JPS6312939A - Space coupling type sensor - Google Patents

Abstract

PURPOSE:To obtain a space coupling type sensor which is small in size and light in weight, by reflecting a light beam from a light emitting part by an oblique polished surface of the tip of a light sending side optical fiber, leading it to an oblique polished surface of the tip of a light receiving side optical fiber, reflecting it again by this oblique polishing surface, and leading it to a light receiving part. CONSTITUTION:A light sending side optical fiber 12 and a light receiving side optical fiber 13 are placed in parallel. As a result, an emitted light A from a light emitting part in a light sending and receiving circuit 11 is propagated through the inside of the optical fiber 12 and led out to a polished surface 12a. Subsequently, by the polished surface 12a which is polished obliquely to an angle theta1 for reflecting said light to the optical fiber 13, it is brought to total reflection to a polished surface of the optical fiber 13. The light beam A which is made incident on the polished surface 13a is brought to total reflection by the polished surface 13a which is polished obliquely to an angle theta4 for reflecting it to the inside of the optical fiber 13, propagated through the inside of the optical fiber 13 and led into a light receiving part of the circuit 11. In such a way, a space coupling type sensor being small in size and light in weight, for measuring the density, etc. of an object to be measured, between the optical fibers 12, 13 by detecting an output of the light beam A by said light receiving part can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to detecting the concentration of fine particles in the atmosphere, detecting changes in the refractive index of liquids and gases, changes in concentration, etc., and detecting the presence or absence of objects such as photoelectric switches. The present invention relates to a spatially coupled sensor used in such cases.

<Prior art> Light emitted from one optical fiber is received by the other optical fiber, and changes in the object to be measured existing in the space between the two optical fibers are detected by measuring the intensity, wavelength, phase, and interference of the light. Spatial coupling sensors, which measure changes in side light, reflection, absorption, etc., are widely used in industry as optical fiber applications. Conventionally, this type of sensor includes, for example, a photoelectric switch (see Figure 4) that detects the presence or absence of an article flowing on a conveyor, and a concentration sensor (see Figure 4) that detects the concentration of liquid or gas flowing in a pipe.
(See Figure 5).

In other words, the photoelectric switch shown in FIG. 4 includes a light-transmitting side optical fiber 1 that leads out light from a light-transmitting circuit having a light-emitting section (not shown), and a light-receiving circuit 3 having a light-receiving section that directs the light from the light-emitting section. The light-receiving side optical fibers 2 to be introduced face each other. When the article 5 flowing on the conveyor 4 passes between the tips of the optical fibers 1 and 2, the optical fiber 1
By blocking the light that enters the optical fiber 2, the intensity of the light changes, and the presence or absence of the article 5 can be detected.

The concentration sensor shown in FIG. 5 also includes a light transmitting side optical fiber 7 that guides light from the light emitting section to a light transmitting/receiving circuit 6 that includes a light emitting section and a light receiving section, and a light transmitting side optical fiber 7 that guides the light from the light emitting section to the light receiving section. A light-receiving side optical fiber 8 to be introduced is integrally provided. The tip of the optical fiber 7.8 is connected to a tube 9 through which liquid or gas flows.
Since the optical fibers 7.8 are arranged facing each other in the radial direction, the distal ends of the optical fibers 7.8 are formed in a curved shape so as to straddle the tube 9.

The intensity of the light incident from the optical fiber 7 to the optical fiber 8 changes due to the liquid or gas passing between the tips of the optical fibers 7.8, thereby increasing the concentration of the liquid or gas flowing in the tube 9. be able to.

<Problems to be Solved by the Invention> However, in the spatially coupled sensor such as the photoelectric switch shown in FIG. This configuration has the disadvantage that the sensor becomes large. Furthermore, since the light transmitting circuit having the light emitting section and the light receiving circuit having the light receiving section are each separately attached to the optical fiber 1.2, there is a drawback that the light transmitting and light receiving circuit system becomes complicated. In addition, a spatially coupled sensor such as a concentration sensor equipped with a light transmitting/receiving circuit 6 that integrates a light emitting part and a light receiving part as shown in FIG. It is necessary to increase the diameter. Therefore, since the curved tips of the optical fibers 7.8 are disposed facing each other, the radius of curvature of the tips becomes large, resulting in a disadvantage that the sensor becomes large.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a small and lightweight spatially coupled sensor.

Means for Solving the Problems> In order to solve the above problems, the present invention provides a light transmitting and receiving circuit that includes a light emitting section and a light receiving section, and a base end of which is provided in the light transmitting and receiving circuit, and a light transmitting and receiving circuit that includes a light emitting section and a light receiving section. A light-transmitting side optical fiber that guides light, and a light-receiving side optical fiber whose base end is provided in the pre-delivery light-receiving circuit in a state lined up with the light-sending side optical fiber and introduces light to the light receiving section. In the spatially coupled sensor, the tip surface of the light-transmitting optical fiber is formed into a polished surface that is obliquely polished to an angle that reflects the light led out from the light-emitting part toward the light-receiving optical fiber. ,
The distal end surface of the light-receiving optical fiber is formed into a polished surface that is obliquely polished to an angle that receives the light reflected from the polished surface of the light-transmitting optical fiber and reflects it into the light-receiving optical fiber. It is characterized by

Effect> The light from the light emitting section is reflected by the obliquely polished surface at the tip of the transmitting side optical fiber, is guided to the obliquely polished surface at the tip of the receiving side optical fiber, is reflected again by this obliquely polished surface, and is received. introduced into the department.

Example of implementation Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

Fig. 1 is a perspective view showing a spatially coupled sensor according to an embodiment of the present invention, and Fig. 2 is a side view thereof. A light transmitting/receiving circuit 11 having a built-in light receiving section is provided with a light transmitting side optical fiber 12 for guiding light from the light emitting section and a light receiving side optical fiber 13 for introducing light into the light receiving section in parallel with an interval t. There is. Further, the tip end face of each optical fiber 12.13 is formed into obliquely polished polished surfaces 12a, t3g, and the polished surfaces 128.degree. 13a are positioned so as to face each other diagonally. The polished surface 12a is polished so that the light A propagating through the optical fiber 12 from the light emitting section in the light transmitting/receiving circuit 11 is totally reflected by the polished surface 12a at the tip toward the polished surface 13a of the optical fiber 13. Diagonal polishing (in this example, the polishing angle is 4)
5°), that is, the total amount of light A determined by the refractive index n of the core of the optical fiber 12 and the refractive index nt of the substance in contact with the polished surface 12a, that is, the object to be measured (where n, < ng). Polish to a reflection angle (above the critical angle). In other words, diagonal polishing is performed to satisfy Snell's formula % formula % (). Here, θl is the critical angle of the light A at the polished surface 12a, θ is the reflection angle of the light A into the object to be measured, which is 90' (sin 90" 1), and (5
) formula is n, sinθ8=n! Therefore, the critical angle θ, becomes t, and when θ, ≦45° (θ, -45° in the figure),
Since the polishing angle θ of the polishing surface 12a satisfies θ1≦909-01, θ≦45” (θ4−!45° in the figure).

In order for the light A that has entered the polished surface 13a of the optical fiber 13 from the polished surface 12a of the optical fiber 12 to be totally reflected by the polished surface 13a toward the light receiving section in the light transmitting/receiving circuit 11, considering the same as above, ( a), (b) According to formula 1, oblique polishing is performed so that θ5≧45° (θ5=a45° in the figure).

That is, the critical angle θ4 of the light A at the polishing surface 13a is θ4 fog θ
, depth 5in-star (□), and when θ4 (-l θd)≦45° (θJ-45° in the figure), the polishing angle θ of the polished surface 13a becomes θ,≧90'-04 Therefore, 05≧45° (θ, -45° in the figure). Therefore,
The polished surfaces 12a and 13a of each optical fiber 12 and 13 are both obliquely polished at an angle of 45 degrees.

Next, the operation of the spatially coupled sensor of the present invention configured as described above will be explained. As described above, in this embodiment, the critical angle θ1 . θ4 is 01-04≦45° (θ in the figure).

-04-45°).

Light A emitted from the light emitting section in the light transmitting/receiving circuit 11 propagates within the optical fiber 12 and is guided to the polished surface 12a. Then, it is totally reflected onto the polished surface 13a of the optical fiber 13 by the polished surface 12a formed at a polishing angle of 45 degrees. At this time, a part of the light A is lost in the object to be measured between the optical fibers 12 and 13, and is incident on the polished surface 13a of the optical fiber 13. The light A incident on the polished surface 13a is totally reflected on the polished surface 13a formed at a polishing angle of 45° in the same manner as described above, propagates through the optical fiber 13, and is introduced into the light receiving section of the light transmitting/receiving circuit 11.
By detecting the output of the light A at the light receiving section, the concentration of the object to be measured between the optical fibers 12 and 13 can be measured.

FIG. 3 shows another embodiment of the invention. In this embodiment, a light transmitting/receiving circuit 11, a light transmitting side optical fiber 12', and a light receiving side optical fiber 13' are constructed in the same manner as in the previous embodiment.

Critical angle θ for light at polished surfaces 12a' and 13a' of 13'
, ', 04' are 45' or more (in this example, the critical angles 01', 04' are 55°) 0 For example, the refractive index of the core of the optical fibers 12', 13' is 1.6200, Assuming that the refractive index of water is 1.3330, (1.6200 ・sin θ+' −1,3330・
sin θyo′. Here, 01' is the critical angle of the light A at the polished surface 12a', and θ,' is the reflection angle of the light A into the object to be measured (water), which is 90''(sin90'=1), so The critical angle 81' is 1.6200, so the polished surface 12a' of the optical fiber 12'
The polishing angle θ,′ is θ,′≦90°−θ1′, so θ,′≦35° (θx′−35° in the figure). The light A incident on the polished surface 13a' of the optical fiber 13'
The polishing angle 05' of the polishing surface 133', which is totally reflected toward the light receiving section in the light transmitting/receiving circuit 11 at 3', is 77 degrees or less, as shown in the figure, considering the same as above. At this time, the optical fiber 13
The critical angle 04' of the light A at the polished surface 13a' is the above-mentioned tc
+, 04'=θl'-55''.

Note that the polishing angles of the polished surfaces of the light transmitting and receiving optical fibers are not limited to the above-mentioned embodiments, and may vary depending on the object to be measured and the type of optical fiber. II (refractive index, structure), etc. to adjust to the optimum value.

Further, by coating the polished surfaces of the light transmitting and light receiving side optical fibers with a reflective film by aluminum vapor deposition or the like, the reflectance of light can be increased.

Further, in the sensor according to the present invention, only one mounting hole is required for the light transmitting and light receiving side optical fibers.

Next, the sensor of the present invention shown in FIGS. 1 and 2, as shown in FIG. As a result of comparing the output with a conventional sensor whose parts face each other, the values shown in Table 1 were obtained.In this case, the sensor of the present invention and the conventional sensor both use the same optical fiber (core The refractive index is 1,516, the core diameter is 1,8 ta), the space to be measured is air, and the distance (is 5 ta).Also,
Polished surfaces 12a, 13a of optical fiber 12.13 of the invention
Polishing angle θ5. θ5 are both 45°, critical angle of light θ1°θ
4 is 41°, and the radius of curvature R (
(outside) is 2 dragons. Furthermore, an LED is used for the light emitting part of the light transmitting/receiving circuit 11, and a phototransistor is used for the light receiving part.

Table 1> As described above, the sensor of the present invention obtained better values for both output and loss than the conventional sensor in which the tips faced each other. In addition, each polished surface 1 of the sensor of the present invention described above
2a.

When 50 μm of aluminum was vapor-deposited on 13a, the optical output was improved to 1.2 V (loss was -10 dB).

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, each optical fiber can be connected to the light transmitting/receiving circuit without arranging the ends of the light transmitting and light receiving side optical fibers to be curved with respect to each other. Since they can be arranged side by side, they can be mounted as long as there is space for the measurement space of the object to be measured and the diameter of each optical fiber, and the sensor can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a spatially coupled sensor according to the present invention;
FIG. 2 is a side view thereof, FIG. 3 is a side view showing another embodiment of the present invention, and FIGS. 4 to 6 are schematic diagrams showing a conventional spatially coupled sensor. In the figure, 11 is a light transmitting/receiving circuit, 12.12' is a light transmitting side optical fiber, 13.13' is a light receiving side optical fiber, 12a, 12a', 13a, 13a' are polished surfaces, θ3. θ2′r Sr θwhis′ is the polishing angle. θ

Claims (3)

[Claims] (1) A light transmitting/receiving circuit incorporating a light emitting section and a light receiving section, a light transmitting side optical fiber whose base end is provided in the light transmitting/receiving circuit and guiding light from the light emitting section, and this light transmitting side optical fiber. and a light-receiving side optical fiber whose base end is provided in the light transmitting/receiving circuit and introduces light to the light receiving section in a state in which the base end is arranged in line with The surface is formed into a polished surface that is obliquely polished to an angle that reflects the light led out from the light emitting part toward the light receiving optical fiber, and the tip surface of the light receiving optical fiber is formed in a polished surface that A space-coupled sensor is formed on a polished surface that is obliquely polished to an angle that receives light reflected from the polished surface and is reflected into the light-receiving optical fiber. (2) The spatially coupled sensor according to claim 1, wherein each of the polished surfaces is polished at an angle such that the light from the light emitting section is totally reflected on each of the polished surfaces. (3) The spatially coupled sensor according to claim 1, wherein each of the polished surfaces is coated with a reflective film.