Fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation

Abstract

The invention discloses a fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation. The device comprises a single-frequency laser, a first optical fiber coupler, a phase modulator, a second optical fiber coupler, a third optical fiber coupler, a feedback module and a control module which are connected in sequence. The control module comprises a parameter setting and data writing unit, a main control unit, a pseudorandom sequence generation unit, a microwave low-pass filter, a pi phase modulation control unit and a radio frequency amplifier. The laser line spacing and the contour spectrum width can be controlled through modulation frequency, code pattern and pi phase modulation, the laser line top flatness can be controlled through modulation depth fine tuning, and discrete fiber laser spectrum planarization broadening based on pseudo-random sequence phase modulation is achieved. The narrow linewidth modulation laser source is high in adaptability, high in intelligent degree, convenient to integrate, good in engineering practicability and capable of effectively improving the stimulated Brillouin scattering threshold power of the system when the linewidth is 10 GHz magnitude.

Description

Technical Field

[0001] The present application belongs to the field of laser technology, and in particular relates to a fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation. Background Art

[0002] At present, the single-channel output power of narrow-linewidth (10GHz level) high-power fiber lasers based on pseudo-random phase modulation at home and abroad is still difficult to reach the 3-kilowatt level, and its π-phase sensitivity under passive modulation reduces its reliability, which limits its application in engineering practice, especially beam-synthesizing high-energy laser systems. Summary of the invention

[0003] The embodiments of the present application provide a fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation, which are used to at least solve the problem of low engineering practicality of laser system phase modulation in related technologies.

[0004] In a first aspect, an embodiment of the present application provides a fiber laser spectrum broadening device based on pseudo-random sequence phase modulation, comprising a single-frequency laser, a first fiber coupler, a phase modulator, a second fiber coupler, a third fiber coupler, a feedback module, and a control module connected in sequence;

[0005] The control module includes a parameter setting and data writing unit, a main control unit, a pseudo-random sequence generating unit, a microwave low-pass filter, a π phase modulation control unit and a radio frequency amplifier, wherein the main control unit is respectively connected to the feedback module, the parameter setting and data writing unit, the pseudo-random sequence generating unit and the π phase modulation control unit, the radio frequency amplifier is respectively connected to the microwave low-pass filter, the π phase modulation control unit and the phase modulator, and the microwave low-pass filter is also connected to the pseudo-random sequence generating unit;

[0006] The main control unit is used to call the phase modulator half-wave voltage data stored in the parameter setting and data writing unit and send a first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and send a first instruction to lock the current working voltage to the π phase modulation control unit when the feedback signal output by the feedback module meets the preset conditions, and drive the pseudo-random sequence generation unit to generate a pseudo-random sequence;

[0007] The microwave low-pass filter is used to perform functional filtering on the pseudo-random sequence to obtain a filtered pseudo-random sequence;

[0008] The radio frequency amplifier is used to perform radio frequency power amplification on the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit to obtain a radio frequency signal;

[0009] The phase modulator is used to perform spectral broadening on the light beam injected through the single-frequency laser and the first optical fiber coupler according to the radio frequency signal, so as to be sequentially input to the second optical fiber coupler, the third optical fiber coupler and the feedback module or output through the second optical fiber coupler.

[0010] In a second aspect, an embodiment of the present application provides a fiber laser spectrum broadening method based on pseudo-random sequence phase modulation, the method being applied to a fiber laser spectrum broadening device based on pseudo-random sequence phase modulation as described in any embodiment of the first aspect, the method comprising:

[0011] The main control unit calls the phase modulator half-wave voltage data stored in the parameter setting and data writing unit and sends a first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and sends a first instruction to lock the current working voltage to the π phase modulation control unit when the feedback signal output by the feedback module meets the preset conditions, and drives the pseudo-random sequence generation unit to generate a pseudo-random sequence;

[0012] Functionally filtering the pseudo-random sequence through a microwave low-pass filter to obtain a filtered pseudo-random sequence;

[0013] A radio frequency amplifier is used to amplify the radio frequency power of the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit to obtain a radio frequency signal;

[0014] The light beam injected through the single-frequency laser and the first optical fiber coupler is spectrally broadened according to the radio frequency signal by a phase modulator, so as to be sequentially input to the second optical fiber coupler, the third optical fiber coupler and the feedback module or output through the second optical fiber coupler.

[0015] The fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation in the embodiment of the present application can control the laser spectrum line spacing and profile spectrum width through modulation frequency, code type and π phase modulation, and can control the flatness of the top of the laser spectrum line through fine tuning of modulation depth, so as to realize the flattening and broadening of discrete fiber laser spectrum based on pseudo-random sequence phase modulation. This narrow linewidth modulated laser source has strong adaptability, high intelligence, easy integration, good engineering practicality, and can effectively improve the system stimulated Brillouin scattering threshold power when the linewidth is on the order of 10GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 It is a structural schematic diagram of a fiber laser spectrum broadening device based on pseudo-random sequence phase modulation provided in an embodiment of the present application;

[0018] Figure 2 It is a structural schematic diagram of another fiber laser spectrum broadening device based on pseudo-random sequence phase modulation provided in an embodiment of the present application;

[0019] Figure 3 It is a schematic flow chart of a fiber laser spectrum broadening method based on pseudo-random sequence phase modulation provided in an embodiment of the present application;

[0020] Figure 4 This is a spectrum diagram of pseudo-random sequence modulation obtained under π phase modulation depth coarse adjustment provided in an embodiment of the present application;

[0021] Figure 5 This is a spectrum diagram of pseudo-random sequence modulation obtained under π phase modulation depth fine tuning provided in an embodiment of the present application.

[0022] Reference numerals:

[0023] Single frequency laser 100, first fiber coupler 200, phase modulator 300, second fiber coupler 400, third fiber coupler 500,

[0024] Feedback module 600, photodetector 610, high pass filter 620, power detector 630, comparator 640,

[0025] Control module 700 , parameter setting and data writing unit 710 , main control unit 720 , pseudo-random sequence generating unit 730 , microwave low-pass filter 740 , π phase modulation control unit 750 , radio frequency fine adjustment control unit 760 , radio frequency amplifier 770 . DETAILED DESCRIPTION

[0026] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0027] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0028] High-power polarization-maintaining fiber lasers with a linewidth of 10 GHz have good monochromaticity, high beam quality, and convenient thermal management. The narrow linewidth reduces the requirements for optical path control accuracy in coherent synthesis and spectral synthesis, and the beam quality after spectral synthesis is high, so it has important application value in beam synthesis high-energy laser systems. However, the threshold of the stimulated Brillouin scattering effect in optical fibers is low, which has become a key factor limiting the further increase in the output power of narrow-linewidth lasers and high-energy laser systems. Highly controllable phase modulation technology can broaden the linewidth of single-frequency lasers to tens of GHz to effectively reduce the peak power of the SBS effect, and the system threshold is greatly improved.

[0029] The flat-top modulation spectrum reduces the peak SBS interaction by making the top of the backscattered Stokes spectrum have a uniform distribution profile, which has a better power threshold improvement effect. Traditional white noise modulation belongs to random non-periodic phase modulation. The dense continuous modulation spectrum generated by it has been verified in experiments to achieve several kilowatts of power output. Its spectrum shape is Gaussian and cannot achieve the theoretical optimal performance. In recent years, programmable electrical drive signals designed based on arbitrary waveform generators have been used for periodic phase modulation to produce discrete flat-top spectra. In 2023, Chu et al. from the China Academy of Engineering Physics generated a nearly flat-top spectrum with a bandwidth of 10.6GHz by optimizing the modulation signal, and achieved a laser output of 3050W. The discrete flat-top spectrum can effectively reduce the power spectral density, and by controlling the longitudinal mode frequency line spacing, the total bandwidth of the SBS gain spectrum can be broadened to further reduce its gain peak. It has initially demonstrated its advantage in improving the SBS threshold in 10GHz linewidth fiber amplifiers.

[0030] Pseudo-random sequence phase modulation, the change of optical phase can be faster than the accumulation time of SBS (4.6ns), thereby preventing the acoustic wave from accumulating to a large amplitude to reduce the SBS gain, and the modulated laser spectrum width is flexible and controllable, which has become the mainstream modulation technology for suppressing SBS. In theory, phase modulation only changes the phase information of the optical carrier, while the amplitude information remains unchanged, and the spectrum shape of the loaded RF signal is consistent with the profile of the modulated spectrum. The laser spectrum modulated by pseudo-random sequence phase modulation has the same Gaussian profile as its signal spectrum, and the spectral line shape only depends on the modulation frequency and the encoding method of the modulation signal. It is currently difficult to achieve a flat-top modulation spectrum output based on it. Secondly, the π phase shift introduced by the high level effectively prevents the generation of the SBS effect to increase the system threshold. Since the modulated laser spectrum will quickly approach a single frequency after the modulation depth is offset, the SBS threshold power will quickly decrease (π phase sensitive characteristics). In addition, due to the nonlinear response of the signal generator, RF amplifier and electro-optical phase modulator at different operating frequencies, the power of the electrical signal will be reduced at high frequencies, thereby affecting the flatness of the laser spectrum after phase modulation. Limited by the above technical difficulties, the single-channel output power of narrow-linewidth (10GHz level) high-power fiber lasers based on pseudo-random phase modulation at home and abroad is still difficult to reach the 3-kilowatt level. In addition, its π-phase sensitivity under passive modulation reduces its reliability, which limits its application in engineering practice, especially beam-synthesizing high-energy laser systems.

[0031] In order to solve the problems of the related art, the embodiments of the present application provide a fiber laser spectrum broadening device and method based on pseudo-random sequence phase modulation, which can realize the flattening and broadening of discrete fiber laser spectrum based on pseudo-random sequence phase modulation.

[0032] The fiber laser spectrum broadening device based on pseudo-random sequence phase modulation provided by the embodiment of the present application is described in detail below through specific embodiments and application scenarios in conjunction with the accompanying drawings.

[0033] refer to Figure 1 , is a schematic diagram of the structure of a fiber laser spectrum broadening device based on pseudo-random sequence phase modulation according to an embodiment of the present application. Figure 1 As shown, the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation includes a single-frequency laser 100, a first fiber coupler 200, a phase modulator 300, a second fiber coupler 400, a third fiber coupler 500, a feedback module 600 and a control module 700 connected in sequence.

[0034] The control module 700 includes a parameter setting and data writing unit 710, a main control unit 720, a pseudo-random sequence generating unit 730, a microwave low-pass filter 740, a π phase modulation control unit 750 and a radio frequency amplifier 770. Specifically, the main control unit 720 is respectively connected to the feedback module 600, the parameter setting and data writing unit 710, the pseudo-random sequence generating unit 730, and the π phase modulation control unit 750, the radio frequency amplifier 770 is respectively connected to the microwave low-pass filter 740, the π phase modulation control unit 750 and the phase modulator 300, and the microwave low-pass filter 740 is also connected to the pseudo-random sequence generating unit 730.

[0035] In some embodiments, the main control unit 720 is used to call the phase modulator half-wave voltage data stored in the parameter setting and data writing unit 710 and send a first voltage value that meets the π phase modulation depth to the π phase modulation control unit 750, and send a first instruction to lock the current working voltage to the π phase modulation control unit 750 when the feedback signal output by the feedback module 600 meets the preset conditions, and drive the pseudo-random sequence generation unit 730 to generate a pseudo-random sequence.

[0036] In some embodiments, the microwave low-pass filter 740 is used to perform functional filtering on the pseudo-random sequence to obtain a filtered pseudo-random sequence.

[0037] In some embodiments, the RF amplifier 770 is used to perform RF power amplification on the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit 750 to obtain a RF signal.

[0038] In some embodiments, the phase modulator 300 is used to spectrally broaden the light beam injected through the single-frequency laser 100 and the first fiber coupler 200 according to the radio frequency signal, so as to be sequentially input to the second fiber coupler 400, the third fiber coupler 500 and the feedback module 600 or output through the second fiber coupler 400.

[0039] As an optional embodiment, Figure 1 As shown, the control module 700 further includes a radio frequency fine adjustment control unit 760. Specifically, the radio frequency fine adjustment control unit 760 is connected to the main control unit 720 and the π phase modulation control unit 750 respectively.

[0040] In some optional embodiments, the main control unit 720 is further configured to calculate a difference signal based on the feedback signal and send the difference signal to the RF fine tuning control unit 760 when the feedback signal output by the feedback module 600 does not meet a preset condition.

[0041] In some optional embodiments, the RF fine-tuning control unit 760 is used to calculate a second voltage value based on the difference signal, and gradually send a third voltage value corresponding to the second voltage value to the π phase modulation control unit 750 according to a preset step size until receiving a second instruction sent by the main control unit 720 when the feedback signal output by the feedback module 600 meets the preset conditions, wherein the second voltage value is the voltage amount to be increased or decreased, and the third voltage value is the voltage value that needs to be changed gradually according to the preset step size corresponding to the second voltage value.

[0042] Optionally, the second instruction instructs the RF fine adjustment control unit 760 to lock the current output voltage value of the operation.

[0043] Furthermore, in some embodiments, Figure 2 A schematic structural diagram of another fiber laser spectrum broadening device based on pseudo-random sequence phase modulation is shown.

[0044] like Figure 2 As shown, the feedback module 600 includes a photodetector 610, a high-pass filter 620, a power detector 630 and a comparator 640 connected in sequence. Among them, one end of the photodetector 610 is connected to the third fiber coupler 500, and the other end of the photodetector 610 is connected to the high-pass filter 620; one end of the comparator 640 is connected to the power detector 630, and the other end of the comparator 640 is connected to the main control unit 720.

[0045] In some optional embodiments, the feedback signal includes a judgment result of the comparator 640; the preset condition includes a judgment result that the power detector 630 outputs a corresponding level of the power of the injected electrical signal to reach a preset reference level, wherein the electrical signal is formed by photoelectric conversion of an optical signal input by the third optical fiber coupler 500 by the photodetector 610.

[0046] In addition, in some embodiments, the first fiber coupler 200 is also connected to the third fiber coupler 500. The first fiber coupler 200 is used to split the light beam injected by the single-frequency laser 100 into two beams to be input to the third fiber coupler 500 and the phase modulator 300 respectively.

[0047] Optionally, the splitting ratios of the first fiber coupler 200 and the second fiber coupler 400 may both be 5:95, and the splitting ratio of the third fiber coupler 500 may be 50:50. In other words, the power of the single-frequency laser 100 is mainly limited in the optical path, and the corresponding power in the circuit can be converted into an electrical signal.

[0048] Optionally, the main control unit 720 includes a microprocessor based on a field programmable gate array chip; the pseudo-random sequence generation unit 730 can be a digital-to-analog conversion module for converting digital data into corresponding analog voltage outputs.

[0049] Optionally, the RF amplifier 770 is a programmable gain-adjustable RF amplifier, with an RF gain greater than 30 dB, an RF operating bandwidth greater than 10 GHz, a saturated output power greater than 30 dBm, and an RF gain response accuracy no greater than 0.2 dB.

[0050] Optionally, the low-pass filtering bandwidth of the microwave low-pass filter 740 is not higher than 5 GHz; and the response bandwidth of the photodetector 610 is not lower than 1 GHz.

[0051] Therefore, the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation in this embodiment can control the laser spectrum line spacing and profile spectrum width through modulation frequency, code type and π phase modulation, and can control the flatness of the top of the laser spectrum line through fine tuning of modulation depth, so as to realize the flattening and broadening of discrete fiber laser spectrum based on pseudo-random sequence phase modulation. This narrow linewidth modulated laser source has strong adaptability, high intelligence, easy integration, good engineering practicality, and can effectively improve the system stimulated Brillouin scattering threshold power when the linewidth is on the order of 10GHz.

[0052] Furthermore, the present application also provides a fiber laser spectrum broadening method based on pseudo-random sequence phase modulation. It should be noted that the fiber laser spectrum broadening method based on pseudo-random sequence phase modulation can be applied to the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation as in any of the above embodiments.

[0053] Figure 3 The schematic diagram of the process of the fiber laser spectrum broadening method based on pseudo-random sequence phase modulation in the embodiment of the present application is shown. Figure 3 As shown, the fiber laser spectrum broadening method based on pseudo-random sequence phase modulation may specifically include the following steps:

[0054] S301, calling the phase modulator half-wave voltage data stored in the parameter setting and data writing unit through the main control unit and sending the first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and sending the first instruction to lock the current working voltage to the π phase modulation control unit when the feedback signal output by the feedback module meets the preset conditions, and driving the pseudo-random sequence generation unit to generate a pseudo-random sequence;

[0055] S302, performing functional filtering on the pseudo-random sequence through a microwave low-pass filter to obtain a filtered pseudo-random sequence;

[0056] S303, performing radio frequency power amplification on the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit through a radio frequency amplifier to obtain a radio frequency signal;

[0057] S304, performing spectral broadening on the light beam injected through the single-frequency laser and the first optical fiber coupler according to the radio frequency signal through a phase modulator, so as to sequentially input the light beam into the second optical fiber coupler, the third optical fiber coupler and the feedback module or output the light beam through the second optical fiber coupler.

[0058] In some embodiments, when the feedback signal output by the feedback module does not meet a preset condition, the main control unit calculates a difference signal according to the feedback signal and sends the difference signal to the RF fine tuning control unit.

[0059] In some embodiments, the RF fine-tuning control unit calculates a second voltage value based on the difference signal, and sends a third voltage value corresponding to the second voltage value to the π phase modulation control unit step by step according to a preset step size until a second instruction sent by the main control unit is received when the feedback signal output by the feedback module meets a preset condition. The second voltage value is the voltage amount to be increased or decreased, the third voltage value is the voltage value that needs to be changed step by step according to a preset step size corresponding to the second voltage value, and the second instruction instructs the RF fine-tuning control unit to lock the current output voltage value of the working state.

[0060] In some embodiments, the feedback signal is monitored in real time by the main control unit, and in response to the feedback signal not satisfying a preset condition, the locking state is canceled and the process returns to the step of calculating a difference signal based on the feedback signal by the main control unit and sending the difference signal to the RF fine tuning control unit.

[0061] In addition, the present application also provides another fiber laser spectrum broadening method based on pseudo-random sequence phase modulation, which can be applied to the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation in any of the above embodiments, and the specific steps are as follows.

[0062] A single-frequency laser is injected into the first fiber coupler and split into two beams, wherein the first beam enters the third fiber coupler through the first beam splitting arm of the third fiber coupler, and the other beam is output to the phase modulator. The RF signal is injected into the phase modulator to achieve spectrum broadening; it is then output to the second fiber coupler through the phase modulator and split into two beams again, wherein one beam is output externally, and the other beam enters the third fiber coupler through the second beam splitting arm of the third fiber coupler and is combined with the laser of its first beam splitting arm.

[0063] Next, the light beam in the third fiber coupler is injected into the photodetector for photoelectric conversion to form an electrical signal; it is filtered through a high-pass filter to filter out the DC current component; it then reaches the power detector and outputs the corresponding level to the comparator based on the power of the injected electrical signal; the comparator compares the level with the reference level and feeds it back to the main control unit.

[0064] Furthermore, the parameter setting and data writing unit writes the modulation signal setting value and the phase modulator half-wave voltage trajectory data into the main control unit; the main control unit drives the pseudo-random sequence generating unit to generate a pseudo-random sequence; the microwave low-pass filter performs functional filtering on the pseudo-random sequence to filter out the high-frequency microwave signal in the pseudo-random sequence, and then injects it into the RF amplifier for amplification; at the same time, the main control unit calls and reads the half-wave voltage value of the phase modulator according to the modulation frequency of the pseudo-random sequence, and sends the voltage value that meets the π phase modulation depth to the π phase modulation control unit; the π phase modulation control unit outputs the voltage to the RF amplifier; the RF amplifier performs RF power amplification on the filtered pseudo-random sequence injected therein, and the RF amplifier injects the amplified filtered pseudo-random sequence into the phase modulator to complete the π phase modulation.

[0065] That is to say, the parameters such as the half-wave voltage of the phase modulator used can be written in advance and stored in the main control unit in the upper computer; the main control unit selects a pseudo-random sequence in a specific frequency band according to demand, and controls the pseudo-random sequence generating unit to generate a pseudo-random sequence signal of the set frequency band, that is, an electrical signal is generated.

[0066] Furthermore, the main control unit makes a reference comparison on the judgment result sent by the comparator. If the reference value is reached, an instruction is sent to the π phase modulation control unit to lock the current working voltage value. If the reference value is not reached, the difference is calculated according to the judgment result and the instruction is sent to the RF fine-tuning control unit; the RF fine-tuning control unit calculates the amount of voltage to be increased or decreased based on the aforementioned difference and gradually sends the voltage value to be changed to the π phase modulation control unit using a set step size until the judgment result sent by the comparator by the main control unit reaches the reference value, and then the main control unit sends an instruction to the RF fine-tuning control unit to lock the current working output voltage value.

[0067] It should be noted that after locking, the main control unit performs a real-time reference comparison on the judgment result sent by the comparator. If there is an abnormality, the locking state is cancelled and the above process is repeated in sequence.

[0068] In specific implementation, since the main control unit is a microprocessor based on an FPGA chip, it can control the pseudo-random sequence generation unit, the π phase modulation control unit, the RF fine-tuning control unit and the comparator. At the same time, the control circuits of the photodetector and the power detector are also recorded here.

[0069] In a specific implementation, the baud rate of the pseudo-random sequence generated by the pseudo-random sequence generating unit is 8 GHz; the gain of the RF amplifier is 30 dB, the RF operating bandwidth is 20 GHz, the saturated output power is greater than 34 dBm, and the RF gain response accuracy is 0.2 dB; the low-pass filter bandwidth of the microwave low-pass filter is 2.2 GHz.

[0070] also, Figure 4 The spectrum diagram of pseudo-random sequence modulation obtained by the above method of this embodiment under π phase modulation depth coarse adjustment is shown, Figure 5 The spectrum diagram of pseudo-random sequence modulation obtained under the π phase modulation depth fine tuning is shown, wherein the horizontal axis is the wavelength in nm, and the vertical axis is the spectrum intensity in dB.

[0071] In the specific implementation, a filtered pseudo-random sequence is used to modulate a single-frequency laser, the wavelength of which is 1064 nm. A pseudo-random sequence with a rate of 8 GHz is used to modulate the single-frequency light after low-pass filtering with a bandwidth of 2.2 GHz. When the modulation depth is close to π, a spectrum of the pseudo-random sequence modulation is obtained, that is, Figure 4 .like Figure 4 As shown, when a pseudo-random sequence is used for phase modulation, the top of the π phase modulation output spectrum presents a Gaussian-like top.

[0072] In specific implementation, after the feedback module and RF fine-tuning control, the spectrum modulated by the pseudo-random sequence under the π phase modulation depth fine-tuning is obtained, that is, Figure 5 .like Figure 5 As shown in the figure, after fine optimization of the modulation depth, the flatness degradation of the modulation spectrum caused by the power fluctuation at the top of the spectrum caused by the nonlinear response of the RF amplifier and the phase modulator under high-frequency signals can be effectively alleviated, a flat-top modulation spectrum with an in-band flatness of less than 1dB can be achieved, the engineering practicality of the pseudo-random sequence phase modulation can be broadened, and a more ideal modulation effect can be obtained.

[0073] It can be seen that the fiber laser spectrum broadening method based on pseudo-random sequence phase modulation in the embodiment of the present application realizes pre-shaping of the modulation signal spectrum by high-precision control of the modulation depth of the filtered PRBS modulated signal and slight tuning of the signal baud rate and code type, which effectively alleviates the degradation of the modulation spectrum flatness caused by the nonlinear response of the RF amplifier and the phase modulator under high-frequency signals causing the power fluctuation at the top of the spectrum; through the feedback module, the system continuously iterates and optimizes near the π phase modulation depth to find the optimal modulation depth value and locks it to stably obtain the optimal flattened broadened spectrum, significantly improving the stimulated Brillouin scattering threshold; through the feedback module, the modulation output state is monitored in real time to solve the problem of reduced reliability caused by the π phase sensitivity of the pseudo-random sequence phase modulation under passive modulation, greatly expanding the application of this type of modulation broadening module in engineering practice; the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation has the advantages of simple structure, high degree of intelligence, flat top of the spectrum profile after broadening, simple linewidth control, etc., which can greatly improve the output power of the fiber laser amplifier with a linewidth of 10GHz.

[0074] It should be noted that the above describes some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the above embodiments and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0075] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0076] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "attached" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0077] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0078] The term "plurality" used in the present application refers to two or more (including two).

[0079] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0080] It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, this application is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be performed simultaneously.

[0081] The above is only a specific implementation of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the protection scope of this application.

Claims

1. A fiber laser spectrum broadening device based on pseudo-random sequence phase modulation, characterized in that: It includes a single-frequency laser, a first optical fiber coupler, a phase modulator, a second optical fiber coupler, a third optical fiber coupler, a feedback module and a control module connected in sequence; The control module includes a parameter setting and data writing unit, a main control unit, a pseudo-random sequence generating unit, a microwave low-pass filter, a π phase modulation control unit and a radio frequency amplifier, wherein the main control unit is respectively connected to the feedback module, the parameter setting and data writing unit, the pseudo-random sequence generating unit and the π phase modulation control unit, the radio frequency amplifier is respectively connected to the microwave low-pass filter, the π phase modulation control unit and the phase modulator, and the microwave low-pass filter is also connected to the pseudo-random sequence generating unit; The main control unit is used to call the phase modulator half-wave voltage data stored in the parameter setting and data writing unit and send a first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and send a first instruction to lock the current working voltage to the π phase modulation control unit when the feedback signal output by the feedback module meets the preset conditions, and drive the pseudo-random sequence generation unit to generate a pseudo-random sequence; The microwave low-pass filter is used to perform functional filtering on the pseudo-random sequence to obtain a filtered pseudo-random sequence; The radio frequency amplifier is used to perform radio frequency power amplification on the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit to obtain a radio frequency signal; The phase modulator is used to perform spectral broadening on the light beam injected through the single-frequency laser and the first optical fiber coupler according to the radio frequency signal, so as to be sequentially input to the second optical fiber coupler, the third optical fiber coupler and the feedback module or output through the second optical fiber coupler.

2. The device according to claim 1, characterized in that The control module also includes a radio frequency fine adjustment control unit, which is connected to the main control unit and the π phase modulation control unit respectively; The main control unit is further configured to calculate a difference signal according to the feedback signal and send the difference signal to the RF fine tuning control unit when the feedback signal output by the feedback module does not meet a preset condition; The RF fine adjustment control unit is used to calculate a second voltage value according to the difference signal, and gradually send a third voltage value corresponding to the second voltage value to the π phase modulation control unit according to a preset step size until a second instruction sent by the main control unit is received when the feedback signal output by the feedback module meets a preset condition, wherein the second voltage value is the voltage amount to be increased or decreased, and the third voltage value is the voltage value that needs to be changed gradually according to the preset step size corresponding to the second voltage value.

3. The device according to claim 2, characterized in that The second instruction instructs the RF fine adjustment control unit to lock the current output voltage value of the operation.

4. The device according to claim 1 or 2, characterized in that: The feedback module includes a photodetector, a high-pass filter, a power detector and a comparator connected in sequence; One end of the photodetector is connected to the third optical fiber coupler, and the other end of the photodetector is connected to the high-pass filter; One end of the comparator is connected to the power detector, and the other end of the comparator is connected to the main control unit.

5. The device according to claim 4, characterized in that The feedback signal includes the judgment result of the comparator; The preset condition includes the judgment result that the power detector outputs a corresponding level according to the power of the injected electrical signal to reach a preset reference level, and the electrical signal is formed by the photoelectric conversion of the optical signal input by the third optical fiber coupler by the photoelectric detector.

6. The device according to claim 1, characterized in that The first optical fiber coupler is also connected to the third optical fiber coupler; The first optical fiber coupler is used to split the light beam injected by the single-frequency laser into two beams so as to input the two beams into the third optical fiber coupler and the phase modulator respectively.

7. The device according to claim 1, characterized in that The main control unit includes a microprocessor based on a field programmable gate array chip.

8. The device according to claim 1, characterized in that The pseudo-random sequence generating unit is a digital-to-analog conversion module, which is used to convert digital data into corresponding analog voltage output.

9. A method for broadening the optical fiber laser spectrum based on pseudo-random sequence phase modulation, characterized in that: The method is applied to the fiber laser spectrum broadening device based on pseudo-random sequence phase modulation as described in any one of claims 1 to 8, and the method comprises: The main control unit calls the phase modulator half-wave voltage data stored in the parameter setting and data writing unit and sends a first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and sends a first instruction to lock the current working voltage to the π phase modulation control unit when the feedback signal output by the feedback module meets the preset conditions, and drives the pseudo-random sequence generation unit to generate a pseudo-random sequence; Functionally filtering the pseudo-random sequence through a microwave low-pass filter to obtain a filtered pseudo-random sequence; A radio frequency amplifier is used to amplify the radio frequency power of the filtered pseudo-random sequence according to the first voltage value input by the π phase modulation control unit to obtain a radio frequency signal; The light beam injected through the single-frequency laser and the first optical fiber coupler is spectrally broadened according to the radio frequency signal by a phase modulator, so as to be sequentially input to the second optical fiber coupler, the third optical fiber coupler and the feedback module or output through the second optical fiber coupler.

10. The method according to claim 9, characterized in that The method further comprises: When the feedback signal output by the feedback module does not meet the preset conditions, the main control unit calculates a difference signal according to the feedback signal and sends the difference signal to the RF fine tuning control unit; The RF fine adjustment control unit calculates a second voltage value according to the difference signal, and gradually sends a third voltage value corresponding to the second voltage value to the π phase modulation control unit according to a preset step size, until a second instruction sent by the main control unit is received when the feedback signal output by the feedback module meets a preset condition, wherein the second voltage value is a voltage value to be increased or decreased according to a preset step size, and the third voltage value is a voltage value to be changed gradually according to a preset step size corresponding to the second voltage value, and the second instruction instructs the RF fine adjustment control unit to lock the current output voltage value of the operation; The feedback signal is monitored in real time by the main control unit, and in response to the feedback signal not satisfying a preset condition, the locking state is canceled and the process returns to the step of calculating a difference signal according to the feedback signal by the main control unit and sending the difference signal to the RF fine tuning control unit.

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