Hybrid optical element and method for producing hybrid optical element

Abstract

A hybrid optical element according to the present disclosure is configured from a p-InP (7), a light absorption layer (9), an n-InP (6), a dielectric thin film (10), an optical waveguide (8), a BOX layer (11), and a core substrate (12) in this order from a surface layer, the n-InP (6) having a first wedge (1), the light absorption layer (9) having a second wedge (2), the light absorption layer (9) being exposed to the second wedge (2), the p-InP (7) having a modulation unit (15), and a third wedge (3) between the second wedge (2) and the modulation unit (15), the second wedge (2) being not applied to the p-InP (7), the dielectric thin film (10) being applied to the p-InP (7) The light absorption is limited in the vicinity of the p-electrode (5), and the wedge length of the third wedge (3) is 5% or less with respect to the length of the modulation unit (15).

Description

Technical Field

[0001] The disclosed technology relates to a hybrid optical element. Background Art

[0002] Hybrid optical elements are known, which are formed by integrating high-efficiency optical devices on silicon waveguides. The term "hybrid" in hybrid optical elements is synonymous with the terms "hybrid IC" and "hybrid integrated circuit" and is used as an antonym for "monolithic."

[0003] Hybrid optical elements are used, for example, as devices for optical Ethernet communications. More specifically, hybrid optical elements are used, for example, as communication devices using transmission methods such as NRZ (Non-Return-to-Zero) and PAM (Pulse Amplitude Modulation).

[0004] High-efficiency optical devices are realized using compound semiconductors, for example. Silicon waveguides and compound semiconductor waveguides are connected through adiabatic transfer using a wedge. The compound semiconductor consists of an n-type semiconductor below and a p-type semiconductor above, forming a pn junction. The wedge has a wedge shape where the n-type semiconductor is exposed on the surface (hereinafter referred to as the "first wedge") and a wedge shape where the p-type semiconductor is exposed on the surface (hereinafter referred to as the "second wedge").

[0005] For example, Patent Document 1 discloses a hybrid light device having a structure for improving the resistance in a light source device.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-140319 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] The hybrid optical element is used, for example, in an electric field absorption modulator (also called an EA modulator). When used in an EA modulator, the end portion of the second wedge of the hybrid optical element is easily coupled with the TM mode reflecting the longitudinal waveguide shape, and in most cases, a Therefore, in order to obtain sufficient coupling, the wedge becomes longer and the device becomes larger. In addition, the above TE and TM represent the propagation mode of electromagnetic waves respectively.

[0011] When hybrid optical components are used in high-speed modulation devices such as EA modulators, the area of the modulator must be minimized to reduce parasitic capacitance (also known as floating capacitance or stray capacitance). Increased parasitic capacitance degrades the device's high-frequency characteristics.

[0012] On the other hand, when the modulator area is reduced, the wedge length becomes shorter, and the above-mentioned coupling cannot be achieved. Furthermore, in the EA modulator, a modulation bias is applied to the wedge portion, causing unintended light absorption in the wedge portion and resulting in insertion loss.

[0013] Therefore, the wedge length must be designed considering the trade-off between sufficient coupling and reduced parasitic capacitance.

[0014] The purpose of the disclosed technology is to resolve the above-mentioned trade-off problem, ensure sufficient coupling in a hybrid optical element, and shorten the wedge shape to achieve reduced parasitic capacitance.

[0015] Means for solving problems

[0016] The hybrid optical element of the disclosed technology is composed of p-InP, a light absorption layer, n-InP, a dielectric film, an optical waveguide, a BOX layer and a core substrate in order from the surface layer. The n-InP has a first wedge, the light absorption layer has a second wedge, the light absorption layer is exposed in the second wedge, the p-InP has a modulation part, and a third wedge is provided between the second wedge and the modulation part. The second wedge is not applied to the p-InP, and light absorption is limited to the vicinity of the p-electrode. The wedge length of the third wedge is less than 5% of the length of the modulation part.

[0017] Effects of the Invention

[0018] The hybrid optical element of the disclosed technology has the above-described structure, and therefore can ensure sufficient coupling, shorten the wedge shape, and achieve reduced parasitic capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of the mixed light element according to Embodiment 1.

[0020] Figure 2 This is one of the explanatory diagrams showing a pasting step as a part of the production process of the mixed light element according to the first embodiment.

[0021] Figure 3 This is a second explanatory diagram showing a pasting step as part of the production process of the mixed light element according to the first embodiment.

[0022] Figure 4 This is a graph showing the state of propagation mode shift occurring in the hybrid optical element according to the first embodiment.

[0023] Figure 5 This is a structural diagram of a case where a conventional hybrid optical element is applied to an EA modulator.

[0024] Figure 6This is a graph showing the state of propagation mode shift occurring in a conventional hybrid optical element.

[0025] Figure 7 Graph showing the coupling efficiency of the hybrid optical element of the disclosed technology in comparison with the conventional technology.

[0026] Figure 8 This is a structural diagram of a mixed light element according to Embodiment 2.

[0027] Figure 9 This is a graph showing the state of propagation mode shift occurring in the hybrid optical element according to the second embodiment.

[0028] Figure 10 This is a structural diagram of a mixed light element according to Embodiment 3.

[0029] Figure 11 This is a structural diagram of a mixed light element in embodiment 7.

[0030] Figure 12 Graphs showing the coupling efficiency of the mixed optical element of Embodiment 1 and the coupling efficiency of the mixed optical element of Embodiment 7 compared with the conventional art.

[0031] Figure 13 This is a graph showing the relationship between the wedge length of the second wedge 2 - 2 and the coupling efficiency in the hybrid optical element according to the seventh embodiment. DETAILED DESCRIPTION

[0032] The hybrid optical element of the disclosed technology is used as an EA modulator.

[0033] Implementation Method 1

[0034] Figure 1 This is a structural diagram (perspective view) of the mixed light element according to the first embodiment.

[0035] like Figure 1 As shown, the hybrid optical element of the first embodiment includes an n-electrode 4 , a p-electrode 5 , an n-InP layer 6 s , a p-InP layer 7 s , an optical waveguide 8 , a light absorbing layer 9 , a dielectric thin film 10 , a BOX layer 11 , and a core substrate 12 .

[0036] A first wedge shape 1 is formed on n-InP 6 . Furthermore, a second wedge shape 2 is formed on the light absorbing layer 9 .

[0037] The optical waveguide 8 utilizes the difference in refractive index and the property that light is localized in a region with a high refractive index, such as silicon, and propagates therein.

[0038] The optical waveguide 8 may be a Si waveguide or a SiN waveguide. In the hybrid optical element of the first embodiment, the optical waveguide 8 is a Si waveguide. The embodiment 5 shows a case where the optical waveguide 8 is a SiN waveguide.

[0039] Production Process of Hybrid Optical Components

[0040] The raw materials of the hybrid optical element include a silicon photonic substrate 14 and an InP epitaxial substrate 13 .

[0041] The silicon photonic substrate 14 has a waveguide structure with a dielectric thin film 10 as the outermost layer. The dielectric 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.

[0042] The InP epitaxial substrate 13 is produced by a process of epitaxially growing a layer structure including the light absorbing layer 9 on an n-InP substrate.

[0043] The production process of the hybrid optical element includes a process of bonding the silicon photonic substrate 14 and the InP epitaxial substrate 13 .

[0044] The silicon photonic substrate 14 and the InP epitaxial substrate 13 are bonded together by wafer bonding using a surface activated bonding technique.

[0045] In principle, the interface between the silicon photonics substrate 14 and the InP epitaxial substrate 13 is formed by the dielectric thin film 10 (SiO2 thin film) and the n-InP layer 6s. Alternatively, by depositing SiO2 on the n-InP6 side, the interface can also be formed by the dielectric thin film 10 (SiO2 thin film) and the SiO2 deposited on the n-InP6.

[0046] A substrate obtained by bonding the silicon photonics substrate 14 and the InP epitaxial substrate 13 is called a hybrid substrate.

[0047] Figure 2 This is one of the explanatory diagrams showing the pasting process as a part of the production process of the mixed light element of the first embodiment. Figure 2 As shown, the bonding between the silicon photonic substrate 14 and the InP epitaxial substrate 13 may be a method of bonding circular substrates to each other.

[0048] Figure 3 This is a second explanatory diagram showing the pasting process as a part of the production process of the hybrid light element of the first embodiment. Figure 3 As shown, the silicon photonic substrate 14 and the InP epitaxial substrate 13 may be bonded together by pasting the InP epitaxial substrate single piece 13 p obtained by cutting the InP epitaxial substrate 13 onto the silicon photonic substrate 14 .

[0049] The thickness of the dielectric thin film 10 in the silicon photonic substrate 14 is preferably 300 nm or less. By setting the thickness to 300 nm or less, optical coupling between the optical waveguide 8 and the light absorbing layer 9 is easily achieved.

[0050] The InP epitaxial substrate 13 is produced by epitaxially growing an n-InP buffer layer, a light-absorbing layer 9, and a p-InP layer 7s on an n-InP substrate. During epitaxial growth during the production of the InP epitaxial substrate 13, a layer structure on the order of several micrometers is generated. The thickness of the n-InP substrate also depends on the substrate diameter, but is generally between 300 μm and 1 mm.

[0051] Mixed crystal materials such as GaInAs, AlInAs, InGaAlAs, or GaInAsP may be inserted into any of the n-InP layer 6s and p-InP layer 7s formed by epitaxial growth. The mixed crystal material may be inserted for purposes such as limiting carriers generated by photocurrent, reducing contact resistance with metal electrodes, or forming an etching stopper required in the processing process.

[0052] In addition, in the field of semiconductors, GaInAs is often referred to as Indium Gallium Arsenide (InGaAs). GaInAs is a ternary alloy (compound) of Indium Arsenide (InAs) and Gallium Arsenide (GaAs). Both Indium Arsenide (InAs) and Gallium Arsenide (GaAs) are 3-5 (罗马数字) family of compound semiconductors.

[0053] Light-absorbing layer 9 has a quantum well structure. A quantum well refers to a state in which the movement of particles such as electrons is restricted. Furthermore, light-absorbing layer 9 is designed to absorb light in the 1.3 μm or 1.55 μm bands through the quantum Stark effect when an electric field is applied. Quantum wells are made of mixed crystal materials such as InGaAlAs or GaInAsP, for example.

[0054] The production process for hybrid optical elements includes semiconductor processes for forming the device structure for the hybrid substrate. Generally speaking, the process of forming the device structure is the process of forming multiple transistors and wiring on a semiconductor chip to configure the circuit. This process is performed after the "circuit design and wiring process" as a pre-process in semiconductor manufacturing. An example of the process of forming the device structure is to use a computer to draw a pattern on a master plate called a photomask and transfer it to a semiconductor wafer to form the circuit.

[0055] In the production process of the hybrid optical element of the disclosed technology, first, the n-InP layer 6s, which is the outermost layer of the hybrid substrate, is mostly removed by etching to reduce the thickness to several hundred [μm] to several [μm].

[0056] Then, photolithography and dry etching techniques are used to form Figure 1 The wedge-shaped structure shown.

[0057] Regarding the thickness of the layers, for example, the thickness of n-InP 6 is 200 nm, the thickness of the light absorbing layer 9 is 500 nm, and the thickness of p-InP 7 is 2 μm.

[0058] The thickness of n-InP6 needs to be thinned to obtain optical coupling between the optical waveguide 8 and the light absorbing layer 9. When the thickness of n-InP6 exceeds about 300 nm, the optical coupling becomes weak and the wedge length required for the transfer of the propagation mode becomes significantly longer.

[0059] Regarding the p-InP 7 , it is important that the p-InP 7 has a sufficient thickness so that the propagation mode reaches the p-electrode 5 without generating optical loss.

[0060] The first wedge shape 1 is processed so that the n-InP 6 is exposed on the surface. In addition, the second wedge shape 2 is processed so that the light absorbing layer 9 is exposed on the surface.

[0061] The light-absorbing layer 9 is composed of a ternary or quaternary mixed crystal with a higher refractive index than n-InP 6. During wedge processing, exposure of the n-InP layer 6s and the light-absorbing layer 9 to the atmosphere is troublesome, so they are sometimes covered with an extremely thin InP protective layer of less than 100 nm.

[0062] In the hybrid optical element formed through the above process, the effective refractive index difference between optical waveguide 8 and the distal end of second wedge 2 is minimal. Therefore, first wedge 1 can be adiabatically transferred over a very short distance. The hybrid optical element of the disclosed technology can have a wedge length of first wedge 1 of 10 μm.

[0063] The longer the modulator 15 in the p-InP layer 7s, the higher the extinction ratio. However, if the modulator 15 in the p-InP layer 7s is too long, parasitic capacitance increases, reducing the operating bandwidth. The length of the modulator 15 also presents a trade-off between extinction ratio and parasitic capacitance.

[0064] When the hybrid optical element is used as a 53GBaud PAM4 device, which is the current mainstream optical Ethernet communication method, the length of the modulator 15 can be approximately 200 [μm]. When the hybrid optical element is used as a 106GBaud PAM4 device, which is the next-generation optical Ethernet communication method, the operating bandwidth is doubled, and the length of the modulator 15 is approximately 100 [μm]. In addition, PAM4 is the abbreviation of 4-level Pulse-Amplitude Modulation, which means 4-value pulse amplitude modulation. More specifically, PAM4 is not the existing 2-value bit string consisting of "0" and "1", but a method of transmitting as a 4-value pulse signal.

[0065] On the Action or Behavior of Light in Mixed Light Elements

[0066] The input light to the hybrid optical element propagates in the TE mode in the optical waveguide 8. TE stands for Transverse Electric. The TE mode is a term used to describe the state of the optical waveguide 8 when no electric field exists in the propagation 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." Furthermore, the TE mode associated with the light absorbing layer 9 is referred to as the "TE fundamental mode," and the two are distinguished.

[0067] The propagating light reaches the modulation unit 15 via the first wedge 1 and the second wedge 2 .

[0068] A reverse bias is applied between the p-electrode 5 and the n-electrode 4. When the reverse bias is applied, light absorption occurs in the light absorbing layer 9 due to the quantum confined Stark effect (abbreviated as "quantum Stark effect"). The Stark effect is a phenomenon in which a spectrum changes when a uniform external electric field is applied to atoms or molecules.

[0069] By changing the magnitude of the reverse bias, it is possible to change the amount of light absorbed by the modulator 15. By utilizing this property, the hybrid optical element of the disclosed technology can perform light intensity modulation such as NRZ or PAM.

[0070] It is considered that absorption of light occurs only in the region where the p-InP 7 is located. The light that has passed through the modulation section 15 passes through the wedge-shaped structure again and returns to the optical waveguide 8.

[0071] Figure 4 Graph showing the state of propagation mode transfer occurring in the hybrid optical element of embodiment 1. Figure 4 In the graph shown, the horizontal axis represents position, and the vertical axis represents the effective refractive index. The effective refractive index is sometimes also called the effective refractive index.

[0072] Figure 4 The graph shown is for Figure 1 Results obtained from mode analysis of a cross section of the waveguide shown. Figure 4 The graph shows the top five modes with high effective refractive index values. The mode with the highest effective refractive index shown by the thick solid curve is the dominant mode.

[0073] like Figure 4 As shown in FIG. 1 , the results of mode analysis show that mode crossing occurs only at one point, designated as "mode crossing 1," in the second wedge 2 of the hybrid optical element of Embodiment 1. Mode crossing refers to a phenomenon in which two propagation modes have the same propagation constant at the same wavelength.

[0074] Light propagating in the TE fundamental mode in the optical waveguide 8 intersects with the TE fundamental mode of the light absorbing layer 9 in the second wedge 2 and is mode-transferred. This mode transfer is an adiabatic behavior.

[0075] The technical feature of the hybrid optical element of the first embodiment is that the light absorbing layer 9 is exposed in the second wedge 2. Figure 5 This is a structural diagram (stereoscopic diagram) of the case where the existing hybrid optical element is applied to the EA modulator. Figure 1 (Implementation 1) Figure 5 By comparing the conventional optical element with the conventional optical element, the technical features of the optical hybrid element of Embodiment 1 become clear. In other words, the technical feature of the optical hybrid element of Embodiment 1 is that the second wedge 2 does not contain p-InP.

[0076] also, Figure 6 This is a graph showing the state of propagation mode shift occurring in a conventional hybrid optical element.

[0077] like Figure 6 As shown in FIG. 1 , the results of mode analysis show that mode crossings occur in the wedge-shaped portion (corresponding to the second wedge 2) of the conventional optical hybrid element at two locations: one designated "mode crossing 1" and one designated "mode crossing 2." In other words, the conventional optical hybrid element undergoes secondary mode transfer via the TM mode.

[0078] It is believed that the reason why secondary mode transfer occurs in the hybrid optical element of the prior art is that the electric field distribution of the TM mode is easily affected by the thickness direction, and the TM fundamental mode of the light absorption layer becomes higher near the wedge end due to the influence of p-InP, resulting in a higher effective refractive index than the TE fundamental mode of the light absorption layer.

[0079] Due to the above technical features, the effective refractive index of the TM fundamental mode near the wedge tip is suppressed low in the hybrid optical element of Embodiment 1. This effect prevents mode crossing between the propagating mode and the TM fundamental mode in the hybrid optical element of Embodiment 1.

[0080] The technical features of the disclosed technology compared with the prior art are shown in the following table.

[0081] Table 1

[0082]

[0083] Figure 7 Graph showing the coupling efficiency (simulation results) of the hybrid optical element of the disclosed technology compared with the prior art. Figure 7 In the graph shown, the horizontal axis represents the wedge length of the second wedge 2, and the vertical axis represents the coupling efficiency. Figure 7 In the graph shown, the simulation results of the mixed light element of embodiment 1 are represented by a solid line curve, and the simulation results of the mixed light element of the conventional structure are represented by a dotted line curve. Figure 7 As shown in FIG. 1 , in the hybrid optical element of the present disclosure, the wedge length for obtaining sufficient coupling is shorter than that of the prior art. Figure 7 In the simulation shown, the wedge length required to achieve a coupling efficiency of 80% is shortened to approximately 1 / 3 compared to the conventional case.

[0084] The hybrid optical element of the first embodiment functions as an EA modulator, and transfers a mode from the optical waveguide 8 to the light absorbing layer 9 via an adiabatic transfer type optical coupler having a wedge shape.

[0085] As described above, the hybrid optical element of the first embodiment has the above-mentioned technical features, and therefore exhibits the following effects: sufficient coupling can be ensured, the wedge shape can be shortened, and the parasitic capacitance can be reduced.

[0086] Implementation Method 2

[0087] The hybrid optical element of Embodiment 2 is a modified example of the hybrid optical element of the disclosed technology. Except where otherwise specified, the same reference numerals as those used in Embodiment 1 are used in Embodiment 2. In addition, descriptions that overlap with those in Embodiment 1 are omitted as appropriate.

[0088] Figure 8 This is a structural diagram (stereoscopic diagram) of the mixed light element of embodiment 2. Figure 8 As shown, the hybrid optical element of the second embodiment includes an extremely short third wedge 3 between the second wedge 2 and the modulation section 15 in the p-InP layer 7 s.

[0089] Figure 9 This is a graph showing the state of propagation mode shift occurring in the hybrid optical element according to the second embodiment.

[0090] and Figure 4(Implementation 1) Comparative Observation Figure 9 (Embodiment 2) It can be seen that in the hybrid optical element of Embodiment 2, the discontinuous and rapid change of the effective refractive index generated at the boundary between the second wedge 2 and the modulation portion 15 is converted into a continuous and gradual change. Figure 9 The properties shown are the result of the fact that the presence or absence of p-InP does not suddenly change along the optical path due to the extremely short third wedge 3 between the second wedge 2 and the modulation portion 15 .

[0091] The unique effect of the hybrid optical element of the second embodiment is that it can adiabatically transfer the mode between the second wedge 2 and the modulation section 15, thereby reducing the optical coupling loss that may occur in this portion.

[0092] However, the effective refractive index difference between the terminal end of the second wedge 2 and the modulation portion 15 is as low as approximately 0.1, so good coupling can be obtained when the wedge length is approximately 10 [μm].

[0093] It is important to note that the wedge length of the third wedge 3 should not be designed to be too long in order to fully achieve the effects described in Embodiment 1. To limit the increase in parasitic capacitance resulting from the addition of the third wedge 3 to, for example, 10% or less, the wedge length of the third wedge 3 can be set to 5% or less relative to the length of the modulation section 15 (this is because the third wedge 3 is located on both sides of the modulation section 15).

[0094] Implementation 3

[0095] The hybrid optical element of embodiment 3 is a modified example of the hybrid optical element of the disclosed technology. In embodiment 3, the same reference numerals as those used in the aforementioned embodiments are used, except where otherwise explicitly stated. Furthermore, in embodiment 3, descriptions that overlap with those in the aforementioned embodiments are omitted as appropriate.

[0096] Figure 10 : is a structural diagram of the mixed light element of embodiment 3. Figure 10 As shown, in the hybrid optical element of the disclosed technology, the first wedge 1 is not an essential component.

[0097] According to the simulation results, the effective refractive index difference between the optical waveguide 8 and the end portion of the second wedge 2 is as low as about 0.02. Therefore, even if a structure without the first wedge 1 is adopted (see Figure 10 ), there will be no significant increase in losses.

[0098] Regarding the structure without the first wedge 1 (see Figure 10), the number of wedges requiring high-precision machining in the production process is reduced, so, for example, alignment accuracy can be reduced, resulting in reduced production costs. Furthermore, since characteristic variations caused by misalignment that may occur in the first wedge 1 are eliminated, it is expected that the yield rate will be improved.

[0099] Implementation 4

[0100] The hybrid optical element of embodiment 4 is a modified example of the hybrid optical element of the disclosed technology. In embodiment 4, the same reference numerals as those used in the aforementioned embodiments are used, except where otherwise explicitly stated. Furthermore, in embodiment 4, descriptions that overlap with those in the aforementioned embodiments are omitted as appropriate.

[0101] In Embodiment 1, the bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 is achieved by wafer bonding using surface activated bonding technology. However, the disclosed technology is not limited thereto. The bonding between the silicon photonics substrate 14 and the InP epitaxial substrate 13 can also be achieved using a resin material such as BCB.

[0102] Using a resin material such as BCB for bonding can prevent adhesion defects that may occur in surface activation bonding.

[0103] Resin materials are relatively soft and can adhere well without gaps even when tiny foreign particles are mixed into the substrate surface.

[0104] Implementation 5

[0105] The hybrid optical element of embodiment 5 is a modified example of the hybrid optical element of the disclosed technology. In embodiment 5, the same reference numerals as those used in the aforementioned embodiments are used, except where otherwise explicitly stated. Furthermore, in embodiment 5, descriptions that overlap with those in the aforementioned embodiments are omitted as appropriate.

[0106] As described in the first embodiment, the optical waveguide 8 provided on the silicon photonic substrate 14 may be a SiN waveguide.

[0107] SiN waveguides have the property of being less likely to produce nonlinear optical effects than Si waveguides, and therefore can be used for applications with higher optical density.

[0108] The refractive index of SiN is lower than that of Si. Therefore, the SiN waveguide can increase the propagation mode and achieve high coupling efficiency with the optical fiber (the light absorbing layer 9 in the figure).

[0109] SiN has a lower electro-optical effect than Si, making it difficult to fabricate optical modulators using SiN itself. However, the production process of the disclosed technology makes it possible to fabricate SiN waveguide modulators.

[0110] Implementation Method 6

[0111] The hybrid optical element of embodiment 6 is a modified example of the hybrid optical element of the disclosed technology. In embodiment 6, the same reference numerals as those used in the aforementioned embodiments are used, except where otherwise explicitly stated. Furthermore, in embodiment 6, descriptions that overlap with those in the aforementioned embodiments are omitted as appropriate.

[0112] In the above embodiment, the hybrid optical element is described as an EA modulator, but the disclosed technology is not limited thereto. The hybrid optical element of the disclosed technology may also be a device in which a directly modulated laser diode is formed on the optical waveguide 8 .

[0113] The device forming the directly modulated laser diode according to the disclosed technology can reduce parasitic capacitance and achieve high-speed response.

[0114] Implementation 7

[0115] The hybrid optical element of embodiment 7 is a modified example of the hybrid optical element of the disclosed technology. In embodiment 7, the same reference numerals as those used in the aforementioned embodiments are used, except where otherwise explicitly stated. In addition, in embodiment 7, descriptions that overlap with those in the aforementioned embodiments are omitted as appropriate.

[0116] Figure 11 This is a structural diagram (stereoscopic diagram) of the mixed light element of embodiment 7. Figure 11 As illustrated, in the hybrid optical element of the present disclosure, the second wedge 2 in the light absorption layer 9 may not be inclined in a strictly straight line, but may be inclined in a broken line with the end portion being the second wedge 2-1 with a small gradient (small wedge ratio) and the base portion being the second wedge 2-2 with a large gradient (large wedge ratio). Figure 11 The illustrated mixed light element is designed so that the wedge length of the second wedge 2 - 1 is long and the wedge length of the second wedge 2 - 2 is short.

[0117] Figure 12 Graphs showing the coupling efficiency of the mixed optical element of Embodiment 1 and the coupling efficiency of the mixed optical element of Embodiment 7 compared with the conventional art. Figure 12 This is a curve graph obtained by simulation. Figure 12 In the graph shown, the horizontal axis represents the wedge length of the second wedge 2 (the second wedge 2 - 1 in the seventh embodiment), and the vertical axis represents the coupling efficiency. Figure 12 The "Taper Length" L recorded in the graph taper "[μm]" means wedge length, and its unit is μm. Figure 12The term “coupling efficiency” described in the graph means coupling efficiency.

[0118] exist Figure 12 In the graph shown, for the plotted curve of Embodiment 7, the wedge length is approximately 100 μm before the coupling efficiency reaches saturation. The wedge length required to achieve saturation of coupling efficiency is ranked in the order of Embodiment 7, Embodiment 1, and the conventional structure, with Embodiment 7 having the shortest wedge length.

[0119] Figure 13 This is a graph showing the relationship between the wedge length of the second wedge 2 - 2 and the coupling efficiency in the hybrid optical element according to the seventh embodiment. Figure 13 The graph shows that the coupling efficiency rises sharply from approximately 0.8 toward 1 when the wedge length ranges from 0 μm to approximately 3 μm. When the wedge length exceeds approximately 3 μm, the coupling efficiency reaches a saturated state, approximately 1. There is no significant difference in coupling efficiency when the wedge length exceeds approximately 3 μm.

[0120] It can be said that Figure 12 This shows the excellent effects of the mixed optical element of Embodiment 7. Specifically, in the mixed optical element of Embodiment 7, the wedge length required to obtain a sufficient coupling efficiency is shorter than that of both the conventional art and Embodiment 1.

[0121] like Figure 13 As shown, in the hybrid optical element of Embodiment 7, the wedge length of the second wedge 2-2 can be approximately 3 μm. In simulation results, when the target coupling efficiency is set at 80%, the wedge length of the structure with the second wedge 2-2 is shorter, approximately one-third, compared to the structure without the second wedge 2-2.

[0122] The shortening mechanism of the structure with the second wedge 2-2 is described by referring to Figure 4 As mentioned above, Figure 4 This is a graph showing the state of propagation mode shift occurring in the hybrid optical element according to the first embodiment. Figure 4 The figure shows how light propagating in the TE fundamental mode in the optical waveguide 8 intersects with the TE fundamental mode of the light absorbing layer 9 at the mode crossing 1 of the second wedge 2, thereby undergoing mode transfer. This mode transfer is adiabatic, so the waveguide width of the light absorbing layer 9 needs to be gradually increased or decreased before and after the mode crossing 1.

[0123] On the other hand, at a position away from the mode intersection 1, the effective refractive indexes of the TE fundamental mode and other modes of the light absorbing layer 9 are sufficiently separated. Therefore, even if the waveguide width of the light absorbing layer 9 at this position increases or decreases sharply, unnecessary mode shift does not occur.

[0124] The above is the background phenomenon that led the inventor to the idea of dividing the second wedge 2 into two areas. The second wedge 2 is divided into the second wedge 2-1 from the end to the location where the module intersection 1 occurs, and the second wedge 2-2 from the location where the module intersection 1 occurs to the base. Figure 11 As shown, the second wedge 2-1 is designed to have a small gradient (small wedge ratio) from the tip to the location where the mode intersection 1 occurs. Furthermore, the second wedge 2-2 is designed to have a large gradient (large wedge ratio) from the location where the mode intersection 1 occurs to the base. This design allows the overall length of the second wedge 2 to be shortened. Furthermore, the width of the tip of the second wedge 2-1 can also be set to the width of the light absorbing layer 9.

[0125] Figure 11 The second wedge 2 is divided into two regions by a so-called broken line gradient, but the disclosed technology is not limited thereto. The hybrid optical element of the disclosed technology may also have a continuously changing gradient of the second wedge 2 (e.g., a gradient that gradually increases from the end).

[0126] As described above, the hybrid optical element of the seventh embodiment has the above-mentioned technical features, and therefore exhibits the following effects: sufficient coupling can be ensured, the wedge shape can be shortened, and the parasitic capacitance can be reduced.

[0127] (Note)

[0128] In the application that serves as the basis for priority of the present application, the initial claims (claims) of the application are as follows.

[0129] (Claim 1)

[0130] A hybrid optical element, wherein:

[0131] The hybrid optical element is composed of p-InP, light absorption layer, n-InP, dielectric film, optical waveguide, BOX layer and core substrate in order from the surface layer.

[0132] The light absorbing layer has a second wedge shape,

[0133] The light absorbing layer is exposed in the second wedge shape.

[0134] (Claim 2)

[0135] The hybrid light element according to claim 1, wherein:

[0136] The mixed light element has a modulation part,

[0137] A third wedge shape is provided between the second wedge shape and the modulation portion.

[0138] (Claim 3)

[0139] The hybrid light element according to claim 1, wherein:

[0140] The optical waveguide is a Si waveguide or a SiN waveguide.

[0141] (Claim 4)

[0142] The hybrid light element according to claim 1, wherein:

[0143] The hybrid optical element functions as an EA modulator,

[0144] The mode is transferred from the optical waveguide to the light absorbing layer by the adiabatic transfer type optical coupler having the second wedge shape.

[0145] (Claim 5)

[0146] The hybrid light element according to claim 1, wherein:

[0147] The hybrid optical element functions as an EA modulator or a directly modulated laser diode.

[0148] (Claim 6)

[0149] A method for producing a hybrid optical element, wherein:

[0150] A hybrid substrate is formed by bonding a silicon photonics substrate and an InP epitaxial substrate.

[0151] The production method of the hybrid optical element includes a process of forming a device structure on the hybrid substrate,

[0152] The light absorbing layer is formed to have a second wedge shape,

[0153] The light absorbing layer is formed so as to be exposed in the second wedge shape.

[0154] (Claim 7)

[0155] The method for producing a hybrid optical element according to claim 6, wherein:

[0156] forming a modulation section,

[0157] A third wedge shape is formed between the second wedge shape and the modulation portion.

[0158] (Claim 8)

[0159] The method for producing a hybrid optical element according to claim 6, wherein:

[0160] The silicon photonic substrate and the InP epitaxial substrate are bonded together by wafer bonding based on a surface activated bonding technique or by using a resin material.

[0161] Industrial applicability

[0162] The hybrid optical element of the disclosed technology can be used as a device for optical Ethernet communication and has industrial applicability.

[0163] Description of labels

[0164] 1: 1st wedge; 2: 2nd wedge; 3: 3rd wedge; 4: n-electrode; 5: p-electrode; 6: n-InP (6s: n-InP layer); 7: p-InP (7s: p-InP layer); 8: Optical waveguide; 9: Light absorption layer; 10: Dielectric thin film; 11: BOX layer; 12: Core substrate; 13: InP epitaxial substrate; 14: Silicon photonic substrate; 15: Modulation unit.

Claims

1. A hybrid optical element, wherein: The hybrid optical element is composed of p-InP, light absorption layer, n-InP, dielectric film, optical waveguide, BOX layer and core substrate in order from the surface layer. The n-InP has a first wedge shape, The light absorbing layer has a second wedge shape, The light absorbing layer is exposed in the second wedge shape, The p-InP has a modulation portion, There is a third wedge between the second wedge and the modulation portion, The second wedge is not applied to the p-InP, Light absorption is confined to the vicinity of the p-electrode. The wedge length of the third wedge is 5% or less of the length of the modulation portion.

2. A method for producing a hybrid optical element, wherein: A hybrid substrate is formed by bonding a silicon photonics substrate and an InP epitaxial substrate. The production method of the hybrid optical element includes a process of forming a device structure on the hybrid substrate, n-InP is formed to have a first wedge shape, The light absorbing layer is formed to have a second wedge shape, The light absorbing layer is formed so as to be exposed in the second wedge shape, A modulation portion is formed on p-InP. A third wedge is formed between the second wedge and the modulation portion so that the wedge length is 5% or less of the length of the modulation portion. wherein the second wedge is not applied to the p-InP, Light absorption is confined to the vicinity of the p-electrode.

3. A hybrid optical element, wherein: The hybrid optical element is composed of p-InP, light absorption layer, n-InP, dielectric film, optical waveguide, BOX layer and core substrate in order from the surface layer. The light absorbing layer has a second wedge shape, The light absorbing layer is exposed in the second wedge shape, When the second wedge shape is divided into a terminal portion extending from the terminal end to a portion where a mold intersection occurs and a base portion extending from the portion where the mold intersection occurs to a base, the terminal portion of the second wedge shape has a smaller wedge ratio than the base portion of the second wedge shape.

4. The hybrid light element according to claim 3, wherein: The mixed light element has a modulation part, A third wedge shape is provided between the second wedge shape and the modulation portion. The hybrid light element according to claim 3 , wherein: The optical waveguide is a Si waveguide or a SiN waveguide. The hybrid light element according to claim 3 , wherein: The hybrid optical element functions as an EA modulator, The mode is transferred from the optical waveguide to the light absorbing layer by the adiabatic transfer type optical coupler having the second wedge shape.

7. The hybrid light element according to claim 3, wherein: The hybrid optical element functions as an EA modulator or a directly modulated laser diode.

8. A method for producing a hybrid optical element, wherein: A hybrid substrate is formed by bonding a silicon photonics substrate and an InP epitaxial substrate. The production method of the hybrid optical element includes a process of forming a device structure on the hybrid substrate, The light absorbing layer is formed to have a second wedge shape, The light absorbing layer is formed so as to be exposed in the second wedge shape, When the second wedge shape is divided into a terminal portion extending from the terminal end to a portion where a mold intersection occurs and a base portion extending from the portion where the mold intersection occurs to a base, the terminal portion of the second wedge shape is formed to have a smaller wedge ratio than the base portion of the second wedge shape.

9. The method for producing a hybrid optical element according to claim 8, wherein: forming a modulation section, A third wedge shape is formed between the second wedge shape and the modulation portion.

10. The method for producing a hybrid optical element according to claim 8, wherein: The silicon photonic substrate and the InP epitaxial substrate are bonded together by wafer bonding based on a surface activated bonding technique or by using a resin material.

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