JPS62145224A - Optical waveguide element - Google Patents

Abstract

PURPOSE:To control the characteristics of an optical waveguide over a wide range by arranging two projection type optical waveguides which are partially parallel to each other adjacently and charging liquid crystal in the recessed area formed between the two waveguides. CONSTITUTION:The liquid crystal 10 is arranged between the projection type optical waveguides to perform electric control to complete coupling length. The liquid crystal 10 has positive dielectric anisotropy and has a molecule array oriented in the traveling direction of light unless a liquid crystal control power source 7 is connected. The refractive index of the liquid crystal 10 to light in TE mode is relatively small, the coupling between the waveguides becomes small, and the complete coupling length is relatively long. When the liquid crystal control power source 7 is turned on, the liquid crystal molecule array becomes parallel to an electric field and the refractive index of the liquid crystal increases in this case. Then, the variation in the refractive index of the liquid crystal is variation of -0.4 from 1.4 to about 1.9 by selecting a proper material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical waveguide element used in the fields of optical communication and optical information processing.

A typical example of a conventional optical waveguide device is one using a directional coupler. The device consists of two adjacent optical waveguides, and each waveguide is provided with means for varying the propagation constant. Here, the length of the element is the fully bonded length. Usually, it is designed as much as possible. The perfect coupling length is a length such that when light enters one waveguide, the light is emitted only from the other waveguide at the output end side. Light switching is then achieved by creating a difference in propagation constants between the two waveguides (eg, using electro-optic effects). In addition, internal all-pair type optical switches have also been devised.

Problems to be Solved by the Invention However, in reality, it is extremely difficult to control the element length to a perfect coupling length due to variations in the refractive index of the waveguide, errors in waveguide fabrication, and the like. Furthermore, the conventional optical waveguide device is LiNb0. However, due to their small electro-optic constants, it has been difficult to improve the performance of the device and make fine adjustments after device fabrication.

The present invention provides an optical waveguide element using liquid crystal with a wide refractive index control range in order to eliminate such drawbacks.

Means for Solving the Problems By filling the concave portion between two convex optical waveguides juxtaposed in close proximity with a liquid crystal whose refractive index can be electrically controlled, the distribution of light between both groove waveguides is controlled. Further, as a means for applying an electric field to the liquid crystal, electrodes are formed on the side surfaces of the convex waveguide. The liquid crystal used here has positive dielectric anisotropy, and its molecules are aligned perpendicular to the direction of the electric field when no voltage is applied.

Effect: By arranging a liquid crystal between two optical waveguide coupling parts and changing its refractive index, the degree of coupling between the waveguides is changed. That is, as the refractive index of the liquid crystal increases, the amount of light seeping out from each waveguide increases, and the interaction between the waveguides increases. This produces the same effect as when the distance between the two waveguides becomes narrower than when the refractive index of the liquid crystal is low. In this case, the complete coupling length of the optical waveguide element of the present invention becomes short. On the other hand, if the refractive index of the liquid crystal is small, the perfect bond length becomes longer based on the same principle. In this way, it is possible to change the refractive index of the liquid crystal by the bias voltage, and it is expected that the device performance will be improved. In addition, liquid crystals can be expected to change their refractive index due to a larger electric field than normal dielectric crystals, and by applying this property to convex waveguide elements arranged in close proximity, it is possible to construct, for example, total internal reflection type optical switches. Become.

Embodiment FIG. 1 is a structural diagram of an optical waveguide device showing an embodiment of the present invention. 1 is an n-type semiconductor substrate, 2 is an optical waveguide layer, 3 is a Schottky electrode, 4 is an insulating film, 5 is a liquid crystal control electrode, 6 is an ohmic electrode on the substrate side, 7 is a liquid crystal control power supply, 8 is an optical waveguide control power supply , 9 is a waveguide coupling portion where an effective refractive index change occurs as the refractive index of the liquid crystal changes, and 10 is a liquid crystal. The semiconductor material used here is a compound semiconductor such as GaAs or InP, but is not limited to these.

FIG. 1 shows the present invention applied to a directional coupler type optical switch. The light (Pin) that is incident on one of the waveguides so that the guided light in TE mode is excited is observed on the output side as Pl and P2 due to the coupling between the waveguides, but normally, a bias is applied to the Schottky electrode 3. If not,
The element length (complete bond length) is selected so that Pl is almost zero. However, it is very difficult to control the element length to this perfect bond length. Therefore, by arranging a liquid crystal 1o between the convex optical waveguides as shown in the figure, it becomes possible to electrically control this complete coupling length. This situation will be explained using FIG. 2. In FIG. 2, the same parts as in FIG. 1 are given the same numbers. Here, the liquid crystal 1° has positive dielectric anisotropy,
As shown in FIG. 2a, when the liquid crystal control power source 7 is not connected, the molecules are aligned in the direction in which the light travels. Here, the refractive index of the liquid crystal 1o for TE mode light is relatively small, the coupling between the waveguides is also small, and the complete coupling length is relatively long.

However, as shown in the figure, when the liquid crystal control power source 7 is turned on, the liquid crystal molecules are aligned parallel to the electric field, and the refractive index of the liquid crystal in this case becomes larger than that shown in the figure. At this time, the change in the refractive index of the liquid crystal can be adjusted to 1.4 by selecting an appropriate material.
It is possible to realize a change in ~Q・4 from 1.8 to about 1.8, and this value is 10-3 to 10-1 for compound semiconductors and dielectrics.
Considering that it is on the order of 4, it can be said to be extremely large. In such a state, the effective refractive index in the waveguide coupling portion 9 becomes large, and therefore the complete coupling length becomes short. These conditions are shown in FIG. FIG. 3 shows the dependence of the power of P2 on the element length.

Let L be the actual element length. It is then assumed that the complete bond length of the element is LO, which is longer than L. This state is shown by the solid line in the figure. In such an element, by applying a voltage to the liquid crystal 10, it is possible to control the bond length to be perfect as shown by the broken line. As described above, by designing the element length to be slightly shorter than the complete bond length, the bond length can be adjusted to
0 enables control. This is considered to be particularly effective when many elements are present, such as in an optical integrated circuit.

Although not shown in the figure, after filling the liquid crystal, it is necessary to create a convex part using the same method as the optical waveguide convex fabrication method to prevent the liquid crystal from flowing out, surround the liquid crystal, and seal the upper part with a glass plate, etc. There is.

Here, the intersection of the convex guide paths is made into a Y-combining configuration so that the light does not pass through the convex r'(<<17 waves formed on the optical waveguide 114ζ through which the original signal light is guided.

Effects of the Invention By utilizing the large refractive index change of liquid crystal, the characteristics of the leading wave element can be controlled over a wide range. Further, by using a convex optical waveguide, it becomes possible to stably hold the liquid crystal, and stable operation of the device becomes possible.

[Brief explanation of drawings]

Figure 1 is a perspective view of an optical waveguide device showing one embodiment of the present invention, and Figure 2 is a cross-sectional view of the device showing the principle of coupling length control of the device.
FIG. 3 is a diagram showing changes in bond length. 1... Semiconductor crystal substrate, 2... Semiconductor optical waveguide layer, 3... Schottky electrode, 4...
・Insulating film, 5...1 night crystal 171I dragon j electrode, 6
...Ohmic electrode, 7...Liquid crystal! t
i control power supply, 8... optical waveguide control power supply. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 L Lθ

Claims (3)

[Claims] (1) Two convex optical waveguides, at least some of which are parallel to each other, are juxtaposed in close proximity, and a recessed area formed between the two waveguides is filled with liquid crystal. An optical waveguide device characterized by: (2) The optical waveguide device according to claim 1, further comprising an electrode so that an electric field can be applied to the liquid crystal. (3) The optical waveguide device according to claim 2, wherein the liquid crystal has positive dielectric anisotropy and molecules are aligned perpendicular to the direction of the electric field when no voltage is applied.