JPS6335962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to the structure of an optical splitter that distributes optical signals from optical fibers.

[Technical background of the invention and its problems]

In general, the distribution of optical signals to a large number of terminals by passive optical circuit elements is particularly important for realizing highly reliable and economical optical networks.

Conventionally, star couplers have been known as such passive circuit elements, which output an optical signal input to one input terminal to all output terminals, and star-shaped networks centered around this type of couplers have been developed. Are known. However, in such a system, it is necessary to wire optical cables from all stations to the star coupler, and when the number of stations is increased, the overall length of the required optical cables increases, resulting in an increase in cost. Also, since many optical cables were connected to one star coupler, the cables were congested and not necessarily easy to use.

If a plurality of the star couplers described above are used and connected in cascade, the number of stations connected to each star coupler will be small even if the total number of stations is large, and the above-mentioned problems can be considered to be eliminated. However, in conventional star couplers, a part of the optical signal is also distributed to the output terminal of the port where the optical signal is input, so a closed loop is formed and oscillation occurs.
Normal optical transmission was impossible.

That is, if the first and second star couplers 1a and 1b have the characteristic of outputting the optical signal supplied to the input terminal of each port to the output terminals of all ports as shown in FIG. The optical signal output from the star coupler 1a passes through a first receiver 2a, a first transmitter 3a, a second star coupler 1b, and then a second receiver 2b and a second transmitter 3b. The signal is then inputted to the first star coupler 1a, and a portion of it is sent out again to the first receiver 2a. In this way, a closed loop is formed and oscillation occurs. Furthermore, the first
In the figure, 4 is a station consisting of an optical transmitter 4a and an optical receiver 4b.

The present inventors previously proposed an optical splitter that is suitable for the above-mentioned system and does not cause oscillations (Japanese Patent Application No. 5671/1983). That is, it is an optical splitter in which no optical signal is output to the output terminal of the port to which the optical signal is supplied. FIG. 2 shows an example of this type of optical splitter.
This optical splitter is an example of an optical splitter having three ports, where the first port consists of an input terminal 11a and an output terminal 11b, and similarly, the second port consists of an input terminal 12a and an output terminal 12b. The third port includes an input terminal 13a and an output terminal 13b. Input terminals 11a, 12 by optical fiber
The optical signals inputted to each of the optical signals a and 13a are given a predetermined phase shift change in the vertical direction by a convex lens 14 made up of three so-called semi-cylindrical lens bodies arranged vertically in parallel, and are further shifted horizontally by a convex lens 15. After being given a change in the amount of phase shift, a deflection matrix plate 16 having six different planes on the radiation side as shown in the figure
incident on . A deflection matrix plate 17 disposed on the output side of the matrix plate 16 has an optical function completely opposite to that of the matrix plate 16. The optical signal incident on the upper stage of the deflection matrix plate 16 is divided into two parts, the first half and the second half, and enters the lower and middle parts of the deflection matrix plate 17. Similarly, the deflection matrix plate 16
The optical signals incident on the middle and lower stages are incident on the upper and lower stages and the middle and upper stages of the deflection matrix plate 17. The optical signal that has passed through the deflection matrix plate 17 passes through convex lenses 15 and 14 and convex lenses 18 and 19 having the same structure, and is output to the output terminal 1 of each port.
It is output to 1b, 12b, and 13b.

In the end, in this optical splitter, the optical signal input to the input terminal 11a of the first port is output to the output terminals 12b and 13b of the second and third ports, but not to the output terminal 11b of the first port. Therefore, the optical distributor has the characteristics described above. However, this optical distributor has a complicated structure and is difficult to adjust, and there are problems in reducing optical loss.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved optical distributor having a characteristic that no optical signal is output to the output terminal of a port to which an optical signal is supplied.

[Summary of the invention]

In the present invention, the end faces of N input optical fibers and output optical fibers constituting N ports (N is an integer of 3 or more) are aligned and arranged in a predetermined positional relationship.
A group of 2N optical fibers, a 1/4 pitch length rod lens or an optical system equivalent to this provided in contact with the end face of the optical fiber group, and the other side of the rod lens or an optical system equivalent to this. The light distributor includes a light reflector having a plurality of reflective surfaces provided in contact with an end face and having at least 2N-3 different surface normals.

The light reflector has a plurality of reflective surfaces so as to distribute the light input from the end of the input optical fiber of any port to all the output optical fibers other than the output optical fiber of the port at a predetermined ratio. normal,
Area and reflectance are set.

〔Effect of the invention〕

According to the invention, a light distributor is obtained that is simple in structure and adjustment.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 3 shows the overall configuration of an optical transmission system to which the optical splitter of the present invention is applied. 20 will be explained in detail later. For example, an optical splitter according to the invention having four ports. Each optical distributor 20 has a first to a fourth optical divider 20.
It has three ports 21, 22, 23, and 24. The first and second ports 21 and 22 of each optical distributor 20 are connected to the adjacent optical distributor 20, and the third,
A station 25 is connected to the fourth ports 23 and 24. Each station 25 has an optical transmitter 26 that transmits an optical signal.
and an optical receiver 27 for receiving optical signals.

Each optical distributor 20 has characteristics as shown in the schematic diagram of FIG. Each port consists of an input optical fiber end that inputs an optical signal and an output optical fiber end that outputs an optical signal. The first port 21 consists of an input optical fiber end M ₁ and an output optical fiber end M ₁ ', and the second port 22 consists of an input optical fiber end M ₂
and an output optical fiber end M ₂ ′. Also, the third
The port 23 consists of an input optical fiber end T ₁ and an output optical fiber end R ₁ , and the fourth port 24 consists of an input optical fiber end T ₂ and an output optical fiber end R ₂ . The optical signal entering each input optical fiber end passes through this optical splitter and enters all output optical fiber ends other than that port. For example, an optical signal entering the input optical fiber end _M1 of the first port 21 is transmitted to the output optical fiber end M1 of this port.
2nd, 3rd, 4th ports 22, 23, other than M ₁ '
24 output optical fiber ends M ₂ ', R ₁ , R ₂ . This optical distributor has the characteristic that optical signals are distributed in the same manner.

FIG. 5 shows the structure of a first embodiment of the present invention having the above characteristics. In Figure 5, 31
~34 connects its end to the input optical fiber end M ₁ ,
M ₂ , T ₁ , T ₂ optical fibers, 41 to 4
4 connects its ends to the output optical fiber ends M ₁ ′, M ₂ ′R ₁ ,
It is an optical fiber with R ₂ . FIG. 6 shows the positional relationship between the ends of each input and output optical fiber. In the figure, a circular portion indicated by a dotted line indicates that an optical fiber having the same size and shape as each optical fiber is provided as a dummy. These optical fibers may be omitted.

As shown in FIG. 5, the end faces of these input/output optical fibers 31 to 34, 41 to 44 have a diameter large enough to include all of these end faces, and 1/
A cylindrical rod lens 35 with a length of 4 pitches is provided so as to abut one end surface thereof. The other end face of the rod lens 35 is provided with a light reflector 45 made of glass and having a large number of reflective planes.

The rod lens 35 is made so that its refractive index gradually decreases outward from its central axis, and the length of one cycle of light bending changes depending on the state of this refractive index change. Assuming that the length of one cycle is one pitch, here the rod lens 35 is 1/4
It is chosen for its length. Actually, this rod lens used had a diameter of 2 mm and a length of 5 mm.

Of course, the rod lens may be an integral multiple of 1/4 pitch.

As shown in FIG. 7, the light reflector 45 has seven reflecting surfaces 51 to 57 when viewed from this direction.
Note that the reflective surfaces 51 and 52 are on the same plane. That is, the normals of these surfaces are in the same direction, and the rod lens 3
The central axes of 5 are also in the same direction. These reflective surfaces 51 to 57 are formed by providing a gold thin film or a dielectric multilayer film on the upper surface of a polyhedron made of glass.

Here, using FIGS. 8 to 11, it will be explained that the optical distributor of the embodiment shown in FIG. 5 has the characteristics shown in FIG. 4.

First, attention will be paid to the optical signal that has passed through the optical fiber 31 and is emitted from the input optical fiber end M ₁ of the first port 21 . This optical signal passes through the rod lens 35 and is incident on the light reflector 45 as a substantially parallel beam with an inclination determined by the distance between the optical fiber 31 and the central axis of the rod lens 35 and the focusing parameter.
Although the light beam incident on the light reflector 45 has a small divergence angle determined strictly by the diameter of the optical fiber 31 and the focusing parameter of the rod lens 35, it can be regarded as a substantially parallel light beam as described above.

As shown in FIG.
The light is reflected by the optical fiber and is incident on a position symmetrical with respect to the x-axis and the y-axis, that is, the end of the output optical fiber M ₂ '.

Incidentally, a rod lens generally has the property of converging a parallel beam of light tilted with respect to its central axis at a position at a distance from the central axis that is proportional to the angle of inclination after 1/4 pitch propagation. Therefore, the reflective surface 54
If this reflective surface 54 is provided so that the normal vector of
The partial light flux incident on the third port 23 is focused at the output optical fiber end R ₁ of the third port 23 . As shown in FIG. 6, in this embodiment, the output optical fiber end R ₁
is placed in the direction of 45° from the output optical fiber end M ₂ ' with respect to the y-axis, so the reflective surface 52 and the reflective surface 5
The intersection line of 4 makes an angle of 45° to the y-axis. In other words, the input of the optical signal to the output optical fiber end _R1 can be described as follows. When the optical signal from the input optical fiber end M ₁ is reflected by the reflecting surfaces 51 and 52 whose normal line is parallel to the central axis of the rod lens 35, it is reflected at a point-symmetrical position, that is, at the output optical fiber end M ₂ ′. The coupling point (displacement vector M ₁ M ₂ ′) is further added with a displacement vector M ₂ ′R ₁ that makes an angle of 45° to the y-axis on the rod lens surface on the side where the fiber group is arranged by the inclined reflecting surface 54. Ru. In Figure 8, these displacement vectors are expressed as 5 using the numbers of the reflective surfaces.
They are shown as 1, 52, 54.

Further, another part of the above-mentioned signal is also reflected by the reflecting surface 56 and eventually enters the output optical fiber end _R2 of the fourth port 24. In this way,
The optical signal launched from the input optical fiber end _M1 is
It is reflected by the reflecting surfaces 51, 52, 54, and 56 of the light reflector 45, and the output optical fiber ends M ₂ ′, R ₁ ,
It will be incident on R ₂ .

Similarly, as shown in FIG.
The optical signal emitted from the input optical fiber end M ₂ of No. 2 is reflected by the reflecting surfaces 51 and 52 and the reflecting surfaces 53 and 55, and enters the output optical fiber ends M ₁ ', R ₁ and R ₂ .

Further, as shown in FIG. 10, the optical signal emitted from the input optical fiber end _T1 of the third port 23 is reflected by the reflecting surfaces 51 and 52 to a position symmetrical with respect to the x-axis. Since it is also reflected by the light beam, it enters the output optical fiber end M ₂ '. Similarly, the optical signal reflected by the reflecting surface 54 enters the output optical fiber end M ₁ ', and the optical signal reflected by the reflecting surface 57 enters the output optical fiber terminal R ₂ .

Furthermore, as shown in FIG. 11, the optical signal emitted from the input optical fiber end _T2 of the fourth port 24 is
The light is reflected by the reflecting surfaces 51 and 52 in a symmetrical position with respect to the x-axis, but it is also reflected by the reflecting surface 56, so that it enters the output optical fiber end M ₁ '. Similarly, the optical signal reflected by the reflecting surface 55 enters the output optical fiber end M ₂ ', and the optical signal reflected by the reflecting surface 57 enters the output optical fiber end R ₁ .

As mentioned above, each input optical fiber end M ₁ ,
The optical signals emitted from M ₂ , T ₁ , and T ₂ are respectively incident on three output fiber ends other than the corresponding output fiber ends M ₁ ′, M ₂ ′, R ₁ , and R ₂ .

According to the embodiment shown in FIG. 5, one surface of the light reflector is a plane perpendicular to the central axis of the rod lens, which has the advantage of being particularly easy to manufacture.

In the above embodiment, the reflective surface 57 of the light reflector 45 that tilts the optical signal in the negative direction on the y-axis is provided on the same surface as the other reflective surface. However, as shown in FIG. 12, a reflective surface 58 for tilting the optical signal in the negative direction on the y-axis may be provided on the other surface of the surface provided with the other reflective surface. In this case, the reflective surface 58 is not a complete reflective surface but reflects some light,
The light reflector 46 is fixed to the rod lens 36 with this surface tilted in the y-axis direction with respect to the central axis of the rod lens 36 (for example, a reflectance of 1%). 13A and 13B are plan views of both sides of the light reflector 46, and arrows in these figures indicate the direction of light deflection. This light reflector 4
6, the displacement vector 57 in FIG. 10 and FIG. It is only different from the case of the embodiment.

According to the above-mentioned embodiment of the present invention, compared to the embodiment shown in FIG. Therefore, loss due to diffraction and unnecessary coupling can be minimized. Also, the reflective surfaces 51 to 5
6 can be set approximately in the shape of a fan, so that the dependence of the excitation mode distribution in the multimode fiber on the optical distribution ratio can be made sufficiently small.

Further, by polishing the surface of the rod lens 36 that is in contact with the light reflector 46 parallel to the reflective surface 58 of the light reflector 46, the following unnecessary coupling can be removed.

If this surface of the rod lens 36 is perpendicular to the central axis and there is residual reflection, there is a possibility that the following displacement vector addition will occur, which may cause unnecessary coupling.

M ₁ M ₂ ′-→+M ₂ ′R ₁ —→+R ₁ M ₁ ′-→(
[51,
52] + [54] + [53]) Next, when the end face of the rod lens 36 is formed by the reflective surface 58, a displacement vector due to this reflective surface is added, so that unnecessary coupling can be avoided. That is, compared to the embodiment shown in FIG. 5, the embodiment shown in FIG. 12 has the effect of further suppressing unnecessary coupling.

The above embodiments are all examples in which the input/output optical fiber ends of the third and fourth ports are arranged on the y-axis via a dummy optical fiber end.
As shown in the figure, the ends of the input and output optical fibers of each port may be arranged with the y-axis narrowed.

That is, as is clear from FIG. 15, which shows the arrangement of the ends of the input and output optical fibers, the first,
The input optical fiber end M ₁ of the second port 21, 22,
M ₂ , input optical fiber ends T ₁ , T ₂ of the third and fourth ports 23 and 24, and output optical fiber ends M of the first and second ports 21 and 22 via a dummy optical fiber end. ₁ ′, M ₂ ′, 3rd and 4th ports 23,
Twenty-four output optical fiber ends R ₁ , R ₂ are sequentially provided.

Reference numeral 37 designates a rod lens having a length of 1/4 pitch, one end surface of which is provided in contact with the end surface of the input/output optical fiber, and a light reflector 47 is provided on the other end surface.

The light reflector 47 has five reflective surfaces 61 to 65 on the surface not in contact with the rod lens 37, and one reflective surface 66 on the surface in contact with the rod lens 37. The reflective surfaces 61 and 62 are planes perpendicular to the rod lens 37, and the reflective surfaces 63 to 62 are planes perpendicular to the rod lens 37.
65 is provided at a predetermined angle so as to reflect the optical signal in the direction of the arrow in FIG. 16A. The reflecting surface 66 is provided so as to reflect the optical signal in the direction of the arrow in FIG. 16B. Reflective surfaces 61-65
is an almost perfect reflective surface formed by providing a thin gold film or a dielectric multilayer film on the surface of a polyhedron made of glass, but the reflective surface 66 has a reflectance of 1, for example.
% is an imperfectly reflective surface.

Here, in the embodiment shown in FIG. 12, how the optical signals emitted from the ends of each input optical fiber enter the ends of the output optical fibers will be explained using FIGS. 17 to 20.

First, the input optical fiber end of the first port 21
The optical signal emitted from _M1 is reflected by the reflecting surfaces 61 to 62 and sent to the second port 2, as shown in FIG.
2 into the output optical fiber end M ₂ '. Further, a part of the light is reflected by the reflecting surface 64 and also enters the output optical fiber end _R1 . Some optical signals are reflected by the reflective surface 65
It is also reflected by the output optical fiber end R ₂ of the fourth port 24 . In this way, the first port 2
The optical signal emitted from the input optical fiber end _M1 of the input optical fiber 1 is reflected by the reflecting surfaces 61, 62, 64, and 65, and is transmitted to the output optical fiber end M1 of the second, third, and fourth ports 22, 23, and 24. ₂ ′, R ₁ , R ₂ .

Similarly, the input optical fiber end of the second port 22
The optical signal emitted from M ₂ is reflected by the reflecting surfaces 61, 62, 63, 65 as shown in FIG _. , R ₁ , R ₂ . The optical signal emitted from the input optical fiber end _T1 of the third port 23 is transmitted to the reflecting surfaces 61 and 6 as shown in FIG.
2, 64, 65, and 66, and enter the output optical fiber ends M ₁ ′, M ₂ ′, and R ₂ of the first, second, and fourth ports 21, 22, and 24, respectively. 4th port 2
The optical signal emitted from the input optical fiber end _T2 of No. 4 is reflected by the reflecting surfaces 61, 62, 6 as shown in FIG.
3, 65, and 66 and reflected by the first, second, and third
Output optical fiber ends of ports 21, 22, 23
incident on M ₁ ′, M ₂ ′, and R ₁ .

Therefore, the characteristics shown in FIG. 4 can also be obtained with the embodiment shown in FIG.

According to this embodiment, the number of reflective surfaces of the light reflector 47 is further reduced by one compared to the embodiment shown in FIG. 12, which has the advantage of reducing light loss and facilitating manufacture. In addition, the ends of the input and output optical fibers are arranged in a short range from the center, allowing the use of rod lenses with small diameters, and the reflective surface of the light reflector 47 is small, making the light distributor compact. There is also.

In each of the optical splitters of the above embodiments, the coupling between the first port and the second port is the strongest, and the coupling between the first port and the second port is the strongest.
The coupling between the port, the third port, and the fourth port is moderate, and the coupling between the third port and the fourth port is set to be the weakest. However, the arrangement, area, and input of the reflective surface of the light reflector By changing the arrangement of the output optical fiber ends, arbitrary coupling conditions can be realized within the range allowed by symmetry.

The optical distributor of the present invention not only has four ports as in the above embodiment, but also has three or five ports.
It can also be applied to an optical distributor having the above ports.

It will be explained below that when there are N ports, it is sufficient that there are at least 2N-3 surface normals of the plurality of reflective surfaces.

First, in the above embodiment, the case where N=4 is explained, and in the configuration shown in FIG. An example of a reflector is shown.
(Here, the reflecting surfaces 61 and 62 in FIG. 14 have the same surface normal.) Therefore, in the case of N=4, the light reflector has (2N-3) surface normals. It can be seen that this is realized by

Next, the case where N>4 will be explained with reference to FIG. 21.

Input port #1~#N, output port #1'~
Let it be #N′. Here, it is assumed that the input port of #K and the output port of #K' form a pair. It is assumed that the positional relationship between the ends of each input and output optical fiber is as shown in FIG.

Distributes the light from input port #1 to output ports other than #1'. Count the number of surface normals required for

First, for #1→#N', light is guided by the first reflecting surface having a surface normal that coincides with the central axis of the rod lens. Also, #1→#1' should not be combined. #1 → #2′, #3′,
...For #N'-1, 2a, 3a, ..., respectively.
(N-1) Surface normals that give N-2 types of deviation vectors of a are required.

As a result, a plurality of reflecting surfaces having (N-1) surface normals are required to perform light distribution of #1→#2', #3', . . . , #N'.

Next, consider distributing the light from input port #2 to output ports other than #2'. Since #2 and #1' are in axially symmetrical positions, the light is coupled by the first reflecting surface. Coupling to the remaining ports requires surface normals corresponding to vectors that give deviations from #1', to #3', #4', ... #N'-1 and #N'. #1′ to #3′, #4′,
..., #N'-1 are 2a, 3a, respectively
..., (N-2)a, surface normals giving (N-3) types of deviation vectors are required, but these have already been counted in the light distribution from #1. The newly required surface normal is one type of vector -a that gives the deviation from #1' to #N'.

Similarly, the new surface normal required to distribute the light from input port #3 to output ports other than #3' is −
This is one type of 2a.

Similarly, the light of input port #N-1 is #N'-1
The number of new surface normals required for distribution to other output ports is one type -(N-2)a.

Similarly, the surface normal required to distribute light from input port #N to output ports other than #N' is −
a, -2a, ..., -(N-2) a and the surface normal corresponding to the first reflecting surface and the surface normal (N-1), but these overlap with those already counted. Therefore, there is no need for new surface normals.

Therefore, the required number of surface normals is (2N-3), which is the sum of (N-1) #1 and (N-2) #2 to #N-1. As explained above, when the number of ports is N, it is understood that the number of surface normals of the plurality of reflective surfaces should be at least 2N-3.

Although the above embodiments all use 1/4 pitch length rod lenses, the present invention is not limited to this.
An equivalent optical system having the characteristics of collimating light and focusing the parallel light may also be used.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an optical transmission system using a conventional star coupler, Fig. 2 is a structural diagram of an optical splitter proposed earlier, and Fig. 3 is an optical transmission system using the optical splitter of the present invention. A system configuration diagram, FIG. 4 is a schematic diagram showing the characteristics of the optical distributor of the present invention, FIG. 5 is a perspective view of an embodiment of the present invention, and FIG. 6 is an input/output optical fiber of the embodiment of the present invention. 7 is a diagram showing the state of the reflective surface of the light reflector in the embodiment of FIG. 5, and FIGS. 8 to 11 are diagrams showing the arrangement of the optical signals in the embodiment of FIG. FIG. 3 is a diagram showing an input/output relationship. FIG. 12 is a perspective view of another embodiment of the present invention, and FIG. 13 is a perspective view of another embodiment of the present invention.
FIG. 14 is a perspective view of still another embodiment of the present invention, and FIG. 15 is a diagram showing the input/output optical fiber end of the embodiment of FIG. 14. Fig. 16 is a diagram showing the arrangement relationship of the parts.
A diagram showing the state of the reflective surface of the light reflector in the example shown in the figure,
17 to 20 are diagrams showing the input/output relationship of optical signals in the embodiment of FIG. 14, and FIG. 21 is a diagram for explaining the number of surface normals of a plurality of reflective surfaces. 20... Optical distributor, 21... First port, 22... Second port, 23... Third port, 24... Fourth port, 25... Station, 26... Optical transmitter, 27... Optical receiver, M ₁ , M ₂ , T ₁ , T ₂ ... input optical fiber end,
M ₁ , M ₂ , R ₁ , R ₂ ...output optical fiber end, 35,
36, 37... Rod lens, 46, 46, 47...
Light reflector, 51-58, 61-66...reflection surface.

Claims (1)

[Claims] 1. 2N optical fibers arranged in a predetermined positional relationship at the end faces of N input optical fibers and N output optical fibers constituting N ports (N is an integer of 3 or more). a fiber group, a 1/4-pitch rod lens or an optical system equivalent thereto with one end surface in contact with the end surface of the fiber group, and a rod lens or an optical system equivalent thereto with one end surface in contact with the other end surface of the rod lens or optical system equivalent thereto. a light reflector provided with a plurality of reflective surfaces having at least 2N-3 different surface normals, and the light reflector reflects light input from the input optical fiber end of an arbitrary port. An optical distributor characterized in that the surface normals, areas, and reflectances of the plurality of reflective surfaces are set so as to distribute the distribution to all output optical fibers other than the output optical fiber of a port at a predetermined ratio. 2. The light distributor according to claim 1, wherein the light reflector has all reflective surfaces on the side that does not come into contact with a rod lens or an optical system equivalent thereto. 3. The light reflector has an imperfect reflective surface that reflects some light and transmits some light on the surface that is in contact with the rod lens or equivalent optical system,
2. The light distributor according to claim 1, wherein the light distributor has a substantially perfect reflective surface on the surface not in contact with a rod lens or an optical system equivalent thereto.