JPS6258102A - Twist detector for optical fiber - Google Patents

Abstract

PURPOSE:To provide the titled detector having a simple structure, easy to manufacture and capable of detecting a twist with high sensitivity, by utilizing two constant polarizing optical fiber fused and connected so that mutually different double refraction axes coincide with each other. CONSTITUTION:Constant polarizing optical fibers 1, 2 are abutted through fixing jigs 4, 5 so that double refraction axes respectively coincide at a fusion connection part 3. The laser beam from a laser oscillator 61 is condensed by a lens 64 through a phase compensation plate 62 and a polarizer 63 to be incident to the optical fiber 1. At this time, the polarizer 63 is rotated so as to allow linear polarized beam to be incident to the double refraction axes. Next, an analyzer 72 is rotated to obtain the ratio of the max. value and min. value of emitted beam, that is, crosstalk. Hereupon, a twist is applied to the part to be twisted between the fixing jigs 4, 5 and, because a polarizing surface rotates when the angular shift of the double refraction axes was generated, the crosstalk increases. There is constant relation between the increase quantity of the crosstalk and the angular shift of the double refraction axes. Then, by measuring the increase quantity of the crosstalk, the quantity of angular shift can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a detector that uses a constant polarization optical fiber to detect minute amounts of twist and rotational deviation.

2. Description of the Related Art Conventionally, torsion detectors constructed using resistance gauges have been mainly used.

On the other hand, as optical fibers, only those that detect temperature and pressure are known, and those that detect twisting are not known.

Problems to be Solved by the Invention Conventional torsion detectors using resistance gauges have complicated structures, are not easy to manufacture, and have poor detection sensitivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a torsion detector that is simple in structure and easy to manufacture, and has high detection sensitivity by using a constant polarization optical fiber.

Means for Solving the Problems The optical fiber torsion detector according to the present invention includes a twisted means to which two polarization-controlled optical fibers are fusion-spliced so that their different birefringence axes coincide with each other. , means for exciting linearly polarized light in one birefringence axis of one of the polarization constant optical fibers, and means for measuring a crosstalk change of light emitted from the other polarization constant optical fiber via the fusion splice. Consisting of

When the vicinity of the fusion spliced portion of the two polarization constant optical fibers of the torsion means is twisted, the state in which the mutually different birefringence axes are made to coincide changes, causing axis misalignment. When this angular shift of the birefringence axis occurs, the plane of polarization rotates,
Crosstalk increases. The increase in crosstalk corresponds to the angular shift of the birefringence axis. Therefore, the amount of twist is detected by measuring the crosstalk.

Embodiment In FIG. 1, a polarization constant optical fiber 1 and a polarization constant optical fiber 2 are fusion-spliced at a point 3.

Reference numeral 4.5 denotes fixtures for fixing the polarization-constant optical fibers 1 and 2, respectively. The fixture 1 is fixed so as not to rotate, and the fixture 2 is rotated. The area between fixture 1 and fixture 2 is the part to which twisting is applied.

In the fusion splicing section 3, the constant polarization optical fiber 1 and the constant polarization optical fiber 2 are butted against each other so that their different birefringence axes coincide with each other. The end faces of the fixed and polarized optical fiber 1 and the end faces of the fixed polarized optical fiber 2 are shown in FIGS. 2 and 3.
As shown in FIG. 4, the polarization-controlled optical fiber 1
so that the birefringence axis They are butted together and fusion spliced. In addition, in these Figures 2 and 3, 11.21 is the core, 12.22 is the cladding,
13.13 and 23.23 are stress applying parts provided in the cladding.

When twisting is applied, the state in which the different birefringence axes coincide with each other as described above is shifted, and an angular deviation φ (deg) of the birefringence axes occurs as shown in FIG. 4.

Linearly polarized light is input into one end of the polarization-constant optical fiber 1 by an input system 6 along one birefringence axis. That is, the laser beam from the laser oscillator 61 passes through the phase compensator 62 and the polarizer 63, is further focused by the lens 64, and is input into one end of the polarization-constant optical fiber 1. At this time, the polarizer 63 is rotated so that linearly polarized light is incident on one birefringence axis. Further, a light receiving system 7 is placed on the output end side of the polarization-constant optical fiber 2. This light receiving system 7 includes a lens 71
It consists of an analyzer 72 and a light receiver 73.

In the light receiving system 7, the analyzer 72 is rotated to obtain the maximum value P rnax and the minimum value P akin of the emitted light. Then, the crosstalk η is expressed as η=P wax/P min. Here, if twist is applied at the twisted part between the fixtures 4 and 5, and an angular shift φ (deg) of the birefringence axis as shown in Fig. 4 occurs, the plane of polarization will rotate, so the cross Although the talk increases, there is a relationship between the amount of increase in crosstalk and the angular shift φ of the birefringence axis: η(φ)−(φ=0), = 5in2φ. Therefore, the angular deviation amount φ can be detected by measuring the amount of increase in crosstalk.

In fact, when the fixed polarization optical fiber 1.2 was twisted with a distance of 1 m between the fixtures 4.5 and the change in crosstalk was measured, the results shown in FIG. 6 were obtained. From now on, 9
Crosstalk is approximately 1 with a twist amount of 0 [deg/ml]
0dB increase, so if the distance between fixed A4.5 is set to 1cm, the crosstalk will increase by about 10dB with a twist amount of only 0,9 [deg], which means that it is possible to detect extremely small twist amounts. Ru.

Furthermore, although the amount of twist θ [deg/m] does not directly correspond to the misalignment φ [deg] of the birefringent axis, the misalignment φ [deg] of the birefringent axis is estimated from the amount of increase in crosstalk. When the relationship with the amount θ [deg/m] was investigated, data as shown in FIG. 7 was obtained. From this Fig. 7, the axis deviation φ [deg] of the birefringence axis is 0 and θ< 1
80 [deg/ml (7) In the range, the twist amount θ[
deg/m].

In addition, as shown in FIG. 5, two optical fiber type polarizers 51.
52 may be orthogonally connected. In this case, since the optical fiber itself is a polarizer, the twisted part (fixture 4.5
In order to excite linearly polarized light to a constant polarization optical fiber between This can be done by injecting the In addition, since the change in the output light is directly a change in crosstalk, the analyzer 72 is also used at the output end as shown in Figure 1.
The amount of twist can be directly read by directly measuring the emitted light with the light receiver 54 without having to rotate it.

Effects of the Invention According to this invention, when two constant polarization optical fibers are fusion spliced so that their different birefringence axes coincide, the rotation of the plane of polarization due to twisting in the vicinity of the fusion splicing point is utilized. Since the amount of twist is detected by using the fusion splice, it is possible to obtain a highly sensitive and stable twist detector that is not affected by twist at locations other than the fusion splice points.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIGS. 2 and 3 are end views showing the end faces of each polarization-controlled optical fiber, and FIG.
The figure is a schematic diagram showing the butt state of two constant polarization optical fibers, Figure 5 is a schematic diagram of another embodiment, Figure 6 is a graph showing the relationship between twist amount and crosstalk, and Figure 7 is twist It is a graph showing the relationship between the amount and the axis deviation angle. 1.2... Constant polarization optical fiber 3... Fusion splicing part 4.5... Fixture 6...
・Incidence system 61 Laser oscillator 62... Phase compensation plate 63... Polarizer 64.71... Lens 7... Light receiving system 72... Analyzer 73
...Receiver 11.21...Core 12.22.
...Clad 13.23...Stress applying part 51.52...Optical fiber polarizer 53...Light source 54...Receiver agent
Patent attorney Yusuke Sato ” Mi J Hide Q Prison Note 5 Drama C Me Kiri F Quantity θEdg Side〕

Claims (1)

[Claims] (1) A twisting means to which a twist is applied, which consists of two polarization-controlled optical fibers that are fusion-spliced so that their different birefringence axes coincide; An optical fiber twist detector comprising means for exciting linearly polarized light and means for measuring crosstalk changes in light emitted from the other polarization-constant optical fiber via the fusion splice.