JPH071358B2 - Optical variable switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an optical device that splits one optical signal into two optical paths in a waveguide type optical device used in the fields of optical communication, optical information processing and the like. The present invention relates to a branching device, and more particularly to an optical variable branching device that makes a branching ratio variable when branching.

[Conventional technology]

Conventionally, a waveguide type optical branching device shown in FIG. 3 is known. The optical branching device shown in FIG. 3 is generally well known as a directional coupling type optical switch, and its operation principle is described in, for example, the explanatory paper RCAlferness, “Guided.
-Wave Devices for Optical Communication ", IEEE Jou
rnal of Quantum Electronics, vol.QE17, No.6, pp, 946−
959, June, 1981 and the like.

The operation will be briefly described below. In the figure, 1 is an electro-optical substrate, 21 and 22 are first and second optical waveguides which are manufactured in parallel and adjacent to the surface of the electro-optical substrate 1, and 3 and 4 are on the optical waveguides 21 and 22, respectively. The produced electrode, E is the voltage applied to the electrode, and L is the length of the substrate in the longitudinal direction, that is, the length of the optical waveguide.

Since the two optical waveguides 21 and 22 are manufactured in parallel and adjacently to each other, a directional coupling effect is generated between the two optical waveguides, for example, the first optical waveguide.
The input optical power P ₀ incident on the optical waveguide 21 is propagated while repeating transition between the two optical waveguides. Here, as the substrate length L, the complete coupling length of the directional coupling between the two optical waveguides (that is, the length at which the power of the light incident on one optical waveguide is completely transferred to the other optical waveguide) L _{If 0} is taken, the optical power P ₀ incident from the optical waveguide 21 is output from the optical waveguide 22. That is, if the output light from the optical waveguide 21 is P ₁ and the output light from the optical waveguide 22 is P ₂ , then P ₂ =
The state of P ₀ , P ₁ = 0 is realized.

On the other hand, since the electro-optical substrate 1 has an electro-optical effect, when an applied voltage E is applied to the electrode 4, the refractive index of the two optical waveguides changes, and the state of directional coupling can be changed.
At this time, the optical power P ₀ incident from the optical waveguide 21 is output from the optical waveguide 21 by adjusting the applied voltage E. That is, the state of P ₂ = 0 and P ₁ = P ₀ is realized.

Therefore, by changing the applied voltage E, the state in which the light incident from the optical waveguide 21 is output from the optical waveguide 21
It can be switched between states output from 22, and can be used as an optical switch. Further, if the applied voltage E is set to a voltage between the two states, an intermediate state between the two states, that is, the light incident from the optical waveguide 21 can be branched and output to the optical waveguides 21 and 22. A turnout is realized.

[Problems to be solved by the invention]

As described above, it is possible to branch one optical signal into two optical paths with the optical branching device of FIG. 3, but when changing the branching power ratio, it is necessary to change the applied voltage for each branching ratio. There is. Therefore, it is necessary to take measures such as preparing a plurality of power supplies having different voltages, and the control circuit becomes complicated.

An object of the present invention is to provide an optical variable branching device capable of varying the branching power ratio while keeping the applied voltage constant.

[Means for solving problems]

To achieve the above object, in the present invention, two first and second linear optical waveguides that are parallel to and adjacent to each other are formed near the surface of an optical substrate having an electro-optical effect, and the substrate length of the optical substrate is It is set to be equal to the complete coupling length of the directional coupling between the two optical waveguides, and the first optical waveguide is provided on the first optical waveguide.
Of the first optical waveguide and the second optical waveguide provided on the second optical waveguide are connected to each other by applying a fixed voltage to the other of the second electrode provided on the second optical waveguide. In an optical variable branching device in which light incident on either one is branched to the other and output from both optical waveguides, the electrode to which the fixed voltage is applied is composed of a plurality of divided electrodes, By selecting any desired number of segment electrodes from the individual segment electrodes and applying a fixed voltage, the branch power ratio of the light split between both optical waveguides can be adjusted according to the number of segment electrodes selected. I made it variable.

[Action]

The voltage applied to the segment electrodes is of a fixed type, and it is possible to provide an optical variable branching device that can be controlled by a simple digital logic circuit.

〔Example〕

FIG. 1 is a perspective view showing a first embodiment of the present invention. In the figure, reference numeral 1 is an electro-optical substrate, and 21 and 22 are first and second parallel fabricated near and adjacent to the surface of the electro-optical substrate 1, respectively.
The optical waveguide 3 is an electrode formed on the optical waveguide 21, 41
Reference numerals 48 to 48 are electrodes formed on the optical waveguide 22. In the figure, the electrodes are divided into eight in the longitudinal direction of the optical waveguide. Generally, the division number is an arbitrary natural number. 51-58 is each electrode 41-
Switch for controlling voltage application to 48, E is applied voltage, L
Is the length of the substrate in the longitudinal direction, that is, the length of the optical waveguide. L _{1 to} L ₈ are the lengths of the electrodes 41 to 48 in the longitudinal direction of the optical waveguide, and the sum of the lengths of L _{1 to} L ₈ is L.

The operation of this embodiment will be described later.

FIG. 2 is a perspective view showing a second embodiment of the present invention. As in the case of FIG. 1, 1 is an electro-optical substrate, and 21 and 22 are first and second parallel electrodes adjacent to the surface of the electro-optical substrate 1.
The optical waveguide 3 is an electrode formed on the optical waveguide 21, 41
Denoted at 45 are electrodes formed on the optical waveguide 22. In the figure, the electrodes are divided into five in the longitudinal direction of the optical waveguide. Generally, the division number is an arbitrary natural number. 51-55 is each electrode 41-
A switch for controlling voltage application to 45, E is applied voltage, L
Is the length of the substrate in the longitudinal direction, that is, the length of the optical waveguide. Further, L _{1 to} L ₅ are the lengths of the electrodes 41 to 45 in the optical waveguide longitudinal direction, and the sum of the lengths of L _{1 to} L ₅ is L. The optical variable branching device of the second embodiment differs from the optical variable branching device of the first embodiment in that the length L _{5 of the} electrode 45 is different.
Is set to half of the substrate length L. That is, L ₅ = L / 2.

Hereinafter, the operation of the variable optical branching device as the embodiment of FIGS. 1 and 2 will be described, but before that, FIG. 4 is for explaining the basic operation of the variable optical branching device according to the present invention. The basic operation will be described with reference to FIG.

In the figure, 1 is an electro-optical substrate, 21 and 22 are first and second optical waveguides produced in parallel and adjacent to the surface of the electro-optical substrate 1, and 3 is an electrode produced on the optical waveguide 21, Reference numeral 4 is an electrode formed on the optical waveguide 22, and its length is L _e . E is the applied voltage, and L is the length of the substrate in the longitudinal direction, that is, the length of the optical waveguide.

Here, when the substrate length L is the complete coupling length L ₀ of directional coupling, all light incident on the optical waveguide 21 is output from the optical waveguide 22 as described in the prior art when no applied voltage is applied. It On the other hand, considering the case where the length L _e of the electrode 4 is L, FIG. 4 has the same configuration as the conventional optical branch circuit shown in FIG. 3, and by adjusting the voltage E applied to the electrode, All the light incident on the optical waveguide 21 can be output from the optical waveguide 21.

When the length L _e of the electrode 4 is shortened as shown in FIG. 4 while maintaining the applied voltage in that state, the refractive index change due to the electro-optic effect occurs only in the optical waveguide where the electrode is present.
The light incident from the optical waveguide 21 is branched into the optical waveguides 21 and 22 to be output, and the branching ratio is determined by the electrode length L _e .

FIG. 5 is an example of calculation of how the branching ratio changes,
The horizontal axis represents the length L _e of the electrode 4, and the vertical axis represents the optical power P ₁ output from the optical waveguide 21 normalized by the input optical power P ₀ . From the figure, the light output from the optical waveguide 22 when the electrode length L _e = 0 is
It is output to 21 and you can see how P ₁ increases.

As described above, the branching ratio can be changed by changing the length of the optical waveguide portion to which the voltage is applied.
Therefore, the same effect can be obtained by dividing the electrodes in advance and applying the applied voltage only to the specific electrodes.

For example, consider the case where the lengths L _{1 to} L ₈ of the electrodes are set as shown in FIG. 6 in the first embodiment shown in FIG. In FIG. 6, the lengths of L _{1 to} L ₈ are such that the optical power output from the optical waveguide 21 is 0,1 / 8,2 / 8,3 / 8,4 / 8,
They are chosen to be 5 / 8,6 / 8,7 / 8,1. In this case, since the curve in the figure are in a relationship of point symmetry with respect to the point of the electrode length _{L e = L 0/2,} L 5 = L 4, L 6 = L 3, L 7 = L 2, L 8 = L ₁ relationship. At this time, "1" when applying voltage to each electrode,
The case where no voltage is applied is represented as "0", and FIG. 7 shows how the branching ratio changes.

In this example, the branching ratio is equal to 1/8, but by setting the electrode length appropriately, it is possible to realize an optical variable brancher that can obtain the branching ratio at any interval.

On the other hand, as described in the first embodiment, the length of each electrode is L ₅ =
When L ₄ , L ₆ = L ₃ , L ₇ = L ₂ , and L ₈ = L ₁ are symmetrical, the number of required electrodes can be reduced. Such a relationship is obtained when the branching ratio is selected as x (0 ≦ x ≦ 1) and (1-x).

For example, in the first embodiment, the relationship is set to 1/8 and 7/8, 2/8 and 6/8 and the like. In such a case, the same operation as in the first embodiment can be performed by setting the length L ₅ of the electrode 45 to L / 2 as in the second embodiment shown in FIG. For example, in the operation of the first embodiment shown in FIG. 7, when the light output P ₁ = 5/8, L _{1 to} L ₅ are “1”, that is, the total electrode length of the portion to which the voltage is applied. Is L ₁ + L ₂
Since there is a relation of + L ₃ + L ₄ + L ₅ = L / 2 + L ₅ = L / 2 + L ₄ , it becomes equal to the length of the portion to which the applied voltage is applied when the electrodes 44 and 45 are set to “1” in the second embodiment. .

Similar to FIG. 7, FIG. 8 shows how the branching ratio changes in the second embodiment. It can be seen from the figure that the same operation as in the case of the first embodiment is performed by controlling the voltage applied to the five electrodes.

In the first or second embodiment, an example in which the first electrode on the first optical waveguide is uniform and the second electrode on the second optical waveguide is divided into a plurality of small electrodes in the longitudinal direction has been described. ,
In addition to this, (a) the second electrode is made uniform and the first electrode is divided, (b) both the first and second electrodes have the same number and length of small electrodes, or Divide by varying the number or the length, (c) Divide the divided state without regard to the longitudinal direction, for example, 2
It can be arranged in a three-dimensional island distribution.

〔The invention's effect〕

In the variable optical branching device according to the present invention, the branching ratio can be changed by applying an applied voltage to an electrode selected from a plurality of divided electrodes according to the branching ratio. There is one kind of applied voltage, and as shown in FIGS. 7 and 8, the voltage applied to each electrode is represented by two states of “0” and “1”. Therefore, the control circuit is simplified and can be controlled by a simple digital logic circuit.

[Brief description of drawings]

1 is a perspective view showing a first embodiment of the present invention, FIG. 2 is a perspective view showing a second embodiment of the present invention, and FIG. 3 is a perspective view showing a conventional variable optical branching device. FIG. 4 is a perspective view for explaining the operating principle of the variable optical branching device according to the present invention, FIG. 5 is a characteristic diagram showing the branching characteristic of optical power, and FIG. 6 is the electrode length of the variable optical branching device according to the present invention. FIG. 7 is a characteristic diagram for showing, FIG. 7 is an explanatory diagram showing an operation example of the first embodiment, and FIG. 8 is an explanatory diagram showing an operation example of the second embodiment. DESCRIPTION OF SYMBOLS 1 ... Electro-optical substrate, 21 ... First optical waveguide, 22 ... Second optical waveguide, 3, 4 ... Electrode, 41-48 ... Electrode, 51-58 ... Switch, L ... Substrate length, E ... Applied voltage, L _{1 to} L ₈ … electrode length, L _e …
Electrode length, P ₀ ... input light power, P ₁ , P ₂ ... output light power

Claims (1)

[Claims] 1. A pair of first and second linear optical waveguides, which are parallel and adjacent to each other, are formed in the vicinity of the surface of an optical substrate having an electro-optical effect, and the substrate length of the optical substrate is set to the two optical waveguides. One of a first electrode provided on the first optical waveguide and a second electrode provided on the second optical waveguide, which is equal to the complete coupling length of the directional coupling between the two. By connecting a reference potential to one side and applying a fixed voltage to the other side, the light incident on one of the first and second optical waveguides is branched to the other and output from both optical waveguides. In the variable optical branching device, the electrode to which the fixed voltage is applied is composed of a plurality of segment electrodes, and an arbitrary desired number of segment electrodes is selected from the plurality of segment electrodes to apply the fixed voltage. By doing so, the split power ratio of the light split between both optical waveguides can be An optical variable branching device, which is variable according to the number of selected segment electrodes.