A measurement device and system based on cascaded optical resonators

Abstract

The application relates to the technical field of measuring devices, in particular to a measuring device and system based on a cascade optical resonant cavity, which comprises a laser light source for emitting a laser light beam to the circulator; the circulator is used for guiding the incident laser light beam to the fixed resonant assembly and outputting reflected light from the fixed resonant assembly to the photoelectric conversion device; the photoelectric conversion device is used for converting the reflected light into an electric signal; the air resonant device is used for reflecting the incident laser light beam with the fixed resonant assembly and defining an optical cavity length; the fixed resonant assembly is used for reflecting the incident laser light beam with the air resonant device, realizing sensing of a to-be-measured signal, and filtering high-order modes of the incident laser light beam, so that the machining difficulty of the measuring device is reduced, and the stability of the measuring device is improved.

Description

Technical Field

[0001] This application relates to the technical field of measuring devices, and in particular to a measuring device and system based on a cascaded optical resonant cavity. Background Technology

[0002] Optical acoustic wave measurement can be mainly divided into two categories based on different sensing principles: inertial and non-inertial. Inertial measurement devices rely on the displacement of mechanical vibration units such as diaphragms to respond to changes in signals such as sound pressure. Their low-frequency response is limited by mechanical inertia, while high-frequency response is constrained by the structural resonant frequency, and they are prone to signal tailing and distortion. Non-inertial optical measurement devices, based on the measurement method of optical resonant cavities, achieve signal demodulation by detecting changes in the refractive index of the medium inside the cavity caused by sound waves. In principle, this avoids mechanical inertia and has a wider frequency response range and lower signal distortion.

[0003] Existing non-inertial optical measurement devices, especially those based on resonant cavities, suffer from limitations in overall performance and reliability due to the structural design and integration of the resonant sensing unit. Current common solutions typically consist of several mirrors. This structure, due to its complex resonant cavity structure and large size, leads to cumbersome fabrication processes and high costs. Furthermore, it is highly sensitive to environmental disturbances such as temperature fluctuations and mechanical vibrations, resulting in insufficient long-term stability. Moreover, existing systems have stringent requirements for optical path alignment and coupling precision; misalignment can cause mode instability or excitation of higher-order modes, leading to decreased sensing sensitivity or even signal failure. These limitations restrict their practical application in complex environments or situations requiring long-term stable operation. These issues need to be addressed. Summary of the Invention

[0004] To reduce the fabrication difficulty of the measuring device and improve its stability, this application provides a measuring device and system based on a cascaded optical resonant cavity, employing the following technical solution:

[0005] In a first aspect, this application provides a measurement device based on a cascaded optical resonant cavity, comprising a laser source, a circulator, a photoelectric conversion device, an air resonator, and a fixed resonant assembly, wherein:

[0006] The laser source is used to emit a laser beam to the circulator;

[0007] The circulator is used to guide the incident laser beam to the fixed resonant component and to output the reflected light from the fixed resonant component to the photoelectric conversion device;

[0008] A photoelectric conversion device for converting the reflected light into an electrical signal;

[0009] An air resonator is used to reflect the incident laser beam in conjunction with the fixed resonator assembly, and defines the optical cavity length;

[0010] A fixed resonant component is used to reflect the incident laser beam with the air resonator to realize the sensing of the signal to be measured, and to filter the incident laser beam into higher-order modes.

[0011] Preferably, the fixed resonant assembly includes a reflective grating and a partially reflective film.

[0012] Preferably, it also includes a collimator;

[0013] The circulator is connected to the collimator;

[0014] The reflective grating is located between the circulator and the collimator;

[0015] The partial reflective film is located at one end of the collimator.

[0016] Preferably, the air resonator includes a reflector.

[0017] Preferably, it further includes a feedback adjustment component for generating an adjustment signal based on an electrical signal to adjust the laser source or the air resonator.

[0018] Preferably, the air resonator includes a movable component connected to the reflector for changing the position of the reflector according to the adjustment signal of the feedback adjustment component.

[0019] Preferably, the feedback adjustment component includes a processing unit and a first feedback unit;

[0020] The processing unit is connected between the output end of the photoelectric conversion device and the input end of the first feedback unit, and the output end of the first feedback unit is connected to the laser light source.

[0021] Preferably, the feedback adjustment component further includes a second feedback unit;

[0022] The second feedback unit is connected between the processing unit and the moving component of the air resonator.

[0023] Preferably, the feedback adjustment component further includes a temperature acquisition unit;

[0024] The temperature acquisition unit is connected between the reflective grating and the processing unit, and is used to acquire the temperature signal of the reflective grating;

[0025] The feedback adjustment component generates an adjustment signal based on the temperature signal to adjust the laser source or the air resonator.

[0026] Secondly, this application provides a measurement system based on a cascaded optical resonator, including the measurement device based on a cascaded optical resonator as described above.

[0027] In summary, compared with the prior art, the beneficial effects of the technical solution provided in this application include at least the following:

[0028] This application utilizes a laser source to emit a laser beam. The laser beam is guided by a circulator to a fixed resonant component and an air resonator for modulation. The air resonator and the fixed resonant component form an air resonant cavity. When the cavity is disturbed by external signals, the air refractive index changes, causing the laser beam to be modulated. The fixed resonant component filters out higher-order modes, and the circulator then transmits the modulated laser beam to a photoelectric conversion device. The photoelectric conversion device converts the laser beam into an electrical signal for output. The combination of the air resonator and the fixed resonant component reduces the manufacturing difficulty of the measuring device, and the filtering of higher-order modes improves the stability of the measuring device. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a measurement device based on a cascaded optical resonant cavity as described in an embodiment of this application.

[0030] Figure 2 This is a schematic diagram of the structure of the measurement device based on a cascaded optical resonant cavity as described in the embodiments of this application.

[0031] Figure 3 This is a schematic diagram of a measurement system based on a cascaded optical resonator as described in an embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Laser source; 2. Circulator; 3. Photoelectric conversion device; 4. Air resonator; 5. Fixed resonator assembly; 51. Reflective grating; 52. Partial reflective film; 6. Collimator; 7. Feedback adjustment assembly; 71. Processing unit; 72. First feedback unit; 73. Second feedback unit; 74. Temperature acquisition unit. Detailed Implementation

[0034] The following combination Figures 1-3 The present application will be described in further detail below. The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0035] Reference Figure 1 and Figure 2 The measurement device based on a cascaded optical resonator disclosed in this application specifically includes a laser source 1, a circulator 2, a photoelectric conversion device 3, an air resonator 4, and a fixed resonator assembly 5, wherein:

[0036] The laser source 1 is used to emit a laser beam to the circulator 2;

[0037] The circulator 2 is used to guide the incident laser beam to the fixed resonant component 5 and to output the reflected light from the fixed resonant component 5 to the photoelectric conversion device 3;

[0038] Photoelectric conversion device 3, used to convert the reflected light into an electrical signal;

[0039] Air resonator 4 is used to reflect the incident laser beam with the fixed resonator 5 and defines the optical cavity length;

[0040] The fixed resonant component 5 is used to reflect the incident laser beam with the air resonant device 4 to realize the sensing of the signal to be measured, and to filter the incident laser beam into higher-order modes.

[0041] Specifically, the measurement device based on the cascaded optical resonator of this application consists of a laser source 1, a circulator 2, a photoelectric conversion device 3, an air resonator 4, and a fixed resonator assembly 5. This application addresses the shortcomings of existing optical resonators, such as their large size, complex fabrication process, susceptibility to external interference, and high coupling requirements. It optimizes the resonator structure by combining the air resonator 4 and the fixed resonator assembly 5 to form the resonator.

[0042] In this embodiment, the laser source 1 emits a laser beam. The laser beam is guided by the circulator 2 and transmitted to the fixed resonant component 5 and the air resonator 4 for modulation. The air resonator 4 and the fixed resonant component 5 form a resonant cavity. The refractive index of the air inside the cavity changes due to interference from external signals, thus modulating the laser beam. The fixed resonant component 5 filters out higher-order modes, and the circulator 2 then transmits the modulated laser beam to the photoelectric conversion device 3. The photoelectric conversion device 3 converts the laser beam into an electrical signal for output. The combination of the air resonator 4 and the fixed resonant component 5 reduces the manufacturing difficulty of the measuring device and improves the stability of the measuring device by filtering out higher-order modes.

[0043] The laser source 1 in this embodiment can be a fixed-wavelength source or a wavelength-tunable source. If it is a fixed-wavelength source, the device can stabilize the operating point of the system by adjusting the position of the reflector. If it is a wavelength-tunable source, the device simultaneously controls the operating points of the position stabilization system for both the source and the reflector.

[0044] In one embodiment, the air resonator 4 includes a reflector.

[0045] Specifically, the air resonator 4 in this application embodiment includes, but is not limited to, a reflector. The reflector can be planar or curved, and can be fixed together with the collimator 6 on the same substrate or connected using a fixed mechanical structure, or can be set separately. As one embodiment, the fixed resonator assembly includes a reflective grating and a partially reflective film.

[0046] Specifically, in this embodiment, the circulator 2 is connected to the collimator 6 via an optical fiber, and a reflective grating 51 is etched on the optical fiber of the collimator 6. The reflective grating 51 not only serves as a reflective surface but also has wavelength selection and filtering functions, which can suppress broadband noise, improve the signal-to-noise ratio, and its angle sensitivity can be used to achieve finer mode control or as a sensing parameter.

[0047] The reflective grating 51 typically provides high wavelength selectivity. In this embodiment, this combination can achieve high precision and narrow bandwidth, and is extremely sensitive to changes near a specific wavelength, tending to achieve high sensitivity, making it suitable for weak acoustic signal detection.

[0048] In this embodiment, the partial reflective film 52 is specifically coated on the light-inlet or light-outlet end of the collimator 6. One embodiment uses the collimator 6 coated with the partial reflective film 52 to directly align with the reflector for optical wave coupling. The integrated reflective film on the end face of the collimator 6 achieves a high degree of integration of optical path components, combining reflection and coupling functions with the fiber optic collimator 6, significantly reducing discrete optical components, improving the system's mechanical stability and anti-interference capability, and reducing assembly difficulty and cost.

[0049] This application embodiment utilizes a high-quality partial reflective film 52, such as a dielectric film, to achieve high reflectivity over an extremely wide bandwidth with extremely low loss. This results in high precision, high FSR, and low loss, maintaining good linearity over a wide dynamic range, making it suitable for scenarios with strong sound fields or where high sound pressure level changes need to be measured.

[0050] The free spectral range and precision of traditional fixed-structure resonant cavities are determined after manufacturing, which locks in the trade-off between sensitivity and dynamic range, making it difficult to adapt to the measurement requirements of different sound field intensities.

[0051] This application embodiment reconstructs the optical length and loss of the resonant cavity by selecting different combinations of cavity components, thereby altering the FSR and precision. This application embodiment is equivalent to providing the system with multiple sensor cores of different ranges and accuracies, selecting the optimal configuration based on the estimated intensity of the target acoustic signal to achieve customized measurement.

[0052] The cascaded structure of this application embodiment has better mode selectivity, suppresses higher-order modes, and reduces alignment requirements; it has better dispersion characteristics, enabling sharper resonant edges for high-sensitivity detection; and it has better potential environmental noise suppression capabilities, making the measurement device more stable.

[0053] In this embodiment, the reflective grating 51 provides primary filtering and selection, and the cavity of the partial reflective film 52 serves as a secondary resonant unit. The dual filtering and resonance generate an exceptionally sharp resonant line or electromagnetically induced transparency-like effect, achieving the highest sensitivity and signal-to-noise ratio among the three.

[0054] Optical wave coupling is achieved by directly aligning a collimator 6 with a partially reflective film 52 to the reflector, while a reflective grating 51 is etched onto the optical fiber of the collimator 6, thus forming a cascaded optical resonant cavity. The position of the reflector is adjusted relative to the center wavelength of the laser using a control system to maintain the stability of the cascaded optical resonant cavity.

[0055] Compared to a single optical resonator, the cascaded optical resonator proposed in this application significantly improves performance indicators such as free spectral width, contrast, and precision, making the overall performance of the acoustic wave measurement device more outstanding. Moreover, compared to the traditional optical resonator with two fixed planes, this application uses a reflective grating 51 and a coating as the reflective surface, which is simple in structure, small in size, easy to manufacture, and more stable.

[0056] The reflective grating 51 and the reflector can form an optical resonant cavity. The reflective film 52 on the end face of the collimator 6 and the reflector can also form an optical resonant cavity. The reflective grating 51, the reflective film 52 on the end face of the collimator 6, and the reflector form a cascaded optical resonant cavity. The three resonant cavities have different performances. Any cavity or multiple cavities can be selected and used in combination as needed.

[0057] In practical optical resonant cavities, due to factors such as fabrication process and beam quality, beams with different equivalent optical paths may satisfy the resonance condition, resulting in a large number of higher-order transverse modes in addition to the fundamental mode. These higher-order modes cause distortion of the interference fringe shape, decreased contrast of the resonance curve, reduced effective precision, and the introduction of additional noise into the measurement signal. However, in this embodiment, a fixed resonant cavity composed of a reflective grating 51 and a partially reflective film 52 is added after the air resonant cavity. This fixed cavity is unaffected by factors such as fabrication process and beam quality. The beam must simultaneously satisfy the resonance conditions of both cavities to be output, thereby effectively eliminating higher-order modes or selectively controlling the film. This concentrates the beam energy more on the fundamental mode required by the system, makes the beam spot output into the air resonator more uniform, and improves the coupling efficiency of the fundamental mode, resulting in significant improvements in performance indicators such as free spectral width, contrast, and precision.

[0058] As one implementation, a collimator 6 is also included;

[0059] Collimator 6 is connected to the second port of circulator 2. Collimator 6 is used to transmit the laser beam output from the second port of circulator 2 to air resonator 4, and to transmit the laser beam output from air resonator 4 to the second port of circulator 2.

[0060] Specifically, in this embodiment, the first port of the circulator 2 is connected to the laser source 1, the second port of the circulator 2 is connected to the collimator 6, and the third port of the circulator 2 is connected to the photodetector. The laser beam enters from the first port of the circulator 2 and exits from the second port. It is then transmitted to the collimator 6 via a transmission method such as optical fiber. The collimator 6 converts the diverging beam in the optical fiber into a parallel beam output. The beam then passes through a resonant cavity composed of an air resonator 4 and a fixed resonant component 5. The air resonator 4 and the fixed resonant component 5 work together to reflect the laser beam. During this process, the refractive index of the air inside the cavity is affected by vibrations from signals such as sound waves. The laser beam interferes during reflection and is then transmitted to the collimator 6. The collimator 6 retransmits the laser beam back to the second port of the circulator 2, and then outputs it from the third port of the circulator 2.

[0061] In the use of measuring devices such as acoustic wave measurement devices, sensitivity and dynamic range are inversely proportional. Higher sensitivity usually indicates a smaller system dynamic range. However, different applications have different requirements. High sensitivity is needed in weak sound signal applications, while a large dynamic range is needed in strong sound signal applications. The three cascaded cavities provided in this application have different sensitivities and dynamic ranges due to their different cavity lengths, i.e., different FSR and fineness. In practical applications, any one cavity or multiple cavities can be selected and used in combination as needed. As one implementation, a feedback adjustment component 7 is also included, used to generate an adjustment signal based on an electrical signal to adjust the laser source 1 or the air resonator 4.

[0062] Specifically, in this embodiment, the laser source 1 or the air resonator 4 can be adjusted by the feedback adjustment component 7, and the laser source 1 and the air resonator can also be adjusted.

[0063] By converting the modulated laser beam into an electrical signal and analyzing the signal, the laser source 1 and the air resonator 4 are adjusted based on the analysis results to stabilize the entire system at the point where the optical resonator slope is at its maximum.

[0064] In one embodiment, the air resonator 4 includes a movable component connected to the reflector for changing the position of the reflector according to the adjustment signal of the feedback adjustment component 7.

[0065] Specifically, in this embodiment, the position of the moving component is adjusted by a feedback adjustment signal, thereby adjusting the optical cavity length. The incident laser resonates cyclically within the cascaded resonant cavity composed of the fixed resonant component 5 and the air resonator 4. The sound wave under test modulates the air refractive index in the region where the resonant cavity is located, changing the effective optical length of the entire resonant cavity, thus causing a shift in the resonant frequency or phase. The reflector is adjusted to a suitable position by the moving component, thereby adjusting the reflected light path to a working state.

[0066] As one implementation, the feedback adjustment component 7 includes a processing unit 71 and a first feedback unit 72;

[0067] The processing unit 71 is connected between the output terminal of the photoelectric conversion device 3 and the input terminal of the first feedback unit 72, and the output terminal of the first feedback unit 72 is connected to the laser source 1.

[0068] Specifically, in this embodiment, the processing unit 71 analyzes the electrical signal of the photoelectric conversion device 3 and compares it with the reference value to obtain the offset value. The adjustment parameters of the laser source 1 are matched according to the offset value, and the adjustment parameters are fed back through the first feedback unit 72 to adjust the laser source 1.

[0069] As one implementation, the feedback adjustment component 7 further includes a second feedback unit 73;

[0070] The second feedback unit 73 is connected between the processing unit 71 and the moving component of the air resonator 4.

[0071] Specifically, in this embodiment, the processing unit 71 analyzes the electrical signal of the photoelectric conversion device 3 and compares it with the reference value to obtain the offset value. The offset value is then matched with the adjustment parameters of the position of the air resonator 4. The adjustment parameters are fed back through the second feedback unit 73 to control the moving component to adjust the position of the air resonator 4.

[0072] In one embodiment, after analyzing the electrical signal, the offset value is obtained as an adjustment parameter for matching the coordinated adjustment of the air resonator 4 and the laser source 1.

[0073] As one implementation, the feedback adjustment component 7 also includes a temperature acquisition unit 74;

[0074] Temperature acquisition unit 74 is connected between reflective grating 51 and processing unit 71, and is used to acquire temperature signal of reflective grating 51;

[0075] The feedback adjustment component generates an adjustment signal based on the temperature signal to adjust the laser source or air resonator.

[0076] Specifically, the reflective grating 51 in the cascaded optical resonant cavity proposed in this application embodiment can serve as a reflective surface, forming a cascaded optical resonant cavity with the partial reflective film 52 and the reflective mirror on the end face of the collimator 6. Moreover, the spectrum of the reflective grating 51 can be measured independently, and the temperature or pressure can be measured through the temperature acquisition unit 74. The measured temperature or pressure is fed back to the first feedback unit 72 and the second feedback unit 73 in real time to control the center wavelength of the laser, so that the center wavelength of the laser is always at the operating point of the cascaded cavity.

[0077] This application employs a cascaded optical resonant cavity composed of a reflective grating 51, a partially reflective film 52 on the collimator 6 end face, and a mirror. This effectively eliminates higher-order modes or selective films, significantly improving performance indicators such as free spectral width, contrast, and precision, resulting in superior performance of the entire acoustic wave measurement device. The reflective grating 51 and the mirror can form an optical resonant cavity; the partially reflective film 52 on the collimator 6 end face and the mirror can also form an optical resonant cavity; and the reflective grating 51, the partially reflective film 52 on the collimator 6 end face, and the mirror can form a cascaded optical resonant cavity. These three types of resonant cavities possess different performance characteristics, and any cavity or multiple cavities can be selected and used in combination as needed. Using the collimator 6 directly aligned with the mirror to form the optical resonant cavity results in a simple structure and manufacturing process, stronger stability, and lower cost. A feedback system is constructed using the reflective grating 51, the laser source 1, the adjustable-position air resonator 4, and the processing unit 71, ensuring that the center wavelength of the laser is always at the operating point of the optical resonant cavity, thus enhancing system stability.

[0078] Reference Figure 3 This application provides a measurement system based on a cascaded optical resonator, which includes the measurement device based on the cascaded optical resonator as described above.

[0079] Specifically, it also includes a data processor electrically connected to the measurement device based on the cascaded optical resonator. The data processor is used to invert the acoustic wave information in the air resonator 4 and the fixed resonator assembly 5 based on the electrical signal converted by the measurement device based on the cascaded optical resonator.

[0080] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the device and product described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0081] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit 71, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0082] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A measurement device based on a cascaded optical resonant cavity, characterized in that, This includes laser light sources, circulators, photoelectric conversion devices, air resonators, and fixed resonator components, among which: The laser source is used to emit a laser beam to the circulator; The circulator is used to guide the incident laser beam to the fixed resonant component and to output the reflected light from the fixed resonant component to the photoelectric conversion device; A photoelectric conversion device for converting the reflected light into an electrical signal; An air resonator is used to reflect the incident laser beam in conjunction with the fixed resonator assembly, and defines the optical cavity length; A fixed resonant component is used to reflect the incident laser beam with the air resonator to realize the sensing of the signal to be measured, and to filter the incident laser beam for higher-order modes; the fixed resonant component includes a reflective grating and a partially reflective film. It also includes a collimator; The circulator is connected to the collimator; The reflective grating is located between the circulator and the collimator; The partial reflective film is located at one end of the collimator; It also includes a processing unit, a first feedback unit, and a second feedback unit; The processing unit is connected between the output end of the photoelectric conversion device and the input end of the first feedback unit, and the output end of the first feedback unit is connected to the laser light source; the second feedback unit is connected between the processing unit and the moving component of the air resonator. The processing unit is used to: analyze the electrical signal of the photoelectric conversion device, compare it with a reference value to obtain an offset value, match the adjustment parameters of the laser source according to the offset value, and adjust the laser source by feeding back the adjustment parameters through the first feedback unit; analyze the electrical signal of the photoelectric conversion device, compare it with a reference value to obtain an offset value, match the adjustment parameters of the air resonator position according to the offset value, and control the moving component to adjust the position of the air resonator by feeding back the adjustment parameters through the second feedback unit.

2. The measuring device based on a cascaded optical resonator according to claim 1, characterized in that, The air resonator includes a reflector.

3. The measuring device based on a cascaded optical resonator according to claim 2, characterized in that, It also includes a feedback adjustment component for generating an adjustment signal based on an electrical signal to adjust the laser source or the air resonator.

4. The measuring device based on a cascaded optical resonator according to claim 3, characterized in that, The air resonator includes a movable component connected to the reflector, used to change the position of the reflector according to the adjustment signal of the feedback adjustment component.

5. The measuring device based on a cascaded optical resonator according to claim 3, characterized in that, The feedback adjustment component also includes a temperature acquisition unit; The temperature acquisition unit is connected between the reflective grating and the processing unit, and is used to acquire the temperature signal of the reflective grating; The feedback adjustment component generates an adjustment signal based on the temperature signal to adjust the laser source or the air resonator.

6. A measurement system based on a cascaded optical resonator, characterized in that, The measuring device based on a cascaded optical resonator as described in any one of claims 1 to 5.

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