Method for detecting solution concentration based on cut-corner square slit whispering gallery optical microcavity

Abstract

The application provides a solution concentration detection method based on a cut-corner square slit echo wall optical microcavity, utilizes a cut-corner square echo wall mode optical microcavity, and proposes a method for completing detection of the concentration of a to-be-detected substance in a slit. Compared with previous solution concentration detection methods based on other echo wall mode optical microcavities, the method has higher detection sensitivity, a smaller detection model volume and more excellent performance. The solution concentration detection is realized directly outside the optical microcavity, and a new idea is provided for development of a slit microcavity and the solution concentration detection method of the optical microcavity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical sensing technology, in particular to a solution concentration detection method based on a cut-corner square slit whispering gallery optical microcavity. BACKGROUND

[0002] Optical sensing technology is divided into contact sensing technology and non-contact sensing technology. In contact sensing technology, when the optical microcavity interacts with the photons in the mode volume of the to-be-detected substance, it will cause the movement, splitting and broadening of the resonance frequency of the whispering gallery mode optical microcavity. The mode movement is the most common sensing mechanism of the whispering gallery mode optical microcavity, and the movement amount of the resonance frequency is used as a parameter to represent the sensing performance of the whispering gallery mode optical microcavity. The specific explanation is as follows: the resonance frequency of the whispering gallery mode optical microcavity will change with the change of the environment, and the whispering gallery mode resonance frequency is generally obtained by monitoring the transmission spectrum, reflection spectrum, etc. of the microcavity. When the to-be-detected substance enters the potential field range of the whispering gallery mode optical microcavity, the effective refractive index of the whispering gallery mode changes, and the resonance condition changes, so that the resonance frequency of the whispering gallery mode moves.

[0003] The present application utilizes a cut-corner square whispering gallery mode optical microcavity, and proposes a method for detecting the concentration of the to-be-detected substance in the slit. Compared with the previous solution concentration detection method based on other whispering gallery mode optical microcavities, the method proposed by the present application has higher detection sensitivity, smaller detection model volume and more excellent performance. The solution concentration detection is realized directly outside the optical microcavity, which provides a new idea for the development of the slit microcavity and the solution concentration detection method of the optical microcavity. SUMMARY

[0004] In view of the above problems in the prior art, the present application proposes a solution concentration detection method based on a cut-corner square slit whispering gallery optical microcavity, comprising the following steps:

[0005] S1, designing the size of the cut-corner square slit whispering gallery mode microcavity and the parameter of the coupled waveguide by using the finite difference time domain method;

[0006] S2, emitting mode light with a wavelength of λ=1250nm-1750nm from one end of the coupled input waveguide by using the mode light source in the finite difference time domain method, and performing finite difference time domain simulation calculation, so as to obtain the resonance frequency of the designed cut-corner square slit whispering gallery mode microcavity;

[0007] S3, adjusting the distance between the upper and lower two cavities of the cut-corner square slit whispering gallery mode optical microcavity, and optimizing the resonance frequency obtained in S2, so as to facilitate the observation of the resonance frequency shift amount during solution concentration sensing;

[0008] S4, selecting the optimized resonance frequency in S3, and calculating the shift amount of different solution concentrations to be detected.

[0009] S5, since the solution to be detected at different concentrations correspond to different optical refractive index, by changing the background refractive index of the simulation region in the time domain finite difference method to simulate the concentration change of the solution to be detected;

[0010] S6, observing the shift of the resonant frequency selected in S4 under different background refractive index, the concentration of the solution to be detected is calculated.

[0011] Preferably, the overall shape of the cut-angle square slit resonant-wall optical microcavity is square, and the vertex is a triangular cut-angle.

[0012] Preferably, the overall shape of the cut-angle square slit resonant-wall optical microcavity is square, and the vertex is a triangular cut-angle.

[0013] Preferably, the device for detecting the concentration of the solution comprises an input waveguide, a cut-angle square slit resonant-wall optical microcavity and an output waveguide coupled in sequence.

[0014] Preferably, the cavity side length l of the cut-angle square slit resonant-wall mode optical microcavity is 1 um; the length of the right angle side of the isosceles triangular cut-angle is 0.25 um; the coupling distance g between the input / output waveguide and the slit resonant cavity is 0.2 um; w is the cross-sectional side length of the input / output waveguide, and the value is 0.3 um; the thickness t of the cut-angle square resonant cavity is 0.2 um; and the slit distance s is 10 nm.

[0015] Preferably, the cut-angle square slit resonant-wall optical microcavity comprises two microcavities parallel to each other, when the incident light E_source is incident from the waveguide, the light satisfying the resonant condition is coupled into the microcavity, and through the coupling of the two microcavities, a stable traveling wave mode is formed in the slit region between the two microcavities; at this time, an output waveguide is used on the other side of the microcavity to receive the resonant frequency.

[0016] Preferably, the sensitivity calculation of the optical sensor comprises:

[0017] After selecting the resonant peak, the change of the solution concentration is simulated by changing the background refractive index of the simulation software, the first background refractive index of the simulation software is set to correspond to the refractive index of the solution to be detected at the first concentration; through calculation, the center wavelength of the first resonant peak is obtained, the second background refractive index of the simulation software is set to correspond to the refractive index of the solution to be detected at the second concentration; through calculation, the center wavelength of the second resonant peak is obtained; the calculation results are linearly fitted: the sensitivity of the solution concentration detection=(the center wavelength of the second resonant peak-the center wavelength of the first resonant peak) / (the refractive index of the solution to be detected at the second concentration-the refractive index of the solution to be detected at the first concentration).

[0018] The above-mentioned technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0019] The present invention provides a solution concentration detection method based on a chamfered square slit whispering-gallery optical microcavity, which has at least the following advantages compared with the prior art:

[0020] 1. Using silicon material to fabricate chamfered square slit optical whispering-gallery mode microcavities and coupling waveguides to improve coupling efficiency;

[0021] 2. This design is suitable for measuring solution concentration, and the solution detection sensitivity is improved by using this chamfered square slit whispering-gallery optical microcavity model;

[0022] 3. Compared with the detection effect of a single chamfered square whispering-gallery optical microcavity with the same model material and size, the detection sensitivity of the chamfered square slit whispering-gallery optical microcavity proposed in this invention can be doubled. Attached Figure Description

[0023] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0024] Figure 1 This is a top view of the microcavity structure;

[0025] Figure 2 This is a 3D diagram of the microcavity structure;

[0026] Figure 3 It is the transmission spectrum seen on the cross-section of the output waveguide;

[0027] Figure 4 yes Figure 3 The last description in the text is a magnified image of the peaks used to observe different solution concentrations;

[0028] Figure 5 This is under two different solution concentrations. Figure 4 The shift of the resonance peak shown. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Figure 1is the top view of the microcavity structure, and is the whole device diagram for detecting the concentration of the solution, where E_source is the mode light incident to the coupling input waveguide, E_out is the outcoupled mode light from the microcavity to the output waveguide, l is the side length of the cut-corner square slot whispering gallery mode optical microcavity, a is the side length of the cut-corner triangle, which is an isosceles triangle, g is the distance between the coupling input / output waveguide and the microcavity, and w is the cross-sectional side length of the coupling input / output waveguide. The model is calculated by using Lumerical FDTD simulation software. The performance of our invention is tested by using ethanol solution. First, the specific parameters in the model are introduced as follows: E_source is the light source incident from the input waveguide, the wavelength range of which is lambda, E_out is the light coupled to the output waveguide after passing through the microcavity, and the resonant frequency of the resonant cavity can be seen by observing the transmission spectrum through the cross section, l is the side length of the cut-corner square slot whispering gallery mode optical microcavity, which is 1 um, the cut corner is four isosceles triangles, a is the length of the right angle side of the triangle, which is 0.25 um, the coupling distance g between the input / output waveguide and the slot resonant cavity is set to 0.2 um, and the transmission spectrum of the cross section of the output waveguide is observed as shown in Figure 2 , which is to illustrate that the cross section of the coupling input / output waveguide is a square, w is the cross-sectional side length of the input / output waveguide, which is 0.3 um, s is the slot distance of the cut-corner square slot whispering gallery mode optical microcavity, the slot distance s is 10 nm, and t is the cavity thickness of the upper and lower microcavities, the cut-corner square resonant cavity thickness t is 0.2 um.

[0031] When the incident light E_source is incident from the waveguide, the light satisfying the resonance condition will be coupled into the microcavity, and through the coupling of the upper and lower microcavities, a stable traveling wave mode will be formed in the slot region in the middle of the microcavity. At this time, the output waveguide is used on the other side of the microcavity to receive the resonant frequency, and the resonant peak is obtained as shown in Figure 3 .

[0032] Figure 3 is the transmission spectrum observed on the cross section of the output waveguide, where the abscissa is the wavelength lambda, and the ordinate is the intensity of the normalized transmission spectrum. The resonant peak indicated by the arrow is the peak that needs to be observed for subsequent detection of the concentration of the solution. As shown in Figure 3 , there are four resonant peaks, and we select the peak with the highest intensity and located in the middle of the transmission spectrum, as shown by the arrow in Figure 3 , and the enlarged view is shown in Figure 4 . Figure 4 is the enlarged view of the cheap peak for observing different solution concentrations described in the last Figure 3 , and the meanings of the horizontal and vertical coordinates are the same as those described in Figure 3 . Figure 5 is the transmission spectrum of the cross section of the output waveguide under two different solution concentrations Figure 4The shift of the resonance peak shown, 1.525um and 1.533um at the arrow means the center wavelength of the two resonance peaks.

[0033] After selecting the resonance peak, we simulate the change of the solution concentration by changing the background refractive index of the simulation software. First, set the background refractive index of the simulation software to 1.3358, which corresponds to the refractive index of the 0.91 mol / L ethanol solution. Through calculation, we get Figure 4 The center wavelength of the resonance peak is 1.525um. Reset the background refractive index of the simulation software to 1.3696, which corresponds to the refractive index of the 17.17 mol / L ethanol solution. Through calculation, we get Figure 4 Figure 4 The center wavelength of the resonance peak is 1.533um.

[0034] Linear fitting calculation is performed on the calculation results: solution concentration detection sensitivity: (1.533-1.525) / (1.3696-1.3358)≈236.6nm / RIU. nm / RIU is used to represent the sensitivity of the optical sensor.

[0035] In summary, the application has designability, small volume, and good solution concentration detection effect. It is suitable for various solution concentration detection fields and has high sensitivity.

[0036] In one embodiment, the cut-corner square-shaped slit acoustic resonant optical microcavity is rectangular.

[0037] In one embodiment, the cut-corner square-shaped slit acoustic resonant optical microcavity is rectangular.

[0038] Although the present application is described herein with reference to particular embodiments, it is to be understood that these embodiments are merely exemplary of the principles and applications of the present application. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It is to be understood that such features of the dependent claims can be combined with such features of the application described herein, in any manner possible. It is also to be understood that features described in relation to one embodiment can be used in other embodiments described herein.

Claims

1. A method for detecting solution concentration based on a chamfered square slit whispering-gallery optical microcavity, characterized in that, Includes the following steps: S1. Design the dimensions and coupling waveguide parameters of a chamfered square slit whispering-gallery mode microcavity using the finite-difference time-domain method. The chamfered square slit whispering-gallery mode optical microcavity consists of two parallel microcavities, one above the other. The microcavity as a whole is square, with isosceles triangular chamfers at the vertices. An output waveguide is used on the other side of the microcavity. The side length of the chamfered square slit whispering-gallery mode optical microcavity is... The chamfered angle is 0.1~10µm; the chamfered angle consists of four isosceles triangles, and the length of the right-angled side 'a' of the chamfered angle of the isosceles triangle is 0.01~1µm; the coupling distance between the input / output waveguide and the slit resonator is g=0.02~1µm; the cross-section of the coupled input / output waveguide is a square, and w is the side length of the cross-section of the input / output waveguide, with a value of 0.1~1µm; the thickness of the chamfered square resonator is t=0.1~1µm; the slit distance is s=5~50nm; S2. Using the mode source in the finite-difference time-domain method, mode light with a wavelength of λ = 1250nm~1750nm is emitted from one end of the coupled input waveguide. The finite-difference time-domain method simulation is performed to obtain the resonant frequency of the designed chamfered square slit whispering-gallery mode microcavity. When the incident light E_source is injected from the waveguide, the light that meets the resonance condition will couple into the microcavity. Through the coupling of the upper and lower microcavities, a stable traveling wave mode will be formed in the slit region between the two microcavities. At this time, the output waveguide is used on the other side of the microcavity to receive the resonant frequency. S3. Adjust the distance between the upper and lower cavities of the chamfered square slit whispering-gallery mode optical microcavity to optimize the resonant frequency obtained in S2, so as to facilitate the observation of the resonant frequency offset when sensing solution concentration. S4. Select the optimized resonant frequency from S3 and calculate the offset of different solution concentrations to be detected. S5. Since the optical refractive index of the solution to be tested varies with different concentrations, the concentration change of the solution to be tested is simulated by changing the background refractive index of the Simulation region in the Finite-Difference Time-Domain method. S6. Observe the shift of the resonant frequency selected in S4 under different background refractive indices, and calculate the concentration of the solution to be tested.

2. The solution concentration detection method based on a chamfered square slit whispering-gallery optical microcavity according to claim 1, characterized in that, The device for detecting solution concentration includes an input waveguide, a chamfered square slit whispering-gallery optical microcavity, and an output waveguide coupled in sequence.

3. The solution concentration detection method based on a chamfered square slit whispering-gallery optical microcavity according to claim 1, characterized in that, The sensitivity calculation of an optical sensor includes: After selecting a suitable resonant peak, the change in solution concentration is simulated by altering the background refractive index of the simulation software. First, the first background refractive index of the simulation software is set to correspond to the refractive index of the solution at the first concentration. The center wavelength of the first resonant peak is then calculated. Next, the second background refractive index of the simulation software is set to correspond to the refractive index of the solution at the second concentration. The center wavelength of the second resonant peak is then calculated. A linear fitting calculation is then performed on the calculation results: Solution concentration detection sensitivity = (Center wavelength of the second resonant peak - Center wavelength of the first resonant peak) / (Refractive index of the solution at the second concentration - Refractive index of the solution at the first concentration).

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