JPH045529A - Optical fiber type temperature distribution measuring instrument - Google Patents

Abstract

PURPOSE:To reduce an investment in facilities and to measure a temperature distribution with high economical efficiency by using a single-mode fusion-spliced coupler which is connected in series and utilizing an existing single-mode optical fiber as an optical fiber for sensing. CONSTITUTION:A light source 1 is driven by a pulse driving circuit 12 which is controlled by a computer 11 to generate a light pulse repeatedly. Then 2nd fusion-spliced couplers 2 and 3 are connected in series by fusion splicing while two single-mode optical fibers are extended longitudinally. A cut filter 5 is connected to the other end of the fusion-spliced coupler 3 on the side of the light source and includes a multi-mode optical fiber on its output side to extract a wavelength component of Stokes light obtained from the single-mode fiber 4 for sensing. A digital averager 10 processes and transfers Rayleigh light and Stokes light detected by photodetector 8 and 6 to the computer 11 to measure the temperature distribution in an area long the fiber 4.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical fiber temperature distribution measuring device that measures temperature distribution using an optical fiber.

[Conventional technology]

Conventionally, a device that measures temperature by detecting backscattered light such as Raman scattering in an optical fiber has been known as a device that simultaneously measures one-dimensional temperature distribution, that is, a location along the length of an optical fiber and the temperature there. It is being Since it is possible to determine the one-dimensional temperature distribution in the area along the optical fiber, it is especially effective for temperature monitoring in very long and narrow areas, such as temperature monitoring of power transmission lines or communication networks. It is believed that there is. This optical fiber type temperature distribution measuring device inputs a light pulse from one end of an optical fiber laid in a sensing area,
This is because the backscattered light such as Raman scattering that returns from various points along the length of the optical fiber is emitted from the input side end and the wavelength components of the Raman scattering etc. are extracted.
In addition to the sensing optical fiber, optical devices such as filters are required. The optical device required here is
These include optical couplers that use semi-transmissive mirrors, spectroscopic optical devices that use dielectric multilayer films, and filters that use diffraction gratings. These optical devices are the fourth choice for boat fishing.
As shown in the figure, the light emitted from the optical fiber 41 on the input side is converted into parallel light by a lens 43, condensed again by another lens 44, and made to enter the other optical fiber 42 on the output side. It is constructed by inserting various optical components 45 such as a prism or a dielectric multilayer film into the parallel light portion between the lens 44 and the lens 44 . Single-mode optical fiber or multi-mode optical fiber can be used as the sensing optical fiber for the optical fiber temperature distribution measuring device, but optical fiber cables for communication are already installed in various places, and one of them is
There is a great practical need to use books as they are as optical fibers for sensing. Particularly in the power field, optical fiber cables for communication are laid along power transmission lines, and even in communication networks, optical fiber cables are laid if they are for optical communication. This existing optical fiber is usually a single mode optical fiber due to its large transmission capacity. Therefore, conventionally, when an existing optical fiber is used as is from the viewpoint of economy, an optical fiber type temperature distribution measuring apparatus is constructed using an optical device for a single mode optical fiber.

[Problem to be solved by the invention]

However, optical devices for single-mode optical fibers usually have problems such as high manufacturing cost and short lifespan, and when using them to configure an optical fiber temperature distribution measurement device, it costs a lot of money. There is a problem that requires significant capital investment. In other words, when the input and output side optical fibers of an optical device are multimode, the core diameter is relatively thick, so there is a large tolerance for positional and angular deviations when adjusting the optical axis. It is possible to create optical devices by fixing optical components using, for example, optical devices, and the completed optical devices can be expected to have a lifespan of several years or more in normal environments. On the other hand, when using single mode optical fibers as the input and output optical fibers of an optical device,
Since the core diameter is smaller than that of multimode optical fiber,
The tolerance for positional and angular deviations is more than one order of magnitude stricter than in the case of multimode optical fibers. Therefore, it is difficult to fix and adjust the position of each optical component, and even if it is fixed after adjustment, it is difficult to maintain stable characteristics thereafter. Under normal circumstances, more advanced techniques such as spot welding, laser welding, or solder fixation techniques are required to obtain a lifespan of several years or more. Therefore, such an optical device for single mode optical fiber is naturally difficult to design and expensive. Therefore, if a single-mode optical fiber is used as the sensing optical fiber and an optical device for the single-mode optical fiber is used to configure an optical fiber temperature distribution measurement device, a large amount of capital investment is required. At the same time, maintenance costs also become high. On the other hand, in order to avoid such problems with optical devices, it is possible to lay a multimode optical fiber as a sensing optical fiber along the area to be measured, but this would require laying a completely new optical fiber. Regardless of the case, in cases such as temperature monitoring of power transmission lines and communication networks, thin mode optical fibers are not used even though they are already installed.
This results in the installation of duplicate optical fibers in the same route, which is unacceptable from the point of view of economic efficiency. This invention eliminates the above-mentioned dilemma and uses an existing single-mode optical fiber as a sensing optical fiber, but does not use an optical device for single-mode optical fiber, thereby reducing the cost and cost of using it. The purpose of the present invention is to provide an optical fiber type temperature distribution measuring device that is improved to avoid problems such as short life, and is inexpensive, highly economical, and has excellent reliability and longevity.

[Means to solve the problem]

In order to achieve the above object, the optical fiber type temperature distribution measuring device according to the present invention has first and second optical fibers connected in series, which are formed by fusing two single mode optical fibers in a longitudinally aligned state. a single mode fusion coupler; a light source coupled to one end of the first fusion coupler; a single mode optical fiber for sensing coupled to one end of the second fusion coupler; The input optical fiber is a single mode optical fiber and the output optical fiber is a multimode optical fiber, which is coupled to the other end of the optical coupler on the light source side and is used to extract the weaker wavelength component of the wavelength components to be measured. a filter having a wavelength-selective optical component fixed therebetween; a first light-receiving element coupled to a multimode optical fiber on the output side of the filter;
A second light receiving element coupled to the other end of the first fusion coupler on the light source side is provided.

[For production]

Light from the light source is input into a single mode optical fiber for sensing through first and second fusion couplers. The scattered light that has returned through the sensing single mode optical fiber is first split by the second fusion coupler, and then branched by the second fusion coupler. Since a fusion coupler is used as an optical coupler/brancher in this way, operation is stable over a long period of time, and insertion loss can be reduced. That is, since the optical components are not mechanically fixed, their positional deviations and instability in operation resulting therefrom are eliminated. The light branched by the second fused coupler is guided to the first light receiving element through a filter. This filter is used to extract a specific wavelength component to be measured.The input optical fiber is a single mode optical fiber, the output optical fiber is a multimode optical fiber, and a wavelength selective optical component is fixed between them. It is composed of As the single mode optical fiber on the input side, the single mode optical fiber extending from the fusion coupler can be used as it is, or the single mode optical fiber connected thereto can be used. Therefore, a single mode optical fiber with a small core diameter is coupled to a multimode optical fiber with a large core diameter, and in order to obtain predetermined characteristics, it is necessary to connect both optical fibers and the wavelength selective optical components between them. The tolerance of positional accuracy is not required to be very strict. Therefore, it is easy to manufacture, stable for long-term use, highly reliable, and has a long life. The light branched by the first fusion coupler is coupled to the second light receiving element and detected. In this way, two wavelength components of the backscattered light are detected from the light split by the first and second fusion couplers, respectively. Of the two wavelengths of backscattered light, the wavelength component with the weaker intensity is the branched light of the fusion coupler (herein referred to as the second fusion coupler) closer to the sensing single mode optical fiber. , and the stronger wavelength component is detected from the branched light of the fusion coupler (herein referred to as the first fusion coupler) on the side far from the sensing single mode optical fiber. Attenuation of the weaker wavelength component is reduced. The two wavelength components of the backscattered light are, for example, any two of Stokes light, anti-Stokes light, and Ray light.
It is the wavelength. When measuring Stokes light and Rage light, since Stokes light is weaker, the Stokes light is detected from the light branched by the second fusion coupler, and the laser light is detected from the light branched by the first fusion coupler. Detect light. In addition, when measuring anti-Stokes light and Stokes light, since the anti-Stokes light is weaker, the anti-Stokes light is detected from the light branched by the second fusion coupler, and the anti-Stokes light is detected from the light branched by the first fusion coupler. Stokes light is detected from the light.

【Example】

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, an optical fiber type temperature distribution measuring device according to an embodiment of the present invention includes a light source 1, first and second fusion couplers 2.3, and a sensing single mode optical fiber 4. are connected in series. These mutual connections may be made by connectors or by fusion splicing. In this embodiment, the light source 1 uses a semiconductor laser-excited solid-state laser with a wavelength of 1.32 μm. Of course, it is possible to use a semiconductor laser with a wavelength of 1.3 μm, but in view of the current lack of optical output, the light source as described above was used. The light source 1 is pulse-driven by a pulse drive circuit 12 controlled by a computer 11 to repeatedly generate light pulses 6 The first and second fusion couplers 2.3 each produce two single-mode lights. It is manufactured by fusion-bonding the fibers vertically to each other. The other ends of the first and second fusion couplers 2.3 on the sensing single mode optical fiber 4 side are left unused. A cut filter 5 is coupled to the other end of the second fusion coupler 3 on the light source 1 side. In this embodiment, the cut filter 5 is for extracting wavelength components of Stokes light in Raman scattering, and is configured as shown in FIG. 2. That is, as shown in FIG.
1, the single mode optical fiber from the second fusion coupler 3 is used as it is (or the single mode optical fiber connected thereto). On the other hand, a multimode optical fiber is used as the optical fiber 52 on the output side. A lens 53 for converting the light emitted from one end of the input side optical fiber 51 into parallel light, a lens 54 for condensing the parallel light and making it enter one end of the output side optical fiber 52, and this lens 53. Dielectric multilayer filters 55 and 56 inserted between .54 and 54 are provided. The dielectric multilayer filter used has wavelength characteristics as shown in FIG. 3, but since a single filter generally does not have sufficient characteristics, a plurality of filters are used in this embodiment. The light that has passed through this cut filter 5 is detected by a light receiving element 6, and its electrical output signal is amplified by an amplifier 7 and then sent to a digital averager 10. On the other hand, the light receiving element 8 is directly coupled to the other end of the first fusion coupler 2 on the light source 1 side. The electrical output signal of this light receiving element 8 is amplified by an amplifier 9 and then sent to a digital averager 10. The digital averager 10 converts the detection signal obtained each time a light pulse is repeatedly incident from the light source 1 to the sensing single mode optical fiber 4 into a digital signal, averages it, and sends the data to the computer 11. Make a transfer. In this embodiment, the light source 1 has a wavelength of 1.32 as described above.
Because it uses a μm semiconductor laser excitation fixed laser,
The wavelength of Stokes light is 1.40a+, and the wavelength of anti-Stokes light is 1.25n. Therefore, the wavelength of the anti-Stokes light may be less than the cutoff wavelength in a normal single mode optical fiber. Therefore, here, the Stokes light component with a wavelength of 1.401 m is extracted by the cut filter 5 and detected by the light receiving element 6. In contrast, the light receiving element 8 detects the beam component. Since the intensity of the Ray light is 3 to 4 orders of magnitude higher than that of the Stokes light, a cut filter for extracting only the Ray light is not necessary. The measurement data of this laser light includes the transmission loss of the single mode optical fiber 4 for sensing,
Used for characteristic calibration of splices, connectors, etc. In this example, as mentioned above, the fused coupler 2.3 is used as an optical coupler/brancher, so it is more stable than a normal optical coupler/brancher that requires mechanical fixation of optical parts. Moreover, insertion loss is reduced. Also, fused coupler 2
．． No. 3 has good characteristics and is also excellent in price. In addition, since the optical device called cut filter 5 used here is of a type that couples a single mode optical fiber to a multimode optical fiber using a lens, the positions of each optical component are similar to the optical device for multimode optical fibers. It is resistant to misalignment, so it is easy to manufacture, has excellent reliability, and has a long life. In other words, since the optical device used here couples a single mode optical fiber to a multimode optical fiber using a lens, it is possible to manufacture an optical device for a conventional multimode optical fiber using the same manufacturing technology. Moreover, the optical devices made in this way are highly reliable because they are not affected by slight positional deviations, and have a long lifespan of several years or more, similar to conventional optical devices for multimode optical fibers. As a result, it is possible to obtain an optical fiber type temperature distribution measuring device that has a simple structure as a whole, is compact, and has high long-term reliability. In the above, Stokes light and Leh light are measured, and since Stokes light is weaker, the Stokes light is detected from the light branched by the second fusion coupler 3, and the Stokes light is detected from the light branched by the second fusion coupler 3. Although the Ray light is detected from the light branched in step 2, it is also possible to measure the anti-Stokes light and the Stokes light, and in that case, since the anti-Stokes light is weaker, the second fusion coupler 3 Anti-Stokes light is detected from the light branched at the first fusion coupler 2, and Stokes light is detected from the light branched at the first fusion coupler 2. Therefore, in this case, in addition to providing the anti-Stokes light detection cut filter 5 between the second fusion coupler 3 and the light receiving element 6, the first fusion coupler 2
It is necessary to provide a cut filter having the same configuration as the cut filter 5 between the light receiving element 8 and the light receiving element 8 in order to extract only the wavelength component of the Stokes light.

【Effect of the invention】

According to this invention, even when a single-mode optical fiber is used as a sensing optical fiber, a fused coupler is used and the ease of manufacturing, reliability, and lifespan equivalent to optical devices for multi-mode optical fibers are achieved. By using an optical device, it is possible to construct an optical fiber type temperature distribution measuring device with low capital investment and high economic efficiency by using an already installed single mode optical fiber.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of a cut filter part used in the same embodiment, and FIG. 3 is a graph showing an example of wavelength characteristics of a dielectric multilayer film of the same cut filter. FIG. 4 is a schematic diagram showing a conventional example of an optical device. DESCRIPTION OF SYMBOLS 1... Light source, 2.3... Fusion coupler, 4... Single mode optical fiber for sensing, 5... Cut filter, 6.8... Light receiving element, 7.9... Amplifier ,
DESCRIPTION OF SYMBOLS 10... Digital averager, 11... Computer, 12... Pulse drive circuit, 41.51... Single mode optical fiber on input side, 42... Single mode optical fiber on output side, 52... ...Output side multimode optical fiber, 53.54.43.44...Lens, 55.56...Dielectric multilayer filter, 45...
・Optical parts.

Claims (1)

[Claims] (1) First and second single-mode fusion couplers connected in series, which are formed by fusing two single-mode optical fibers in a longitudinally aligned state, and coupled to one end of the first fusion coupler. a single-mode optical fiber for sensing coupled to one end of the second fusion coupler, and a single-mode optical fiber for sensing the wavelength component to be measured coupled to the other end of the second fusion coupler on the light source side. In order to extract the weaker wavelength component, the input optical fiber is a single-mode optical fiber, the output optical fiber is a multi-mode optical fiber, and a wavelength-selective optical component is fixed between them. , comprising a first light receiving element coupled to the multimode optical fiber on the output side of the filter, and a second light receiving element coupled to the other end of the first fusion coupler on the light source side. Optical fiber type temperature distribution measuring device.