A dynamic reconstruction method of spatiotemporal light field based on monochromatic numerical pattern decomposition

Abstract

The present invention discloses a method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical mode decomposition, belonging to the fields of spatiotemporal mode-locked pulsed fiber lasers and multimode nonlinear fiber optics. The method comprises the following steps: S1: establishing an analysis platform comprising a spatiotemporal mode-locked laser, a folding mirror, a spectral filter, a processing device, and an acquisition device, wherein the processing device adjusts the state of the spectral filter and the acquisition device points toward the folding mirror; S2: calibrating the analysis platform; S3: the spatiotemporal mode-locked laser generates an incident light beam, which, after spectral filtering, is continuously collected by the acquisition device for each spectral component to obtain spectral-spatial intensity information; and S4: converting the spectral-spatial intensity information into spatiotemporal structure information. The present invention employs the above method to monitor the output mode of the spatiotemporal mode-locked pulse in real time and feedback-control the mode-selective excitation within the spatiotemporal mode-locked laser cavity, providing a solution for high-performance spatiotemporal mode-locked fiber lasers with controllable output modes.

Description

Technical Field

[0001] The present invention relates to the fields of spatiotemporal mode-locked pulsed fiber lasers and multimode nonlinear fiber optics, and in particular to a spatiotemporal light field dynamic reconstruction method based on monochromatic numerical mode decomposition. Background Art

[0002] Spatiotemporally mode-locked fiber lasers have a larger mode area and additional spatial degrees of freedom, promising higher-performance ultrafast laser output. However, they also face the challenge of uncontrollable spatial mode distribution and output beam quality. For multimode nonlinear processes, the measurement system challenge is how to effectively obtain all the information needed to fully characterize broadband and highly multimode beams. An effective measurement system needs to minimize measurement time, experimental cost, and complexity, while facilitating accurate comparisons between theoretical analysis and experimental results in order to optimize and control laser output performance. Currently commonly used single-mode fiber scanning or sampling methods facilitate qualitative analysis but cannot be directly compared with theory. Spatial mode multiplexing passive devices based on photon lanterns or multi-channel beam control can only achieve physical decomposition of a small number of modes and are not suitable for multimode light fields. Full-field measurement methods using holographic wavelength scanning can perform mode decomposition based on wavelength. Although the device is relatively simple, it is time-consuming and cannot achieve dynamic reconstruction of spatiotemporal light fields. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition. A quasi-4-f system is formed by a programmable digital micromirror device, a cylindrical lens, and a transmission diffraction grating to realize a tunable optical filter. The spectral bands are opened in sequence to realize wavelength scanning and the corresponding spatial distribution is recorded by a high-speed camera. Spatial-spectral intensity information can be obtained. The collected spectral-spatial distribution data is subjected to pattern decomposition using a non-iterative algorithm to restore the amplitude and phase of the light field in real time. The spectral-spatial distribution is then subjected to a frequency domain to time domain Fourier transform to obtain spatiotemporal structure information. The reconstruction time can be shortened to the order of 1 ms. This can deepen the understanding of the mode selection of three-dimensional spatiotemporal mode-locked pulses and the spatiotemporal characteristic regulation mechanism, and provide an effective solution for the design optimization and mode control of adaptively controlled spatiotemporal mode-locked fiber lasers.

[0004] To achieve the above object, the present invention provides a method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition, comprising the following steps:

[0005] S1: Establishing an analysis platform, including a spatiotemporal mode-locked laser, a folding mirror, a spectral filter, a processing device, and a collection device connected in sequence, wherein the processing device adjusts the working state of the spectral filter, and the collection device points to the folding mirror;

[0006] S2: Calibrate the analytical platform using a spontaneous emission fluorescence light source and spectrometer;

[0007] S3: A spatiotemporally mode-locked laser generates an incident light beam, which is processed by the transmission surface of the folding mirror and the spectral filter to obtain a spectral filter and return along the original optical path. The spectral filter is finally output from the refractive surface of the folding mirror. The acquisition device continuously collects the spectrally filtered light field, records the spatial light intensity corresponding to each spectral component, and obtains spectral-spatial intensity information.

[0008] S4: Perform non-iterative numerical calculation on the spectral-spatial intensity information to recover the amplitude and phase of the light field, and then perform Fourier transform on it to obtain the spatiotemporal structure information.

[0009] Preferably, in step S1, a scanning galvanometer is provided behind the optical path of the spatiotemporal mode-locked laser, which can increase the refresh rate of the spectral filter.

[0010] Preferably, in step S1, the spectral filter includes a transmissive diffraction grating, a cylindrical mirror and a digital micromirror device arranged in sequence along the optical path, and the processing device is connected to the digital micromirror device to adjust the switching state of different positions of the digital micromirror device to achieve adjustable wavelength scanning spectral filtering.

[0011] Preferably, in step S2, the calibration process is as follows: using a spontaneous radiation fluorescence light source to output spontaneous radiation fluorescence input to the folding mirror, the spontaneous radiation fluorescence is incident on a digital micromirror device with all pixels turned on, and its fluorescence spectrum is measured using a spectrometer; then some pixel units on the digital micromirror device are turned off, the spontaneous radiation fluorescence is incident on the digital micromirror device with the pixel units turned off, and its output spectrum is measured using a spectrometer. By comparing the interval of the attenuated spectral components on the two output spectra with the pixel interval of the corresponding turned-off pixel units on the digital micromirror device, the center wavelength and the wavelength interval corresponding to each unit pixel can be located, and the functional parameters of the analysis platform can be calibrated and calibrated.

[0012] Preferably, the specific process in step S3 is as follows: the bandwidth of the spectral filter is set to 70nm, the spectral resolution is set to 0.04nm, the refresh rate is set to 32kHz, the spectral filter will select a specific spectral band to constitute spectral filtering, the processing device is set to a computer, and the acquisition device is set to a high-speed camera or a photodiode array. The high-speed camera or photodiode array is used to record the spatial light intensity distribution map corresponding to each spectral component, and finally the spectral-spatial intensity information is obtained.

[0013] Preferably, in step S4, the process of converting the spectral-spatial intensity information into the spatiotemporal structure information is as follows: a non-iterative algorithm is used to perform pattern decomposition on the collected spectral-spatial intensity information, the nonlinear pattern is converted into a cumbersome linear part and a simple nonlinear part, and a pseudo-inverse matrix and the optical fiber intrinsic mode light intensity distribution are used to perform matrix solution to restore the amplitude and phase of the light field, and then the spectral-spatial distribution is Fourier transformed from the frequency domain to the time domain to obtain the spatiotemporal structure information.

[0014] Therefore, the present invention adopts the above-mentioned spatiotemporal light field dynamic reconstruction method based on monochromatic numerical pattern decomposition, which has the following advantages:

[0015] (1) In the present invention, the spectral filter device composed of a programmable digital micromirror device and a transmission diffraction grating has the advantages of a wide spectral range and real-time scanning. Compared with other tunable optical filter solutions, it can obtain a higher degree of freedom and has the advantages of quick operation, simple structure and programmability.

[0016] (2) In the present invention, the pattern decomposition technology is used, and the pattern decomposition time is less than 1ms. The total reconstruction time is determined by the time of scanning the spectral band of the digital micromirror device. The refresh rate of the existing digital micromirror device determines that the reconstruction time is on the order of tens of ms. The refresh rate can be increased to tens of MHz by using a scanning galvanometer, and the total reconstruction time can be reduced to less than 1ms. This pattern-resolved spatiotemporal measurement system is simple, efficient, low-cost, and can dynamically reconstruct spatiotemporal pattern information.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of the analysis platform in a method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition according to the present invention;

[0019] Figure numerals: 1. folding mirror; 2. transmission diffraction grating; 3. cylindrical mirror; 4. digital micromirror device; 5. processing device; 6. acquisition device; 7. spatiotemporal mode-locked laser. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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 part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. The specific model specifications need to be selected and determined based on the actual specifications of the device, etc. The specific selection calculation method adopts the existing technology in this field, so it will not be described in detail.

[0021] Example

[0022] like Figure 1 As shown, the present invention provides a method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition, comprising the following steps:

[0023] S1: Establish an analysis platform, including a space-time mode-locked laser 7, a folding mirror 1, a spectral filter, a processing device 5 and a collection device 6 connected in sequence. The processing device 5 adjusts the working state of the spectral filter, and the collection device points to the folding mirror 1. The spectral filter includes a transmission diffraction grating 2, a cylindrical mirror 3 and a digital micromirror device 4 arranged in sequence along the optical path. The processing device 5 is connected to the digital micromirror device 4 to adjust the switching state of the digital micromirror device 4 at different positions; a scanning galvanometer can be optionally set after the optical path of the space-time mode-locked laser 7 to increase the refresh rate of the spectral filter and thereby speed up the subsequent reconstruction time.

[0024] S2: Use the auto-emission fluorescence light source and spectrometer to calibrate the analysis platform. The calibration process is as follows:

[0025] A spontaneous fluorescence light source is used to output spontaneous fluorescence, which is input into the transmission surface of the folding mirror 1 and ultimately incident on the digital micromirror device 4 with all pixels turned on, forming a spectral filter return, which is output through the refractive surface of the folding mirror 1, and its output spectrum is measured using a spectrometer; some pixel units in the digital micromirror device 4 are turned off. In this embodiment, two vertical pixel units are turned off, and then the spontaneous fluorescence is incident on the digital micromirror device 4 with the pixel units turned off, and its new output spectrum is measured using a spectrometer. By comparing the interval between the two attenuated spectral components in the two output spectra with the pixel interval of the corresponding turned-off pixel units on the digital micromirror device 4, the center wavelength and the wavelength interval corresponding to each unit pixel can be located, thereby calibrating and calibrating functional parameters such as the working wavelength and spectral selection resolution of the analysis platform;

[0026] S3: The spatiotemporally mode-locked laser 7 generates an incident light beam, which is processed by the transmission surface of the folding mirror 1 and the spectral filter to obtain a spectral filter and return along the original optical path. The spectral filter is finally output from the refractive surface of the folding mirror 1;

[0027] The bandwidth of the spectral filter is set to 70 nm, the spectral resolution is set to 0.04 nm, the processing device 5 is set to a computer, the acquisition device 6 is set to a high-speed camera or a photodiode array, with a wide wavelength tuning range and a refresh rate of 32 kHz to achieve high-speed wavelength scanning, and a specific spectral band is selected from the refractive surface output of the folding mirror 1 to form spectral filtering, and the spatial light intensity corresponding to each spectral component is recorded by the acquisition device 6 to obtain spectral-spatial intensity information;

[0028] S4: The collected spectral-spatial intensity information is subjected to pattern decomposition using a non-iterative algorithm, converting the nonlinear pattern into a linear part and a simple nonlinear part. The matrix is ​​solved using the pseudo-inverse matrix and the fiber intrinsic mode intensity distribution to recover the amplitude and phase of the light field. The spectral-spatial distribution is subjected to a Fourier transform from the frequency domain to the time domain to obtain the spatiotemporal structure information. The calculation process is as follows:

[0029] The lateral distribution of the electric field in the optical fiber corresponding to the wavelength-scanned spectral band can be expressed as a linear combination of characteristic modes. :

[0030] ;

[0031] ;

[0032] In the above formula, Representing coordinates The electric field at is the complex coefficient representing the kth order eigenmode, represents the amplitude of the kth order eigenmode, represents the relative phase of the k-th eigenmode.

[0033] The experiment uses a high-speed camera or photodiode array to measure the spatial intensity distribution corresponding to the wavelength scan. The formula is as follows:

[0034] ;

[0035] In the above formula, Representing coordinates The spatial intensity distribution at the output of the optical fiber is used to determine the coefficients of the mode decomposition. , for support The optical fiber with characteristic modes needs to be determined Amplitude and Phase (assuming ), a total of If the spectral intensity distribution is captured by a high-speed camera or a photodiode array, the resulting image can be used to recover the coefficients .

[0036] For example: Consider a The input image consists of pixels, then it is written as The system of equations is as follows:

[0037] ;

[0038] In the above formula, Indicates the spatial intensity distribution of the mth point, the subscript and Indicates the kth and jth order eigenmodes, with a value range of 1 to N , represents the conjugate of the jth eigenmode complex coefficient.

[0039] Combined with the pseudo-Moore-Penrose inverse matrix calculation of the eigenmode of the optical fiber at a given wavelength, the complex coefficients of the characteristic mode, namely the amplitude and phase parts, are calculated. The obtained spectral-spatial distribution is then transformed from the frequency domain to the time domain by Fourier transform to obtain the spatiotemporal structure information.

[0040] Therefore, the present invention adopts a dynamic reconstruction method of spatiotemporal light fields based on monochromatic numerical pattern decomposition, in which the accuracy of the spectral filter based on programmable digital micromirror devices can be controlled in real time to realize the acquisition of spatial mode intensity information by wavelength scanning. The three-dimensional light field is reconstructed with the help of the monochromatic numerical pattern decomposition method, providing a new method for full-field measurement of spatiotemporal light fields. Compared with other light field measurement systems, this system has the advantages of less time consumption, simple structure and programmability, and can further promote the adaptive control and optimization of high-energy spatiotemporal mode-locked fiber lasers with customizable output characteristics.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for dynamic reconstruction of spatiotemporal light fields based on monochromatic numerical pattern decomposition, characterized in that: The following steps are involved: S1: Establishing an analysis platform, including a spatiotemporal mode-locked laser, a folding mirror, a spectral filter, a processing device, and a collection device connected in sequence, wherein the processing device adjusts the working state of the spectral filter, and the collection device is directed to the folding mirror; the spectral filter includes a transmissive diffraction grating, a cylindrical mirror, and a digital micromirror device arranged in sequence along the optical path, and the processing device is connected to the digital micromirror device to adjust the switching state of different positions of the digital micromirror device to achieve adjustable wavelength scanning spectral filtering; S2: Use the spontaneous emission fluorescence light source and spectrometer to calibrate the analysis platform. The calibration process is as follows: A spontaneous fluorescence light source is used to output spontaneous fluorescence, which is input into a folding mirror. The spontaneous fluorescence is incident on a digital micromirror device with all pixels turned on, and its fluorescence spectrum is measured using a spectrometer. Then, some of the pixel units on the digital micromirror device are turned off, and the spontaneous radiation fluorescence is incident on the digital micromirror device with some of the pixel units turned off. The output spectrum is measured using a spectrometer. By comparing the intervals of the attenuated spectral components in the two output spectra with the pixel intervals of the corresponding turned-off pixel units on the digital micromirror device, the central wavelength and the wavelength interval corresponding to each unit pixel can be located, and the functional parameters of the analysis platform can be calibrated and calibrated. The functional parameters include the operating wavelength and spectral selection resolution of the analysis platform; S3: A spatiotemporally mode-locked laser generates an incident light beam, which is processed by the transmission surface of the folding mirror and the spectral filter to obtain a spectral filter and return along the original optical path. The spectral filter is finally output from the refractive surface of the folding mirror. The acquisition device continuously collects the spectrally filtered light field, records the spatial light intensity corresponding to each spectral component, and obtains spectral-spatial intensity information. S4: Perform non-iterative numerical calculation on the spectral-spatial intensity information to recover the amplitude and phase of the light field, and then perform Fourier transform on it to obtain the spatiotemporal structure information.

2. The method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition according to claim 1, characterized in that: In step S1, a scanning galvanometer is provided behind the optical path of the spatiotemporal mode-locked laser, which can increase the refresh rate of the spectral filter.

3. The method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition according to claim 1, characterized in that: The specific process in step S3 is as follows: The bandwidth of the spectral filter is set to 70nm, the spectral resolution is set to 0.04nm, and the refresh rate is set to 32kHz. The spectral filter will select a specific spectral band to form spectral filtering. The processing device is set to a computer, and the acquisition device is set to a high-speed camera or a photodiode array. The high-speed camera or photodiode array is used to record the spatial light intensity distribution map corresponding to each spectral component, and finally the spectral-spatial intensity information is obtained.

4. The method for dynamic reconstruction of a spatiotemporal light field based on monochromatic numerical pattern decomposition according to claim 3, characterized in that: In step S4, the process of converting the spectral-spatial intensity information into the spatiotemporal structure information is as follows: The collected spectral-spatial intensity information is subjected to pattern decomposition using a non-iterative algorithm. The matrix solution is performed using the pseudo-inverse matrix and the fiber eigenmode intensity distribution to recover the amplitude and phase of the light field. The spectral-spatial distribution is then transformed from the frequency domain to the time domain by Fourier transform to obtain the spatiotemporal structure information.

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