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

Abstract

The purpose of the present invention is to provide an optical waveguide element capable of shortening a distance between a side surface of an optical waveguide substrate and an electrode, and capable of suppressing the occurrence of chipping when cutting a wafer.　An optical waveguide element according to the present invention comprises: an optical waveguide substrate 1 on which an optical waveguide is formed; an upper layer UPL and a lower layer UNL that are disposed so as to sandwich the optical waveguide substrate 1; and a support substrate SS that is disposed on a side of the lower layer UNL opposite to the optical waveguide substrate 1. The optical waveguide element is characterized in that both the upper layer UPL and the lower layer UNL are composed of materials having a refractive index lower than a refractive index of the optical waveguide substrate 1, and a Young's modulus of the upper layer UPL is smaller than a Young's modulus of the lower layer UNL.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element including an optical waveguide substrate on which an optical waveguide is formed, an upper layer and a lower layer disposed so as to sandwich the optical waveguide substrate, and a support substrate disposed on the side opposite to the optical waveguide substrate of the lower layer, an optical modulator using the same, and an optical transmission device.

Background Art

[0002] In the fields of optical measurement technology and optical communication technology, optical waveguide elements using substrates on which optical waveguides are formed, such as optical modulators, are widely used. In a general optical waveguide element, an optical waveguide is formed on a substrate having an electro-optic effect such as lithium niobate (LN), and an electrode for applying an electric field to the optical waveguide is formed on the substrate.

[0003] In recent years, a high bandwidth coherent driver modulator (HB-CDM) has attracted attention, and the development of optical waveguide elements corresponding to high speed and miniaturization is expected. In the optical waveguide element used in HB-CDM, in order to suppress the propagation loss of high frequency signals, the distance between the electrode on the optical waveguide substrate and the driver circuit element is shortened and the wiring length is shortened. For this reason, the electrode is disposed close to the side surface of the optical waveguide substrate. In addition, in order to obtain more chips from one wafer, the cutting end face of the optical waveguide substrate is set close to the electrode on the optical waveguide substrate.

[0004] Thus, when cutting an optical waveguide substrate in close proximity to the electrodes on the substrate, the edge of the substrate may chip during cutting, potentially causing the electrodes to detach or break. Figure 1 shows an optical waveguide substrate 1 bonded to a support substrate SS1 made of silicon or the like via an intermediate layer IL made of SiO2 or the like, in order to improve the modulation efficiency of the optical waveguide element. A rib-type optical waveguide 10 is shown, but it is also possible to form it by thermally diffusing a high refractive index material such as Ti into the optical waveguide substrate 1. In addition, electrodes EL are formed on the optical waveguide substrate 1 to apply an electric field to the optical waveguide 10. When SiO2 is used for this intermediate layer IL, chipping of the intermediate layer itself is likely to occur when the intermediate layer is cut, and as a result, chipping of the optical waveguide substrate 1 also becomes more likely.

[0005] Furthermore, as shown in Patent Document 1, in order to broaden the bandwidth of optical modulators, glass-based substrates with low dielectric loss are sometimes used as support substrates for optical waveguide elements. Figure 2 shows a support substrate SS2 using a glass-based substrate such as quartz, to which the optical waveguide substrate 1 is bonded via a Si adhesive layer BL and an SiO2 intermediate layer IL. Since such glass-based substrates are hard materials that are difficult to cut, chipping of the support substrate SS2 itself occurs when the wafer is cut, making it easy for the electrodes to peel off or break.

[0006] Patent Document 2 presents a method for cutting wafers in which a shallow groove is formed with a wide blade (cutter), and then the remaining portion is cut with a narrow blade. This method can suppress the occurrence of chipping, but as a result, the width required for cutting becomes larger, and the number of chips that can be obtained from one wafer decreases.

[0007] Furthermore, as shown in Figure 3, Patent Document 3 describes a method in which a thin resin film RE is placed on a semiconductor substrate wafer WH so as to straddle the cut portion CL during the manufacturing of a semiconductor element. The role of this thin resin film RE is to relieve the stress applied to the sealing resin when the outer surface of the semiconductor element is sealed with another resin after the wafer has been cut. Moreover, by using such a thin resin film RE during cutting, it is possible to suppress the occurrence of chipping. However, in order to secure a separate area for forming the thin resin film RE, it is necessary to widen the distance between the side surface (cutting position) of the optical waveguide substrate and the electrode, which, as mentioned above, can cause propagation loss of high-frequency signals in HB-CDM and a reduction in the number of chips that can be obtained from the wafer. In addition, since a resin with high dielectric loss is placed near the high-frequency signal electrode, degradation of high-frequency signal characteristics also occurs. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] China Patent Publication CN111061071B [Patent Document 2] Japanese Patent Publication No. 2013-235113 [Patent Document 3] Japanese Patent Publication No. 2014-116333 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to provide an optical waveguide element that solves the above-mentioned problems, shortens the distance between the side surface of the optical waveguide substrate and the electrode, and suppresses the occurrence of chipping during wafer cutting. Furthermore, it aims to provide an optical modulator and an optical transmitter using this optical waveguide element. [Means for solving the problem]

[0010] To solve the above problems, the optical waveguide element, optical modulator using the same, and optical transmission device of the present invention have the following technical features. (1) An optical waveguide element comprising an optical waveguide substrate on which an optical waveguide is formed, and an upper layer and a lower layer arranged so as to sandwich the optical waveguide substrate, wherein a support substrate is arranged on the side of the lower layer opposite to the optical waveguide substrate, characterized in that both the upper layer and the lower layer are made of a material having a refractive index lower than that of the optical waveguide substrate, and the Young's modulus of the upper layer is smaller than that of the lower layer.

[0011] (2) The optical waveguide element described in (1) above, wherein the upper layer and the lower layer contain an inert gas, and the content of the inert gas in each layer is greater in the upper layer than in the lower layer.

[0012] (3) The optical waveguide element described in (2) above is characterized in that the content of the inert gas in the upper layer is 1.0 atm% or more and 3.0 atm% or less.

[0013] (4) In the optical waveguide element described in any of (1) to (3) above, the thickness of the upper layer is characterized in that it is thinner than the thickness of the lower layer.

[0014] (5) In the optical waveguide element described in any of (1) to (4) above, the upper layer is characterized in that it is arranged at least in the peripheral part of the optical waveguide substrate.

[0015] (6) In the optical waveguide element described in any of (1) to (5) above, the material constituting the upper layer is the same material as the material constituting the lower layer.

[0016] (7) An optical waveguide element according to any of (1) to (6) above, wherein an electrode layer is arranged on the upper or lower side of the optical waveguide substrate, and the shortest distance from the side surface of the optical waveguide substrate to the side surface of the electrode layer is set to 30 μm or less.

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

[0018] (9) In the optical modulator according to (8) above, the optical waveguide element includes a modulation electrode for modulating light waves propagating through the optical waveguide, and an electronic circuit for amplifying a modulation signal input to the modulation electrode, and the electronic circuit is provided inside the housing.

[0019] (10) An optical transmission device comprising: the optical modulator according to (8) or (9) above; a light source for inputting light waves to the optical modulator; and an electronic circuit for outputting a modulation signal to the optical modulator.

Advantages of the Invention

[0020] The present invention provides an optical waveguide element including an optical waveguide substrate on which an optical waveguide is formed, an upper layer and a lower layer disposed so as to sandwich the optical waveguide substrate, and a support substrate disposed on the side opposite to the optical waveguide substrate of the lower layer. In this optical waveguide element, both the upper layer and the lower layer are made of a material having a refractive index lower than that of the optical waveguide substrate, and the Young's modulus of the upper layer is smaller than that of the lower layer. Therefore, at the time of wafer dicing, the occurrence of chipping in the optical waveguide substrate or the like can be suppressed, and as a result, it becomes possible to provide an optical waveguide element in which the distance between the side surface of the optical waveguide substrate and the electrode is shortened. Furthermore, by using an optical waveguide element having such excellent characteristics, it is also possible to provide an optical modulator and an optical transmission device having similar effects.

Brief Description of the Drawings

[0021] [Figure 1] A cross-sectional view showing an example of a conventional optical waveguide element. [Figure 2] A cross-sectional view showing another example of a conventional optical waveguide element. [Figure 3] A cross-sectional view showing an example of a semiconductor substrate wafer disclosed in Patent Document 3. [Figure 4]It is a cross-sectional view showing an example of the optical waveguide device of the present invention. [Figure 5] It is a cross-sectional view showing an example in which an upper layer is disposed under an electrode layer in the optical waveguide device of the present invention. [Figure 6] It is a cross-sectional view showing an example in which an upper layer is disposed on an electrode layer in the optical waveguide device of the present invention. [Figure 7] It is a plan view showing an example of an optical waveguide device using a segment electrode shown in Patent Document 2. [Figure 8] It is a cross-sectional view showing an example when the segment electrode of FIG. 7 is applied to the optical waveguide device of the present invention. [Figure 9] It is a cross-sectional view showing another example when the segment electrode of FIG. 7 is applied to the optical waveguide device of the present invention. [Figure 10] It is a plan view for explaining a state in the vicinity of a side surface of an optical waveguide substrate of the optical waveguide device of the present invention. [Figure 11] It is a view showing an example of the optical transmission device of the present invention.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, the optical waveguide device of the present invention, the optical modulator using the same, and the optical transmission device will be described in detail using preferred examples. FIG. 4 shows a cross-sectional view showing an example of the optical waveguide device of the present invention. The optical waveguide device of the present invention includes an optical waveguide substrate 1 on which an optical waveguide is formed, an upper layer UPL and a lower layer UNL disposed so as to sandwich the optical waveguide substrate 1, and a support substrate SS disposed on the opposite side of the lower layer UNL from the optical waveguide substrate 1. In the optical waveguide device, both the upper layer UPL and the lower layer UNL are made of a material having a refractive index lower than that of the optical waveguide substrate 1, and the Young's modulus of the upper layer UPL is smaller than the Young's modulus of the lower layer UNL.

[0023] The optical waveguide substrate 1 used in the optical waveguide element of the present invention can be a substrate having an electro-optic effect. Specifically, single crystal materials such as lithium niobate (LN), lithium tantalate (LT), and PLZT (lead lanthanum zirconate titanate), or materials doped with MgO or the like, can be used. These materials can also be formed into films using vapor phase growth methods such as sputtering, vapor deposition, or CVD. Furthermore, a substrate can be used in which an electro-optic effect substrate is bonded to another substrate, and then the electro-optic effect substrate is thin-film processed onto it. In addition, semiconductor substrates and organic material substrates such as EO polymers can also be used.

[0024] As the optical waveguide 10, it is possible to use an optical waveguide formed by thermal diffusion of a high refractive index material such as Ti into the optical waveguide substrate 1, an optical waveguide formed by the proton exchange method, or a rib-type optical waveguide 10 in which the substrate has a convex shape corresponding to the optical waveguide, as shown in Figure 5 or 6, by etching the substrate 1 other than the optical waveguide or forming grooves on both sides of the optical waveguide. Furthermore, it is possible to further increase the refractive index by diffusing Ti or other materials onto the substrate surface by the thermal diffusion method or the proton exchange method in accordance with the rib-type optical waveguide. In order to enhance light confinement, the rib-type optical waveguide has a fine structure with a width and height of about 1 μm or less.

[0025] The thickness (maximum thickness) of the optical waveguide substrate 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 match the speed of the microwave and optical waves of the modulated signal. In addition, the height of the rib-type optical waveguide 10 (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 to 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.

[0026] To increase the mechanical strength of the optical waveguide substrate 1 on which the optical waveguide is formed, a support substrate SS is bonded to the underside of the optical waveguide substrate 1. The optical waveguide substrate 1 and the support substrate SS are bonded together either directly or via an adhesive layer such as resin. For direct bonding, it is preferable that the support substrate has a lower refractive index than the optical waveguide or the substrate on which the optical waveguide is formed, but it is not limited to this. 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 support substrate SS is preferably made of a material with a coefficient of thermal expansion similar to that of the optical waveguide substrate 1, such as a substrate containing an oxide layer, such as a low dielectric constant substrate of SiO2 or Al2O3, including glass, quartz, fused silica, synthetic silica, alkali glass, alkali-free glass, lead glass, borosilicate glass, soda glass, sapphire, alumina, etc. In addition, it is also possible to use the same LN substrate as the optical waveguide substrate 1, or a composite substrate in which a silicon oxide layer is formed on a silicon substrate abbreviated as SOI or LNOI, or a composite substrate in which a silicon oxide layer is formed on an LN substrate. If the refractive index of the support substrate SS is higher than that of the optical waveguide substrate 1, a layer with a lower refractive index than that of the optical waveguide substrate 1 is provided between the optical waveguide substrate 1 and the support substrate SS. Furthermore, as will be described later, the support substrate according to the present invention is not limited to one formed from a single substrate, but also includes a substrate formed by stacking and integrating multiple substrates.

[0027] In Figure 4, as an example, a glass substrate is used for the support substrate SS, and a bonding layer (intermediate layer) of SiO2 or the like is provided on the upper surface of the support substrate SS via an adhesive layer BL of Si or the like, and the optical waveguide substrate 1 is placed thereon. In the optical waveguide element of the present invention, the intermediate layer that is placed below the optical waveguide substrate 1 and in contact with the optical waveguide substrate 1 is called the lower layer UNL. In addition, the upper layer UPL, which is a feature of the present invention, is placed above the optical waveguide substrate 1.

[0028] In the optical waveguide element of the present invention, the upper layer UPL and lower layer UNL sandwiching the optical waveguide substrate 1 function as cladding layers for the optical waveguide, and therefore dielectric materials with a lower refractive index and higher transparency than the optical waveguide substrate 1 are used. Specifically, oxides and fluorides of metal elements from groups 1 to 17 of the periodic table, such as SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, CaF2, and Y2O3, are used.

[0029] Furthermore, the upper layer UPL is softer than the lower layer to mitigate mechanical shock during wafer cutting and suppress chipping of the optical waveguide substrate 1, the lower layer (intermediate layer) UNL, and the support substrate SS. In other words, the Young's modulus of the upper layer UPL is smaller than that of the lower layer UNP. Specifically, the Young's modulus of the upper layer UPL is set to 90 GPa or less.

[0030] To adjust the Young's modulus in the upper and lower layers, at least one oxide of a semiconductor element from groups 3 to 8 of the periodic table may be included in the upper or lower layers. For example, metal oxides such as indium, titanium, zinc, tin, chromium, aluminum, and germanium are used. Furthermore, for the purpose of adjusting the refractive index, the upper layer (UPL) may consist of two or more layers of different materials. In this case, the Young's modulus of each layer is set so that the Young's modulus of the layer with the smallest Young's modulus among the layers is smaller than the Young's modulus of the lower layer (UNL).

[0031] Furthermore, to adjust the Young's modulus, it is possible to include inert gas in the upper and lower layers. Since the upper and lower layers are formed by sputter deposition of the material to become the film, the amount of inert gas contained in each layer can be changed by adjusting the concentration of the inert gas used for sputtering. The higher the amount of inert gas, the lower the density of the formed film, resulting in a soft film with a low Young's modulus. For this reason, the amount of inert gas in each layer is higher in the upper layer (UPL) than in the lower layer (UNL). Sputter deposition results in a uniform composition within the film, and can stably prevent chipping regardless of its location on the chip or wafer.

[0032] The inert gas used can be noble gases from Group 18 of the periodic table (He, Ne, Ar, Kr, Xe, Rn) or nitrogen. One type of inert gas may be used, or a mixture of multiple inert gases may be used. For example, only Ar may be used, and the Young's modulus may be adjusted by changing the Ar content. Similarly, Ar and nitrogen can be mixed, and their content can be varied. It is preferable to set the nitrogen content lower than the noble gas content. This is because noble gases do not react with other elements, while nitrogen forms nitrides. Therefore, considering the stability of the device after fabrication, a lower nitrogen content is preferable.

[0033] The advantage of using an inert gas such as Ar in the upper layer is that even after the optical waveguide element (chip) is mounted in a housing, hermetically sealed, and assembled into a device, the inert gas does not react with other functional layers such as electrodes, thus preventing deterioration of device characteristics. For example, even if an inert gas such as Ar is released inside the housing after packaging, it does not affect other functional layers such as the oxidation of electrodes, thus ensuring stable device characteristics over the long term.

[0034] In the case of the lower layer UNL, the inert gas content is preferably set to 1.0 atm% or less to avoid affecting the bonding strength, as the lower layer functions as a bonding layer, resulting in a rigid film.

[0035] On the other hand, the upper layer UPL is designed to be a flexible film, so the inert gas content is preferably 1.0 atm% or higher. However, if there is too much inert gas such as Ar, the film will have many defects, and the device characteristics and reliability will decrease due to water content, etc., so it is preferable to set it to 3.0 atm% or lower. The inert gas content in the film can be measured by RBS (Rutherford Backscattering Spectrometry) analysis.

[0036] The film thickness h2 of the upper layer UPL can be set to be thinner than the film thickness h1 of the lower layer UNL. The thickness h1 of the lower layer is preferably 1 μm or more, and preferably 2 μm or more to suppress light absorption by the support substrate SS. The thickness h2 of the upper layer is 100 nm or more, and more preferably 200 nm or more to suppress chipping of the optical waveguide substrate 1.

[0037] The materials that make up the upper layer (UPL) may be the same as those that make up the lower layer (UNL), or they may be different. When the same material is used, the upper layer UPL and the lower layer UNL sandwiching the optical waveguide substrate 1 will have the same coefficient of linear expansion, making it possible to provide an optical waveguide element that suppresses the occurrence of drift phenomena due to temperature changes.

[0038] It is also possible to form the layers using different materials, such as using SiO2 for the upper layer (UPL) and Al2O3 for the lower layer (UNL). This makes it possible to select the optimal material according to the required properties of each layer.

[0039] Figures 5 and 6 show an example in which an electrode layer EL for applying an electric field to the optical waveguide 10 is placed on the upper side of the optical waveguide substrate 1. In Figure 5, the upper layer UPL is placed below the electrode layer EL, but it may also be placed so as to cover the electrode layer EL, as shown in Figure 6. When placed below the electrode layer as in Figure 5, it relieves stress on the optical waveguide substrate and optical waveguide caused by the electrodes. When placed above the electrode layer as in Figure 6, it is possible to increase the electric field efficiency applied to the optical waveguide by the electrodes.

[0040] Figure 7 is a plan view of an optical waveguide element using a segment electrode SE as shown in Patent Document 1. The segment electrode SE is electrically connected to a transmission line ME that propagates a high-frequency signal using a bridge electrode BE. An example of applying such a segment electrode SE to the optical waveguide element of the present invention is shown in Figures 8 and 9. Figures 8 and 9 are enlarged cross-sectional views showing only the vicinity of the segment electrode SE on either side of the optical waveguide 10. As shown in Figure 8, it is possible to arrange the segment electrode SE, bridge electrode, and transmission line ME on the upper side of the upper layer UPL.

[0041] For example, using a glass substrate for the support substrate SS results in a decrease in the dielectric constant around the electrodes, but by using segment electrodes, it becomes possible to adjust (increase) Nm (effective refractive index of light). Furthermore, as shown in Figure 9, it is also possible to configure the system so that only the segment electrodes SE and bridge electrodes BE are placed on the optical waveguide substrate 1, and the transmission line ME is placed on top of the upper layer UPL. In Figure 9, a portion of the transmission line ME, which is placed above the upper layer UPL, is positioned to straddle the optical waveguide substrate 1, but this role can also be performed by the bridge electrode BE.

[0042] As shown in Figure 9, the upper layer UPL does not need to be placed over the entire upper surface of the optical waveguide substrate 1. Since the upper layer UPL needs to be placed at least in the cut portion, in the chip state (after the wafer has been cut), the configuration ensures that the upper layer UPL is placed at least around the periphery of the optical waveguide substrate 1.

[0043] As shown in Figure 10, electrode layers (EL1 to EL3) are arranged on the upper or lower side of the optical waveguide substrate 1, and the shortest distance (S1, S2) from the side surface of the optical waveguide substrate 1 (left edge and bottom edge in the drawing) to the side surface of the electrode layer is set to 30 μm or less, more preferably 20 μm or less. The shorter the distance S1, the less margin there is around the chip's periphery, and the more chips can be obtained from a single wafer. Furthermore, a shorter distance S1 allows for shorter wiring lengths connecting to the electrode EL2 from the outside, which can, for example, suppress the degradation of high-frequency signals.

[0044] Next, we will describe examples of applying the optical waveguide element of the present invention to optical modulators and optical transmitting devices. In the following description, we will use an example of HB-CDM, but the present invention is not limited to this and can also be applied to optical phase modulators, optical modulators with polarization combining functions, optical modulators integrating more or fewer Mach-Zehnder type optical waveguides, bonding devices with optical waveguide substrates made of other materials such as silicon, and devices for sensor applications.

[0045] As shown in Figure 11, the optical waveguide element has an optical waveguide 10 formed on an optical waveguide substrate 1 and electrodes (not shown), such as modulation electrodes, that modulate the light waves propagating through the optical waveguide 10, and the substrate 1 is housed in a housing CA. Furthermore, by providing an optical fiber (F) for inputting and outputting light waves to the optical waveguide, an optical modulator MD can be constructed. In Figure 11, the optical fiber (F) is introduced into the housing CA through a through-hole penetrating the side wall of the housing CA, and the optical waveguide substrate 1 and the optical fiber are directly joined. Alternatively, the light waves L1 incident from the optical fiber F and the light waves L2 emitted from the optical fiber F can be optically coupled to the optical waveguide 10 in the optical waveguide substrate 1 via an optical block equipped with an optical lens, a lens barrel, a polarization multiplexer, etc. In addition, to ensure stable joining with the optical fiber and optical block, a reinforcing member RI can be placed on top of the optical waveguide substrate 1 along the end face of the substrate 1.

[0046] An optical transmitter (OTA) can be configured by connecting an electronic circuit (digital signal processor, DSP) that outputs a modulation signal S0 to the optical modulator MD 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 also be amplified. For this reason, in Figure 11, a driver circuit DRV is used to amplify the modulation signal. The driver circuit DRV and the digital signal processor DSP can be placed outside the housing CA, or they can be placed inside the housing CA. In particular, placing the driver circuit DRV inside the housing makes it possible to further reduce the propagation loss of the modulation signal from the driver circuit. If the degradation of the modulation signal is small, the DRV is not necessary, and the modulation operation of the optical modulator MD can be performed directly by the DSP.

[0047] The input light L1 to the optical modulator MD may be supplied from outside the optical transmitter OTA, but it is also possible to use a semiconductor laser (not shown) as the light source and integrate it integrally within the optical transmitter OTA. The output light L2 modulated by the optical modulator MD is output externally via an optical fiber F.

[0048] It is also possible to configure the system so that electrical connections can be made simply by plugging devices into connection plugs, such as by installing the optical modulator MD inside the optical transmission device OTA, or by integrating the unitized optical transmission device OTA into a rack within the transceiver equipment. Furthermore, while the above-described example of an optical waveguide element involves housing the optical waveguide element inside a casing to form an optical modulator, and then incorporating the optical modulator into an optical transmitter, it is also possible to directly mount the optical waveguide element onto an optical transceiver or to combine it with other functional elements within the optical transceiver to create a subassembly. [Industrial applicability]

[0049] As described above, the present invention makes it possible to provide an optical waveguide element that shortens the distance between the side surface of the optical waveguide substrate and the electrode, and suppresses the occurrence of chipping during wafer cutting. Furthermore, it is possible to provide an optical modulator and an optical transmitting device using the optical waveguide element. [Explanation of Symbols]

[0050] 1 Optical waveguide substrate (thin plate, film body) 10 Optical waveguide UPL upper layer UNL lower tier SS support board BL adhesive layer EL electrode layer M Upper electrode F Optical Fiber CA cabinet MD Optical Modulator DRV driver circuit DSP (Digital Signal Processor) OTA Optical Transmitter

Claims

1. An optical waveguide element comprising an optical waveguide substrate on which an optical waveguide is formed, and an upper layer and a lower layer arranged so as to sandwich the optical waveguide substrate, wherein a support substrate is arranged on the side of the lower layer opposite to the optical waveguide substrate, Both the upper layer and the lower layer are composed of a material having a refractive index lower than that of the optical waveguide substrate. An optical waveguide element characterized in that the Young's modulus of the upper layer is smaller than that of the lower layer.

2. An optical waveguide element according to claim 1, wherein the upper layer and the lower layer contain an inert gas, and the content of the inert gas in each layer is greater in the upper layer than in the lower layer.

3. An optical waveguide element according to claim 2, characterized in that the content of the inert gas in the upper layer is 1.0 atm% or more and 3.0 atm% or less.

4. An optical waveguide element according to claim 1, characterized in that the thickness of the upper layer is thinner than the thickness of the lower layer.

5. An optical waveguide element according to claim 1, characterized in that the upper layer is arranged at least in the peripheral portion of the optical waveguide substrate.

6. An optical waveguide element according to claim 1, characterized in that the material constituting the upper layer is the same material as the material constituting the lower layer.

7. An optical waveguide element according to claim 1, characterized in that an electrode layer is arranged on the upper or lower side of the optical waveguide substrate, and the shortest distance from the side surface of the optical waveguide substrate to the side surface of the electrode layer is set to 30 μm or less.

8. The optical waveguide element according to claim 1, A housing for the optical waveguide element, An optical modulator characterized by comprising an optical waveguide and an optical fiber for inputting or outputting optical waves.

9. In the optical modulator according to claim 8, The optical waveguide element includes a modulation electrode for modulating the light wave propagating through the optical waveguide. An optical modulator characterized by having an electronic circuit inside the housing that amplifies the modulation signal input to the modulation electrode.

10. The optical modulator according to claim 8, A light source that inputs light waves to the optical modulator, An optical transmitting device characterized by having an electronic circuit that outputs a modulation signal to the optical modulator.

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