Optical whispering gallery mode resonator, and method for manufacturing and performance adjustment thereof

Abstract

This invention discloses an optical whispering-gallery mode resonator, its fabrication method, and its performance adjustment method. The method includes: forming a thin tubular structure on a capillary and inflating it with gas to form a microbubble cavity; maintaining the internal gas pressure higher than the external pressure, heating and softening the microbubble cavity, and then applying pressure along the axial direction to form a flat microbubble cavity with an equatorial diameter to axial length ratio greater than 1; stretching one side of the microbubble cavity to form a contact probe; and heating and melting the probe tip to seal it, forming a closed cavity. The resonator includes a capillary body, a flat microbubble cavity, a contact probe, and a closed cavity. The performance adjustment method includes: obtaining the current fundamental resonant frequency; determining the target range and sensitivity based on the mechanical properties of the sample to be measured; and changing the stress state of the microbubble cavity wall by adjusting the gas pressure inside the closed cavity to shift the fundamental resonant frequency to a matched set frequency range. This invention solves the problems of low sensitivity and unadjustable performance, achieving high-sensitivity measurement and dynamically adjustable range.

Description

Technical Field

[0001] This invention relates to the field of optical sensing technology, and in particular to an optical whispering-gallery mode resonator, its fabrication method, and its performance tuning method. Background Technology

[0002] Whispering-gallery mode optical microcavities possess high quality factor and extremely small mode volume, making them widely used in the field of micro-mechanical sensing. When external pressure is applied to the microcavity, its resonant spectrum shifts, and high-precision mechanical measurements can be achieved by detecting the shift. To realize pressure measurement of small areas or single points, it is usually necessary to integrate the microcavity with a force transmission structure.

[0003] A typical integration method involves using a carbon dioxide laser to sequentially heat and stretch a quartz capillary, inflate it with gas, and then pull a probe to form a contact probe integrally connected to the microbubble cavity. A waveguide is then coupled to the equatorial plane of the microbubble cavity. During measurement, the contact probe contacts the point being measured, transmitting pressure to the microbubble cavity, causing a change in the equatorial radius and a shift in the resonance peak.

[0004] However, this integration method still has shortcomings. On the one hand, the shape of the microbubble cavity mainly depends on the inflation and expansion, and the ratio of its equatorial diameter to its axial length is limited by the laser spot and the expansion process, making it difficult to obtain a flat structure greater than 1, thus limiting mechanical sensitivity. On the other hand, the microbubble cavity is an open structure, with internal gas pressure balanced with the environment. After fabrication, the sensitivity and range are fixed, and cannot be flexibly adjusted according to the measurement scenario, limiting the applicability of a single device. Summary of the Invention

[0005] This invention provides an optical whispering-gallery mode resonator, its fabrication method, and its performance adjustment method. It solves the problems that optical whispering-gallery mode resonators are difficult to obtain with high mechanical sensitivity due to shape limitations, and that the open structure leads to fixed performance parameters that cannot be flexibly adjusted according to the measurement scenario. By axially compressing the microbubble cavity to form a flat structure, mechanical sensitivity is improved. At the same time, by sealing the end of the probe to form a closed cavity with independently adjustable air pressure, dynamic adjustment of sensitivity and range is achieved.

[0006] This invention provides a method for fabricating an optical whispering-gallery mode resonator, the method comprising: A capillary structure is formed on the capillary, and gas is filled into the capillary structure. The capillary structure is then heated to cause local expansion of the capillary structure, forming a microbubble cavity. After the microbubble cavity is formed, the internal air pressure of the microbubble cavity is kept higher than that of the outside, and the microbubble cavity is softened by heating. At the same time, pressure is applied along the axial direction of the microbubble cavity to form a flat microbubble cavity with a ratio of equatorial plane diameter to axial length greater than 1. A contact probe is formed by stretching one side of the flat microbubble cavity; The end of the contact probe is heated to melt and seal it, forming a closed cavity.

[0007] Optionally, the step of applying pressure along the axial direction of the microbubble cavity includes: Real-time monitoring of the deformation morphology of the microbubble cavity; If axial tilting of the microbubble cavity is detected, the pressure-applying component is controlled to retract in the opposite direction to release stress. After the microbubble cavity regains its coaxiality, the axial pressure action is performed again until a flat microbubble cavity is formed.

[0008] Optionally, the step of applying pressure along the axial direction of the microbubble cavity further includes: Control the pressure application rate to match the deformation rate of the microbubble cavity with the viscous flow rate of the material; During the extrusion process, the pressure rate is dynamically adjusted according to the thinning rate of the microbubble cavity wall to prevent the microbubble cavity wall from rupturing due to stress concentration.

[0009] Optionally, the step of maintaining the internal pressure of the microbubble cavity higher than that of the external environment includes: Gas is introduced into the microbubble cavity, and the stress state of the microbubble cavity wall is monitored in real time; The inflation flow rate is dynamically adjusted based on the monitoring results to maintain the internal air pressure within the critical support pressure range that can support the microbubble cavity wall from collapsing.

[0010] Optionally, prior to the step of heating the tip of the contact probe, the following steps are included: The stretching equipment is controlled to stretch the capillary tubes after they have formed flat microbubble cavities; Real-time monitoring of the probe length formed by stretching; The extension stops when the probe length reaches a preset safe distance to prevent the heat-affected zone during end heating and sealing from affecting the microbubble cavity structure.

[0011] Furthermore, to achieve the above objectives, embodiments of the present invention also provide an optical whispering-gallery mode resonator, the optical whispering-gallery mode resonator comprising: Capillary body; A flat microbubble cavity is disposed on the capillary body, and the ratio of its equatorial diameter to its axial length is greater than 1; A contact probe is located at one end of the capillary body and is formed by stretching the capillary. The enclosed cavity, formed by the melting and shrinking of the end of the contact probe, is used to encapsulate the internal gas.

[0012] Furthermore, to achieve the above objectives, embodiments of the present invention also provide a method for adjusting the performance of an optical whispering-gallery mode resonator, the method comprising: Obtain the fundamental resonant frequency of the optical whispering-gallery mode resonator in the current state; Based on the mechanical properties of the sample to be tested, determine the required target range and sensitivity; By adjusting the air pressure inside the closed cavity, the stress state of the microbubble cavity wall is changed, causing the fundamental resonant frequency to shift to a set frequency range that matches the target range and sensitivity.

[0013] Optionally, the step of changing the stress state of the microbubble cavity wall by adjusting the air pressure inside the closed cavity includes: The capillary body is punctured using a microneedle; The gas is injected into or extracted from the closed cavity through the microneedles to change the pre-tightening force of the microbubble cavity wall. Remove the microneedles and seal the puncture site to alter the stress state of the microbubble cavity wall.

[0014] Optionally, the step of changing the stress state of the microbubble cavity wall by adjusting the air pressure inside the closed cavity includes: Connect one side of the capillary body to an external air pressure regulating device; The preload of the microbubble cavity is changed by injecting gas into or extracting gas from the closed cavity through the external air pressure regulating device. The air pressure inside the sealed cavity is monitored in real time until the target air pressure is reached.

[0015] Optionally, before the step of adjusting the air pressure within the sealed cavity, the method further includes: Obtain the estimated hardness range of the sample to be tested; The standard sample is tested, and the current air pressure in the closed cavity is determined to match the estimated hardness range based on the resonant peak shift of the test results. If there is a mismatch, the air pressure inside the sealed cavity is adjusted until the resonant peak offset falls within the preset threshold range.

[0016] Optionally, after the step of shifting the fundamental resonant frequency to a set frequency range matching the target range and sensitivity, the method further includes: During continuous measurement, if the detected resonant peak shift exceeds the linear response range of the detection device, the internal air pressure is increased to reduce the sensitivity and expand the range, so that the resonant peak returns to the linear response range.

[0017] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. By axially extruding, a flat microbubble cavity with a ratio of equatorial diameter to axial length greater than 1 is formed. Under the same axial pressure, the change in equatorial radius is greater and the resonant peak shift is more significant, thereby greatly improving the device's sensitivity to the measurement of minute forces and displacements.

[0018] 2. By melting and sealing the end of the contact probe to form an independent closed cavity, the internal air pressure can be independently adjusted, thereby changing the pre-tightening force of the microbubble cavity wall. This allows the same device to dynamically switch between high sensitivity-small range and low sensitivity-large range modes, adapting to materials of different hardness and measurement scenarios.

[0019] 3. By adopting process measures such as coaxiality correction, dynamic speed matching, and safety probe length control, the microbubble cavity is effectively prevented from tilting, stress rupture, and thermal impact damage, ensuring the symmetry and surface quality of the microbubble cavity, and improving product consistency and optical resonance stability. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the fabrication method of the optical whispering-gallery mode resonator of the present invention; Figure 2 This is a schematic diagram of the optical whispering-gallery mode resonator of the present invention; Figure 3 This is a flowchart illustrating the performance adjustment method of the optical whispering-gallery mode resonator of the present invention. Detailed Implementation

[0021] To address the limitations of current optical whispering-gallery mode resonators in achieving high mechanical sensitivity due to the restricted microbubble shape, and the fixed performance parameters resulting from their open structure, which cannot be flexibly adjusted according to the measurement scenario, this invention first applies axial pressure to the microbubble after its formation, shaping it into a flat microbubble with an equatorial diameter-to-axial length ratio greater than 1. This results in a larger equatorial deformation under the same axial pressure, significantly improving mechanical sensitivity. Simultaneously, the contact probe tip is melt-sealed, forming a closed cavity with independently adjustable internal gas pressure. By changing the gas pressure within the closed cavity, the stress state of the microbubble cavity wall is altered, achieving dynamic adjustment of mechanical sensitivity and measurement range. This approach not only gives the resonator higher pressure measurement sensitivity but also endows a single device with the ability to flexibly switch between high-sensitivity-small-range and low-sensitivity-large-range modes in different measurement scenarios, significantly expanding its applicability.

[0022] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0023] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0024] Example 1 In this embodiment, a method for fabricating an optical whispering-gallery mode resonator is provided. The method involves heating, stretching, inflating, expanding, extruding, and sealing the end of a capillary tube to form an optical whispering-gallery mode resonator with a flat microbubble cavity and a closed cavity.

[0025] Reference Figure 1 The fabrication method of the optical whispering-gallery mode resonator in this embodiment includes the following steps: Step S1: Form a capillary structure on the capillary and fill the capillary structure with gas. Heat the capillary structure to cause local expansion and form microbubble cavities. In this embodiment, the capillary refers to a glass tube open at both ends. Quartz glass is preferred in this embodiment due to its high heat resistance and chemical stability. The microbubble cavity refers to a cavity structure formed by locally heating and softening the thin tube structure, then expanding it outwards through internal air pressure. Its smooth inner wall allows for continuous total internal reflection of light signals near the equatorial plane, i.e., the whispering gallery mode.

[0026] For example, the two ends of a quartz capillary are fixed to two three-dimensional displacement platforms. The spot of a carbon dioxide laser is adjusted to focus on a predetermined position on the capillary. The laser is turned on to locally heat the capillary to a softened state. Then, the two displacement platforms are controlled to move in opposite directions along the axial direction, thinning the softened area to form a thin tube structure. The laser is then turned off. A gas source is connected to one end of the capillary to fill it with gas. The laser spot is moved to another predetermined position on the thin tube structure, and the laser is turned on again to locally heat and soften that position. Simultaneously, the internal gas expands due to heat, expanding the softened area outward to form a microbubble cavity. The laser is then turned off, and the capillary is allowed to cool and solidify naturally.

[0027] Step S2: After the microbubble cavity is formed, the internal air pressure of the microbubble cavity is kept higher than that of the outside, and the microbubble cavity is softened by heating. At the same time, pressure is applied along the axial direction of the microbubble cavity to form a flat microbubble cavity with a ratio of equatorial plane diameter to axial length greater than 1. In this embodiment, a ratio of equatorial diameter to axial length greater than 1 means that, assuming L is the axial length of the microbubble cavity and D is the equatorial diameter (i.e., the diameter of the largest cross-section perpendicular to the axis), D / L > 1 indicates that the microbubble cavity is oblate or disc-shaped. (Refer to...) Figure 2 This flat shape allows axial pressure to be converted more efficiently into radial expansion of the equatorial surface, thereby improving mechanical sensitivity.

[0028] As an optional implementation, after the microbubble cavity is formed, the internal gas pressure is maintained higher than the external pressure, for example, 0.15-0.20 MPa. The microbubble cavity is reheated to a softened state using a laser, and two displacement platforms are controlled to move slowly towards each other to apply axial pressure to the microbubble cavity. The shortening of its axial length and the increase of its equatorial diameter are observed. When the ratio of the equatorial diameter to the axial length reaches a target value greater than 1, the pressure is stopped, and the gas pressure is maintained until it cools and solidifies.

[0029] Optionally, this embodiment does not limit the heating method of capillary, thin tube structure, microbubble cavity or contact probe. Any heat source that can locally soften quartz or glass material can be used, such as carbon dioxide laser, oxyhydrogen flame, electric heating wire, infrared lamp focusing heating, resistance hot plate contact heating, etc. The appropriate heat source can be selected according to the equipment conditions and process requirements.

[0030] As an optional implementation, the deformation morphology of the microbubble cavity is monitored in real time when pressure is applied along its axial direction. If axial tilting of the microbubble cavity is detected, the pressure-applying component is controlled to retract in the opposite direction to release stress. After the microbubble cavity regains its coaxiality, the axial pressure application is repeated until a flat microbubble cavity is formed. Controlling the retraction of the pressure-applying component in the opposite direction refers to moving the displacement platform in the opposite direction to release the compressive stress, allowing the microbubble cavity to automatically regain its coaxiality under its own surface tension. Through tilt monitoring and stress release, the coaxiality of the flat microbubble cavity and the capillary body is ensured, avoiding resonance peak broadening, deterioration of optical performance, and inconsistent response under pressure in different directions due to tilting. The flat microbubble cavity refers to a microbubble cavity with an equatorial diameter to axial length ratio greater than 1, an angle less than 1° between the axis of the microbubble cavity and the axis of the capillary body, no obvious tilting, symmetrical shape, uniform wall thickness, and no obvious surface defects.

[0031] For example, during the extrusion process, a vision system equipped with a microscope is used to observe the contours of the microbubble cavities in real time. If the angle between the microbubble cavity axis and the capillary axis exceeds a preset angle threshold, such as 5°, the pressure is stopped, and the two displacement platforms are moved in opposite directions a small distance, such as 2–5 μm, to release stress. The microbubble cavities gradually return to coaxiality under the action of surface tension. The pressure direction is then adjusted, for example, by fine-tuning the lateral position of the displacement platforms, and extrusion is restarted. The above monitoring and correction operations are repeated until a regular, flat microbubble cavity with an axial deviation angle of less than 1° is obtained.

[0032] As another optional implementation, when applying pressure along the axial direction of the microbubble cavity, the pressure application rate also needs to be controlled to match the deformation rate of the microbubble cavity with the viscous flow rate of the material. During the extrusion process, the pressure application rate is dynamically adjusted according to the thinning rate of the microbubble cavity wall to prevent the microbubble cavity wall from rupturing due to stress concentration. By dynamically matching the deformation rate with the viscous flow rate of the material, stress concentration caused by excessively rapid deformation is avoided, thereby preventing the microbubble cavity wall from rupturing and improving the yield and structural consistency of the prepared product.

[0033] Optionally, the thickness of the microbubble cavity wall is measured in real time during extrusion, for example, by optical coherence tomography or a microscope scale. The extrusion speed is dynamically adjusted according to the wall thickness change. A slightly faster speed is possible when the initial wall thickness is thicker, but it should not exceed 10 μm / s. As the wall thickness decreases, the speed is gradually reduced, such as to 5 μm / s, 2 μm / s, and 1 μm / s. This keeps the wall thickness reduction rate within the range that the material's viscous flow can withstand, avoiding the formation of microcracks or localized ruptures.

[0034] As an optional implementation, during the extrusion process, the internal air pressure of the microbubble cavity should be maintained higher than that of the external environment. When gas is introduced into the microbubble cavity, the stress state of the cavity wall is monitored in real time, and the inflation flow rate is dynamically adjusted based on the monitoring results to maintain the internal air pressure within a critical support pressure range that can prevent the microbubble cavity wall from collapsing. The stress state refers to the stress condition of the microbubble cavity wall under the combined action of the internal and external pressure difference and the external extrusion force, which can be indirectly monitored through changes in wall curvature or internal pressure sensors.

[0035] Optionally, the critical support pressure range can be set to 150-200 kPa. Within this pressure range, the microbubble cavity wall will not collapse inward due to excessively low pressure, nor will it expand excessively outward or rupture due to excessively high pressure.

[0036] Step S3: Stretch one side of the flat microbubble cavity to form a contact probe; In this embodiment, a predetermined position on the capillary located on one side of the microbubble cavity is softened by heating, and then stretched axially to narrow and eventually separate at that position, forming a slender needle-like structure with one end connected to the microbubble cavity and the other end free. A contact probe is used to directly contact the target point, transmitting axial pressure to the microbubble cavity as a mechanical transmission component. Its axis should be perpendicular to the equatorial plane of the microbubble cavity to ensure that the pressure direction is consistent with the sensitive direction. The contact probe enables point-contact mechanical loading, efficiently transmitting external pressure to the sensitive area of ​​the microbubble cavity while avoiding positioning errors caused by surface contact.

[0037] As an alternative implementation, the laser spot is moved to a thin tubular structure on one side of the flat microbubble cavity and heated to a softened state. Then, the two displacement platforms are controlled to move in opposite directions along the axial direction, or one displacement platform moves away from the other displacement platform along the axial direction, stretching and thinning the softened area until it breaks naturally, forming a contact probe with one end connected to the microbubble cavity and the other end being a free end.

[0038] Optionally, before forming the contact probe, a stretching device can be used to stretch the thin tubular structure on one side of the flat microbubble cavity to a preset safe length, such as ≥250μm. Then, the stretched thin tubular structure is heated and melted to form a long probe of sufficient length. This method ensures that the probe length meets the safe distance requirement before melting, facilitating the removal of the heat-affected zone from the microbubble cavity during subsequent end-sealing operations.

[0039] Optionally, after forming the contact probe and before forming the closed cavity, the capillary after forming the flat microbubble cavity is stretched by controlling the stretching device; the length of the probe formed by stretching is monitored in real time; when the length of the probe reaches a preset safe distance, the stretching is stopped to prevent the heat-affected zone when the end is heated and sealed from affecting the microbubble cavity structure.

[0040] Optionally, the preset safety distance refers to a probe length that is large enough to prevent the heat-affected zone from extending into the microbubble cavity during subsequent end-heat sealing. It should be noted that during the heating and sealing process, the probe gradually shortens towards the microbubble side, the laser irradiation point needs to be adjusted accordingly, and the through-hole at the probe end does not close immediately but requires continuous heating. Therefore, to ensure complete probe sealing and prevent the heat-affected zone from affecting the microbubble cavity, a relatively long length is required to cope with this shortening effect. In this embodiment, the preset safety distance can be set to 250 μm or longer, ensuring that the length of the contact probe is greater than or equal to 250 μm. After end-heat sealing, the probe length is generally shortened to 30-50 μm, and the end diameter is larger than the diameter before sealing.

[0041] Step S4: Heat the end of the contact probe to melt and seal it, forming a closed cavity.

[0042] In this embodiment, the microbubble cavity, which was originally open to the outside world, is transformed into a closed system, allowing the internal air pressure to be adjusted independently, thus providing a structural basis for subsequent performance regulation. By changing the air pressure inside the closed cavity, the preload of the microbubble cavity can be altered, thereby adjusting the mechanical response characteristics of the device.

[0043] As an alternative implementation, a laser spot is focused on the end of the contact probe and heated with appropriate power to melt the end material. Under the action of surface tension, the molten glass contracts towards the center, ultimately completely sealing the through-hole inside the probe. The laser is then turned off, and natural cooling forms a closed cavity.

[0044] In this embodiment, after inflating and expanding to form a microbubble cavity, an axial extrusion step yields a flat structure with an equatorial diameter to axial length ratio greater than 1, thereby improving mechanical sensitivity. The contact probe tip is melt-sealed to form a closed cavity with independently adjustable internal pressure, providing a basis for dynamic adjustment of sensitivity and range. Furthermore, real-time monitoring and coaxiality correction prevent microbubble cavity skew, ensuring consistency between optical performance and measurement. Controlling the pressure application rate to match the material's viscous flow and dynamically adjusting it according to wall thickness prevents rupture and improves yield. Dynamically maintaining the internal pressure within the critical support pressure range ensures stable extrusion. A probe safety length of ≥250μm is reserved to prevent heat-affected zone damage to the microbubble cavity during end-heating and sealing. These measures enable the fabricated optical whispering-gallery mode resonator to possess high sensitivity, adjustable performance, and good structural regularity.

[0045] Based on the same inventive concept, this invention also provides an optical whispering-gallery mode resonator corresponding to the method in Embodiment 1, as shown in Embodiment 2.

[0046] Example 2 This embodiment provides an optical whispering-gallery mode resonator, which includes: Capillary body 1; A flat microbubble cavity 2 is disposed on the capillary body, and the ratio of its equatorial diameter to its axial length is greater than 1; In this embodiment, the flattened microbubble cavity is located on the enlarged structure of the capillary body, with an equatorial diameter to axial length ratio greater than 1, i.e., it is oblate or disc-shaped. This shape can be obtained through the extrusion step in Embodiment 1. The flattened structure exhibits greater radial deformation of the equatorial surface under axial pressure, thereby improving mechanical sensitivity.

[0047] Contact probe 3 is located at one end of the capillary body and is formed by stretching the capillary. In this embodiment, the contact probe is an elongated needle-like structure extending from one end of the capillary body, integrally connected to the flat microbubble cavity, and formed by stretching the capillary material. Its axis is perpendicular to the equatorial plane of the microbubble cavity, and its end is sharp or blunt, used to contact the target point being measured and transmit axial pressure to the microbubble cavity.

[0048] The enclosed cavity, formed by the melting and shrinking of the end of the contact probe, is used to encapsulate the internal gas.

[0049] In this embodiment, the sealed cavity is formed by the material shrinking and sealing the internal through-holes under the action of surface tension after being melted by laser heating at the end of the contact probe. This sealed cavity is connected to the microbubble cavity and contains a certain pressure of gas, isolating it from the outside atmosphere, so that the internal gas pressure can be adjusted independently.

[0050] The entire optical whispering-gallery mode resonator is an integrated structure consisting of a capillary body, a flat microbubble cavity, and a contact probe. The waveguide can be coupled to the equatorial circumference of the microbubble cavity for input optical signals and output resonant spectra. Since the equatorial wall thickness of the microbubble cavity is the smallest, this region experiences the greatest deformation under stress, thus causing a shift in the resonant peak.

[0051] Optionally, when a flat microbubble cavity is subjected to axial pressure transmitted by a contact probe, the radial expansion of the equatorial surface is greater than that of a spherical microbubble cavity, resulting in a more significant shift in the resonant wavelength of the whispering-gallery mode, thereby achieving higher mechanical sensitivity.

[0052] Optionally, the sealed cavity allows for independent adjustment of the internal air pressure. When the air pressure changes, the preload of the microbubble cavity wall changes accordingly. When the air pressure increases, the internal gas exerts more pressure on the inner wall, resulting in smaller deformation of the cavity wall under the same external force. When the air pressure decreases, the pressure on the inner wall weakens, and under the same external force, the microbubble experiences less resistance from the internal gas molecules during deformation, thus allowing for greater deformation. Therefore, by adjusting the internal air pressure, dynamic switching of sensitivity and measurement range can be achieved to adapt to different measurement scenarios.

[0053] Optionally, the needle-like structure of the contact probe can achieve precise loading of a single point on the target being tested, avoiding positional errors caused by surface contact.

[0054] Exemplarily, the optical whispering-gallery mode resonator prepared by the method described in Example 1 is a specific implementation of this embodiment. The capillary body, the flat microbubble cavity, the contact probe, and the sealed cavity are all integrally formed. The outer diameter of the capillary body can be 100-200 μm, the equatorial diameter of the flat microbubble cavity can be 100-300 μm, the axial length can be 30-100 μm, the contact probe length is 30-50 μm, the contact probe tip diameter is 1-10 μm, and the encapsulated gas in the sealed cavity is at atmospheric pressure or a preset pressure of 100-200 kPa. The above dimensions are merely examples, and the scope of protection of this invention is not limited to these specific values.

[0055] Optionally, when the contact probe is subjected to axial pressure, the pressure is transmitted to the flat microbubble cavity. Since the ratio of the equatorial diameter to the axial length is greater than 1, the microbubble cavity is more prone to deformation under axial pressure, resulting in a larger change in the equatorial radius. According to the whispering-gallery mode resonance principle, the shift of the resonance peak is positively correlated with the change in the equatorial radius; therefore, the greater the change in the equatorial radius, the higher the mechanical sensitivity.

[0056] The optical whispering-gallery mode resonator provided in this embodiment utilizes a flat microbubble cavity with an equatorial diameter-to-axial length ratio greater than 1, which enhances the measurement sensitivity of axial pressure. Simultaneously, the adjustable air pressure structure of the closed cavity enables flexible switching between high sensitivity and small measurement range for a single device, and low sensitivity and large measurement range for the same measurement range. A contact probe ensures high spatial resolution point-contact measurement. This resonator features a compact structure, high sensitivity, adjustable range, and good measurement direction consistency, and can be widely used in fields such as micromechanical probing, material surface mechanical characterization, biological tissue hardness testing, and precision displacement sensing.

[0057] Example 3 Based on the optical whispering-gallery mode resonator of Embodiment 2, this embodiment provides a method for adjusting the performance of the optical whispering-gallery mode resonator by adjusting its internal air pressure to change its mechanical sensitivity and range. The method includes: Step S5: Obtain the fundamental resonant frequency of the optical whispering-gallery mode resonator in the current state; In this embodiment, the fundamental resonant frequency refers to the resonant wavelength corresponding to a certain whispering-gallery mode of the microbubble cavity under the current internal air pressure, which is directly related to the equatorial radius of the microbubble cavity under the current stress state.

[0058] Optionally, the optical whispering-gallery mode resonator is connected to an optical measurement system. A scanning laser is input through a waveguide, and the output optical signal is acquired to obtain the resonance spectrum. A characteristic resonance peak is identified in the spectrum, and its center wavelength or frequency is recorded, which is the current fundamental resonant frequency. During subsequent performance adjustment, the degree of adjustment can be quantitatively controlled by comparing the frequency offset before and after adjustment.

[0059] For example, the waveguide input of an optical whispering-gallery mode resonator is connected to a tunable laser, and the output is connected to a detection device, such as a spectrometer. The tunable laser is controlled to scan within a desired wavelength range, and the spectrometer simultaneously acquires the output light intensity. In the acquired spectrum, the resonant peak with the maximum extinction ratio is identified, and its center wavelength is recorded. This center wavelength is the fundamental resonant frequency in the current state.

[0060] Optionally, before obtaining the fundamental resonant frequency, a standard sample can be used for testing to assess whether the current air pressure is suitable for the hardness range of the sample to be tested. Specifically, the estimated hardness range of the sample to be tested is obtained; the standard sample is tested, and the current air pressure in the closed cavity is determined based on the resonant peak shift in the test results to determine whether it matches the estimated hardness range; if it does not match, the air pressure in the closed cavity is adjusted until the resonant peak shift falls within a preset threshold range. The preset threshold range can be set according to the resolution of the detection equipment and the actual measurement accuracy requirements; within this range, the measurement accuracy and range can meet the testing requirements. This pre-calibration method ensures that the current air pressure matches the hardness range of the sample to be tested, improving measurement accuracy.

[0061] For example, the hardness range of the sample to be tested is estimated based on its material type. A standard sample with similar hardness is selected, and a contact probe is pressed with the same force, recording the resonant peak shift. This shift is compared with a preset reasonable threshold range. If the shift is small, it indicates that the current air pressure is too high, resulting in insufficient sensitivity; if the shift is large, it indicates that the air pressure is too low, resulting in excessive sensitivity. The internal air pressure is adjusted using a microneedle or similar method, and the standard sample is tested repeatedly until the shift falls within the preset threshold range. The air pressure at this point is the matching air pressure suitable for the hardness range of the sample to be tested. Alternatively, the internal air pressure can be adjusted using a microneedle or an external air pressure regulating device, and the standard sample can be tested repeatedly until the shift falls within the preset threshold range.

[0062] Step S6: Determine the required target range and sensitivity based on the mechanical properties of the sample to be tested; In this embodiment, the mechanical properties of the sample under test include the estimated hardness, elastic modulus, and expected maximum pressure or displacement range. The target range refers to the maximum pressure or displacement value that the sensor can measure; a large range is suitable for hard materials or high-force measurements, while a small range is suitable for soft materials or low-force measurements. Sensitivity refers to the sensor's ability to resolve minute pressure or displacement changes. High sensitivity is suitable for detecting minute rates of change, while low sensitivity is suitable for detecting large changes. Based on the mechanical properties of the sample under test, the required sensitivity and range for the current measurement are determined, allowing the operator to purposefully select the performance mode and avoid blind adjustments.

[0063] For example, if the sample to be tested is a soft material, such as biological tissue, gel, or rubber, then high sensitivity and a small measurement range are required; therefore, the target mode is high sensitivity with a small measurement range. If the sample to be tested is a hard material, such as metal, ceramic, or glass, then a large measurement range and lower sensitivity are required; therefore, the target mode is low sensitivity with a large measurement range.

[0064] Step S7: By adjusting the air pressure inside the closed cavity, the stress state of the microbubble cavity wall is changed, so that the fundamental resonant frequency is shifted to the set frequency range that matches the target range and sensitivity.

[0065] In this embodiment, the stress state of the microbubble cavity wall refers to the pre-tightening force or initial stress of the microbubble cavity wall. The lower the internal air pressure, the softer the wall surface; the higher the internal air pressure, the harder the wall surface. The set frequency range corresponds to a resonant frequency interval of the target range and sensitivity. This can be obtained through pre-calibration, for example, in high-sensitivity mode, the resonant frequency has a positive or negative offset relative to the fundamental frequency.

[0066] As an alternative implementation, when adjusting the gas pressure inside the closed cavity, a microneedle can be used to puncture the end of the contact probe or the capillary body; gas can be injected into or extracted from the closed cavity through the microneedle to change the pre-tightening force of the microbubble cavity wall; the microneedle can be removed and the puncture point can be sealed to change the stress state of the microbubble cavity wall.

[0067] For example, a microneedle with a tip diameter of 5 μm is held in place using a micromanipulator and slowly inserted under a microscope into the tip of a contact probe or the capillary body wall, entering the sealed cavity. A certain volume of gas is injected or withdrawn as needed using a microsyringe connected to the microneedle. For example, 0.1–0.5 μL of air is withdrawn to reduce the pressure, and an equal volume of gas is injected to increase the pressure. After removing the microneedle, the puncture point is sealed to restore the seal. The resonant frequency is then remeasured until it is confirmed to have shifted within the set frequency range.

[0068] As an alternative implementation, when adjusting the air pressure within the sealed cavity, one side of the capillary tube can be connected to an external air pressure regulating device via an air tube. The external air pressure regulating device includes an air pump, gas cylinder, or vacuum pump, etc. Gas is injected into or extracted from the sealed cavity through this external air pressure regulating device, while a pressure monitoring meter connected to the air circuit reads the internal air pressure value in real time until the desired target air pressure is reached, at which point the valve is closed and the connection is disconnected. This method is suitable for scenarios requiring repeated adjustments or batch testing, enabling faster and more precise air pressure control.

[0069] Optionally, after adjusting the air pressure within the sealed cavity, if the resonant peak shift exceeds the linear response range of the detection device during continuous measurement, the internal air pressure is increased to reduce sensitivity and expand the measurement range, bringing the resonant peak back into the linear response range. Specifically, if the shift is found to be close to the upper limit of the spectrometer's linear response during continuous measurement, it indicates that the current sensitivity is too high and the measurement range is insufficient. At this point, the measurement is paused, and the internal air pressure is increased using a microneedle or an external air pressure adjustment device to reduce sensitivity, expand the measurement range, and bring the resonant peak shift back into the linear range before continuing the measurement. By dynamically adjusting the measurement range during the measurement process, measurement interruptions due to signal saturation are avoided.

[0070] Alternatively, the testing equipment can be a spectrometer, oscilloscope, spectrum analyzer, or other testing devices.

[0071] The performance adjustment method in this embodiment achieves flexible switching between high sensitivity and small measurement range for the optical whispering-gallery mode resonator and low sensitivity and large measurement range by changing the air pressure inside the sealed cavity. The pre-calibration step ensures that the current air pressure matches the hardness of the sample under test, and the dynamic adjustment step avoids signal saturation during the measurement process. Ultimately, this allows a single device to adapt to various measurement scenarios, from soft to hard, and from micro-force to high-force.

[0072] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0074] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0075] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0076] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, third, etc., does not indicate any order. These words can be interpreted as names.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method of fabricating an optical whispering gallery mode resonator, characterized by, The preparation method includes: A capillary structure is formed on the capillary, and gas is filled into the capillary structure. The capillary structure is then heated to cause local expansion of the capillary structure, forming a microbubble cavity. After the microbubble cavity is formed, the internal air pressure of the microbubble cavity is kept higher than that of the outside, and the microbubble cavity is softened by heating. At the same time, pressure is applied along the axial direction of the microbubble cavity to form a flat microbubble cavity with a ratio of equatorial plane diameter to axial length greater than 1. During the process of applying pressure along the axial direction of the microbubble cavity, the deformation of the microbubble cavity is monitored in real time. If axial tilting of the microbubble cavity is detected, the pressure-applying component is controlled to retract in the opposite direction to release stress. After the microbubble cavity returns to coaxiality, the axial pressure application is performed again. Furthermore, when gas is filled into the microbubble cavity, the stress state of the microbubble cavity wall is monitored in real time, and the gas flow rate is dynamically adjusted according to the monitoring results to maintain the internal gas pressure within the critical support pressure range that can support the microbubble cavity wall from collapsing. A contact probe is formed by stretching one side of the flat microbubble cavity; The end of the contact probe is heated to melt and seal it, forming a closed cavity; Prior to the step of heating the tip of the contact probe, the following steps are included: The stretching equipment is controlled to stretch the capillary tubes after they have formed flat microbubble cavities; Real-time monitoring of the probe length formed by stretching; The extension stops when the probe length reaches a preset safe distance to prevent the heat-affected zone during end heating and sealing from affecting the microbubble cavity structure.

2. The production method according to claim 1, wherein The step of applying pressure along the axial direction of the microbubble cavity further includes: Control the pressure application rate to match the deformation rate of the microbubble cavity with the viscous flow rate of the material; During the extrusion process, the pressure rate is dynamically adjusted according to the thinning rate of the microbubble cavity wall to prevent the microbubble cavity wall from rupturing due to stress concentration.

3. An optical whispering gallery mode resonator, characterized by The optical whispering-gallery mode resonator, prepared using the method described in claim 1 or 2, comprises: Capillary body; A flat microbubble cavity is disposed on the capillary body, and the ratio of its equatorial diameter to its axial length is greater than 1; A contact probe is located at one end of the capillary body and is formed by stretching the capillary. The enclosed cavity, formed by the melting and shrinking of the end of the contact probe, is used to encapsulate the internal gas.

4. A method of performance adjustment of an optical whispering gallery mode resonator according to claim 3, characterized by The performance tuning method includes: Obtain the fundamental resonant frequency of the optical whispering-gallery mode resonator in the current state; Based on the mechanical properties of the sample to be tested, determine the required target range and sensitivity; By adjusting the air pressure inside the closed cavity, the stress state of the microbubble cavity wall is changed, causing the fundamental resonant frequency to shift to a set frequency range that matches the target range and sensitivity.

5. The performance adjustment method as described in claim 4, characterized in that, The step of changing the stress state of the microbubble cavity wall by adjusting the air pressure inside the closed cavity includes: Connect one side of the capillary body to an external air pressure regulating device; The preload of the microbubble cavity is changed by injecting gas into or extracting gas from the closed cavity through the external air pressure regulating device. The air pressure inside the sealed cavity is monitored in real time until the target air pressure is reached.

6. The performance adjustment method as described in claim 5, characterized in that, Before the step of adjusting the air pressure inside the sealed cavity, the method further includes: Obtain the estimated hardness range of the sample to be tested; The standard sample is tested, and the current air pressure in the closed cavity is determined to match the estimated hardness range based on the resonant peak shift of the test results. If there is a mismatch, the air pressure inside the sealed cavity is adjusted until the resonant peak offset falls within the preset threshold range.

7. The performance adjustment method as described in claim 5, characterized in that, After the step of shifting the fundamental resonant frequency to a set frequency range that matches the target range and sensitivity, the method includes: During continuous measurement, if the detected resonant peak shift exceeds the linear response range of the detection device, the internal air pressure is increased to reduce the sensitivity and expand the range, so that the resonant peak returns to the linear response range.

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