JPH08189864A - Photo-coupler - Google Patents

Abstract

PURPOSE: To provide a photo-coupler which can make light transmission by coupling optical fibers inside an outside a vacuum vessel inn such a state that the transmission loss and its variation are reduced. CONSTITUTION: The photo-coupler 10 has a convergence lens system 3 to make light transmission from a light source in a vacuum vessel 6 through optical fiber to another optical fiber which is provided outside the vacuum vessel 6. The incident side optical fiber 9 is installed in a position which allows incidence of all beams of light incident on the photo-coupler 10 on the convergence lens system 3, whose magnification is set smaller than ×1 and has a larger core diameter than the optical fiber or the incidence side. At the point of image 5, the emission side optical fiber 11 is positioned as having a greater aperture number than the product of the aperture number of the incident side optical fiber and the inverse umber of the magnification of the lens system 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an optical coupler that couples optical fibers inside and outside a vacuum container for optical transmission, and is particularly used for optical transmission of a radiation thermometer to reduce transmission loss and fluctuation of transmission loss. The present invention relates to an optical coupler that can be used.

[0002]

2. Description of the Related Art An optical fiber type radiation thermometer has a mechanism for guiding heat radiation from a temperature-measured object to a radiation thermometer using an optical fiber as an optical transmission path and converting the amount of light into temperature to measure the temperature. Since a flexible optical fiber can be used as an optical transmission line, there is an advantage that the work efficiency of temperature measurement is extremely high. However, in order to accurately perform temperature measurement operation using this radiation thermometer, it is necessary to transmit the heat radiation from the object to be measured incident on the optical fiber to the optical sensor section of the radiation thermometer without loss. Therefore, it is preferable that the transmission loss due to the coupling connection of the optical fibers is as small as possible.

Further, when the ratio of transmission loss fluctuates due to the coupling connection of optical fibers, the amount of light received by the optical sensor section of the radiation thermometer also fluctuates, and the apparent temperature measurement value changes.
In order to obtain an accurate temperature measurement value, it is necessary to calibrate the temperature conversion scale every time the optical fiber is connected and connected, which significantly reduces the work efficiency. Therefore, it is important for the optical coupler of the optical fiber type radiation thermometer that not only the transmission loss due to the coupling connection of the optical fibers is small but also the fluctuation of the transmission loss is small.

As a method of connecting optical fibers to each other, there is a direct connecting method of directly connecting optical fibers to each other, and methods such as precision ferrule type and mold cone type have been put into practical use. In this case, when the optical fibers cannot be directly coupled to each other, a lens coupling method is adopted in which a glassy substance having a high light transmittance is interposed between the optical fibers to perform optical transmission.

As a lens coupling system, for example, Japanese Patent Laid-Open No.
JP-A-4-110851 discloses an optical transmission line coupling method in which a light source is coupled to a first optical transmission line, wherein the first optical transmission line is provided between the light source and the first optical transmission line. A second optical transmission line having a larger numerical aperture and a smaller diameter, and a lens material for guiding the output light of the second optical transmission line to the first optical transmission line. A coupling method of an optical transmission line that leads to the first optical transmission line through the second optical transmission line and the lens material has been proposed. In this system, a spherical lens is used to approximately collimate the output light. Are optically coupled. Further, JP-A-55-113007 discloses an optical fiber coupling structure in which a lens-shaped converging medium for converging light emitted from the semiconductor laser is arranged between the semiconductor laser and the optical fiber. An optical fiber coupling structure has been proposed in which the refractive index between the optical fiber and the optical fiber is continuous, and the optical fiber coupling structure has been proposed. Is being prevented.

[0006]

However, in these coupling systems, the relative displacement between the optical fibers,
That is, when the optical axis is deviated, there is a drawback that a part of the emitted light is not incident on the optical fiber on the light receiving side and the transmission loss increases.

When the temperature of an object to be measured in a vacuum container is measured by an optical fiber type radiation thermometer, the optical fibers cannot be directly connected to each other in order to seal the vacuum container. In such a case, the lens coupling method is effective.However, if the transmission loss fluctuates due to the mutual coupling of optical fibers, the temperature measurement value fluctuates. Calibration for conversion is required, and reducing the fluctuation of transmission loss is an important factor for accurate temperature measurement and efficient temperature measurement operation.

The present inventor, when the optical fibers inside and outside the vacuum vessel are coupled, has the core diameters of the optical fibers entering and exiting the optical coupler, the numerical apertures, the arrangement positions with respect to the converging lens system, and the magnification of the converging lens system. It has been found that the transmission loss can be reduced and the fluctuation of the transmission loss can be suppressed even if the optical axes of the incident side optical fiber and the outgoing side optical fiber are deviated to some extent by appropriately setting the above.

The present invention was developed on the basis of the above findings, and its purpose is to reduce the transmission loss when optical fibers are coupled to the inside and outside of a vacuum vessel for optical transmission, and to reduce the frequency of attachment / detachment to / from an optical coupler. An object of the present invention is to provide an optical coupler capable of suppressing fluctuations in transmission loss due to attachment / detachment of many outgoing side optical fibers.

[0010]

To achieve the above object, an optical coupler according to the present invention is an optical coupler having a converging lens system for transmitting light from a light source in a vacuum container to an optical fiber outside the vacuum container by an optical fiber. In, the incident side optical fiber is arranged at a position where all the light incident on the optical coupler can be incident on the converging lens system, the magnification of the converging lens system is set smaller than 1, and the core diameter is larger than that of the incident side optical fiber. A structural feature is that an exit side optical fiber having a numerical aperture larger than the product of the numerical aperture of the entrance side optical fiber and the reciprocal of the magnification of the converging lens system is arranged at the image point.

In general, when light is incident on a converging lens system to form an image, as shown in FIG. 1, an incident light beam 2 from an object point 1, which is the tip of an incident side optical fiber, passes through a converging lens system 3 and is emitted. The light ray 4 forms an image at the image point 5. The radiation angle (θ) of the incident light ray 2 has a relationship of [NA = n · sin θ] with the numerical aperture (NA) of the incident side optical fiber. In the above equation, n is the refractive index of air (≈1).
Therefore, in order to make all the light rays from the incident side optical fiber enter the converging lens system 3, the object point 1 and the converging lens system 3
When the distance to is rd, the relationship of the equation (1) is established with the outer diameter R of the converging lens system 3. R ≧ 2 · rd · NA / (1-NA ² ) ^1/2 (1) Therefore, if the tip of the incident side optical fiber (object point 1) is placed at a position that satisfies the relationship of the following equation (2). All the light rays can be made incident on the converging lens system 3. rd ≦ R · (1-NA ² ) ^1/2/2 · NA (2)

An incident ray 2 from the object point 1 forms an image at an image point 5 which is determined by the focal length of the converging lens system 3 and the distance rd between the object point 1 and the converging lens system 3. By arranging the end face of the exit side optical fiber at the position and setting the magnification (β) of the converging lens system 3 to a value smaller than 1, the image of the outgoing light is formed smaller than the image of the incoming light. Therefore, if the core diameter (Co) of the output side optical fiber is set larger than the core diameter (Ci) of the input side optical fiber, even if the optical axis is slightly displaced when the output side optical fiber is attached to or detached from the optical coupler, the output side The side optical fiber can receive the total amount of light.

In this case, since the angle (θ ') of the outgoing ray 4 sent from the converging lens system 3 to the outgoing optical fiber is larger than the emission angle (θ) of the incoming ray 2, the numerical aperture of the outgoing optical fiber. NAo needs to be set larger than the product of the numerical aperture NAi of the incident side optical fiber and the reciprocal of the magnification β of the converging lens system.
The relationship of equation (3) must be satisfied between Ao and the numerical aperture NAi of the incident side optical fiber. NAo ≧ NAi / β (3)

By thus arranging the incident side optical fiber, the emitting side optical fiber and the converging lens system to form an optical coupler, the optical transmission loss and the optical transmission loss generated when the emitting side optical fiber is attached to and detached from the optical coupler are eliminated. Fluctuations can be suppressed.

[0015]

According to the optical coupler of the present invention, in the optical coupler for coupling the optical fibers with each other through the converging lens system, the cores of the incident side optical fiber entering the converging lens system and the emitting side optical fiber emitting from the converging lens system. By specifying the relationship between the diameter and the numerical aperture, and setting the positions of the incident-side optical fiber and the outgoing-side optical fiber with respect to the converging lens system and the magnification of the converging lens system, the total incident light from the incident-side optical fiber to the converging lens system can be determined. The amount of light can be efficiently transmitted to the output side optical fiber. Therefore, it becomes possible to effectively reduce the optical transmission loss and the fluctuation of the optical transmission loss.

Therefore, if it is applied as an optical coupler for connecting and connecting optical fibers inside and outside the vacuum container, for example, as an optical coupler for an optical fiber type radiation thermometer, the amount of transmitted light is reduced due to the coupling connection of the emission side optical fiber which is frequently attached or detached. It is possible to effectively reduce fluctuations in the amount of transmitted light. As a result, during temperature measurement, that is, when the outgoing side optical fiber is connected to the optical coupler, accurate temperature measurement can be performed without calibrating the conversion table of the received light amount and temperature, and the temperature can be efficiently measured. .

[0017]

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is an overall explanatory view of an apparatus used as an optical coupler of a radiation thermometer. In FIG. 2, the temperature-measured object 7 in the vacuum container 6 is heated by the heater 8, and the amount of heat radiation from the temperature-measured object 7 is detected by the probe and is incident on the optical coupler 10 by the incident side optical fiber 9. . The incident light is transmitted to the emission side optical fiber 11 through the coupling connection portion outside the vacuum container of the optical coupler 10 and transmitted to the optical sensor portion of the radiation thermometer 12 to convert the detected light amount into temperature and measure the temperature. It is carried out.

FIG. 3 is a schematic cross-sectional view showing an enlarged example of the optical coupler 10 of the present invention. The light incident on the converging lens system 3 from the incident side optical fiber 9 is transmitted to the emitting side optical fiber 11 through the hemispherical lens 13 and the spherical lens 14. The light beam is refracted by the converging lens system 3 and forms an image at the image point 5 which is the end face of the output side optical fiber. The flow of the image forming light beam is schematically illustrated in FIG. In FIG. 4, from the object point 1 which is the tip of the incident side optical fiber 9 to the hemispherical lens 13
The light incident on is refracted by the hemispherical lens 13 and the spherical lens 14, and the light ray 15 forms an image at the image point 5 which is the end face of the output side optical fiber. When the object point 1 is displaced from the object point 1 by the distance D from FIG. 4, the image point 5 is imaged on the object point 5 ′ which is displaced by the distance d (D> d), and the deviation of the optical axis is reduced on the object point 5 to form an image. It can be seen that it is formed.

Using this optical coupler 10, the heat radiation from the temperature-measured object 7 in the vacuum chamber 6 is made to have a core diameter (Ci) of 200 μm.
The incident side optical fiber 9 with m and numerical aperture (NAi) of 0.25 receives light, and the core diameter (Co) is 400 μm outside the vacuum container.
, Exit side optical fiber 11 with numerical aperture (NAo) of 0.38
Light transmitted to. The outer diameter of the converging lens system 3 is 3 mm.
Using the hemispherical lens (F = 2.9) and spherical lens (F = 2.2) of
The magnification (β) was 0.75. Further, the object point 1 which is the front end surface of the incident side optical fiber 9 is 1.9 from the hemispherical lens 13.
At the position of mm, the end face of the output side optical fiber 11 is arranged at the image point 5 of 0.5 mm from the spherical lens 14. As a result of imaging in this way, the core diameter on the object point 1 is 200 μm
The tip of the optical fiber on the incident side of
An image of 0 μm is formed, and the angle of the ray on this image point 5 (θ
′) Was sin θ ′ = 0.32.

Therefore, the core diameter (Co) of the output side optical fiber 11 is Co> 150 μm, and the numerical aperture (N)
Ao) becomes NAo> 0.32, and when the output side optical fiber 11 is coupled and connected to the optical coupler 10, there is some deviation. In this case, even if the optical axis is shifted by about 120 μm, it is transmitted from the input side optical fiber 9. The entire amount of light can be received.

[0022]

As described above, according to the optical coupler of the present invention, the values of the core diameter and the numerical aperture of the optical fiber entering and exiting the converging lens system are set to a specific value range, and the optical fiber on the incident side and the outgoing side are output. By specifying the position of the optical fiber on the side and the magnification of the converging lens system, etc., the optical transmission loss and fluctuation of the optical transmission loss due to the optical axis shift when coupling the optical fiber on the output side to the optical coupler can be effectively performed. It can be reduced. Therefore, it becomes possible to measure the object temperature in the vacuum container accurately and efficiently, for example, by an optical fiber type radiation thermometer.

[Brief description of drawings]

FIG. 1 is an explanatory diagram when an image is formed by a convergent lens system of the present invention.

FIG. 2 is an overall explanatory diagram of an apparatus used in an example of the present invention.

FIG. 3 is a schematic cross-sectional view showing an enlarged example of the optical coupler of the embodiment.

FIG. 4 is a schematic view illustrating the flow of image-forming light rays in the converging lens system of the example.

[Explanation of symbols]

 1, 1'Object point 2 Incident ray 3 Converging lens system 4 Exit ray 5, 5'Image point 6 Vacuum container 7 Temperature-measuring object 8 Heater 9 Incident side optical fiber 10 Optical coupler 11 Exit side optical fiber 12 Radiation thermometer 13 Hemispherical lens 14 spherical lens 15 rays

Claims (1)

[Claims] 1. In an optical coupler having a converging lens system for transmitting light from a light source inside the vacuum container to an optical fiber outside the vacuum container by an optical fiber, the light incident on the optical coupler is incident on a position where all the light can enter the converging lens system. Side optical fiber is arranged, the magnification of the converging lens system is set to be smaller than 1, the core diameter is larger than that of the incident side optical fiber, and the aperture is larger than the product of the numerical aperture of the incident side optical fiber and the reciprocal of the magnification of the converging lens system. An optical coupler characterized in that a plurality of output side optical fibers are arranged at an image point.