A mode-locked system and mode-locked method suitable for microcavity ultrasound detection

Abstract

The application discloses a mode locking system and mode locking method suitable for micro-cavity ultrasonic detection, and the system comprises a control module, a laser output module and a detection module; the laser output module comprises a single-frequency laser, a temperature adjusting unit, a temperature detecting unit and a heat transfer unit, the detection module is used for detecting transmission spectrum lines of the micro-cavity ultrasonic probe and transmitting the transmission spectrum lines to the control module; the control module is used for controlling the intracavity temperature of the single-frequency laser through linear interpolation data, realizing linear regulation and scanning of the intracavity wavelength, screening and locking the micro-cavity mode of the micro-cavity ultrasonic probe; and the control module is also used for detecting the locking point of the micro-cavity mode by adopting temperature detection and light intensity voltage feedback design, automatically adjusting the temperature for wavelength adjustment in the mode drift process, and correcting the mode drift of the micro-cavity. The application can independently complete the functions of micro-cavity ultrasonic probe mode scanning, active mode selection and mode locking, and provides a new scheme which is stable, reliable, low in cost and high in sensitivity for ultrasonic detection.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic detection technology, and more particularly to a mode-locking system and mode-locking method suitable for microcavity ultrasonic detection. Background Technology

[0002] Research on ultrasound has spread across various fields, including scientific research, medicine, industry, and the military. Among these, ultrasonic testing, as a non-contact, high-resolution, and highly sensitive non-destructive testing method, is of great significance for many applications, such as underwater target detection, semiconductor packaging testing, and non-destructive testing of metallic materials. Efficient, sensitive, and accurate ultrasonic testing technology is now widely used in many interdisciplinary fields. Research has found that whispering-gallery mode (WGM) microcavities possess excellent acoustic measurement capabilities. Microcavity ultrasonic probes, as ultra-high sensitivity miniature probe devices, offer new possibilities for ultrasonic testing.

[0003] For microcavity ultrasonic probes, a whispering-gallery mode (hereinafter referred to as a mode) is a specific standing wave structure formed by light within the cavity. The mode of a microcavity ultrasonic probe is closely related to the wavelength of the incoming laser. By changing the wavelength of the laser entering the microcavity ultrasonic probe or adjusting the physical parameters of the cavity (such as temperature or external pressure), different modes can be selectively excited, each with a different Q-value (quality factor). Within a laser resonant cavity, the Q-value represents the ratio of the energy stored within the cavity to the energy lost per unit cycle. In ultrasonic testing, selecting a mode with a higher Q-value is beneficial for obtaining better detection sensitivity.

[0004] For the same mode, the acoustic sensitivity of a microcavity ultrasonic probe varies significantly depending on its operating position within that mode. Therefore, the measurement sensitivity of a microcavity ultrasonic probe is closely related to its operating point. During complex, dynamic measurements, the probe is affected by external factors such as temperature and pressure, making it difficult to maintain stability and operate at the same mode point for extended periods. Currently, there is no compact and complete integrated system that can integrate the complex optical path system of a microcavity ultrasonic probe while maintaining mode locking.

[0005] The existing technology has at least the following problems and defects:

[0006] (1) Microcavity ultrasonic probes typically have multiple modes, each with a different Q value. This results in varying sensitivities to the same ultrasonic signal across different modes. Therefore, the use of microcavity ultrasonic probes necessitates mode scanning, scanning a specific wavelength range of modes and then selecting the appropriate ones. Generally, a narrower mode width results in higher sensitivity to ultrasonic signals; however, a narrower mode width also makes it more difficult for the microcavity ultrasonic probe to stabilize within that mode, hindering the detection of complex and variable ultrasonic signals outside the laboratory. Furthermore, mode scanning of microcavity ultrasonic probes relies on a tunable laser to change the laser wavelength entering the cavity, increasing the overall system cost and size. Currently, there is no universal algorithm for mode scanning of microcavity ultrasonic probes that can scan and select suitable modes without using a tunable laser for practical applications.

[0007] (2) The mode of a microcavity ultrasonic probe is related to both the laser wavelength entering the cavity and the physical parameters of the microcavity itself. To provide high-sensitivity ultrasonic detection, existing microcavity ultrasonic probes typically use high-Q microcavities, making them extremely sensitive to perturbations during the measurement process. When the physical parameters of the microcavity, such as temperature and pressure, change due to external environmental influences, the mode of the microcavity will change even if the laser wavelength entering the cavity remains unchanged. Therefore, microcavity ultrasonic probes often exhibit mode drift during long-term use, frequently requiring manual mode stabilization by the user, which increases the difficulty and complexity of using microcavity ultrasonic probes.

[0008] Therefore, there is an urgent need for a sensitive and efficient pattern-locking algorithm, and a highly integrated and stable measurement system to provide lightweight, durable, robust, and highly sensitive ultrasonic testing. Summary of the Invention

[0009] This invention provides a mode-locking system and method suitable for microcavity ultrasonic detection, which can autonomously complete the functions of microcavity ultrasonic probe mode scanning, active mode selection and mode locking, providing a stable, reliable, low-cost and high-sensitivity new solution for ultrasonic detection.

[0010] This system is suitable for microcavity ultrasonic probes made of various materials, replacing expensive tunable lasers with low-cost single-frequency lasers.

[0011] In a first aspect, the present invention provides a mode-locking system suitable for microcavity ultrasonic detection, comprising a control module, a laser output module, and a detection module; the control module is connected to both the laser output module and the detection module; the laser output module includes:

[0012] A single-frequency laser is used to generate single-frequency laser light; a microcavity ultrasonic probe is disposed at the output end of the single-frequency laser; a temperature detection unit is used to detect the intracavity temperature of the single-frequency laser.

[0013] A temperature regulation unit is used to compare the error value between the cavity temperature and the given temperature output by the control module and output a temperature adjustment command; a heat transfer unit is used to receive the temperature adjustment command and adjust the cavity temperature of the single-frequency laser; wherein, the center wavelength of the single-frequency laser is linearly related to the cavity temperature;

[0014] The detection module is used to detect the transmission spectrum of the microcavity ultrasonic probe and transmit it to the control module;

[0015] The control module is used to control the intracavity temperature of the single-frequency laser through linear interpolation data, realize linear control and scanning of the inlet wavelength, and screen and lock the microcavity mode of the microcavity ultrasonic probe; it is also used to detect the locking point of the microcavity mode by adopting temperature detection and light intensity voltage feedback design, and automatically adjust the temperature to adjust the wavelength during mode drift, so as to correct the microcavity mode drift.

[0016] Optionally, the detection module includes:

[0017] A photodetector is used to detect the transmission spectrum and mode drift of the microcavity ultrasonic probe and convert them into electrical signals; a high-pass filter is used to receive the electrical signals and filter out low-frequency noise and baseline drift to acquire high-frequency signals; and a data acquisition card is used to acquire and record the high-frequency signals and transmit them to the control module.

[0018] Optionally, a polarization controller is also included, disposed at the output end of the single-frequency laser and connected to the microcavity ultrasonic probe; used to adjust and control the polarization characteristics of the single-frequency laser.

[0019] Optionally, the single-frequency laser is connected to the microcavity ultrasonic probe via an optical fiber, the optical fiber including a polarization-maintaining fiber.

[0020] Secondly, embodiments of the present invention also provide a mode-locking system suitable for microcavity ultrasound detection, wherein the mode-locking system for microcavity ultrasound detection provided by the first invention is used for mode locking, characterized in that the mode-locking method includes:

[0021] The temperature control unit linearly adjusts the center wavelength of the single-frequency laser output by the single-frequency laser according to the linear relationship between the cavity temperature and the center wavelength, and performs pattern scanning on the microcavity ultrasonic probe.

[0022] Obtain the transmission spectrum corresponding to each scanning wavelength, calculate the Q value corresponding to each transmission spectrum, screen the high Q value mode of single-frequency laser, and use the high Q value mode as the optimal mode of microcavity ultrasonic probe.

[0023] The temperature control unit adjusts the single-frequency laser to operate in high-Q mode, and locks the microcavity ultrasonic probe at the midpoint of the hypotenuse of the optimal mode.

[0024] The transmission spectrum in the optimal mode is obtained. Based on the transmission spectrum, the mode drift of the microcavity ultrasonic probe is obtained. Based on the linear relationship between the cavity temperature and the center wavelength, the center wavelength of the single-frequency laser is adjusted to compensate for the mode drift when the microcavity ultrasonic probe is working.

[0025] Optionally, when performing pattern scanning on a microcavity ultrasonic probe, the scanning mode includes wide temperature scanning and narrow temperature scanning;

[0026] First, the temperature control unit is controlled to perform a wide temperature scan to obtain the wide scan temperature of the microcavity ultrasound probe in the optimal mode. Then, based on the wide scan temperature, the temperature control unit is controlled to perform a narrow temperature scan to obtain the narrow scan temperature of the microcavity ultrasound probe in the optimal mode. The high Q value mode corresponding to the narrow scan temperature is taken as the optimal mode of the microcavity ultrasound probe. The wide scan temperature and the narrow scan temperature are determined by the Q value of the transmission spectrum.

[0027] Optionally, when performing mode scanning on the microcavity ultrasonic probe, the control module controls the temperature adjustment unit to perform wide temperature scanning and narrow temperature scanning along the temperature increase direction and temperature decrease direction respectively, and filters the Q value corresponding to the transmission spectrum obtained by the scan.

[0028] Optionally, when screening high Q-value modes of a single-frequency laser, based on the mode thermal broadening phenomenon, when there are multiple high Q-value modes and corresponding multiple spectral lines, the dual side of the mode with the largest mode slope k in the spectral curve is selected as the optimal mode for the microcavity ultrasonic probe; wherein, the dual side is determined by the symmetry of the transmission spectral lines.

[0029] Optionally, when screening high Q-value modes of single-frequency lasers, the control module pre-sets the rated depth and rated width of the spectral lines, and screens spectral curves with a depth greater than the rated depth and a width less than the rated width.

[0030] Optionally, the center wavelength of the single-frequency laser is adjusted based on the mode drift of the microcavity ultrasonic probe obtained from the transmission spectrum and the linear relationship between the cavity temperature and the center wavelength. Specifically, adjusting the center wavelength of the single-frequency laser includes:

[0031] In the optimal mode, the mode slope k, lockout voltage U and actual voltage U' of the transmission spectrum are obtained, and the mode drift ΔU and its corresponding temperature adjustment d are calculated using the first formula.

[0032] Wherein, the first formula satisfies: ΔU=U′-U,d=(U′-U) / k;

[0033] If ΔU > 0 and k > 0, or ΔU < 0 and k < 0, control the temperature adjustment unit to increase the cavity temperature of the single-frequency laser according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

[0034] If ΔU < 0 and k > 0, or if ΔU > 0 and k < 0, control the temperature adjustment unit to lower the cavity temperature of the single-frequency laser according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

[0035] In summary, the mode-locking system for microcavity ultrasonic detection provided by this invention uses a control module to adjust the intracavity temperature of a single-frequency laser through linear interpolation data control of the temperature regulation unit. This achieves linear control and uniform scanning of the inlet wavelength, enabling detailed scanning and accurate reproduction of the microcavity mode. Furthermore, the system can automatically select the most suitable mode for ultrasonic detection, calculate the ultrasonic signal based on the detected effective data, receive the mode drift of the microcavity ultrasonic probe, determine the mode compensation method, calculate the temperature change required to compensate for the mode drift, and transmit this calculation to the temperature regulation unit for mode drift correction. This system achieves mode scanning of the microcavity ultrasonic probe and can actively select the optimal mode for easy use, eliminating the need for an expensive tunable laser and reducing system costs. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a mode-locking system for microcavity ultrasonic detection provided by the present invention;

[0037] Figure 2 These are the ultrasonic signal intensity test diagrams of the microcavity ultrasonic probe provided by this invention at different operating points;

[0038] Figure 3 This is a linear relationship graph of intracavity temperature and center wavelength for the single-frequency laser provided by the present invention.

[0039] Figure 4 This is a pattern result diagram of a microcavity ultrasonic probe obtained by scanning through temperature changes of a single-frequency laser;

[0040] Figure 5 This is a test diagram of the intracavity temperature control effect of the single-frequency laser provided by the present invention;

[0041] Figure 6 This is a schematic diagram of a mode locking method for microcavity ultrasonic detection provided by the present invention;

[0042] Figure 7 This is a test graph showing the temperature scan results of the pattern locking system provided by this invention.

[0043] Figure 8 This is a schematic diagram of the thermal broadening of the microcavity ultrasonic probe mode in a mode-locking system.

[0044] Figure 9 This is a flowchart of a mode-locking method for microcavity ultrasonic detection provided by the present invention. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0046] In view of one or more of the above-mentioned problems existing in the prior art, the present invention proposes a mode locking system suitable for microcavity ultrasonic detection. Figure 1 This is a schematic diagram of a mode-locking system for microcavity ultrasonic detection provided by the present invention. (Reference) Figure 1 The mode-locking system for microcavity ultrasonic detection provided in this embodiment of the invention includes a control module 10, a laser output module 20, and a detection module 30; the control module 10 is connected to both the laser output module 20 and the detection module 30. The control module 10 includes at least one processor, which can be a microprocessor, such as a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The control module 10 has a built-in self-written intelligent program that can receive mode drift signals, automatically determine the mode compensation method, calculate the temperature change required to compensate for mode drift, and transmit this information to the temperature adjustment unit 23 for active drift correction. Specifically, the control module 10 controls the intracavity temperature of the single-frequency laser through linear interpolation data to achieve linear modulation and scanning of the inlet wavelength, and to screen and lock the microcavity mode of the microcavity ultrasonic probe. It also adopts a temperature detection and light intensity voltage feedback design to detect the locking point of the microcavity mode, and automatically adjusts the temperature to adjust the wavelength during mode drift, thereby correcting the microcavity mode drift and locking the mode.

[0047] Specifically, the laser output module 20 includes:

[0048] A single-frequency laser 21 is used to generate single-frequency laser light. This invention uses a low-cost single-frequency laser 21 as the light source for a microcavity ultrasonic probe. The single-frequency laser 21 can be temperature-tuned through hardware modules, such as using a single-frequency laser 21 with a laser center wavelength of 1064nm or 1550nm.

[0049] A microcavity ultrasonic probe 40 is disposed at the output end of a single-frequency laser 21. The output mode of the microcavity ultrasonic probe 40 changes with the center wavelength of the single-frequency laser output by the single-frequency laser 21, specifically manifested as changes in the shape and peak position of the transmission spectrum.

[0050] When an ultrasonic signal is transmitted to the vicinity of the microcavity ultrasonic probe 40, the internal coupling state of the microcavity ultrasonic probe 40 changes, resulting in a change in the output mode, which reflects the intensity and frequency of the ultrasonic signal. In ultrasonic testing using a microcavity ultrasonic probe as the main component, for the same signal (i.e., the external ultrasonic signal intensity and frequency input to the microcavity ultrasonic probe 40 are the same), the measured ultrasonic response amplitude is not the same when the microcavity ultrasonic probe is operating at different positions in the mode, such as... Figure 2 As shown, when the microcavity ultrasonic probe is stably working at the midpoint of the hypotenuse of the mode curve (i.e., Figure 2 (c) point C), corresponding to Figure 2 (g) indicates the strongest ultrasonic response to the same signal.

[0051] in, Figure 2 (a)~ Figure 2 (d) shows the transmission spectral lines of the microcavity ultrasonic probe locked at points A, B, C, and D in the microcavity mode. Figure 2 (e) The ultrasonic signal intensity corresponding to point A Figure 2 (f) Ultrasonic signal intensity corresponding to point B Figure 2 (g) The ultrasonic signal intensity corresponding to point C. Figure 2 (h) corresponds to the ultrasonic signal intensity at point D.

[0052] Temperature detection unit 22 is used to detect the intracavity temperature of single-frequency laser 21 and feed it back to temperature adjustment unit 23. Temperature detection unit 22 detects the intracavity temperature of single-frequency laser 21 in real time. Temperature adjustment unit 23 compares the actual intracavity temperature of single-frequency laser 21 with the given temperature output by control module 10, and outputs a temperature adjustment command. For example, the error value is expressed as ΔT = T 实际 -T 给定 Calculation. The judgment criteria given by the temperature control command are:

[0053] When the temperature inside the resonant cavity is greater than the given temperature of the control module 10, the temperature adjustment unit 23 will control the heat transfer unit 24 to lower the temperature inside the resonant cavity of the single-frequency laser 21.

[0054] When the temperature inside the resonant cavity is less than the given temperature of the control module 10, the temperature adjustment unit 23 will control the heat transfer unit 24 to increase the temperature inside the resonant cavity of the single-frequency laser 21.

[0055] The temperature control command is transmitted to the heat transfer unit 24 through the temperature regulation unit 23, which directly controls the magnitude and direction of the current in the heat transfer unit 24 to control the temperature of the laser.

[0056] The heat transfer unit 24 can be composed of a sensitive thermally conductive patch and a thermoelectric cooler (TEC). When current flows through it, the heat transfer unit 24 can cool or heat the single-frequency laser 21. Specifically, the heat transfer unit 24 can be attached to the underside of the resonant cavity of the single-frequency laser 21. The heat transfer unit 24 receives temperature adjustment commands and adjusts the cavity temperature of the single-frequency laser 21 through the thermoelectric cooler (TEC). The TEC achieves heating or cooling according to the direction of the current.

[0057] The center wavelength of the single-frequency laser output by the single-frequency laser 21 provided in this embodiment of the invention has a linear relationship with the cavity temperature. Specifically, Figure 3 This is a linear relationship graph of cavity temperature versus center wavelength for the single-frequency laser provided by the present invention, wherein... Figure 3 The horizontal axis represents the scanning temperature, and the vertical axis represents the center wavelength of the single-frequency laser output by single-frequency laser 21. (Reference) Figure 3 When the internal temperature of the single-frequency laser 21 changes, the cavity length of the resonant cavity changes slightly, and the cavity length of the internal resonant cavity expands or contracts accordingly, thereby changing the output wavelength of the laser and achieving the effect of temperature tuning. This system uses the linear interpolation result of the laser wavelength-temperature to fine-tune the heat transfer unit 24, so as to achieve uniform scanning and linear control of the center wavelength of the single-frequency laser output by the single-frequency laser 21.

[0058] Specifically, the center wavelength of the single-frequency laser output by the single-frequency laser 21 increases with rising temperature. This is because the cavity length of the resonant cavity expands due to increased temperature, thereby changing the resonance conditions and causing a redshift in the output wavelength. This embodiment of the invention uses linear interpolation to linearly fit this change, confirming the linear relationship between the center wavelength of the single-frequency laser output by the single-frequency laser 21 and the cavity temperature of the laser, and generating a wavelength-temperature correspondence data table for fine-tuning at temperature. In this invention, reference... Figure 3 The intracavity temperature-wavelength relationship of the single-frequency laser 21 is linear, and the goodness of fit R 2 =0.99. This further proves that the output wavelength of the single-frequency laser 21 changes with temperature at a uniform and linear rate.

[0059] Regarding temperature control precision, the system employs a PID (Proportional-Integral-Derivative) control algorithm to precisely control the temperature of the single-frequency laser 21. By adjusting the proportional, integral, and derivative parameters, a temperature tuning accuracy of over 0.01℃ / s and a wavelength adjustment interval of less than 10pm are achieved. By temperature tuning the single-frequency laser 21, the center wavelength of the single-frequency laser output by the laser 21 can be changed, thereby exciting different modes of the microcavity ultrasonic probe 40 and achieving mode scanning.

[0060] Further, refer to Figure 1 The detection module 30 is used to detect the transmission spectrum of the microcavity ultrasonic probe 40 and transmit it to the control module 10. Specifically, Figure 4 This is a pattern result diagram of a microcavity ultrasonic probe obtained by scanning through temperature changes of a single-frequency laser. Figure 4 The horizontal axis represents the scan time, and the vertical axis represents the transmission line voltage. (Reference) Figure 4 The temperature scanning range is 12℃ to 33℃, and the entire scanning time is 0 to 20 seconds. The mode of the microcavity ultrasonic probe 40 can be scanned in detail by changing the temperature of the single-frequency laser 21. The mode-locking program autonomously selects the optimal mode by comparing the Q value and slope of the transmission spectrum. After the mode scan is completed, the system stores the mode scan signal and then enters the mode selection program for selection.

[0061] Based on the above embodiments, continue to refer to Figure 1The detection module 30 includes a photodetector 31, a high-pass filter 32, and a data acquisition card 33. The photodetector 31 detects the transmission spectrum and mode drift of the microcavity ultrasonic probe 40 and converts them into electrical signals. Specifically, in this embodiment, the photodetector 31 is composed of a photodiode. The photodiode is designed and manufactured using a large-area PN junction to receive incident light. Under reverse voltage operation, the reverse current of the photodiode is extremely weak in the absence of light, called dark current; under light, the reverse current rapidly increases to tens of microamps, called photocurrent. The greater the light intensity, the greater the reverse current. Changes in light cause changes in the photodiode current, thus converting the optical signal into an electrical signal. In this system, the output of the photodetector 31 is divided into two paths: the unfiltered portion is used to monitor the mode baseline drift of the microcavity ultrasonic probe 40, and the portion filtered by the high-pass filter 32 is used to extract the effective ultrasonic signal to enhance the signal-to-noise ratio. The high-pass filter 32 receives the electrical signal and filters out low-frequency noise and baseline drift to obtain the high-frequency signal (i.e., the ultrasonic signal). In this system, the selected high-pass filter 32 is configured to cover the ultrasonic frequency band, which effectively enhances the ultrasonic signal and suppresses static mode baselines. The acquisition card 33 is used to acquire and record high-frequency signals and transmit them to the control module 10. Specifically, the acquisition card 33 can acquire valid data from the high-pass filter 32, and the control module 10 calculates the valid data to obtain the ultrasonic signal.

[0062] Figure 5 This is a test diagram showing the intracavity temperature control effect of the single-frequency laser provided by the present invention, wherein... Figure 5 The horizontal axis represents the scan time, and the vertical axis represents the scan temperature. (Reference) Figure 5 When the heat transfer unit 24 receives a temperature adjustment command, it controls the temperature of the single-frequency laser 21 to rise uniformly, maintaining a uniform rate of increase or decrease during each temperature fine-tuning. When a specific temperature needs to be maintained, the temperature fluctuation of the heat transfer unit 24 is less than 1 mK.

[0063] During mode locking, the photodetector 31 detects the mode drift of the microcavity ultrasonic probe 40 and converts the mode drift into an electrical signal. The acquisition card 33 collects the electrical signal. The control module 10 automatically identifies whether mode drift occurs based on the electrical signal fed back in real time by the acquisition card 33 and sends the command to the temperature adjustment unit 23. The output wavelength is changed by dynamically tuning the cavity temperature of the single-frequency laser 21 resonant cavity, thereby adjusting the mode of the microcavity ultrasonic probe 40 in reverse to compensate for the mode drift.

[0064] This invention, through the program design of temperature control and light intensity voltage feedback, uses a single-frequency laser 21 to achieve microcavity mode scanning, automatically finds the optimal mode curve, and after finding the optimal mode, can automatically lock the microcavity ultrasonic probe 40 at the midpoint of the hypotenuse of the optimal mode. Based on the hardware and software design provided by this solution, highly sensitive measurement of ultrasonic signals can be achieved.

[0065] The mode-locking system provided in this invention is applicable to microcavity ultrasonic probes made of various materials. It replaces expensive tunable lasers with low-cost single-frequency lasers, and linear tuning of temperature and wavelength can be achieved through hardware module control. This system can autonomously perform microcavity ultrasonic probe mode scanning, active mode selection, and mode locking, providing a stable, reliable, low-cost, and highly sensitive new solution for ultrasonic testing.

[0066] It should be noted that the system provided in this embodiment of the invention is compatible with microcavity ultrasonic probes 40 made of various materials, including but not limited to polymers, polymer-silica double shells, etc. The microcavity ultrasonic probes 40 in the system can be replaced with microcavity ultrasonic probes 40 made of other materials.

[0067] Based on the above embodiments, continue to refer to Figure 1 The mode locking system also includes a polarization controller 50, located at the output end of the single-frequency laser 21 and connected to the microcavity ultrasonic probe 40; it is used to adjust and control the polarization characteristics of the single-frequency laser entering the microcavity ultrasonic probe 40. Specifically, the polarization controller 50 adjusts the single-frequency laser output from the single-frequency laser 21 to linear polarization, improving the detection accuracy of laser scanning.

[0068] Based on the above embodiments, continue to refer to Figure 1 The single-frequency laser 21 is connected to the microcavity ultrasonic probe 40 via optical fiber, including polarization-maintaining fiber. Specifically, the optical fiber in the system can be replaced with a polarization-maintaining fiber to keep the polarization of the optical path unchanged, thus replacing the polarization controller 50. The fiber optic connector can be a commonly used (commercial) standard interface, such as FC / APC or ST / UPC. The optical fiber is matched to the laser wavelength of the single-frequency laser, for example, it can transmit laser light with wavelengths of 1064nm or 1550nm.

[0069] Based on the same inventive concept, embodiments of the present invention provide a mode-locking system suitable for microcavity ultrasonic probing, and use the mode-locking system provided in the above embodiments for microcavity ultrasonic probing mode locking. The following details the method for mode locking in microcavity ultrasonic probing using the mode-locking system provided in the embodiments of the present invention. Figure 6 This is a schematic diagram of a mode-locking method for microcavity ultrasonic detection provided by the present invention, see reference. Figures 1-6Pattern locking methods include:

[0070] S101, the control module controls the temperature adjustment unit to linearly adjust the center wavelength of the single-frequency laser output according to the linear relationship between the cavity temperature and the center wavelength, and performs pattern scanning on the microcavity ultrasonic probe.

[0071] Specifically, the control module 10 starts running, each module powers on in turn, the control module 10 checks whether each module is working properly, and initializes each module.

[0072] For example, the control module 10 controls the temperature adjustment unit 23 to adjust the temperature scanning direction, for example, the default is reverse (i.e., the temperature decreases), to perform a wide temperature scan. Based on the linear relationship between the cavity temperature and the center wavelength, the scanning temperature is linearly adjusted so that the center wavelength (hereinafter referred to as the scanning wavelength) of the single-frequency laser output by the single-frequency laser 21 is scanned uniformly over a wide range. The default temperature scanning range is 20℃, the scanning speed is 1℃ / s, and the wavelength tuning range is approximately 2nm. The scanning range of the wide temperature scan or the scanning sampling time can also be modified according to actual needs. The wavelength-temperature data table provided by linear interpolation and the temperature control accuracy of the temperature adjustment unit 23 together ensure the accuracy and uniformity of the temperature scan.

[0073] S102. The control module acquires the transmission spectrum corresponding to each scanning wavelength, calculates the Q value corresponding to each transmission spectrum, filters the high Q value mode of single-frequency laser, and uses the high Q value mode as the best mode for the microcavity ultrasonic probe.

[0074] Specifically, during the scanning process, the photodetector 31 detects the transmission spectrum of the microcavity ultrasonic probe 40 and converts it into an electrical signal. The high-pass filter 32 receives the electrical signal and filters out low-frequency noise and baseline drift, acquiring high-frequency signals (ultrasonic signals). The acquisition card 33 acquires and records the high-frequency signals and transmits them to the control module 10, establishing a database of various scanning temperatures, scanning wavelengths, and transmission spectra.

[0075] The sensitivity of the microcavity ultrasonic probe 40 is related to its Q-value (quality factor). A high Q-value means lower energy loss in the cavity and a longer residence time of photons within the cavity, thereby enhancing interaction with the environment or sample. Therefore, the higher the Q-value, the higher the sensitivity of the microcavity ultrasonic probe 40. In this embodiment of the invention, the mode with a high Q-value is selected as the optimal mode when choosing the microcavity ultrasonic probe 40 mode.

[0076] Specifically, the Q value of the microcavity ultrasonic probe 40 is calculated using the following formula:

[0077] Q = λ / Δλ.

[0078] Where λ is the resonant wavelength of the mode, i.e., the scanning wavelength, and Δλ is the full width at half maximum (FWHM) of the mode. It can be understood that when the overall resonant wavelength does not change significantly, the deeper and narrower the mode, the smaller the FWHM, and the higher the corresponding Q value. Therefore, this embodiment of the invention uses a mode selection procedure to prioritize high-Q modes with large depth and narrow width. Optionally, when selecting high-Q modes for single-frequency lasers, the control module 10 pre-sets the rated depth and rated width of the spectral lines, selecting spectral curves with a depth greater than the rated depth and a width greater than the rated width.

[0079] It should be noted that a higher Q value for a mode is not always better. Modes with high Q values ​​may exhibit drastic changes and struggle to maintain stability in complex external environments. In practical applications of ultrasonic testing, this invention requires only a Q value higher than the 5th power for the selected mode to meet measurement needs. Based on this, the control module 10 of this invention includes a mode selection program that sets a lower limit for the mode width. Only modes with a width higher than the set value can be locked by the program; modes with a width lower than the set value are not conducive to long-term stability and are generally not used. The set limits for the rated depth and rated width of the transmission spectrum can be reasonably set according to actual needs or obtained from the optimal dynamic values ​​based on the mode scanning results.

[0080] S103, the control module controls the temperature adjustment unit to adjust the single-frequency laser to work in high Q value mode, and locks the microcavity ultrasonic probe at the midpoint of the hypotenuse of the optimal mode.

[0081] Specifically, after confirming the optimal mode, the control module 10 sets a center point for the optimal mode, typically located at the midpoint of the hypotenuse of one side of the mode (see reference). Figure 2 (c) Point C), and calculate the cavity temperature of the single-frequency laser 21 corresponding to the center point based on the wavelength-temperature linear interpolation result. Reference Figure 1 Subsequently, the control module 10 issues a mode-lock command, controlling the temperature adjustment unit 23 to initiate a tuning program and issue a temperature adjustment command for temperature scanning. The heat transfer unit 24 then adjusts the temperature of the single-frequency laser 21 to this temperature, bringing the microcavity ultrasonic probe 40 into its optimal operating mode. After the microcavity ultrasonic probe 40 enters its optimal operating mode, the system records the transmission spectrum of the microcavity ultrasonic probe 40 at this time and records the current voltage value, setting it as the lockout voltage U. Simultaneously, the mode slope k of the transmission spectrum in this locked mode is recorded. These two constants, the lockout voltage U and the mode slope k, will serve as important references for subsequent locking.

[0082] S104. The control module acquires the transmission spectrum in the optimal mode, obtains the mode drift of the microcavity ultrasonic probe based on the transmission spectrum, and adjusts the center wavelength of the single-frequency laser based on the linear relationship between the cavity temperature and the center wavelength to compensate for the mode drift of the microcavity ultrasonic probe during operation.

[0083] Specifically, after the microcavity ultrasonic probe 40 is locked in the optimal mode, the acquisition card 33 begins to record the actual voltage U' of the current transmission spectrum of the microcavity ultrasonic probe 40 at fixed intervals, and compares the actual voltage U' with the locked voltage U, allowing a maximum error of 0.8% of the mode depth. The transmission spectrum of the microcavity ultrasonic probe 40 can reflect the mode drift of the microcavity ultrasonic probe 40 in real time. When the mode is stable, the transmission spectrum of the microcavity ultrasonic probe 40 should remain stable accordingly. When the voltage error value exceeds 0.8% of the mode depth, the system corrects the mode drift and temperature-tunes the single-frequency laser 21 to stabilize the microcavity ultrasonic probe 40 in the optimal mode.

[0084] Optionally, in step S104, the mode drift of the microcavity ultrasonic probe is obtained based on the transmission spectrum, and the center wavelength of the single-frequency laser is adjusted based on the linear relationship between the cavity temperature and the center wavelength. Specifically, this includes:

[0085] Step S11: The control module acquires the mode slope k, lockout voltage U, and actual voltage U' of the transmission spectrum in the optimal mode, and calculates the mode drift ΔU and its corresponding temperature adjustment d using the first formula.

[0086] The first formula satisfies: ΔU=U′-U,d=(U′-U) / k.

[0087] Step S12: The control module determines whether ΔU > 0 and k > 0; or whether ΔU < 0 and k < 0, and controls the temperature adjustment unit to increase the cavity temperature of the single-frequency laser according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

[0088] Specifically, when d > 0, it means that the actual voltage U' > the lockout voltage U, and the mode slope k > 0; or the actual voltage U' < the lockout voltage U, and k < 0. Both cases require controlling the drift of the laser wavelength actively following the mode to bring the operating point of the microcavity ultrasonic probe 40 back to the locked position. At this time, the system positively adjusts the cavity temperature of the single-frequency laser 21 resonant cavity in 0.002℃ increments, which can also be adjusted according to actual needs to ensure the speed of temperature tuning. Since the wavelength-temperature relationship is linear, as the output wavelength of the single-frequency laser 21 increases, the operating point of the microcavity ultrasonic probe 40 moves upward, and the mode drift is corrected. After the first correction, the system compares the actual voltage U' of the transmitted spectrum of the microcavity ultrasonic probe 40 with the locking voltage U again to calculate the difference. If the difference ΔU is still greater than the maximum tolerable error, the temperature adjustment operation is performed cyclically. The temperature detection unit 22 detects the intracavity temperature of the resonant cavity of the single-frequency laser 21 in real time and transmits it to the temperature adjustment unit 23. The acquisition card 33 records the actual voltage U' of the current transmitted spectrum of the microcavity ultrasonic probe 40 at fixed intervals and performs tuning feedback until the difference ΔU between the actual voltage U' and the locking voltage U is less than the maximum tolerable error.

[0089] Step S13: The control module determines that ΔU < 0 and k > 0; or, ΔU > 0 and k < 0, and controls the temperature adjustment unit to lower the cavity temperature of the single-frequency laser 21 according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

[0090] Specifically, when d < 0, it means that the actual voltage U' < the lockout voltage U, and the mode slope k > 0; or the actual voltage U' > the lockout voltage U, and k < 0. In this case, the system reverses the temperature adjustment of the cavity of the single-frequency laser 21 resonant cavity, with a temperature step of 0.002℃. As the cavity temperature of the single-frequency laser 21 decreases, the output wavelength of the single-frequency laser 21 decreases, the operating point of the microcavity ultrasonic probe 40 moves downward, and the mode drift is corrected. Afterward, the system again compares the actual voltage U' of the transmitted spectrum of the microcavity ultrasonic probe 40 with the lockout voltage U to calculate the difference. If the difference ΔU is still greater than the maximum tolerable error, the temperature adjustment operation is repeated. The temperature detection unit 22 detects the cavity temperature of the single-frequency laser 21 resonant cavity in real time and transmits it to the temperature adjustment unit 23. The acquisition card 33 records the actual voltage U' of the current transmitted spectrum of the microcavity ultrasonic probe 40 at fixed intervals for tuning feedback until the difference ΔU between the actual voltage U' and the lockout voltage U is less than the maximum tolerable error. The mode lock program runs in a loop until it is manually closed.

[0091] Based on the above embodiments, in step S101, when performing mode scanning on the microcavity ultrasonic probe, the scanning methods include temperature narrow scanning and temperature narrow scanning. The control module first controls the temperature adjustment unit to perform temperature wide scanning to obtain the wide scanning temperature of the microcavity ultrasonic probe in the optimal mode; using the wide scanning temperature as a reference, it controls the temperature adjustment unit to perform temperature narrow scanning to obtain the narrow scanning temperature of the microcavity ultrasonic probe in the optimal mode; the high Q-value mode corresponding to the narrow scanning temperature is taken as the optimal mode of the microcavity ultrasonic probe. The wide scanning temperature and the narrow scanning temperature are determined by the Q-value of the transmission spectrum.

[0092] Figure 7 This is a test graph showing the temperature scan results of the mode locking system provided by the present invention, wherein... Figure 7 (a) shows the pattern results of a wide scan using a microcavity ultrasound probe. Figure 7 (b) shows the results of a narrow scan using a microcavity ultrasonic probe. Figure 7 (c) shows the mode-locking diagram for a wide-scan microcavity ultrasound probe. (Reference) Figures 1-7 As shown, specifically:

[0093] First, the control module 10 controls the temperature regulation unit 23 to perform a wide temperature scan in sequence.

[0094] Step S21: The control module 10 controls the temperature adjustment unit 23 to output a first temperature adjustment command according to the first temperature range, and the heat transfer unit 24 linearly adjusts the cavity temperature of the single-frequency laser 21 based on the first temperature adjustment command, and outputs the single-frequency laser corresponding to each first scanning temperature.

[0095] For example, the first temperature range can be 12℃~33℃, the scanning speed is 1℃ / s, and the wavelength tuning range is approximately 2nm. The control module 10 controls the temperature adjustment unit 23 to adjust the temperature scanning direction, which is reversed (cooling) by default, performing a wide-range temperature scan to ensure the output wavelength of the single-frequency laser 21 is scanned uniformly over a wide range. The default range is 20℃, the scanning speed is 1℃ / s, and the wavelength tuning range is approximately 2nm. The scanning range of the wide-range temperature scan or the scanning sampling time can be modified according to actual needs. The wavelength-temperature data table provided by linear interpolation and the temperature control accuracy of the temperature adjustment unit 23 together ensure the accuracy and uniformity of the temperature scan. Figure 7 As shown in (a).

[0096] It should be noted that when adjusting the temperature of the single-frequency laser 21 to near the optimal mode, the direction of adjustment must be the same as the scanning direction corresponding to the optimal mode. For example, if the optimal mode is obtained during temperature backscan, the system will first rapidly increase the temperature, then slowly decrease the temperature, adjusting it to near the temperature corresponding to the optimal mode, ensuring that the microcavity ultrasonic probe 40 enters the mode during temperature backscan.

[0097] Step S22: The control module 10 acquires the first transmission spectrum corresponding to each first scanning wavelength, calculates the first Q value corresponding to each first transmission spectrum, filters the first high Q value mode of single-frequency laser, and acquires the first high Q value scanning temperature corresponding to the first high Q value mode.

[0098] Furthermore, the control module 10 controls the temperature regulation unit 23 to perform a narrow temperature scan, including:

[0099] In step S23, the control module 10 controls the temperature adjustment unit 23 to output a second temperature adjustment command according to the second temperature range, and the heat transfer unit 24 linearly adjusts the cavity temperature of the single-frequency laser 21 based on the second temperature adjustment command, and outputs the single-frequency laser corresponding to each second scanning temperature.

[0100] The first high Q value scanning temperature is located within the second temperature range, the second temperature range is located within the first temperature range, and the number of second scanning temperatures is greater than the number of first scanning temperatures.

[0101] For example, the second temperature range is 20℃~25℃, the scanning speed is 0.1℃ / s, and the wavelength tuning range is approximately 0.2nm. The control module 10 narrows the tuning range and controls the temperature adjustment unit 23 to adjust the temperature scanning direction, which defaults to reverse (cooling), performing a narrow temperature scan within a small range. This ensures that the output wavelength of the single-frequency laser 21 is scanned uniformly within a narrow range, with a default range of 5℃, a scanning speed of 0.1℃ / s, and a wavelength tuning range of approximately 0.2nm. The scanning range of the narrow temperature scan or the scanning sampling time can also be modified according to actual needs. The wavelength-temperature data table provided by linear interpolation and the temperature control accuracy of the temperature adjustment unit 23 together ensure the accuracy and uniformity of the narrow temperature scan. Figure 7 As shown in (b).

[0102] Step S24: Obtain the second transmission spectrum corresponding to each second scanning wavelength, calculate the second Q value corresponding to each second transmission spectrum, screen the second high Q value mode of single-frequency laser, and use the second high Q value mode as the optimal mode of microcavity ultrasonic probe 40.

[0103] It should be noted that the second temperature scan, performed by increasing the sampling data, further confirms the specific location of the optimal mode, while minimizing mode drift that may occur during the system's bidirectional scanning and mode selection process. After the narrow temperature scan, the system compares the data from the two scans to accurately locate the optimal mode and verifies its depth and width, ultimately locking the microcavity ultrasound probe 40 onto the optimal mode. Figure 7 As shown in (c).

[0104] Based on the above embodiments, during wide-temperature scanning, the thermal broadening phenomenon of modes needs to be considered. Thermal broadening is a thermal nonlinear effect within the microcavity. The positive accumulation of this thermal nonlinear effect is achieved by factors such as high Q-values, small modal volumes, miniature cavity dimensions, and temperature-sensitive polymer cavity materials. This leads to a bistable effect in the 40 modes of the microcavity ultrasonic probe, specifically manifested as broadening or compression of high-Q modes during both forward (heating) and reverse (cooling) laser scanning.

[0105] Figure 8 This is a schematic diagram of the thermal broadening of the microcavity ultrasonic probe mode in a mode-locking system. (Reference) Figure 8 Since thermal broadening is essentially a forward and reverse scan of the same single mode, it does not change the Q-value of the mode, but it does change the linearity of the forward and reverse scans. Specifically, one side of the mode narrows while the other side broadens. Figure 8 (a) is the pattern in its normal form. Figure 8 (b) To generate the same thermally broadened mode, it can be seen that there is a single-sided slope of the mode (hereinafter referred to as the mode slope) in the broadened mode. Without changing the mode Q value, the mode slope k of the mode slope is reduced, thus making it easier for the system to lock and making it one of the preferred modes. In addition, since the thermal broadening direction of the mode is related to the material used in the microcavity and is not completely fixed, optionally, when performing mode scanning on the microcavity ultrasonic probe 40, the control module 10 controls the temperature adjustment unit 23 to perform narrow temperature scanning and narrow temperature scanning along the temperature rising direction and temperature falling direction respectively, to screen out all Q values ​​corresponding to the transmission spectrum lines. It can also be understood that the mode locking system provided in this embodiment of the invention performs two wavelength scans in the forward heating direction and the reverse cooling direction during temperature scanning to find the optimal mode line shape.

[0106] In step S102 above, the mode Q value is calculated. After the temperature wide scan is completed, the system records the scan data, stores the transmission line voltage values ​​of the microcavity ultrasonic probe 40 at each temperature, and calculates the Q value of all modes within the scanning range to select the optimal mode. During data processing, the calculation of the mode Q value is simplified to the calculation of the depth U, width Δλ, and mode slope k of one side of the mode.

[0107] The depth of a single mode can be directly obtained from the voltage value of the transmission spectrum. By traversing the maximum and minimum values ​​of the data through the peak-finding function, the minimum value obtained is the valley point of each mode, and all modes can be screened out in this way.

[0108] The mode width is defined as the half-width at half maximum (HWHM) Δλ of a single side of the mode. Based on the linear relationship between wavelength and temperature, it can be represented by the temperature of the single-frequency laser 21. A mode with a HWHM of 0.05℃ means scanning the entire HWHM range, and the temperature of the single-frequency laser 21 needs to be adjusted by 0.05℃. The mode slope k of a single side is obtained by dividing the mode depth by the full HWHM of the single side, i.e., k = U / 2Δλ. Since thermal broadening causes the shape of the two sides of the mode to be different, when selecting the best mode, the two sides of the same mode are considered as different parts, and the selection result of the best mode will be accurate to the single side of the mode.

[0109] For a single-sided mode, the greater the maximum depth U and the higher the slope k of the single-sided mode, the higher the Q value of the mode. Optionally, when screening high Q-value modes of single-frequency lasers, the control module 10 pre-sets the rated depth and rated width of the spectral lines, screening spectral curves with a depth greater than the rated depth and a width less than the rated width. In other words, during system screening, a predetermined depth and width are set, and only single-sided modes with a depth greater than the predetermined depth and a width less than the predetermined width will be selected. Simultaneously, since excessively narrow single-sided modes change too drastically, which is not conducive to mode locking, the system sets a minimum width for the single-sided mode based on the adjustable accuracy of the temperature control module. Only modes with a width greater than the set value can be locked through the program.

[0110] After the Q-value calculation is completed, the system provides a set of mode sides that meet the above conditions, and finds the mode side with the largest mode slope k. Considering that thermal broadening is a phenomenon of narrowing on one side and broadening on the opposite side of the mode, and that modes without thermal broadening exhibit symmetry, the mode side ultimately selected in this invention is the dual side of the mode side with the largest mode slope k, as the optimal mode. Optionally, when screening high Q-value modes of single-frequency lasers, if multiple high Q-value modes exist and correspond to multiple spectral lines, the dual side of the mode side with the largest mode slope among the multiple spectral curves is selected as the optimal mode of the microcavity ultrasonic probe 40.

[0111] It should be noted that when the control module 10 adjusts the temperature of the single-frequency laser 21 to near the optimal mode, the adjustment direction must be the same as the scanning direction corresponding to the optimal mode. For example, if the optimal mode is obtained during temperature backscan, the system will first rapidly increase the temperature, then slowly decrease it, adjusting it to near the temperature corresponding to the optimal mode, ensuring that the microcavity ultrasonic probe 40 enters the mode during temperature backscan. After performing a wide temperature scan, the tuning range is narrowed to perform a narrow temperature scan. A second temperature scan is performed by increasing the sampling data to further confirm the specific location of the optimal mode, while minimizing mode drift that may occur during the system's bidirectional scanning and mode selection. After the narrow temperature scan, the system compares the data from the two scans to accurately locate the position of the optimal mode and verifies the depth and width of the optimal mode.

[0112] Figure 9 This is a flowchart of a mode-locking method for microcavity ultrasonic detection provided by the present invention, see reference. Figures 1-9 As shown, the following describes the process control of the mode locking method for microcavity ultrasonic detection provided by the embodiments of the present invention:

[0113] Step S31: System startup and operation. Control module 10 starts running, and each module powers on in sequence. Control module 10 checks whether each module is working properly and initializes each module.

[0114] Step S32: Confirm that each module is working properly.

[0115] Step S33: Adjust the temperature scan direction, which is reverse (cooling) by default. The control module 10 controls the temperature adjustment unit 23 to adjust the temperature scan direction, which is reverse (i.e., the direction of temperature reduction) by default.

[0116] Step S34: The temperature control unit performs a wide temperature scan.

[0117] The temperature control unit 23 initiates the scanning program and issues a scanning command to perform a wide temperature scan. It controls the heat transfer unit 24 to perform a uniform temperature scan of the single-frequency laser 21 over a wide range. The default temperature scan range is 20℃, the scan speed is 1℃ / s, and the wavelength tuning range is approximately 2nm. The single-frequency laser 21 is abbreviated as DFB (Distributed Feedback).

[0118] Step S35: Wide signal processing. The control module acquires the high-frequency signal transmitted by the acquisition card 33 and establishes a database of parameters such as scanning temperature, scanning wavelength, and transmission spectrum.

[0119] Step S36: Temperature scan has been performed twice. If the answer is Y, proceed to step S37; otherwise, proceed to step S38.

[0120] Step S37: Calculate the Q-value of the mode and select the optimal mode. The control module 10 calculates the Q-value of the mode according to the formula Q = λ / Δλ for the Q-value of the microcavity ultrasonic probe 40. The mode with the highest Q-value is selected as the optimal mode. In the transmission spectrum statistics, high Q-value modes with large depth and narrow width are preferentially selected.

[0121] When screening high Q-value modes of single-frequency lasers, the control module 10 pre-sets the rated depth and rated width of the spectral lines, and screens spectral curves with a depth greater than the rated depth and a width greater than the rated width.

[0122] When multiple high-Q modes exist and correspond to multiple spectral lines, the dual side of the mode with the largest slope k in the spectral curve is selected as the optimal mode for the microcavity ultrasonic probe. The dual side is determined by the symmetry of the transmission spectral lines.

[0123] Step S38: Adjust the temperature scan direction to positive (heating). The control module 10 controls the temperature adjustment unit 23 to adjust the temperature scan direction to positive (i.e., the direction of temperature increase). Then, execute steps S34 to S36 in sequence.

[0124] Step S39: Adjust the DFB temperature to near the optimal mode. The control module 10 controls the temperature adjustment unit 23 to adjust the intracavity temperature of the single-frequency laser 21 to near the scanning temperature corresponding to the optimal mode.

[0125] Step S310: Narrowing the temperature range for a narrow temperature scan. The temperature adjustment unit 23 initiates the scanning program and issues a scanning command to perform a narrow temperature scan. The heat transfer unit 24 controls the single-frequency laser 21 to perform a uniform temperature scan within a narrow range. The default temperature scan range is 5℃, the scan speed is 0.1℃ / s, and the wavelength tuning range is approximately 0.2nm. By increasing the sampling data for a second temperature scan, the specific location of the optimal mode can be further confirmed, while minimizing mode drift that may occur during the system's bidirectional scanning and mode selection. After the narrow temperature scan, the system compares the data from the two scans, including O-value calculation, to accurately locate the optimal mode and verify the depth and width of the optimal mode, ultimately locking the microcavity ultrasonic probe 40 onto the optimal mode.

[0126] Step S311: Lock the optimal mode and adjust the working point to this mode. The control module 10 controls the microcavity ultrasonic probe 40 to lock in the optimal mode, realize mode locking, and enter the mode drift compensation program.

[0127] Step S312: Record the voltage at this time as the lockout voltage.

[0128] Step S313, Mode Voltage Detection. The control module 10 acquires the transmission line voltage value of the microcavity ultrasonic probe 40 in real time.

[0129] Step S314: Determine if |actual voltage - lockout voltage| > error value. If yes, proceed to step S315; otherwise, proceed to step S313.

[0130] Step S315: Calculate the temperature adjustment amount d = (actual voltage - lockout voltage) / mode slope. Calculate the mode drift ΔU and its corresponding temperature adjustment amount d using the first formula. The first formula satisfies: ΔU = U′ - U, d = (U′ - U) / k. If d > 0, proceed to steps S317–S319 sequentially; if d ≤ 0, proceed to steps S320–S321 sequentially.

[0131] Step S317: Increase the DFB temperature.

[0132] Step S318: Increase the DFB output wavelength.

[0133] Step S319: Move the working point upwards.

[0134] Step S320: Adjust DFB temperature.

[0135] Step S321: The DFB output wavelength decreases.

[0136] Step S322: Move the working point downwards.

[0137] In summary, the mode-locking method for microcavity ultrasonic detection provided by this invention allows the control module to adjust the intracavity temperature of a single-frequency laser using linear interpolation data to control the temperature regulation unit. This achieves linear control and uniform scanning of the entry wavelength, enabling detailed scanning and accurate reproduction of the microcavity mode. Furthermore, the most suitable mode for ultrasonic detection can be automatically selected through a program, eliminating the need for an expensive tunable laser and reducing system costs. Further, the mode-locking method enables mode scanning and automatic locking of microcavity ultrasonic probes made of various materials. It receives mode drift from the microcavity ultrasonic probe, determines the compensation method, calculates the temperature change required to compensate for the drift, and transmits this calculation to the temperature regulation unit for mode drift correction. This allows the microcavity ultrasonic probe to autonomously stabilize at its optimal operating point, with temperature stability at the 1 mK level. Based on this stable operating point, the ultrasonic signal can be retrieved from the effective data detected by the microcavity ultrasonic probe. The highly stable mode-locking program design allows the microcavity ultrasonic probe to operate in its optimal mode for extended periods, exhibiting excellent anti-interference capabilities and maintaining high consistency in complex environments outside the laboratory, while also reducing the difficulty of mode locking for the microcavity ultrasonic probe.

[0138] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A mode-locking system suitable for microcavity ultrasonic detection, characterized in that, It includes a control module, a laser output module, and a detection module; the control module is connected to both the laser output module and the detection module; the laser output module includes: A single-frequency laser is used to generate single-frequency laser light; a microcavity ultrasonic probe is disposed at the output end of the single-frequency laser; a temperature detection unit is used to detect the intracavity temperature of the single-frequency laser. A temperature regulation unit is used to compare the error value between the cavity temperature and the given temperature output by the control module and output a temperature adjustment command; a heat transfer unit is used to receive the temperature adjustment command and adjust the cavity temperature of the single-frequency laser; wherein, the center wavelength of the single-frequency laser is linearly related to the cavity temperature; The detection module is used to detect the transmission spectrum of the microcavity ultrasonic probe and transmit it to the control module; The control module is used to control the intracavity temperature of the single-frequency laser through linear interpolation data, thereby achieving linear modulation and scanning of the inlet wavelength, and screening and locking the microcavity mode of the microcavity ultrasonic probe. It is also used to employ temperature detection and light intensity voltage feedback design to detect the locking point of the microcavity mode, and to automatically adjust the temperature to regulate the wavelength during mode drift, thus correcting microcavity mode drift. Specifically, it includes the following control steps: The temperature control unit linearly adjusts the center wavelength of the single-frequency laser output by the single-frequency laser according to the linear relationship between the cavity temperature and the center wavelength, and performs pattern scanning on the microcavity ultrasonic probe. Obtain the transmission spectrum corresponding to each scanning wavelength, calculate the Q value corresponding to each transmission spectrum, screen the high Q value mode of single-frequency laser, and use the high Q value mode as the optimal mode of microcavity ultrasonic probe. The temperature control unit adjusts the single-frequency laser to operate in high-Q mode, locks the microcavity ultrasonic probe at the midpoint of the hypotenuse of the optimal mode, and obtains the mode slope k and locking voltage U of the transmission spectrum in this locked mode. In the optimal mode, the mode slope k, lockout voltage U and actual voltage U' of the transmission spectrum are obtained, and the mode drift ∆U and its corresponding temperature adjustment d are calculated using the first formula. Wherein, the first formula satisfies: , ; judge ;or, The temperature control unit adjusts the cavity temperature of the single-frequency laser according to the temperature adjustment amount to adjust the center wavelength of the single-frequency laser. judge ;or, The temperature control unit lowers the cavity temperature of the single-frequency laser according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

2. The pattern locking system according to claim 1, characterized in that, The detection module includes: A photodetector is used to detect the transmission spectrum and mode drift of the microcavity ultrasonic probe and convert them into electrical signals; a high-pass filter is used to receive the electrical signals and filter out low-frequency noise and baseline drift to acquire high-frequency signals; and a data acquisition card is used to acquire and record the high-frequency signals and transmit them to the control module.

3. The pattern locking system according to claim 1, characterized in that, It also includes a polarization controller, which is disposed at the output end of the single-frequency laser and connected to the microcavity ultrasonic probe; used to adjust and control the polarization characteristics of the single-frequency laser.

4. The pattern locking system according to claim 1, characterized in that, The single-frequency laser and the microcavity ultrasonic probe are connected by an optical fiber, which includes a polarization-maintaining fiber.

5. A mode-locking method suitable for microcavity ultrasonic probing, comprising using the mode-locking system for microcavity ultrasonic probing as described in any one of claims 1 to 4 for microcavity ultrasonic probing mode locking, characterized in that, include: The temperature control unit linearly adjusts the center wavelength of the single-frequency laser output by the single-frequency laser according to the linear relationship between the cavity temperature and the center wavelength, and performs pattern scanning on the microcavity ultrasonic probe. Obtain the transmission spectrum corresponding to each scanning wavelength, calculate the Q value corresponding to each transmission spectrum, screen the high Q value mode of single-frequency laser, and use the high Q value mode as the optimal mode of microcavity ultrasonic probe. The temperature control unit adjusts the single-frequency laser to operate in high-Q mode, locks the microcavity ultrasonic probe at the midpoint of the hypotenuse of the optimal mode, and obtains the mode slope k and locking voltage U of the transmission spectrum in this locked mode. In the optimal mode, the mode slope k, lockout voltage U and actual voltage U' of the transmission spectrum are obtained, and the mode drift ∆U and its corresponding temperature adjustment d are calculated using the first formula. Wherein, the first formula satisfies: , ; judge ;or, The temperature control unit adjusts the cavity temperature of the single-frequency laser according to the temperature adjustment amount to adjust the center wavelength of the single-frequency laser. judge ;or, The temperature control unit lowers the cavity temperature of the single-frequency laser according to the temperature adjustment amount, so as to adjust the center wavelength of the single-frequency laser.

6. The pattern locking method according to claim 5, characterized in that, When performing pattern scanning on a microcavity ultrasonic probe, the scanning methods include wide temperature scanning and narrow temperature scanning. First, the temperature control unit is controlled to perform a wide temperature scan to obtain the wide scan temperature of the microcavity ultrasound probe in the optimal mode. Then, based on the wide scan temperature, the temperature control unit is controlled to perform a narrow temperature scan to obtain the narrow scan temperature of the microcavity ultrasound probe in the optimal mode. The high Q value mode corresponding to the narrow scan temperature is taken as the optimal mode of the microcavity ultrasound probe. The wide scan temperature and the narrow scan temperature are determined by the Q value of the transmission spectral line.

7. The pattern locking method according to claim 6, characterized in that, During the mode scanning of the microcavity ultrasonic probe, the control module controls the temperature adjustment unit to perform wide temperature scanning and narrow temperature scanning along the temperature increase direction and temperature decrease direction respectively, and selects the Q value corresponding to the transmission spectrum obtained by the scan.

8. The pattern locking method according to claim 5, characterized in that, When screening high Q-value modes of a single-frequency laser, based on the mode thermal broadening phenomenon, when there are multiple high Q-value modes and corresponding multiple spectral lines, the dual side of the mode with the largest mode slope k in the spectral curve is selected as the optimal mode for the microcavity ultrasonic probe; wherein, the dual side is determined by the symmetry of the transmission spectral lines.

9. The pattern locking method according to claim 6, characterized in that, When screening high Q-value modes of single-frequency lasers, the control module pre-sets the rated depth and rated width of the spectral lines, and screens spectral curves with a depth greater than the rated depth and a width less than the rated width.

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