A device and method for detecting instantaneous broadband and phase-modulated light source signals.

Abstract

This invention discloses a detection device and method for instantaneous broadband and phase-modulated light source signals, belonging to the field of laser signal processing. The detection device includes a polarization-maintaining transmission fiber, a waveguide-type amplitude modulator, a high-speed photodetector, and a signal frequency detector. The detection device provided by this invention features an all-fiber structure, resulting in efficient and accurate detection. It simplifies the performance requirements for the signal generator and facilitates demodulation of the frequency-interval periodic signal carried by the phase-modulated pulse, exhibiting high overall reliability. Furthermore, it can beat the signals of the two branches simultaneously, reducing the bandwidth requirements of the photodetector and avoiding integration of the time-domain signal. This allows for direct differentiation of whether the injected signal is broadband or single-frequency in a specific time slice using ordinary photodetector methods. The invention also provides a calculation process and judgment criteria for analyzing and identifying light source signals. After obtaining the modulation parameters of the injected light source signal, it can automatically and quickly determine whether the signal is an instantaneous broadband light source signal or a phase-modulated light source signal, achieving automatic analysis and judgment of the signal category throughout the entire process.

Description

Technical Field

[0001] This invention belongs to the field of laser signal processing, and specifically relates to a device and method for detecting instantaneous broadband and phase-modulated light source signals. Background Technology

[0002] In laser-driven inertial confinement fusion research, laser energy is injected into a black cavity and converted into a quasi-symmetric X-ray radiation field. This radiation field drives the implosion of the target sphere at the center of the black cavity, causing the fusion fuel inside the target sphere to reach a specific high-temperature, high-density state, thereby achieving fusion ignition. However, during laser irradiation, the black cavity fills with material blown out from the walls and the target sphere, thus generating plasma that fills the black cavity.

[0003] Black cavity plasma induces laser-plasma interactions, such as SRS (stimulated Raman scattering), SBS (stimulated Brillouin scattering), and CBET (beam transfer), which can cause up to 30-50% of the laser beam energy to be redirected during the process from the laser injection hole to the wall. Currently, the dynamics of indirectly driven black cavities and the problems of directly driven laser-plasma interaction (LPI), as well as hydrodynamic instabilities, remain persistent challenges to achieving significant combustion efficiency in ICF (inertial confinement fusion). Extrapolation of LPI shows that the LPI response intensity of the ICF target increases with increasing laser driving energy. The National Ignition Facility (NIF) in the United States observed strong LPI in targets with the smallest cavity-to-target ratio at an energy of approximately 1 MJ. Therefore, the LPI problem needs to be effectively addressed.

[0004] With the increasing scale and control capabilities of lasers, broadband light is considered a primary technical means to solve the LPI problem and a typical characteristic of next-generation lasers. Estimates of the required bandwidth indicate that 10% bandwidth will completely suppress all three-wavelength LPI, while 1% bandwidth can significantly improve the instability threshold. Further research shows that suppressing LPI requires each time slice to contain all frequency components; such a light source is called an instantaneous broadband light source. Broadband light is meaningful only when light of different frequencies interacts with the plasma simultaneously and suppresses LPI. Therefore, determining the type of injected light source is crucial for solving the LPI problem. Currently, the broadband light sources used in traditional ICF laser drivers are mainly phase-modulated broadband sources, which contain only a single frequency component in any given time slice. Instantaneous broadband sources and phase-modulated sources cannot be directly distinguished by the naked eye when used as injection sources. Limited by the response bandwidth of optoelectronic devices, it is currently impossible to directly detect the frequency components in the time slices of either type of light source. Therefore, existing technologies lack effective methods for analyzing and judging the signals from both types of light sources. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems. Based on the frequency domain characteristics of instantaneous broadband light sources, this invention proposes a detection device and method for instantaneous broadband and phase-modulated light source signals, which analyzes and judges the instantaneous broadband characteristics of the injected light source signal.

[0006] The technical solution adopted in this invention is as follows:

[0007] A detection device for instantaneous broadband and phase-modulated light source signals is disclosed. The detection device includes, along the optical path, a polarization-maintaining transmission fiber 1, a waveguide-type amplitude modulator 2, a high-speed photodetector 3, and a signal frequency detector 4. The injected light source signal enters the waveguide-type amplitude modulator 2 along the polarization-maintaining transmission fiber 1 and undergoes amplitude modulation. By analyzing the frequency components of the modulated output signal, it is determined whether the light source signal is an instantaneous broadband light source signal or a phase-modulated light source signal.

[0008] On the other hand, the present invention also provides a method for detecting instantaneous broadband and phase-modulated light source signals. The detection method modulates the light source signal by phase amplitude to obtain the modulated signal parameters, calculates the frequency component parameters based on the modulated signal parameters, and further analyzes and determines whether the light source signal is an instantaneous broadband light source signal or a phase-modulated light source signal based on the frequency component parameters and corresponding conditions.

[0009] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0010] This invention provides a detection device and method for instantaneous broadband and phase-modulated light source signals, used for modulating and analyzing injected light source signals. Firstly, the detection device can achieve an all-fiber structure, which, although simple in structure, yields efficient and accurate detection results, simplifies the performance requirements of the signal generator, and facilitates demodulation of the frequency interval periodic signal carried by the phase modulation pulse, resulting in good overall reliability. Secondly, the device can beat the signals of the two branches simultaneously, reducing the bandwidth requirements of the photodetector and avoiding integration of the time-domain signal. It allows for direct differentiation of whether the injected signal is broadband or single-frequency in a specific time slice using ordinary photodetector methods. Thirdly, this invention provides a calculation process and judgment criteria for analyzing and identifying light source signals. After obtaining the modulation parameters of the injected light source signal, it can automatically and quickly determine whether the light source signal is an instantaneous broadband light source signal or a phase-modulated light source signal, achieving automatic analysis and judgment of the signal category throughout the entire process. Attached Figure Description

[0011] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0012] Figure 1 This is a schematic diagram of the detection device structure in an embodiment of the present invention;

[0013] Figure 2 This is a schematic diagram of the signal modulation process in an embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram illustrating the time-frequency domain relationship of an instantaneous broadband light source signal.

[0015] Figure 4 This is a schematic diagram illustrating the time-frequency domain relationship of a phase-modulated light source signal.

[0016] Figure 5 A schematic diagram of the time-domain pulse shape of a phase-modulated light source signal after passing through a modulator;

[0017] Figure 6 This is a schematic diagram of the time-domain pulse shape of an instantaneous broadband light source signal after passing through a modulator.

[0018] Among them: 1-polarization-maintaining transmission fiber, 2-waveguide amplitude modulator, 3-high-speed photodetector, 4-signal frequency detector. Detailed Implementation

[0019] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0020] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0021] Example 1

[0022] This embodiment discloses a device for detecting instantaneous broadband and phase-modulated light source signals, such as... Figure 1 As shown. The detection device includes a polarization-maintaining transmission fiber 1, a waveguide-type amplitude modulator 2, a high-speed photodetector 3, and a signal frequency detector 4 along the optical path.

[0023] The polarization-maintaining fiber 1 mainly serves as a transmission fiber to transmit the light source signal output by the light source to the waveguide-type amplitude modulator 2 and maintain the stability of the polarization state of the optical signal.

[0024] The two modulation arms of the waveguide amplitude modulator 2 have good consistency, which enables a high modulation extinction ratio.

[0025] The working principle of the waveguide-type amplitude modulator 2 is as follows: Figure 2 As shown:

[0026] Assuming the light field of the injected light source signal is E, after traveling a certain distance, it is output at the first branch and divided into two equal parts, represented as the first branch E1 and the second branch E2 respectively; the first branch E1 and the second branch E2 pass through the two branches of the optical waveguide respectively, and then meet at the second branch to form a new light wave E'.

[0027] In this process, the first branch E1 and the second branch E2 acquire additional phases in the electro-optic effect region of the waveguide-type amplitude modulator 2, respectively. The two branch signals carrying the additional phases are coherently combined with linearly polarized light at the second branch. In a preferred embodiment, the modulation voltages of the two branch signals are different, and their additional phases are also different.

[0028] Therefore, when the input light source signal contains multiple frequencies, interference modulation of the two branch signals will occur during the amplitude modulation process described above, i.e., beat frequency phenomenon. Since the waveguide-type electro-optic amplitude modulator beats the signals of the two branch arms at the same time, the beat frequency process can preserve the signal difference between signals of different frequencies. It still reflects the pulse frequency domain information on a specific time slice, thus avoiding the integration of the time domain signal. Ultimately, it can be directly or indirectly distinguished whether the injected signal is a broadband signal or a single-frequency signal on a specific time slice. In addition, beat frequency can also achieve frequency downsampling to reduce the detection bandwidth requirements of photodetectors and achieve frequency demodulation.

[0029] If the injected light source signal is an instantaneous broadband light source signal, meaning the light source signal contains a large number of frequency components at any given moment, then the output signal through photoelectric conversion can demodulate rich frequency information; the time-domain-frequency domain characteristics of the instantaneous broadband light source signal are as follows: Figure 3 As shown. If the injected light source signal is not an instantaneous broadband light source signal, i.e., a phase-modulated light source signal, then the phase-modulated light source signal has only a single frequency or a few frequency components at any given time. Therefore, the output signal after photoelectric conversion will have no characteristic frequency signal or only a few single-point frequency components in the frequency domain. The time-frequency domain characteristics of the phase-modulated light source signal are shown in the attached figure. Figure 4 As shown.

[0030] In a preferred embodiment, the waveguide-type amplitude modulator 2 is a Mach-Zehnder interferometer amplitude modulator.

[0031] The photodetector 3 is mainly used to respond to signals with large frequency intervals. In a preferred embodiment, the photodetector 3 is a 45 GHz high-speed photodetector.

[0032] The signal frequency detector 4 is mainly used to detect the frequency of the modulated signal to determine whether the corresponding injected light source signal is an instantaneous broadband pulse signal. The signal frequency detector 4 can be a digital oscilloscope or a spectrum analyzer. In a preferred embodiment, the bandwidth of the signal frequency detector 4 is 50 GHz.

[0033] In a preferred embodiment of frequency detection, when the signal frequency detector 4 uses a digital oscilloscope, it is only necessary to detect the top of the modulated square wave optical pulse output signal. If there is no modulation at the top of the square wave pulse, it indicates that the injected light source signal is single-frequency in any time slice, as shown in the attached figure. Figure 5 As shown; if periodic modulation exists, it indicates that the injected light source signal is broadband on any time slice, as shown in the attached figure. Figure 6 As shown.

[0034] In a preferred embodiment of frequency detection, when the signal frequency detector 4 uses a spectrum analyzer, it is only necessary to extract and detect the frequency information of the modulated pulse. If the extracted frequency has only a single or a few characteristic frequencies, it indicates that the injected light source signal is not broadband on any time slice, that is, the light source signal is a non-instantaneous broadband light source signal.

[0035] In this embodiment, the coherence requirement of the injected light is met by using an MZ-type fiber waveguide amplitude modulator. By modulating the amplitude of the injected light source pulse signal, the instantaneous broadband characteristics of the laser pulse are judged, and the purpose of distinguishing between instantaneous broadband laser and phase-modulated laser is finally achieved.

[0036] Example 2

[0037] This embodiment discloses a method for detecting instantaneous broadband and phase-modulated light source signals, the detection method comprising:

[0038] The light source signal output from the light source is acquired and then fed into the waveguide-type amplitude modulator 2; the light field of the light source signal is E;

[0039] The light source signal is split into two equal parts at the first branch of the waveguide-type amplitude modulator 2: a first branch E1 and a second branch E2, which are respectively represented as (for simplicity, taking an example containing two frequency components):

[0040]

[0041]

[0042] Where f1 and f2 are two different frequencies contained in the light source, t is time, and A is the electric field amplitude. The first branch E1 and the second branch E2 pass through two branches of the optical waveguide, and respectively obtain additional phase in the electro-optic effect region, resulting in the first branch E1′ and the second branch E2′ carrying the additional phase, expressed as:

[0043]

[0044]

[0045] in, These are the first additional phase and the second additional phase, respectively.

[0046] Then, the first branch E1′ and the second branch E2′, carrying additional phase, are combined at the second branch to form a coherent superimposed optical field E′. The combined optical field is represented as:

[0047]

[0048] As can be seen in the entire modulation process, the first branch E1 and the second branch E2 first obtain additional phase in the electro-optic effect region of the waveguide amplitude modulator 2, and then the two branch signals are coherently combined with linearly polarized light at the second branch to achieve amplitude modulation.

[0049] In a preferred embodiment, since the waveguide-type amplitude modulator 2 adopts a push-pull branched optical waveguide structure, the relationship between the magnitudes of the first additional phase and the second additional phase is preferably set as follows in the phase modulation step: And let

[0050] The light intensity I of the output light signal is expressed as:

[0051]

[0052] Finally, let β = f1 - f2, then I can be expressed as:

[0053]

[0054] It is evident that the light intensity I of the output optical signal has a frequency difference of β = f1 - f2.

[0055] At this time, the light intensity I of the output light signal is frequency detected, and the number of single-point frequencies in the light intensity I is calculated using the value of the frequency difference β: if there is no single-point frequency in the spectrum, or if there is a single-point frequency and the number of single-point frequencies is higher than the preset threshold condition, then the injected light source signal is considered to be an instantaneous broadband light source signal; if there is a single-point frequency in the spectrum and the number of single-point frequencies does not exceed the preset threshold condition, then the injected light source signal is considered to be a phase-modulated light source signal.

[0056] In a preferred embodiment, the aforementioned preset threshold condition is that when the calculated number of single-point frequencies exceeds five times the theoretical number of single-point frequency signals of the phase-modulated pulse, the injected light source can be considered as an instantaneous broadband light source signal. In other embodiments, the multiple value can be changed according to the parameter settings required in specific application scenarios.

[0057] Taking the phase-modulated pulse commonly used in typical high-power laser driving devices as an example, the center wavelength λ of the phase-modulated pulse... c The wavelength is 1053 nm, and the spectral broadening is Δλ. The value of Δλ varies depending on the system. In this embodiment, Δλ = 0.15 nm. Based on λ = c / f, Δf ≈ 40 GHz can be calculated, and the phase modulation frequency f is... m The value of f is the same as that of the frequency difference β in this embodiment. m =2.5GHz (i.e., β value). Using the light source signal detection method in this embodiment to perform feature detection on the frequency of the injected light source, theoretically, the maximum value that can be obtained is no more than Δf / f. m =16 single-point frequency signals, and the signal strength value decreases as the frequency increases. If the number of detected frequency points far exceeds 16 (limited to 5 times, i.e., 80), the injected signal can be considered as an instantaneous broadband pulse light source signal.

[0058] By modulating and analyzing the injected light source signal using the detection device and method provided by this invention, it is possible to effectively determine whether the light source signal is an instantaneous broadband light source signal or a phase-modulated light source signal. The detection device in this invention can achieve an all-fiber structure. Although the structure is relatively simple, the detection results are highly efficient and accurate. It also simplifies the performance requirements for the signal generator and facilitates demodulation of the frequency interval periodic signal carried by the phase modulation pulse, resulting in good overall reliability. Furthermore, the device can beat the signals of the two branches at the same time, reducing the bandwidth requirements of the photodetector and avoiding the integration of the time-domain signal. It allows for direct differentiation of whether the injected signal is broadband or single-frequency in a specific time slice using ordinary photodetector methods. Based on this, this invention also provides a method and calculation process for distinguishing and judging light source signals. After obtaining the modulation parameters of the injected light source signal, it can automatically and quickly distinguish the category of the light source, realizing full-process signal type analysis and judgment.

[0059] This invention is not limited to the specific embodiments described above, nor to the application scenarios described above. It can be applied to any laser signal application scenario, and this invention does not limit it. Furthermore, this invention extends to any new features or any new combinations disclosed in this specification, as well as any new steps or any new combinations of any disclosed new methods or processes.

Claims

1. A detection device for instantaneous broadband and phase-modulated light source signals, used for detecting and analyzing injected light source signals, characterized in that, The detection device includes a polarization-maintaining transmission fiber (1), a waveguide amplitude modulator (2), a high-speed photodetector (3), and a signal frequency detector (4) along the optical path. The polarization-maintaining transmission fiber (1) is used as a transmission fiber to transmit the injected light source signal to the waveguide amplitude modulator (2) and maintain the stability of the polarization state of the optical signal; the waveguide amplitude modulator (2) is used to perform amplitude modulation on the light source signal; the photodetector (3) is used to respond to the modulated pulse signal; the signal frequency detector (4) is used to perform frequency detection on the modulated signal to determine whether the injected light source signal is an instantaneous broadband light source signal; after the light source signal enters the waveguide amplitude modulator (2), it is divided into two equal parts at the first branch, namely the first branch and the second branch; after the first branch and the second branch obtain additional phase through the electro-optic effect region of the two branches of the optical waveguide, they are coherently synthesized at the second branch and recombined to form a coherent superimposed electric field to realize amplitude modulation.

2. The detection device for instantaneous broadband and phase-modulated light source signals as described in claim 1, characterized in that, When the voltages applied to the first branch and the second branch are the same or different, the additional phases are also the same or different.

3. The detection device for instantaneous broadband and phase-modulated light source signals as described in claim 1, characterized in that, The signal frequency detector (4) is a digital oscilloscope or a spectrum analyzer.

4. The detection device for instantaneous broadband and phase-modulated light source signals as described in claim 3, characterized in that, The signal frequency detector (4) is a digital oscilloscope used to detect the top of the modulated square wave optical pulse output signal. If there is no modulation at the top of the square wave pulse, the injected light source signal is single-frequency in any time slice; if there is periodic modulation, the injected light source signal is broadband in any time slice.

5. The detection device for instantaneous broadband and phase-modulated light source signals as described in claim 3, characterized in that, The signal frequency detector (4) is a spectrum analyzer used to extract and detect the frequency information of the modulated pulse; if the number of extracted single-point frequencies is lower than the preset threshold condition, the injected light source signal is a phase-modulated signal. If the number of extracted single-point frequencies exceeds the preset threshold, the injected light source signal is an instantaneous broadband signal.

6. A method for detecting instantaneous broadband and phase-modulated light source signals, characterized in that, The detection method includes: Acquire a light source signal injected from a signal source, wherein the light field of the light source signal is E; The light intensity I of the modulated output light signal is obtained by amplitude modulation of the light source signal: the light source signal is divided into two equal parts at the first branch, namely the first branch and the second branch; after the first branch and the second branch obtain additional phase through the electro-optic effect region of the two branches of the optical waveguide, they are coherently combined at the second branch to form a coherent superimposed electric field, thereby realizing amplitude modulation; Frequency detection is performed on the light intensity I of the output light signal. If there is no single-point frequency in the spectrum or there is a single-point frequency and the number of single-point frequencies is higher than the preset threshold condition, then the injected light source signal is an instantaneous broadband light source signal; if there is a single-point frequency in the spectrum and the number of single-point frequencies does not exceed the preset threshold condition, then the injected light source signal is a phase-modulated light source signal.

7. The method for detecting instantaneous broadband and phase-modulated light source signals as described in claim 6, characterized in that, The process of amplitude modulating the light source signal to obtain the light intensity I of the modulated output light signal specifically includes: The light source signal is divided into two equal parts at the first branch: the first branch E1 and the second branch E2, which are respectively represented as: ， ； Where f1 and f2 are two different frequencies contained in the light source, t is time, and A is the electric field amplitude; By giving the first branch E1 and the second branch E2 additional phases respectively, a first branch containing additional phases is obtained. Second branch : ， ， in, , These are the first additional phase and the second additional phase, respectively. First branch carrying additional phase Second branch At the second branch, they are combined into a coherent superposition light field. : ； make , and let , The light intensity I of the output light signal is: make Then I is represented as: 。 8. A method for detecting instantaneous broadband and phase-modulated light source signals as described in claim 6 or 7, characterized in that, The preset threshold condition is that the number of single-point frequencies is 5 times the theoretical value of the phase modulation pulse.

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