JP3445226B2 - Directional coupler, optical modulator, and wavelength selector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device. More specifically, the present invention relates to a vertical directional coupler.

[0002]

2. Description of the Related Art In recent years, in an optical transmission system which has been remarkably developed, a directional coupler is a powerful element applicable to an optical switch, an intensity modulator, a wavelength selection filter, and the like.

A directional coupler usually includes two optical waveguides 100 and 101 arranged close to each other in parallel as shown in FIG. Since the two optical waveguides 100 and 101 are sufficiently close to each other, the waveguide modes of the light propagating therethrough are coupled to each other, so that the light power is transferred between the optical waveguides. The state of this power transfer is determined by the propagation constants β1, β2 of the optical waveguide.
And the coupling coefficient κ. FIG. 1 schematically shows this propagation state. The light intensity is shown in a chevron, and the intensity corresponds to the height of the chevron. As can be seen in FIG.
The power distribution between the two optical waveguides changes along the light traveling direction. The distance L at which the light incident on one optical waveguide shifts to the other and its power is maximized is called the coupling length.
This bond length is represented by L = π / 2 · γ. Here, γ and Δ are represented by the following equations.

Γ = (κ ² + Δ ² ) ^1/2 Δ = (β 1 −β 2) / 2 FIG. 2 shows a state of power transfer of the directional coupler. In FIG. 2, the horizontal axis represents the normalized distance, and the vertical axis represents the normalized light output intensity. When Δ is 0, (√3)
For the case of κ, the output in the first optical waveguide and the output in the second optical waveguide are shown. In the specification of the present application, $ 3
Alternatively, (√3) indicates a cubic root of 3. When Δ is 0, it is indicated by a solid line, and when (√3) κ, it is indicated by a dotted line. From the curves in the figure, the ratio of the output in the first optical waveguide and the output in the second optical waveguide can be seen. When the propagation constants β1 and β2 of the two optical waveguides match, the coupling length L becomes π /
(2κ). At this time, when the normalized output of the first optical waveguide shown by the solid line is 1.0, the second optical waveguide shown by the solid line
The case where the normalized output of the optical waveguide is zero appears. Here, the power of light has shifted 100% from one optical waveguide to the other. The propagation constant β of the two optical waveguides
The case where 1 and β2 coincide corresponds to the case where Δ is 0. On the other hand, when there is a difference in the propagation constant, the transition of the optical power becomes small. That is, it can be understood by looking at the example of Δ = √3 by the dotted line in FIG. Light output appears in the second optical waveguide, and some light is transferred from the first optical waveguide to the second optical waveguide, but the output of the transferred light remains small.

FIG. 3 shows an example of a conventional directional coupler. In this example, two optical waveguides 27 and 28 having the same propagation constant are arranged in parallel on the substrate, and the length of the coupling portion is set to L or an odd multiple thereof. Therefore, when no voltage is applied, for example, light incident from the first input port 20 is
The light completely shifts to the other optical waveguide and can be taken out from the second output port 23. When switching is performed, an electric field is applied to the coupling portion of the optical waveguides 27 and 28 through the first electrode 24, and the length of the coupling portion is set to be an even multiple of the coupling length L. At this time, light incident from the first input port 20 can be extracted from the first output port 22. The same operation can be realized for the first output port 22 or the second output port 23 with respect to the light incident from the second input port 21. 25 is the second
Electrodes.

Here, the cladding layer 26 between the optical waveguides plays an important role in determining the coupling state. The smaller the width of this layer and the closer the refractive index to the optical waveguide, the stronger the coupling between the two optical waveguides and the shorter the coupling distance.

However, due to limitations in lithography and processing accuracy, usually the refractive index of the cladding layer 23 must be set to the same as the refractive index of the cladding layer outside the optical waveguide.
The width could not be much less than 1 micron.

[0008]

As described above, in the conventional directional coupler, the thickness of the cladding layer between the optical waveguides cannot be reduced, so that the coupling length cannot be reduced and the element size is inevitably increased. . Therefore, when a matrix switch is configured by combining such directional couplers, there is a problem that the size of the switch itself becomes very large.

The present invention makes it possible to reduce the size of a directional coupler and increase the degree of freedom in design.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a vertical directional coupler for performing switching, light intensity modulation, and wavelength selection in an optical communication system. The present invention controls the thickness and the refractive index of the cladding layer between the devices, thereby enabling the miniaturization of the devices and increasing the degree of freedom in design.

In order to achieve the above object, according to the present invention, two optical waveguides are arranged in a direction perpendicular to the substrate, and between the two optical waveguides to apply an electric field independently to the two optical waveguides. A conductive layer is provided. With the vertical arrangement, each optical waveguide layer and cladding layer can be independently controlled at the stage of crystal growth. Therefore, for example, the thickness of the cladding layer between the optical waveguides can be reduced to a level that cannot be achieved with a planar directional coupler. As a result, the coupling length is significantly reduced, and the size of the entire device can be significantly reduced.
Alternatively, a structure in which the refractive index of the two optical waveguides is changed can be easily realized, so that the degree of freedom in design is greatly increased.
Further, in this structure, it is easy to control the refractive index by applying an electric field to the cladding layer between the optical waveguides, so that the directional coupler can be provided with a new function by utilizing this.

The gist of the present invention is to have at least a first optical waveguide, a cladding layer, and a second optical waveguide which are arranged on a substrate in a direction perpendicular to the substrate, and wherein the first optical waveguide is provided. It can be said that it is a directional coupler having an electrode for applying an electric field to either the waveguide or the region of the second optical waveguide where each optical waveguide is performed, or any one of the cladding layers.

Further, the present invention has at least a first optical waveguide, a cladding layer, and a second optical waveguide disposed on a substrate in a direction perpendicular to the substrate, and
An electric field is applied to one of the cladding layer and the optical waveguide or the second optical waveguide, in which each optical waveguide is applied, and the refractive index of the region to which the electric field is applied is changed to change the first and second optical waveguides.
Or the directional coupler that changes the propagation characteristics of each optical waveguide of the second optical waveguide or the second optical waveguide.

The operation differs between the case where an electric field is applied to a region of the first optical waveguide or the second optical waveguide where each optical waveguide is performed and the case where an electric field is applied to any one of the cladding layers. However, in either method, the relative refractive index of the core region of the first and second optical waveguides and the relative refractive index of the cladding layer disposed between the first and second optical waveguides are increased. This changes the optical coupling state of the first and second optical waveguides.

One embodiment changes the propagation state of light between two optical waveguides, and allows light to travel from one optical waveguide to another optical waveguide. Still another form allows modulation of light intensity, ie, use as a light modulator.
Yet another configuration allows for wavelength selection.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing specific embodiments of the present invention, main modes of the present invention will be specifically listed.

(1) In a first mode, a first waveguide formed on a substrate and a cladding layer in a direction perpendicular to the first waveguide and the substrate in a direction of the first optical waveguide are provided. A vertical directional coupler having a second optical waveguide formed therethrough, wherein at least one layer is provided in a cladding layer between the plane including the first optical waveguide and the plane including the second optical waveguide. A directional coupler including a conductive layer for applying an electric field.

(2) In the second aspect, the directional coupler is characterized in that a quantum well is formed in at least one of the first optical waveguide and the second optical waveguide. Is a directional coupler described in 1. above.

(3) In a third mode, the directional coupler according to the above item (1) or (2) comprises a first optical waveguide and a second optical waveguide.
A directional coupler is characterized in that a quantum well is formed in a cladding layer between the optical waveguides.

(4) In a fourth mode, the directional coupler according to any one of the above items (1) to (3) includes a first optical waveguide and a second optical waveguide.
A directional coupler, comprising at least one p-type and n-type conductive layers in a cladding layer between the optical waveguides described above, and applying an electric field to the cladding layer.

(5) A fifth mode is an optical matrix switch constituted by connecting a plurality of the directional couplers according to the above items (1) to (4).

(6) A sixth mode is an optical modulator characterized in that the directional coupler according to any of the above items (1) to (4) is used for intensity modulation of light.

(7) In a seventh mode, a voltage is applied to the cladding layer of the directional coupler according to the item (4) to change a coupling state between two optical waveguides of the directional coupler. Thus, the wavelength selector changes the wavelength of light output from at least one output port.

The present invention is advantageous for miniaturization of the apparatus, and it is advantageous to use the directional coupler, the optical modulator, the optical switch, the wavelength selector, and the like for a module for optical communication. Furthermore, an optical communication system using these can be constructed. The following is such an example.

(8) An eighth mode is the optical modulator according to the item (6), a light condensing means for optically coupling input light to the modulator, and output light from the modulator. This is an optical communication module having a built-in condensing means for optically coupling the optical fiber to an external optical fiber.

(8) A ninth embodiment is directed to a transmitting unit having the semiconductor optical modulator according to the item (6), a waveguide unit for guiding output light from the transmitting unit, and a waveguide unit. And a receiving unit for receiving the output light from the wave unit.

<First Embodiment> FIG. 4 is a perspective view showing an example of an embodiment of a directional coupler according to the present invention. FIG. 5 is a cross-sectional view of the directional coupler element shown in FIG.

A first cladding layer 9 is provided on a predetermined substrate. The embedded second optical waveguide 2 is formed on the first clad layer 9 by the embedded layer 8 made of a semiconductor material. A first conductive type first semiconductor layer 11 is disposed above the buried second optical waveguide 2, and further covers the first semiconductor layer 11 and the buried layer 8.
A second conductive second semiconductor layer 3 is formed. On the side opposite to the first conductive type first semiconductor layer 11 with the second conductive type second semiconductor layer 3 interposed therebetween, the first optical waveguide 1 is formed by a buried layer 7. Formed with embedded side surfaces. Note that a second conductive semiconductor layer 10 for applying an electric field of the first optical waveguide 1 is provided above the first optical waveguide 1. A second conductive type electrode and a first conductive type electrode are provided on the back surface of the second conductive type second semiconductor layer 3 and the back surface of the cladding layer 9, respectively.

In the structure of the present invention, the sum of the thicknesses of the first semiconductor layer 11 and the second semiconductor layer 3 defines the distance between the first optical waveguide 1 and the second optical waveguide 2. ing. The distance between the two waveguides is set in the stacking direction of the components of the directional coupler. Then, an electric field is applied to the first optical waveguide 1 or the second optical waveguide 2 by the first, second, and third electrodes, and light is transferred from one optical waveguide to the other optical waveguide. Is what you do. In this element, an electric field can be independently applied to the optical waveguide 1 through the front n-electrode 4 and the p-electrode 5 and to the optical waveguide 2 through the back n-electrode 6 and the p-electrode 5.

The following is a specific example of each of the above members. Reference numerals 1 and 2 are i-In _0.58 Ga _0.42 A
s _0.1 P _0.9 / i-In _0.81 Ga _0.19 As _0.45 P _0.55 composed of multiple quantum wells (MQW: Multi Qua)
3) p-InP layer, 4)
Denotes a front surface n electrode, 5 denotes a P electrode, and 6 denotes a rear surface n electrode. 7, 8 are i-InP buried layers, 9 is n-InP
The clad layer 10 is an n-InP layer for applying an electric field to the MQW waveguide, and similarly, 11 is a p-InP layer. The optical waveguide has a width and depth of 2 μm on each side and is a single mode optical waveguide. The distance between the optical waveguides, which is the sum of the thicknesses of 3 and 11, was 0.5 μm. The MQW layer comprises 10 pairs of a 6-nm wide i-In _0.58 Ga _0.42 As _0.1 P _0.9 (band gap 0.790 eV) quantum well and a 15-nm wide i-In _0.81 Ga _0.19 As _0.45 P _0.55 (band gap 1. 06eV) formed from a combination of barriers.
Both the well layer and the barrier layer are lattice-matched to InP without distortion. The length along the optical waveguide of No. 4 is 400 microns. Through the n-side electrode 4 and the p-side electrode 5 on the front side, the MQW
A voltage can be independently applied to the optical waveguide 1 and to the MQW optical waveguide 2 through the n-side electrode 6 and the p-side electrode 5 on the back surface.

Next, a method of manufacturing the present element will be described with reference to FIGS.
This will be described with reference to F.

As illustrated in FIG. 6A, a metal organic chemical vapor deposition (MOCVD) method is used on an n-InP substrate.
n-InP layer 9, M using i-InGaAsP-based material
Each layer of the QW layer 30 and the p-InP layer 31 was sequentially epitaxially grown. In the drawings, the substrate is omitted.
In the following figures, since the substrate and the n-InP layer are made of the same material, they are denoted by the same reference numeral 9. Accordingly, the semiconductor denoted by reference numeral 9 indicates the substrate and this upper layer together.

Next, a resist pattern is formed in the shape of the optical waveguide by using a photolithography technique. Then, using this resist pattern as a mask region, the MQW layer 30 and the p-InP layer 3 are formed by ordinary dry etching.
1 was formed. FIG. 6B shows this state. Again, after growing the i-InP layer 8 by MOCVD and embedding this mesa shape, the p-InP layer 3
Each layer of the i-InGaAs PMQW layer 32 and the n-InP layer 33 was grown (FIG. 6C). Next, a mesa shape was formed immediately above the embedded optical waveguide as shown in FIG. 6D by using a process similar to that for forming the state in FIG. 6B.
This mesa shape is constituted by the MQW optical waveguide, 1 and the p-InP layer 9. Thereafter, the ridge was completely buried with the i-InP layer 7 as shown in FIG. 6E by using the MOCVD method.

Next, a part of the p-InP layer 3 is exposed by photolithography and wet etching (FIG. 6F).
An electrode material was deposited and then subjected to photolithography milling to form an n-electrode 4 and a p-electrode 5 as shown in FIG. 6G. Finally, the substrate is polished to a desired thickness (FIG. 6).
H), the back surface n-electrode 6 was formed (FIG. 6I). An AuGe alloy was used for both of the electrodes, and was formed by vapor deposition. For these electrodes, a laminated film of Au and a heat-resistant metal such as Ti, Pt, or Mo can be used.

According to the present invention, the distance between the two optical waveguides and the composition thereof are determined by the crystal growth conditions. Therefore, it is possible to completely set these conditions and characteristics arbitrarily. In the present embodiment, the compositions and shapes of the two optical waveguides are exactly the same. However, as described above, these settings can be freely selected by changing the crystal growth conditions.

For example, in the present embodiment, an InGaAsP quantum well structure lattice-matched to an InP substrate is used.
A group III-V compound semiconductor material having a composition containing at least one of In, Ga, and Al as a material of a group II element and at least one of As, P, and N as a material of a group V element may be used. I can do it.

In this embodiment, the compositions and shapes of the two optical waveguides are completely the same. However, it is also possible to form optical waveguide groups having different compositions and shapes by changing the conditions for crystal growth. Can be done.

Next, the operation of the vertical directional coupler of this embodiment will be described.

FIG. 7 is a plan view showing an embodiment of the directional coupler according to the present invention. 8 and 9 are cross-sectional views of the directional coupler element shown in FIG. 7 taken along the line AA. Each figure shows a different operation state. FIG. 10 is a diagram showing a refractive index distribution of a main part of the directional coupler. FIG. 11 is a diagram illustrating the refractive index dependence of the intensity distribution of light guided to the first optical waveguide, and FIG. 12 is a diagram illustrating the refractive index dependence of the intensity distribution of light guided to the second optical waveguide. . FIG. 13 shows the first and second
FIG. 5 is a diagram showing the dependence of the output intensity from the output end of each optical waveguide on the voltage applied to the first optical waveguide.

When no voltage is applied to the directional coupler, as shown by the solid line in FIG. 10, the two optical waveguides constituting the directional coupler have the same refractive index. As shown in FIG. 9, when a voltage is applied between the upper electrode 4 and the conductive layer 3 with respect to the substrate, the refractive index of the first optical waveguide 1 to which the voltage is applied increases, and the refractive index distribution becomes Becomes asymmetric. FIGS. 11 and 12 show the power distribution of the propagating light when the refractive index of one optical waveguide of the directional coupler is changed as described above. In each figure, the horizontal axis indicates the distance in the light propagation direction, and the vertical axis indicates the normalized light power. 11 shows the power in the optical waveguide 1, and FIG. 12 shows the power in the optical waveguide 2. In each case, the difference Δn between the refractive indices of the optical waveguides 1 and 2 is set to 0.
³ shows the result when the value is changed from 1.2 × 10 ⁻³ to 1.2 × 10 ⁻³ . In each figure, the curves of Δn = 0 and Δn = 1.2 × 10 ⁻³ are indicated, but the group of curves shown between these curves is the case where there is a refractive index difference between them. The characteristics are shown. In FIG. 11, when the distance is 0 and the optical power is 1, it indicates a state in which light is incident only on the first optical waveguide 1. As the light propagation distance increases, FIG.
In the first optical waveguide 1 shown in FIG. 12, the optical power decreases, and in the second optical waveguide 2 shown in FIG. 12, the optical power increases. This shows how light moves from the optical waveguide 1 to the optical waveguide 2. Further, as the propagation distance increases, the optical power in the optical waveguide 1 increases again, and the normalized power starts to return to 1. In the same state, the second optical waveguide 2 exhibits a light state opposite to that of the first optical waveguide 1. As described above, as the propagation distance increases, the power of light reciprocates between the first optical waveguide 1 and the second optical waveguide 2. Δn = 0
Comparing the curves in the case of FIG. 11 with FIG.
It can be seen that the transition completely occurs near 0.4 mm. In each figure, the position is indicated by a dotted line when the distance is 0.4 mm.

In the present embodiment, the length of the coupler is 0.4 mm. By doing so, when no voltage is applied to the first optical waveguide 1, the first optical waveguide 1
100% of the light incident on the second optical waveguide 2 is extracted from the exit of the second optical waveguide 2. This state is illustrated in FIG.

In general, the distance required for complete transfer of optical power is smaller as the distance between two optical waveguides is shorter. Such a phenomenon relating to light transfer is exactly the same whether the two optical waveguides are arranged in a plane or in the stacking direction. In the present embodiment, by taking the structure of the vertical coupling, it is possible to make the interval between the two optical waveguides extremely short. Therefore, it is possible to realize a length of the coupling portion which is shorter than the planar directional coupler by about one digit. Thus, the present invention can provide a very small directional coupler. In the case of this example, specifically, for example, the interval between the optical waveguides is 0.5 μm, and the length of the coupling portion is 0.4 mm.
Met.

Referring to FIGS. 11 and 12, it is understood that when an electric field is applied to one of the optical waveguides and Δn increases, the transition of the optical power becomes incomplete and the transition period becomes shorter. This is because the refractive index distribution becomes asymmetric and the light is biased toward the optical waveguide having a high refractive index. Δn is 1.2 ×
At 10 ^-3 , the transition cycle becomes just half as compared with the case where Δn is 0. That is, in this example, specifically, the propagation distance is 0.4 mm and the optical power is localized in the first optical waveguide 1. FIG. 9 shows this state. At this time, the light that has entered the first optical waveguide 1 is extracted 100% from the exit of the first optical waveguide 1.

FIG. 13 collectively shows switching states described in detail above. The vertical axis represents the output power of the first and second optical waveguides 1 and 2, and the horizontal axis represents the voltage applied to the first optical waveguide 1. In this example, the light is completely switched at a voltage of 1V. This voltage is a voltage necessary for giving the Δn of 1.2 × 10 ⁻³ .

In this embodiment, when no electric field is applied,
The configuration was such that the refractive index distribution was symmetric and asymmetric when an electric field was applied. However, as described above, the material composition and the refractive index of the two optical waveguides can be arbitrarily set. Therefore, it is of course possible to adopt a configuration that is asymmetric when no voltage is applied and symmetric when voltage is applied.

<Embodiment 2> This embodiment is an example in which a voltage is applied to a clad layer between at least two optical waveguides. This example is specifically an example of an optical device suitable for an optical switch, an optical intensity modulator, a wavelength selector, or the like.

First, the configuration of the optical device of this embodiment will be described. FIG. 14 is a schematic view showing another embodiment of the directional coupler according to the present invention. FIG. 15 is a cross-sectional view taken along the line AA of the structure of FIG. FIG. 16 is a diagram for explaining the operation of the present example.

The structure shown in FIGS. 14 and 15 has a structure similar to the structure of the first embodiment illustrated in FIGS. 4 and 5, but differs particularly in the arrangement of electrodes for applying a voltage.

A first cladding layer 47 is provided on a predetermined substrate. A buried second photoconductive path 41 is formed on the first clad layer 47 by a buried layer 48 made of a semiconductor material. Embedded second optical waveguide 41
A first semiconductor layer of a first conductivity type is disposed on top of
Further, covering the first semiconductor layer and the buried layer 48,
First second semiconductor layer of the conductivity type of 44 and the cladding layer 43
Is formed. A second conductive third semiconductor layer 42 is formed on the cladding layer 43. These semiconductor layers 42, 43, and across the 44, on the opposite side of the first semiconductor layer of the first conductivity type, a first optical waveguide 40 is embedded its side by a buried layer 46 Formed. The electrode 6 is provided on the semiconductor layer 42 and the electrode 45 is provided on the semiconductor layer 44. In this device, a voltage is applied to both electrodes to change the refractive index of the cladding layer 43. FIG. 16 shows a state in which the refractive index of the cladding layer 43 changes by applying a voltage. The change is indicated by a dotted line.

First, a specific configuration of the embodiment will be described below. In the present embodiment, the compositions of the optical waveguides 40 and 41 are i-In _0.58 Ga _0.42 As _0.1 P _0.9, and p
I-In sandwiched between -InP layer 42 and n-InP layer 44
_0.58 Ga _0.42 As _0.1 P _0.9 / i-In _0.81 Ga _0.19 As
_An MQW layer 43 made of _0.45 P _0.55 was provided. This MQW
The structured optical waveguide itself is sufficient according to customary methods.
The p-side electrode 5 is provided on the p-InP layer 42 and the n-InP layer 44.
Are formed with n-side electrodes 45, respectively. The claddings 46 and 47 surrounding the two optical waveguides are i-In
P layer. The feature of the operation of the present embodiment is that the refractive index of the cladding layer between the optical waveguides is changed without changing the refractive index of the two optical waveguides. Therefore, the coupling length can be changed while maintaining the maximum transition power at 100%.

It goes without saying that the device of this embodiment is suitable for an optical switch and a light intensity modulator, but is particularly suitable for a wavelength selector. FIGS. 17 and 18 show the concept of the operation.
It is. They show examples of selectively extracting light of another wavelength.

Since the propagation constant β differs depending on the wavelength of light, the coupling length has wavelength dependence. Therefore, when light in a wide wavelength range is incident on the directional coupler, only light having a wavelength having a coupling length equal to the length of the element is transferred to the optical waveguide on the opposite side. For example, in the example of FIG. 17, the first optical waveguide 40
, Light beams having wavelengths λ0, λ1, λ2, λ3, and λ4 are incident. Since the length of the coupling length varies depending on the wavelength of the light, if the coupling length is set so that only the light of wavelength λ0 is transferred to the second optical waveguide, only the light of wavelength λ0 is converted into the second optical waveguide. The light travels to

In this example, the refractive index of the cladding layer 43 between the two optical waveguides 40 and 41 is changed by applying a voltage to the electrodes 6 and 45. Thus, the wavelength of the light extracted from the second optical waveguide can be selected. FIG. 18 shows an example in which only the light of wavelength λ1 is transferred to the second optical waveguide by control by applying a voltage. As in the example of FIG.
In the first optical waveguide 40, wavelengths λ0, λ1, λ2, λ3,
And λ4, only light of wavelength λ1 transfers to the second optical waveguide. In this example, it is also possible to select another wavelength by the applied voltage. Thus, in this example, it is possible to freely select the wavelength to be selected. Further, in this example, there is no need to use a quantum well structure having a large loss in a core portion where light propagates, and thus there is an advantage that a propagation loss can be reduced.

<Third Embodiment> Next, some apparatuses and systems to which the optical device of the present invention is applied will be described.

FIG. 19 shows an optical matrix switch in which the directional coupler 50 exemplified in the first embodiment is integrated. The directional couplers are connected in a matrix by an optical waveguide as shown. Eight incident lights 601 to 608 become eight outgoing lights 701 to 708. That is, 8
A matrix of × 8 is formed. In the drawing, only the arrangement of the directional couplers 50 is shown, but the electrodes for switching the voltage application described above in each directional coupler 50 are omitted from the drawing. With these electrode groups, a matrix optical switch operation can be performed.

FIG. 20 shows a communication module for optical modulation using the directional coupler exemplified in the first embodiment as an optical modulator. An optical communication modulator module 55 in which a directional coupler 51 according to the first embodiment is mounted on a submount 101 and a desired optical transmission path, for example, an optical fiber 52 and a lens 53 are fixed on the optical axis thereof. By the operation of the directional coupler 51,
It is possible to enable or disable the transmission of light from one optical fiber to the other optical fiber, thereby performing light modulation.

FIG. 21 shows a trunk optical communication system using the optical communication modulator module 55 described above. The transmitting device 60 includes a semiconductor laser 61 for inputting light to the modulator module 54 and a drive system 62 for driving the modulator module. The light from the semiconductor laser 61 is converted into an optical signal by the modulator module 54, passes through the optical fiber 63, and is detected by the light receiving unit 65 in the receiving device 64. Each element of the optical system, for example, a semiconductor laser, a light receiving unit, and the like, is a conventional one.

[0058]

As described above, according to the present invention, it is possible to obtain a directional coupler which can be applied to an optical switch, an optical modulator, and a wavelength selective filter which are small and can be integrated. Further, according to the present invention, an inexpensive and highly reliable optical communication module and an optical communication system using them can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation principle of a general directional coupler.

FIG. 2 is a diagram illustrating a state of light wave power transfer of a general directional coupler.

FIG. 3 is a plan view showing an example of a conventional directional coupler.

FIG. 4 is a perspective view showing an example of the directional coupler of the present invention.

FIG. 5 is a sectional view showing an example of the directional coupler of the present invention.

FIG. 6A is a cross-sectional view of the device in a predetermined manufacturing process of the directional coupler of the present invention.

FIG. 6B is a sectional view of the device in a predetermined manufacturing process of the directional coupler of the present invention.

FIG. 6C is a cross-sectional view of the device in a predetermined manufacturing process of the directional coupler of the present invention.

FIG. 6D is a cross-sectional view of the device in a predetermined manufacturing step of the directional coupler of the present invention.

FIG. 6E is a sectional view of the device in a predetermined manufacturing step of the directional coupler of the present invention.

FIG. 6F is a cross-sectional view of the device in a predetermined manufacturing step of the directional coupler of the present invention.

FIG. 6G is a sectional view of the device in a predetermined manufacturing step of the directional coupler of the present invention.

FIG. 6H is a cross-sectional view of the device in a predetermined manufacturing step of the directional coupler of the present invention.

FIG. 6I is a sectional view of the device in a predetermined manufacturing process of the directional coupler of the present invention.

FIG. 7 is a plan view showing an example of the directional coupler of the present invention.

FIG. 8 is a sectional view showing an example of a first operation state of the directional coupler of the present invention.

FIG. 9 is a sectional view showing an example of a second operation state of the directional coupler of the present invention.

FIG. 10 is a diagram for explaining the operation of another embodiment of the present invention.

FIG. 11 is a diagram illustrating the refractive index dependence of the intensity distribution of light guided to the first optical waveguide.

FIG. 12 is a diagram showing a refractive index dependence of an intensity distribution of light guided to a second optical waveguide.

FIG. 13 is a diagram showing the output intensity from the output end of each of the first and second optical waveguides and the voltage dependency applied to the first optical waveguide.

FIG. 14 is a schematic view showing another embodiment of the optical device according to the present invention.

FIG. 15 is a sectional view taken along the line AA of the structure of FIG. 14;

FIG. 16 is a diagram for explaining the operation of another example of the optical device of the present application.

FIG. 17 is a diagram showing a first operation state of the variable wavelength filter of the present application.

FIG. 18 is a diagram illustrating a second operation state of the variable wavelength filter of the present application.

FIG. 19 is a diagram showing an example of an optical matrix switch using the directional coupler of the present invention.

FIG. 20 is a schematic diagram of an optical communication module on which the optical device of the present invention is mounted.

FIG. 21 is a schematic diagram of an optical communication system using the optical communication module of the present invention.

[Explanation of symbols]

1: MQW optical waveguide of i-InGaAsP / InP 2: MQW optical waveguide of i-InGaAsP / InP 3: p-InP conductive layer 4: 4: n-electrode, 5: p-electrode,
6: n-electrode, 7: i-InP buried layer, 8: i-I
nP buried layer, 9: n-InP layer, 10: n-InP layer, 11: n-InP layer, 20: input port 1, 21: input port 2, 22: output port 1,
23: Output port 2, 24: Electrode 25: Electrode, 26: Cladding layer between waveguides 30: MQW layer 31 of i-InGaAsP / InP 31: p-InP layer, 32: i-InGaAsP / In
P MQW layer 33: n-InP layer, 40: i-InGaAsP optical waveguide 41: i-InGaAsP optical waveguide, 42: pI
nP layer 43: i-InGaAsP / InP MQW layer, 44: n
-InP layer 45: n-electrode, 46: i-InP clad layer, 47:
i-InP cladding layer 50: optical modulator, 51: submount, 52: optical fiber, 53: lens 54: modulator module for optical communication, 60: transmitter, 6
1: semiconductor laser 62: drive system, 63: optical fiber, 64: receiving device,
65: light receiver.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/015 G02F 1/31

Claims (4)

(57) [Claims] To 1. A substrate, a first optical waveguide, and i-type click <br/> Rudd layer has at least are arranged in a vertical direction and a second optical waveguide to the substrate, on the cladding layer
The lower surface of each at least includes a semiconductor <br/> layer of either conductivity type p-type and n-type, and the first optical waveguide, a semiconductor
The layer, the cladding layer, the semiconductor layer , and the second optical waveguide are
Having an area arranged to be superimposed on the substrate in a vertical direction,
An electrode is provided on each of the p-type or n-type conductivity type semiconductor layers.
Voltage is applied between the electrodes to apply an electric current to the cladding layer.
The first light guide is applied by the electric field.
Changing the optical coupling state between the waveguide and the second optical waveguide,
Changing the coupling length between the first optical waveguide and the second optical waveguide
A directional coupler, characterized in that the directional coupler is capable of being operated. 2. The method according to claim 1, wherein a half of an i-type multiple quantum well structure is formed on the substrate.
Sandwiching the conductor layer and the semiconductor layer having the multiple quantum well structure,
The semiconductor of the multiple quantum well structure is formed by a first cladding layer.
First optical waveguide embedded except for a surface facing a body layer
And a half of the multiple quantum well structure by another cladding layer.
Second optical waveguide embedded except for the surface facing the conductor layer
And at least vertically disposed with respect to the substrate
And a p-type semiconductor layer on the upper and lower surfaces of the semiconductor layer having the multiple quantum well structure.
And at least one of n-type conductive semiconductor layers
And electrically charges each of the p-type or n-type conductive semiconductor layers.
Poles are provided and in the direction along the substrate surface,
One optical waveguide, a semiconductor layer, and a half having a multiple quantum well structure.
A conductor layer, a semiconductor layer , and a second optical waveguide are paired with the substrate.
And the area vertically overlapped
And the first optical waveguide and the second optical waveguide are positioned at the front.
Areas at different positions along the substrate surface.
Then , an electric field can be applied to the semiconductor layer having the multiple quantum well structure by applying a voltage between the electrodes, and the electric coupling state between the first optical waveguide and the second optical waveguide is changed by the electric field. Changing the coupling length between the first optical waveguide and the second optical waveguide so that light can be transferred between the first optical waveguide and the second optical waveguide. Combiner. 3. An optical modulator, which comprises using the intensity modulation of the light the directional coupler according to claim 2 from claim 1. 4. A first optical waveguide and an i-type multi- layer structure on a substrate.
A semiconductor layer having a quantum well structure, and a second optical waveguide disposed at least in a direction perpendicular to the substrate, and p-type and n-type are formed on upper and lower surfaces of the semiconductor layer having the multiple quantum well structure. At least a semiconductor layer of any one of the conductivity types, and each of the p-type or n-type conductivity semiconductor layer
And the first optical waveguide, p-type or
Semiconductor layer of n-type conductivity, semiconductor having multiple quantum well structure
Body layer, n-type or p-type conductivity type semiconductor layer , and second photoconductive layer
Where the waveguides are arranged vertically overlapping the substrate.
Having an area , an electric field can be applied to the clad layer by applying a voltage between the electrodes , and the electric field changes an optical coupling state between the first optical waveguide and the second optical waveguide, A wavelength selector, wherein the wavelength of light propagated to at least one of the first optical waveguide and the second optical waveguide can be changed.