CN115629442B - Device and method for parallel direct writing of large-core-diameter fiber gratings by long-focus deep femtosecond laser - Google Patents
Device and method for parallel direct writing of large-core-diameter fiber gratings by long-focus deep femtosecond laser Download PDFInfo
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Abstract
The invention belongs to the technical field of fiber gratings, and particularly discloses a device and a method for parallel direct writing of a large-core fiber grating by long-focus deep femtosecond laser. The method comprises the following steps: the femtosecond laser output module is used for outputting femtosecond laser; a dichroic mirror; the focusing module is used for modulating the femtosecond laser to form a one-dimensional multi-focus point which is distributed in parallel along the axial direction of the large-core-diameter optical fiber, and the one-dimensional multi-focus point forms long focal depth distribution on the cross section of the large-core-diameter optical fiber; the vision positioning module is used for identifying the one-dimensional multi-focus position information; the three-dimensional workbench module is used for loading the large-core-diameter optical fiber and adjusting the position of the large-core-diameter optical fiber; and the control module is used for controlling the femtosecond laser output module, the vision positioning module and the three-dimensional workbench module to cooperatively act so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter optical fiber core. The invention has the characteristics of high scanning efficiency and uniform and controllable etching lattice.
Description
Technical Field
The invention belongs to the technical field of fiber gratings, and particularly relates to a device and a method for parallel direct writing of a large-core fiber grating by long-focus deep femtosecond laser.
Background
The high-power optical fiber laser occupies an increasingly important strategic position in the fields of national defense and military, processing and manufacturing and the like. The high-power fiber grating is used as a key device of the high-power fiber laser, and the quality of the performance of the high-power fiber grating directly influences the output power, the beam quality and the stability of the whole high-power fiber laser.
At present, there are two main approaches for preparing fiber gratings based on femtosecond laser: (1) The phase mask plate is utilized to assist ultraviolet laser to perform grating writing, which is called a phase mask method for short; (2) The femtosecond laser is directly inscribed, and is called a femtosecond direct writing method for short. The phase mask method is the only commercial preparation method of the large-scale fiber grating, ultraviolet light forms interference fringes with alternate light and shade after passing through a phase mask plate, and the photosensitive fiber is subjected to ultraviolet exposure under the interference fringes to periodically change the refractive index of a fiber core to form the fiber grating. The method has obvious defects, is limited by the photosensitive wavelength of the optical fiber, and the etching light source generally adopts a 193nm or 248nm excimer laser which has extremely high requirements on coherence and high price; a phase mask plate matched with the grating design needs to be customized, so that the price is high, and the grating writing flexibility is seriously influenced; and stripping the coating layer of the optical fiber to carry out hydrogen-carrying sensitization on the optical fiber to be etched. The femtosecond direct writing method directly irradiates the fiber core of the optical fiber by using femtosecond laser with high peak power to cause permanent change of the refractive index of the fiber core, and provides a new approach for preparing the fiber grating. Because the writing mechanism is different, in the process of preparing the fiber grating by the femtosecond direct writing method, the hydrogen-carrying sensitization of the optical fiber is not needed, and the strict requirement on the coherence of a light source is not needed; the optical fiber coating layer does not need to be stripped; has the characteristics of good thermal stability, flexible preparation, low damage threshold, high temperature resistance and the like.
In the traditional method, the hydrogen-carrying pressure required in the process of carrying hydrogen and sensitizing the optical fiber is large, and the time consumption is long. For ordinary single mode fiber, hydrogen is downloaded at room temperature for about 2 weeks. The large-core-diameter double-cladding fiber grating widely used for the resonant cavity mirror of the high-power fiber laser at present has larger fiber core and cladding sizes, and the time for hydrogen-carrying sensitization is greatly prolonged. The process of writing the grating by the femtosecond direct writing method is a nonlinear process, does not depend on the photosensitivity of the optical fiber, does not need to carry out hydrogen sensitization on the optical fiber, can carry out rapid writing and reduces the influence caused by the instability of a writing system. And the grating structure etched by the femtosecond direct writing method can resist high temperature, and can bear the temperature of 1000 ℃ without being erased. Therefore, the femtosecond direct writing large-core fiber grating is necessary.
The femtosecond laser direct writing is divided into the following steps according to different writing modes: point-by-point direct writing, line-by-line direct writing, face-by-face direct writing and fiber core scanning direct writing. Among them, the point-by-point direct writing method is most commonly used. If the femtosecond laser is adopted to directly write the large-core fiber grating point by point, the area of the single-point refractive index change region depends on the size of an etching focal spot, and the area ratio of the single-point refractive index change region to the effective mode field area of the fundamental mode is extremely small, the coupling efficiency of the prepared fiber grating is low, and the fiber grating with high reflectivity is difficult to form. The line-by-line direct writing method can effectively overcome the problem of small modulation area of the single-point refractive index by moving the optical fiber and connecting points to lines one by one. Therefore, the femtosecond line-by-line direct writing method is more suitable for preparing the large-core fiber grating.
However, the line-by-line direct writing fiber grating requires compact point-by-point etching and connecting into lines on the cross section of the fiber at different positions along the axial direction of the fiber, and the number of the etching points is large. The method is realized by frequently controlling the high-precision electric control displacement table fixed by the optical fiber to repeatedly move in the Y direction and the X direction, so that the etching dot matrix is not uniform, and the uniform and stable grating track is difficult to obtain.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a device and a method for long-focus deep femtosecond laser parallel direct writing large-core-diameter fiber bragg grating, wherein the device for long-focus deep femtosecond laser point-by-point direct writing and multi-beam parallel processing of the grating is correspondingly designed by combining the characteristics of a large-core-diameter fiber and the grating writing process characteristics thereof, and the structures and specific arrangement modes of key components of the device, such as a femtosecond laser output module, a dichroic mirror, a focusing module, a visual positioning module and a three-dimensional worktable module are researched and designed, so that the problems of low multi-point scanning efficiency and uneven etching dot matrix in the traditional femtosecond line-by-line direct writing process of the large-core-diameter fiber bragg grating are correspondingly and effectively solved, the femtosecond laser forms multi-focus distribution in the fiber axial direction and the long-focus deep distribution on the cross section of the fiber, and the device is suitable for preparing the uniform and stable large-core-diameter fiber bragg grating, and has important value in the line-by line direct writing aspect of the high-speed large-core-diameter fiber bragg grating.
To achieve the above object, according to one aspect of the present invention, there is provided an apparatus for parallel direct writing of a large core fiber grating by a long-focus deep femtosecond laser, comprising:
the femtosecond laser output module is used for outputting the collimated femtosecond laser with specified energy;
a dichroic mirror for receiving the collimated femtosecond laser and changing a direction of the collimated femtosecond laser;
the focusing module comprises a diffraction cone lens, a one-dimensional diffraction beam splitter and a focusing lens which are sequentially arranged along a light path, collimated femtosecond laser reflected by the dichroic mirror sequentially passes through the diffraction cone lens, the one-dimensional diffraction beam splitter and the focusing lens to form one-dimensional multiple focuses which are axially distributed in parallel along the large-core-diameter optical fiber, and the one-dimensional multiple focuses form long focal depth distribution on the cross section of the large-core-diameter optical fiber;
the vision positioning module is used for identifying the one-dimensional multi-focus position information;
the three-dimensional workbench module is used for loading the large-core-diameter optical fiber and adjusting the position and the motion track of the large-core-diameter optical fiber according to the position information;
and the control module is used for controlling the femtosecond laser output module, the vision positioning module and the three-dimensional workbench module to cooperatively act, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter fiber core, and the long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter fiber grating by the one-dimensional multi-focus along the X direction is realized.
As a further preferred, the femtosecond laser output module comprises a femtosecond light source, an attenuation unit and a beam expansion unit which are sequentially arranged, the femtosecond light source outputs femtosecond laser with specified power under the action of the control module, and the attenuation unit is used for receiving the femtosecond laser and adjusting the power of the femtosecond laser.
As a further preferred, the attenuation unit comprises a half-wave plate and a polarization splitting prism which are arranged along the optical path in sequence.
As a further preference, the beam expanding unit includes a plano-concave lens and a plano-convex lens arranged in this order along the optical path.
Preferably, the femtosecond laser output module further comprises a first diaphragm arranged between the femtosecond light source and the attenuation unit;
and the optical shutter and the second diaphragm are arranged between the beam expanding unit and the dichroic mirror, and the optical shutter is in communication connection with the control module.
Preferably, the vision positioning module includes a first imaging unit and a second imaging unit, the first imaging unit is used for identifying the position information of the one-dimensional multifocal lens along the axial direction of the large-core-diameter optical fiber, and the second imaging unit is used for identifying the position information of the one-dimensional multifocal lens along the radial section of the large-core-diameter optical fiber.
Further preferably, the first imaging unit and the second imaging unit each include a CCD camera, a spectroscope, and an illumination light source.
Preferably, the three-dimensional workbench module comprises a high-precision three-dimensional electric control displacement table and an optical fiber clamp arranged on the high-precision three-dimensional electric control displacement table, and the high-precision three-dimensional electric control displacement table is in communication connection with the control module.
According to another aspect of the present invention, there is also provided a method for parallel direct writing of a large-core fiber grating by a long-focus deep femtosecond laser, which is implemented by using the above apparatus, and comprises the following steps:
s1, outputting a collimated femtosecond laser with specified energy;
s2, after passing through the dichroic mirror, the collimated femtosecond laser enters a diffraction cone lens, a one-dimensional diffraction beam splitter and a focusing lens which are arranged along a light path to form a one-dimensional multifocal parallel distributed along the axial direction of the large-core-diameter optical fiber, and the one-dimensional multifocal forms long focal depth distribution on the cross section of the large-core-diameter optical fiber;
s3, identifying the position information of the one-dimensional multi-focus, and adjusting the position of the large-core-diameter optical fiber according to the position information to enable the one-dimensional multi-focus to be focused on the junction of the fiber core and the cladding of the large-core-diameter optical fiber in the Z direction;
and S4, the control module controls the three-dimensional workbench module to act, and simultaneously adjusts the output power of the collimated femtosecond laser according to the etching path, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter optical fiber core, and long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter optical fiber grating by the one-dimensional multi-focus in the Y direction are realized.
Preferably, the control module adjusts pump power of a femtosecond light source main amplification stage or a rotating half-wave plate, so as to control the femtosecond laser transmitted from the polarization splitting prism to reach an optimal etching energy range.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. the invention enables the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction to cover the mode field diameter of the large-core-diameter fiber core, so as to realize that the one-dimensional multi-focus performs long-focus depth and multi-row parallel point-by-point direct writing on the large-core-diameter fiber grating along the X direction, and the invention has the characteristics of high scanning efficiency and uniform and controllable etching dot matrix.
2. According to the invention, a single beam of femtosecond laser is expanded by a beam expanding unit, the on-off of the laser is controlled by an optical shutter, and the expanded laser is focused on a large-core-diameter optical fiber core to be processed by a focusing system; the method comprises the following steps of (1) assisting in positioning a grating track and leveling a sample table through a visible light imaging unit consisting of a CCD camera, an illumination light source and the like; and then, the periodic fiber bragg grating point-by-point direct writing is carried out by matching with the movement of the high-precision electric control displacement table. The invention utilizes a focusing system consisting of the diffraction cone lens, the one-dimensional diffraction beam splitter and the focusing lens to ensure that the femtosecond laser forms multi-focus distribution in the axial direction of the optical fiber and long focal depth distribution on the cross section of the optical fiber, and the mode of point-by-point direct writing of the long focal depth femtosecond laser and multi-beam parallel processing effectively solves the problems of low multi-point scanning efficiency and uneven etching dot matrix in the traditional femtosecond line-by-line direct writing process of the large-core-diameter optical fiber grating, is suitable for preparing the uniform and stable large-core-diameter optical fiber grating, and has important value in the aspect of line-by-line direct writing of the high-speed large-core-diameter optical fiber grating.
Drawings
FIG. 1 is a schematic diagram of an apparatus for parallel write-through of a large-core fiber grating by a long-focus deep femtosecond laser according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the optical path of a focusing system according to an embodiment of the present invention;
FIG. 3 is a schematic view of a one-dimensional multi-focal distribution of etched spots formed in the fiber axis direction in accordance with one embodiment of the present invention;
FIG. 4 is a schematic diagram of a long depth of focus profile of an etched spot formed on a cross-section of an optical fiber according to one embodiment of the present invention.
In all the figures, the same reference numerals denote the same features, in particular: 1-a femtosecond light source; 2-a first diaphragm; 3-a half-wave plate; 4-a polarization beam splitter prism; 5-a beam expanding unit; 6-light shutter; 7-a second diaphragm; an 8-dichroic mirror; 9-a focusing system; 10-large core diameter optical fiber to be etched; 11-a fiber clamp; 12-a high-precision three-dimensional electric control displacement table; 13-a first imaging unit; 14-a second imaging unit; 15-a computer; 001-plano-concave lens; 002-plano-convex lens; a 003-diffractive axicon; 004-one-dimensional diffractive beam splitter; 005-a focusing lens; 006-CCD camera; 007-spectroscope; 008-illumination light source; 100-a fiber core; 101-an optical fiber inner cladding; 102-etching the light spot.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, an apparatus for parallel direct writing a large-core fiber grating by a long-focus deep femtosecond laser according to an embodiment of the present invention includes: the femtosecond laser output module is used for outputting the collimated femtosecond laser with specified energy; a dichroic mirror 8 for receiving the collimated femtosecond laser and changing a direction of the collimated femtosecond laser; the focusing module 9 comprises a diffraction cone lens 003, a one-dimensional diffraction beam splitter 004 and a focusing lens 005 which are sequentially arranged along a light path, collimated femtosecond laser reflected by the dichroic mirror 8 sequentially passes through the diffraction cone lens 003, the one-dimensional diffraction beam splitter 004 and the focusing lens 005 to form one-dimensional multiple focuses which are axially distributed in parallel along the large-core-diameter optical fiber, and the one-dimensional multiple focuses form long focal depth distribution on the cross section of the large-core-diameter optical fiber; the vision positioning module is used for identifying the one-dimensional multi-focus position information; the three-dimensional workbench module is used for loading the large-core-diameter optical fiber and adjusting the position and the motion track of the large-core-diameter optical fiber according to the position information; and the control module is used for controlling the femtosecond laser output module, the vision positioning module and the three-dimensional workbench module to cooperatively act, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter fiber core, and the long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter fiber grating by the one-dimensional multi-focus along the X direction is realized.
Based on the content of the above device embodiment, as an optional embodiment, the femtosecond laser output module includes a femtosecond light source 1, an attenuation unit and a beam expansion unit 5, which are sequentially arranged, the femtosecond light source 1 outputs femtosecond laser with specified power under the action of the control module, and the attenuation unit is used for receiving the femtosecond laser and adjusting the power of the femtosecond laser. The attenuation unit comprises a half-wave plate 3 and a polarization beam splitter prism 4 which are sequentially arranged along an optical path. The beam expanding unit 5 includes a plano-concave lens 001 and a plano-convex lens 002 arranged in this order along the optical path.
Based on the content of the above device embodiment, as an optional embodiment, the femtosecond laser output module further includes a first diaphragm 2 disposed between the femtosecond light source 1 and the attenuation unit; and a light shutter 6 and a second diaphragm 7 arranged between the beam expanding unit 5 and the dichroic mirror 8, wherein the light shutter 6 is in communication connection with the control module.
Based on the content of the above device embodiment, as an alternative embodiment, the vision positioning module includes a first imaging unit 13 and a second imaging unit 14, the first imaging unit 13 is configured to identify position information of the one-dimensional multifocal along the axial direction of the large-core optical fiber, and the second imaging unit 14 is configured to identify position information of the one-dimensional multifocal along a radial cross section of the large-core optical fiber.
Based on the above description of the embodiment of the apparatus, as an alternative embodiment, the first imaging unit 13 and the second imaging unit 14 each include a CCD camera 006, a spectroscope 007, and an illumination light source 008.
Based on the content of the above device embodiment, as an optional embodiment, the three-dimensional workbench module includes a high-precision three-dimensional electronic control displacement table 12 and an optical fiber clamp 11 disposed on the high-precision three-dimensional electronic control displacement table 12, and the high-precision three-dimensional electronic control displacement table 12 is in communication connection with the control module.
Based on the content of the above-mentioned apparatus embodiment, as an optional embodiment, this embodiment provides an apparatus for parallel direct writing of a large-core fiber grating by using a long-focus deep femtosecond laser, where the apparatus includes: the device comprises a femtosecond light source 1, a first diaphragm 2, a half-wave plate 3, a polarization beam splitter prism 4, a beam expanding unit 5, a light shutter 6, a second diaphragm 7, a dichroic mirror 8, a focusing system 9, a large-core-diameter optical fiber 10 to be etched, an optical fiber clamp 11, a high-precision three-dimensional electric control displacement table 12, a first imaging unit 13, a second imaging unit 14 and a computer 15. In this embodiment, the half-wave plate 3 and the polarization beam splitter prism 4 constitute an attenuation device for continuously adjusting the femtosecond laser pulse energy involved in the etching process. The optical shutter 6 is connected with a computer 15 and used for controlling the on-off time of the femtosecond laser. The first diaphragm 2 and the second diaphragm 7 are used for adjusting the positions of optical elements in a femtosecond etching light path; after the femtosecond laser passes through the beam expanding unit 5 for expansion, the femtosecond laser sequentially passes through the optical shutter 6 and the central position of the dichroic mirror 8; and then the fiber is focused to the junction position of the fiber core and the cladding of the large-core-diameter optical fiber 10 to be etched through the focusing module 9. The optical fiber clamp 11 is arranged on the high-precision three-dimensional electric control displacement table 12 and used for fixing the large-core-diameter optical fiber 10 to be etched; the computer 15 is used for linkage control of the optical shutter 6 and the high-precision three-dimensional electric control displacement table 12. The first imaging unit 13 is coaxially confocal with the femtosecond etching light path, and is used for positioning the position of an etching light spot in the optical fiber axial direction and assisting in leveling the objective table; the second imaging unit 14 is used for positioning the position of the etching light spot on the cross section of the optical fiber.
The femtosecond light source 1 adopts a high repetition frequency femtosecond laser system consisting of an SESAM seed source, a CFBG stretcher, a multi-stage flexible optical fiber amplifier and a grating pair compressor, the central wavelength of output pulse is 1030nm, the repetition frequency is 1MHz, the pulse width is 300fs, and the diameter of collimation output light spot is about 4mm. And the output energy of the femtosecond light source can be controlled by adjusting the size of the pumping current of the main amplification stage through the computer.
The beam expanding unit 5 is composed of a plano-concave lens 001 with a focal length of-75 mm and a plano-convex lens 002 with a focal length of 300mm, so that the light spot is expanded by 4 times.
The optical shutter 6 adopts a single-blade type optical shutter model: SH1/M and a matched shutter controller model: SC10, response time 10ms, exposure in the range of 80% -20%.
The dichroic mirror 8 is plated with a high-transmittance dielectric film in a visible light waveband and a high-reflection dielectric film in a 1um waveband.
The focusing module 9 is composed of a diffraction cone lens 003, a one-dimensional diffraction beam splitter 004 and a focusing lens 005, so that a one-dimensional multi-focus distribution is formed in the axial direction of the optical fiber, a long focal depth distribution is formed on the cross section of the optical fiber, and the light path schematic diagram of the part is shown in fig. 2.
Assuming that the prepared large-core fiber grating has a core diameter D, a grating period T and a grating length L, the diffraction cone lens 003 and the focusing lens 005 act together, and the realized focal length needs to be equivalent to the diameter of the fiber core, namely the focal depth D depth D is approximately distributed; the one-dimensional diffractive beam splitter 004 splits the femtosecond laser into N beams, forming N focal points in the fiber axis direction. Therefore, the movement interval of the high-precision three-dimensional electric control displacement table 12 needs to be set to Δ T = T × N; the moving frequency is set to N 0 = L/Δ T. The computer 15 controls the high-precision three-dimensional electric control displacement table 12 to move, and then parallel direct writing of multiple beams of femtosecond lasers can be realized. The one-dimensional multi-focal distribution of the etched spots formed in the fiber axis is schematically shown in fig. 3. The etched spot forms a schematic long focal depth profile over the cross-section of the fiber as shown in fig. 4.
The diffraction cone lens 003 and the one-dimensional diffraction beam splitter 004 need to be designed according to the requirements of the fiber grating, such as corresponding tele DOE elements and multi-focus DOE elements.
Taking the preparation of a large-core diameter Bragg fiber grating with the core diameter of 25um as an example, according to the Bragg grating formula
Calculation, assuming core effective index
Center wavelength 1064nm, bandwidth 3nm, reflectivity>99%, the required grating period is about 70um and the grating length is about 36mm. Calculated, if the incident light spot diameter of the diffraction cone lens expands to 16mm, the separation angle theta is adopted f The (1 × N type) one-dimensional diffraction beam splitter with the angle of 28.346 ° and the focusing lens with the focal length F =2mm can realize one-dimensional multi-focus (N =15, the distance of 70 um) distribution in the optical fiber axial direction after passing through the focusing module, and the focal depth on the optical fiber cross section reaches 25um, and the optical fiber fundamental mode area to be etched with large core diameter is completely covered.
Based on the content of the above device embodiment, this embodiment provides a method for parallel direct writing of a large-core fiber grating by using a long-focus deep femtosecond laser, which includes the following steps:
s1, outputting the collimated femtosecond laser with the designated energy.
Specifically, the femtosecond light source is fixed and turned on, the main amplification level pumping power of the femtosecond light source is adjusted through a computer, and weak light output is set firstly so as to facilitate light path debugging; opening the optical shutter; inserting a half-wave plate, a polarization splitting prism, a beam expanding unit, a light shutter, a dichroic mirror and a focusing module into a light path in sequence, and building the light path as required; the positions of the optical elements are adjusted by utilizing the first diaphragm and the second diaphragm; and fixing the large-core-diameter optical fiber to be etched on a high-precision three-dimensional electric control displacement table by using an optical fiber clamp.
S2, after passing through the dichroic mirror 8, the collimated femtosecond laser enters the diffraction cone lens 003, the one-dimensional diffraction beam splitter 004 and the focusing lens 005 which are arranged along the optical path to form a one-dimensional multi-focus point which is distributed in parallel along the axial direction of the large-core-diameter optical fiber, and the one-dimensional multi-focus point forms long focal depth distribution on the cross section of the large-core-diameter optical fiber.
Specifically, a light path of a first imaging unit is required to be built, the light path is coaxially confocal with a femtosecond etching light path, the relative position of an optical fiber to be etched with a large core diameter is adjusted, and the position of an etching light spot in the axial direction of the optical fiber is positioned by utilizing visible light output by an illumination light source in the first imaging unit; the high-precision three-dimensional electric control displacement platform is moved in the X direction, the track of an etching light spot in the axial direction of the optical fiber is observed in real time through a CCD camera in the first imaging unit, and the relative position of the optical fiber to be etched with the large core diameter and an object carrying platform on the high-precision three-dimensional electric control displacement platform is adjusted, so that the etching light spot is always positioned in the center of the optical fiber core without relative movement and the appearance of the etching light spot is kept unchanged.
And S3, identifying the position information of the one-dimensional multi-focus, and adjusting the position of the large-core-diameter optical fiber according to the position information, so that the one-dimensional multi-focus is focused on the junction of the fiber core and the cladding of the large-core-diameter optical fiber in the Z direction. Specifically, in this step, the femtosecond laser transmitted from the polarization splitting prism is controlled to reach the optimal etching energy range by adjusting the pump power of the femtosecond light source main amplification stage or rotating the half-wave plate through the computer.
And S4, the control module controls the three-dimensional workbench module to act, and simultaneously adjusts the output power of the collimated femtosecond laser according to the etching path, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter optical fiber core, and long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter optical fiber grating by the one-dimensional multi-focus in the Y direction are realized.
And S5, setting relevant parameters (moving interval and moving frequency) of the high-precision three-dimensional electric control displacement platform and relevant parameters (shutter opening/closing time) of the optical shutter through the computer, and controlling the large-core-diameter optical fiber to be etched to move until the preparation of the large-core-diameter optical fiber grating is finished.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A device for parallel direct writing of large-core fiber gratings by long-focus deep femtosecond laser is characterized by comprising:
the femtosecond laser output module is used for outputting the collimated femtosecond laser with specified energy;
a dichroic mirror (8) for receiving the collimated femtosecond laser light and changing a direction of the collimated femtosecond laser light;
the focusing module (9) comprises a diffraction cone lens (003), a one-dimensional diffraction beam splitter (004) and a focusing lens (005) which are sequentially arranged along a light path, collimated femtosecond laser reflected by the dichroic mirror (8) sequentially passes through the diffraction cone lens (003), the one-dimensional diffraction beam splitter (004) and the focusing lens (005) to form one-dimensional multiple focuses which are axially distributed in parallel along the large-core-diameter optical fiber, and the one-dimensional multiple focuses form long focal depth distribution on the cross section of the large-core-diameter optical fiber to completely cover a large-core-diameter basic mode area of the optical fiber to be etched;
the vision positioning module is used for identifying the one-dimensional multi-focus position information;
the three-dimensional workbench module is used for loading the large-core-diameter optical fiber and adjusting the position and the motion track of the large-core-diameter optical fiber according to the position information;
and the control module is used for controlling the femtosecond laser output module, the vision positioning module and the three-dimensional workbench module to cooperatively act, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter fiber core, and the long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter fiber grating by the one-dimensional multi-focus along the X direction is realized.
2. The apparatus for parallel direct writing of a large-core fiber grating by using a long-focus deep femtosecond laser according to claim 1, wherein the femtosecond laser output module comprises a femtosecond light source (1), an attenuation unit and a beam expansion unit (5) which are sequentially arranged, the femtosecond light source (1) outputs the femtosecond laser with a specified power under the action of the control module, and the attenuation unit is used for receiving the femtosecond laser and adjusting the power of the femtosecond laser.
3. The device for parallel direct writing of the large-core fiber grating by the long-focus deep femtosecond laser according to the claim 2, wherein the attenuation unit comprises a half-wave plate (3) and a polarization splitting prism (4) which are arranged along the optical path in sequence.
4. The device for parallel direct writing of the large-core fiber grating by the long-focus deep femtosecond laser according to claim 2, wherein the beam expanding unit (5) comprises a plano-concave lens (001) and a plano-convex lens (002) which are sequentially arranged along the optical path.
5. The apparatus for parallel direct writing of a large core fiber grating by a long-focus deep femtosecond laser according to claim 2, wherein the femtosecond laser output module further comprises a first diaphragm (2) disposed between the femtosecond light source (1) and the attenuation unit;
and a light shutter (6) and a second diaphragm (7) arranged between the beam expanding unit (5) and the dichroic mirror (8), wherein the light shutter (6) is in communication connection with the control module.
6. The apparatus for parallel direct writing of a large-core fiber grating by a long-focus deep femtosecond laser according to claim 1, wherein the vision positioning module comprises a first imaging unit (13) and a second imaging unit (14), the first imaging unit (13) is used for identifying the position information of the one-dimensional multifocal along the axial direction of the large-core fiber, and the second imaging unit (14) is used for identifying the position information of the one-dimensional multifocal along the radial section of the large-core fiber.
7. The device for parallel direct writing of the large-core fiber grating by the long-focus deep femtosecond laser according to claim 6, wherein the first imaging unit (13) and the second imaging unit (14) each comprise a CCD camera (006), a spectroscope (007) and an illumination light source (008).
8. The device for parallel direct writing of the large-core fiber grating by the long-focus deep femtosecond laser according to claim 1, wherein the three-dimensional workbench module comprises a high-precision three-dimensional electronic control displacement table (12) and a fiber clamp (11) arranged on the high-precision three-dimensional electronic control displacement table (12), and the high-precision three-dimensional electronic control displacement table (12) is in communication connection with the control module.
9. A method for parallel direct writing of large-core fiber gratings by long-focus deep femtosecond laser, which is realized by the device according to any one of claims 1 to 8, and comprises the following steps:
s1, outputting a collimated femtosecond laser with specified energy;
s2, after passing through a dichroic mirror (8), the collimated femtosecond laser enters a diffraction cone lens (003), a one-dimensional diffraction beam splitter (004) and a focusing lens (005) which are arranged along a light path to form a one-dimensional multifocal parallel distributed along the axial direction of the large-core-diameter optical fiber, and the one-dimensional multifocal forms long focal depth distribution on the cross section of the large-core-diameter optical fiber;
s3, identifying the position information of the one-dimensional multi-focus, and adjusting the position of the large-core-diameter optical fiber according to the position information to enable the one-dimensional multi-focus to be focused on the junction of the fiber core and the cladding of the large-core-diameter optical fiber in the Z direction;
and S4, the control module controls the three-dimensional workbench module to act, and simultaneously adjusts the output power of the collimated femtosecond laser according to the etching path, so that the etching depth of the one-dimensional multi-focus with specified energy for etching in the Z direction covers the mode field diameter of the large-core-diameter optical fiber core, and long-focus depth and multi-row parallel point-by-point direct writing of the large-core-diameter optical fiber grating by the one-dimensional multi-focus in the X direction are realized.
10. The method for parallel direct writing of large-core fiber gratings by long-focus deep femtosecond laser according to claim 9, wherein the control module adjusts the pump power of the main amplification stage of the femtosecond light source (1) or rotates the half-wave plate (3), so as to control the femtosecond laser transmitted from the polarization splitting prism (4) to reach the optimal etching energy range.
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