Chromatic dispersion measurement system and measurement method of chirp Bragg grating

Abstract

The invention discloses a dispersion measurement system and a dispersion measurement method for a chirp Bragg grating. The dispersion measurement system comprises an interference module, a dispersion compensation module and an electric control module. In the first working mode, the dispersion compensation module is located outside the signal light path, a first interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a first dispersion value of a first chirp Bragg grating to be tested according to the first interference signal; in the second working mode, the dispersion compensation module is located in the signal light path, the dispersion compensation module provides preset dispersion compensation for the signal light path, a second interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a second dispersion value of a second chirp Bragg grating to be measured according to the second interference signal and the preset dispersion compensation. The dispersion measurement system provided by the embodiment of the invention provides a dispersion measurement method which is more accurate and larger in measuring range, and cross-measuring-range measurement from small dispersion to large dispersion is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical testing, and in particular to a dispersion measurement system and a measurement method for a chirped Bragg grating. Background Art

[0002] Ultrashort pulse lasers, with their advantages of extremely short duration, high peak power and ultra-wide bandwidth, have become an effective means of studying ultrafast phenomena and have been widely used in many fields such as strong field physics, information science, materials science and biomedicine. In the field of ultrafast lasers, dispersion management technology is an important means to achieve high-performance femtosecond lasers. In fiber mode-locked lasers, ultra-narrow pulse width laser output can be achieved by balancing the intracavity dispersion through dispersion compensation elements; dispersion elements can also be used in chirped pulse amplification systems as stretchers to stretch pulses, thereby increasing the output power of the laser. The former requires a smaller amount of dispersion to be compensated, usually around 0.5ps. 2 The latter needs to provide a larger dispersion, usually in the range of several to tens of ps. 2 Commonly used dispersion elements include grating pairs, prism pairs, dispersion-compensating fibers, chirped fiber Bragg Gratings (CFBG), etc. Among them, CFBG has attracted much attention due to its stable structure and all-fiber advantages. Therefore, how to achieve cross-range measurement of CFBG dispersion parameters to meet the needs of different application scenarios has become a hot and difficult problem that needs to be solved in the field of ultrafast optics and applications.

[0003] Chirped Fiber Bragg Grating (CFBG) is a non-uniform periodic grating structure based on a uniform grating fiber structure (FBG). Fiber Bragg Grating (FBG) refers to an optical fiber with a periodic change in the refractive index of the core layer in a certain area along the length of the optical fiber. Only a specific wavelength λ with equal phase B The partial Fresnel reflection of the light wave due to the change of refractive index is enhanced, and only at a specific wavelength λ B A back-reflected light wave is generated at this location. This wavelength is called the Bragg wavelength and satisfies:

[0004]

[0005] Where q is an integer; is the effective or average refractive index of the guided mode, called the mode refractive index; Λ refers to the period of the grating. The grating period of CFBG varies linearly along the fiber direction, and the Bragg reflection resonance wavelength also varies linearly. Assuming that a beam of light is coupled into the CFBG from the short-period direction, the short-wavelength light is reflected at the near end of the CFBG, and the long-wavelength light is reflected at the far end. There is a time delay between the long and short waves, which is the dispersion phenomenon. CFBG can not only compensate for the dispersion caused by several meters of optical fiber in the fiber mode-locked laser cavity through design and processing, but also provide more than 40ps at a length of cm. 2 The dispersion and broadening amount are equivalent to those of single-mode optical fibers with a length of km. CFBG has been widely used in fiber femtosecond laser systems due to its unique advantage of large dispersion span. In order to achieve high-output fiber femtosecond laser systems, it is very important to accurately grasp the dispersion parameters of CFBG. Group delay (GD) and group delay dispersion (GDD) are the two most critical dispersion parameters of CFBG, representing the first-order derivative and second-order derivative of the optical phase delay with respect to the angular frequency ω, respectively. Their accurate measurement is of great significance to ensure the stability and reliability of system performance.

[0006] The time-of-flight method and the modulation phase shift method are two widely used conventional dispersion measurement methods. The former measures the relative time delay of pulses of different wavelengths to calculate the dispersion, while the latter measures the phase delay of the modulated signal as a function of the wavelength and finally calculates the dispersion. However, these two methods are limited by the large number of sampling points and bandwidth, and are usually suitable for large dispersion measurements of optical fibers longer than 100 meters, but are not applicable when the dispersion is small. White light interferometry (WLI) is usually used for dispersion measurements of short-length optical fibers and small dispersion mirrors, which combines a broadband light source with a standard Michelson or Mach-Zehnder interferometer. However, existing dispersion measurement methods for large chirp dispersion compensation devices are scarce, and there is a problem of poor accuracy in measuring large dispersion coefficients; moreover, existing systems cannot continuously tune the measurement range and cannot perform cross-range dispersion measurements from small dispersion to large dispersion. Therefore, a more accurate and larger-range dispersion measurement method is urgently needed. Summary of the invention

[0007] The embodiment of the present invention provides a dispersion measurement system and a measurement method for a chirped Bragg grating. The dispersion measurement system provides a more accurate and larger-range dispersion measurement method to achieve cross-range measurement from small dispersion to large dispersion, in order to solve the problems that existing dispersion measurement methods for large chirp dispersion compensation devices (chirped Bragg gratings) are scarce, the measurement accuracy of large dispersion coefficients is poor, and the existing system cannot continuously tune the measurement range and cannot perform cross-range dispersion measurement from small dispersion to large dispersion.

[0008] According to one aspect of the present invention, a dispersion measurement system for a chirped Bragg grating is provided, comprising an interference module, a dispersion compensation module and an electric control module, wherein the interference module and the dispersion compensation module are both connected to the electric control module;

[0009] The optical path in the interference module includes a signal optical path and a reference optical path, and the chirped Bragg grating to be measured is located in the signal optical path;

[0010] The dispersion measurement system includes a first working mode and a second working mode. In the first working mode, the dispersion compensation module is located outside the signal optical path, the first interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a first dispersion value of a first chirped Bragg grating to be measured according to the first interference signal;

[0011] In the second working mode, the dispersion compensation module is located in the signal optical path, the dispersion compensation module provides preset dispersion compensation for the signal optical path, the second interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a second dispersion value of the second chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation;

[0012] The first dispersion value is smaller than the second dispersion value.

[0013] Optionally, the interference module includes a light source, a beam splitter, a circulator, an electrically controlled delay line, a beam combiner and a spectrometer, and the first chirped Bragg grating to be measured or the second chirped Bragg grating to be measured is connected to the second end of the circulator;

[0014] In the first working mode, the output beam of the light source is incident on the beam splitter and is divided into a first signal beam and a first reference beam, the first signal beam is incident on the first end of the circulator, is output from the second end of the circulator to the first chirped Bragg grating to be measured, is reflected by the first chirped Bragg grating to be measured, is incident on the second end of the circulator, and is output from the third end of the circulator to the beam combiner;

[0015] The first reference beam is incident on the electrically controlled delay line, and is incident on the beam combiner after being delayed by the electrically controlled delay line;

[0016] The first signal beam and the first reference beam are combined by the beam combiner to generate the first interference signal, and the first interference signal is incident on the spectrometer;

[0017] In the second working mode, the output beam of the light source is incident on the beam splitter and is divided into a second signal beam and a second reference beam, the second signal beam is incident on the first end of the circulator, is output from the second end of the circulator to the second chirped Bragg grating to be measured, is reflected by the second chirped Bragg grating to be measured, is incident on the second end of the circulator, is output from the third end of the circulator to the dispersion compensation module, and is output to the beam combiner after the preset dispersion compensation is generated by the dispersion compensation module;

[0018] The second reference beam is incident on the electrically controlled delay line, and is incident on the beam combiner after being delayed by the electrically controlled delay line;

[0019] The second signal beam and the second reference beam are combined by the beam combiner to generate the second interference signal, and the second interference signal is incident on the spectrometer.

[0020] Optionally, the interference module further includes a first collimator and a second collimator;

[0021] In the first working mode, the first signal beam output by the beam splitter is collimated by the first collimator and then incident to the first end of the circulator, and the first signal beam output by the circulator is collimated by the second collimator and then incident to the beam combiner;

[0022] In the second working mode, the second signal beam output by the beam splitter is collimated by the first collimator and then incident on the first end of the circulator, and the second signal beam output by the circulator is collimated by the second collimator and then incident on the dispersion compensation module.

[0023] Optionally, the electrically controlled delay line includes two right-angle mirrors and a first displacement platform, the right-angle mirrors are fixed on the first displacement platform, the first displacement platform is connected to the electrically controlled module, and the first displacement platform is used to drive the right-angle mirrors to translate to achieve the delay of the first reference beam or the second reference beam.

[0024] Optionally, the dispersion compensation module includes a first reflector, a second reflector, a first grating, a second grating, a second displacement platform and a climbing reflector, the first reflector and the second reflector are arranged in different planes, the first grating and the second grating are parallel, the position of the first grating is fixed, the second grating is arranged on the second displacement platform, the second displacement platform is connected to the electric control module, and the second displacement platform is used to drive the second grating to translate so as to provide preset dispersion compensation for the second signal light beam.

[0025] Optionally, in the second operating mode, the second signal light beam output from the third end of the circulator is reflected by the first reflector and then incident on the first grating to generate angular dispersion, and then becomes parallel light after passing through the second grating. After being reflected by the climbing reflector, the light moves to the plane where the second reflector is located, and then passes through the second grating and the first grating again and then incident on the second reflector, and then reflected by the second reflector and then incident on the combiner.

[0026] Optionally, the preset dispersion compensation is determined according to the distance between the first grating and the second grating, and the corresponding relationship between the distance between the first grating and the second grating and the dispersion compensation value is pre-calibrated according to experiments.

[0027] Optionally, the electronic control module includes a computer and a controller, the spectrometer and the controller are both connected to the computer, the electronically controlled delay line and the dispersion compensation module are both connected to the controller, the computer is used to calculate the dispersion value according to the interference spectrum signal received by the spectrometer, and the controller is used to adjust the delay of the electronically controlled delay line and the preset dispersion compensation provided by the dispersion compensation module.

[0028] According to another aspect of the present invention, a dispersion measurement method for a chirped Bragg grating is provided, which is performed by the dispersion measurement system for the chirped Bragg grating. The dispersion measurement method comprises:

[0029] Connecting the chirped Bragg grating to be measured into the signal optical path of the interference module;

[0030] The dispersion compensation module is arranged outside the signal optical path, and the dispersion value of the chirped Bragg grating to be measured is measured in a first working mode;

[0031] If the dispersion value of the chirped Bragg grating to be measured exceeds the measurement range of the first working mode, the dispersion compensation module is arranged in the signal optical path, and the dispersion value of the chirped Bragg grating to be measured is measured in the second working mode;

[0032] Wherein, in the first working mode, the first interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the first interference signal; in the second working mode, the dispersion compensation module provides preset dispersion compensation to the signal optical path, and the second interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation.

[0033] Optionally, if it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the first working mode, the dispersion value of the chirped Bragg grating to be measured is measured using the first working mode;

[0034] If it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the second working mode, the second working mode is adopted to measure the dispersion value of the chirped Bragg grating to be measured.

[0035] The dispersion measurement system of a chirped Bragg grating provided in an embodiment of the present invention comprises an interference module, a dispersion compensation module and an electric control module, wherein the interference module and the dispersion compensation module are both connected to the electric control module; the optical path in the interference module comprises a signal optical path and a reference optical path, and the chirped Bragg grating to be measured is located in the signal optical path; the dispersion measurement system comprises a first working mode and a second working mode, wherein in the first working mode, the dispersion compensation module is located outside the signal optical path, a first interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a first dispersion value of a first type of chirped Bragg grating to be measured according to the first interference signal; in the second working mode, the dispersion compensation module is located in the signal optical path, the dispersion compensation module provides a preset dispersion compensation for the signal optical path, a second interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a second dispersion value of a second type of chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation; wherein the first dispersion value is less than the second dispersion value. The dispersion measurement system provided in the embodiment of the present invention is divided into two modes. One mode is a small dispersion measurement mode, which directly uses the interference method to measure the small dispersion amount; the other mode is a large dispersion measurement mode. On the basis of the first mode, a dispersion compensation module is added to the signal optical path to provide a certain known dispersion compensation amount. After measuring the dispersion, the test value is added to the compensation amount to obtain the dispersion value of the large dispersion amount.

[0036] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 A schematic structural diagram of a dispersion measurement system for a chirped Bragg grating provided in an embodiment of the present invention;

[0039] Figure 2 A schematic flow chart of a dispersion measurement method for a chirped Bragg grating provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] In the prior art, white light interferometry (WLI) is usually used to measure the dispersion of short-length optical fibers and small dispersion mirrors. It combines a broadband light source with a standard Michelson or Mach-Zehnder interferometer. The light beam emitted by the light source is collimated and then split into two beams by a beam splitter. One beam of light is input into one arm of the optical fiber to be measured, namely the arm to be measured; the other beam of light enters the air arm as the reference arm. The light beam emitted from the optical fiber is collimated again and enters the beam combiner together with the light in the air arm through a reflector. Interference occurs at the beam combiner, and the cross-correlated interference information is transmitted to the spectrometer for analysis. There are roughly two ways to obtain interference patterns: spectral WLI and scanning WLI. Spectral WLI extracts the dispersion curve by measuring the intensity of the spectral interference pattern once. There are no moving parts in the system. However, since only one spectral pattern is obtained in the whole process, there are problems such as few sampling points and large dispersion influence introduced by the system. Scanning WLI overcomes this shortcoming. In scanning WLI, the return mirror of the reference arm of the interferometer moves under the drive of the motor, changing the optical path difference between the arm to be measured and the reference arm, thereby changing the time delay between the reference light and the light to be measured at the beam combining point, that is, the phase difference. The spectrometer measures the image of the spectral intensity distribution with wavelength after spectral interference. The interference spectral intensity distribution is different at different step positions of the motor. Finally, the time intensity distribution corresponding to a specific wavelength, that is, the interference pattern, is obtained. The phase is recovered from the interference pattern, and the dispersion curve of the material can be calculated.

[0043] The scanning WLI method is used to measure the dispersion of CFBG, which can overcome the problems of small number of sampling points and large measurement errors caused by the resolution limitation of the spectrometer in the traditional WLI method. The scanning WLI method can obtain the dispersion curve of CFBG with small dispersion, but the fringes in the interference spectrum of CFBG are extremely dense when the dispersion amount is large. If the motor step distance is set too short, the resolution ability of the spectrometer will be seriously restricted, resulting in the difficulty in accurately identifying the interference maximum in the adjacent interference pattern; if the step distance is too long, the number of sampling points will be reduced, and the dispersion curve cannot be accurately depicted. In addition, the dispersion curve of CFBG is relatively steep, requiring multiple differentiation and smoothing, and the error generated by the algorithm is very large. The method of extracting the local extreme value of the fringes in the interference pattern is more suitable. This method requires that there are more fringes in the interference pattern and each fringe is clearly distinguishable, and it also puts forward high requirements on the resolution ability of the spectrometer. Therefore, it is necessary to improve the original white light interferometry method to solve the problem that the scanning WIL method cannot measure small dispersion and large dispersion at the same time.

[0044] Based on this, an embodiment of the present invention provides a dispersion measurement system for a chirped Bragg grating to achieve a cross-range measurement problem of simultaneously measuring small dispersion amounts and large dispersion amounts. Figure 1 A schematic diagram of a dispersion measurement system for a chirped Bragg grating provided in an embodiment of the present invention, referring to Figure 1The dispersion measurement system includes an interference module 20, a dispersion compensation module 30 and an electric control module 40, and the interference module 20 and the dispersion compensation module 30 are both connected to the electric control module 40; the optical path in the interference module 20 includes a signal optical path a and a reference optical path b, and the chirped Bragg grating 5 to be measured is located in the signal optical path; the dispersion measurement system includes a first working mode and a second working mode, in the first working mode, the dispersion compensation module 30 is located outside the signal optical path, the first interference signal generated by the interference module 20 is transmitted to the electric control module 40, and the electric control module 40 determines the first dispersion value of the first chirped Bragg grating to be measured according to the first interference signal; in the second working mode, the dispersion compensation module 30 is located in the signal optical path, the dispersion compensation module 30 provides a preset dispersion compensation for the signal optical path, the second interference signal generated by the interference module 20 is transmitted to the electric control module 40, and the electric control module 40 determines the second dispersion value of the second chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation; wherein the first dispersion value is less than the second dispersion value.

[0045] The chirped Bragg grating to be measured can be CFBG, which is an optical dispersion compensation device with large dispersion and narrow bandwidth, and its dispersion curve is short and steep. The traditional white light interferometry method not only has insufficient number of sampling points, but also has large errors in the obtained dispersion parameters. In addition, it is limited by the motor displacement accuracy and the resolution of the spectrometer, and the dispersion that can be measured has an upper limit. For a spectrometer with a minimum optical resolution of 0.02nm, the dispersion value is greater than 8ps. 2 After that, the interference fringes will not be distinguishable within the 10dB bandwidth.

[0046] The dispersion measuring instrument designed in the present invention is divided into two modes. One mode is a small dispersion CFBG measurement mode, which uses the white light interferometry method plus phase shift method to measure small dispersion CFBG; the other is a large dispersion CFBG measurement mode. On the basis of the first mode, a dispersion compensation module is added to the end to be measured to provide a certain known dispersion compensation amount. After measuring the dispersion, the test value is added to the compensation amount to obtain the dispersion value of the large dispersion CFBG.

[0047] Optional, continue to refer to Figure 1The interference module 20 includes a light source 1, a beam splitter 2, a circulator 4, an electrically controlled delay line 19, a beam combiner 13 and a spectrometer 16. The first chirped Bragg grating to be measured or the second chirped Bragg grating to be measured is connected to the second end of the circulator 4. In the first working mode, the output light beam of the light source 1 is incident on the beam splitter 2 and is divided into a first signal beam and a first reference beam. The first signal beam is incident on the first end of the circulator 4, and is output from the second end of the circulator 4 to the first chirped Bragg grating to be measured. After being reflected by the first chirped Bragg grating to be measured, it is incident on the second end of the circulator 4, and is output from the third end of the circulator 4 to the beam combiner 13. The first reference beam is incident on the electrically controlled delay line 19, and is incident on the beam combiner 13 after being delayed by the electrically controlled delay line 19. The first signal beam and the first reference beam pass through the beam combiner 13. After beam combining, a first interference signal is generated, and the first interference signal is incident on the spectrometer 16; in the second working mode, the output light beam of the light source 1 is incident on the beam splitter 2 and is divided into a second signal beam and a second reference beam, the second signal beam is incident on the first end of the circulator 4, and is output from the second end of the circulator 4 to the second chirped Bragg grating to be measured, and is reflected by the second chirped Bragg grating to be measured and is incident on the second end of the circulator 4, and is output from the third end of the circulator 4 to the dispersion compensation module 30, and is output to the beam combiner 13 after the preset dispersion compensation is generated by the dispersion compensation module 30; the second reference beam is incident on the electrically-controlled delay line 19, and is incident on the beam combiner 13 after being delayed by the electrically-controlled delay line 19; the second signal beam and the second reference beam are combined by the beam combiner to generate a second interference signal, and the second interference signal is incident on the spectrometer.

[0048] Optionally, the electrically controlled delay line 19 includes two right-angle mirrors 14 and a first displacement platform 15. The right-angle mirror 14 is fixed on the first displacement platform 15. The first displacement platform 15 is connected to the electronic control module 40. The first displacement platform 15 is used to drive the right-angle mirror 15 to translate to achieve the delay of the first reference beam or the second reference beam.

[0049] Among them, the light source 1 is a broadband light source, for example, a white light source, and the beam splitter 2 and the beam combiner 13 can be semi-transparent and semi-reflective mirrors. In the small dispersion mode, the CFBG is inserted in the measuring arm (signal optical path), and the first displacement platform 15 is used to change the length of the air reference arm (reference optical path) through motor movement. The moving direction is consistent with the light propagation direction. By changing the optical path of the air arm in the interference system, a time delay is generated, and the intensity of the interference signal is changed by changing the time delay. The spectrometer 16 scans to obtain different spectral interference patterns; in the large dispersion mode, a dispersion compensation module 30 is set after the CFBG of the measuring arm, so as to perform dispersion compensation in advance. The dispersion compensation module 30 can be calibrated using a standard optical fiber before the experiment.

[0050] The dispersion measurement system provided in the embodiment of the present invention is divided into two modes. One mode is a small dispersion measurement mode, which directly uses the interference method to measure the small dispersion amount; the other mode is a large dispersion measurement mode. On the basis of the first mode, a dispersion compensation module is added to the signal optical path to provide a certain known dispersion compensation amount. After measuring the dispersion, the test value is added to the compensation amount to obtain the dispersion value of the large dispersion amount.

[0051] Optional, continue to refer to Figure 1 The interference module 20 also includes a first collimator 3 and a second collimator 6; in the first working mode, the first signal light beam output by the beam splitter 2 is collimated by the first collimator 3 and then incident on the first end of the circulator 4, and the first signal light beam output by the circulator 4 is collimated by the second collimator 6 and then incident on the beam combiner 13; in the second working mode, the second signal light beam output by the beam splitter 2 is collimated by the first collimator 3 and then incident on the first end of the circulator 4, and the second signal light beam output by the circulator 4 is collimated by the second collimator 6 and then incident on the dispersion compensation module 30.

[0052] By providing the first collimator 3 and the second collimator 6, the light beam quality can be improved, which is beneficial to improving the dispersion measurement effect.

[0053] Optional, continue to refer to Figure 1 The dispersion compensation module 30 includes a first reflector 7, a second reflector 12, a first grating 8, a second grating 9, a second displacement platform 10 and a climbing reflector 11. The first reflector 7 and the second reflector 12 are arranged in different planes, the first grating 8 and the second grating 9 are parallel, the position of the first grating 8 is fixed, the second grating 9 is arranged on the second displacement platform 10, the second displacement platform 10 is connected to the electric control module 40, and the second displacement platform 10 is used to drive the second grating 9 to translate to provide preset dispersion compensation for the second signal light beam.

[0054] Optionally, the preset dispersion compensation is determined according to the distance between the first grating 8 and the second grating 9, and the corresponding relationship between the distance between the first grating 8 and the second grating 9 and the dispersion compensation value is pre-calibrated according to experiments.

[0055] Among them, the first grating 8 and the second grating 9 form a Treacy grating pair, and the grating pair is placed in parallel at a certain angle (the two gratings are blazed gratings, and the incident angle of the incident light is equal to the blazed angle of the grating). The length of the standard optical fiber is changed by an equal amount, and the spacing of the grating pair is moved. The residual second-order dispersion after compensation is measured by the measurement mode for the small dispersion amount, and the dispersion of the standard optical fiber of a certain length is known, so the dispersion compensation amount corresponding to the grating spacing is calibrated. Since the spacing of the grating pair is linearly related to the dispersion amount it provides, the dispersion amount provided by the grating pair with different spacings can be obtained using the calibrated data. During the measurement, the second displacement platform 10 is vertically connected to one of the grating pairs (the second grating 9), and the large dispersion amount is compensated for as small dispersion or zero dispersion. The result can be obtained by observing the interference image on the spectrometer 16. This step reduces the error generated by the subsequent fitting dispersion curve. Finally, the dispersion compensated by the grating pair is added back to the calculation result. In this embodiment, both the first displacement platform 15 and the second displacement platform 10 can be selected as pzt displacement platforms.

[0056] Optionally, in the second working mode, the second signal light beam output from the third end of the circulator 4 is reflected by the first reflector 7 and then incident on the first grating 8 to generate angular dispersion, and then becomes parallel light after passing through the second grating 9. After being reflected by the climbing reflector 11, the light height moves to the plane where the second reflector 12 is located, and then passes through the second grating 9 and the first grating 8 again and then incident on the second reflector 12, and then reflected by the second reflector 12 and then incident on the combiner 13.

[0057] Specifically, when the measured dispersion is small, the light does not pass through the dispersion compensation module 30 and can leave the optical path by lifting the first reflector 7 and the second reflector 12, so that the two beams of light directly interfere with each other.

[0058] The beam transmission process of the second working mode is as follows: the output beam of the light source 1 is divided by the beam splitter 2 into two beams of light as the two arms of the interference system, one of which is dispersed by the CFBG, and the other is used as an air arm and is combined with the electrically controlled delay line 19 to scan the interference spectrum; the first beam of light is collimated and coupled into the optical fiber by the collimator 3, enters the CFBG through the second end of the circulator 4, is reflected in the CFBG, and is output from the third end of the circulator 4, and then enters the dispersion compensation module 30 through the collimator 6.

[0059] The light reflected by the first reflector 7 is incident on the first grating 8 at an angle, and first produces angular dispersion. After passing through the second grating 9, it becomes parallel light again, and then enters the climbing reflector 11, which is composed of two right-angle reflectors. After being reflected twice, the light is emitted in parallel with the original direction, and the light height moves to the same plane as the second reflector 12. The second reflector 12 and the first reflector 7 are in an up-down relationship in the vertical direction of space, that is, at this time, the light height moves to the same plane as the second reflector 12; then it passes through the grating pair (9, 8) again to obtain the light after dispersion compensation. The dispersion compensation amount of the grating pair is related to the distance between the two gratings and the angle between the grating and the incident light. In the experiment, the angle between the incident light and the grating should be adjusted to make the diffraction strongest; the moving direction of the second displacement platform 10 should be perpendicular to the direction of the second grating 9 to ensure the parallelism of the grating pair. In this process, the positive dispersion of light passing through CFBG is compensated by the negative dispersion of the grating pair, the dispersion amount becomes smaller, and the time delay provided by the air arm can also be reduced. The scanned interference spectrum will not cause the phase difference to be greater than 2π due to too many sampling points, which cannot be distinguished in the spectrometer; the compensated light is reflected by the second reflector 12 and enters the beam combiner 13 to interfere with the light of the other arm. The other beam of light separated by the beam splitter 2 enters the beam combiner 13 through two right-angle reflectors 14 for interference. The two right-angle reflectors 14 are connected to the first displacement platform 15, and the platform movement direction is parallel to the propagation direction of the light. During the movement of the two right-angle reflectors 14, the time delay generated by this arm is different, and the intensity of interference with the other arm is different. The spectrometer 16 receives a new image every time it moves a certain distance.

[0060] Optional, continue to refer to Figure 1 The electronic control module 40 includes a computer 17 and a controller 18. The spectrometer 16 and the controller 18 are both connected to the computer 17. The electronically controlled delay line 19 and the dispersion compensation module 30 (the second displacement platform 10 therein) are both connected to the controller 18. The computer 17 is used to calculate the dispersion value according to the interference spectrum signal received by the spectrometer 16. The controller 18 is used to adjust the delay of the electronically controlled delay line 19 and the preset dispersion compensation provided by the dispersion compensation module 30.

[0061] The computer 17 is used to analyze the spectral interference data. The spectrometer 16 receives the spectral interference graph of the number of steps of the first displacement platform 15, and converts the three variables into a two-dimensional image, whose horizontal axis represents a spectral scan and the vertical axis represents an interference image, thereby obtaining an interference graph of the number of steps to the intensity. The envelope fitting function and the error function are used to extract the fitting parameters that correspond to the maximum and minimum values ​​of the interference intensity, wherein a certain parameter represents the group delay GD value. The controller 18 receives the grating position signal, and then calculates the original dispersion value provided by the CFBG. The controller 18 provides a control signal to adjust the compensation amount of the grating pair (8, 9), and then moves the electrically controlled delay line 19 again, which is received by the spectrometer 16 and analyzed in the same way as above.

[0062] Figure 2 A flow chart of a dispersion measurement method for a chirped Bragg grating provided in an embodiment of the present invention is provided. The dispersion measurement method is performed by the dispersion measurement system for a chirped Bragg grating provided in the above embodiment. Figure 2 , the dispersion measurement method comprises:

[0063] S110, connecting the chirped Bragg grating to be measured to the signal optical path of the interference module.

[0064] The chirped Bragg grating may be a CFBG, and the specific structure may refer to the aforementioned embodiment and will not be described in detail here.

[0065] S120, setting a dispersion compensation module outside the signal optical path, and measuring the dispersion value of the chirped Bragg grating to be measured in a first working mode.

[0066] S130: If the dispersion value of the chirped Bragg grating to be measured exceeds the measurement range of the first working mode, a dispersion compensation module is arranged in the signal optical path, and the dispersion value of the chirped Bragg grating to be measured is measured in the second working mode.

[0067] It is understandable that if the dispersion range of the chirped Bragg grating to be measured is unknown, the dispersion measurement can be performed using the first working mode for measuring small dispersion values. If the measurement exceeds the range, the second working mode for measuring large dispersion values ​​is used.

[0068] Among them, in the first working mode, the first interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the first interference signal; in the second working mode, the dispersion compensation module provides a preset dispersion compensation to the signal optical path, and the second interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation.

[0069] The dispersion measurement method of the chirped Bragg grating provided in the embodiment of the present invention has the same or corresponding technical effects as the dispersion measurement system provided in the above embodiment, which will not be described in detail here.

[0070] Optionally, if it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the first operating mode, the first operating mode is used to measure the dispersion value of the chirped Bragg grating to be measured; if it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the second operating mode, the second operating mode is used to measure the dispersion value of the chirped Bragg grating to be measured.

[0071] The specific range of small dispersion and large dispersion can be determined according to the accuracy of the spectrometer, and can be selected according to actual conditions during implementation.

[0072] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A dispersion measurement system for a chirped Bragg grating, characterized in that: It includes an interference module, a dispersion compensation module and an electric control module, wherein the interference module and the dispersion compensation module are both connected to the electric control module; The optical path in the interference module includes a signal optical path and a reference optical path, and the chirped Bragg grating to be measured is located in the signal optical path; The dispersion measurement system includes a first working mode and a second working mode. In the first working mode, the dispersion compensation module is located outside the signal optical path, the first interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a first dispersion value of a first chirped Bragg grating to be measured according to the first interference signal; In the second working mode, the dispersion compensation module is located in the signal optical path, the dispersion compensation module provides preset dispersion compensation for the signal optical path, the second interference signal generated by the interference module is transmitted to the electric control module, and the electric control module determines a second dispersion value of the second chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation; The first dispersion value is smaller than the second dispersion value.

2. The dispersion measurement system of a chirped Bragg grating according to claim 1, characterized in that: The interference module includes a light source, a beam splitter, a circulator, an electrically controlled delay line, a beam combiner and a spectrometer, and the first chirped Bragg grating to be measured or the second chirped Bragg grating to be measured is connected to the second end of the circulator; In the first working mode, the output beam of the light source is incident on the beam splitter and is divided into a first signal beam and a first reference beam, the first signal beam is incident on the first end of the circulator, is output from the second end of the circulator to the first chirped Bragg grating to be measured, is reflected by the first chirped Bragg grating to be measured, is incident on the second end of the circulator, and is output from the third end of the circulator to the beam combiner; The first reference beam is incident on the electrically controlled delay line, and is incident on the beam combiner after being delayed by the electrically controlled delay line; The first signal beam and the first reference beam are combined by the beam combiner to generate the first interference signal, and the first interference signal is incident on the spectrometer; In the second working mode, the output beam of the light source is incident on the beam splitter and is divided into a second signal beam and a second reference beam, the second signal beam is incident on the first end of the circulator, is output from the second end of the circulator to the second chirped Bragg grating to be measured, is reflected by the second chirped Bragg grating to be measured, is incident on the second end of the circulator, is output from the third end of the circulator to the dispersion compensation module, and is output to the beam combiner after the preset dispersion compensation is generated by the dispersion compensation module; The second reference beam is incident on the electrically controlled delay line, and is incident on the beam combiner after being delayed by the electrically controlled delay line; The second signal beam and the second reference beam are combined by the beam combiner to generate the second interference signal, and the second interference signal is incident on the spectrometer.

3. The dispersion measurement system of a chirped Bragg grating according to claim 2, characterized in that: The interference module also includes a first collimator and a second collimator; In the first working mode, the first signal beam output by the beam splitter is collimated by the first collimator and then incident to the first end of the circulator, and the first signal beam output by the circulator is collimated by the second collimator and then incident to the beam combiner; In the second working mode, the second signal beam output by the beam splitter is collimated by the first collimator and then incident on the first end of the circulator, and the second signal beam output by the circulator is collimated by the second collimator and then incident on the dispersion compensation module.

4. The dispersion measurement system of a chirped Bragg grating according to claim 2, characterized in that: The electrically controlled delay line includes two right-angle mirrors and a first displacement platform, the right-angle mirrors are fixed on the first displacement platform, the first displacement platform is connected to the electrically controlled module, and the first displacement platform is used to drive the right-angle mirrors to translate to achieve the delay of the first reference beam or the second reference beam.

5. The dispersion measurement system of a chirped Bragg grating according to claim 2, characterized in that: The dispersion compensation module includes a first reflector, a second reflector, a first grating, a second grating, a second displacement platform and a climbing reflector, the first reflector and the second reflector are arranged in different planes, the first grating and the second grating are parallel, the position of the first grating is fixed, the second grating is arranged on the second displacement platform, the second displacement platform is connected to the electric control module, and the second displacement platform is used to drive the second grating to translate to provide preset dispersion compensation for the second signal light beam.

6. The dispersion measurement system of a chirped Bragg grating according to claim 5, characterized in that: In the second working mode, the second signal light beam output from the third end of the circulator is reflected by the first reflector and then incident on the first grating to generate angular dispersion. After passing through the second grating, it becomes parallel light again. After being reflected by the climbing reflector, the light moves to the plane where the second reflector is located. After passing through the second grating and the first grating again, it is incident on the second reflector, and after being reflected by the second reflector, it is incident on the combiner.

7. The dispersion measurement system of a chirped Bragg grating according to claim 5, characterized in that: The preset dispersion compensation is determined according to the distance between the first grating and the second grating, and the corresponding relationship between the distance between the first grating and the second grating and the dispersion compensation value is pre-calibrated according to experiments.

8. The dispersion measurement system of a chirped Bragg grating according to claim 2, characterized in that: The electronic control module includes a computer and a controller, the spectrometer and the controller are both connected to the computer, the electronically controlled delay line and the dispersion compensation module are both connected to the controller, the computer is used to calculate the dispersion value according to the interference spectrum signal received by the spectrometer, and the controller is used to adjust the delay of the electronically controlled delay line and the preset dispersion compensation provided by the dispersion compensation module.

9. A method for measuring dispersion of a chirped Bragg grating, characterized in that: The dispersion measurement method is performed by the dispersion measurement system of the chirped Bragg grating according to any one of claims 1 to 8, and the dispersion measurement method comprises: Connecting the chirped Bragg grating to be measured into the signal optical path of the interference module; The dispersion compensation module is arranged outside the signal optical path, and the dispersion value of the chirped Bragg grating to be measured is measured in a first working mode; If the dispersion value of the chirped Bragg grating to be measured exceeds the measurement range of the first working mode, the dispersion compensation module is arranged in the signal optical path, and the dispersion value of the chirped Bragg grating to be measured is measured in the second working mode; Wherein, in the first working mode, the first interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the first interference signal; in the second working mode, the dispersion compensation module provides preset dispersion compensation to the signal optical path, and the second interference signal generated by the interference module is transmitted to the electronic control module, and the electronic control module determines the dispersion value of the chirped Bragg grating to be measured according to the second interference signal and the preset dispersion compensation.

10. The dispersion measurement method of a chirped Bragg grating according to claim 9, characterized in that: If it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the first working mode, the dispersion value of the chirped Bragg grating to be measured is measured using the first working mode; If it is known that the dispersion value of the chirped Bragg grating to be measured is within the measurement range of the second working mode, the second working mode is adopted to measure the dispersion value of the chirped Bragg grating to be measured.

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