JPH05265055A - Integrated optical element, optical switch and optical switch array - Google Patents

Abstract

PURPOSE:To simplify the process for forming the element and to decrease switching currents by integrating optical amplifiers and providing the P-N junctions formed by the growth of the same crystals in an optical amplifying part and an optical switching part. CONSTITUTION:The element constituted by integrating the optical amplifiers to carrier implantation type optical switches having a single bridge crossed structure is constituted of an optical waveguide 1, an optical switching current implantation part 2 and the optical amplifying part 3. The angle of an X branch is specified to be 10 deg. and the angle of a Y branch to be 5 deg.. This element is used as a unit cell constituting an optical switch array. The optical switching part is formed by growing the optical waveguide layer 22, a barrier layer 23, an optical amplifying part 24, a clad layer 25 and a gap layer 26 on a substrate 21. Since the P-N junction is formed by such crystal growth, the control of the joining position with sufficient accuracy is possible. An oxide film is deposited by evaporation over the entire surface to form an oxide mask by using photolithography only in the parts of the optical amplifying part 3 and the current implantation part 2 and the upper four layers exclusive of the optical amplifying part are successively removed by a selective etching method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of optical fiber communication and optical information processing, and more particularly to a method for manufacturing a semiconductor optical device suitable for integrating optical devices having an optical waveguide structure.

[0002]

2. Description of the Related Art Conventionally, integration of a semiconductor optical switch and an optical amplifier has been discussed in JP-A-2-199430.

[0003]

In the above-mentioned prior art, no consideration is given to the ease of making when integrating the optical switch and the optical amplifier, and the optical amplifier and the optical switch are sequentially arranged. In addition to the problem of having to fabricate, there was a problem that the reproducibility of the fabrication of the optical switch section by Zn diffusion was poor. Furthermore, the prior art does not consider the current confinement in the lateral direction of the optical switch current injection portion, and causes a large proportion of the injected current to act as effective carriers, resulting in an increase in switching current.

An object of the present invention is to simplify the manufacturing process when the optical switch and the optical amplifier are integrated and reduce the switching current.

[0005]

The above object can be achieved by constructing an optical switch using a layer structure common to that of an optical amplifier portion.

[0006]

The carrier injection type optical switch is realized by utilizing the physical phenomenon that the refractive index of the semiconductor decreases when a current is injected, and using the current injection section as a total reflection mirror.
According to Snell's law, the relation between the angle θ of total reflection and the refractive index difference ΔNtr of the medium is given by ΔNtr = Ne (1-cos [θ / 2]) .......... (Equation 1) Be done. Here, Ne is the equivalent refractive index of the optical waveguide and is represented by Ne = βλ / 2π. β is a propagation constant and λ is a wavelength. If the angle θ is determined from this equation, the refractive index change ΔNtr required to satisfy total reflection is determined.

An optical waveguide having a multilayer structure can be characterized by an equivalent refractive index. In order to determine whether or not an optical switch can be constructed using the layer structure of the optical amplifier, the equivalent refractive index Nwg due to the multilayer structure of the optical waveguide and the equivalent refractive index of the optical switch part due to the multilayer structure common to the optical amplifying part are used. Compare with the rate Nsw. Since current injection is limited to the optical switch section, Nwg does not change and Nsw only decreases when current is injected. Let ΔNcmax be the maximum change in refractive index caused by current injection. In order to realize the switching, it is sufficient to satisfy the relationship of ΔNtr ≦ Nwg- (Nsw-ΔNcmax) .... (Equation 2). By analogy with the conventional structure, sufficient switching is possible at least when Nwg = Nsw. As Nwg <Nsw changes to Nwg> Nsw, the amount of change in the refractive index required for total reflection decreases, so that the current required for switching can be reduced. Further, under the condition of Nwg> Nsw, the change in the refractive index becomes large when the same current as that in the conventional case is flowed, so that the switching becomes possible even if the total reflection angle is large.

By the way, when Nwg> Nsw, there is a condition that satisfies (Equation 2) even when there is no current injection, that is, when ΔNcmax = 0, total reflection occurs from the initial state, and switching due to current is caused. I cannot turn it on and off. For this reason, when Nwg> Nsw, the limiting condition of ΔNtr> Nwg-Nsw ..... (Equation 3) is required.

Therefore, Nwg and Nsw satisfying the conditions of (Equation 1) to (Equation 3) should be obtained. Nwg calculated using the layer structure of FIG. 2 with the thickness of the optical waveguide layer as a parameter
And the results of Nsw are shown in FIG. If the equivalent refractive index is 3.30 and the thickness of the optical waveguide layer of the optical waveguide section is 0.8 μm and the thickness of the optical waveguide layer of the optical switch section is 0.3 μm, the condition of Nwg = Nsw is satisfied. Further, if the film thickness of the optical waveguide layer of the optical switch unit is made thinner or the film thickness of the optical waveguide layer of the optical waveguide unit is made thicker, N
The relationship of wg> Nsw can also be satisfied.

From the above, a carrier injection type optical switch can be realized by using the layer structure common to the optical amplifier, and the current can be reduced if the condition of Nwg> Nsw is satisfied under the restriction of (Equation 3). I understand.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a top view of an element in which an optical amplifier is integrated in a carrier injection type optical switch having a single-pass crossing structure. It is composed of an optical waveguide 1 for guiding light, an optical switch current injection section 2 and an optical amplification section 3. The X-branch angle was 10 ° and the Y-branch angle was 5 °. This element can be used as a unit cell when forming an optical switch array.

A sectional structure AA 'of the optical switch portion is shown in FIG. Hereinafter, a method for manufacturing an element will be described with reference to this drawing.
In this embodiment, an n-type InP substrate 21 is provided with an n-type InGaAsP optical waveguide layer 22 (absorption edge wavelength λg = 1.15 μm), an n-type InP barrier layer 23, and an n-type InGaAs.
Five layers, that is, a P optical amplification layer 24 (absorption edge wavelength λg = 1.3 μm), a p-type InP clad layer 25, and a p-type InGaAsP cap layer 26, were multilayer-grown by the MOCVD crystal growth method. The junction position can be controlled with sufficient accuracy to form a PN junction by crystal growth. An oxide film is vapor-deposited on the entire surface, and an oxide film mask is formed only by photolithography on the optical amplification section and the current injection section of the optical switch. The upper four layers other than the optical amplification section are sequentially etched by a selective etching method. Removed. Next, using the above-mentioned oxide film mask, the n-type InGaAsP optical waveguide layer 27
Two layers of the semi-insulating InP clad layer 28 (absorption edge wavelength λg = 1.15 μm) were selectively grown by the MOCVD crystal growth method. After that, an optical waveguide having the shape shown in FIG. 1 was formed by using photolithography and dry etching technology by RIE.

FIG. 3 shows the equivalent refractive index Nsw of the optical switch section according to the layer structure CC ′ of FIG. 2 and the optical structure according to the layer structure DD ′ of FIG. 2 when the film thickness of the optical waveguide layer is used as a parameter. The equivalent refractive index Nwg of the waveguide is shown. According to the above discussion, in order to satisfy Nwg = Nsw, the film thickness of the optical waveguide layer 22 of the first crystal growth is
The thickness of the optical waveguide layer 27 at the time of the second crystal growth was 0.5 μm. In the optical switch created under these conditions, 1.3 μm semiconductor laser light was guided and switching was possible at a current of about 50 mA. Furthermore, in an element in which the optical waveguide layer 22 is 0.2 μm and the optical waveguide layer 27 is 0.5 μm, the switching current can be reduced by about 20 μm.
It was confirmed that switching was performed with mA.

FIG. 4 shows a cross-sectional structure of the optical amplifying portion corresponding to BB 'in FIG. The layer structure of the optical amplification section is common to that of the optical switch section. In the optical amplifier of this structure, a gain of canceling the insertion loss was obtained with a current of 150 mA.

FIG. 5 shows the structure of an optical switch section of the conventional structure taken along the line AA 'in FIG. After the crystal structure of the layer structure of the optical amplification section was grown in the same manner as in the above-mentioned preparation method, only the optical amplification section was left and the upper part 4 was formed.
The InGaAsP optical waveguide layer 27 (absorption edge wavelength λg
= 1.15 μm), InP clad layer 31, InGaAsP cap layer 32
3 layers were selectively grown by the MOCVD crystal growth method. The current injection part of the optical switch part was made by Zn diffusion. Here, the depth control of the current injection part was an important factor that determines the switching characteristics, but sufficient reproducibility was not obtained by Zn diffusion by the closed tube method. Moreover, as can be seen from the structure of FIG. 4, the current confinement in the layer direction is well confined in the optical waveguide layer by the double hetero structure, but there is no lateral potential barrier in the optical waveguide layer, so that the expansion occurs. For this reason, the carrier density in the optical waveguide layer rises slowly with respect to the injected current, leading to an increase in the switching current. On the other hand, in this embodiment shown in FIG. 2, carrier confinement is improved because a hetero barrier is formed in the lateral direction in addition to the double hetero structure in the layer direction. The switching current of the optical switch according to the conventional structure is about 100 mA, which requires twice to five times the current of the embodiment of the present invention.

In the present embodiment, the rib type structure is used for the optical waveguide in order to confirm the basic function with a simple structure, but it goes without saying that the current of the optical amplifier can be reduced by using the embedded structure similar to that of the semiconductor laser. .. Moreover, since the PN junction of the current injection part of the optical switch part is formed by crystal growth, re-diffusion does not occur even if heat treatment is performed during embedded crystal growth like the PN junction formed by Zn diffusion and the optical switch part The property is saved.

[0017]

According to the present embodiment, the optical switch can be realized by using the same layer structure as that of the optical amplifier, so that the device manufacturing process can be greatly simplified. Furthermore, by adopting the layer structure satisfying the relationship of the equivalent refractive index shown in the embodiment, the current required for switching can be greatly reduced. Furthermore,
When the same layer structure as the above is used and driven at the same current value as the conventional one, a large equivalent change in the refractive index can be obtained, so that the total reflection angle can be increased. As a result, the element can be downsized and a large-scale array can be realized.

[Brief description of drawings]

FIG. 1 is a top view when an optical switch and an optical amplifier according to an embodiment of the present invention are integrated.

FIG. 2 is a sectional structural view of the optical switch of the embodiment shown in FIG.

FIG. 3 Calculation of equivalent refractive index using optical waveguide layer film thickness as a parameter for designing the layer structure of the example

FIG. 4 is a sectional structure of an optical amplification section.

FIG. 5 is a cross-sectional structure of a conventional optical switch section.

[Explanation of symbols]

1 ... Optical waveguide, 2 ... Carrier injection region, 3 ... Optical amplifier,
4 ... Single-pass optical waveguide, 21 ... n-type InP substrate, 22 ... n-type InGaA
sP optical waveguide layer, 23 ... n type InP barrier layer, 24 ... n type InGaAsP optical amplification layer, 25 ... p type InP clad layer, 26 ... p type InGaAsP cap layer, 27 ... n type InGaAsP optical waveguide layer, 28 ... half Insulation
InP clad layer, 31 ... n type InP clad layer, 32 ... n type In
GaAsP cap layer, 33 ... Zn diffusion region.

Claims (5)

[Claims] 1. An integrated optical device in which an optical waveguide for guiding a light wave and an optical switch for switching light are formed on the same semiconductor substrate.
An integrated optical device characterized by producing a PN junction by crystal growth. 2. An integrated optical device characterized in that an optical amplifier is integrated with the integrated optical device according to claim 1, and the optical amplifier part and the optical switch part have PN junctions formed by the same crystal growth. .. 3. A carrier injection type optical switch in which the optical integrated device according to claim 2 is constructed in a crossover structure. 4. The optical switch according to claim 3, wherein an optical amplifier is integrated at a crossover. 5. An optical switch array in which the optical switch according to claim 1 is integrated as a basic unit cell.