JP2549668B2 - Optical fiber coil for sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical fiber coil for a sensor, and more specifically, to an optical fiber coil for a sensor in which a portion used as a sensor portion is wound in a coil shape. .

<Prior arts and problems to be solved by the invention> Conventionally, as a sensor used for various applications, high sensitivity, small size and light weight, good environmental resistance, etc. Fiber optic sensors having the are being used.

The optical fiber sensor includes a physical quantity conversion element for converting a change in a physical quantity into a change in light in addition to an optical fiber and a photodetector, and a part of the optical fiber as a physical quantity conversion element. It is roughly divided into those that are configured to function as.

Among these, in the configuration, it is considered to increase the physical quantity conversion efficiency by forming the portion functioning as the physical quantity conversion element into a coil shape. For example, in an optical fiber gyroscope, in order to improve the sensitivity, The optical fiber is wound into a coil to increase the area surrounded by the fiber. However, in the state where the optical fiber is wound in a coil shape and moreover in a multi-layer,
It is known that the temperature of each part of the optical fiber becomes different from each other, resulting in a decrease in measurement accuracy (“Fiber resonatorgyroscope: sensitivity and t
hermal nonreciprocity "David M. Shupe, APPLIED OPTICS
/ See Vol.20, No.2 / 15January1981). In order to reduce the influence of such a temperature difference, a method of symmetrically winding the optical fiber has been considered. As shown in FIG. 3, the optical fiber is wound in a coil shape from the middle portion of the entire length of the optical fiber. The optical fibers are alternately coiled with the winding start as a reference for every one layer or every two layers when the winding is started. Specifically, as shown in FIG. 4, an optical fiber having a desired length is wound around two coils so as to be equal in length to each other, and then these coils are used as the supply side, and It is created by replacing the coils on the supply side for each.

When the optical fiber is symmetrically wound in this way, the clockwise light and the counterclockwise light propagating through the optical fiber coil must propagate in the portions spatially close to each other at the same time. Even if the refractive index of the optical fiber changes as a result of non-uniform temperature fluctuation of the optical fiber, the above two lights propagate almost the same optical path length, greatly reducing the measurement accuracy due to the temperature fluctuation. The width can be suppressed.

However, in the above-described coil wound symmetrically, it is necessary to temporarily create two coils, which not only complicates the process as a whole, but also has a problem that the winding method is complicated. Because the optical fiber jumps over only one or two layers at the end of each layer,
There is a problem that the optical fiber is twisted and distorted to deteriorate the light propagation characteristics. More specifically, when the optical fiber is twisted and distorted, not only the transmission loss increases, but also when the polarization maintaining fiber is used as the optical fiber, the polarization maintaining characteristic deteriorates and crosstalk occurs. Will increase. Further, since crosstalk directly affects the measurement accuracy in an optical fiber gyroscope or the like that performs measurement based on light interference, it cannot be ignored at all.

<Object of the Invention> The present invention has been made in view of the above problems, and provides an optical fiber coil for a sensor, which can simplify the manufacturing process and can maintain high measurement accuracy. It is an object.

<Means for Solving the Problems> An optical fiber coil for a sensor according to the present invention for achieving the above object is provided with a winding frame having high thermal conductivity and an optical fiber wound around the winding frame in a multilayer coil shape. And a metal heat conducting layer having high heat conductivity interposed between the layers of the optical fiber, and the metal heat conducting layer and the winding frame are in contact with each other so as to be electrically conducted through the flange. are doing.

However, the heat conductive layer is preferably a metal thin film layer, and particularly preferably a copper foil or an aluminum foil.

Further, it is preferable that the optical fiber is wound around a winding frame and that the winding frame is made of a material having high thermal conductivity.

<Operation> In the case of the optical fiber coil for a sensor having the above configuration, the center portion of the optical fiber is wound in a multilayer coil shape, and a heat conductive layer having a high thermal conductivity is interposed between layers. The temperature difference between the optical fibers that make up the
It is possible to reduce variations in light propagation characteristics. Therefore, the physical quantity detection sensitivity can be increased by causing the portion wound in the multilayer coil shape to function as the physical quantity conversion element.

And, even when the heat conduction layer is a metal thin film layer,
Particularly when the metal thin film is a copper foil or an aluminum foil, the same action as above can be achieved.

Further, when the optical fiber is wound around a winding frame and the winding frame is formed of a material having a high thermal conductivity, the light constituting each layer is formed by both the heat conductive layer and the winding frame. It is possible to further reduce the temperature difference between the fibers and further reduce the variation in the light propagation characteristics. Therefore,
The physical quantity detection sensitivity can be further increased by causing the portion wound in the multilayer coil shape to function as the physical quantity conversion element.

More specifically, regarding the case where the temperature T of a 1 m-long portion near one end of an optical fiber having a length L changes by α = dT / dt, the phase of light propagating inside the optical fiber The change dφ / dt is given by dφ / dt = (dT / dt) (dφ / dT).

Here, dφ / dT is 315 rad / ° C for 1 m of optical fiber length.
Therefore, for example, if the temperature change rate α is 1 ° C./sec, the phase change dφ / dt is 315 rad / sec.

Further, the difference τ between the times when the clockwise light and the counterclockwise light propagates in the 1 m portion is τ = nL / c (where n is the refractive index of the fiber and c is the speed of light in vacuum). , L = 200 m, τ = 1 × 10 ⁻⁶ . Therefore, the phase φ is φ = (dφ / dt) τ = 3.15 × 10 ⁻⁴ rad = 0.018 deg.

Furthermore, considering an optical fiber gyroscope with a light source wavelength λ = 0.83 × 10 ^-6 m and a coil diameter of 50 mm, the rotational angular velocity Ω
Since the relationship between and the Zagnec phase difference φs is given by φs = 0.25Ω, the angular velocity detection performance is Ω = 0.07deg / sec.

That is, if the temperature change rate α is 1 ° C./sec, the angular velocity detection performance will drop to Ω = 0.07 deg / sec.

However, in the present invention, since the winding frame and the metal heat conducting layer, both of which have high thermal conductivity, are in contact with each other so as to be electrically conducted, the temperature is evenly distributed between the heat conducting layers via the winding frame. In addition, the temperature of the optical fiber close to the winding frame and the temperature of the optical fiber distant from the winding frame become uniform. As a result, the temperature distribution becomes uniform over the entire coil-constituting portion of the optical fiber. As a result, it is possible to reduce the temperature variation as a whole, reduce the phase difference φ that acts as an error, and improve the measurement accuracy.

Also, when used as an electrostrictive voltage sensor, a pressure sensor, an acoustic sensor, etc., the measurement accuracy can be improved as in the case of the optical fiber gyroscope.

<Example> Hereinafter, an example will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view showing the structure of an optical fiber coil for a sensor according to the present invention, in which an optical fiber (2) is wound around a winding frame (1) to form a multi-layer coil and is wound. A copper foil (3) is wound around each layer of the optical fiber (2).

More specifically, the winding frame (1) is entirely made of copper, and the optical fiber (2) is wound in a multilayer coil shape between both flanges (11) of the winding frame (1). It The winding state of the optical fiber (2) is different from the conventional symmetrical winding, and the optical fiber is only sequentially wound in one direction from one end side, and the winding operation is simple as a whole. Has been converted. Further, the copper foil (3) is wound around the outer circumference of the optical fiber layer every time the optical fiber (2) is wound by one layer, and both edges are formed on the both flanges (11). It is formed to have a contact width.

In the optical fiber coil having the above structure, the copper foil (3) wound between the optical fiber layers and the winding frame (1).
The heat is conducted therethrough, and the temperature difference between the outer optical fiber layer and the inner optical fiber layer of the copper foil (3) is remarkably reduced over the entire range.

Therefore, by causing the portion wound in the multilayer coil shape to function as the physical quantity conversion element, the phase difference acting as an error can be significantly reduced, and the physical quantity measurement accuracy can be significantly improved.

FIG. 2 is a schematic view showing a reference example, and the point different from the above-mentioned embodiment is that the optical fiber (2) is wound around the reel (1) having no flange. Therefore, in the case of this reference example, heat conduction through the bobbin (1) is not performed at all, and the effect of reducing the temperature difference is reduced to some extent. Therefore, the physical quantity measurement accuracy can be improved.

The present invention is not limited to the above-described embodiment, and other metal foil such as aluminum foil can be used instead of the copper foil (3). It is possible to form a large number of grooves to increase the contact area with the optical fiber, and it is also possible to provide a flange with a slit for passing the optical fiber between both flanges. Various design changes can be made within the scope of the present invention.

<Effects of the Invention> As described above, according to the present invention, an optical fiber is wound in a multilayer coil shape so as to function as a physical quantity conversion element, and a winding frame having high heat conductivity and a metal heat conduction layer are provided. In addition, since the heat conductive layer and the winding frame are in contact with each other so as to be electrically conducted, the temperature distribution becomes uniform over the entire coil constituent portion of the optical fiber. Therefore, the unbalanced temperature distribution in the case of the multi-layer coil, which has been a problem in the past, can be surely eliminated, and the variation in the temperature of the entire optical fiber coil can be remarkably reduced, and the physical quantity measurement accuracy can be remarkably improved. It has the unique effect of being able to.

[Brief description of drawings]

1 is a schematic view showing an embodiment of an optical fiber coil for a sensor of the present invention, FIG. 2 is a schematic view showing a reference example of an optical fiber coil for a sensor, and FIG. 3 is a conventional optical fiber coil for a sensor. FIG. 4 is a schematic diagram showing the method of manufacturing a conventional optical fiber coil for a sensor. (1) …… Reel, (2) …… Optical fiber, (3) …… Copper foil

Claims (1)

(57) [Claims] 1. A winding frame having high heat conductivity, an optical fiber wound in a multilayer coil shape on the winding frame, and a metallic heat conducting layer having high heat conductivity interposed between respective layers of the optical fiber. An optical fiber coil for a sensor, comprising: and a metallic heat conducting layer and a winding frame, which are in contact with each other via a flange so as to be electrically conducted.