JPS59197829A - Optical fiber vibration sensor - Google Patents

Abstract

PURPOSE:To detect a minute vibration whose amplitude is small by placing two semicylindrical refractive index distribution type lenses having a meridian surface so that meridian surfaces are opposed to each other in a distance which is below a distance as long as the wavelength of a light. CONSTITUTION:A light which is made incident to a semicylindrical refractive index distribution type lens 5 from an incident optical fiber 3 reaches a meridian surface of the semicylindrical refractive index distribution type lens 5. On this surface, the light is reflected, and made incident to an emitting optical fiber installed at a position of an image forming relation to an optical fiber 1. When a vibration 2 is applied to an exciting part 7, a distance between two semicylindrical refractive index distribution type lenses 5, 6 is varied, therefore, a reflection factor in the meridian surface of the semicylindrical refractive index distribution type lens 5 is varied in accordance with the vibration. Therefore, the coupling efficiency between the incident optical fiber 3 and the emitting optical fiber 4 is varied, and a light for propagating the emitting optical fiber 4 receives an optical intensity variation. An optical signal which has been subjected to an intensity modulation is detected by a photodetector and brought to a signal processing, by which the vibration is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber transmission sensor that detects vibrations using an optical fiber or a detection section added to the optical fiber.

This conventional glaze device has a configuration as shown in FIG. In Figure 1, two optical fibers (1
The light incident from the end face of the optical fiber (1) propagates throughout the optical fiber (1) and is guided from one end face of the optical fiber to the photodetector. Vibration (2) is applied to the optical fiber (1).

When vibration (2) is applied to the optical fiber (1), the central axis of the optical fiber (11) curves in accordance with the vibration (2+), an fCC shim is generated, the refractive index changes due to the photoelastic effect, and the propagating light changes. This causes changes in phase and rotation of the plane of polarization.

The transmission loss fluctuates, resulting in an optical intensity modulated signal. Full detection is achieved by detecting this signal with a photodetector.

However, in a motion sensor that utilizes such a photoelastic effect, in order for the optical signal to undergo intensity modulation of several percent, the layer width must be subjected to vibrations of several fl mL.

Therefore, this type of sensor has the disadvantage that it cannot detect minute vibrations whose width is lJ-. Also.

Fluctuations in the phase and rotation of the plane of polarization of light propagating through optical fibers are highly sensitive to changes in hot water temperature.

For this reason, there was a drawback of low reliability.

In order to solve these drawbacks, the present invention is characterized in that two semi-cylindrical graded refractive index lenses each having a meridional plane are arranged so that the meridional planes are aligned with each other at a distance of less than the wavelength of light. The purpose is to detect minute vibrations with small amplitude.

The present invention will be described in detail below based on two drawings.

FIG. 2 is a perspective view showing an embodiment of the optical fiber vibration sensor according to the present invention, and FIGS. 2 and 3 are cross-sectional views of FIG. 2. FIG. 4 is a diagram illustrating the entire Goose-Hendien effect. (3) is the input optical fiber (4) is the output optical fiber, (51F6) is a semi-cylindrical graded index lens with a meridional plane, (7) is the addition part, (8) is the trajectory of the ray, (
9) is a medium with a refractive index n1, 00) is a medium with a refractive index n2, n
, an is a medium H having a refractive index n2.

In Figures 2 and 4, medium 1 (9) is shown in Figure 4 (a).
) is larger than the refractive index n2 of the medium ■00), when a ray of light enters the boundary surface from the W, quality 1 (9) side at an angle of incidence exceeding the critical angle, a part of the incident light is medium ffQ
The light immerses into the medium I(9) for several lengths, and is totally reflected again into the medium I(9). However, as in (bJ) in Fig. 4, medium II (
10) If there exists a medium Imf that is as thin as the wavelength and has a refractive index of nl, part of the light energy will enter the medium. This is the goosehennen effect. At this time, if the thickness of the medium ■α■ is thick, the leakage of light energy into the medium plate αυ (1 small, medium IIQO) is thin, the leakage of energy will be large. For this reason, medium 1 (9
) and the medium ■00) at the interface.

Depends on the thickness of the medium n (10). Such a Gooshenschen effect occurs when the thickness of the medium n (10) is about the wavelength of light.

Next, the operating principle of the optical fiber and motion sensor according to the present invention will be explained with reference to FIG.

If the light ray that enters the semi-cylindrical gradient index lens (5) from the input optical fiber (3) follows the trajectory shown in Fig. 3,
It reaches the meridian plane of the semi-cylindrical gradient index lens (5). In this plane, the light rays are reflected and the optical fiber (1)
The light enters an output optical fiber (4) installed at a position in relation to image formation. When the vibration (2) is applied to the vibrating part (7), two semi-cylindrical gradient index lenses +51. (6) varies, so the reflectance of the semi-cylindrical gradient index lens (5) on the meridian plane varies depending on the distance. Therefore, 2 input optical fibers < +3) and output optical fibers (4)
The coupling efficiency between the two changes, and the light propagating through the output optical fiber (4) undergoes light intensity fluctuations. Vibration is detected by detecting the intensity-modulated optical signal with a photodetector and processing the signal.

By the way, the 2 dozen pendien effect is caused by the Fi quality I1. (10) Thickness 1 The distance between the two semi-cylindrical gradient index lenses (5) (61) in the present invention,
Since this is an effect when the amplitude is about the wavelength of light, the optical fiber magnetic sensor according to the present invention has the advantage of being able to detect minute vibrations whose amplitude is about the wavelength of light. Ushita.

The Goose-Henryon effect has the advantage of producing highly reliable sensors because it is not affected by temperature or counterfeiting.

In the above, the case where the input optical fiber and the output optical fiber are installed at a position where the light from the optical fiber forms an image with the meridian plane of the semi-cylindrical gradient index lens as the reflection surface is explained. The present invention is not limited to this, and may be used in cases where a beam-firing optical fiber is installed at another position in an image-forming relationship with respect to a beam-forming optical fiber.

Also, 9 and above explained the case of a vibration sensor, but 2
The present invention is not limited to this, but it is possible to measure displacement by converting fluctuations in physical quantities to be measured such as displacement and pressure into fluctuations in the distance between semi-cylindrical gradient index lenses.

It may also be used as a pressure sensor and other sensors.

As described above, in the optical fiber vibration sensor according to the present invention, f! , 1 can be used to detect tracing motion, and has the advantage of being able to detect minute vibrations whose amplitude is about the wavelength of light.

It has the advantage of high reliability.

[Brief explanation of the drawing]

Figure 1 shows a conventional optical fiber dynamic sensor;
Figure I'i is a perspective view showing an embodiment of the present invention. FIG. 3 is a diagram of FIG. 2 illustrating the operating principle of the present invention. In the figure, (1) is an optical fiber, (2) is a vibration, (3) is an input optical fiber, [4] i-1: an output optical fiber, (5)
) and (6) a semi-cylindrical gradient index lens with the side surface facing the meridian plane, (7) a curved part, (8) a light ray trace, (9)
is a medium 1p whose refractive index is nl [Iol has a refractive index n2
medium II, (Ill is I whose refractive index is nl
2!11: Quality ■. In the two figures, the same or similar parts are designated by the same reference numerals. Agent Masuo Oiwa Figure 2 Figure 4 ((L) Figure 4 (b)

Claims (1)

[Claims] In an optical fiber vibration sensor that performs full detection using an optical fiber or a detection unit attached to an optical fiber, two semi-cylindrical graded index lenses with meridian planes as sides, an input optical fiber, an output optical fiber, and an external The stationary total receiver from
Two cylindrical/FFL graded index lenses are arranged at a distance of less than the wavelength of light so that their meridional planes are aligned with each other, and the output optical fiber is placed in an imaging relationship with the input optical fiber. An optical fiber peristaltic sensor that is installed at a certain position and has an 8A structure in which the distance between two semi-cylindrical gradient index lenses changes in response to external vibrations.