Micro-ring resonant cavity acoustic sensor based on vernier effect

Abstract

The invention provides a vernier effect-based micro-ring resonant cavity acoustic sensor, and belongs to the technical field of optical-acoustic sensors. Comprising a coupling unit; the light source is used for generating light signals; the cascade sensing ring unit comprises a front-stage sensing ring and a rear-stage reference ring, one end of the front-stage sensing ring is connected with a light path of the light source, and the other end of the front-stage sensing ring is connected with a light path of one end of the rear-stage reference ring through the coupling unit; wherein each of the front-stage sensing ring and the rear-stage reference ring comprises a hollow plate glass substrate, a first PDMS thin film, a micro-nano optical fiber knot and a second PDMS thin film which are sequentially stacked, and the two ends of the micro-nano optical fiber knot in the axial extension direction serve as the two ends of the sensing ring; the radius and the free spectral range of the micro-nano optical fiber junctions of the front-stage sensing ring and the rear-stage reference ring are different. The micro-nano optical fiber knot and the multi-stage sensing ring structure are adopted, the acoustic sensor can accurately detect weak acoustic pressure change, and the sensing ring is very sensitive to wavelength drift and acoustic pressure change.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic sensors, and in particular, to a micro-ring resonator acoustic sensor based on the Vernier effect. Background Art

[0002] Traditional acoustic signal detection technologies, such as piezoelectric transducers for acoustic measurement, usually encounter problems such as excessive electromagnetic interference, large structural size, and low sensitivity. Photoacoustic detection technology based on the interaction between the strain field and the optical field avoids the above disadvantages to a certain extent, but traditional optical technologies such as Fabry-Perot interferometers still have problems such as narrow frequency response range and difficulty in integration. Compared with piezoelectric transducers and traditional optical technologies in the application of acoustic sensing, micro-nano fiber knot resonators based on the whispering gallery mode have the advantages of anti-electromagnetic interference, small structural size, and high sensitivity, and have been widely studied in recent years. Acoustic sensors based on micro-ring resonators usually have two signal demodulation methods: intensity modulation and wavelength modulation. For the wavelength demodulation method, the sensitivity can be amplified in acoustic signal measurement by using the optical Vernier effect.

[0003] Therefore, it is very necessary to provide a micro-ring resonator acoustic sensor based on the Vernier effect, which has high sensitivity by adopting a cascaded double-ring micro-nano fiber knot resonator, and can achieve anti-interference, easy packaging and array integration. Summary of the Invention

[0004] In view of this, the present invention proposes a micro-nano fiber knot and a multi-stage sensing ring structure, and a micro-ring resonator acoustic sensor based on the Vernier effect that can accurately detect weak sound pressure changes and is very sensitive to wavelength drift and sound pressure changes.

[0005] The present invention provides a micro-ring resonator acoustic sensor based on the Vernier effect, comprising:

[0006] A coupling unit;

[0007] A light source for generating an optical signal;

[0008] A cascaded sensing ring unit, including a front-stage sensing ring and a rear-stage reference ring. One end of the front-stage sensing ring is optically connected to the light source, and the other end of the front-stage sensing ring is optically connected to one end of the rear-stage reference ring through the coupling unit;

[0009] Wherein, both the front-stage sensing ring and the rear-stage reference ring include a hollow flat glass substrate, a first PDMS film, a micro-nano fiber knot, and a second PDMS film that are sequentially stacked, and both ends of the micro-nano fiber knot in the axial extension direction are used as the two ends of the sensing ring; the radii and free spectral ranges of the micro-nano fiber knots of the front-stage sensing ring and the rear-stage reference ring are different.

[0010] Based on the above technical solutions, preferably, the micro-nano optical fiber knot is formed by stretching a single-mode optical fiber in a molten state, tying a knot in the reduced-diameter section of the molten optical fiber to form a knot loop, and the two ends of the micro-nano optical fiber knot extend outward along the direction tangent to the contour of the knot loop; the first PDMS film and the second PDMS film respectively cover one surface of the knot loop close to the hollow flat glass substrate and the surface of the knot loop far from the hollow flat glass substrate; an opening is provided at the corresponding position of the hollow flat glass substrate to the knot loop, and the opening penetrates along the radial direction of the knot loop.

[0011] Preferably, pigtails are respectively arranged at both ends of the micro-nano optical fiber knot, the pigtails are fusion-spliced with the micro-nano optical fiber knot, and the diameter of the pigtails is larger than that of the micro-nano optical fiber knot.

[0012] Preferably, let ΔFSR be the difference in the free spectral range of the micro-nano optical fiber knots of the front-stage sensing ring and the rear-stage reference ring, and FWHM be the full width at half maximum of the front-stage sensing ring. The two micro-nano optical fiber knots satisfy the following constraint relationship: 0.034FWHM ≤ ΔFSR ≤ FWHM; where R1 and R2 are the radii of the micro-nano optical fiber knots of the front-stage sensing ring and the rear-stage reference ring respectively, α is the transmission loss factor of the micro-nano optical fiber knot, t is the transmission coefficient of the coupling region, and π is the pi.

[0013] Based on the above technical solutions, preferably, it further includes a signal generator for generating a sound signal; the output end of the signal generator is arranged in the radial direction of the knot loop of the front-stage sensing ring and is arranged at a gap with the knot loop of the front-stage sensing ring.

[0014] Preferably, let the sound pressure sensitivity of the cascaded sensing ring unit be S D , the wavelength drift change amount of the cascaded sensing ring unit be Δλ D , Δλ D = Δλ1·M, where Δλ1 is the wavelength drift change amount of the front-stage sensing ring acting alone on the sound signal, M is the magnification factor of the cascaded sensing ring unit for the free spectral range of the front-stage sensing ring, ΔP is the sound pressure change amount, and it satisfies S is the sound pressure sensitivity of the front-stage sensing ring.

[0015] Based on the above technical solutions, preferably, the coupling unit is a flange or an optical fiber coupler, and both the front-stage sensing ring and the rear-stage reference ring are detachably connected to the coupling unit.

[0016] Preferably, it further includes a spectral analyzer, and the spectral analyzer is optically connected to the other end of the rear-stage reference ring.

[0017] Preferably, when the coupling unit uses an optical fiber coupler, the input end of the optical fiber coupler is optically connected to the output end of the front-stage sensing loop, the first output end of the optical fiber coupler is optically connected to the input end of the rear-stage reference loop, the second output end of the optical fiber coupler is optically connected to a photodetector, and the output end of the photodetector is electrically connected to a spectrum analyzer.

[0018] Based on the above technical solutions, preferably, the light source is an ASE broadband light source or a tunable laser.

[0019] A micro-ring resonator acoustic sensor based on the Vernier effect provided by the present invention has the following beneficial effects compared with the prior art:

[0020] (1) By adopting a micro-nano fiber knot and a multi-stage sensing loop structure, the acoustic sensor of the present invention can accurately detect weak acoustic pressure changes, and the sensing loop is very sensitive to wavelength drift and acoustic pressure changes; the free spectral ranges of the micro-nano fiber knots of the front-stage sensing loop and the rear-stage reference loop are slightly different, and this design can cause the transmission spectrum to change, improving the test sensitivity through the optical Vernier effect, thereby enhancing the overall acoustic signal detection ability;

[0021] (2) The micro-nano fiber knot is formed by stretching and knotting a single-mode fiber in a molten state to form a knot loop, which has good sensing characteristics, and its size design makes the sensing effect of sound waves more sensitive. The design of the first and second PDMS films helps to improve the stability and sensitivity of the sensor;

[0022] (3) By adopting a coupling unit, the front-stage sensing loop and the rear-stage reference loop can be conveniently disassembled and maintained, increasing the adjustability and service life of the device. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a schematic structural diagram of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0025] Figure 2 It is a schematic structural diagram of the sensing loop of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0026] Figure 3 It is a schematic diagram of the Vernier effect amplification principle of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0027] Figure 4 Wavelength drift diagram caused by refractive index difference of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0028] Figure 5 Test experimental device diagram of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0029] Figure 6 Power spectrum diagram after cascading different micro-ring resonators of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention;

[0030] Figure 7 Wavelength drift diagram and sensitivity diagram of the micro-ring resonator No. 17 of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 500 Hz;

[0031] Figure 8 Wavelength drift diagram and sensitivity diagram of the micro-ring resonator No. 17 of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 800 Hz;

[0032] Figure 9 Wavelength drift diagram of the first combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 500 Hz;

[0033] Figure 10 Acoustic sensing sensitivity diagram and frequency domain response diagram of the first combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 500 Hz;

[0034] Figure 11 Wavelength drift diagram of the first combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 800 Hz;

[0035] Figure 12 Acoustic sensing sensitivity diagram and frequency domain response diagram of the first combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 800 Hz;

[0036] Figure 13 Wavelength drift diagram of the second combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 800 Hz;

[0037] Figure 14 Acoustic sensing sensitivity diagram and frequency domain response diagram of the second combination of a micro-ring resonator acoustic sensor based on the Vernier effect of the present invention at 800 Hz. Detailed implementation manner

[0038] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] As Figure 1 shown, the present invention provides a micro-ring resonator acoustic sensor based on the cursor effect, including:

[0040] A coupling unit 3;

[0041] A light source for generating an optical signal;

[0042] A cascaded sensing ring unit, including a front-stage sensing ring 1 and a rear-stage reference ring 2. One end of the front-stage sensing ring 1 is optically connected to the light source optical path, and the other end of the front-stage sensing ring 1 is optically connected to one end of the rear-stage reference ring 2 through the coupling unit 3;

[0043] Wherein, both the front-stage sensing ring 1 and the rear-stage reference ring 2 include a hollow flat glass substrate 4, a first PDMS film 5, a micro-nano fiber knot 6, and a second PDMS film 7 that are sequentially stacked. The two ends in the axial extension direction of the micro-nano fiber knot 6 are used as the two ends of the sensing ring; the radii and free spectral ranges (FSRs) of the micro-nano fiber knots 6 of the front-stage sensing ring 1 and the rear-stage reference ring 2 are different.

[0044] This structure uses a hollow flat glass substrate to achieve dual-functional optimization: First, the micro-nano fiber knot is only coated with two upper and lower ultra-thin PDMS films, ensuring that the acoustic signal can directly act on the sensitive area during the sensing process, thereby effectively eliminating the influence of the substrate material on the sensitive unit; Second, since the optical fiber is a sensitive material vulnerable to external interference, the glass substrate can provide a stable support for the end of the optical fiber, which can not only fix and protect the two end optical fibers, but also effectively avoid the influence of external interference such as vibration of the two end optical fibers on the core sensitive unit. This design improves the sensitivity of the acoustic signal response of the sensor and ensures its long-term stability in a complex environment.

[0045] The structural feature of the present invention is to adopt a series structure of two micro-ring resonators, that is, the front-stage sensing ring 1 and the rear-stage reference ring 2 respectively form a micro-nano fiber knot type resonator structure. After the two micro-ring resonators are cascaded through the coupling unit 3, an interference type sensor structure with a cursor amplification effect is formed.

[0046] The cascaded structure of the two micro-ring resonators in the cascaded sensing ring unit will cause the transmission spectrum to change, improving the sensitivity of the test through the optical cursor effect, and this modular architecture provides further development space for the high-density integration of the resonator array through the standardized design of the flange interface.

[0047] In this embodiment, the micro-nano fiber knot 6 is formed by stretching a single-mode fiber in a molten state to obtain a micro-nano fiber with a diameter of 3 microns, knotting the reduced-diameter section of the molten micro-nano fiber to form a knot loop, and the two ends of the micro-nano fiber knot extending outward along the direction tangent to the contour of the knot loop; the first PDMS film 5 and the second PDMS film 7 respectively cover one surface of the knot loop close to the hollow flat glass substrate 4 and the surface far from the hollow flat glass substrate 4; an opening is provided at the corresponding position of the hollow flat glass substrate 4 to the knot loop, and the opening penetrates along the radial direction of the knot loop.

[0048] It is composed of the thinnest part of the micro-nano fiber drawn from a single-mode fiber in a molten state. The two tapered parts at both ends are supported and protected by two layers of PDMS films and a flat glass substrate, and then the pigtail is fusion-spliced. With the assistance of a microscope and a three-dimensional displacement platform, the size of the micro-nano fiber knot can be well controlled, and the preparation success rate of the micro-nano fiber knot can be greatly improved.

[0049] As Figure 2 shown, pigtails are respectively arranged at both ends of the micro-nano fiber knot, the pigtails are fusion-spliced with the micro-nano fiber knot, and the diameter of the pigtail is larger than that of the micro-nano fiber knot.

[0050] In this structure, there are specific requirements for the free spectral range FSR of the two micro-nano fiber knots. An overly large ΔFSR will cause the equivalent amplification factor of the cascaded system to decay and reduce the sensing sensitivity; an overly small ΔFSR will trigger the overlapping effect of adjacent resonance peak groups, resulting in a decrease in the contrast of the transmission spectrum envelope and making it difficult to identify characteristic peaks. This phenomenon stems from the beat frequency characteristics of the reference ring and the sensing ring in the Vernier effect - when the free spectral ranges FSR of the two micro-nano fiber knots are close but have a moderate difference, effective spectral shifting and signal amplification can be achieved. In one embodiment, let △FSR be the difference in the free spectral ranges of the micro-nano fiber knots 6 of the front-stage sensing ring 1 and the rear-stage reference ring 2, and FWHM be the full width at half maximum of the front-stage sensing ring 1. The two micro-nano fiber knots 6 satisfy the following constraint relationship: 0.034FWHM ≤ ΔFSR ≤ FWHM; where R1 and R2 are the radii of the micro-nano fiber knots 6 of the front-stage sensing ring 1 and the rear-stage reference ring 2 respectively, α is the transmission loss factor of the micro-nano fiber knot 6, t is the transmission coefficient of the coupling region, and π is the pi. In one embodiment, let both the transmission loss factor and the transmission coefficient of the coupling region be 0.9. At this time, the radii of the two micro-nano fiber knots have the following relationship: 0.975R1 ≤ R2 ≤ 0.999R1.

[0051] As Figure 3 of (a) and Figure 3(b) shows the simulated transmission spectra of two micro-nano fiber knot resonant cavity structures formed by the front-stage sensing ring 1 and the back-stage reference ring 2, respectively, with radii of 600 μm and 500 μm, respectively. Figure 3 (c) is the transmission spectrum after two micro-nano fiber knot-type resonant cavity structures are cascaded. After two micro-nano fiber knot-type resonant cavities with similar free spectral ranges FSR are cascaded, the resonance peaks of the output transmission spectrum will overlap at a certain position to obtain a maximum resonance peak, and stagger at another position to obtain a minimum resonance peak. The overall periodic cycle will present an envelope. Two similar but unequal free spectral ranges FSR will allow this overlap to reappear after several resonance peaks, and the maximum and minimum peaks and the overall envelope are also periodic. Figure 4 As shown in the figure, the theoretical resonance spectrum drift caused by the change of refractive index difference is shown. It can be seen that when the simulated refractive index difference gradually increases, the resonance spectrum after cascading moves toward the shorter wavelength direction as a whole. The wavelength drift can be read from the maximum peak of the envelope line. The larger the refractive index difference, the greater the wavelength drift.

[0052] In order to better respond to external sound signals, the sensor structure is also equipped with a signal generator for generating sound signals; the output end of the signal generator is arranged in the radial direction of the coil of the front-stage sensor ring 1, and is arranged with a gap from the coil of the front-stage sensor ring 1. Under the vertical action of the external sound field, the change of sound pressure causes the medium to change, and the interaction with the evanescent wave causes the change of the effective refractive index, which will cause the change of the resonant wavelength and produce wavelength drift.

[0053] Let the sound pressure sensitivity of the cascade sensor ring unit be S D , the wavelength drift variation of the cascade sensing ring unit is Δλ D , Δλ D =Δλ1·M, where is the wavelength drift variation of the sound signal of the front-stage sensor ring 1 before cascading, and M is the magnification of the free spectrum range of the front-stage sensor ring 1 by the cascade sensor ring unit as a whole, FSR1 and FSR2 are the free spectral ranges of the front-stage sensor ring 1 and the back-stage reference ring 2 respectively; ΔP is the sound pressure change, satisfying S is the sound pressure sensitivity of the front stage sensor ring 1.

[0054] In this embodiment, the coupling unit 3 is a flange or an optical fiber coupler, and the front-stage sensor ring 1 and the rear-stage reference ring 2 are both detachably connected to the coupling unit 3. The detachable coupling structure allows the front-stage sensor ring and the rear-stage reference ring to be easily disassembled and maintained, thereby increasing the adjustability and service life of the device, such as configuring the front-stage sensor ring 1 and the rear-stage reference ring 2 of different radii to form different combination structures, thereby forming a specific frequency domain detection and amplification effect.

[0055] like Figure 5As shown in (a), the figure shows an experimental setup of a micro-ring resonator acoustic sensor based on the cursor effect. Two micro-fiber junction resonators are defined. One end of the front-stage sensing ring is connected to the output of an ASE broadband light source 8 (ASE-CL-50-B), and the other end is connected to the rear-stage reference ring. The other end of the reference ring is connected to a spectral analyzer 9 (YOKOGAWAAQ6374). Light is emitted from the broadband light source 8, passes through the sensing ring, then enters the reference ring and then enters the spectral analyzer 9 to perform real-time scanning and display of the output spectrum.

[0056] Further, as Figure 5 As shown in (a), a signal generator 10 (DG4162) is used to drive a speaker 11 to emit a sine-wave acoustic signal, and the magnitude of the emitted acoustic signal is adjusted by changing the amplitude of the signal generator 10. The speaker 11 is aligned with the sensing ring and fixed at the same position. A sound level meter 12 is placed near the sensing ring to ensure that it receives the same sound pressure as the sensing ring, and the sound pressure value of the current acoustic signal is recorded. The acoustic signal is kept acting until the spectral analyzer 9 finishes scanning, and the output spectral line obtained on the spectral analyzer 9 is saved. By changing the voltage amplitude of the signal generator 10 multiple times, multiple output power spectrograms with the same frequency but different sound pressures can be obtained.

[0057] Figure 5 Figure (b) is a diagram of the experimental setup for the cascaded dual-ring air acoustic frequency response. Similarly, two micro-fiber junction resonators are defined, one is the front-stage sensing ring and the other is the rear-stage reference ring. One end of the front-stage sensing ring is connected to the output of a tunable laser 13 (TOPTICA PHOTONICS DLC pro), and the other end is connected to a 1×2 type 3dB fiber coupler 14. One end of the coupler is connected to the reference ring, and the other end is connected to a photodetector 15. After the photodetector 15, there is a spectrum analyzer 16 (ROHDE&SCHWARZ FSV3030). Light is emitted from the laser 13, passes through the front-stage sensing ring, and then one path enters the rear-stage reference ring, and the other path is converted into an electrical signal by the photodetector 15 (THORLABS PDB450C) and then enters the spectrum analyzer 16 to perform frequency-domain analysis and display of the output signal. Since the air acoustic test only applies an acoustic signal to the front-stage sensing ring and the rear-stage reference ring only plays a role in spectral coupling, the photodetector and the spectrum analyzer are directly connected to the output position of the front-stage sensing ring to detect the received signal in the frequency domain.

[0058] Change the connection of the experimental setup as Figure 5 shown in (b), and apply an acoustic signal with the same frequency to the front-stage sensing ring at the same position. The frequency-domain output signal of the sensor under the excitation of the current acoustic signal is obtained on the spectrum analyzer 16.

[0059] The following content is a comparative experiment of different series combinations:

[0060] Let the parameters of the micro-nano fiber knot-type resonant cavity structure numbered 17 be FSR 17 = 0.4 nm, FWHM 17 = 0.26 nm; the parameters of the micro-nano fiber knot-type resonant cavity structure numbered 18 are FSR 18 = 0.51 nm, FWHM 18 = 0.33 nm; the parameters of the micro-nano fiber knot-type resonant cavity structure numbered 19 are FSR 19 = 0.46 nm, FWHM 19 = 0.19 nm. And the radii of the corresponding micro-nano fiber knots satisfy R 18 = 0.78R 17 ,R 19 = 0.87R 17 . Denote the series connection of the micro-nano fiber knot-type resonant cavity structure numbered 17 and the micro-nano fiber knot-type resonant cavity structure numbered 18 as the first combination, that is, the micro-nano fiber knot-type resonant cavity structure numbered 17 is used as the front-stage sensing ring, and the micro-nano fiber knot-type resonant cavity structure numbered 18 is used as the rear-stage reference ring; the series connection of the micro-nano fiber knot-type resonant cavity structure numbered 17 and the micro-nano fiber knot-type resonant cavity structure numbered 19 is the second combination, that is, the micro-nano fiber knot-type resonant cavity structure numbered 17 is used as the front-stage sensing ring, and the micro-nano fiber knot-type resonant cavity structure numbered 19 is used as the rear-stage reference ring.

[0061] As Figure 6 shown, (a) is the power spectrum diagram of the first combination, and (b) is the power spectrum diagram of the second combination. According to the amplification relationship of M times of the free spectral range of the front-stage sensing ring 1 by the cascaded sensing ring unit mentioned in the foregoing content, the theoretical free spectral range FSR of the cascaded spectrum generated by the first combination should be 1.9 nm. In Figure 6 (a), the free spectral range FSR after the actual series connection of the two micro-nano fiber knot-type resonant cavity structures can be read as 2.1 nm; the theoretical free spectral range FSR of the cascaded spectrum generated by the second combination should be 3.1 nm. In Figure 6 (b), the free spectral range FSR after the actual series connection of the two micro-nano fiber knot-type resonant cavity structures can be read as 3 nm, which is basically consistent with the theoretical value.

[0062] As Figure 7 shown, Figure 7 (a) is the wavelength drift diagram of the micro-nano fiber knot-type resonant cavity structure numbered 17 at 500 Hz, Figure 7(b) is its corresponding sensitivity diagram. That is, when the frequency of the signal generator is constant and the voltage amplitude increases, the sound pressure received by the sound level meter increases from 59.1 dB to 73.1 dB. The output spectrum with an obvious period obtained by the spectrometer is subjected to envelope fitting to make the upper / lower envelope fit the output spectrum as much as possible. The position of the maximum peak of a certain envelope is selected to record the corresponding wavelength, and the drift amount of this maximum peak, 0.122 nm, is recorded during the increase of the sound pressure. The sound pressure recorded by the sound level meter is converted into the sound pressure magnitude in Pa units. Fitting the wavelength and sound pressure of the measurement points can obtain the sound pressure sensitivity of the 17th micro-ring resonator at 500 Hz as 1.7 nm / Pa.

[0063] Repeat the above operations and change the frequency of the signal generator to 800 Hz. As Figure 8 shown, Figure 8 (a) is the wavelength drift diagram of the micro-nano fiber junction resonator structure numbered 17 at 800 Hz, Figure 8 (b) is its corresponding sensitivity diagram. The sound pressure received by the sound level meter increases from 68.1 dB to 82.1 dB. The position of the maximum peak of a certain envelope is selected to record the corresponding wavelength, and the drift amount of this maximum peak, 0.119 nm, is recorded during the increase of the sound pressure. Fitting the wavelength and sound pressure of the measurement points can obtain the sound pressure sensitivity of the micro-nano fiber junction resonator structure numbered 17 at 800 Hz as 0.58 nm / Pa.

[0064] Repeat the above operations. As Figure 9 shown is the wavelength drift diagram of the first combination at 500 Hz. The sound pressure received by the sound level meter increases from 59.1 dB to 73.1 dB. The position of the maximum peak of a certain envelope is selected to record the corresponding wavelength, and the drift amount of this maximum peak, 0.512 nm, is recorded during the increase of the sound pressure. Fitting the wavelength and sound pressure of the measurement points can obtain the sound pressure sensitivity of the cascaded dual-ring resonator acoustic sensor at 500 Hz as 7.2 nm / Pa. As Figure 10 (a) shows the acoustic sensing sensitivity diagram of the present invention at 500 Hz, Figure 10 (b) is the acoustic sensing frequency domain response diagram at 500 Hz. It can be clearly observed from the frequency spectrum diagram that there is a prominent peak at the abscissa corresponding to 500 Hz, indicating that the sensor responds to the 500 Hz acoustic signal at this time. Comparing Figure 9 , Figure 10 with Figure 7 , it can be clearly observed that the vernier effect amplifies the tiny wavelength drift. The acoustic sensing sensitivity of the cascaded micro-ring resonator is 4.2 times that of the single micro-ring resonator, which is close to the theoretical amplification factor of 4.6 times.

[0065] Only change the frequency of the signal generator to make the speaker emit an acoustic signal of 800 Hz. The wavelength drift curve of the first combination at 800 Hz is obtained through the same experimental procedure as shown in Figure 11 . The sound pressure received by the sound level meter increases from 68.1 dB to 82.1 dB. Select the maximum peak position of a certain envelope curve to record the corresponding wavelength, and record the drift amount of this maximum peak, which is 0.545 nm, during the increase of the sound pressure. By fitting the wavelength and sound pressure of the measurement points, the sound pressure sensitivity of the cascaded microring resonator acoustic sensor at 800 Hz can be obtained as 2.8 nm / Pa. As shown in Figure 12 (a) is the acoustic sensing sensitivity diagram of the present invention at 800 Hz, Figure 12 (b) is the acoustic sensing frequency domain response diagram at 800 Hz. It can be clearly observed from the frequency spectrum diagram that there is a prominent peak at the place corresponding to 800 Hz on the abscissa, indicating that the sensor responds to the acoustic signal of 800 Hz at this time. Comparing Figure 11 、 Figure 12 with Figure 8 , it can be clearly observed that the Vernier effect amplifies the tiny wavelength drift. The acoustic sensing sensitivity of the cascaded microring resonator is 4.8 times that of the single microring resonator, which is close to the theoretical amplification factor of 4.6 times.

[0066] Keep the frequency of the signal generator unchanged at 800 Hz. The wavelength drift curve of the second combination at 800 Hz is obtained through the same experimental procedure as shown in Figure 13 . The sound pressure received by the sound level meter increases from 68.0 dB to 73.4 dB. Select the maximum peak position of a certain envelope curve to record the corresponding wavelength, and record the drift amount of this maximum peak, which is 0.948 nm, during the increase of the sound pressure. By fitting the wavelength and sound pressure of the measurement points, the sound pressure sensitivity of the cascaded microring resonator acoustic sensor at 800 Hz can be obtained as 4.5 nm / Pa. As shown in Figure 14 (a) is the acoustic sensing sensitivity diagram of the present invention at 800 Hz, Figure 14 (b) is the acoustic sensing frequency domain response diagram at 800 Hz. It can be clearly observed from the frequency spectrum diagram that there is a prominent peak at the place corresponding to 800 Hz on the abscissa, indicating that the sensor responds to the acoustic signal of 800 Hz at this time. Comparing Figure 13 、 Figure 14 with Figure 8 , it can be clearly observed that the Vernier effect amplifies the tiny wavelength drift. The acoustic sensing sensitivity of the cascaded microring resonator is 7.8 times that of the single microring resonator, which is close to the theoretical amplification factor of 7.7 times.

[0067] In the micro-ring resonator acoustic sensor based on the Vernier effect provided by the present invention, the two micro-nano fiber junction resonator structures are connected in the form of coupling units such as flanges instead of direct fiber fusion splicing. On the one hand, it is because different diameter sensing rings can be conveniently replaced to obtain different magnification factors. Compared with directly splicing two micro-ring resonators, this method is more conducive to observing the relationship between rings with different diameters and the magnification factor under the Vernier effect. On the other hand, compared with the connection method relying on discrete couplers in the traditional parallel architecture, the insertion loss introduced by the coupler is effectively avoided.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A micro-ring resonator acoustic sensor based on the cursor effect, characterized in that, Comprising: A coupling unit; A light source for generating an optical signal; A cascaded sensing loop unit, including a pre-stage sensing loop and a post-stage reference loop. One end of the pre-stage sensing loop is optically connected to the light source optical path, and the other end of the pre-stage sensing loop is optically connected to one end of the post-stage reference loop through the coupling unit; Wherein, both the pre-stage sensing loop and the post-stage reference loop include a hollow flat glass substrate, a first PDMS film, a micro-nano fiber knot, and a second PDMS film that are sequentially stacked. The two ends in the axial extension direction of the micro-nano fiber knot serve as the two ends of the sensing loop; the radii and free spectral ranges of the micro-nano fiber knots of the pre-stage sensing loop and the post-stage reference loop are different.

2. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 1, wherein The micro-nano fiber knot is formed by stretching a single-mode fiber in a molten state, knotting the reduced-diameter section of the molten fiber to form a knot loop, and the two ends of the micro-nano fiber knot extend outward along the direction tangent to the contour of the knot loop; the first PDMS film and the second PDMS film respectively cover one side surface of the knot loop close to the hollow flat glass substrate and the other side surface of the knot loop far from the hollow flat glass substrate; an opening is provided at the corresponding position of the hollow flat glass substrate with respect to the knot loop, and the opening penetrates along the radial direction of the knot loop.

3. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 2, wherein, Tail fibers are respectively arranged at the two ends of the micro-nano fiber knot, the tail fibers are fusion-spliced to the micro-nano fiber knot, and the diameter of the tail fibers is larger than the diameter of the micro-nano fiber knot.

4. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 3, characterized in that Let ΔFSR be the difference in the free spectral range of the micro-nano fiber junctions between the pre-stage sensing loop and the post-stage reference loop, and FWHM be the full width at half maximum of the pre-stage sensing loop. The two micro-nano fiber junctions satisfy the following constraint relationship: 0.034FWHM ≤ ΔFSR ≤ FWHM; where R1 and R2 are the radii of the micro-nano fiber junctions of the pre-stage sensing loop and the post-stage reference loop respectively, α is the transmission loss factor of the micro-nano fiber junction, t is the transmission coefficient of the coupling region, and π is the ratio of a circle's circumference to its diameter.

5. A micro-ring resonator acoustic sensor based on the cursor effect according to claim 1, characterized in that, It further includes a signal generator for generating a sound signal; the output end of the signal generator is arranged in the radial direction of the knot loop of the pre-stage sensing loop and is arranged with a gap from the knot loop of the pre-stage sensing loop.

6. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 4, characterized in that, Let the sound pressure sensitivity of the cascaded sensing ring unit be S D , and the wavelength drift change of the cascaded sensing ring unit be Δλ D , Δλ D = Δλ1·M, where Δλ1 is the wavelength drift change of the previous-stage sensing ring acting alone on the sound signal, M is the magnification factor of the cascaded sensing ring unit for the free spectral range of the previous-stage sensing ring, ΔP is the sound pressure change, and it satisfies S is the sound pressure sensitivity of the previous-stage sensing ring.

7. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 1, characterized in that, The coupling unit is a flange or an optical fiber coupler, and both the pre-stage sensing loop and the post-stage reference loop are detachably connected to the coupling unit.

8. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 7, characterized in that, It further includes a spectral analyzer, and the spectral analyzer is optically connected to the other end of the post-stage reference loop.

9. The micro-ring resonator acoustic sensor based on the cursor effect according to claim 7, wherein When the coupling unit uses an optical fiber coupler, the input end of the optical fiber coupler is optically connected to the output end of the pre-stage sensing loop, the first output end of the optical fiber coupler is optically connected to the input end of the post-stage reference loop, the second output end of the optical fiber coupler is optically connected to a photodetector, and the output end of the photodetector is electrically connected to a spectrum analyzer.

10. A micro-ring resonator acoustic sensor based on the cursor effect according to claim 1, characterized in that, The light source is an ASE broadband light source or a tunable laser.

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