High-precision intermediate infrared microcavity quality factor measuring device and method

Abstract

The invention discloses a high-precision mid-infrared micro-cavity quality factor measuring device and method, and solves the problem that a high micro-cavity quality factor cannot be measured due to the frequency tuning precision of a laser in an existing frequency sweeping method. In order to solve the problem that a relatively low microcavity quality factor cannot be measured due to the fact that a pumping unit A emits mid-infrared pumping laser with a fixed frequency, and the mid-infrared pumping laser is modulated by a mid-infrared intensity modulator to generate an optical frequency sideband with a movable frequency, so that the quality factor of the microcavity can be measured. The problem that the quality factor of the mid-infrared microcavity cannot be measured due to the lack of a frequency sweep laser and a high-speed optical switch device at the mid-infrared band at present is solved, and the measuring device is simple in structure and high in practicability.

Description

Technical Field

[0001] This invention relates to a device and method for measuring the quality factor of a microcavity, specifically to a high-precision mid-infrared microcavity quality factor measuring device and method. Background Technology

[0002] Mid-infrared lasers exist within atmospheric windows and are also the "fingerprint region" of various molecular spectra. Therefore, mid-infrared lasers have unique advantages in free-space optical communication, environmental gas detection, and other fields, and have wide applications in scientific research, industry, and medicine. Optical microcavities are important fundamental components in integrated optics, serving as core components for devices including optical filters, sensors, and lasers. With the development of modern micro-nano fabrication technology, various systems based on optical microcavities have demonstrated high integration, low power consumption, high repetition rate, and large bandwidth, showing promising application prospects and widespread value in high-speed communication, microwave photonics, and precision measurement. Mid-infrared microcavities include different forms such as microrings, microspheres, and micropillars, and can be fabricated from mid-infrared transparent (or low absorption loss) materials such as silicon, germanium, silicon nitride, fluorides, sulfides, lithium niobate, and aluminum nitride. Compared to the near-infrared band, mid-infrared microcavities still face significant technical challenges in testing, characterization, and system construction.

[0003] Among the parameters used to evaluate the performance of a microcavity, the quality factor (Q) is defined as the ratio of the optical field energy within the cavity to the energy lost per unit time. It is determined by the absorption loss of the waveguide material constituting the microcavity and the structural losses introduced during the actual fabrication process. Q directly reflects the microcavity's ability to store an optical field and also determines the threshold power required to excite nonlinear effects (such as parametric oscillations). Therefore, accurate measurement of the microcavity quality factor is crucial not only for assessing the fabrication effect and providing feedback and optimization for the fabrication process, but also for the selection of the pump source and supporting devices, and the overall system construction.

[0004] Currently, the measurement of the quality factor of microcavities in the near-infrared band is mainly achieved using either the frequency sweep method or the ring-down method. The former relies on a high-performance, rapidly tunable laser to scan the microcavity to obtain the resonant peak transmission curve, while the latter uses an ultra-high-speed optical switch to rapidly cut off the pump laser to observe the ring-down curve of the intracavity optical field. On the one hand, the frequency sweep method is limited by the laser's frequency tuning accuracy (i.e., the minimum step size, typically tens of MHz), making it unable to measure higher (>10) quality factors. 7 The microcavity quality factor is on the order of magnitude (in terms of orders of magnitude); however, the ring-down rule is limited by the available optical switching rate, making it impossible to measure lower (<10) microcavity quality factors. 5The quality factor of microcavities in the mid-infrared band is crucial. Especially for the mid-infrared band, there is a current lack of both high-performance, tunable lasers and high-speed (GHz and above) optical switching devices. Therefore, measuring the quality factor of mid-infrared optical microcavities has become a common challenge for both academia and industry, severely hindering the key performance characterization and processing effect evaluation of mid-infrared photonic integrated devices and chips, and impacting the realization and long-term technological development of mid-infrared optical systems. Summary of the Invention

[0005] To address the limitation of existing frequency sweep methods in measuring high frequencies (>10) due to the laser frequency tuning accuracy requirement. 7 The microcavity quality factor is on the order of magnitude (in terms of orders of magnitude); however, the ring-down rule is limited by the available optical switching rate, making it impossible to measure lower (<10) microcavity quality factors. 5 To address the technical problem of microcavity quality factor (on the order of magnitude), this invention provides a high-precision mid-infrared microcavity quality factor measurement device and method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-precision mid-infrared microcavity quality factor measurement device is characterized by comprising a pumping unit A, a frequency shifting scanning unit B, a frequency tuning unit C, and a monitoring unit D connected in sequence. The pump unit A is used to emit a mid-infrared pump laser at a fixed frequency; The frequency-shifting scanning unit B includes a mid-infrared intensity modulator and a first focusing lens arranged sequentially along the emission direction in the optical path of the mid-infrared pump laser, as well as a microwave signal generator and a DC power supply electrically connected to the mid-infrared intensity modulator. The mid-infrared intensity modulator is used to modulate the mid-infrared pump laser to generate a frequency-shiftable optical sideband. The microwave signal generator is used to output microwave signals of different frequencies to the mid-infrared intensity modulator. The DC power supply is used to output a bias voltage to control the operating state of the mid-infrared intensity modulator. The first focusing lens is used to compress the optical mode field size of the modulated mid-infrared pump laser so that it is input into the microcavity under test. The frequency tuning unit C is used to place the microcavity under test and to tune it; The monitoring unit D is used to monitor the laser power and spectrum after being acted upon by the microcavity under test.

[0007] Furthermore, the frequency shift scanning unit B also includes a bias unit; The microwave signal output terminal of the microwave signal generator is electrically connected to the microwave signal input terminal of the biaser. The output terminal of the DC power supply is electrically connected to the DC signal input terminal of the biaser. The output of the bias unit is electrically connected to the electrical signal input of the mid-infrared intensity modulator.

[0008] Furthermore, the pump unit A includes a mid-infrared narrow-linewidth laser and a second focusing lens; The mid-infrared narrow-linewidth laser is used to emit a fixed-frequency mid-infrared pump laser. The second focusing lens is used to compress the spot size of the mid-infrared pump laser, so that it can be incident on the mid-infrared intensity modulator with higher efficiency; The frequency tuning unit C includes a three-dimensional displacement platform and a semiconductor thermoelectric cooler disposed on the three-dimensional displacement platform; The semiconductor thermoelectric cooler is used to support the microcavity under test and control its temperature.

[0009] Furthermore, the monitoring unit D includes a spectroscope, a power meter, and a spectrometer; The beam splitter is disposed at the output end of the microcavity under test and is used to split the light beam after the microcavity under test into a first beam and a second beam. The power meter is installed in the optical path of the first beam to monitor the optical power of the first beam; The spectrometer is positioned in the optical path of the second beam to monitor the spectrum of the second beam.

[0010] A high-precision mid-infrared microcavity quality factor measurement method, employing the aforementioned high-precision mid-infrared microcavity quality factor measurement device, is characterized by including the following steps: Step 1: Place the microcavity under test in the frequency tuning unit C; Step 2: Start pump unit A and monitoring unit D. Pump unit A emits mid-infrared pump laser, and its initial wavelength λ0 is obtained through monitoring unit D. Step 3: Start and adjust the frequency tuning unit C so that the edge frequency of the resonant peak of the microcavity under test coincides with the frequency of the mid-infrared pump laser. Step 4: Start the frequency shift scanning unit B, adjust the microwave signal generator and DC power supply to make the mid-infrared intensity modulator work in push-pull mode, so as to suppress the optical power of the mid-infrared pump laser and generate a frequency-shiftable optical sideband. Step 5: Adjust the microwave signal output frequency of the microwave signal generator to continuously shift the frequency of the mid-infrared pump laser, thereby scanning the microcavity under test, acquiring the output frequency data of the microwave signal generator during the scanning process, and acquiring the corresponding optical power data through the monitoring unit D. Calculate the mid-infrared microcavity quality factor of the microcavity under test based on the initial wavelength λ0, the output frequency data, and the corresponding optical power data, thus completing the mid-infrared microcavity quality factor measurement.

[0011] Further, step 1 specifically involves placing the microcavity to be tested at the active end of the semiconductor thermoelectric cooler.

[0012] Further, step 2 specifically involves starting the mid-infrared narrow-linewidth laser, power meter, and spectrometer, with the mid-infrared narrow-linewidth laser emitting mid-infrared pump laser; adjusting the positions of the second focusing lens, the first focusing lens, and the three-dimensional displacement platform so that the mid-infrared pump laser can be incident on the mid-infrared intensity modulator, the microcavity under test, the beam splitter, the power meter, and the spectrometer, and recording the initial wavelength λ0 shown by the spectrometer.

[0013] Further, step 3 specifically involves starting the semiconductor thermoelectric cooler and gradually increasing or decreasing its temperature until the power value shown by the power meter first reaches its lowest value P. min It then reached a maximum value P again. max Reaching the highest value P max If the temperature of the semiconductor thermoelectric cooler is kept constant, the edge frequency of the resonant peak of the microcavity under test will coincide with the frequency of the mid-infrared pump laser.

[0014] Furthermore, step 4 specifically includes: Step 4.1: Start the microwave signal generator and DC power supply, and adjust the output voltage of the DC power supply until the power value shown on the power meter reaches the minimum value P. min At that time, maintain the output voltage V of the DC power supply. π If it remains unchanged, the phase difference between the optical wave modes of the two arms of the mid-infrared intensity modulator is set to π; Step 4.2: Adjust the output voltage of the microwave signal generator so that the mid-infrared intensity modulator operates in push-pull mode to suppress the optical power of the mid-infrared pump laser and generate two frequency-shiftable optical sidebands.

[0015] Furthermore, step 5 specifically includes: Step 5.1: Gradually increase the microwave signal output frequency of the microwave signal generator to continuously shift the frequency of the mid-infrared pump laser, thereby scanning the microcavity under test until the power value shown by the power meter first reaches its lowest value T. min It then reached another peak value T. max Record the output frequency data of the microwave signal generator and the corresponding optical power data shown by the power meter, and plot the change curve with the output frequency data as the X-axis and the optical power data as the Y-axis; Step 5.2: Calculate the optical power (T) based on the change curve plotted in Step 5.1. max -T min The resonant frequency with a full width at half maximum (FWHM) of f when the value is 1 / 2 is f. avg ; Step 5.3: Calculate the mid-infrared microcavity quality factor of the microcavity under test. Q : Q =c / (λ0×f avg ) Where c is the speed of light.

[0016] The beneficial effects of this invention are: 1. The present invention provides a high-precision mid-infrared microcavity quality factor measurement device and method, which utilizes a pump unit A to emit a fixed-frequency mid-infrared pump laser, and modulates the mid-infrared pump laser through a mid-infrared intensity modulator to generate a frequency-movable optical sideband. This solves the problem that the mid-infrared microcavity quality factor cannot be measured due to the lack of frequency-sweeping lasers with fast frequency adjustment and high-speed optical switching devices in the current mid-infrared band. The measurement device has a simple structure and is highly practical.

[0017] 2. The present invention provides a high-precision mid-infrared microcavity quality factor measurement device and method. By changing the temperature of the microcavity under test, the pump laser frequency is equivalently preset to coincide with the edge frequency of the microcavity resonance peak. On the one hand, it eliminates the need for a large and costly tunable laser, requiring only a miniaturized and economical mid-infrared narrow-linewidth laser. On the other hand, it effectively solves the problem of possible mismatch between the initial mid-infrared pump laser and the edge frequency of the microcavity resonance peak. Therefore, it eliminates the need to select a specific frequency laser source based on the microcavity resonance position. Only the same mid-infrared narrow-linewidth laser is needed to measure various microcavities with different materials, configurations, and repetition frequencies, exhibiting high compatibility and versatility.

[0018] 3. The present invention provides a high-precision mid-infrared microcavity quality factor measurement device and method. By specially setting the mid-infrared intensity modulator to generate a frequency-shiftable optical sideband, it solves the problem that the existing frequency sweeping method is limited by the linewidth and minimum step size of the frequency sweeping laser (usually tens of MHz), resulting in limited measurement accuracy (the minimum resolvable spectrum is tens of MHz). Thanks to the continuous and free frequency shifting of the microwave signal driving the optical sideband to move and scan, the theoretical maximum resolution value of the quality factor measurement of the present invention has no upper limit and is only determined by the actual mid-infrared narrow linewidth laser used (up to kHz level), thus having extremely high measurement accuracy.

[0019] 4. The present invention provides a high-precision mid-infrared microcavity quality factor measurement device and method. By specially setting the mid-infrared intensity modulator to operate in push-pull mode, it achieves continuously frequency-shiftable optical frequency sidebands, breaking the limitations of sweep-frequency and ring-down methods that are restricted by laser frequency tuning step size and optical switching rate, thus preventing the measurement of higher (≤10) microcavity quality factors. 7 (Level) or lower (≥10) 5 This invention addresses the bottleneck issue of measuring the quality factor of microcavities at the order of magnitude (on the order of magnitude); by employing only a commonly used mid-infrared narrow-linewidth laser, the measurable quality factor range can cover 10. 3 ~10 7 It has a large measurement range and strong versatility.

[0020] 5. The present invention provides a high-precision mid-infrared microcavity quality factor measurement device and method. By making special settings on the mid-infrared intensity modulator, it can generate a continuously frequency-shiftable optical sideband while suppressing the optical power of the mid-infrared pump laser, effectively reducing the background noise of the continuous laser. Therefore, the optical power changes more significantly during the frequency-shifting scanning process, and the contrast and accuracy of the measurement results are higher.

[0021] 6. The high-precision mid-infrared microcavity quality factor measurement device and method provided by the present invention consists of readily available and replaceable product devices, which have the advantages of high compactness and low cost; at the same time, the operation steps are simple and the time consumption is short, avoiding the problems of pump laser frequency drift and power fluctuation, and the measurement speed is faster and the error is smaller.

[0022] 7. The high-precision mid-infrared microcavity quality factor measurement device and method provided by the present invention can efficiently and accurately obtain the quality factor of mid-infrared microcavities. It can not only provide a direct basis for judging the fabrication effect of microcavities and the feedback optimization of the processing, but also provide key parameters for selecting the appropriate light source type and supporting devices for mid-infrared optical systems based on integrated microcavities. It has significant scientific value and application significance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an embodiment of a high-precision mid-infrared microcavity quality factor measuring device according to the present invention; Figure 2 This is a graph showing the relative positions of the mid-infrared pump laser and the target resonant frequency of the microcavity under test in an embodiment of the present invention; wherein, a is the graph showing the relative positions of the mid-infrared pump laser and the target resonant frequency of the microcavity under test after step 2 is completed; b is the graph showing the relative positions of the mid-infrared pump laser and the target resonant frequency of the microcavity under test as the temperature increases or decreases in step 3; c is the graph showing the relative positions of the newly generated optical frequency sideband after modulation of the mid-infrared pump laser and the target resonant frequency of the microcavity under test after step 4.2 is completed; d is the graph showing the relative positions of the optical frequency sideband and the target resonant frequency of the microcavity under test as the microwave signal output frequency is adjusted in step 5.1. Figure 3 This is a graph of the optical frequency sideband spectrum newly generated after modulation of the mid-infrared pump laser in step 4 of the present invention. Figure 4 This is a graph showing the change in optical power with the output frequency of the microwave signal from the microwave signal generator after frequency shift scanning in an embodiment of the present invention.

[0024] The attached figures are labeled as follows: 1. Mid-infrared narrow linewidth laser; 2. Second focusing lens; 3. Mid-infrared intensity modulator; 4. Microwave signal generator; 5. DC power supply; 6. Bias setter; 7. First focusing lens; 8. Semiconductor thermoelectric cooler; 9. Microcavity under test; 10. Beam splitter; 11. Power meter; 12. Spectrometer. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a high-precision mid-infrared microcavity quality factor measurement device, such as... Figure 1 As shown, it includes a pumping unit A, a frequency shifting and scanning unit B, a frequency tuning unit C, and a monitoring unit D connected in sequence.

[0027] Pump unit A is used to emit a fixed-frequency mid-infrared pump laser; pump unit A includes a mid-infrared narrow-linewidth laser 1 and a second focusing lens 2; the mid-infrared narrow-linewidth laser 1 is used to emit a fixed-frequency mid-infrared pump laser to pump the microcavity 9 under test; the second focusing lens 2 is used to compress the spot size of the mid-infrared pump laser so that it can be incident on the mid-infrared intensity modulator 3 with higher efficiency.

[0028] In this embodiment, the mid-infrared narrow linewidth laser 1 is a mid-infrared interband cascade laser with a working wavelength of 3μm. In other embodiments, different types of mid-infrared lasers with working wavelengths of other wavelengths can also be used, such as fiber or semiconductor narrow linewidth lasers with working wavelengths of around 2μm, or mid-infrared quantum cascade lasers with working wavelengths of around 8μm. The second focusing lens 2 can also be a fiber lens with focusing function.

[0029] Frequency-shifting scanning unit B is used to modulate the mid-infrared pump laser and perform frequency-shifting scanning on the microcavity 9 under test. Frequency-shifting scanning unit B includes a mid-infrared intensity modulator 3 and a first focusing lens 7 arranged sequentially along the output direction of the mid-infrared pump laser, as well as a microwave signal generator 4 and a DC power supply 5 electrically connected to the mid-infrared intensity modulator 3 via a biaser 6. The microwave signal output terminal of the microwave signal generator 4 is electrically connected to the microwave signal input terminal of the biaser 6; the output terminal of the DC power supply 5 is electrically connected to the DC signal input terminal of the biaser 6; and the output terminal of the biaser 6 is connected to the mid-infrared intensity modulator 3. The electrical signal input terminal is electrically connected; the mid-infrared intensity modulator 3 is used to receive and modulate the mid-infrared pump laser to generate a frequency-shiftable optical sideband; the microwave signal generator 4 is used to output microwave signals of different frequencies to the mid-infrared intensity modulator 3; the DC power supply 5 is used to output a specific bias voltage to control the working state of the mid-infrared intensity modulator 3; the biaser 6 is used to simultaneously input the signals generated by the microwave signal generator 4 and the DC power supply 5 into the mid-infrared intensity modulator 3; the first focusing lens 7 is used to compress the optical mode field size of the modulated mid-infrared pump laser so that it is input into the microcavity under test 9.

[0030] The frequency tuning unit C is used to place the microcavity under test 9 and tune the resonance peak of the microcavity under test 9; the frequency tuning unit C includes a three-dimensional displacement platform and a semiconductor thermoelectric cooler 8 set on the three-dimensional displacement platform; the semiconductor thermoelectric cooler 8 has a temperature regulation function, is used to support the microcavity under test 9 and control its temperature.

[0031] In this embodiment, the microcavity 9 to be tested is a lithium niobate microring cavity with a working wavelength around 3μm. It can also be an optical microcavity working at other wavelengths, such as an optical microcavity made of silicon, lithium niobate, magnesium fluoride or aluminum gallium arsenide, and in the form of microspheres, microdisks or micropillars.

[0032] Monitoring unit D is used to observe the optical power and spectrum of the microcavity 9 under test after frequency shift scanning. Monitoring unit D includes a beam splitter 10, a power meter 11, and a spectrometer 12; the beam splitter 10 is set outside the output end of the microcavity 9 under test, and is used to split the light beam after the microcavity 9 under test into a first beam and a second beam; the power meter 11 is set in the optical path of the first beam, and is used to monitor the optical power of the first beam; the spectrometer 12 is set in the optical path of the second beam, and is used to monitor the spectrum of the second beam.

[0033] The mid-infrared microcavity quality factor measurement using the aforementioned high-precision mid-infrared microcavity quality factor measurement device includes the following steps: Step 1: Place the microcavity under test 9 in the frequency tuning unit C; specifically: The microcavity to be tested 9 is placed at the active end of the semiconductor thermoelectric cooler 8.

[0034] Step 2: Start pump unit A and monitoring unit D. Pump unit A emits mid-infrared pump laser, and its initial wavelength λ0 is obtained through monitoring unit D; specifically: Start the mid-infrared narrow-linewidth laser 1, power meter 11, and spectrometer 12. The mid-infrared narrow-linewidth laser 1 emits mid-infrared pump laser. Adjust the positions of the second focusing lens 2 and the first focusing lens 7 in the optical path, as well as the three-dimensional displacement platform, so that the mid-infrared pump laser can be incident on the mid-infrared intensity modulator 3, the microcavity under test 9, the beam splitter 10, the power meter 11, and the spectrometer 12. Record the initial wavelength λ0 shown by the spectrometer 12.

[0035] like Figure 2 As shown in Figure a, since the mid-infrared pump laser has a fixed wavelength, while the resonant frequency of the microcavity under test 9 (i.e. the target resonant frequency of the microcavity under test) is unknown, the positions of the two are randomly distributed and cannot overlap.

[0036] Step 3: Activate and adjust the frequency tuning unit C so that the edge of the resonant peak of the microcavity under test 9 coincides with the frequency of the mid-infrared pump laser; specifically: The semiconductor thermoelectric cooler 8 is activated, and its temperature is gradually increased or decreased. The temperature of the microcavity 9 under test increases or decreases accordingly. At the same time, the power meter 11 is observed until the power value shown by the power meter 11 first reaches a minimum value P. min It then reached a maximum value P again. max Reaching the highest value P max If the temperature of the semiconductor thermoelectric cooler 8 is kept constant, the edge frequency of the resonant peak of the microcavity 9 under test has been tuned to coincide with the frequency of the mid-infrared pump laser.

[0037] like Figure 2 As shown in Figure b, as the temperature increases (or decreases) unidirectionally, the trough position of the resonance curve will gradually shift towards the longer (or shorter) wave direction. When the trough position of the resonance curve moves to the same frequency as the mid-infrared pump laser, the mid-infrared pump laser is well confined by the microcavity under test 9, so the power value shown by the power meter 11 will reach its lowest value P. min As the temperature continues to change, the mid-infrared pump laser gradually moves from the trough to the peak of the microcavity resonance curve. The confinement capability of the microcavity under test 9 for the mid-infrared pump laser weakens, so the power value shown by the power meter 11 will gradually increase; when the power value reaches the highest value P... max At this time, the corresponding state is that the edge of the resonant peak frequency of the microcavity under test 9 has been tuned to just coincide with the mid-infrared pump laser.

[0038] Step 4: Start the frequency shift scanning unit B, adjust the microwave signal generator 4 and DC power supply 5 to make the mid-infrared intensity modulator 3 work in push-pull mode, so as to suppress the optical power of the mid-infrared pump laser and generate a frequency-shiftable optical sideband; specifically including: Step 4.1: Start the microwave signal generator 4 and DC power supply 5, and adjust the output voltage of DC power supply 5 until the power value shown on power meter 11 reaches the minimum value P. min At this time, maintain the output voltage V of DC power supply 5. π If it remains unchanged, the phase difference of the optical wave modes of the two arms of the mid-infrared intensity modulator 3 is set to π; Step 4.2: Adjust the output voltage of microwave signal generator 4 so that its output drive voltage is V. π 1.17 times that of the mid-infrared intensity modulator 3, at which point the working state of the mid-infrared pump laser 3 has been set to push-pull mode to suppress the optical power of the mid-infrared pump laser and generate two new frequency-movable optical sidebands.

[0039] like Figure 2 As shown in Figure c, by adjusting the output voltage of the microwave signal generator 4, the mid-infrared intensity modulator 3 is made to work in push-pull mode. Therefore, the initial center wavelength frequency component of the mid-infrared pump laser will be completely suppressed, and a new ±1-order optical frequency sideband will be generated, the position of which is determined by the specific frequency of the microwave modulation signal.

[0040] like Figure 3 As shown, when the center wavelength of the pump laser used is 3μm and the output voltage V of the DC power supply 5 is... π When the voltage is 11.5V and the output voltage of microwave signal generator 4 is 13.46V, the two optical frequency sidebands are located at 2999.7nm and 3000.3nm, respectively.

[0041] Step 5: Adjust the microwave signal output frequency of microwave signal generator 4 to continuously shift the frequency of the mid-infrared pump laser, thereby scanning the microcavity 9 under test. Acquire the output frequency data of microwave signal generator 4 during the scanning process, and obtain the corresponding optical power data through monitoring unit D. Calculate the mid-infrared microcavity quality factor of the microcavity 9 under test based on the initial wavelength λ0, output frequency data, and corresponding optical power data; specifically including: Step 5.1: Gradually increase the microwave signal output frequency of microwave signal generator 4, causing continuous frequency shifting of the mid-infrared pump laser to scan the microcavity 9 under test. During this process, the frequency of the optical frequency sideband gradually shifts towards longer wavelengths, similar to the temperature tuning process in step 3. When the optical frequency sideband reaches the trough of the microcavity resonance curve, the power measured by power meter 11 drops to its lowest value T. min Continue tuning, and when the optical frequency sideband reaches the peak of the resonance curve, the power rises back to its highest value T. max This completes the frequency-shift scanning of the resonance curve of the microcavity 9 under test, and the system state is as follows: Figure 2 As shown in d. At this time, record the output frequency data of the microwave signal generator 4 and the corresponding optical power data shown by the power meter 11, and plot as shown in Figure d. Figure 4The curves shown are plotted with output frequency data on the X-axis and optical power data on the Y-axis; where the X-axis represents the output frequency increasing continuously from 0 to 15 GHz.

[0042] Step 5.2: Calculate the optical power (T) based on the change curve plotted in Step 5.1. max -T min The resonant frequency with a full width at half maximum (FWHM) of f when the value is 1 / 2 is f. avg ; Step 5.3: Calculate the mid-infrared microcavity quality factor of the microcavity to be tested 9. Q : Q =c / (λ0×f avg ) Where c is the speed of light.

[0043] like Figure 4 As shown, the pump laser wavelength λ0 used in this embodiment is 3μm, and the optical power reaches (T). max -T min The resonant frequency with a full width at half maximum (FWHM) of f when the value is 1 / 2 is f. avg The final measured quality factor of the microcavity was 676.48 MHz. Q It is 1.48×10 5 .

[0044] The principle of this invention is as follows: a mid-infrared narrow-linewidth laser 1 with a fixed frequency is used. First, the pump frequency is preset to the edge of the resonant peak frequency of the microcavity 9 under test by changing the temperature of the microcavity 9 under test. Then, the mid-infrared intensity modulator 3 is set to generate a frequency-shiftable optical sideband. Finally, the continuous frequency shift scanning of the microcavity 9 under test is achieved by adjusting the microwave signal output frequency, thereby completing the quality factor measurement of the microcavity 9 under test. On the one hand, it solves the problem that the quality factor is difficult to measure in the mid-infrared band due to the lack of frequency-sweeping lasers with fast frequency tunability and high-speed optical switching devices. On the other hand, by using the optical frequency sideband with continuous frequency shifting to scan the microcavity under test 9, it solves the problems of the sweeping method commonly used in other bands being limited by the sweeping rate and minimum step size, resulting in limited measurement accuracy and inability to measure extremely high quality factors, as well as the problem of the ring-down method being limited by the optical switching rate and unable to measure extremely low quality factors. Moreover, it only requires a miniaturized narrow-linewidth laser with a fixed frequency for pumping without the need for a high-performance, large-volume precision tunable light source. Therefore, it has the characteristics of high accuracy, large measurement range, wide applicability, simple structure, low cost, and easy operation.

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-precision mid-infrared microcavity quality factor measurement device, characterized in that: It includes a pump unit A, a frequency shift scanning unit B, a frequency tuning unit C, and a monitoring unit D connected in sequence; The pump unit A is used to emit a mid-infrared pump laser at a fixed frequency; The frequency shift scanning unit B includes a mid-infrared intensity modulator (3) and a first focusing lens (7) arranged sequentially along the output direction on the optical path of the mid-infrared pump laser, as well as a microwave signal generator (4) and a DC power supply (5) electrically connected to the mid-infrared intensity modulator (3); the mid-infrared intensity modulator (3) is used to modulate the mid-infrared pump laser to generate a frequency-shiftable optical sideband; the microwave signal generator (4) is used to output microwave signals of different frequencies to the mid-infrared intensity modulator (3); the DC power supply (5) is used to output a bias voltage to control the working state of the mid-infrared intensity modulator (3); the first focusing lens (7) is used to compress the optical mode field size of the modulated mid-infrared pump laser so that it is input to the microcavity under test (9). The frequency tuning unit C is used to place the microcavity to be tested (9) and to tune it; The monitoring unit D is used to monitor the laser power and spectrum after being acted upon by the microcavity under test (9).

2. The high-precision mid-infrared microcavity quality factor measuring device according to claim 1, characterized in that: The frequency shift scanning unit B also includes a bias unit (6); The microwave signal output terminal of the microwave signal generator (4) is electrically connected to the microwave signal input terminal of the bias device (6). The output terminal of the DC power supply (5) is electrically connected to the DC signal input terminal of the bias (6); The output terminal of the bias device (6) is electrically connected to the electrical signal input terminal of the mid-infrared intensity modulator (3).

3. The high-precision mid-infrared microcavity quality factor measuring device according to claim 1 or 2, characterized in that: The pump unit A includes a mid-infrared narrow linewidth laser (1) and a second focusing lens (2). The mid-infrared narrow linewidth laser (1) is used to emit a mid-infrared pump laser at a fixed frequency; The second focusing lens (2) is used to compress the spot size of the mid-infrared pump laser so that it can be incident on the mid-infrared intensity modulator (3) with higher efficiency. The frequency tuning unit C includes a three-dimensional displacement platform and a semiconductor thermoelectric cooler (8) disposed on the three-dimensional displacement platform. The semiconductor thermoelectric cooler (8) is used to carry the microcavity to be tested (9) and control its temperature.

4. The high-precision mid-infrared microcavity quality factor measuring device according to claim 3, characterized in that: The monitoring unit D includes a spectroscope (10), a power meter (11), and a spectrometer (12). The beam splitter (10) is disposed at the output end of the microcavity (9) under test and is used to split the beam after the microcavity (9) under test into a first beam and a second beam. The power meter (11) is set in the optical path of the first beam and is used to monitor the optical power of the first beam; The spectrometer (12) is set in the optical path of the second beam to monitor the spectrum of the second beam.

5. A high-precision mid-infrared microcavity quality factor measurement method, employing the high-precision mid-infrared microcavity quality factor measurement device according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Place the microcavity to be tested (9) in the frequency tuning unit C; Step 2: Start pump unit A and monitoring unit D. Pump unit A emits mid-infrared pump laser, and its initial wavelength λ0 is obtained through monitoring unit D. Step 3: Start and adjust the frequency tuning unit C so that the edge frequency of the resonant peak of the microcavity under test (9) coincides with the frequency of the mid-infrared pump laser. Step 4: Start the frequency shift scanning unit B, adjust the microwave signal generator (4) and DC power supply (5) to make the mid-infrared intensity modulator (3) work in push-pull mode to suppress the optical power of the mid-infrared pump laser and generate a frequency-shiftable optical sideband. Step 5: Adjust the microwave signal output frequency of the microwave signal generator (4) to continuously shift the frequency of the mid-infrared pump laser, thereby scanning the microcavity (9) under test, acquiring the output frequency data of the microwave signal generator (4) during the scanning process, and acquiring the corresponding optical power data through the monitoring unit D. Calculate the mid-infrared microcavity quality factor of the microcavity under test (9) based on the initial wavelength λ0, the output frequency data and the corresponding optical power data, and complete the mid-infrared microcavity quality factor measurement.

6. The high-precision mid-infrared microcavity quality factor measurement method according to claim 5, characterized in that: Step 1 specifically involves placing the microcavity to be tested (9) at the active end of the semiconductor thermoelectric cooler (8).

7. The high-precision mid-infrared microcavity quality factor measurement method according to claim 6, characterized in that: Step 2 specifically involves starting the mid-infrared narrow-linewidth laser (1), power meter (11), and spectrometer (12), with the mid-infrared narrow-linewidth laser (1) emitting mid-infrared pump laser; adjusting the positions of the second focusing lens (2), the first focusing lens (7), and the three-dimensional displacement platform so that the mid-infrared pump laser can be incident on the mid-infrared intensity modulator (3), the microcavity under test (9), the beam splitter (10), the power meter (11), and the spectrometer (12), and recording the initial wavelength λ0 shown by the spectrometer (12).

8. The high-precision mid-infrared microcavity quality factor measurement method according to claim 7, characterized in that: Step 3 specifically involves starting the semiconductor thermoelectric cooler (8) and gradually increasing or decreasing its temperature until the power value shown by the power meter (11) first reaches its lowest value P. min It then reached a maximum value P again. max Reaching the highest value P max If the temperature of the semiconductor thermoelectric cooler (8) is kept constant, the edge frequency of the resonant peak of the microcavity (9) to be tested coincides with the frequency of the mid-infrared pump laser.

9. The high-precision mid-infrared microcavity quality factor measurement method according to claim 6, 7, or 8, characterized in that, Step 4 specifically includes: Step 4.1: Start the microwave signal generator (4) and DC power supply (5), and adjust the output voltage of the DC power supply (5) until the power value shown by the power meter (11) reaches the minimum value P. min At the same time, maintain the output voltage V of the DC power supply (5). π If it remains unchanged, the phase difference of the light wave modes of the two arms of the mid-infrared intensity modulator (3) is set to π; Step 4.2: Adjust the output voltage of the microwave signal generator (4) so ​​that the mid-infrared intensity modulator (3) works in push-pull mode to suppress the optical power of the mid-infrared pump laser and generate two frequency-movable optical sidebands.

10. The high-precision mid-infrared microcavity quality factor measurement method according to claim 9, characterized in that, Step 5 specifically includes: Step 5.1: Gradually increase the microwave signal output frequency of the microwave signal generator (4) to continuously shift the frequency of the mid-infrared pump laser, thereby scanning the microcavity (9) under test until the power value shown by the power meter (11) first reaches the lowest value T. min It then reached another peak value T. max Record the output frequency data of the microwave signal generator (4) and the corresponding optical power data shown by the power meter (11), and plot the change curve with the output frequency data as the X-axis and the optical power data as the Y-axis; Step 5.2: Calculate the optical power (T) based on the change curve plotted in Step 5.

1. max -T min The resonant frequency with a full width at half maximum (FWHM) of f when the value is 1 / 2 is f. avg ; Step 5.3: Calculate the mid-infrared microcavity quality factor of the microcavity to be tested (9). Q : Q =c / (λ0×f avg ) Where c is the speed of light.

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