An ammonia sensor based on graphene modified optical microcavity

Abstract

The application relates to an ammonia sensor based on a graphene-modified optical microcavity. The ammonia sensor comprises a sensing unit, a tapered optical fiber, a tunable laser, a photodetector and an oscilloscope. The sensing unit comprises an optical microcavity, and the outer surface of the optical microcavity is attached with graphene. The tapered optical fiber is arranged at the equator of the optical microcavity, one end of the tapered optical fiber is connected with the tunable laser, and the other end of the tapered optical fiber is connected with the photodetector. The oscilloscope is connected with the photodetector and is used for displaying the optical resonance frequency of the sensing unit. The optical resonance frequency is used for determining the ammonia concentration information collected by the ammonia sensor. The ammonia sensor provided by the application can improve the accuracy of ammonia concentration measurement.

Description

Technical Field

[0001] This application relates to the field of gas sensing, to nanomaterials and micro / nano fabrication technology, and in particular to an ammonia sensor based on a graphene-modified optical microrod cavity. Background Technology

[0002] Gas sensing technology plays a vital role in modern industry, environmental monitoring, public safety, and healthcare. Ammonia, in particular, is widely used in agriculture (e.g., fertilizers), chemicals, and refrigeration. Leaks of ammonia can cause not only environmental pollution but also serious health consequences (e.g., respiratory illnesses). Therefore, developing highly sensitive and selective ammonia sensors is crucial to meeting increasingly stringent environmental monitoring requirements and industrial safety standards.

[0003] Optical gas sensors detect gases based on their absorption and scattering properties of light, offering numerous advantages including high sensitivity (detecting gas concentrations at the ppb level), real-time monitoring, and non-contact operation. These characteristics make them widely applicable in gas detection. However, optical sensors also have significant drawbacks: their cost is relatively high, especially the expense of high-performance light sources and detectors; furthermore, their size and weight are often large, limiting their use in portable applications; and they are sensitive to changes in ambient temperature and humidity, which can affect the accuracy and repeatability of measurements.

[0004] Therefore, ammonia gas sensors in traditional technologies suffer from low measurement accuracy. Summary of the Invention

[0005] Therefore, it is necessary to provide an ammonia sensor based on a graphene-modified optical microrod cavity that can improve the accuracy of ammonia concentration detection, addressing the aforementioned technical problems.

[0006] In one aspect, this application provides an ammonia sensor based on a graphene-modified optical microrod cavity, comprising: a sensing unit, a tapered optical fiber, a tunable laser, a photodetector, and an oscilloscope;

[0007] The sensing unit includes an optical microrod cavity, and graphene is attached to the outer surface of the optical microrod cavity.

[0008] The tapered optical fiber is disposed at the equator of the optical microrod cavity, one end of the tapered optical fiber is connected to the tunable laser, and the other end of the tapered optical fiber is connected to the photodetector;

[0009] The oscilloscope is connected to the photodetector and is used to display the optical resonant frequency of the sensing unit. The optical resonant frequency is used to determine the ammonia concentration information collected by the ammonia sensor.

[0010] In one embodiment, the laser output from the tunable laser passes through an optical fiber polarization controller and enters one end of a tapered optical fiber.

[0011] In one embodiment, the other end of the tapered optical fiber is connected to the photodetector via an optical fiber attenuator.

[0012] In one embodiment, the graphene has a thickness of a single carbon atom layer and a surface area of ​​400~1600 μm. 2 .

[0013] In one embodiment, the diameter of the optical microrod cavity is 2-3 mm.

[0014] In one embodiment, the quality factor Q of the optical microrod cavity is ≥10. 7 .

[0015] In one embodiment, the optical microrod cavity is made of silicon dioxide.

[0016] In one embodiment, the diameter of the tapered region of the tapered optical fiber is 1~3μm.

[0017] In one embodiment, the tapered optical fiber has a length of 1.5 to 3 cm.

[0018] In one embodiment, the tapered optical fiber is made of silicon dioxide.

[0019] The aforementioned ammonia sensor based on a graphene-modified optical microrod cavity includes: a sensing unit, a tapered optical fiber, a tunable laser, a photodetector, and an oscilloscope. The sensing unit includes an optical microrod cavity with graphene attached to its outer surface. The tapered optical fiber is positioned at the equator of the optical microrod cavity, with one end connected to the tunable laser and the other end connected to the photodetector. The oscilloscope is connected to the photodetector and is used to display the optical resonant frequency of the sensing unit. This optical resonant frequency is used to determine the ammonia concentration information collected by the ammonia sensor. When ammonia molecules are adsorbed onto the graphene surface, the ammonia molecules react with the graphene. Electron exchange causes a change in the electrical conductivity of graphene, which in turn alters its optical refractive index. Since the optical signal within the sensing unit interacts with the graphene through an evanescent field, the change in the graphene's optical refractive index also changes the optical refractive index of the sensing unit, ultimately altering its optical resonant frequency. This allows the correlation between the change in the sensing unit's optical resonant frequency and the ammonia concentration value to determine the ammonia concentration currently collected by the ammonia sensor. This application's ammonia sensor combines microcavity optics and graphene optoelectronics, solving the problem of insensitivity to gases in traditional optical microcavity materials. This application uses a graphene-modified optical microrod cavity for ammonia sensing, exhibiting high sensitivity and rapid response, capable of detecting low concentrations of ammonia. Furthermore, graphene's excellent stability and conductivity allow it to adapt to various environmental conditions, and combined with miniaturization, it provides a low-cost, easily integrated sensing solution. These characteristics make it an ideal choice for ammonia monitoring.

[0020] The design of graphene-modified optical microrod cavities effectively overcomes the shortcomings of traditional optical gas sensors and microcavity sensors. First, the chemical stability and physical strength of graphene ensure the sensor's reliability in harsh environments, reducing dependence on external conditions. Second, the optical signal in the optical microcavity interacts with the graphene through an evanescent field. Gas molecules adsorb onto the graphene surface and undergo electron exchange, affecting the graphene's conductivity and thus altering its optical refractive index, further influencing optical signal transmission. Furthermore, advanced nanofabrication techniques allow for precise control of the microrod cavity, optimizing its optical properties and improving the sensor's sensitivity and stability in practical applications.

[0021] In summary, this application has the advantages of low system complexity, high gas sensing sensitivity, and low cost. It effectively solves the problems of traditional microcavity materials being insensitive to gas, having complex systems, and being difficult to operate. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of a sensing module of an ammonia sensor in one embodiment;

[0024] Figure 2 This is a schematic diagram of an ammonia sensor system in one embodiment;

[0025] Figure 3 This is an example of how the transmission spectrum of an optical microrod cavity changes with gas concentration.

[0026] Figure 4 This is a response graph of the optical resonant frequency of an optical microrod cavity as a function of gas concentration in one embodiment.

[0027] The reference numerals and their meanings in the attached figures are as follows:

[0028] 1. Optical microrod cavity; 2. Graphene; 3. Tapered optical fiber; 4. Tunable laser; 5. Fiber polarization controller; 6. Fiber attenuator; 7. Photodetector; 8. Oscilloscope; 9. Sensing module. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] To facilitate understanding of this disclosure, a more complete description will now be given with reference to the accompanying drawings, in which preferred embodiments of the present disclosure are shown. However, this disclosure may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or parts, these elements, components, areas, layers, and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or part from another element, component, area, layer, or part. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or part discussed below may be referred to as the second element, component, area, layer, or part.

[0033] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below” or “under” the other element or feature will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprise” and / or “comprising,” when used in this specification, identify the presence of features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0035] Figure 1 This is a schematic diagram of a sensing module for an ammonia gas sensor; wherein, as shown... Figure 1As shown, the sensing module 9 of the ammonia sensor includes a sensing unit and a tapered optical fiber 3. The sensing unit includes an optical microrod cavity 1 and graphene 2. The graphene is attached to the outer surface of the optical microrod cavity 1. The tapered optical fiber 3 is located at or near the equator of the optical microrod cavity 1.

[0036] Graphene, as a novel two-dimensional material, is an ideal choice for optical sensors due to its excellent optical, electrical, and chemical properties. Modifying optical microrod cavities with graphene can significantly improve sensor sensitivity by enhancing the interaction between light and ammonia molecules within the cavity. Specifically, graphene's high specific surface area and excellent gas adsorption capacity enhance ammonia adsorption, resulting in a more pronounced optical signal within the optical microcavity. Furthermore, graphene's high conductivity and rapid electron mobility can shorten the sensor's response time and improve its dynamic performance.

[0037] Figure 2 This is a schematic diagram of an ammonia gas sensor system; such as Figure 2 As shown, the ammonia sensor also includes a tunable laser 4, a photodetector 7, and an oscilloscope 8; wherein, one end of the tapered optical fiber 3 is connected to the tunable laser 4, and the other end of the tapered optical fiber 3 is connected to the photodetector 7.

[0038] The laser output from the tunable laser 4 enters one end of the tapered optical fiber 3 through the fiber polarization controller 5, and the other end of the tapered optical fiber 3 is connected to the photodetector 7 through the fiber attenuator 6.

[0039] The oscilloscope 8 is connected to the photodetector 7 and is used to display the optical resonant frequency of the sensing unit. The optical resonant frequency is used to determine the ammonia concentration collected by the ammonia sensor.

[0040] In practice, the working process of the ammonia sensor described above is as follows:

[0041] A tunable laser 4 outputs a laser with a uniformly scanning wavelength. The laser output from the tunable laser 4 is transmitted via a fiber polarization controller 5 to a tapered fiber 3, which is positioned close to the equator of the optical microrod cavity 1. The laser light enters the optical microrod cavity 1 from the tapered fiber 3 through an evanescent field, and the optical signal in the optical microrod cavity 1 is coupled back to the tapered fiber 3 for output. Since graphene 2 is attached to the outer surface of the optical microrod cavity 1, graphene 2 can interact with the optical signal inside the optical microrod cavity 1 through the evanescent field. The other end of the tapered fiber 3 is connected to a photodetector 7 via a fiber attenuator 6. The photodetector 7 converts the detected optical signal into an electrical signal and outputs it to an oscilloscope 8. By uniformly scanning the tunable laser 4 and acquiring the electrical signal output from the photodetector 7 through the oscilloscope 8, the optical resonant frequency of the sensing unit can be obtained.

[0042] Figure 3This is an example of the transmission spectrum of an optical microrod cavity varying with gas concentration, combined with... Figure 3 When ammonia molecules adsorb onto the surface of graphene 2, they exchange electrons with graphene 2, causing a change in the conductivity of graphene 2 and further altering its optical refractive index. The optical signal within the sensing unit of the graphene 2-modified optical microrod cavity 1 interacts with graphene 2 through an evanescent field. When the optical refractive index of graphene 2 changes, the effective optical refractive index of the sensing unit also changes, ultimately leading to a change in the optical resonant frequency of the graphene 2-modified optical microrod cavity sensing unit.

[0043] Figure 4 This is a response graph of the optical resonant frequency of the optical microrod cavity as a function of gas concentration in one embodiment; combined with Figure 4 Different concentrations of ammonia correspond to different changes in the optical resonant frequency of the graphene-modified optical microrod cavity sensing unit. Therefore, the ammonia sensor of this application can accurately determine the ammonia concentration currently collected by the sensor by utilizing the correspondence between the change in the optical resonant frequency of the sensing unit and the ammonia concentration value.

[0044] The ammonia sensor of this embodiment includes: a sensing unit, a tapered optical fiber, a tunable laser, a photodetector, and an oscilloscope. The sensing unit includes an optical microrod cavity, the outer surface of which is coated with graphene. The tapered optical fiber is positioned at the equator of the optical microrod cavity, one end of which is connected to the tunable laser, and the other end is connected to the photodetector. The oscilloscope is connected to the photodetector and is used to display the optical resonant frequency of the sensing unit. The optical resonant frequency is used to determine the ammonia concentration information collected by the ammonia sensor. When ammonia molecules are adsorbed onto the graphene surface, electron exchange occurs between the ammonia molecules and the graphene, causing... The change in the electrical conductivity of graphene alters its optical refractive index. Since the optical signal within the sensing unit interacts with the graphene through an evanescent field, the change in the graphene's optical refractive index also changes the sensing unit's optical refractive index, ultimately altering the sensing unit's optical resonant frequency. This allows the correlation between the change in the sensing unit's optical resonant frequency and the ammonia concentration value to determine the ammonia concentration currently collected by the ammonia sensor. This ammonia sensor combines microcavity optics and graphene optoelectronics, solving the problem of insensitivity to gases in traditional optical microcavity materials. This application utilizes a graphene-modified optical microrod cavity for ammonia sensing, exhibiting high sensitivity and rapid response, capable of detecting low concentrations of ammonia. Furthermore, graphene's excellent stability and conductivity allow it to adapt to various environmental conditions, and combined with miniaturization, it provides a low-cost, easily integrated sensing solution. These characteristics make it an ideal choice for ammonia monitoring.

[0045] The design of graphene-modified optical microrod cavities effectively overcomes the shortcomings of traditional optical gas sensors and microcavity sensors. First, the chemical stability and physical strength of graphene ensure the sensor's reliability in harsh environments, reducing dependence on external conditions. Second, the optical signal in the optical microcavity interacts with the graphene through an evanescent field. Gas molecules adsorb onto the graphene surface and undergo electron exchange, affecting the graphene's conductivity and thus altering its optical refractive index, further influencing optical signal transmission. Furthermore, advanced nanofabrication techniques allow for precise control of the microrod cavity, optimizing its optical properties and improving the sensor's sensitivity and stability in practical applications.

[0046] In summary, the ammonia sensor of this application has the advantages of low system complexity, high gas sensing sensitivity, and low cost. It effectively solves the problems of traditional microcavity materials being insensitive to gases, having complex systems, and being difficult to operate.

[0047] In some embodiments, the thickness of the graphene is the thickness of a single carbon atom layer, and the surface area of ​​the graphene is 400~1600 μm. 2 .

[0048] In practice, the graphene in the ammonia sensor of this application can be prepared by mechanical exfoliation and then transferred to the surface of the optical microrod cavity by dry method. The specific preparation method is as follows:

[0049] Select a high-purity graphite block and repeatedly stick and peel it off with adhesive tape until a thin layer of graphite is obtained. Transfer the peeled graphite layer onto a silicon wafer and observe and confirm its thickness using a microscope. Place a PDMS film on the graphene surface and gently apply pressure to ensure good contact. Carefully peel the PDMS film off the silicon wafer; the graphene should adhere to the PDMS. Align the PDMS film with graphene onto the surface of the microrod cavity, ensuring accurate positioning. Use appropriate pressure to ensure tight contact between the PDMS and the microrod cavity surface, ensuring graphene transfer. Heat to 65-80 degrees Celsius and gently peel off the PDMS film; the graphene will remain on the surface of the microrod cavity.

[0050] In some embodiments, the diameter of the optical microrod cavity is 2-3 mm, and the quality factor Q of the optical microrod cavity is ≥10. 7 The optical microrod cavity is made of silicon dioxide.

[0051] In practice, the optical microrod cavity of this application can be fabricated by laser etching, specifically using the following fabrication method:

[0052] Using optical microrods as raw materials and a CO2 laser as the light source, the optical microrods (2-3 mm in diameter) are first fixed on an electrically driven rotary fixture, which is then fixed on an electrically driven displacement stage. The CO2 laser is turned on, and the laser emitted by the light source passes through a beam expander and a focusing lens, ultimately focusing onto the surface of the optical quartz rod. Step 1: The electrically driven rotary fixture and automatic control program are started, with the output set to 15W and the laser focus point set to 5-7 mm from the quartz rod surface. The electrically driven displacement stage is set to reciprocate, allowing the CO2 laser output to scan and pre-process the quartz rod surface. The reciprocating length of the stage is 5-20 mm, and the moving speed is 0.5-2 mm / s. Step 2: The electrically driven displacement stage is stopped, allowing the CO2 laser output to focus on the pre-processed central area. The control program is then started to automatically process the optical microrod cavity. Step 3: Step 1 is repeated to anneal the optical microrod cavity. The resulting optical microrod cavity has a quality factor Q ≥ 10. 7 .

[0053] In some embodiments, the diameter of the tapered region of the tapered optical fiber is 1~3μm, the length of the tapered optical fiber is 1.5~3cm, and in some embodiments, the material of the tapered optical fiber is silicon dioxide.

[0054] In practice, the tapered optical fiber of this application can be obtained from single-mode fiber (SMF28) through an optical fiber tapering mechanism, specifically using the following fabrication method:

[0055] First, gently peel off the coating of ordinary commercial optical fiber and wipe the fiber surface with test paper to ensure it is clean. Secure the stripped fiber below the hydrogen outlet of the fiber tapering machine. Connect both ends of the fiber using a bare fiber adapter; one end connects to the power port of the tapering machine, and the other end connects to a 1550nm wavelength laser. Start the laser; the power meter interface will display the laser power and fiber loss. Next, turn on the hydrogen flame switch of the fiber tapering machine to start the tapering process. During the tapering process, monitor the loss of the tapered fiber through the working interface. When the tapered length displays 20000μm, turn off the flame. The entire tapering process lasts approximately 4 minutes.

[0056] It is understood that the sensing module prepared by the above-described embodiment is the ammonia sensor based on this sensing module. When ammonia molecules are adsorbed onto the graphene surface of the ammonia sensor, electron exchange occurs between the ammonia molecules and the graphene, causing a change in the conductivity of the graphene and thus a change in its optical refractive index. Since the optical signal within the sensing unit interacts with the graphene through an evanescent field, the optical refractive index of the sensing unit also changes after the graphene's optical refractive index changes, ultimately altering the optical resonant frequency of the sensing unit. This allows the correlation between the change in the optical resonant frequency of the sensing unit and the ammonia concentration value to determine the ammonia concentration information currently collected by the ammonia sensor. This application's ammonia sensor combines microcavity optics and graphene optoelectronics, solving the problem of insensitivity to gases in traditional optical microcavity materials. The graphene-modified optical microrod cavity used in this application for ammonia sensing exhibits high sensitivity and rapid response, enabling the detection of low-concentration ammonia. Furthermore, graphene's excellent stability and conductivity make it adaptable to various environmental conditions, and combined with miniaturization design, it provides a low-cost, easily integrated sensing solution. These characteristics make it an ideal choice for ammonia monitoring.

[0057] In summary, this application has the advantages of low system complexity, high gas sensing sensitivity, and low cost. It effectively solves the problems of traditional microcavity materials being insensitive to gas, having complex systems, and being difficult to operate.

[0058] It should be understood that, unless explicitly stated herein, there is no strict order in which the steps are performed; these steps may be performed in other orders. Moreover, at least some steps in the preparation process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but may be performed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but may be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0059] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0062] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An ammonia sensor based on a graphene-modified optical microrod cavity, characterized in that, include: Sensing unit, tapered optical fiber, tunable laser, photodetector, oscilloscope; The sensing unit includes an optical microrod cavity, and graphene is attached to the outer surface of the optical microrod cavity. The tapered optical fiber is disposed at the equator of the optical microrod cavity, one end of the tapered optical fiber is connected to the tunable laser, and the other end of the tapered optical fiber is connected to the photodetector; The oscilloscope is connected to the photodetector and is used to display the optical resonant frequency of the sensing unit. The optical resonant frequency is used to determine the ammonia concentration collected by the ammonia sensor. In this process, the optical signal within the sensing unit based on the graphene-modified optical microrod cavity interacts with the graphene through an evanescent field. The effective optical refractive index of the sensing unit changes with the optical refractive index of the graphene, thereby altering the optical resonant frequency of the sensing unit in the graphene-modified optical microrod cavity.

2. The ammonia sensor according to claim 1, characterized in that, The laser output from the tunable laser enters one end of the tapered optical fiber after passing through an optical fiber polarization controller.

3. The ammonia sensor according to claim 1, characterized in that, The other end of the tapered optical fiber is connected to the photodetector via an optical fiber attenuator.

4. The ammonia sensor according to claim 1, characterized in that, The graphene has a thickness of a single carbon atom layer and a surface area of ​​400~1600 μm. 2 .

5. The ammonia sensor according to claim 1, characterized in that, The diameter of the optical microrod cavity is 2~3mm.

6. The ammonia sensor according to claim 5, characterized in that, The quality factor Q of the optical microrod cavity is ≥10. 7 .

7. The ammonia sensor according to claim 5, characterized in that, The optical microrod cavity is made of silicon dioxide.

8. The ammonia sensor according to claim 1, characterized in that, The diameter of the tapered region of the tapered optical fiber is 1~3μm.

9. The ammonia sensor according to claim 8, characterized in that, The tapered optical fiber has a length of 1.5~3cm.

10. The ammonia sensor according to claim 8, characterized in that, The tapered optical fiber is made of silicon dioxide.

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