CN116661061A

CN116661061A - Semiconductor optical element and method for manufacturing the same

Info

Publication number: CN116661061A
Application number: CN202310193349.0A
Authority: CN
Inventors: 河野直哉; 藤原直树; 齐藤晋圣; 藤泽刚; 佐藤孝宪
Original assignee: Hokkaido University NUC; Sumitomo Electric Industries Ltd
Current assignee: Hokkaido University NUC; Sumitomo Electric Industries Ltd
Priority date: 2022-02-28
Filing date: 2023-02-23
Publication date: 2023-08-29

Abstract

Provided are a semiconductor optical element which is easy to manufacture and can improve coupling efficiency, and a method for manufacturing the same. The semiconductor optical element is provided with: a substrate having a first optical waveguide formed of silicon; and a semiconductor element bonded to an upper surface of the substrate, the semiconductor element having a second optical waveguide formed of a group III-V compound semiconductor, the first optical waveguide and the second optical waveguide forming a directional coupler.

Description

Semiconductor optical element and method for manufacturing the same

Technical Field

The present disclosure relates to semiconductor optical elements and methods of manufacturing the same.

Background

A technique of bonding a semiconductor element formed of a group III-V compound semiconductor to a substrate such as an SOI (Silicon On Insulator: silicon on insulator) substrate (so-called silicon photonics) on which an optical waveguide is formed is known (for example, non-patent document 1 and the like).

Prior art literature

Non-patent literature

Non-patent document 1: R.Kou et al, "Inter-layer light transition in hybrid III-V/Si wavguides integrated by μ -transfer printing" optical Express28 (13), 19772-19782, june 2020

Disclosure of Invention

Problems to be solved by the invention

In order to improve the coupling efficiency between the optical waveguide provided on the substrate and the optical waveguide of the III-V semiconductor element, the tip of the optical waveguide of the III-V semiconductor element may be tapered. However, for example, it is difficult to perform processing such as dry etching to make the width of the tip of the taper 400nm or less. Accordingly, an object of the present disclosure is to provide a semiconductor optical element which is easy to manufacture and can improve coupling efficiency, and a method for manufacturing the same.

Means for solving the problems

The semiconductor optical element of the present disclosure includes: a substrate having a first optical waveguide formed of silicon; and a semiconductor element bonded to an upper surface of the substrate, the semiconductor element having a second optical waveguide formed of a group III-V compound semiconductor, the first optical waveguide and the second optical waveguide forming a directional coupler.

The manufacturing method of the semiconductor optical element of the present disclosure includes: a step of bonding a semiconductor element formed of a group III-V compound semiconductor to an upper surface of a substrate having a first optical waveguide formed of silicon; and forming a second optical waveguide in the semiconductor element, wherein the first optical waveguide and the second optical waveguide form a directional coupler.

Effects of the invention

According to the present disclosure, a semiconductor optical element that can be manufactured easily and can improve coupling efficiency and a method for manufacturing the same can be provided.

Drawings

Fig. 1A is a plan view illustrating a semiconductor optical element of the first embodiment.

Fig. 1B is an enlarged plan view of a part of the semiconductor optical element.

Fig. 2A is a cross-sectional view taken along line A-A of fig. 1B.

Fig. 2B is a cross-sectional view taken along line B-B of fig. 1B.

Fig. 3A is a diagram illustrating an effective refractive index.

Fig. 3B is a diagram illustrating an effective refractive index.

Fig. 4 is a graph illustrating transmittance.

Fig. 5A is a graph illustrating the dependence of the transmittance on the amount of overlap.

Fig. 5B is a graph illustrating the wavelength dependence of transmittance.

Fig. 6 is a cross-sectional view of a semiconductor optical element illustrating a modification.

Fig. 7A is a plan view illustrating a semiconductor optical element of the second embodiment.

Fig. 7B is a cross-sectional view taken along line C-C of fig. 7A.

Fig. 8A is a plan view illustrating a semiconductor optical element of the third embodiment.

Fig. 8B is an enlarged plan view of a part of the semiconductor optical element.

Fig. 9A is a sectional view taken along line D-D of fig. 8A.

Fig. 9B is a cross-sectional view along line E-E of fig. 8A.

Fig. 10A is a plan view illustrating a method of manufacturing a semiconductor optical element.

Fig. 10B is a cross-sectional view taken along line D-D of fig. 10A.

Fig. 10C is a cross-sectional view taken along line E-E of fig. 10A.

Fig. 11A is a plan view illustrating a method of manufacturing a semiconductor optical element.

Fig. 11B is a sectional view taken along line D-D of fig. 11A.

Fig. 11C is a cross-sectional view taken along line E-E of fig. 11A.

Fig. 12A is a plan view illustrating a method of manufacturing a semiconductor optical element.

Fig. 12B is a cross-sectional view taken along line D-D of fig. 12A.

Fig. 13A is a plan view illustrating a semiconductor optical element of the fourth embodiment.

Fig. 13B is a cross-sectional view taken along line E-E of fig. 13A.

Fig. 14 is a plan view illustrating a semiconductor optical element of the fifth embodiment.

Fig. 15A is a diagram illustrating a calculation result of the coupling efficiency.

Fig. 15B is a diagram illustrating a calculation result of the coupling efficiency.

Detailed Description

[ description of embodiments of the present disclosure ]

First, the contents of the embodiments of the present disclosure will be described.

One aspect of the present disclosure is (1) a semiconductor optical element including: a substrate having a first optical waveguide formed of silicon; and a semiconductor element bonded to an upper surface of the substrate, the semiconductor element having a second optical waveguide formed of a group III-V compound semiconductor, the first optical waveguide and the second optical waveguide forming a directional coupler. Since the directional coupler is formed by bringing the first optical waveguide and the second optical waveguide into proximity, manufacturing is easy. By forming the directional coupler, the coupling efficiency can be improved.

(2) In the above (1), the first optical waveguide may have a shape curved so as to approach the second optical waveguide. The directional coupler is formed by the proximity of the first optical waveguide to the second optical waveguide. By forming the directional coupler, the coupling efficiency can be improved.

(3) In the above (1) or (2), the first optical waveguide may have a first portion and a second portion, a distance between the second portion and the second optical waveguide may be smaller than a distance between the first portion and the second optical waveguide, and the second portion and the second optical waveguide may form the directional coupler. By forming the directional coupler, the coupling efficiency can be improved.

(4) In any one of the above (1) to (3), the second optical waveguide may be located above one end portion of the first optical waveguide in the width direction and not extend to the other end portion of the first optical waveguide. The directional coupler is formed by the first optical waveguide and the second optical waveguide, so that the coupling efficiency can be improved.

(5) In any one of the above (1) to (4), the center of the second portion of the first optical waveguide may be separated from the center of the second optical waveguide in the width direction of the first optical waveguide and the second optical waveguide. The directional coupler is formed by the first optical waveguide and the second optical waveguide, so that the coupling efficiency can be improved.

(6) In the above (5), at least a part of the second portion of the first optical waveguide may not overlap with the second optical waveguide in a direction in which the substrate and the semiconductor element are bonded. The directional coupler is formed by the first optical waveguide and the second optical waveguide, so that the coupling efficiency can be improved.

(7) In any one of the above (3) to (6), a phase adjustment portion provided in the first portion of the first optical waveguide may be provided. The phase of the light can be adjusted.

(8) In any one of the above (1) to (7), the first optical waveguide and the second optical waveguide may form a plurality of the directional couplers, and the plurality of the directional couplers may be arranged along an extending direction of the first optical waveguide and the second optical waveguide. Multiple directional couplers can be utilized to improve coupling efficiency.

(9) In any one of the above (1) to (8), the semiconductor element may have a first semiconductor layer bonded to the upper surface of the substrate and a mesa protruding from the first semiconductor layer to a side opposite to the substrate, and the semiconductor element may have the second optical waveguide. The directional coupler is formed by the first optical waveguide and the second optical waveguide, so that the coupling efficiency can be improved.

(10) In the above (9), the mesa may have a second semiconductor layer, a third semiconductor layer, and a fourth semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer may be sequentially stacked on the first semiconductor layer, and the third semiconductor layer may have a multi-quantum well structure. The third semiconductor layer serves as a core of the second optical waveguide, and can enclose light in the third semiconductor layer.

(11) In any one of the above (1) to (10), the substrate may have a first layer, a second layer, and a third layer which are stacked in this order, the first layer and the third layer may be formed of silicon, the second layer may be formed of silicon oxide, and the semiconductor element may be bonded to the third layer. The directional coupler is formed by the first optical waveguide provided in the third layer and the second optical waveguide provided in the semiconductor element, whereby the coupling efficiency can be improved.

(12) In any one of the above (1) to (11), the substrate may have 2 of the first optical waveguides, and the 2 first optical waveguides and the second optical waveguide may form the directional coupler. The coupling length of the first optical waveguide and the second optical waveguide can be shortened.

(13) In any one of the above (1) to (12), the semiconductor element may have an optical gain, and the semiconductor element may function as a laser element. Light generated by the semiconductor element can propagate in the second optical waveguide and migrate in the directional coupler between the second optical waveguide and the first optical waveguide.

(14) In any one of the above (1) to (13), the first optical waveguide may have a tapered portion, the tapered portion being thinner as it approaches a tip end of the first optical waveguide, and the tapered portion of the first optical waveguide and the second optical waveguide may form the directional coupler. The coupling efficiency of the first optical waveguide and the second optical waveguide becomes high. Tolerance against dimensional errors increases.

(15) In the above (14), the taper portion of the first optical waveguide may have an asymmetric shape with respect to a direction in which the first optical waveguide extends. The coupling efficiency of the first optical waveguide and the second optical waveguide becomes high. Tolerance against dimensional errors increases.

(16) In the above (15), the tapered portion may be formed in the asymmetric shape such that a first end portion of the first optical waveguide is parallel to an extending direction of the first optical waveguide and a second end portion of the first optical waveguide is adjacent to the second optical waveguide. The coupling efficiency of the first optical waveguide and the second optical waveguide becomes high. Tolerance against dimensional errors increases.

(17) In the above (14), the taper portion of the first optical waveguide may have a symmetrical shape with respect to a direction in which the first optical waveguide extends. The coupling efficiency of the first optical waveguide and the second optical waveguide becomes high. Tolerance against dimensional errors increases.

(18) A method of manufacturing a semiconductor optical element, comprising: a step of bonding a semiconductor element formed of a group III-V compound semiconductor to an upper surface of a substrate having a first optical waveguide formed of silicon; and forming a second optical waveguide in the semiconductor element, wherein the first optical waveguide and the second optical waveguide form a directional coupler. Since the directional coupler is formed by bringing the first optical waveguide and the second optical waveguide into proximity, manufacturing is easy. By forming the directional coupler, the coupling efficiency can be improved.

[ details of embodiments of the present disclosure ]

Specific examples of the semiconductor optical device and the method of manufacturing the same according to the embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is intended to be indicated by the appended claims, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

< first embodiment >

Fig. 1A is a plan view illustrating a semiconductor optical element 100 according to a first embodiment. Fig. 1B is an enlarged plan view of a part of the semiconductor optical element 100. Fig. 2A is a cross-sectional view taken along line A-A of fig. 1B. Fig. 2B is a cross-sectional view taken along line B-B of fig. 1B.

As shown in fig. 1A, 2 sides of the semiconductor optical element 100 extend parallel to the X-axis direction. The other 2 sides extend parallel to the Y-axis direction. The Z-axis direction is the normal direction of the XY plane, and is the lamination direction of the layers. The X-axis direction, the Y-axis direction and the Z-axis direction are orthogonal to each other. The semiconductor optical element 100 may be a single rectangular chip or a part of a rectangular region of a large chip (a wavelength variable laser or the like) in which a plurality of elements are integrated.

The semiconductor optical element 100 is a hybrid optical element including a substrate 10 and a semiconductor element 40. The substrate 10 has an upper surface parallel to the XY plane. The semiconductor element 40 is bonded to the upper surface of the substrate 10. In a top view, the semiconductor element 40 is seen through, illustrating the upper surface of the substrate 10.

The substrate 10 has an optical waveguide 20 (first optical waveguide). The semiconductor element 40 has an optical waveguide 41 (second optical waveguide). The optical waveguide 20 and the optical waveguide 41 extend from one end portion to the other end portion of the semiconductor optical element 100 in the X-axis direction.

As shown in fig. 1A, the optical waveguide 41 extends linearly and is parallel to the X-axis direction, for example. The optical waveguide 20 has a wave-like shape in the XY plane, and approaches the optical waveguide 41 at the antinode portion. The linear portion of the optical waveguide 20 is parallel to the X-axis direction. The optical waveguide 20 is bent to approach the optical waveguide 41. The optical waveguide 20 has a portion 30 (first portion) distant from the optical waveguide 41 and a portion 32 (second portion, portion corresponding to an antinode) close to the optical waveguide 41.

As shown in fig. 1B and 2A, a part of the portion 32 of the optical waveguide 20 extends downward of the optical waveguide 41, and overlaps the optical waveguide 41. At the portion 32 the optical waveguide 20 is closely spaced from the optical waveguide 41, the optical waveguide 20 and the optical waveguide 41 forming a directional coupler (DC: directional Coupler) 21. The number of the directional couplers 21 may be plural or 1. In the first embodiment, the number of directional couplers 21 is plural, for example, 3 or more, 5 or more. The plurality of directional couplers 21 are arranged in the X-axis direction.

The optical waveguide 20 is provided with a phase adjustment section 23 at a portion extending in the X-axis direction. The number of the phase adjustment units 23 may be 1 or a plurality thereof. The phase adjuster 23 is provided with a heater having a predetermined length so as to extend along the optical waveguide 20. The heater changes the temperature of the phase adjustment unit 23. The refractive index of the phase adjustment unit 23 is changed by the temperature change, so that the phase of the light passing through the phase adjustment unit 23 is changed. The heater is formed of a metal such as tantalum (Ta), for example. The length of the phase adjustment unit 23 in the X-axis direction is, for example, 100 μm.

As shown in fig. 1B and 2A, the substrate 10 has an optical waveguide 20, a groove 22, and a step 24. The grooves 22 are located on both sides of the optical waveguide 20 and extend along the optical waveguide 20. As shown in fig. 1B, the planar shape of the optical waveguide 20 is a wave-type. The support 26 is linear and parallel to the X-axis direction. The support 26 is formed of the Si layer 16 and is disposed so as to be away from the optical waveguide 20. The step 24 is a portion of the Si layer 16 that spreads in a planar manner.

As shown in fig. 2A and 2B, the substrate 10 is an SOI substrate having a substrate 12 (first layer), a buried layer 14 (second layer) (BOX layer), and a silicon (Si) layer 16 (third layer). The substrate 12 is formed of Si having a thickness of 500 μm, for example. The buried layer 14 is made of, for example, silicon oxide (SiO) having a thickness of 3 μm ₂ ) Is formed and laminated on the upper surface of the substrate 12. The Si layer 16 is formed of Si having a thickness of 220nm, for example, and is stacked on the upper surface of the buried layer 14.

The groove 22 is a portion of the Si layer 16 recessed from the upper surface in the Z-axis direction, and is formed by etching the Si layer 16, for example. In the Z-axis direction, the trench 22 may extend to the middle of the Si layer 16, or may extend through the Si layer 16 and to the buried layer 14. That is, the depth of the groove 22 is, for example, 220nm or less (the thickness of the Si layer 16). The refractive index of the substrate 12 and the Si layer 16 is 3.48 at a wavelength of 1.55 μm, for example. The refractive index of the buried layer 14 is lower than the refractive index of the substrate 12 and the Si layer 16, for example, 1.44 at a wavelength of 1.55 μm.

The optical waveguide 20, the step 24, and the support 26 are formed on the Si layer 16 and protrude in the Z-axis direction from the bottom surface of the groove 22. In the etching process for forming the groove 22, the unetched portion becomes the optical waveguide 20, the stage 24, and the support 26. The upper surfaces of the optical waveguide 20, the stage 24, and the support 26 are parallel to the XY plane, and form 1 plane, i.e., the upper surface of the substrate 10. The thickness T1 of the optical waveguide 20 shown in fig. 2A is equal to the depth of the groove 22, for example, 220nm. The width W1 of the optical waveguide 20 is 880nm, for example.

The semiconductor element 40 has a bonding layer 42 (first semiconductor layer), cladding layers 44 and 48, light blocking layers 45 and 47, an active layer 46 (third semiconductor layer), and a contact layer 49. The bonding layer 42 covers the upper surface of the Si layer 16 of the substrate 10 and is bonded to the upper surface. The bonding layer 42 may be in contact with the upper surface of the Si layer 16, or another layer may be provided between the bonding layer 42 and the Si layer 16.

The semiconductor element 40 has a mesa 43. As described in the third embodiment, the mesa 43 is formed in the semiconductor element 40 by bonding the semiconductor element 40 to the substrate 10 and etching. Mesa 43 protrudes from the upper surface of Si layer 16 in the Z-axis direction. Mesa 43 includes cladding layers 44 and 48, light blocking layers 45 and 47, active layer 46, and contact layer 49. Over the bonding layer 42, a clad layer 44 (second semiconductor layer), a light blocking layer 45, an active layer 46, a light blocking layer 47, a clad layer 48 (fourth semiconductor layer), and a contact layer 49 are sequentially stacked in the Z-axis direction. The mesa 43 extends from one end to the other end of the substrate 10 in the X-axis direction in parallel with the X-axis direction, and functions as the optical waveguide 41. The active layer 46 becomes a core layer of the optical waveguide 41.

As shown in fig. 2A and 2B, the bonding layer 42 of the semiconductor element 40 is bonded to the stage 24 of the substrate 10 and is supported by the stage 24. In the region shown in fig. 1B, the central portion (the portion close to the portion 32 of the optical waveguide 20) in the X-axis direction in the mesa 43 of the semiconductor element 40 is located above the optical waveguide 20 in an overlapping manner, and the portions on both sides thereof in the X-axis direction are located above the support 26 in an overlapping manner. The table 43 is supported by the support 26.

The insulating film 25 covers the side surfaces of the mesa 43 and the upper surface of the bonding layer 42. The insulating film 25 is made of, for example, silicon nitride (SiN), silicon oxide (SiO) ₂ ) And an insulator such as silicon oxynitride (SiON). The thickness of the insulating film 25 is, for example, 100nm or more and 600nm or less. The insulating film 25 has an opening on the upper surface of the mesa 43. An electrode 27 is provided on the upper surface of the contact layer 49. The electrode 27 is formed of a metal such as gold (Au), for example.

The bonding layer 42 is formed of, for example, indium phosphide (InP) having a thickness of 182 nm. The cladding layer 44 is formed of, for example, n-type indium phosphide (n-InP) having a thickness of 180 nm. As the n-type dopant, si is used, for example. The cladding layer 48 is formed of, for example, p-type indium phosphide (p-InP) having a thickness of 1700 nm. The refractive index of each of the bonding layer 42, the cladding layers 44 and 48 is lower than that of the active layer 46, for example, 3.17 at a wavelength of 1.55 μm. The contact layer 49 is formed of, for example, p+ -type indium gallium arsenide ((p+) -GaInAs). As the p-type dopant, for example, zinc (Zn) is used.

The active layer 46 has a multiple quantum well structure (MQW: multi Quantum Well) including a plurality of well layers and a plurality of barrier layers. The plurality of well layers and the plurality of barrier layers are alternately stacked. The 1 well layer is formed of GaInAsP having a thickness of 6nm, for example. The 1 barrier layer is formed of GaInAsP having a thickness of 10nm, for example. The thickness of the active layer 46 is, for example, 90nm. The refractive index of the active layer 46 is, for example, 3.44 at a wavelength of 1.55 μm.

The light blocking layers 45 and 47 are formed of undoped gallium indium arsenide phosphide (i-GaInAsP), for example. The thickness of the light blocking layer 45 is, for example, 80nm. The thickness of the light blocking layer 47 is, for example, 100nm. The band gap wavelength of the light blocking layers 45 and 47 is, for example, 1.2 μm, which is shorter than the wavelength of light input and output from the semiconductor optical element 100. The refractive index of the light blocking layers 45 and 47 is, for example, 3.34 at a wavelength of 1.55 μm. The semiconductor layers of the semiconductor element 40 may be formed of a group III-V compound semiconductor, or may be formed of a semiconductor other than the above.

The width W2 of the mesa 43 is, for example, 500nm, 550nm or 600nm, or the like, and several hundred nm. The distance between mesa 43 and portion 30 of optical waveguide 20 is greater than the distance between mesa 43 and portion 32 of optical waveguide 20. The distance D1 in the Y-axis direction between the phase adjustment section 23 and the portion 32 of the optical waveguide 20 shown in fig. 1B is, for example, 0.9 μm. Portion 32 of optical waveguide 20 extends below mesa 43. The width direction of the optical waveguide is orthogonal to the extending direction of the optical waveguide. In fig. 1B, the width direction is parallel to the Y-axis direction. At the portion 32 of the optical waveguide 20, the mesa 43 is located above one end portion in the width direction of the optical waveguide 20, and does not extend to the other end portion. That is, one end of the optical waveguide 20 is located below the mesa 43, and the other end is located outside the optical waveguide 20. Mesa 43 overlaps a portion of portion 32 of optical waveguide 20 when viewed from the Z-axis direction. The width W3 of the overlapped portion (the overlapping amount, see fig. 2A) is, for example, 300nm or more and 400nm or less, or several hundred nm.

Line C1 of fig. 2A represents the center of the optical waveguide 20 in the Y-axis direction. Line C2 represents the center of the optical waveguide 41 in the Y-axis direction. The center of the optical waveguide 20 and the center of the optical waveguide 41 do not overlap and are separated from each other.

The semiconductor element 40 is evanescently optically coupled to the substrate 10. The portion 32 of the optical waveguide 20 and the optical waveguide 41 of the semiconductor element 40 form a directional coupler 21, which is optically coupled. The coupling length L in 1 directional coupler 21 shown in fig. 1B, that is, the length of the portion where the optical waveguide 20 and the optical waveguide 41 overlap and are parallel, is, for example, 50 μm. The distance D2 from the coupled portion to the phase adjustment unit 23 is, for example, 20 μm.

For example, one end IN the extending direction of the optical waveguide 20 is defined as an entrance port IN, and one end of the optical waveguide 41 is defined as an exit port OUT. Light is incident on an entrance port IN the extending direction of the optical waveguide 20. Light propagates through the optical waveguide 20, and migrates from the optical waveguide 20 to the optical waveguide 41 in the directional coupler 21. The light that has migrated to the optical waveguide 41 exits from the end of the optical waveguide 41. The refractive index of the optical waveguide 20 changes at a heater provided in the phase adjustment section 23 of the optical waveguide 20. The phase of light can be adjusted by the change of the refractive index, and phase matching can be performed. The semiconductor optical element 100 functions as a mach-zehnder interferometer. By applying a voltage to the electrode 27 provided to the optical waveguide 41, the optical waveguide 41 has an optical gain.

Fig. 3A and 3B are diagrams illustrating effective refractive indices. The horizontal axis represents the width of the optical waveguide. The vertical axis represents the effective refractive index of the optical waveguide at a wavelength of 1.55 μm.

Fig. 3A shows the effective refractive index of the optical waveguide 20. Fig. 3B shows the effective refractive index of the optical waveguide 41. As shown in fig. 3A and 3B, when the width of the optical waveguide increases, the effective refractive index increases. The widths of the optical waveguides 20 and 41 are preferably adjusted so that the effective refractive index of the optical waveguide 20 and the effective refractive index of the optical waveguide 41 are the same. The effective refractive indices of the 2 optical waveguides become approximately equal, so that the coupling efficiency between the optical waveguide 20 and the optical waveguide 41 can be improved in the directional coupler 21.

Fig. 4 is a graph illustrating transmittance, and shows the result of calculation of transmittance of light from the optical waveguide 20 to the optical waveguide 41. The horizontal axis represents the coupling efficiency X in 1 directional coupler 21. The vertical axis represents the transmittance T (maximum transmittance) of light from the optical waveguide 20 to the optical waveguide 41 when light having a wavelength of 1.55 μm is guided. The number of directional couplers 21 is set to 3. The method comprises the following steps: the coupling efficiencies X of the 3 directional couplers 21 are equal to each other.

The coupling efficiency X is designed by adjusting the effective refractive index of the optical waveguide 20 and the optical waveguide 41, the coupling length L, and the overlap amount W3. The transmittance T is expressed by the following expression as a function of the coupling efficiency X.

T＝16X ³ -24X ² +9X

The range in which the coupling efficiency X of the maximum transmittance t=100% can be achieved is represented by the following formula. In the following formula, regarding X, 100% is treated as 1.

Case where n is an odd number 1. Gtoreq.X. Gtoreq.sin ² (π/(2n))

Case 1-sin where n is an even number ² (π/(2n))≥X≥sin ² (π/(2n))

n is the number of directional couplers 21, n=3 in the example of fig. 4. When specific numerical values are input to the above two formulas, X (%) becomes as follows.

When n=1, x=100%.

When n=2, x=50%.

When n=3, 100 percent is more than or equal to X is more than or equal to 25 percent

When n=4, 85.35 percent is more than or equal to X is more than or equal to 14.64 percent

When n=5, 100 percent or more of X is or more than 9.54 percent or more

When n=6, 93.30 percent is more than or equal to X is more than or equal to 6.69 percent

That is, when n is 3 or more, the range of the coupling ratio X in which the transmittance T can be set to 100% is wider when n is an odd number than when n is an even number. As shown in fig. 4, when n=3, the transmittance T becomes 100% when the coupling efficiency X becomes 25% or more. That is, light can be incident on the optical waveguide 20 and all of the light can be emitted from the optical waveguide 41.

Fig. 5A is a graph illustrating the dependence of the transmittance on the amount of overlap. The horizontal axis represents the overlap amount W3. The vertical axis represents the maximum transmittance from the optical waveguide 20 to the optical waveguide 41. The transmittance was calculated by setting the wavelength of light to 1550nm and the overlap amount W3 to a variable.

The broken line in fig. 5A shows an example in which the width W2 of the optical waveguide 41 is 550 nm. The solid line is an example of a width W2 of 600 nm. The dotted line is an example of a width W2 of 650 nm. In all of the 3 examples, the loss of light can be suppressed to less than 1dB in the range of the overlap amount W3 of 290nm to 360nm.

Fig. 5B is a graph illustrating the wavelength dependence of transmittance. The horizontal axis represents the wavelength of light. The vertical axis represents transmittance. In the solid line example, the width W2 of the optical waveguide 41 is 600nm, and the overlap W3 is 330nm. In the example of the dotted line, the width W2 is 650nm and the overlap W3 is 330nm. In the example of the dotted line, the width W2 is 550nm and the overlap W3 is 330nm. In the example of the one-dot chain line, the width W2 is 600nm and the overlap amount W3 is 300nm. In the example of the two-dot chain line, the width W2 is 600nm, and the overlap W3 is 360nm. In the entire region of the C band (1530 nm to 1565 nm), the optical loss is suppressed to less than 1.8dB.

Due to the resist pattern misalignment and the like in the manufacturing process, variations occur in the width W1 of the optical waveguide 20, the width W2 of the optical waveguide 41, and the overlap amount W3. As shown in fig. 5A, if, for example, the width W2 of the mesa 43 is in the range of 600±50nm and the overlap amount W3 is in the range of 290nm to 360nm, the loss of light is suppressed to less than 1dB. As shown in fig. 5B, in the case where the width W2 of the optical waveguide 41 is in the range of 600±50nm and the overlap amount W3 is 300nm to 330nm, the loss of light in the whole of the C-band is suppressed to less than 1.8dB.

According to the first embodiment, the substrate 10 has the optical waveguide 20 formed of Si. The semiconductor element 40 is bonded to the upper surface of the substrate 10, and has an optical waveguide 41 formed of a group III-V compound semiconductor. The directional coupler 21 is formed by the optical waveguide 20 and the optical waveguide 41, and a high coupling efficiency can be obtained. Light is transferred between the optical waveguide 20 and the optical waveguide 41 in the directional coupler 21. As shown in fig. 5A and 5B, light loss can be suppressed, and light can be propagated through 2 optical waveguides.

By providing the optical waveguide 41 with a thin taper portion having a width of several hundred nm or less, for example, the coupling efficiency can be improved. However, it is difficult to form the taper by etching with a high aspect ratio (a high ratio of thickness to width). According to the first embodiment, the taper portion may not be formed in the optical waveguide 41. By bringing the optical waveguide 20 and the optical waveguide 41 close to each other, the directional coupler 21 is formed, and the coupling efficiency can be improved.

As shown in fig. 1A and 1B, the optical waveguide 20 has a planar shape of a wave form and is curved so as to approach the optical waveguide 41. The directional coupler 21 is formed by approaching the optical waveguide 20 to the optical waveguide 41.

Specifically, optical waveguide 20 has a portion 30 and a portion 32. The distance between the portion 32 and the optical waveguide 41 is smaller than the distance between the portion 30 and the optical waveguide 41. Since the portion 32 is close to the optical waveguide 41, the directional coupler 21 is formed. The wavelike optical waveguide 20 is formed in the Si layer 16, for example by etching. Mesa 43 is formed in semiconductor element 40 at a position close to optical waveguide 20 by etching. The semiconductor optical element 100 having the directional coupler 21 can be manufactured in a simple process.

As shown in fig. 2A, the center (line C1) of the portion 32 of the optical waveguide 20 is separated from the center (line C2) of the optical waveguide 41. That is, the optical waveguide 20 is separated from the optical waveguide 41 in the width direction (Y-axis direction) and is also separated from the optical waveguide 41 in the thickness direction (Z-axis direction). In other words, the optical waveguide 20 and the optical waveguide 41 are disposed obliquely to each other in a plane parallel to the YZ plane. The obliquely arranged optical waveguide 20 and optical waveguide 41 form a directional coupler 21. The coupling efficiency can be improved and light can be transferred between 2 optical waveguides.

For example, as shown in fig. 2A, the optical waveguide 41 is located above one end portion of the optical waveguide 20 in the width direction (Y-axis direction) so as not to extend to the other end portion. That is, in the Z-axis direction, a part of the optical waveguide 20 overlaps with the optical waveguide 41, and the other part does not overlap with the optical waveguide 41. The overlap amount W3 between the optical waveguide 20 and the optical waveguide 41 is, for example, 300nm±30nm with respect to the width W1 (880 nm or the like) of the optical waveguide 20. The overlap amount W3 may be half or less of the width W1 or may be half or more.

The bonding layer 42 of the semiconductor element 40 is bonded to the upper surface of the substrate 10. Mesa 43 protrudes from bonding layer 42 in the Z-axis direction and has optical waveguide 41. The optical waveguide 41 is located above the substrate 10. The obliquely arranged optical waveguide 20 and optical waveguide 41 form a directional coupler 21. The coupling efficiency can be improved and light can be transferred between 2 optical waveguides.

In mesa 43, cladding layer 44, photo-sealing layer 45, active layer 46, photo-sealing layer 47, cladding layer 48, and contact layer 49 are laminated in this order. The active layer 46 has a multi-quantum well structure and functions as a core layer of the optical waveguide 41. The active layer 46 is sandwiched by cladding layers 44 and 48. The light can be blocked to the active layer 46, and loss can be suppressed.

The substrate 10 is an SOI substrate, and has a substrate 12, a buried layer 14, and a Si layer 16. An optical waveguide 20 is provided in the Si layer 16. The directional coupler 21 is formed by the optical waveguide 20 of Si and the optical waveguide 41 of the III-V compound semiconductor, and the coupling efficiency can be improved.

As shown in fig. 1B and 2B, the substrate 10 includes a support 26. The support 26 is separated from the optical waveguide 20, is located below the mesa 43, extends in the same direction (X-axis direction) as the mesa 43, and supports the mesa 43. This improves the mechanical strength of the semiconductor optical element 100. The width of the support 26 is smaller than the width W1 of the optical waveguide 20, and is preferably 100nm or less, for example. The support 26 is thin, and thus the effective refractive index of the support 26 is lower than the effective refractive indices of the optical waveguide 20 and the optical waveguide 41. Light does not readily spread toward the support 26. The support 26 may not be provided on the substrate 10, and the mesa 43 in the substrate 10 may be provided above the groove 22. The loss of light can be suppressed.

The mechanical strength can be improved, for example, by providing the step 24 below the mesa 43. However, the refractive index discontinuity between the directional coupler 21 and the stage 24 becomes large, and the loss of light may increase. By disposing the mesa 43 on the support 26, the mechanical strength can be improved and the refractive index discontinuity can be reduced.

As shown in fig. 1A, the semiconductor optical element 100 has a plurality of directional couplers 21. Since the plurality of directional couplers 21 are arranged along the X-axis direction, the coupling efficiency between the optical waveguide 20 and the optical waveguide 41 becomes high. The number of directional couplers 21 is, for example, 3 or more, 5 or more, and preferably an odd number.

The phase adjustment section 23 is provided in the portion 30 of the optical waveguide 20. The heater provided in the phase adjuster 23 generates heat, so that the temperature of the phase adjuster 23 changes, and the refractive index of the optical waveguide 20 changes. The phase of the light propagating in the optical waveguide 20 can be adjusted. By using an electrode provided on the mesa 43 to flow a current to the mesa 43, light can be generated in the active layer 46. The generated light is optically coupled from the optical waveguide 41 to the optical waveguide 20 in the directional coupler 21. The light transferred to the optical waveguide 20 can be optically coupled to the optical waveguide 41 with high coupling efficiency at the next directional coupler 21 by adjusting the phase by the phase adjusting section 23. The refractive index of the optical waveguide 41 can also be changed using the electrode 27 provided on the mesa 43. The coupling efficiency can be improved by making the effective refractive index of the optical waveguide 20 and the effective refractive index of the optical waveguide 41 equal in magnitude.

(modification)

Fig. 6 is a cross-sectional view of a semiconductor optical element 100A illustrating a modification, and illustrates a cross-section corresponding to fig. 2A. In the example of fig. 6, the entire optical waveguide 41 does not overlap with the optical waveguide 20. In other words, the overlap amount is zero. The distance between the optical waveguide 20 and the optical waveguide 41 in the Y-axis direction is, for example, about 500 nm. The directional coupler 21 is formed by the proximity of the optical waveguide 20 and the optical waveguide 41.

As shown in fig. 2A and 6, at least a part of the end portion of the optical waveguide 20 does not overlap with the optical waveguide 41 in a plan view in which the semiconductor element 40 is seen in perspective. The directional coupler 21 is formed by the proximity of the optical waveguide 20 and the optical waveguide 41.

< second embodiment >

Fig. 7A is a plan view illustrating a semiconductor optical element 200 of the second embodiment. Fig. 7B is a cross-sectional view taken along line C-C of fig. 7A. The same configuration as in the first embodiment will not be described.

As shown in fig. 7A and 7B, the substrate 10 has 2 optical waveguides 20. The 2 optical waveguides 20 are line-symmetrical with respect to an axis (axis parallel to the X axis) extending along the center of the optical waveguide 41 in the width direction. Each of the 2 optical waveguides 20 and the optical waveguide 41 form a directional coupler 21.

According to the second embodiment, since the directional coupler 21 is formed by 2 optical waveguides 20 and 41, the coupling efficiency can be improved. By setting the number of optical waveguides 20 to 2, the coupling length between the optical waveguides (length L in fig. 1B) can be set to 1/(v2) times as large as that in the case where the number of optical waveguides 20 is 1.

In the example of fig. 7B, 2 optical waveguides 20 do not overlap with the optical waveguide 41. A part of the 2 optical waveguides 20 may overlap the optical waveguide 41, but the entirety of the 2 optical waveguides 20 may not overlap the optical waveguide 41.

< third embodiment >

Fig. 8A is a plan view illustrating a semiconductor optical element 300 according to a third embodiment. Fig. 8B is an enlarged plan view of a part of the semiconductor optical element 300. The same configuration as in the first embodiment will not be described.

As shown in fig. 8A, the substrate 10 has an optical waveguide 20, 2 ring resonators 50, and 2 loop mirrors 52. The optical waveguide 20 extends from one end portion to the other end portion of the substrate 10 in the X-axis direction. 2 ring resonators 50 and 2 loop mirrors 52 are provided in the middle of the optical waveguide 20. The ring resonator 50 and the loop mirror 52 are provided on the Si layer 16 of the substrate 10, and have a core made of Si, similarly to the optical waveguide 20.

A semiconductor element 40 is bonded in the center in the upper surface of the substrate 10. The optical waveguide 41 of the semiconductor element 40 and the optical waveguide 20 of the substrate 10 form a plurality of directional couplers 21. The optical waveguide 20 is separated from the optical waveguide 41 at a portion other than the directional coupler 21. The end of the semiconductor element 40 is separated from the end of the substrate 10.

As shown in fig. 8B, the semiconductor element 40 has tapered portions 54 at both ends in the X-axis direction. Taper 54 is separated from optical waveguide 41 and is located above optical waveguide 20. The taper portion 54 protrudes outward of the semiconductor element 40, and has a tapered shape that becomes thinner as it moves away from the semiconductor element 40.

As shown in fig. 8A, the ring resonator 50 and the loop mirror 52 are separated from the semiconductor element 40 in the X-axis direction. From one end of the semiconductor element 40 toward one end of the substrate 10, 1 ring resonator 50 and 1 loop mirror 52 are arranged in order. From the other end portion of the semiconductor element 40 toward the other end portion of the substrate 10, 1 ring resonator 50 and 1 loop mirror 52 are arranged in order. The ring resonator 50 and the loop mirror 52 are optically coupled to the optical waveguide 20.

Fig. 9A is a cross-sectional view along line D-D of fig. 8A, illustrating a cross-section including the directional coupler 21. As shown in fig. 8A and 9A, the optical waveguide 20 and the optical waveguide 41 overlap. The semiconductor element 40 has electrodes 60 and 62. The electrode 60 and the electrode 62 are separated from each other.

As shown in fig. 9A, the insulating film 25 has an opening above the bonding layer 42 and an opening above the mesa 43. The electrode 60 is an n-type electrode, is provided in the opening of the insulating film 25, and is in contact with the bonding layer 42 to be electrically connected to the bonding layer 42. The electrode 62 is a p-type electrode, and has a pad 62a and a connection portion 62b. The pad 62a and the connection portion 62b are formed of 1 metal layer and are electrically connected. The pad 62a is separated from the optical waveguide 41 and is provided on the insulating film 25. The connection portion 62b is provided on the mesa 43, and is in contact with the contact layer 49 through the opening of the insulating film 25, and is electrically connected to the contact layer 49.

The electrode 60 is formed of an alloy (augenci) of gold, germanium, and nickel (Ni), for example. The electrode 62 is formed of, for example, a laminate of titanium, platinum, and gold (Ti/Pt/Au). The electrodes 60 and 62 also have a wiring layer composed of gold (Au).

Fig. 9B is a cross-sectional view along line E-E of fig. 8A, illustrating a cross-section including the top end of the mesa 43 and excluding the directional coupler 21. As shown in fig. 9B, the optical waveguide 20 and the optical waveguide 41 are separated. The electrode 62 is not provided at the top end of the mesa 43, and is covered with the insulating film 25. Taper 54 is formed by bonding layer 42. Taper 54 does not include light blocking layer 45, active layer 46, light blocking layer 47, cladding layer 48, and contact layer 49. Thus, the aspect ratio of etching when forming the taper portion 54 is suppressed low.

The semiconductor element 40 has an optical gain and is evanescently optically coupled to the substrate 10. By applying a voltage to the semiconductor element 40 using the electrode 60 and the electrode 62, a current flows to the mesa 43. By injecting carriers into the active layer 46, the active layer 46 generates light. In the directional coupler 21, light migrates from the optical waveguide 41 of the semiconductor element 40 to the optical waveguide 20 of the substrate 10.

Light propagating in optical waveguide 20 is reflected by loop mirror 52. The light is repeatedly reflected by the 2 loop mirrors 52, and laser oscillation is performed. The laser light is emitted to the outside of the semiconductor optical element 300.

(manufacturing method)

Fig. 10A, 11A, and 12A are plan views illustrating a method of manufacturing the semiconductor optical element 300. Fig. 10B, 11B and 12B are cross-sectional views taken along the line D-D of the corresponding plan view. Fig. 10C and 11C are cross-sectional views along the line E-E of the corresponding plan view.

Before the process shown in fig. 10A to 10C, the Si layer 16 of the substrate 10 is dry etched to form the grooves 22. The optical waveguide 20, the stage 24, the ring resonator 50, and the loop mirror 52 are formed in portions that are not etched. For example, the bonding layer 42, the clad layer 44, the photo-sealing layer 45, the active layer 46, the photo-sealing layer 47, the clad layer 48, and the contact layer 49 are epitaxially grown on a wafer of a group III-V compound semiconductor by an organometallic vapor phase growth method (OMVPE: organometallic Vapor Phase Epitaxy) or the like. The semiconductor element 40 is formed by dicing a wafer. The mesa 43 and the electrode are not formed in the semiconductor element 40.

As shown in fig. 10A to 10C, the semiconductor element 40 is bonded to the substrate 10. Specifically, nitrogen (N) is applied to the upper surface of the Si layer 16 of the substrate 10 (the upper surface of the substrate 10) and the surface of the bonding layer 42 of the semiconductor element 40 ₂ ) And (3) performing plasma treatment to activate the particles. The activated surface was subjected to ultrasonic cleaning in water. The activated surfaces are brought into contact with each other, and the semiconductor element 40 is temporarily bonded to the upper surface of the substrate 10. After the temporary bonding, for example, annealing is performed at 300℃for 2 hours to release moisture and strengthen the bonding strength (O ₂ Coupling). 2 ring resonators 50 and 2 loop mirrors 52 are located outside the semiconductor element 40. The wavy portion in the optical waveguide 20 is covered with the semiconductor element 40.

An insulating film serving as an etching mask is formed over the substrate 10 and the semiconductor element 40. A resist pattern is formed over the insulating film by photolithography or the like, and the pattern (the etching mask and the resist pattern are not shown) is transferred to the insulating film by etching. Etching is performed using an etching mask. For example, a mixed gas (CH) using methane and hydrogen is used ₄ /H ₂ ) Or RIE with chlorine-based gas, and wet etching, to form mesa 43 on semiconductor element 40. At a portion other than the mesa 43, the bonding layer 42 is exposed. Absolute used as maskThe edge film was removed by wet etching using buffered hydrofluoric acid (BHF: buffered Hydrogen Fluoride). The bonding layer 42 is further etched to form a taper 54. Since taper 54 does not include photo-seal layer 45, active layer 46, photo-seal layer 47, cladding layer 48, and contact layer 49, the aspect ratio of the etch when taper 54 is formed is low. Thus, the shape of the thin tip of the taper portion 54 can be formed with high accuracy.

As shown in fig. 11A to 11C, the insulating film 25 is formed by, for example, a chemical vapor deposition method (CVD: chemical Vapor Deposition) or the like. The insulating film 25 covers the substrate 10 and the semiconductor element 40. An opening is formed in the insulating film 25 by, for example, wet etching. As shown in fig. 11B, 1 opening 25a is provided at a position separated from the mesa 43, and 1 opening 25B is formed on the mesa 43.

As shown in fig. 12A and 12B, the electrodes 60 and 62 are formed by vacuum deposition and peeling, for example. The wiring layer of Au may be formed by, for example, a plating process. The semiconductor optical element 300 is formed by dicing the substrate 10 in a wafer state.

According to the third embodiment, the semiconductor optical element 300 functions as a laser element. The semiconductor element 40 having an optical gain generates light. Since the optical waveguide 41 of the semiconductor element 40 and the optical waveguide 20 of the substrate 10 form the directional coupler 21, light migrates between 2 optical waveguides. The light propagates through the optical waveguide 20, is reflected by the 2 loop mirrors 52, and oscillates. The semiconductor optical element 300 can emit laser light from the end of the substrate 10 to the outside.

In the semiconductor optical element 300, the optical waveguide 20 and the optical waveguide 41 may be separated as shown in fig. 6. It is also possible to provide 2 optical waveguides 20. Optical elements other than the ring resonator 50 and the loop mirror 52 may be provided on the substrate 10.

< fourth embodiment >

Fig. 13A is a plan view illustrating a semiconductor optical element 400 according to the fourth embodiment. Fig. 13B is a cross-sectional view taken along line E-E of fig. 13A. The same configuration as in any of the first to third embodiments is not described. As shown in fig. 13A, the semiconductor optical element 400 includes the optical waveguide 20 and the optical waveguide 41. The optical waveguide 20 and the optical waveguide 41 form 1 directional coupler 21.

The optical waveguide 20 and the optical waveguide 41 extend in the X-axis direction. The optical waveguide 20 extends from one end portion of the substrate 10 in the X-axis direction beyond the center of the substrate 10 to a position not reaching the other end portion of the substrate 10. One end of the optical waveguide 20 is located at an end of the substrate 10 and functions as an entrance port IN. The other end of the optical waveguide 20 has a taper 70. The portion of the optical waveguide 20 other than the taper portion 70 is linear. A portion of the optical waveguide 20 near the entrance opening IN is exposed from the bonding layer 42 of the semiconductor element 40. The taper 70 and the portion near the taper 70 in the optical waveguide 20 are covered with the bonding layer 42.

The optical waveguide 41 extends from substantially the center of the substrate 10 IN the X-axis direction to an end of the substrate 10 opposite to the entrance port IN. The end of the optical waveguide 41 is the exit OUT.

The optical waveguide 20 has a tapered portion 70 at a tip end portion opposite to the entrance port IN. Taper 70 of optical waveguide 20 and optical waveguide 41 form directional coupler 21. The taper 70 has a symmetrical shape with respect to the X-axis. One end 20a (first end) and the other end 20b (second end) of the optical waveguide 20 in the Y-axis direction are inclined from the X-axis to approach the optical waveguide 41. The end 20a and the end 20b form a taper 70. The taper 70 is thicker as it is farther from the tip of the optical waveguide 20, and is thinner as it is closer to the tip.

The coupling length L1 between the optical waveguide 20 and the optical waveguide 41 in the directional coupler 21 shown in fig. 13A is, for example, 200 μm. The distance L2 from the end of the bonding layer 42 to the taper portion 70 in the optical waveguide 20 is, for example, 15 μm. The width W4 at one of the 2 end portions of the tapered portion 70, which is closer to the entrance port IN, is, for example, 1200nm. The width W5 of the optical waveguide 20 at the other end (tip) of the taper 70 is smaller than the width W4, for example, 400nm. The thickness T1 of the optical waveguide 20 shown in fig. 13B is 220nm, for example. The distance g between the center of the optical waveguide 20 (line C1) and the center of the optical waveguide 41 (line C2) may be 0nm or more, or several hundred nm. At a distance g of 0nm, the center of the optical waveguide 20 and the center of the optical waveguide 41 overlap.

Light is incident on the optical waveguide 20 from the entrance port IN. Light propagates in the optical waveguide 20 and migrates from the optical waveguide 20 to the optical waveguide 41 at the directional coupler 21. The light that has migrated to the optical waveguide 41 exits from the exit port OUT of the optical waveguide 41.

According to the fourth embodiment, the taper 70 of the optical waveguide 20 and the optical waveguide 41 form the directional coupler 21. Thus, high coupling efficiency can be obtained. Light is transferred from the optical waveguide 20 to the optical waveguide 41 in the directional coupler 21. The loss of light can be suppressed, and the light can be emitted from the emission port OUT.

The Si layer 16 can be etched, and the taper 70 can be provided in the optical waveguide 20. The semiconductor element 40 may not be formed with a multi-step taper. The process is simplified. There are cases where there are variations in the dimensions such as the widths W4 and W5 of the optical waveguide 20, the width W2 of the optical waveguide 41, and the distance g between the optical waveguides. According to the fourth embodiment, since the optical waveguide 20 has the taper portion 70, tolerance against dimensional deviation is improved. Even when an error occurs in size, high coupling efficiency is maintained, and deterioration of characteristics is suppressed.

< fifth embodiment >

Fig. 14 is a plan view illustrating a semiconductor optical element 500 according to a fifth embodiment. The same configuration as in any of the first to fourth embodiments is not described. Taper 70 of optical waveguide 20 and optical waveguide 41 form directional coupler 21. The taper 70 has an asymmetric shape with respect to the X-axis. One end 20a (first end) of the optical waveguide 20 in the Y-axis direction extends linearly in parallel with the X-axis. The other end 20b (second end) of the optical waveguide 20 is inclined from the X-axis toward the optical waveguide 41. The end 20a and the end 20b form a taper 70.

According to the fifth embodiment, the taper 70 of the optical waveguide 20 and the optical waveguide 41 form the directional coupler 21. Thus, high coupling efficiency can be obtained. Light is transferred from the optical waveguide 20 to the optical waveguide 41 in the directional coupler 21. The light can be emitted from the emission port OUT while suppressing the loss of light. According to the fifth embodiment, since the optical waveguide 20 has the taper portion 70, tolerance against dimensional deviation is improved.

Fig. 15A and 15B are diagrams illustrating calculation results of coupling efficiency. The method comprises the following steps: the TE0 mode is incident from the optical waveguide 20 and excited in the optical waveguide 41. The worst value of the coupling efficiency at 3 wavelengths (1530 nm, 1547.5nm, 1565 nm) was calculated by the full vector beam propagation method. The coupling efficiency of fig. 15A and 15B is normalized by the maximum value of the coupling efficiency in the fifth embodiment (example of a one-sided cone). The numerical values (0.3, 0.8, 0.9, etc.) in fig. 15A and 15B represent the normalized coupling efficiency. The maximum value of the normalized coupling efficiency is 1. The coupling efficiency decreases from 1, the characteristic deteriorates.

The horizontal axis in fig. 15A and 15B represents the distance g between the centers of the optical waveguides. The vertical axis represents the width W2 of the optical waveguide 41. The coupling efficiency with respect to the change in the distance g and the width W2 was evaluated.

Fig. 15A shows the coupling efficiency in the fourth embodiment. As shown in FIG. 15A, the distance g is varied approximately in the range of-800 nm to 800 nm. When the distance g is 0, the center of the optical waveguide 20 overlaps the center of the optical waveguide 41. When the distance g is a positive value, the center of the optical waveguide 20 is located on the left side from the center of the optical waveguide 41 in fig. 13B. When the distance g is a negative value, the center of the optical waveguide 20 is located on the right side from the center of the optical waveguide 41 in fig. 13B. The width W2 is varied in the range of 450nm to 700 nm.

In the example of fig. 13A, the taper 70 is symmetrical in shape, and thus the coupling efficiency of fig. 15A is symmetrical with reference to the distance g=0. When the distance g is near 0 and the width W2 is 450nm to 600nm, the normalized coupling efficiency is 0.8 or more. In the case where the distance g is 500nm to 600nm and the width W2 is 550nm to around 600nm, the coupling efficiency is 0.8 or more. When the distance g is about 100nm to 400nm and the width W2 is about 450nm to 550nm, the coupling efficiency is 0.5 or less. When the coupling efficiency is 0.5 or less, it is considered that an unnecessary mode conversion occurs.

Fig. 15B shows the coupling efficiency in the fifth embodiment. As shown in FIG. 15B, the distance g is varied in the range of-600 nm to 600 nm. The width W2 is varied in the range of 450nm to 700 nm.

When the distance g is from about 0 to 200nm and the width W2 is from 450nm to 550nm, the coupling efficiency is 0.5 or less. When the distance g is 200nm or more, a high coupling efficiency is obtained in a wide range. When the distance g is around 400nm and the width W2 is 450nm to 650nm, the coupling efficiency is 0.9 or more.

As shown in fig. 15A and 15B, the coupling efficiency can be improved by making the distance g and the width W2 in appropriate ranges. In the example of fig. 15A, even if an error of about 100nm occurs around 0 as the center with respect to the distance g, the coupling efficiency can be made to be 0.8 or more by making the width W2 in the range of 150nm from 450nm to 600 nm. In the example of fig. 15B, even if the distance g is about 400nm and an error of about ±150nm is generated and the width W2 is about 550nm and an error of about ±100nm is generated, the coupling efficiency can be made to be 0.8 or more. High coupling efficiency can be obtained in the C-band full domain.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the specific embodiments, and various modifications and changes can be made within the gist of the present disclosure described in the claims.

Description of the reference numerals

10. 12 substrate

14. Buried layer

16 Si layer

20. 41 optical waveguide

21. Directional coupler

22. Groove(s)

23. Phase adjustment unit

24. Stage

25. Insulating film

25a, 25b opening portions

26. Support body

27. 60, 62 electrode

30. 32 portions

40. Semiconductor device with a semiconductor element having a plurality of electrodes

42. Bonding layer

43. Table top

44. 48 coating layer

45. 47 light blocking layer

46. Active layer

49. Contact layer

50. Ring resonator

52. Loop mirror

54. Taper part

62a bonding pad

62b connecting part

70. Taper part

20a, 20b end portions

100. 100A, 200, 300, 400, 500 semiconductor optical element

IN entrance port

OUT exit.

Claims

1. A semiconductor optical element is provided with:

a substrate having a first optical waveguide formed of silicon; and

A semiconductor element bonded to an upper surface of the substrate and having a second optical waveguide formed of a III-V compound semiconductor,

the first optical waveguide and the second optical waveguide form a directional coupler.

2. The semiconductor optical device according to claim 1,

the first optical waveguide has a shape curved so as to approach the second optical waveguide.

3. The semiconductor optical element according to claim 1 or 2,

the first optical waveguide has a first portion and a second portion,

the distance between the second portion and the second optical waveguide is smaller than the distance between the first portion and the second optical waveguide,

the second portion and the second optical waveguide form the directional coupler.

4. The semiconductor optical element according to claim 1 or 2,

The second optical waveguide is located above one end portion of the first optical waveguide in a width direction and does not extend to the other end portion of the first optical waveguide.

5. The semiconductor optical element according to claim 1 or 2,

the center of the second portion of the first optical waveguide is separated from the center of the second optical waveguide in the width direction of the first optical waveguide and the second optical waveguide.

6. The semiconductor optical device according to claim 5,

at least a part of the second portion of the first optical waveguide does not overlap with the second optical waveguide in a direction in which the substrate and the semiconductor element are bonded.

7. The semiconductor optical device according to claim 3,

the optical waveguide device includes a phase adjustment unit provided in the first portion of the first optical waveguide.

8. The semiconductor optical element according to claim 1 or 2,

the first optical waveguide and the second optical waveguide form a plurality of the directional couplers,

the plurality of directional couplers are arranged along an extending direction of the first optical waveguide and the second optical waveguide.

9. The semiconductor optical element according to claim 1 or 2,

the semiconductor element has a first semiconductor layer and a mesa,

The first semiconductor layer is bonded to the upper surface of the substrate,

the mesa protrudes from the first semiconductor layer to a side opposite to the substrate, and has the second optical waveguide.

10. The semiconductor optical device according to claim 9,

the mesa has a second semiconductor layer, a third semiconductor layer and a fourth semiconductor layer,

a second semiconductor layer, a third semiconductor layer and a fourth semiconductor layer are sequentially laminated on the first semiconductor layer,

the third semiconductor layer has a multiple quantum well structure.

11. The semiconductor optical element according to claim 1 or 2,

the substrate has a first layer, a second layer and a third layer laminated in this order,

the first layer and the third layer are formed of silicon,

the second layer is formed of silicon oxide,

the semiconductor element is bonded to the third layer.

12. The semiconductor optical element according to claim 1 or 2,

the substrate has 2 of the first optical waveguides,

the 2 first optical waveguides and the second optical waveguide form the directional coupler.

13. The semiconductor optical element according to claim 1 or 2,

the semiconductor element has an optical gain and,

the semiconductor device functions as a laser device.

14. The semiconductor optical element according to claim 1 or 2,

the first optical waveguide has a tapered portion,

the taper becomes thinner as it approaches the tip of the first optical waveguide,

the taper of the first optical waveguide and the second optical waveguide form the directional coupler.

15. The semiconductor optical device according to claim 14,

the taper portion of the first optical waveguide has an asymmetric shape with respect to a direction in which the first optical waveguide extends.

16. The semiconductor optical device according to claim 15,

the first end of the first optical waveguide is parallel to the extending direction of the first optical waveguide, and the second end of the first optical waveguide is close to the second optical waveguide, so that the taper portion forms the asymmetric shape.

17. The semiconductor optical device according to claim 14,

the taper portion of the first optical waveguide has a symmetrical shape with respect to a direction in which the first optical waveguide extends.

18. A method of manufacturing a semiconductor optical element, comprising:

a step of bonding a semiconductor element formed of a group III-V compound semiconductor to an upper surface of a substrate having a first optical waveguide formed of silicon; and

A step of forming a second optical waveguide in the semiconductor element,