CN207556708U - An optical fiber temperature sensing system and temperature sensing optical fiber - Google Patents

Abstract

The utility model discloses an optical fiber temperature sensing system and a temperature sensing optical fiber. The system includes a laser light source, a wavelength division multiplexer, an avalanche diode, a data acquisition device, a host computer and the temperature sensing optical fiber. The optical fiber includes a core layer, a cladding layer and a coating layer in sequence from the inside to the outside; the radius of the core layer is 23.75-26.25 μm, the refractive index profile of the core layer is a graded refractive index distribution, and the refractive index distribution index α is 1.80-1.89 , The relative refractive index difference Δ1% of the core layer is 0.9% to 1.15%, and the welding loss is less than or equal to 0.08dB. The optical fiber temperature sensing system provided by the utility model has the advantages of simple structure, high signal-to-noise ratio and accurate results. The temperature sensing optical fiber provided by the utility model has strong spatial resolution of temperature measurement, high temperature measurement precision and long distance.

Description

An optical fiber temperature sensing system and temperature sensing optical fiber

technical field

The utility model belongs to the field of multi-mode optical fiber for temperature measurement, and more specifically relates to an optical fiber temperature sensing system and a temperature sensing optical fiber.

Background technique

Temperature measurement and control play an extremely important role in aerospace, materials, energy, metallurgy and other fields. Distributed optical fiber temperature measurement is an emerging contact temperature measurement technology. It uses optical fiber as the carrier of temperature information sensing and signal transmission. It has continuous temperature measurement, distributed temperature measurement, real-time temperature measurement, anti-electromagnetic interference, intrinsic Safety, remote monitoring, high sensitivity, easy installation, long life and other characteristics, widely used in pipelines, tunnels, cables, petroleum and petrochemical, coal mines and other industries.

The fiber-optic temperature sensing system combines the principle of Raman scattering and optical time-domain reflectometry, and collects the anti-Stokes light in the backward spontaneous Raman scattering carrying temperature information in the optical fiber as a signal channel, and at the same time collects the Stokes The Sri Lankan light or Rayleigh scattered light is used as a contrast channel, and the temperature field distribution along the optical fiber is restored through data processing after photoelectric conversion and analog-to-digital conversion. The key performance parameters of the distributed optical fiber temperature sensing system include temperature resolution, spatial resolution, temperature measurement length, single measurement time, etc. Spatial resolution is an important index in the distributed optical fiber temperature sensing system. It refers to the minimum temperature-sensing length of the optical fiber in the optical fiber temperature sensing system. Specifically, it can be expressed as: The corresponding response distance when the temperature response curve of the temperature measuring optical fiber rises from 10% to 90%.

In the existing optical fiber temperature sensing system, the sensing optical fiber usually adopts multimode optical fiber for communication. Multimode fiber has large mode field area and high Raman gain coefficient, and it is easy to obtain temperature information along the fiber through spontaneous Raman scattering. However, the disadvantage of multimode fiber for communication is that the loss of the fiber is large. In order to obtain higher spatial resolution, it is often used to select a working wavelength with better conductivity and optimize the parameters of the multimode fiber for this working wavelength. For example, the Chinese patent The sensing optical fiber mentioned in the document CN102539015A.

However, more importantly, the pulse broadening of the laser source due to the intermodal dispersion (mode differential group delay) of the multimode fiber leads to insufficient spatial resolution for longer distance sensing, which is required for temperature measurements with higher spatial resolution. In this scenario, the sensing distance of the optical fiber is actually limited, resulting in insufficient temperature measurement length.

Utility model content

Aiming at the above defects or improvement needs of the prior art, the utility model provides an optical fiber temperature sensing system and a temperature sensing optical fiber, the purpose of which is to realize the working band, anti-Stokes Raman The light attenuation of scattered light (1450nm) and Stokes Raman scattered light (1660nm) is significantly reduced, thereby solving the technical problems of limited sensing distance and insufficient temperature measurement length of the existing optical fiber temperature sensing system.

In order to achieve the above purpose, according to a solution of the utility model, an optical fiber temperature sensing system is provided, including a laser light source, a wavelength division multiplexer, an avalanche diode, a data acquisition device, a host computer and a temperature sensing optical fiber;

The laser light emitted by the laser light source is connected to the temperature sensing optical fiber through a wavelength division multiplexer;

The wavelength division multiplexer is used to receive the temperature sensing optical fiber signal and is connected to the avalanche diode;

The avalanche diode is used to convert the light signal into a current signal, and is connected with the data acquisition device;

The data acquisition device is connected with the host computer;

The host computer receives the data collected by the data acquisition device;

The temperature sensing optical fiber is a multimode optical fiber, which includes a core layer, a cladding layer and a coating layer from the inside to the outside; the radius of the core layer is 23.75-26.25 μm, and the refractive index profile of the core layer is a graded refractive index distribution. The rate distribution index α is 1.80-1.89, and the relative refractive index difference Δ1% of the core layer is 0.9%-1.15%.

Preferably, in the optical fiber temperature sensing system, the numerical aperture of the temperature sensing optical fiber is 0.190-0.205.

Preferably, in the optical fiber temperature sensing system, the fusion loss of the temperature sensing optical fiber fusion point is lower than 0.08dB.

Preferably, the optical fiber temperature sensing system uses a 1550nm pulsed light source as the laser light source.

Preferably, in the optical fiber temperature sensing system, the wavelength division multiplexer and the avalanche diode are used to transmit optical signals of 1450nm and 1660nm.

According to another solution of the utility model, a temperature sensing optical fiber is provided, which includes a core layer, a cladding layer and a coating layer in sequence from the inside to the outside; the radius of the core layer is 23.75-26.25 μm, and the refractive index profile of the core layer is gradually changing Type refractive index distribution, the refractive index distribution index α is 1.80-1.89, the relative refractive index difference Δ1% of the core layer is preferably 1.0%-1.15%, and the welding loss is less than or equal to 0.08dB.

Preferably, the numerical aperture of the temperature sensing optical fiber is 0.190-0.205.

Preferably, the core material of the temperature sensing optical fiber is SiO ₂ quartz glass of germanium/fluorine co-doped system; the cladding material is high-purity quartz glass.

Preferably, the temperature sensing optical fiber has a cladding radius of 62.0-63.0 μm.

Preferably, the temperature sensing optical fiber has a core radius of 24.5-25.5 μm, a refractive index distribution index α of 1.84-1.86, and a numerical aperture of the temperature sensing optical fiber of 0.195-0.200.

The longest temperature measurement distance of the temperature sensing optical fiber can reach 27km, and the fusion loss at the fusion point is lower than 0.08dB, which can reduce the temperature jump caused by the fusion point and avoid false alarms of the optical fiber temperature sensing system.

Generally speaking, compared with the prior art, the above technical solutions conceived by the utility model can achieve the following beneficial effects:

(1) The optical fiber temperature sensing system provided by the utility model has a simple structure, low noise, high signal-to-noise ratio, accurate temperature measurement results, and a temperature measurement distance of 10km to 27km due to low fiber fusion loss and high bandwidth.

(2) The temperature sensing optical fiber provided by the utility model has optimized the bandwidth of 1550nm and the loss of 1450nm at the same time compared with the general communication multimode optical fiber, enhanced the spatial resolution of the optical fiber temperature sensing system, improved the temperature measurement accuracy and temperature measurement distance, so that the multimode optical fiber provided by the utility model can be applied to a medium-long distance optical fiber temperature sensing system, and the temperature measurement distance can reach 10km to 27km.

The optimal solution optimizes the radius and numerical aperture of the core layer to reduce the fusion loss of the optical fiber and ensure the effect of long-distance optical transmission.

Description of drawings

Fig. 1 is a schematic structural diagram of an optical fiber temperature sensing system provided by the utility model;

Fig. 2 is a schematic structural diagram of the temperature sensing optical fiber provided by the utility model;

Fig. 3 is a schematic cross-sectional view of the temperature sensing optical fiber refractive index provided by the utility model;

Fig. 4 is the optical fiber attenuation spectrum of the temperature sensing optical fiber provided by the utility model;

Fig. 5 is a test result diagram of the spatial resolution of the optical fiber temperature sensing system provided by Embodiment 8 of the present utility model.

Detailed ways

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not intended to limit the utility model. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute conflicts with each other.

The optical fiber temperature sensing system provided by the utility model, as shown in Figure 1, includes a laser light source, a wavelength division multiplexer (WDM), an avalanche diode (APD), a data acquisition device, a host computer and the temperature sensor provided by the utility model. Sensing fiber;

The laser light that described laser light source sends is connected with described temperature sensing fiber through wavelength division multiplexer (WDM); Described laser light source adopts 1550nm pulse light source;

The host computer receives the data collected by the data collection device. The wavelength division multiplexer (WDM) is used to receive the temperature sensing optical fiber signal, connect with the avalanche diode (APD), and transmit the optical signals of 1450nm and 1660nm;

The avalanche diode (APD) is used to convert the optical signal into a current signal, and is connected with a data acquisition device to transmit optical signals of 1450nm and 1660nm;

The data acquisition device is connected with the host computer;

The host computer receives the data collected by the data collection device.

The longest temperature measurement distance of the temperature sensing optical fiber can reach 27km, and the fusion loss at the fusion point is lower than 0.08dB, which can reduce the temperature jump caused by the fusion point and avoid false alarms of the optical fiber temperature sensing system.

The temperature sensing optical fiber, as shown in Figure 2, includes a core layer, a cladding layer coated outside it, and a polymer material coated on the surface of the cladding layer;

The radius of the core layer is 23.75-26.25 μm, preferably 24.5-25.5 μm; the refractive index profile of the core layer is a gradual refractive index distribution, and the refractive index distribution index α is 1.80-1.89, preferably 1.84-1.86; the relative refractive index of the core layer is The rate difference Δ1% is 1.0% to 1.15%, as shown in Figure 3, the fusion loss is less than or equal to 0.08dB; the core material is preferably SiO ₂ quartz glass of germanium/fluorine co-doped system.

The radius of the cladding is 62.0-63.0 μm, preferably 62.1-62.7 μm, and the material is preferably high-purity quartz glass.

The polymer material is preferably acrylic resin or high temperature resistant polyimide coating; when the polymer material is acrylic resin, the outer diameter of the temperature sensing optical fiber is 245±10 μm; when the polymer material is When the high temperature resistant polyimide coating is used, the outer diameter of the temperature sensing optical fiber is 160±10 μm.

The numerical aperture of the multimode optical fiber is 0.190-0.205, preferably 0.195-0.200; its fusion loss is less than or equal to 0.08dB, which can reduce the temperature jump caused by the fusion point and avoid false alarms of the optical fiber temperature sensing system, especially During long-distance transmission, splice loss has a great influence on the temperature measurement effect.

The temperature sensing optical fiber provided by the utility model has an effective mode bandwidth of more than 500MHz*km at 1550nm, and an optimal bandwidth of more than 1000MHz*km; the attenuation at 1450nm is lower than 0.5dB/km

Multimode fiber has large mode field area and high Raman gain coefficient, and it is easy to obtain temperature information along the fiber through spontaneous Raman scattering. A typical optical fiber temperature sensing system uses a 1550nm light source as the excitation light. The anti-Stokes Raman scattered light (1450nm) corresponding to this light source is used as the temperature measurement signal channel, and the Stokes Raman scattered light (1660nm) is used as the temperature measurement reference. aisle. The utility model breaks through the previous thinking of optical fiber design for detecting laser light, and optimizes the transmission of Stokes Raman scattered light and anti-Stokes Raman scattered light in the optical fiber temperature sensing system. Through a large number of experiments, it is obtained The core layer parameter of described multimode optical fiber is carried out combined experiment in many respects, finally draws the multimode temperature measurement optical fiber that the utility model provides, it is in Stokes Raman scattered light and Stokes Raman scattered light Unexpected decrease in light attenuation occurs in bands near the band. As shown in Figure 4: It is known in the art that multimode optical fibers for communication will have a high peak of light attenuation in the 1385nm band, which will lead to an increase in the light attenuation of anti-Stokes Raman scattered light and Stokes Raman scattered light, while The attenuation curve of the optical fiber provided by the utility model fluctuates smoothly in the 1385nm band, and the influence on the anti-Stokes Raman scattering light and the Stokes Raman scattering light band can be almost ignored.

At the same time, the optical fiber provided by the utility model also has excellent performance in terms of splicing loss. Generally speaking, the temperature sensing optical fiber provided by the utility model can be applied to a medium and long-distance optical fiber temperature sensing system, and the spatial resolution of the system reaches 5m. , the temperature resolution is less than 2°C, and the temperature measurement distance reaches 27km, which breaks through the temperature measurement distance of the existing temperature measurement optical fiber, and realizes medium and long-distance high-resolution temperature measurement, as shown in Figure 5.

The temperature sensing optical fiber provided by the utility model can be prepared by the PCVD in-pipe method.

The temperature sensing optical fiber provided by the utility model is a medium and long-distance optical fiber temperature sensing system, and the temperature measuring distance of the system reaches 27km.

The following are examples:

Embodiments 1 to 4 temperature sensing optical fiber

According to the above scheme design, a group of optical fibers were prepared. The core layer is _SiO2 silica glass of germanium/fluorine co-doped system, and the cladding is high-purity silica glass. The relevant parameters are shown in Table 1:

Table 1

Embodiments 5 to 8 The optical fiber temperature sensing system uses the multimode optical fiber in Embodiments 1 to 4, and the results are as follows:

Including laser light source, wavelength division multiplexer (WDM), avalanche diode (APD), data acquisition device, host computer and temperature sensing optical fiber provided by the utility model;

The laser light sent by the laser light source is connected to the temperature sensing fiber through a wavelength division multiplexer (WDM); the laser light source is a 1550nm pulsed laser light source;

The temperature measuring distance of the temperature sensing optical fiber can reach 10 to 27km, and the fusion loss at the fusion point is lower than 0.08dB, which can reduce the temperature jump caused by the fusion point and avoid false alarms of the optical fiber temperature sensing system.

The wavelength division multiplexer (WDM) is used to receive the temperature sensing optical fiber signal, connect with the avalanche diode (APD), and transmit the optical signals of 1450nm and 1660nm;

The avalanche diode (APD) is used to convert the optical signal into a current signal, and is connected with a data acquisition device to transmit optical signals of 1450nm and 1660nm;

The data acquisition device is connected with the host computer;

The host computer receives the data collected by the data collection device.

The parameters are shown in Table 2:

Table 2

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements and modifications made within the spirit and principles of the utility model Improvements and the like should all be included within the protection scope of the present utility model.

Claims (5)

1. An optical fiber temperature sensing system, characterized in that, comprises a laser light source, a wavelength division multiplexer, an avalanche diode, a data acquisition device, an upper computer and a temperature sensing optical fiber; The laser light emitted by the laser light source is connected to the temperature sensing optical fiber through a wavelength division multiplexer; The wavelength division multiplexer is used to receive the temperature sensing optical fiber signal and is connected to the avalanche diode; The avalanche diode is used to convert the light signal into a current signal, and is connected with the data acquisition device; The data acquisition device is connected with the host computer; The host computer receives the data collected by the data acquisition device; The temperature sensing optical fiber is a multimode optical fiber, which includes a core layer, a cladding layer and a coating layer from the inside to the outside; the radius of the core layer is 23.75-26.25 μm, and the refractive index profile of the core layer is a graded refractive index distribution. The rate distribution index α is 1.80-1.89, and the relative refractive index difference Δ1% of the core layer is 0.9%-1.15%. 2 . The optical fiber temperature sensing system according to claim 1 , wherein the numerical aperture of the temperature sensing optical fiber is 0.190˜0.205. 3. The optical fiber temperature sensing system according to claim 1, characterized in that the fusion loss of the fusion point of the temperature sensing optical fiber is lower than 0.08dB. 4. The fiber-optic temperature sensing system according to claim 1, wherein the laser light source is a 1550nm pulsed light source. 5. The fiber optic temperature sensing system according to claim 1, wherein the wavelength division multiplexer and the avalanche diode are used to transmit optical signals of 1450nm and 1660nm.