JPH02238441A - light switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical waveguide type optical switch.

BACKGROUND OF THE INVENTION In recent years, optical waveguide type optical switches of this type used in optical devices that utilize electro-optic effects have been actively developed. Of these, the one that has received particular attention is
LiNbO. An optical waveguide is formed by diffusing Ti into a ferroelectric material.

Also, LiTaO. Some use ferroelectric materials or PLZT thin films. Furthermore, research into compound semiconductor epitaxial crystal optical waveguides made of GaAs, InP, etc. is also active for the purpose of integration with semiconductor lasers and the like.

In any case, in the case of these optical waveguide type optical switches,
Basically, light switching is performed by changing the phase and mode of light waves propagating in an optical waveguide.

Problems to be Solved by the Invention However, in the case of the above-mentioned optical waveguide type using ferroelectric material,
Since the electro-optic effect is not very large, the element length becomes long. Furthermore, integration with a semiconductor laser is also difficult.

In addition, in the case of compound semiconductor epitaxial crystal optical waveguides such as GaAs, most of them utilize the plasma effect due to carrier injection as an electro-optic effect, and the refractive index change is more pronounced than the electro-optic effect in the case of ferroelectric optical waveguides. Although it is large, the change in refractive index is still small enough to perform switching.

In this regard, recently, a multi-quantum well structure (Multi Quantum Well structure) has been developed as a structure with a large electro-optic effect.
) has been proposed (while the refractive index change in the carrier injection type described above is several 0.0%, this MQW type shows a refractive index change of several % when an electric field is applied). . However, only total reflection type optical switches have been considered.

Means for Solving the Problems A directional coupler including two semiconductor optical waveguides having a multi-quantum well structure arranged in parallel, a pair of electrodes formed by sandwiching a multi-quantum structure between the semiconductor optical waveguides, and It was composed of a power source means for selectively applying a voltage between the electrodes.

Effect The light incident on one semiconductor optical waveguide propagates while being confined in this semiconductor optical waveguide due to the difference in refractive index.
According to its action as a directional coupler, a part of it is coupled into the other semiconductor optical waveguide that is arranged in parallel nearby, and after propagating through the complete coupling length, it completely migrates into the other semiconductor optical waveguide. It is emitted. However, when a voltage is applied to a pair of electrodes formed between two semiconductor optical waveguides sandwiching a multiple quantum structure, and an electric field is applied to the multiple quantum structure, the refractive index of this portion decreases. In this state, the light propagated in one semiconductor optical waveguide is confined therein and is not coupled into the other semiconductor optical waveguide.

Therefore, the incident light is emitted from this one semiconductor optical waveguide. In other words, by controlling the refractive index of the multi-quantum structure between two semiconductor optical waveguides by applying an electric field using electrodes, the confinement state of light is changed and the optical coupling between the two semiconductor optical waveguides is controlled. By doing so, optical switching can be performed.

Example An embodiment of the present invention will be described based on the drawings.

This embodiment utilizes a semiconductor optical waveguide structure having a rib-type multiple quantum well structure (MQW). First, a low refractive index layer 2 for light confinement is formed on a semiconductor substrate l. On this low refractive index layer 2, a rib-shaped MQW semiconductor optical waveguide is formed. That is, a multiple quantum structure 3 is formed on a low refractive index layer 2, and a low refractive index cladding layer is formed in a convex shape as shown in the figure on the top layer of this multiple quantum structure 3. Two semiconductor optical waveguides 4
．． 5 is formed. Here, these semiconductor optical waveguides 4 and 5 are close to each other near the center (area E), and are configured as a directional coupler 6.

On the other hand, in a region E where such two semi-dedicated optical waveguides 4 and 5 are located close to each other, the semiconductor optical waveguides 4 and 5 are located between the front and back surfaces (multi-weight [one structure part 3 surface and the semiconductor substrate l ) has a pair of lengths equivalent to the length of area E. talfs 27a and 7b are provided. A voltage is selectively applied between these electrodes 7a and 7b by a power supply means (not shown) according to a switching signal.

In such a configuration, it is assumed that light is now incident on the semiconductor optical waveguide 4. Moreover, the electrode 7a, ? Assume that no voltage is applied between b.

Then, this light propagates while being confined within this semiconductor optical waveguide 4 due to the refractive index difference (see FIG. 4(b)). However, all the light is not localized in the semiconductor optical waveguide 4, and the electric field seeps out from the semiconductor optical waveguide 4 (see FIG. 4(c)). At this time, if another semiconductor optical waveguide 5 exists in parallel nearby as in the present embodiment, the leakage of this electric field causes the fifth As shown in the figure, it is gradually coupled to the other semiconductor optical waveguide 5,
After propagating through the complete coupling length, 100% of the light moves into this semiconductor optical waveguide 5 and is emitted. That is,
The light incident on the semiconductor optical waveguide 4 is emitted from the semiconductor optical waveguide 5.

On the other hand, consider a case where a voltage is applied between electrodes 7a and 7b. When a voltage is applied between these electrodes 7a and 7b and an electric field is applied to both sides of the multiquantum +1'17 structure 3 between the semi-central optical waveguides 4 and 5, as shown in FIG. 3(a), The refractive index changes. This refractive index change is a change in which the refractive index of the electric field application region becomes smaller, as shown in FIG. 2(b). Therefore, as shown in FIG. 4C, the light that enters and propagates into the semiconductor optical waveguide 4 is completely confined within the semiconductor optical waveguide 4 without any electric field seeping out, and even if it is in the region E, the light that propagates in the semiconductor optical waveguide 4 is completely confined within the semiconductor optical waveguide 4. It is in a state where it is not coupled to the semiconductor optical waveguide 5 of. As a result, unlike when no electric field is applied, the light incident on the semiconductor optical waveguide 4 is directly emitted from the semi-dedicated optical waveguide 4.

That is, the refractive index of the multi-quantum structure 3 changes as shown in FIGS. 3(b) and 4(b) depending on whether or not an electric field is applied by the electrodes 7a and 7b, so the light confinement state changes. As a result, the optical coupling between the two semiconductor optical waveguides 4.5 can be changed, and optical switching becomes possible. Here, the refractive index change due to the application of an electric field to the MQW enables high-speed operation, and since the refractive index change is large, a high-speed optical switch with a large extinction ratio can be realized.

Moreover, it is an optical switch that can be integrated and configured, and can be easily applied to, for example, an optical modulator using a semiconductor laser as a light source.

FIG. 6 shows an example of application to a light intensity modulator. This is 2
An optical waveguide 8 forming a loss region is formed in parallel to the semiconductor optical waveguides 4 and 5 by separating the adjacent locations of the two semiconductor optical waveguides 4 and 5, and electrodes 7a and 7b are connected to the respective optical waveguides. It is arranged so that it is divided on both sides, and a voltage is applied through a common electrode 9. Light from the semiconductor laser lo is incident on the optical waveguide 8.

According to such a configuration, the light from the semiconductor laser 10 enters the optical waveguide 8, is coupled to the semiconductor optical waveguides 4 and 5, and is emitted. When a voltage is applied between the electrodes 7a and 7b via the common electrode 9, the refractive index of both sides of the optical waveguide 8 changes, and the state is such that it is not coupled to the semiconductor optical waveguides 4 and 5.
The light from the semiconductor laser 10 enters the optical waveguide 8 and is emitted from the optical waveguide 8 as it is. At this time, electrodes 7a, 7
By controlling the voltage to b and, therefore, the strength of the electric field to be generated, the amount of loss in the optical waveguide 8 can also be controlled, and therefore intensity-modulated light can be emitted from the optical waveguide 8. In this way, in this example, since the optical switch described above is used as a modulator, modulated light with a narrow spectral linewidth and a large extinction ratio can be obtained under high-speed operation. In particular, according to this example, the optical switch described above can be manufactured using a normal semiconductor laser manufacturing process, and as shown in FIG. It can also be formed in an integrated manner.

Therefore, the optical switch or optical intensity modulator of the present invention can be said to be promising as a light source device for use in long-distance, large-capacity optical fiber communications.

Effects of the Invention As described above, the present invention provides a directional coupler using two multi-quantum well structure semiconductor optical waveguides arranged in parallel;
Since a pair of electrodes are formed between the semiconductor optical waveguides and sandwich the multiple quantum structure and to which a voltage is selectively applied by the power supply means, light is It is possible to perform switching, therefore, it is possible to operate at high speed and to provide a switching element with a large extinction ratio.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is a plan view, FIG. 2 is a front view, and FIG. 3 is a diagram showing the state near the multiple quantum structure when voltage is applied, the refractive index distribution, and the electric field distribution. FIG. 4 is an explanatory diagram showing the relationship between the state near the multiple quantum structure when no voltage is applied, the refractive index distribution, and the electric field distribution.
The figure is an explanatory plan view showing the optical coupling operation between semiconductor optical waveguides when no voltage is applied, and FIG. 6 is a plan view showing an example of application to a light intensity modulator.

Claims (1)

[Claims] A directional coupler including two semiconductor optical waveguides having a multiple quantum well structure arranged in parallel, a pair of electrodes formed by sandwiching a multiple quantum structure between the semiconductor optical waveguides, and selectively applying a voltage between these electrodes. An optical switch characterized by comprising a power source means for applying .