JPH01129127A - Few-core optical fiber cable incorporating temperature sensor and monitoring method of temperature - Google Patents

Abstract

PURPOSE:To monitor a temperature precisely and inexpensively, by providing an optical coupling element in a part of a multicore optical fiber core wire and by covering its periphery with a material whose refractive index changes in accordance with the temperature. CONSTITUTION:A multicore optical fiber 3 comprising first and second cores 1a and 1b and a clad 2 surrounding these cores commonly is surrounded by a plastic coating 4 and a sheath 5, and thereby an optical fiber cable is constituted. A biconical taper region (optical coupling element) 6 is made in the optical fiber 3 and the periphery thereof is covered with a material 7 whose refractive index is dependent on temperature. The rate of a power P1 transmitted through the optical coupling element 6 and emitted to the other end of the first core 1a, in a power P0 of a light entering the core 1a at one end thereof, changes in accordance with the refractive index of the material 7. The temperature can be monitored by observing the power P1 of the transmitted light or the power of the back scattering light thereof. A power P2 of the light coupled from the core 1a to the core 1b is not dependent on the refractive index of the material 7 nearly at all, and therefore it is used for communication.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a small-core optical fiber cable with a built-in temperature sensor that can accurately detect temperature changes, and a temperature monitoring method.

(Prior art and its problems) It is known that optical fiber breakage occurs due to the growth of minute scratches existing on the glass surface. As the ambient temperature increases, the growth of fiber surface scratches is promoted (H, C,
Chandan, and D. Kallsh.

“'remperature dependence
of 5tattc fatigueor optlc
al fibers coated with a U
V-curable polyurethane aer
ylate', J, Amer, Cerm, S
oc.

65, p, l? 1.1982). In a normal design, the average temperature is about 10 to 20 degrees Celsius, but if exposed to high temperatures such as 40 to 60 degrees Celsius for a long period of time due to unforeseen external factors, the fiber may break prematurely. To prevent this, it is necessary to monitor the temperature of the cable.

General temperature sensors have the Seebeck effect (thermoelectromotive force)
thermocouples that utilize metal resistance, resistance thermometers that utilize the temperature dependence of metal resistance, resistance thermometers that utilize the temperature dependence of resistance of oxide and non-oxide semiconductors, and critegisters that utilize semiconductor-metal phase transition ( CTR), a crystal thermometer that uses the temperature dependence of the piezoelectric constant of a ferroelectric, a thermometer that uses the temperature dependence of the wavelength distribution of reflected light in a liquid crystal, a gas thermometer that uses the thermal expansion of gases and liquids, and mercury. There were thermometers, but these had the disadvantage that they were installed far away from the cable itself, making it impossible to accurately detect the temperature inside the cable. In addition, it was difficult to insert it into the cable because it was too large and the shape was not suitable. Furthermore, for remote monitoring, a constant flow of temperature sensor control and detection signals is required.

The disadvantage was that it required separate construction and maintenance of a dedicated line for this purpose, making it impossible to construct an economical line configuration.

On the other hand, conventional optical fiber temperature sensors using stimulated Raman scattering effects (J, P, DAKIN, D, J, PRAT
T:'Distributed 0ptical PH
+er RamanTeIlperature 5en
Sor Uslng a Semiconductor
rLight 5source and Detect
r', ELECTRONIC8LETTER8,
Vol, 21. No. 11 (June 1985))
was there.

This technology is an excellent method because the sensor is in the form of a fiber, so it can be inserted into the cable and can monitor the location where temperature changes occur along the length of the cable. DR (Optic
Al Tll1e Domajn Reflect
ometry) requires a laser with higher output than a normal 0TDR and an optical directional coupler with low loss and high separation, making the measurement equipment expensive, and the drawback is that it is not possible to reduce the cost of the maintenance system using temperature sensing. was there. In addition to the optical signal transmission fiber, a temperature sensor fiber is also required. This fiber has a large core diameter and high NA
This made it difficult to use it in common with communication fibers, as it required measures to improve measurement accuracy, such as increasing the measurement accuracy. Therefore, in the drop-in line to the subscriber terminal, which requires only one fiber for communication, there are two fibers including the fiber for the sensor, which has a major disadvantage in that the cost of the drop-in line inevitably increases. When a cable is exposed to high temperatures due to environmental changes, the temperature of the fibers within the cable increases significantly in the case of a cable with a small number of cores. For this reason, the conventional technology has the disadvantage that the cost increases, especially due to the required small number of core cables.

An object of the present invention is to solve the above-mentioned problems, to detect the temperature of an optical fiber cable, and to provide a small-core optical fiber cable with a built-in temperature sensor that can be constructed at a low cost and with good sensing accuracy. An object of the present invention is to provide a temperature monitoring method using an optical fiber cable.

(Means for Solving the Problems) In order to achieve the above object, the first invention provides a multi-core optical system in which a plurality of cores for transmitting optical signals exist, and the cladding has a shape that commonly surrounds the plurality of cores. In a small-core optical fiber cable that accommodates at least one multi-core optical fiber core, the multi-core optical fiber core wire is provided with an optical coupling portion at a small length at an arbitrary location in the longitudinal direction, and is temperature-controlled. In the second invention, there is a plurality of cores for transmitting optical signals, and the cladding is made of a material whose refractive index changes depending on the optical coupling part. An optical coupling part to the multi-core optical fiber at any location in the longitudinal direction of a small-core optical fiber cable that accommodates at least one multi-core optical fiber having a shape that commonly surrounds a plurality of cores. In an optical fiber cable that has a part covered with a material whose refractive index changes depending on the temperature, the communication light is connected to one core of the multi-core optical fiber at one end of the cable. A signal is inputted to the core, and the optical coupling part couples the optical signal to another multi-core core so that the output light can be separated and taken out, and among the output lights, the core is the same as the core into which the communication optical signal is input. The third invention is characterized in that a temperature change is detected from a change in the intensity of light emitted from the multi-core. A small-core optical fiber cable containing at least one multi-core optical fiber is provided with an optical coupling part in the longitudinal direction of the multi-core optical fiber, and the optical coupling part is provided in the multi-core optical fiber at an arbitrary location in the longitudinal direction, and In an optical fiber cable that has a part covered around the coupling part with a material whose refractive index changes, a communication optical signal is input into one core of the multi-core optical fiber at one end of the cable, and the same A temperature detection optical pulse is input to a core different from the core into which the optical signal of the ground was input, and the intensity of the backscattered light returning from the core is detected, and the intensity changes due to changes in the refractive index of the coating material due to temperature changes. The temperature change is detected from the intensity change of the backscattered light returning from the optical coupling part.

(Function) According to the first invention, when the temperature changes around the optical coupling portion, the refractive index of the portion surrounding the optical coupling portion changes with this temperature change. A change occurs in the power of the coupled light at . Therefore, temperature changes can be detected from this power change.

According to the second invention, a communication optical signal is input into one core of the multi-core optical fiber at one end of the optical fiber cable,
By coupling the optical signal to other multi-core cores at the optical coupling part and making it possible to separate and extract the emitted light,
When a temperature change occurs around the optical coupling part, based on the change in the refractive index of the surrounding material, the intensity of the outgoing light from the same core as the one into which the communication optical signal was input will change. This allows temperature changes to be detected.

According to the third invention, at one end of the optical fiber cable, a communication optical signal is input into one core of the multi-core optical fiber, and a core different from the core into which the optical signal was input at the same location is By injecting a temperature detection optical pulse and detecting the intensity of the backscattered light returning from the core, the backscattered light returning from the optical coupling portion is detected based on the change in the refractive index of the coating material due to temperature change. A change in intensity occurs, which allows a temperature change to be detected.

(Example) Hereinafter, an example of an optical fiber cable with a built-in temperature sensor according to the present invention will be shown.

FIG. 1 shows an embodiment of an optical fiber cable accommodating a multi-core optical fiber capable of temperature sensing according to the present invention, in which 1a is the first core, 1b is the second core, and 1b is the second core.
2 is a cladding that commonly surrounds the cores 1a and 1b, 3 is a multi-core optical fiber including two cores, 4 is a plastic coating that surrounds the multi-core optical fiber 3, and 5 is an outer jacket.

FIG. 2 is a cross-sectional view of a temperature sensor section formed by creating an optical coupling section in the two-core multi-core optical fiber cable shown in FIG. 1, and the same reference numerals as in FIG. shows. 6 in the figure is the piconical taber region after stretching,
Configures an optical coupling section.

Reference numeral 7 denotes a material whose refractive index is temperature dependent, and is provided around the outer periphery of the Taber region (optical coupling portion) 6 .

In such a configuration, light propagating through the first core 1a leaks out of the core la at the Taber region 6, is reflected at the interface between the outer cladding layer 2 and the refractive index temperature-dependent material 7, and is transmitted to the second core 1a. or directly into the core 1b of the box 2 through the inner cladding. In reality, as will be described later, the former case is predominant, and a change in the refractive index on the outside of the cladding 2 has a large effect on transmitted light or coupled light. Furthermore, by designing the taper of the optical coupling section 6, various coupling ratios can be obtained. In this method, the tapered portion is produced by heating and drawing, but there is no need to twist the fiber at this time.

This is because the symmetrical fiber is a multi-core optical fiber as shown in FIG. 1, and a part of the cladding is fused in advance. That is, since there is a common rad 2, the tapered portion is formed simply by heating and stretching a part of the multi-core. As shown in Figure 1, multi-core optical fibers are made by bundling multiple single-core optical fibers in parallel, and their circumscribed contact lines are fused to each other, and the non-contact surfaces are curved almost in the original shape. A certain cross-sectional shape is desirable.

That is, it has a groove-like portion in the length direction of the outer circumferential surface.

When such a multi-core optical fiber is heated and drawn, the molten glass portion tends to approximate a circular shape due to surface tension, and a force acts to bring the internal cores to the center. That is, the tapered portion can be effectively produced. In the conventional method, a large number of single-core optical fibers are twisted together multiple times and heated and drawn. At this time, in order to melt and draw a plurality of optical fibers, the fibers must be properly bonded to each other. If the optical fibers are simply heated and stretched, each optical fiber will only become soft and thin, and it will be difficult to melt them together. For this purpose, a twist is added, and as a result,
It is not easy to obtain optimal optical coupling conditions. That is, since the core draws a complicated curve in the melted part, it becomes difficult to accurately set manufacturing conditions that determine optical coupling. In this way, in addition to the heating temperature and the stretching distance, twist is one more parameter added to the manufacturing conditions, making it difficult to obtain stable reproducibility.

On the other hand, the coupling part in the multi-core optical fiber used in the present invention does not have the twist parameter among the three parameters, so the manufacturing conditions are easy to understand and the reproducibility is good. That is, once the heating temperature is set, the optical fiber can be melted and drawn as it is, so it can be produced extremely easily, and the manufacturing conditions that determine optical coupling can be easily controlled. Furthermore, since multi-core optical fibers are used, advanced processing technology is not required to create the optical coupling part.
Moreover, it can be easily manufactured on-site.

Figure 3 shows the multi-core optical fiber shown in Figure 1 with a second
The piconical taber region 6 shown in the figure is fabricated, its periphery is covered with a material 7 whose refractive index changes depending on the temperature, the optical power PO is input to the first core 1a, and the first core 1 at the other end is
a and the power emitted from the second core 1b are respectively PL
, P2 is a diagram showing the results of measuring the refractive index dependence of each power. Here, Pl is transmitted light, P2
is the combined light. However, the mode field diameter of each core of the multi-core optical fiber used was 8.3 μm, the cutoff wavelength was 1.12 μm, the long axis of the outer diameter was 160 μm, and the short axis of the outer diameter was 80 μm.
μ-. Further, as material 7, a mixed solution of benzene and ethyl alcohol was used in order to facilitate measurement of the refractive index dependence of emitted light. By changing the mixing ratio, the refractive index was selected within the range of 1.37 to 1.50.

From this figure, the coupled light P2 has hardly changed, but
It can be seen that the transmitted light Pl shows refractive index dependence, and the maximum power occurs near 1.45. For example, if the optical coupling part is covered with a plastic material having a refractive index of 1.45 at room temperature, the transmitted light P1 will have maximum power. Generally, the refractive index of a plastic material decreases as the temperature increases, so when the temperature around the optical fiber coupling section increases, the output of the transmitted light P1 decreases. As can be seen from the figure, when the refractive index decreases to around 1.44, the power P1 also decreases rapidly. By detecting this power drop, it is possible to quickly sense that the surrounding temperature has become high. Additionally, by monitoring the power level during this time, it becomes possible to accurately detect temperatures from room temperature to high temperatures.

On the contrary, if a material with a refractive index of 1.44 is used at room temperature, the refractive index of the material will increase when the ambient temperature becomes low, so the power pt will suddenly increase and the temperature will decrease. Detected. That is, it functions as a temperature sensor on the low temperature side. In the above method, when the temperature exceeds a certain set point from normal temperature to the high temperature side or from normal temperature to the low temperature side, the output power changes to h.
This is temperature sensing that takes advantage of rapid changes. On the other hand, in FIG. 3, the refractive index varies by about 1.
In the range of 38 to 1.43, the transmitted light Pl changes almost linearly with respect to the refractive index. Therefore, if we select a material whose refractive index changes within this range due to temperature changes and which has the median value of this refractive index range at room temperature, the power of transmitted light P
By monitoring i, sensing is possible in a temperature range beyond room temperature. Materials 7 that can be used here include fluororesins with relatively low refractive index values (1.3 to 1.42) and relatively high refractive index values (1.46 to 1.42).
1.51), cellulose-derived resins such as ethyl cellulose and acetate fibers, and polyethylene. The above embodiment is a temperature monitoring method by detecting only the power of transmitted light passing through an optical coupling section.

The above method is the principle of the temperature monitoring method using a small-core optical fiber cable with a built-in temperature sensor according to the present invention. Practically speaking, a known method of monitoring backscattered light at one end is more effective than observing changes in transmitted light.

FIG. 4 is a diagram showing an embodiment for explaining a method of monitoring power changes at one end using backscattered light,
a is the first core, 1b is the second core, 2 is common to the two cores, 3 is a multi-core optical fiber including two cores, 7 is a plastic material whose refractive index is temperature dependent, 8 is a plastic material whose refractive index is temperature dependent. A laser light source, 9 a light directional coupler, 10 a light receiver, 11 an amplification/processing device, 12 a waveform display device,
8 to 12 together constitute an optical pulse tester 13. As shown in FIG. 3, the combined light P2 has a larger power compared to the transmitted light Pl, and has a smaller dependence on the refractive index. Therefore,
As shown in FIG. 4, this power P2 is used for optical signal communication. That is, the optical signal incident on the core 1a is coupled to the core 1b at the optical coupling section 6, and the optical signal that enters the core 1a after the complete coupling section is
The combined light propagating through b is detected as the main signal. On the other hand, due to the symmetry of the structure of the coupling part, the optical coupling characteristics at the coupling part when the optical pulse PsO is input from the core 1b for temperature detection are similar to those when the optical power PO is input from the core 1a. It's the same. That is, the incident light pulse PsO is divided into the transmitted light Pggl (propagated through the core 1b) and the coupled light Pggl at the optical coupling part.
d (propagates through core 1a). Here, the transmitted light Pa
l changes depending on the change in the refractive index of the material 7 due to the symmetry described above. Along with this, the directional coupler 9 connects the light receiver 1.
The reflected light P ml' incident on 0 also changes, causing a level change in the observed waveform.

In this way, the optical pulse tester 13 measures changes in the level of the detected waveform of Rayleigh backscattered light at the optical coupling section due to temperature changes.
By observing the temperature using , it is possible to detect the temperature around the optical coupling part in real time without affecting the communication line. With the above sensing method, the regular signal line and the sensing line can be set up in the same optical fiber, so there is no need to provide another fiber exclusively for sensing, and the maintenance system can be configured economically.

(Effects of the Invention) As explained above, according to the optical fiber cable with a small number of cores with a built-in temperature sensor according to the present invention, the cable can be constructed with high sensing accuracy and at a low cost. Further, according to the temperature monitoring method of the present invention, the temperature detection section can be easily manufactured on-site, can accurately measure temperature over a wide range, and can perform sensing without affecting the communication line used. Therefore, even after the cable has been constructed, it can be easily manufactured at a required location, and a track maintenance system that can economically detect temperature can be configured. Further, the optical fiber used in the present invention can be a commonly used quartz fiber, and there is no need to use a special fiber for temperature detection that uses Raman amplification.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a central optical fiber cable with a built-in temperature sensor according to the present invention, FIG. 2 is a cross-sectional view showing a sensor section according to the present invention, and FIG. FIG. 4 is a diagram showing the experimental results of measuring the refractive index dependence of the output power of the coupled light, and FIG. 4 is a diagram showing an embodiment of the temperature monitoring method of the present invention. la, lb...Core 2...Clad 3...Multi-core optical fiber 4...Plastic coating 5...Sheath 6...Piconical tapered portion 7...Refractive index is temperature dependent Material 8... Laser light source 9... Optical directional coupler 10... Light receiver 11... Amplification/processing device 12... Waveform display device 13... Optical pulse tester Patent applicant Nippon Telegraph and Telephone Corporation

Claims (4)

[Claims] (1) A small-core optical fiber containing at least one multi-core optical fiber consisting of a multi-core optical fiber having a plurality of cores for transmitting optical signals, the cladding of which has a shape that commonly surrounds the plurality of cores. In the fiber cable, the multi-core optical fiber core is provided with an optical coupling part at a small length at any location in the longitudinal direction, and the optical coupling part is covered with a material whose refractive index changes depending on the temperature. A small-core optical fiber cable with a built-in temperature sensor. (2) The cross-sectional outer circumferential shape of the multi-core optical fiber is such that a plurality of single-core optical fibers with a circular core and a circular cladding are bundled in parallel, and the circumscribed contact lines of the single-core optical fibers are fused to each other, and the non-contact surface The small-core optical fiber cable with a built-in temperature sensor according to claim 1, wherein the cores remain substantially in their original shape, and the adjacent cores are located at substantially equal intervals. (3) A small-core optical fiber having a plurality of cores for transmitting optical signals, the cladding of which accommodates at least one multi-core optical fiber consisting of a multi-core optical fiber having a shape that commonly surrounds the plurality of cores. An optical fiber in which an optical coupling part is provided in the multi-core optical fiber core at any location in the longitudinal direction of the fiber cable, and a part is coated around the coupling part with a material whose refractive index changes depending on temperature. In a cable, a communication optical signal is inputted into one core of a multi-core optical fiber at one end of the cable, and the optical signal is coupled to other multi-core cores at the optical coupling part, so that the output light can be separated and extracted. A temperature monitoring method characterized in that a temperature change is detected from a change in the intensity of the emitted light from the same core as the core into which the communication optical signal is input. (4) A small-core optical fiber containing at least one multi-core optical fiber consisting of a multi-core optical fiber having a plurality of cores for transmitting optical signals, the cladding of which has a shape that commonly surrounds the plurality of cores. An optical fiber in which an optical coupling part is provided in the multi-core optical fiber core at any location in the longitudinal direction of the fiber cable, and a part is coated around the coupling part with a material whose refractive index changes depending on temperature. In the cable, a communication optical signal is input into one core of the multi-core optical fiber at one end of the cable,
A temperature detection optical pulse is input to a core different from the core into which the optical signal is input at the same end, and the intensity of the backscattered light returning from the core is detected, and the refractive index change of the coating material due to temperature change is detected. A temperature monitoring method characterized in that a temperature change is detected from a change in the intensity of backscattered light returning from the optical coupling section.