EIT-like-based whispering gallery mode coupled cavity sensor for micro gas type identification

Abstract

The invention provides a miniature gas detection echo wall mode coupled cavity sensor based on an electromagnetism-like induced transparency effect. The device comprises a coupling cavity and a waveguide, the coupling cavity is two echo wall mode double-ring cavities with different sizes, and the waveguide is used for waveguide transmission with the coupling cavity and microcavity coupling. The echo wall mode coupled cavity sensor has the advantages that the echo wall mode coupled cavity is high in integration level and quality factor and easy to induce an electromagnetically induced transparency effect, and the intensity and the stability of a transparency peak are ensured. The excited electromagnetism-like induced transparency effect can be used for detecting and identifying the types of micro gases.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to an EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor. Background Art

[0002] Electromagnetic induced transparency (EIT-like) originates from the nonlinear optical effect of destructive interference of quantum excitation paths. It induces destructive interference of the system by applying a coherent light field, thereby offsetting the absorption of light of a specific frequency by the medium and transforming the originally opaque material into a transparent state. It has extremely important application value in the fields of optical communication, optical sensors and quantum information. It is usually manifested as a wide transparent window in the transmission spectrum of the probe light, accompanied by a sharp phase change and high group delay. Whispering gallery mode optical microcavity has attracted widespread attention due to its ultra-high quality factor and tiny mode volume, and is of great value in the research of sensing.

[0003] Optical microcavities can confine light fields in extremely small spatial regions, greatly enhancing the interaction between light and matter, and providing a reliable platform for studying EIT-like effects. In addition, when studying the process of electromagnetically induced transparency and microcavity mode coupling, it is crucial to select a probe light source that matches the energy level transition, because only when the frequency of the probe light matches the energy level interval in the microcavity can effective energy level coupling be achieved, thereby producing a transparent effect, and the mode stability and ease of regulation of the microcavity provide a guarantee for this.

[0004] Usually, the microcavity sensing principle is to observe the movement of the resonance spectrum peak and explore its linear relationship with the numerical change of the sensing parameter. However, the resonance peak is not fully utilized, and the detection sensitivity of trace gas changes is low, the response time is slow, and the response frequency band is narrow, which is not conducive to observation. Summary of the invention

[0005] The object of the present invention is to provide a sensor which has high detection sensitivity, wide spectrum response and rapid response when detecting gas types.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a micro gas type identification whispering gallery mode coupling cavity sensor based on EIT-like, comprising a whispering gallery mode coupling cavity and a waveguide, wherein the whispering gallery mode coupling cavity has a first annular microcavity and a second annular microcavity, the first annular microcavity and the second annular microcavity have different sizes and the same structure; the first annular microcavity and the second annular microcavity resonate in a band with a central wavelength of 1550nm, and the first annular microcavity and the second annular microcavity have two optical modes with the same frequency, clockwise and counterclockwise; when the counterclockwise rotating mode of the first annular microcavity is coupled with the clockwise rotating mode of the second annular microcavity to interfere, coherent light with higher deflection loss is introduced to make the first annular microcavity transparent at a specific frequency, thereby generating an EIT-like phenomenon;

[0007] The forward propagating continuous field in the waveguide excites the mode field in the second annular microcavity, which is mainly manifested as a counterclockwise rotating mode field in the second annular microcavity. The counterclockwise rotating mode field excites many modes including the clockwise rotating mode field in the second annular microcavity. Then, the corresponding modes with a phase difference of π between the counterclockwise rotating mode field and the clockwise rotating mode field of the first annular microcavity are coupled to excite the high-order mode required for EIT-like.

[0008] The counterclockwise rotating mode field in the second annular microcavity scatters back and excites the clockwise rotating mode field of the first annular microcavity, thereby exciting the low-order mode required for EIT-like;

[0009] The clockwise rotating mode field in the second annular microcavity is then indirectly coupled with the counterclockwise rotating mode field of the first annular microcavity and finally returns to the waveguide.

[0010] Preferably, the whispering gallery mode coupling cavity is a silicon-based, silicon dioxide, lithium niobate, silicon nitride or silicon nitride material coupling cavity.

[0011] Preferably, when the counterclockwise rotating mode field and the clockwise rotating mode field are coupled, destructive interference occurs to generate a composite light field, and the field intensity of the composite light field is enhanced or suppressed by interference by controlling the frequency difference between the counterclockwise rotating mode field and the clockwise rotating mode field, thereby changing the spacing between the first annular microcavity and the second annular microcavity, so as to regulate the coupling loss to gradually stimulate the EIT-like effect.

[0012] Preferably, during operation, the EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor is placed in the standard gas respectively, and the redshift standard value of the EIT-like display window is recorded; the EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor is placed in the gas to be detected respectively, the transmission spectrum line shape corresponding to the gas to be detected does not undergo visual changes, and the EIT-like display window will undergo a visible redshift. The redshift result of the gas to be detected is compared with the redshift standard value of the EIT-like display window to determine the type of the gas to be detected.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The present invention discloses a miniature gas type identification whispering gallery mode coupled cavity sensor based on EIT-like. Due to the quantum interference effect generated by EIT-like, the absorption characteristics of light are significantly reduced at a specific frequency, thereby greatly enhancing the transmittance. In the gas sensor, when the concentration of the gas molecules to be measured changes, a slight change in the EIT-like state will cause a significant fluctuation in the sensor output signal, so that the gas sensor based on EIT-like can detect extremely low concentrations of gas molecules, and can even achieve ppb-level detection capabilities, meeting the needs of various application fields for high-sensitivity sensors.

[0015] 2. The present invention discloses a micro gas type identification whispering gallery mode coupled cavity sensor based on EIT-like, which has the characteristics of wide-band response, enabling it to operate in a relatively wide spectral range. This feature not only improves the applicability of the sensor, but also allows it to effectively detect under different gas types and concentration conditions. By adjusting the geometric parameters of the coupling cavity and the properties of the medium, selective tuning of light of different wavelengths can be achieved, which enables the gas sensor to detect multiple gas components at the same time. In practical applications, this wide-spectrum response capability significantly improves the versatility of gas sensors and provides an effective solution for the analysis of gas mixtures in complex environments.

[0016] 3. The present invention discloses a micro gas type identification whispering gallery mode coupled cavity sensor based on EIT-like, which exhibits a faster response speed. This advantage is mainly attributed to the high efficiency and inherent quantum properties of its optical transmission mechanism. When external conditions change, such as fluctuations in gas concentration or ambient temperature, the EIT-like system can quickly capture these changes and respond in a very short time. This rapid response capability enables EIT-like gas sensors to meet the needs of real-time monitoring, especially in scenarios such as industrial production, environmental monitoring, and safety alarms, where timely detection of rapidly changing gas concentrations is of great significance.

[0017] 4. The present invention discloses a micro gas type identification whispering gallery mode coupled cavity sensor based on EIT-like, which has good integrability and is easy to link with other devices and systems. This integrability is not only reflected in hardware design, but also in software control and data processing. Due to its miniaturized structure and high efficiency, the sensor can be easily embedded in various devices, such as smart phones, drones, wearable devices, etc. In addition, combined with modern communication technology, the micro gas detection whispering gallery mode coupled cavity sensor based on EIT-like can also realize remote monitoring and data transmission, providing new possibilities for smart cities, environmental protection, health monitoring and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of a whispering gallery mode coupled cavity micro gas detection sensor based on the EIT-like effect.

[0019] Figure 2 (a) is a schematic diagram of the change in electric field distribution after changing the distance between the two cavities (from opaque to transparent), and (b) is the change in electric field distribution when d = 0 μm, 0.2 μm, 0.4 μm, and 0.6 μm.

[0020] Figure 3 These are the EIT-like transmission spectra of the dual-ring cavity structure at d = 0 μm, 0.2 μm, 0.4 μm, and 0.6 μm (the left side is the theoretical result, and the right side is the actual result).

[0021] Figure 4 The transmission spectra of different gases in the coupling cavity. (a) is the transmission spectra of different gases when d = 0 μm, (b) is the wavelength shift and Q value change of different gases when d = 0 μm, (c) is the transmission spectra of different gases when d = 0.2 μm, and (d) is the wavelength shift and Q value change of different gases when d = 0.2 μm.

[0022] Figure 5The transmission spectra of different gases based on the EIT-like effect. (a) is the transmission spectra of different gases when d = 0.4 μm, (b) is the wavelength shift and Q value change of different gases when d = 0.4 μm, (c) is the transmission spectra of different gases when d = 0.6 μm, and (d) is the wavelength shift and Q value change of different gases when d = 0.6 μm.

[0023] Figure 6 is the wavelength shift variation under different dual-ring cavity spacings. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solution method of the present invention, the present invention is further described in detail below with reference to specific embodiments in conjunction with the accompanying drawings. However, this method is not limited to a specific example and can be applied to similar situations.

[0025] Please refer to the attached Figure 1 To Attachment Figure 6 The specific preparation process of the EIT-like-based micro gas detection whispering gallery mode coupled cavity sensor is as follows:

[0026] 1) First, a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of about 7:3 is used to rinse the dual-ring cavity device; then a mixed solution consisting of a hydrofluoric acid solution with a concentration of about 0.001 mol / L at room temperature and other solvents is prepared; then the mixed solution is passed into the coupled cavity device for etching for a period of time, rinsed with deionized water and then dried to form a coupled cavity device; then the coupled cavity and waveguide are prepared by steps such as preset waveguide geometry, exposure, and wet etching. After the above preparation and processing, the desired whispering gallery mode coupled cavity EIT-like sensor is obtained. Figure 1 shown.

[0027] 2) Figure 2 The process of the coupled cavity producing an EIT-like effect is demonstrated. When the CCW mode of microcavity M1 is coupled with the CW mode of microcavity M2 and interferes, coherent light with higher deflection loss is introduced, making microcavity M1 transparent at a specific frequency, that is, an electromagnetically induced transparency phenomenon is generated. Since both microcavity M1 and microcavity M2 have two optical modes with the same frequency, CW and CCW, assuming that these optical modes are not scattered due to additional disturbances, the EIT-like effect of the coupled cavity system can be explained by the coupled mode equation:

[0028]

[0029] in, Corresponding to the light field energy of CCW mode of microcavity M1 and CW mode of microcavity M2; Δω 1(2) =ω-ω 1(2)is the frequency detuning of M1(2) to the incident light field; ε 1(2) and τ 1(2) is the intrinsic loss and coupling loss of microcavity M1(2); E in is the incident light field energy; g is the coupling factor of the interaction between the CCW mode of microcavity M1 and the CW mode of M2, which affects the energy transfer rate and the intensity of the interference effect; E out is the energy of the transmitted light field. By combining equations (1), (2), (3), and (4), the normalized transmittance of the system can be obtained as:

[0030]

[0031] Among them, X1 = -iΔω1+ε1+τ1, X2 = -iΔω2+ε2+τ2. From the normalized transmittance formula, it can be seen that the normalized transmittance depends on parameters such as Δω1, Δω2 and τ1. First, the forward propagating continuous field in the waveguide excites the mode field in the microcavity M2, which is mainly manifested as the CCW field in the microcavity M2. These CCW fields will excite many modes including the CW field in the microcavity M2. Then, energy transfer and exchange occur between the multiple mode fields of the microcavity M1, especially the corresponding mode coupling with a phase difference of π between the CCW field and the CW field, thereby forming an excited EIT-lik e In addition, the CCW field in microcavity M2 will also scatter back and excite the CW field in microcavity M1, similar to the former, to excite the EIT-like e The desired low-order mode. Finally, the CW field in the microcavity M2 is indirectly coupled with the CCW field in the microcavity M1 and finally returns to the waveguide, which also explains why the normalized transmittance T depends on parameters such as Δω1, Δω2 and τ1. From the above formula, it can be seen that destructive interference occurs when the two modes are coupled to produce a composite light field, and the intensity of the composite light field can be controlled by controlling the frequency difference, enhancing the interference, or being suppressed by interference, and changing the spacing between the microring cavities, thereby regulating the coupling loss to gradually stimulate the EIT-like effect.

[0032] 3) In order to specifically demonstrate the process of changing the spacing between the coupled cavities and then regulating the coupling loss to gradually stimulate the EIT-like effect. The whispering gallery mode coupling cavity uses a double ring cavity, including two whispering gallery mode microcavities. The lower one is a micro-ring cavity M2 with an inner diameter of 15.5μm and an outer diameter of 16μm, and the upper one is a micro-ring cavity M1 with an inner diameter of 29μm and an outer diameter of 30μm. The spacing between the two micro-ring cavities is set to gradually increase from 0μm to 0.6μm with a step of 0.2μm, and the electric field distribution is explored as the spacing between the two micro-ring cavities increases, such as Figure 2As shown in the electric field distribution diagram, the degree of microcavity M1's participation in coupling gradually decreases, and the electric field energy gradually decreases, which is reflected in the deepening of the transparency of microcavity M1, that is, the enhancement of the EIT-like effect. Further analysis of the transmission spectrum, Figure 3 The results of the EIT-like theory based on the dual-ring cavity and the actual control were compared, and the overlap between the two was high, which also verified the reliability of the theoretical and actual control. From top to bottom, as the distance between microcavity M1 and microcavity M2 increases, the coupling loss increases, causing the transparent peak to be gradually absorbed, and microcavity M2 slowly decays back to the Lorentz spectrum line shape. A more obvious transparent peak appears from d = 0.4μm, and the transparent peak is very obvious when the microcavity d = 0.6μm.

[0033] 4) In order to explore the gas sensing application of the EIT-like effect of the whispering gallery mode coupled cavity, several common gases in the industry were selected as research materials, and our system was placed in a standard laboratory environment filled with hydrogen, oxygen, carbon dioxide, and chlorine. The refractive indices of these four gases are hydrogen: 1.000140, oxygen, 1.000276, carbon dioxide: 1.000449; chlorine: 1.000768. The spacing between the two ring cavities was set to 0μm, and the changes in the spectrum and the effects were observed, such as Figure 4As shown in the figure, it can be observed that as the refractive index gradually increases, the transmission line shapes corresponding to the four common gases in this model do not change significantly in the wavelength range of 1540μm to 1550μm, but the EIT-like window will redshift accordingly, because the gas molecules cause changes in the system coupling loss. Specifically, since the generation of the EIT-like effect depends on the balance between the light field attenuation rate and the coupling strength in the microring cavity, the increased refractive index of the external gas environment will affect the waveguide transmission efficiency of the coupled mode, causing the coupling loss to increase, thereby changing the attenuation rate and coherence time of the light field in the microring cavity, and this change will cause the transparency peak in the EIT-like effect to redshift, further indicating the linear relationship between the wavelength change based on the transparency peak and the gas refractive index. By monitoring this redshift, the concentration of different gases can be effectively identified and quantified, and high-sensitivity gas sensing can be achieved. In order to define the sensitive characteristics of the EIT-like effect of the dual ring cavity with the change of refractive index, the quality factor (Quality factor, Q), sensitivity (S), and limit of detection (LOD) can be used as the refractive index sensing performance indicators to measure the EIT-like effect of the dual ring cavity. The quality factor calculation formula of the EIT-like effect in the dual ring cavity is: Q = λ / FWHM, which represents the wavelength corresponding to the EIT-like resonance peak, and FWHM is the half-maximum full width of the EIT-like resonance peak. The quality factor Q reflects the accuracy and reliability of the EIT-like effect in the dual ring cavity. The higher the Q value, the smaller the detection limit LOD value. The sensitivity S can be calculated by the following formula: S = Δλ / Δn, Δλ is the wavelength offset of the EIT-like resonance peak, and Δn is the refractive index change of the gas to be measured on the surface of the dual ring cavity. The sensitivity S represents the wavelength drift caused by a unit refractive index change. The larger the S value, the more sensitive it is to the refractive index change. Furthermore, the detection limit LOD can be calculated by the following formula: L 0D = FWHM / S, the detection limit LOD is an important sensor performance indicator reflecting the EIT-like effect in the dual ring cavity. It refers to the minimum refractive index change value that can be detected by the EIT-like effect in the dual ring cavity, reflecting the ability to effectively distinguish the refractive index change signal from other interference signals. Figure 4 (c) It can be seen that when the distance between the double ring cavities is d = 0 μm and d = 0.2 μm, although the complete EIT-like has not been excited, the transparent peak gradually becomes sharper, indicating that the EIT-like effect has begun to take effect. Figure 4 (b) shows that when d = 0 μm, the corresponding refractive index sensitivity S is about 251.804 nm / RIU in different gas environments, and the Q value changes between 1972.2 and 1972.4. ODWhen d = 0.2 μm, the corresponding refractive index sensitivity S is about 188.853 nm / RIU, the Q value changes between 1972.3 and 1972.5, and the LOD value is about 4.1×10 -3 RIU. From the change from d = 0 μm to d = 0.2 μm, the Q value hardly changes, which may be the evidence that EIT-like is not fully realized. In addition, the enhancement of EIT-like effect may lead to a decrease in sensitivity and an increase in resolution and detection limit indicators. Further changing the distance between the two micro-ring cavities, the distance between the two micro-ring cavities is adjusted to 0.4 μm and 0.6 μm respectively. Figure 6 shown. Figure 5 (a) It can be observed that the EIT-like effect begins to take effect when d = 0.4 μm, which is consistent with the previous electric field simulation results. Figure 5 (b) shows that the refractive index sensitivity is reduced by 18.5% to 205.16nm / RIU compared to d = 0μm, and is slightly improved compared to d = 0.2μm, which may be attributed to the recovery of the coupling between the M1 and M2 optical modes. However, the Q value has reached nearly 2.2 times that of the previous EIT-like intermediate stage, varying between 4371.9 and 4372.4, and its L OD The value is about 0.0017RIU, which means that increasing the spacing between the dual ring cavities within an appropriate range can induce a more complete EIT-like. Although the refractive index sensitivity will be reduced, the sensor resolution and detection limit performance will be greatly improved. When d = 0.6μm, it is similar to the case of d = 0.4μm. Figure 5 (c) shows that in this case, a more obvious EIT-like is induced compared with d = 0.4 μm. Figure 5 (d) shows that compared with d = 0 μm, its refractive index sensitivity is 205.16 nm / RIU, which is consistent with the case of d = 0.4 μm, which may be used as a criterion for the successful excitation of the EIT-like effect. The Q value range is 10086.5~10087.5, L OD The value is about 7.46×10 -4 RIU is about 4.16 times that of the case when EIT-like is not excited. In summary, when the EIT-like effect begins to work, even if the EIT-like effect is not fully realized, its comprehensive sensing performance, especially the resolution, will be greatly improved due to its resonance peak characteristics. This feature will provide important reference value for the research of ultra-high resolution refractive index sensors based on EIT-like.

[0034] 5) In order to summarize and analyze the wavelength shift changes under different dual-ring cavity spacings, Figure 6It shows that when the distance between the two ring cavities is increased within an appropriate range and the EIT-like effect is gradually excited, its sensitivity decreases but the decrease is not large; as the EIT-like effect is fully excited, its sensitivity remains almost unchanged, and there is not much difference when the EIT-like effect is just started. At this time, the sensitivity is not affected by the change of refractive index or the distance between the two ring cavities. This is a very special sensing phenomenon, which shows that the influence of gas on the sensing characteristics is limited to the change of the refractive index of the gas itself. This is also the unique advantage of the EIT-like effect, which is different from the traditional micro-resonant cavity sensing combined with sensitive materials, and is more conducive to the realization of high-precision sensing.

[0035] The invention discloses a micro gas type identification whispering gallery mode coupled cavity sensor based on EIT-like, which gradually induces electromagnetic induced transparency in the microcavity, and makes it participate in sensing as a resonance peak with a higher quality factor, which has a significant beneficial effect. In addition, the steep transparent peak presented when the EIT-like induced transparency based on the microcavity also makes the phenomenon easy to observe, and the easy-to-regulate characteristic also provides considerable convenience for inducing the phenomenon. The whispering gallery mode coupled cavity has different optical paths, which can excite two modes with different quality factors, providing conditions for the interference and destructive interaction between the modes. It not only has the advantages of high quality factor and high EIT-like transmission efficiency, but also has high integration, high quality factor and low coupling loss, ensuring the intensity and stability of the transparent peak. As a traveling wave cavity, the whispering gallery mode coupled cavity will not be reflected back into the input waveguide at any wavelength, and the number of modes therein is large, which makes it easier to achieve energy level difference matching, thereby successfully inducing the EIT-like effect. Relying on the whispering gallery mode optical microcavity to achieve electromagnetic induced transparency provides the possibility for the regulation of optical devices, and provides important tools and theoretical support for the detection and identification of micro gas types.

[0036] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present invention shall also fall within the protection scope of the present invention. The present invention does not elaborate on some of the known technologies of those skilled in the art.

Claims

1. A micro gas type identification whispering gallery mode coupled cavity sensor based on EIT-like, characterized in that: The invention comprises a whispering gallery mode coupling cavity and a waveguide, wherein the whispering gallery mode coupling cavity comprises a first annular microcavity and a second annular microcavity, wherein the first annular microcavity and the second annular microcavity have different sizes and the same structure; the first annular microcavity and the second annular microcavity resonate in a wavelength band with a central wavelength of 1550 nm, and the first annular microcavity and the second annular microcavity have two optical modes with the same frequency, clockwise and counterclockwise; when the counterclockwise rotating mode of the first annular microcavity is coupled with the clockwise rotating mode of the second annular microcavity to interfere, coherent light with higher deflection loss is introduced, making the first annular microcavity transparent at a specific frequency, thereby generating an EIT-like phenomenon; The forward propagating continuous field in the waveguide excites the mode field in the second annular microcavity, which is mainly manifested as a counterclockwise rotating mode field in the second annular microcavity. The counterclockwise rotating mode field excites many modes including the clockwise rotating mode field in the second annular microcavity. Then, the corresponding modes with a phase difference of π between the counterclockwise rotating mode field and the clockwise rotating mode field of the first annular microcavity are coupled to excite the high-order mode required for EIT-like. The counterclockwise rotating mode field in the second annular microcavity scatters back and excites the clockwise rotating mode field of the first annular microcavity, thereby exciting the low-order mode required for EIT-like; The clockwise rotating mode field in the second annular microcavity is then indirectly coupled with the counterclockwise rotating mode field of the first annular microcavity and finally returns to the waveguide.

2. The EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor according to claim 1, characterized in that: The whispering gallery mode coupling cavity is a silicon-based, silicon dioxide, lithium niobate, silicon nitride or silicon nitride material coupling cavity.

3. The EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor according to claim 1, characterized in that: When the counterclockwise rotating mode field and the clockwise rotating mode field are coupled, destructive interference occurs to generate a composite light field. The field intensity of the composite light field is enhanced or suppressed by interference by controlling the frequency difference between the counterclockwise rotating mode field and the clockwise rotating mode field, thereby changing the distance between the first annular microcavity and the second annular microcavity, so as to regulate the coupling loss and gradually stimulate the EIT-like effect.

4. The EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor according to claim 1, characterized in that: During operation, the EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor is placed in the standard gas respectively, and the redshift standard value of the EIT-like display window is recorded; the EIT-like-based micro gas type identification whispering gallery mode coupled cavity sensor is placed in the gas to be detected respectively, the transmission spectrum shape corresponding to the gas to be detected does not undergo visual changes, and the EIT-like display window will undergo a visible redshift. The redshift result of the gas to be detected is compared with the redshift standard value of the EIT-like display window, and the type of the gas to be detected can be determined based on the linear relationship between the redshift standard value of the EIT-like display window and the refractive index of the surrounding environment.

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