JPS63280224A - Waveguide type optical control element - Google Patents

Abstract

PURPOSE:To reduce a difference between a refractive indexes and to suppress crosstalk to a low level by comparatively independently controlling a band gap in accordance with the well of a multiplex quantum well (MQW) and the component and thickness of a barrier and an average refractive index based on the ratio of the well and the component and thickness of the barrier. CONSTITUTION:When control light 10 is not made incident upon an optical waveguide 11, signal light 12 made incident upon an optical waveguide 13a is straight advanced as it is and emitted. When the control light having 0.85mum wavelength lambdaex equal to the exciton peak wavelength of the MQW is made incident upon the waveguide 11, the control light 10 is arrived from the waveguide 11 to an MQW reflecting part 6. The control light 10 is absorbed into the MQW at the part 6, the exciton peak of the MQW disappears and a refractive index is reduced at wavelength lambda1(>lambdaex), so that the signal light 12 is totally reflected by the reflection part 6 and outputted from an optical waveguide 13b. At that time, the refractive index is sharply changed by the control light 10 only in the reflection part 6 and an interface generating the change of the refractive index is extremely sharpened. Consequently, crosstalk at the time of total reflection can be extremely reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a waveguide type optical control element for switching the optical path of an optical signal, selecting a wavelength, and converting a wavelength in the field of optical switching and optical information processing. It is something.

[Conventional technology]

With the ultra-high speed of optical communication systems, the advancement of systems such as coherent transmission, and the progress of research into optical switching equipment, optical computers, etc., there is a strong desire to realize optical control elements that control optical signals with light. It is now possible to To meet these demands, we have developed an "optical NOA" system that utilizes the change in refractive index caused by light absorption in a multiple quantum well (MQW) structure.
"Gate" (1986 Autumn Academic Conference of the Japan Society of Applied Physics 2)
8a-X-7) is considered.

This optical Noah gate forms a Fabry-Perot etalon (hereinafter referred to as etalon) in the vertical direction to the MQW layer.
The refractive index of the MQW is changed by inputting excitation light having a wavelength near the exciton peak wavelength of the MQW into the MQW, and the signal light is controlled by changing the peak wavelength of the etalon for the signal light.

The specific operation of this optical Noah gate will be briefly explained below. First, one of the interference peak wavelengths of the MQW etalon is made to match the wavelength of the signal light. In this state, the signal light that is perpendicularly incident on the MQW etalon passes through the etalon and enters the ON state. Next, the excitation light is incident on the MQW etalon along the same optical path as the signal light. The refractive index of the MQW etalon changes depending on the excitation light, and the interference peak wavelength of the etalon changes, thereby causing a wavelength mismatch with the signal light. Then, the signal light passing through the etalon is reduced compared to when the etalon is in the ON state, and the Etalon is in the OFF state. In this way, the excitation light is OF
An optical NOR gate is realized in which the signal light is turned on when F, and the signal light is turned off when the excitation light is turned on.

[Problem that the invention seeks to solve]

This type of light control element has an etalon configuration, and its operating principle is to shift the interference peak wavelength of the etalon using a change in the refractive index caused by the excitation light. Therefore, the conditions for setting the wavelength of the signal light are very strict, and the signal light and If there is a temperature change in the semiconductor laser light or wavelength fluctuation due to returned light, sufficient characteristics as a gate may not be obtained. In addition, since it has a solid structure in which the signal light and excitation light are incident perpendicularly to the MQW layer, it can be connected in cascade with the next stage of devices, and even with multiple light control devices via optical waveguides. The disadvantage was that it was difficult to integrate.

An object of the present invention is to provide a waveguide type light control element that solves the above problems.

[Means for solving problems]

The waveguide type light control device according to the present invention has first lattice plates on a semiconductor substrate that intersect with each other. a second optical waveguide; and the first optical waveguide. It is composed of a reflective surface arranged on the center line of the intersection of the second optical waveguide, and a third optical waveguide for inputting light to the reflective surface, and the reflective surface has a thickness of approximately the de Broglie wavelength. It has a multi-quantum well structure in which a first semiconductor layer is sandwiched between second semiconductor layers having a wider band gap than the first semiconductor layer, and quantum wells are multiplexed in the layer thickness direction.
The second optical waveguide has a higher band width than the multiple quantum well structure.
The gap is wide and the effective refractive index is approximately equal, and the first
．． A signal light having a wavelength longer than the exciton peak wavelength of the multi-quantum well is incident on the second optical waveguide, and a control light having a wavelength substantially equal to the exciton peak wavelength is incident on the third optical waveguide. It is characterized by:

[Effect]

The present invention utilizes changes in the refractive index of MQW caused by absorption of light near the exciton peak wavelength of MQW. First, regarding this refractive index change, G a A s /
This will be explained by taking an A It Ga As quantum well (QW) structure as an example.

In the case of a QW, since room temperature excitons exist due to the quantum size effect, the optical absorption coefficient spectrum shows a rapid change near the exciton absorption peak wavelength. The refractive index spectrum, which has a Kramers-Kronig relationship with each other, also changes significantly with wavelength. This situation is shown by solid lines in Figures 2(a) and 2). Here, λ, 8 indicates the peak wavelength of excitons. When light with a wavelength near the exciton peak wavelength of the QW is incident on this QW, the QW absorbs the light, and the exciton level is filled with carriers generated thereby, causing so-called absorption saturation. This kind of development was published in the magazine "Physical Review
Letters (Physical Review Letts)
-ers) J Vol. 56, 1986, p. 1191.

Due to this absorption saturation, the exciton level disappears, and the state of the optical absorption spectrum at that time is shown by the broken line in Figure 2 (a), and the related refractive index spectrum is shown by the broken line in Figure 2 (bl). Due to the disappearance of the levels, the gap in the refractive index spectrum drawn by the solid line in Figure 2) is averaged as shown by the broken line, resulting in a shape similar to the refractive index spectrum in the bulk case.

The change in the refractive index due to the input of optical power becomes positive at wavelengths shorter than the exciton peak and negative at wavelengths longer than the exciton peak. The situation is shown in Figure 3.

In addition, the value of the refractive index change Δn/n obtained by averaging the gear and p is 6X10-'0 The present invention utilizes the change in the refractive index due to the incidence of optical power on the QW. be.

Next, the basic operation of the device of the present invention will be briefly explained. First, this MQ
Light with a wavelength λ□ approximately equal to the exciton peak wavelength of W (
Consider the case where control light (hereinafter referred to as control light) is not incident through an optical waveguide. , λ, It is assumed that light having a wavelength λ on the longer wavelength side than X (hereinafter referred to as signal light) is incident on the MQW reflecting section at a certain angle through an optical waveguide. At this time, since the optical waveguide and the MQW reflecting section have substantially the same refractive index, the light passes through the reflecting section as is.

Next, consider the case where control light is incident on this MQW. At this time, as mentioned above and shown in FIG. 3, the refractive index of the MQW reflecting portion for light having a wavelength λ on the longer wavelength side than λ, X decreases. As a result, the signal light incident on the MQW reflection section at a certain angle undergoes total reflection, and does not pass through the MQW reflection section.

Based on the configuration and operating principle as described above, the waveguide type optical control element of the present invention can be realized.

Furthermore, in the MQW structure, the bandgap can be controlled to some extent independently by the composition and thickness of the well and barrier of the MQW, and the average refractive index by the ratio of the composition and thickness of the well and barrier. Therefore, even if the composition changes between the reflective part and its surroundings, it is possible to effectively design the refractive index difference to be sufficiently small, and crosstalk can also be suppressed to a small level.

〔Example〕

FIG. 1 is a diagram showing the structure of an embodiment of a waveguide type light control element according to the present invention, (a) is a perspective view thereof, and (b) is an A-
It is a sectional view between A'.

Here, GaAs/Ajl! The case where GaAs-based material is used is shown.

First, the fabrication of the waveguide type light control element of this example will be explained. A 1-Aj2GaAs cladding layer 3.1 is formed on an n''-GaAs substrate l via an i-GaAs buffer layer 2.
-GaAs/AffGaAs multiple quantum well (MQW) layer 4 (4 to 100 GaAs wells, AlGaAs
CAR molar ratio x = 0.55) Barrier thickness ~ 100 people)
, 1-AIlGaAs cladding layer 5 is successively grown by the MBE method. Next, this wafer has a width of 2 μm and a length of 100 μm.
The 1-GaAs buffer layer 2 is etched by reactive ion beam etching until the 1-GaAs buffer layer 2 is reached. After that, by LPE method, this MQW reflection color 6-AlGaAs (x=0.28)
Cladding layer 7.1-AIGaAs (x=0.2) Guide layer 8.1-AnGaAs (x=0.28) Buried by cladding layer 9. At this time, a protective film such as SiQ is applied to the top of the MQW reflecting section 6 to prevent the growth of MQW.
1-AIGaA grown by BH! ! Clad N3.
5 and the thickness of the 1-AIGaAs cladding layer 7.9 grown by the LPE method, and
/AffiGaAsMQW layer 4 thickness and i-/'1Ga
The thickness of the As guide layer 8 was made almost equal to that of the As guide layer 8.

On the wafer grown in this way, a pattern of a striped rib optical waveguide 11 for the control light 10 and a pattern of the rib optical waveguide 1 after the MQW reflection color 6 with a new width of the MQW reflection color 6 are formed.
A pattern of intersecting rib optical waveguides 13a and 13b for the signal light 12 is formed by etching such that 1 is the center line.

Considering here that the wavelength λ of the signal light 12 is near = 0.86 μm, the i-MQW layer 4.1-AjiGaAs guide layer 8.1-Ai! The refractive index of the GaAs cladding layer 7.9 is 3
．． 45.3.47.3.42 and 1-AIGaAS
The effective refractive index for light propagating through the guide layer 8 is i-MQ
The refractive index was set to be approximately equal to the refractive index of the W layer 4. At this time, 1-AfGaAs guide layer 8.1-Aj! The bandgap wavelength of the GaAs cladding layer 7.9 is 0.74 μm,
The amount of absorption loss is 0.7 μl, which is a sufficiently small value for absorption loss at a wavelength of λ=0.86 μm.

Next, the operation of the waveguide type light control element of this embodiment will be explained. To simplify the explanation, the signal light 12 is shown in FIG. 1(a).
It is assumed that the light enters the optical waveguide 13a from before. When the control light 10 is not incident on the optical waveguide 11, the signal light 12 that is incident on the optical waveguide 13a continues straight and exits. When the control light 10 having a wavelength λ, .=0.85 μm, which is equal to the exciton peak wavelength of this MQW is incident on the optical waveguide 11, the control light 10 passes through the optical waveguide 11 and reaches the MQW reflection section 6. As explained earlier, here the control light 10
is absorbed by the MQW, the exciton peak of the MQW disappears, and the refractive index decreases at the wavelength λjI (>λIIX). Therefore, the signal light 12 is totally reflected by the MQW reflection section 6 and output from the optical waveguide 13b. The magnitude of the refractive index change at this time reaches about 0.6%, so the crossing angle should be about 10''.Moreover, only the MQW reflection section 6 has a large change in refractive index due to the control light 10. Since the interface where the refractive index changes is very steep, crosstalk during total reflection is also very small.

Although the above description has been made regarding the IX2 changeover switch, 2×2 switching is also possible with the same effect when signal light is incident on each of the optical waveguides 13a and 13b.

Furthermore, in this example, the material is GaAs/Aj! GaA
Although we have explained about s-based materials, InGaAsP/1nP
, 1nGaAs/InAjtAs, and other material systems. Although a rib type optical waveguide is used as the optical waveguide, other three-dimensional optical waveguides such as a buried type can also be used.

〔Effect of the invention〕

As explained in detail above, according to the present invention, it is possible to realize a 1×2 or 2×2 optical switch that is waveguide type and is controlled using light. It has great utility value in fields such as computers.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of an embodiment of a waveguide type light control element according to the present invention, (a) is a perspective view thereof, and (b) is an A-A'
2 and 3 are diagrams for explaining changes in the refractive index of the multiple quantum well structure due to excitation light used in the present invention. 1...n" -GaAs substrate 2...1-GaAs buffer layer 3.5, 7.9...i -A I2 G a A
s cladding layer 4---i-GaAslAItGaAsM
QW layer 6...MQW reflecting section 8 ・"i-AIGaAs guide layer 10
...Control light 11, 13a, 13b...Optical waveguide 12...Signal light agent Yoshiyuki Iwasa (a) Figure 1 (a) (b) Figure 2 Brocade 3

Claims (1)

[Claims] (1) First and second optical waveguides that intersect with each other on a semiconductor substrate, a reflective surface arranged on the center line of the intersection of the first and second optical waveguides, and light incident on the reflective surface a third optical waveguide for the purpose of converting a first semiconductor layer having a thickness of approximately the de Broglie wavelength into a second semiconductor layer having a wider band gap than the first semiconductor layer; The first and second optical waveguides have a wider band gap and substantially equal effective refractive indexes than the multi-quantum well structure, and 1. A signal light having a wavelength longer than the exciton peak wavelength of the multiple quantum well is incident on the second optical waveguide, and a control light having a wavelength substantially equal to the exciton peak wavelength is incident on the third optical waveguide. A waveguide type optical control element characterized by: