JPH0339689Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an optical fiber coil, and particularly to an optical fiber coil used as a sensor thereof.

BACKGROUND OF THE INVENTION At present, gyroscopes that detect rotational angular velocity are used for inertial navigation and attitude control of aircraft, ships, flying objects (missiles, rockets, etc.), automobiles, robots, and the like. By using this gyro, it is possible to obtain not only angular velocity but also data such as azimuth by integrating the angular velocity.

Gyroscopes are broadly divided into mechanical and optical types, but compared to the former mechanical type, the latter type (1) has no moving parts and is resistant to acceleration, (2) has a simple structure, and (2) has a simple structure. It has the following advantages: 3) short startup time, (4) high sensitivity, (5) high linearity, (6) low power consumption, and (7) high reliability, so it has been put into practical use in many fields in recent years. .

The ring laser gyro was first developed as a type of optical gyro. This ring laser gyroscope uses a triangular block of fused silica as the optical path.
Laser beams are oscillated in both left and right directions,
The angular velocity with respect to inertial space is determined by measuring the beat frequency of both laser beams caused by the optical path difference proportional to the angular velocity.

However, the ring laser gyroscope has the following problems.

Output at low angular velocity shows nonlinearity (lock-in development).

Causes output drift due to laser gas flow.

To stabilize the laser oscillation mode, thermal expansion,
It is necessary to control optical path length changes due to pressure changes and mechanical strain.

Of these, lock-in development (1) in particular has a big problem in that the frequency difference between the left and right laser beams becomes small in the low angular velocity region, causing mutual development and the beat frequency becoming 0, making it impossible to detect rotation. It is a point. This is because the optical loop itself that detects rotation is actively composed of a laser oscillator. Therefore, lock-in development will not occur if the light source is placed outside the light loop and is configured passively.

Therefore, with the recent progress in optical communication technology, optical fibers that have achieved low loss have attracted attention, and gyroscopes using optical fiber coils have been developed.
This fiber optic gyroscope has no moving parts and can be miniaturized. Furthermore, it has excellent minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and stability of scale factor. There is.

Examples of such optical fiber sensors include, for example, "Gearo Range T.G., Bucaro G.A. et al., ``Optical Fiber Sensor Technology'' I.
EE Journal of Quantum Electronics (Giallorenzi TG,
Bucaro JAet al. “Optical Fiber Sensor
Technology”，IEEE J.of Quantum
Electronics) QE−18 , No.4, pp626−662,
(1982) and Culshaw and IPGiles, Journal of Physics and Electronics Science Instruments.
“Fiber Optic Gyroscopes” J.Phys.E:Sci.
Instvrm.) 16 , pp5-15 (1983), Tsubokawa, Otsuka, "Optical Fiber Gyroscope" Laser Research, 11 ,
No. 12, pp. 889-902 (1983), etc., for details.

Figure 3 shows the basic optical system of an optical fiber gyro. The laser light emitted from light source 1 passes through beam splitter BS1, polarizer PL and spatial filter SF.
It becomes a single-mode polarized wave, enters the second beam splitter BS2, and is split into two directions there. The demultiplexed laser beams pass through the single mode optical fiber coil 2 clockwise and counterclockwise, respectively, and then return to the beam splitter BS.
2, passes through the spatial filter SF and the polarizing plate PL, is reflected by the beam splitter BS1, and enters the light receiver 3. After this, an electric circuit (not shown) detects the phase difference φ between the clockwise light and the counterclockwise light.
Furthermore, the angular velocity Ω of rotation is calculated.

Here, the relationship between the phase difference Δφ and the angular velocity Ω is as follows.

△φ=4π1a/cλΩ ...(1) However, 1: Length of optical fiber a: Radius of optical fiber coil c: Speed of light λ: Problem to be solved by wavelength The optical fiber coil 2 in Fig. 3 is generally a solenoid. Since the optical fiber forming the coil 2 is wound around the coil 2, one end of the optical fiber forming the coil 2 is located inside the coil 2, and the other end is located outside the coil 2, so there is no symmetry. That is, the laser light passing through the optical fiber enters from the outside of the coil 2 and exits from the inside, or enters from the inside and exits from the outside. Therefore, when affected by external temperature changes,
The temperature of the optical fiber has non-uniform fluctuations along its length, and the optical path difference between the clockwise and counterclockwise lights of the coil varies, resulting in output drift.

This problem becomes more serious as the optical fiber gyroscope becomes smaller and more sensitive. This is because, as can be seen from equation (1) above, in order to increase the sensitivity, it is necessary to increase the optical fiber length 1, and in order to reduce the size, it is necessary to decrease the optical fiber coil radius a. . To meet these two requirements, the optical fiber coil must be wound thickly and in multiple layers.
As the coil winding layer becomes thicker in this way, the temperature difference between the inside and outside of the layer increases.

Regarding this development, see, for example, M. Day. ``Thermally Induced Nonreciprocity in Optical Fiber Interferometers'' Applied Optical (MDShupe: Thermally Induced
Nonreciprocity in the Fiber−Optic
Interferometer, Appl.Opt.) 19-5. pp654/655
(1980).

Incidentally, temperature fluctuations that are symmetrical about the center of the optical fiber have the same effect on the clockwise and counterclockwise lights, so the optical path difference between them does not change, and no output drift occurs. Therefore, one countermeasure is to wind the coil symmetrically about the center of the optical fiber.

Regarding how to wind this type of coil, R. A. RABergh “All-fiber Gyroscope with Optical Kerr Effect Correction” PhD Dissertation, Stanford University (RABergh: “All-fiber Gyroscope”
with Optical Kerr Effect Compensation”，ph.
(Doctor Report Stanford Univ.) (1983) P. 74, and cross-sectional views of coils based on this proposal are shown in Figures 4a and b. These coils are made by bending the optical fiber in two at the center M.
is located at the innermost part of the coil, and two optical fibers (indicated by black and white circles) are wound together at the same time, and both ends S and T of the optical fiber are located at the outermost part of the coil. Furthermore, the fourth
The coil in Figure a is wound in such a way that the half of the optical fiber indicated by the black circle is always outside the half of the optical fiber indicated by the white circle. In each case, the optical fibers indicated by black circles and the optical fibers indicated by white circles are wound in opposite positions. Therefore, both coils are nearly symmetrical compared to the conventional one, especially the coil in Fig. 4b.
In each round, among the optical fibers indicated by black circles and white circles, the outer optical fibers are more affected by temperature fluctuations in the outside world than the inner optical fibers, but in the next round, the optical fibers indicated by black circles and white circles Since the positions of the optical fibers swapped, the optical fibers that were greatly affected in the previous round will be affected less in this round, and in this way, the influence of temperature fluctuations on both the optical fibers in the black circle and the white circle each time they go through multiple rounds is reduced. The sums are almost equal.

However, these coils are only nearly symmetrical with respect to the center M of the optical fiber, and do not have perfect symmetry, so they have problems such as residual noise.

The object of the present invention is to provide an optical fiber coil that has perfect symmetry about the center of the optical fiber and does not suffer from output drift due to temperature fluctuations.

Means for Solving the Problems In other words, the optical fiber coil of the present invention has an optical fiber coil wound around a bobbin in both left and right directions with the midpoint of its entire length as a reference, and intersecting each other every turn. The bobbin is symmetrical about the midpoint, and a plurality of parallel grooves are formed on a part of the outer surface of the bobbin, each having a depth approximately equal to the diameter of the optical fiber. When the strands are wound around the bobbin and crossed, the inner parts of the crossed wires are accommodated in the grooves.

In a preferred embodiment of the present invention, similar grooves are provided in a plurality of cylindrical bobbins with different radii, and the optical fiber is first wound on the bobbin with the smallest radius as described above, and then on the outside of the bobbin with the smallest radius. A multi-layered optical fiber coil may be obtained by wrapping a bobbin with a smaller radius and winding the continuation of the optical fiber wire in the same manner, and in this way winding the optical fiber wire sequentially up to the bobbin with a larger radius.

Function First, the method of winding the optical fiber coil according to the present invention will be explained with reference to FIGS. 5 and 6.

The midpoint 41 of the entire length of the optical fiber 4 is brought into contact with the side surface of the bobbin 5. At this time, if the total length of the optical fiber 4 is long, it is sufficient to wind it onto a spare bobbin from both ends. Next, the optical fiber 4 is simultaneously wound around the bobbin 5 from both sides with the intermediate point 41 as the center. Figures 5a and 5b are a perspective view and a plan view of the coil at this time. Furthermore, after crossing the optical fibers 4 on both sides, they are wound a second time in the same manner (FIGS. 6a and 6b). By winding the optical fiber 4 in this manner, a coil having symmetry with respect to the midpoint 41 of the optical fiber 4 can be formed.

Thus, the optical fiber coil for an optical fiber coil of the present invention is completely symmetrical with respect to the midpoint 41 for each turn, and therefore the optical fiber as a whole is also symmetrical with respect to the midpoint 41. ing. Therefore, even if a temperature difference occurs partially in the optical fiber coil, the locally low-temperature or high-temperature portion has a right side portion and a left side portion of the same length from the midpoint 41 (however, only half the circumference of the maximum coil (with a corresponding length offset) are located adjacent to each other. Therefore, the locally low-temperature or high-temperature portions are located symmetrically around the midpoint 41 of the optical fiber, and have the same effect on both clockwise and counterclockwise light, canceling each other out and reducing the phase difference between the two. It does not appear in
No temperature drift occurs. Therefore, the optical fiber coil using the optical fiber coil of the present invention is
There is almost no temperature drift, allowing stable and highly accurate measurements.

However, as shown in FIGS. 6a and 6b, at the intersection A of the optical fibers 4, the optical fibers 4 bulge outward by the diameter of the outer optical fibers 4 and bend. Because of this bending, microbending occurs when the optical fiber is an optical fiber having only a primary coating. This microbending brings about a serious drawback in that it increases the transmission loss of laser light.

Therefore, as shown in FIGS. 7a and 7b, a groove with a depth equal to the diameter of the optical fiber 4 is formed in a part of the side surface of the bobbin 6.
1 is provided, and the optical fiber 4 is wound around the bobbin 6 in the above-described winding method, and when the inner fiber is placed in the groove 61 at the intersection of the optical fibers 4, the top view of the coil becomes as shown in FIG. It is possible to prevent microbending from occurring due to intersections.

In addition, in all intersections of optical fibers, if only one of the clockwise and counterclockwise parts is on the upper side,
There is a difference in the length of one circumference between the clockwise portion and the counterclockwise portion. Therefore, it is preferable that the clockwise portion and the counterclockwise portion are alternately placed on the upper side at the intersection.

Example Examples of the present invention will be described below.

FIGS. 1A, 1B, and 1C are a front view, a sectional view, and a plan view of a bobbin 7 used in an optical fiber coil for an optical fiber gyro according to an embodiment of the present invention. The bobbin 7 has a cylindrical shape with a thickness D and an outer diameter R, and a plurality of parallel grooves 71 with a pitch and a depth of d are provided on a part of the outer surface. The value d is equal to the diameter of the optical fiber wound around the bobbin 7.
Furthermore, it has the same shape as bobbin 7 in Fig. 1 and has a radius of R+D.
The bobbins 8 and 9 are sequentially set larger by the thickness and the diameter of the optical fiber, such as +d, R+2 (D+d), and R+3 (D+d).

Next, a method for forming the optical fiber coil of this example will be explained.

First, the optical fiber 4 having a diameter d is wound in only one layer around the bobbin 7 having the smallest radius in the manner shown in FIGS. 4 and 5. When the winding is completed, the next bobbin 8 is fitted on the outside thereof, and the rest of the optical fiber 4 is wound around the bobbin 8 in the same manner. By sequentially winding the optical fibers 4 around the bobbin 9 in this manner, a three-layer optical fiber coil whose plan view is shown in FIG. 2 is formed.

Furthermore, by stacking bobbins in the same manner, it is possible to form many layers of coils.

The implemented example was a core diameter of 7 μm and a cladding diameter.
125μm, primary coat outer diameter 400μm, length 200m
A 0.85 μm band single mode optical fiber was used, and the pitch and depth of the grooves on the bobbin were set to 400 μm.

Note that the innermost bobbin 7 does not need to be cylindrical, and may be cylindrical. Therefore, when forming a coil with only one layer, it is not necessary to form a cylindrical bobbin.

Effects of the invention As explained above, the optical fiber coil according to the invention is completely symmetrical with respect to the center of the optical fiber, so the optical path difference between clockwise light and counterclockwise light does not change at all even when affected by temperature changes. Therefore, no output drift occurs.

That is, by applying the optical fiber coil of the present invention, it is possible to realize an optical fiber coil with significantly improved stability and sensitivity.

[Brief explanation of the drawing]

1a, b, and c are a front view, a sectional view, and a plan view of a bobbin 7 used in an optical fiber coil for an optical fiber coil according to an embodiment of the present invention; FIG. 2 is a plan view of the embodiment; The figure shows the basic optical system of an optical fiber coil, FIG. 4 is an explanatory diagram showing a conventional method of winding an optical fiber coil, and FIGS. 5 to 8 are explanatory diagrams showing the principle of the present invention. Main reference numbers, 4... optical fibers, 5-9...
Bobbin, 41...middle point, 61, 71...groove.

Claims (1)

[Claims for Utility Model Registration] (1) In an optical fiber coil for an optical fiber gyro in which an optical fiber is wound around a bobbin,
The optical fiber wire is wound around the bobbin in both left and right directions with the midpoint of its entire length as a reference, crossing each other every turn so as to be symmetrical with respect to the midpoint, and the bobbin includes: , a plurality of parallel grooves having a depth approximately the same as the diameter of the optical fiber strand are formed in a part of the outer surface thereof, and when the optical fiber strand is wound around the bobbin and intersects, An optical fiber coil for an optical fiber gyroscope, characterized in that the intersecting inner portions are accommodated in the grooves. (2) The optical fiber coil for an optical fiber gyroscope according to claim 1, wherein the bobbin is cylindrical. (3) It has multiple cylindrical bobbins with different radii,
The above-mentioned grooves are provided in the same way on each bobbin,
First, the optical fiber wire is wound around the bobbin with the smallest radius in both left and right directions with the midpoint of its entire length as a reference, and is crossed every turn. The optical fiber wire is wound symmetrically so that when the optical fiber wire is wound around the bobbin and intersects, the intersecting inner part is accommodated in the groove, and the outer part is wrapped with a wire having the next smallest radius. Cover the bobbin and wrap the rest of the optical fiber wire in the same way,
In this way, the optical fiber wire is sequentially wound around bobbins with larger radii to obtain a multilayer optical fiber coil. Optical fiber coil for optical fiber coils.