Reflection-type optical fiber humidity sensing device

Abstract

The utility model relates to the technical field of optical fiber humidity detection, in particular to a reflective optical fiber humidity sensing device. Comprising a transmitting optical fiber, a collecting optical fiber, a sleeve, a humidity-sensitive layer and a reflecting layer. The transmitting optical fiber and the collecting optical fiber are arranged side by side and jointly embedded into one end of the sleeve, the other end of the sleeve is closed, the humidity sensitive layer covers the outer side face of the sleeve, and the reflecting layer is arranged at the bottom of the closed end in the sleeve. The humidity-sensitive layer is made of a material which expands after absorbing moisture. The device measures the humidity through the change of the light intensity, does not need a complex fiber bragg grating or interference structure, and reduces the manufacturing cost. A bar closed structure is adopted to replace precise coating, so that the production process is simplified, and the stability and reliability of the sensor are improved. The overall design is suitable for environment monitoring, industrial detection, smart home and other applications, and is an economical and efficient humidity sensing solution.

Description

TECHNICAL FIELD

[0001] The utility model relates to optical fiber humidity detection technical field, concretely relates to a reflection type optical fiber humidity sensor device. BACKGROUND

[0002] Humidity sensing technology has important applications in industry, environmental monitoring, medical treatment and other fields. Traditional humidity sensors mainly include capacitive, impedance and optical fiber sensors. Among them, optical fiber humidity sensing device has wide application in high-precision measurement field due to its advantages of anti-electromagnetic interference, strong remote transmission capability and high sensitivity.

[0003] At present, common optical fiber humidity sensing devices mainly include: humidity sensors based on fiber Bragg grating (FBG), humidity sensors based on long period fiber grating (LPG), humidity sensors based on interference optical fiber, humidity sensors based on surface plasmon resonance (SPR) optical fiber. The humidity sensor based on fiber Bragg grating uses humidity-sensitive material coated on the fiber Bragg grating, and the change of humidity causes the drift of Bragg wavelength, so as to measure the humidity; the manufacturing process of fiber Bragg grating is complex, and ultraviolet writing or femtosecond laser writing technology is needed, resulting in high cost. The humidity sensor based on long period fiber grating modulates the transmission spectrum of long period fiber grating through humidity-sensitive material, so as to realize humidity measurement; this method needs accurate grating structure, and the uniformity of humidity-sensitive material coating layer is required to be high, so the manufacturing cost is high. The humidity sensor based on interference optical fiber needs high-precision optical fiber end face processing, and the mirror coating layer is complex to make, and a precise interferometer system is needed, resulting in high manufacturing cost and great debugging difficulty. The humidity sensor based on surface plasmon resonance optical fiber combines metal nanometer layer and humidity-sensitive material, and uses plasmon resonance effect to realize humidity measurement. This kind of sensor has strict requirements on metal film thickness and structure, and has high manufacturing cost, and is sensitive to environmental temperature change, which affects the measurement precision.

[0004] Therefore, the market needs an optical fiber humidity sensing device which maintains the advantages of optical fiber humidity sensor and reduces the cost. INVENTION CONTENTS

[0005] In order to solve the above problems, the utility model provides a reflection type optical fiber humidity sensor device, including transmitting optical fiber, collection optical fiber, sleeve, humidity sensitive layer and reflection layer. Transmitting optical fiber and collection optical fiber are arranged side by side, and are embedded in one end of sleeve together, the other end of sleeve is closed, humidity sensitive layer covers the outside of sleeve, and reflection layer is arranged at the bottom of closed end in sleeve. The humidity sensitive layer is a material that expands after absorbing moisture.

[0006] The transmitting optical fiber transmits the optical signal to the reflecting layer inside the sleeve, and part of the light is reflected into the collecting optical fiber. The moisture-sensitive layer covers the outer side of the sleeve, and the material of the moisture-sensitive layer expands after absorbing moisture, causing the wall of the sleeve to deform slightly or change the refractive index, thereby changing the optical path of the optical fiber and the coupling efficiency of the reflected light. With the increase of environmental humidity, the expansion of the moisture-sensitive layer causes the fine adjustment of the reflection path of the optical signal, causing the light intensity entering the collecting optical fiber to change. By detecting the change rule of the light intensity, humidity measurement can be realized.

[0007] Further, the material of the moisture-sensitive layer is polyvinyl alcohol or polyimide.

[0008] Further, the material of the sleeve is polycarbonate or polymethyl methacrylate.

[0009] Further, the reflecting layer is a silver film or an aluminum film.

[0010] Further, the moisture-sensitive layer covers the part of the sleeve extending out of the end face of the transmitting optical fiber and the end face of the collecting optical fiber. This design ensures that the expansion of the moisture-sensitive layer mainly acts on the optical path outside the end face of the optical fiber, and does not directly affect the light propagation inside the optical fiber, avoiding the excessive interference of the moisture-sensitive layer with the coupling area of the optical fiber, thereby reducing the nonlinear error. In addition, since the moisture-sensitive layer only exists in the area outside the end face of the optical fiber, its expansion will not cause the deformation of the optical fiber body, but can change the distance between the end face of the optical fiber and the reflecting layer after absorbing moisture, thereby affecting the collection efficiency of the reflected light.

[0011] Further, the end faces of the transmitting optical fiber and the collecting optical fiber are flush.

[0012] Further, the collecting optical fiber is a plurality of collecting optical fibers, and the collecting optical fibers are coaxially arranged to surround the transmitting optical fiber. This structure increases the total effective receiving area of the collecting optical fiber, so that more reflected light can be collected, thereby improving the utilization rate of the optical signal and enhancing the signal strength and signal-to-noise ratio of the system. Secondly, since the expansion of the moisture-sensitive layer will cause dynamic changes in the optical path, this design can reduce the angle deviation problem when a single optical fiber collects light signals, making the optical coupling more stable and reducing the measurement error caused by non-uniform expansion of the moisture-sensitive layer. In addition, the plurality of collecting optical fibers are uniformly distributed around the transmitting optical fiber, which can more comprehensively obtain reflected light signals returned from different directions, making the measurement result more uniform and reliable, and improving the overall response capability to environmental humidity changes.

[0013] Furthermore, the transmitting fiber is a single-mode fiber, while the collecting fiber is a multimode fiber. Single-mode fiber has a smaller mode field diameter and a lower numerical aperture, enabling it to emit a more directional beam with a smaller divergence angle. This makes the optical signal more stable during transmission, reduces mode interference, and improves the coherence and consistency of the light source. Multimode fiber, on the other hand, has a larger numerical aperture and a wider mode field, effectively collecting reflected light from different angles and positions, improving optical coupling efficiency. Since the expansion of the humidity-sensitive layer causes changes in the optical signal path, the beam emitted by single-mode fiber changes more stably, while multimode fiber can receive optical signals over a wider range, thus reducing signal loss caused by uneven expansion of the humidity-sensitive layer or slight beam deviation. This single-mode-multimode fiber combination not only enhances the system's sensitivity to humidity changes and improves measurement accuracy but also optimizes the stability of optical signal collection, ensuring that the humidity sensor maintains good response performance under different humidity conditions.

[0014] Furthermore, the distance between the end face of the transmitting fiber and the surface of the reflective layer is 200 micrometers to 600 micrometers.

[0015] The beneficial effects of this utility model are:

[0016] (1) The present invention uses a simple method of detecting reflected light intensity, which avoids the complex fiber Bragg grating writing, long period fiber grating or interference structure (such as Fabry-Perot cavity) in traditional fiber optic humidity sensors, thereby reducing the cost of high-precision fiber processing and expensive laser writing.

[0017] (2) The transmitting optical fiber and the collecting optical fiber of this utility model are arranged side by side in the same sleeve, which has a compact structure, reduces the complexity of fixing and aligning the optical fiber, and reduces the assembly cost.

[0018] (3) The reflective layer of this utility model is located at the bottom of the closed end of the sleeve. Its preparation does not require a precise optical coating process. Inexpensive metal coatings (such as silver or aluminum) can be used directly. The reflective layer can even be formed by inserting a smooth metal or plastic rod to block the bottom of the sleeve without additional complex manufacturing steps. This sealing method is not only simple in structure, but also easy to mass-produce, further reducing manufacturing costs.

[0019] (4) The moisture-sensitive layer of this utility model can be made of low-cost polymer materials (such as polyimide, PVA or nano oxide coating), without the need for expensive nano deposition or vacuum coating processes.

[0020] In summary, this invention significantly reduces production costs by simplifying the fiber optic structure, optimizing the reflective layer preparation method, and using low-cost humidity-sensitive materials, making it more economical than traditional fiber optic humidity sensors and suitable for large-scale, low-cost applications. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a reflective fiber optic humidity sensor.

[0022] In the diagram: 1. Transmitting optical fiber; 2. Collecting optical fiber; 3. Sleeve; 4. Humidity-sensitive layer; 5. Reflective layer. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments.

[0024] This invention provides a reflective fiber optic humidity sensing device, such as... Figure 1 As shown, the structure includes a transmitting fiber 1, a collecting fiber 2, a sheath 3, a humidity-sensitive layer 4, and a reflective layer 5. The transmitting fiber 1 and collecting fiber 2 are arranged side-by-side and embedded in one end of the sheath 3, with the other end of the sheath 3 closed to form a reflection and detection structure for the optical signal. The transmitting fiber 1 is a single-mode fiber (SMF-28, numerical aperture NA≈0.12, mode field diameter MFD≈810 micrometers) used to transmit the optical signal to the reflective layer 5. The collecting fiber 2 is a multimode fiber (NA≈0.22), with multiple collecting fibers 2 coaxially arranged around the transmitting fiber 1 to receive the reflected optical signal, improving optical coupling efficiency and signal stability. The end faces of the transmitting fiber 1 and collecting fiber 2 are flush to optimize the optical signal collection path. The sheath 3 is made of polycarbonate (PC) or polymethyl methacrylate (PMMA), and its outer surface is uniformly covered with the humidity-sensitive layer 4. The humidity-sensitive layer 4 is made of polyvinyl alcohol (PVA) or polyimide (PI), with a thickness of approximately 20-50 micrometers. It expands upon absorbing moisture, modulating the reflection and coupling efficiency of the optical signal. The humidity-sensitive layer 4 only covers the portion of the sleeve 3 extending from the end face of the transmitting fiber 1 and the end face of the collecting fiber 2, enhancing the effect of humidity changes on the optical signal and improving measurement sensitivity. The reflective layer 5 is located at the bottom of the closed end inside the sleeve 3, made of a silver film (Ag, approximately 100 nm thick) or an aluminum film (Al, approximately 200 nm thick). Its high reflectivity (>90%) ensures effective reflection of the optical signal. The distance between the end face of the transmitting fiber 1 and the surface of the reflective layer 2 is set to 200-600 micrometers to optimize the transmission and collection of the optical signal and improve the dynamic range of the humidity response.

[0025] When the humidity environment changes, the expansion of the humidity-sensitive layer 4 causes a change in the optical path between the fiber end face and the reflective layer 5, which in turn changes the intensity of reflected light in the collecting fiber 2. By detecting the change in light intensity, accurate measurement of the ambient humidity can be achieved.

[0026] In the fabrication process, a single-mode transmitting fiber 1 and a multimode collecting fiber 2 are selected, and multiple collecting fibers 2 are coaxially arranged to surround the transmitting fiber 1. The fiber positions are adjusted so that all fiber end faces are flush to optimize optical signal transmission and collection. A sleeve 3 with through holes at both ends, made of polycarbonate or polymethyl methacrylate, is used to insert the fiber assembly from one end, ensuring that the fiber end face is flush with the opening of the sleeve 3. Subsequently, a rod with a reflective layer 5 is inserted into the other end of the sleeve 3. The end face of the rod is pre-coated with a high-reflectivity silver film (Ag, approximately 100 nm thick) or aluminum film (Al, approximately 200 nm thick) to ensure efficient reflection of the optical signal. After the rod is inserted, its robustness and sealing can be ensured by bonding, mechanical fixing, or thermoforming. A humidity-sensitive layer 4 is uniformly deposited on the outside of the sleeve 3, which can be achieved by spin coating, dip coating, or spray coating, to uniformly cover the portion of the sleeve 3 extending from the end face of the transmitting fiber 1 and the end face of the collecting fiber 2, thereby enhancing the sensitivity of humidity detection. The humidity-sensitive layer 4 can be made of polyvinyl alcohol or polyimide, with a thickness controlled between 20 and 50 micrometers. It is then thermo-cured or UV-cured to ensure its stability and humidity response characteristics. After assembly, the alignment of the fiber end face with the reflective layer 5 is checked to ensure optical path stability. Optical adhesive is used to fix the fiber to the sleeve 3 structure, and a humidity calibration experiment is conducted to measure the effect of the expansion of the humidity-sensitive layer 4 on the optical signal. The distance between the fiber end face and the reflective layer 5 (200–600 micrometers) is optimized to ensure optimal humidity response characteristics. This fabrication method uses a modular assembly approach, avoiding the complex fiber grating writing or precision coating processes of traditional humidity sensors. It has the advantages of simple process, low cost, and ease of mass production, while ensuring the stability and high sensitivity of the sensor.

[0027] In operation, the sensing device is first fixed in the environment to be measured, ensuring that the humidity-sensitive layer 4 is fully exposed to the air to respond to humidity changes in real time. Then, a light source and photodetector system are used for signal measurement. Specifically, the light source (such as an 850 nm or 1310 nm LED / laser) transmits a light signal to the reflective layer 5 through a single-mode transmitting fiber 1. The reflected light is modulated by the humidity-sensitive layer 4 and collected by a coaxially surrounded multimode collecting fiber 2, then transmitted to the photodetector. The photodetector converts the received light signal into an electrical signal and measures the change in light intensity using a data acquisition system (DAQ) or an optical power meter. Combined with a humidity calibration curve, the ambient humidity value can be calculated. Additionally, a microprocessor can be optionally added for real-time data processing, and the humidity data can be transmitted to a remote monitoring terminal via a wireless transmission module. The overall system structure is simple and suitable for applications such as industrial humidity monitoring, environmental monitoring, smart homes, and agriculture. It eliminates the need for complex spectral analyzers or precision interferometers, significantly reducing operating costs and improving the convenience and reliability of measurements.

[0028] Preferably, in this invention, the central part of the reflective layer 5 adopts a protruding conical structure, which can effectively improve the sensitivity of humidity detection. The height of this conical structure is controlled at 100 micrometers, the bottom diameter matches the inner diameter of the sleeve 3, and the top curvature radius is less than 50 micrometers. After optimized reflection, the light enters the collecting optical fiber more concentratedly. In this way, when the light signal exits from the transmitting optical fiber 1 and reaches the conical reflective layer 5, the conical surface can focus the reflected beam, reduce divergence loss, improve the optical coupling efficiency of the collecting optical fiber 2, and make the reflected light signal more sensitive to the optical path changes caused by the expansion of the humidity-sensitive layer 4. In addition, the tilt angle of the conical structure (30 degrees to 60 degrees) can enhance the change of the incident angle of the optical path, making the optical path modulation caused by the expansion of the humidity-sensitive layer more significant, thereby improving the resolution of humidity measurement.

[0029] In this invention, the fiber optic end face is covered by a sleeve 3, which effectively reduces interference from external environmental factors on the fiber optic cable, improving the stability and measurement accuracy of the sensor. Since the fiber optic end face is not directly exposed to the air, the influence of dust, moisture condensation, or mechanical damage on optical signal transmission is avoided, thereby reducing signal fluctuations and improving measurement consistency.

[0030] In summary, this invention provides a low-cost, simple, and easy-to-manufacture reflective fiber optic humidity sensor. The device employs a coaxial arrangement of a single-mode transmitting fiber 1 and a multimode collecting fiber 2, with flush end faces. These fibers are embedded within a closed-end sleeve 3. A reflective layer 5 is formed by inserting a rod with a silver or aluminum film. A humidity-sensitive layer 4, made of polyvinyl alcohol or polyimide, covers the outside of the sleeve 3, modulating the reflected light intensity by humidity changes to achieve high-sensitivity detection. This device measures humidity by changes in light intensity, eliminating the need for complex fiber gratings or interference structures, thus reducing manufacturing costs. The use of a closed rod structure instead of precision coating simplifies the production process and improves the stability and reliability of the sensor. The overall design is suitable for applications such as environmental monitoring, industrial inspection, and smart homes, representing an economical and efficient humidity sensing solution.

[0031] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A reflective optical fiber humidity sensing device, characterized by: It comprises a transmitting optical fiber, a collecting optical fiber, a sleeve, a moisture sensitive layer and a reflecting layer, the transmitting optical fiber and the collecting optical fiber are arranged side by side and embedded in one end of the sleeve, the other end of the sleeve is closed, the moisture sensitive layer covers the outer side of the sleeve, and the reflecting layer is arranged at the bottom of the closed end of the sleeve.

2. The reflective fiber-optic humidity-sensing device of claim 1, wherein: The moisture sensitive layer is a material that expands after absorbing moisture.

3. The reflective fiber-optic humidity-sensing device of claim 2, wherein: The material of the moisture sensitive layer is polyvinyl alcohol or polyimide.

4. The reflective fiber-optic humidity-sensing device of claim 1, wherein: The reflecting layer is a silver film or an aluminum film.

5. The reflective fiber-optic humidity-sensing device of claim 1, wherein: The moisture sensitive layer covers the part of the sleeve extending out of the end face of the transmitting optical fiber and the end face of the collecting optical fiber.

6. A reflective optical fiber humidity sensor device according to any one of claims 1-5, characterized in that: The end faces of the transmitting optical fiber and the collecting optical fiber are flush.

7. The reflective fiber-optic humidity-sensing device of claim 6, wherein: The collecting optical fiber is a plurality of optical fibers, and the collecting optical fibers surround the transmitting optical fiber in coaxial arrangement.

8. The reflective fiber-optic humidity-sensing device of claim 7, wherein: The transmitting optical fiber is a single-mode optical fiber, and the collecting optical fiber is a multi-mode optical fiber.

9. The reflective fiber-optic humidity-sensing device of claim 8, wherein: The distance between the end face of the transmitting optical fiber and the surface of the reflecting layer is 200-600 microns.

Images