Optical waveguide element and method for manufacturing optical waveguide element

Abstract

To relax positional accuracy when a compound semiconductor waveguide including a light source or the like is stuck to an Si optical waveguide.SOLUTION: The optical waveguide device includes a clad, a silicon waveguide core buried in the clad or formed to be exposed on an upper surface of the clad and extending in parallel with the upper surface of the clad, and a compound semiconductor thin film waveguide obliquely crossing the silicon waveguide core on the upper surface of the clad, wherein a width of the silicon waveguide core is 700 nm or more, the width being a length in a direction orthogonal to both a thickness direction orthogonal to the upper surface of the clad and a direction in which the silicon waveguide core extends.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical waveguide element that combines a silicon optical waveguide with a compound semiconductor, and a manufacturing method thereof, and more particularly to an optical waveguide element suitable for use in many fields, such as optical biosensors and optical communications, and a manufacturing method thereof. [Background technology]

[0002] In recent years, Si optical waveguide technology, which uses silicon (Si) as a waveguide material with the aim of miniaturization and mass production, has begun to attract attention. However, it is difficult to realize a light source using Si. For this reason, compound semiconductor light sources using III-V group compound semiconductors are sometimes used as light sources.

[0003] Many methods have been proposed for combining compound semiconductor light sources with Si optical waveguides.

[0004] One is to use a completely external light source, in which light is input to the Si optical waveguide via a grating coupler.

[0005] Another method is to integrate a light source on the same chip as the Si optical waveguide by directly growing compound semiconductors, but it is difficult to achieve a high-performance light source using this method.

[0006] Another method is to connect the light source to the end of the optical waveguide via a spot size converter, but this requires alignment work to align the optical axis, which makes it unsuitable for mass production.

[0007] In contrast to this method, a method has been proposed in which a light source is attached to a Si optical waveguide from above in order to enable mass production (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication 2021-093627 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the above-mentioned conventional method requires strict positional accuracy and is therefore not a very practical method.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical waveguide element in which the positional accuracy requirement is relaxed when a compound semiconductor waveguide including a light source and the like is attached to a Si optical waveguide, and a method for manufacturing the same. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the optical waveguide element of the present invention comprises a clad, a silicon waveguide core that is embedded in the clad or formed exposed on an upper surface of the clad and extends parallel to the upper surface of the clad, and a compound semiconductor thin film waveguide on the upper surface of the clad and obliquely intersects with the silicon waveguide core, wherein the width of the silicon waveguide core, which is the length in a direction perpendicular to both a thickness direction perpendicular to the upper surface of the clad and a direction in which the silicon waveguide core extends, is 700 nm or more.

[0012] According to a preferred embodiment of the optical waveguide element of the present invention, the width of the silicon waveguide core is 1800 nm or less.

[0013] According to another preferred embodiment of the optical waveguide element of the present invention, the equivalent refractive index of the compound semiconductor thin film waveguide is equal to the equivalent refractive index of the silicon waveguide core.

[0014] According to another preferred embodiment of the optical waveguide element of the present invention, the width of the compound semiconductor thin film waveguide, which is the length in a direction perpendicular to both the thickness direction perpendicular to the upper surface of the cladding and the direction in which the compound semiconductor thin film waveguide extends, is equal to the width of the silicon waveguide core.

[0015] According to another preferred embodiment of the optical waveguide element of the present invention, the compound semiconductor constituting the compound semiconductor thin film waveguide is InP.

[0016] According to another preferred embodiment of the optical waveguide element of the present invention, the distance between the silicon waveguide core and the compound semiconductor thin film waveguide in a direction perpendicular to the upper surface of the cladding is 100 nm or more and 200 nm or less.

[0017] According to another preferred embodiment of the optical waveguide element of the present invention, the silicon waveguide core and the compound semiconductor thin film waveguide intersect with each other at an angle in the range of 5 to 8 degrees in the extension direction.

[0018] According to another preferred embodiment of the optical waveguide element of the present invention, the optical waveguide element further comprises a rib waveguide and a tapered waveguide, each of which comprises a ridge portion and a terrace portion.

[0019] The rib waveguide, the tapered waveguide, and the compound semiconductor thin film waveguide are connected in this order, and the thicknesses of the ridge portions of the rib waveguide and the tapered waveguide are equal to each other, and the thicknesses of the terrace portions of the rib waveguide and the tapered waveguide are equal to the thickness of the compound semiconductor thin film waveguide. At the connecting end face of the rib waveguide and the tapered waveguide, the widths of the rib waveguide and the tapered waveguide are equal to each other, and the widths of the ridge portions of the rib waveguide and the tapered waveguide are equal to each other. In the tapered waveguide, the width of the ridge portion gradually narrows toward the compound semiconductor thin film waveguide, and at the connecting end face of the tapered waveguide and the compound semiconductor thin film waveguide, the tapered waveguide consists only of the terrace portion. At the connecting end face of the tapered waveguide and the compound semiconductor thin film waveguide, the widths of the tapered waveguide and the compound semiconductor thin film waveguide are equal to each other.

[0020] In this case, the compound semiconductor constituting the compound semiconductor thin film waveguide and the terrace portions of the rib waveguide and the tapered waveguide is InP, and the ridge portion of the rib waveguide can be provided with an active layer of InGaAsP as a quaternary material.

[0021] According to another preferred embodiment of the optical waveguide element of the present invention, the optical waveguide element further comprises a holding waveguide and a connecting waveguide formed of the same material and with the same thickness as the terrace portions of the compound semiconductor thin film waveguide, tapered waveguide, and rib waveguide. The holding waveguide is arranged parallel to the extending directions of the compound semiconductor thin film waveguide, tapered waveguide, and rib waveguide, and the end of the compound semiconductor thin film waveguide opposite to the end connected to the tapered waveguide is connected to the holding waveguide via the connecting waveguide, and the terrace portions of the rib waveguide are connected to the holding waveguide.

[0022] According to another preferred embodiment of the optical waveguide element of the present invention, there is provided a clad, and a first silicon waveguide core and a second silicon waveguide core which are embedded in the clad or formed exposed on an upper surface of the clad, extend parallel to the upper surface of the clad, and are parallel to each other, and further provided on the upper surface of the clad, in this order, a first compound semiconductor thin film waveguide which obliquely intersects with the first silicon waveguide core, a first tapered waveguide, a rib waveguide, a second tapered waveguide, and a second compound semiconductor thin film waveguide which obliquely intersects with the second silicon waveguide core.

[0023] The first tapered waveguide, the rib waveguide, and the second tapered waveguide are each configured to have a ridge portion and a terrace portion, the ridge portions of the first tapered waveguide, the rib waveguide, and the second tapered waveguide have the same thickness, and the first compound semiconductor thin film waveguide, the terrace portion of the first tapered waveguide, the terrace portion of the rib waveguide, the terrace portion of the second tapered waveguide, and the second compound semiconductor thin film waveguide have the same thickness.

[0024] At a connection end face between the rib waveguide and the first tapered waveguide, the widths of the rib waveguide and the first tapered waveguide are equal to each other, and the widths of the ridge portions of the rib waveguide and the first tapered waveguide are equal to each other. Also, at a connection end face between the rib waveguide and the second tapered waveguide, the widths of the rib waveguide and the second tapered waveguide are equal to each other, and the widths of the ridge portions of the rib waveguide and the second tapered waveguide are equal to each other.

[0025] In the first tapered waveguide, the width of the ridge portion gradually narrows toward the first compound semiconductor thin film waveguide, and at the connection end face between the first tapered waveguide and the first compound semiconductor thin film waveguide, the first tapered waveguide consists of only a terrace portion.

[0026] In the second tapered waveguide, the width of the ridge portion gradually narrows toward the second compound semiconductor thin film waveguide, and at the connection end face between the second tapered waveguide and the second compound semiconductor thin film waveguide, the second tapered waveguide consists of only a terrace portion.

[0027] At a connection end face of the first tapered waveguide and the first compound semiconductor thin film waveguide, the widths of the first tapered waveguide and the first compound semiconductor thin film waveguide are equal to each other, and at a connection end face of the second tapered waveguide and the second compound semiconductor thin film waveguide, the widths of the second tapered waveguide and the second compound semiconductor thin film waveguide are equal to each other.

[0028] The width of the first and second silicon waveguide cores, which is the length in a direction perpendicular to both the thickness direction perpendicular to the upper surface of the cladding and the direction in which the first and second silicon waveguide cores extend, is 700 nm or more.

[0029] Furthermore, a method for manufacturing an optical waveguide element according to the present invention is a method for manufacturing the above-described optical waveguide element, and includes the steps of: preparing a silicon semiconductor chip having the cladding and the silicon waveguide core; preparing a compound semiconductor chip having the compound semiconductor thin film waveguide; and directly bonding the silicon semiconductor chip and the compound semiconductor chip.

[0030] Furthermore, according to a preferred embodiment of the method for manufacturing an optical waveguide element of the present invention, the method comprises the steps of: preparing a silicon semiconductor chip having the cladding and the silicon waveguide core; preparing a compound semiconductor chip having a compound semiconductor thin film; directly bonding the silicon semiconductor chip and the compound semiconductor chip; and patterning the compound semiconductor thin film to obtain the compound semiconductor thin film waveguide. [Effects of the Invention]

[0031] According to the optical waveguide element and its manufacturing method of the present invention, the positional accuracy required when bonding a compound semiconductor waveguide including a light source and the like to a Si optical waveguide can be relaxed to about 2 μm or more. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 2 is a schematic diagram illustrating a first optical waveguide element. [Figure 2] 1 shows the results of the simulation. [Figure 3] Figure (2) shows the results of the simulation. [Figure 4] Figure (3) shows the results of the simulation. [Figure 5] FIG. 4 is a schematic diagram illustrating a second optical waveguide element. [Figure 6] FIG. 10 is a schematic diagram illustrating a third optical waveguide element. [Figure 7] FIG. 1 is a schematic diagram for explaining a compound semiconductor thin film waveguide having a rib waveguide structure. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and positional relationship of each component are merely shown in a schematic manner to enable understanding of the present invention. Furthermore, preferred configuration examples of the present invention will be described below. However, the materials and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many modifications and variations that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention. Note that, although some hatching is applied in the plan view, it should be understood that this does not represent a cross section, but is added to facilitate understanding of the invention.

[0034] In the following description, the direction perpendicular to the upper surface of the cladding is defined as the thickness direction, and the direction perpendicular to both the light propagation direction and the thickness direction is defined as the width direction.

[0035] (First optical waveguide element) An example of the configuration of an optical waveguide element (hereinafter also referred to as a first optical waveguide element) according to a first embodiment of the present invention will be described with reference to Fig. 1. Figs. 1(A) to 1(C) are schematic diagrams for explaining the first optical waveguide element. Fig. 1(A) is a schematic plan view of the first optical waveguide element. Figs. 1(B) and 1(C) are diagrams showing cut end faces of the first optical waveguide element taken along line AA and line BB, respectively.

[0036] The first optical waveguide element is configured to include a silicon semiconductor chip 10 and a compound semiconductor chip 20 provided on the upper surface of the silicon semiconductor chip 10.

[0037] The silicon semiconductor chip 10 comprises a support substrate 100, a cladding 200, and a silicon waveguide core 300. The silicon semiconductor chip 10 can be easily manufactured by a standard silicon photonics manufacturing method, for example, by using a commercially available SOI (Silicon On Insulator) substrate. In this case, the support substrate layer of the SOI substrate, which is formed by sequentially stacking a Si support substrate layer, an SiO2 layer, and a Si layer, serves as the support substrate 100. The SiO2 layer serves as the lower cladding.

[0038] The Si layer is patterned by dry etching or the like to form the silicon waveguide core 300 .

[0039] Then, SiO is deposited on the lower clad by a chemical vapor deposition (CVD) method or the like to form an upper clad. The upper clad is formed so as to cover the silicon waveguide core 300 or to the same height as the upper surface of the silicon waveguide core 300.

[0040] As a result, a silicon waveguide core 300 is obtained that is embedded in the clad 200 consisting of the lower clad and the upper clad, or is formed exposed on the upper surface of the clad 200 and extends parallel to the upper surface of the clad 200.

[0041] The silicon semiconductor chip 10 has an output port 310 at one end in the propagation direction of the silicon waveguide core 300, and an antireflection portion 320 at the other end. The output port 310 is used to connect the silicon waveguide core 300 to another Si optical waveguide circuit, for example, to extract light propagating through the silicon waveguide core 300 from the silicon semiconductor chip 10 and send it to another Si optical waveguide circuit. The antireflection portion 320 is provided to prevent light propagating through the silicon waveguide core 300 in the direction opposite to the direction toward the output port 310 from being reflected back toward the output port 310. The antireflection portion 320 can be configured, for example, with a tapered structure whose width gradually narrows along the propagation direction of the light sent from the silicon waveguide core 300 to the antireflection portion 320.

[0042] The compound semiconductor chip 20 is configured to include a compound semiconductor thin film waveguide 400 .

[0043] The silicon semiconductor chip 10 and the compound semiconductor chip 20 are bonded together so that the silicon waveguide core 300 and the compound semiconductor thin film waveguide 400 intersect obliquely. The bonding of the silicon semiconductor chip 10 and the compound semiconductor chip 20 is performed using, for example, CFB (Crystal Film Bonding) technology. In the CFB technology, the bonding of the silicon semiconductor chip 10 and the compound semiconductor chip 20 is performed using only the intermolecular forces acting between the chips, without using an adhesive or the like.

[0044] The compound semiconductor forming the compound semiconductor thin film waveguide 400 is, for example, InP. The compound semiconductor chip 20 may include a compound semiconductor element such as a laser diode (LD) or a semiconductor optical amplifier (SOA).

[0045] The compound semiconductor device can be fabricated by any suitable conventionally known fabrication method, for example, as a rib waveguide having a ridge portion and a terrace portion, and a tapered waveguide may be provided between the rib waveguide and the compound semiconductor thin film waveguide.

[0046] Here, an example will be described in which the compound semiconductor device is an LD, and the compound semiconductor chip 20 is configured to include a rib waveguide and a tapered waveguide. When the compound semiconductor device is an LD, the active layer of the LD uses, for example, InGaAsP as a quaternary material. In this case, the rib waveguide 600, tapered waveguide 500, and compound semiconductor thin film waveguide 400 are connected in this order.

[0047] The rib waveguide 600 is configured to include a ridge portion 610 and a terrace portion 620. The terrace portions 620 are provided on both sides of the ridge portion 610. The two terrace portions 620 are provided at positions sandwiching the ridge portion 610, and the ridge portion 610 and the two terrace portions 620 extend parallel to each other. The ridge portion 610 is configured by stacking a lower cladding layer 612, an active layer 614, and an upper cladding layer 616 in this order. The lower cladding layer 612 and the upper cladding layer 616 are made of, for example, InP, and the active layer 614 is made of, for example, InGaAsP. Furthermore, the position of the upper surface of the lower cladding layer 612 in the ridge portion 610 is higher than the position of the upper surface of the terrace portions 620.

[0048] The tapered waveguide 500 is configured to include a ridge portion 510 and a terrace portion 520. The cross-sectional shape of the ridge portion 510 of the tapered waveguide 500 is similar to the cross-sectional shape of the ridge portion 610 of the rib waveguide 600, and is configured by laminating a lower cladding layer, an active layer, and an upper cladding layer in this order. The thicknesses of the lower cladding layer, the active layer, and the upper cladding layer are equal to the thicknesses of the lower cladding layer 612, the active layer 614, and the upper cladding layer 616 of the rib waveguide 600, respectively. That is, the thicknesses of the ridge portions 610 and 510 of the rib waveguide 600 and the tapered waveguide 500 are equal to each other. Furthermore, the materials of the lower cladding layer, the active layer, and the upper cladding layer are equal to the materials of the lower cladding layer 612, the active layer 614, and the upper cladding layer 616 of the rib waveguide 600, respectively, and can be formed using the same process.

[0049] The terrace portion 620 of the rib waveguide 600, the terrace portion 520 of the tapered waveguide 500, and the compound semiconductor thin film waveguide 400 are made of the same compound semiconductor, InP in this example, and have the same thickness.

[0050] At the connecting end faces of the rib waveguide 600 and the tapered waveguide 500, the widths of the rib waveguide 600 and the tapered waveguide 500 are equal to each other, and the widths of the ridge portions 610 and 510 of the rib waveguide 600 and the tapered waveguide 500 are equal to each other.

[0051] In the tapered waveguide 500, the width of the ridge portion 510 gradually narrows from the rib waveguide 600 side toward the compound semiconductor thin film waveguide 400 side, and the ridge portion 510 disappears midway in the propagation direction. The width of the tapered waveguide 500 also gradually narrows from the width of the rib waveguide 600 at the connection end face of the rib waveguide 600 and the tapered waveguide 500 to the width of the compound semiconductor thin film waveguide 400 at the connection end face of the tapered waveguide 500 and the compound semiconductor thin film waveguide 400. At the connection end face of the tapered waveguide 500 and the compound semiconductor thin film waveguide 400, the widths of the tapered waveguide 500 and the compound semiconductor thin film waveguide 400 are equal to each other.

[0052] Oscillation (laser) light generated in the ridge portion 610 of the rib waveguide 600 propagates from the rib waveguide 600 to the tapered waveguide 500. In the tapered waveguide 500, the width of the ridge portion 510 narrows toward the compound semiconductor thin film waveguide 400, so that the light propagating through the active layer in the ridge portion 510 of the tapered waveguide 500 transfers to the lower cladding layer and terrace portion 520 of the ridge portion 510. The laser light that has transferred to the lower cladding layer and terrace portion 520 is sent to the compound semiconductor thin film waveguide 400 and propagates through the compound semiconductor thin film waveguide 400. The laser light propagating through the compound semiconductor thin film waveguide 400 interferes at the intersection with the Si waveguide core 300 and transfers to the Si waveguide core 300. The light that has moved to the Si waveguide core 300 propagates through the Si waveguide core 300 and is extracted from the output port 310 to the outside of the first optical waveguide element.

[0053] An antireflection portion 420 is provided at the end of the compound semiconductor thin film waveguide 400 opposite to the end connected to the tapered waveguide 500. The antireflection portion 420 can be formed, for example, by slanting the end face of the compound semiconductor thin film waveguide 400.

[0054] In this case, by appropriately setting the design conditions for the intersection between the compound semiconductor thin film waveguide 400 and the Si waveguide core 300, the amount of light that moves from the compound semiconductor thin film waveguide 400 to the Si waveguide core 300 can be maximized.

[0055] 1(C), the side surfaces of the terrace portions 620 of the rib waveguide 600 are provided in a direction perpendicular to the upper surface of the cladding 200, but this is not limiting. For example, the width of the rib waveguide 600 at the surface (bottom surface) on the silicon semiconductor chip 300 side may be wider than the width at a height corresponding to the upper surface of the terrace portions 620 of the rib waveguide 600, i.e., the side surfaces of the terrace portions 620 may be inclined.

[0056] Although the method for manufacturing the first optical waveguide element has been described as a method in which a silicon semiconductor chip 10 and a compound semiconductor chip 20 are prepared and then bonded together, it is also possible to manufacture the compound semiconductor thin film waveguide 400 and the terrace portion 520 of the tapered waveguide 500 with the same extremely wide width as the terrace portion 620 of the rib waveguide 600, and after bonding them together, pattern the terrace portion 520 of the tapered waveguide 500 and the compound semiconductor thin film waveguide 400 by etching. In this method, the width of the compound semiconductor thin film waveguide is wider when bonded together compared to the above-mentioned method, and therefore damage to the compound semiconductor thin film waveguide 400 during the bonding process can be prevented.

[0057] (Design conditions) Simulations obtained using the three-dimensional BPM (Beam Propagation Method) method will be described with reference to Figures 2 to 4. Figures 2 to 4 are diagrams showing the results of the simulations.

[0058] Here, the silicon waveguide core 300 and the compound semiconductor thin film waveguide 400 have the same width, and the width of the silicon waveguide core and the compound semiconductor thin film waveguide is referred to as the waveguide width. The equivalent refractive index is also made uniform by the thickness of the silicon waveguide core 300 and the compound semiconductor thin film waveguide 400. In this simulation, the thickness of the silicon waveguide core is 220 nm, and the thickness of the compound semiconductor thin film waveguide is 400 nm. The wavelength of the light is 1550 nm.

[0059] 2(A) shows the angular tolerance when there is no gap at the intersection of the silicon waveguide core and the compound semiconductor thin film waveguide, in other words, when the silicon waveguide core 300 is exposed on the top surface of the cladding 200.

[0060] In Figure 2(A), the horizontal axis represents the waveguide width (unit: nm) and the vertical axis represents the angular tolerance (unit: °). As shown in Figure 2(A), the narrower the waveguide width, the larger the angular tolerance. An angular tolerance of approximately 0.2° or more is preferable, and the waveguide width should be 1800 nm or less.

[0061] 2(B) shows the thickness and width tolerances when there is no gap at the intersection of the silicon waveguide core and the compound semiconductor thin film waveguide. In other words, it shows the thickness and width tolerances when the silicon waveguide core is exposed on the top surface of the cladding.

[0062] In FIG. 2(B), the horizontal axis represents the waveguide width (unit: nm), and the vertical axis represents the thickness and width tolerance (unit: nm).

[0063] The wider the waveguide width, the larger the width tolerance (InP width and Si width). When the waveguide width is 700 nm or more, the width tolerance of both the compound semiconductor thin film waveguide 400 and the silicon waveguide core 300 is 100 nm or more. On the other hand, the thickness tolerance (InP thickness and Si thickness) remains almost unchanged even when the waveguide width is wider.

[0064] The fewer parameters that need to be controlled during manufacturing, the better. To avoid the need for tighter control of the waveguide width, a width tolerance of 100 nm or better is required.

[0065] Therefore, from the viewpoint of width tolerance, it is preferable to set the waveguide width to 700 nm or more. Also, as mentioned above, from the viewpoint of angle tolerance, it is preferable to set the waveguide width to 1800 nm or less. Thus, it is preferable to set the waveguide width to 700 to 1800 nm.

[0066] Until now, it was not known that this diagonal cross structure would work in waveguides other than single-mode waveguides, but this invention has confirmed that the diagonal cross structure works in waveguides other than single-mode waveguides as well.

[0067] In a waveguide with an oblique crossing structure (crossing waveguide), when the waveguide width is W, the equivalent refractive index is n, and the wavelength is λ, the maximum crossing angle Θ is given by the following equation (1).

[0068]

number

[0069] From the above formula (1), it can be seen that the larger the waveguide width W, the smaller the maximum crossing angle Θ.

[0070] A larger crossing angle is preferable because it reduces the requirement for positional accuracy when attaching the compound semiconductor chip 20 including the compound semiconductor thin film waveguide 400 to the silicon semiconductor chip 10 including the Si waveguide core 300. However, if the crossing angle is too large, it becomes difficult for light to transfer from the compound semiconductor thin film waveguide 400 to the silicon waveguide core 300. On the other hand, if the crossing angle is too small, the number of interference orders increases, and the usable wavelength band becomes narrower due to wavelength dependency. For this reason, the crossing angle should be set within the range of 5° to 8°.

[0071] Fig. 3 shows the change in the output amount from the output port when the silicon waveguide core is misaligned in the width direction of the propagation direction. In Fig. 3, the horizontal axis shows the magnitude (unit: μm) of the misalignment in the width direction of the compound semiconductor thin film waveguide 400 with respect to the silicon waveguide core 300, and the vertical axis shows the output amount from the output port 310 as transmittance when the amount of light propagating through the compound semiconductor thin film waveguide 400 is set to 1.

[0072] As shown in Figure 3, it is clear that a transmittance of 90% or more can be ensured with a misalignment of up to 3 μm.

[0073] FIG. 4 is a diagram showing wavelength bands when the gap at the intersection of the silicon waveguide core and the compound semiconductor thin film waveguide is changed, that is, when the thickness of the cladding 200 on the silicon waveguide core 300 is changed.

[0074] In FIG. 4, the horizontal axis represents the gap (unit: nm) at the intersection of the silicon waveguide core 300 and the compound semiconductor thin film waveguide 400, the left axis represents the wavelength band (unit: nm), and the right axis represents the wavelength change coefficient with respect to the gap change.

[0075] In Figure 4, the maximum crossing angle Θ is used with the waveguide width W set to 1 μm. When the gap is 0 nm, the maximum crossing angle Θ is 14.5°, when the gap is 100 nm, the maximum crossing angle Θ is 12.8°, and when the gap is 200 nm, the maximum crossing angle Θ is 6.0°. The wavelength band is the full width band up to a 1 dB drop.

[0076] As shown in Figure 4, the larger the gap, the narrower the wavelength band. Therefore, it is best to set the gap to 200 nm or less, and more preferably 150 nm or less. Note that a gap smaller than 100 nm results in operation similar to that of a single-layer cross waveguide, while a gap larger than 100 nm results in operation similar to that of a directional coupler.

[0077] The change in optical output due to the gap deviation Δg from the design value in the vicinity of the design wavelength λ is given by the following equation (2), where m is the interference order.

[0078]

number

[0079] where (dλ / dg) is the wavelength change coefficient for gap fluctuation, Δn is the equivalent refractive index difference between the even and odd modes, and Δng is the group refractive index difference between the even and odd modes.

[0080] The gap dependency of this wavelength change coefficient is also shown in Figure 4. The larger the gap, the smaller the wavelength change coefficient becomes. In other words, there is a trade-off between the wavelength change coefficient and the wavelength band.

[0081] On the other hand, the wavelength band Δλr is given by the following equation (3) with respect to the reduction rate d from the peak using a similar calculation.

[0082]

number

[0083] In both of the above equations (2) and (3), it is preferable that the interference order m is as small as 1.

[0084] In these formulas (2) and (3), if d is common, Δg=Δλr / (dλ / dg) becomes the deviation tolerance.

[0085] As shown in Figure 4, the larger the gap, the more resistant it is to deviations from the design value, but a value around 150 nm is a good value due to the trade-off with the wavelength band. Although we evaluated gap changes here, the tolerance values ​​Δw and Δh for the waveguide width (w) and thickness (h) can also be calculated from Δλr using dλ / dw and dλ / dh obtained from the simulation.

[0086] (Second optical waveguide element) An example of the configuration of an optical waveguide element according to a second embodiment of the present invention (hereinafter also referred to as a second optical waveguide element) will be described with reference to Fig. 5. Fig. 5 is a schematic diagram for explaining the second optical waveguide element. Fig. 5 is a schematic plan view of the second optical waveguide element.

[0087] The second optical waveguide element differs from the first optical waveguide element in the configuration of the compound semiconductor chip, whereas the configuration of the silicon semiconductor chip is the same as that of the first optical waveguide element, and therefore a redundant description will be omitted.

[0088] In the second optical waveguide element, the compound semiconductor chip includes a compound semiconductor thin film waveguide 400, a tapered waveguide 500, and a rib waveguide 602, as well as a holding waveguide 630 and a connecting waveguide 640.

[0089] The holding waveguide 630 and the connecting waveguide 640 are formed of the same material and thickness as, for example, the compound semiconductor thin film waveguide 400, the tapered waveguide 500, and the terrace portions 520 and 622 of the rib waveguide 602.

[0090] The holding waveguide 630 is disposed parallel to the extending directions of the compound semiconductor thin film waveguide 400, the tapered waveguide 500, and the rib waveguide 602. The holding waveguide 630 is connected to the end of the compound semiconductor thin film waveguide 400 opposite to the end connected to the tapered waveguide 500 by a connecting waveguide 640. In addition, the terrace portion 622 of the rib waveguide 602 is connected to the holding waveguide 630. According to this second optical waveguide element, the compound semiconductor thin film waveguide 400 is held by the holding waveguide 630 and the connecting waveguide 640, thereby increasing the strength.

[0091] (Third optical waveguide element) An example of the configuration of an optical waveguide element according to a third embodiment of the present invention (hereinafter also referred to as a third optical waveguide element) will be described with reference to Fig. 6. Fig. 6 is a schematic diagram for explaining the third optical waveguide element. Fig. 6 is a schematic plan view of the third optical waveguide element, showing only the waveguide cores, omitting a support substrate and a lower cladding, which will be described later.

[0092] The third optical waveguide element includes two first optical waveguide elements, one of which is rotated by 180° relative to the other first optical waveguide element in a plane parallel to the upper surface of the clad, and the rib waveguides are then coupled together. In this case, the compound semiconductor element is, for example, an SOA.

[0093] Specifically, the waveguide includes a first silicon waveguide core 301 and a second silicon waveguide core 302 as silicon waveguide cores, a first compound semiconductor thin film waveguide 401 and a second compound semiconductor thin film waveguide 402 as compound semiconductor thin film waveguides, and a first tapered waveguide 501 and a second tapered waveguide 502 as tapered waveguides.

[0094] The compound semiconductor chip is configured by connecting a first compound semiconductor thin film waveguide 401, a first tapered waveguide 501, a rib waveguide 600, a second tapered waveguide 502, and a second compound semiconductor thin film waveguide 402 in this order.

[0095] The relationship between the first silicon waveguide core 301, the first compound semiconductor thin film waveguide 401, the first tapered waveguide 501, and the rib waveguide 600 is the same as that in the first optical waveguide element. The relationship between the second silicon waveguide core 302, the second compound semiconductor thin film waveguide 402, the second tapered waveguide 502, and the rib waveguide 600 is also the same as that in the first optical waveguide element.

[0096] An input port 311 is connected to the first silicon waveguide core 301. An output port 312 is connected to the second silicon waveguide core 302. The input port 311 and the output port 312 are ports used to connect to an external silicon optical waveguide circuit and are configured similarly. Therefore, the third optical waveguide element is point-symmetric with respect to the center point in a plane parallel to the upper surface of the cladding of the rib waveguide.

[0097] In the third optical waveguide element, light input from the input port 311 propagates through the first silicon optical waveguide core 301 and transitions to the first compound semiconductor thin film waveguide 401 at the intersection. The light that transitions to the first compound semiconductor thin film waveguide 401 passes through the first tapered waveguide 501 and is amplified in the rib waveguide 600. The light amplified in the rib waveguide 600 propagates through the second tapered waveguide 502 to the second compound semiconductor thin film waveguide 402. The light sent to the second compound semiconductor thin film waveguide 402 transitions to the second silicon optical waveguide core 302 at the intersection. The light that transitions to the second silicon optical waveguide core 302 propagates through the second silicon optical waveguide core 302 and is output from the output port 312.

[0098] For example, in the first optical waveguide element described with reference to FIG. 1, when a positional deviation occurs in the width direction of the compound semiconductor thin film waveguide 400, the propagation distance through the silicon optical waveguide core 300 becomes shorter while the propagation distance through the compound semiconductor thin film waveguide 400 becomes longer, or conversely, the propagation distance through the silicon optical waveguide 300 becomes longer while the propagation distance through the compound semiconductor thin film waveguide 400 becomes shorter, resulting in a change in the optical path length.

[0099] In contrast to this, in the third optical waveguide element, when a positional deviation occurs in the width direction of the compound semiconductor thin film waveguide, if the propagation distance through first silicon optical waveguide core 301 becomes shorter, the propagation distance through second silicon optical waveguide core 302 becomes longer accordingly, and conversely, if the propagation distance through first silicon optical waveguide core 301 becomes longer, the propagation distance through second silicon optical waveguide core 302 becomes shorter accordingly. Similarly, when a positional deviation occurs in the width direction of the compound semiconductor thin film waveguide, if the propagation distance through first compound semiconductor thin film waveguide 401 becomes shorter, the propagation distance through second compound semiconductor thin film waveguide 402 becomes longer accordingly, and conversely, if the propagation distance through first compound semiconductor thin film waveguide 401 becomes longer, the propagation distance through second compound semiconductor thin film waveguide 402 becomes shorter accordingly.

[0100] In this way, even if a positional deviation occurs in the width direction of the compound semiconductor thin film waveguide, there is no change in the optical path length from the input port 301 to the output port 302. As a result, the third optical waveguide element can realize a structure with higher positional tolerance.

[0101] Although the third optical waveguide element has been described here as incorporating two first optical waveguide elements, it may also be configured using a second optical waveguide element.

[0102] Although the compound semiconductor thin film waveguides 400 to 402 included in the first to third optical waveguide elements are wire-type in the above example, the present invention is not limited to this. The compound semiconductor thin film waveguides may have a rib waveguide structure having ridge portions and terrace portions.

[0103] Fig. 7 is a schematic diagram for explaining a compound semiconductor thin film waveguide with a rib waveguide structure, which corresponds to Fig. 1(B) and shows a cut end surface of the compound semiconductor thin film waveguide with a rib waveguide structure.

[0104] 1 serves as the ridge portion, and on both sides of the ridge portion are provided 200-nm-thick InP layers as terrace portions 405. The terrace portions 405 function as supports for the ridge portion 400, which is more preferable because it increases the strength.

[0105] For example, when the width of the ridge portion 400 of the compound semiconductor thin film waveguide is 1000 nm and the terrace portion 405 is provided, the optimum crossing angle between the ridge portion 400 of the compound semiconductor thin film waveguide and the silicon waveguide core 300 is 7 degrees. At this time, the loss increases by about 0.5 dB. Note that, because the transition to higher-order modes in the silicon waveguide core 300 becomes dominant, when the width of the ridge portion 400 of the compound semiconductor thin film waveguide is 1800 nm or more, the characteristics are not suitable for use.

[0106] Here, an example has been described in which the compound semiconductor thin film waveguide of the first optical waveguide element has a rib waveguide structure, but the compound semiconductor thin film waveguides of the second and third optical waveguide elements can also have a rib waveguide structure. [Explanation of symbols]

[0107] 10 Silicon semiconductor chip 20 Compound semiconductor chips 100 Support substrate 200 Clad 300, 301, 302 Silicon waveguide core 310, 312 output ports 311 input port 320, 420 Anti-reflection section 400, 401, 402 Compound semiconductor thin film waveguide 405, 520, 620, 622 terrace area 500, 501, 502 Tapered waveguide 510, 610 ridge part 600, 602 Rib waveguide 612 Lower cladding layer 614 Active layer 616 Upper cladding layer 630 Holding Waveguide 640 Connected Waveguide

Claims

1. Clad and a silicon waveguide core that is embedded in the cladding or is formed exposed on an upper surface of the cladding and extends parallel to the upper surface of the cladding; a compound semiconductor thin film waveguide on the upper surface of the cladding, the compound semiconductor thin film waveguide diagonally intersecting the silicon waveguide core; Equipped with The width of the silicon waveguide core, which is the length in a direction perpendicular to both the thickness direction perpendicular to the upper surface of the cladding and the direction in which the silicon waveguide core extends, is 700 nm or more. Optical waveguide element.

2. The width of the silicon waveguide core is 1800 nm or less. The optical waveguide element according to claim 1 .

3. The equivalent refractive index of the compound semiconductor thin film waveguide is equal to the equivalent refractive index of the silicon waveguide core. The optical waveguide element according to claim 1 .

4. The width of the compound semiconductor thin film waveguide, which is the length in a direction perpendicular to both the thickness direction perpendicular to the upper surface of the cladding and the direction in which the compound semiconductor thin film waveguide extends, is equal to the width of the silicon waveguide core. The optical waveguide element according to claim 3 .

5. The compound semiconductor constituting the compound semiconductor thin film waveguide is InP. The optical waveguide element according to claim 1 .

6. The distance between the silicon waveguide core and the compound semiconductor thin film waveguide in the direction perpendicular to the upper surface of the cladding is 100 nm or more and 200 nm or less. The optical waveguide element according to claim 1 .

7. The silicon waveguide core and the compound semiconductor thin film waveguide intersect at an angle in the range of 5 to 8 degrees in the extending direction. The optical waveguide element according to claim 1 .

8. The optical waveguide further includes a rib waveguide and a tapered waveguide, each of which includes a ridge portion and a terrace portion; the rib waveguide, the tapered waveguide, and the compound semiconductor thin film waveguide are connected in this order; the thicknesses of the rib waveguide and the ridge portions of the tapered waveguide are equal to each other; the thickness of the terrace portions of the rib waveguide and the tapered waveguide is equal to the thickness of the compound semiconductor thin film waveguide; At the connection end faces of the rib waveguide and the tapered waveguide, the widths of the rib waveguide and the tapered waveguide are equal to each other, and the widths of the ridge portions of the rib waveguide and the tapered waveguide are equal to each other; a width of a ridge portion of the tapered waveguide gradually narrows toward the compound semiconductor thin film waveguide, and at a connection end face of the tapered waveguide and the compound semiconductor thin film waveguide, the tapered waveguide consists of only a terrace portion; The widths of the tapered waveguide and the compound semiconductor thin film waveguide at the connection end faces of the tapered waveguide and the compound semiconductor thin film waveguide are equal to each other. The optical waveguide element according to claim 1 .

9. the compound semiconductor constituting the compound semiconductor thin film waveguide and the terrace portions of the rib waveguide and the tapered waveguide is InP; The rib waveguide has an active layer made of InGaAsP as a quaternary material. The optical waveguide element according to claim 8 .

10. moreover, A holding waveguide and a connecting waveguide formed of the same material and with the same thickness as the terrace portion of the compound semiconductor thin film waveguide, tapered waveguide, and rib waveguide. Equipped with the holding waveguide is arranged in parallel to the extending direction of the compound semiconductor thin film waveguide, the tapered waveguide, and the rib waveguide; an end of the compound semiconductor thin film waveguide opposite to an end connected to the tapered waveguide is connected to the holding waveguide via the connecting waveguide; The terrace portion of the rib waveguide and the holding waveguide are connected. The optical waveguide element according to claim 8 .

11. Clad and a first silicon waveguide core and a second silicon waveguide core, which are embedded in the clad or formed exposed on an upper surface of the clad, extend parallel to the upper surface of the clad, and are parallel to each other; Equipped with a first compound semiconductor thin film waveguide obliquely intersecting the first silicon waveguide core, a first tapered waveguide, a rib waveguide, a second tapered waveguide, and a second compound semiconductor thin film waveguide obliquely intersecting the second silicon waveguide core, in this order, on an upper surface of the cladding; the first tapered waveguide, the rib waveguide, and the second tapered waveguide each include a ridge portion and a terrace portion; the thicknesses of the ridge portions of the first tapered waveguide, the rib waveguide, and the second tapered waveguide are equal to one another; the first compound semiconductor thin film waveguide, the terrace portion of the first tapered waveguide, the terrace portion of the rib waveguide, the terrace portion of the second tapered waveguide, and the second compound semiconductor thin film waveguide have the same thickness; At a connection end face between the rib waveguide and the first tapered waveguide, the widths of the rib waveguide and the first tapered waveguide are equal to each other, and the widths of ridge portions of the rib waveguide and the first tapered waveguide are equal to each other; At a connection end face between the rib waveguide and the second tapered waveguide, the widths of the rib waveguide and the second tapered waveguide are equal to each other, and the widths of the ridge portions of the rib waveguide and the second tapered waveguide are equal to each other; a width of a ridge portion of the first tapered waveguide gradually narrows toward the first compound semiconductor thin film waveguide, and the first tapered waveguide has only a terrace portion at a connection end face between the first tapered waveguide and the first compound semiconductor thin film waveguide; a width of a ridge portion of the second tapered waveguide gradually narrows toward the second compound semiconductor thin film waveguide, and the second tapered waveguide has only a terrace portion at a connection end face between the second tapered waveguide and the second compound semiconductor thin film waveguide; the widths of the first tapered waveguide and the first compound semiconductor thin film waveguide are equal to each other at a connection end face of the first tapered waveguide and the first compound semiconductor thin film waveguide; the widths of the second tapered waveguide and the second compound semiconductor thin film waveguide are equal to each other at a connection end face of the second tapered waveguide and the second compound semiconductor thin film waveguide; The width of the first and second silicon waveguide cores, which is the length in a direction perpendicular to both a thickness direction perpendicular to the upper surface of the cladding and a direction in which the first and second silicon waveguide cores extend, is 700 nm or more. Optical waveguide element.

12. A method for producing the optical waveguide element according to any one of claims 1 to 11, comprising: providing a silicon semiconductor chip having the cladding and the silicon waveguide core; preparing a compound semiconductor chip having the compound semiconductor thin film waveguide; a step of directly bonding the silicon semiconductor chip and the compound semiconductor chip; A method for manufacturing an optical waveguide element comprising:

13. A method for producing the optical waveguide element according to any one of claims 1 to 11, comprising: providing a silicon semiconductor chip having the cladding and the silicon waveguide core; providing a compound semiconductor chip having a compound semiconductor thin film; a step of directly bonding the silicon semiconductor chip and the compound semiconductor chip; a step of patterning the compound semiconductor thin film to obtain the compound semiconductor thin film waveguide; A method for manufacturing an optical waveguide element comprising:

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