A capillary bubble microcavity array preparation device and method based on machine vision closed-loop control

Abstract

The application discloses a kind of based on machine vision closed-loop control's capillary bubble microcavity array preparation device and method, comprising: high-voltage discharge module, including programmable AC power supply and high-voltage transformer, the input end of programmable AC power supply is connected to AC mains;Air pressure control module, vision acquisition module, automatic positioning and fine adjustment module and host computer, for real-time analysis and output control instruction.The application realizes micron level position compensation by spatial symmetry closed-loop correction loop, and dynamically reduces discharge intensity with wall thickness thinning by energy self-adaptive control loop, effectively solves the problem that traditional manual operation is subjective, poor consistency and low yield, ensures the high quality and high consistency of bubble microcavity;At the same time, it provides a reliable device preparation solution for ultra-low concentration chemical gas / biomolecule high-sensitivity detection, narrow linewidth laser, optical sensing and quantum optics.

Description

Technical Field

[0001] This invention relates to the field of capillary microbubble fabrication technology, and in particular to a device and method for fabricating capillary bubble microcavity arrays based on machine vision closed-loop control. Background Technology

[0002] Currently, common methods for fabricating bubble-type microcavities either involve using a commercial fiber optic fusion splicer to discharge a quartz capillary while simultaneously pressurizing the inside of the capillary to cause it to bulge into a bubble. This method places high demands on the adjustability of the fusion splicer, requiring it to be able to collimate the quartz capillary and move it up and down in the z-axis to find the center of the arc. This is because the arc is usually not along the line connecting the two discharge needles, but rather spindle-shaped between them. To our knowledge, fiber optic fusion splicers are increasingly being developed towards facilitating fiber splicing, which cannot meet the requirements for fabricating bubble-type microcavities. On the other hand, the range of movement along the capillary direction provided by the fusion splicer is very small, making it difficult to fabricate a series of bubble-type microcavities on a single section of capillary.

[0003] Existing discharge melting methods for fabricating bubble-type microcavities suffer from uneven heating of the capillary due to the spindle-shaped and narrow arc in the front-to-back direction, resulting in asymmetrical bubble expansion. This is caused by the non-ideal symmetry of the arc's thermal field. While this problem can be mitigated by operators visually observing under a microscope and manually adjusting the capillary's position relative to the arc, this open-loop manual fine-tuning method has three major drawbacks: first, it heavily relies on human experience, making it difficult to precisely quantify the adjustment direction and step size; second, visual observation is often delayed, intervening only after significant asymmetry has occurred, leading to irreversible microcavity distortion; and third, it results in low yield, poor microcavity morphology consistency, and difficulty in large-scale continuous fabrication.

[0004] Another commonly used method for preparing bubble microcavities is carbon dioxide laser melting. By constructing a carbon dioxide laser optical path, the focused laser beam is directed onto a quartz capillary. Pressure is applied using a syringe or gas cylinder, causing one side of the capillary to melt while the other side expands, forming a bubble-shaped optical microcavity. To ensure symmetrical expansion of the capillary, the laser beam is typically split into two paths, symmetrically irradiating the same point on the capillary. The morphology of the bubble can be controlled by adjusting the output and power of the carbon dioxide laser. However, carbon dioxide laser systems require the construction of a spatial optical path, occupying a large optical platform. The adjustment and focusing process of a 10.6µm wavelength laser is complex and carries certain risks, requiring extensive experience in laser experimental operations. Furthermore, after focusing, the carbon dioxide laser beam is perpendicular to the beam direction, resulting in a narrow heating range, still presenting the problem of asymmetrical expansion of the bubble-shaped microcavity. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for preparing capillary bubble microcavity arrays based on machine vision closed-loop control, which can greatly improve the symmetry of bubble-type microcavities and the consistency of continuous microcavities.

[0006] The technical solution adopted in this invention is as follows: A device for fabricating capillary bubble microcavity arrays based on machine vision closed-loop control, comprising: The high-voltage discharge module includes a programmable AC power supply and a high-voltage transformer. The input terminal of the programmable AC power supply is connected to AC mains power, and the output terminal is electrically connected to the primary coil of the high-voltage transformer. The secondary coil of the high-voltage transformer is electrically connected to a pair of discharge tungsten needle electrodes distributed on both sides of the capillary tube. The high-voltage transformer is configured to multiply and boost the low-voltage / medium-voltage AC power received at the primary terminal, and output high-voltage AC power at the secondary terminal that is sufficient to break down the air between the electrodes and form a plasma arc. The pneumatic control module includes a precision pneumatic pump for applying an adjustable constant pneumatic pressure inside the quartz capillary. The visual acquisition module includes a monocular microscope with a CCD camera, which is aligned with the discharge area to acquire dynamic image sequences of the capillary thermal expansion in real time. The automatic positioning and fine-tuning module includes a first three-axis manual displacement stage, a second three-axis manual displacement stage, a three-axis electrically controlled displacement stage, and a fixture for fixing the quartz capillary. The fixture is fixedly mounted on the three-axis electrically controlled displacement stage to drive the quartz capillary to translate in three-dimensional space. The first three-axis manual displacement stage and the second three-axis manual displacement stage are respectively used to adjust the spacing and alignment between a pair of discharge tungsten needle electrodes. The main control computer is communicatively connected to the programmable AC power supply, the precision air pump, the CCD camera, the first three-axis manual displacement stage, the second three-axis manual displacement stage, and the three-axis electrically controlled displacement stage. The main control computer runs image processing algorithms and closed-loop control programs to analyze the morphological parameters of the bubble microcavities in real time and output control commands to drive the three-axis electrically controlled displacement stage and the programmable AC power supply.

[0007] The turns ratio of the primary coil to the secondary coil of the high-voltage transformer is 1:40.

[0008] The programmable AC power supply has a voltage output range of 0-250V and is continuously steplessly adjustable. The programmable AC power supply has built-in timing control logic, and the setting step resolution for the single discharge duration is 1ms, with a setting range of 50ms-200ms for the single discharge duration.

[0009] The precision pneumatic pump outputs a relative pressure range of 0-70 kPa, corresponding to an absolute pressure range of 101-171 kPa, with a pressure accuracy of ±0.5 kPa. It employs high-precision pressure sensing and closed-loop control.

[0010] The monocular microscope uses a 0.75×-5× continuous zoom main unit, with a 0.5×-2× objective lens and a working distance of 30-40mm; the CCD camera has anti-saturation technology, which can continuously and clearly image during arc discharge.

[0011] The single-axis closed-loop positioning accuracy of the three-axis electrically controlled displacement stage is ±1μm, and the minimum single-step movement step size is 0.2μm.

[0012] A method for fabricating a bubble-type optical microcavity using the aforementioned device includes the following steps: Step 1, Pre-treatment and loading of quartz capillary tube: First, pre-clean the quartz capillary tube, then seal and fix one end of the cleaned quartz capillary tube on the fixture of the three-axis electric displacement stage, so that the quartz capillary tube is suspended and extended forward between the two discharge tungsten needles, and connect the other end of the quartz capillary tube to the output air circuit of the precision pneumatic pump. Step 2, System Initialization and Automatic Visual Alignment: The main control computer extracts the tip coordinates of the two tungsten discharge needles using an image recognition algorithm, calculates the theoretical center point of the arc thermal field, and drives the three-axis electrically controlled displacement stage to automatically translate the quartz capillary to the center point. Step 3, Constant Pressure Inflation and Initial Discharge Molding: The main control computer sends instructions to the precision air pump to apply and maintain a constant air pressure inside the capillary; at the same time, it controls the programmable AC power supply to output an initial voltage, which breaks down the air between the two discharge tungsten needles through the high-voltage transformer to form an electric arc, causing the quartz capillary to soften and expand initially. Step 4: Spatial position closed-loop compensation and symmetry control based on machine vision: During the capillary discharge expansion process, the main control computer acquires the CCD video stream in real time through the CCD camera, extracts the dynamic contours of the upper and lower sidewalls of the bubble, and calculates the symmetry error of the expansion area; when the symmetry error is greater than the preset tolerance threshold, the main control computer controls the electronically controlled displacement stage to drive the capillary to the side with smaller expansion for step compensation, so that the capillary is always at the center of the electric arc thermal field during the expansion. Step 5: Dynamic degradation of discharge energy and single-cavity shaping: The main control computer dynamically adjusts the output voltage and discharge pulse width of the programmable AC power supply based on the total diameter of the bubble calculated in real time by vision. When the real-time diameter reaches the target diameter, the main control computer cuts off the high-voltage trigger signal, and the bubble-shaped optical microcavity is prepared and cooled and shaped.

[0013] In step four, the main control computer obtains the first expansion radius R1 and the second expansion radius R2 of the bubble through the edge extraction algorithm, and calculates the asymmetry parameter ΔR=R1−R2; when |ΔR| is greater than the preset tolerance threshold, the error is input into the PID position control algorithm to solve the reverse space compensation step size, and drives the three-axis electric control displacement stage to perform micron-level step compensation.

[0014] In step five, when the total diameter of the bubble is less than the set diameter threshold, a high-voltage long pulse mode is adopted, with an output voltage of 165V and a single discharge duration of 150-200ms; when the total diameter of the bubble reaches or exceeds the diameter threshold, a flexible discharge mode is switched to, and the output voltage is reduced to 125V with a single discharge duration of 90-120ms.

[0015] After the single bubble microcavity is shaped, the main control computer drives the electronically controlled displacement stage to move the quartz capillary along its central axis by a preset distance. Then, it returns to step two and repeats the process on the new unmelted tube segment until the preset number of microcavities are processed to obtain a bubble-type microcavity array.

[0016] The bubble-type optical microcavity fabrication system and method proposed in this invention introduces machine vision and a dual-closed-loop control algorithm into the fabrication process for the first time. It achieves micron-level position compensation through a spatially symmetrical closed-loop correction loop and dynamically reduces discharge intensity as the wall thickness decreases through an energy adaptive control loop. This effectively solves the problems of high subjectivity, poor consistency, and low yield associated with traditional manual operations, ensuring the high quality of the bubble-type microcavities (quality factor up to 10). 7 The system achieves high consistency (level); simultaneously, based on digital energy injection from a programmable AC power supply and precise stepping of an electrically controlled displacement stage, it can automatically fabricate precisely spaced microcavity arrays on a single capillary, and all process parameters can be programmed for storage and reproduction, providing a reliable device fabrication solution for fields such as high-sensitivity detection of ultra-low concentration chemical gases / biomolecules, narrow-linewidth lasers, optical sensing, and quantum optics. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a system structure diagram of the present invention; Figure 2 This is a partially enlarged schematic diagram of the discharge tungsten needle described in this invention; Figure 3 This is a diagram illustrating the bubble-shaped optical microcavity prepared according to the present invention; Figure 4 This is the optical whispering-gallery mode transmission spectrum of the bubble-type optical microcavity prepared in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figure 1 , 2 As shown in Figures 3 and 4, the present invention includes: The high-voltage discharge module includes a programmable AC power supply 2 and a high-voltage transformer 3. The input terminal of the programmable AC power supply 2 is connected to AC mains power, and it is connected to a 220V power socket in the figure. The output terminal is electrically connected to the primary coil of the high-voltage transformer 3. The secondary coil of the high-voltage transformer 3 is electrically connected to a pair of discharge tungsten needle electrodes 4 distributed on both sides of the capillary tube. The high-voltage transformer is configured to multiply and boost the low-voltage / medium-voltage AC power received at the primary terminal, and output high-voltage AC power at the secondary terminal that is sufficient to break down the air between the electrodes and form a plasma arc. The air pressure control module includes a precision air pressure pump 5, which is used to apply an adjustable constant air pressure inside the quartz capillary. The visual acquisition module includes a monocular microscope 6 with a CCD camera. The monocular microscope 6 is aligned with the discharge area and is used to acquire dynamic image sequences of capillary thermal expansion in real time. There are at least two monocular microscopes 6, which are arranged vertically and fixed to the output shaft of the manual displacement stage 9, respectively, for adjusting the relative position of the distance from the tungsten needle electrode by the manual displacement stage 9.

[0021] The automatic positioning and fine-tuning module includes a first three-axis manual displacement stage, a second three-axis manual displacement stage, a three-axis electrically controlled displacement stage 7, and a clamp 11 for fixing the quartz capillary. The clamp 11 is fixedly mounted on the three-axis electrically controlled displacement stage 7 to drive the quartz capillary to translate in three-dimensional space. The first three-axis manual displacement stage 9 and the second three-axis manual displacement stage are respectively used to adjust the spacing and alignment between a pair of discharge tungsten needle electrodes. The main control computer is communicatively connected to the programmable AC power supply, the precision air pump, the CCD camera, the first three-axis manual displacement stage, the second three-axis manual displacement stage, and the three-axis electrically controlled displacement stage. The main control computer runs image processing algorithms and closed-loop control programs to analyze the morphological parameters of the bubble microcavities in real time and output control commands to drive the three-axis electrically controlled displacement stage and the programmable AC power supply.

[0022] The turns ratio of the primary coil to the secondary coil of the high-voltage transformer is 1:40.

[0023] The high-voltage transformer is internally sealed and vacuum-cured using epoxy resin potting compound, and its outer shell is made of flame-retardant ABS plastic.

[0024] The programmable AC power supply has a voltage output range of 0-250V and is continuously steplessly adjustable. The programmable AC power supply has built-in timing control logic, and the setting step resolution for the single discharge duration is 1ms, with a setting range of 50ms-200ms for the single discharge duration.

[0025] The precision pneumatic pump outputs a relative pressure range of 0-70 kPa, corresponding to an absolute pressure range of 101-171 kPa, with a pressure accuracy of ±0.5 kPa. It employs high-precision pressure sensing and closed-loop control.

[0026] The monocular microscope uses a 0.75×-5× continuous zoom main unit, with a 0.5×-2× objective lens and a working distance of 30-40mm; the CCD camera has anti-saturation technology, which can continuously and clearly image during arc discharge.

[0027] The single-axis closed-loop positioning accuracy of the three-axis electrically controlled displacement stage is ±1μm, and the minimum single-step movement step size is 0.2μm.

[0028] The quartz capillary is bonded to the fixture with UV-curable adhesive and extends between the two tungsten needles.

[0029] A method for fabricating a bubble-type optical microcavity using the aforementioned device includes the following steps: Step 1, Pre-treatment and loading of quartz capillary tube: First, pre-clean the quartz capillary tube, then seal and fix one end of the cleaned quartz capillary tube on the fixture of the three-axis electric displacement stage, so that the quartz capillary tube is suspended and extended forward between the two discharge tungsten needles, and connect the other end of the quartz capillary tube to the output air circuit of the precision pneumatic pump. Step 2, System Initialization and Automatic Visual Alignment: The main control computer extracts the tip coordinates of the two tungsten discharge needles using an image recognition algorithm, calculates the theoretical center point of the arc thermal field, and drives the three-axis electrically controlled displacement stage to automatically translate the quartz capillary to the center point. Step 3, Constant Pressure Inflation and Initial Discharge Molding: The main control computer sends instructions to the precision air pump to apply and maintain a constant air pressure inside the capillary; at the same time, it controls the programmable AC power supply to output an initial voltage, which breaks down the air between the two discharge tungsten needles through the high-voltage transformer to form an electric arc, causing the quartz capillary to soften and expand initially. Step 4: Spatial position closed-loop compensation and symmetry control based on machine vision: During the capillary discharge expansion process, the main control computer acquires the CCD video stream in real time through the CCD camera, extracts the dynamic contours of the upper and lower sidewalls of the bubble, and calculates the symmetry error of the expansion area; when the symmetry error is greater than the preset tolerance threshold, the main control computer controls the electronically controlled displacement stage to drive the capillary to the side with smaller expansion for step compensation, so that the capillary is always at the center of the electric arc thermal field during the expansion. Step 5: Dynamic degradation of discharge energy and single-cavity shaping: The main control computer dynamically adjusts the output voltage and discharge pulse width of the programmable AC power supply based on the total diameter of the bubble calculated in real time by vision. When the real-time diameter reaches the target diameter, the main control computer cuts off the high-voltage trigger signal, and the bubble-shaped optical microcavity is prepared and cooled and shaped.

[0030] In step four, the main control computer obtains the first expansion radius R1 and the second expansion radius R2 of the bubble through the edge extraction algorithm, and calculates the asymmetry parameter ΔR=R1−R2; when |ΔR| is greater than the preset tolerance threshold, the error is input into the PID position control algorithm to solve the reverse space compensation step size, and drives the three-axis electric control displacement stage to perform micron-level step compensation.

[0031] In step five, when the total diameter of the bubble is less than the set diameter threshold, a high-voltage long pulse mode is adopted, with an output voltage of 165V and a single discharge duration of 150-200ms; when the total diameter of the bubble reaches or exceeds the diameter threshold, a flexible discharge mode is switched to, and the output voltage is reduced to 125V with a single discharge duration of 90-120ms.

[0032] After the single bubble microcavity is shaped, the main control computer drives the electronically controlled displacement stage to move the quartz capillary along its central axis by a preset distance. Then, it returns to step two to repeat the visual alignment, gas discharge and closed-loop compensation on the new unmelted tube section until the preset number of microcavities are processed to obtain a bubble-shaped microcavity array.

[0033] The main control computer controls the stepping translation of the electronically controlled displacement stage according to preset array parameters, and the axial spacing between adjacent microcavities is preset by the user.

[0034] To address the symmetry issue in the fabrication of bubble-type microcavities, this invention presents a bubble-type optical microcavity fabrication device based on machine vision closed-loop control. This device uses a CCD camera to extract the dynamic contour line of the capillary expansion region in real time, calculates the symmetry error, and uses a PID control algorithm to drive an electrically controlled displacement stage carrying the capillary for fine-tuning, ensuring that the capillary remains at the center of the electric arc's dynamic thermal field throughout the expansion process. This invention's core innovation lies in "visual recognition replacing human observation, closed-loop algorithms replacing experience-based judgment, and digital parameters replacing manual adjustment," upgrading the traditional open-loop fabrication process, which relies on operator experience, into an automated closed-loop system with rigorous mathematical logic. Among them, a high-voltage transformer with a turns ratio of 1:40, combined with a programmable power supply with 1ms resolution, precisely maps the fine adjustments made by the host computer to the low-voltage end to the high-voltage discharge end, realizing digital fine control of the arc thermal field intensity; the combination of an anti-saturation CCD and a continuous zoom microscope ensures continuous clear imaging during arc discharge, providing real-time image data unaffected by strong light for closed-loop control; the spatial symmetry closed-loop correction circuit dynamically compensates for the capillary position with micron-level steps, forcing it to always be at the absolute center of the arc thermal field, completely solving the asymmetric distortion of the long axis of the microcavity caused by uneven heating; the energy adaptive control circuit synchronously reduces the discharge intensity as the wall thickness decreases, effectively avoiding tube wall rupture caused by heat overload, ensuring that the finished product quality factor can reach 10. 7 The ±1μm positioning accuracy of the three-axis electrically controlled displacement stage, combined with the fully digital parameters of the programmable power supply, eliminates the sudden mechanical stress changes caused by manual operation and allows all process parameters to be programmatically stored and reproduced, enabling highly consistent batch fabrication of microcavity arrays on a single capillary. This invention achieves a systematic breakthrough in three dimensions: fabrication efficiency, device quality, and batch production consistency, providing a reliable device fabrication solution for cutting-edge applications such as ultra-low concentration gas / biomolecule sensing, narrow linewidth lasers, and quantum optics.

[0035] We have independently designed and built a system for preparing bubble-type optical microcavities using the discharge melting method. The following specific examples will further explain and illustrate the content of this application.

[0036] High-voltage transformer: In terms of working logic and function, this high-voltage transformer is configured to perform distortion-free voltage multiplication and boosting of the low / medium voltage AC power (e.g., 0-250V range) received at the primary end, thereby outputting high-voltage AC power (e.g., up to 8kV) at the secondary end sufficient to break down the air between electrodes and form a stable plasma arc. In a preferred embodiment of the invention, the primary to secondary turns ratio of the high-voltage transformer is set to 1:40. This defined linear boost ratio allows the fine adjustment of the low-voltage output of the programmable power supply by the host computer to be precisely and linearly mapped to the high-voltage discharge end, thereby achieving micron-level smooth control of the arc thermal field intensity.

[0037] In terms of structural design and safety assurance, in order to meet the harsh working conditions of frequent millisecond-level short high-frequency discharges when preparing bubble microcavities, the high-voltage transformer is fully sealed and vacuum-encapsulated with epoxy resin potting compound, and its outer shell is made of flame-retardant ABS plastic material.

[0038] Programmable AC power supply: The high-voltage discharge module includes a programmable AC power supply. The input terminal of the power supply is connected to the standard AC mains power, and the output terminal is connected to the primary coil of the high-voltage transformer. Its communication control interface (such as RS-232 or LAN port) enables bidirectional data communication with the main control computer 10.

[0039] The programmable AC power supply is configured to precisely output an AC voltage with a specific amplitude and pulse width according to digital instructions issued in real time by the main control computer. Specifically, this device undertakes two core control functions in the entire preparation system: (1) High-precision discharge energy (voltage) regulation: The power supply has digital voltage output regulation capability (e.g., continuous stepless adjustment within the range of 0-250V). By adjusting the primary voltage output to the transformer, the thermal field intensity of the arc between the discharge tungsten needles can be precisely controlled.

[0040] (2) Millisecond-level discharge timing (time) control: The power supply has built-in high-precision timing control logic, which can accurately control the conduction and cut-off time of AC output (i.e., single discharge duration, 50ms-200ms range) with a millisecond-level set step size (resolution of 1ms), fundamentally eliminating the contact jitter and delay error of traditional mechanical time relays.

[0041] In the closed-loop fabrication process of this invention, the programmable AC power supply and the vision recognition module of the main control computer constitute a dynamic energy feedback loop. During the initial expansion stage of the bubble microcavity, the main control computer instructs the power supply to output a higher voltage (e.g., 165V) and a longer discharge pulse width (e.g., 150-200ms) to rapidly melt the quartz tube wall. When the vision module detects that the bubble diameter has expanded and the tube wall has thinned, the main control computer sends new program instructions to the power supply in real time, so that it can dynamically and smoothly reduce the output voltage (e.g., to 125V) without interrupting the processing, and switch the discharge mode to short high-frequency discharge (e.g., 70-120ms each time).

[0042] This dynamic multi-segment energy injection method based on programmable AC power not only effectively avoids the rupture of the ultra-thin tube wall caused by excessive discharge time or heat overload, greatly improving the yield of bubble microcavities; at the same time, it realizes the complete digitalization and programmatic reproduction of discharge energy, which is the key electrical guarantee for the system to automatically and consistently prepare "bubble-type microcavity arrays" on a single capillary tube.

[0043] Pressure control module: The adjustable precision air pump can stably output precise air pressure within the relative pressure range of 0-70 kPa, corresponding to an absolute pressure range of 101-171 kPa. The pressure accuracy is ±0.5 kPa, employing high-precision pressure sensing and closed-loop control.

[0044] Visual Acquisition Module: This module includes a monocular microscope with a CCD camera, which is aligned with the arc discharge area to acquire real-time dynamic image sequences of the capillary's thermal expansion. The monocular microscope uses a 0.75X-5X continuous zoom main unit, paired with 0.5X-2X objectives, with a working distance of 30-40mm, obtaining clear magnified images while avoiding contact damage to the lens. The monocular microscope is equipped with a special-condition observation CCD camera, which not only provides clear imaging of the capillary but also features anti-saturation technology, preventing image saturation and blackouts when capturing arc discharges.

[0045] Automatic Positioning and Fine-tuning Module: This module is the core mechanical actuator of the device, consisting of a high-precision three-axis electrically controlled displacement stage, a precision motor, a motor drive controller 8, and a custom-designed fixture for fixing the quartz capillary. This module provides high-degree-of-freedom translational adjustment of the capillary in three-dimensional space. To meet the requirements for fabricating bubble-type microcavities, this module possesses high spatial resolution and smooth motion. Its single-axis closed-loop positioning accuracy can reach ±1µm, and the minimum single-step movement size can be refined to the 0.2µm level. Its smooth acceleration curve eliminates the sudden changes in mechanical stress caused by human hand tremors during traditional manual adjustment, significantly reducing the rupture rate of the bubble's thin wall.

[0046] In its workflow, this module operates in real-time with the main control computer via a communication bus. When the main control computer determines, through visual feature extraction, that there is an asymmetry in the current expansion state of the capillary, it uses a built-in PID algorithm to solve for the spatial position deviation vector and sends a fine-tuning pulse command to the motor drive controller. Upon receiving the command, the displacement stage immediately drives the capillary towards the absolute thermal field center of the discharge arc for dynamic position compensation through its internal precision transmission components.

[0047] Main control computer: Communicates with the vision acquisition module, automatic positioning and fine-tuning module, and high-voltage discharge module. Internally, it runs image processing algorithms and closed-loop control programs to analyze the symmetry of the bubble microcavities in real time and outputs control commands to drive the electrically controlled displacement stage.

[0048] Figure 1 The solid black lines represent high-voltage circuit connections and pneumatic circuit connections; the dashed black lines represent signal line connections.

[0049] A pair of tungsten discharge needles are mounted on two triaxial displacement stages, such as Figure 2As shown, this provides good degrees of freedom for the tungsten needles. The tungsten needles can be easily aligned and the distance between them adjusted using a three-axis displacement stage. The capillary is bonded to a self-made aluminum part with UV-cured adhesive and extends between the two tungsten needles. The capillary is mounted on a precision electrically controlled three-axis displacement stage, allowing for easy adjustment of its position. Because the discharge arc between the tungsten needles is not along the line connecting the two needle tips, the capillary position needs to be adjustable to ensure it is positioned in the middle of the arc.

[0050] The quartz capillary with a polyimide coating is rapidly heated in a heat source (such as the inner flame of an alcohol lamp) to remove the coating and clean it with lens paper, exposing a clean quartz tube section (e.g., with an original diameter of 160 μm). One end of the exposed tube section is bonded and fixed to a custom fixture on a triaxial electrically controlled displacement stage using UV-cured adhesive, allowing the capillary to extend forward between two tungsten discharge needles; the other end of the capillary is connected to the sealed air circuit of a precision pneumatic pump.

[0051] Input the target preparation parameters (e.g., target bubble diameter D) into the control software of the main control computer. target = 320μm, total number of array microcavities N, and axis spacing between adjacent microcavities L). The main control computer activates the microscopic CCD camera and extracts the tip coordinates of the two discharging tungsten needles using an image recognition algorithm to calculate the theoretical center point of the arc thermal field. Subsequently, the main control computer drives a three-axis electrically controlled displacement stage to automatically translate the quartz capillary to this center point.

[0052] The main control computer sends commands to the precision air pump to pressurize and maintain a constant air pressure inside the capillary (e.g., relative atmospheric pressure of 0.67 atm). Subsequently, the main control computer controls the programmable AC power supply to output an initial high voltage (e.g., 165V from the regulator), and through the high-voltage transformer, breaks down the air between the tungsten needles to form an electric arc. At the same time, a relatively long initial discharge pulse time is set (e.g., 150ms-200ms), causing the quartz capillary to soften upon heating and begin to expand initially.

[0053] During the capillary multi-frequency discharge expansion process, the main control computer acquires CCD video streams in real time, uses edge extraction algorithms to obtain the dynamic contours of the upper and lower sidewalls of the bubble, and calculates the first expansion radius R1 and the second expansion radius R2. If the detected symmetry error ΔR=|R1−R2| is greater than the preset tolerance threshold (indicating that the capillary deviates from the absolute center of the arc and is unevenly heated), the PID algorithm in the main control computer responds immediately, controlling the electronically controlled displacement stage to move the capillary towards the side with smaller expansion for micron-level step compensation, forcing the capillary to always be at the absolute center of the dynamic thermal field throughout the entire expansion period.

[0054] As the total diameter of the bubble increases, the bubble wall thickness gradually decreases. Based on the real-time total diameter calculated visually, the main control computer dynamically adjusts the output parameters of the programmable AC power supply: smoothly reducing the driving voltage (e.g., from 165V to 125V to reduce arc intensity) and switching the discharge mode to short pulses (e.g., 90ms-120ms) to prevent the tube wall from rupturing. When the real-time diameter reaches the target diameter (320μm), the main control computer automatically cuts off the high-voltage trigger signal, completing the fabrication and cooling of the single-bubble optical microcavity.

[0055] After the individual bubble microcavities are shaped, the main control computer drives the electrically controlled displacement stage to precisely translate the quartz capillary along its central axis by a preset distance L, according to the set array parameters. After translation, the system automatically returns to step 2 to re-perform visual alignment, gas discharge, and closed-loop compensation on the new unmelted tube segment. The system automatically repeats the above steps until the processing of N microcavities is completed, and finally stops the pneumatic pump and indicates that the preparation is complete, thus obtaining a bubble-shaped microcavity array with precise spacing and highly consistent morphology on a single quartz capillary.

[0056] Furthermore, the main control computer described in this invention is embedded with a self-developed multi-dimensional closed-loop control algorithm. This algorithm uses real-time images acquired by a monocular microscope and CCD camera as input parameters, and through digital feature calculation, simultaneously outputs "spatial position fine-tuning commands" and "electrical discharge adjustment commands," achieving fully automated control of the preparation process. The specific algorithm logic includes the following three core steps: 1. Image preprocessing and real-time calculation of dilation features After each brief discharge, the main control computer acquires the current frame image of the capillary captured by the CCD camera. The algorithm then performs the following processing sequentially: Image binarization and edge extraction: An image contour detection operator is used to identify the upper and lower sidewall boundary lines of the capillary. Baseline construction: Identify the center position of the unexpanded region (the original tube segments at both ends of the capillary) and fit a "center baseline" to generate; Feature parameter calculation: The maximum vertical pixel distance from the left wall of the expansion region to the center baseline is measured (converted to actual physical size, denoted as the first expansion radius R1), and the maximum vertical distance from the right wall to the center baseline is measured (denoted as the second expansion radius R2). The total diameter D of the current bubble microcavity is then calculated in real time. total =R1+R2, and the morphological asymmetry parameter ΔR=R1−R2.

[0057] 2. Spatial symmetry closed-loop correction algorithm (first feedback loop) This control loop aims to force the capillary to always be at the absolute center of the electric arc thermal field, overcoming uneven heating caused by electrode wear or installation errors. The main control computer sets a symmetry tolerance threshold Th. sym (For example, set it to 1.0μm).

[0058] Logical judgment is performed on the asymmetry parameter ΔR calculated in real time: if |ΔR|≤Th sym If the bubble is determined to be uniformly heated and symmetrically expanded, no displacement command is sent; if ΔR > Th sym This indicates that the first side (as above) receives more heat and expands faster. The main control computer immediately inputs the error into the PID position control algorithm, calculates the corresponding reverse spatial compensation step size ΔS, and drives the precision three-axis displacement stage through the motor controller, causing the capillary to move slightly towards the second side (as below) by a corresponding distance. The reverse is also true. Through this closed-loop mechanism of "high-frequency acquisition - digital comparison - motor fine-tuning," the relative spatial coordinates of the capillary and the discharge arc are dynamically corrected in real time.

[0059] 3. Energy Adaptive Dynamic Regulation Algorithm (Second Feedback Loop) As the bubble expands, the tube wall thickness decreases exponentially. Maintaining the initial discharge energy at this point could easily lead to the bubble rupturing instantly or losing its morphology. Therefore, this circuit is based on the real-time total diameter D of the bubble. total To dynamically adjust the output parameters of the programmable AC power supply: Initial shaping stage: when D total Less than the set diameter threshold D threshold When the wall thickness is relatively thick, the main control computer sends a command to the programmable AC power supply to use a high-voltage long pulse mode (such as setting the output voltage to 165V and the single discharge duration to 150-200ms) to quickly melt the quartz material.

[0060] Thinning approximation stage: When the algorithm determines D total ≥D threshold At this time, the main control computer triggers the "flexible discharge mode" and sends a new instruction to the programmable power supply through the communication bus: synchronously reduce the discharge voltage (such as step or linearly reducing it to 125V) and significantly shorten the single discharge time (such as adjusting it to 90-120ms) to perform multi-frequency, low-energy "point discharge".

[0061] Automatic termination determination: When D total To achieve the preset final target diameter D final When the microcavity reaches a depth of 320μm (e.g., 320μm), the main control computer immediately cuts off the output of the programmable AC power supply and shuts down the precision air pump, automatically terminating the preparation process and allowing the microcavity to cool and solidify.

[0062] The aforementioned dual closed-loop control algorithm upgrades the original open-loop fabrication process, which relied on operator visual observation and manual pressure and position adjustments based on experience, into an automated system with rigorous mathematical logic. The first feedback loop (spatial control) completely solves the distortion problem caused by the asymmetry of the long axis of the microcavity; the second feedback loop (energy control) perfectly matches the thermodynamic requirements during the wall thickness reduction process, ultimately achieving a high quality factor (10). 7 High-yield and extremely consistent fabrication of (level) microcavities.

[0063] The bubble-type optical microcavity we fabricated, such as Figure 3 As shown in the figure, the original diameter of the quartz glass capillary is 160 μm. After the above experiment, it can expand to form a bubble-shaped microcavity with a diameter of approximately 320 μm. Furthermore, based on the above experimental method, we can continuously prepare multiple bubble microcavities on the quartz capillary, and the morphology of the microcavities is highly consistent.

[0064] We characterized the optical whispering-gallery mode transmission spectrum of the fabricated microcavity, such as... Figure 4 As shown in (a). Select Figure 4 (a) Lorentz fitting was performed on the peak within the blue dashed box, yielding a full width at half maximum (FWHM) of 0.0019 GHz. Figure 4 As shown in (b). Its quality factor is then obtained as follows: Therefore, it can be seen that the optical microcavities prepared according to the above method can not only produce a series of microcavities with good morphological uniformity, but also achieve an optical whispering-gallery mode quality factor of 10. 7 above.

[0065] In the description of this invention, it should be noted that directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0066] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0067] Note that the above description is merely a preferred embodiment and application of the technical principles of the present invention. 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, 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 specific embodiments described herein, and may include many other effective 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 device for fabricating capillary bubble microcavity arrays based on machine vision closed-loop control, characterized in that: include: The high-voltage discharge module includes a programmable AC power supply and a high-voltage transformer. The input terminal of the programmable AC power supply is connected to AC mains power, and the output terminal is electrically connected to the primary coil of the high-voltage transformer. The secondary coil of the high-voltage transformer is electrically connected to a pair of discharge tungsten needle electrodes distributed on both sides of the capillary tube. The high-voltage transformer is configured to multiply and boost the low-voltage / medium-voltage AC power received at the primary terminal, and output high-voltage AC power at the secondary terminal that is sufficient to break down the air between the electrodes and form a plasma arc. The pneumatic control module includes a precision pneumatic pump for applying an adjustable constant pneumatic pressure inside the quartz capillary. The visual acquisition module includes a monocular microscope with a CCD camera, which is aligned with the discharge area to acquire dynamic image sequences of the capillary thermal expansion in real time. The automatic positioning and fine-tuning module includes a first three-axis manual displacement stage, a second three-axis manual displacement stage, a three-axis electrically controlled displacement stage, and a fixture for fixing the quartz capillary. The fixture is fixedly mounted on the three-axis electrically controlled displacement stage to drive the quartz capillary to translate in three-dimensional space. The first three-axis manual displacement stage and the second three-axis manual displacement stage are respectively used to adjust the spacing and alignment between a pair of discharge tungsten needle electrodes. The main control computer is communicatively connected to the programmable AC power supply, the precision air pump, the CCD camera, the first three-axis manual displacement stage, the second three-axis manual displacement stage, and the three-axis electrically controlled displacement stage. The main control computer runs image processing algorithms and closed-loop control programs to analyze the morphological parameters of the bubble microcavities in real time and output control commands to drive the three-axis electrically controlled displacement stage and the programmable AC power supply.

2. The apparatus for fabricating a bubble-type optical microcavity according to claim 1, characterized in that, The turns ratio of the primary coil to the secondary coil of the high-voltage transformer is 1:

40.

3. The apparatus for fabricating a bubble-type optical microcavity according to claim 1, characterized in that, The programmable AC power supply has a voltage output range of 0-250V and is continuously steplessly adjustable. The programmable AC power supply has built-in timing control logic, and the setting step resolution for the single discharge duration is 1ms, with a setting range of 50ms-200ms for the single discharge duration.

4. The apparatus for fabricating a bubble-type optical microcavity according to claim 1, characterized in that, The precision pneumatic pump outputs a relative pressure range of 0-70 kPa, corresponding to an absolute pressure range of 101-171 kPa, with a pressure accuracy of ±0.5 kPa. It employs high-precision pressure sensing and closed-loop control.

5. The apparatus for fabricating a bubble-type optical microcavity according to claim 1, characterized in that, The monocular microscope uses a 0.75×-5× continuous zoom main unit, with a 0.5×-2× objective lens and a working distance of 30-40mm; the CCD camera has anti-saturation technology, which can continuously and clearly image during arc discharge.

6. The apparatus for fabricating a bubble-type optical microcavity according to claim 1, characterized in that, The single-axis closed-loop positioning accuracy of the three-axis electrically controlled displacement stage is ±1μm, and the minimum single-step movement step size is 0.2μm.

7. A method for fabricating a bubble-type optical microcavity using the apparatus according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1, Pre-treatment and loading of quartz capillary tube: First, pre-clean the quartz capillary tube, then seal and fix one end of the cleaned quartz capillary tube on the fixture of the three-axis electric displacement stage, so that the quartz capillary tube is suspended and extended forward between the two discharge tungsten needles, and connect the other end of the quartz capillary tube to the output air circuit of the precision pneumatic pump. Step 2, System Initialization and Automatic Visual Alignment: The main control computer extracts the tip coordinates of the two tungsten discharge needles using an image recognition algorithm, calculates the theoretical center point of the arc thermal field, and drives the three-axis electrically controlled displacement stage to automatically translate the quartz capillary to the center point. Step 3, Constant Pressure Inflation and Initial Discharge Molding: The main control computer sends instructions to the precision air pump to apply and maintain a constant air pressure inside the capillary; at the same time, it controls the programmable AC power supply to output an initial voltage, which breaks down the air between the two discharge tungsten needles through the high-voltage transformer to form an electric arc, causing the quartz capillary to soften and expand initially. Step 4: Spatial position closed-loop compensation and symmetry control based on machine vision: During the capillary discharge expansion process, the main control computer acquires the CCD video stream in real time through the CCD camera, extracts the dynamic contours of the upper and lower sidewalls of the bubble, and calculates the symmetry error of the expansion area; when the symmetry error is greater than the preset tolerance threshold, the main control computer controls the electronically controlled displacement stage to drive the capillary to the side with smaller expansion for step compensation, so that the capillary is always at the center of the electric arc thermal field during the expansion. Step 5: Dynamic degradation of discharge energy and single-cavity shaping: The main control computer dynamically adjusts the output voltage and discharge pulse width of the programmable AC power supply based on the total diameter of the bubble calculated in real time by vision. When the real-time diameter reaches the target diameter, the main control computer cuts off the high-voltage trigger signal, and the bubble-shaped optical microcavity is prepared and cooled and shaped.

8. The method for preparing a bubble-type optical microcavity according to claim 7, characterized in that, In step four, the main control computer obtains the first expansion radius R1 and the second expansion radius R2 of the bubble through the edge extraction algorithm, and calculates the asymmetry parameter ΔR=R1−R2; when |ΔR| is greater than the preset tolerance threshold, the error is input into the PID position control algorithm to solve the reverse space compensation step size, and drives the three-axis electric control displacement stage to perform micron-level step compensation.

9. The method for preparing a bubble-type optical microcavity according to claim 7, characterized in that, In step five, when the total diameter of the bubble is less than the set diameter threshold, a high-voltage long pulse mode is adopted, with an output voltage of 165V and a single discharge duration of 150-200ms; when the total diameter of the bubble reaches or exceeds the diameter threshold, a flexible discharge mode is switched to, and the output voltage is reduced to 125V with a single discharge duration of 90-120ms.

10. The method for preparing a bubble-type optical microcavity according to claim 7, characterized in that, After the single bubble microcavity is shaped, the main control computer drives the electronically controlled displacement stage to move the quartz capillary along its central axis by a preset distance. Then, it returns to step two and repeats the process on the new unmelted tube segment until the preset number of microcavities are processed to obtain a bubble-type microcavity array.

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