Optical fiber microcavity humidity sensor and manufacturing method thereof

Abstract

The present invention provides an optical fiber microcavity humidity sensor and a manufacturing method thereof. The optical fiber microcavity humidity sensor includes a silicon wafer, a moisture-sensitive material layer, a single-mode optical fiber and a sensor housing. The moisture-sensitive material layer is sputtered on the inner surface of the silicon wafer, and a silicon wafer cavity is formed between the moisture-sensitive material layer and the outer surface of the silicon wafer; the single-mode optical fiber extends toward and does not contact the moisture-sensitive material layer, and an air cavity is formed between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer; the sensor housing includes a first support platform for fixing the moisture-sensitive material layer and a second support platform for fixing the single-mode optical fiber, the single-mode optical fiber is passed through the second support platform and extends toward the first support platform, and is used to form the air cavity between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer; wherein the air cavity and the silicon wafer cavity are constructed into a cascade structure to achieve amplification of the sensor sensitivity by the optical vernier effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to an optical fiber microcavity humidity sensor and a manufacturing method thereof. Background Art

[0002] Fiber-optic humidity sensors play a vital role in a wide range of applications, including human-related humidity detection, biochemical sensing, environmental monitoring, and food / pharmaceutical storage. Traditional resistive or capacitive humidity sensors suffer from shortcomings such as poor stability, susceptibility to corrosion under high humidity conditions, and susceptibility to electromagnetic interference. To address these issues, various fiber-based humidity sensors have been extensively studied, including long-period fiber gratings (LPGs), fiber Bragg gratings (FBGs), side-polished fibers (SPFs), and interferometers. Notably, LPG-based humidity sensors offer a wider measurement range, but their sensitivity requires higher core size and period length. In contrast, FBG-based humidity sensors offer significant multiplexing capabilities, making them suitable for multi-point measurements. However, they suffer from low sensitivity and are susceptible to ambient temperature fluctuations. Finally, SPF-based humidity sensors have a simpler structural design, but their humidity measurement range is limited and their sensitivity is low. Consequently, interferometer-based humidity sensors have garnered significant attention. Summary of the Invention

[0003] The object of the present invention is to provide an optical fiber microcavity humidity sensor and a manufacturing method thereof, so as to realize humidity sensing with small size and high sensitivity.

[0004] The first aspect of the present invention discloses an optical fiber microcavity humidity sensor, comprising a silicon wafer, a moisture-sensitive material layer, a single-mode optical fiber, and a sensor housing, wherein the moisture-sensitive material layer is sputtered on the inner surface of the silicon wafer, and a silicon wafer cavity is formed between the moisture-sensitive material layer and the outer surface of the silicon wafer; the single-mode optical fiber extends toward and does not contact the moisture-sensitive material layer, and an air cavity is formed between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer; the sensor housing comprises a first support platform for fixing the moisture-sensitive material layer and a second support platform for fixing the single-mode optical fiber, the single-mode optical fiber is passed through the second support platform and extends toward the first support platform, and is used to form the air cavity between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer; wherein the air cavity and the silicon wafer cavity are constructed into a cascade structure to achieve amplification of the sensor sensitivity by the optical vernier effect.

[0005] Optionally, the humidity-sensitive material layer is a layered nanomaterial with a thickness of 260 nm to 300 nm.

[0006] Optionally, the thickness of the air cavity is 50 μm-100 μm.

[0007] Optionally, a first through hole is provided on the first support platform, and a second through hole is provided on the second support platform. The single-mode optical fiber is passed through the second through hole and extends into the first through hole. The inner wall of the first through hole, the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer form the air cavity.

[0008] Optionally, the first support platform and the second support platform are circular ring structures with the same outer diameter, and the outer diameter R3 of the first support platform and the outer diameter R3 of the second support platform satisfy: 3.0mm≤R3≤5.0mm; the thickness H1 of the first support platform satisfies: 1.0mm≤H1≤1.3mm; the thickness H3 of the second support platform satisfies: 1.5mm≤H3≤2.5mm.

[0009] Optionally, the aperture of the second through hole satisfies: 1.25 mm ≤ R1 ≤ 1.35 mm; the aperture of the first through hole satisfies: R1 ≤ R2 ≤ R3-1.0 mm.

[0010] Optionally, the sensor housing further includes a plurality of connecting columns, both ends of which are respectively connected to the first supporting platform and the second supporting platform, so that a housing hollow cavity is formed between the first supporting platform and the second supporting platform.

[0011] Optionally, the width W of the connecting column satisfies: 1.0mm≤W≤R3-R2; the height H2 of the connecting column satisfies: 2.5mm≤H2≤3.2mm; the thickness H1 of the first support platform, the thickness H3 of the second support platform and the height H2 of the connecting column satisfy: 5.0mm≤H1+H2+H3≤7.0mm.

[0012] A second aspect of the present invention discloses a method for manufacturing the above-mentioned optical fiber microcavity humidity sensor, comprising:

[0013] Prepare a moisture-sensitive material layer by sputtering a moisture-sensitive material target onto a single-side polished silicon wafer using a coating machine in a vacuum environment to form a moisture-sensitive material layer;

[0014] Prepare the sensor housing by using a high-temperature resin to print the three-dimensional model of the sensor housing into a physical sensor housing through a 3D printer;

[0015] To assemble the optical fiber microcavity humidity sensor, the silicon wafer with the humidity-sensitive material layer is assembled and fixed to the sensor housing, and then the single-mode optical fiber is inserted into the sensor housing to form an air cavity between the protruding end face of the single-mode optical fiber and the humidity-sensitive material layer.

[0016] Optionally, the assembling of the optical fiber microcavity humidity sensor includes:

[0017] Using curing glue to bond the moisture-sensitive material layer to the outer surface of the first support platform of the sensor housing to achieve the fixation of the silicon chip;

[0018] The single-mode optical fiber is passed through the second through hole of the second support platform of the sensor housing and extended into the first through hole of the first support platform, so that the air cavity is formed between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer, and then the outer surface of the single-mode optical fiber is bonded to the wall of the second through hole using curing glue to fix the single-mode optical fiber.

[0019] The beneficial effects of the present invention are:

[0020] This fiber-optic microcavity humidity sensor utilizes a cascaded FP cavity structure, connecting an air cavity and a silicon chip cavity. This amplifies the sensor's sensitivity through the optical vernier effect. Due to the mode field differences between the quartz fiber and the microcavity, higher-order optical modes are effectively excited, resulting in intermodal interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of the optical fiber microcavity humidity sensor;

[0022] Figure 2 Schematic cross-sectional view of the optical fiber microcavity humidity sensor;

[0023] Figure 3 It is a structural diagram of the sensor housing;

[0024] Figure 4 It is the main view of the sensor housing;

[0025] Figure 5 is a side view of the sensor housing;

[0026] Figure 6 Schematic diagram of the structure of a single-mode optical fiber;

[0027] Figure 7 Schematic diagram of the MoS2 material layer thickness measured by the step profiler;

[0028] Figure 8 Surface image of the MoS2 material layer;

[0029] Figure 9 This is a cross-sectional image of the MoS2 material layer;

[0030] Figure 10 This is the reflection spectrum of the optical fiber microcavity humidity sensor;

[0031] Figure 11 This is the spectral drift diagram of the optical fiber microcavity humidity sensor when the relative humidity increases gradually within the range of 28.5%-84.1%;

[0032] Figure 12 This is a schematic diagram of the sensitivity fitting of the optical fiber microcavity humidity sensor during the humidity rising process;

[0033] Figure 13 Schematic diagram of the temperature response of the optical fiber microcavity humidity sensor;

[0034] Figure 14 Schematic diagram of the temperature sensitivity of the optical fiber microcavity humidity sensor;

[0035] Figure 15 Schematic diagram of the stability of the optical fiber microcavity humidity sensor.

[0036] Description of reference numerals:

[0037] 10. Silicon wafer; 20. MoS2 material layer; 30. Single-mode optical fiber; 40. Sensor housing; 41. First support platform; 411. First through hole; 42. Second support platform; 421. Second through hole; 43. Connecting column; 50. Silicon wafer cavity; 60. Air cavity. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, an indirect connection through an intermediate medium, or a communication between the internal parts of two components. For those skilled in the art, the specific meanings of the terms in the present invention can be understood according to specific circumstances.

[0040] Interferometer-based humidity sensors have attracted widespread attention, including the Mach-Zehnder interferometer (MZI), Michelson interferometer (MI), Sagnac interferometer (SI), and Fabry-Pérot interferometer (FPI). Among these interferometers, the FPI not only shares the inherent advantages of fiber-optic humidity sensors, such as small size, good environmental adaptability, immunity to electromagnetic interference, and long-distance measurement, but also does not include a fiber coupler. Its fabrication process is simple, its structure is compact, and its sensitivity is high.

[0041] See also Figure 1-6 The optical fiber microcavity humidity sensor of the present invention includes a silicon chip 10, a moisture-sensitive material layer 20, a single-mode optical fiber 30 and a sensor housing 40. The moisture-sensitive material layer 20 is sputtered on the inner surface of the silicon chip 10, and a silicon chip cavity 50 is formed between the moisture-sensitive material layer 20 and the outer surface of the silicon chip 10; the single-mode optical fiber 30 extends toward and does not contact the moisture-sensitive material layer 20, and an air cavity 60 is formed between the protruding end face of the single-mode optical fiber 30 and the moisture-sensitive material layer 20; the sensor housing 40 includes a first support platform 41 for fixing the moisture-sensitive material layer 20 and a second support platform 42 for fixing the single-mode optical fiber 30, and the single-mode optical fiber 30 is passed through the second support platform 42 and extends toward the first support platform 41, so as to form an air cavity 60 between the protruding end face of the single-mode optical fiber 30 and the moisture-sensitive material layer 20; wherein, the air cavity 60 and the silicon chip cavity 50 are constructed into a cascade structure to realize the amplification of the sensor sensitivity by the optical vernier effect.

[0042] The humidity sensitive material in this solution is preferably MoS2 material, graphene material or carbon nanotube material. This embodiment is described using MoS2 material as the raw material.

[0043] MoS2 is a typical two-dimensional layered nanomaterial. Each layer of MoS2 consists of molybdenum atoms sandwiched between two layers of hexagonal close-packed sulfur atoms. At the edges of the MoS2 material layer 20, the Mo-S bonding with a 2-H structure exhibits excellent hydrophilicity, allowing water molecules to easily adsorb and aggregate, resulting in a change in the effective refractive index of the MoS2 material layer 20.

[0044] Multiple reflection surfaces exist between the extended end face of the single-mode fiber 30 and the MoS2 material layer 20 and silicon wafer 10, causing the incident light to reflect multiple times, resulting in multi-beam interference. Moisture absorption causes changes in the length of the FP cavity and the effective refractive index of the MoS2 material layer 20, which in turn changes the reflected optical path difference, thus causing optical signal modulation. The spectra of two reflected light beams with different but similar optical path lengths superimpose, producing periodic interference fringes. By analyzing the envelope curve underlying these periodic interference fringes, the Vernier effect can be exploited to improve sensor sensitivity.

[0045] The fiber optic humidity sensor proposed in this proposal utilizes a cascaded FP cavity structure, constructed by cascading an air cavity 60 and a silicon cavity 50. This amplifies the sensor's sensitivity through the optical vernier effect. The mode field differences between the quartz fiber and the microcavity effectively excite high-order optical modes, resulting in intermodal interference. This interferometer, based on the optical vernier effect of the MoS2 material layer 20 and the optical microcavity, exhibits high humidity sensitivity.

[0046] like Figure 2 As shown in the figure, the sensor's principle is as follows: Multiple reflection surfaces exist between the extended end face (M1) of the single-mode optical fiber 30, the MoS2 material layer 20 (M2), and the silicon wafer 10 (M3). The incident light undergoes multiple reflections, resulting in multi-beam interference. Moisture absorption changes the length of the FP cavity and the effective refractive index of the MoS2 material layer 20, causing a corresponding change in the reflected optical path difference, thus generating optical signal modulation. The spectra of two reflected light beams with different but similar optical path lengths superimpose, producing periodic interference fringes. By analyzing the envelope curve underlying these periodic interference fringes, the vernier effect can be exploited to improve the sensor's sensitivity.

[0047] The thickness of the air cavity 60 is 50 μm-100 μm.

[0048] Specifically, the first support platform 41 is provided with a first through hole 411, and the second support platform 42 is provided with a second through hole 421. The single-mode optical fiber 30 is passed through the second through hole 421 and extends into the first through hole 411. The inner wall of the first through hole 411, the extended end surface of the single-mode optical fiber 30, and the MoS2 material layer 20 enclose an air cavity 60. The first support platform 41 and the second support platform 42 are annular structures with the same outer diameter. The outer diameter R3 of the first support platform 41 and the outer diameter R3 of the second support platform 42 satisfy the following conditions: 3.0 mm ≤ R3 ≤ 5.0 mm. The thickness H1 of the first support platform 41 satisfies the following conditions: 1.0 mm ≤ H1 ≤ 1.3 mm; the thickness H3 of the second support platform 42 satisfies the following conditions: 1.5 mm ≤ H3 ≤ 2.5 mm. The aperture of the second through hole 421 satisfies the following conditions: 1.25 mm ≤ R1 ≤ 1.35 mm; and the aperture of the first through hole 411 satisfies the following conditions: R1 ≤ R2 ≤ R3 - 1.0 mm. The sensor housing 40 also includes several connecting posts 43, each connected at its ends to the first support platform 41 and the second support platform 42, forming a hollow housing cavity between the first and second support platforms 41, 42. The width W of the connecting posts 43 satisfies the following conditions: 1.0 mm ≤ W ≤ R3 - R2; the height H2 of the connecting posts 43 satisfies the following conditions: 2.5 mm ≤ H2 ≤ 3.2 mm; and the thickness H1 of the first support platform 41, the thickness H3 of the second support platform 42, and the height H2 of the connecting posts 43 satisfy the following conditions: 5.0 mm ≤ H1 + H2 + H3 ≤ 7.0 mm.

[0049] See also Figure 3-5 In this embodiment, the sensor housing 40 is designed with a 2.85mm hollow section to allow water molecules to fully contact the humidity-sensitive membrane. The dimensions of each component are W = 1.5mm, H1 = 1.15mm, H2 = 2.85mm, H3 = 2mm, R1 = 1.3mm, R2 = 2.5mm, and R3 = 4mm.

[0050] The manufacturing method of the sensor includes:

[0051] The first step is to prepare the MoS2 film by magnetron sputtering. First, a 50μm thick single-side polished (SSP) silicon wafer is fixed to the sample stage of the coating machine using high-temperature tape. Then, the sample stage is loaded into the coating machine, and the MoS2 target is installed at the target position corresponding to the RF power supply. Secondly, the pump is started for automatic exhaust. When the vacuum gauge ionization gauge shows 6.6×10 -4 The coating process was carried out at a pressure of about 1 Pa, and the pumping speed was adjusted to control the argon flow rate, and the resistance gauge value was adjusted between 1 Pa and 5 Pa. Finally, the sample rotation button was turned on and the speed was set to 8 r / min, the sputtering current was set to 0.4 A, the sputtering power was set to 120 W, and the coating time was set to 3000 s. The thickness of the MoS2 film was measured to be 280 nm using a step profiler. Figure 7 shown. Figure 8 and Figure 9 The surface and cross-sectional images of the MoS2 film were obtained using a scanning electron microscope (SEM).

[0052] The second step is to prepare the sensor housing by laser 3D printing. Figure 3 As shown, a 3D model of the sensor housing was constructed using 3D modeling software. After slicing the model, selecting the print path, and setting printing parameters, the sensor housing was printed using a commercial laser 3D printer (Formlabs, Form3). High-temperature resin (High Temp V2) was selected as the printing material. Considering print speed and Z-axis accuracy, the layer thickness was set to 0.025mm, with optimal detail mode. The system default settings were used for print settings, which primarily control printing performance such as print speed and support end shape. After printing, the sample was removed from the laser 3D printer and cleaned of residual resin on the surface with anhydrous ethanol. The sample was then irradiated with a point light source for 15 minutes to further enhance its mechanical strength.

[0053] The third step is to assemble the sensor. Use UV curing adhesive (ERGO 8500) to assemble the SSP silicon wafer with MoS2 film deposited by magnetron sputtering and the sensor housing printed by laser 3D printing. The SSP silicon wafer is fixed on the top of the sensor housing, with the MoS2 film on the inside and the SSP silicon wafer on the outside. Figure 1 shown. Figure 10 The sensor is a single-mode optical fiber with an Ultra Physical Contact (UPC) interface. Finally, after adjusting the sensor housing's position on a micro-displacement platform to obtain the desired spectrum, it is secured to the UPC interface using UV-curable adhesive (ERGO 8500), creating the humidity sensor probe. The fabricated sensor probe is then placed in a thermostat and aged at 50°C for one hour to improve its stability.

[0054] See also Figure 10 , the lower curve in the figure is the lower envelope curve, and the upper curve is the spectrum. Figure 11 The spectral drift diagram of the sensor when the relative humidity is increased gradually in the range of 28.5%-84.1%. The diagram shows a clear red shift. The wavelength is tracked near 1530nm, and the fitting relationship between wavelength and humidity is obtained, as shown in the figure. Figure 11 As shown. The humidity sensitivity of the sensor is 1.057nm / %RH. It is worth noting that the sensor responds well at a relative humidity of 28.5%-84.1%, showing a wide frequency response and high sensitivity. In addition, the sensitivity of the sensor was measured as the humidity decreased from 84.1% to 28.5%. The sensitivity comparison of the two processes is shown in the figure below. Figure 12As shown, it shows that the humidity sensitivity of the sensor has good repeatability.

[0055] Figure 13-15 The temperature response, temperature sensitivity and stability of the optical fiber microcavity humidity sensor are demonstrated in turn. Figure 13 is the change of the sensor's reflection spectrum with temperature, Figure 14 is the temperature sensitivity of the sensor, which shows that the sensor has relatively good temperature stability. Figure 15 The fluctuation diagram of the characteristic wavelength of the sensor in a humidity environment of 59.1% RH within ten hours shows that the sensor has good stability.

[0056] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An optical fiber microcavity humidity sensor, characterized in that: include: silicon wafers, A moisture-sensitive material layer is sputtered on the inner surface of the silicon wafer, forming a silicon wafer cavity between the moisture-sensitive material layer and the outer surface of the silicon wafer, and the moisture-sensitive material layer is MoS2 material; a single-mode optical fiber extending toward and not contacting the moisture-sensitive material layer, wherein an air cavity is formed between an extended end face of the single-mode optical fiber and the moisture-sensitive material layer; The sensor housing includes a first support platform for fixing the moisture-sensitive material layer and a second support platform for fixing the single-mode optical fiber. The extended end face of the single-mode optical fiber is passed through the second support platform and extends toward the first support platform, so as to form the air cavity between the extended end face of the single-mode optical fiber and the moisture-sensitive material layer. The sensor housing also includes a plurality of connecting columns, the ends of which are respectively connected to the first support platform and the second support platform, so that a housing hollow cavity is formed between the first support platform and the second support platform. The air cavity and the silicon chip cavity are constructed into a cascade structure to achieve amplification of the sensor sensitivity by the optical vernier effect.

2. The optical fiber microcavity humidity sensor according to claim 1, characterized in that: The humidity sensitive material layer is a layered nanomaterial with a thickness of 260nm-300nm.

3. The optical fiber microcavity humidity sensor according to claim 1, characterized in that: The thickness of the air cavity is 50 μm-100 μm.

4. The optical fiber microcavity humidity sensor according to claim 1, characterized in that: A first through hole is provided on the first support platform, and a second through hole is provided on the second support platform. The single-mode optical fiber is passed through the second through hole and extends into the first through hole. The inner wall of the first through hole, the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer form the air cavity.

5. The optical fiber microcavity humidity sensor according to claim 4, characterized in that: The first support platform and the second support platform are circular ring structures with the same outer diameter. The outer diameter R3 of the first support platform and the outer diameter R3 of the second support platform satisfy: 3.0mm≤R3≤5.0mm; the thickness H1 of the first support platform satisfies: 1.0mm≤H1≤1.3mm; the thickness H3 of the second support platform satisfies: 1.5mm≤H3≤2.5mm.

6. The optical fiber microcavity humidity sensor according to claim 5, characterized in that: The aperture of the second through hole satisfies: 1.25 mm ≤ R1 ≤ 1.35 mm; the aperture of the first through hole satisfies: R1 ≤ R2 ≤ R3-1.0 mm.

7. The optical fiber microcavity humidity sensor according to claim 6, characterized in that: The width W of the connecting column satisfies: 1.0mm≤W≤R3-R2; the height H2 of the connecting column satisfies: 2.5mm≤H2≤3.2mm; the thickness H1 of the first support platform, the thickness H3 of the second support platform and the height H2 of the connecting column satisfy: 5.0mm≤H1+H2+H3≤7.0mm.

8. A method for manufacturing an optical fiber microcavity humidity sensor according to any one of claims 1 to 7, characterized in that: include: Prepare a moisture-sensitive material layer by sputtering a moisture-sensitive material target onto a single-side polished silicon wafer using a coating machine in a vacuum environment to form a moisture-sensitive material layer; Prepare the sensor housing by using a high-temperature resin to print the three-dimensional model of the sensor housing into a physical sensor housing through a 3D printer; To assemble the optical fiber microcavity humidity sensor, the silicon wafer with the humidity-sensitive material layer is assembled and fixed to the sensor housing, and then the single-mode optical fiber is inserted into the sensor housing to form an air cavity between the protruding end face of the single-mode optical fiber and the humidity-sensitive material layer.

9. The method for manufacturing the optical fiber microcavity humidity sensor according to claim 8, characterized in that: The assembled optical fiber microcavity humidity sensor comprises: Using curing glue to bond the moisture-sensitive material layer to the outer surface of the first support platform of the sensor housing to achieve the fixation of the silicon chip; The single-mode optical fiber is passed through the second through hole of the second support platform of the sensor housing and extended into the first through hole of the first support platform, so that the air cavity is formed between the protruding end face of the single-mode optical fiber and the moisture-sensitive material layer, and then the outer surface of the single-mode optical fiber is bonded to the wall of the second through hole using curing glue to fix the single-mode optical fiber.

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