JPS606802Y2 - optical distribution circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to optical fiber communications, and more particularly to an optical distribution circuit for an optical fiber that distributes light from an optical fiber to a plurality of other optical fibers.

Communication systems often require a signal distribution circuit for the purpose of distributing signals to multiple locations.

Among communication systems, optical communication has been gaining popularity in recent years due to its broadband nature and
Optical fiber communication systems, which use optical fibers as transmission paths, are attracting attention due to various features such as resistance to electromagnetic induction. It is considered to be promising due to various advantages such as sex.

Conventionally, optical distribution circuits in the field of optical fiber communications have been made by combining a glass plate (a type of optical transmission body) with a thickness of about 80 μm, for example, and optical fibers arranged in a plate shape along the end face of this glass plate. was used.

However, in this conventional optical distribution circuit, the thickness of the glass plate is as thin as about 80 μm, which makes it difficult to manufacture the glass plate and assemble the optical distribution circuit.

Furthermore, in this optical distribution circuit, the light is transmitted through the thickness of the glass plate, which is approximately 80 mm thick.
Since the light is configured to undergo multiple reflections and propagation on both sides of the μ skin, there is a drawback that loss occurs due to the multiple reflections of light due to imperfections such as dirt on these surfaces.

Furthermore, if the thickness of the glass plate in this optical distribution circuit is increased, the core diameter of the optical fiber becomes smaller than the thickness of the glass plate, resulting in a disadvantage that the coupling loss of light from the glass plate to the optical fiber increases.

Furthermore, in order to reduce the coupling loss of light from the glass plate to the optical fiber in this optical distribution circuit, it was necessary to remove the cladding portion of the optical fiber by etching or the like, leaving only the core portion.

The object of this invention is to provide an optical distribution circuit for optical fibers that has low loss and is easy to manufacture optical transmission bodies and assemble circuits.

According to this invention, there is provided an optical transmission body having two end faces substantially perpendicular to the optical axis plane, and one or more optical transmission bodies having one end face disposed close to one of the two end faces of the optical transmission body. an optical fiber, a plurality of cylindrical lenses disposed close to the other of the two end faces so that the optical axis thereof is substantially perpendicular to the optical axis plane of the optical transmission body; a plurality of optical fibers having one end face disposed close to the side opposite to the side where the optical transmission body is located of the cylindrical lens, and the optical transmission body It has a refractive index distribution that decreases approximately in proportion to the square of the distance from the optical axis plane, and has a length of approximately (172 m pitch - D), where skin is a positive integer and D is the diameter of the cylindrical lens. An optical distribution circuit for an optical fiber is obtained, which is characterized by having the following.

The optical transmission body used in the optical distribution circuit of this invention is a transparent object whose refractive index n (r) decreases approximately according to the following formula as the distance r from the optical axis plane increases in a cross section perpendicular to the front axis plane. It is.

n (r) = η0(1-ar”)...
...(1) However, η0 is the refractive index on the optical axis plane, and a is a positive constant.

Such an optical transmitter is made using ion exchange or the like, and even if both end surfaces are flat, it has a lens effect in the direction perpendicular to the optical axis plane.

Since the refractive index has a square distribution in the direction perpendicular to the optical axis plane,
For example, light incident on a different axis plane parallel to the optical axis plane of a light transmitting body travels along the optical axis plane in a sinusoidal meandering manner.

In other words, the incident position of the light that enters the optical transmission body whose refractive index has a square distribution is rl from the optical axis plane, the incidence angle is 01, the output position is r2, the output angle is 02, and the length of the optical transmission body is L. Then, the following relationship holds true.

1 ・r2=Cos (Ja L) r1+product-7=ytn
(J a L) θ1...(2) θ2=-nOjaSin(jaL)r□...
(3) If b is the length of the optical transmission body at which the light is emitted at the zero point of incidence, the position and angle of exit, that is, the length of one pitch, then (2), from equation (3), Lo = 2? r/ja・
...(4).

In addition, if r = 0 in equations (2) and (3), that is, the light is incident on the optical axis plane at the end face of the optical transmission body at an angle θ1, then the length is 172LO, that is, 1/ r2=0 at 2 pitch length. Since θ2=-〇□, if the optical transmission body has a length of 172 pinches, the light will be emitted from the optical axis plane at the other end face of the optical transmission body at an angle of -01.

However, since there is no refractive index distribution in the direction parallel to the optical axis plane as in the perpendicular direction, if diverging light is incident on the optical transmission body, the light will spread as it is in the direction parallel to the optical axis plane, and in the case In some cases, the light may be reflected by the side wall of the optical transmission body and reach the other end of the optical transmission body.

Therefore, when a spot-shaped light output from an optical fiber is incident on one end face of the optical transmission body, the light becomes an elongated beam in a direction parallel to the optical axis plane at the other end face on the incident side of 1/2 pitch length.

Furthermore, a plurality of cylindrical lenses are arranged close to the end face on the output side of the optical transmission body so that the optical axis is perpendicular to the optical axis plane of the optical transmission body, and the length of the optical transmission body is approximately the same as that of the cylindrical lenses. If the beam is shortened by the diameter of , the elongated beam is divided into a plurality of locations and focused by a plurality of cylindrical lenses.

Note that since the optical transmission body has periodicity in the length direction as expressed by equations (2) and (3), a similar phenomenon occurs even if the length is an integral multiple of 172 pitches.

As described above, the present invention is based on the output from an optical fiber located at one end face of an optical transmission body with a length of (1/2 m, pitch - D, where skin is a positive integer, and D is the diameter of a cylindrical lens). Utilizing the fact that the emitted light is divided into multiple locations and emitted from the multiple cylindrical lenses placed close to the other end surface, multiple beams of light are emitted from these multiple condensing positions. Light is made incident on a plurality of optical fibers and distributed by arranging the end faces on one side of each fiber.

According to this invention, the light incident on the optical axis plane at the end face of the optical transmission body is emitted so as to be condensed on an extended plane of the optical axis plane, and also in the direction parallel to the optical axis plane, a plurality of lights are emitted. Since the cylindrical lens acts as a condenser, the incident light can be distributed to a plurality of optical fibers efficiently, that is, with low loss.

That is, in the present invention, since there is a cylindrical lens, almost no light enters the cladding part other than the core part of the optical fiber, so the loss can be lower than when there is no cylindrical lens.

Furthermore, since the optical transmission body does not need to be particularly thin, its production and circuit assembly are easy.

Furthermore, since almost no light enters the cladding portion of the optical fiber other than the core portion, there is no particular need to remove the cladding portion of the optical fiber by etching or the like to leave only the core portion.

Next, this invention will be explained with reference to the drawings.

Figure 1 is a diagram showing the configuration of the most preferred embodiment of this invention, in which a is a plan view, b is an elevational view, and C is a distribution of refractive index in the direction perpendicular to the optical axis plane of the optical transmission body. It is a diagram.

One end face of the optical fibers 11 to 16 is attached to the end face 2 of the optical transmission body 1, which is slightly shorter than 1/2 pitch length, and the optical transmission body 1
Cylindrical lenses 21-26 are arranged close to the other end face 3, and end faces of other optical fibers 31-36 on one side are arranged close to the cylindrical lenses 21-26.

Both end surfaces 2 and 3 of the optical transmission body 1 are substantially perpendicular to the optical axis plane 4, and the optical fibers 11 to 16 and the optical fibers 31 to 36
The end faces on one side of the optical fibers 11 to 16 are substantially parallel to the end faces 2 and 3, respectively, and the optical axes of the optical fibers 11 to 16 and 31 to 36 are arranged on an extension of the optical axis surface 4 of the optical transmission body 1. There is.

The cylindrical lenses 21 to 26 are arranged so that their central axes are substantially perpendicular to the optical axis plane 4 of the optical transmission body 1.

Further, the side walls 9 and 10 of the optical transmission body 1 are optically polished perpendicular to the optical axis plane 4 and the end faces 2 and 3.

In the direction perpendicular to the optical axis plane 4 of the optical transmission body 1, the refractive index is (1)
Since there is a square distribution as shown in the equation and FIG. For example, the ray 5 in Figure 1 travels through the cylindrical lenses 21 to 2.
6 and is focused on the end faces of optical fibers 31 to 36.

On the other hand, since the refractive index is constant in the direction parallel to the optical axis plane 4 of the optical transmission body 1, for example, the light incident on the optical transmission body 1 from the optical fiber 13 is parallel to the optical axis plane 4 of the optical transmission body 1. For example, the light rays 6, 7° 8 in Fig. 1a,
It reaches end face 3.

In this case, the light rays 6 and 7 are transmitted to the side wall 8 of the light transmitting body 1.
．． It may also be reflected at 9.

Therefore, the output light of the optical fiber 13 that enters the optical transmission body 1 from the end face 2 as a spot-like light becomes an elongated beam in a direction parallel to the optical axis plane and reaches the other end face 3.

By the way, since the cylindrical lenses 21 to 26 are arranged close to the end surface 3 so that their central axes and the optical axis plane 4 are perpendicular, the end surface 3
The emitted light is separated and condensed by the cylindrical lenses 21-26 at one end face of the optical fibers 31-36.

Therefore, the light emitted from the optical fiber 13 is transmitted to the optical fibers 31 to 3.
6 efficiently, that is, with low loss.

Similarly, the light emitted from the optical fibers 11, 12 and the optical fibers 14 to 16 is divided and input into the optical fibers 31 to 36.

The optical transmission body 1 having a refractive index distribution in the thickness direction as shown in FIG.
Obtained by dipping a 5 mm glass substrate into high temperature molten potassium salt, no = 1.63? a = 1.
6mm-2 has been realized.

In this case, the length of 172 pinches can be calculated by using equation (4), 1/
2Lo=2.5m.

For example, the optical fibers 11 to 16, 31 to 36 have a core diameter of 100ILrrL1, a cladding diameter of 150μ, N
, A of 0.26 can be used.

For example, the cylindrical lenses 21 to 26 have a diameter of 150 IL?
71. , and a refractive index of 1.63 can be used.

When using an optical fiber or a cylindrical lens as described above in FIG.
The thickness is 0.5mm and the width is 0.9rmn.

Manufacturing such an optical transmission body 1 and assembling the circuit are easy because the thickness of the optical transmission body 1 is as thick as 0.5 mm.

In addition, in distributing light to each of the six optical fibers, the light is mostly focused on the core portions of the optical fibers 31 to 36,
Since the light does not enter the cladding portion, a low-loss optical distribution circuit can be constructed.

Therefore, there is no particular need to remove the cladding portion of the optical fiber by etching or the like to leave only the core portion as is the case in the past.

In the case of the embodiment shown in FIG. 1 in which light is distributed to six optical fibers, the distribution loss to each of the six optical fibers is as low as about 100%.

In the first embodiment, since a portion of the light is reflected by the side walls 4 and 5, the side walls 4 and 5 are optically polished, but they may also be coated with a reflective coating.

Further, if the optical fiber disposed close to the end face 2 of the optical transmission body 1 is, for example, only the optical fiber 13, the optical fiber 1
If the emission angle of the emitted light 3 is small and the light is not reflected by the side walls 4 and 5, optical polishing or reflective coating of the side walls 4 and 5 is not necessary.

In this embodiment, the optical transmission body 1 is (112 pitch-D
), but it may be slightly shorter than the length (112 pitch-D), in which case the optical fiber 1
1 to 16 and the optical transmission body 1 may be opposed to each other with a slight distance from each other.

Furthermore, the optical transmission body 1 has a length of (1 pitch - D) and a length of (11/
It goes without saying that the length may be approximately an integral multiple of the 1/2 pitch length minus the diameter of the cylindrical lens, such as the length of 2 pitches (D).

In addition, in this embodiment, the optical fibers 11-16°31-3
6 is assumed to be on the extended plane of the optical axis plane 4 of the optical transmission body 1, but when the optical transmission body 1 has a pitch length of (k+l/2) (k is a positive integer), the optical axis of the optical fiber 11 ~16. The optical axes of 31 to 36 and the optical axis plane 4 are almost parallel, and the optical fiber 11
16 and the optical axes of the optical fibers 31 to 36 may be on a symmetrical plane with respect to the optical axis plane 4.

In addition, the pitch length of the optical transmission body 1 is (however, e is a positive integer)
In this case, the optical axes of optical fibers 11 to 16 and optical fiber 3
The optical axes 1 to 36 may be on the same plane parallel to the optical axis plane 4.

Furthermore, in these cases, the optical fibers 11-16, 31-3
The optical axis 6 may be slightly inclined by the same angle with respect to the optical axis plane 4 of the optical transmission body 1.

However, the direction of the inclination of the optical axes of the optical fibers 11 to 16 and the direction of the inclination of the optical axes of the optical fibers 31 to 36 are different from each other in the optical transmission body 1.
It is necessary to do the opposite when the pitch length is (k + 172), and the same when the pitch length is l.

Further, the cylindrical lens may be a semi-cylindrical lens cut into two in a direction parallel to its tip axis, and in this case, the cut plane of the semi-cylindrical lens is connected to the end surface of the optical transmission body It should be placed parallel to 3.

Note that the cylindrical lens and semi-cylindrical lens may be made of a material such as epoxy resin or acrylic resin.

Furthermore, a matrix in the form of a semi-cylindrical lens may be prepared separately, and a replica thereof may be formed on the end surface 3 of the optical transmission body 1 using epoxy resin or the like.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of an embodiment of this invention, in which a is a plan view, b is an elevational view, and C is a distribution of refractive index in the direction perpendicular to the optical axis plane 4 of the optical transmitter 1. It is a diagram. In the figure, 1... optical transmission body, 2, 3...
... end face, 4 ... optical axis surface, 5. 6.7
．． 8... Ray, 9,10... Side wall,
11-16.31-36...Optical fiber, 21
~26... It is a cylindrical lens.

Claims (1)

[Scope of utility model registration request] A convergent light having a refractive index distribution that decreases approximately in proportion to the square of the distance from the optical axis plane in a cross section perpendicular to the optical axis plane including the optical axis, and having two end faces perpendicular to the optical axis. a transmission body;
An optical fiber disposed on one end surface of the convergent light transmission body, a plurality of cylindrical lenses whose central axes are disposed substantially perpendicular to the optical axis plane on the other end surface, and a plurality of optical fibers having optical axes perpendicular to the central axis arranged to be sandwiched between the light transmitting body, and the sum of the length of the converging light transmitting body and the diameter of the cylindrical lens is approximately the converging property. An optical distribution circuit characterized in that the pitch is an integral multiple of 172 of the pitch of propagation while meandering through an optical transmission body.