2/m2以上,该高能量区域长度远远超过多一般光纤的纤芯的尺寸250μm。图14中D为图14中A在z=1200μm处沿x方向的光能分布。由图14中D可知光片沿着x轴方向场强2V2/m2对应的光片厚度约为70μm,且光片旁瓣的强度明显低于主瓣强度。在实际刻写光纤光栅的过程中,采用此方案形成的光片,将光纤放置于x-y平面的光片高亮度区域,其与光片正交放置,进行光纤光栅的刻写。如果将2V2/m2当做刻写阈值,则光片的厚度小于刻写周期,且旁瓣不会对刻写过程造成不利影响,同时光片的宽度大于250μm,满足刻写光纤光栅的要求,可以实现高效刻写。当然,在实际情况中由于光纤材料的不同刻写阈值存在差异,可以调节激光系统的入射功率来改变光片的能量来实现高效刻写。The results of the light energy distribution can be obtained according to the size modeling of the metasurface structure in the above specific example. 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. C in FIG. 14 is the light energy distribution along the z direction of A in FIG. 14 at the position of x=0 μm. It can be seen from C in Figure 14 that the light intensity of the light sheet is maintained above 2V2/m2 in the range of about 500-1500μm, and the length of this high-energy region is far longer than the core size of many ordinary fibers, which is 250μm. D in FIG. 14 is the light energy distribution along the x direction at z=1200 μm in A in FIG. 14 . It can be seen from D in Fig. 14 that the thickness of the light sheet corresponding to the field strength 2V2/m2 along the x-axis direction is about 70 μm, and the intensity of the side lobes of the light sheet is significantly lower than that of the main lobe. In the actual process of writing the fiber grating, 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. If 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. At the same time, the width of the optical sheet is greater than 250μm, which meets the requirements for writing fiber gratings, and can achieve efficient writing. Of course, in practice, due to the difference in writing thresholds of different fiber materials, the incident power of the laser system can be adjusted to change the energy of the optical sheet to achieve efficient writing.
在本申请的一些实施例中,光片生成系统包括至少一个光片生成器,该光片生成器为圆锥状光片生成器或三棱柱状光片生成器。这些实施例中,光片生成器的材料可以包括硅、氮化硅、锗、二氧化钛、石英玻璃、液晶、氧化铟锡或铌酸锂中的至少一种,本申请对此不做限定。In some embodiments of the present application, 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. In these embodiments, 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.
图15是本申请的一个实施例的通过圆锥状光片生成器产生光片来刻写光纤光栅的示意图。如图15所示,使用圆锥状光片生成器可以产生细长的光束,其也可以视为光片。该光片所在平面处于y-z平面,x方向与光片垂直,光片在x方向体现的是其厚度,该光片在y方向的光斑较小,即光片在y方向较窄,一次可以照射一条路径上的多条纤芯。圆锥状光片生成器对纤芯线性排列的多芯光纤的刻写效果较好。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. As shown in Figure 15, the use of 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.
图16是本申请的一个实施例的通过三棱柱状光片生成器产生光片来刻写光纤光栅的示意图。如图16所示,使用三棱柱状光片生成器可以产生一个平面状的光束,平面状的光束所在平面处于y-z平面,x方向与光片垂直,光片在x方向体现的是其厚度,这样可以一次性照射不同位置处的纤芯,刻写效率将大大提高。三棱柱状光片生成器对纤芯线性排列的多芯光纤和非线性排列的多芯光纤的刻写效果均较好。三棱柱状光片生成器的功耗较圆锥状光片生成器的功耗稍大。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. As shown in Figure 16, 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.
图17是对应于图16的三棱柱状光片生成器的侧视图。由于生成的光片在图17中y方向上延伸,因此在图17中用省略号表示,DA为形成光片的厚度,W为光片的宽度,Zmax为形成光片的无衍射传输距离。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.
图18是圆锥状光片生成器和三棱柱状光片生成器的形成方式示意图。图15和图16所使用的光片生成器的截面的形状均为三角形。不同的是图15的圆锥状光片生成器由截面三角形沿轴线旋转得到,而图16的三棱柱状光片生成器则是使用截面三角形沿y方向延伸得到的,如图18的A和B分别所示。由圆锥状光片生成器和三棱柱状光片生成器得到的光束均为轴对称的光片。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.
以圆锥状光片生成器为例,其产生的无衍射传输距离Z
max和光斑尺寸D
A大小分别可以通过以下公式2表示。
Taking a cone-shaped light sheet generator as an example, 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.
图19是本申请的一个实施例的圆锥状光片生成器的设计参数示意图。如图19所示,阴影部分表示圆锥状光片生成器,D表示圆锥状光片生成器的口径大小,上式在光充满整个口径的情况下推导得到。因此,D也可以认为是入射光的直径;n代表圆锥状光片生成器的材料折射率;α表示圆锥状光片生成器的底角(以弧度为单位);Z
max表示贝塞尔光斑的长度,即“无衍射传输距离”;D
A表示光片(光斑)的厚度,λ表示热射光的波长,此处以10.6μm的波长为例进行说明。
FIG. 19 is a schematic diagram of design parameters of a conical light sheet generator according to an embodiment of the present application. As shown in Figure 19, the shaded part represents the conical light sheet generator, and 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; α 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), and λ represents the wavelength of the heat radiated light. Here, the wavelength of 10.6 μm is used as an example for description.
在一个具体的例子中,要实现高效刻写,一次照射即可覆盖所有纤芯,要求光片的无衍射传输距离Z
max应大于待刻写光纤的包层直径,以一般多芯光纤的经验参数为例,可以取250μm。对于三棱柱状光片生成器,入射光的宽度W也应大于包层直径(250μm),同时光片直径D
A应小于光纤光栅的周期。其中,圆锥状光片生成器的材料可以选取为石英玻璃,折射率为1.53,综合上述要求,通过公式(2)计算可以得到,圆锥状光片生成器的口径应选择250μm,底角应选为18.13度,此时光片的宽度为250μm,无衍射传输距离为751μm,光片最小处的半径约为10μm,光片完全可以覆盖所有纤芯截面,实现高效精确刻写。
In a specific example, in order to achieve efficient writing, 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 μm. For the triangular prism light sheet generator, the width W of the incident light should also be larger than the cladding diameter (250μm), and the light sheet diameter D A should be smaller than the period of the fiber grating. Among them, the material of the cone-shaped light sheet generator can be selected as quartz glass, and the refractive index is 1.53. Based on the above requirements, it can be calculated by formula (2), the diameter of the cone-shaped light sheet generator should be 250μm, and the bottom angle should be selected At this time, the width of the optical sheet is 250 μm, the non-diffraction transmission distance is 751 μm, and the minimum radius of the optical sheet is about 10 μm. The optical sheet can completely cover all the core sections and realize efficient and accurate writing.
在本申请的一些实施例中,光片生成系统包括至少一个光片生成器,该光片生成器为衍射光学元件(diffractive optical elements,DOE)。这些实施例中,光片生成器的材料可以包括硅、氮化硅、锗、二氧化钛、石英玻璃、液晶、氧化铟锡或铌酸锂中的至少一种,本申请对此不做限定。In some embodiments of the present application, the light sheet generation system includes at least one light sheet generator, which is a diffractive optical element (DOE). In these embodiments, 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.
图20是本申请的一个实施例的DOE的结构示意图。DOE采用光刻技术,提供透射光的全相位控制。DOE由对称的两部分构成,通过将入射光衍射到固定的角度,在空间上预设位置进行干涉相长,从而形成光片。与传统的折射光学器件相比,DOE无需通过器件厚度积累光程差,厚度较薄,有利于光纤光栅刻写装置的小型化。DOE作为光片生成器时,光从如图20所示的DOE的上方或下方入射。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. Compared with traditional refractive optical devices, 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. When the DOE acts as a light sheet generator, light is incident from above or below the DOE as shown in Figure 20.
在本申请的一些实施例中,光片生成系统可以包括至少三个光片生成器,至少三个光片生成器串行级联设置,包括可移动的第一光片生成器、位置固定的第二光片生成器和位置固定的第三光片生成器,光从第一光片生成器的底面入射,经第一光片生成器后入射到第二光片生成器的非底面上,第二光片生成器的底面与第三光片生成器的底面相对设置,使得光从第二光片生成器平行出射并平行入射第三光片生成器。应理解,本申请的光片生成系统还可以包括类似第二光片生成器和第三光片生成器的更多的底面相对的光片生成器组合,从而可以任意调整光纤被光片照射的位置和大小。In some embodiments of the present application, 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. It should be understood that 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.
图21是光片生成系统包括串行级联设置的至少三个光片生成器的示意图。以前三个光片生成器为例说明光片生成系统的工作原理。三个光片生成器串行级联,第一光片生成器可以移动,光从其底面入射。第二、第三光片生成器底面与底面相对,保证光可以从第二光片生成器平行出射并平行入射第三光片生成器,且第二、第三光片生成器位置固定。后面如果设置更多的光片生成器,则其传播过程重复前述过程。从图21示出的光路可以看出,通过移动第一光片生成器或者后续的光片生成器,可以把光片移动到任意位置进行调整以刻写光纤的不同位置,同时光片的大小也可能会发生变化。这样光片生成系统可以使得光纤光栅刻写装置能够适应于单芯光纤或多芯光纤,从而实现灵活刻写。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. From the optical path shown in Figure 21, it can be seen that by moving the first optical sheet generator or the subsequent optical sheet generators, the optical sheet can be moved to any position for adjustment to write different positions of the optical fiber, and the size of the optical sheet is also subject to change. In this way, 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.
应理解,光片生成器的底面可以理解为光片生成器接收入射光的一面。例如,可以是超表面结构的基底这一面。再如,可以是图20示出的DOE的上边一面或下边一面。It should be understood that the bottom surface of the light sheet generator can be understood as the side of the light sheet generator that receives incident light. For example, it can be the substrate side of the metasurface structure. For another example, it may be the upper side or the lower side of the DOE shown in FIG. 20 .
在本申请的一些实施例中,光片生成系统可以包括至少两个光片生成器,该至少两个光片生成器并行级联设置,每个光片生成器形成一个独立的光片。In some embodiments of the present application, 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.
图22是光片生成系统包括并行级联设置的至少两个光片生成器的示意图。如图22所示,光片生成系统使用可同时产生沿光纤轴向即沿着x方向周期性排列的多个光片的多个光片生成器,即多个产生单光片的光片生成器并行级联。如图22所示,阴影部分代表多个光片生成器,将其并行级联,可以形成多个独立分布的光片。光片在x方向代表其厚度,在y方向上延展宽度W,当这些独立光片的间隔满足刻写光纤光栅的周期时,将光纤放置于x-y平面光片中心的位置,可以实现单次刻写多个光纤光栅周期,因此能大大能提高刻写效率。Figure 22 is a schematic diagram of a light sheet generation system comprising at least two light sheet generators arranged in parallel cascade. As shown in Figure 22, 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. As shown in Figure 22, 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. When the interval between these independent light sheets meets the period of writing the fiber grating, the optical fiber is placed at the center of the xy plane light sheet, which can realize a single writing multiple times. Therefore, the writing efficiency can be greatly improved.
在本申请的一些实施例中,光纤光栅刻写装置还可以包括在光路上位于光片生成系统之后的倒置望远镜系统。In some embodiments of the present application, the fiber grating writing device may further include an inverted telescope system located behind the light sheet generation system in the optical path.
图23是本申请的一个实施例的光片生成系统与倒置望远镜系统的组合设计的示意图。由前述公式(1)可以看出,光片的长度(无衍射传输距离)Z
max和光片的厚度均与光片生成器的底角大小有关,底角越小,则Z
max越大,DA越大,这对于光纤光栅刻写是不利的。因此,本申请的一些实施例提出如图23所示的方案,在光片生成系统后加倒置望远系统,可以任意调控无衍射传输距离Z
max和光片厚度大小。
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. As can be seen from the above equation (1), 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.
在一个实施例中,倒置望远镜系统可以包括第一透镜和第二透镜,第一透镜的右焦点与第二透镜的左焦点重合。In one embodiment, 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.
如图23所示,倒置望远镜系统可以由两个透镜组成,透镜可以使用传统的透镜或基于超表面的超透镜。第一透镜的焦距是f1,第二透镜的焦距是f2,且第一透镜的右焦点与第二透镜的左焦点重合,此时公式(1)可以变为如下形式的公式(3)。As shown in Figure 23, 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, and the right focus of the first lens is coincident with the left focus of the second lens. At this time, formula (1) can be transformed into formula (3) in the following form.
假设规定光片生成器的底角为4°,如果D、f2/f1分别为250μm和0.448,则可以得到Z
max为751μm,厚度小于100μm,宽度为250μm的光片。此时可以一次性刻写光纤中所有的纤芯。在光片生成系统之后设置倒置望远镜系统可以帮助设计任意长度和厚度的光片。对于刻写光纤光栅的而言,即可以任意调整光纤被光片照射的位置和大小,对于纤芯折射率变化的精确控制具有有益价值。
Assuming that the base angle of the specified light sheet generator is 4°, if D and f2/f1 are 250 μm and 0.448, respectively , a light sheet with Z max of 751 μm, a thickness of less than 100 μm and a width of 250 μm can be obtained. At this point, all the cores in the fiber can be written at once. Setting up an inverted telescope system after the light sheet generation system can help design light sheets of arbitrary length and thickness. For writing fiber gratings, the position and size of the optical fiber irradiated by the light sheet can be adjusted arbitrarily, which has beneficial value for the precise control of the refractive index change of the fiber core.
在其他实施例中,倒置望远镜系统还可以是其他的结构,本申请对此不做限定。In other embodiments, the inverted telescope system may also have other structures, which are not limited in this application.
本申请还提供了一种计算机可读介质,用于存储计算机程序,该计算机程序包括用于执行前文的光栅光纤刻写方法的指令。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.
所属领域的技术人员可以清楚地了解到,为描述的方便和简洁,上述描述的方法的各步骤的执行,可以基于前述产品实施例中的对应模块、单元和器件来实现,在此不再赘述。Those skilled in the art can clearly understand that, for the convenience and conciseness of description, the execution of each step of the above-described method can be implemented based on the corresponding modules, units and devices in the foregoing product embodiments, which will not be repeated here. .
应理解,本文中涉及的各种数字编号仅为描述方便进行的区分,并不用来限制本申请的范围。It should be understood that the various numbers and numbers involved in this document are only for the convenience of description, and are not used to limit the scope of the present application.
应理解,在本申请实施例中,上述各过程的序号的大小并不意味着执行顺序的先后,各过程的执行顺序应以其功能和内在逻辑确定,而不应对本申请实施例的实施过程构成任何限定。It should be understood that, in the embodiments of the present application, the size of the sequence numbers of the above-mentioned processes does not mean the order of execution, and the execution order of each process should be determined by its functions and internal logic, rather than the implementation process of the embodiments of the present application. constitute any limitation.
本领域普通技术人员可以意识到,结合本文中所公开的实施例描述的各示例的单元及算法步骤,能够以电子硬件、或者计算机软件和电子硬件的结合来实现。这些功能究竟以硬件 还是软件方式来执行,取决于技术方案的特定应用和设计约束条件。专业技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能,但是这种实现不应认为超出本申请的范围。Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of this application.
在本申请所提供的几个实施例中,应该理解到,所揭露的系统、装置和方法,可以通过其它的方式实现。例如,以上所描述的装置实施例仅仅是示意性的,例如,所述单元的划分,仅仅为一种逻辑功能划分,实际实现时可以有另外的划分方式,例如多个单元或组件可以结合或者可以集成到另一个系统,或一些特征可以忽略,或不执行。另一点,所显示或讨论的相互之间的耦合或直接耦合或通信连接可以是通过一些接口,装置或单元的间接耦合或通信连接,可以是电性,机械或其它的形式。In the several embodiments provided in this application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not implemented. On the other hand, 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.
所述作为分离部件说明的单元可以是或者也可以不是物理上分开的,作为单元显示的部件可以是或者也可以不是物理单元,即可以位于一个地方,或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部单元来实现本实施例方案的目的。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.
另外,在本申请各个实施例中的各功能单元可以集成在一个处理单元中,也可以是各个单元单独物理存在,也可以两个或两个以上单元集成在一个单元中。In addition, 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.
所述功能如果以软件功能单元的形式实现并作为独立的产品销售或使用时,可以存储在一个计算机可读取存储介质中。基于这样的理解,本申请的技术方案本质上或者说对现有技术做出贡献的部分或者该技术方案的部分可以以软件产品的形式体现出来,该计算机软件产品存储在一个存储介质中,包括若干指令用以使得一台计算机设备(可以是个人计算机,服务器,或者网络设备等)执行本申请各个实施例所述方法的全部或部分步骤。而前述的存储介质包括:U盘、移动硬盘、只读存储器(read-only memory,ROM)、随机存取存储器(random access memory,RAM)、磁碟或者光盘等各种可以存储程序代码的介质。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. Based on this understanding, 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 .
以上所述,仅为本申请的具体实施方式,但本申请的保护范围并不局限于此,任何熟悉本技术领域的技术人员在本申请揭露的技术范围内,可轻易想到变化或替换,都应涵盖在本申请的保护范围之内。因此,本申请的保护范围应以所述权利要求的保护范围为准。The above are only specific embodiments of the present application, but the protection scope of the present application is not limited to this. should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims (17)
- 一种光纤光栅刻写装置,其特征在于,包括至少一组激光系统和光片生成系统,以及位移台,其中,A fiber grating writing device, characterized in that it includes at least one set of laser system and light sheet generation system, and a displacement stage, wherein,所述激光系统用于发出用于刻写的光;the laser system for emitting light for writing;所述光片生成系统用于使所述光通过以形成光片,所述光片为片状光场,所述光片的厚度方向沿所述光纤的轴向,所述光片的宽度方向和长度方向形成的平面与所述光纤的径向横截面平行;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 axial direction of the optical fiber, and the width direction of the light sheet is along the axis of the optical fiber. and the plane formed by the length direction is parallel to the radial cross-section of the optical fiber;所述位移台用于装载并周期性移动所述光纤,使所述光纤曝光在所述光片下以完成所述光纤的光栅刻写。The displacement stage is used for loading and periodically moving the optical fiber to expose the optical fiber under the light sheet to complete the grating writing of the optical fiber.
- 根据权利要求1所述的装置,其特征在于,所述装置包括至少两组所述激光系统和所述光片生成系统,所述至少两组所述激光系统和所述光片生成系统被设置为均匀环绕所述光纤的径向横截面。The apparatus of claim 1, wherein the apparatus comprises at least two sets of the laser systems and the light sheet generation systems, the at least two sets of the laser systems and the light sheet generation systems being provided is a radial cross-section that evenly surrounds the fiber.
- 根据权利要求1所述的装置,其特征在于,所述装置还包括分束器和反射元件,经所述光片生成系统形成的光片被所述分束器分为多束后被所述反射元件反射到所述光纤上。The device according to claim 1, characterized in that, the device further comprises 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 A reflective element reflects onto the optical fiber.
- 根据权利要求1至3中任一项所述的装置,其特征在于,所述光片生成系统包括至少一个光片生成器,所述光片生成器基于超表面结构,所述超表面结构包括多个单元,每个所述单元包括基底和微纳结构,所述激光系统发出的所述光由所述基底入射后经过所述微纳结构的相位调控形成所述光片。The apparatus according to any one of claims 1 to 3, wherein the light sheet generation system comprises at least one light sheet generator, the light sheet generator is based on a metasurface structure, the metasurface structure comprises A plurality of units, each of which includes a substrate and a micro-nano structure, and the light emitted by the laser system is incident on the substrate and undergoes phase regulation of the micro-nano structure to form the light sheet.
- 根据权利要求4所述的装置,其特征在于,所述微纳结构的材料包括硅、氮化硅、锗、二氧化钛、石英玻璃、金、银、铜、液晶、氧化铟锡或铌酸锂中的至少一种。The device according to claim 4, wherein the material of the micro-nano structure comprises silicon, silicon nitride, germanium, titanium dioxide, quartz glass, gold, silver, copper, liquid crystal, indium tin oxide or lithium niobate. at least one of.
- 根据权利要求1至3中任一项所述的装置,其特征在于,所述光片生成系统包括至少一个光片生成器,所述光片生成器为圆锥状光片生成器或三棱柱状光片生成器。The device according to any one of claims 1 to 3, wherein the light sheet generating system comprises at least one light sheet generator, and the light sheet generator is a conical light sheet generator or a triangular prism. Light sheet generator.
- 根据权利要求1至3中任一项所述的装置,其特征在于,所述光片生成系统包括至少一个光片生成器,所述光片生成器为衍射光学元件DOE。The device according to any one of claims 1 to 3, wherein the light sheet generating system comprises at least one light sheet generator, and the light sheet generator is a diffractive optical element DOE.
- 根据权利要求6或7所述的装置,其特征在于,所述光片生成器的材料包括硅、氮化硅、锗、二氧化钛、石英玻璃、液晶、氧化铟锡或铌酸锂中的至少一种。The device according to claim 6 or 7, wherein the material of the light sheet generator comprises at least one of silicon, silicon nitride, germanium, titanium dioxide, quartz glass, liquid crystal, indium tin oxide or lithium niobate kind.
- 根据权利要求4至8中任一项所述的装置,其特征在于,所述光片生成系统包括至少三个光片生成器,所述至少三个光片生成器串行级联设置,包括可移动的第一光片生成器、位置固定的第二光片生成器和位置固定的第三光片生成器,所述光从所述第一光片生成器的底面入射,经所述第一光片生成器后入射到所述第二光片生成器的非底面上,所述第二光片生成器的底面与所述第三光片生成器的底面相对设置,使得所述光从所述第二光片生成器平行出射并平行入射所述第三光片生成器。The device according to any one of claims 4 to 8, wherein the light sheet generating system comprises 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 second light sheet generator and a fixed position third light sheet generator, the light is incident from the bottom surface of the first light sheet generator, and passes through the first light sheet generator. A light sheet generator is then incident on the non-bottom surface of the second light sheet generator, and the bottom surface of the second light sheet generator is disposed opposite to the bottom surface of the third light sheet generator, so that the light from the The second light sheet generator is parallel to exit and parallel to the third light sheet generator.
- 根据权利要求4至8中任一项所述的装置,其特征在于,所述光片生成系统包括至少两个光片生成器,所述至少两个光片生成器并行级联设置,每个光片生成器形成一个独立的光片。The device according to any one of claims 4 to 8, wherein the light sheet generating system comprises at least two light sheet generators, the at least two light sheet generators are cascaded in parallel, each The light sheet generator forms an independent light sheet.
- 根据权利要求1至10中任一项所述的装置,其特征在于,所述装置还包括在光路上位于所述光片生成系统之后的倒置望远镜系统。The apparatus according to any one of claims 1 to 10, characterized in that the apparatus further comprises an inverted telescope system located behind the light sheet generation system in the optical path.
- 根据权利要求11所述的装置,其特征在于,所述倒置望远镜系统包括第一透镜和第二透镜,所述第一透镜的右焦点与所述第二透镜的左焦点重合。The apparatus of claim 11, wherein the inverted telescope system comprises a first lens and a second lens, and the right focus of the first lens coincides with the left focus of the second lens.
- 根据权利要求1至12中任一项所述的装置,其特征在于,所述光纤为单模光纤、少模光纤、多模光纤、超模光纤或多芯少模光纤。The device according to any one of claims 1 to 12, wherein the optical fiber is a single-mode optical fiber, a few-mode optical fiber, a multi-mode optical fiber, a super-mode optical fiber, or a multi-core few-mode optical fiber.
- 根据权利要求1至13中任一项所述的装置,其特征在于,光栅刻写后所述光纤的纤芯区域的折射率分布为阶跃型分布、多阶跃型分布、渐变型分布或槽式渐变型分布。The device according to any one of claims 1 to 13, wherein the refractive index distribution of the core region of the optical fiber after the grating is written is a step-type distribution, a multi-step-type distribution, a gradient-type distribution or a groove gradient distribution.
- 根据权利要求1至14中任一项所述的装置,其特征在于,所述装置还包括控制模块,用于控制所述激光系统发出所述光,或控制所述光片生成系统形成所述光片,或控制所述位移台周期性移动所述光纤。The apparatus according to any one of claims 1 to 14, characterized in that, the apparatus further comprises a control module for controlling the laser system to emit the light, or controlling the light sheet generating system to form the light sheet light sheet, or control the displacement stage to periodically move the optical fiber.
- 一种光纤光栅刻写方法,其特征在于,所述方法由光纤光栅刻写装置执行,所述装置包括至少一组激光系统和光片生成系统,以及位移台,所述方法包括:A fiber grating writing method, characterized in that the method is performed by a fiber grating writing device, the device comprising at least one set of a laser system and a light sheet generation system, and a displacement stage, the method comprising:控制所述激光系统发出用于刻写的光;controlling the laser system to emit light for writing;使所述光通过所述光片生成系统并形成光片,所述光片为片状光场,所述光片的厚度方向沿所述光纤的轴向,所述光片的宽度方向和长度方向形成的平面与所述光纤的径向横截面平行;Passing the light through the light sheet generating system and forming a light sheet, the light sheet is a sheet-like light field, the thickness direction of the light sheet is along the axial direction of the optical fiber, and the width direction and length of the light sheet are the plane formed by the direction is parallel to the radial cross-section of the optical fiber;控制所述位移台周期性移动所述光纤,使所述光纤曝光在所述光片下以完成所述光纤的光栅刻写。The displacement stage is controlled 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.
- 一种计算机可读介质,其特征在于,用于存储计算机程序,所述计算机程序包括用于执行权利要求16所述的方法的指令。A computer-readable medium for storing a computer program, the computer program comprising instructions for performing the method of claim 16 .
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