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

Abstract

This application discloses a fiber laser spectral broadening device and method based on pseudo-random sequence phase modulation. The device includes 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. The control module includes a parameter setting and data writing unit, a main control unit, a pseudo-random sequence generation unit, a microwave low-pass filter, a π-phase modulation control unit, and an RF amplifier. The laser spectral line spacing and profile spectral width can be controlled by modulation frequency, code pattern, and π-phase modulation. The flatness of the laser spectral top can be controlled by fine-tuning the modulation depth, thereby achieving discrete fiber laser spectral flattening and broadening based on pseudo-random sequence phase modulation. This narrow-linewidth modulated laser source is highly adaptable, intelligent, easy to integrate, and has good engineering practicality. It can effectively improve the stimulated Brillouin scattering threshold power of the system when the linewidth is on the order of 10 GHz.

Description

Technical Field

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

[0002] Currently, the single-channel output power of narrow-linewidth (10GHz-level) high-power fiber lasers based on pseudo-random phase modulation is still difficult to reach the 3kW level, both domestically and internationally. Furthermore, their reliability is reduced due to the π-phase sensitivity under passive modulation, which limits their application in practical engineering, especially in beam-combining high-energy laser systems. Summary of the Invention

[0003] This application provides a fiber laser spectral broadening device and method based on pseudo-random sequence phase modulation, which at least solves the problem of low engineering practicality of laser system phase modulation in related technologies.

[0004] In a first aspect, embodiments of this application provide a fiber laser spectral 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 generation unit, a microwave low-pass filter, a π-phase modulation control unit, and an RF amplifier. The main control unit is connected to the feedback module, the parameter setting and data writing unit, the pseudo-random sequence generation unit, and the π-phase modulation control unit, respectively. The RF amplifier is connected to the microwave low-pass filter, the π-phase modulation control unit, and the phase modulator, respectively. The microwave low-pass filter is also connected to the pseudo-random sequence generation 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 the 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 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;

[0009] The phase modulator is used to broaden the spectrum of the beam injected through the single-frequency laser and the first fiber coupler according to the radio frequency signal, so as to input it sequentially to the second fiber coupler, the third fiber coupler and the feedback module, or output it through the second fiber coupler.

[0010] Secondly, embodiments of this application provide a fiber laser spectral broadening method based on pseudo-random sequence phase modulation, the method being applied to a fiber laser spectral broadening apparatus 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 parameter setting and data writing unit to store the phase modulator half-wave voltage data and sends the first voltage value that meets the π phase modulation depth to the π phase modulation control unit. When the feedback signal output by the feedback module meets the preset conditions, the first instruction to lock the current working voltage is sent to the π phase modulation control unit, and the pseudo-random sequence generation unit is driven to generate a pseudo-random sequence.

[0012] The pseudo-random sequence is functionally filtered by a microwave low-pass filter to obtain a filtered pseudo-random sequence.

[0013] The filtered pseudo-random sequence is amplified by an RF amplifier according to the first voltage value input by the π phase modulation control unit to obtain an RF signal.

[0014] The phase modulator broadens the spectral density of the beam injected through the single-frequency laser and the first fiber coupler according to the radio frequency signal, so that it can be sequentially input to the second fiber coupler, the third fiber coupler and the feedback module, or output through the second fiber coupler.

[0015] The fiber laser spectral broadening device and method based on pseudo-random sequence phase modulation of this application can control the laser spectral line spacing and profile spectral width through modulation frequency, code pattern, and π-phase modulation, and can control the flatness of the laser spectral top through fine tuning of modulation depth, thereby realizing discrete fiber laser spectral flattening and broadening based on pseudo-random sequence phase modulation. This narrow-linewidth modulated laser source has strong adaptability, high intelligence, and is easy to integrate, with good engineering practicality. It can effectively improve the stimulated Brillouin scattering threshold power of the system when the linewidth is on the order of 10 GHz. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a fiber laser spectral broadening device based on pseudo-random sequence phase modulation provided in an embodiment of this application;

[0018] Figure 2 This is a schematic diagram of another fiber laser spectral broadening device based on pseudo-random sequence phase modulation provided in this application embodiment;

[0019] Figure 3 This is a flowchart illustrating a fiber laser spectral broadening method based on pseudo-random sequence phase modulation provided in an embodiment of this application.

[0020] Figure 4 This is a spectrum of pseudo-random sequence modulation obtained under coarse tuning of π phase modulation depth, as provided in the embodiments of this application.

[0021] Figure 5 This is a spectrum of pseudo-random sequence modulation obtained under π-phase modulation depth fine-tuning, as provided in the embodiments of this application.

[0022] Figure label:

[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] The system includes a control module 700, a parameter setting and data writing unit 710, a main control unit 720, a pseudo-random sequence generation unit 730, a microwave low-pass filter 740, a π-phase modulation control unit 750, an RF fine-tuning control unit 760, and an RF amplifier 770. Detailed Implementation

[0026] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0028] High-power polarization-maintaining fiber lasers with linewidths in the 10 GHz range exhibit excellent monochromaticity, high beam quality, and convenient thermal management. Their narrow linewidth reduces the precision requirements for optical path control in coherent and spectral combining, while also ensuring high beam quality after spectral combining. Therefore, they hold significant application value in beam-combining high-energy laser systems. However, the low threshold of stimulated Brillouin scattering (SBS) in optical fibers has become a key factor limiting further increases in the output power of narrow-linewidth lasers and high-energy laser systems. Highly controllable phase modulation techniques can broaden the linewidth of single-frequency lasers to the tens of GHz range, effectively reducing the peak power of the SBS effect and significantly improving the system threshold.

[0029] Flat-top modulation spectra reduce peak SBS interactions by creating a uniformly distributed profile at the top of the backscattered Stokes spectrum, resulting in a better power threshold enhancement. Traditional white noise modulation, a random aperiodic phase modulation, has produced dense, continuous modulation spectra that have been experimentally verified to achieve kilowatt-level power output, but its spectral shape is Gaussian and cannot reach theoretically optimal performance. In recent years, programmable electrically driven signals based on arbitrary waveform generators have been used for periodic phase modulation, generating discrete flat-top spectra. In 2023, Chu et al. from the China Academy of Engineering Physics generated a near-flat-top spectrum with a bandwidth of 10.6 GHz by optimizing the modulation signal and achieved a laser output of 3050 W. Discrete flat-top spectra 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 widened to further reduce its gain peak, demonstrating its initial advantage in improving the SBS threshold in 10 GHz linewidth fiber amplifiers.

[0030] Pseudo-random sequence phase modulation (PSI) allows the optical phase to change faster than the SBS accumulation time (4.6 ns), thus preventing the acoustic wave from accumulating to a large amplitude and reducing the SBS gain. Furthermore, the modulated laser spectral width is flexible and controllable, making it the mainstream modulation technique for suppressing SBS. Theoretically, phase modulation only changes the phase information of the optical carrier while keeping the amplitude information unchanged, resulting in a consistent spectral shape between the loaded RF signal and the modulated spectrum. The laser spectrum modulated by PSI has a Gaussian-like profile, and the spectral shape depends only on the modulation frequency and the encoding method of the modulation signal. Currently, it is difficult to achieve a flat-top modulated spectrum output based on this. Secondly, the π phase shift introduced by the high level effectively prevents the SBS effect and increases the system threshold. Because the modulated laser spectral line rapidly approaches a single frequency after the modulation depth shift, the SBS threshold power decreases rapidly (π phase sensitivity characteristic). Additionally, due to the nonlinear responses of the signal generator, RF amplifier, and electro-optic phase modulator at different operating frequencies, the power of the electrical signal decreases at high frequencies, thus affecting the flatness of the phase-modulated laser spectral line. Due to the aforementioned technical challenges, the single-channel output power of current domestic and international narrow-linewidth (10GHz-level) high-power fiber lasers based on pseudo-random phase modulation is still difficult to reach the 3kW level. Furthermore, their π-phase sensitivity under passive modulation reduces their reliability, limiting their application in practical engineering, especially in beam-combining high-energy laser systems.

[0031] To address the problems in related technologies, this application provides a fiber laser spectral broadening device and method based on pseudo-random sequence phase modulation, which can realize the flattening and broadening of discrete fiber laser spectra based on pseudo-random sequence phase modulation.

[0032] The fiber laser spectral broadening device based on pseudo-random sequence phase modulation provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0033] refer to Figure 1 This is a schematic diagram of a fiber laser spectral broadening device based on pseudo-random sequence phase modulation, according to an embodiment of this application. Figure 1 As shown, the fiber laser spectral 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 generation unit 730, a microwave low-pass filter 740, a π-phase modulation control unit 750, and an RF amplifier 770. Specifically, the main control unit 720 is connected to the feedback module 600, the parameter setting and data writing unit 710, the pseudo-random sequence generation unit 730, and the π-phase modulation control unit 750, respectively. The RF amplifier 770 is connected to the microwave low-pass filter 740, the π-phase modulation control unit 750, and the phase modulator 300, respectively. The microwave low-pass filter 740 is also connected to the pseudo-random sequence generation 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 the 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 operating 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 radio frequency amplifier 770 is used to amplify the radio frequency power of the filtered pseudo-random sequence according to the first voltage value input to the π phase modulation control unit 750 to obtain a radio frequency signal.

[0038] In some embodiments, the phase modulator 300 is used to broaden the spectrum of the beam injected through the single-frequency laser 100 and the first fiber coupler 200 according to the radio frequency signal, so as to input sequentially 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, such as Figure 1 As shown, the control module 700 also includes a radio frequency fine-tuning control unit 760, which is specifically connected to the main control unit 720 and the π phase modulation control unit 750.

[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 radio frequency fine-tuning control unit 760 when the feedback signal output by the feedback module 600 does not meet the preset conditions.

[0041] In some optional embodiments, the radio frequency 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 it receives a second instruction sent by the main control unit 720 when the feedback signal output by the feedback module 600 meets the preset conditions. The second voltage value is the amount of voltage to be increased or decreased, and the third voltage value is the voltage value corresponding to the second voltage value that needs to be changed gradually according to the preset step size.

[0042] Optionally, the second instruction is to instruct the radio frequency fine-tuning control unit 760 to lock the current operating output voltage value.

[0043] Furthermore, in some embodiments, Figure 2 A schematic diagram of another fiber laser spectral 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. One end of the photodetector 610 is connected to the third fiber optic coupler 500, and the other end 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 is connected to the main control unit 720.

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

[0046] 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 beam injected by the single-frequency laser 100 into two beams for input to the third fiber coupler 500 and the phase modulator 300, respectively.

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

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

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

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

[0051] Therefore, the fiber laser spectral broadening device based on pseudo-random sequence phase modulation in this embodiment can control the laser spectral line spacing and profile spectral width through modulation frequency, code pattern, and π-phase modulation, and can control the flatness of the laser spectral top through fine tuning of modulation depth, thereby achieving discrete fiber laser spectral flattening broadening based on pseudo-random sequence phase modulation. This narrow-linewidth modulated laser source is highly adaptable, intelligent, easy to integrate, and has good engineering practicality, effectively improving the stimulated Brillouin scattering threshold power of the system when the linewidth is on the order of 10 GHz.

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

[0053] Figure 3 A schematic flowchart of the fiber laser spectral broadening method based on pseudo-random sequence phase modulation, according to an embodiment of this application, is shown. Figure 3 As shown, the fiber laser spectral broadening method based on pseudo-random sequence phase modulation may specifically include the following steps:

[0054] S301, The main control unit calls the phase modulator half-wave voltage data stored in the parameter setting and data writing unit and sends the first voltage value that meets the π phase modulation depth to the π phase modulation control unit, and sends 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 drives the pseudo-random sequence generation unit to generate a pseudo-random sequence.

[0055] S302. The pseudo-random sequence is functionally filtered using a microwave low-pass filter to obtain a filtered pseudo-random sequence;

[0056] S303. The filtered pseudo-random sequence is amplified by an RF amplifier according to the first voltage value input by the π phase modulation control unit to obtain an RF signal;

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

[0058] In some embodiments, if the feedback signal output by the feedback module does not meet the preset conditions, the main control unit calculates the difference signal based on the feedback signal and sends the difference signal to the radio frequency fine-tuning control unit.

[0059] In some embodiments, the radio frequency fine-tuning control unit calculates a second voltage value based on 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 is received from the main control unit when the feedback signal output by the feedback module meets a preset condition. The second voltage value is the amount of voltage to be increased or decreased, the third voltage value is the voltage value corresponding to the second voltage value that needs to be changed gradually according to a preset step size, and the second instruction is to instruct the radio frequency fine-tuning control unit to lock the current output voltage value.

[0060] In some embodiments, the main control unit monitors the feedback signal in real time, and in response to the feedback signal not meeting the preset conditions, the locking state is canceled and the process returns to the step of the main control unit calculating the difference signal based on the feedback signal and sending the difference signal to the radio frequency fine-tuning control unit.

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

[0062] A single-frequency laser is injected into the first fiber coupler and split into two beams. The first beam enters the third fiber coupler through the first beam splitter arm, while the other beam is output to the phase modulator. The radio frequency signal is injected into the phase modulator to achieve spectral broadening. The laser is then output to the second fiber coupler through the phase modulator and split into two beams again. One beam is output to the outside, while the other beam enters the third fiber coupler through the second beam splitter arm and is combined with the laser from the first beam splitter arm.

[0063] Next, the beam in the third fiber coupler is injected into the photodetector for photoelectric conversion to form an electrical signal; it is then filtered by a high-pass filter to remove the DC current component; subsequently, it reaches the power detector and outputs a corresponding level to the comparator based on the power of the injected electrical signal; the comparator compares this 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 half-wave voltage trajectory data of the phase modulator into the main control unit; the main control unit drives the pseudo-random sequence generation 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 conforms to the π-phase modulation depth to the π-phase modulation control unit; the π-phase modulation control unit outputs voltage to the RF amplifier; the RF amplifier amplifies the RF power of the filtered pseudo-random sequence injected into it, and the RF amplifier injects the amplified filtered pseudo-random sequence into the phase modulator to complete the π-phase modulation.

[0065] In other words, parameters such as the half-wave voltage of the phase modulator used can be pre-written and stored in the main control unit in the host computer; the main control unit selects a pseudo-random sequence in a specific frequency band according to the requirements, and generates a pseudo-random sequence signal of the set frequency band by controlling the pseudo-random sequence generation unit, which generates an electrical signal.

[0066] Furthermore, the main control unit compares the judgment result sent by the comparator with the reference value. If the reference value is reached, it sends a command to the π-phase modulation control unit to lock the current operating voltage value. If the reference value is not reached, it calculates the difference based on the judgment result and sends the command 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 sends the voltage value to be changed to the π-phase modulation control unit step by step using a set step size until the judgment result sent by the main control unit to the comparator reaches the reference value. Then, the main control unit sends a command to the RF fine-tuning control unit to lock the current operating output voltage value.

[0067] It should be noted that after locking, the main control unit compares the judgment result sent by the comparator in real time. If an abnormality is found, the locking state is canceled and the above process is repeated.

[0068] In practice, 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 radio frequency 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 practice, the pseudo-random sequence generated by the pseudo-random sequence generation unit has a baud rate of 8 GHz; the RF amplifier has a gain of 30 dB, an RF operating bandwidth of 20 GHz, a saturated output power greater than 34 dBm, and an RF gain response accuracy of 0.2 dB; and the microwave low-pass filter has a low-pass filtering bandwidth of 2.2 GHz.

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

[0071] In practice, a filtered pseudo-random sequence is used to modulate the single-frequency laser. The single-frequency laser wavelength is 1064 nm. A pseudo-random sequence with a rate of 8 GHz is used, which is then low-pass filtered with a bandwidth of 2.2 GHz to modulate the single-frequency light. The spectrum of the pseudo-random sequence modulation is obtained when the modulation depth is close to π. 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 exhibits a Gaussian-like apex.

[0072] In practical implementation, after feedback module and RF fine-tuning control, the spectrum of pseudo-random sequence modulation obtained under π phase modulation depth fine-tuning is obtained, i.e. Figure 5 .like Figure 5 As shown, after finely optimizing the modulation depth, the degradation of modulation spectrum flatness caused by the power fluctuation at the top of the spectrum due to the nonlinear response of the RF amplifier and phase modulator under high-frequency signals can be effectively alleviated, achieving a flat-top modulation spectrum with in-band flatness <1dB, broadening the engineering practicality of pseudo-random sequence phase modulation, and obtaining a more ideal modulation effect.

[0073] As can be seen, the fiber laser spectral broadening method based on pseudo-random sequence phase modulation in this application achieves pre-shaping of the modulation signal spectrum by performing high-precision control of the modulation depth of the filtered PRBS modulation signal and fine-tuning of the signal baud rate and code pattern. This effectively alleviates the degradation of modulation spectrum flatness caused by power fluctuation at the top of the spectrum due to the nonlinear response of the RF amplifier and phase modulator under high-frequency signals. The feedback module enables the system to continuously iterate and optimize near the π-phase modulation depth to find and lock the optimal modulation depth value to stably obtain the optimal flattened broadened spectrum, significantly improving the stimulated Brillouin scattering threshold. The feedback module monitors the modulation output status in real time, solving the problem of reduced reliability caused by the π-phase sensitivity of pseudo-random sequence phase modulation under passive modulation, greatly expanding the application of this type of modulation broadening module in engineering practice. The applied fiber laser spectral broadening device based on pseudo-random sequence phase modulation has the advantages of simple structure, high intelligence, flat top of the broadened spectral profile, and simple linewidth control, which can significantly improve the output power of 10GHz linewidth-level fiber laser amplifiers.

[0074] It should be noted that the above description describes some embodiments of this 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 a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

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

[0076] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0077] In the embodiments of this application, the same reference numerals denote 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 this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0078] In this application, "multiple" means two or more (including two).

[0079] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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 methods or systems based on a series of steps or apparatus. 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 embodiments, or in a different order, or several steps can be performed simultaneously.

[0081] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A fiber laser spectrum broadening device based on phase modulation of a pseudo-random sequence, characterized in that, It includes 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. The control module includes a parameter setting and data writing unit, a main control unit, a pseudo-random sequence generation unit, a microwave low-pass filter, a π-phase modulation control unit, and an RF amplifier. The main control unit is connected to the feedback module, the parameter setting and data writing unit, the pseudo-random sequence generation unit, and the π-phase modulation control unit, respectively. The RF amplifier is connected to the microwave low-pass filter, the π-phase modulation control unit, and the phase modulator, respectively. The microwave low-pass filter is also connected to the pseudo-random sequence generation 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 the 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 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 phase modulator is used to broaden the spectrum of the beam injected through the single-frequency laser and the first fiber coupler according to the radio frequency signal, so as to input it sequentially to the second fiber coupler, the third fiber coupler and the feedback module or output it through the second fiber coupler. The control module also includes a radio frequency fine-tuning 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 based on the feedback signal and send the difference signal to the radio frequency fine-tuning control unit when the feedback signal output by the feedback module does not meet the preset conditions. The radio frequency fine-tuning control unit 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 according to a preset step size, until the main control unit receives a second instruction sent by the main control unit when the feedback signal output by the feedback module meets the preset conditions. The second voltage value is the amount of voltage to be increased or decreased, and the third voltage value is the voltage value corresponding to the second voltage value that needs to be changed gradually according to the preset step size. The first fiber optic coupler is also connected to the third fiber optic coupler; The first fiber coupler is used to split the beam injected by the single-frequency laser into two beams for input to the third fiber coupler and the phase modulator, respectively.

2. The apparatus of claim 1, wherein, The second instruction is to instruct the radio frequency fine-tuning control unit to lock the current output voltage value.

3. The apparatus of claim 1, wherein, 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 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.

4. The apparatus of claim 3, wherein, The feedback signal includes the judgment result of the comparator; The preset conditions include the judgment result being that the power detector outputs a level corresponding to the power of the injected electrical signal that reaches a preset reference level, wherein the electrical signal is formed by photoelectric conversion of the optical signal input to the third fiber coupler by the photodetector.

5. The apparatus of claim 1, wherein, The main control unit includes a microprocessor based on a field-programmable gate array (FPGA) chip.

6. The apparatus of claim 1, wherein, The pseudo-random sequence generation unit is a digital-to-analog converter module, used to convert digital data into corresponding analog voltage output.

7. A method for fiber laser spectrum broadening based on phase modulation of a pseudo-random sequence, characterized in that, The method is applied to a fiber laser spectral broadening device based on pseudo-random sequence phase modulation as described in any one of claims 1-6, and the method includes: The main control unit calls the parameter setting and data writing unit to store the phase modulator half-wave voltage data and sends the first voltage value that meets the π phase modulation depth to the π phase modulation control unit. When the feedback signal output by the feedback module meets the preset conditions, the first instruction to lock the current working voltage is sent to the π phase modulation control unit, and the pseudo-random sequence generation unit is driven to generate a pseudo-random sequence. The pseudo-random sequence is functionally filtered by a microwave low-pass filter to obtain a filtered pseudo-random sequence. The filtered pseudo-random sequence is amplified by an RF amplifier according to the first voltage value input by the π phase modulation control unit to obtain an RF signal. The phase modulator broadens the spectral density of the beam injected through the single-frequency laser and the first fiber coupler according to the radio frequency signal, so that it can be sequentially input to the second fiber coupler, the third fiber coupler and the feedback module, or output through the second fiber coupler.

8. The method according to claim 7, characterized in that, The method further includes: If the feedback signal output by the feedback module does not meet the preset conditions, the main control unit calculates the difference signal based on the feedback signal and sends the difference signal to the radio frequency fine-tuning control unit. The radio frequency fine-tuning control unit calculates the second voltage value based on the difference signal, and sends the 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 it receives a second instruction sent by the main control unit when the feedback signal output by the feedback module meets the preset conditions. The second voltage value is the amount of voltage to be increased or decreased, the third voltage value is the voltage value corresponding to the second voltage value that needs to be changed step by step according to a preset step size, and the second instruction is to instruct the radio frequency fine-tuning control unit to lock the current output voltage value. The main control unit monitors the feedback signal in real time. If the feedback signal does not meet the preset conditions, the locking state is canceled and the process returns to the step of calculating the difference signal based on the feedback signal and sending the difference signal to the radio frequency fine-tuning control unit.

Images