WO2023243045A1 - 方向性結合器及びその製造方法 - Google Patents

方向性結合器及びその製造方法 Download PDF

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Publication number
WO2023243045A1
WO2023243045A1 PCT/JP2022/024158 JP2022024158W WO2023243045A1 WO 2023243045 A1 WO2023243045 A1 WO 2023243045A1 JP 2022024158 W JP2022024158 W JP 2022024158W WO 2023243045 A1 WO2023243045 A1 WO 2023243045A1
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Prior art keywords
core layer
optical
refractive index
directional coupler
optical waveguides
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French (fr)
Japanese (ja)
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敬太 望月
一誠 岸本
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Priority to PCT/JP2022/024158 priority Critical patent/WO2023243045A1/ja
Priority to US18/729,007 priority patent/US20250110278A1/en
Priority to JP2022559438A priority patent/JP7205678B1/ja
Priority to CN202280089980.XA priority patent/CN119301490A/zh
Publication of WO2023243045A1 publication Critical patent/WO2023243045A1/ja
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/125—Bends, branchings or intersections
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12097—Ridge, rib or the like
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/12147—Coupler

Definitions

  • the present disclosure relates to a directional coupler configured with an InP-based high mesa optical waveguide and a method for manufacturing the same.
  • Materials for optical semiconductor devices include silicon (Si), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), lithium niobate (LiNbO 3 ), or compound semiconductors based on these.
  • Various materials are used.
  • Optical waveguides are widely used as a basic component in such optical semiconductor devices. An optical waveguide confines light in a certain local area by making the refractive index higher than the surrounding area, and allows the light to propagate in a desired direction by forming that area in a linear shape.
  • directional couplers are also widely used as one of the basic components of optical semiconductor devices for realizing various functions.
  • a directional coupler optically couples the optical propagation modes of two independent optical waveguides by bringing them close to each other at a distance less than the wavelength of the propagating light. This allows arbitrary power of propagating light to be transferred.
  • the tolerance range for the device length to obtain the desired transfer rate is approximately 1 micrometer. There is also the issue of being narrow. The fact that the device length within the tolerance range is smaller than the overall device length indicates that the directional coupler is a device that is more susceptible to manufacturing errors.
  • the SWG structure is a periodic structure in which two optical waveguides that are close to each other at a distance on the order of a wavelength have different waveguide widths, and are provided in a direction perpendicular to the two optical waveguides and have a period equal to or less than the propagation light.
  • the optical power transfer distance is shortened by introducing an asymmetric waveguide width, and the SWG structure compensates for the decrease in the optical power transfer rate, which becomes a problem at this time.
  • the optical waveguide width is 0.5 micrometer or less, and it is easy to form a structure in which two optical waveguides are disposed close to each other at 0.2 micrometer or less. It is difficult to apply the conventional technology to anything other than such Si thin wire waveguides. In particular, since confinement in the height direction of the optical waveguide is weak, deep recesses are required.
  • the optical waveguide width is 0.5 micrometer or more, and a distance between two optical waveguides is required. Therefore, it is difficult to apply the conventional technology to a high mesa optical waveguide based on InP.
  • the present disclosure has been made in order to solve the above-mentioned problems, and the purpose is to provide a directional coupler that can be applied to InP-based high mesa optical waveguides, has a small device size, and is resistant to manufacturing errors, and the like. A manufacturing method is obtained.
  • a directional coupler includes a semiconductor substrate, first and second optical waveguides having a high mesa structure formed side by side on the semiconductor substrate, and surroundings of the first and second optical waveguides. a surrounding cladding formed therein, the first and second optical waveguides are configured to transmit light propagating through one of the first and second optical waveguides to the first and second optical waveguides at a desired power ratio.
  • first curved waveguide that is connected to the input side of the optical power transition section and reduces the distance between the first and second optical waveguides toward the optical power transition section; a second curved waveguide connected to the output side of the optical power transition section and increasing the distance between the first and second optical waveguides as the distance from the optical power transition section increases;
  • the distance between the first and second optical waveguides is equal to or less than the wavelength of the light, and each of the first and second optical waveguides includes a lower cladding layer, a core layer, and a core layer formed in this order on the semiconductor substrate.
  • the first optical waveguide and the second optical waveguide have different widths, and the core layer of the first and second optical waveguides of the optical power transition section has a high mesa structure having an upper cladding layer.
  • a gap core layer is formed on the lower cladding layer between the first and second optical waveguides, and the equivalent refractive index of the gap core layer is such that the equivalent refractive index of the first and second optical waveguides takes into account the leakage of the light in the height direction.
  • the refractive index is lower than the equivalent refractive index of the core layer.
  • the gap core layer is designed such that the equivalent refractive index of the gap core layer is lower than the equivalent refractive index of the core layer of the optical waveguide when light leakage in the height direction is taken into consideration. .
  • the equivalent refractive index of the gap core layer is lower than the equivalent refractive index of the core layer of the optical waveguide when light leakage in the height direction is taken into consideration.
  • FIG. 1 is a top view showing a directional coupler according to Embodiment 1.
  • FIG. FIG. 2 is a perspective view showing an optical power transfer section of the directional coupler according to the first embodiment.
  • FIG. 7 is a diagram showing the results of calculating the branching ratio of a directional coupler for the structure of Embodiment 1, the conventional high mesa waveguide structure, and the conventional buried waveguide structure.
  • FIG. 4 is a cross-sectional view showing the structure of Embodiment 1 used in the calculation of FIG. 3.
  • FIG. 4 is a cross-sectional view showing a conventional high mesa waveguide structure used in the calculation of FIG. 3.
  • FIG. 4 is a cross-sectional view showing a conventional buried waveguide structure used in the calculation of FIG. 3.
  • FIG. 4 is a diagram showing the results of calculating the ratio of optical power contained in each of two optical waveguides by overlapping integration with respect to the optical power distribution at each z position in FIG. 3;
  • FIG. 6 is a diagram showing the results of calculating the branching rate of optical power with respect to the position in the length direction of a directional coupler.
  • FIG. 6 is a diagram showing the results of calculating the branching rate of optical power with respect to the position in the length direction of a directional coupler.
  • FIG. 6 is a diagram showing the results of calculating the branching rate of optical power with respect to the position in the length direction of a directional coupler.
  • FIG. 6 is a diagram showing the results of calculating the branching rate of optical power with respect to the position in the length direction of a directional coupler.
  • FIG. 3 is a perspective view showing a directional coupler according to a second embodiment.
  • FIG. 7 is a diagram showing the results of calculating the branching ratio of the directional coupler in the structure of Embodiment 2; 14 is a diagram showing the results of calculating the ratio of optical power contained in each of the first optical waveguide and the second optical waveguide on the input side by overlap integration with respect to the optical power distribution at each z position in FIG. 13.
  • FIG. FIG. 7 is a perspective view showing a directional coupler according to Embodiment 3;
  • FIG. 3 is a plan view showing a mask used when forming a waveguide.
  • FIG. 7 is a perspective view showing a directional coupler according to a fourth embodiment.
  • FIG. 7 is a perspective view showing a directional coupler according to a fifth embodiment.
  • FIG. 7 is a perspective view showing a directional coupler according to a sixth embodiment.
  • FIG. 1 is a top view showing a directional coupler according to a first embodiment.
  • Two optical waveguides 2 and 3 are formed side by side on a semiconductor substrate 1.
  • the optical waveguides 2 and 3 are regions having a higher refractive index than the surrounding area. Light is locally confined in this region. Light propagation is allowed only in a certain direction of the optical waveguides 2 and 3.
  • the optical waveguide 2 has optical waveguides 2a to 2e.
  • the optical waveguide 3 has optical waveguides 3a to 3e.
  • the light 4a input to the directional coupler and the output lights 4b and 4c branched by the directional coupler are schematically shown by arrows.
  • the optical waveguides 2a and 3a on the input side of the directional coupler are arranged side by side.
  • the distance between the optical waveguides 2a and 3a is a sufficient distance that is several times the wavelength of the propagating light.
  • One ends of the optical waveguides 2b and 3b are connected to the optical waveguides 2a and 3a, respectively.
  • the shape of the optical waveguides 2b and 3b is a combination of circular arcs, a combination of a sine wave and a cosine wave, a cycloid curve, a clothoid curve, or the like.
  • the optical waveguides 2b and 3b connected to the input side of the optical power transition section are curved waveguides that reduce the distance between the optical waveguides 2 and 3 toward the optical power transition section. To bring light from several times the wavelength of light to around the same wavelength without optical loss.
  • the length of the optical waveguides 2b and 3b is about 10 times or more than the wavelength of the propagating light.
  • One end of the optical waveguides 2c, 3c of the optical power transfer section is connected to the other end of the optical waveguides 2b, 3b, respectively.
  • the optical waveguides 2c and 3c are arranged parallel to and close to each other.
  • the distance between the optical waveguides 2c and 3c is about the wavelength of propagating light or less.
  • the optical power transfer section branches the light propagating through one of the optical waveguides 2c and 3c to the optical waveguides 2c and 3c at a desired power ratio.
  • optical waveguides 2d and 3d One end of the optical waveguides 2d and 3d is connected to the other end of the optical waveguides 2c and 3c, respectively.
  • the shape of the optical waveguides 2d and 3d is a combination of circular arcs, a combination of a sine wave and a cosine wave, or a cycloid curve.
  • the optical waveguides 2d and 3d connected to the output side of the optical power transition section are curved waveguides in which the distance between the optical waveguides 2 and 3 increases as the distance from the optical power transition section increases. To expand light from about the wavelength of light to several times the wavelength without optical loss.
  • the length of the optical waveguides 2d and 3d is about 10 times or more than the wavelength of the propagating light.
  • Optical waveguides 2e and 3e on the output side of the directional coupler are connected to the other ends of optical waveguides 2d and 3d, respectively.
  • FIG. 2 is a perspective view showing the optical power transfer section of the directional coupler according to the first embodiment. Note that the x-axis and y-axis are shown in the figure so that the correspondence between the directions in FIGS. 1 and 2 can be understood.
  • the optical waveguide 2c has a high mesa structure including a lower cladding layer 5, a core layer 6a, and an upper cladding layer 7a, which are laminated in this order on the semiconductor substrate 1.
  • the optical waveguide 3c has a high mesa structure including a lower cladding layer 5, a core layer 6b, and an upper cladding layer 7b which are laminated in this order on the semiconductor substrate 1.
  • the core layers 6a and 6b are made of a material having a higher refractive index than the lower cladding layer 5 and the upper cladding layers 7a and 7b, and are regions that confine light.
  • a gap core layer 6c is formed on the lower cladding layer 5 between the core layers 6a and 6b of the optical waveguides 2c and 3c of the optical power transition section.
  • the gap core layer 6c is made of the same material as the core layers 6a, 6b, and the height of the upper surface thereof is dug lower than that of the core layers 6a, 6b.
  • a peripheral cladding 8 is formed around the optical waveguides 2c, 3c.
  • the peripheral cladding 8 is made of a material such as SiO 2 or SiN, which has a refractive index lower than that of the lower cladding layer 5, the core layers 6a, 6b, the upper cladding layers 7a, 7b, and the gap core layer 6c.
  • the width of the optical waveguide 2c is approximately 1.5 times the width of the optical waveguide 3c.
  • the width of the optical waveguides 2a to 2e is approximately 1.5 times the width of the optical waveguides 3a to 3e. Therefore, the directional coupler according to this embodiment is an asymmetric directional coupler in which the optical waveguide 2 and the optical waveguide 3 have different widths. Note that the width of the optical waveguides 2 and 3 is less than or equal to the net wavelength of the propagating light, and the overall height is greater than or equal to the net wavelength.
  • the height of the bottom surface of the gap core layer 6c is the same as the height of the bottom surface of the core layers 6a, 6b. Further, the gap core layer 6c and the core layers 6a and 6b are in contact with each other.
  • the equivalent refractive index of the gap core layer 6c is calculated taking into account the leakage of light from the gap core layer 6c to the surrounding cladding 8 and lower cladding layer 5.
  • the equivalent refractive index of the core layers 6a, 6b is calculated taking into account the leakage of light from the core layers 6a, 6b to the upper cladding layers 7a, 7b and the lower cladding layer 5. Generally, the thinner the core layer is, the more light leaks into the upper and lower cladding layers, and the lower the equivalent refractive index is.
  • the equivalent refractive index of the gap core layer 6c is lower than the equivalent refractive index of the core layers 6a, 6b of the optical waveguides 2c, 3c when light leakage in the height direction is taken into consideration.
  • the gap core layer 6c is dug lower than the core layers 6a, 6b of the optical waveguides 2c, 3c.
  • the gap core layer 6c is adjusted so that the equivalent refractive index n eff of the gap core layer 6c satisfies the following formula (1) with an error of 10% or less when light leakage in the height direction is taken into account. Adjust the amount of digging.
  • n core is the refractive index of the core layers 6a, 6b and the gap core layer 6c.
  • n clad is the refractive index of the surrounding cladding 8.
  • k 0 is the wave number of light propagating in vacuum.
  • w gap is the proximity distance between the optical waveguides 2c and 3c in the optical power transfer section, that is, the width of the gap core layer 6c.
  • a high mesa waveguide has stronger light confinement within the optical waveguide than other optical waveguides such as a buried waveguide or a thin wire waveguide. Furthermore, since deep etching is required to create a gap between the two optical waveguides of the optical power transition section, the width w gap of the gap needs to be at least a certain value. In such a structure, the optical propagation modes in the two optical waveguides are not sufficiently optically coupled to each other, making it difficult for sufficient optical power transfer to occur. Therefore, in this embodiment, by leaving a portion of the gap core layer 6c in the gap portion, each light propagation mode is intentionally expanded toward the gap portion, thereby strengthening the optical coupling.
  • the widths of the optical waveguides 2c and 3c in the optical power transition section are different, the difference in the propagation constant of each optical propagation mode becomes large, so that the optical waveguides 2c and 3c in the optical power transition section have different widths.
  • the transfer distance of optical power can be shortened. As a result, it is possible to realize a directional coupler that achieves both a short optical power transfer distance and a maximum optical power transfer rate of about 50%.
  • FIG. 3 is a diagram showing the results of calculating the branching ratio of the directional coupler for the structure of Embodiment 1, the conventional high mesa waveguide structure, and the conventional buried waveguide structure.
  • FIG. 4 is a cross-sectional view showing the structure of Embodiment 1 used in the calculation of FIG.
  • FIG. 5 is a cross-sectional view showing a conventional high mesa waveguide structure used in the calculation of FIG. In the conventional high mesa waveguide structure, the gap portion is completely dug.
  • FIG. 6 is a cross-sectional view showing a conventional buried waveguide structure used in the calculation of FIG. In the conventional buried waveguide structure, after the gap portion is completely dug, the surrounding area is completely buried with an InP layer 9 having a refractive index of 3.17.
  • Both structures are asymmetric directional couplers in which the optical waveguide 2c on the optical input side and the optical waveguide 3c on the optical output side are adjacent to each other with a gap portion having a width of 0.6 micrometers in between.
  • the optical waveguides 2c and 3c are surrounded by a peripheral cladding 8 made of SiO 2 with a refractive index of 1.45.
  • the width of the optical waveguide 2c is 0.6 micrometers.
  • the width of the optical waveguide 3c is 0.4 micrometers.
  • the optical waveguide 2c includes an upper cladding layer 7a with a thickness of 1.2 micrometers made of InP with a refractive index of 3.17, and a core layer 6a with a thickness of 0.5 micrometers made of AlGaInAs multiple quantum wells with an average refractive index of 3.32. and a lower cladding layer 5 having a thickness of 1.2 micrometers and made of InP with a refractive index of 3.17.
  • the optical waveguide 3c includes an upper cladding layer 7b with a thickness of 1.2 micrometers made of InP with a refractive index of 3.17, and a core layer 6b with a thickness of 0.5 micrometers made of AlGaAsAs multiple quantum wells with an average refractive index of 3.32. and a lower cladding layer 5 having a thickness of 1.2 micrometers and made of InP with a refractive index of 3.17.
  • the equivalent refractive index of the gap core layer 6c is 3.129.
  • the horizontal axis in FIG. 3 represents the position of the directional coupler in the width direction, and corresponds to the x-axis in FIGS. 1 and 2.
  • the vertical axis in FIG. 3 represents the position of the directional coupler in the length direction, and corresponds to the z-axis in FIGS. 1 and 2.
  • the plurality of curves in FIG. 3 are superimposed displays of the power distribution of light every 0.5 micrometers in the z direction, and are illustrated so that the x position where the light is localized can be easily understood visually.
  • FIG. 7 is a diagram showing the results of calculating the ratio of the optical power contained in each of the two optical waveguides by overlapping integration with respect to the optical power distribution at each z position in FIG. 3. From these calculation results, it can be seen that the conventional buried waveguide structure requires a length of 25 micrometers until the optical branching rate reaches 50%. It can be seen that in the conventional high mesa waveguide structure, the optical coupling between the two optical waveguides is too weak, and no matter how long the directional coupler is, almost no optical power transfer occurs. On the other hand, in the structure of Embodiment 1, the optical power branching rate is 50% when the length of the directional coupler is about 8 micrometers, which is about 1/3 of the directivity of the conventional structure. It can be seen that both the shortening of the coupler and the power transfer rate of 50% can be achieved.
  • FIG. 8 to 11 are diagrams showing the results of calculating the branching ratio of optical power with respect to the position in the length direction of the directional coupler.
  • the optical power branching ratio is the ratio of optical power included in each of the two optical waveguides.
  • the height of the gap core layer is changed to change the equivalent refractive index of the gap part from the refractive index of SiO 2 of the surrounding cladding of 1.45 to the refractive index of the multiple quantum well of the core layer of 3.21.
  • 8 to 11 show cases where the gap width w gap between the two optical waveguides is set to 0.2 micrometer, 0.4 micrometer, 0.6 micrometer, and 0.8 micrometer, respectively.
  • the equivalent refractive index conditions indicated by thick lines are the conditions closest to formula (1). From each figure, it can be seen that when the condition of equation (1) is satisfied, the optical power branching rate at the peak position of the graph is approximately 50%. The optical power branching ratio becomes 50% at the peak position of the graph where the slope of the graph becomes small, that is, the region where the change in the optical power branching ratio is the smallest. Therefore, the range of z positions where the optical power branching rate is approximately 50% is widened, and a directional coupler that is robust against manufacturing errors can be realized. At this time, for example, if the error in the optical power branching rate is set to ⁇ 10%, the condition of equation (1) allows an error of about 10% from the optimum condition.
  • the equivalent refractive index of the gap core layer 6c is lower than the equivalent refractive index of the core layers 6a, 6b of the optical waveguides 2c, 3c when light leakage in the height direction is taken into consideration.
  • the gap core layer 6c is designed so that. Specifically, the gap core layer 6c is dug so that the equivalent refractive index n eff of the gap core layer 6c satisfies equation (1) with an error of 10% or less when light leakage in the height direction is taken into account. Adjust the amount of filling. As a result, it is possible to obtain a directional coupler that can be applied to a high mesa optical waveguide based on InP, has a small device size, and is resistant to manufacturing errors.
  • the shape, material, and positional relationship of the directional coupler are not limited to those in this embodiment.
  • the positions of the input-side optical waveguide and the output-side optical waveguide may be swapped.
  • the material of the semiconductor substrate 1 may be Si, GaAs, SiO 2 , SiN or other materials such as LiNbO 3 .
  • the core layer does not need to be a multiple quantum well, but only needs to be a material with a higher refractive index than the cladding layer, and may be, for example, SiO 2 in which the SiO 2 cladding is doped with Ge or the like. In this case, the refractive index of the device is reduced overall, which is disadvantageous for increasing the device size, but the optical loss of propagating light is reduced, so a low-loss device can be realized.
  • FIG. 12 is a perspective view showing a directional coupler according to the second embodiment.
  • the gap core layer 6c is made of the same material as the core layers 6a, 6b, and is partially dug so that its height is lower than that of the core layers 6a, 6b, and has first and second regions 10a, which have different heights.
  • 10b is an SWG (sub-wavelength grating) structure that is periodically repeated at a pitch equal to or less than the net wavelength of light propagating in the optical waveguides 2c and 3c.
  • n gap1 of the first region 10a and the equivalent refractive index n gap2 of the second region 10b when considering the leakage of front light in the height direction are expressed by the following formula (2) with an error of 10% or less. I'm satisfied with that.
  • the equivalent refractive index, that is, the height, of the gap core layer 6c had to be uniquely determined based on the gap width and the refractive index of the material of the optical waveguide.
  • the equivalent refractive index of the gap core layer 6c felt by light propagating in the optical waveguide is the average refractive index of the first and second regions 10a and 10b having different heights determined according to the filling factor. It has a refractive index. Therefore, by introducing the SWG structure, the combination of the two heights of the first and second regions 10a and 10b and the filling factor allows for optimal optical power branching, regardless of the gap width and the refractive index of the material of the optical waveguide. It becomes possible to realize a directional coupler having a ratio.
  • FIG. 13 is a diagram showing the results of calculating the branching ratio of the directional coupler in the structure of the second embodiment.
  • the equivalent refractive index n gap1 in the height direction of the first region 10a is 3.055
  • the equivalent refractive index n gap2 of the second region 10b is 3.205
  • the period of the SWG structure is 0.22 micrometers
  • the filling factor is It was set to 0.5.
  • FIG. 14 is a diagram showing the results of calculating the ratio of optical power contained in each of the first optical waveguide and the second optical waveguide on the input side using overlap integration for the optical power distribution at each z position in FIG. 13. It is. Due to the limitations of the calculation program, the structure had an equivalent refractive index that was approximately 10% smaller than the target value. Therefore, although the optical power transfer rate is smaller than the calculation result of the first embodiment, a characteristic of an optical power transfer rate of around 50%, which is generally as desired, is obtained. From this result, it can be seen that in order to suppress the branching ratio of optical power to 50% ⁇ 10%, the allowable error from the optimum condition of equation (2) is about 10%, which is the same as in the first embodiment.
  • FIG. 15 is a perspective view showing a directional coupler according to the third embodiment. Similar to the second embodiment, in the gap core layer 6c, the first and second regions 10a and 10b are periodically repeated at a pitch equal to or less than the length of the net wavelength of light propagating in the optical waveguides 2c and 3c. It has an SWG structure. The height of the second region 10b is lower than the first region 10a.
  • the width of the optical waveguides 2c, 3c is formed on the side surfaces of the upper cladding layers 7a, 7b of the optical waveguides 2c, 3c, which are opposite to each other, with the same period and the same filling factor as the first and second regions 10a, 10b.
  • Digged portions 11a and 11b are formed with the following widths and depths that do not reach the core layers 6a and 6b.
  • the positions of the dug portions 11a and 11b match the positions of the second region 10b.
  • the positions of the non-engraved portions 12a and 12b on the side surfaces coincide with the position of the first region 10a.
  • FIG. 16 is a plan view showing a mask used when forming a waveguide.
  • the opening 13a of the mask 13 has walls in three directions and has a small aperture ratio. By etching at this opening 13a, dug portions 11a and 11b are formed.
  • the opening 13b has two walls and has a small aperture ratio.
  • a shallow first region 10a is formed by etching at this opening 13b.
  • the opening 13c has no wall and has a large aperture ratio.
  • a deep second region 10b is formed by etching at this opening 13c.
  • the optical waveguides 2c and 3c can be formed by one deep etching. Note that since the actual opening shape of the mask largely depends on the etching apparatus or conditions, the mask shape shown in FIG. 16 is just an example.
  • the regions where the first and second regions 10a and 10b are formed by etching The mask opening area ratio becomes a constant value according to the filling factor.
  • the dug portions 11a and 11b are allowed to be formed on the mutually opposing side surfaces of the upper cladding layers 7a and 7b of the optical waveguides 2c and 3c.
  • the condition of equation (2) of the second embodiment can be used as is.
  • FIG. 17 is a perspective view showing a directional coupler according to Embodiment 4.
  • the gap core layer 6c has a height lower than that of the core layers 6a, 6b, and first and second regions 10a, 10b having the same height and different refractive indexes extend inside the optical waveguides 2c, 3c. It has a structure that repeats periodically at a pitch equal to or less than the net wavelength of the propagating light.
  • the equivalent refractive index n gap1 of the first region 10a and the equivalent refractive index n gap2 of the second region 10b satisfy equation (2) with an error of 10% or less.
  • the height of the gap core layer 6c, the refractive index of the first and second regions 10a and 10b, the filling factor, etc. are set so as to.
  • the first and second regions 10a and 10b can be formed by doping with impurities or the like.
  • impurities or the like.
  • Other configurations and effects are similar to those of the first embodiment.
  • FIG. 18 is a perspective view showing a directional coupler according to the fifth embodiment.
  • the gap core layer 6c has the same height as the core layers 6a, 6b, and is made of a material having a lower refractive index than the core layers 6a, 6b.
  • the refractive index of the gap core layer 6c is set so that the equivalent refractive index n eff of the gap core layer 6c satisfies equation (1) with an error of 10% or less when light leakage in the height direction is taken into account.
  • the gap core layer 6c having a low refractive index can be formed by doping with impurities or the like.
  • the structure of this embodiment can also be formed by embedding another material, which expands the options for manufacturing methods. Other configurations and effects are similar to those of the first embodiment.
  • FIG. 19 is a perspective view showing a directional coupler according to Embodiment 6.
  • the gap core layer 6c has an SWG structure in which first and second regions 10a and 10b having different refractive indexes are periodically repeated at a pitch equal to or less than the length of the net wavelength of light propagating in the optical waveguides 2c and 3c. It is.
  • the first and second regions 10a, 10b have the same height as the core layers 6a, 6b, and are made of a material having a lower refractive index than the core layers 6a, 6b.
  • the equivalent refractive index n gap1 of the first region 10a and the equivalent refractive index n gap2 of the second region 10b satisfy equation (2) with an error of 10% or less.
  • the refractive index, filling factor, etc. of the first and second regions 10a and 10b are set so as to.
  • the first and second regions 10a and 10b of the gap core layer 6c can be formed by doping with impurities or the like.
  • the structure of this embodiment can also be formed by embedding another material, which expands the options for manufacturing methods. Other configurations and effects are similar to those of the first embodiment.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Optical Integrated Circuits (AREA)
PCT/JP2022/024158 2022-06-16 2022-06-16 方向性結合器及びその製造方法 Ceased WO2023243045A1 (ja)

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US18/729,007 US20250110278A1 (en) 2022-06-16 2022-06-16 Directional coupler and method of manufacturing the same
JP2022559438A JP7205678B1 (ja) 2022-06-16 2022-06-16 方向性結合器及びその製造方法
CN202280089980.XA CN119301490A (zh) 2022-06-16 2022-06-16 定向耦合器及其制造方法

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