JPS63273044A - Refractive index detecting sensor - Google Patents

Abstract

PURPOSE:To easily obtain detecting sensitivity characteristics in the neighborhood of a refractive index desired to be obtained by forming the end face of an light emitting optical fiber so as to have an angle smaller than a right angle with respect to an axial direction, leading emitted light to a light receiving optical fiber by providing a reflector for reflecting the emitted light once or more and detecting the intensity of reflected light by the difference of a medium to be measured. CONSTITUTION:A sensor is constructed such that, for example, light emitted from a light emitting side optical fiber 10 with an obliquely cut end face is reflected from a reflecting surface 18 and incident upon a light receiving side optical fiber 20 with a rectangularly formed end face to be led to a photodetector. The light is emitted in an oblique direction with respect to an optical axis to be expanded whereby an optical path difference after a reflection is increased. Accordingly, when the angle of a reflector is set in accordance with a medium to be measured in advance even though the emitted light has a wide distribution, the reflected light can be received when the medium has a refractive index corresponding to the angle of the reflector. Since reflection characteristics are added other than an emitted light distribution when the refractive index of the medium is not aligned to last-said refractive index, a sensitivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a refractive index detection sensor. More specifically, the present invention relates to a sensor for detecting the refractive index of a medium to be measured, which utilizes the fact that light is refracted at a boundary surface depending on the refractive index of the medium.

(Prior art and problems to be solved by the invention) A conventional example will be described below with reference to the accompanying drawings.

As shown in FIG. 5 or 6, this type of sensor that has been used conventionally is an optical fiber sensor that detects and measures the refractive index of a medium, particularly a liquid or gas.
When the medium to be measured is placed in the vicinity of the sensor by processing it into a letter or helical shape, the bending loss of the optical fiber changes at the curved part. Measurements, etc. are being carried out. However, since optical fibers are originally intended for the transmission of light, they consist of a core section that is a light transmission section and a cladding section that serves to trap light. Now, when light enters the optical fiber at an aperture angle greater than or equal to the aperture angle, the light is emitted to the outside and the transmission is
. Conventional example. Refractive index detection sensors apply this principle, and detect changes in radiation loss, or bending loss, caused by the bending of the waveguide, which occurs when an optical fiber is intentionally bent and a different medium is interposed at the bend. By measuring, the refractive index of the medium is detected. However, refractive index detection using this method has the following drawbacks.

(1) It is necessary to make the radius of curvature of the optical fiber extremely small, and an optical fiber with a large diameter cannot be detected, so there is a limit to the amount of incident light.

(2) When an optical fiber is processed, it should be structured so that its processed state will not recover, or a material such as glass fiber that does not recover itself should be used. Therefore, it is difficult to process or maintain the bent state, and it is impossible to use other means than using a specific optical fiber.

(3) Since the refractive index of an optical fiber is usually 1.5, it is difficult to detect if the refractive index of the medium to be measured placed near the optical fiber is close to 1.5. Furthermore, since the detection sensitivity changes depending on the radius of curvature of the optical fiber, stable detection cannot always be obtained.

Therefore, it is impossible to particularly improve the sensitivity characteristics near the refractive index of the medium to be measured.

(4) Since the cladding layer is interposed between the light transmission section and the object, the refractive index of the medium to be measured cannot be directly detected, resulting in a decrease in sensitivity characteristics.

Furthermore, it is known that the end face of an optical fiber is cut diagonally with respect to the axial direction, and the emitted light is refracted at the boundary face, so a sensor for detecting the refractive index of the medium using this principle can be considered. The light emitted from the fiber propagates from the end face with a predetermined spread, so in order to receive the refracted light, the fiber must be a considerable distance away from the output end.
Furthermore, with the above configuration, the amount of light received at the light receiving end becomes small, and the sensitivity characteristics of the refractive index deteriorate. On the other hand, a SELFOC lens is installed on the end face of the optical fiber to make the emitted light into parallel light beams.
It is also possible to install optical elements such as spherical lenses and prisms, but these elements complicate the structure and change the refractive index due to differences in the medium to be measured, making it difficult for light to be refracted and degrading sensitivity characteristics. do.

In short, as described above, conventional optical fiber type refractive index sensors: (1) cannot easily obtain detection sensitivity characteristics near the refractive index of the desired medium;

(2) Processing work for the sensor is relatively difficult, and many types of optical fibers cannot be used, so a specific optical fiber must be used.

There were problems such as.

(Means and effects for solving the problem) The present invention utilizes the principle of refraction of light, and has a configuration in which the end face of the optical fiber on the outgoing light side is cut at a predetermined angle with respect to a plane perpendicular to the axial direction. The emitted light from the light emitting end is refracted by a medium existing around the light emitting end, and the refracted light is reflected more than - times on a separately provided reflective surface, and the reflected light is converted into the emitting side light. The problem can be easily solved by providing a refractive index detection sensor that is configured to receive light using an optical fiber whose end face is processed like a fiber or an optical fiber whose end face is formed perpendicular to the optical axis. can.

The light emitted from the optical fiber on the output side that has a predetermined angle with respect to the plane perpendicular to the axial direction is refracted by a medium existing around the light output end, and the refracted light is refracted one or more times by a separately provided reflective surface. The reflected light is guided to the light receiving section through the light receiving side optical fiber, and the refractive index of the medium to be measured is detected at the light receiving section.

(Examples) Examples according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an embodiment showing the overall structure of an optical fiber type refractive index detection sensor.

Reference numeral 1 denotes a board mounting bracket, which is a support member for the refractive index sensor. 2
is the outbound optical fiber. Reference numeral 3 denotes an optical fiber connector, and an optical fiber connector holding member 5 is attached to the outside thereof to form a connector portion. The emitted light reflecting metal fitting 7 and the connector cover portion are connected by the guide bin 6 . 4 is a return optical fiber.

The light emitted from the light emitting section passes through the outgoing optical fiber 2, is refracted at its end face, is reflected twice by the emitted light reflecting fitting 7, and the reflected light reaches the incoming optical fiber 4. If there is a medium with a refractive index nl near the emitted light reflecting fitting 7 whose refractive index has been adjusted to n1 in advance, a large amount of light reaches the return optical fiber 4, and the light passes through the return optical fiber 4. The light is received by the light receiving detector 30.

However, if a medium with a refractive index of n2 exists, the emitted light will be reflected twice and will not reach the return optical fiber, or even if it does reach the fiber, the incident angle of the fiber will be significantly different, so it will not be transmitted through the return fiber 4. Therefore, the light never reaches the light receiving part. The second embodiment is shown in FIG. 2, which is an output side fiber lO whose end face is cut obliquely with respect to the optical axis.
The optical path of the light B emitted from the optical fiber is bent by the first reflective surface 12 and the second reflective surface 14, and the reflected light is guided to the light-receiving fiber 16 whose end face is cut obliquely to the optical axis, as will be described later. The light reaches the light receiving detector 30. A third embodiment is shown in FIG. 3, in which the output side fiber 10 has an end face cut obliquely to the optical axis.
The light B emitted from the light receiving side fiber 2 is reflected by the reflecting surface 18 and bent to the side.
0 and is guided to the light receiving detector 30.

As in this embodiment, the end face of the light-receiving fiber 20 may be formed perpendicular to the optical axis.

Furthermore, the fourth embodiment is shown in FIG. 4, in which a single fiber 22 whose end face is cut obliquely with respect to the optical axis is commonly used as an output fiber and an input fiber. Light B emitted from the light source 24 is emitted from the end face of the optical fiber 22 formed obliquely with respect to the optical axis to the medium to be measured, enters the first reflecting surface 2B, is bent in any direction, and is connected to the optical fiber 22. The light B that is almost perpendicularly incident on the second reflective surface 2B, which is disposed in parallel and faces the first reflective surface 26, and simultaneously reflected on the second reflective surface 28 changes direction and travels backward on the outward path. The first reflective surface 26 again
, and is further refracted by the oblique end face of the optical fiber 22.
The light passes through the optical fiber 22, is reflected by a half mirror or splitter 32, and reaches the light receiving detector 30. Since the amount of light reaching the light receiving detector 30 changes depending on the magnitude of the refractive index of the medium to be measured, the refractive index of the medium to be measured can be determined from this, as in the previous embodiment.

(Function) According to the present invention, since the output end of the optical fiber is cut at a predetermined angle with respect to a plane perpendicular to the axial direction of the fiber, the output light from the optical fiber is refracted according to Snell's law of refraction. That is, nr 5in01 = n2 sin θ2n1. n2 is: The refractive index θ1,02 of each substance is: The angle of incidence and output light with respect to the normal line of each end face. Now, suppose the fiber cutting angle is 40'', and the numerical aperture N,
When using an optical fiber with A = 1.5, light within an axial tilt angle of the fiber of -15° to 15'' will propagate through the optical fiber.

When this light reaches the end face of the optical fiber and is emitted into a medium such as an air layer, the end face of the optical fiber is emitted from a surface inclined at 40 degrees with respect to the plane perpendicular to the axial direction. -0.7° to the cable axis direction
It emits with a spread of ~50° (see Figure 8 (A)), while Maim Beamc7) has a spread of 34.6
°.

Also, in the case of other media, such as water, instead of an air layer, the refractive index of water is n = 1.33, so the degree of spread of the emitted light is similarly -11.6° to 27.4°. (Figure 8 (
In the conventional method, in such a case, these emitted lights were directly detected, so the amount of change in the output light amount distribution of the optical fiber was measured, and the sensitivity characteristics due to the difference in refractive index were I couldn't get it. When light enters a reflective surface, it is reflected at an angle equal to the normal to the reflective surface.

Therefore, when two lights at different angles are reflected in the same normal direction, if the difference between the angles of the two lights is Δθ, the optical path difference after reflection becomes large.

By setting the angle and configuring a reflecting surface so that it can receive the reflected light after n times of reflection according to the refractive index of the object to be measured, it is possible to measure two objects with very similar refractive indexes. When a measurement medium is used, the refractive index of the medium to be measured can be measured as described above.

As explained above, according to the present invention, even if the distribution of light emitted from an optical fiber is wide, the angle of the reflector can be set in advance according to the refractive index of the specific medium to be measured. If it has that refractive index, the receiving optical fiber can receive the reflected light, but if it does not match that refractive index, the sensitivity is good because reflection characteristics are added to the light distribution of the emitted light. It becomes ゛.

Figure 7 shows the case where the cutting angle of the optical fiber, that is, the angle with the plane perpendicular to the axial direction, is 40° and the angle of the reflector is 62.3°. When the medium to be measured is air, the light is This shows that it is possible to transmit data inside.

Furthermore, FIG. 9 shows a case where the optical fiber is cut at an angle of 40' and the angle of the reflecting surface is 48 degrees, indicating that light can be transmitted when the medium to be measured is water.

(Effects) As explained in detail above, the refraction vehicle inspection/output sensor of the present invention has the following advantages: (1) Sensitivity characteristics near the refractive index to be measured can be freely changed.

(2) The structure is simple.

(3) There should be little variation between product lofts.

(4) It can be applied to all kinds of optical fibers, especially large-diameter fibers, so a large amount of light can be input.

It has the following characteristics and has the advantage that it can be applied to a wide range of applications, such as measuring the content of impurities in a medium to be measured, such as a liquid, detecting the liquid level, and detecting the type of liquid.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the optical refractive index detection sensor according to the present invention;
FIG. 2 is a route diagram showing the arrangement of fibers and reflective surfaces of an optical refractive index detection sensor according to an embodiment. FIG. 3 is a layout diagram of the fiber and reflective surface of another embodiment different from that shown in FIG. 2, and FIG. 4 is a layout diagram of the fiber and reflective surface of another embodiment. 5 and 6 are route diagrams of a conventional refractive index detection sensor using an optical fiber. Figure 7 (A), (
B) is a cross-sectional view showing the angle formed by the optical fiber end face and the reflector with respect to the plane perpendicular to the axial direction when the medium to be measured is air, and Fig. 8 (A) is a cross-sectional view when the medium to be measured is air. A route map showing the spread of the emitted light; Fig. 9 (B) is a route map showing the spread of the emitted light when the measurement medium is water; The route map which shows the angle formed by the optical fiber end face and the reflector. 2... Outgoing optical fiber, 4... Returning optical fiber, 7... Outgoing light reflecting fitting, 10... Outgoing fiber, 12... First reflecting surface, 14... Second reflective surface, 16
...Receiving side fiber, 18...Reflecting surface, 20...
Light-receiving side fiber, 22... Optical fiber, 26... First reflecting surface, 28... Second reflecting surface, 30... Light-receiving detector Applicant Delphi Co., Ltd. Agent Patent attorney Eiji Kobayashi Figure 1 Figure 3 Figure 4 Crane 5 Figure 6 Figure g7 (A) (B)

Claims (1)

[Claims] 1. An output optical fiber having one end cut at an angle less than orthogonal to the axial direction, and a reflector that reflects the emitted light from the one end one or more times, and the reflected light is A refractive index detection sensor that detects the strength of reflected light based on a difference in the refractive index of a medium to be measured that is guided into a light-receiving optical fiber and exists near an end face of the optical fiber. 2. The refractive index detection sensor according to claim 1, wherein each of the optical fiber end faces on the emitting light side and the light receiving side are tilted at about 10° to 70° with respect to the axial direction. 3. A refractive index detection sensor as claimed in claim 1, which is capable of emitting light and receiving reflected light using the same optical fiber. 4. A refractive index detection sensor according to claim 1, wherein optical fibers for emitting and receiving light are arranged parallel to each other or at right angles to each other.