HYBRID OPTICAL ELEMENT AND METHOD FOR PRODUCING HYBRID OPTICAL ELEMENT - Patent application

Abstract

A hybrid optical element according to the present disclosure comprises, sequentially from the surface layer: a p-InP (7); a light-absorbing layer (9); an n-InP (6); a dielectric thin film (10); an optical waveguide (8); a BOX layer (11); and a core substrate (12). The n-InP (6) has a first taper (1). The light-absorbing layer (9) has a second taper (2). The light-absorbing layer (9) is exposed in the second taper (2). The p-InP (7) is equipped with a modulation unit (15). A third taper (3) is provided between the second taper (2) and the modulation unit (15). The second taper (2) is not provided to the p-InP (7). Light absorption is restricted to the vicinity of a p-electrode (5). The third taper (3) has a taper length that is 5 percent or less of the length of the modulation unit (15).

Description

[Technical field]

[0001] The disclosed technology relates to hybrid optical devices. [Background technology]

[0002] Hybrid optical elements are known that are made by integrating highly efficient optical devices on a silicon waveguide. The term "hybrid" in hybrid optical elements is synonymous with that used in "hybrid IC" and "hybrid integrated circuit," and is used as the opposite of "monolithic." Hybrid optical devices are used, for example, as devices for optical Ethernet communication. More specifically, hybrid optical devices are used, for example, as communication devices for transmission methods such as Non-Return-to-Zero (NRZ) or Pulse Amplitude Modulation (PAM).

[0003] Highly efficient optical devices are realized, for example, by compound semiconductors. A silicon waveguide and a compound semiconductor waveguide are connected by an adiabatic transition using a taper. The compound semiconductor has an n-type semiconductor on the bottom and a p-type semiconductor on the top, forming a pn junction. There are two types of tapers: one where the n-type semiconductor is exposed on the surface (hereinafter referred to as the "first taper"), and one where the p-type semiconductor is exposed on the surface (hereinafter referred to as the "second taper").

[0004] For example, Patent Document 1 discloses a hybrid optical device having a structure that improves the electrical resistance in a light source device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-140319 A Summary of the Invention [Problem to be solved by the invention]

[0006] Hybrid optical elements are applied, for example, to electroabsorption modulators (also called EA modulators). When applied to EA modulators, the tip of the second taper of the hybrid optical element is easily coupled to the TM mode reflecting the vertically long waveguide shape, and in many cases, a transition is obtained as follows: (1) TE [Si waveguide] ⇒ (2) TM [taper tip] ⇒ (3) TE [taper base] ⇒ TE [EA modulator]. For this reason, in order to obtain sufficient coupling, the taper becomes long, and the device becomes large. Note that the above TE and TM respectively represent the propagation modes of electromagnetic waves.

[0007] When applying a hybrid optical element to a high-speed modulation element such as an EA modulator, the area of ​​the modulator needs to be as small as possible in order to reduce the parasitic capacitance (also called floating capacitance or stray capacitance). An increase in the parasitic capacitance degrades the high-frequency characteristics of the device. On the other hand, if the area of ​​the modulator is reduced, the taper length becomes shorter, and the above coupling cannot be obtained. Furthermore, in the EA modulator, the modulation bias is applied to the taper section, which causes unintended optical absorption in the taper section, resulting in insertion loss. For this reason, the taper length must be designed taking into consideration the trade-off between sufficient coupling and reduced parasitic capacitance.

[0008] The disclosed technology aims to solve the above trade-off problem, and shortens the taper while ensuring sufficient coupling in a hybrid optical element, thereby realizing a reduction in parasitic capacitance. [Means for solving the problem]

[0009] The hybrid optical element according to the disclosed technique comprises, in order from the surface, p-InP, an optical absorption layer, n-InP, a dielectric thin film, an optical waveguide, a BOX layer, and a core substrate, the n-InP having a first taper, the optical absorption layer having a second taper, the optical absorption layer being exposed at the second taper, the p-InP having a modulation section, and between the second taper and the modulation section: Formed in p-InPThe third taper is provided, the second taper is not provided on the p-InP, the light absorption is limited to the vicinity of the p-electrode, and the taper length of the third taper relative to the length of the modulation section is 5% or less. Effect of the Invention

[0010] Since the hybrid optical element according to the disclosed technique has the above-described configuration, the taper is shortened while ensuring sufficient coupling, and thus the parasitic capacitance is reduced. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a structural diagram of a hybrid optical device according to the first embodiment. [Diagram 2] FIG. 2 is a first explanatory diagram showing a bonding process which is a part of the production process of the hybrid optical element according to the first embodiment. [Diagram 3] FIG. 3 is a second explanatory diagram showing the bonding process which is a part of the production process of the hybrid optical element according to the first embodiment. [Figure 4] FIG. 4 is a graph showing a state of propagation mode transition occurring in the hybrid optical device according to the first embodiment. [Diagram 5] FIG. 5 is a structural diagram of a conventional hybrid optical element applied to an EA modulator. [Figure 6] FIG. 6 is a graph showing the state of propagation mode transition occurring in a conventional hybrid optical element. [Figure 7] FIG. 7 is a graph showing the coupling efficiency of a hybrid optical device according to the disclosed technique compared to the prior art. [Figure 8] FIG. 8 is a structural diagram of a hybrid optical device according to the second embodiment. [Figure 9] FIG. 9 is a graph showing a state of propagation mode transition occurring in the hybrid optical device according to the second embodiment. [Figure 10] FIG. 10 is a structural diagram of a hybrid optical device according to the third embodiment. [Figure 11]FIG. 11 is a structural diagram of a hybrid optical device according to the seventh embodiment. [Figure 12] FIG. 12 is a graph showing the coupling efficiency of the hybrid optical element according to the first embodiment and the coupling efficiency of the hybrid optical element according to the seventh embodiment in comparison with the conventional techniques. [Figure 13] FIG. 13 is a graph showing the relationship between the taper length of the second taper 2-2 and the coupling efficiency in the hybrid optical device according to the seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The hybrid optical element according to the present disclosure is applied as an EA modulator.

[0013] Embodiment 1 FIG. 1 is a structural diagram (perspective view) of a hybrid optical element according to the first embodiment.

[0014] As shown in FIG. 1, the hybrid optical device of the first embodiment includes an n-electrode 4, a p-electrode 5, an n-InP layer 6s, a p-InP layer 7s, an optical waveguide 8, a light absorption layer 9, a dielectric thin film 10, a BOX layer 11, and a core substrate 12. A first taper 1 is formed in the n-InP 6. Furthermore, a second taper 2 is formed in the light absorption layer 9.

[0015] The optical waveguide 8 utilizes the difference in refractive index. The optical waveguide 8 utilizes the property that light is localized and propagates in a region with a high refractive index, such as silicon. The optical waveguide 8 may be a Si waveguide or a SiN waveguide. In the hybrid optical device according to the first embodiment, the optical waveguide 8 is a Si waveguide. An example in which the optical waveguide 8 is a SiN waveguide will be described in the fifth embodiment.

[0016] <Production process of hybrid optical elements> The raw materials of the hybrid optical device include a silicon photonics substrate 14 and an InP epitaxial substrate 13 . The silicon photonics substrate 14 has a waveguide structure with the dielectric thin film 10 as the outermost layer. The dielectric material in the dielectric thin film 10 is generally SiO2 or Al2O3. In this specification, the dielectric thin film 10 is assumed to be a SiO2 thin film. The InP epitaxial substrate 13 is produced by a process in which a layer structure including the light absorbing layer 9 is formed by epitaxial growth on an n-InP substrate.

[0017] The manufacturing process of the hybrid optical device includes a bonding process between the silicon photonics substrate 14 and the InP epitaxial substrate 13. The silicon photonics substrate 14 and the InP epitaxial substrate 13 are bonded together by wafer bonding using a surface activated bonding technique. In principle, the bonding surface between the silicon photonics substrate 14 and the InP epitaxial substrate 13 is the dielectric thin film 10 (SiO2 thin film) and the n-InP layer 6s. Alternatively, by depositing SiO2 on the n-InP6 side, the bonding surface can be made to be SiO2-SiO2 between the dielectric thin film 10 (SiO2 thin film) and the SiO2 deposited on the n-InP6. The substrate obtained by bonding the silicon photonics substrate 14 and the InP epitaxial substrate 13 is called a hybrid substrate.

[0018] Fig. 2 is a first explanatory diagram showing a bonding process which is a part of the production process of the hybrid optical element according to the embodiment 1. As shown in Fig. 2, the bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 may be a mode in which circular substrates are bonded to each other.

[0019] 3 is a second explanatory diagram showing a bonding process which is a part of the production process of the hybrid optical element according to the embodiment 1. As shown in FIG. 3, the bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 may be performed by bonding an InP epitaxial substrate piece 13p, which is obtained by fragmenting the InP epitaxial substrate 13, onto the silicon photonics substrate 14.

[0020] The dielectric thin film 10 in the silicon photonics substrate 14 preferably has a thickness of 300 nm or less. By making the thickness 300 nm or less, optical coupling between the optical waveguide 8 and the light absorption layer 9 can be easily obtained.

[0021] The InP epitaxial substrate 13 is produced by epitaxially growing an n-InP buffer layer, an optical absorption layer 9, and a p-InP layer 7s on an n-InP substrate. In the epitaxial growth for producing the InP epitaxial substrate 13, a layer structure on the order of several μm is generated. The thickness of the n-InP substrate is approximately 300 μm to 1 mm, depending on the diameter of the substrate.

[0022] In either the n-InP layer 6s or the p-InP layer 7s formed by epitaxial growth, a mixed crystal material such as GaInAs, AlInAs, InGaAlAs, or GaInAsP may be inserted. The mixed crystal material is inserted for the purpose of confining carriers generated by photocurrent, reducing contact resistance with a metal electrode, forming an etch stop layer required in the processing process, etc. In the semiconductor field, GaInAs is often called indium gallium arsenide (InGaAs). GaInAs is a ternary alloy (compound) of indium arsenide (InAs) and gallium arsenide (GaAs). Indium arsenide (InAs) and gallium arsenide (GaAs) are both 3-5 (ローマ数字) It is a group compound semiconductor.

[0023] The light absorbing layer 9 has a quantum well structure. A quantum well means a state in which the direction of movement of particles such as electrons is restricted. The light absorbing layer 9 is designed to absorb light in the 1.3 [μm] wavelength band or the 1.55 [μm] wavelength band due to the quantum Stark effect when an electric field is applied. For the quantum well, a mixed crystal material such as InGaAlAs or GaInAsP is used.

[0024] The manufacturing process of hybrid optical elements includes a semiconductor process for forming a device structure on a hybrid substrate. In general, the process for forming a device structure can be said to be a process for forming a large number of transistors and wiring on a semiconductor chip to arrange an electric circuit. This process is carried out after the "process for designing wiring circuits," which is a pre-process of semiconductor manufacturing. One example of the process for forming a device structure is to use a computer to draw a pattern on a master plate called a photomask, and then transfer this onto a semiconductor wafer to form a circuit. In the manufacturing process of the hybrid optical element according to the disclosed technique, first, most of the n-InP layer 6s, which is the outermost layer of the hybrid substrate, is removed by etching, and thinned to a thickness of several hundred μm to several μm. Then, using lithography and dry etching techniques, the tapered structure shown in FIG. 1 is formed.

[0025] Regarding the thickness of the layers, for example, the thickness of the n-InP 6 is 200 [nm], the thickness of the light absorption layer 9 is 500 [nm], and the thickness of the p-InP 7 is 2 [μm]. The thickness of the n-InP 6 needs to be thin so as to obtain optical coupling between the optical waveguide 8 and the light absorption layer 9. If the thickness of the n-InP 6 exceeds approximately 300 nm, the optical coupling weakens and the taper length required for the transition of the propagation mode becomes significantly long. It is essential that the p-InP 7 has a sufficient thickness so that the propagation mode does not reach the p-electrode 5 and cause optical loss.

[0026] The first taper 1 is processed so that the n-InP 6 is exposed on the surface, and the second taper 2 is processed so that the light absorbing layer 9 is exposed on the surface. The light absorbing layer 9 is made of a ternary or quaternary mixed crystal having a higher refractive index than the n-InP 6. Since it is problematic for the n-InP layer 6s and the light absorbing layer 9 to be exposed to the atmosphere during the taper processing, they may be covered with a very thin InP protective layer of 100 nm or less.

[0027] In the hybrid optical element formed by the above process, the effective refractive index difference between the optical waveguide 8 and the tip of the second taper 2 is small. Therefore, the first taper 1 is capable of adiabatic transition over a very short distance. In the hybrid optical element according to the present disclosure, the taper length of the first taper 1 can be set to 10 μm.

[0028] The longer the length of the modulation section 15 in the p-InP layer 7s, the higher the extinction ratio becomes, but if it is too long, the parasitic capacitance increases and the operating band decreases. The length of the modulation section 15 also poses a trade-off between the extinction ratio and the parasitic capacitance. If the hybrid optical element is used as a device for 53GBaud PAM4, which is the current mainstream optical Ethernet communication method, the length of the modulation section 15 may be approximately 200[μm]. If the hybrid optical element is used as a device for 106GBaud PAM4, which is the next-generation optical Ethernet communication method, the operating band is doubled and the length of the modulation section 15 is suitable to be approximately 100[μm]. Note that PAM4 is an abbreviation for 4-level Pulse-Amplitude Modulation, which means four-value pulse amplitude modulation. More specifically, PAM4 is a method of transmitting four-value pulse signals instead of the conventional binary bit string consisting of "0" and "1".

[0029] <<About the operation or behavior of light in hybrid optical devices>> The input light to the hybrid optical element propagates in the optical waveguide 8 in the TE mode. TE is an abbreviation for Transverse Electric. The TE mode is a term that indicates the state when no electric field exists in the transmission direction. In this specification, the mode in which the input light propagates in the optical waveguide 8 is referred to as the "TE fundamental mode." Also, in this specification, the TE mode for the light absorption layer 9 is referred to as the "TE fundamental mode," and the two are distinguished from each other. The propagating light reaches the modulation section 15 via the first taper 1 and the second taper 2 .

[0030] A reverse bias is applied between the p-electrode 5 and the n-electrode 4. When a reverse bias is applied, light absorption occurs in the light absorbing layer 9 due to the quantum confined Stark effect (also simply called the "quantum Stark effect"). The Stark effect is a phenomenon in which the spectrum changes when a uniform external electric field is applied to an atom or molecule. By changing the magnitude of the reverse bias, it is possible to change the amount of light absorption in the modulation section 15. By utilizing this property, the hybrid optical element according to the disclosed technique is capable of performing light intensity modulation such as NRZ or PAM.

[0031] It is believed that light absorption occurs only in the region containing the p-InP 7. The light that has passed through the modulation section 15 passes through the tapered structure again and returns to the optical waveguide 8.

[0032] Fig. 4 is a graph showing the state of the propagation mode transition occurring in the hybrid optical element according to the embodiment 1. In the graph shown in Fig. 4, the horizontal axis represents the position, and the vertical axis represents the effective refractive index. The effective refractive index is also called the effective refractive index. The graph in Figure 4 is the result of performing a mode analysis on the cross section of the waveguide shown in Figure 1. The top five modes with the highest effective refractive index are shown in the graph in Figure 4. The mode with the highest effective refractive index, indicated by the thick solid curve, is the dominant mode. 4, as a result of the mode analysis, the mode crossing occurring in the second taper 2 of the hybrid optical device according to the first embodiment is only one place indicated as “mode crossing 1.” Here, the mode crossing refers to a phenomenon in which two propagation modes have the same propagation constant at the same wavelength.

[0033] The light propagating through the optical waveguide 8 in the TE fundamental mode intersects with the TE fundamental mode of the light absorption layer 9 in the second taper 2 and undergoes mode conversion. This mode conversion is an adiabatic behavior.

[0034] The technical feature of the hybrid optical element according to the first embodiment is that the optical absorption layer 9 is exposed in the second taper 2. FIG. 5 is a structural diagram (perspective view) of a conventional hybrid optical element applied to an EA modulator. By comparing FIG. 1 (first embodiment) with FIG. 5 (conventional), the technical feature of the hybrid optical element according to the first embodiment becomes clear. In other words, the technical feature of the hybrid optical element according to the first embodiment is that p-InP is not present in the second taper 2.

[0035] FIG. 6 is a graph showing the state of propagation mode transition occurring in a conventional hybrid optical element. 6, the mode analysis results show that there are two mode crossings in the taper section (corresponding to the second taper 2) of the hybrid optical element according to the conventional technology: a location marked "mode crossing 1" and a location marked "mode crossing 2." In other words, in the conventional hybrid optical element, two mode conversions occur via the TM mode. The reason why two mode conversions occur in the hybrid optical element according to the conventional technology is believed to be that the electric field distribution of the TM mode is easily affected in the thickness direction, the TM fundamental mode of the optical absorption layer becomes stronger near the taper tip due to the influence of p-InP, and the effective refractive index becomes higher than that of the TE fundamental mode of the optical absorption layer.

[0036] Due to the above technical features, the hybrid optical element according to the first embodiment keeps the effective refractive index of the TM fundamental mode low near the taper tip. Due to this effect, in the hybrid optical element according to the first embodiment, no mode crossing occurs between the propagating mode and the TM fundamental mode. The technical features of the present disclosure compared to the prior art are as shown in the table below. TIFF0007646097000001.tif67166

[0037] FIG. 7 is a graph showing the coupling efficiency (simulation result) of the hybrid optical element according to the disclosed technology compared with the conventional technology. In the graph shown in FIG. 7, the horizontal axis represents the taper length of the second taper 2, and the vertical axis represents the coupling efficiency. In the graph shown in FIG. 7, the simulation result of the hybrid optical element according to the first embodiment is shown by a solid curve, and the simulation result of the hybrid optical element according to the conventional structure is shown by a dashed curve. As shown in FIG. 7, in the hybrid optical element according to the disclosed technology, the taper length for obtaining sufficient coupling is shorter than that of the conventional technology. More specifically, in the simulation shown in FIG. 7, the taper length for obtaining a coupling efficiency of 80[%] is so short that it is approximately 1 / 3 of that of the conventional technology.

[0038] The hybrid optical element according to the first embodiment functions as an EA modulator, and transition of the mode is achieved from the optical waveguide 8 to the optical absorption layer 9 by an adiabatic transition type optical coupler having a tapered shape.

[0039] As described above, the hybrid optical element according to the first embodiment has the above technical features, and therefore has the effect of shortening the taper and reducing the parasitic capacitance while ensuring sufficient coupling.

[0040] Embodiment 2 The hybrid optical element according to the second embodiment is a modified example of the hybrid optical element according to the present disclosure. Unless otherwise specified, the same reference numerals as those used in the first embodiment are used in the second embodiment. Furthermore, in the second embodiment, descriptions that overlap with those in the first embodiment are omitted as appropriate.

[0041] Fig. 8 is a structural diagram (perspective view) of a hybrid optical element according to embodiment 2. As shown in Fig. 8, the hybrid optical element according to embodiment 2 includes a very short third taper 3 between the second taper 2 and the modulation section 15 in the p-InP layer 7s.

[0042] FIG. 9 is a graph showing a state of propagation mode transition occurring in the hybrid optical device according to the second embodiment. As can be seen from Fig. 9 (embodiment 2) in comparison with Fig. 4 (embodiment 1), in the hybrid optical element according to embodiment 2, the discontinuous and sudden change in the effective refractive index that occurred at the boundary between the second taper 2 and the modulation section 15 has become a continuous and gradual change. The property shown in Fig. 9 is the result of the provision of a very short third taper 3 between the second taper 2 and the modulation section 15, so that the presence or absence of p-InP does not occur suddenly along the optical path.

[0043] The effect unique to the hybrid optical element according to the second embodiment is that the mode between the second taper 2 and the modulation section 15 can be converted adiabatically, thereby reducing the optical coupling loss that may occur in this portion.

[0044] Incidentally, since the effective refractive index difference occurring between the end portion of the second taper 2 and the modulation section 15 is low at about 0.1, good coupling can be obtained with a taper length of about 10 [μm]. It is necessary to design the taper length of the third taper 3 so that it is not too long, so as to fully obtain the effects shown in the embodiment 1. In order to keep the increase in parasitic capacitance resulting from the addition of the third taper 3 to, for example, 10% or less, it is advisable to set the taper length of the third taper 3 to 5% or less with respect to the length of the modulation section 15 (because the third taper 3 is on both sides of the modulation section 15).

[0045] Embodiment 3 The hybrid optical element according to the third embodiment is a modified example of the hybrid optical element according to the present disclosure. Unless otherwise specified, the same reference numerals as those used in the previous embodiments are used in the third embodiment. Furthermore, in the third embodiment, descriptions that overlap with those in the previous embodiments are omitted as appropriate.

[0046] Fig. 10 is a structural diagram of a hybrid optical element according to embodiment 3. As shown in Fig. 10, in the hybrid optical element according to the disclosed technique, the first taper 1 is not an essential component. According to the simulation results, the effective refractive index difference between the optical waveguide 8 and the tip of the second taper 2 is low, about 0.02. Therefore, even if a structure without the first taper 1 (see FIG. 10) is adopted, no significant increase in loss occurs.

[0047] In the structure without the first taper 1 (see FIG. 10), the number of tapers that require high-precision processing in the production process is small, so that, for example, the alignment precision can be lowered, resulting in reduced production costs. In addition, the variation in characteristics caused by misalignment that may occur in the first taper 1 is eliminated, and it is expected that the yield will improve.

[0048] Embodiment 4 The hybrid optical element according to the fourth embodiment is a modified example of the hybrid optical element according to the disclosed technology. Unless otherwise specified, the same reference numerals as those used in the previous embodiments are used in the fourth embodiment. Furthermore, in the fourth embodiment, descriptions that overlap with those in the previous embodiments are omitted as appropriate.

[0049] In the first embodiment, the bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 is realized by wafer bonding using a surface activated bonding technique, but the disclosed technique is not limited to this. The bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 may be realized by using a resin material such as BCB.

[0050] Using a resin material such as BCB for bonding can prevent adhesion defects that can occur with surface activated bonding. Resin materials are relatively soft, and even if minute foreign matter is mixed into the substrate surface, good bonding can be achieved without voids.

[0051] Embodiment 5. The hybrid optical element according to the fifth embodiment is a modified example of the hybrid optical element according to the present disclosure. Unless otherwise specified, the same reference numerals as those used in the previous embodiments are used in the fifth embodiment. Furthermore, in the fifth embodiment, descriptions that overlap with those in the previous embodiments are omitted as appropriate.

[0052] As described in the first embodiment, the optical waveguide 8 provided in the silicon photonics substrate 14 may be a SiN waveguide. SiN waveguides are less susceptible to nonlinear optical effects than Si waveguides, and can therefore be used in applications requiring higher optical density. The refractive index of SiN is lower than that of Si. Therefore, the SiN waveguide can increase the propagation mode and obtain high coupling efficiency with the optical fiber (light absorption layer 9 in the figure). SiN does not have a high electro-optic effect compared to Si, so it is difficult to create an optical modulator using SiN itself, but the production process according to the disclosed technology makes it possible to produce a modulator using a SiN waveguide.

[0053] Embodiment 6 The hybrid optical element according to the sixth embodiment is a modified example of the hybrid optical element according to the disclosed technology. Unless otherwise specified, in the sixth embodiment, the same reference numerals as those used in the previous embodiments are used. In the sixth embodiment, descriptions that overlap with those in the previous embodiments are omitted as appropriate.

[0054] In the above-mentioned embodiment, the hybrid optical element is described as an EA modulator, but the disclosed technology is not limited to this. The hybrid optical element according to the disclosed technology may be a device in which a direct modulation laser diode is formed on an optical waveguide 8. A device in which a directly modulated laser diode according to the disclosed technique is formed has reduced parasitic capacitance and is capable of high-speed response.

[0055] Embodiment 7 The hybrid optical element according to the seventh embodiment is a modified example of the hybrid optical element according to the present disclosure. Unless otherwise specified, the same reference numerals as those used in the previous embodiments are used in the seventh embodiment. Furthermore, in the seventh embodiment, descriptions that overlap with those in the previous embodiments are omitted as appropriate.

[0056] Fig. 11 is a structural diagram (perspective view) of a hybrid optical element according to the seventh embodiment. As illustrated in Fig. 11, in the hybrid optical element according to the disclosed technology, the second taper 2 in the light absorption layer 9 does not have a strictly linear inclination, but may have a broken line in which the tip portion is a second taper 2-1 with a small gradient (taper ratio is also small) and the base portion is a second taper 2-2 with a large gradient (taper ratio is also large). The hybrid optical element illustrated in Fig. 11 is designed so that the taper length of the second taper 2-1 is long and the taper length of the second taper 2-2 is short.

[0057] FIG. 12 is a graph showing the coupling efficiency of the hybrid optical element according to the first embodiment and the coupling efficiency of the hybrid optical element according to the seventh embodiment in comparison with the conventional technology. FIG. 12 is a graph obtained by performing a simulation. In the graph shown in FIG. 12, the horizontal axis represents the taper length of the second taper 2 (second taper 2-1 in the seventh embodiment), and the vertical axis represents the coupling efficiency. The "Taper Length L" shown in the graph of FIG. taper "[μm]" refers to the taper length, and its unit is μm. The term "Coupling Efficiency" in the graph of FIG. 12 refers to coupling efficiency. 12, the plot curve according to the seventh embodiment has a taper length of about 100 μm until the coupling efficiency is saturated. The taper length required until the coupling efficiency is saturated is in the order of the seventh embodiment, the first embodiment, and the conventional structure, with the seventh embodiment being the shortest.

[0058] Fig. 13 is a graph showing the relationship between the taper length of the second taper 2-2 and the coupling efficiency in the hybrid optical element according to the seventh embodiment. The graph shown in Fig. 13 shows that the coupling efficiency rises sharply from about 0.8 to 1 when the taper length is from 0 [μm] to about 3 [μm], and when the taper length is in the range longer than about 3 [μm], the coupling efficiency is saturated at about 1. When the taper length is in the range longer than about 3 [μm], there is no significant difference in the coupling efficiency.

[0059] 12 shows the excellent effect of the hybrid optical element according to the seventh embodiment. Specifically, the hybrid optical element according to the seventh embodiment has a shorter taper length for obtaining a necessary and sufficient coupling efficiency than both the conventional technology and the hybrid optical element according to the first embodiment. 13, in the hybrid optical element according to the seventh embodiment, a taper length of about 3 μm for the second taper 2-2 is sufficient. In the simulation results, when the target coupling efficiency is set to 80%, the taper length of the structure having the second taper 2-2 is about 1 / 3 of that of the structure not having the second taper 2-2, which is shorter.

[0060] The mechanism by which the structure having the second taper 2-2 achieves a shorter length can be seen with reference to Fig. 4. As described above, Fig. 4 is a graph showing the state of propagation mode transition occurring in the hybrid optical element according to the first embodiment. Fig. 4 shows the state in which light propagating in the optical waveguide 8 in the TE fundamental mode crosses the TE fundamental mode of the optical absorption layer 9 at the mode crossing 1 in the second taper 2 and undergoes mode conversion. Since this mode conversion is an adiabatic behavior, the waveguide width of the optical absorption layer 9 needs to increase or decrease gradually before and after the mode crossing 1.

[0061] On the other hand, at a position away from the mode crossing 1, the effective refractive index of the TE fundamental mode of the light absorption layer 9 and the other modes are sufficiently different from each other. Therefore, even if the waveguide width of the light absorption layer 9 at this position increases or decreases sharply, no unnecessary mode conversion occurs.

[0062] The above is the background phenomenon that gave the inventor the idea of ​​dividing the second taper 2 into two regions. The second taper 2 is divided into a second taper 2-1 from the tip to the location where the mode crossing 1 occurs, and a second taper 2-2 from the location where the mode crossing 1 occurs to the base. As shown in FIG. 11, the second taper 2-1 from the tip to the location where the mode crossing 1 occurs is designed to have a small gradient (small taper ratio). Meanwhile, the second taper 2-2 from the location where the mode crossing 1 occurs to the base is designed to have a large gradient (large taper ratio). By designing in this way, the second taper 2 can have a short taper length as a whole. The width of the tip of the second taper 2-1 may be the width of the light absorbing layer 9.

[0063] 11 shows an embodiment in which the second taper 2 is divided into two regions and has a so-called broken line gradient, but the disclosed technology is not limited to this. In the hybrid optical element according to the disclosed technology, the gradient of the second taper 2 may be continuously changed, for example, the gradient may be gradually increased from the tip.

[0064] As described above, the hybrid optical element according to the seventh embodiment has the above technical features, and therefore has the effect of shortening the taper and reducing the parasitic capacitance while ensuring sufficient coupling.

[0065] (Additional Note) In the application on which this application is based, the claims as originally filed (claims) are as follows: (Claim 1) From the surface, it consists of p-InP, an optical absorption layer, n-InP, a dielectric thin film, an optical waveguide, a BOX layer, and a core substrate. the light absorbing layer has a second taper; The light absorbing layer is exposed at the second taper. Hybrid optical element. (Claim 2) A modulation section is provided, A third taper is provided between the second taper and the modulation section. The hybrid optical element according to claim 1. (Claim 3) The optical waveguide is a Si waveguide or a SiN waveguide. The hybrid optical element according to claim 1. (Claim 4) It acts as an EA modulator, a mode transition is performed from the optical waveguide to the optical absorption layer by an adiabatic transition type optical coupler having the second taper; The hybrid optical element according to claim 1. (Claim 5) Functioning as an EA modulator or a directly modulated laser diode, The hybrid optical element according to claim 1. (Claim 6) A hybrid substrate is made by bonding a silicon photonics substrate and an InP epitaxial substrate. forming a device structure on the hybrid substrate; The light absorbing layer is formed to have a second taper; The light absorbing layer is formed so as to be exposed at the second taper. A method for producing a hybrid optical element. (Claim 7) Forming a modulation section, forming a third taper between the second taper and the modulation section; A method for producing the hybrid optical element of claim 6. (Claim 8) The bonding between the silicon photonics substrate and the InP epitaxial substrate is This is carried out by wafer bonding using surface activated bonding techniques or by using resin materials. A method for producing the hybrid optical element of claim 6. [Industrial Applicability]

[0066] The hybrid optical element according to the disclosed technique can be applied as an optical Ethernet communication device and has industrial applicability. [Explanation of symbols]

[0067] 1 first taper, 2 second taper, 3 third taper, 4 n electrode, 5 p electrode, 6 n-InP (6s n-InP layer), 7 p-InP (7s p-InP layer), 8 optical waveguide, 9 optical absorption layer, 10 dielectric thin film, 11 BOX layer, 12 core substrate, 13 InP epitaxial substrate, 14 silicon photonics substrate, 15 modulation section.

Claims

1. The structure is made up of, in order from the surface layer, p-InP, an optical absorption layer, n-InP, a dielectric thin film, an optical waveguide, a BOX layer, and a core substrate. the n-InP has a first taper; the light absorbing layer has a second taper; The light absorbing layer is exposed at the second taper, The p-InP includes a modulation section, a third taper formed in the p-InP between the second taper and the modulation section; The second taper is not applied to the p-InP. The optical absorption is limited to the vicinity of the p-electrode, The taper length of the third taper is 5% or less with respect to the length of the modulation section. Hybrid optical element.

2. A silicon photonics substrate and an InP epitaxial substrate are bonded to form a hybrid substrate. forming a device structure on the hybrid substrate; The n-InP is formed to have a first taper, The light absorbing layer is formed to have a second taper; The light absorbing layer is formed so as to be exposed at the second taper, A modulation section is formed in p-InP. forming a third taper in the p-InP between the second taper and the modulation section such that the taper length is 5% or less with respect to the length of the modulation section; However, the second taper is not applied to the p-InP. The optical absorption is limited to the vicinity of the p-electrode. A method for producing a hybrid optical element.

3. The structure is made up of, in order from the surface layer, p-InP, an optical absorption layer, n-InP, a dielectric thin film, an optical waveguide, a BOX layer, and a core substrate. the light absorbing layer has a second taper; the light absorbing layer is exposed at the second taper, when the second taper is divided into a tip portion from a tip to a position where mode crossing occurs between light in the TE fundamental mode propagated through the optical waveguide and light in the TE fundamental mode propagated through the optical absorption layer, and a base portion from the position where mode crossing occurs to a base, the tip portion of the second taper has a smaller taper ratio than the base portion of the second taper. Hybrid optical element.

4. A modulation section is provided, a third taper formed in the p-InP between the second taper and the modulation section; The hybrid optical element according to claim 3 .

5. The optical waveguide is a Si waveguide or a SiN waveguide. The hybrid optical element according to claim 3 .

6. It functions as an EA modulator. a mode transition is performed from the optical waveguide to the optical absorption layer by an adiabatic transition type optical coupler having the second taper; The hybrid optical element according to claim 3 .

7. Functions as an EA modulator or a directly modulated laser diode; The hybrid optical element according to claim 3 .

8. A method for producing a hybrid optical element comprising, in order from the surface layer, p-InP, an optical absorption layer, n-InP, a dielectric thin film, an optical waveguide, a BOX layer, and a core substrate, the method comprising the steps of: A silicon photonics substrate and an InP epitaxial substrate are bonded to form a hybrid substrate. forming a device structure on the hybrid substrate; The light absorbing layer is formed to have a second taper; The light absorbing layer is formed so as to be exposed at the second taper, the second taper is formed such that when the second taper is divided into a tip portion from a tip to a position where mode crossing occurs between light in a TE fundamental mode propagated through the optical waveguide and light in a TE fundamental mode propagated through the optical absorption layer, and a base portion from the position where mode crossing occurs to a base, the tip portion of the second taper has a smaller taper ratio than the base portion of the second taper. A method for producing a hybrid optical element.

9. Forming a modulation section, forming a third taper in the p-InP between the second taper and the modulation section; A method for producing the hybrid optical device of claim 8.

10. The bonding between the silicon photonics substrate and the InP epitaxial substrate is This is carried out by wafer bonding using surface activated bonding techniques or by using resin materials. A method for producing the hybrid optical device of claim 8.

Images