Optical waveguide element, optical modulator using same, and optical transmission device

Abstract

The objective of the present invention is to provide an optical waveguide element in which an increase in three-dimensional volume related to the optical waveguide elements is restrained while ensuring the effective area of a chip on an optical waveguide substrate, and in which the manufacturing process related to electrical wiring is also simplified, and to provide an optical modulator with a simplified wiring structure of a substrate on which an optical waveguide is formed.　An optical waveguide element according to the present invention comprises an optical waveguide substrate (1) on which an optical waveguide (10) is formed and a support substrate (SS) disposed on top of the optical waveguide substrate (1) and bonded to the optical waveguide substrate (1), the optical waveguide element being characterized in that electrical wiring (EP11, EP21, EPG1, EL1, EL2, ELG, EP12, EP22, EPG2) is provided on the surface of the support substrate (SS) on the opposite side from the surface that is bonded to the optical waveguide substrate (1).

Description

Optical waveguide element, optical modulator using the same, and optical transmitter

[0001] The present invention relates to an optical waveguide element, an optical modulator using the same, and an optical transmitter, and more particularly to an optical waveguide element including an optical waveguide substrate on which an optical waveguide is formed, and an auxiliary substrate disposed on the optical waveguide substrate and bonded to the optical waveguide substrate, and an optical modulator and an optical transmitter using the same.

[0002] As optical communication systems become faster and larger in capacity, the optical modulators used in them are becoming increasingly sophisticated and denser. As optical waveguide devices (chips) such as high-bandwidth coherent driver modulators (HB-CDMs) become smaller, the wiring that electrically connects the inside and outside of the chips becomes more complex.

[0003] 1 is a plan view illustrating a portion of the wiring connected to an optical waveguide element, and light-receiving elements (PD1, PD2) for monitoring light waves propagating through the optical waveguide are arranged on an optical waveguide substrate 1 on which an optical waveguide 10 is formed. The optical waveguide element is housed in a housing CA, and connection pins (PS1, PS2, PG) that lead out electrical signals from inside the housing are directly connected (wire-bonded) to the light-receiving elements by wires (W1, W2, WG).

[0004] On the other hand, the input and output sections of the lightwaves to the optical waveguide element are arranged on one side of the optical waveguide substrate, thereby shortening the longitudinal direction (horizontal direction in FIG. 1) of the optical waveguide element and simplifying the input and output of the lightwaves to the optical waveguide element. As shown in FIG. 1, by folding the optical waveguide 10, the width of the chip (vertical direction in FIG. 1) increases. As a result, the wires (W1, etc.) become longer and may fall over and come into contact with other wires or wiring formed on the optical waveguide substrate 1, causing a short circuit.

[0005] 2, relay wiring (EL1, EL2, ELG) is provided on the optical waveguide substrate 1, and the wires (W11, W21, WG1 and W12, W22, WG2) are configured to be short. Such relay wiring occupies a part of the optical waveguide substrate, so the space (effective area of ​​the chip) required for arranging the optical waveguide 10 and the control electrodes for controlling the light waves arranged on the substrate 1 is limited, which also causes the chip size to increase.

[0006] FIG. 3 shows a relay substrate RS shown in Patent Document 1, which is disposed above the optical waveguide substrate 1 at a distance from the substrate 1. In FIG. 3, the signal from the light-receiving element PD disposed on the optical waveguide substrate 1 is configured to be guided to the outside of the substrate 1 via wiring EL on the relay substrate. By arranging the relay substrate three-dimensionally in this manner, stable electrical wiring is possible without reducing the effective chip area. However, the optical waveguide substrate 1 and the relay substrate must be fixed at a fixed distance and then electrically wired. This complicates the manufacturing process and increases the thickness of the optical waveguide substrate 1 in the direction perpendicular to the drawing in FIG. 3 , as well as the thickness of the housing (package) that houses the optical waveguide substrate 1, hindering miniaturization.

[0007] The above explanation has been given using wiring to a light-receiving element as an example, but this is not limited to this, and similar problems occur with many other types of wiring, such as wiring for a DC bias electrode that applies an electric field to an optical waveguide, or electrical wiring when other optical elements or electrical elements such as a semiconductor laser light source are incorporated together with an optical waveguide element.

[0008] Japanese Patent Application Laid-Open No. 2017-187521

[0009] The object of the present invention is to solve the above-mentioned problems by providing an optical waveguide element that suppresses an increase in the three-dimensional volume of the optical waveguide element while ensuring the effective area of ​​the chip of the optical waveguide substrate and further simplifies the manufacturing process for the electrical wiring, and also to provide an optical modulator and an optical transmitter that use the optical waveguide element.

[0010] In order to solve the above problems, the optical waveguide element of the present invention and the optical modulator and optical transmitter using the same have the following technical features: (1) An optical waveguide element including an optical waveguide substrate on which an optical waveguide is formed, and an auxiliary substrate disposed on the optical waveguide substrate and bonded to the optical waveguide substrate, characterized in that electrical wiring is provided on the surface of the auxiliary substrate opposite to the surface bonded to the optical waveguide substrate.

[0011] (2) In the optical waveguide element described in (1) above, a part of the electrical wiring is used as a signal line of a light-receiving element that detects a part of the light wave propagating through the optical waveguide, or as a DC line that applies a DC voltage to a control electrode arranged in the optical waveguide element.

[0012] (3) In the optical waveguide element according to (1) or (2) above, a part of the electrical wiring is used as an electrical element wiring that connects to an electrical element provided outside the optical waveguide substrate.

[0013] (4) In the optical waveguide element according to any one of (1) to (3) above, an end face of the auxiliary substrate is arranged in alignment with an end face of the optical waveguide substrate on which the input end and / or output end of the optical waveguide is arranged, and an optical component is arranged in contact with the end face of the optical waveguide substrate and the end face of the auxiliary substrate, and is optically coupled to the input end and / or the output end.

[0014] (5) In the optical waveguide element according to any one of (1) to (4) above, a light-receiving element is disposed on the auxiliary substrate to detect a part of the light wave propagating through the optical waveguide, and a part of the electrical wiring is used as a signal line for the light-receiving element.

[0015] (6) In the optical waveguide element according to any one of (1) to (5) above, the auxiliary substrate is made of a material that is transparent to visible light and has a dielectric constant of 15 or less.

[0016] (7) In the optical waveguide element according to any one of (1) to (6) above, a wire for electrical connection is connected to the electrical wiring from outside the auxiliary substrate.

[0017] (8) An optical modulator comprising: the optical waveguide element according to any one of (1) to (7) above; a housing for accommodating the optical waveguide element; and an optical fiber for inputting or outputting a light wave to or from the optical waveguide.

[0018] (9) The optical modulator according to (8) above is characterized in that a modulation electrode for modulating a light wave propagating through the optical waveguide is disposed on the optical waveguide substrate, and an amplifier circuit for amplifying a modulation signal input to the modulation electrode is provided inside the housing.

[0019] (10) An optical transmitter comprising the optical modulator according to (8) or (9), a light source for inputting a light wave to the optical modulator, and a signal circuit for inputting a modulated signal to the optical modulator.

[0020] The optical waveguide element of the present invention comprises an optical waveguide substrate having an optical waveguide formed thereon and an auxiliary substrate disposed on the optical waveguide substrate and bonded to the optical waveguide substrate, and electrical wiring is provided on the surface of the auxiliary substrate opposite to the surface bonded to the optical waveguide element, thereby making it possible to provide an optical waveguide element that ensures the effective area of ​​the chip of the optical waveguide substrate while suppressing an increase in the three-dimensional volume of the optical waveguide element and further simplifies the manufacturing process for the electrical wiring.Furthermore, by using the optical waveguide element, it is also possible to provide an optical modulator or an optical transmitter having the above-mentioned effects.

[0021] FIG. 10 is a plan view illustrating a conventional optical waveguide element. FIG. 11 is a plan view illustrating another conventional optical waveguide element. FIG. 12 is a plan view illustrating an optical waveguide element described in Patent Document 1. FIG. 13 is a plan view illustrating a first embodiment of an optical waveguide element of the present invention. FIG. 14 is a cross-sectional view illustrating the optical waveguide element of FIG. 4. FIG. 15 is a plan view illustrating electrical wiring used in an optical waveguide element of the present invention. FIG. 16 is a cross-sectional view illustrating electrical wiring used in an optical waveguide element of the present invention. FIG. 17 is a cross-sectional view illustrating a second embodiment of an optical waveguide element of the present invention. FIG. 18 is a plan view illustrating the optical waveguide element of FIG. 15. FIG. 19 is a plan view illustrating a third embodiment of an optical waveguide element of the present invention. FIG. 20 is a plan view illustrating a fourth embodiment of an optical waveguide element of the present invention. FIG. 21 is a plan view illustrating a fifth embodiment of an optical waveguide element of the present invention. FIG. 22 is a plan view illustrating a sixth embodiment of an optical waveguide element of the present invention. FIG. 23 is a plan view illustrating an optical transmitting device of the present invention.

[0022] The optical waveguide element according to the present invention, and the optical modulator and optical transmitter using the same will be described in detail below. The optical waveguide element according to the present invention comprises an optical waveguide substrate 1 on which an optical waveguide 10 is formed, and an auxiliary substrate SS disposed on the optical waveguide substrate and bonded to the optical waveguide substrate, as shown in Figures 4 and 5, for example, and is characterized in that electrical wiring (EP11, EP21, EPG1, EL1, EL2, ELG, EP12, EP22, EPG2) is provided on the surface of the auxiliary substrate SS opposite to the surface bonded to the optical waveguide substrate.

[0023] The substrate (optical waveguide substrate) 1 used in the optical waveguide element of the present invention can be a substrate having an electro-optic effect. Specifically, substrates such as lithium niobate (LN), lithium tantalate (LT), and PLZT (lead lanthanum zirconate titanate), as well as substrates made of these substrate materials doped with MgO or the like, can be used. These materials can also be used to form films using vapor phase growth methods such as sputtering, evaporation, or CVD. Furthermore, a substrate made by bonding a substrate having an electro-optic effect to another substrate and then thin-film processing the electro-optic substrate can also be used. Furthermore, semiconductor substrates and substrates made of organic materials such as EO polymers can also be used.

[0024] The optical waveguide 10 can be an optical waveguide in which a high refractive index material such as Ti is thermally diffused into the substrate (optical waveguide substrate) 1, an optical waveguide formed by proton exchange, or even a rib-type optical waveguide 10 in which the portion corresponding to the optical waveguide is convex on the surface of the substrate 1, such as by etching the substrate 1 other than the optical waveguide or by forming grooves on both sides of the optical waveguide. Furthermore, in accordance with the rib-type optical waveguide, it is also possible to further increase the refractive index by diffusing Ti or the like into the surface of the substrate by thermal diffusion or proton exchange.

[0025] The thickness (maximum thickness) of the optical waveguide substrate (thin plate) 1 on which the optical waveguide 10 is formed is set to 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less, in order to achieve velocity matching between the microwave and light waves of the modulation signal. The height of the rib-type optical waveguide 10 (the height of the portion protruding from the slab waveguide) is set to 80% or less of the maximum thickness of the optical waveguide substrate, specifically, 4 μm or less, more preferably 3 μm or less, and even more preferably 0.8 μm or less or 0.4 μm or less. The width of the rib-type optical waveguide 10 is set to 2 μm or less, or 1 μm or less.

[0026] To enhance the mechanical strength of the optical waveguide substrate 1 having the optical waveguide formed thereon, a holding substrate 2 is bonded to the underside of the optical waveguide substrate 1. The optical waveguide substrate 1 and the holding substrate 2 are bonded together by direct bonding or via an adhesive layer such as a resin. The holding substrate to be directly bonded preferably has a lower refractive index than the optical waveguide and the substrate on which the optical waveguide is formed, but is not limited thereto. In the case of direct bonding, an intermediate layer such as a metal oxide or metal may be included in the bonding portion. Furthermore, the holding substrate 2 is preferably made of a material having a thermal expansion coefficient similar to that of the optical waveguide substrate 1, such as a substrate containing an oxide layer of quartz or glass. Furthermore, it is also possible to use the same LN substrate as the optical waveguide substrate 1, or a composite substrate formed with a silicon oxide layer on a silicon substrate (abbreviated as SOI or LNOI), or a composite substrate formed with a silicon oxide layer on an LN substrate. If the refractive index of the holding substrate 2 is higher than that of the optical waveguide substrate 1, a layer with a lower refractive index than the optical waveguide substrate 1 is provided between the optical waveguide substrate 1 and the holding substrate 2. The holding substrate is not limited to a substrate formed from a single substrate, but also includes a substrate formed by stacking a plurality of substrates together.

[0027] To apply an electric field to the optical waveguide 10, a control electrode (not shown) is formed on the optical waveguide substrate 1. The control electrode has a multilayer structure consisting of an upper electrode and an underlayer. The upper electrode is made of a metal such as Au or Cu. The underlayer is used to improve adhesion between the optical waveguide substrate 1 and the upper electrode. The upper electrode is formed to cover the underlayer by electrolytic plating using the underlayer, electroless plating using a resist pattern, gas phase methods such as vapor deposition and sputtering, or a combination of these. The underlayer is made of material such as Ti, Nb, Ni, Cr, or Al, and is formed on the optical waveguide substrate by sputtering, vapor deposition, or the like.

[0028] The optical waveguide element of the present invention is characterized in that, as shown in Figures 4 and 5, electrical wiring is provided on the upper surface (the surface of the auxiliary substrate SS opposite to the surface that is bonded to the optical waveguide substrate 1) of the auxiliary substrate SS that is placed on the optical waveguide substrate 1 and bonded to the optical waveguide substrate 1.

[0029] 4 and 5, the auxiliary substrate SS also serves to increase the bonding area when bonding an optical component OP to the optical waveguide substrate 1. The end face of the auxiliary substrate SS is aligned with the end face of the optical waveguide substrate 1 where the input or output end of the optical waveguide 10 is located, and an optical component is disposed in contact with the end face of the optical waveguide substrate and the end face of the auxiliary substrate to optically couple with the input or output end. The optical waveguide substrate 1 (including the holding substrate 2) and the auxiliary substrate SS are bonded to the optical component OP by adhesive AD1. The optical waveguide substrate 1 and the auxiliary substrate SS are bonded by adhesive AD2, and the optical waveguide substrate 1 and the light-receiving elements (PD1, PD2) are bonded by adhesive AD3. The optical component OP does not necessarily have to be bonded to the auxiliary substrate SS.

[0030] The electrical wiring arranged on the auxiliary substrate SS is made of metal such as Au or Cu, similar to the control electrodes described above. If the adhesive strength between these metals and the auxiliary substrate is weak, a base layer can be provided, similar to the control electrodes.

[0031] 6 is a plan view illustrating a portion of the electrical wiring formed on the auxiliary substrate SS. The electrical wiring is also called an "electrode pad," and is composed of portions (EP11, EP21, EPG1, EP12, EP22, EPG2) where wires (W11, W21, WG1, W12, W22, WG2) are connected and arranged, and wiring portions (EL1, EL2, ELG) that connect the electrode pads together. Of course, an electrode pad with only an electrode pad and no wiring portions, such as the electrode pad EP1 in FIG. 11 described below, in which multiple wires (W11, W12) are connected to the electrode pad EP1, is also included in the electrode wiring of the present invention.

[0032] The size (width H x length I) of the electrode pad (EP11, etc.) in Fig. 6 is set such that both the lengths H and I are 100 µm or more, ensuring a size large enough to reliably align the wire and electrode pad during wire bonding. The width J of the wiring portion (EL1, etc.) must be large enough to prevent problems such as wire breakage, and is 10 µm or more, preferably 30 µm or more.

[0033] The thickness K (see Figure 7) of the electrical wiring (electrode pad, wiring portion) is set to 300 nm or more to ensure that the wire and electrode pad can be reliably bonded during wire bonding and that the wiring portion is unlikely to break.

[0034] 5 depends on the thickness of the auxiliary substrate SS and the thickness of the light receiving elements (PD1, PD2). If a lens is to be bonded as the optical component OP, the thickness D of the auxiliary substrate SS is set to 500 μm or more to ensure a sufficient bonding area. The loop height G at which the wire loop does not become straight and the wire does not collapse is set in the range of 400 μm or more and 750 μm or less.

[0035] The auxiliary substrate SS is made of a material that is transparent to the light waves propagating through the optical waveguide, for example, a material that is transparent to visible light, and preferably has a dielectric constant of 15 or less. Materials with a low dielectric constant have the advantage of excellent insulation properties and small dielectric loss. Specific materials that are suitable include inorganic metal oxides and resins, such as glass, quartz, and alumina.

[0036] 4 and 5, by using an auxiliary substrate SS to adhesively fix the optical component OP, there is no need to prepare a new relay substrate, and since this is a material that has been used in optical waveguide elements traditionally, there is no increase in the number of parts, and the conventional manufacturing process is not complicated. As shown in Fig. 4, the light receiving elements (PD1, PD2) are electrically connected to connection pins (PS1, PS2, PG). Specifically, the light receiving element (PD1) is connected to two wiring systems from the signal connection pin (PS1) and the ground connection pin (PG2) via respective wires (W11, WG1), electrode pads (EP11, EPG1), wiring portions (EL1, ELG), electrode pads (EP12, EPG2), and wires (W12, WG2).

[0037] 4, the adhesive AD1 may overflow and spread in the direction of the electrical wiring (EP21, EL2, etc.), so it is preferable to ensure that the distance C from the edge of the auxiliary substrate to the electrical wiring is 200 μm or more. Furthermore, an increase in the width A of the auxiliary member SS also reduces the effective area of ​​the chip, so it is preferable to set the width A to 1000 μm or less.

[0038] The distance B between the light-receiving elements (PD1, PD2) arranged on the optical waveguide substrate 1 and the auxiliary substrate SS depends on the size of the light-receiving elements and the shape of the arrangement of the optical waveguide 10 (the position of the multiplexing section, etc.), but when the step between the light-receiving elements (PD1, PD2) and the surface of the auxiliary substrate SS is in the range of 350 μm to 500 μm, it is set to 700 μm or less, more preferably 650 μm or less, and even more preferably 600 μm or less. Furthermore, to avoid sudden bending of the wire, it is set to 400 μm or more.

[0039] In the above explanation, an example has been shown in which the auxiliary substrate SS also serves as an adhesive member for the optical component OP, but this is not limiting, and it is also possible to use an auxiliary substrate SS2 dedicated to relay in addition to the auxiliary substrate SS1, as shown in Fig. 12. Furthermore, in cases where the light receiving elements and the auxiliary substrate SS1 are separated from each other, it is also possible to use only the auxiliary substrate SS2 dedicated to relay, which is electrically connected directly to the light receiving elements (PD1, PD2), without using the wiring of the auxiliary substrate SS1.

[0040] 8 and 9 are diagrams illustrating a second embodiment of the optical waveguide element of the present invention. As shown in Fig. 8 and Fig. 9, a light-receiving element PD is disposed on the upper surface of an auxiliary substrate SS to detect a portion of the light wave propagating through the optical waveguide 10. A portion of the electrical wiring (EP, EL) provided on the upper surface of the auxiliary substrate SS is used as a signal line for the light-receiving element PD. The light-receiving element PD is adhered to the auxiliary substrate SS with adhesive AD4.

[0041] A grating GT is disposed close to the optical waveguide 10 so that a part of the light wave propagating through the optical waveguide 10 is detected by the photodetector PD. The grating GT can be configured as a separate member, or can be processed and formed on the lower surface of the auxiliary substrate SS. Also, instead of a grating, it is possible to change part or all of the auxiliary member to a member having a refractive index higher than that of the optical waveguide 10.

[0042] As in the second embodiment, by placing the light receiving element PD on the auxiliary substrate SS, the length of the wire W can be made shorter, and it is also possible to secure a larger effective area for the optical waveguide substrate (chip).

[0043] 10 is a diagram illustrating a third embodiment of the optical waveguide element of the present invention. A semiconductor laser (light source LD) serving as a light source is disposed adjacent to the optical waveguide substrate (chip). If necessary, the light source LD and the optical waveguide substrate 1 may be bonded together. When an electrical element such as the light source LD is provided outside the optical waveguide substrate 1, it is also possible to use electrical wiring (EP11, EP21, EL1, EL2, EP12, EP22) provided on the auxiliary substrate SS as part of the electrical element wiring for supplying power and transmitting signals to the electrical element.

[0044] FIG. 11 is a diagram illustrating a fourth embodiment of the optical waveguide element of the present invention. This diagram illustrates an example in which a portion of the electrical wiring on the auxiliary substrate SS is used to supply a DC bias to a control electrode, particularly a DC bias electrode (not shown), arranged on the optical waveguide substrate. The symbols DCP1 and DCP2 indicate electrode pads connected to the DC bias electrodes arranged on the optical waveguide substrate. These electrode pads receive DC bias from connection pins (P1 and P2) that supply the DC bias from the outside via two wiring systems (wire W11 → electrode pad EP1 → wire W12, wire W21 → electrode pad EP21 → wiring portion EL → electrode pad EP22 → wire W22).

[0045] As shown by the electrode pad (EP1), in the optical waveguide element of the present invention, the electrical wiring formed on the auxiliary substrate SS includes only electrode pads and no wiring portion. Also, although not shown, it is possible to electrically connect with wires as the electrical wiring of the auxiliary substrate instead of wiring portions.

[0046] 12 is a diagram illustrating a fifth embodiment of the optical waveguide element of the present invention. For the electrical connection between the connection pins (PS1, PS2, PG) and the light-receiving element (PD1, etc.), in addition to the auxiliary substrate SS1 used for bonding optical components, a relay-only auxiliary substrate SS2 disposed on the optical waveguide substrate 1 can also be used. The light-receiving element PD1 is electrically connected from the connection pins (PS1, PG) via two wiring systems (wire W11 → electrode pad EP11 → wiring portion EL11 → electrode pad EP12 → wire W12 → electrode pad EP13 → wiring portion EL12 → electrode pad EP14 → wire W13; wire WG1 → electrode pad EPG1 → wiring portion ELG1 → electrode pad EPG2 → wire WG2 → electrode pad EPG3 → wiring portion ELG2 → electrode pad EPG4 → wire WG3).

[0047] When an auxiliary substrate SS2 dedicated to relaying is placed on the optical waveguide substrate 1, it is preferable to configure it so that the light waves propagating through the optical waveguide 10 are not absorbed or scattered, and the electric field generated by the electrical wiring is not applied to the optical waveguide, thereby affecting the modulated light. To achieve this, it is necessary to configure the structure so that the electrical wiring is not placed directly above the optical waveguide. However, even if the electrical wiring is placed directly above the optical waveguide, if it is placed perpendicular to the extension direction of the optical waveguide, the effect of the electric field generated by the electrical wiring on the optical waveguide can be suppressed. In the above explanation, the electrical wiring is formed on the top surfaces of the auxiliary substrate SS, auxiliary substrate SS1, auxiliary substrate SS2, etc., but some of the electrical wiring may be formed on the side surfaces or bottom surfaces other than the top surfaces. Also, as shown in Figure 13, if the distance between the connection pins (PS1, PG) and the light receiving element (PD1) is short, they can be directly connected with wires (W1, WG), and if the distance between the connection pins (PS2, PG) and the light receiving element (PD2) is long, it is also possible to connect the wiring system via electrode pads (EP21, EP22, PGG1, EPG2) or wiring parts (EL2, ELG) on the auxiliary substrate SS.

[0048] Next, examples of application of the optical waveguide element of the present invention to an optical modulator or an optical transmitter will be described. While the following describes an optical waveguide element having a nested optical waveguide, the present invention is not limited to this, and can also be applied to HB-CDM, optical phase modulators, optical modulators with polarization combining functions, optical modulators integrating more or fewer Mach-Zehnder optical waveguides, bonding devices with optical waveguide substrates made of other materials such as silicon, devices for sensor applications, and the like.

[0049] As shown in FIG. 14 , the optical waveguide element includes an optical waveguide 10 formed on an optical waveguide substrate 1 and an electrode (not shown), such as a modulation electrode, that modulates the light wave propagating through the optical waveguide 10. The substrate 1 is housed within a housing CA. Furthermore, an optical modulator MD can be configured by providing an optical fiber (F) that inputs and outputs light waves to the optical waveguide. In FIG. 14 , the optical fiber (F) is introduced into the housing CA through a through-hole penetrating the sidewall, and the optical waveguide substrate 1 and the optical fiber are directly bonded. Alternatively, the light wave L1 incident from the optical fiber F and the light wave L2 emitted from the optical fiber F can be optically coupled to the optical waveguide 10 within the optical waveguide substrate 1 via an optical block equipped with an optical lens, a lens barrel, a polarization multiplexer, or the like. Furthermore, to ensure stable bonding with optical components such as an optical fiber or an optical block, an auxiliary member SS is placed on the optical waveguide substrate 1 along the end face of the substrate 1.

[0050] An optical transmitter OTA can be configured by connecting an electronic circuit (digital signal processor, DSP) that outputs a modulation signal S0 that causes the optical modulator MD to perform modulation operations to the optical modulator MD. To obtain the modulation signal S to be applied to the optical waveguide element, the modulation signal S0 output from the digital signal processor DSP can be amplified. For this reason, in FIG. 14, a driver circuit DRV is used to amplify the modulation signal. The driver circuit DRV and digital signal processor DSP can be located outside the housing CA, but they can also be located inside the housing CA. In particular, locating the driver circuit DRV inside the housing can further reduce the propagation loss of the modulation signal from the driver circuit. If degradation of the modulation signal is minimal, a DRV is not necessary, and the optical modulator MD can be directly modulated by the DSP.

[0051] The input light L1 to the optical modulator MD may be supplied from outside the optical transmitter OTA, but it may also be incorporated integrally into the optical transmitter OTA using a semiconductor laser LD as the light source as shown in Figure 10. The output light L2 modulated by the optical modulator MD is output to the outside via an optical fiber F.

[0052] As described above, according to the present invention, it is possible to provide an optical waveguide element that can suppress an increase in the three-dimensional volume of the optical waveguide element while ensuring the effective area of ​​the chip of the optical waveguide substrate, and further, can simplify the manufacturing process for the electrical wiring. Furthermore, it is possible to provide an optical modulator and an optical transmitter that use the optical waveguide element.

[0053] REFERENCE SIGNS LIST 1 Optical waveguide substrate (thin plate, film body) 2 Holding substrate 10 Optical waveguide SS Auxiliary substrate EP11, EP12, EPG1, EPG2, etc. Electrical wiring (electrode pad) EL1, ELG, etc. Electrical wiring (wiring portion) PD1, PD2 Light receiving element OP Optical component F Optical fiber CA Housing MD Optical modulator DRV Driver circuit DSP Digital signal processor OTA Optical transmitter

Claims

1. An optical waveguide element comprising an optical waveguide substrate having an optical waveguide formed thereon and an auxiliary substrate disposed on the optical waveguide substrate and bonded to the optical waveguide substrate, characterized in that electrical wiring is provided on the surface of the auxiliary substrate opposite to the surface bonded to the optical waveguide substrate.

2. An optical waveguide element according to claim 1, characterized in that part of the electrical wiring is used as a signal line for a light-receiving element that detects part of the light waves propagating through the optical waveguide, or as a DC line for applying a DC voltage to a control electrode arranged in the optical waveguide element.

3. An optical waveguide element according to claim 1, wherein a portion of the electrical wiring is used as electrical element wiring to connect to an electrical element provided outside the optical waveguide substrate.

4. An optical waveguide element according to claim 1, characterized in that the end face of the auxiliary substrate is arranged in alignment with the end face of the optical waveguide substrate on which the input end and / or output end of the optical waveguide is arranged, and an optical component is arranged in contact with the end face of the optical waveguide substrate and the end face of the auxiliary substrate, and is optically coupled to the input end and / or output end.

5. An optical waveguide element according to claim 1, characterized in that a light-receiving element for detecting a part of the light wave propagating through the optical waveguide is disposed on the auxiliary substrate, and a part of the electrical wiring is used as a signal line for the light-receiving element.

6. An optical waveguide element according to claim 1, wherein the auxiliary substrate is made of a material that is transparent to visible light and has a dielectric constant of 15 or less.

7. An optical waveguide element according to claim 1, wherein the electrical wiring is connected to an electrical connection wire from outside the auxiliary substrate.

8. An optical modulator comprising: the optical waveguide element according to claim 1; a housing for accommodating said optical waveguide element; and an optical fiber for inputting or outputting a light wave to said optical waveguide.

9. An optical modulator according to claim 8, wherein a modulation electrode for modulating the light wave propagating through the optical waveguide is disposed on the optical waveguide substrate, and an amplifier circuit for amplifying the modulation signal input to the modulation electrode is provided inside the housing.

10. An optical transmitter comprising: the optical modulator according to claim 8; a light source for inputting a light wave to said optical modulator; and a signal circuit for inputting a modulated signal to said optical modulator.

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