CN109655964B - Method and device for preparing long-period fiber grating with fixed-point coating on line - Google Patents
Method and device for preparing long-period fiber grating with fixed-point coating on line Download PDFInfo
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- CN109655964B CN109655964B CN201910151131.2A CN201910151131A CN109655964B CN 109655964 B CN109655964 B CN 109655964B CN 201910151131 A CN201910151131 A CN 201910151131A CN 109655964 B CN109655964 B CN 109655964B
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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
- G02B6/02152—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating involving moving the fibre or a manufacturing element, stretching of the fibre
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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
- G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
- G02B6/021—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the core or cladding or coating, e.g. materials, radial refractive index profiles, cladding shape
- G02B6/02104—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the core or cladding or coating, e.g. materials, radial refractive index profiles, cladding shape characterised by the coating external to the cladding, e.g. coating influences grating properties
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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
- G02B6/02147—Point by point fabrication, i.e. grating elements induced one step at a time along the fibre, e.g. by scanning a laser beam, arc discharge scanning
Abstract
The invention designs a method and a device for preparing a long-period fiber grating with a fixed-point coating on line. A pulse counter located at the laser receives the pulses and begins counting. And when the counting value reaches a set value, triggering the laser to emit laser pulses. The laser pulse passes through the phase/amplitude mask plate, and a periodic variation structure is formed on the refractive index of a local area on the fiber core of the optical fiber. And simultaneously, a pulse counter positioned on the coating device starts the coating device according to a pulse counting set value. The coating device adjusts the length and the thickness of a coating layer through the starting time, and the coating material can be various functional materials.
Description
Technical Field
The invention belongs to the technical field of fiber grating preparation, and particularly relates to a method and a device for preparing a long-period fiber grating with a fixed-point coating on line.
Background
With the development of the times, the requirements on the optical fiber sensor are continuously increased. Currently, the optical fiber sensor is developing towards high performance, large capacity, multi-parameter and array. The development of a new generation of optical fiber sensor network has become a major topic of a new information wave.
The long-period fiber grating is a new-generation optical passive device, has good stability, small volume and flexible use, and is also applied to the fields of optical sensing and optical communication increasingly widely. By periodic index modulation on the longitudinal axis of the fiber, the fundamental mode is coupled into the cladding mode, which spectrally exhibits a loss of a specific wavelength. By coating different materials on the surface of the long-period grating, the long-period grating can measure various parameters such as temperature, humidity, refractive index, strain, hydrogen and the like. Conventional methods of fabricating long period grating sensors are typically based on off-line fabrication. After the optical fiber is prepared, the coating layer is removed, then the optical fiber is etched by a laser, and finally various sensitive coating materials are coated. The long-period grating sensor prepared by the method can be applied to the sensing fields of temperature, humidity, refractive index and the like. However, this method is inefficient to produce and requires a long time to produce when a large number of long-period grating sensors need to be used. In addition, the surface of the optical fiber is easily damaged in the process of removing the optical fiber coating layer. This causes a significant reduction in sensor strength.
Chinese patent CN107632336A discloses a long period grating and a method for manufacturing the same. The optical fiber with high numerical aperture is heated by emitting laser light by a carbon dioxide laser after removing the optical fiber coating layer. By diffusing the doping elements in the core with a high numerical aperture, the mode field is enlarged. This repetitive structure constitutes a long period grating. The method needs to peel off the coating layer, so that the preparation efficiency is low, the sensor is easy to damage, and the strength of the sensor is reduced.
Chinese patent CN106018350A discloses an SPR heavy metal ion sensing head of long-period fiber grating and a manufacturing method thereof. The invention plates a layer of metal film on the surface of the long-period fiber grating, and then prepares another layer of modified chitosan film on the surface of the metal film. The sensor is able to detect heavy metal ions by coupling light to the surface excitation SPR signal through the long period grating. However, when the method is used in large quantity, the preparation is long and the rapid large-scale preparation is difficult.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method and a device for preparing a long-period fiber grating with a fixed-point coating on line, and realizing rapid large-scale preparation.
The technical scheme adopted by the invention for solving the technical problems is as follows: the invention firstly provides a device for preparing long-period fiber grating with fixed-point coating on line, which comprises: the device comprises an optical fiber preform, a feeding device, a graphite furnace, a coating device, a curing furnace, a driving traction wheel and a phase mask plate; the optical fiber preform rod and the feeding device are used for feeding the preform rod into the graphite furnace at a preset speed, the temperature gradient and the temperature in the graphite furnace are controllable, the tip end of the preform rod is melted, the active traction wheel drives the optical fiber to rotate according to the set speed, and a photoelectric encoder arranged behind the active traction wheel sends pulses according to the rotating arc length; according to the instruction of a pulse counter, a laser emits laser pulses, the laser pulses form interference fringes through a phase mask plate, periodic fringes are formed on an optical fiber, and a long-period fiber grating is engraved; the coating device receives the instruction, coats a special coating with set thickness, length and material on the partial area of the surface of the grating and enters a curing furnace; the coating device coats special coatings with set thickness, length and material on the partial area of the grating surface according to the instruction, and then enters the curing device.
The invention also provides a method for preparing the long-period fiber grating with the fixed-point coating on line by using the device, which comprises the following steps:
step one, after a prefabricated rod is melted and drawn into an optical fiber through a graphite furnace of a wire drawing tower, the optical fiber is irradiated by laser through interference fringes formed by a lens group and a phase mask plate; step two, the femtosecond laser forms periodic defect areas on the surface of the optical fiber and the fiber core area to form a long-period grating; thirdly, according to a pulse signal sent by a light spot encoder positioned behind a driving traction wheel of the wire drawing tower, a pulse counter positioned in the femtosecond laser receives the pulse signal and sends laser pulse according to a set value; a counter positioned on the coating device receives the pulse signal and is started when the counting reaches a set value; fifthly, the coating device controls the length and the thickness of the coating material coated on the partial area of the surface of the grating according to the starting time and then enters a curing furnace for curing; and step six, connecting a plurality of coating devices in series to form a plurality of grating sensors with different coating areas on the surface of the fiber grating.
According to the technical scheme, the active traction wheel clamps the optical fiber, sends a pulse signal according to the unit rotating distance of the outer arc edge, and is calculated by the following formula:
r＝2×π*R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the unit rotation distance of the outer arc edge; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
According to the technical scheme, the set value of a pulse counter in the laser is L/r, L is the interval of writing the grating according to actual needs, and the pulse counter is cleared when the count value reaches.
According to the technical scheme, when the system is started, the laser emits the first laser pulse, then all the pulse counters are cleared, the pulse counters serve as counting starting points, and the inscribed gratings are symmetrically distributed according to the inscribed positions.
According to the technical scheme, when a pulse counter in the coating device counts for the first time, the set value is (L0 +/-k)/r, wherein L0 is the interval between the position of the laser pulse on the optical fiber and the position of the coating device on the optical fiber, and k is the length deviating from the center of the grating; the pulse counter count is then cleared and the subsequent set value is L/r.
The invention also provides a method for preparing the long-period fiber grating with the fixed-point coating on line, which comprises the following steps that firstly, a prefabricated rod is melted and drawn into an optical fiber through a graphite furnace of a wire drawing tower and is irradiated by laser through interference fringes formed by a lens group and a phase mask plate; step two, the femtosecond laser forms periodic defect areas on the surface of the optical fiber and the fiber core area to form a long-period grating; thirdly, according to a pulse signal sent by a light spot encoder positioned behind the active traction wheel of the drawing tower, a pulse counter positioned in the active traction wheel receives the pulse signal and sends the pulse signal according to a set value; and step four, the laser receives the pulse signal and emits laser pulse. The coating device receives the pulse signal, and after a time delay program, the special coating device is started; fifthly, the coating device controls the length and the thickness of the coating material coated on the partial area of the surface of the grating according to the starting time and then enters a curing furnace for curing; and step six, connecting a plurality of coating devices in series, and forming a plurality of grating sensors with different coating areas on the surface of the fiber grating.
According to the technical scheme, the active traction wheel clamps the optical fiber, sends a pulse signal according to the unit rotating distance of the outer arc edge, and is calculated by the following formula:
r＝2×π*R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the unit rotation distance of the outer arc edge; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
According to the technical scheme, the set value of the pulse counter is L/r, and L is the interval of the written grating according to actual needs; and clearing when the count value reaches.
According to the technical scheme, the delay time length of the delay program is (L0 +/-k)/v, wherein L0 is the interval between the position of the laser pulse on the optical fiber and the coating position of the coating device on the optical fiber, k is the length deviating from the center of the grating, and v is the fiber drawing speed; then when the grating interval L is smaller than L0, the delay duration of the delay procedure is (LL ± k)/v, where LL is L0 mod L, i.e., LL is the remainder of L0 divided by L, and when the grating interval L is greater than or equal to L0, the duration of the delay procedure is (L0 ± k)/v, and mod is the remainder.
The invention has the following beneficial effects: the long-period fiber grating is prepared on line, and the long-period fiber grating can be prepared in a large scale, at low cost, with high efficiency and good consistency; when the long-period fiber grating is etched on line, different coating materials are coated on the surface of the long-period fiber grating, so that the long-period fiber grating sensor can measure a plurality of parameters simultaneously. The long-period fiber grating with the fixed-point coating is engraved on line, so that the long-period fiber grating sensor with the simultaneous multi-parameter measurement capability can be prepared in a large scale, high efficiency and low cost.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic structural diagram of an apparatus for on-line mass-writing a long period grating with a fixed-point coating in an embodiment of the present invention;
FIG. 2 is a flow chart of a method according to a first embodiment of the present invention;
FIG. 3 is a flowchart of a method according to a second embodiment of the present invention;
FIG. 4 is a schematic structural view of a long-period optical fiber sensor with a spot-on coating prepared in an embodiment of the present invention;
FIG. 5 is a transmission spectrum of a long-period fiber sensor prepared according to an embodiment of the present invention;
in fig. 1: 101-optical fiber preform and feeding device, 102-graphite furnace, 103-coating device, 104-curing device, 105-coating device, 106-curing device, 107-active traction wheel and take-up device, 108-phase mask plate and 109-laser.
In fig. 4: 401-fiber outer coating, 402-fiber quartz coating, 403-fiber inner coating, 404-grating, 405-fiber one coating material, 406-fiber core, 407-fiber other coating material, 408-fiber other coating material.
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.
The first embodiment is as follows:
in an embodiment of the present invention, an apparatus for on-line large-scale preparation of a long-period fiber grating with a fixed-point coating is provided, as shown in fig. 1, including: the device comprises an optical fiber preform and feeding device, a graphite furnace 102, a coating device 103, a curing furnace 104, a coating device 105, a curing device 106, a driving traction wheel 107, a phase mask plate 108 and a laser 109.
The optical fiber preform and feeding apparatus 101 is used to feed the preform into the graphite furnace at a prescribed rate. The temperature gradient and the temperature magnitude in the graphite furnace 102 can be controlled, and the tip of the prefabricated rod is melted. The driving traction wheel 107 drives the optical fiber to rotate according to the set speed. And a photoelectric encoder arranged behind the driving traction wheel sends pulses according to the length of the rotating arc. Laser 109 emits laser pulses according to the pulse counter instructions. The laser pulses form interference fringes through the phase mask 108, forming periodic fringes on the fiber, and writing a long period fiber grating. The coating device 103 receives the instruction and coats the special coating with the set thickness, length and material on the partial area of the grating surface. And then into curing oven 104. The coating device 105 then applies a special coating of a set thickness, length, material on the grating surface partial area according to the instructions, and then enters the curing oven 106. And finally, winding and collecting the optical fiber by using a take-up device.
The number and the position of the coating device and the curing oven can be changed according to the actual requirement.
Example two:
the present embodiment provides a method for on-line mass production of a long-period fiber grating having a spot coating, as shown in fig. 2, using an apparatus for on-line mass production of a long-period fiber grating having a spot coating.
The optical fiber perform rod enters a curing furnace to be melted under the feeding device, and the driving traction wheel drives the optical fiber to rotate. And the photoelectric encoder positioned behind the driving traction wheel transmits pulse signals according to the rotating arc length of the driving traction wheel. The pulse signal period corresponds to the minimum resolution of the optical fiber length, and the minimum resolution is determined according to the code number of the photoelectric encoder and the radius of the active traction wheel. The minimum resolution is calculated according to the following formula:
r＝2×π×R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the minimum resolution; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
When the whole system is started, the laser emits a laser pulse, then all pulse counts are completely cleared, and the counting starting point is set.
When the operation is formally started, when the counting of the first pulse counter reaches a set value, the laser is triggered to emit laser pulses, and the laser pulses form interference fringes through the phase mask plate. The interference fringes form regions with a periodic distribution of refractive index on the optical fiber, forming a long-period fiber grating. The first pulse counter is then cleared and recounted. The set value of the first pulse counter is L/r, and L is the interval of the written grating according to actual needs.
According to the rule that a photoelectric encoder transmits pulse signals, the numerical value of a first pulse counter is multiplied by the minimum distinguishable distance to be converted into the optical fiber drawing length, and the optical fiber length is the distance between adjacent gratings; when the fiber drawing length is smaller than the distance between adjacent gratings, the pulse counter continues to count; and if the length of the drawn wire is equal to the distance between the adjacent gratings, starting a driving program. And if the grating interval is L, when the number of the signals received by the first pulse counter reaches L/r, emitting pulse signals to trigger the laser to complete the writing of one grating. The first pulse counter is cleared and begins counting again.
When the count of the second pulse counter reaches a set value, the coating device 1 is triggered, and the coating device 1 coats a certain length, thickness and material coating layer on a specific area of the surface of the fiber bragg grating according to a set program. And simultaneously, the second pulse counter is cleared and starts counting again.
And the second pulse counter is used for clearing the count and restarting the count when the laser emits the first laser pulse. The first set value of the pulse counter is related to the specific area of the coating device 1 on the surface of the fiber grating according to the position of the laser emitted by the laser on the fiber. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The first set value of the second pulse counter is as follows:
(L0±k)/r，
where L0 is the spacing between the location of the laser pulse on the fiber and the location of the coating apparatus 1 coating the fiber, and k is the length offset from the center of the grating. The second pulse counter count is then cleared and the subsequent set value is L/r.
The optical fiber is then fed into a curing oven for curing.
The optical fiber continues to run under the drive of the driving traction wheel. When the count of the third pulse counter reaches a set value, the coating device 2 is triggered, and the coating device 2 coats a certain length, thickness and material coating on a specific area of the surface of the fiber bragg grating according to a set program. And simultaneously, the third pulse counter is cleared and starts counting again.
And the third pulse counter is used for clearing the count and restarting counting when the laser emits the first laser pulse. The first set value of the pulse counter is related to the specific area of the coating device 2 on the surface of the fiber grating according to the position of the femtosecond laser emitted by the laser on the fiber. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The first setting value of the third pulse counter is as follows:
(L1±k)/r，
where L1 is the spacing between the location of the laser pulse on the fiber and the location of the coating device 2 coating the fiber, and k is the length offset from the center of the grating. The second pulse counter count is then cleared and the subsequent set value is L/r.
The optical fiber is then cured in a curing oven.
More coating devices and curing devices can be installed according to actual needs. The set values are set according to the method described above.
And (4) the coated optical fiber enters a take-up device, and the optical fiber is stored on the upper disc.
Example three:
using the apparatus for on-line mass production of long-period fiber gratings with spot coatings according to the first embodiment, this embodiment provides a method for on-line mass production of long-period fiber gratings with spot coatings, as shown in fig. 3.
The optical fiber perform rod enters a curing furnace to be melted under the feeding device, and the driving traction wheel drives the optical fiber to rotate. And the photoelectric encoder positioned behind the driving traction wheel transmits pulse signals according to the rotating arc length of the driving traction wheel. The pulse signal period corresponds to the minimum resolution of the optical fiber length, and the minimum resolution is determined according to the code number of the photoelectric encoder and the radius of the active traction wheel. The minimum resolution is calculated according to the following formula:
r＝2×π×R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the minimum resolution; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
And a pulse counter positioned in the driving traction wheel receives the pulse signal and transmits the pulse signal according to a set value. The set value of the pulse signal is L/r, and L is the interval of the written grating according to actual needs. The laser receives the pulse signal and emits a laser pulse. The laser pulses form interference fringes through the phase mask. The interference fringes form regions with a periodic distribution of refractive index on the optical fiber, forming a write grating. The pulse counter is then cleared and recountd.
According to the rule that a photoelectric encoder transmits a pulse signal, the numerical value of a pulse counter is multiplied by the minimum distinguishable distance to be converted into the optical fiber drawing length, and the optical fiber length is the distance between adjacent gratings; when the fiber drawing length is smaller than the distance between adjacent gratings, the pulse counter continues to count; and if the wire drawing length is equal to the distance between the adjacent gratings, transmitting a pulse signal. If the interval of the grating is L, when the number of the signals received by the pulse counter reaches L/r, the pulse counter transmits pulse signals, and the pulse counter is cleared and starts counting again.
The coating device 1 receives the pulse signal, triggers the driving program 2 after passing through the delay program 1, and then starts the coating device 1. The coating device 1 coats a certain length, thickness and material of a coating layer on a specific area of the surface of the fiber grating according to a set program.
The delay time of the delay program depends on the position of the laser on the fiber, which is emitted by the laser, and the specific area of the coating device 1 on the surface of the fiber grating. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse.
When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The delay time of the delay program is as follows:
(L0±k)/v，
where L0 is the spacing between the location of the laser pulse on the fiber and the location of the coating apparatus 1 coating the fiber, k is the length of the offset from the center of the grating, and v is the fiber draw speed.
After the delay program 1 is completed for the first time, when the grating interval L is less than L0, the delay duration of the delay program is changed to: (LL ± k)/v, where LL is L0 mod L, i.e., LL is the remainder of L0 divided by L. When the grating interval is greater than or equal to L0, the duration of the time delay program is (L0 + -k)/v.
The coating device 2 receives the pulse signal, triggers the driving program 3 after passing through the delay program 2, and then starts the coating device 2. The coating device 2 coats a certain length, thickness and material of the coating layer on a specific area of the surface of the fiber grating according to a set program.
The delay time of the delay program depends on the position of the laser on the fiber, which is emitted by the laser, and the specific area of the coating device 1 on the surface of the fiber grating. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The delay time of the delay program is as follows:
(L1±k)/v，
where L1 is the spacing between the location of the laser pulse on the fiber and the location of the coating device 2 on the fiber, k is the length of the offset from the center of the grating, and v is the fiber draw speed.
After the delay program 2 completes the first time, when the grating interval L is less than L1, the delay duration of the delay program is changed to: (LL1 ± k)/v, where LL1 ═ L1 mod L, i.e., LL1 is the remainder of L1 divided by L. When the grating interval is greater than or equal to L0, the duration of the time delay program is (L0 + -k)/v.
More coating devices and curing devices can be installed according to actual needs. The set values are set according to the method described above.
And (4) the coated optical fiber enters a take-up device, and the optical fiber is stored on the upper disc.
Fig. 4 shows a long-period optical fiber sensor with a fixed-point coating prepared by the second embodiment and the third embodiment, in which a grating 404 is written on a fiber core, a fiber quartz layer 402 outside the fiber core 406, an optical fiber inner coating 403, an optical fiber outer coating 401 outside the optical fiber inner coating, an optical fiber one-coating material 405, an optical fiber another-coating material 407, and an optical fiber another-coating material 408 are written on the fiber core. The transmission spectrum is shown in fig. 5.
Example four:
a method for preparing long-period optical fiber grating with fixed-point coating on line in large scale is carried out by melting optical fiber prefabricated rod in solidifying furnace under feeding device, driving traction wheel to drive optical fiber to rotate. And the photoelectric encoder positioned behind the driving traction wheel transmits pulse signals according to the rotating arc length of the driving traction wheel. The pulse signal period corresponds to the minimum resolution of the optical fiber length, and the minimum resolution is determined according to the code number of the photoelectric encoder and the radius of the active traction wheel. The minimum resolution is calculated according to the following formula:
r＝2×π×R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the minimum resolution; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
When the whole system is started, the laser emits a laser pulse, then all pulse counts are completely cleared, and the counting starting point is set.
When the operation is formally started, when the counting of the first pulse counter reaches a set value, the laser is triggered to emit laser pulses, and the laser pulses form interference fringes through the phase mask plate. The interference fringes form regions with a periodic distribution of refractive index on the optical fiber, forming a long-period fiber grating. The first pulse counter is then cleared and recounted. The set value of the first pulse counter is L/r, and L is the interval of the written grating according to actual needs.
According to the rule that a photoelectric encoder transmits pulse signals, the numerical value of a first pulse counter is multiplied by the minimum distinguishable distance to be converted into the optical fiber drawing length, and the optical fiber length is the distance between adjacent gratings; when the fiber drawing length is smaller than the distance between adjacent gratings, the pulse counter continues to count; and if the length of the drawn wire is equal to the distance between the adjacent gratings, starting a driving program. And if the grating interval is L, when the number of the signals received by the first pulse counter reaches L/r, emitting pulse signals to trigger the laser to complete the writing of one grating. The first pulse counter is cleared and begins counting again.
When the count of the second pulse counter reaches a set value, the coating device 1 is triggered, and the coating device 1 coats a certain length, thickness and material coating layer on a specific area of the surface of the fiber bragg grating according to a set program. And simultaneously, the second pulse counter is cleared and starts counting again.
And the second pulse counter is used for clearing the count and restarting the count when the laser emits the first laser pulse. The first set value of the pulse counter is related to the specific area of the coating device 1 on the surface of the fiber grating according to the position of the laser emitted by the laser on the fiber. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The first set value of the second pulse counter is as follows:
(L0±k)/r，
where L0 is the spacing between the location of the laser pulse on the fiber and the location of the coating apparatus 1 coating the fiber, and k is the length offset from the center of the grating. The second pulse counter count is then cleared and the subsequent set value is L/r.
The optical fiber is then fed into a curing oven for curing.
The optical fiber continues to run under the drive of the driving traction wheel. When the count of the third pulse counter reaches a set value, the coating device 2 is triggered, and the coating device 2 coats a certain length, thickness and material coating on a specific area of the surface of the fiber bragg grating according to a set program. And simultaneously, the third pulse counter is cleared and starts counting again.
And the third pulse counter is used for clearing the count and restarting counting when the laser emits the first laser pulse. The first set value of the pulse counter is related to the specific area of the coating device 2 on the surface of the fiber grating according to the position of the femtosecond laser emitted by the laser on the fiber. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The first setting value of the third pulse counter is as follows:
(L1±k)/r，
where L1 is the spacing between the location of the laser pulse on the fiber and the location of the coating device 2 coating the fiber, and k is the length offset from the center of the grating. The second pulse counter count is then cleared and the subsequent set value is L/r.
Example five:
a method for preparing long-period optical fiber grating with fixed-point coating on line in large scale is carried out by melting optical fiber prefabricated rod in solidifying furnace under feeding device, driving traction wheel to drive optical fiber to rotate. And the photoelectric encoder positioned behind the driving traction wheel transmits pulse signals according to the rotating arc length of the driving traction wheel. The pulse signal period corresponds to the minimum resolution of the optical fiber length, and the minimum resolution is determined according to the code number of the photoelectric encoder and the radius of the active traction wheel. The minimum resolution is calculated according to the following formula:
r＝2×π×R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the minimum resolution; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
And a pulse counter positioned in the driving traction wheel receives the pulse signal and transmits the pulse signal according to a set value. The set value of the pulse signal is L/r, and L is the interval of the written grating according to actual needs. The laser receives the pulse signal and emits a laser pulse. The laser pulses form interference fringes through the phase mask. The interference fringes form regions with a periodic distribution of refractive index on the optical fiber, forming a write grating. The pulse counter is then cleared and recountd.
According to the rule that a photoelectric encoder transmits a pulse signal, the numerical value of a pulse counter is multiplied by the minimum distinguishable distance to be converted into the optical fiber drawing length, and the optical fiber length is the distance between adjacent gratings; when the fiber drawing length is smaller than the distance between adjacent gratings, the pulse counter continues to count; and if the wire drawing length is equal to the distance between the adjacent gratings, transmitting a pulse signal. If the interval of the grating is L, when the number of the signals received by the pulse counter reaches L/r, the pulse counter transmits pulse signals, and the pulse counter is cleared and starts counting again.
The coating device 1 receives the pulse signal, triggers the driving program 2 after passing through the delay program 1, and then starts the coating device 1. The coating device 1 coats a certain length, thickness and material of a coating layer on a specific area of the surface of the fiber grating according to a set program.
The delay time of the delay program depends on the position of the laser on the fiber, which is emitted by the laser, and the specific area of the coating device 1 on the surface of the fiber grating. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The delay time of the delay program is as follows:
(L0±k)/v，
where L0 is the spacing between the location of the laser pulse on the fiber and the location of the coating apparatus 1 coating the fiber, k is the length of the offset from the center of the grating, and v is the fiber draw speed.
After the delay program 1 is completed for the first time, when the grating interval L is less than L0, the delay duration of the delay program is changed to: (LL ± k)/v, where LL is L0 mod L, i.e., LL is the remainder of L0 divided by L. When the grating interval is greater than or equal to L0, the duration of the time delay program is (L0 + -k)/v.
The coating device 2 receives the pulse signal, triggers the driving program 3 after passing through the delay program 2, and then starts the coating device 2. The coating device 2 coats a certain length, thickness and material of the coating layer on a specific area of the surface of the fiber grating according to a set program.
The delay time of the delay program depends on the position of the laser on the fiber, which is emitted by the laser, and the specific area of the coating device 1 on the surface of the fiber grating. The fiber grating is symmetrically distributed at the writing position of the fiber with laser pulse. When the laser emits laser pulses, the corresponding vertical position on the optical fiber is the position of the grating on the optical fiber. The delay time of the delay program is as follows:
(L1±k)/v，
where L1 is the spacing between the location of the laser pulse on the fiber and the location of the coating device 2 on the fiber, k is the length of the offset from the center of the grating, and v is the fiber draw speed.
After the delay program 2 completes the first time, when the grating interval L is less than L1, the delay duration of the delay program is changed to: (LL1 ± k)/v, where LL1 ═ L1 mod L, i.e., LL1 is the remainder of L1 divided by L. When the grating interval is greater than or equal to L0, the duration of the time delay program is (L0 + -k)/v.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (9)
1. An apparatus for on-line preparation of long period fiber gratings with spot coatings, comprising: the device comprises an optical fiber preform, a feeding device, a graphite furnace, a coating device, a curing furnace, a driving traction wheel and a phase mask plate;
the optical fiber preform rod and the feeding device are used for feeding the preform rod into the graphite furnace at a preset speed, the temperature gradient and the temperature in the graphite furnace are controllable, the tip end of the preform rod is melted, the active traction wheel drives the optical fiber to rotate according to the set speed, and a photoelectric encoder arranged behind the active traction wheel sends pulses according to the rotating arc length; according to the instruction of a pulse counter, a laser emits laser pulses, the laser pulses form interference fringes through a phase mask plate, periodic fringes are formed on an optical fiber, and a long-period fiber grating is engraved; the coating device receives the instruction, coats a special coating with set thickness, length and material on the partial area of the surface of the grating and enters a curing furnace; the coating device coats special coatings with set thickness, length and material on the partial area of the grating surface according to the instruction, and then enters the curing device.
2. A method for in-line preparation of long period fiber gratings with spot coating using the apparatus of claim 1, comprising the steps of:
step one, after a prefabricated rod is melted and drawn into an optical fiber through a graphite furnace of a wire drawing tower, the optical fiber is irradiated by laser through interference fringes formed by a lens group and a phase mask plate; step two, the femtosecond laser forms periodic defect areas on the surface of the optical fiber and the fiber core area to form a long-period grating; thirdly, according to a pulse signal sent by a light spot encoder positioned behind a driving traction wheel of the wire drawing tower, a pulse counter positioned in the femtosecond laser receives the pulse signal and sends laser pulse according to a set value; a counter positioned on the coating device receives the pulse signal and is started when the counting reaches a set value; fifthly, the coating device controls the length and the thickness of the coating material coated on the partial area of the surface of the grating according to the starting time and then enters a curing furnace for curing; sixthly, connecting a plurality of coating devices in series to form a plurality of grating sensors with different coating areas on the surface of the fiber grating; the active traction wheel clamps the optical fiber, sends a pulse signal according to the unit rotating distance of the outer arc edge, and is calculated by the following formula:
r＝2×π*R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the unit rotation distance of the outer arc edge; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
3. The method according to claim 2, wherein the pulse counter in the laser has a setting value of L/r, L is the interval of writing the grating according to actual needs, and the counting value is cleared when the counting value reaches.
4. The method of claim 2 or 3, wherein when the system is started, the laser emits the first laser pulse, and then all the pulse counters are cleared and used as the starting counting point, and the written gratings are distributed symmetrically at the writing position.
5. The method of claim 2 or 3, wherein the pulse counter of the coating apparatus is set to (L0 ± k)/r when counting for the first time, wherein L0 is the distance between the position of the laser pulse on the optical fiber and the position of the coating apparatus on the optical fiber, and k is the length deviated from the center of the grating; the pulse counter count is then cleared and the subsequent set value is L/r.
6. The method for preparing long-period fiber grating with fixed-point coating on line by using the device of claim 1 is characterized by comprising the following steps of, after a prefabricated rod is melted and drawn into optical fiber by a drawing tower graphite furnace, irradiating the optical fiber by interference fringes formed by laser through a lens group and a phase mask plate; step two, the femtosecond laser forms periodic defect areas on the surface of the optical fiber and the fiber core area to form a long-period grating; thirdly, according to a pulse signal sent by a light spot encoder positioned behind the active traction wheel of the drawing tower, a pulse counter positioned in the active traction wheel receives the pulse signal and sends the pulse signal according to a set value; step four, the laser receives the pulse signal and emits a laser pulse; the coating device receives the pulse signal, and after a time delay program, the special coating device is started; fifthly, the coating device controls the length and the thickness of the coating material coated on the partial area of the surface of the grating according to the starting time and then enters a curing furnace for curing; and step six, connecting a plurality of coating devices in series, and forming a plurality of grating sensors with different coating areas on the surface of the fiber grating.
7. The method of claim 6, wherein the active traction wheel clamps the optical fiber and sends a pulse signal according to the unit rotation distance of the outer arc edge, and the pulse signal is calculated by the following formula:
r＝2×π*R/N，
in the formula, r is the arc length interval of signals sent by the photoelectric encoder, namely the unit rotation distance of the outer arc edge; r is the radius of the driving traction wheel; and N is the number of pulse signals sent by the photoelectric encoder when the driving traction wheel rotates for one circle.
8. The method for preparing the long period fiber grating with the fixed point coating on line according to claim 6 or 7, wherein the set value of the pulse counter is L/r, and L is the interval of the grating to be written according to actual needs; and clearing when the count value reaches.
9. The method of on-line preparing a long period fiber grating with a spot coating according to claim 6 or 7, wherein the delay time duration of the delay program is (L0 ± k)/v, wherein L0 is the interval between the position of the laser pulse on the fiber and the position of the coating device on the fiber, k is the length deviated from the center of the grating, and v is the fiber drawing speed; then when the grating interval L is smaller than L0, the delay duration of the delay procedure is (LL ± k)/v, where LL is L0 mod L, i.e., LL is the remainder of L0 divided by L, and when the grating interval L is greater than or equal to L0, the duration of the delay procedure is (L0 ± k)/v, and mod is the remainder.
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