Echo-wall mode resonator laser refrigeration system and working method thereof

Abstract

The application sets a temperature measurement channel and a feedback control loop based on echo wall mode resonance drift by introducing refrigeration pumping light and different wavelength detection light in the same rare earth doped crystal disc-shaped echo wall mode resonant cavity, so that the resonant cavity realizes bulk optical refrigeration, and achieves the effects of non-contact, high-sensitivity temperature measurement and stable closed-loop control. Compared with the prior art, the method has the advantages of compact structure, small measurement disturbance, more direct temperature characterization and convenient long-term stable operation.

Description

Technical Field

[0001] This invention relates to the fields of laser cooling, microcavity photonics, and precision measurement, and particularly to an ambient pressure optical cooling device based on a rare-earth-doped crystal whispering-gallery mode (WGM mode) resonator, and an online temperature measurement and control method based on dual-wavelength coupling. This technology can be applied to low thermal noise photonic devices, narrow linewidth lasers, frequency reference cavities, precision sensing, and quantum optics related systems. Background Technology

[0002] Optical cooling (also known as solid-state laser cooling) is a type of all-optical cooling technology that uses anti-Stokes fluorescence to remove heat from the material's crystal lattice in the form of photons, thereby achieving a temperature reduction. Rare-earth-doped low-phonon-energy materials, especially ytterbium-doped fluoride crystals, are currently an important platform for realizing this technology.

[0003] In existing technologies, cooling solutions have emerged that enhance pump absorption through whispering-gallery mode structures. Chinese patent CN204494901U discloses a tapered fiber microsphere solid-state laser cooler. Its core design utilizes a microsphere WGM resonator, couples pump light through a tapered fiber to form a whispering-gallery mode, and thermally connects the microsphere to the object being cooled. The entire unit is placed within a vacuum insulation cavity to achieve the cooler function. However, these existing technologies suffer from at least the following shortcomings: complex system structure, limited engineering adaptability and stability; primarily targeting external objects for cooling rather than self-cooling the crystal resonator itself; and difficulty in achieving real-time temperature characterization and feedback control.

[0004] Therefore, there is an urgent need for an improved optical cooling method that can achieve feedback control while the resonant cavity is self-cooled. Summary of the Invention

[0005] Purpose of the invention: To address the problems existing in the prior art, this invention proposes a whispering-gallery mode resonant cavity laser cooling system and its working method, which enables the resonant cavity to achieve non-contact, highly sensitive temperature measurement and steady-state closed-loop control while realizing optical cooling of the resonant cavity.

[0006] Technical solution:

[0007] On one hand, the present invention proposes a laser cooling system for a whispering-gallery mode resonator, comprising: a light source module, a coupling element, a prism, a whispering-gallery mode resonator, a temperature measurement module, and a feedback control module;

[0008] The material of the whispering-gallery mode resonant cavity is a rare-earth-doped crystal.

[0009] The light source module includes a pump light source and a waveplate for the pump light source, a probe light source and a waveplate for the probe light source, used to output and adjust the pump light and the probe light; the operating wavelength of the pump light source is located in the anti-Stokes cooling band of the rare earth doped crystal, and the operating wavelength of the probe light source is separate from the operating wavelength of the pump light source.

[0010] The coupling module includes a first dichroic beam splitter, an optical fiber coupler, an optical fiber transmission unit, and a GRIN lens, used to control the pump light and the probe light to enter the prism along the same path; the first dichroic beam splitter is placed in opposite directions.

[0011] The reflective surface of the prism is adjacent to the whispering-gallery mode resonator, so that the pump light and the probe light form a near-field coupling between the prism and the whispering-gallery mode resonator, and the pump light and the probe light enter the whispering-gallery mode resonator through the prism.

[0012] The temperature measurement module includes a second dichroic beam splitter, a photodetector for the pump light, and a photodetector for the probe light, used to receive the pump light and probe light emitted from the whispering-gallery mode resonant cavity, respectively, to form the resonant transmission spectrum corresponding to the pump light and probe light.

[0013] The feedback control module includes a feedback loop and an electro-optic modulator. The feedback loop is used to connect the photodetector of the probe light and the electro-optic modulator. The electro-optic modulator is disposed between the pump light source and the waveplate to modulate the pump light.

[0014] Furthermore, the whispering-gallery mode resonator is a disk-shaped crystal that supports the propagation of whispering-gallery modes, with a smooth outer edge; the whispering-gallery mode resonator is mounted on a support.

[0015] On the other hand, the present invention also proposes a method for operating a whispering-gallery mode resonant cavity laser cooling system as described above, comprising:

[0016] S1, activate the detection light source of the light source module, output detection light, and form a detection light path;

[0017] S2, Adjust the position of the waveplate of the probe light source in the light source module, the gap between the prism and the whispering-gallery mode resonator, so that the probe light forms a probe whispering-gallery mode in the whispering-gallery mode resonator.

[0018] S3, Temperature calibration of the whispering-gallery mode resonant cavity;

[0019] S4, activate the pump light source of the light source module, output pump light, and form a pump light path;

[0020] S5 uses the same method as S2 to adjust the waveplate position of the pump light source in the light source module, so that the pump light forms a pump whispering mode in the whispering mode resonant cavity, thereby exciting the optical cooling effect.

[0021] S6. The photodetector of the probe light is used to collect the resonant transmission spectrum of the probe light, and the drift of the resonant frequency of the probe whispering gallblade mode is recorded. Based on the temperature calibration results, the temperature change of the whispering gallblade mode resonant cavity is calculated.

[0022] S7, compare the temperature change with the preset target cooling amount, and adjust the pump light through the feedback loop based on the comparison result to keep the system in a cooling state.

[0023] Furthermore, the detection optical path includes: the detection light is directed to the prism through the coupling module, passes through the evanescent field of the prism, and enters the whispering-gallery mode resonant cavity; after exiting the whispering-gallery mode resonant cavity, the detection light enters the photodetector of the detection light through the second dichroic beam splitter.

[0024] Furthermore, the pump optical path includes: the pump light is directed to the prism through the coupling module, passes through the evanescent field of the prism, and enters the whispering-gallery mode resonator; after exiting the whispering-gallery mode resonator, the pump light enters the photodetector of the pump light through the second dichroic beam splitter.

[0025] Furthermore, the probe light forms a probe whispering-gallery mode within the whispering-gallery mode resonant cavity, including:

[0026] Adjust the gap between the prism and the whispering-gallery mode resonant cavity, and use a probe photodetector to record the range of clear resonance valley values ​​in the probe light resonant transmission spectrum;

[0027] Within the range of the clear resonance valley value, the waveplate of the probe light source is adjusted to adjust the polarization direction of the probe light incident on the whispering-gallery mode resonator, so that the polarization direction of the probe fiber matches the polarization state of the target whispering-gallery mode; the target whispering-gallery mode is an inherent property of the whispering-gallery mode resonator.

[0028] The system controls the detection light source to scan the resonant frequency of the target's whispering galaxy mode, and records the transmission signal of the detection channel through the detection photodetector until the system reaches the target absorption state.

[0029] Furthermore, the system reaches the target absorption state, including:

[0030] Using the resonant absorption depth D as the state criterion, , where I off I is the intensity of transmitted light at resonance. res The intensity of transmitted light at the resonance point is denoted as . When the resonance absorption depth D reaches 30%–90%, the system is considered to have entered an effective absorption state, and a target whispering-gallery mode is formed within the whispering-gallery mode resonator.

[0031] Furthermore, the temperature calibration includes:

[0032] Within a preset temperature range, record the resonant frequency drift data for the whispering gallery mode, including the resonant frequency drift Δν and the temperature change ΔT; linearly fit the resonant frequency drift Δν and the temperature change ΔT to obtain the temperature calibration formula: , where K is the temperature tuning coefficient.

[0033] Furthermore, the calculation of the temperature change of the whispering-gallery mode resonator includes:

[0034] The resonant frequency shift of the detection mode is defined as follows: ,in ν is the resonant frequency at the initial temperature, and ν is the resonant frequency at the current moment;

[0035] Based on the temperature calibration formula, we obtain Under known temperature change conditions, the frequency drift Δν of the detection mode is recorded, and the temperature change ΔT is calculated.

[0036] Furthermore, the feedback control includes:

[0037] The calculated temperature change ΔT is compared with the preset target cooling amount, and a control signal is output to the electro-optic modulator based on the comparison result to adjust the pump light output power.

[0038] When the temperature change ΔT is lower than the preset target cooling amount, the driving voltage of the electro-optic modulator is increased to increase the output power of the pump light; when the temperature change ΔT reaches or exceeds the preset target cooling amount, or when the system experiences temperature oscillation, the driving voltage of the electro-optic modulator is decreased to reduce the output power of the pump light.

[0039] Beneficial effects: Compared with the prior art, the present invention has the following significant technical improvements:

[0040] (1) This invention constructs an integrated working mechanism of "optical cooling-mode drift temperature measurement" by introducing cooling pump light and probe light of different wavelengths into the resonant cavity of the same rare earth-doped crystal. This allows the resonant cavity to cool down using one set of WGM modes while simultaneously reading temperature changes using the resonant drift of another set of WGM modes, thereby achieving non-contact, real-time, and highly sensitive temperature measurement. Compared with existing technologies where the cooling and temperature measurement functions are separated and usually require an additional thermal imager or external temperature probe, this invention has the advantages of a more compact structure, a more direct measurement link, and a more sensitive response to the temperature of the resonant cavity itself.

[0041] (2) This invention utilizes a dual-wavelength cooperative coupling method to directly invert the temperature change of the resonant cavity by taking advantage of the resonance peak drift corresponding to the detection wavelength. This avoids the spatial averaging error and response lag problems caused by relying solely on external thermal imaging, external temperature measuring elements, or ambient temperature estimation. This allows the measured temperature to more accurately reflect the local thermal state of the WGM resonant mode region, thereby improving the accuracy of the cooling state characterization. At the same time, this invention does not require the introduction of an additional independent temperature sensor, thus reducing additional disturbances to the resonant cavity thermal field, mechanical support, and optical path structure. It has the advantages of small additional thermal load, small structural disturbance, easy integration, and high measurement accuracy.

[0042] (3) By setting up a detection channel, calibration relationship, and feedback control loop, the present invention enables the detected mode drift signal to be directly used to adjust the pump laser power, thereby enabling the system to achieve steady-state cooling and maintain it within the target temperature range. Compared with the existing technology, which only achieves passive cooling and lacks online correction capability, the present invention further possesses a closed-loop optimization capability consisting of "measurement-judgment-adjustment", which can effectively reduce system temperature fluctuations and improve long-term operational stability. Attached Figure Description

[0043] Figure 1 This is a structural diagram of the laser cooling system of the present invention;

[0044] Figure 2 This is a structural diagram of the sound-gallery mode resonator and its support structure.

[0045] Figure 3 Calibration curves for detecting the WGM mode resonant frequency shift as a function of temperature. Detailed Implementation

[0046] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0047] Firstly, such as Figure 1 The diagram shows the structure of a whispering-gallery mode resonator laser cooling system according to the present invention. Specifically, it includes: a light source module comprising a pump light source 1, a waveplate 31 for the pump light source, a probe light source 2, and a waveplate 32 for the probe light source; a coupling module comprising a first dichroic beam splitter 4, an optical fiber coupler 5, an optical fiber transmission unit 6, and a GRIN lens 7; a prism 8; a whispering-gallery mode resonator 9; a temperature measurement module comprising a second dichroic beam splitter 10, a pump photodetector 11, and a probe photodetector 12; and a feedback control module comprising a feedback loop 13 and an electro-optic modulator 14. Different optical paths are distinguished by different colors.

[0048] The light source module includes a pump source 1 for outputting and adjusting pump light and a waveplate 31 for the pump source, and a probe source 2 for outputting and adjusting probe light and a waveplate 32 for the probe source. The operating wavelength of the pump source is preferably located in the anti-Stokes cooling band of the rare-earth-doped crystal, and the output of the probe source is preferably a narrow-linewidth laser with a different wavelength than the pump light. In this embodiment, the pump light is a laser near 1020 nm, combined with Yb 3+ The spectral characteristics of YLF crystals are selected based on their properties, with those preferably located in the Yb region. 3+ The anti-Stokes cooling absorption band of ions is within the range to satisfy Yb 3+ The anti-Stokes cooling condition of the YLF crystal is used to excite the target WGM mode; the target WGM mode is determined by the inherent properties of the whispering-gallery mode resonator. The probe light is used to excite another set of stably readable WGM modes under low absorption conditions and to achieve temperature measurement. In this embodiment, Yb is selected. 3+ The pump light and probe light preferably have sufficient wavelength separation to achieve signal separation and reduce channel crosstalk through a beam splitter.

[0049] The coupling module includes a first dichroic beam splitter 4 placed in opposite directions, an optical fiber coupler 5, an optical fiber transmission unit 6, and a GRIN lens 7, used to control the pump light and probe light to be incident on the prism 8 along the same path. After the pump light and probe light are output from the light source module, they are first combined by the first dichroic beam splitter 4 placed in opposite directions, then formed into a coupled beam by the optical fiber coupler 5, and finally transmitted to the GRIN lens 7 for collimation through the optical fiber transmission unit 6. In this embodiment, the GRIN lens used is a Thorlabs GRIN2910.

[0050] The prism 8 is placed adjacent to the whispering-gallery mode resonator 9, such that the gap between the reflecting surface of the prism 8 and the whispering-gallery mode resonator 9 is less than half the operating wavelength of the pump light or probe light. When the probe light and the pump light are incident on the prism 8 along the same path, the two beams form near-field coupling between the prism 8 and the whispering-gallery mode resonator 9. In this embodiment, the prism is Thorlabs, ADG-6. The principle of coupling between the prism and the whispering-gallery mode resonator is specifically referred to in the prior art (Tang Shuijing, Li Beibei, Xiao Yunfeng. Whispering-gallery mode optical microcavity sensing [J]. Physics, 2019, 48(3): 137-147.DOI: 10.7693 / wl20190301). Optionally, the gap is adjusted by a piezoelectric-driven high-precision displacement machine to switch between undercoupled, critically coupled and overcoupled states to meet the experimental requirements under different conditions.

[0051] The whispering-gallery mode resonator 9 is a millimeter-scale disk-shaped crystal resonator made of Yb. 3+ Doping YLF crystals can also be extended to other rare-earth-doped low-phonon energy materials suitable for anti-Stokes fluorescence cooling. For example... Figure 2 As shown, the sounding-gallery mode resonant cavity 9 is mounted on a low thermal conductivity support 91. In this embodiment, the support 91 is made of polyvinyl chloride (PVC). Those skilled in the art will know that the material of this support can be replaced with polytetrafluoroethylene (PTFE), PEEK, aerogel, a low thermal conductivity polymer column, or other low thermal conductivity materials. The support is preferably a cylindrical fixing rod to reduce the thermal load introduced by the support. The support and the sounding-gallery mode resonant cavity preferably employ a small-area contact, central support, or point contact support method to minimize the thermal load introduced by the mechanical support, thereby improving the net cooling effect.

[0052] In this embodiment, the rare-earth-doped crystal disk-shaped whispering-gallery mode resonator has a diameter of 5 mm and a thickness of 0.5 mm. The outer edge of the resonator is polished to form a smooth edge structure suitable for supporting the propagation of high-Q whispering-gallery modes. The diameter of the support is preferably smaller than the diameter of the resonator disk surface to reduce the thermal bridging effect.

[0053] The coupled light passes through the whispering-gallery mode resonator 9 to obtain output light, which then enters the temperature measurement module. The temperature measurement module includes a second dichroic beam splitter 10 and photodetectors 11 and 12, used to separate the output light from the whispering-gallery mode resonator into pump beam splitter and probe beam splitter, and to acquire signals from the separated output light respectively. In this embodiment, photodetector 12 is set to receive the probe beam splitter, and photodetector 11 is set to receive the pump beam splitter.

[0054] The feedback control module includes a feedback loop 13 and an electro-optic modulator 14 (EOM). The feedback loop connects the photodetector 12 and the EOM, which is placed between the pump light source 1 and the corresponding waveplate 31 to modulate the pump light output from the pump light source.

[0055] Secondly, based on the aforementioned whispering-gallery mode resonant cavity laser cooling system, this invention proposes a method for operating the system, specifically including the following steps:

[0056] S1: The detection light source of the light source module is activated, outputting detection light to form a detection optical path. The detection light passes through the coupling module and is directed towards the prism. Through the evanescent field of the prism, it enters the whispering-gallery mode resonator. After exiting the whispering-gallery mode resonator, the detection light passes through the second dichroic beam splitter and enters the photodetector of the detection light (hereinafter referred to as PD1). In the coupling module, the detection light sequentially passes through the first dichroic beam splitter placed in opposite directions, the fiber coupler, the fiber transmission unit, and the GRIN lens.

[0057] S2, by adjusting the polarization of the probe light source in the light source module, the gap between the prism and the whispering-gallery mode resonator, the probe light forms a probe WGM mode in the whispering-gallery mode resonator.

[0058] The WGM mode is a stable resonance mode formed when a wave is confined to the boundary by total internal reflection in a curved structure, and coherently superimposes after completing one revolution. In this invention, the sub-steps include:

[0059] (1) Adjust the gap between the prism and the whispering-gallery mode resonant cavity, and use PD1 to record the range of clear resonance valley values ​​in the probe light resonant transmission spectrum;

[0060] (2) Within the range obtained in (1), adjust the waveplate of the probe light source to adjust the polarization direction of the probe light incident on the resonant cavity to match the polarization state of the target WGM mode;

[0061] (3) Control the detection light source to scan the resonant frequency of the target WGM mode, and record the transmission signal of the detection channel through PD1 to make the system reach the target absorption state. Here, the resonant absorption depth D is used as the coupling state criterion, where: , among which, I off I is the intensity of transmitted light at resonance. res The transmitted light intensity is at the resonance point. When the resonant absorption depth D reaches 30%–90%, the system is considered to have entered an effective absorption state, and a set of probe WGM modes is formed within the whispering-gallery mode resonator. In this embodiment, the probe light is a narrow-linewidth laser light around 1550 nm.

[0062] S3, temperature calibration of the whispering-gallery mode resonator, specifically the calibration of the temperature change and resonant frequency drift. This step is achieved using an external temperature control device to obtain the temperature calibration relationship under specified experimental conditions.

[0063] like Figure 3 As shown, in this embodiment, the resonant frequency drift data of the detected WGM mode is recorded within a temperature range of 25.3℃ to 26.8℃. Figure 3 The horizontal axis represents the rate of temperature change, and the vertical axis represents the resonant frequency drift. The calibration results show that the resonant frequency drift Δν and the temperature change ΔT approximately satisfy a linear relationship within this temperature range. The temperature tuning coefficient K is approximately 1.9 GHz / ℃. When the temperature increases from 25.3℃ to 26.8℃, the resonant frequency drift is approximately 2.9 GHz; when the temperature increases by approximately 1.0℃, the corresponding resonant frequency drift is also approximately 1.9 GHz, demonstrating good linearity. The temperature change of the crystal resonator in whispering-gallery mode is inverted. Subsequently, during the cooling process, this calibration relationship allows for non-contact, highly sensitive measurement of the crystal resonator temperature.

[0064] S4, activate the pump light source of the light source module to output pump light and form a pump light path. After being processed by the coupling module, the pump light is combined with the probe light to form a coupled beam, which is then directed toward the prism. The pump light in the coupled beam passes through the evanescent field of the prism and enters the whispering-gallery mode resonator. After exiting the whispering-gallery mode resonator, the pump light passes through the second dichroic beam splitter and enters the photodetector of the pump light (hereinafter referred to as PD2).

[0065] The processing of the coupling module includes: the pump light and the probe light are incident on opposite sides of the first dichroic beam splitter to achieve beam combining, the combined beam enters the fiber coupler to obtain the coupled beam, the coupled beam is transmitted through the fiber transmission unit, and finally collimated by the GRIN lens.

[0066] S5, adjust the polarization of the pump light source in the light source module so that the pump light forms a pump WGM mode in the whispering-gallery mode resonator.

[0067] The pump light has a different wavelength than the probe light, which is used to excite another set of WGM modes in the whispering-gallery mode resonator that are different from the probe WGM mode described in S2. Similar to the probe light source, the polarization adjustment of the pump light source is achieved by adjusting the waveplate at the exit position of the pump light source. Specifically, using the same method as sub-steps (2) to (3) of S2, the transmission signal of the pump channel is recorded using PD2, and the waveplate of the pump light source is adjusted to form another set of WGM modes in the whispering-gallery mode resonator. In this embodiment, the pump light is a narrow linewidth laser near 1020 nm, which enters the Yb 3+ A set of pump WGM modes is formed in the YLF disk-shaped whispering galvanic mode resonant cavity, and the pump light is locked at the resonant point of the pump WGM mode.

[0068] At this time, the wavelength of the pump light is located in the anti-Stokes cooling operating range of the rare earth doped crystal. After the rare earth ions in the crystal absorb the pump photon, they absorb the lattice thermal vibration energy and emit fluorescent photons with higher average energy, which carries some of the heat energy out of the crystal, causing the temperature of the whispering-gallery mode resonator to drop, forming an optical cooling effect and achieving the purpose of self-cooling of the resonator.

[0069] Optionally, under normal pressure, the whispering-gallery mode resonator is simultaneously subjected to heat loads such as air convection, support conduction, and radiation heat transfer. By employing low thermal conductivity supports, optimizing prism coupling conditions, and adjusting pump power and pump detuning, the whispering-gallery mode resonator can achieve net cooling.

[0070] S6. Use PD1 to collect the resonant transmission spectrum of the probe light, record the position change of the WGM resonance peak, and calculate the temperature change of the whispering-gallery mode resonator based on the temperature calibration results in the previous steps.

[0071] Because the refractive index and geometry of a whispering-gallery mode resonator change with temperature, its resonant frequency or wavelength also drifts with temperature. This is achieved by monitoring the change in the position of the WGM resonance peak corresponding to the probe light, specifically including:

[0072] (1) Define the resonant frequency drift of the detection mode as: ,in, ν is the resonant frequency at the initial temperature, and ν is the resonant frequency at the current moment.

[0073] (2) Based on the temperature calibration results in the preceding steps, within a certain temperature range, the resonant frequency drift and temperature change approximately satisfy a linear relationship: Where K is the temperature tuning coefficient.

[0074] (3) Record the frequency drift Δν of the detection mode under known temperature change conditions, and fit it to obtain the temperature tuning coefficient K. Then, according to the formula... Inverting temperature changes.

[0075] S7 compares the temperature change obtained from the inversion with the preset target cooling amount, generates a feedback control signal, and adjusts the output power of the pump light source through the feedback loop to keep the temperature change of the resonant cavity consistent with the preset target cooling amount.

[0076] To further improve cooling stability and measurement accuracy, this invention designs a closed-loop feedback control system. The feedback control is implemented through the control unit, which compares the temperature change calculated by S6 with the preset target cooling amount to obtain the temperature deviation; based on the temperature deviation, a control signal is output to the EOM driver to adjust the pump light output power.

[0077] In this embodiment, when the temperature change is less than the target cooling amount, the control unit increases the EOM driving voltage, thereby increasing the modulation output power of the pump light; when the temperature change exceeds the target value, or when the system exhibits temperature oscillation, overshoot, or instability, the EOM driving voltage decreases, thereby reducing the pump light output power. The control unit is preferably a PID controller, microcontroller, or FPGA, all of which can be implemented using conventional photoelectric detection and automatic control technologies in the art.

[0078] Through the aforementioned feedback adjustment, the whispering-gallery mode resonator is maintained at the target temperature and temperature fluctuations are reduced, thereby improving the long-term operational stability of the system and enhancing the net cooling capacity and temperature measurement accuracy of the rare-earth-doped crystal disk-shaped whispering-gallery mode resonator under normal pressure. Furthermore, the feedback control loop can also adjust the modulation state, scanning parameters, or lock state of the pump laser as needed to further optimize coupling efficiency and cooling performance.

Claims

1. A whispering-gallery mode resonant cavity laser cooling system, characterized in that, include: The light source module, coupling module, prism, whispering-gallery mode resonant cavity, temperature measurement module, and feedback control module; The material of the whispering-gallery mode resonant cavity is a rare-earth-doped crystal. The light source module includes a pump light source and a waveplate for outputting and adjusting pump light, and a probe light source and a waveplate for outputting and adjusting probe light; the operating wavelength of the pump light source is located in the anti-Stokes cooling band of the rare earth doped crystal, and the operating wavelength of the probe light source is separate from the operating wavelength of the pump light source. The coupling module includes a first dichroic beam splitter, an optical fiber coupler, an optical fiber transmission unit, and a GRIN lens, used to control the pump light and the probe light to enter the prism along the same path; the first dichroic beam splitter is placed in opposite directions. The reflective surface of the prism is adjacent to the whispering-gallery mode resonator, so that the pump light and the probe light form a near-field coupling between the prism and the whispering-gallery mode resonator, and the pump light and the probe light enter the whispering-gallery mode resonator through the prism. The temperature measurement module includes a second dichroic beam splitter, a photodetector for the pump light, and a photodetector for the probe light, used to receive the pump light and probe light emitted from the whispering-gallery mode resonant cavity, respectively, to form the resonant transmission spectrum corresponding to the pump light and probe light. The feedback control module includes a feedback loop and an electro-optic modulator. The feedback loop is used to connect the photodetector of the probe light and the electro-optic modulator. The electro-optic modulator is disposed between the pump light source and the waveplate of the pump light source to modulate the pump light.

2. The whispering-gallery mode resonant cavity laser cooling system according to claim 1, characterized in that, The whispering-gallery mode resonator is a disk-shaped crystal that supports the propagation of whispering-gallery modes, with a smooth outer edge; the whispering-gallery mode resonator is mounted on a support.

3. A method for operating the whispering-gallery mode resonant cavity laser cooling system as described in claim 1 or 2, characterized in that, include: S1, activate the detection light source of the light source module, output detection light, and form a detection light path; S2, Adjust the position of the waveplate of the probe light source in the light source module, the gap between the prism and the whispering-gallery mode resonator, so that the probe light forms a probe whispering-gallery mode in the whispering-gallery mode resonator. S3, Temperature calibration of the whispering-gallery mode resonant cavity; S4, activate the pump light source of the light source module, output pump light, and form a pump light path; S5 uses the same method as S2 to adjust the waveplate position of the pump light source in the light source module, so that the pump light forms a pump whispering mode in the whispering mode resonant cavity, thereby exciting the optical cooling effect. S6. The photodetector of the probe light is used to collect the resonant transmission spectrum of the probe light, and the drift of the resonant frequency of the probe whispering gallblade mode is recorded. Based on the temperature calibration results, the temperature change of the whispering gallblade mode resonant cavity is calculated. S7. The temperature change is compared with the preset target cooling amount. Based on the comparison result, the output power of the pump light is adjusted through the feedback loop to keep the temperature change consistent with the preset target cooling amount.

4. The working method according to claim 3, characterized in that, The detection optical path includes: the detection light is directed to the prism through the coupling module, passes through the evanescent field of the prism, and enters the whispering-gallery mode resonant cavity; after exiting the whispering-gallery mode resonant cavity, the detection light enters the photodetector of the detection light through the second dichroic beam splitter.

5. The working method according to claim 4, characterized in that, The pump optical path includes: pump light passing through a coupling module and directed towards a prism, passing through the evanescent field of the prism, and entering a whispering-gallery mode resonant cavity; after exiting the whispering-gallery mode resonant cavity, the pump light passes through a second dichroic beam splitter and enters a photodetector for the pump light.

6. The working method according to claim 5, characterized in that, The probe light forms a probe whispering-gallery mode within the whispering-gallery mode resonant cavity, including: Adjust the gap between the prism and the whispering-gallery mode resonant cavity, and use a probe photodetector to record the range of clear resonance valley values ​​in the probe light resonant transmission spectrum; Within the range of the clear resonance valley value, the waveplate of the probe light source is adjusted to adjust the polarization direction of the probe light incident on the whispering-gallery mode resonator, so that the polarization direction of the probe fiber matches the polarization state of the target whispering-gallery mode; the target whispering-gallery mode is an inherent property of the whispering-gallery mode resonator. The system controls the detection light source to scan the resonant frequency of the target's whispering galaxy mode, and records the transmission signal of the detection channel through the detection photodetector until the system reaches the target absorption state.

7. The working method according to claim 6, characterized in that, The system reaches the target absorption state, including: Using the resonant absorption depth D as the state criterion, , where I off I is the intensity of transmitted light at resonance. res The intensity of transmitted light at the resonance point is denoted as . When the resonance absorption depth D reaches 30%–90%, the system is considered to have entered an effective absorption state, and a target whispering-gallery mode is formed within the whispering-gallery mode resonator.

8. The working method according to claim 7, characterized in that, The temperature calibration includes: Within a preset temperature range, record the resonant frequency drift data for the whispering gallery mode, including the resonant frequency drift Δν and the temperature change ΔT; linearly fit the resonant frequency drift Δν and the temperature change ΔT to obtain the temperature calibration formula: , where K is the temperature tuning coefficient.

9. The working method according to claim 8, characterized in that, The calculation of the temperature change of the whispering-gallery mode resonator includes: The resonant frequency shift of the detection mode is defined as follows: ,in ν is the resonant frequency at the initial temperature, and ν is the resonant frequency at the current moment; Based on the temperature calibration formula, we obtain Under known temperature change conditions, the frequency drift Δν of the detection mode is recorded, and the temperature change ΔT is calculated.

10. The working method according to claim 9, characterized in that, The feedback control includes: The calculated temperature change ΔT is compared with the preset target cooling amount, and a control signal is output to the electro-optic modulator based on the comparison result to adjust the pump light output power. When the temperature change ΔT is lower than the preset target cooling amount, the driving voltage of the electro-optic modulator is increased to increase the output power of the pump light; when the temperature change ΔT exceeds the preset target cooling amount, or when the system experiences temperature oscillation, the driving voltage of the electro-optic modulator is decreased to reduce the output power of the pump light.

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