CN108645444A - The temperature and strain gauge of optical-fiber probe type based on single spherical welding - Google Patents

Abstract

The invention discloses an optical fiber probe-type temperature and stress sensor based on single spherical fusion. The optical fiber is any single-mode optical fiber. The upper reflective layer (gold, silver, aluminum can be used) is used to form the structure of the optical fiber probe, and the M-Z interference effect is formed after reflection. Fix the fused fiber probe on the strain regulator, then the light enters the fiber probe through the circulator, and then the reflected light passes through the circulator again, and observes the spectrum with the spectrum analyzer. When the temperature changes, the fiber expands and the fiber diameter It changes accordingly, and when the stress is applied, the length and spherical diameter of the fiber will change, which will lead to the change of the transmission spectrum, and realize the measurement of temperature and stress. This new type of M‑Z fiber optic probe sensor is more sensitive than the traditional M‑Z fiber optic sensor, and it can be used as a probe directly inserted into the object or solution to be measured, which is more convenient for detection. The invention can be applied in the fields of chemical and biological sensing.

Description

Fiber-optic probe-type temperature and stress sensor based on single spherical fusion

technical field

The invention belongs to the field of optical fiber sensing, and in particular relates to the temperature and stress sensing technology realized by using a single spherical structure, in particular to an optical fiber probe type temperature and stress sensor based on single spherical fusion.

Background technique

In the past few decades, with the rapid development of optical fiber communication and optoelectronic technology, optical fiber sensing technology has also been relatively comprehensive development. Optical fiber sensors are widely used in the fields of construction engineering, power industry, aerospace and navigation, medicine and chemistry due to their advantages such as small size, light weight, anti-electromagnetic interference, corrosion resistance, high sensitivity, bendable twist, and point and distributed measurement. be widely used. The United States was the first to develop fiber optic sensing systems such as fiber optic gyroscopes, hydrophones, and magnetometers, and fiber optic sensors for nuclear radiation monitoring. Many countries such as Japan, Britain, France and Germany have also actively participated in the research competition of optical fiber sensors. At present, fiber optic sensors have been widely used in both military and civilian applications.

Optical fiber M-Z sensor has attracted great research interest in the field of optical fiber sensing in recent years. It is small in size, firm in structure, and high in sensitivity. The principle of Mach-Zehnder interferometer (M-Z) separates a beam of light into two beams first, and the two beams The light goes through different optical paths and recombines. Due to the different optical paths experienced by the two beams of light, an optical path difference occurs, and interference occurs when the two beams of light recombine.

Contents of the invention

The purpose of the present invention is to provide a temperature and stress sensor based on a single spherical fusion-bonded optical fiber probe based on the above technical analysis. and stress measurements.

The present invention adopts the following technical solutions to achieve the above object. A temperature and stress sensor based on a single spherical fusion-bonded fiber optic probe, including a broadband light source and a spectrum analyzer. The broadband light source and spectrum analyzer are respectively connected to the circulator through a single-mode fiber, and the circulator is connected through a spherical fusion point on the single-mode fiber. Optical fiber probe, the optical fiber probe is fixedly placed on the stress regulator, then the light enters the optical fiber probe through the circulator, and then the reflected light passes through the circulator again, and the spectrum is observed through the spectrum analyzer to monitor and record the change of the reflection spectrum;

One end of the spherical fusion splicing point is the left section of the optical fiber, and the other end is the right section of the optical fiber. The end surface is coated with a reflective layer, which forms an M-Z interference effect after reflection. When the temperature changes, the fiber expands, and the fiber diameter also changes accordingly. And when stress is applied to the optical fiber, the length and spherical diameter of the optical fiber will change, resulting in a change in the transmission spectrum, and the measurement of temperature and stress can be realized.

Further, the diameter of the spherical welding point is 150-190um.

Furthermore, the length of the optical fiber probe is 1-3 cm from the dislocation fusion point to the reflective layer on its end face.

Further, the reflective layer is gold, silver or aluminum coating.

The invention is based on a temperature and stress sensor of a single spherically welded optical fiber probe type, adopts a single-mode optical fiber, and has convenient material acquisition and low price. The reflective layer is not only beneficial to enhance the reflection, but also used to protect the fiber end face from contamination. This optical fiber structure can resist greater pulling force, and also increases the range of stress measurement. Interference between the fiber cladding mode and the fiber core mode improves the sensitivity to temperature and stress. When the temperature changes, the fiber expands, and the fiber diameter also changes accordingly. When stress is applied, the fiber length and spherical diameter change. Changes, resulting in changes in the transmission spectrum, to achieve the measurement of temperature and stress. The novel M-Z optical fiber probe sensor of the present invention has higher sensitivity than the traditional M-Z optical fiber sensor, and it can be directly inserted into the object or solution to be measured as a probe, which is more convenient for detection. The structure designed by the invention has great application in optical fiber temperature and stress sensing.

Description of drawings

Fig. 1 is a schematic diagram of the overall structure of the present invention;

Fig. 2 is the optical structure figure in the optical fiber among the present invention;

Fig. 3 is a transmission spectrum graph of the present invention;

In the figure: 1. Broadband light source, 2. Spectrum analyzer, 3. Single-mode fiber, 4. Circulator, 5. Fiber probe, 6. Stress regulator; 01. Left section of fiber, 02. Spherical fusion point, 03. The right section of optical fiber, 04. Reflective layer.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Referring to FIGS. The analyzer 2 is respectively connected to the circulator 4 through the single-mode optical fiber 3, the circulator 4 is connected to the optical fiber probe 5 through the spherical fusion point 02 on the single-mode optical fiber 3, the optical fiber probe 5 is fixedly placed on the strain regulator 6, and then the light passes through the circulator Circulator 4 enters fiber optic probe 5, then the reflected light passes through circulator 4 again, and observes the spectrum through spectrum analyzer 2 to monitor and record changes in the reflected spectrum;

One end of the spherical fusion splice 02 is the left section of the optical fiber 01, and the other end is the right section of the optical fiber 01. The end surface is coated with a reflective layer, which forms an M-Z interference effect after reflection. When the temperature changes, the fiber expands, and the fiber diameter also changes with the temperature. When the stress is applied to the optical fiber, the length and spherical diameter of the optical fiber will change, and the transmission spectrum will change, so as to realize the measurement of temperature and stress.

The single-mode fiber 3 is any single-mode fiber. The diameter of the spherical welding point 02 is 150-190um. , the length L of the optical fiber probe 5 is 1-3 cm from the dislocation fusion point to the reflective layer on its end face.

The broadband light source 1 in the present invention has optical interference in the fiber probe 5, and in the case of optical fiber M-Z, the interference generated by the reflected light considers the core mode, because the fiber pigtail is long enough to attenuate the cladding mode energy. However, in fiber optic probes, the reflected cladding modes cannot be ignored due to the length of L. Therefore, the entire interference process in the fiber optic probe 5 is divided into two steps. First, the input light propagates through the optical fiber and interferes with the spherical fusion point 02. The total light intensity at the output end is:

Where: I ₁ and I ₂ are the light intensity of the core mode and cladding mode, and ΔΦ is the phase difference between them. ΔΦ=2πΔn _eff L _eff /λ, where Δn _eff is the effective refractive index difference between the core and cladding modes, L _eff is the effective length of the fiber probe interferometer, and λ is the wavelength of the input light. Secondly, the reflected light is reflected by the reflective layer and returns to the spherical welding point 02 to generate the second interference.

When a single-mode fiber is subjected to axial stress, its fiber length and spherical diameter change slightly. Because the elasto-optic coefficient of the germanium-doped silica core is greater than that of the cladding made of pure silica, the effective refractive index difference between the core and the cladding decreases. At this time, the transmission line is also affected. Then the variation of the output wavelength can be expressed as:

In the formula: ν is the Poisson coefficient of the optical fiber, _pe is the effective elastic-optic coefficient, and ε is the deformation per unit length. It can be seen from the formula that when the axial stress is applied, the transmission spectrum curve will shift to the direction.

When the temperature changes, the formula The partial derivative of the temperature can be obtained, and the influence of the temperature change on the sensor can be expressed as:

In the formula, T is the change of temperature, according to the formula (5), we can get the temperature-wavelength formula:

where is the thermo-optic coefficient of the M-Z sensor, and is the thermal expansion coefficient of the sensor. It can be seen from the formula (6) that the relationship between the wavelength change of the sensor spectrum and the temperature change is linear, and the proposed M-Z sensor can be used for temperature sensing .

As shown in Figure 2, the broadband light source 1 is input in the core mode of the left fiber 1, and when it passes through the spherical fusion point 02, it excites the cladding mode of the input light, and after being reflected by the reflective layer 04, the cladding mode passes through the spherical fusion point again. Interference with core mode coupling occurs. The diameter of the fiber expands as the temperature changes, and the fiber length and spherical diameter change when stress is applied. As a result, the transmission spectrum changes, and the measurement of temperature and stress is realized.

As shown in Figure 3, the a-peak interference extinction is better, the FSR is appropriate, and the loss is lower. Select the troughs near 1500nm and 1550nm, and select peak a in the figure as a reference point to observe the response characteristics of temperature and stress respectively. When the relative temperature around the single-mode fiber 3 changes and the single-mode fiber 3 is affected by stress, its length and diameter will change, and the transmission spectrum will also red-shift according to the direction of the figure, so as to achieve the purpose of temperature and stress measurement.

In the model of the present invention, the left section of optical fiber 01 is first fused into a spherical structure, and then fused with the right section of optical fiber 03, and a reflective layer (gold, silver, or aluminum can be used) is put on the end surface, and the M-Z interference effect is formed through reflection. The input light is transmitted in the fundamental mode of the core of the left fiber 01, and when it passes through the spherical fusion point 02, the cladding mode of the input light is excited. Both the cladding mode and the core mode are transmitted in the fiber probe, and after being reflected by the reflective layer, The coupling of the cladding mode and the fiber core mode interferes when passing through the spherical fusion point. When the ambient temperature changes, the fiber expands, and the fiber diameter changes accordingly, and when stress is applied, the length and spherical diameter of the fiber will also change, resulting in a change in the transmission spectrum, enabling the measurement of temperature and stress.

Claims (3)

1. the temperature and strain gauge of the optical-fiber probe type based on single spherical welding, including wideband light source and spectrum analysis Instrument, which is characterized in that wideband light source and spectroanalysis instrument are connect by single mode optical fiber with circulator respectively, and circulator passes through single mode Spherical fusion point on optical fiber connects fibre-optical probe, and fibre-optical probe fixed placement is on answering draught control mechanism, and then light passes through cycle Device enters fibre-optical probe, and then reflected light observes spectrum again by circulator, and by spectroanalysis instrument, to monitor and record Reflectance spectrum changes；

One end of the spherical shape fusion point is left section of optical fiber, and the other end is right section of optical fiber, and reflecting layer is coated on its end face, is passed through M-Z interference effects are reflected to form, optical fiber expands in temperature change, while fibre diameter also changes correspondingly, and works as and applied to optical fiber When adding stress, cause fiber lengths and spherical diameter to change, and transmission spectrum is caused to change, realizes to temperature and stress Measurement.

2. the temperature and strain gauge of the optical-fiber probe type according to claim 1 based on single spherical welding, special Sign is, a diameter of 150-190um of the spherical shape fusion point.

3. the temperature and strain gauge of the optical-fiber probe type according to claim 1 based on single spherical welding, special Sign is, the length of the fibre-optical probe is that the distance of misplaces fusion point to its end face reflection layer is 1-3cm.