JPS6218890B2 - - 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, a star coupler is known as such a passive circuit element, which outputs an optical signal input to one input terminal to all output terminals, and a star-shaped network centered on this type of coupler is known. It is being 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. Furthermore, since many optical cables are connected to one star coupler, the cables become congested and are 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, as shown in FIG. 1, 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 terminal of all ports, the first 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. Note that in FIG. 1, 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 oscillation (Japanese Patent Application No. 57-5651). That is, it is an optical splitter in which no optical signal is output to the output terminals of the port pair to which the optical signal is supplied. FIG. 2 shows an example of this type of optical splitter. This distributor is an example of an optical distributor having three port pairs, where the first port pair is the input terminal 11a.
Similarly, the second port pair consists of an input terminal 12a, an output terminal 12b, and an output terminal 11b.
The third port pair is input terminal 13a and output terminal 13b
Each consists of Optical signals input to input terminals 11a, 12a, and 13a through optical fibers are given a predetermined phase shift change in the vertical direction by a convex lens 14 made up of three so-called semicylindrical lens bodies arranged vertically in parallel. Further, after being given a phase shift change in the horizontal direction by a convex lens 15, the light enters a deflection matrix plate 16 having six different planes on the radiation side as shown in the figure. This matrix plate 16
The deflection matrix plate 17 arranged on the emission side of
It has an optical effect completely opposite to that of No. 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 optical signals incident on the middle and lower stages of the deflection matrix plate 16 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 18 and 19 having the same structure as convex lenses 15 and 14, and is output to output terminals 11b, 12b, and 13b of each port pair.

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

[Purpose of the invention]

The present invention provides an optical splitter suitable for an optical transmission system having many stations, that is, an improved optical splitter having a characteristic that no optical signal is output to the output terminal of a pair of ports to which an optical signal is supplied. The purpose is to

[Summary of the invention]

The present invention uses a group of reflective plates in which a plurality of reflective plates each having a transmitting surface that transmits an optical signal and a reflective surface that reflects the optical signal are stacked and held at a predetermined inclination.
Then, the optical signals reflected from each input optical fiber end of the plurality of port pairs consisting of the input optical fiber end and the output optical fiber end are transmitted to the reflector group through a rod lens or an optical system equivalent thereto. As a result, this optical signal is reflected so as to be incident on the output fiber end of a port pair other than the port pair at the input fiber end from which it was emitted.

〔Effect of the invention〕

According to the present invention, an optical splitter suitable for an optical transmission system having many stations can be obtained. In addition, in the present invention, the desired reflection characteristics are obtained by a group of stacked reflectors having transmitting surfaces and reflecting surfaces as described above held at a predetermined inclination, so that a light distributor that is easy to adjust can be obtained. It will be done.

[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. Reference numeral 20 denotes an optical distributor according to the present invention having, for example, four port pairs, which will be described in detail later. Each optical distributor 20 has four port pairs 21, 22, 23, and 24, first to fourth. First and second port pair 2 of each optical splitter 20
1 and 22 are connected to adjacent optical distributors 20, and a third and fourth port pair 23 and 24 are connected to a station 25. Each station 25 includes an optical transmitter 26 that transmits an optical signal and an optical receiver 27 that receives the optical signal.
It consists of

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

FIG. 5 shows the structure of an embodiment of the present invention having the above characteristics. In Figure 5, 31-3
4 connects its ends to input optical fiber ends M ₁ , M ₂ ,
These are optical fibers T ₁ , T ₂ , and 41 to 44 are 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. If accurate positional relationships can be maintained only with the input/output optical fibers 31 to 34 and 41 to 44, the dummy optical fibers may be omitted. Also, in FIG. 6, the ends M ₁ , M ₂ , T ₁ , T ₂
The tip fires toward you, and the ends M ₁ ′, M ₂ ′,
R ₁ and R ₂ indicate that light enters the fiber.

As shown in FIG. 5, the end faces of these input/output optical fibers 31 to 34 and 41 to 44 have diameters that are 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 group of reflective plates 45 in which a plurality of reflective plates having a reflective surface that reflects an optical signal and a transmitting surface that transmits an optical signal are stacked and held at a predetermined inclination. There is.

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. Assuming that the length of one cycle is one pitch, the rod lens 35 is selected to have a length of 1/4 pitch. For example, a rod lens with a diameter of 2 mm and a length of 5 mm was used.

The reflector group 45 consists of four light reflectors 50 to 53. As shown in FIG. 7, the light reflecting plate 53 has front and back surfaces forming an angle of 2θ in the y direction, and has a reflecting surface 60 having the shape shown in the figure on the back surface (the surface on the rod lens side). Here, θ is an angle that causes a deviation corresponding to the outer diameter of one optical fiber at the end face of the fiber array. The reflective surface 60 is perpendicular to the axis of the rod lens. Therefore, due to this reflective surface, the optical signal emitted from the input optical fiber end M ₁ of the first port pair 21 is directed to the output optical fiber end M ₂ ' of the second port pair 22 as shown in FIG. The optical signal incident and emitted from the input optical fiber end M ₂ of the second port pair 22 enters the output optical fiber end M ₁ ' of the first port pair 21.

Further, as shown in FIG. 8, the light reflecting plate 52 provided on the light reflecting plate 53 has front and back surfaces with an angle θ in the -y direction, and reflective surfaces 61 and 62 having the shapes shown in the figure are provided on the back and front surfaces. is provided. The reflective surface 61 is film-like and has a low reflectance of about 1%, which is different from other reflective surfaces. The back surface of the light reflecting plate 53 forms an angle of 2θ with respect to the end surface of the rod lens 35, and as shown in _{FIG .} Light is the fourth
Output optical fiber end of third port pair 24, 23
Inject into R ₂ and R ₁ . In addition, the reflective surface 62 with an apex angle of 45° on the front side is y with respect to the end surface of the rod lens 35.
It forms an angle of 2θ-θ=θ in the direction. Therefore, as shown in FIG.
Accordingly, the optical signals emitted from the input optical fiber ends M ₁ and M ₂ of the first and second port pair 21 and 22 are transmitted to the second port pair 21 and 22.
Output optical fiber end of first port 22, 21
Input to R ₂ and R ₁ . In addition, these reflective surfaces allow the end of the input optical fiber to be reflected as shown in FIG.
The optical signals emitted from T ₁ and T ₂ enter the output optical fiber ends M ₂ ′ and M ₁ ′.

The reflecting plate 51 laminated on the light reflecting plate 52 is
As shown in FIG. 9, both the front and back surfaces have a reflective surface 63 in the -x direction. As shown in FIG. 15, the reflective surfaces 63 and 60 allow the optical signals emitted from the input optical fiber ends M ₂ and T ₂ to enter the output optical fiber ends R ₂ and M ₂ '.

The reflecting plate 50 stacked on the light reflecting plate 51 has front and back surfaces having an angle of 2θ in the x direction, as shown in FIG. 10, and has a reflecting surface 64 on this surface. 16th
As shown in the figure, the reflective surfaces 64 and 60 allow the optical signals emitted from the input optical fiber ends M ₁ and T ₁ to enter the output optical fiber ends R ₁ and M ₁ '.

Therefore, when these light reflecting plates 50 to 53 are stacked, the optical signal emitted from the input optical fiber end _M2 of the second port pair 22, for example,
13 and 15, the light enters the output optical fiber ends M ₁ ', R ₁ and R ₂ other than the second port pair. In this way, the characteristics shown in FIG. 4 are obtained.

In the above embodiment, a single-wavelength optical signal is wavefront-split into a light beam according to a designed scattering matrix, but even in the case of multiple wavelengths, an optical circuit element that combines the wavelength dependence of a reflective film and wavefront splitting is used. Easy to configure.

According to the above-described embodiment of the present invention, the wavefront splitting can be freely set by the shape of the reflecting surface of the light reflecting plate, and the deflection necessary for coupling is given by setting the normal line of the laminated plane, thereby fulfilling two roles. Can be divided. Therefore, the degree of freedom in configuration increases, and it becomes possible to realize an optical circuit element with a complicated scattering matrix using a single rod lens.

By being able to consist of a single rod lens,
It is possible to reduce the size, and moreover, it is easier to reduce imperfection loss due to rod lens aberrations, fiber array position errors, etc., compared to the case where a plurality of rod lenses are used.

Incidentally, the optical distributor of the present invention has four parts as in the above embodiment.
It is clear that the invention is applicable not only to those with one port, but also to optical splitters with three or more than five ports.

Further, although the above embodiment uses a rod lens with a length of 1/4 pitch, the present invention is not limited to this, but an equivalent optical system having the characteristics of collimating light and narrowing the parallel light can also be used. May 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 to 10 are perspective views of the light reflecting plate used in the embodiment of FIG. 5, and FIGS. 11 to 16 are diagrams showing the arrangement of the optical signals in the embodiment of FIG. FIG. 3 is a diagram showing an input/output relationship. 20... Optical distributor, 21... First port pair, 22...
2nd port pair, 23...3rd port pair, 24...4th port pair
port pair, 25...station, 26...optical transmitter, 7...optical receiver, _M1 , _M2 , _T1 , _T2 ...input optical fiber end,
M ₁ ′, M ₂ ′, R ₁ , R ₂ ... Output light optical fiber end, 3
5...Rod lens, 45...Reflector group, 50-53
...Light reflector.

Claims (1)

[Scope of Claims] 1. A port pair group consisting of a plurality of port pairs each consisting of an input optical fiber end and an output optical fiber end, each of which inputs and outputs an optical signal, and which are arranged in parallel at a predetermined position; a transmitting surface that transmits the optical signal such that the optical signal emitted from the end of each input fiber of the input fiber is incident on the output fiber end of the port other than the output fiber of the port pair of the input fiber from which the optical signal was emitted; A group of reflectors stacked with a plurality of reflectors each having a reflective surface that reflects an optical signal held at a predetermined inclination, and a rod lens interposed between the group of reflectors and the port group for transmitting the optical signal. An optical distributor characterized by comprising an optical system equivalent to this.