Optical fiber device in-line process optimization method and apparatus

Abstract

The application provides an optical fiber device online process optimization method and device, which comprises determining N process parameters of an optical fiber device to be optimized, adopting a control variable method, optimizing one process parameter each time until the optimization of the N process parameters is completed, and the output state of the optical fiber device reaches a target effect. The application is based on the existing test results of internal mode coupling of the optical fiber device, and for the process parameter optimization of the online preparation of the optical fiber device, the internal mode coupling state can be improved by optimizing the key process parameters, so that the output end of the device has as few mode degenerations as possible. The optimization of the key process parameters includes but is not limited to the optimization of ablation parameters, the optimization of the draw-tower ratio, the optimization of mode field matching, the increase of relay optical fibers and the like. The application can realize the online detection of mode components and the real-time optimization of key process parameters in the preparation process of the optical fiber device, realize the effective mode maintenance of the optical fiber device, and avoid the local degradation of the beam quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber device preparation, and particularly relates to an online process optimization method and device for optical fiber devices. BACKGROUND

[0002] High-power fiber lasers based on all-fiber structures have made great progress in power improvement and defense industry applications in recent years, which is largely due to the wide application of all-fiber structures. In the all-fiber structure laser system, the combination of few-mode gain fibers, energy transmission fibers and fiber devices makes the overall structure compact and strong in anti-interference. Among them, the most widely used fiber devices include pump combiner (signal-pump combiner), power combiner, mode field adapter, cladding light filter, fiber end cap, etc.

[0003] Because the fiber device usually involves integration between different fibers or mechanical / optical processing of the fiber structure, with the change of the waveguide structure, the transmission of laser in it is prone to mode coupling, which leads to serious mode degradation, especially at medium and high power output levels. For example, a fiber combiner is usually composed of at least two types of few (multi) mode fibers, the mode coupling between the fibers is complex, and the mode matching between the input fiber and the output fiber is affected by multiple factors such as the mode composition of the front-stage laser and the preprocessing process. At present, there is still a lack of effective mode composition measurement and online process optimization means. In the existing method, the device manufacturing quality is usually evaluated subjectively based on the output power measurement or the direct acquisition of the output spot pattern, and it is difficult to establish a "point-to-point" quantitative relationship between the key preparation process of the device and the mode preservation characteristics. In addition, the data obtained by direct power monitoring has no direct correspondence with the mode-related characteristics of the device, and is insufficient to indirectly represent the beam quality preservation characteristics of the device. Although the output spot pattern implies mode content information, the mode composition and the spot intensity distribution have a many-to-one relationship, which easily leads to incorrect interpretation of the mode degradation of the fiber device. The mode preservation effect of the fiber device is evaluated by the method of direct beam quality measurement, which is low in testing efficiency, and the beam quality M 2 and the internal mode evolution of the fiber device have no direct correspondence. Therefore, in order to truly clarify the main causes of the internal mode degradation of the fiber device, quantify the mode content change rule, and explore the corresponding relationship between the process parameters and the internal mode state, a new tool for measuring the internal mode coupling of the fiber device is needed.

[0004] For example, the fiber end cap is usually made by fusing the energy transmission fiber and the fused quartz block to reduce the output power density of the laser, and the quality of the fusion has a significant impact on the output beam quality. It is necessary to carry out online mode coupling analysis to quantify and optimize the fusion process and realize the mode characteristic preservation of high beam quality laser. For the preparation of beam combiner, mode field adapter and other devices containing tapering process, although the process objectively meets the adiabatic tapering condition, the key process parameters still significantly affect the mode transmission characteristics, resulting in the degradation of the output beam quality. On the one hand, for the prepared fiber device, in addition to the need for testing the overall transmission efficiency of the device, the internal mode coupling characteristics of the device also need to be tested for the beam quality preservation characteristics. On the other hand, for the online preparation of fiber devices, it is necessary to develop an online mode measurement method to explore the influence of process parameters on the mode coupling characteristics of fiber devices, guide online process optimization, and improve the beam quality preservation ability of devices. SUMMARY

[0005] In view of the problems in the prior art, the present application provides an online process optimization method and device for fiber devices, which can quantitatively measure the mode coupling state and output mode composition of fiber devices.

[0006] To achieve the above technical purposes, the technical scheme adopted by the present application is:

[0007] On the one hand, the present application provides an online process optimization method for fiber devices, comprising:

[0008] S1. determining N process parameters of the fiber device to be optimized;

[0009] S2. using the control variable method to optimize one process parameter at a time until the optimization of N process parameters is completed, and the output state of the fiber device reaches the target effect, wherein the optimization process of the nth process parameter is as follows:

[0010] S2.1 under the current process parameter, injecting a probe laser into the input signal fiber of the fiber device in the manufacturing process;

[0011] S2.2 the probe laser starts from the input signal fiber, passes through the process treatment area of the fiber device, is affected by the external process treatment parameters in the manufacturing process of the fiber device, and there is non-ideal mode degradation in the internal fiber device. The core transmission mode of the probe laser changes in the process treatment area, and the modulated probe laser is transmitted to the output signal tail fiber of the fiber device in a new mode state;

[0012] S2.3 collecting the light field information output by the output signal tail fiber of the fiber device and analyzing the mode field characteristics to obtain the number of modes, the type of high-order modes and the relative content induced by mode coupling during the internal transmission of the fiber device under the current process parameter;

[0013] S2.4 keeping other process parameters unchanged, changing the nth process parameter, repeating steps S2.1 to S2.4 until the high-order mode content induced by mode coupling during the transmission of the probe laser in the optical fiber device is the lowest under the current process parameter, and the current corresponding nth process parameter is the optimal value of the nth process parameter.

[0014] Further, in step S2 of the present application, the probe laser is a swept laser;

[0015] The optical fiber device produces a periodic interference light field at the output signal tail fiber output end of the optical fiber device as the wavelength of the injected swept laser changes, and the periodic interference light field contains multiple characteristic frequencies, and the frequency size is the differential mode group delay between different modes.

[0016] The intensity information of the periodic interference light field at different wavelengths output by the output signal tail fiber is collected, the intensity data at all positions in two-dimensional space at different wavelengths is extracted, the Fourier transform is performed on the intensity data at all positions in two-dimensional space, and the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device are obtained based on the Fourier transform result.

[0017] Further, in step S2 of the present application, the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device are obtained based on the Fourier transform result, and the method is as follows:

[0018] If all the output signal fibers of the optical fiber device are two-mode fibers, the peak values in the Fourier transform result are the characteristic peak, the first high-order mode LP 01 , the second high-order mode LP 11 , and so on.

[0019] If all the output signal fibers of the optical fiber device are fibers supporting more modes, the peak values in the Fourier transform result are the characteristic peak, the first high-order mode LP 01 , the second high-order mode LP 11 , the third high-order mode LP 21 , and so on.

[0020] Under the premise that the total output power of the optical fiber device is constant, the greater the peak intensity in the Fourier transform result, the higher the content of the corresponding mode, so that the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device are obtained.

[0021] In one aspect, an optical fiber device online process optimization device is provided, comprising:

[0022] A probe laser injection unit is configured to generate a probe laser and inject the probe laser into an input signal fiber of the fiber device;

[0023] The fiber device comprises at least two ports, i.e., an input signal fiber and an output signal pigtail.

[0024] An image acquisition and mode component analysis unit is configured to acquire light field information output by the output signal pigtail and analyze mode field characteristics to obtain mode quantity, high-order mode type and relative content induced by mode coupling during internal transmission of the fiber device under current process parameters.

[0025] A control unit is configured to control process parameters, evaluate fiber device performance in real time according to mode component analysis results, use mode analysis results as feedback parameters to control process equipment step adjuster to adjust device processing parameters, and iteratively optimize to determine optimal process parameters.

[0026] Further, the control unit determines the advantages and disadvantages of the fiber device in terms of mode retention and beam quality according to mode quantity, high-order mode type and relative content induced by mode coupling during internal transmission of the fiber device under current process parameters.

[0027] Further, in the present application, the probe laser injection unit comprises a tunable laser and a single-mode jumper.

[0028] Further, in the present application, the tunable laser has three controllable parameters, i.e., wavelength tuning range, wavelength tuning resolution and wavelength tuning speed.

[0029] Further, in the present application, the cutoff wavelength of the single-mode jumper is not greater than the working wavelength of the device, and the numerical aperture NA is not greater than 0.1 at the working wavelength.

[0030] Further, in the present application: the optical fiber device is any optical fiber device with laser transmission purposes, the optical fiber device has an external processing area, and the external processing area has an induced mode coupling factor or a mechanical, chemical, or optical processing-induced mode coupling factor.

[0031] Further, in the present application: the image acquisition and mode component analysis unit comprises an imaging optical assembly, a high-frame-rate camera, and a mode interference optical field processing assembly.

[0032] The imaging optical assembly transmits the mode interference optical field output by the output signal tail fiber to the high-frame-rate camera.

[0033] The high-frame-rate camera records the intensity data of the mode interference optical field.

[0034] The mode interference optical field processing assembly performs Fourier transform on the intensity data of the mode interference optical field, and obtains the mode number, high-order mode type, and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device based on the Fourier transform result.

[0035] Compared with the prior art, the present application can produce the beneficial technical effects that:

[0036] The present application can quantitatively measure the mode coupling state and output mode component of the prepared optical fiber device. Specifically, for the prepared optical fiber device, the probe laser is injected into the input signal optical fiber of the optical fiber device. The probe laser starts from the input signal optical fiber, passes through the waveguide structure change area of the optical fiber device, is affected by the external processing parameters in the production process of the optical fiber device, the internal waveguide structure of the optical fiber device deviates from the ideal state, there is mode mismatch during the fusion of the optical fiber, the core transmission mode of the probe laser changes in the corresponding area, the modulated probe laser is transmitted to the output signal tail fiber of the optical fiber device with a new mode state, the output optical field information of the optical fiber device is collected and the mode field characteristics are analyzed, the mode number and relative content of the current internal transmission optical field of the device reaching the output end are obtained, and the advantages and disadvantages of the mode component analysis optical fiber device mode retention characteristics are analyzed.

[0037] The present application can evaluate the mode retention performance of the prepared optical fiber device by accurately measuring the mode coupling state inside the optical fiber device. On the one hand, the internal mode component of the optical fiber device under different process parameters is quantified, which is beneficial to the targeted optimization of the device preparation process, and on the other hand, the mode retention performance of the optical fiber device is effectively improved, and the output beam quality is optimized.

[0038] The present application is based on the existing test results of the mode coupling inside the fiber device. For the process parameter optimization of the online preparation of the fiber device, the mode coupling state can be improved by optimizing the key process parameters, so as to ensure that the output end of the device has as few mode degenerations as possible. The mode of optimizing the key process parameters includes but is not limited to optimizing the ablation parameters, optimizing the tapering ratio, optimizing the mode field matching, and increasing the relay optical fiber. The present application can realize the online detection of the mode components and the real-time optimization of the key process parameters in the preparation process of the fiber device, realize the effective mode maintenance of the fiber device, and avoid the local degradation of the beam quality. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0040] Figure 1 The flowchart of an embodiment;

[0041] Figure 2 The mode coupling schematic diagram in the fiber device;

[0042] Figure 3 The structural schematic diagram of an embodiment;

[0043] Figure 4 The test fiber link diagram of an embodiment;

[0044] Figure 5 The internal mode coupling test result diagram of two first-type mode field adapters (6 / 125 μm-20 / 400 μm specification mode field adapters) in an embodiment, wherein (a) is the internal mode coupling test result diagram of the first first-type mode field adapter (6 / 125 μm-20 / 400 μm specification mode field adapter), and (b) is the internal mode coupling test result diagram of the second first-type mode field adapter (6 / 125 μm-20 / 400 μm specification mode field adapter);

[0045] Figure 6 The internal mode coupling test result diagram of two second-type mode field adapters (6 / 125 μm-25 / 250 μm specification mode field adapters) in an embodiment, wherein (a) is the internal mode coupling test result diagram of the first second-type mode field adapter (6 / 125 μm-25 / 250 μm specification mode field adapter), and (b) is the internal mode coupling test result diagram of the second second-type mode field adapter (6 / 125 μm-25 / 250 μm specification mode field adapter);

[0046] The objectives, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. Specific implementation method

[0047] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly explain the spirit of the present application with the aid of the drawings and detailed description. Any person skilled in the art, after understanding the embodiments of the present application, can make changes and modifications to the technology taught by the present application without departing from the spirit and scope of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application but not to limit the present application.

[0048] Reference Figure 1 For a flowchart of an embodiment, a method for online process optimization of an optical fiber device is provided, comprising:

[0049] S1. determining N process parameters of the optical fiber device to be optimized;

[0050] S2. using the control variable method to optimize one process parameter at a time until the optimization of the N process parameters is completed and the output state of the optical fiber device reaches the target effect.

[0051] In an embodiment, a method for optimizing process parameters is proposed. The optimization process for the nth process parameter is as follows:

[0052] S2.1 under the current process parameter, injecting a probe laser into the input signal fiber of the optical fiber device in the manufacturing process;

[0053] S2.2 the probe laser, starting from the input signal fiber, passes through the process treatment area of the optical fiber device and is affected by the external process treatment parameters in the manufacturing process of the optical fiber device. There are non-ideal mode degenerations in the internal transmission of the optical fiber device. The core transmission mode of the probe laser changes in the process treatment area. The modulated probe laser is transmitted to the output signal pigtail of the optical fiber device in a new mode state;

[0054] S2.3 collecting the light field information output by the output signal pigtail of the optical fiber device and analyzing the mode field characteristics to obtain the number of modes, the type of high-order modes and the relative content induced by mode coupling in the internal transmission of the optical fiber device under the current process parameter;

[0055] S2.4 keeping other process parameters unchanged, changing the nth process parameter, and repeating steps S2.1 to S2.4 until the content of high-order modes induced by mode coupling in the internal transmission of the optical fiber device under the current process parameter is the lowest. The current corresponding nth process parameter is the optimal value of the nth process parameter.

[0056] In an embodiment, a method for optimizing process parameters is proposed, and the optimization process of the nth process parameter is as follows:

[0057] S2.1 injecting a probe laser into the input signal fiber of the fiber device in the manufacturing process under the current process parameter, wherein the probe laser is a swept-frequency laser;

[0058] S2.2 the probe laser travels through the process treatment area of the fiber device, and the fiber device is affected by the external process treatment parameter in the manufacturing process. Non-ideal mode degradation exists in the fiber device, the core transmission mode of the probe laser changes in the process treatment area, and the modulated probe laser is transmitted to the output signal tail fiber of the fiber device in a new mode state;

[0059] Specifically, in the embodiment, the periodic interference light field of each core mode is generated at the output end of the output signal tail fiber of the fiber device with the change of the wavelength of the injected swept-frequency laser. The periodic interference light field contains multiple characteristic frequencies, and the frequency size is the differential mode group delay between different modes.

[0060] S2.3 collecting the light field information output by the output signal tail fiber and analyzing the mode field characteristics to obtain the mode number, high-order mode type and relative content induced by mode coupling in the internal transmission of the fiber device under the current process parameter;

[0061] Specifically, the intensity information of the periodic interference light field at different wavelengths output by the output signal tail fiber is collected, the intensity data at all positions in two-dimensional space at different wavelengths is extracted, the intensity data at all positions in two-dimensional space is subjected to Fourier transform, and the mode number, high-order mode type and relative content induced by mode coupling in the internal transmission of the probe laser in the fiber device are obtained based on the Fourier transform result.

[0062] S2.4 keeping other process parameters unchanged, changing the nth process parameter, and repeating steps S2.1 to S2.4 until the high-order mode content induced by mode coupling in the internal transmission of the fiber device under the current process parameter is the lowest. The current corresponding nth process parameter is the optimal value of the nth process parameter.

[0063] In an embodiment, a method for obtaining the mode number, high-order mode type and relative content induced by mode coupling in the internal transmission of the probe laser in the fiber device based on the Fourier transform result is proposed, and the steps are as follows:

[0064] If all the output signal fibers of the fiber device are two-mode fibers, the peak values in the Fourier transform result are the base mode LP 01 characteristic peak, first high-order mode LP 11 characteristic peak;

[0065] All output signal fibers of the fiber device are multimode fibers, and the peak values in the Fourier transform result are in turn the fundamental mode LP 01 Characteristic peak, first high-order mode LP 11 Characteristic peak, second high-order mode LP 21 Characteristic peak, and so on. The order of the high-order mode characteristic peaks is determined by the relative differential delay of the current mode and the fiber fundamental mode. The smaller the differential delay, the higher the order.

[0066] Under the premise that the total output power of the fiber device is constant, the greater the peak intensity in the Fourier transform result, the higher the content of the corresponding mode, thereby obtaining the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the fiber device.

[0067] In any of the above embodiments, according to the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the fiber device under the current process parameters, the advantages and disadvantages of the fiber device in terms of mode retention and beam quality are determined. The fewer the number of high-order modes and the lower the relative content, the better the characteristics of the fiber device in terms of mode retention and beam quality under the current process parameters.

[0068] In any of the above embodiments, the fiber device includes at least two ports of input signal fiber and output signal fiber. The fiber device includes no less than two types of fibers, or the fiber device is a non-single-mode fiber device processed by mechanical, optical or hybrid process, or the fiber device is any fiber device used for laser transmission purposes, such as a mode field adapter, a fiber combiner, a cladding optical filter, a fiber end cap, etc.

[0069] The fiber device has an external process treatment area, and there are external treatment factors that induce coupling of the fiber core mode state in the external process treatment area, or there are mechanical, chemical, optical processing techniques that induce coupling of the fiber core mode state.

[0070] The main types of mode coupling that cause mode degradation inside fiber optic devices include: (1) excitation of higher-order modes caused by changes in fiber waveguide structure, (2) inter-mode energy exchange during waveguide coupling between fibers, and (3) defects in fiber waveguide structure caused by external process disturbances. Ideally, laser transmission inside fiber optic devices should not generate new mode components, and the beam quality of the output beam should not degrade compared to the input beam. In actual fiber optic devices, due to process limitations, mode coupling inevitably exists in the disturbance region inside the device. The single transverse mode beam (high beam quality beam) injected into the fiber optic device undergoes energy coupling to the adjacent higher-order mode beam in the mode disturbance region. The newly generated higher-order mode components then induce the generation of even higher-order higher-order modes, causing the single transverse mode beam (high beam quality beam) to degrade into a multimode beam (low beam quality beam) at the output end of the fiber optic device.

[0071] Reference Figure 2 The diagram illustrates mode coupling in an optical fiber device, where (a) represents the excitation of higher-order modes caused by changes in the fiber waveguide structure; (b) represents inter-mode energy exchange during waveguide coupling between fibers; and (c) represents defects in the fiber waveguide structure caused by external process disturbances. Mode coupling within an optical fiber device manifests as energy transfer from lower-order modes to higher-order modes, exhibiting a degradation effect. Once a higher-order mode is generated, it will tend to couple to that higher-order mode during subsequent transmission, especially in regions where there are changes in the waveguide structure within the optical fiber device. Higher-order modes have larger propagation divergence angles and losses; therefore, mode degradation not only affects the beam quality of the device's output beam but may also lead to increased local energy leakage, abnormal temperature rise in the device, and compromise safe operation. After the new higher-order mode component is generated, it propagates within the device waveguide along with the lower-order mode optical field. Since their frequencies are similar, they generate optical beats with characteristic frequencies under interference. Under the premise that the fundamental mode (lower-order mode) dominates the transmission, the higher the content of higher-order modes, the larger the amplitude of the optical beat at the corresponding characteristic frequency.

[0072] On the one hand, an online process optimization device for optical fiber devices is provided, including an optical fiber device mode coupling test device and a control unit for controlling process parameters and evaluating the performance of optical fiber devices in real time based on mode composition analysis results to determine the optimal process parameters.

[0073] Reference Figure 3 One embodiment provides an optical fiber device mode coupling test apparatus, comprising:

[0074] The probe laser injection unit 100 is used to generate a probe laser and inject the probe laser into the input signal fiber of the optical fiber device;

[0075] The optical fiber device 200 at least includes two ports of input signal optical fiber and output signal pigtail; after the probe laser is transmitted from the input signal optical fiber and through the process treatment area of the optical fiber device, the core transmission mode of the probe laser is changed in the process treatment area due to the influence of external process treatment parameters in the manufacturing process of the optical fiber device, and the modulated probe laser is transmitted to the output signal pigtail of the optical fiber device in a new mode state.

[0076] The image acquisition and mode component analysis unit 300 is used for acquiring the light field information output by the output signal pigtail and analyzing the mode field characteristics, and obtaining the mode number, high-order mode type and relative content induced by mode coupling during the internal transmission of the optical fiber device under the current process parameters.

[0077] The control unit is used for controlling the process parameters, real-time evaluating the performance of the optical fiber device according to the mode component analysis result, taking the mode analysis result as a feedback parameter to control the process equipment step adjuster to adjust the device processing parameters, and iteratively optimizing to determine the optimal process parameters.

[0078] The control unit according to the mode number, high-order mode type and relative content induced by mode coupling during the internal transmission of the optical fiber device under the current process parameters determines the advantages and disadvantages of the optical fiber device in terms of mode retention and beam quality, wherein the fewer the high-order mode number and the lower the relative content, the better the characteristics of the optical fiber device in terms of mode retention and beam quality under the current process parameters.

[0079] In the present application, the mode excitation device injects the probe laser into the input signal optical fiber of the optical fiber device, the probe laser is transmitted from the input signal optical fiber, passes through the process treatment area of the optical fiber device, and the core transmission mode of the probe laser is changed in the process treatment area due to the influence of external process treatment parameters in the manufacturing process of the optical fiber device, and the modulated probe laser is transmitted to the output signal pigtail of the optical fiber device in a new mode state, the image acquisition and mode component analysis unit acquires the light field information output by the optical fiber device and analyzes the mode field characteristics, and obtains the mode number, high-order mode type and relative content induced by mode coupling during the internal transmission of the optical fiber device under the current process parameters, and establishes the numerical correspondence between the current process parameters and the mode transmission characteristics. The injection state of the probe laser of the input signal pigtail is kept unchanged, the process treatment area of the optical fiber device is modulated with monotonically increasing intensity for one of the process parameters, and the process parameter value under the condition of better mode characteristics is obtained through online measurement. In this way, one process parameter is optimized each time, and the mode component measurement experiment is performed again after each optimization is completed, until the high-order mode content is the lowest, and the next process parameter optimization link is entered, until the output state of the optical fiber device reaches the target optimization effect.

[0080] In order to reduce the influence of environmental noise and jitter, during the test, the laser can be repeatedly scanned in any state of the optical fiber device 200, the mode component is measured multiple times and the average value is taken as the final evaluation result of the mode component.

[0081] The present application can perform online testing of the process of the optical fiber device 200. During the preparation of the optical fiber device, the tunable laser is swept cyclically, and the mode component measurement is performed continuously. For a certain process parameter, the processing is implemented in a step-by-step manner, and during the process, the device performance is evaluated in real time according to the mode component measurement result to determine the optimal process parameter.

[0082] Based on the existing test results of the internal mode coupling of the optical fiber device, for the process parameter optimization of the online preparation of the optical fiber device, the internal mode coupling state can be improved by optimizing the key process parameters to ensure that the output end of the device has as few mode degenerations as possible. The way of optimizing the key process parameters includes but is not limited to optimizing the ablation parameters, optimizing the tapering ratio, optimizing the mode field matching, and increasing the relay optical fiber.

[0083] The probe laser injection system 100 includes a tunable laser and a single-mode jumper. After the swept laser is output through the tunable laser and the single-mode jumper, it is injected into the next stage system. The tunable laser has three controllable parameters of wavelength tuning range, wavelength tuning resolution, and wavelength tuning speed. The minimum wavelength tuning range of the tunable laser is not less than 5 nm, the minimum wavelength tuning interval is not greater than 0.5 nm, and the fastest wavelength tuning speed is not less than 0.1 nm / s. The cutoff wavelength of the single-mode jumper is not greater than the working wavelength of the device application, and the numerical aperture NA is not greater than 0.1 at the working wavelength. In the optional range, the smaller the values of the cutoff wavelength and the numerical aperture NA are, the better.

[0084] The single-mode jumper can be a polarization maintaining single-mode optical fiber, which generates a single polarization swept laser and injects it into the next stage system for measuring the polarization maintaining and stress characteristics of the next stage system.

[0085] After the swept laser is output through the tunable laser and the single-mode jumper, it can be directly fused with the next stage system, i.e. the single-mode jumper is directly fused with the input signal optical fiber of the optical fiber device 200, and the swept laser is input into the optical fiber device 200 from the input signal optical fiber.

[0086] As an optional solution, after the swept laser is output through the tunable laser and the single-mode jumper, it can also be injected into the next stage system through a spatial optical system, i.e. the swept laser is input into the optical fiber device 200 from the input signal optical fiber, and the spatial optical system can include a power attenuation element and a polarization optical element.

[0087] The fiber device 200 contains at least two ports, an input signal fiber and an output signal fiber. The fiber device 200 contains no less than two types of fibers, or the fiber device 200 is a non-single mode fiber device processed by mechanical, optical or hybrid process, or the fiber device 200 is any fiber device used for laser transmission purposes such as a mode field adapter, a fiber combiner, a cladding light filter, a fiber end cap, etc.

[0088] The fiber device 200 has an external process treatment area, and there are external treatment factors inside the external process treatment area that induce the coupling of the core mode state, or there are mechanical, chemical, optical process treatment that induces the coupling of the core mode state.

[0089] The output signal fiber of the fiber device 200 can be connected to the same type of fiber or other types of fiber as an output relay fiber.

[0090] The image acquisition and mode component analysis unit 300 contains an imaging optical assembly, a high-frame-rate camera and a mode interference light field processing assembly; the imaging optical assembly transmits the mode interference light field output by the output signal tail fiber to the high-frame-rate camera; the high-frame-rate camera records the intensity data of the mode interference light field; the mode interference light field processing assembly Fourier transforms the intensity data of the mode interference light field, and obtains the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the fiber device based on the Fourier transform results.

[0091] As an optional solution, the imaging optical assembly can perform near-field imaging on the previous stage system, or perform far-field imaging on the previous stage system.

[0092] As a preferred solution, the acquisition frame rate of the high-frame-rate camera can be greater than 500 fps, realizing real-time mode interference light field data acquisition and processing.

[0093] For the measurement of the internal mode characteristics of the fiber device, during the mode coupling test, the probe laser injection system 100 generates a swept frequency laser, which is transmitted through the fiber device 200, and the mode components are affected by the internal mode coupling of the device, and the proportion of each core mode changes.

[0094] As the wavelength of the injected swept frequency laser changes during the injection of the swept frequency laser into the fiber device 200, periodic interference light fields are generated at the output end of the output signal tail fiber of the fiber device 200, and the periodic interference light fields contain multiple characteristic frequencies, and the frequency size is the differential mode group delay between different modes.

[0095] The image acquisition and mode component analysis system 300 acquires intensity information of the periodic interference light field at different wavelengths, extracts intensity data at all positions in the two-dimensional space at different wavelengths, Fourier transforms the intensity data at all positions in the two-dimensional space, and obtains the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device based on the Fourier transform result.

[0096] According to the type of the output signal fiber of the optical fiber device, if the output signal fiber of the optical fiber device is a two-mode fiber, the peak values in the Fourier transform result are the fundamental mode (LP 01 ) characteristic peak, the first high-order mode (LP 11 ) characteristic peak in turn; if the output signal fiber of the optical fiber device is a fiber supporting more modes, the peak values in the Fourier transform result are the fundamental mode (LP 01 ) characteristic peak, the first high-order mode (LP 11 ) characteristic peak, the second high-order mode (LP 21 ) characteristic peak, and so on. Under the premise that the total output power of the optical fiber device is constant, the greater the peak intensity in the Fourier transform result, the higher the content of the corresponding mode, so as to obtain the mode number, high-order mode type and relative content induced by mode coupling during the transmission of the probe laser in the optical fiber device.

[0097] Through the above test process, the high-order mode type and content induced by mode coupling during the transmission of the single-mode laser in the optical fiber device can be analyzed, so as to accurately quantify the device mode degradation behavior and determine the advantages and disadvantages of the current optical fiber device in terms of mode maintenance and beam quality.

[0098] In order to verify the effectiveness of the present application, a specific application example is provided below to test and analyze the internal mode coupling characteristics of the prepared mode field adapter. Through the mode coupling test of the optical fiber device, the test and analysis results obtained can be used for the yield screening of the prepared optical fiber device, and provide a "dissecting sparrow" single device in-depth analysis perspective for the subsequent construction of the optical fiber laser system based on the tested optical fiber device, which is helpful for the analysis of the system mode degradation causes.

[0099] In this embodiment, two types of mode field adapters, 6 / 125μm-20 / 400μm and 6 / 125μm-25 / 250μm, are tested, and each type of mode field adapter has 2 devices for direct comparison.

[0100] The system is built as shown in Figure 4The shown test fiber link, single transverse mode swept fiber laser transmitted by single mode fiber SMF is injected into the fiber device, i.e. mode field adapter (MFA), through 6 / 125 μm single mode fiber. After the transmission of single transverse mode swept fiber laser inside the mode field adapter, mode coupling behavior is generated. The degraded laser mode is output through the 20 / 400 μm output signal fiber of the mode field adapter. Since the output signal fiber is short, a fiber with the same specification parameter, i.e. delay fiber, is spliced as a relay fiber or delay fiber. It can be understood that, Figure 4 The shown test fiber link is a test fiber link for the first type of mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter). For the second type of mode field adapter (6 / 125 μm-25 / 250 μm specification type mode field adapter), only the 6 / 125 μm-20 / 400 μm specification type mode field adapter in Figure 4 is replaced by a 6 / 125 μm-25 / 250 μm specification type mode field adapter.

[0101] Referring to Figure 5 The internal mode coupling test results of two first type mode field adapters (6 / 125 μm-20 / 400 μm specification type mode field adapters) are shown. (a) is the internal mode coupling test result diagram of the first first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter), and (b) is the internal mode coupling test result diagram of the second first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter). From the test results, it can be seen intuitively that the ② type LP 11 mode content of the second first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter) is lower, and the rest of the high-order mode components are equivalent to those of the first first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter). Therefore, it is preliminarily inferred that the second first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter) is better. In the actual construction process of the fiber laser system, from the perspective of system optimization of system mode control, the second first type mode field adapter (6 / 125 μm-20 / 400 μm specification type mode field adapter) can be preferably selected as a system component.

[0102] Referring to Figure 6The internal mode coupling test results of two second type of mode field adapters (6 / 125 μm-25 / 250 μm mode field adapter) are shown in (a) and (b). From the test results, it can be seen that the LP 11 The mode contents are equivalent. However, the ③ and ④ type of LP modes of the first second type of mode field adapter (6 / 125 μm-25 / 250 μm mode field adapter) are lower than those of the second second type of mode field adapter (6 / 125 μm-25 / 250 μm mode field adapter). 02 The mode contents are obviously lower, so it is preliminarily inferred that the first second type of mode field adapter (6 / 125 μm-25 / 250 μm mode field adapter) is better. In the actual construction process of the fiber laser system, from the perspective of system optimization of system mode control, the first second type of mode field adapter (6 / 125 μm-25 / 250 μm mode field adapter) can be preferably selected as a system component.

[0103] The remaining matters of the present application are known technologies.

[0104] The technical features of the above embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0105] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. An online process optimization method for optical fiber devices, characterized in that, include: S1. Determine which fiber optic devices need optimization. N One process parameter; S2. Using the controlled variable method, optimize one process parameter at a time until completion. N Optimization of process parameters resulted in the fiber optic device output achieving the target effect, among which the first... n The optimization process for each process parameter is as follows: S2.1 Under the current process parameters, a probe laser is injected into the input signal fiber of the fiber optic device during the fabrication process, wherein the probe laser is a frequency-sweeping laser; S2.2 The probe laser originates from the input signal fiber, passes through the fiber optic device processing area, and is affected by the external processing parameters applied during the fiber optic device fabrication process. Due to the influence of these external processing parameters, non-ideal mode degradation exists within the fiber optic device, and the core transmission mode of the probe laser changes in the processing area. The modulated probe laser is then transmitted to the output signal pigtail of the fiber optic device in a new mode state. As the wavelength of the injected sweep laser changes, each core mode of the fiber optic device generates a periodic interference light field at the output end of the output signal pigtail. The periodic interference light field contains multiple characteristic frequencies, the magnitude of which is the differential mode group delay between different modes. S2.3 Acquire the optical field information of the output signal pigtail of the fiber optic device and analyze the mode field characteristics to obtain the number of modes, higher-order mode types, and relative abundance induced by mode coupling during transmission within the fiber optic device under the current process parameters. This includes: acquiring the intensity information of the periodic interference optical field at different wavelengths of the output signal pigtail; extracting the intensity data at all positions in two-dimensional space at different wavelengths; performing a Fourier transform on the intensity data at all positions in two-dimensional space; and obtaining the number of modes, higher-order mode types, and relative abundance induced by mode coupling during transmission of the probe laser within the fiber optic device based on the Fourier transform results. If all output signal fibers of the fiber optic device are two-mode fibers, the peak values ​​in the Fourier transform results are, in order, the fundamental mode LP. 01 Characteristic peaks, first higher-order mode LP 11 Characteristic peaks; if all output signal fibers of the optical fiber device support more modes, the peak values ​​in the Fourier transform results are, in order, the fundamental mode LP. 01 Characteristic peaks, first higher-order mode LP 11 Characteristic peaks, second higher-order mode LP 21 Characteristic peaks, and so on, the order of higher-order mode peaks is determined by the relative differential delay between the current mode and the fiber fundamental mode. The smaller the differential delay, the higher the order. Under the premise that the total output power of the fiber device is constant, the greater the peak intensity in the Fourier transform result, the higher the content of the corresponding mode. In this way, the number of modes, the type of higher-order mode and the relative content induced by mode coupling when the probe laser is transmitted inside the fiber device can be obtained. S2.4 Keeping other process parameters unchanged, change the first... n For each process parameter, repeat steps S2.1 to S2.4 until the content of higher-order modes induced by mode coupling during transmission within the optical fiber device is minimized under the current process parameters. n The process parameter is the first one. n The optimal value of each process parameter.

2. An online process optimization device for optical fiber devices, characterized in that, include: A probe laser injection unit is used to generate a probe laser and inject the probe laser into the input signal fiber of the fiber optic device, wherein the probe laser is a frequency-sweeping laser; The optical fiber device includes at least two ports: an input signal fiber and an output signal pigtail. After the probe laser originates from the input signal fiber and is transmitted through the optical fiber device, it passes through the fiber device's processing area. Due to the influence of external processing parameters applied during the fabrication of the optical fiber device, the core transmission mode of the probe laser changes in the processing area. The modulated probe laser is then transmitted to the output signal pigtail of the optical fiber device in a new mode. As the wavelength of the injected sweep laser changes, each core mode of the optical fiber device generates a periodic interference optical field at the output end of the output signal pigtail. The periodic interference optical field contains multiple characteristic frequencies, the magnitude of which is the differential mode group delay between different modes. The image acquisition and mode composition analysis unit is used to acquire the optical field information output from the output signal pigtail and analyze the mode field characteristics. It obtains the number of modes, higher-order mode types, and relative abundance induced by mode coupling during transmission within the fiber optic device under the current process parameters. This includes: acquiring the intensity information of the periodic interference optical field at different wavelengths output from the output signal pigtail; extracting the intensity data at all locations in two-dimensional space at different wavelengths; performing a Fourier transform on the intensity data at all locations in two-dimensional space; and obtaining the number of modes, higher-order mode types, and relative abundance induced by mode coupling during the transmission of the probe laser within the fiber optic device based on the Fourier transform results. If all output signal fibers of the fiber optic device are two-mode fibers, the peak values ​​in the Fourier transform results are, in order, the fundamental mode LP. 01 Characteristic peaks, first higher-order mode LP 11 Characteristic peaks; if all output signal fibers of the optical fiber device support more modes, the peak values ​​in the Fourier transform results are, in order, the fundamental mode LP. 01 Characteristic peaks, first higher-order mode LP 11 Characteristic peaks, second higher-order mode LP 21 Characteristic peaks, and so on, the order of higher-order mode peaks is determined by the relative differential delay between the current mode and the fiber fundamental mode. The smaller the differential delay, the higher the order. Under the premise that the total output power of the fiber device is constant, the greater the peak intensity in the Fourier transform result, the higher the content of the corresponding mode. In this way, the number of modes, the type of higher-order mode and the relative content induced by mode coupling when the probe laser is transmitted inside the fiber device can be obtained. The control unit controls the process parameters, evaluates the performance of optical fiber devices in real time based on the mode composition analysis results, uses the mode analysis results as feedback parameters to control the process equipment to step-adjust the device processing parameters, and iteratively optimizes to determine the optimal process parameters.

3. The online process optimization device for optical fiber devices according to claim 2, characterized in that, The control unit determines the quality of the fiber optic device in terms of mode retention and beam quality based on the number of modes, higher-order mode types, and relative content induced by mode coupling during transmission within the fiber optic device under the current process parameters. The fewer the number of higher-order modes and the lower the relative content, the better the fiber optic device in terms of mode retention and beam quality under the current process parameters.

4. The online process optimization device for optical fiber devices according to claim 2 or 3, characterized in that, The probe laser injection unit includes a tunable laser and a single-mode jumper. The probe laser is output through the tunable laser and the single-mode jumper and then injected into the input signal fiber of the optical fiber device.

5. The online process optimization device for optical fiber devices according to claim 4, characterized in that, The tunable laser features controllable wavelength tuning range, wavelength tuning resolution, and wavelength tuning speed.

6. The online process optimization device for optical fiber devices according to claim 5, characterized in that, The tunable laser has a minimum wavelength tuning range of not less than 5 nm, a minimum wavelength tuning interval of not more than 0.5 nm, and a maximum wavelength tuning speed of not less than 0.1 nm / s.

7. The online process optimization device for optical fiber devices according to claim 2, characterized in that, The optical fiber device is any type of optical fiber device used for laser transmission. The optical fiber device has an external processing area. The external processing area contains external processing factors that induce coupling of the fiber core mode state, or there are mechanical, chemical, or optical processing processes that induce coupling of the fiber core mode state.

8. The online process optimization device for optical fiber devices according to claim 2, 3, 5, 6, or 7, characterized in that, The image acquisition and pattern composition analysis unit includes an imaging optical component, a high frame rate camera, and a pattern interference light field processing component. The imaging optics component transmits the mode interference light field output from the output signal pigtail to the high frame rate camera; High frame rate cameras record the intensity data of the interferometric light field. The mode interference optical field processing component performs a Fourier transform on the intensity data of the mode interference optical field, and obtains the number of modes, higher-order mode types, and relative content induced by mode coupling when the probe laser propagates inside the optical fiber device based on the Fourier transform result.

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