JP2002107546A - Light guide, optical transmission device using the same, and x-ray ct apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide having high conversion efficiency from incident light to exit light. SOLUTION: A light scattering film 14 having as much large area as approaching to the tip part of the direction of light propagation is arranged at prescribed cycles on a second end surface 13B which meets in the longitudinal direction of a transparent board 13 disposed so that incident light 12 is received on a first end surface 13A of one end side in the longitudinal direction. Light which propagates within the transparent board 13 is scattered by these light scattering films 14, and emitted from a third end surface 13C facing the end surface 13B of the transparent board 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide applied to, for example, guidance of illumination light in an image scanner and light transmission between relatively moving objects, and an optical transmission apparatus and an X-ray CT apparatus using the same. About.

[0002]

2. Description of the Related Art In an image scanner which reads an image on a document surface by a CCD image sensor or the like and outputs it as an electric signal, it is necessary to illuminate the document surface.
In such a case, in addition to the method of directly irradiating the light from the light source onto the document surface, a method of guiding the light from the light source onto the document surface by a light guide and illuminating the light linearly has been considered.

FIG. 11 shows a configuration based on the prior art of a light guide used for such an application. Light emitting element 101
Is emitted from one end of the transparent plate 103. On one side surface of the transparent plate 103, a light scattering film 104 is formed so as to be gradually widened toward the tip in the light propagation direction, and the incident light 102 from the light emitting element 101 propagates through the transparent plate 103. While the light is scattered by the light scattering film 104, and the band-like emission light 1 is emitted from the light emission surface perpendicular to the light incidence surface.
It is taken out as 05. This outgoing light 1
05 is irradiated on the document surface, for example.

However, in a light guide having such a structure,
It is necessary to increase the intensity of the light emitted from the light emitting element 101 in order to obtain the external light with sufficient light intensity because the conversion efficiency from the incident light to the emitted light is low, which causes an increase in power consumption and a decrease in reliability. .

When an optical transmission device for transmitting light between a light-emitting element and a light-receiving element that move relatively using such a light guide is manufactured, the conversion efficiency of the light guide from incident light to output light is reduced. Due to the small size, the relative movement distance between the light emitting element and the light receiving element, the amount of axial deviation, and the like are limited.

[0006]

As described above, in the conventional light guide, since the conversion efficiency from incident light to outgoing light is small, it is necessary to increase the intensity of the outgoing light from the light emitting element. In addition, when an optical transmission device in which the light emitting element and the light receiving element relatively move is manufactured, the conversion efficiency is small, so that the light emitting element and the light receiving element have a problem. However, there is a problem that the relative movement distance and the amount of axis deviation are limited.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a light guide having high conversion efficiency from incident light to outgoing light.

It is another object of the present invention to provide an optical transmission device for transmitting light from a light emitting element which moves relatively using the light guide to a light receiving element, and an X-ray CT apparatus using the same.

[0009]

In order to solve the above-mentioned problems, a light guide according to the present invention comprises a transparent plate arranged so as to receive incident light at a first end face at one end in a longitudinal direction, and a transparent plate provided with the transparent plate. It is formed at intervals on a second end surface along the longitudinal direction of the plate, and scatters light propagating in the transparent plate to form a second transparent plate.
A plurality of light scattering films for emitting light from a third end surface facing the end surface, wherein the plurality of light scattering films have an area ratio per unit length in a longitudinal direction of the transparent plate toward a front end in a light propagation direction in the transparent plate. Is formed so as to increase in accordance with. More specifically, the plurality of light-scattering films are formed such that, for example, the area of the light-scattering film closer to the tip in the light propagation direction in the transparent plate becomes larger.

[0010] The light guide according to the present invention having the above-described configuration is capable of diffusing incident light from the first end face, which is the light incident face of the transparent plate, on the second end face along the longitudinal direction of the transparent plate. Since the light is scattered by the film and the light is emitted from the light exit surface, which is the third end surface opposite to the second end surface, the surface on which the light scattering film is formed is orthogonal to the light exit surface. The conversion efficiency from incident light to outgoing light is significantly improved as compared with the comparison guide. In addition, since the light scattering film closer to the front end in the light propagation direction in the transparent plate has a larger area ratio, for example, its area is larger, the intensity distribution of the emitted light is made uniform.

Another light guide according to the present invention is a transparent plate arranged to receive incident light at a first end face on one end side in a longitudinal direction, and formed on a second end face along the longitudinal direction of the transparent plate. Then, the light propagating in the transparent plate is scattered and the second
A light scattering film for emitting light from a third end face facing the end face, wherein the distance between the second end face and the third end face gradually decreases in the transparent plate toward the front end in the light propagation direction in the transparent plate. It is characterized by being formed in.

In the light guide having such a configuration, the conversion efficiency from incident light to outgoing light is improved by the same principle, and the distance between the second end face and the third end face of the transparent plate is tapered. As a result, the intensity distribution of the emitted light is made uniform.

Still another light guide according to the present invention has a configuration in which the above two types of light guides are combined, and the plurality of light scattering films are light scattering films near the front end of the transparent plate in the light propagation direction. The light scattering film at the tip of the propagation direction is formed continuously in the propagation direction, and the transparent plate is transparent in an area where the light scattering film is continuously formed. The distance between the second end face and the third end face is gradually reduced toward the front end in the light propagation direction in the plate. With such a configuration, it is possible to realize a light guide that can efficiently emit light with a uniform intensity over a wide range.

Further, the optical transmission device according to the present invention comprises the above-described light guide, a light emitting element for making the outgoing light incident on the first end face of the light guide, and a relative movement with respect to the light emitting element and the light guide. And a light receiving element that receives light emitted from the third end face of the light guide.

Further, the light guide according to the present invention is arranged on the rotating body for transmitting data as a light beam between the rotating body and the fixed body facing each other, and emits light according to the data to be transmitted. At least one light emitting element, at least one light receiving element disposed on the fixed body and receiving light from the light emitting element, and the rotating body and the fixed body located between the fixed body and the rotating body. And a light guide that guides the light from the light emitting element to the light receiving element.

[0016]

Embodiments of the present invention will be described below. (First Embodiment) FIG. 1 shows the configuration of a light guide according to a first embodiment of the present invention. This light guide is an element for converting the outgoing light from the light emitting element 11 into incident light 12 and converting this into external outgoing light 15 in a predetermined direction. The light guide is a rectangular transparent plate 13 and a light scattering film 14 applied thereto. Is composed mainly of.

That is, the incident light 12, which is the light emitted from the light emitting element 11, enters the first end face 13 A at one end in the longitudinal direction of the transparent plate 13. On one side surface of the transparent plate 13, that is, on the second end surface 13B along the longitudinal direction, a plurality of light scattering films 14 are provided.
Are applied and formed at intervals. The transparent plate 13 is made of, for example, an acrylic resin, and the light scattering film 14 is formed by silk printing. Thus, the light guide can be manufactured with high productivity.

The incident light from the first end face 13A of the transparent plate 13 is scattered by the scattering film 14 while propagating through the transparent plate 13, and is emitted as external outgoing light 15 from the third end face 13C facing the second end face 13B. Is done. Here, the light scattering film 14
As shown in the figure, is formed such that the light scattering film closer to the tip in the light propagation direction in the transparent plate 13 has a larger area.

Next, the operating principle and effects of the light guide according to this embodiment will be described with reference to FIG. One feature of the present embodiment is that the light scattering film 14 is formed on the second end face 13B facing the third end face 13C, which is the light exit surface of the transparent plate 13. The reason will be described with reference to FIG. The radiation directivity of light (scattered light) incident on the transparent plate 13 from the first end face 13A and scattered by the light scattering film 14 becomes spherical as shown in FIG. 2 according to Lambert's law. Of the scattered light, a part of the light having the highest light intensity, which is close to the direction perpendicular to the light scattering film 14, is converted into the outgoing light 15, and the other light is totally reflected light. Therefore, if the light scattering film 14 is formed on the second end face 13B opposite to the third end face 13C, which is the light emitting face, the portion having the highest light intensity is converted into the outgoing light 15, which is shown in FIG. The conversion efficiency is improved as compared with the conventional light guide.

Further, in this embodiment, since the incident light 12 is attenuated as it propagates through the transparent plate 13, the area of the light scattering film 14 is increased toward the front end in the light propagation direction, so that the outgoing light 15 To keep the intensity constant. The area of the light scattering film 14 obtained analytically is as follows.

As shown in FIG. 3, an x coordinate is set in the length direction of the transparent plate 13, and a minute unit of the length x in this direction is dx. The area ratio of the light scattering film 14 in the minute unit dx is represented by y, the intensity of the propagating light incident on the minute unit dx is represented by P (x), and the light scattering film in the minute unit dx (hereinafter referred to as a minute light scattering film). ), The intensity of the light that is scattered and becomes the emission light 15 is defined as a unit emission light intensity H (x). A cross section is taken in a direction perpendicular to x, and it is assumed that the light intensity in this cross section is uniform.

Unit output light intensity H (x) in minute unit dx
Is considered to be proportional to the area ratio y of the minute light scattering film and the intensity P (x) of the propagating light incident on the minute unit dx, so that the proportionality constant is C ₁ and H (x) = C ₁ · y · P (x ) (1)

When it is considered that, for example, the document surface is uniformly illuminated by the output light 15, the unit output light intensity H
(x) is desired to be a constant value irrespective of the position x. Therefore, when the constant value is C ₂ , it is preferable to satisfy the relationship of Expression (2). C ₂ = yP (x) (2) On the other hand, the intensity P (x) of the propagating light incident on the minute unit dx,
Difference P (x) from transmitted light intensity P (x + dx) from minute unit dx
Since −P (x + dx) is proportional to the area y · dx of the minute light scattering film, the proportional constant is C ₃ , and P (x) −P (x + dx) = C ₃ · y · dx (3 ). That is, −dP (x) / dx = C ₃ · y (4) Solving to erase the y using equation (2), the incident light intensity P of the minute unit dx (x) is represented by the following equation the proportionality constant as the C _4.

(Equation 1)

Here, P _i is the intensity of incident light on the transparent plate 13. Area ratio of the light scattering film 14 y is determined by the following equation as C ₅ proportionality constant using equation (2).

(Equation 2)

If the light scattering film 14 is formed so that P (x) = 0 at x = 100 mm, C ₄ = 1.0 × 10 ⁻² / m
m. The proportionality constant C ₅ is the incident light intensity P _i of the transparent plate 12.
And the unit output light intensity H (x).

FIG. 4 shows that C ₄ = 1.0 × 10 ^-2 / mm, PI = 1, C
The relation between P (x) and y with respect to x when 5 = 0.5 is shown. FIG. 4 shows that when x is 75 mm or more, y exceeds 1. Although not shown in the figure, it is easily understood from the equation (6) that when x = 100 mm, y becomes infinite. A practically effective range is 0 ≦ y ≦ 1.

When the area of each light scattering film 14 is determined based on the area ratio y thus obtained, the unit output light intensity H (x) can be made uniform efficiently. Transparent plate 1
In the case where the light intensity in the cross section in the direction orthogonal to x is non-uniform near the light incident surface (first end surface 13A) of No. 3 or the like, the light scattering near the incident surface depends on the degree of non-uniformity. If the area of the film 14 is increased, the intensity of the emitted light is made uniform.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
FIG. 4 is a diagram illustrating a configuration of a light guide according to the first embodiment, which is different from the first embodiment in that a transparent plate 13 is tapered in a width direction. That is, the width of the transparent plate 13 (the distance between the second end surface 13B and the third end surface 13C which is the light exit surface facing the second end surface 13B) gradually decreases toward the front end in the propagation direction of the light incident on the transparent plate 13. It is formed so that it becomes.

This embodiment is particularly effective when 1 ≦ y in the description of the first embodiment. That is,
In the first embodiment, the light-scattering film 14 is formed on the second end face 13B of the transparent plate 13 in a plurality of parts, whereas in the present embodiment, one light-scattering film 14 is formed continuously. Have been. As described above, in the present embodiment, since the light scattering film 14 is formed continuously, the width of the transparent plate 13 is reduced so that the light density inside the transparent plate 13 does not decrease, and the emission light intensity is reduced. Keep it even. This transparent plate 1
The width of 3 is analytically obtained as follows.

As shown in FIG. 6, as in FIG.
The x-coordinate is taken in the length direction of 3, and a minute unit of the length x in this direction is dx. The thickness of the transparent plate 13, that is, the width of the light scattering film 14 is a, and the intensity of the propagating light incident on the minute unit dx is P.
(x), and the intensity of light that is scattered by the light scattering film (hereinafter, referred to as a minute light scattering film) in the minute unit dx to become the emission light 15 is defined as the unit emission light intensity H (x). A cross section is taken in a direction perpendicular to x, and it is assumed that the light intensity in this cross section is uniform.

Unit output light intensity H (x) in minute unit dx
Is proportional to the intensity P (x) of the propagating light incident on the minute unit dx and the width a of the light scattering film 14, and the peripheral length 2 (a +
it is considered to be inversely proportional to h), it is expressed as H (x) a proportional constant as _{C 6 = C 6 · P (} x) · a / 2 (a + h) (7).

When it is considered that the document surface is uniformly illuminated by the output light 15, for example, the unit output light intensity H
(x) since it is desired that a constant value regardless of the position x, when the predetermined value C _7, it is preferable to satisfy the relation of equation (8). C ₇ = P (x) · a / (a + h) (8) On the other hand, the intensity P (x) of the propagating light incident on the minute unit dx is:
Difference P (x) from transmitted light intensity P (x + dx) from minute unit dx
Since −P (x + dx) is considered to be proportional to a / (a + h) and dx, the proportionality constant is set to C ₈ and P (x) −P (x + dx) = C ₈ · dx · a / ( a + h) and becomes (9) ie -dP (x) / dx = C 8 · a / (a + h) (10). Using equation (9), clearing a / a (a + h), the -dP (x) / dx = C 7 · C 8 / P (x) (11). Result of solving the differential equation of Formula (11) is a proportional constant as C ₉

(Equation 3)

## EQU1 ## Here, _Pi is the incident light intensity of the transparent plate 13. The width h at the position of the minute unit dx of the transparent plate 13, as C ₁₀ proportional constant using equation (8) determined by the following equation.

(Equation 4)

Assuming that the taper of the transparent plate 13 is formed so that P (x) = 0 at x = 25 mm, C ₉ = 4 × 10 ⁻² /
mm.

FIG. 7 shows that C ₉ = 4 × 10 ^-2 / mm, a = 1 mm, C
P (x) and h (x) for x when ₁₀ = 6 (transparent plate 1
3 = the distance between the second end face 13B and the third end face 13C). In FIG. 7, h is negative in the vicinity of x = 25 mm. However, the area where h is positive is physically significant.
When the taper of the transparent plate 13 is formed according to the width h (x) obtained in this manner, the unit output light intensity H (x) can be made uniform efficiently.

(Third Embodiment) From the above description,
An area ratio y of the minute light scattering film in the first embodiment;
It can be seen that the width h of the transparent plate 13 in the second embodiment has the same meaning. Here, the effective range of y in the first embodiment is 0 ≦ y ≦ 1, and in the embodiment of FIG.
From h, it is clear that combining these first and second embodiments can realize a light guide that can efficiently irradiate light over a wide range.

FIG. 8 shows a configuration of a light guide according to the third embodiment of the present invention based on such a concept. The fixed width region 16 in the drawing corresponds to the range of 0 ≦ y ≦ 1 as in the first embodiment, and the tapered region 17 corresponds to the range of 1 ≦ h as in the second embodiment. That is, the light guide according to the present embodiment is formed such that the light scattering film 14 is formed such that the area becomes larger as the light scattering film is closer to the front end in the light propagation direction in the transparent plate 13 and the light scattering film at the front end in the propagation direction. Are formed continuously in the propagation direction. The transparent plate 13 is formed such that the distance between the second end face 13B and the third end face 13C gradually decreases toward the front end in the light propagation direction in the region where the light scattering film 14 is continuously formed. It is characteristic.

As a design method of the light guide of the present embodiment, first, the constant width region 16 is designed using the equations (5) and (6). Since the constants C ₄ and C ₅ depend on the shape of the transparent plate 13, the components of the light scattering film 14, the intensity of incident light, and the like, they need to be obtained in advance through experiments and the like.

As a result, assuming that the parameters are the same as those shown in FIG.
And it is sufficient. Since the range of 75 mm ≦ x is the tapered region 17, it is designed using the equations (12) and (13). FIG.
If the parameters are the same as in FIG. 7, 0 ≦ x ≦ 2
It can be seen that the area up to 4 mm is an effective area, and the area is effective up to 0 ≦ x ≦ 99 mm together with the constant width area 17.

According to FIG. 4, when x = 75 mm, P (x) = 0.5
It can be seen that half the light intensity enters the tapered region 17. Then, the light intensity after transmitting 24 mm in the tapered region 17 becomes about 10%, and 90% light intensity is used as the output light intensity. Therefore, according to the present embodiment, it is possible to realize a light guide that can efficiently emit light to a wide range.

(Fourth Embodiment) Next, as a fourth embodiment of the present invention, a light emitting element and a light receiving element are combined with the light guide described in the first to third embodiments. An optical transmission apparatus that transmits an optical signal while relatively moving between light guides will be described.

FIGS. 9A and 9B are a side view and a front view showing the configuration of the optical transmission device according to the present embodiment. The rotating body 21 is formed in an annular shape, and a fixed body 22 is opposed to a part of the rotating body 21 in the circumferential direction. In the present embodiment, four light emitting elements 23 are arranged at equal intervals on the circumference of the rotating body 21, and one light receiving element 24 is arranged on the surface of the fixed body 22 facing the rotating body 21. .

The light guide 25 is basically the same as the light guide described in the first to third embodiments, but is formed in an arc shape corresponding to the annular rotating body 21. In the light guide 25, a light incident surface corresponding to the first end surface 13A of the transparent plate 13 described in the first to third embodiments is formed as a reflective surface 26, and the reflective surface 26 bends the incident light at a right angle. It has a 45 degree inclination to guide it into the light guide 25.

The light emitting element 23 is, for example, an LED or a laser light source, and emits an optical signal when an electric signal is applied. This optical signal is applied to the light guide 25 by the reflecting surface 26.
And is emitted by the light guide 25 with uniform light intensity over a length of １ ／ of the circumference. In this way, a part of the optical signal emitted from the light guide 25 is received by the light receiving element 23 and converted into an electric signal.

As described above, according to the optical transmission device of the present embodiment, it is possible to transmit an optical signal between the rotating body 21 and the fixed body 22. In this case, by using the light guide according to the present invention having the configuration described in the first to third embodiments as the light guide 25, the number of light emitting elements 23 can be significantly reduced, and power consumption, high reliability, and low cost can be achieved. Further, it is possible to increase the allowable amount such as the moving distance and the amount of axis deviation.

Next, an example of an X-ray CT apparatus to which the optical transmission device of the present embodiment is applied will be described. FIG.
It is a perspective view which cuts out and shows some gantry parts of a line CT apparatus. The ring-shaped rotating body 1 is rotatably supported by a ring-shaped fixed body 2 arranged substantially perpendicular to the stand 3. The rotor 1 is provided with permanent magnets and an annular magnetic rotor yoke 4 attached at equal intervals along the circumference thereof, and a motor 5 is attached to the rotor 1 by the coils 5 attached to the fixed body 2. Rotating body 1 by directly transmitting the driving force
A direct drive motor system is configured to rotationally drive the motor.

In the rotating body 1, for example, an X-ray tube 6 for irradiating X-rays in a cone beam shape and a multi-slice type X-ray detector 7 are opposed to each other with a subject on a bed (not shown) interposed therebetween. It is equipped with. The rotator 1 further includes a current-voltage converter for converting a current signal from the X-ray detector 7 into a voltage signal, an integrator for periodically integrating the voltage signal, and a preamplifier for amplifying an output signal of the integrator. And a data acquisition system (DAS: dataacquisit) comprising an A / D converter for converting the output signal of the preamplifier into digital data.
ion system) 8 is provided.

Digital data output from the data collection system 8 is supplied to a light emitting element (not shown) provided on the rotating body 1 and transmitted from this light emitting element to a light receiving element provided on the fixed body 2 as a light beam. .

The optical transmission apparatus described in the present embodiment is suitable as an optical transmission apparatus for transmitting digital data output from the data acquisition system 8 as a light beam in such an X-ray CT apparatus.

The present invention is not limited to the above-described embodiment, but can be implemented with various modifications. For example,
In the first embodiment, the light scattering film 14 is formed so that the area becomes larger as the light scattering film is closer to the tip of the light propagation direction, that is, the length of the light scattering film in the light propagation direction gradually increases. However, for example, the length of the plurality of light scattering films in the light propagation direction may be fixed, and the interval between the light scattering films may be gradually reduced toward the front end side in the propagation direction. In short, it is only necessary that the transparent plate 13 be formed such that the area ratio per unit length (constant length) in the longitudinal direction increases toward the front end of the transparent plate 13 in the light propagation direction.

In using the light guide according to the present invention, the first end face 13A (light incident face) of the transparent plate 13 and the second end face 13A are used.
An exterior may be formed so that the whole or a part of the surface other than the end surface (light emission surface) is wrapped with a light reflector such as a white object or a mirror. By doing so, the transparent plate 13
Can be reflected by a white object or a mirror surface and returned to the inside of the transparent plate 13 again, and the conversion efficiency can be further improved. In addition, when the light guide is held, the outer case can be held without increasing light loss.

The optical transmission device according to the present invention is applicable not only to the transmission of light (optical signal) between the rotating body and the fixed body, but also to the transmission of light between relatively linearly moving objects. Further, the light guide according to the present invention can also be applied to a document surface illumination device in an image scanner.

[0053]

As described above, according to the present invention, it is possible to provide a light guide having a high conversion efficiency from incident light to outgoing light, so that the output of the light emitting element can be greatly reduced and low power consumption can be achieved. Power consumption, high reliability, and low cost can be achieved.

In an optical transmission device in which a light emitting element and a light receiving element move relatively, an allowable amount such as a moving distance or an axis shift increases, and the number of light emitting elements can be reduced, so that the assembling time is also reduced. Can be Furthermore, since the optical signal can be efficiently transmitted to the light receiving element, the speed can be easily increased. Further, a high-performance optical transmission device can be realized between the rotating body and the fixed body, and is suitable for an X-ray CT apparatus.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a light guide according to a first embodiment of the present invention.

FIG. 2 is a view for explaining an operation principle of the embodiment.

FIG. 3 is a diagram illustrating an area distribution of a light scattering film in a light propagation direction according to the first embodiment.

FIG. 4 is a diagram showing the relationship between the length of the light scattering film in the light propagation direction, the intensity of propagating light incident on a minute unit, and the area ratio of the minute scattering film according to the first embodiment.

FIG. 5 is a perspective view showing a configuration of a light guide according to a second embodiment of the present invention.

FIG. 6 is a view showing a modeled light guide according to a second embodiment;

FIG. 7 is a diagram showing the relationship between the length of a light scattering film in the light propagation direction, the intensity of propagating light incident on a minute unit, and the width of a transparent plate according to the second embodiment.

FIG. 8 is a perspective view showing a configuration of a light guide according to a third embodiment of the present invention.

FIG. 9 is a side view and a front view showing a configuration of an optical transmission device according to a fourth embodiment of the present invention.

FIG. 10 is a perspective view showing a schematic configuration of an X-ray CT apparatus to which the optical transmission device is applied;

FIG. 11 is a perspective view showing a conventional light guide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Light emitting element 12 ... Incident light 13 ... Transparent plate 13A ... 1st end surface (light incidence surface) 13B ... 2nd end surface (light scattering film formation surface) 13C ... 3rd end surface (light emission surface) 14 ... Light scattering film 15 ... Outgoing light 21 ... Rotating body 22 ... Fixed body 23 ... Light emitting element 24 ... Light receiving element 25 ... Light guide 26 ... Reflective surface (light incident surface)

Continued on the front page F term (reference) 2H038 AA55 BA06 4C093 AA22 BA03 CA32 CA35 CA50 EC41 EC60 FH06 5B047 AA17 AA30 BC01 BC04 5C072 AA01 BA05 DA16 DA17 DA21 EA05

Claims (9)

[Claims] 1. A transparent plate arranged to receive incident light at a first end face on one end side in a longitudinal direction; and a transparent plate formed at intervals on a second end face along the longitudinal direction of the transparent plate. A plurality of light-scattering films that scatter light propagating in the plate and emit the light from a third end surface of the transparent plate facing the second end surface, wherein the plurality of light-scattering films are formed in a longitudinal direction of the transparent plate. A light guide characterized in that an area ratio of the light scattering film per unit length in a direction becomes larger toward a front end in a light propagation direction in the transparent plate. 2. A transparent plate arranged to receive incident light at a first end face on one end side in a longitudinal direction; and a transparent plate formed at intervals on a second end face along the longitudinal direction of the transparent plate. A plurality of light scattering films for scattering light propagating in the plate and emitting the light from a third end surface of the transparent plate facing the second end surface, wherein the plurality of light scattering films are arranged in the transparent plate. A light guide, wherein the light scattering film is formed so that the area becomes larger as the light scattering film is closer to the front end in the light propagation direction. 3. A transparent plate arranged to receive incident light at a first end face on one end side in a longitudinal direction, and formed on a second end face along the longitudinal direction of the transparent plate, and propagates in the transparent plate. And a light scattering film that scatters the emitted light and emits the light from the third end face of the transparent plate facing the second end face, wherein the transparent plate gradually moves toward the front end in the light propagation direction in the transparent plate. A light guide, wherein a distance between the second end face and the third end face is reduced. 4. A transparent plate arranged to receive incident light at a first end face on one end side in a longitudinal direction, and a transparent plate formed at a second end face along the longitudinal direction of the transparent plate with a space therebetween. A plurality of light scattering films for scattering light propagating in the plate and emitting the light from a third end surface of the transparent plate facing the second end surface, wherein the plurality of light scattering films are arranged in the transparent plate. The light scattering film closer to the front end in the light propagation direction is formed to have a larger area, and the light scattering film on the front end side in the propagation direction is formed continuously in the propagation direction. In a region where the light scattering film is continuously formed, the distance between the second end surface and the third end surface is gradually reduced toward the front end in the light propagation direction in the transparent plate. And light guide. 5. The light guide according to claim 1, wherein the transparent plate is made of an acrylic resin, and the light scattering film is formed by silk printing. 6. The light guide according to claim 1, wherein at least a part of a surface of the transparent plate other than the first end surface and the third end surface is surrounded by a light reflector. 7. A light guide according to any one of claims 1 to 6, a light emitting element for emitting outgoing light to a first end face of the light guide, and a light emitting element relative to the light emitting element and the light guide. And a light receiving element for receiving light emitted from the third end face of the light guide. 8. An optical transmission device for transmitting data as a light beam between a rotating body and a fixed body opposed to each other, wherein at least one light emitting device arranged on the rotating body and emitting light according to data to be transmitted. An element, at least one light receiving element disposed on the fixed body and receiving light from the light emitting element; and one of the rotating body and the fixed body positioned between the fixed body and the rotating body. An optical transmission device, comprising: a light guide fixed to one side and guiding light from the light emitting element to the light receiving element. 9. An X-ray CT apparatus using the optical transmission apparatus according to claim 8, wherein digital data obtained by processing an output signal from an X-ray detector is transmitted as the light beam.