Optical device, transmitter, and transceiver

Abstract

To suppress occurrence of a slot line mode with simple structure.SOLUTION: An optical device includes: an optical modulation section 113 that is provided on a first surface side of a board 101 and includes multiple electrodes 116, 117 for modulating a light signal; and multiple vias 118 that extend in a thickness direction of the board 101 and are connected to multiple ground electrodes 117 for composing the multiple electrodes. The optical device also includes an electrode 119 on a second surface side that is provided on a second surface side that opposes a first surface side of the board 101 and is connected to the multiple vias 118. The electrode 119 on the second surface side may be provided on a lower surface of the board 101 or inside the board 101, or may be provided on another board different from the board 101 and may be connected to the vias 118 by movement of the board 101.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to optical devices, transmitters and transceivers. [Background technology]

[0002] In order to cope with the recent rapid increase in optical transmission capacity of IP data, there is an urgent need to develop communication devices and equipment that support this. For example, optical modulators for high-speed data transmission are beginning to be put into practical use at 400 Gbit / sec level (64 Gbaud symbol rate for multi-level modulation, e.g., 16QAM modulation). In addition, standardization toward 800 Gbit / sec level (128 Gbaud symbol rate) is currently underway, requiring optical modulators with even wider bandwidth. On the other hand, increasing transmission capacity in data centers and other facilities requires the installation of more optical transmission equipment and optical transceivers, which also necessitates the miniaturization of optical devices.

[0003] Silicon modulators are optical modulators capable of high-speed operation of 400 Gbit / sec (symbol rate of 64 Gbaud) and miniaturization. However, these silicon modulators have limitations in modulation speed, and while they can handle up to 64 Gbaud, they are known to be difficult to apply to higher-speed transmissions. For this reason, development of modulator materials other than silicon is gaining momentum. On the other hand, silicon photonics-based optical elements have the advantage of being able to be integrated compactly on a silicon substrate. For this reason, methods for integrating modulator materials other than silicon on a silicon substrate are being considered, such as integrating only the modulator portion of a silicon photonics integrated circuit using materials such as EO polymers that are capable of high-speed modulation and have a high electro-optic constant (referred to as a high EO coefficient).

[0004] The following patent documents disclose prior art techniques for providing a silicon substrate with photoelectric conversion functionality. For example, a semiconductor substrate having a photoelectric conversion element is provided with a through electrode as a gate electrode, and source and drain regions are provided around the through electrode, with the electrode of the photoelectric conversion element being connected to the gate electrode of the through electrode. Another example relates to integrated silicon photonics devices for broadband communications, and provides multiple through silicon vias in the substrate of an optoelectronic module based on silicon photonics. Another example relates to photonic integrated circuits, and provides multiple optical ICs on an insulating wafer and connects them via substrate vias. Another example is a spatial light modulator that includes a substrate and multiple laminates, and has through holes connecting the front and back of the substrate to increase speed. There are also circuit boards and electronic devices that include optoelectronic modules with circuit patterns and through electrodes on semiconductor substrates such as silicon wafers (see, for example, Patent Documents 1 to 5 below).

[0005] Also disclosed is a technique for suppressing high-frequency electrical propagation modes (slot-line modes) by connecting ground electrodes on a substrate with bonding wires or ground shields (see, for example, Non-Patent Documents 1 and 2 below). Also disclosed is a technique for suppressing slot-line modes inside an optical modulator by connecting ground electrodes with vias and metal layers along part of the length (see, for example, Non-Patent Document 3 below). Also disclosed is a technique for propagating light through multiple optical waveguides in a thin-film LN optical modulator having a thin-film LN substrate (see, for example, Non-Patent Document 4 below). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 138197 [Patent Document 2] U.S. Patent Application Publication No. 2020 / 0152574 [Patent Document 3] U.S. Patent Application Publication No. 2021 / 0302654 [Patent Document 4] International Publication No. 2021 / 132374 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-277927 [Non-patent literature]

[0007] [Non-Patent Document 1] Hao Xu,et.al,“Demonstration and Characterization of High-Speed ​​Silicon Depletion-Mode Mach-Zehnder Modulators”,Journal of selected topics in quantum electronics,Vol.20,No.4,p.3400110,July / August2014. [Non-patent document 2] Xiaoguang Tu,et.al,“Silicon optical modulator with shield coplanar waveguide electrodes”, optics express vol.22,no.19,September,2014. [Non-patent document 3] Ran Ding, et.al, “High-Speed ​​Silicon Modulator With Slow-Wave Electrodes and Fully Independent Differential Drive”, Journal of lightwave technology, Vol. 12, No. 12, p. 2240-2247, June, 2014. [Non-patent document 4] Nicholas Boynton, et al, “A Heterogeneously integrated silicon photonic / lithium niobate traveling wave electro-optic modulator”, optics express vol.28, no.2, p.1868, January, 2020. Summary of the Invention [Problem to be solved by the invention]

[0008] By integrating high EO materials into silicon photonics devices, it is possible to address the challenges of silicon modulators, such as modulation speed and voltage reduction, but it is not possible to suppress the conversion from CPW mode to slotline mode that accompanies signal propagation in the high-frequency electrodes. Conventional modulators have been unable to suppress the characteristic degradation caused by the electrodes and achieve a broadband.

[0009] In one aspect, an object of the present invention is to be able to suppress the occurrence of slot-line modes with a simple structure. [Means for solving the problem]

[0010] According to one aspect of the present invention, an optical device has an optical modulation section provided on a first surface side of a substrate and including a plurality of electrodes that modulate an optical signal, a plurality of vias extending in the thickness direction of the substrate and connected to a plurality of ground electrodes that constitute the plurality of electrodes, and electrodes on the second surface side of the substrate that are opposite to the first surface side and connected to the plurality of vias. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to suppress the occurrence of slot-line modes with a simple structure. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an optical device according to an embodiment. [Figure 2] FIG. 2 is a top view showing an example of the configuration of an optical modulator including an optical device. [Figure 3A] FIG. 3A is a top perspective view of an optical device according to an embodiment. [Figure 3B] FIG. 3B is a bottom perspective view of the optical device according to the embodiment. [Figure 4]FIG. 4 is a diagram illustrating a configuration example in which the optical device according to the embodiment is applied to a transmitter / receiver. [Figure 5] FIG. 5 is a cross-sectional view showing an optical modulator according to the prior art. [Figure 6] FIG. 6 is a cross-sectional view showing the occurrence of slot line modes according to the prior art. [Figure 7] Figure 7 is a cross-sectional view of an example of a conventional countermeasure against slot line modes. (Part 1) [Figure 8] Figure 8 is a cross-sectional view of an example of a conventional countermeasure against slot line modes. (Part 2) [Figure 9] Figure 9 is a cross-sectional view of a conventional countermeasure against slot line mode (part 3). [Figure 10] FIG. 10 is a cross-sectional view showing an example of the configuration of a conventional EO polymer optical modulator. [Figure 11] FIG. 11 is a cross-sectional view showing an example of the configuration of a thin-film LN optical modulator according to the prior art. [Figure 12A] FIG. 12A is a diagram showing the results of a simulation of the transfer characteristics of a high-frequency electrical signal in an optical modulator (prior art). [Figure 12B] 12B is a diagram showing the results of a simulation of the transfer characteristics of a high-frequency electrical signal in an optical modulator. [Figure 13] FIG. 13 is a cross-sectional view showing the silicon photonics integrated thin film LN optical modulator according to the first embodiment. [Figure 14A] FIG. 14A is a diagram showing a configuration example of a thin-film LN optical modulator with a GSG structure applied to Example 2. (Part 1) [Figure 14B] FIG. 14B is a diagram showing a configuration example of a thin-film LN optical modulator with a GSG structure applied to the second embodiment. (Part 2) [Figure 14C] FIG. 14C is a cross-sectional view showing a configuration example of a thin-film LN optical modulator with a GSG structure according to the second embodiment. [Figure 15A] FIG. 15A is a cross-sectional view showing a configuration example of an EO polymer optical modulator according to a third embodiment. [Figure 15B]FIG. 15B is a cross-sectional view showing a configuration example of the EO polymer optical modulator of Example 3. (Part 2) [Figure 16] FIG. 16 is a cross-sectional view showing an example of the configuration of a thin-film LN optical modulator according to a fourth embodiment. [Figure 17] FIG. 17 is a cross-sectional view showing a configuration example of a silicon optical modulator according to a fifth embodiment. [Figure 18] FIG. 18 is a top view showing a configuration example of an optical modulator with segmented electrodes according to a sixth embodiment. [Figure 19] FIG. 19 is a top view illustrating a configuration example of a transmitter / receiver according to a seventh embodiment. [Figure 20A] FIG. 20A is a cross-sectional view showing a photoelectric conversion device according to Example 8 (part 1). [Figure 20B] FIG. 20B is a cross-sectional view showing the photoelectric conversion device of Example 8 (part 2). [Figure 21A] FIG. 21A is a cross-sectional view of a conventional photoelectric conversion device for comparison with Example 8 (part 1). [Figure 21B] FIG. 21B is a cross-sectional view of a conventional photoelectric conversion device for comparison with Example 8 (part 2). DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, with reference to the drawings, embodiments of the disclosed optical device, transmitter, transceiver, and optical-electrical conversion device will be described in detail.

[0014] (Configuration Example of Optical Device According to Embodiment) Fig. 1 is a cross-sectional view showing an optical device according to an embodiment. Fig. 2 is a top view showing a configuration example of an optical modulator including the optical device. Fig. 1 corresponds to the cross-sectional view taken along line A-A' in Fig. 2. The optical device according to the embodiment is formed by compactly integrating optical elements on a silicon substrate by using, for example, silicon photonics technology.

[0015] 1 shows an example of the configuration of an EO polymer optical modulator 100 as an optical device. A silicon dioxide (SiO2) layer 111, which is a first insulating layer, and a second SiO2 layer 112 are laminated on a first surface (upper surface, front surface) of a silicon substrate 101. A pair of optical modulation units (optical modulation elements) 113 (113a, 113b) are provided on the first SiO2 layer 111 (second SiO2 layer 112).

[0016] The optical modulation section 113 is composed of a silicon slab section 121 doped with p-type or n-type impurities to provide conductivity and a silicon rib section 122, which has a protruding shape for guiding light, arranged opposite each other with a gap of several hundred nanometers between them. An EO polymer section 124 is arranged between and around the silicon slab section 121 and the silicon rib section 122.

[0017] EO polymer materials exhibit electro-optical effects when heated to a temperature above their glass transition temperature (e.g., 150°C or higher), subjected to a molecular orientation process called poling, and then cooled. In the configuration of Figure 1, most of the light passes through the EO polymer portion 124 between the silicon rib portions 122, and the device functions as an EO polymer optical modulator.

[0018] In one optical modulation section 113a, one silicon slab section 121 is connected to a signal electrode S (116a) on the second SiO2 layer 112 through a via 123 extending in the thickness direction of the second SiO2 layer 112. The other silicon slab section 121 is connected to a ground electrode G (117a) on the second silicon layer 112 through a via 123 extending in the thickness direction of the second silicon layer 112.

[0019] In the other optical modulation section 113b, one silicon slab section 121 is connected to the signal electrode S (116b) on the second SiO2 layer 112 through a via 123 extending in the thickness direction of the second SiO2 layer 112. The other silicon slab section 121 is connected to the ground electrode G (117b) on the second SiO2 layer 112 through a via 123 extending in the thickness direction of the second SiO2 layer 112.

[0020] A ground electrode G (117c) is provided between the pair of signal electrodes S (116a, 116b) on the second SiO2 layer 112. In the example shown in Fig. 1, the ground electrode G (117c) is arranged as a GSGSG electrode in the width direction Y of the substrate 101 on which the pair of optical modulation sections 113 (113a, 113b) are provided.

[0021] The substrate 101 is provided with vias 118 extending in the thickness direction Z of the substrate 101. The ground electrode G (117) is connected to a second surface electrode (also referred to as a back surface electrode or a ground electrode) 119 provided on a second surface side (lower surface) opposite to the first surface side of the substrate 101 via the first SiO2 layer 111, the second SiO2 layer 112, and the vias 118 extending in the thickness direction of the substrate 101. The ground electrode G (117a) is connected to the back surface electrode 119 via a via 118a. The ground electrode G (117b) is connected to the back surface electrode 119 via a via 118b. The ground electrode G (117c) is connected to the back surface electrode 119 via a via 118c.

[0022] In the example of FIG. 1, the electrode 119 on the second surface side is provided on the second surface (lower surface, back surface) of the substrate 101. However, as will be described later, the electrode 119 on the second surface side may be provided between the first surface (upper surface) and the second surface (lower surface) of the substrate 101, i.e., inside the substrate 101 (see, for example, FIG. 16). Furthermore, the electrode 119 on the second surface side may be provided on a substrate separate from the substrate 101, and the ground electrode 117 of the substrate 101 may be grounded by moving the substrate 101 (see, for example, FIG. 15A). In this way, the electrode 119 on the second surface side is an electrode provided at a predetermined position on the second surface side in the thickness direction of the substrate 101, rather than at the position on the first surface (upper surface) of the substrate 101.

[0023] Figure 2 corresponds to a top view of the optical modulator 100 in Figure 1 and shows a Mach-Zehnder optical modulator. Figure 2 also shows the components of a more general optical modulator. An optical input is split into two by an optical splitter 201 and guided to a pair of optical waveguides 202. The pair of optical waveguides 202 have a predetermined length in the longitudinal direction X, and are combined by an optical combiner 203 to produce an optical output.

[0024] 1 is provided in the predetermined length of the optical waveguide 202, and a ground electrode G (117a) and a signal electrode S(+) 116a are provided on both sides of one optical modulation section 113a. A signal electrode S(-) 116b and a ground electrode G (117b) are provided on both sides of the other optical modulation section 113b. A ground electrode G (117c) is provided between the signal electrode S(+) 116a and the signal electrode S(-) 116b.

[0025] A signal from a transmission signal source 211 is supplied to one end of a signal electrode S(+) 116a and one end of a signal electrode S(-) 116b via a driver amplifier 212. The other ends of the signal electrodes S(+) 116a and S(-) 116b are terminated by a termination resistor 213.

[0026] An optical input output from a wavelength tunable laser light source or the like is split by an optical splitter 201 and then guided to a pair of optical waveguides 202. The light guided through the optical waveguide 202 is optically modulated by a pair of optical modulation units 113 (113a, 113b) based on a signal from a transmission signal source 211, and after being combined by an optical combiner 203, is optically output as modulated signal light.

[0027] 3A is a top perspective view of the optical device according to the embodiment, and FIG. 3B is a bottom perspective view of the optical device according to the embodiment.

[0028] As shown in FIG. 3A, the three ground electrodes G (117a to 117c) on the upper surface are connected to one end of a plurality of vias 118 (118a to 118c) provided at different positions (three locations) in the length direction.

[0029] These multiple vias 118 (118a to 118c) extend in the thickness direction of the substrate 101, and the other ends are connected to back surface electrodes 119 provided on the lower surface side shown in Fig. 3B. In the example shown in Fig. 3B, three back surface electrodes 119 (119a, 119b, 119c) are provided along the width direction Y at different positions in the length direction X of the ground electrode G (117a to 117c). However, the back surface electrodes 119 may be provided over the entire back surface of the optical modulator 100.

[0030] Fig. 4 is a diagram showing an example of a configuration in which an optical device according to an embodiment is applied to a transceiver. The transceiver 400 is fabricated using semiconductor fabrication technology together with an optical waveguide and an optical functional element on a silicon substrate 403 using silicon photonics technology. The transmitter 401 is composed of an optical integrated element for polarization multiplexed coherent optical transmission fabricated using silicon photonics technology. The transceiver 400 shown in Fig. 4 has the transmitter 401 and receiver 402 provided on the same silicon substrate 403.

[0031] The optical modulation section 410 of the transmitter 401 (corresponding to the optical modulator 100 in FIG. 1) is a Mach-Zehnder modulator having a plurality of modulators 411 and an optical waveguide 412. The optical modulation section 410 includes, for example, two parent Mach-Zehnder interferometers 411 (411a, 411b) roughly divided into X- and Y-polarized waves and four child Mach-Zehnder interferometers for the eight-branched optical waveguide 412. The portion indicated by the dotted line in FIG. 4 corresponds to the optical modulator 100 (a pair of optical modulation sections 113a, 113b) shown in FIGS. 1 and 2.

[0032] In the transmitter 401, light from a wavelength-tunable laser light source (not shown) is incident on the optical waveguide end face, which is the optical input port 421, and a portion of the light is branched and output to the optical modulation unit 410. The optical modulation unit 410 performs the desired optical modulation, and the polarization of the modulated signal light from one parent modulator 411a is rotated by 90 degrees by the polarization rotation unit 413. The polarization combining unit 414 performs polarization combining (X+Y) of the modulated signal light from one parent modulator 411b and the modulated signal light from the other parent modulator 411b, and emits the modulated signal light from the optical waveguide end face, which is the transmitted light output port 422.

[0033] In the receiver 402, received signal light is input to a received light input port 431, which is an end face of the optical waveguide, from an optical transmission fiber of an installed optical transmission line, and is separated into two polarized waves (X, Y) and branched into two by a polarization separator 432. One of the two branched polarized received signal lights is input to a 90-degree hybrid (HB) element 433a, and the other is input to a 90-degree hybrid element 433b via a polarization rotator 434.

[0034] On the other hand, a portion of the light incident from the optical waveguide end face of the optical input port 421 is branched and similarly input to two 90-degree hybrid elements 433a and 433b, respectively. A portion of the light from the wavelength-tunable laser light source is used as local light for the receiver 402. The 90-degree hybrid elements 433 (433a and 433b) of the receiver 402 have the function of converting the phase state of the received signal light into optical intensity using the local light as reference light. The optical intensity output from the 90-degree hybrid elements 433 (433a and 433b) is detected and output by eight Ge-doped PDs (photodetectors) 435.

[0035] According to the transceiver 400 shown in FIG. 4, by providing the transmitter 401 and the receiver 402 on the same silicon substrate 403, it is possible to achieve miniaturization and cost reduction.

[0036] (Regarding the prior art) Here, the prior art and the problems that led to the present invention will be described with reference to FIGS.

[0037] 5 is a cross-sectional view showing an optical modulator according to the prior art. In the conventional optical modulator 500, a first SiO2 layer 511 and a second SiO2 layer 512 are formed on a silicon substrate 501, and an optical modulation section 513 is formed in the first SiO2 layer 511 and the second SiO2 layer 512. The optical modulation section 513 has a p-type doped region 501, which is doped p-type, and an n-type doped region 502. The p-type doped region 501 and the n-type doped region 502 are connected to their respective electrodes 504 and 505 via vias 506.

[0038] The pn junction is connected to a silicon optical waveguide, and the refractive index of the pn junction changes by controlling the carrier density through the voltage applied to electrodes 504 and 505. The electrodes include a signal electrode S (504) and a ground electrode G (505) that form the differential transmission.

[0039] Although not shown, the optical modulator 500 includes a transmission signal source, a driver amplifier, an optical splitter, a pair of optical waveguides, an optical combiner, and a termination resistor, similar to those in FIG. 2. In the configuration example shown in FIG. 1, the electrodes are arranged in a GSGSG configuration in the width direction Y where the pair of optical modulation units 513 are provided. The direction of change in the optical phase changes when the voltages of the two signal electrodes S (504) have opposite polarities. After splitting by the optical splitter, the phase of the light from one optical modulation unit 513 lags, and the phase of the light from the other optical modulation unit 513 advances. This generates a phase difference, and the light interferes when combined by the optical combiner, making it possible to modulate the phase and intensity of the light and output it.

[0040] The electrical signal output from the transmission signal source is amplified by the driver amplifier to the voltage required by the optical modulation section, and then propagates in the X-axis direction in Figure 5 to the terminal end of the signal electrode S (504). In order to properly convert the electrical modulation signal into an optical modulation signal, it is necessary for the electric field to propagate correctly through the signal electrode S (504) from the driver amplifier to the terminal resistor.

[0041] Figure 6 is a cross-sectional view showing the generation of a slot line mode in the prior art. Figure 6 shows the electric field lines of the optical modulation unit 513 described in Figure 5. The prior art has problems in propagating high-frequency signals of several tens of GHz. When transmitting differential electrical signals, the desired transmission mode is one in which the potential of one signal electrode S(+) 504 of the GSGSG is higher than the potential of the ground electrode 505, and the potential of the other signal electrode S(-) 504 is lower than the potential of the ground electrode 505, as shown in Figure 6(a). This transmission mode is usually called a CPW mode (coplanar transmission mode).

[0042] However, since a pn junction optical modulation section is formed on only one side of each pair of GSG electrodes, and the pair of optical modulation sections 513 has poor symmetry, it is known that a high-frequency electrical propagation mode such as that shown in FIG. 6(b) actually occurs. This is called a slot-line mode. When this high-frequency electrical propagation mode conversion occurs, electrical signals cannot be transmitted properly, and accordingly, optical signals cannot be modulated properly, resulting in degradation of optical modulation characteristics. For example, the above-mentioned Non-Patent Documents 1 to 3 disclose conventional techniques for dealing with such slot-line modes.

[0043] 7 to 9 are cross-sectional views of examples of countermeasures against slot-line mode according to conventional techniques. The components of the optical modulation unit shown in these Figs. 7 to 9 are given the same reference numerals as in Fig. 5. First, in the optical modulator 700 shown in Fig. 7 (corresponding to Non-Patent Document 1), the ground electrode G (505) of the GSGSG electrode is connected by a bonding wire 701 to have the same potential. This suppresses conversion from CPW mode to slot-line mode.

[0044] 8 (corresponding to Non-Patent Document 2), the ground electrodes G (505) of the GSGSG electrodes are connected with a ground shield 801 to achieve the same potential, thereby suppressing conversion from the CPW mode to the slot-line mode.

[0045] In addition, in the configuration example of the optical modulator 900 shown in FIG. 9 (corresponding to Non-Patent Document 3), the cross-sectional structure is not uniform, and the silicon layers 511 and 512 inside the optical modulator 900 have a structure in which the structures of FIG. 9(a) and FIG. 9(b) are periodically repeated in the longitudinal direction X.

[0046] 9(a), at a predetermined position in the longitudinal direction X of the optical modulator 900, the optical modulation section 513 is connected to a first metal layer 902 by a via 901, and second metal layers 504 and 505 connected by a via 903 are formed on the first metal layer 902. These second metal layers 504 and 505 serve as a signal electrode 504 and a ground electrode 505 for applying a modulated electrical signal from the outside.

[0047] 9(b), the ground electrodes 505 of the GSGSG are connected by vias 904 and a third metal layer 905 at positions different from those shown in FIG. 9(a) in the longitudinal direction X of the optical modulator 900.

[0048] In the configuration of Fig. 9(a), conversion of the electrical signal to the slot-line mode occurs, but with the configuration of Fig. 9(b), the slot-line mode is suppressed and the mode becomes CPW mode based on the same principle as in Fig. 7 (Non-Patent Document 1) and Fig. 8 (Non-Patent Document 2). However, in the section of the configuration shown in Fig. 9(b) in the longitudinal direction X of the optical modulator 900, an electrical signal cannot be supplied to the optical modulator 900 (optical modulation section 513), and therefore optical modulation is not possible, and the modulation efficiency of the entire modulator decreases by an amount corresponding to the length of the section of Fig. 9(b) x the arrangement period.

[0049] As mentioned above, silicon optical modulators operate on the principle that the carrier density at the pn junction is changed by an external electric field, thereby changing the refractive index at the pn junction and modulating the phase of the light passing through.

[0050] However, this operating principle has limitations on modulation speed. For example, while it can handle up to about 64 Gbaud, it is known that it is difficult to apply it to higher-speed transmission. In addition, the degree of optical phase modulation relative to voltage is small, so it is necessary to amplify the amplitude of the modulated electrical signal, which limits how low the voltage can be. To address these issues, there has been active development of modulator materials other than silicon.

[0051] On the other hand, silicon photonics-based optical elements (optical waveguides, optical combiners, optical splitters, Ge photodetectors, 90-degree hybrids, etc.) such as the transceiver 400 shown in Fig. 4 have the advantage of being able to be compactly integrated on a silicon substrate 403. Therefore, a promising approach is to integrate modulator materials other than silicon on a silicon substrate.

[0052] Specifically, this is a method of integrating a material capable of high-speed modulation and having a high electro-optic constant (called a high EO coefficient) only in the optical modulation section 410 of a silicon photonics integrated circuit. Materials with a high EO coefficient that are being considered include EO polymer, thin-film LN (lithium niobate), PLZT (lanthanum-doped lead zirconate titanate), and BTO (barium titanate).

[0053] FIG. 10 is a cross-sectional view showing an example of the configuration of a conventional EO polymer optical modulator, and FIG. 11 is a cross-sectional view showing an example of the configuration of a conventional thin film LN optical modulator.

[0054] In Fig. 10, the same components as in Fig. 5 are denoted by the same reference numerals. The optical modulation section 1003 of the EO polymer optical modulator 1000 in Fig. 10 has a silicon slab section 1001 doped with p-type or n-type impurities to provide conductivity, and a silicon rib section 1002 with a protruding shape for guiding light. The silicon rib sections 1002 are arranged opposite each other with a gap of several hundred nanometers between them, and an EO polymer section 1004 is arranged between and around them.

[0055] EO polymer exhibits an electro-optic effect when it is heated to a temperature above its glass transition temperature (e.g., 150°C or higher), subjected to a molecular orientation process called poling, and then cooled. In the configuration of Figure 10, most of the light passes through the EO polymer portion 1004 between the silicon rib portions 1002, functioning as an EO polymer optical modulator 1000. A typical method for manufacturing such an EO polymer optical modulator 1000 using silicon photonics integration is to apply a dissolved EO polymer solution from above the silicon substrate 501 to the position of the EO polymer portion 1004 using a precision dispenser or the like, and then cure it.

[0056] 11 includes electrodes 504 and 505 and two optical waveguides 1102 and 1103 arranged vertically on a silicon substrate 501. A thin-film LN substrate 1104 is bonded onto the electrodes 504 and 505 and the optical waveguides 1102 and 1103.

[0057] The thin-film LN substrate 1104 is formed by forming an insulating film such as SiO2 on an LN substrate or the like, and then forming a thin-film LN layer on top of that, and is bonded with the thin-film LN layer facing downwards. The LN substrate and light propagation are disclosed in the above-mentioned Non-Patent Document 4.

[0058] 11, light input through a tapered optical transition structure (not shown) travels in the depth direction X of the figure and transitions from optical waveguide 1102 to optical waveguide 1103, with most of the light propagating while seeping into the LN portion, functioning as a thin-film LN optical modulator 1100. After undergoing optical phase modulation in the thin-film LN substrate 1104, the light transitions again to optical waveguide 1102 and is output. The thin-film LN substrate 1104 is integrated on a silicon substrate 501 on which an SiO2 layer 511 and an SiO2 layer 512 are laminated by a technique such as microtransfer printing.

[0059] As shown in Figures 10 and 11, integrating high EO materials into silicon photonics elements can address the challenges of silicon modulators, such as modulation speed and voltage reduction. However, optical modulators using high EO materials still suffer from the challenge of conversion from CPW mode to slot-line mode as the signal propagates through the high-frequency electrodes.

[0060] However, it is difficult to address the issue of slot-line mode generation in the conventional techniques (corresponding to Non-Patent Documents 1 to 3) shown in Figures 7 to 9. The reason is that in all of these conventional techniques, the ground electrodes 505 of the GSGSG electrodes are connected on the upper surface side of the optical modulation section 513.

[0061] Furthermore, in modulators using high EO materials, both the EO polymer optical modulator 1000 shown in Fig. 10 and the thin-film LN optical modulator 1100 shown in Fig. 11 are formed by applying or attaching a different material to the upper surface of the silicon substrate 501. When fabricating the EO polymer optical modulator 1000, the spacing between the GSGSG electrodes 504, 505, i.e., the spacing in the width direction Y of the region where the EO polymer solution is applied (the optical modulation section 513), is several tens of microns. For this reason, when the EO polymer solution is applied in practice, the solution spreads to the electrodes 504, 505, making it difficult to perform wire bonding or other processes.

[0062] 11, the electrodes 504, 505 are not exposed on the top surface, making it difficult to implement wire bonding as shown in FIG. 7 or the shield ground arrangement as shown in FIG. 8. Furthermore, the thin-film LN optical modulator 1100 requires that the optical waveguides 1102, 1103 and the thin-film LN substrate 1104 be located close to each other. This makes it difficult to provide a structure such as a metal layer for connecting the ground electrodes 505 to the upper inner layer (second SiO layer 512) of the optical modulator 900 shown in FIG.

[0063] As described above, in the conventional optical modulator, when a structure in which different materials are integrated on a silicon substrate is used, it is not possible to suppress the occurrence of high-frequency electrical propagation mode conversion (slot-line mode).

[0064] (Comparison between the prior art and the embodiment) 1 and the like, the optical device of the embodiment is an optical modulator 100 in which different materials are integrated, and an EO polymer portion 124 is formed on a silicon substrate 101. Furthermore, the optical modulator 100 of the embodiment has vias 118 (118a to 118c) formed in each ground electrode G (117; 117a to 117c) of the GSGSG structure, the vias 118 extending in the thickness direction of the SiO2 layers 111 and 112. The vias 118 are connected to a back electrode 119 of the silicon substrate 101.

[0065] For example, the via 118 is formed by etching the silicon substrate 101 and filling it with a metal material. Also, an insulating film having a thickness of several microns or less is formed around the hole of the via 118 to insulate it from the silicon substrate 101. Then, the back electrode 119 is also wired after an insulating film is formed to insulate it from the silicon substrate 101.

[0066] The via 118 is generally called a TSV (Through Silicon Via), has a diameter of several microns to several tens of microns, is filled with copper, and has a surrounding insulating film of SiO2 with a thickness of several microns or less. The via 118 can be formed in the silicon substrate 101 by polishing the silicon substrate 101 using a CMP (Chemical Mechanical Polishing) method and thinning it to about 100 microns.

[0067] In a silicon photonics device such as the optical modulator 100 of the embodiment, the optical waveguide, optical modulator, optical receiver, etc. are all formed within a few microns from the surface of the silicon substrate 101. For this reason, in conventional technology, there is no need to thin the silicon substrate itself, and thinning is generally not performed. On the other hand, in semiconductor memory devices and the like, a configuration is used in which the silicon substrate is thinned to increase capacity, and TSVs are formed and stacked three-dimensionally.

[0068] In the embodiment, this is realized by applying a technology for thinning a silicon substrate to a silicon photonics substrate. In the embodiment, the ground electrode G (117) of the GSGSG electrode is connected to the back side of the silicon substrate 101 by a GND bridge using TSV, so that it is easy to integrate different materials on the front side of the silicon substrate 101.

[0069] Next, the suppression of high-frequency electrical propagation mode conversion by the optical modulator 100 according to the embodiment was verified by electromagnetic field simulation. The perspective views of the optical modulator 100 shown in FIGS. 3A and 3B correspond to the simulation model. In the simulation model, as shown in FIGS. 3A and 3B, vias 118 (118a to 118c) extending in the thickness direction of the silicon substrate 101 are used, and the back electrode 119 of the silicon substrate 101 connects the ground electrodes G (117; 117a to 117c) of the GSGSG electrode. For example, the diameter of the vias 118 is 10 μm, the thickness of the silicon substrate is 100 μm, the thickness of the insulating film is 1 μm, and the conductive material is copper, with the electrical conductivity of copper being used.

[0070] 12A and 12B are diagrams showing the results of a simulation of the transfer characteristics of a high-frequency electrical signal in an optical modulator. FIG. 12A shows the results of a simulation of the transfer characteristics of a high-frequency electrical signal when there is no GND bridge using a TSV, which corresponds to the prior art. FIG. 12B shows the results of a simulation of the transfer characteristics of a high-frequency electrical signal when there is a GND bridge using a TSV, which corresponds to an embodiment. The horizontal axis of these FIGS. 12A and 12B shows frequency, and the vertical axis shows S-parameter. Furthermore, since the optical modulator 100 transmits differential signals, the differential transmission characteristic Sdd 21 , operational reflex characteristics Sdd 11 This shows:

[0071] In Fig. 12A, large dips occur in the transmission characteristics near 45 GHz and 95 GHz, but in Fig. 12B, the occurrence of the dips is suppressed. According to the embodiment shown in Fig. 12B, it is shown that the high-frequency electrical propagation mode (slot-line mode) that occurs in the conventional technology shown in Fig. 12A can be suppressed. Note that the occurrence of dips in the frequency characteristics as a phenomenon when high-frequency electrical propagation mode conversion occurs is also shown in the above-mentioned Non-Patent Documents 1 and 2.

[0072] Example 1 Next, each embodiment of the optical modulator will be described. Fig. 13 is a cross-sectional view showing a silicon photonics integrated thin film LN optical modulator according to Example 1. In Fig. 13, an SiO2 layer 112 includes optical modulation sections 113a and 113b having optical waveguides 1301 and 1302 above and below. In the silicon photonics integrated thin film LN optical modulator 1300 shown in Example 1, a TSV via 118 is formed in the substrate 101 in the same manner as described above, and the ground electrode G (117) of the GSGSG electrode is connected to (ground electrode) 119 on the back side of the substrate 101.

[0073] Here, the upper surface of substrate 101 is not affected by the formation of via 118, and the upper surface remains the same as in Figure 11, so that thin-film LN chip 1303 can be mounted on the upper surface of substrate 101 by a method such as microtransfer printing. Also, a substrate on which thin-film LN is formed at the wafer stage can be attached to the upper surface of substrate 101. Note that via 118 and back surface electrode 119 may be formed before or after attaching thin-film LN chip 1303.

[0074] Example 2 14A and 14B are diagrams showing an example of the configuration of a thin-film LN optical modulator with a GSG structure applied to Example 2. Fig. 14A shows a top view of a Mach-Zehnder type optical modulator, and Fig. 14B shows a cross-sectional view taken along line A-A' in Fig. 14A. In Fig. 14A and Fig. 14B, the same components as those in Fig. 2 are assigned the same reference numerals.

[0075] EO polymers and LN have the property of delaying or advancing the phase of light depending on the direction of the applied electric field, which makes it possible to configure a Mach-Zehnder type optical modulator 1400 with the GSG structure shown in Figures 14A and 14B.

[0076] The electrical modulation signal is a single output that drives the signal electrode S (116) at the center of the optical modulator. The electric field is generated toward the ground electrodes G (117a, 117b) located on both sides of the signal electrode S (116). This results in a push-pull drive in which the phase changes in opposite directions, and the GSG structure also functions as an optical modulator. In this case, the diagram shows that the structure is uniform from the center signal electrode S (116) to the ground electrodes G (117a, 117b), and ideally, high-frequency propagation mode conversion would not occur. However, in reality, imperfections such as manufacturing variations or bent electrode structures can impair uniformity, causing degradation in high-frequency electrical signal propagation.

[0077] An important characteristic index of the optical modulator 1400 is the phase shift per unit length. The voltage required to change the phase of light by 180 degrees is called the half-wave voltage and is defined as voltage × length. Increasing the length of the optical modulator 1400 along the X-axis is an effective way to reduce the driving voltage for power consumption, but this increases the size of the optical modulator 1400. When arranging the driver amplifier 212 and other components that drive the optical modulator 1400 shown in Figure 14A on the substrate 101, bending the high-frequency electrode structure from the driver amplifier 212 to the optical modulator 1400 can sometimes be advantageous for overall device layout, given the increased size of the optical modulator 1400. In this case, even with a GSG electrode structure, the propagation distance of the high-frequency electrical signal differs between the left and right grounds at the bend, resulting in asymmetry.

[0078] 14C is a cross-sectional view showing a configuration example of a thin-film LN optical modulator with a GSG structure according to Example 2. In the thin-film LN optical modulator 1400 according to Example 2, as shown in FIG. 14C, the left and right ground electrodes G (171a, 117b) are connected to the ground by the back electrode 119 of the substrate 101 through vias 118a, 118b. This makes it possible to suppress mode conversion by connecting the left and right ground electrodes G (171a, 117b) even in the case of a curved electrode structure, for example.

[0079] Example 3 15A and 15B are cross-sectional views showing a configuration example of an EO polymer optical modulator of Example 3. In the above-described configuration example, among the electrodes of the GSGSG structure of the optical modulator, three ground electrodes G (117a to 117c) or two ground electrodes G (117a and 117b) of the GSG structure are connected by a back electrode 119 of the substrate 101. In Example 3, the ground electrodes G are connected to each other on a substrate 1510 separate from the substrate 101 of the optical modulator 1500.

[0080] As shown in FIG. 15A, bumps 1518 (1518a, 1518b) that are electrically connected to vias 118a, 118b are provided on the back surface of substrate 101. In the example of FIG. 15A, bumps 1518 are made of copper pillars and solder caps. Another substrate (second substrate) 1510 is disposed on the back surface of substrate 101, with its upper surface facing the back surface of substrate 101. Ground electrodes 1511 that are electrically connected to bumps 1518 (1518a, 1518b) are provided on the other substrate 1510. Then, bumps 1518 on the substrate 101 side of optical modulator 1500 are connected on the other substrate 1510. With this configuration, mode conversion in high-frequency signal propagation can be suppressed using the same principle as above.

[0081] In this way, a configuration in which a separate substrate 1510 is provided in addition to the substrate 101 of the optical modulator 1500 is necessary when the optical modulator is, for example, an EO polymer optical modulator 1500 as shown in Fig. 15A. In order for the silicon photonics integrated EO polymer optical modulator 1500 to function as an optical modulator, after an EO polymer solution is applied to the silicon waveguide, a poling process, which is a molecular orientation process for providing an electro-optic effect, must be performed.

[0082] To perform poling with the GSG electrode structure, it is necessary to apply a voltage to the EO polymer part 124. To apply a voltage during poling, it is necessary to apply a voltage to one of the ground electrodes G (117a) of the GSG structure, leave the signal electrode S (116) unconnected, and ground the other ground electrode G (117b). Therefore, the ground electrodes G (117a, 117b) on both sides of the GSG electrode must be electrically isolated only during the poling process.

[0083] Fig. 15B shows a state in which another substrate 1510 is separated from the substrate 101 of the optical modulator 1500. A poling process is performed on the substrate 101 of the optical modulator 1500 shown in Fig. 15B with the other substrate 1510 separated. Thereafter, by mounting the substrate 101 of the optical modulator 1500 on the other substrate 1510 as shown in Fig. 15A, it becomes possible to connect the ground electrodes G (117a, 117b) on both sides of the GSG structure to each other, and high-frequency propagation mode conversion can be suppressed when used as the optical modulator 1500.

[0084] In the above description, the bumps 1518 are formed on the second surface side of the substrate 101. However, the bumps 1518 may be formed on the second substrate 1510 at positions corresponding to the vias 118. Furthermore, the substrate 101 may be mounted after ball bumps are placed on the second substrate 1510 at positions corresponding to the vias 118.

[0085] Example 4 16 is a cross-sectional view showing an example of the configuration of a thin-film LN optical modulator of Example 4. In the above-described example, the ground electrode 117 on the top surface of the substrate 101 is connected to the backside electrode 119 or ground electrode 1511 on the back side of the substrate 101 through a via 118. In this thin-film LN optical modulator 1600 of Example 4, the optical modulation section is formed in a portion close to the LN substrate 1303. The ground electrodes 117 of the GSGSG structure or the GSG structure on the upper side of the substrate 101 are connected by ground wiring 1601.

[0086] In silicon modulators and EO polymer optical modulators, an SOI (Silicon On Insulator) substrate is used as the substrate 101, and the modulator is formed by etching the silicon layer above the SiO2 layer 111 on the upper side of the SOI substrate. In the thin-film LN optical modulator 1600 of Example 4, the etched silicon layer 1601 is doped to impart conductivity, and ground connections are made within the SiO2 layers 111 and 112. Using this method eliminates the need to form vias in the substrate 101, allowing for inexpensive manufacturing.

[0087] Example 5 17 is a cross-sectional view showing an example of the configuration of a silicon optical modulator according to a fifth embodiment. The present invention is primarily intended for application to modulators in which different materials are integrated on a silicon photonics substrate, but it can also be applied to conventional silicon modulators. The conventional silicon optical modulator 500 corresponds to FIG. 5.

[0088] The optical modulation sections 113 (113a, 113b) of the fifth embodiment each have a p-type doped region 1701 and an n-type doped region 1702. The p-type doped region 1701 and the n-type doped region 1702 are connected to the electrodes 116 and 117, respectively. The ground electrodes 117 (117a to 117c) are connected to the back electrode 119 of the substrate 101 through vias 118 (118a to 118c), respectively.

[0089] As will be explained in Example 8 below, there are cases where vias are formed for other purposes, and in such cases, if via 118 is formed at the same time, high-frequency electrical propagation mode conversion can be suppressed. This eliminates the need for dedicated measures such as the ground connection described in the prior art (FIGS. 7 to 9). Furthermore, because the ground connection described in FIG. 9 of the prior art is the only part that does not perform modulation, the modulator length can be shortened compared to the prior art of FIG. 9, which also has the advantage of enabling miniaturization.

[0090] Example 6 Fig. 18 is a top view showing a configuration example of an optical modulator with segmented electrodes according to Example 6. In Fig. 18, the same components as those in Figs. 2, 3A, and 3B are assigned the same reference numerals. As shown in Fig. 18, the electrodes of the GSGSG electrode structure are arranged in a plurality of positions along the longitudinal direction X when viewed from above, and each electrode has a substantially T-shape and is arranged opposite each other with an optical waveguide in between (see, for example, Non-Patent Document 3 mentioned above). This electrode shape is also called a capacitively loaded type, a slow wave type, a T-rail type, etc., in addition to the segment type.

[0091] In the high-frequency electrode of an optical modulator, it is necessary to match the propagation speed of electricity with the propagation speed of light, and the structure shown in Fig. 18 can reduce the propagation speed of the electrical signal, so it is often used as an electrode structure for optical modulators. In Example 6, the ground electrode G (117) of the T-shaped electrode is connected to a back electrode 119 on the back surface of the substrate 101 through a via 118. By using the structure of Example 6, it is no longer necessary to periodically arrange the connection parts between the modulation part and the ground in the length direction X, as in the conventional technology shown in Fig. 9, for example, and it is possible to shorten the length of the modulator in the length direction X and make it more compact.

[0092] Example 7 Fig. 19 is a top view showing an example of the configuration of a transceiver according to the seventh embodiment. In Fig. 19, the same components as those in Fig. 4 are assigned the same reference numerals. A transceiver 1900 shown in Fig. 19 is obtained by replacing the optical modulation section 410 (corresponding to the optical modulator 100) by silicon photonics integration shown in Fig. 4 with an optical modulation section 1910 integrated with a different material (for example, a high EO material). Although not shown, the ground electrodes G (117) of the modulation section 1910 are connected to each other on the back surface of the silicon substrate 403 or below the modulation section 1910 in the thickness direction, as in the above-described embodiments.

[0093] According to the seventh embodiment, it becomes possible to integrate a high EO material from the upper surface side of a silicon chip (silicon substrate 403). This makes it possible to manufacture an optical integrated device that can perform high-speed modulation using a heterogeneous material modulator while taking advantage of the advantage of silicon photonics technology, that is, the ability to integrate optical components with required functions in a small size.

[0094] Example 8 20A and 20B are cross-sectional views showing an optoelectric conversion device of Example 8. An optoelectric conversion device 2001 shown in FIG. 20A includes, as the silicon chip in Example 7, a silicon photonics element (SiPh element) 2011, a driver (DRV) 2012 for driving the SiPh element 2011, an optical fiber 2013 for inputting and outputting light, and the like. Reference numeral 2013a denotes a fiber block for fixing the optical fiber 2013. These optical components are mounted on an interposer 2014.

[0095] In the SiPh element 2011, for example, a ground electrode G (117) of an optical modulation unit 2021 made of a high EO material is connected to a back electrode 119 by a via 118. Between the optical modulation unit 2021 and the DRV 2012, a signal electrode (S) 116 and a ground electrode G (117) are respectively connected by wiring 2021a on the SiPh element 2011.

[0096] In order to form vias in the SiPh element 2011, the silicon photonics substrate is thinned to a thickness of about 100 microns, for example, by polishing, and by mounting it on the interposer 2014, the strength of the SiPh element 2011 can be reinforced and stress caused by the difference in thermal expansion between the SiPh element 2011 and the lowermost PCB substrate 2015 can be alleviated. Also, it is possible to provide the function of widening the spacing between the wiring on the back surface of the SiPh element 2011 to a spacing that makes it easier to mount on the PCB substrate 2015.

[0097] The photoelectric conversion device 2001 is also connected to a digital signal processing element (DSP) 2016 via a PCB substrate 2015. In the SiPh element 2011, the ground electrodes G (117) of the optical modulation section 2021 are connected to each other by vias 118 through back surface electrodes 119, as described above. In the eighth embodiment, another via 118A provided in the SiPh element 2011 is also used as a path for inputting an electrical signal output from the DSP 2016 to the DRV 2012.

[0098] The DSP 2016 to the DRV 2012 are connected via a via 2018A in the DPS substrate 2018, wiring 2015A on the PCB substrate 2015, a via 2014A in the interposer 2014, and a via 118A in the SiPh element 2011.

[0099] In addition to the optical modulation unit 2021 (corresponding to the optical modulation unit 113 in Figure 1), the SiPh element 2011 may also be equipped with a DRV 2012, a receiving signal amplification element (not shown), and a DSP 2016, and any combination of these may be installed.

[0100] 20A, the photoelectric conversion device 2002 shown in FIG. 20B is almost the same as that shown in FIG. 20A, but the connection of the ground electrode G (117) is different. In the photoelectric conversion device 2001 shown in FIG. 20A, the ground connection is made by the back surface electrode 119 shown in Example 2 (see FIG. 14C, etc.). In contrast, the photoelectric conversion device 2002 shown in FIG. 20B(b) is connected to the ground by the method shown in FIG. 15A, etc., i.e., via a separate substrate, for example, a ground pattern 2014a on an interposer 2014, without using the back surface electrode 119 of the SiPh element 2011.

[0101] As is clear from Fig. 20B, this method can be easily applied when mounting SiPh element 2011 on interposer 2014. Either the method shown in Fig. 20A or the method shown in Fig. 20B can be selected as needed.

[0102] 21A and 21B are cross-sectional views showing a conventional photoelectric conversion device for comparison with Example 8. For convenience, in these Figs. 21A and 21B, the same components as those in Figs. 20A and 20B are denoted by the same reference numerals, and a DRV 2012 is disposed on an interposer 2014. The photoelectric conversion device 2101 in Fig. 21A shows an example in which an optical modulation section 2021 and a DRV 2012 are connected by wire bonding 2111.

[0103] 21B is an example in which both the input and output of the DRV 2012 are connected by wire bonding. The DRV 2012 is connected by wire bonding 2111 on the optical modulation unit 2021 side and by wire bonding 2112 on the DSP 2016 side.

[0104] As described above, the photoelectric conversion device 2001 is required to support high-speed signal transmission such as 64 Gbaud or 128 Gbaud as the transmission speed. The silicon photonics substrate (SiPh element) 2011 of Example 8 (FIGS. 20A and 20B) is thinned to about 100 microns by polishing, for example, and the length (depth) of the via 118A portion can be made shorter than that of the wire bonding 2111 shown in FIG. 21A. Therefore, Example 8 can reduce the attenuation of high-frequency signals compared to that of wire bonding, which is advantageous for high-speed transmission devices.

[0105] In the eighth embodiment, when via 118A is formed in silicon photonics device 2011 for the purpose of high-speed transmission, via 118 for connecting the ground electrodes of the optical modulator, which is an application of the present invention, can also be formed. This allows the present invention to be applied without any additional cost increase.

[0106] The embodiments of the present invention, including the above examples, have been described on the premise of the formation of a silicon substrate 101 and vias 118 extending in the thickness direction of the substrate 101. Since the higher the resistivity of the substrate 101, the lower the high-frequency loss, the further improved characteristics can be achieved by using a quartz substrate or the like for the substrate 101. Formation of vias 118 in a glass substrate 101 such as quartz can be achieved by TGV (Through Glass Via) technology. Furthermore, a passivation film may be provided on the electrodes (signal electrode 116, ground electrode 117) on the substrate 101 described in each example.

[0107] As described above, the optical modulator described in the embodiments can suppress conversion of the high-frequency electrical propagation mode (slot-line mode) caused by the asymmetry of the structure that occurs when an optical modulator function is introduced into the high-frequency electrode structure, thereby preventing deterioration of the optical modulator's characteristics. For example, the present invention can be applied to optical modulators that integrate heterogeneous materials, which are necessary for high-speed modulation of 64 Gbaud or more. Furthermore, by applying the present invention to silicon photonics integrated elements as shown in each embodiment, it becomes possible to provide small-sized optical devices that can operate at high speeds.

[0108] The present invention does not limit the materials used for the modulator integrated on the substrate. It is clear that, in addition to the EO polymer and LN described above, dielectrics such as BTO and PLZT, and semiconductors such as InP, can also be used. Furthermore, heterogeneous material integrated optical modulators do not necessarily need to be formed on a silicon substrate, such as when forming a standalone optical modulator. For example, a wafer with an SiO2 film formed on an LN substrate and a thin film of LN formed on top of that can be used. While LN is more difficult to process than silicon, as long as the ground electrodes can be connected on the backside or under the optical modulator, the processing accuracy of this part is not an issue. By applying the present invention, for example, it is possible to suppress characteristic degradation caused by electrodes in a wide variety of optical modulators and enable the broadband of optical modulators.

[0109] The optical device according to the above-described embodiment includes an optical modulation unit provided on a first surface of a substrate and including a plurality of electrodes for modulating an optical signal, a plurality of vias extending in the thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes, and electrodes provided on a second surface of the substrate opposite the first surface and connected to the plurality of vias. This makes it possible to suppress slot-line mode conversion with a simple structure and avoid deterioration of the modulator characteristics.

[0110] Furthermore, the optical device according to the embodiment may have an optical waveguide on the first surface side of the substrate, and the optical modulation section may include a material having a higher electro-optic constant than the optical waveguide. In this way, by integrating a material having a high electro-optic constant (high EO coefficient) in the optical modulation section, high-speed modulation operation becomes possible.

[0111] In addition, the optical device according to the embodiment may have a substrate made of silicon, quartz, or quartz. Substrates made of these materials allow optical elements such as modulators to be integrated on the substrate in a compact size.

[0112] In addition, the optical device according to the embodiment may have an optical modulation section with a Mach-Zehnder structure. By connecting the ground electrode of the Mach-Zehnder optical modulation section to the electrode on the rear surface side through a plurality of vias, it becomes possible to suppress conversion of the slot-line mode with a simple structure.

[0113] In addition, in the optical device according to the embodiment, the optical modulation section may have a GSGSG arrangement (G: ground electrode, S: signal electrode) in which the electrodes correspond to a differential driving signal. Alternatively, the optical modulation section may have a GSG arrangement in which the electrodes correspond to a single output driving signal. By providing vias in the ground electrodes in accordance with these electrode arrangements, it becomes possible to suppress slot-line mode conversion with a simple structure.

[0114] In addition, the optical device according to the embodiment may have a second substrate different from the substrate, the second substrate having a ground electrode on a surface opposite to the second surface of the substrate, and the ground electrode of the second substrate may be connected to the via and the bump. In this case, by moving the substrate toward the second substrate, the ground electrode of the substrate can be connected to the ground electrode of the second substrate at the bump portion through the via. This allows, for example, in an EO polymer optical modulator, by separating the substrate from the second substrate, an EO polymer solution can be applied to the silicon waveguide, and then a poling process can be performed to enable the device to function as an optical modulator. Thereafter, the substrate can be moved toward the second substrate to connect the ground, simplifying manufacturing and testing.

[0115] In addition, in the optical device of the embodiment, the electrode on the second surface side may be provided between the first surface and the second surface inside the substrate. For example, by providing the electrode on the second surface side inside the SiO2 layer inside the substrate, it is not necessary to form a via in the substrate below the silicon layer, and manufacturing costs can be reduced.

[0116] In addition, in the optical device according to the embodiment, the plurality of electrodes may be segmented electrodes. Even in this case, by providing vias in the ground electrode corresponding to the arrangement of these electrodes, it becomes possible to suppress the conversion of the slot-line mode with a simple structure.

[0117] Furthermore, the transmitter of the embodiment may include the above-described optical device and an optical element having an optical transmission function on a substrate. Furthermore, the transceiver of the embodiment may include a transmitter including the above-described optical device and an optical element having an optical transmission function, and an optical element having an optical receiving function on a substrate. By mounting a transmitter including an optical device, or the functions of a transmitter and a receiver, on the same substrate, it is possible to reduce the size and cost of the entire device.

[0118] Furthermore, the optical device of the embodiment may have the above-mentioned optical modulation unit, and either or both of a drive element for the optical modulation unit and a signal processing unit mounted on the substrate. In this way, when a function other than the optical modulation unit is mounted on the substrate, the vias for the optical modulation unit and the vias used by the functional units other than the optical modulation unit can be formed simultaneously in the substrate, thereby making it possible to easily manufacture the photoelectric conversion device.

[0119] Furthermore, the optical device of the embodiment may be mounted on an interposer by thinning the substrate to a predetermined thickness, thereby shortening the length (depth) of the vias, and using the vias to connect the optical modulation unit with a functional unit other than the optical modulation unit, such as a driver, can more easily reduce attenuation of high-frequency signals than, for example, wire bonding.

[0120] The following additional notes are provided regarding the above-described embodiment.

[0121] (Note 1) An optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; a plurality of vias extending in a thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; electrodes provided on a second surface of the substrate opposite to the first surface and connected to the plurality of vias; An optical device comprising:

[0122] (Note 2) An optical waveguide is provided on the first surface side of the substrate, 2. The optical device according to claim 1, wherein the optical modulation section includes a material having a higher electro-optic constant than the optical waveguide.

[0123] (Appendix 3) The optical device according to appendix 1, wherein the material of the substrate is either silicon, quartz, or quartz.

[0124] (Supplementary Note 4) The optical device according to Supplementary Note 1, wherein the optical modulation section has a Mach-Zehnder type structure.

[0125] (Appendix 5) The optical device according to appendix 1, wherein the optical modulation section has electrodes in a GSGSG arrangement (G: ground electrode, S: signal electrode) corresponding to a differential signal for driving.

[0126] (Appendix 6) The optical device according to appendix 1, wherein the optical modulation section has the electrodes in a GSG arrangement corresponding to a single output signal for driving.

[0127] (Supplementary Note 7) A second substrate different from the substrate is provided, and the second substrate has a ground electrode on a surface opposite to the second surface of the substrate; the via and the ground electrode of the second substrate are connected by a bump; 2. The optical device according to claim 1,

[0128] (Appendix 8) The optical device according to appendix 1, wherein the electrode on the second surface side is provided between the first surface and the second surface within the substrate.

[0129] (Supplementary Note 9) The optical device according to Supplementary Note 1, wherein the plurality of electrodes are segmented electrodes.

[0130] (Supplementary Note 10) A transmitter having an optical modulator and an optical element for an optical transmission function on a substrate, The optical modulator comprises: an optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; a plurality of vias extending in a thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; electrodes provided on a second surface of the substrate opposite to the first surface and connected to the plurality of vias; A transmitter comprising:

[0131] (Supplementary Note 11) A transceiver having an optical modulator, an optical element for an optical transmission function, and an optical element for an optical reception function on a substrate, The optical modulator comprises: an optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; a plurality of vias extending in a thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; electrodes provided on a second surface of the substrate opposite to the first surface and connected to the plurality of vias; A transceiver comprising:

[0132] (Appendix 12) The optical device according to appendix 1, wherein the substrate is thinned to a predetermined thickness and mounted on an interposer. [Explanation of symbols]

[0133] 100,1300,1400,1500,1600 Optical Modulator 101 Substrate (silicon substrate) 111 First SiO2 layer 112 Second SiO2 layer 113 (113a, 113b) Optical modulation section 116 Signal electrode 117 Ground electrode 118,118A via 119 Electrode on the second surface side (rear surface electrode) 124 EO Polymer Section 201 Optical Splitter 202,412 Optical waveguide 203 Optical Combiner 211 Transmitting signal source 212 driver amplifier 213 Termination Resistor 400,1900 Transceiver 401 Transmitter 402 Receiver 410,1910 Optical modulation section 413,434 Polarization Rotation Unit 414 Polarization combining unit 421 Optical Input Port 422 Transmit optical output port 431 Receive optical input port 432 Polarization Separator 433 90-degree hybrid element 1301,1302 Optical waveguide 1303 LN chip 1510 board 1511 Ground electrode 1518 Bump 1601 Ground wiring 2001, 2002 Photoelectric conversion devices 2011 Silicon photonics devices 2012 Driver (DRV) 2013 Optical Fiber 2014 Interposer 2015 PCB board

Claims

1. An optical modulation unit provided on the first surface side of a substrate and including a plurality of electrodes for modulating an optical signal; A plurality of vias extending in the thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; An optical device, comprising: a second surface side electrode provided on a second surface side facing the first surface side of the substrate and connected to the plurality of vias.

2. The optical device according to claim 1, further comprising an optical waveguide on the first surface side of the substrate, wherein the optical modulation unit includes a material having an electro-optic constant higher than that of the optical waveguide.

3. The optical device according to claim 1, wherein the material of the substrate is any one of silicon, quartz, or quartzite.

4. The optical device according to claim 1, wherein the optical modulation unit has a Mach-Zehnder type structure.

5. The optical device according to claim 1, wherein the optical modulation unit has a GSGSG arrangement (G: ground electrode, S: signal electrode) in which the electrodes correspond to a differential signal for driving.

6. The optical device according to claim 1, wherein the optical modulation unit has a GSG arrangement in which the electrodes correspond to a single output signal for driving.

7. The optical device according to claim 1, further comprising a second substrate different from the substrate, wherein the second substrate has a ground electrode on a surface facing the second surface of the substrate, and the via and the ground electrode of the second substrate are connected by a bump. The optical device according to claim 1, wherein the second surface side electrode is provided in the substrate between the first surface and the second surface.

8. The optical device according to claim 1, wherein the plurality of electrodes are segment type electrodes.

9. A transmitter having an optical modulator and an optical element related to an optical transmission function on a substrate,

10. wherein the optical modulator includes: An optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; A plurality of vias extending in the thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; A second surface side electrode provided on a second surface side facing the first surface of the substrate and connected to the plurality of vias. The transmitter is characterized by having the above components.

11. A transceiver having an optical modulator, an optical element related to an optical transmission function, and an optical element related to an optical reception function on a substrate, wherein the optical modulator includes: An optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; An optical modulation unit provided on the first surface side of the substrate and including a plurality of electrodes for modulating an optical signal; A plurality of vias extending in the thickness direction of the substrate and connected to a plurality of ground electrodes constituting the plurality of electrodes; A second surface side electrode provided on the second surface side facing the first surface of the substrate and connected to the plurality of vias; A transceiver characterized by comprising the above.

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