JPS62127805A - Optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To obtain an optical multiplexer and demultiplexer whose productivity is high and whose loss is small, by applying a torsion to a multicore fiber, and setting a component difference in the longitudinal axial direction in a propagation constant of a single mode core of the center part and a single mode core of the outside peripheral part, to zero. CONSTITUTION:A multicore fiber 10 has two pieces of single mode cores 11, 12 as a wave director. An arrangement of the single mode cores 11, 12 is set so that one and the other are positioned in the center part and its outside peripheral part, respectively. Also, the respective propagation constants are set to beta1>beta2, when that of one core 11 and that of the other are denoted as beta1 and beta2, respectively. When setting this propagation constant, when a radius of one core 11, and that of the other are denoted as gamma1, and gamma2, respectively, and a refractive index of one core 11, and that of the other are denoted as n1, and n2, respectively, the propagation constant beta1>beta2 is set by setting as gamma1>gamma2. By adjusting a torsion applied to the multicore fiber 10, beta2costheta=beta1 can be set, and by executing the setting in this way, a component difference in the longitudinal axial direction of the propagation constant can be set to zero.

Description

[Detailed description of the invention] (Industrial application field) The invention relates to a parallel waveguide type optical multiplexer/demultiplexer.

(Conventional technology) The following two types of conventional single-mode optical multiplexing/demultiplexing bases are used.
Two types are known as representative ones.

The first method is called a fiber-processed interference filter method, which uses two fibers, 1 and 2, as shown in FIG.
1 is connected to a single mode fiber 3 via an interference filter 2.

The second method is called the planar waveguide diffraction grating method, which is used to connect the input optical fiber to the
5, the number of diffraction gratings 8a, 6b, 8 according to the wavelength used
diodes 7a, 7b, 7c are installed, and the light from the input optical fiber 4 is connected to the diffraction gratings 8a, 6b, Be.
It is also said that the waves are separated by

(Problems to be solved by the invention) In the conventional examples described above, processing is generally time-consuming;
There is a problem with productivity.

For example, in the former type, it is necessary to polish the end face of the optical fiber 4.

In addition, the latter method has the disadvantage that the loss of the waveguide is large (for example, 1.38 dB/Cm).

The present invention was made to solve these problems, and an object of the present invention is to obtain an optical multiplexer/demultiplexer with good productivity and low loss.

(Means for Solving the Problems) The present invention twists a multi-core fiber in which at least one outer peripheral single mode core is arranged around the outer periphery of one central single mode core arranged at the center. The component difference in the longitudinal axis direction in the propagation constant between the central single mode core and the outer peripheral single mode core is made zero,
That is what it is.

(Function) Under certain conditions, when artificial light of input 2 is made incident on the central single mode core, the artificial light comes from the central single mode core, and the input 2 light comes from the outer single mode core. Each emits light and functions as an optical demultiplexer.

Also, if the input light 1 is input from the central single mode core and the input light 2 is input from the outer peripheral single mode core, then the central single mode core enters! , and outputs the two input lights, functioning as an optical multiplexer.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 1, 10 is a multi-core fiber,
It has two single mode cores 11 and 12 as waveguides.

The single mode cores 11 and 12 are arranged such that one tt is located at the center fill and the other 12 is located at the outer periphery.

Then, the respective propagation constants are β1>
It is set to β2.

Setting this propagation constant is such that the radius of one core 11 is γ1,
If the other is γ2, the refractive index of one core 11 is Ill, and the other is γ2, then γl>γ2. Or r+1>n
This can be realized by setting it to z.

Here, by setting γl>γ2, the propagation constant β1
Set the input β2.

The multicore fiber 10 configured as described above is twisted as shown in FIG.

As shown in FIG. 3, the component of the propagation constant in the longitudinal axis direction at this time is β! for one core 11. .

In the case of the other core 12, β2 Coal θ is obtained. Here, θ is the angle between the traveling direction of the light traveling through the other core 12 and the longitudinal axis direction of the multi-core fiber IO.

Therefore, by applying a twist of 31 WI to the multi-core fiber 10, it is possible to set β2 cas O=β1, and by setting in this way, the difference in the longitudinal axis component of the propagation constant can be made zero.

Next, a case will be described in which the optical multiplexer/demultiplexer having the above configuration is used.

Wavelength input to one of the cores 11 above! , when the light of input 2 is input, the wavelength is input! The light of wavelength λ2 is emitted from one core 11, and the light of wavelength λ2 is emitted from the other core 12.
By setting the coupling constant of 1.12 and the length of the multi-core fiber IO, the fiber 10 can be used as an optical demultiplexer.

Also, the wavelength is input from one core 11! If light with a wavelength of 2 is input from the other core 12, one core 11
Light with a wavelength λ1 and input 2 is emitted from the light source, and can be used as an optical multiplexer.

FIG. 4 shows another embodiment of the present invention, in which a multi-core fiber 13 has one central single-mode core 14 located at the center and n-tree fibers arranged around the outer periphery of the core 14. Outer single mode core N1. Nz・・・・・・
・Nn.

The propagation constant is that of the central single mode core 14 as β
0, Outer single mode core N1...Nn is β! , β2...βn.

Set βo x β amount = β2 . . . = βn = β.

When such a multi-core fiber 13 is twisted, the longitudinal component of the transmission constant becomes β0 for the central single-mode core 14 and βco for the outer single-mode core.
S θ becomes.

β0 and βCogθ can be adjusted by adjusting the torsion.
=βCOSθ, and each core 14, Nl...
...The longitudinal axis direction components of the propagation constants of Nn can be made equal.

Now, assume that the coupling constants between the central single mode core 14 and the outer peripheral single mode cores NI...Nn are Ci (iml, 2...n).

Outer single mode core N! It is assumed that Nn are sufficiently separated from each other and there is no bond between them.

In the multi-core fiber 13 with such a coupling relationship, ■ When the coupling constants are all different (C1≠C2≠...
...≠Cn) The coupling constant Ci and the length of the multi-core fiber 13 are set so that when light with a wavelength i is input to the central single mode core 14, light with a wavelength i is input from the outer core N1. By setting , the multi-core fiber 13 can be used as an optical demultiplexer.

Furthermore, if light with a wavelength i is input from the outer peripheral core Nn, light with a wavelength i can be input from the central core 14, and can be used as an optical multiplexer.

(For example, if we divide the coupling constant Ci into several groups so that they are equal within a certain group,
The number of outer single mode cores N is Nz5, the coupling constant Ci is divided into two groups, and in one group,
C1=Cz, in the other group C3=C4=C5
shall be.

In this setting, when light of wavelength A is incident on the central core 14, the outer peripheral core N1. From Nz to wavelength λA
The coupling constant Ci and the multi-core fiber are set so that the light of wavelength λB is divided into two equal parts and emitted, and when the light of wavelength λB is made incident, the light of sunset wavelength is divided into three equal parts and emitted from the cores Nz, Nn, and Ns. By setting the length of 13, the function of an optical branching device can be added to the optical demultiplexer.

Further, the light of wavelength A incident from the outer peripheral single mode cores Nt and N2 is transferred from the central single mode core 14 to the outer peripheral core N3. N4. It can also be used as an optical multiplexer with an optical multiplexing function in which light of wavelength B incident from the NS is output from the central core 14.

However, in this case, it is necessary to adjust the phase of the incident light by 7JR.

The following is a case where Nz5 and C1=C2 and C3=Ca=Cs, but it can be similarly used as an optical multiplexer/demultiplexer with an optical multiplexing/demultiplexing function added in a general case.

(Effects of the Invention) As is clear from the above, since the present invention uses a single mode fiber as a waveguide, the loss is small.

Since the loss of a single fiber is about 0.5 dB/km, for example, when the length of the waveguide is about 10 cm, the loss is almost zero.

Also, the coupling loss with the optical fiber is small.

A loss of about 0.1 dB can be easily obtained.

Furthermore, since the spacing between the waveguides is controlled at the stage of manufacturing the preform, the spacing between the waveguides can be set with high precision.

[Brief explanation of drawings]

Figure 1 shows the state of the optical multiplexer/demultiplexer according to the present invention before twisting! 2 is a perspective view of the optical multiplexer/demultiplexer according to the present invention; FIG. 3 is an explanatory diagram showing the traveling direction of the light after twisting;
FIG. 4 is a perspective view of another embodiment of the present invention before twisting;
5 and 6 are perspective views of the conventional example. 11.14・・・・・・Central single mode core 12・・・・・・・・・Outer single mode core Nl”Nn・・・Outer single mode core Agent Patent attorney Yoshio SaitotlXf Figure 3 Figure 4 Figure 5 wi 6 Flash

Claims (1)

[Claims] A multi-core fiber in which at least one outer single mode core is arranged around the outer periphery of one central single mode core arranged at the center is twisted, and the propagation between the central single mode core and the outer single mode core is twisted. An optical multiplexer/demultiplexer characterized in that the component difference in the constant along the longitudinal axis is made zero.