JPH05273607A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To obtain the waveguide type optical switch which eliminates the absorption of light by a substrate, can be reduced in the thickness of a lower clad layer to enable miniaturization, is improved in electrical sepn. in a first clad layer, can be reduced in the thickness of core layers and can be easily produced at a high yield. CONSTITUTION:This optical switch has a semi-insulating substrate 32, the first clad layers 33, 33 which are separated from each other and are provided on this substrate 32, the first core layers 34, 34 which are provided on the respective first clad layers 33 and are parallel with each other, the second core layer 36 which is provided on the first core layers 34, 34, the second clad layer 37 which is provided on the second core layer 36 and is of the same conduction type as the conduction type of the first clad layer 33, a first electrode 39 which is provided on the second core layer 36 and second electrodes 40, 40 which are provided on the substrate 32. Optical waveguides 41, 42 are constituted of the first core layers 34, 34 and the second core layer 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system for transmitting information by light, an optical switch suitable for use as a key device for an arithmetic unit and an information processing system using light.

[0002]

2. Description of the Related Art Conventionally, there are the following two typical structures of this type of semiconductor waveguide type optical switch. First, as a first example, as shown in FIG. 10, there is a directional coupler type optical switch (hereinafter, abbreviated as an optical switch) 1 that utilizes a change in refractive index due to current injection. This optical switch 1 is formed on a high-concentration n-type indium phosphide (n-InP) semiconductor substrate 2 by an epitaxial crystal growth method.
Low concentration n-InP lower cladding layer 3, low concentration n-I
An nGaAsP first core layer 4 and a non-doped InP etch stop layer 5 are sequentially grown, and non-doped InGaAsP is formed at a predetermined position on the non-doped InP etch stop layer 5.
The second core layers 6, 6 are grown and these second core layers 6, 6 are
A non-doped or high-resistance InP upper clad layer 7 is grown so as to fill the upper portion 6 and zinc (Zn) is diffused at a predetermined position of the upper clad layer 7 to form high-concentration p-type semiconductor zinc diffusion layers 8 and 8. An insulating film 9 made of silicon dioxide (SiO ₂ ) is formed around these zinc diffusion layers 8 and, and an upper electrode for independently applying a voltage or injecting a current is provided on the zinc diffusion layers 8 and 8. 10 and 10 are formed, and the lower electrode 11 is formed on the bottom surface of the n-InP substrate 2. The first core layer 4 and the second core layer 6 constitute an optical waveguide 12 (13) (reference document: E. Lallier et al., ECOC'91 PD papers, p44-p47, 1991).

In order to operate the optical switch 1, a forward voltage, that is, a positive voltage is applied to the upper electrode 10 across both ends of the pin structure described above, and a current is injected into the second core layer 6. The refractive index of the second core layer 6 changes depending on the injected carriers. As a result, the propagation state of the light of the second core layer 6 to which the current is injected changes, and the perfect coupling condition of the directional coupler is broken, whereby the optical path of the light is switched and switching is performed. In addition, a reverse voltage, that is, a negative voltage is applied to the upper electrode 10,
Even if an electric field is applied to the core layer 6, the second
The refractive index of the core layer 6 changes, and similar switching is performed.

As a second example, as shown in FIG. 11, a directional coupler type optical switch (hereinafter abbreviated as an optical switch) 2 which utilizes the change in the refractive index with the application of voltage.
There is one. The optical switch 21 comprises a high-concentration n-InP lower clad layer 22 and a non-doped InGa layer formed on a high-concentration n-InP substrate 2 by an epitaxial crystal growth method.
A first core layer 23 having a multiple quantum well structure in which a number of well layers made of As and barrier layers made of non-doped InAlAs are stacked, and a non-doped InGaAsP etch stop layer 2
4. The non-doped InP etch stop layer 5 is sequentially grown, and the InGaAsP second core layer 25 made of a non-doped or p-type semiconductor is formed at a predetermined position on the etch stop layer 5.
25 is grown, and the high-concentration p-InP upper cladding layers 26, 2 are filled so as to fill these second core layers 25, 25.
6, high-concentration p-InGaAs contact layers 27, 27
Is grown, and the periphery of the upper cladding layers 26, 26 and the contact layers 27, 27 is filled with a high-resistance or non-doped or low-concentration n-type InP burying layer 28, and the upper electrodes 10, 27 are formed on the contact layers 27, 27. 10 is formed, and the lower electrode 11 is formed on the bottom surface of the n-InP substrate 2. The first core layer 23 and the second core layer 25 form an optical waveguide 29 (30).

In order to operate the optical switch 21, a reverse voltage, that is, a negative voltage is applied to the upper electrode 10 across the pin structure as described above, and the first core layer 2 is operated.
When an electric field is applied to the quantum well of the first core layer 23, the quantum well of the first core layer 23 becomes a quantum confined Stark effect.
The absorption coefficient and the refractive index are changed by the fined Stark Effect. As a result, the light propagation state of the first core layer 23 to which the voltage is applied also changes, and the perfect coupling condition of the directional coupler is broken, whereby the optical path of the light is switched and switching is performed.

[0006]

By the way, in the conventional optical switch 1, it is necessary to apply a voltage or inject a current to each of the optical waveguides 12 and 13 independently. Since the n-InP substrate 2 is commonly used as a common conductor, the electrical isolation of the optical waveguides 12 and 13 must be achieved by forming a p-type conductive layer. Therefore, in this optical switch 1, the upper clad layer 7
P-type zinc diffusion layers 8 and 8 are formed inside the non-doped or high-resistance upper cladding layer 7 by diffusing zinc into the upper cladding layer 7.

However, this diffusion process has a drawback that the production yield is remarkably lowered because of the risk of device damage due to the high temperature treatment required for diffusion and the high control of the diffusion distance. It was Furthermore, the use of a conductive substrate causes an increase in stray capacitance associated with the wiring on the substrate, which makes it difficult to separate elements in monolithic integration with other electric elements. It also has the drawback of adversely affecting. Further, since the lower electrode 11 has to be arranged on the bottom surface of the n-InP substrate 2, the process is complicated and the cost of the product is increased.

Further, in the optical switch 21, since the conductive n-InP substrate 2 is shared as a common conductor, the electrical separation of the optical waveguides 29 and 30 is achieved by the second core layers 25 and 25. It is inevitable that the p-type conductive layer of the upper clad layer 26 is processed into a ridge shape and then buried and grown again.

However, this burying growth is necessary for confining light and avoiding optical loss due to the electrodes, in addition to the problem that the region selectivity between the burying portion and the other portion is difficult. It is extremely difficult to flatly embed the upper clad layers 26, 26 having a thickness of about 5 to 2 μm into a high-resistance layer below the ridge shape having a large step, and there is a drawback that a high degree of controllability is required. there were. Further, when the buried layer 28 is made to have a high resistance, it is affected by the impurity diffusion from the p-type semiconductor in the ridge portion which is the buried layer 28, so that it becomes more difficult to control the growth condition and the manufacturing yield is increased. It had the drawback of significantly reducing it.

Further, the use of a conductive substrate has a problem that it causes an increase in stray capacitance due to the wiring on the substrate and makes it difficult to separate elements from each other in monolithic integration with other electric elements. However, there is also a drawback that the device performance is adversely affected. In addition, the lower electrode 11 is formed of the n-InP.
Since it has to be arranged on the bottom surface of the substrate 2, there is a drawback that the process becomes complicated and the cost of the product increases.

As described above, the conventional optical switch 1
In (21), each of the optical waveguides 12, 13 (2
(9, 30) to perform electrical control independently, each waveguide 1
2,13 (29,30) electrical isolation is required.

The present invention has been made in view of the above circumstances, and solves various problems and drawbacks in the related art, and in addition to the steps of element processing or crystal growth associated with electrical isolation between optical waveguides. Another object of the present invention is to provide a waveguide type optical switch that can solve the above-mentioned difficulties and improve the manufacturing yield.

[0013]

In order to solve the above problems, the present invention employs the following waveguide type optical switch. That is, the waveguide type optical switch according to claim 1,
A semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate separately from each other, and a plurality of first clad layers provided on each of the first clad layers and parallel to each other. A core layer, a second core layer provided on the first core layer, and a second clad provided on the second core layer and having the same conductivity type as the first clad layer. A layer, a first electrode provided on the second core layer, and a plurality of second electrodes provided on the semi-insulating substrate, and each of the first core layers An optical waveguide is configured by the second core layer, and the optical path of the light propagating in the optical waveguide is switched by controlling the magnitude of the voltage applied to these optical waveguides or the current injected. There is.

According to another aspect of the waveguide type optical switch, a semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate and separated from each other, and the first clad layer and the first clad layer. First core layer provided on the clad layer, and a plurality of second core layers provided on the first core layer and above the plurality of first clad layers in parallel with each other. A second clad layer having the same conductivity type as that of the first clad layer, the second clad layer being provided on the second core layer;
A first electrode provided on the core layer, and a plurality of second electrodes provided on the semi-insulating substrate, wherein each of the first core layer and the second core layer comprises: Each of the optical waveguides is configured by, and the optical path of the light propagating in the optical waveguide is switched by controlling the magnitude of the voltage applied to these optical waveguides or the injected current.

Further, a waveguide type optical switch according to a third aspect is the waveguide type optical switch according to the first or second aspect, wherein at least the wider core layer of the first and second core layers is used. Is characterized by being constituted by any one of a quantum well structure, a quantum wire structure, and a quantum box structure.

A waveguide type optical switch according to a fourth aspect of the present invention is a semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate and separated from each other, and the first clad layer and the first clad layer. A plurality of first core layers provided on each of the clad layers in parallel to each other, a second core layer provided on the first core layers, and a second core layer provided on the second core layers. A second clad layer that is provided and has a conductivity type opposite to that of the first clad layer; and a first electrode that is provided on the second core layer,
A plurality of second electrodes provided on the semi-insulating substrate are provided, and an optical waveguide is constituted by each of the first core layer and the second core layer, and applied to these optical waveguides. It is characterized in that the optical path of the light propagating in the optical waveguide is switched by controlling the magnitude of the voltage or the injected current.

According to a fifth aspect of the waveguide type optical switch, a semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate and separated from each other, and a first of these first clad layers. First core layer provided on the clad layer, and a plurality of second core layers provided on the first core layer and above the plurality of first clad layers in parallel with each other. A second clad layer provided on the second core layer and having a conductivity type opposite to that of the first clad layer; and a first electrode provided on the second core layer, A plurality of second electrodes provided on the semi-insulating substrate are provided, and an optical waveguide is constituted by each of the first core layer and the second core layer, and applied to these optical waveguides. Light propagating in the optical waveguide by controlling the magnitude of voltage or injected current It is characterized by switching the optical path.

A waveguide type optical switch according to a sixth aspect is the waveguide type optical switch according to the fourth or fifth aspect, wherein at least the wider core layer of the first and second core layers is used. Is characterized by being constituted by any one of a quantum well structure, a quantum wire structure, and a quantum box structure.

The waveguide type optical switch according to claim 7 is the waveguide type optical switch according to claim 4 or 5, wherein at least the wider core layer of the first and second core layers is used. Is a non-doped quantum well layer, an n-type conductive layer having n-type conductivity, and conductivity intermediate between these layers, at least a part of which has p-type conductivity and It is characterized by having a three-layer structure including an intermediate layer made of a semiconductor having a bandgap wider than that of the semiconductor forming the quantum well layer and the n-type conductive layer.

The waveguide type optical switch according to claim 8 is the waveguide type optical switch according to claim 7, wherein the wider core layer has a multilayer structure in which the three-layer structure is repeated. It is characterized by being done.

The above-mentioned semi-insulating substrate is one that becomes an insulator in the vicinity of room temperature among semiconductor substrates, and is, for example, a III-V group compound semiconductor such as indium phosphide (InP) or gallium arsenide (GaAs). Is mentioned.

[0022]

In the waveguide type optical switch according to claim 1 or 2, the use of the semi-insulating substrate eliminates absorption of light by the substrate, and the semi-insulating substrate is used as a part of the lower clad. It becomes possible to do. Therefore, the lower clad layer can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of first clad layers provided on the semi-insulating substrate are separated from each other,
The electrical isolation in these first cladding layers is good. Further, by forming a plurality of optical waveguides with the first core layer and the second core layer, it is possible to reduce the thickness of the core layer and to reduce the step difference at the time of buried growth to about 0.5 μm or less. Therefore, the difficulty of burying growth can be alleviated. Therefore, it becomes possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

Further, in the optical waveguide switch according to the present invention, at least the wider core layer of the first and second core layers has a quantum well structure, a quantum wire structure or a quantum box structure. With either configuration, the operating voltage required for switching is reduced.

In the waveguide type optical switch according to the present invention, since the semi-insulating substrate is used, the absorption of light by the substrate is extremely small, and the semi-insulating substrate is used as a part of the lower clad. It becomes possible to use.
Therefore, the lower clad layer can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of first cladding layers provided on the semi-insulating substrate are separated from each other,
The electrical isolation in these first cladding layers is good. Further, by forming a plurality of optical waveguides with the first core layer and the second core layer, it is possible to reduce the thickness of the core layer and to reduce the step difference at the time of buried growth to about 0.5 μm or less. Therefore, the difficulty of burying growth can be alleviated. Therefore, it becomes possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

In the waveguide type optical switch according to a sixth aspect of the present invention, at least the wider core layer of the first and second core layers has a quantum well structure, a quantum wire structure or a quantum box structure. With either configuration, the operating voltage required for switching is reduced.

According to a seventh aspect of the present invention, in the waveguide type optical switch, at least the wider core layer of the first and second core layers is a non-doped quantum well layer and an n-type conductive layer. An n-type conductive layer having, and conductivity intermediate between these layers, at least a part of which has a p-type conductivity type,
Further, by adopting a three-layer structure including an intermediate layer made of a semiconductor having a bandgap wider than that of the semiconductor forming the quantum well layer and the n-type conductive layer, the operating voltage required for switching is further reduced.

Further, in the waveguide type optical switch according to the present invention, the operating voltage required for switching is further reduced by forming the wider core layer with a multilayer structure in which the three-layer structure is repeated. To do.

[0030]

Embodiments of the waveguide type optical switch according to the present invention will be described below. (First Embodiment) FIGS. 1 and 2 show a waveguide type optical switch (hereinafter abbreviated as an optical switch) 31 according to a first embodiment of the present invention.
And a directional coupler type optical switch that operates by injecting a current or applying a voltage. Here, FIG. 1 is a perspective view of the waveguide type optical switch 31, and FIG. 2 is A of FIG.
It is sectional drawing which follows the -A line.

The optical switch 31 has a pin vertical conductive structure and is a semi-insulating semiconductor substrate of InP.
A conductive n-InP lower cladding layer 3 doped with impurities at a concentration of 5 × 10 ¹⁷ cm ⁻³ is formed on the substrate 32.
3. The non-doped InGaAsP first core layer 34 is sequentially epitaxially grown, the lower clad layer 33 and the first core layer 34 are processed into a predetermined shape and electrically separated, and a high resistance or non-doped InP buried layer is formed on them. Embedded layer 35, non-doped InGaAsP second core layer 36,
P doped with impurities to a concentration of 5 × 10 ¹⁷ cm ^-3
-InP upper clad layer 37, impurities 5 × 10 ¹⁸ cm
^The p-InGaAs contact layer 38 doped to a concentration of ^-3 is sequentially epitaxially grown, the InP buried layer 35 or the contact layer 38 is processed into a structure of a waveguide type optical switch, and AuZnNi alloy and Au are formed on the contact layer 38. Is formed on the lower clad layers 33, 33.
The lower electrodes 40, 40 made of a metal vapor deposition film in which a uGeNi alloy and Au are laminated are formed. The optical waveguide 41 is formed by the first core layer 34 and the second core layer 36.
(42) is configured.

In this optical switch 31, a positive voltage is applied to the upper electrode 39 and a negative voltage is applied to the lower electrode 40, and
When the structure is forward biased, a current flows through the electrodes to each layer. Since the carriers injected into the second core layer 36 by this current change the refractive index of the second core layer 36, the propagation constant of light passing through the first core layer 34 of each of the optical waveguides 41 and 42 is directionally coupled. A change in the fully coupled state of the device causes switching of light.

Further, when a negative voltage is applied to the upper electrode 39 and a positive voltage is applied to the lower electrode 40 to make a reverse bias state with respect to the pin structure, an electric field is applied to each layer via the electrodes.
A change in the refractive index occurs in the first core layer 34 due to the electro-optic effect based on this electric field, and light switching similar to that in the case of current injection occurs.

As described above, this optical switch 31
According to the above, since the InP substrate 32, which is a semi-insulating substrate, is used, light absorption by the substrate is eliminated and the InP substrate 32 is removed.
Can be utilized as part of the lower cladding. Therefore, the lower clad layer 33 can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of lower clad layers 33, 33 provided on the InP substrate 32 are separated from each other, good electrical isolation can be achieved in these first clad layers 33, 33. Also, the first core layers 34, 3
4 and the second core layer 36 form a plurality of optical waveguides 41, 42.
Since the core layers are formed, the thickness of these core layers can be reduced, the level difference at the time of embedded growth can be reduced to about 0.5 μm or less, and the difficulty of embedded growth can be eased. Therefore, it is possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

Although the InP substrate 32 is used as the semi-insulating substrate in the first embodiment, it is not limited to the InP substrate 32, and semi-insulating substrates made of various materials can be applied. is there. For example, when a GaAs substrate is used, the same effect can be obtained by epitaxially growing GaAs and AlGaAs on the GaAs substrate.

(Second Embodiment) FIGS. 3 and 4 show a waveguide type optical switch 51 according to a second embodiment of the present invention, which is a directional coupler which operates by injecting a current or applying a voltage. Type optical switch. Here, FIG. 3 is a perspective view of the waveguide type optical switch 51, and FIG. 4 is a sectional view taken along the line BB of FIG. In the figure, the same components as those of the optical switch 31 described above are designated by the same reference numerals, and description thereof will be omitted.

The optical switch 51 has a conductive vertical structure of pin, and the lower clad layer 33 is epitaxially grown on the InP substrate 32, and the lower clad layer 33 is processed into a predetermined shape and electrically. Separated from each other, the InP buried layer 35 and the undoped InGaAl are formed on these.
A first core layer 52 having a multiple quantum well structure including an As quantum well layer and an InAlAs barrier layer, a non-doped InP etch stop layer 53, and a p-InGaAsP second core layer doped with impurities at a concentration of 5 × 10 ¹⁷ cm ^−3. 54 is sequentially epitaxially grown, the InP buried layer 35 or the second core layer 54 is processed into a structure of a waveguide type optical switch,
Further, the upper clad layer 37 and the contact layer 38 are sequentially epitaxially grown, the upper electrode 39 is formed on the contact layer 38, and the lower electrodes 40, 40 are formed on the lower clad layers 33, 33, respectively. The first core layer 52 and each second core layer 54 form an optical waveguide 55 (56).

In this optical switch 51, a positive voltage is applied to the upper electrode 39 and a negative voltage is applied to the lower electrode 40, and the pin
When the structure is forward biased, a current flows through the electrodes to each layer. Since the carriers injected into the second core layer 54 by this current change the refractive index of the second core layer 54, the propagation constant of light passing through the second core layer 54 of each of the optical waveguides 55 and 56 is directionally coupled. A change in the fully coupled state of the device causes switching of light.

Further, when a negative voltage is applied to the upper electrode 39 and a positive voltage is applied to the lower electrode 40 to make a reverse bias state with respect to the pin structure, an electric field is applied to each layer via the electrodes.
By the quantum confined Stark effect based on this electric field,
A change in refractive index occurs in the first core layer 52 having a multiple quantum well structure, and light switching similar to that in the case of current injection occurs.

As described above, this optical switch 51
According to the above, since the InP substrate 32, which is a semi-insulating substrate, is used, light absorption by the substrate is eliminated and the InP substrate 32 is removed.
Can be utilized as part of the lower cladding. Therefore, the lower clad layer 33 can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of lower clad layers 33, 33 provided on the InP substrate 32 are separated from each other, good electrical isolation can be achieved in these first clad layers 33, 33. In addition, the first core layer 52 and the second core layers 54, 54 form a plurality of optical waveguides 55, 56.
Since the core layers are formed, the thickness of these core layers can be reduced, the level difference at the time of embedded growth can be reduced to about 0.5 μm or less, and the difficulty of embedded growth can be eased. Therefore, it is possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

The first core layer 52 is made of non-doped InG.
Since the multiple quantum well structure including the aAlAs quantum well layer and the InAlAs barrier layer is used, the operating voltage required for switching can be further reduced.

In the second embodiment as well, similar to the first embodiment, the semi-insulating substrate is not limited to the InP substrate 32, and semi-insulating substrates of various materials can be applied. is there.

(Third Embodiment) FIG. 5 shows a waveguide type optical switch 61 according to a third embodiment of the present invention, which is a directional coupler type optical switch which operates by injecting a current or applying a voltage. Is. The optical switch 61 has the same epitaxial layer structure as that of the optical switch 31 of the first embodiment, except that the InP burying layer 35 or the contact layer 38 is not processed into a waveguide type optical switch structure. , Through holes 62, 62 extending from the surface to the lower clad layer 33 on both sides thereof, and an insulating film 63 is formed over these through holes 62, 62 to avoid unnecessary electrical contact with each layer.
The metal film 64 to be an ohmic electrode is vapor-deposited on the lower cladding layer 33, and the wiring metal film 65 is formed in the through holes 62, 62. In this case, in order to reduce the ohmic contact with the lower cladding layer 33, a high concentration n-type impurity diffusion layer 66 is formed in the lower cladding layer 33 by an ion implantation method or a diffusion method. Also in this optical switch 61, the same operation and effect as those of the optical switch 31 can be obtained.

(Fourth Embodiment) FIG. 6 shows a waveguide type optical switch 71 according to a fourth embodiment of the present invention, which is a directional coupler type optical switch which operates by injecting current or applying voltage. Is. The optical switch 71 has the same epitaxial layer structure as the above-described optical switches 31 and 61. The difference is that the upper clad layer 37 and the contact layer 38 are processed into a structure of a waveguide type optical switch, and both sides thereof are processed. Through holes 72, 72 extending from the second core layer 36 to the first core layer 34 are formed in the portion, and an insulating film 63 is formed in these through holes 72, 72 in order to avoid unnecessary electric contact with each layer.
It is formed around 72, and thereafter, a metal film 64 to be an ohmic electrode is vapor-deposited on the first core layer 34, and a wiring metal film 65 is formed in these through holes 62, 62. In this case, in order to reduce the resistance of ohmic contact with the lower cladding layer 33, a high concentration n-type impurity diffusion layer 73 is formed in the first core layer 34 by an ion implantation method or a diffusion method. Also in this optical switch 71,
The same action and effect as those of the optical switches 31 and 61 can be obtained.

In this optical switch 71, needless to say, it can be applied even when the conductivity of the lower clad layer 33 is p-type, which is the opposite of that of this embodiment.
If the lower cladding layer 33 is p-type, InGaAsP
Contacting the layer is a very effective means for ensuring a low resistance ohmic contact between the lower cladding layer and the metal electrode.

(Fifth Embodiment) FIGS. 7 to 9 show a waveguide type optical switch 81 according to a fifth embodiment of the present invention, which is a directional coupler type optical switch which operates by applying a voltage. is there. Here, FIG. 7 is a cross-sectional view of the optical switch 81,
8 and 9 are band diagrams of the second core layer of the optical switch 81.

The optical switch 81 has a conductive vertical structure of the same conductivity type, and the lower clad layer, the upper clad layer and the contact layer have the same conductivity type structure.
Another feature is that the second core layer has a quantum well structure in which the refractive index changes significantly by applying a voltage.

In this optical switch 81, a lower clad layer 33 and a first core layer 34 are sequentially epitaxially grown on an InP substrate 32, and the lower clad layer 33 and the first core layer 34 are sequentially grown.
The core layer 34 is processed into a predetermined shape and electrically separated, and the InP burying layer 35, the second core layer 82, and
N doped with impurities to a concentration of 5 × 10 ¹⁷ cm ⁻³
-InP upper clad layer 83, impurities 5 × 10 ¹⁸ cm
^The n-InGaAs contact layer 84 doped to a concentration of ^-3 is sequentially epitaxially grown, the InP buried layer 35 or the contact layer 84 is processed into a structure of a waveguide type optical switch, and an AuGeNi alloy and Au are formed on the contact layer 84. An upper electrode 85 made of a metal vapor deposition film in which the above are laminated is formed, and the lower electrodes 40, 40 are formed on the lower clad layers 33, 33, respectively. Then, the optical waveguide 86 is formed by the first core layer 34 and the second core layer 82.
(87) is configured.

The second core layer 82 is made of n-InGaAlAs.
Layer 82a, p-InAlAs layer 82b, non-doped I
The InGaAs layer 82c is composed of four layers of an nGaAs layer 82c and an n-InGaAlAs layer 82d, and the InGaAs layer 82c serves as a quantum well.

The band diagram of the second core layer 82 will be described. When no electric field is applied to the second core layer 82, as shown in FIG.
Since the first quantum level E _e1 of the electron in the quantum well is above the Fermi level E _f , the electron concentration in the quantum well is low.

Here, when an electric field is applied to the second core layer 82, for example, as shown in FIG. 9, a positive potential is applied to the right side in the figure, that is, the n-InGaAlAs layers 82a and p.
When the pn junction with the -InAlAs layer 82b is reverse-biased, the first quantum level E _e1 of the electron in the quantum well falls below the Fermi level E _f , so the electron is n-InGaAl.
It moves from the As layer 82d into the quantum well of the InGaAs layer 82c. As a result, the effect of excitons in the quantum well is suppressed by the band-filling effect of the moved electrons, so that the refractive index of the second core layer 82 changes. Therefore, according to this operation principle, the propagation constant of light passing through the two optical waveguides 86 and 87 changes from the fully coupled state of the directional coupler, and light switching occurs.

As described above, this optical switch 81
According to the above, since the InP substrate 32, which is a semi-insulating substrate, is used, light absorption by the substrate is eliminated and the InP substrate 32 is removed.
Can be utilized as part of the lower cladding. Therefore, the lower clad layer 33 can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of lower clad layers 33, 33 provided on the InP substrate 32 are separated from each other, good electrical isolation can be achieved in these first clad layers 33, 33. Also, the first core layers 34, 3
4 and the second core layer 82 form a plurality of optical waveguides 86, 87.
Since the core layers are formed, the thickness of these core layers can be reduced, the level difference at the time of embedded growth can be reduced to about 0.5 μm or less, and the difficulty of embedded growth can be eased. Therefore, it is possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

Further, the second core layer 82 is formed of n-InGa.
The InGaAs layer 82c has a quantum well structure, which is composed of four layers of the AlAs layer 82a, the p-InAlAs layer 82b, the undoped InGaAs layer 82c, and the n-InGaAlAs layer 82d. Therefore, the operating voltage required for switching can be further reduced. ..

Although the second core layer is a single quantum well in the fifth embodiment, the n-InGaAlAs layer 82 is used.
a, p-InAlAs layer 82b, undoped InGa
A multi-quantum well structure having a structure in which four layers of the As layer 82c and the n-InGaAlAs layer 82d are periodically repeated may be used. In this case, the operating voltage required for switching can be further reduced.

[0058]

As described above, according to the first aspect of the present invention.
Alternatively, according to the waveguide type optical switch described in 2, since the semi-insulating substrate is used, light absorption by the substrate is eliminated and the semi-insulating substrate can be used as a part of the lower clad. Therefore, the lower clad layer can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of lower clad layers provided on the semi-insulating substrate are separated from each other, good electrical isolation can be achieved in these first clad layers. Further, since the plurality of optical waveguides are configured by the first core layer and the second core layer, the thickness of these core layers can be reduced, and the step difference at the time of buried growth can be reduced to about 0.5 μm or less. Therefore, it is possible to alleviate the difficulty of embedded growth. Therefore, it is possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

According to a third aspect of the waveguide type optical switch of the present invention, in the waveguide type optical switch according to the first or second aspect, at least the wider one of the first and second core layers is used. The core layer is a quantum well structure, a quantum wire structure,
Since it is configured to have any of the quantum box structures, the operating voltage required for switching can be reduced.

According to the fourth aspect of the waveguide type optical switch, since the semi-insulating substrate is used, light absorption by the substrate is eliminated and the semi-insulating substrate is used as a part of the lower clad. can do. Therefore, the lower clad layer can be thinned and the size can be reduced. In addition, it becomes easy to separate the elements from other elements that perform electrical operation, and monolithic integration with other elements on the same substrate becomes possible, and stray capacitance such as wiring can be reduced, and high-speed element operation can be achieved. Can be realized.

Further, since the plurality of lower clad layers provided on the semi-insulating substrate are separated from each other, good electrical isolation can be achieved in these first clad layers. Further, since the plurality of optical waveguides are configured by the first core layer and the second core layer, the thickness of these core layers can be reduced, and the step difference at the time of buried growth can be reduced to about 0.5 μm or less. Therefore, it is possible to alleviate the difficulty of embedded growth. Therefore, it is possible to provide a waveguide type optical switch which is easy to manufacture and has a high yield.

According to a sixth aspect of the waveguide type optical switch of the fourth or fifth aspect, in the waveguide type optical switch, at least the wider one of the first and second core layers is used. The core layer is a quantum well structure, a quantum wire structure,
Since it is configured to have any of the quantum box structures, the operating voltage required for switching can be reduced.

According to a seventh aspect of the waveguide type optical switch of the present invention, in the waveguide type optical switch according to the fourth or fifth aspect, at least the wider one of the first and second core layers is used. The core layer includes a non-doped quantum well layer and n
-Type conductive layer having p-type conductivity, and an intermediate conductivity between these layers, at least a part of which has p-type conductivity, and constitutes the quantum well layer and the n-type conductive layer Since it is configured to have a three-layer structure including an intermediate layer made of a semiconductor having a wider band gap than the semiconductor, the operating voltage required for switching can be further reduced.

According to the waveguide type optical switch described in claim 8, in the waveguide type optical switch described in claim 7, the wider core layer has a multi-layer structure in which the three-layer structure is repeated. Since it was decided to be composed of
The operating voltage required for switching can be further reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing a waveguide type optical switch according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a perspective view showing a waveguide type optical switch according to a second embodiment of the present invention.

4 is a cross-sectional view taken along the line BB of FIG.

FIG. 5 is a sectional view showing a waveguide type optical switch according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing a waveguide type optical switch according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view showing a waveguide type optical switch according to a fifth embodiment of the present invention.

FIG. 8 is a diagram showing a band diagram of a second core layer of a waveguide type optical switch according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a band diagram of a second core layer of a waveguide type optical switch according to a fifth embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a conventional waveguide type optical switch.

FIG. 11 is a cross-sectional view showing a conventional waveguide type optical switch.

[Explanation of symbols]

31 waveguide type optical switch 32 InP substrate (semi-insulating substrate) 33 n-InP lower cladding layer 34 non-doped InGaAsP first core layer 35 InP buried layer 36 non-doped InGaAsP second core layer 37 p-InP upper cladding layer 38 p -InGaAs contact layer 39 Upper electrode 40 Lower electrode 41,42 Optical waveguide 51 Waveguide optical switch 52 First core layer with multiple quantum well structure 53 Undoped InP etch stop layer 54 p-InGaAsP second core layer 55,56 Optical waveguide 61 waveguide type optical switch 62 through hole 63 insulating film 64 metal film 65 wiring metal film 66 n type impurity diffusion layer 71 waveguide type optical switch 72 through hole 73 n type impurity diffusion layer 81 waveguide type optical switch 82 second core Layer 82a n-InGaAlAs layer 2b p-InAlAs layer 82c undoped InGaAs layer (quantum well structure) 82d n-InGaAlAs layer 83 n-InP upper cladding layer 84 n-InGaAs contact layer 85 upper electrode 86 and 87 first quantum optical waveguide E _e1 quantum wells electronic Level E _f Fermi level

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hiroaki Takeuchi 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Naoto Yoshimoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Masaki Shintoku 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (8)

[Claims] 1. A semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate separately from each other, and provided on each of the first clad layers and parallel to each other. A plurality of first core layers, a second core layer provided on these first core layers,
A second clad layer provided on the second core layer and having the same conductivity type as the first clad layer; a first electrode provided on the second core layer; and the semi-insulating layer. A plurality of second electrodes provided on a flexible substrate, and an optical waveguide is configured by each of the first core layer and the second core layer, and a voltage or injection applied to these optical waveguides. A waveguide type optical switch characterized in that the optical path of light propagating in the optical waveguide is switched by controlling the magnitude of a current to be applied. 2. A semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate and separated from each other, and a first clad layer provided on these first clad layers. A core layer, a plurality of second core layers provided on the first core layer and above the plurality of first cladding layers in parallel with each other, and on the second core layers; A second clad layer having the same conductivity type as the first clad layer, a first electrode provided on the second core layer, and a plurality of electrodes provided on the semi-insulating substrate. And a second electrode, wherein each of the first core layer and the second core layer constitutes an optical waveguide, and a voltage applied to these optical waveguides or a magnitude of an injected current is controlled. A waveguide characterized in that the optical path of light propagating in the optical waveguide is switched by Light switch. 3. The optical waveguide switch according to claim 1, wherein at least the wider core layer of the first and second core layers has a quantum well structure, a quantum wire structure, and a quantum box. A waveguide type optical switch characterized in that it is constituted by any one of the structures. 4. A semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate separately from each other, and provided on each of the first clad layers and parallel to each other. A plurality of first core layers, a second core layer provided on the first core layers, and a conductivity type opposite to the first clad layer provided on the second core layers; Second clad layer, a first electrode provided on the second core layer, and a plurality of second electrodes provided on the semi-insulating substrate. Optical waveguides are respectively constituted by the first core layer and the second core layer, and the optical path of light propagating in the optical waveguides is controlled by controlling the voltage applied to these optical waveguides or the magnitude of the injected current. A waveguide type optical switch characterized by switching. 5. A semi-insulating substrate, a plurality of first clad layers provided on the semi-insulating substrate and separated from each other, and a first clad layer provided on these first clad layers. A core layer, a plurality of second core layers provided on the first core layer and above each of the plurality of first cladding layers in parallel with each other, and on top of the second core layers; A second clad layer which is provided and has a conductivity type opposite to that of the first clad layer, a first electrode which is provided on the second core layer, and a plurality of electrodes which are provided on the semi-insulating substrate. And a second electrode, wherein each of the first core layer and the second core layer constitutes an optical waveguide, and a voltage applied to these optical waveguides or a magnitude of an injected current is controlled. Guided light characterized by switching the optical path of light propagating in the optical waveguide by Type optical switch. 6. The waveguide type optical switch according to claim 4, wherein at least the wider core layer of the first and second core layers has a quantum well structure, a quantum wire structure, and a quantum box. A waveguide type optical switch characterized in that it is constituted by any one of the structures. 7. The waveguide type optical switch according to claim 4, wherein at least the wider core layer of the first and second core layers is a non-doped quantum well layer and an n-type core layer. An n-type conductive layer having conductivity, and a semiconductor having conductivity between these layers, at least a part of which has p-type conductivity, and which constitutes the quantum well layer and the n-type conductive layer. 3 with an intermediate layer made of a semiconductor having a wider band gap than
A waveguide type optical switch having a layered structure. 8. The waveguide type optical switch according to claim 7, wherein the wider core layer has a multi-layer structure in which the three-layer structure is repeated. switch.