CN206618528U - A kind of optical fiber air pressure sensing device based on multiple Fabry-Perot micro-cavities - Google Patents

Abstract

The utility model provides an optical fiber air pressure sensing device based on a plurality of Fabry-Perot microcavities, comprising a broadband light source, a circulator, a sensing head and a spectrum analyzer. The sensing head is composed of a capillary and a single-mode optical fiber. The characteristic is that the single-mode optical fiber and the capillary are continuously welded by discharge in the welding mode with a discharge power of 45bit and a discharge time of 3000ms until a part of the capillary expands into a hollow spherical cavity. , and a thin layer of capillary is formed at the splice of the single-mode fiber-capillary. This structure forms multiple Fabry-Perot cavities. The circulator receives the light from the broadband light source and transmits it to the sensor head, and the sensor head reflects the light back to the circulator, and then transmits the light to the spectrum analyzer through the circulator, forming a similar Fabry-Perot interferometer to measure reflection The value of the measured environmental parameter can be calculated by the wavelength shift of the spectral characteristic trough. The utility model has the advantages of small volume, simple preparation and the like, and can be applied to the measurement of air pressure and temperature.

Description

A Fiber Optic Air Pressure Sensing Device Based on Multiple Fabry-Perot Microcavities

technical field

The utility model provides an optical fiber air pressure sensing device based on a plurality of Fabry-Perot microcavities, which belongs to the technical field of optical fiber sensing.

Background technique

Atmospheric pressure is a very important parameter in the fields of meteorological telemetry, aircraft altitude determination, and field operations. Especially in recent years, with the revolutionary development of the field of UAVs, it is very urgent to monitor the height of UAVs quickly, in real time and accurately through remote measurement of atmospheric pressure. In the field of traditional atmospheric pressure measurement, force balance, resonant and piezoresistive air pressure sensing technologies are mostly used. In contrast, the fiber optic air pressure sensor has attracted more and more attention in the market due to its advantages of small size, anti-electromagnetic interference, high temperature resistance, strong chemical stability, and many adjustable parameters.

Among the various configurations of fiber-optic pressure sensors, fiber-optic pressure sensors based on Fabry-Perot microcavities are particularly attractive in the research field due to their high sensitivity, small size, and easy operation in reflection mode. . There are two different mechanisms of operation for these sensors: cavity length variation and refractive index variation in the cavity. The gas pressure sensitivity of the Fabry-Perot interferometer gas pressure sensor based on the variable cavity length is relatively low. After adding an ultra-thin diaphragm on the end face of the optical fiber, although this type of sensor can achieve an ultra-high sensitivity of up to 100nm/MPa, it only has a limited measurement range of tens of kPa. More importantly, the sensing head of an optical fiber with an ultra-thin diaphragm is less robust and difficult to maintain in hazardous environments. For gas pressure sensors based on Fabry-Perot interferometers based on changes in the refractive index in the cavity, although a larger range of measurement and better robustness can be achieved, the sensitivity is usually as low as tens of μm/MPa.

To sum up, fiber optic gas pressure sensors have great development prospects and are one of the most potential research directions. Although, there are still many problems to be solved urgently, such as improving the sensitivity, increasing the measurement range, enhancing the robustness and considering the temperature cross property, etc.

Utility model content

The utility model aims to solve the defects of the above-mentioned prior art, and provides an optical fiber air pressure sensing device based on a plurality of Fabry-Perot microcavities, which has a simple manufacturing process, small volume, low cost, high sensitivity, It has the advantages of wide measurement range and strong robustness.

1. The technical scheme adopted by the utility model to solve the technical problems is: a kind of optical fiber air pressure sensing device based on a plurality of Fabry-Perot microcavities, comprising a broadband light source, a circulator, a sensor head, a spectrum analyzer, The connection method is as follows: the inlet end of the circulator is connected to the broadband light source, the outlet end of the circulator is connected to the sensing head, and the feedback end of the circulator is connected to the spectrum analyzer; it is characterized in that: the sensing head is composed of a quartz capillary and single-mode fiber optics. Under the continuous discharge of the fusion splicer, a part of the capillary expands into a hollow spherical cavity, and a capillary thin layer is formed on the fusion surface of the single-mode fiber-capillary.

The core diameter of the single-mode optical fiber is 8.2 μm, and the fiber diameter is 125 μm.

The quartz capillary is about 0.8 mm in length and is attached to a single-mode optical fiber. It has an inner diameter of 50 μm and an outer diameter of 150 μm.

The manufacturing method of the sensing head is as follows: using a fusion splicing machine, in the fusion splicing mode with a discharge power of 45 bits and a discharge time of 400 ms, the capillary section with a length of about 0.8 mm is first fused to the single-mode optical fiber. Under the action of the stress at both ends provided by the fusion splicer, the other end of the capillary and another single-mode fiber are spliced by continuous discharge in the fusion splicing mode with a discharge power of 45bit and a discharge time of 3000ms until a part of the capillary expands into a hollow spherical cavity, and forms a thin layer at the single-mode fiber-capillary fusion splice. Finally, on the capillary side, cut the capillary approximately 410 μm away from the single-mode fiber-capillary fusion.

The beneficial effects of the utility model compared with the prior art are:

1. The material of the sensing head is single-mode optical fiber and quartz capillary, which has the advantages of simple manufacturing method, low material price and stable chemical performance.

2. The sensing head is sensitive to both air pressure and temperature, and can be used for simultaneous measurement of dual parameters of temperature and air pressure.

3. The air pressure sensitivity of the sensor head is high (4.067nm/MPa), and the air pressure measurement range is large.

Description of drawings

In order to illustrate the embodiments or technical solutions of the utility model more clearly, the utility model will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the implementation and application system of the utility model.

Fig. 2 is a structural diagram of the optical fiber sensing head of the present invention.

In the figure, 1. Broadband light source, 2. Circulator, 3. Sensing head, 4. Spectrum analyzer, 5. Single-mode fiber, 5a. Single-mode fiber core, 5b. Single-mode fiber cladding, 6. Capillary Lamina, 6a. Front wall of capillary laminae, 6b. Rear wall of capillary laminae, 7. Spherical air cavity, 7a. Rear wall of spherical air cavity, 8. Capillary, 8a. Cutting end face of capillary.

detailed description

Below in conjunction with accompanying drawing and embodiment example, the utility model is further described:

FIG. 1 is a schematic diagram of an implementation and application system of the present invention, including a broadband light source 1 , a circulator 2 , a sensor head 3 , and a spectrum analyzer 4 . The connection method is as follows: the circulator 2 has three interface ports, namely: the light source inlet port, the light source outlet port, and the feedback port. The inlet port is connected to the broadband light source 1 , the outlet port is connected to the connecting sensor head 3 , and the feedback port is connected to the spectrum analyzer 4 .

Fig. 2 shows the structural representation of the optical fiber sensing head 3 of the present utility model, and described sensing head 3 is made of single-mode optical fiber 5, capillary thin layer 6, spherical air chamber 7 and capillary 8, single-mode optical fiber 5 includes a single-mode fiber core 5a and a single-mode fiber cladding 5b, the core and fiber diameters of the single-mode fiber are 8.2 μm and 125 μm respectively; the capillary thin layer 6 in the sensor head 3 includes the capillary thin layer front wall 6a and The capillary thin layer rear wall 6b has a thickness of about 27 μm; the spherical air cavity 7 in the sensor head 3 includes the spherical air cavity rear wall 7a, and the length of the spherical air cavity is about 118.5 μm. The capillary 8 in the sensing head 3 is cut to form a capillary cutting end face 8a; the capillary 8 in the sensing head 3 is made of pure quartz, with an inner diameter of 50 μm and an outer diameter of 150 μm.

The manufacturing method of the sensing head is: placing the single-mode optical fiber 5 and the capillary 8 at both ends of the optical fiber fusion splicer, and under the action of the stress at both ends provided by the fusion splicer, the end surface of the capillary is close to the end surface of the single-mode optical fiber. Continuous discharge is carried out in the welding mode with a discharge power of 45bit and a discharge time of 3000ms until a part of the capillary 8 expands into a hollow spherical cavity 7, and a thin capillary layer 6 is formed at the fusion of the single-mode fiber-capillary. This capillary thin layer 6. The spherical air cavity 7 and the capillary cutting end surface 8a together form a plurality of Fabry-Perot microcavity structures.

Combined with Figures 1 and 2, the specific working principle is introduced: the sensor head 3 receives the light from the broadband light source 1 and passes through the circulator 2, and multi-beam interference occurs when the light is incident from one side of the single-mode fiber. Due to the change in refractive index from the core of the single-mode fiber to the capillary, a first reflection occurs at the front wall 6a of the capillary lamina, followed by another reflection at the back wall of the capillary lamella due to the change in the refractive index of the capillary lamina 6 to air A second reflection occurs at 6b. Part of the transmitted light enters the spherical air cavity 7 and is reflected by the rear wall 7a of the spherical air cavity, and the other part of the light propagates along the thin wall of the capillary and is reflected by the cut end surface 8a of the capillary. Therefore, the sensor 3 is composed of four main reflective surfaces, the capillary thin layer front wall 6a, the capillary thin layer rear wall 6b, the spherical air cavity rear wall 7a and the capillary cut end face 8a, and the light reflected by the four reflective end faces forms a 6 There are three different interference modes, in which the three interference modes composed of three pairs of reflective surfaces play a major role. These three pairs of reflective surfaces are:

1. Capillary laminar front wall 6a and capillary laminar rear wall 6b.

2. The back wall 6b of the capillary thin layer and the back wall 7a of the spherical air cavity.

3. The rear wall 7a of the spherical air cavity and the cutting end surface 8a of the capillary.

These three pairs of reflective surfaces form the main interference fringes. When the sensor head is subjected to changes in gas pressure or temperature, the cavity length or the refractive index of the cavity medium will change, which leads to a change in the optical path difference of the Fabry-Perot cavity and results in a shift in the output spectral pattern. Since there are multiple troughs in the output spectrum, the simultaneous detection of gas pressure and temperature can be achieved by tracking the shift of the two trough wavelengths.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above descriptions are only specific embodiments of the utility model and are not intended to limit the utility model. For the utility model, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the utility model shall be included in the protection scope of the utility model.

Claims (3)

1. A fiber optic air pressure sensing device based on multiple Fabry-Perot microcavities, including a broadband light source, a circulator, a sensor head, and an optical fiber spectrum analyzer, and its connection mode is: the inlet end of the circulator and the broadband light source connection, the outlet end of the circulator is connected to the optical fiber sensing head, and the feedback end of the circulator is connected to the fiber optic spectrometer; it is characterized in that: the sensing head is composed of a quartz capillary and a single-mode optical fiber; under the continuous discharge of the fusion splicer , a part of the capillary expands into a hollow spherical cavity, and a thin layer of quartz capillary is formed on the fusion surface of the single-mode fiber-capillary. 2. A fiber optic air pressure sensing device based on a plurality of Fabry-Perot microcavities according to claim 1, characterized in that: the core diameter of the single-mode fiber is 8.2 μm, and the fiber diameter is 125 μm. 3. A kind of optical fiber air pressure sensing device based on a plurality of Fabry-Perot microcavities according to claim 1, characterized in that: the quartz capillary is about 0.8mm in length, attached to the single-mode optical fiber Capillary segment; its inner diameter is 50 μm and its outer diameter is 150 μm.