CN115901193B - Method and system for measuring fiber grating parameters during etching and writing of integrated resonant cavity - Google Patents
Method and system for measuring fiber grating parameters during etching and writing of integrated resonant cavity Download PDFInfo
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- CN115901193B CN115901193B CN202310026249.9A CN202310026249A CN115901193B CN 115901193 B CN115901193 B CN 115901193B CN 202310026249 A CN202310026249 A CN 202310026249A CN 115901193 B CN115901193 B CN 115901193B
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Abstract
The invention relates to a fiber grating parameter measurement method and a fiber grating parameter measurement system during writing an integrated resonant cavity, because a scale fiber grating is arranged between the fiber grating being written and a measurement system, when the writing of the high-reflection fiber grating is carried out, the first reflection spectrums of the high-reflection fiber grating and the scale fiber grating can be obtained in real time through the measurement system, and spectral parameters such as the reflectivity of the high-reflection fiber grating being written can be calculated on line according to the first reflection spectrums until the spectral parameters of the high-reflection fiber grating meet target parameters; and when the writing of the low reflection fiber grating is started, acquiring the second reflection spectrums of the scale fiber grating, the high reflection fiber grating and the low reflection fiber grating which is being written in real time. The inscribed high-reflection fiber grating can be regarded as a scale and a preset scale fiber grating to be used as a reference for completing the spectral parameter measurement of the low-reflection fiber grating. The invention can accurately measure the spectral parameters of the integrated resonant cavity in real time.
Description
Technical Field
The application relates to the technical field of fiber bragg grating testing, in particular to a fiber bragg grating parameter measurement method and system during etching and writing of an integrated resonant cavity.
Background
Since the first fiber grating in the world was reported, fiber gratings have been rapidly developed, and have been widely used in the fields of fiber communication, fiber sensing, fiber lasers, and the like. In particular, in a fiber laser oscillator, a fiber bragg grating is a critical fiber optic device as a cavity mirror of a resonant cavity. Because the traditional ultraviolet exposure method is used for writing the fiber bragg grating and has requirements on the photosensitivity of the optical fiber, the fiber bragg grating used as a cavity mirror is mainly written on the passive optical fiber at present, the passive optical fiber is required to be subjected to hydrogen carrying and annealing treatment before and after writing, and finally, the fiber bragg grating and the active optical fiber form a resonant cavity in a fusion mode, and the fiber laser oscillator is built. Obviously, the steps from the optical fiber grating writing to the construction of the fiber laser oscillator are more and the period is longer.
With the development of femtosecond laser writing technology, there is a report of directly writing a fiber grating on an active fiber. The two fiber gratings are directly prepared on the active optical fiber and used as the cavity mirrors to form the integrated resonant cavity, so that the manufacturing period of the fiber laser oscillator can be greatly shortened, and the production efficiency is improved. In addition, the femtosecond laser can also write the fiber grating through the fiber coating layer, so that the integrated resonant cavity can be continuously prepared on one active fiber. However, in the process of continuously preparing an integrated resonant cavity on one active optical fiber based on femto-second laser, on-line measurement of spectral parameters of two cavity mirror fiber gratings is a challenging problem. On the one hand, two fiber gratings serving as a cavity mirror are inscribed on the same active optical fiber, measurement spectrums of the two fiber gratings overlap, and the reflectivity of the low-reflection fiber grating cannot be read by the measurement transmission spectrum. On the other hand, when the integrated resonant cavity is continuously prepared, the inscribed integrated resonant cavity can influence the subsequent measurement of the inscribed integrated resonant cavity.
Disclosure of Invention
Based on the above, it is necessary to provide a method and a system for measuring parameters of fiber grating during writing of an integrated resonant cavity.
A fiber grating parameter measurement method during writing an integrated resonant cavity comprises the following steps:
after focusing of the fiber core of the optical fiber to be inscribed is completed, inscribing of the high-reflection fiber grating of the current integrated resonant cavity is started, and a measurement system of the parameters of the fiber grating built in advance is adopted to acquire the first reflection spectrums of the high-reflection fiber grating being inscribed and the scale fiber grating in real time; the scale fiber bragg grating is arranged between the fiber bragg grating which is being inscribed and the measuring system;
calculating a first spectral parameter of the high-reflection fiber grating on line according to the first reflection spectrum, and completing inscription of the high-reflection fiber grating when the first spectral parameter meets a first target parameter;
after the optical fiber to be inscribed is controlled to slide for a preset distance and the focusing of the fiber core is completed, inscribing of the low-reflection fiber grating of the current integrated resonant cavity is started, and a measuring system is adopted to acquire the second reflection spectrums of the scale fiber grating, the inscribed high-reflection fiber grating and the inscribed low-reflection fiber grating in real time; the preset distance is the target cavity length of the current integrated resonant cavity;
and calculating a second spectral parameter of the low-reflection fiber grating on line according to the second reflection spectrum, finishing writing of the low-reflection fiber grating when the second spectral parameter meets a second target parameter, obtaining a current integrated resonant cavity with the writing completed and sending the current integrated resonant cavity out of a writing area, and shearing the current integrated resonant cavity before the next integrated resonant cavity starts writing so as to separate the current integrated resonant cavity from the optical fiber to be written.
An optical fiber grating parameter measurement system during writing of an integrated resonant cavity, comprising:
the device comprises a broadband light source, an optical fiber circulator, a spectrometer, a scale optical fiber grating and an optical fiber shearing device;
the optical fiber circulator, the scale optical fiber grating and the optical fiber to be inscribed are connected in sequence and are positioned on the same horizontal line; the broadband light source, the optical fiber circulator and the spectrometer are connected in sequence;
the broadband light source is used for synchronously emitting broadband light when the current integrated resonant cavity is inscribed after the last integrated resonant cavity is sheared and separated from the optical fiber to be inscribed;
the optical fiber ring is used for receiving broadband light emitted by the broadband light source and sequentially transmitting the broadband light to the scale optical fiber grating and the optical fiber grating which is being inscribed;
the method comprises the steps that broadband light is reflected by a scale fiber bragg grating and a fiber bragg grating which is being inscribed, a reflection spectrum of the fiber bragg grating which is being inscribed and the scale fiber bragg grating is formed on a spectrometer through a fiber circulator, spectral parameters of the fiber bragg grating which is being inscribed are obtained according to the reflection spectrum, and when the spectral parameters meet preset target parameters, the fiber bragg grating which is being inscribed is inscribed; the method for obtaining the spectral parameters of the fiber bragg grating in the integrated resonant cavity under inscription according to the reflection spectrum comprises the following steps: calculating a first spectral parameter of the high-reflection fiber grating on line according to the first reflection spectrums of the scale fiber grating and the high-reflection fiber grating in the inscribed integrated resonant cavity; calculating second spectral parameters of the low-reflection fiber grating on line according to the second reflection spectrums of the scale fiber grating, the inscribed high-reflection fiber grating and the inscribed low-reflection fiber grating in the integrated resonant cavity;
the optical fiber shearing device is used for shearing and inscribing the integrated resonant cavity before the broadband light source emits broadband light.
According to the method and the system for measuring the optical fiber grating parameters during the writing of the integrated resonant cavity, the scale optical fiber grating is arranged between the optical fiber grating being written and the measuring system, so that when the writing of the high-reflection optical fiber grating is carried out, the first reflection spectrums of the high-reflection optical fiber grating and the scale optical fiber grating can be obtained in real time through the measuring system, and as the reflectivity of the scale optical fiber grating is known, spectral parameters such as the reflectivity of the high-reflection optical fiber grating being written can be calculated on line according to the first reflection spectrums until the spectral parameters of the high-reflection optical fiber grating meet target parameters; when the writing of the low reflection fiber grating is started, a measuring system is adopted to acquire the second reflection spectrums of the scale fiber grating, the high reflection fiber grating after the writing and the low reflection fiber grating during the writing in real time, and the high reflection fiber grating and the low reflection fiber grating serving as the cavity mirrors of the integrated resonant cavity are written on the same active optical fiber at the moment, so that the reflection spectrums of the high reflection fiber grating and the low reflection fiber grating overlap, and the spectral parameters of the low reflection fiber grating cannot be read generally. In addition, considering that the integrated resonant cavity after writing can affect the optical fiber grating being written and measured, the scheme can send the current integrated resonant cavity after writing out of the writing area and cut the current integrated resonant cavity to separate from the optical fiber to be written before the next integrated resonant cavity starts writing/measuring. In summary, the invention can accurately measure the spectral parameters of the inscribed integrated resonant cavity in real time.
Drawings
FIG. 1 is a flow chart of a method for measuring parameters of an optical fiber grating when writing an integrated resonant cavity in one embodiment;
FIG. 2 is a schematic diagram of a fiber grating parameter measurement system for writing an integrated resonant cavity according to an embodiment;
FIG. 3 is a schematic diagram of a fiber grating writing system in an integrated resonant cavity according to one embodiment;
FIG. 4 is a schematic diagram of camera imaging in one embodiment; wherein (a) is that an included angle exists between the interference fringe image and the fiber core of the optical fiber; (b) Misalignment exists between the interference fringe image and the fiber core of the optical fiber; (c) the interference fringe image coincides with the fiber core;
FIG. 5 is a schematic diagram of a reflection spectrum of an integrated resonant cavity in another embodiment; wherein (a) is to measure and obtain the reflection spectrum of the scale fiber grating and the high reflection fiber grating in the inscribed integrated resonant cavity; (b) The superposition reflection spectrum of the low reflection fiber grating and the high reflection fiber grating in the integrated resonant cavity which is being inscribed is obtained for measurement.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
In one embodiment, as shown in fig. 1, a method for measuring parameters of a fiber grating during writing of an integrated resonant cavity is provided, including:
The scale fiber grating is arranged between the fiber grating which is being inscribed and the measuring system.
Considering that the high reflection fiber grating is usually a chirped fiber grating with larger bandwidth, the direction requirement exists when measuring the reflection spectrum, and the reflection spectrum needs to be measured along the direction that the high reflection fiber grating is connected in the resonant cavity, so the high reflection fiber grating needs to be written and measured first.
And 104, calculating a first spectral parameter of the high reflection fiber grating on line according to the first reflection spectrum, and completing the inscription of the high reflection fiber grating when the first spectral parameter meets a first target parameter.
The optical spectrum parameters of the scale optical fiber grating are known, and the inscribed target optical spectrum parameters are known, so that the scale optical fiber grating with proper optical spectrum parameters can be selected according to the known target optical spectrum parameters, and the method is suitable for online measurement during inscription of the integrated resonant cavity of various target optical spectrum parameters, and has high practicability.
And 106, after the optical fiber to be inscribed is controlled to slide for a preset distance and the focusing of the fiber core is completed, inscribing of the low-reflection fiber grating of the current integrated resonant cavity is started, and a measuring system is adopted to acquire the second reflection spectrums of the scale fiber grating, the inscribed high-reflection fiber grating and the inscribed low-reflection fiber grating in real time.
The preset distance is the target cavity length of the current integrated resonant cavity, namely the optical fiber length between the high-reflection fiber grating and the low-reflection fiber grating.
It can be understood that after the optical fiber to be inscribed is controlled to slide for a preset distance, the inscribed high-reflection fiber grating is sent out of the inscribed area, and the low-reflection fiber grating of the current integrated resonant cavity is sent into the inscribed area. The high-reflection fiber grating or the low-reflection fiber grating needs refocusing positioning before writing, so that writing is ensured to be free of offset, and writing is performed after focusing is completed.
And step 108, calculating a second spectral parameter of the low reflection fiber grating on line according to the second reflection spectrum, finishing writing of the low reflection fiber grating when the second spectral parameter meets a second target parameter, obtaining a current integrated resonant cavity with the writing completed and sending the current integrated resonant cavity out of a writing area, and shearing the current integrated resonant cavity before the next integrated resonant cavity starts writing so as to separate the current integrated resonant cavity from the optical fiber to be written.
After the writing of the low-reflection fiber grating is finished, the current integrated resonant cavity is prepared, and then the integrated resonant cavity is sent out of the writing area and sheared. The integrated resonant cavity after writing does not affect the focusing positioning of the next integrated resonant cavity, but affects the spectrum measurement of the next integrated resonant cavity, and the writing process and the spectrum online measurement are performed synchronously, so that the integrated resonant cavity after writing must be sheared before the next integrated resonant cavity is written. That is, the focusing of the fiber core of the high reflection fiber grating of the next integrated resonant cavity is not required to be staggered with the shearing of the current integrated resonant cavity, so that the preparation time of the integrated resonant cavity can be further reduced.
In the method for measuring the optical fiber grating parameters during the writing of the integrated resonant cavity, since the scale optical fiber grating is arranged between the optical fiber grating being written and the measuring system, when the writing of the high-reflection optical fiber grating is carried out, the first reflection spectrums of the high-reflection optical fiber grating and the scale optical fiber grating can be obtained in real time through the measuring system, and since the reflectivity of the scale optical fiber grating is known, the spectral parameters such as the reflectivity of the high-reflection optical fiber grating being written can be calculated on line according to the first reflection spectrums until the spectral parameters of the high-reflection optical fiber grating meet the target parameters; when the writing of the low reflection fiber grating is started, a measuring system is adopted to acquire the second reflection spectrums of the scale fiber grating, the high reflection fiber grating after the writing and the low reflection fiber grating during the writing in real time, and the high reflection fiber grating and the low reflection fiber grating serving as the cavity mirrors of the integrated resonant cavity are written on the same active optical fiber at the moment, so that the reflection spectrums of the high reflection fiber grating and the low reflection fiber grating overlap, and the spectral parameters of the low reflection fiber grating cannot be read generally. In addition, considering that the integrated resonant cavity after writing can affect the optical fiber grating being written and measured, the scheme can send the current integrated resonant cavity after writing out of the writing area and cut the current integrated resonant cavity to separate from the optical fiber to be written before the next integrated resonant cavity starts writing/measuring. In summary, the invention can accurately measure the spectral parameters of the inscribed integrated resonant cavity in real time.
In addition, when the reflection spectrum width of the low reflection fiber grating is narrower than that of the high reflection fiber grating, the reflection spectrum of the low reflection fiber grating can be obviously seen to be convex from the overlapped spectrum of the low reflection fiber grating and the high reflection fiber grating. In this case, the reflectivity of the low reflection fiber grating can be calculated by overlapping the intensity variation of the spectrum convex portion without depending on the scale fiber grating. That is, when the reflection spectrum width of the low reflection fiber grating is narrower than that of the high reflection fiber grating, the reflection spectrum of the scale fiber grating may not be measured, and the reflection spectrum of the high reflection fiber grating which is inscribed and obtained according to the scale fiber grating before may be used as the reference to obtain the spectrum parameter of the low reflection fiber grating, which may reduce the resource loss of the measurement system to some extent.
In summary, the invention can accurately measure the spectral parameters of the inscribed integrated resonant cavity in real time.
In one embodiment, the first spectral parameters include a first bandwidth, a first center wavelength, and a first reflectivity;
on-line calculating a first spectral parameter of the high reflection fiber grating according to the first reflection spectrum, including:
reading a first bandwidth and a first bandwidth center wavelength of the high-reflection fiber grating through a first reflection spectrum;
on-line calculating a first reflectivity of the high-reflectivity fiber grating according to the first reflection spectrum:
R 20-1 =R 22 ×10^[(I 20-1 -I 22 ) /10]
wherein R is 20-1 For the reflectivity of the high reflection fiber grating 20-1 in the integrated resonant cavity currently being inscribed, R 22 For the reflectivity of the scale fiber grating 22, I 22 For the reflection spectrum intensity of the scale fiber bragg grating 22, I 20-1 The reflection spectrum intensity of the high reflection fiber grating 20-1 in the integrated resonant cavity is written in dB.
In one embodiment, the second spectral parameters include a second bandwidth, a second center wavelength, and a second reflectivity;
on-line calculating a second spectral parameter of the low reflection fiber grating according to the second reflection spectrum, including:
reading a second bandwidth and a second bandwidth center wavelength of the low-reflection fiber grating through a second reflection spectrum;
calculating the second reflectivity of the low-reflection fiber grating on line according to the second reflection spectrum:
R 20-2 ={R 22 ×10^[(I 20-2 -I 22 ) /10]}/ R 20-1
wherein R is 20-2 For the reflectivity of the low reflection fiber grating 20-2 in the integrated resonant cavity being inscribed, I 20-2 The unit is dB of the superposition reflection spectrum intensity of the low reflection fiber grating 20-2 and the high reflection fiber grating 20-1 in the integrated resonant cavity being inscribed.
In one embodiment, a system for measuring parameters of an optical fiber grating during writing of an integrated resonant cavity is provided, comprising:
broadband light source, fiber optic circulator, spectrometer, scale fiber grating, and fiber shearing device. Wherein the broadband light source may be an ASE light source.
The optical fiber circulator, the scale optical fiber grating and the optical fiber to be inscribed are sequentially connected and are positioned on the same horizontal line. The broadband light source, the optical fiber circulator and the spectrometer are connected in sequence.
The broadband light source is used for synchronously emitting broadband light when the current integrated resonant cavity is inscribed after the last integrated resonant cavity is sheared and separated from the optical fiber to be inscribed. Therefore, the last integrated resonant cavity for completing writing can be prevented from affecting the spectral measurement of the currently writing integrated resonant cavity.
The optical fiber ring is used for receiving broadband light emitted by the broadband light source and sequentially transmitting the broadband light to the scale optical fiber grating and the optical fiber grating of the integrated resonant cavity which is being inscribed.
The optical fiber grating of the scale and the optical fiber grating of the integral resonant cavity being inscribed reflect broadband light, the integral resonant cavity being inscribed and the reflection spectrum of the scale optical fiber grating are formed on the spectrometer through the optical fiber circulator, the spectral parameters of the optical fiber grating in the integral resonant cavity being inscribed are obtained according to the reflection spectrum, and when the spectral parameters meet preset target parameters, the inscribed optical fiber grating is inscribed. The scale fiber grating is connected between the integral resonant cavity being inscribed and the fiber circulator, so that the reflection spectrum obtained in the spectrometer comprises the integral resonant cavity being inscribed and the reflection spectrum of the scale fiber grating, and the spectral parameters of the fiber grating in the integral resonant cavity being inscribed can be conveniently and intuitively read and calculated in real time, thereby accurately judging whether the fiber grating of the integral resonant cavity being inscribed at present meets the inscribed finishing condition.
The optical fiber shearing device is used for shearing the integrated resonant cavity after writing before the broadband light source emits broadband light, namely before the next integrated resonant cavity is prepared, so that the written integrated resonant cavity is prevented from affecting the measurement of the optical fiber grating parameters in the subsequent integrated resonant cavity writing process. The method can realize continuous preparation of the integrated resonant cavities on one active optical fiber and online measurement of the spectral characteristics of each integrated resonant cavity, and effectively improves the production efficiency of the integrated resonant cavities of the fiber laser oscillator.
In one embodiment, the system further comprises a movable fiber holding device and a conveyor belt.
The movable optical fiber clamping device can be an optical fiber clamping device with a pulley and is used for enabling the grating to be inscribed to slide for a preset distance, sending the high-reflection optical fiber grating inscribed in the current integrated resonant cavity out of the inscribing area, enabling the low-reflection optical fiber grating to be inscribed in the current integrated resonant cavity to enter the inscribing area, conveying the integrated resonant cavity to be inscribed to the position of the optical fiber shearing device, and shearing the integrated resonant cavity to be inscribed before the broadband light source emits broadband light, namely continuously preparing the next integrated resonant cavity. The conveyor belt is used for conveying the sheared integrated resonant cavity after inscription to the next production link. That is, the optical fiber clamping device with the pulley can also transmit the integrated resonant cavity after writing to the outside of the writing area through the pulley besides playing a clamping role, thereby realizing continuous writing of the integrated resonant cavity in the same optical fiber.
As shown in fig. 2, a schematic structural diagram of a fiber grating parameter measurement system during writing of an integrated resonant cavity is provided. Wherein, 4: an active optical fiber to be inscribed; 11: a computer; 13: an optical fiber clamping device with a pulley; 17: an ASE light source; 18: an optical fiber circulator; 19: a spectrometer; 20-1: a high reflection fiber grating in the integrated resonant cavity being inscribed; 20-2: a low reflection fiber grating in the integrated resonant cavity being inscribed; 21-1: writing a high reflection fiber grating in the finished integrated resonant cavity; 21-2: writing a low reflection fiber grating in the finished integrated resonant cavity; 22: a scale fiber grating; 23: an optical fiber shearing device; 24: a conveyor belt.
In one embodiment, the system further comprises a femtosecond laser, a cylindrical mirror and a phase mask;
the first femtosecond laser passes through the cylindrical mirror and the phase mask plate to form interference fringes and focuses the interference fringes in the active optical fiber to be inscribed; the output power corresponding to the first femtosecond laser is smaller than the write threshold power of the fiber grating. The interference fringes can excite blue fluorescence in the active optical fiber containing germanium ions, and images of the interference fringes can be seen by collecting the blue fluorescence.
The femtosecond laser is also used for outputting second femtosecond laser and starting to write the current fiber grating; the output power corresponding to the second femtosecond laser is not smaller than the write threshold power of the fiber grating.
The femtosecond laser is also used for outputting third femtosecond laser and ending the writing of the current fiber grating when the spectrum parameter meets the preset target parameter; the output power corresponding to the third femtosecond laser is smaller than the write threshold power of the fiber grating.
In one embodiment, the system further comprises an objective lens, a filter, a camera, a red light source, and a fiber optic coupler.
The objective lens comprises a first direction objective lens and a second direction objective lens; the first direction and the second direction are perpendicular to each other.
The filter plate comprises a first direction filter plate and a second direction filter plate, and the filter plate is used for filtering femtosecond laser.
The cameras include a first direction camera and a second direction camera.
The first direction objective lens, the first direction filter and the first direction camera are sequentially arranged in the first direction of the active optical fiber to be inscribed; the second direction objective lens, the second direction filter and the second direction camera are sequentially arranged in the second direction of the active optical fiber to be inscribed.
The optical fiber coupler is welded with one end of the optical fiber to be inscribed and is used for coupling the red light emitted by the red light source into the fiber core of the optical fiber and forming red scattered light in the fiber core. The red scattered light is formed by the Rayleigh scattering of the red light during the transmission of the fiber core, and the scattered red light is collected to see the image of the fiber core.
And when the interference fringes and the red scattered light of the first image and the second image are completely overlapped, the focusing of the femtosecond laser on the fiber core of the optical fiber to be written is completed, and the second femtosecond laser is output by the femtosecond laser to start writing of the current fiber grating, wherein the output power corresponding to the second femtosecond laser is not less than the writing threshold power of the fiber grating. The multi-dimensional adjustment of the displacement and rotation angle of the optical fiber can be realized by an electrically controlled multi-dimensional combination table. The adjustment in the first direction and the adjustment in the second direction can be performed in parallel, and the adjustment efficiency is greatly improved without mutual influence, so that the writing preparation time is saved.
As shown in fig. 3, a schematic structural diagram of a fiber grating writing system in an integrated resonant cavity is provided, wherein 1: a femtosecond laser; 2: a cylindrical mirror; 3: a phase mask; 4: an active optical fiber to be inscribed; 5: a Y-direction objective lens; 6: a Z-direction objective lens; 7: a Y-direction filter; 8: a Z-direction filter; 9: a Y-direction visible light CCD;10: a Z-direction visible light CCD;11: a computer; 12: an electric control multidimensional combination table; 13: an optical fiber clamping device with a pulley; 14: a red light source; 15: an optical fiber coupler.
As shown in fig. 4, a camera imaging schematic is provided, wherein (a) is that an included angle exists between the interference fringe image and the fiber core; (b) Misalignment exists between the interference fringe image and the fiber core of the optical fiber; (c) the interference fringe image coincides with the fiber core; 4-1: an optical fiber cladding; 4-2: an optical fiber core; 16: interference fringe images. The color of the optical fiber cladding 4-1 in the image is coincident with the noise background color of the Z-direction visible light CCD 10, and is normally black, the optical fiber core 4-2 is shown in red in the image, and the interference fringe image 16 is shown in blue. The positional relationship between the fiber core 4-2 and the interference fringe image 16 generally occurs in three ways, namely (a) that an included angle exists between the interference fringe image 16 and the fiber core 4-2, (b) that there is a dislocation between the interference fringe and the fiber core, and (c) that the interference fringe coincides with the fiber core. If the interference fringe image 16 is at an angle or offset from the fiber core 4-2, the position of the active fiber 4 to be inscribed needs to be adjusted so that the two coincide.
In one embodiment, the reflectance spectra of the scale fiber grating 22 and the high-reflectance fiber grating 20-1 in the integral cavity being inscribed may be measured from the spectrometer 19, followed by a measurement of the superimposed reflectance spectra of the low-reflectance fiber grating 20-2 and the high-reflectance fiber grating 20-1 in the integral cavity being inscribed. The center wavelength of the scale fiber grating 22 is different from the center wavelength of the high reflection fiber grating 20-1 and the low reflection fiber grating 20-2 in the integrated resonant cavity being inscribed, and the reflection spectrums are not overlapped.
As shown in fig. 5, a schematic diagram of the reflectance spectrum measured by the spectrometer is shown. Fig. 5 (a) shows the reflection spectrum of the scale fiber grating 22 and the highly reflective fiber grating 20-1 in the integrated cavity being inscribed. Fig. 5 (b) shows the superimposed reflection spectrum of the scale fiber grating 22 and the low reflection fiber grating 20-2 and the high reflection fiber grating 20-1 in the integrated cavity being inscribed. In this embodiment, the center wavelength of the marked fiber grating 22 is 1070nm, and the center wavelengths of the high reflection fiber grating 20-1 and the low reflection fiber grating 20-2 in the integrated resonant cavity being marked are 1080nm. When the highly reflective fiber grating 20-1 in the integrated cavity is first written in the optical fiber 4, the spectrometer 19 transmits the spectral data to the computer 11 in real time, as shown in fig. 5 (a). The wavelength and bandwidth of the highly reflective fiber grating 20-1 in the integrated resonant cavity being inscribed can be directly obtained from its reflection spectrum, and its reflectivity is calculated by the scale fiber grating 22. The reflectivity of the scale fiber grating 22 is known, in this embodiment 99%, i.e. R 22 =99%. Reflection spectrum intensity I of the scale fiber bragg grating 22 in this example 22 = -12.5dB, reflection spectrum intensity I of high reflection fiber grating 20-1 in integrated resonant cavity being inscribed 20-1 At the moment, the reflectivity R of the high-reflection fiber grating 20-1 in the inscribed integrated resonant cavity is calculated by the method of= -13.75dB 20-1 =74.24%. When the low reflection fiber grating 20-2 in the integrated cavity is subsequently written in the optical fiber 4, the spectrometer 19 also transmits the spectral data in real time into the computer 11, as shown in fig. 5 (b). Since the bandwidth of the low reflection fiber grating 20-2 is smaller than that of the high reflection fiber grating 20-1, the reflection spectrum protrusion of the low reflection fiber grating 20-2 can be clearly seen in the superimposed reflection spectrum of the two. The wavelength and bandwidth of the low reflection fiber grating 20-2 can be obtained directly from the convex portion of the superimposed reflection spectrum. The superimposed reflection spectrum intensity I of the low reflection fiber grating 20-2 and the high reflection fiber grating 20-1 in this example 20-2 At the moment, the reflectivity R of the low-reflection fiber grating 20-2 in the inscribed integrated resonant cavity is calculated by the method of= -10dB 20-2 =2.34%。
In conclusion, the method determines the moment of starting the inscription through image recognition, determines the moment of finishing the inscription through an online measurement result, does not need manual intervention in the whole process, and can adaptively determine the inscription period.
In one embodiment, the system further comprises a length recording module;
the length recording module is used for recording the transmitted accumulated fiber length, comparing the accumulated fiber length with the total length of the fiber to be inscribed, and judging whether the remaining fiber length meets the requirement of continuing inscribing the fiber grating. When the requirements are met, continuing to write the next fiber bragg grating; and when the requirements are not met, the femtosecond laser is turned off, and the writing is finished.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
Claims (8)
1. The method for measuring the parameters of the fiber bragg grating during the writing of the integrated resonant cavity is characterized by comprising the following steps:
after focusing of the fiber core of the optical fiber to be inscribed is completed, inscribing of the high-reflection fiber grating of the current integrated resonant cavity is started, and a measurement system of a pre-built fiber grating parameter is adopted to acquire a first reflection spectrum of the high-reflection fiber grating and a first reflection spectrum of the scale fiber grating which are inscribed in real time; the scale fiber bragg grating is arranged between the fiber bragg grating which is being inscribed and the measuring system;
calculating a first spectral parameter of the high-reflection fiber grating on line according to the first reflection spectrum, and completing the inscription of the high-reflection fiber grating when the first spectral parameter meets a first target parameter;
after the optical fiber to be inscribed is controlled to slide for a preset distance and the focusing of the fiber core is completed, inscribing of the low-reflection fiber grating of the current integrated resonant cavity is started, and a second reflection spectrum of the scale fiber grating, the inscribed high-reflection fiber grating and the inscribed low-reflection fiber grating is acquired in real time by adopting the measuring system; the preset distance is the target cavity length of the current integrated resonant cavity;
and calculating a second spectral parameter of the low-reflection fiber grating on line according to the second reflection spectrum, finishing writing of the low-reflection fiber grating when the second spectral parameter meets a second target parameter, obtaining a current integrated resonant cavity after writing is finished, sending the current integrated resonant cavity out of a writing area, and shearing the current integrated resonant cavity before writing of the next integrated resonant cavity is started to separate the current integrated resonant cavity from the optical fiber to be written.
2. The method of claim 1, wherein the first spectral parameters comprise a first bandwidth, a first center wavelength, and a first reflectivity;
calculating a first spectral parameter of the high reflection fiber grating on line according to the first reflection spectrum, including:
reading a first bandwidth and a first bandwidth center wavelength of the high-reflection fiber grating through the first reflection spectrum;
calculating the first reflectivity of the high-reflectivity fiber grating on line according to the first reflection spectrum:
R 20-1 =R 22 ×10^[(I 20-1 -I 22 ) /10]
wherein R is 20-1 For the reflectivity of the high-reflectivity fiber grating (20-1) in the integrated resonant cavity currently being inscribed, R 22 Is the reflectivity of the scale fiber grating (22), I 22 Is the reflection spectrum intensity of the scale fiber bragg grating (22), I 20-1 The unit is dB of reflection spectrum intensity of the high reflection fiber grating (20-1) in the inscribed integrated resonant cavity.
3. The method of claim 2, wherein the second spectral parameters comprise a second bandwidth, a second center wavelength, and a second reflectivity;
calculating a second spectral parameter of the low reflection fiber grating on line according to the second reflection spectrum, including:
reading a second bandwidth and a second bandwidth center wavelength of the low-reflection fiber grating through the second reflection spectrum;
calculating the second reflectivity of the low-reflection fiber grating on line according to the second reflection spectrum:
R 20-2 ={R 22 ×10^[(I 20-2 -I 22 ) /10]}/ R 20-1
wherein R is 20-2 For the reflectivity of the low-reflection fiber grating (20-2) in the integrated resonant cavity being inscribed, I 20-2 The unit is dB of the superposition reflection spectrum intensity of the low reflection fiber grating (20-2) and the high reflection fiber grating (20-1) in the integrated resonant cavity being inscribed.
4. An optical fiber grating parameter measurement system during writing of an integrated resonant cavity, characterized in that the system comprises:
the device comprises a broadband light source, an optical fiber circulator, a spectrometer, a scale optical fiber grating and an optical fiber shearing device;
the optical fiber circulator, the scale optical fiber grating and the optical fiber to be inscribed are connected in sequence and are positioned on the same horizontal line; the broadband light source, the optical fiber circulator and the spectrometer are connected in sequence;
the broadband light source is used for synchronously emitting broadband light when the current integrated resonant cavity is inscribed after the last integrated resonant cavity is sheared and separated from the optical fiber to be inscribed;
the optical fiber circulator is used for receiving broadband light emitted by the broadband light source and sequentially transmitting the broadband light to the scale optical fiber grating and the optical fiber grating of the integrated resonant cavity which is being inscribed;
the scale fiber bragg grating and the optical fiber bragg grating which is being inscribed reflect the broadband light, the integral resonant cavity which is being inscribed and the reflection spectrum of the scale fiber bragg grating are formed on the spectrometer through the fiber circulator, the spectral parameters of the fiber bragg grating in the integral resonant cavity which is being inscribed are obtained according to the reflection spectrum, and when the spectral parameters meet preset target parameters, the optical fiber bragg grating which is being inscribed is inscribed; the method for obtaining the spectral parameters of the fiber bragg grating in the integrated resonant cavity under inscription according to the reflection spectrum comprises the following steps: calculating a first spectral parameter of the high-reflection fiber grating on line according to the first reflection spectrums of the scale fiber grating and the high-reflection fiber grating in the inscribed integrated resonant cavity; calculating second spectral parameters of the low-reflection fiber grating on line according to the second reflection spectrums of the scale fiber grating, the inscribed high-reflection fiber grating and the inscribed low-reflection fiber grating in the integrated resonant cavity;
the optical fiber shearing device is used for shearing and inscribing the integrated resonant cavity before the broadband light source emits broadband light.
5. The system of claim 4, further comprising a movable fiber holding device and a conveyor belt;
the movable optical fiber clamping device is used for enabling the grating to be inscribed to slide for a preset distance, sending the high-reflection optical fiber grating which is inscribed in the current integrated resonant cavity out of the inscribing area, enabling the low-reflection optical fiber grating to be inscribed in the current integrated resonant cavity to enter the inscribing area, and transmitting the current integrated resonant cavity which is inscribed to the position of the optical fiber shearing device, and shearing the current integrated resonant cavity which is inscribed by the optical fiber shearing device before the broadband light source emits broadband light; the preset distance is the target cavity length of the current integrated resonant cavity;
the conveyor belt is used for conveying the sheared current integrated resonant cavity which is written to the next production link.
6. The system of claim 4, further comprising a femtosecond laser, a cylindrical mirror, a phase mask;
the first femtosecond laser is used for outputting first femtosecond laser, and the first femtosecond laser passes through the cylindrical mirror and the phase mask plate to form interference fringes and is focused in the optical fiber to be inscribed; the output power corresponding to the first femtosecond laser is smaller than the write threshold power of the fiber grating;
the femtosecond laser is also used for outputting second femtosecond laser and starting to write the current fiber grating; the output power corresponding to the second femtosecond laser is not less than the write threshold power of the fiber grating;
the femtosecond laser is also used for outputting third femtosecond laser and ending the writing of the current fiber grating when the spectrum parameter meets the preset target parameter; and the output power corresponding to the third femtosecond laser is smaller than the write threshold power of the fiber grating.
7. The system of claim 6, further comprising an objective lens, a filter, a camera, a red light source, and a fiber optic coupler;
the objective lens comprises a first direction objective lens and a second direction objective lens; the first direction and the second direction are perpendicular to each other;
the filter plate comprises a first direction filter plate and a second direction filter plate; the filter is used for filtering the femtosecond laser;
the camera comprises a first direction camera and a second direction camera;
the first direction objective lens, the first direction filter and the first direction camera are sequentially arranged in the first direction of the optical fiber to be inscribed;
the second direction objective lens, the second direction filter and the second direction camera are sequentially arranged in the second direction of the optical fiber to be inscribed;
the optical fiber coupler is welded with one end of the optical fiber to be inscribed and is used for coupling the red light emitted by the red light source into the fiber core of the optical fiber and forming red scattered light in the fiber core;
and the interference fringes and the red scattered light are imaged in the first direction camera through a first direction objective lens and a first direction filter plate to obtain a first image, the interference fringes and the red scattered light are imaged in the second direction camera through a second direction objective lens and a second direction filter plate to obtain a second image, the displacement and the rotation angle of the optical fiber are iteratively adjusted according to the relative positions of the interference fringes and the red scattered light in the first image and the second image, and when the interference fringes and the red scattered light of the first image and the second image are completely overlapped, the focusing of the femtosecond laser on the fiber core of the optical fiber to be inscribed is completed, and the second femtosecond laser is output by the femtosecond laser to start inscription of the current fiber grating.
8. The system of claim 5, further comprising a length recording module;
the length recording module is used for recording the transmitted accumulated fiber length, comparing the accumulated fiber length with the total length of the fiber to be inscribed, and judging whether the length of the rest fiber meets the requirement of continuing inscribing the fiber grating;
when the requirements are met, continuing to write the next fiber grating;
and when the requirement is not met, the femtosecond laser is turned off, and the writing is finished.
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