A device and method for screening microspheres with similar sizes by using whispering gallery mode splitting spectrum

Abstract

The application discloses a device and method for screening microspheres with similar sizes by using echo wall mode split spectrum, which comprises a tapered optical fiber, a first microsphere cavity, a second microsphere cavity, a third microsphere cavity, and a coupling region of the microspheres to be measured and the three microsphere cavities; the tapered optical fiber has a long taper region, which provides spatial positions for coupling with the three microsphere cavities; the three microsphere cavities with different radius sizes are used as reference standards, and are coupled with microspheres with similar sizes corresponding to the three microsphere cavities respectively, so as to cause mode splitting phenomenon. When the size of the microspheres to be measured is smaller than the size of the microsphere cavities, the split spectrum direction tends to the left side; when the size of the microspheres to be measured is equal to the size of the microsphere cavities, the split peaks of the split spectrum are equal and the split peak spacing is maximum; when the size of the microspheres to be measured is larger than the size of the microsphere cavities, the split spectrum direction tends to the right side. The application can effectively expand the measurement range of the microsphere size, and realize rapid measurement of the microsphere size and differentiation of microspheres with similar sizes according to the split spectrum direction and the split spacing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical sensing, and particularly relates to a device and method for screening microspheres with similar sizes by using whispering gallery mode splitting spectrum. BACKGROUND

[0002] The whispering gallery mode in optics refers to a phenomenon that light waves propagate along the boundary inside a small circular or spherical structure and are confined within the boundary due to total internal reflection. The light waves propagating in the resonant cavity must satisfy the resonance condition, i.e. the wavelength and the mode splitting are common in the process of whispering gallery mode transmission. Compared with the conventional whispering gallery mode, the mode splitting has higher quality factor, double-spectrum detection capability and higher sensitivity. The essential reason for the mode splitting is the degeneration of the mode in the microcavity, which forms multiple modes with similar frequencies, including the fundamental mode and the azimuthal mode. The mode splitting caused by the coupling of two resonators is due to the coupling and interaction between different modes. For the coupling of two microspheres with the same material, the difference in the radius of the two microspheres affects the coupling efficiency and the strength of the two split peaks generated by the mode splitting. Therefore, the fundamental mode and the azimuthal mode and their splitting direction can be determined according to the difference in the strength of the split peaks, and the size difference of the two microspheres can be determined according to the split spacing. When the radius of the standard microsphere is known, the size of the microsphere to be measured can be obtained. The condition for the coupling of two spherical resonators with the same material that can generate whispering gallery mode is that they have similar sizes. Microspheres with similar sizes have similar optical properties and are easy to couple to generate mode splitting; microspheres with large size difference have large differences in transmission mode and properties, resulting in low coupling efficiency or even no coupling.

[0003] Generally, the measurement methods for microspheres (nanometer, micrometer level) include optical microscopy, electron microscopy, dynamic light scattering, atomic force microscopy and confocal microscopy, etc. Considering the price of the measurement equipment, the difficulty of operation and the measurement range, the optical microscopy is often used to measure the size of the microspheres due to its simple operation and low cost, but its resolution is limited. When different magnification objectives are used to measure the same microsphere to be measured, errors will be caused, and it is difficult to distinguish or screen microspheres with similar sizes. Therefore, a more accurate measurement method is needed to distinguish or screen microspheres with similar sizes. The whispering gallery mode splitting phenomenon is used to calculate the size of the microspheres, and by analyzing the split peak strength characteristics (split direction) and split spacing of the two coupled microspheres, the size difference and specific size of the microspheres can be accurately measured. This method not only overcomes the resolution limitation of the optical microscopy, but also can measure the microspheres without damaging them, providing a new method for screening microspheres with similar sizes. SUMMARY

[0004] The application aims to provide a device and method for screening microspheres with similar sizes by using whispering gallery mode split spectrum.

[0005] The application aims to provide a device and method for screening microspheres with similar sizes by using whispering gallery mode split spectrum.

[0006] The application aims to provide a device and method for screening microspheres with similar sizes by using whispering gallery mode split spectrum.

[0007] The incident light from the light source module enters the measuring module from the input end, is emitted into the first microsphere cavity through the tapered optical fiber, and is coupled with the first microsphere cavity to form the first whispering gallery mode; the remaining uncoupled incident light continues to pass through the tapered optical fiber and enters the second microsphere cavity, and is coupled with the second microsphere cavity to form the second whispering gallery mode; the remaining uncoupled incident light continues to pass through the tapered optical fiber and enters the third microsphere cavity, and is coupled with the third microsphere cavity to form the third whispering gallery mode.

[0008] The three microspheres to be measured are coupled with the corresponding three microsphere cavities to form mode splitting, and the spectral receiving module receives the information of the split spectrum.

[0009] Further, the light source module includes a tunable laser, a spontaneous emission amplification light source and a polarization controller; the tunable laser is connected with the spontaneous emission amplification light source to form a measuring module, and then the measuring module is connected with the polarization controller; the tunable laser and the spontaneous emission amplification light source provide a continuous and stable tunable light source for the measuring module, and the polarization controller adjusts the input polarization state of the light source to be TM or TE, so as to ensure that the input light source maintains a relatively single input polarization state, and then adjusts the resonance wavelength of the whispering gallery mode, so as to facilitate the analysis of the subsequent received spectrum.

[0010] Further, the tapered optical fiber has a long taper zone with a core diameter of 2 μm, and the light wave transmitted in the tapered optical fiber is coupled into the three microsphere cavities from the long taper zone; the uniform long taper zone structure ensures that the transmitted evanescent waves satisfy the matching conditions with the first microsphere cavity, the second microsphere cavity and the third microsphere cavity respectively, and the whispering gallery mode is formed.

[0011] Further, the three regions for measuring the size of the microspheres are the spatial positions where the microspheres to be measured are in contact with the first, second and third microsphere cavities and coupled with each other; the three microsphere cavities are coupled with the microspheres to be measured with similar sizes, the microspheres with similar sizes have similar optical properties, and the two microspheres in direct contact with each other have stable mode splitting phenomenon, and different size differences cause different degrees of mode splitting characteristics (splitting direction and splitting interval).

[0012] Further, the first, second and third microsphere cavities are in a cascade form, which increases the size measurement range of the microspheres to be measured; the size of the microsphere cavities is determined by the free spectral range: FSR = λ 2 / 2πnR, where λ represents the center wavelength of the incident light, n represents the refractive index of the microsphere cavity, and R represents the corresponding radius of the three microsphere cavities.

[0013] Further, the sizes of the first, second and third microsphere cavities increase in sequence, and the difference between the radii of each two microsphere cavities is not more than 50 μm.

[0014] Further, when the size of the microsphere to be measured is smaller than the size of the microsphere cavity, the splitting spectrum direction tends to the left; when the size of the microsphere to be measured is equal to the size of the microsphere cavity, the splitting peaks of the splitting spectrum are equal and the splitting interval is maximum; when the size of the microsphere to be measured is larger than the size of the microsphere cavity, the splitting spectrum direction tends to the right; and the splitting interval of the splitting spectrum is: δλ ≈ 2(g 2 -((κ1-κ2) / 2) 2 ) 1 / 2 where g is the coupling strength of the standard microsphere cavity and the microsphere to be measured, which is related to the coupling distance between the two, in the measurement process, the microsphere to be measured is coupled with the standard microsphere cavity in direct contact, and the coupling strength is constant, κ1 is the mode dissipation rate of the microsphere cavity, and κ2 is the mode dissipation rate of the microsphere to be measured, and the mode dissipation rate is inversely proportional to the radius of the microsphere.

[0015] Further, the spectrum receiving module includes a spectrum analyzer, a photodetector and an oscilloscope; the photodetector is connected with the oscilloscope after converting the light signal into an electrical signal; the spectrum analyzer receives the corresponding whispering gallery spectrum of the first, second and third microsphere cavities through the connected photodetector and oscilloscope; when the size of the microsphere to be measured is measured, the mode splitting phenomenon occurs on the basis of the corresponding whispering gallery mode, and the spectrum receiving module receives the information of the splitting spectrum.

[0016] The utility model provides a device for screening microspheres with similar sizes by using echo wall mode split spectrum, which comprises a measuring module; the input end of the measuring module is connected with a light source module, and the output end is connected with a spectrum receiving module; the light source module provides incident light to the measuring module; the measuring module is jointly constituted by a first microsphere cavity, a second microsphere cavity and a third microsphere cavity in a cascade form; the incident light enters the three microsphere cavities to form three echo wall modes; the three microspheres to be measured are coupled with the microsphere cavities with similar sizes to cause mode splitting; and the spectrum receiving module analyzes the received split spectrum.

[0017] The utility model has the advantages of:

[0018] 1. The main components of the measuring module, i.e. the tapered optical fiber and the microsphere cavity, are common optical devices, so the cost of the main device is low;

[0019] 2. The cascade structure of the three standard microsphere cavities with large differences in radius size expands the measurement range of the sizes of the microspheres to be measured;

[0020] 3. The size of the microspheres to be measured is determined according to the change characteristics of the split peak intensity characteristics (split direction) and the split spacing of the split spectrum;

[0021] 4. The measurement process is simple, and the actual operation is relatively easy; the sizes of the microspheres with similar sizes can be accurately measured or screened. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a schematic view of a device for screening microspheres with similar sizes by using echo wall mode split spectrum;

[0023] Figure 2 It is a structural view of the coupling of the microspheres to be measured with the three cascade microsphere cavities in the measuring module;

[0024] Figure 3 It is a corresponding relationship between the split direction and the split peak spacing of the split spectrum and the size of the microspheres to be measured. DETAILED DESCRIPTION

[0025] The utility model will be further described below with reference to the drawings.

[0026] According to the utility model, Figure 1 a device for screening microspheres with similar sizes by using echo wall mode split spectrum, which comprises a light source module composed of a tunable laser 1, a spontaneous emission amplification light source 2 and a polarization controller 3; a measuring module composed of three microsphere cavities (403, 404, 405) with different sizes and a tapered optical fiber 402 coupled in a cascade structure; and a spectrum receiving module composed of a photodetector 5, an oscilloscope 6 and a spectrum analyzer 7.

[0027] According to the utility model, Figure 2The taper fiber 402 with a long taper region in the measuring module is coupled with the first microsphere cavity 403, the second microsphere cavity 404, the third microsphere cavity 405, etc. to excite the whispering gallery mode, and provides the first measuring area 406, the second measuring area 407, the third measuring area 408 and the microspheres with similar sizes to be measured to be coupled to generate the mode splitting phenomenon.

[0028] Specifically, the measuring module 4 includes an input end 401, a taper fiber 402, a first microsphere cavity 403, a second microsphere cavity 404, a third microsphere cavity 405, a first measuring area 406, a second measuring area 407, a third measuring area 408, a first microsphere to be measured 409 with a size similar to the first microsphere cavity, a second microsphere to be measured 410 with a size similar to the second microsphere cavity, a third microsphere to be measured 411 with a size similar to the third microsphere cavity, and an output end 412.

[0029] The taper fiber 402 has a long taper region with a core diameter of 2 μm, and the light wave transmitted in the taper fiber 402 is coupled into the microsphere cavity. The uniform long taper region structure can ensure that the transmitted evanescent wave can meet the matching condition with the first microsphere cavity 403, the second microsphere cavity 404 and the third microsphere cavity 405 respectively, and form the whispering gallery mode.

[0030] The sizes of the first microsphere cavity 403, the second microsphere cavity 404 and the third microsphere cavity 405 should have a large gap, and the difference between the radii of each two microsphere cavities should not exceed 50 μm, so as to ensure the continuity of the overall measuring range. For example, when the radius size of the first microsphere cavity 403 is 50 μm, the radius size of the second microsphere cavity 404 is 75 μm, and the radius size of the third microsphere cavity 405 is 100 μm, the microsphere size measuring range that can be achieved is about 35 μm to 115 μm, and the microspheres in this radius range can be accurately measured or screened by using this part.

[0031] The first microsphere cavity 403, the second microsphere cavity 404 and the third microsphere cavity 405 are directly coupled at equal intervals on the long taper region of the taper fiber 402 to form a cascade structure, so as to ensure the long-term transmission of the light wave energy and achieve the best coupling efficiency.

[0032] The taper fiber 402 is fixed in the measuring module 4, the first microsphere cavity 403, the second microsphere cavity 404 and the third microsphere cavity 405 are fixed in the measuring module 4 after being optimally coupled with the taper fiber 402, and the measuring areas for the microspheres to be measured are designed as the first measuring area 406, the second measuring area 407 and the third measuring area 408.

[0033] In the measurement process, the microspheres to be measured are directly coupled with the microsphere cavities (the first microsphere cavity 403, the second microsphere cavity 404 or the third microsphere cavity 405) of similar sizes, ensuring that the coupling strength remains consistent and guaranteeing that the mode splitting is caused by the size difference between the microspheres to be measured and the standard microsphere cavities, and then selecting a suitable measurement area (the first measurement area 406, the second measurement area 407 or the third measurement area 408).

[0034] The output end 412 of the measurement module 4 is connected with a spectrum receiving module, wherein the photodetector 5 is connected with an oscilloscope 6, and the received light signal is converted into an electrical signal for output. The spectrum analyzer 7 and the oscilloscope 6 jointly collect the split spectrum, judge the two split peak intensity characteristics (split direction) and the split interval of the split spectrum, record the size of the corresponding microspheres to be measured and the characteristic parameters (the two split peak intensity characteristics and the split interval) of the split spectrum, and make a corresponding microsphere size-split spectrum corresponding database, which is beneficial to the rapid analysis of subsequent microsphere measurement and accurate acquisition of the size of the microspheres to be measured.

[0035] In summary, the method for screening microspheres of similar sizes by using the whispering gallery mode split spectrum first provides incident light in the form of evanescent waves in the tapered optical fiber 402 by the light source module, the incident light satisfying the resonance condition of the first microsphere cavity 403 enters the first microsphere cavity 403 and is coupled therewith to form a first whispering gallery mode; the remaining uncoupled incident light continues to be transmitted in the tapered zone of the tapered optical fiber 402, the incident light energy satisfying the resonance condition of the second microsphere cavity 404 enters the second microsphere cavity 404 and is coupled therewith to form a second whispering gallery mode; the remaining uncoupled incident light continues to be transmitted in the tapered zone of the tapered optical fiber 402, the incident light satisfying the resonance condition of the third microsphere cavity 405 enters the third microsphere cavity 405 and is coupled therewith to form a third whispering gallery mode; the first microspheres to be measured 409, the second microspheres to be measured 410 and the third microspheres to be measured 411 are coupled with the microsphere cavities of similar sizes to cause mode splitting, and finally the split spectrum is obtained by the spectrum receiving module and further analyzed.

[0036] According to Figure 3 In the measurement process, the radius size R2 of the microspheres to be measured and the size R1 of the standard microsphere cavities have three relationships: the radius size R2 of the microspheres to be measured is smaller than the size R1 of the microsphere cavities, and the corresponding split spectrum is split to the left; the radius size R2 of the microspheres to be measured is equal to the size R1 of the microsphere cavities, and the corresponding split spectrum has the same intensity of the two split peaks and the maximum interval of the split peaks; the radius size R2 of the microspheres to be measured is greater than the size R1 of the microsphere cavities, and the corresponding split spectrum is split to the right; after preliminarily judging the relationship between the radius size R2 of the microspheres to be measured and the size R1 of the microsphere cavities, the real size of the microspheres to be measured is analyzed according to the split interval of the split peaks.

[0037] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A device for screening microspheres of similar size using whispering-gallery mode splitting spectroscopy, characterized in that: The system includes a measurement module (4), which includes an input terminal (401), a tapered optical fiber (402), a first microsphere cavity (403), a second microsphere cavity (404), a third microsphere cavity (405), a first microsphere to be measured (409) with a size similar to that of the first microsphere cavity, a second microsphere to be measured (410) with a size similar to that of the second microsphere cavity, a third microsphere to be measured (411) with a size similar to that of the third microsphere cavity, and an output terminal (412). The input terminal (401) is connected to a light source module, and the output terminal (412) is connected to a spectral receiving module. The incident light supplied by the light source module enters the measurement module from the input end (401), passes through the tapered optical fiber (402) and enters the first microsphere cavity (403), where it couples with the first microsphere cavity (403) to form a first whispering wall mode; the remaining uncoupled incident light continues to pass through the tapered optical fiber (402) and enters the second microsphere cavity (405), where it couples with the second microsphere cavity (405) to form a second whispering wall mode; The remaining uncoupled incident light continues to pass through the tapered fiber (402) and enters the third microsphere cavity (405), where it couples with the third microsphere cavity (405) to form the third whispering gallblade mode; The three microspheres to be measured are coupled to the corresponding three microsphere cavities to generate mode splitting, and the spectral receiving module receives the information of the split spectrum.

2. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 1, characterized in that: The light source module includes a tunable laser (1), a spontaneous emission amplified light source (2), and a polarization controller (3); the tunable laser (1) is connected to the spontaneous emission amplified light source (2) to form a measurement module (4), and then connected to the polarization controller (3); the tunable laser (1) and the spontaneous emission amplified light source (2) provide a continuous and stable tunable light source, and the polarization controller (3) adjusts the input polarization state of the light source to TM or TE, so that the input light source is a single input polarization state.

3. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 1, characterized in that: The tapered optical fiber (402) has a long tapered region with a core diameter of 2μm. The light waves transmitted in the tapered optical fiber (402) are coupled into the three microsphere cavities. The uniform long tapered region structure ensures that the transmitted evanescent wave meets the matching conditions with the first microsphere cavity (403), the second microsphere cavity (404), and the third microsphere cavity (405), respectively, forming a whispering gallery mode.

4. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 1, characterized in that: The measurement area of ​​the three microspheres to be measured is the spatial position where the microspheres to be measured are in contact with the first microsphere cavity (403), the second microsphere cavity (404), and the third microsphere cavity (405) respectively and are coupled. The three microsphere cavities are coupled with the microspheres to be measured with corresponding sizes that are similar. The two microspheres with similar sizes have similar optical properties. The two are in direct contact and a stable mode splitting phenomenon occurs. Different size differences cause different degrees of mode splitting characteristics.

5. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 4, characterized in that: The first microsphere cavity (403), the second microsphere cavity (404), and the third microsphere cavity (405) are cascaded, which increases the size measurement range of the microspheres to be measured; the size of the microsphere cavity is determined by the free spectral range: FSR=λ 2 / 2πnR, where λ represents the center wavelength of the incident light, n represents the refractive index of the microsphere cavity, and R represents the corresponding radii of the three microsphere cavities.

6. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 5, characterized in that: The sizes of the first microsphere cavity (403), the second microsphere cavity (404), and the third microsphere cavity (405) increase sequentially, and the maximum difference in radius between any two microsphere cavities does not exceed 50 μm.

7. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 5, characterized in that: When the size of the microsphere to be measured is smaller than the size of the microsphere cavity, the direction of the splitting spectrum tends to the left; when the size of the microsphere to be measured is equal to the size of the microsphere cavity, the splitting peaks of the splitting spectrum are equal and the splitting interval is the largest; when the size of the microsphere to be measured is larger than the size of the microsphere cavity, the direction of the splitting spectrum tends to the right; the splitting peak interval of the splitting spectrum is: δλ≈2(g 2 -((κ1-κ2) / 2) 2 ) 1 / 2 Where g is the coupling strength between the standard microsphere cavity and the microsphere to be measured, which is related to the coupling distance between them. During the measurement process, the microsphere to be measured and the standard microsphere cavity are coupled in direct contact, and the coupling strength remains unchanged. κ1 is the mode dissipation rate of the microsphere cavity, and κ2 is the mode dissipation rate to be measured. The mode dissipation rate is inversely proportional to the microsphere radius.

8. The device for screening microspheres of similar size using echo-gallery mode splitting spectroscopy according to claim 1, characterized in that: The spectral receiving module includes a spectral analyzer (7), a photodetector (5), and an oscilloscope (6); the photodetector (5) converts the optical signal into an electrical signal and connects to the oscilloscope (6); the spectral analyzer (7), the connected photodetector (5), and the oscilloscope (6) receive the whispering-gallery spectra corresponding to the first microsphere cavity (403), the second microsphere cavity (404), and the third microsphere cavity (405); when measuring the size of the microsphere to be measured, a mode splitting phenomenon occurs based on the corresponding whispering-gallery mode, and the spectral receiving module receives the information of the split spectrum.

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