JPH07183483A - Light switch array - Google Patents

Abstract

PURPOSE:To realize a light switch array of large quenching ratio and rapid response velocity by constituting a light switch comprised of a photosensitive part, an amplification part and an output part formed of a vertical resonator type surface light emitting laser monolithically on a substrate. CONSTITUTION:A layer comprised of an i-GaAs optical absorption layer 102, an n<->-GaAs channel layer 103 and an n<+>-GaAs contact layer 104 is formed on a semiinsulation GaAs substrate 101 as a photosensitive part and an amplification part. Furthermore, a layer comprised of a surface light emission layer including an InGaP layer 105 as an etching stop layer, an n-DBR layer 106 constituted by forming 30 periods of n-AlAs/n-AlGaAs alternately as a light modulation part, an i-AlGaAs active layer 107, a p-DBR layer 108 constituted by forming 25 periods of P-AlAs/p-AlGaAs alternately is formed by molecular beam epitaxy. The formed wafer is processed and a light switch is prepared.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch array driven and controlled by an optical signal.

[0002]

2. Description of the Related Art The development of an optical switch array as a key device for optical signal processing and optical information processing is highly desired. Conventionally, as an element of this type, for example, a document (IEEE)
E PHOTONICS TECHNOLOGY LE
TTERS, Vol. 1, p. 62 (1989)), a photodetector consisting of a photodiode, a load resistor and a constant voltage source, an amplifying part consisting of an FET, a multiple quantum well (M
QW) pin type optical modulator, which is an optical modulator,
An element called "field effect transistor seed (FET-SEED)" having a function of changing the transmitted light intensity of the light applied to the -pin type optical modulator has been proposed. In this element, the transmitted light intensity of the light biased at a constant intensity can be controlled by the input light having the same wavelength as the quantum confined Stark effect. The configuration and characteristics will be described with reference to FIG.

P-AlGaAs on a p-GaAs substrate
Layer, i-MQW layer, n ^-- GaAs layer and n ⁺ -Ga layer
FIG. 15 shows an epitaxial substrate laminated in the order of As.
It is processed as shown in (A). FET is MQW- on the right side
In the pin structure, the n ⁻ -GaAs layer is used as a channel. Now, assuming that the light incident on the left MQW-pin structure is the input light, the light incident on the right MQW-pin structure is the bias light, and the transmitted light thereof is the output light, FIG.
The characteristic shown in (B) appears.

[0004]

However, the above-mentioned device has the following problems.

First, since the MQW-pin diode is used as the light modulator, the extinction ratio is low and the loss is large.

Secondly, since it is necessary to enter bias light into the light modulator, the optical system becomes complicated.

Thirdly, since the operating voltage of the light modulator is as large as about 10V, the response speed is slow.

Fourthly, the operating wavelength range of the optical modulator using the quantum confined Stark effect is limited to several nm, and the operating wavelength of the optical modulator fluctuates due to heat or the like, so that the wavelength of the bias light source is limited. Is tough.

The object of the present invention is to solve the above problems,
It is to realize an optical switch array having a large extinction ratio and a high response speed.

[0010]

[Means for Solving the Problems]

1) The optical switch array of the present invention includes a light receiving section for converting an input signal into an electric signal, an amplifying section for amplifying the electric signal, and a vertical cavity surface emitting device for oscillating output light by the amplified electric signal. An optical switch composed of an output section composed of a laser is monolithically formed on the substrate.

2) Further, in the optical switch array of the present invention, in the element described in 1) above, the light receiving portion is MSM (M
etal-Semiconductor-Metal)
It is characterized by comprising a photodiode or a photoconductor.

3) Further, the optical switch array of the present invention comprises:
The element described in 1) above is characterized in that the light receiving portion is composed of a plurality of light receiving elements.

[0013]

In order to solve the above problems, the present invention solves the above problems as follows.

That is, in the optical switch array according to the present invention, since the surface emitting laser (SELD) is used as the optical modulator, high contrast can be obtained. Further, since an operating voltage of about 2V is sufficient, high speed operation can be realized. Further, since this element does not require bias light and operates only with a light source for input, the wavelength of the light source is not limited, and the optical system is simplified. In addition, when the present device is configured in multiple stages and the optical connection such that the output light from the previous stage is used as the input light is performed to perform processing such as optical interconnection, SELD
Is difficult to control because the oscillation wavelength is very sensitive to the fluctuation of the film thickness,
If an MSM photodiode or the like is used, almost uniform photosensitivity can be obtained in a wide range of wavelengths of 100 nm or more, so that there is no limitation on the oscillation wavelength of the SELD in the preceding stage, which is also advantageous for multi-stages.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail with reference to the accompanying drawings, but it goes without saying that the present invention is not limited thereto.

First, the structure of the device of the present invention will be described with reference to FIG. 1, and then the operating principle and characteristics thereof will be described with reference to FIGS. 2 to 8. In the following, as the light receiving unit, M
An example in which the SM photodiode is used as the amplifying section and the FET is used will be described. However, other than this, the light receiving section can be configured by using a pin diode or a photoconductor, and the amplifying section can be formed by using a bipolar transistor such as a heterojunction transistor. Further, with reference to FIGS. 9 to 14, specific examples of the layer structure of the element and the optical switch characteristics will be shown.

FIG. 1 shows the structure of the device.
FIG. 1A shows the basic structure of the device. The surface emitting laser 12 as the light modulator 10 and the F as the amplifier 20 are shown.
The ET22 is connected in series with a constant voltage source. At this time, the surface emitting laser 12 is connected so as to be forward biased. Reference numerals 24, 26 and 28 are the source, gate and drain of the FET 22, respectively. M as the light receiving unit 30
The SM photodiode 32 and the load resistor 34 are also connected in series together with the constant voltage source, and the contact 36 of the MSM photodiode 32 and the load resistor 34 is connected to the gate 26 of the FET. P _in and P _out are input light and output light, respectively.
The input light P _in enters the MSM photodiode 32.
FIG. 1B shows an MSM photodiode 3 having two light receiving parts.
It is a figure at the time of comprising and connecting 2 and 32 series. In this case, when an optical signal to be input to each of the MSM photodiode and P _A and P _B, only the gate voltage of the FET22 is changed if both P _A and P _B are entered simultaneously, as described below, V ₁ A NAND operation is performed when> V ₂ , and an AND operation when V ₁ <V ₂ . In FIG. 1C, the light receiving unit 30 is provided with two MSM photodiodes 32, 32.
It is a figure in the case of connecting and connecting in parallel. When the optical signals input to the respective MSM photodiodes are P _A and P _B , the gate voltage of the FET changes when either P _A or P _B is input, and as described later, V ₁ > V ₂ NOR operation when, OR when V ₁ <V ₂
To work.

Next, the operating principle of the device of the present invention will be described.

FIG. 2 shows an example of the relationship between the current-voltage characteristics and the current-output light intensity of the surface emitting laser. The threshold current is 1.5 mA and the voltage at that time is 2.2V. The light output light intensity increases as the voltage increases.
For example, the output light intensity is 1 mW when the current is 3.1 mA.
Is.

FIG. 3A shows M in the configuration of FIG.
The change of the gate voltage with respect to the incident light intensity which is incident on the SM photodiode is shown. FET gate voltage V _G
When V is changed from V _G1 to V _G2 (V _G1 <V _G2 ) by the input light, it is slightly smaller than V ₁ (about 0.1 V) and V ₂
Is set to be larger than V _G2 (freely set as long as it is smaller than the withstand voltage of the MSM photodiode). Therefore, the gate voltage increases as the input light intensity increases. Also, F
The gate voltage dependence of the ET drain current is shown in FIG. As a result, the dependency of the drain current on the input light intensity is as shown in FIG.

FIG. 4 is a diagram for explaining the operating characteristics of the element shown in FIG. FIG. 3C shows the dependency of the drain current on the input light intensity and the characteristics when the current-voltage characteristics of the surface emitting laser are considered together with the power supply voltage. First, when the input light is P ₀ , the operating point is at a, and almost no current flows in the surface emitting laser. Therefore, from FIG. 2, the output light intensity is almost zero. When the input light intensity is set to P ₂ , the operating point shifts to c, and the current flowing through the surface emitting laser becomes the oscillation threshold. When the input light intensity is further increased, the surface emitting laser starts oscillating and the output light rapidly increases. Therefore, the output characteristics are as shown in FIG. At this time, when V _b is small, the input light is saturated at a certain current value even if the input light is increased, and in this case, the output light intensity is saturated as shown in the figure.

Further, in this element, the input / output characteristics can be inverted by inverting the voltages applied to V ₁ and V ₂ . In the case of FIG. 6A, V ₁ is set to be slightly larger than V _G2 (about 0.1 V), and V ₂ is set to be smaller than V _G1 , that is, a negative polarity. Therefore, in this case, the gate voltage decreases as the input light intensity increases. As a result, the dependency of the drain current on the input light intensity is shown in FIG.
The drain current decreases as the input light intensity increases.

FIG. 7 is a diagram for explaining the operating characteristics of the device. The current-voltage characteristics are shown as in the case of FIG. First, when the input light is P ₀ , the operating point is at a, and a large current is flowing through the surface emitting laser, so that a large output light intensity can be obtained. When the input light intensity is increased, the output light gradually becomes smaller, and the current flowing through the surface emitting laser becomes equal to the threshold value when the input light intensity is P ₃ . When the input light intensity is further increased, the surface emitting laser no longer oscillates but only spontaneous emission light is emitted. Therefore, the input / output characteristics are as shown in FIG. Also at this time, when V _b is small, the current value does not decrease up to a certain gate voltage even if the gate voltage of the FET becomes small. Therefore, in the region where the input light intensity is small, the output light intensity is constant as shown in the figure. Area.

(Specific Example) Next, a specific example of the optical switch array of the present invention shown in FIG. 1 is shown in FIG. Figure 9 shows GaAs /
It is a sectional view of an element when AlGaAs is used.

A light receiving portion on the semi-insulating GaAs substrate 101,
A layer composed of an i-GaAs light absorption layer 102 (2 μm) n ⁻ -GaAs channel layer 103 (0.2 μm) n ⁺ -GaAs contact layer 104 (0.4 μm) as an amplification section, and InGa as an etching stop layer.
P layer 105 (10 nm) Further, as an optical modulator, n-AlAs (71.5 nm) / n-Al _0.15 Ga _0.85
N-DBR (Distributed Bragg) having a structure in which As (62.9 nm) is alternately laminated for 30 periods.
Reflector) layer 106, i-AlGaAs active layer 107, p-AlAs (71.5 nm) / p-Al
_A layer made of a surface emitting laser including a p-DBR layer 108 having a structure in which 25 cycles of _0.15 Ga _0.85 As (62.9 nm) were alternately laminated was formed by a molecular beam epitaxial growth method. Be and Si are used as p-type and n-type dopants, respectively.
Was used.

This grown wafer was processed as shown in FIG. 9 to prepare an optical switch. AuZn as the p-type electrode 110
Ni, AuGeNi was used as the n-type electrode 111, Ti / Pt / Au was used as the Schottky electrode 112, and Cr / Au was used as the inter-element wiring metal 113. in this case,
Although the tungsten silicide thin film is used as the load resistor 114, an active resistor using a metal thin film or FET other than this is also possible. Further, the step is filled with the polyimide 115. Further, it is also possible to carry out an ion implantation method or the like to fabricate the element without performing the mesa separation. In the case of arraying, these elements may be arranged two-dimensionally.

FIG. 10 shows the device characteristics of this embodiment. In FIG. 10A, V _b and V ₂ are 3 V and V ₁ is −
This is the case when set to 0.2V. When the input light is 10 μW or less, the output light is only spontaneous emission light of 1 μW or less, but when the input light is further increased, the output light intensity increases,
When the input light intensity was 100 μW, the output light intensity was 1 mW. In FIG. _10B , V _b is 3 V, V ₂ is −3 V, V
_This is the case when ₁ is set to 0.2V. When there was no input light, the output light was 1 mW or more, but when the input light was further increased, the output light intensity decreased, and when the input light intensity was 100 μW, the output light intensity became 1 μW or less. In both cases, the response speed of this element was 1 ns or less for both the on-time and the off-time when the input light intensity was 100 μW. Furthermore, the characteristics did not change even if the wavelength of the input light was changed from 750 nm to 870 nm.

In the first embodiment shown in FIG. 9, by inserting an etching stop layer, n ^{+ of the} FET portion is inserted.
The head of the -GaAs contact layer (0.4 µm) was pierced. This in forming the recess by etching the gate portion of the FET, n ^- if there is unevenness in thickness of the remaining layer above the -GaAs channel layer n ^- fluctuations in the thickness of the -GaAs channel layer out This is to prevent the current-voltage characteristics of the FET from fluctuating. In order to further suppress this fluctuation, it is possible to make the channel layer thickness uniform by using HEMT or the like.

Further, as a method which does not use an etching stop layer, which is the second embodiment, there is selective growth. In this case, MOCVD is used as a method for growing the surface emitting laser portion.
The method was used. The procedure is shown in FIG. First, the light receiving portion and the amplifying portion are grown with the same layer structure as in the first embodiment. The growth method at this time is MOC even if it is a molecular beam epitaxial growth method.
The VD method may be used. That is, the i-GaAs substrate 101,
The i-GaAs light absorption layer 102, the n ⁻ -GaAs channel layer 103, and the n ⁺ -GaAs contact layer 104 are sequentially stacked (FIG. 11A). Next, an insulating film 1 such as SiO ₂
05a is vapor-deposited, and thereafter the insulating film is removed by etching only where the surface emitting laser is grown (FIG. 11).
(B)). Then, the surface emitting laser portion is grown by the MOCVD method (FIG. 11C). Finally, it is processed as shown in FIG. The size of the window of the insulating film is 100 μm, and n
The influence of the resistance of the DBR layer was reduced, and only the active layer portion was set to 10 μm. In this case, the p-DBR layer is made of a semiconductor, but the dielectric multilayer film 11 of SiO ₂ / TiO ₂ or the like is used.
It is also possible to configure with 6. This example is shown in FIG.

In addition to this, there is a method of forming an FET by an ion implantation method as a method without using an etching stop layer.

In this case, a layer composed of an i-GaAs light absorbing layer (2 μm) as a light receiving portion and an amplifying portion on a semi-insulating GaAs substrate is used as an optical modulating portion. N-AlAs (7.15 nm) / n-Al _0.15 Ga _0.85
N-DBR (Distributed Bragg) having a structure in which As (62.9 nm) is alternately laminated for 30 periods.
g Reflector) layer, i-AlGaAs active layer, p-AlAs (71.5 nm) / p-Al _0.15 Ga
_A layer made of a surface emitting laser including a p-DBR layer having a structure in which 25 periods of _0.85 As (62.9 nm) were alternately laminated was formed by a molecular beam epitaxial growth method. p-type,
Be and Si were used as n-type dopants, respectively.

After forming a surface emitting laser by performing mesa etching on the layer for the light modulating portion of this epitaxial substrate, Si is used to form an n-channel layer on the i-GaAs light absorbing layer exposed on the surface. Ion implantation and FET
To form.

In the above embodiments, the MSM photodiode and the FET are used as the light receiving portion and the amplifying portion.
n-diode and HBT (Hetero Bipolar)
FIG. 14 shows an example in which an optical switch array is composed of Transistor).

A light receiving portion on the semi-insulating GaAs substrate 101,
N ⁺ -GaAs contact layer 120 (0.5 μm) n-AlGaAs emitter layer 121 (0.2 μm) p-GaAs base layer 122 (0.1 μm) i-GaAs light absorption layer and collector layer 123 (1. 0
μm) n ⁺ -GaAs contact layer 124 (0.2 μm) was grown. The surface emitting laser portion can form an element in the same manner as in the first and second embodiments. However, in this case, similarly to FIG. 5, only the input / output characteristic in which the output light intensity increases as the input light intensity increases can be realized.

Although the embodiments described so far are grown on a GaAs substrate, similar devices can be constructed on an AlGaAs substrate. In this case, since the substrate is transparent to the oscillation wavelength of the surface emitting laser, there is an advantage that light can be input from both sides.

In the above embodiment, GaAs / AlGa is used.
Although the optical switch array is composed of As, it is not limited to this, and InGaAs / InP, InAlAs / In
It can also be applied to other material systems such as GaAs and GaAs / InGaAs.

[0037]

As described above, the optical switch array according to the present invention has an optical amplification function, a large extinction ratio, and can operate at high speed with low input intensity.
Further, in the optical switch array according to the present invention, the FET
The one using the as an amplifier has a feature that the operation can be inverted by the operating voltage. Due to these characteristics, it is very promising as the optical switch array according to the present invention and an optical information processing device in the future.

[Brief description of drawings]

1 (A), (B) and (C) are circuit diagrams showing the structure of an element of the present invention.

FIG. 2 is a characteristic diagram showing an example of a relationship between current-voltage characteristics and current-output light intensity of a surface emitting laser.

FIG. 3 (A) shows that V ₁ is slightly smaller than V _G1 (0.1 V
Degree), the V ₂ can be freely set smaller than the breakdown voltage of greater than V _G2 (MSM photodiode) characteristic diagram showing the change of the gate voltage with respect to the incident light intensity incident on the MSM photodiode in the case of setting, (B) Is a characteristic diagram showing the gate voltage dependence of the drain current of the FET, (C)
FIG. 3 is a characteristic diagram showing the dependency of drain current on the intensity of input light.

FIG. 4 is a characteristic diagram illustrating operating characteristics of the device of FIG.

5 is a characteristic diagram illustrating input / output characteristics of the device of FIG.

FIG. 6 (A) shows that V ₁ is slightly larger than V _G2 (0.1 V
), V ₂ is smaller than V _G1 , that is, a characteristic diagram showing the dependency of the gate voltage on the input light intensity when the negative polarity is set, and (B) is the drain to FET drain current when the input light intensity changes. It is a characteristic view which shows the relationship of a voltage.

FIG. 7 is a characteristic diagram illustrating operating characteristics of an element.

FIG. 8 is a characteristic diagram showing input / output characteristics in the case of FIG.

FIG. 9 is a cross-sectional view of an element when GaAs / AlGaAs is used.

10A and 10B are characteristic diagrams of the device of the present invention.

11A and 11B are process diagrams showing a procedure for selectively growing a surface emitting laser portion by using a MOCVD method, FIG. 11A is a sectional view showing growth of a light receiving portion and an amplifying portion, and FIG. FIG. 3C is a cross-sectional view showing patterning, and FIG. 6C is a cross-sectional view showing partial surface emitting laser partial growth (selective growth by MOCVD method).

12 is a configuration diagram of an element in the case of FIG.

FIG. 13 is a configuration diagram of an element when a dielectric multilayer film is used.

FIG. 14 is a cross-sectional view showing a configuration of an element using an HBT and a pin diode.

15A is a configuration diagram of an element of a conventional example, and FIG. 15B is a characteristic diagram thereof.

[Explanation of symbols]

10 Light Modulation Section 12 Surface Emitting Laser 20 Amplification Section 22 FET 24 Source 26 Gate 28 Drain 30 Photoreception Section 32 MSM Photodiode 34 Load Resistor 36 Contact 101 Semi-insulating AlGaAs Substrate 102 i-GaAs Layer 103 n ^- GaAs Channel Layer 104 n ⁺ -GaAs contact layer 105 InGaP layer 106 n-DBR layer 107 i-AlGaAs active layer 108 p-DBR layer 110 p-type electrode 111 n-type electrode 112 Schottky electrode 113 Cr / Au 114 load resistance layer 115 polyimide layer 116 dielectric multilayer mirror 120 n ⁺ -GaAs contact layer 121 n-AlGaAs emitter layer 122 p-GaAs base layer 123 i-GaAs layer light-absorbing layer and the collector layer 124 n ⁺ -GaAs contact layer P _in input Light P _out output light P _A, P _B light signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Fukushima 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Taketaka Obama 1-1-6 Uchisai-cho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corp. (72) Inventor Yoshitaka Oiso 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (3)

[Claims] 1. A light receiving section for converting an input signal into an electric signal, an amplifying section for amplifying the electric signal, and an output section including a vertical cavity surface emitting laser for oscillating output light by the amplified electric signal. An optical switch array characterized in that an optical switch including and is monolithically formed on a substrate. 2. The light receiving portion is an MSM (Metal-Semi).
2. The optical switch array according to claim 1, wherein the optical switch array comprises a photo diode or a photo conductor. 3. The optical switch array according to claim 1, wherein the light receiving section is composed of a plurality of light receiving elements.