阅读说明：本技术 光调制器 (Optical modulator ) 是由 开达郎 硴塚孝明 松尾慎治 于 2019-02-08 设计创作，主要内容包括：本发明使得在使用由基于InP的半导体构成的芯的光调制器中能够更容易地提高调制效率。根据本发明的光调制器设置有：下包层(102),形成在衬底(101)上；芯(103),形成在下包层(102)上；以及上包层(104),形成在芯(103)上。芯(103)由带隙与期望波长相对应的基于InP的半导体构成。下包层(102)和上包层(104)被配置为折射率等于或小于InP的折射率。(The present invention enables modulation efficiency to be more easily improved in an optical modulator using a core composed of an InP-based semiconductor. An optical modulator according to the present invention is provided with: a lower cladding layer (102) formed on the substrate (101); a core (103) formed on the lower cladding (102); and an upper cladding layer (104) formed on the core (103). The core (103) is composed of an InP-based semiconductor having a band gap corresponding to a desired wavelength. The lower cladding (102) and the upper cladding (104) are configured to have a refractive index equal to or less than the refractive index of InP.)

1. An optical modulator, comprising:

a lower cladding layer formed on the substrate and having a refractive index equal to or less than that of InP;

a core formed on the lower cladding layer, made of an InP-based semiconductor having a band gap corresponding to a desired wavelength;

an upper cladding layer formed on the core and having a refractive index equal to or less than that of InP; and

an electric field applying device that applies an electric field to the core.

2. The optical modulator of claim 1, wherein the core is made of InGaAsP.

3. The optical modulator of claim 1 or 2, wherein the lower cladding layer and the upper cladding layer are made of silicon oxide.

4. The optical modulator according to any one of claims 1 to 3, wherein the electric field applying device includes a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type, the first semiconductor layer and the second semiconductor layer being formed so as to: the core is interposed between the first semiconductor layer and the second semiconductor layer in a direction horizontal to a plane of the substrate.

5. The optical modulator of claim 4, wherein the core comprises a first core of a first conductivity type and a second core of a second conductivity type.

6. The optical modulator according to claim 5, wherein the first core and the second core are formed in a state of being arranged in a direction parallel to a plane of the substrate.

7. The optical modulator according to claim 5, wherein the first core and the second core are formed in a state of being stacked on the lower cladding layer.

8. The optical modulator of claim 7, wherein:

on one side of the cores, the first semiconductor layer is formed in contact with only the first one of the cores; and

on the other side of the cores, the second semiconductor layer is formed in contact with only the second one of the cores.

Technical Field

The present invention relates to an optical modulator using a core made of an InP-based semiconductor.

Background

Optical modulators are key devices for high-capacity optical communications. In the optical modulator, a portion (such as a core) for performing optical modulation is made of a material such as lithium niobate (LiNbO)₃) InP-based materials, and silicon (Si). Among them, InP-based materials can have a large refractive index change by F-K (Franz-Keldysh) effect, Pockels (Pockels) effect, QCSE (quantum confinement Stark effect) effect, carrier plasmon effect, band filling effect, and the like, and are expected to be used as modulator materials.

For example, patent document 1 describes an optical modulator including a refractive index control region in which, as shown in fig. 3, a refractive index control layer 302 made of n-type InGaAsP is provided on an n-type cladding layer 301 made of InP, and a p-type cladding layer 303 made of InP is provided on the refractive index control layer 302. Patent document 1 reports that by applying a reverse bias to the refractive index control layer 302 as a core, refractive index modulation due to the F-K effect, carrier plasmon effect, and band filling effect is allowed.

Reference list

Patent document

Patent document 1: japanese patent application laid-open No. 2010-113084

Disclosure of Invention

Technical problem

In the above-described optical modulator in which the core is made of an InP-based material, it is necessary to increase a portion where the electric field distribution of light overlaps with the charge depletion region in order to improve the modulation efficiency. For this purpose, it is important to increase the refractive index difference between the core and the cladding, thereby increasing the light confinement. However, in the conventional optical modulator, a cladding layer sandwiching the layer from above and below is made of an InP-based semiconductor such as InP, as compared with InGaAsP that is made into a core. Therefore, the refractive index difference between them cannot be increased, and there are problems that it is difficult to increase the portion where the electric field distribution of light overlaps with the charge depletion region and to improve the modulation efficiency.

The present invention has been made to solve the above-described problems, and an object of the present invention is to enable modulation efficiency in an optical modulator using a core made of an InP-based semiconductor to be more easily improved.

Means for solving the problems

An optical modulator according to the present invention includes: a lower cladding layer formed on the substrate and having a refractive index equal to or less than that of InP; a core formed on the lower cladding layer, made of an InP-based semiconductor having a band gap corresponding to a desired wavelength; an upper cladding layer formed on the core and having a refractive index equal to or less than that of InP; and an electric field applying device that applies an electric field to the core.

In the above optical modulator, the core may be made of InGaAsP. In addition, the lower cladding layer and the upper cladding layer may be made of silicon oxide.

In the above-described optical modulator, the electric field applying means includes a first semiconductor layer of the first conductivity type and a second semiconductor layer of the second conductivity type, the first semiconductor layer and the second semiconductor layer being formed as: the core is interposed between the first semiconductor layer and the second semiconductor layer in a direction horizontal to a plane of the substrate.

In the above optical modulator, the core may include a first core of a first conductivity type and a second core of a second conductivity type. In this case, the first core and the second core may be formed in a state of being arranged in a direction parallel to the plane of the substrate, or may be formed in a state of being stacked on the under clad layer.

In the above-described optical modulator, on one side of the core, the first semiconductor layer may be formed in contact with only a first core of the cores, and on the other side of the core, the second semiconductor layer may be formed in contact with only a second core of the cores.

Effects of the invention

As described above, according to the present invention, since the lower cladding and the upper cladding having the refractive index equal to or less than that of InP are provided above and below the core made of an InP-based semiconductor, an excellent effect can be obtained in the optical modulator using the core made of an InP-based semiconductor, that is, the modulation efficiency can be more easily improved.

Drawings

Fig. 1A is a cross-sectional view showing the structure of a light modulator according to an embodiment of the present invention.

Fig. 1B is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

FIG. 1C is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

Fig. 1D is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

FIG. 1E is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

FIG. 1F is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

FIG. 1G is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

FIG. 1H is a cross-sectional view showing another structure of a light modulator according to an embodiment of the present invention.

Fig. 1I is a cross-sectional view showing another structure of the optical modulator according to the embodiment of the present invention.

Fig. 2A is a top view schematically showing a partial structure of a light modulator according to an embodiment of the present invention.

Fig. 2B is a top view schematically illustrating a partial structure of a light modulator according to an embodiment of the present invention.

Fig. 3 is a sectional view showing a partial structure of a conventional light modulator.

Detailed Description

Hereinafter, an optical modulator according to an embodiment of the present invention will be described with reference to fig. 1A to 1I. Note that fig. 1A to 1I show cross sections perpendicular to the waveguide direction.

As shown in fig. 1A, the optical modulator according to the embodiment includes a lower cladding layer 102 formed on a substrate 101, a core 103 formed on the lower cladding layer 102, and an upper cladding layer 104 formed on the core 103. The lower cladding 102, the core 103, and the upper cladding 104 constitute an optical waveguide. For example, the lower cladding 102, the core 103, and the upper cladding 104 may constitute an optical waveguide satisfying a single mode condition.

The refractive indices of the lower cladding layer 102 and the upper cladding layer 104 are equal to or less than the refractive index of InP. The lower cladding layer 102 and the upper cladding layer 104 are made of, for example, silicon oxide. The core 103 is made of an InP-based semiconductor having a band gap corresponding to a desired wavelength. The core 103 is made of, for example, InGaAsP. In this case, the wavelength of the light to be modulated is in the communication wavelength band of 1.5 μm. The substrate 101 may be, for example, a silicon substrate. The lower cladding layer 102 and the upper cladding layer 104 may be made of a material having a lower refractive index than InP and are not limited to silicon oxide.

The optical modulator includes a first semiconductor layer 105 of a first conductivity type and a second semiconductor layer 106 of a second conductivity type, the first semiconductor layer 105 and the second semiconductor layer 106 being formed as: the core 103 is interposed between the first semiconductor layer 105 and the second semiconductor layer 106 in a direction horizontal to the plane of the substrate 101. The first conductivity type is, for example, n-type, and the second conductivity type is, for example, p-type. A first electrode 107 is formed on the first semiconductor layer 105 through ohmic connection, and a second electrode 108 is formed on the second semiconductor layer 106 through ohmic connection.

These first semiconductor layer 105, second semiconductor layer 106, first electrode 107, and second electrode 108 constitute electric field applying means for the core 103. The first electrode 107 and the second electrode 108 are provided so as not to overlap with the core 103 in a plan view. The first semiconductor layer 105 and the second semiconductor layer 106 have a smaller refractive index than the core 103, and also function as a cladding layer that confines light in the core 103 in a direction parallel to the plane of the substrate 101.

The core 103 is introduced with n-type or p-type impurities and has a conductivity type. When an electric field is applied to the core 103 by the above electric field applying device, a part of the core 103 is depleted and the phase of light propagating (guided) through the optical waveguide is modulated. As described above, since each electrode is provided so as not to overlap with the core 103 in a plan view, the core 103 can be thinned in a state where the absorption of light by the electrode is reduced, and the propagating optical mode field diameter can be reduced.

According to the optical modulator of the above-described embodiment, since the lower cladding layer 102 and the upper cladding layer 104 are made of a material having a refractive index equal to or less than that of InP, such as silica, light confinement to the core 103 becomes stronger than in the case of being made of an InP-based semiconductor. Thereby, a portion where the electric field distribution of the propagating light of the core 103 overlaps with the charge depletion region can be increased, and improvement of the modulation efficiency can be more easily achieved.

Here, a method of manufacturing the optical modulator according to the above-described embodiment will be briefly described. For example, a growth substrate made of InP is prepared, and a growth layer made of InGaAsP is epitaxially grown on the growth substrate by a known organometallic vapor phase growth method. Next, the grown growth layer is patterned by known photolithography and etching techniques to form the core 103. Next, the first semiconductor layer 105 and the second semiconductor layer 106 are formed by growing InP again on the growth substrates on both sides of the core 103.

Next, the substrate 101 having the lower cladding layer 102 formed thereon is bonded on the core 103, the first semiconductor layer 105, and the second semiconductor layer 106 formed on the growth substrate by a known bonding technique. For example, the lower cladding layer 102 may be formed on the substrate 101 made of silicon by depositing silicon oxide using a known deposition method such as a CVD (chemical vapor deposition) method. Then, by removing the growth substrate, the following states were obtained: a lower cladding layer 102 is formed on a substrate 101, and a core 103, a first semiconductor layer 105, and a second semiconductor layer 106 are formed on the lower cladding layer 102.

Next, a first electrode 107 and a second electrode 108 are formed on the first semiconductor layer 105 and the second semiconductor layer 106, respectively. After that, silicon oxide is deposited by a sputtering method or the like on the first semiconductor layer 105 and the second semiconductor layer 106 where the first electrode 107 and the second electrode 108 are formed, and the core 103, respectively, to form the upper cladding layer 104, and the optical modulator according to the above-described embodiment is obtained.

As shown in fig. 1B, the semiconductor layer 111 and the semiconductor layer 112 may be disposed above and below the core 103. The semiconductor layer 111 and the semiconductor layer 112 are made of, for example, InP. In addition, the first electrode 107 may be connected to the first semiconductor layer 105 via a contact layer 113. Similarly, the second electrode 108 may be connected to the second semiconductor layer 106 via a contact layer 114. The contact layer 113 and the contact layer 114 may be made of, for example, InGaAs. The contact layer 113 may be formed by introducing an impurity of the first conductivity type at a higher concentration, and the contact layer 114 may be formed by introducing an impurity of the second conductivity type at a higher concentration.

The core 103 may have, for example, a multiple quantum well structure. Note that the core 103 may be in an undoped state.

As shown in fig. 1C, the core 103 may include a first core 131 of a first conductive type and a second core 132 of a second conductive type. In this example, the first core 131 and the second core 132 are formed in a state of being arranged in a direction parallel to the plane of the substrate 101. In this way, by forming the core 103 from the first core 131 and the second core 132, the peak of the optical electric field and the p-n junction (charge depletion region) are close to each other, the portion where they overlap increases, and high modulation efficiency is expected to be achieved.

When the core 103 is made of InGaAsP, the acceptor introduced into the second core 132 to be made, for example, of p-type has a large optical absorption coefficient, and the amount of change in refractive index due to the carrier plasmon effect is very small. Therefore, it is preferable that the density of the acceptor is lower than that of the donor introduced into the first core 131 to be made into the n-type so that the second core 132 is easily depleted.

As shown in fig. 1D, a first core 133 of a first conductive type and a second core 134 of a second conductive type may be formed in a state of being stacked on the lower cladding layer 102. With this structure, both the first core 133 and the second core 134 constituting the core 103 are formed in contact with the first semiconductor layer 105 and the second semiconductor layer 106. In the case of this structure, an electric field is also applied to the core 103 in a direction perpendicular to the plane of the substrate 101. This structure in which the depletion layer extends in the vertical direction makes the portion of light overlapping the depletion region larger because the mode diameter of light propagating through the core 103 in the direction perpendicular to the substrate 101 is smaller.

The semiconductor layer 111 and the semiconductor layer 112 may be doped with impurities and have a conductivity type. For example, the semiconductor layer 111 may have a first conductivity type, and the semiconductor layer 112 may have a second conductivity type. When the semiconductor layer 111 and the semiconductor layer 112 are made of InP, as shown in fig. 1E, a structure including a first semiconductor layer 151 of a first conductivity type and a second semiconductor layer 161 of a second conductivity type is obtained, the first semiconductor layer 151 and the second semiconductor layer 161 being formed: the core 103 is interposed between the first semiconductor layer 151 and the second semiconductor layer 161 in directions horizontal and vertical to the plane of the substrate 101.

As shown in fig. 1F, the structure may include a first semiconductor layer 152 of a first conductivity type and a second semiconductor layer 162 of a second conductivity type, the first semiconductor layer 152 and the second semiconductor layer 162 being formed as: the core 103 is interposed between the first semiconductor layer 152 and the second semiconductor layer 162 in a direction horizontal to the plane of the substrate 101. The first semiconductor layer 152 and the second semiconductor layer 162 are thinned on both sides of the core 103. The thinned portion is buried by the upper cladding 141. With this structure, light confinement to the core 103 can be further improved, and high modulation efficiency is expected. In this case, the first semiconductor layer 152 and the second semiconductor layer 162 do not need to have the function of a cladding layer.

The structure described with reference to fig. 1F is made into a structure as shown in fig. 1G in which the lower surface of the core 103 is formed in contact with the lower cladding 102, and the upper cladding 141 is formed in contact with the upper surface of the core 103. This structure is a state where the semiconductor layer 111 and the semiconductor layer 112 shown in fig. 1F are not provided.

As shown in fig. 1H, the first semiconductor layer 153 may be formed to be in contact with only the first core 133 of the cores 103 at one side of the cores 103, and the second semiconductor layer 163 may be formed to be in contact with only the second core 134 of the cores 103 at the other side of the cores 103. The first semiconductor layer 153 has a first conductivity type (e.g., n-type), and the second semiconductor layer 163 has a second conductivity type (e.g., p-type).

On one side of the core 103, a lateral cladding 115 made of a semi-insulating semiconductor is formed in contact with the second core 134. On the other side of the core 103, a lateral cladding 116 made of a semi-insulating semiconductor is formed in contact with the first core 133. The first semiconductor layer 153, the second semiconductor layer 163, the lateral cladding layer 115, and the lateral cladding layer 116 may be made of, for example, InP. For example, the lateral cladding layer 115 and the lateral cladding layer 116 may be made of InP that is doped with Fe to be semi-insulating.

By constituting as described above, a p-n junction is formed in a direction perpendicular to the substrate 101 (in which a portion where an electric field distribution of light guided through the core 103 overlaps with the charge depletion region is large), and an electric field is applied thereto. On the other hand, a p-n junction is not formed in a direction horizontal to the plane of the substrate 101 (in which a portion where the electric field distribution of light guided through the core 103 overlaps with the charge depletion region is small). As a result, the parasitic capacitance can be reduced, which is advantageous for high speed. Note that lateral cladding 115 and lateral cladding 116 may be formed of, for example, SiO₂Such as an insulator or air.

As shown in fig. 1I, a first semiconductor layer 154 of a first conductive type and a second semiconductor layer 164 of a second conductive type may be formed on the lower cladding layer 102.

The first semiconductor layer 154 is formed separately from the lower cladding layer 102 in the core forming region 201. In a region separated from the lower cladding layer 102, a lateral cladding layer 117 formed of an air layer is disposed between the lower cladding layer 102 and the first semiconductor layer 154. On the other hand, the second semiconductor layer 164 is formed in the core forming region 201 so as to be separated from the upper cladding layer 142. In a region separated from the upper cladding layer 142 in the core formation region 201, the first semiconductor layer 154 is disposed between the second semiconductor layer 164 and the upper cladding layer 142.

In the optical modulator having the above-described structure, in the core formation region 201, a part of the first semiconductor layer 154 and a part of the second semiconductor layer 164 are stacked to form the core 103. The first semiconductor layer 154 in the core formation region 201 becomes the first core 135 of the first conductivity type, and the second semiconductor layer 164 in the core formation region 201 becomes the second core 136 of the second conductivity type.

As described with reference to fig. 1D, 1H, and 1I, when the core 103 made of InGaAsP is composed of the portions of the first conductivity type and the portions of the second conductivity type and these portions (p-n junctions) are stacked on the lower cladding layer 102, the extending direction of the core 103 is preferably aligned with the crystallization direction of the InGaAsP.

For example, as shown in fig. 2A, when a p-type first core is disposed on the substrate side and an n-type second core is disposed thereon, the upper surface of the core 103 made of InGaAsP is set to (001), and preferably the extending direction of the core 103 (the propagation direction of the optical mode) is set to the [110] axial direction of InGaAsP. This is because, in this structure, since an electric field is applied to the core 103 in a direction perpendicular to the substrate 101, the pockels effect contributes to a refractive index change. By setting the extending direction of the core 103 to the [110] direction, the sign of the refractive index change due to the pockels effect coincides with the F-K effect, the carrier plasma effect, and the band filling effect. Therefore, a large amount of refractive index variation can be obtained for the reverse bias applied to the core 103.

As shown in fig. 2B, when the n-type first core is disposed on the substrate side and the p-type second core is disposed thereon, the upper surface of the core 103 made of InGaAsP is set to (001), and the extending direction of the core 103 (the propagation direction of the optical mode) is preferably set to the [1-10] axial direction of the InGaAsP. This is because, in this structure, the direction of the electric field is opposite to that in the above case for the realized structure.

As described above, according to the present invention, in an optical modulator using a core made of an InP-based semiconductor, since lower and upper claddings having refractive indices equal to or less than that of InP are provided above and below the core made of an InP-based semiconductor, modulation efficiency can be more easily improved.

The present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by those skilled in the art within the technical idea of the present invention.

List of reference numerals

101 substrate

102 lower cladding layer

103 core

104 upper cladding layer

105 a first semiconductor layer

106 second semiconductor layer

107 first electrode

108 a second electrode.