JPS5960425A - Optical switch - Google Patents

Abstract

PURPOSE:To enable operation at a low voltage by providing an electrode having a symmetrical construction in the central part where crossed optical guides intersect so that the waveguides are changed over by an increase in the refractive index when a voltage is applied on the electrode. CONSTITUTION:Two optical waveguides are formed as a layer 3 having the refractive index higher than the refractive index of a substrate 1 by diffusing a thin titanium film layer 2 on the substrate 1. An electrode 4 having a rectangular shape is provided in the part where the waveguides intersect in parallel with the line connecting the vertex P of the crossing angle of parts 31, 32 on the incident side and the vertex Q at the crossing angle of parts 33, 34 on an exit side. A signal voltage is then applied on the electrode 4 to change the refractive index in the region of the optical waveguides where the waveguides face to the electrode 4, thereby branching the light made incident from a direction X to a direction Y or Z. Since the optical switch of a 2X2 type is formed, the integration of the optical circuit element is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an optical circuit element, and particularly to an optical switch using crossed optical waveguides.

(b) Background of the technology In optical circuits currently in practical use, circuit components such as lenses, filters, isolators, and switches are each independent, making it difficult to miniaturize and integrate them, as well as to form circuits. At times, highly accurate optical axis adjustment between these circuit components is required, and the formed optical circuit is also required to have sufficient earthquake resistance.

In addition to the above conventional optical circuit components, 1. Optical circuits using optical waveguides formed on a substrate are being actively developed to solve the various problems described above.

(c) Prior Art and Problems Conventionally, directional coupling type and total reflection type optical switches have been proposed as basic optical switches for optical circuit elements using optical waveguides.

The former has problems such as long element length and requires a high degree of dimensional accuracy, while the latter has the drawback of high operating voltage.

The present inventors have already discovered that an optical switch with low operating voltage can be obtained by increasing the refractive index at the intersection of the leading waveguides (Japanese Patent Application No. 55-1640).
! 11).

(d) Purpose of the Invention An object of the present invention is to provide an optical switch with a novel structure that uses crossed optical waveguides and is capable of low voltage operation.

(e) Structure of the Invention The present invention provides an optical switch using a pair of intersecting guide waveguides, in which the intersection angle apex formed by the light input side waveguide end side and the intersection angle apex formed by the light output side waveguide end side. For the line connecting
A cycle in which a rectangular electrode is provided at the intersection iJ1 of the optical waveguide so that its long sides are parallel and symmetrical with respect to the original line, and waveguide switching by applying a voltage to the electrode is performed at least by increasing the refractive index. It is characterized by including.

(f) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sawtooth diagram schematically showing a crossed optical waveguide.
For example, by forming two strips of titanium 'FiHfAm2 so as to cross each other on the surface of a substrate 1 made of electro-optic crystal such as lithium niobate (LiNb03), and heat-treating this at, for example, 1040° C. for 5 hours, The titanium thin film layer 2 is diffused into the substrate 1 to form a layer 3 having a refractive index lower than that of the substrate 1, which is used as an optical waveguide.

FIG. 2 is a diagram schematically showing one configuration example of an optical switch according to the present invention using the optical waveguide formed as described above.

In FIG. 2, a rectangular electrode 4 is located at the intersection of two leading waveguides, and its long side is the intersection angle apex P formed by the end sides of the light incident side parts 31 and 32 of the two leading wavepaths, and the light output side part. It is provided so as to be parallel to the line connecting the intersection angle vertices Q formed by the end sides of 33 and 34 and symmetrical with respect to the original line.

The shape of the electrode here refers not to the shape of the electrode itself, but to the shape of the refractive index changing region formed in the leading waveguide section under the electrode by applying a signal voltage to the electrode. Therefore, this expression will be used in the following explanation for convenience.

In the above configuration, by applying a signal voltage to the electrode 4 and changing the refractive index of the region of the optical waveguide facing the electrode 4, light incident from the direction of the arrow X is directed straight in the direction of the arrow Y. , or deflect (branch) in the direction of arrow 2.

In this case, the refractive index of the region (refractive index change region) facing the electrode 4 increases (
+Δn effect) or decrease (−Δn effect).

In the present invention, when switching the leading waveguide along which light travels,
It differs from conventional total reflection optical switches in that it uses at least the above-mentioned 10Δn effect, and this point enables the optical switch according to the present invention to operate at low voltage and achieve low crosstalk between optical waveguides. be.

FIG. 3 is a diagram showing an example of changes in straight optical output (S) and branched optical output (B) with respect to changes in refractive index caused by application of a signal voltage to the optical switch having the configuration shown in FIG. be.

The optical switch in the figure uses LiNbO3 as a substrate,
An optical waveguide was formed by diffusing titanium into this, and the optical waveguide width was 7.5 μm, the crossing angle was 1.7°, the electrode width was 4 μm,
The refractive index difference between the substrate and the optical waveguide (when there is no signal) is 0.004.

As shown in FIG. 3, in the optical switch of this example,
When there is no signal (Δn-0), the straight optical output (S) and the branched optical output (B) are almost equal. That is, in FIG. 2, approximately 1/2 of the light incident in the direction of arrow X is branched and emitted in the direction of arrow Z.

Now, when a signal voltage is applied to increase the refractive index, the branched light output (B) becomes maximum and the straight light output (S) becomes minimum near Δn = 0.0012.

On the other hand, when a signal voltage is applied to decrease the refractive index, the straight optical output (S') increases around Δn = -0,0012.
becomes the maximum, and the branched light output (B) becomes the minimum.

On the other hand, in the case of a conventional total reflection type optical switch, the straight optical output is maximum when there is no signal (Δn=0),
It is designed so that the branched light output is maximum when a signal voltage is applied (Δn×0).

Another important point in which the optical switch of the present invention differs from the conventional total reflection type is that the optical switch of the present invention has electrodes with a symmetrical structure as shown in FIG. A switch with a 2x2 type element (one switch element has two input light direction valves and two output light directions,
The point is that it can function as a device having a switch function for any combination of the incident light power direction and the output light power direction. In contrast, conventional total internal reflection type optical switches
It can only function as an XZ type switch (having one direction of incident light and two directions of output light power, and the combination of these directions is two), and is equivalent to a 2 x 2 type switch. Four optical switch elements were required to make it functional.

Therefore, the optical switch of the present invention is advantageous in integrating optical circuit elements.

As can be inferred from the above description, the optical switch of the present invention is based on a different operating mechanism from the conventional total reflection type optical switch, and the operations of the two will be compared and explained below.

In the optical switch of the present invention, as shown in FIG. 2, the electrodes 4 are arranged symmetrically at the center of the intersection of the optical waveguides, and the width of the electrodes 4 depends on the width of the optical waveguide, the shape of the waveguide such as the intersection angle, the wavelength of the light, etc. It has an optimal value depending on the conditions, and generally takes a value smaller than the width of the leading wavepath.

On the other hand, in a total reflection type optical switch, as shown in Fig. 4, the electrode 4 is generally biased toward the side opposite to the light incident side (arrow Placed. In addition, the width is made as large as possible in order to completely branch the light to the branching side (arrow Z), thereby making the barrier for total reflection thicker.

FIGS. 5 to 8 show the results of investigating the propagation state of light in the total internal reflection type optical switch of the present invention and the conventional optical switch using a theoretical analysis method.

5 and 6 show the operating mechanism of the total internal reflection type optical switch, FIG. 5 shows the signal in the OFF state, and FIG. 6 shows the signal in the ON state.

In a total internal reflection type optical switch, light travels straight in the off state, and in this state, light leaks to the branch side (1 to 1).
In order to make the intersection angle sufficiently small, it is necessary to choose a large intersection angle. In the example shown in Figure 5, the intersection angle is 2°, and most of the optical power propagates almost straight through the intersection. However, a slight leakage of light is observed on the branching side.On the other hand, when this optical switch is in the on state, the optical power propagates while the fundamental mode state is maintained, and the total reflective barrier 7
It is reflected and goes to the branch side. This optical switch mechanism expresses the phenomenon of total reflection of light from a lightning strike.

On the other hand, Figs. 7 and 8 show the operating mechanism of the optical switch of the present invention, and Fig. 7 corresponds to the off state (straight forward) of a total internal reflection type optical switch, whereas Fig. 8 corresponds to the on state (branching). This is shown in Figure 8. In the cases shown in both figures, unlike the example in FIG. 3, the light travels straight due to the 10Δn effect and is split due to the −Δn effect.

In the case of FIG. 7, the refractive index change Δn is +0.001,
Furthermore, the trajectory of the light is not a straight line, but meanderes twice as it travels through the optical waveguide on the straight side. In this way, the trajectory differs from the case of straight travel in FIG. 5, not only in that a signal voltage is applied, but also in the trajectory. In addition, in the case of Fig. 8, the refractive index change Δ
n is −0,0005, and the light travels to the branch side with approximately one bend. However, the place where this direction changes is not in front of the barrier, but rather near the wall of the optical waveguide.
This point also differs from the case of a total internal reflection type optical switch.

The light propagation phenomenon in these optical switches of the present invention is similar to the power transition in a directional coupler.

In addition, the crossed leading waveguide shown in Figure 3 (crossing angle 1.7°
), going straight goes to 1 due to the 〇 effect, and branching goes to +
It is noteworthy that while this is achieved by the Δn effect, in the case of FIGS. 7 and 8 (crossing angle of 1°), the operation is performed by the opposite refractive index change.

In other words, in the optical switch of the present invention, the magnitude and polarity of the voltage for performing the Suinochi operation can be set to be variously different depending on the design conditions of the leading waveguide and electrodes. In the optical switch of the present invention, as shown in FIG.
Straight optical output (S) and branched optical output CB) for Δn)
determines the periodicity, and the zero voltage state on such a period depends on the design conditions of the leading waveguide (diffusion material concentration, optical waveguide width,
This is because it can be set at various points on the Δn axis depending on the electrode width, crossing angle, etc.). Therefore, depending on this design condition, it is possible to have a straight state in the 0 voltage state (Δn = O) or a branched state, and it is also possible to create a state in which adjacent It is also possible to perform a switching operation by selecting the maximum of the straight light and the maximum of the branched light.

(g) Effects of the Invention According to the present invention, it is possible to provide an optical switch with low operating voltage and low crosstalk, and since it is possible to configure a 2×2 type optical switch, it is possible to provide a highly integrated optical switch. This has the effect of

[Brief Description of the Drawings] Fig. 1 is a diagram showing the basic structure of an optical waveguide, Fig. 2 is a diagram showing the configuration of an optical switch according to the present invention, and Fig. 3 is a diagram showing the refractive index change in the optical switch according to the present invention. Figure 4 is a diagram for explaining the electrode arrangement and operation in a total reflection type optical switch. Figures 5 and 6 are diagrams showing an optical waveguide of a total reflection type optical switch. FIGS. 7 and 8 are diagrams showing examples of light propagation conditions within the optical waveguide of the optical switch of the present invention, and FIG. FIG. 3 is a diagram illustrating an example of periodicity of the refractive index change and the optical output. In the figure, 1 is a substrate, 2 is a titanium thin film layer, 3 is an optical waveguide, 4 is an electrode, 7 is a total reflection barrier, 31 and 32 are 63 minutes on the light incidence side of the optical waveguide, and 33 and 34 are light outputs of the optical waveguide. In the side portions, P and Q are the crossing angle vertices of the optical waveguides, S is the straight optical output, and B is the branched optical output. Tsutaq Tsukuku vinegar obscene hina) l', i Jll 5η4'・2・2if Ill
, the table of f1 is 3, jdi +1 is 4-h 'Iit'l to UI HI ↑l', l'l
Applicant 11 Location Kawasaki Yamanaka 11, Kanayo Prefecture;
・1) Address 1015 (522) in 1 (Ro, Fujitsu Ltd. 4 Agent IL Office Kawasaki Yamanaka, Shinzenyo Prefecture 11 ifl < l) I Yama 1 Naka] 015ff'i Location Fujitsu Ltd. Office ＼ Showa January 11 Yoni (1) The scope of the claims of the present application is amended as follows. (2) A patent characterized in that a bar-shaped electrode is provided at the center of the intersection of crossed optical waveguides formed on an electro-optic crystal, and optical path history is performed by switching and applying positive and negative voltages to the electrode. An optical switch according to claim 1. (3) In an optical switch using a pair of intersecting optical waveguides, with respect to the line connecting the intersection angle apex formed by the end of the light input side waveguide and the intersection angle apex formed by the end side of the light output side waveguide, A rectangular electrode is provided at the intersection of the patterned optical waveguides so that its long sides are parallel and symmetrical with respect to the original line, and a cycle is established in which waveguide switching is performed by at least an increase in the refractive index by applying a voltage to the visiting electrode. An optical switch according to claim 1, characterized in that the optical switch comprises: (4) Power on the electro-optic crystal, LiNb0: Optical switch with + plate. ” (2) Page 4 of the specification, lines 10 to 11, “This is a figure shown.
Figure 2(b) is a perspective view of the optical switch when using a 2-cut LiNbO3 substrate, and the ground voltage w.
15 is also shown. In FIG. 2(a)," the correction is made as follows. (3) Page 5, line 17 of the specification [It makes it possible. 1
In the above example, Z-cut-LiNb03.1 is used as the upper plate of the electro-optic crystal.
However, by applying the present invention, it is possible to use a Y-cut as a substrate.
- Using LiNb03, in order to cause a change in the refractive index formed in the optical waveguide section by applying a signal voltage to the electrode, see Figure 2 ('Fff, 1lliy
4 and 5 for crossed optical waveguides? 1Kri4. 5
The space between the optical waveguides is formed to be narrower than that in the optical waveguide. In addition, in Fig. 2 (C), Y-cut--Li N b O
1 is a perspective view of an optical switch of the present invention using three substrates; FIG. ” 1 patent attorney Hiroshi Matsuoka vq1H 124-

Claims (1)

[Claims] (1) A bar-shaped electrode is provided at the center of the intersection of the crossed optical waveguides formed on the electro-optic crystal, and the optical path is changed by applying positive and negative voltages to the electrode while switching between them. Optical switch (2) In an optical switch using a pair of intersecting optical waveguides, for the line connecting the intersection angle apex formed by the light output side waveguide end side and the intersection angle apex formed by the light output side waveguide end side. A rectangular electrode is provided at the intersection of the optical waveguide with its long sides parallel and symmetrical with respect to the line, and waveguide switching by applying a voltage to the electrode is performed at least by increasing the refractive index. The optical switch according to claim 1, characterized in that the optical switch includes a cycle in which