Optical waveguide element, optical modulator, optical modulation module, and optical transmission device

Abstract

The present invention provides an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmission device. In the optical waveguide element, without causing deterioration or degradation of optical characteristics, the optical absorption loss of waveguide light caused by electrode metal that may be generated at the intersection of the optical waveguide and the electrode is effectively reduced. In the optical waveguide element including a substrate, an optical waveguide formed on the substrate, and an electrode for controlling light waves propagating in the optical waveguide, the optical waveguide and the electrode have an intersection where they cross each other. At the intersection, the electrode forms a multilayer structure including a plurality of metal layers made of a metal material, and a resin layer made of a resin material is formed between the electrode and the substrate.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmission device. Background Art

[0002] In high-speed / large-capacity optical fiber communication systems, optical modulators incorporating optical modulation elements are often used. The optical modulation elements are optical waveguide elements formed by optical waveguides on a substrate. Among them, LiNbO3 (hereinafter also referred to as LN) having an electro-optic effect is widely used in high-speed / large-capacity optical fiber communication systems because of its low optical loss and broadband optical modulation characteristics. In an optical modulation element using such an LN substrate, for example, a Mach-Zehnder type optical waveguide and a signal electrode for applying a high-frequency electrical signal as a modulation signal to the optical waveguide are provided.

[0003] In particular, the modulation methods in optical fiber communication systems have been influenced by the trend of increasing transmission capacity in recent years, and multi-value modulations such as QPSK (Quadrature Phase Shift Keying) and DP-QPSK (Dual Polarization - Quadrature Phase Shift Keying), and transmission systems incorporating polarization multiplexing into multi-value modulations have become mainstream. They are used not only in backbone optical transmission networks but also introduced into metropolitan area networks.

[0004] An optical modulator for QPSK modulation (QPSK optical modulator) or an optical modulator for DP-QPSK modulation (DP-QPSK optical modulator) includes a plurality of Mach-Zehnder type optical waveguides having a so-called nested structure, each of which has at least one signal electrode. Moreover, in an optical modulator using such a Mach-Zehnder type optical waveguide, generally, a bias electrode for compensating for changes in the bias point caused by so-called DC drift is also formed.

[0005] These signal electrodes or bias electrodes (hereinafter also collectively referred to simply as electrodes) are formed so as to extend near the outer periphery of the LN substrate for connection to an electrical circuit outside the substrate. Therefore, on the substrate, a plurality of optical waveguides and a plurality of electrodes cross each other complexly, forming a plurality of crossing portions of the optical waveguides and the electrodes.

[0006] In the above-described crossing portion, when the optical waveguide and the electrode are formed in direct contact with each other, in the above-described crossing portion, since the light propagating in the optical waveguide is absorbed by the metal constituting the electrode, light loss (light absorption loss) occurs. Such light loss generates, for example, a light loss difference between two parallel waveguides constituting a Mach-Zehnder type optical waveguide, and deteriorates the extinction ratio of the modulated light. The higher the modulation speed required for the optical modulator, the stricter the requirement conditions for the extinction ratio. Therefore, it can be expected that such deterioration of the extinction ratio becomes more and more obvious along with the high-speedization of the modulation speed accompanying the increase in the transmission capacity.

[0007] In addition, the above-described crossing portion is generally formed widely not only in an optical modulator using a Mach-Zehnder type optical waveguide but also in optical waveguide elements such as an optical modulator and / or an optical switch using a directional coupler or an optical waveguide constituting a Y-branch. And if the optical waveguide pattern and the electrode pattern become complicated along with the further miniaturization, multi-channelization and / or high integration of the optical waveguide element, the number of crossing portions on the substrate continuously increases, becoming a non-negligible cause of loss and restricting the performance of the optical waveguide element.

[0008] As a technique for reducing the light absorption loss generated by the electrode metal formed on the optical waveguide, conventionally, a technique of providing a buffer layer made of SiO2 on the surface of the substrate on which the optical waveguide is formed and forming the electrode metal on the upper part of the buffer layer is known (for example, Patent Document 1).

[0009] However, since SiO2 has higher rigidity than the LN substrate, when a SiO2 film is formed on the LN substrate, not only stress acts on the substrate from the SiO2 film itself, but also stress is applied to the substrate from the electrode metal formed on its upper part via the SiO2 film. And such stress also has an adverse effect on the optical characteristics or electrical characteristics of the optical waveguide element via the photoelastic effect of the LN substrate.

[0010] Especially in an optical waveguide element in which the LN substrate is formed thin (for example, with a thickness of several tens of μm) in order to further enhance the interaction between the signal electric field and the waveguide light in the substrate (that is, to improve the electric field efficiency), the stress applied to the substrate from the SiO2 film and the electrode metal on its upper part has a non-negligible influence on the optical characteristics and / or electrical characteristics, and also may cause mechanical damage such as cracks or fractures in the LN substrate due to the difference in the linear expansion coefficients of the SiO2 film and the LN substrate.

[0011]

Prior Art Documents

[0012]

Patent Documents

[0013]

Patent Document 1

[0014]

Summary of the Invention

[0015]

Problems to be Solved by the Invention

[0016] In the optical waveguide element based on the above background, it is required to effectively reduce the optical absorption loss of the waveguide light caused by the electrode metal that may occur at the intersection of the optical waveguide and the electrode without deteriorating or worsening the optical characteristics of the optical waveguide element.

[0017]

Solutions to the Problems

[0018] One aspect of the present invention is that in an optical waveguide element including a substrate, an optical waveguide formed on the substrate, and an electrode for controlling light waves propagating in the optical waveguide, the optical waveguide and the electrode have an intersection where they cross each other. At the intersection, the electrode forms a multilayer structure including a plurality of metal layers made of a metal material, and a resin layer made of a resin material is formed between the electrode and the substrate.

[0019] According to another aspect of the present invention, in the multilayer structure of the electrode, at least one layer of the metal layers other than the lowermost layer closest to the substrate is thicker than the lowermost layer.

[0020] According to another aspect of the present invention, the resin layer is formed to have a length in the waveguide direction of the optical waveguide longer than the length in the waveguide direction of the adjacent metal layer.

[0021] According to another aspect of the present invention, the resin layer is configured such that the length in the waveguide direction of the portion where the adjacent metal layer is not formed is longer than the wavelength of the light propagating in the optical waveguide.

[0022] According to another aspect of the present invention, the metal layer adjacent to the resin layer is formed to have a length in the waveguide direction of the optical waveguide equal to or longer than the length in the waveguide direction of the other adjacent metal layer.

[0023] According to another aspect of the present invention, the metal layer adjacent to the resin layer is configured such that the length in the waveguide direction of the portion where the other metal layer is not formed is longer than the wavelength of the light propagating in the optical waveguide.

[0024] According to another aspect of the present invention, the resin layer is formed such that at both end portions in the waveguide direction of the optical waveguide, the width in the direction orthogonal to the waveguide direction is equal to or less than the width of the optical waveguide and becomes narrower as it separates from the intersection.

[0025] According to another aspect of the present invention, the resin layer is formed such that its thickness becomes thinner as it separates from the crossing portion at both ends in the waveguide direction of the optical waveguide.

[0026] According to another aspect of the present invention, at least one of the metal layers in the metal layer constituting the multilayer structure, other than the metal layer formed on the uppermost part, is formed with a slit.

[0027] According to another aspect of the present invention, the resin layer is formed across at least two of the crossing portions.

[0028] Another aspect of the present invention relates to an optical modulator including any one of the above optical waveguide elements as an optical modulation element for modulating light, a housing that houses the optical waveguide element, an optical fiber that inputs light to the optical waveguide element, and a second optical fiber that guides the light output from the optical waveguide element to the outside of the housing.

[0029] Another aspect of the present invention relates to an optical modulation module including any one of the above optical waveguide elements as an optical modulation element for modulating light, and a drive circuit that drives the optical waveguide element.

[0030] Another aspect of the present invention relates to an optical transmission device including the optical modulator or the optical modulation module, and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform a modulation operation.

[0031]

Advantages of the Invention

[0032] According to the present invention, in the optical waveguide element, it is possible to effectively reduce the optical absorption loss of the waveguide light caused by the electrode metal that may occur at the crossing portion of the optical waveguide and the electrode on the substrate, without causing deterioration or degradation of the optical characteristics of the optical waveguide element. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a diagram showing the configuration of an optical modulator according to the first embodiment of the present invention.

[0034] Figure 2 is shown in Figure 1 a diagram showing the configuration of an optical modulation element used in the optical modulator.

[0035] Figure 3 is Figure 2 a partial detailed view of part A of the optical modulation element shown.

[0036] Figure 4 is Figure 3 a sectional view taken along line IV-IV of part A shown.

[0037] Figure 5 is Figure 3The V-V sectional view of part A shown and a diagram for explaining the function of this section.

[0038] Figure 6 It is a diagram showing an example of another configuration of the signal electrode of part A.

[0039] Figure 7 It is Figure 2 The partial detailed view of part B of the optical modulation element shown.

[0040] Figure 8 It is Figure 7 The VIII-VIII sectional view of part B shown.

[0041] Figure 9 It is Figure 7 The IX-IX sectional view of part B shown and a diagram for explaining the function of this section.

[0042] Figure 10 It is a diagram showing an example of an alternative configuration of part B.

[0043] Figure 11 It is a diagram showing another example of an alternative configuration of part B.

[0044] Figure 12 It is Figure 2 The partial detailed view of part C of the optical modulation element shown.

[0045] Figure 13 It is Figure 12 The XIII-XIII sectional view of part C shown.

[0046] Figure 14 It is Figure 12 The XIV-XIV sectional view of part C shown and a diagram for explaining the function of this section.

[0047] Figure 15 It is a diagram showing the configuration of the optical modulation module according to the second embodiment of the present invention.

[0048] Figure 16 It is a diagram showing the configuration of the optical transmission device according to the third embodiment of the present invention.

[0049] Figure 17 It is a top view showing an example of the configuration of the intersection of the optical waveguide and the electrode in a conventional optical waveguide element.

[0050] Figure 18 It is Figure 17 The XVIII-XVIII sectional view of the intersection shown.

[0051] Figure 19 It is Figure 17Cross-sectional view taken along the XIX-XIX plane of the intersection shown.

[0052]

Reference Numeral Explanation

[0053] 100… Optical modulator, 102… Housing, 104… Optical modulation element, 106… Relay substrate, 108… Through-hole, 110a, 110b, 110c, 110d… Signal pins, 112a, 112b… Terminator, 114… Input optical fiber, 116… Optical unit, 118, 130, 134… Lenses, 120… Output optical fiber, 122, 124… Supports, 230, 2130… Substrates, 232… Input waveguide, 234… Branch waveguide, 240a, 240b… Nested Mach-Zehnder optical waveguide, 244a, 244b, 246a, 246b… Mach-Zehnder optical waveguide, 244b-1, 2134… Optical waveguide, 248a, 248b… Output waveguide, 250a, 250b, 250b’, 252a, 252b, 252b’… Signal electrodes, 254a, 254b, 256a, 256b, 258a, 258b, 260a, 260b… Pads, 262a, 262b, 264a, 264b… Bias electrodes, 280a, 280b, 280c, 280d… Sides, 370, 770, 1270, 2140… Intersections, 450-1, 450-2, 650-1, 650-2, 650-3, 650-4, 850-1, 850-1’, 850-2, 1350-1, 1350-2… Metal layers, 452, 852, 852’, 1352, 1352’, 2138… Resin layers, 490, 2142… Adhesive layers, 492, 2144… Support substrates, 1500… Optical modulation module, 1506… Circuit board, 1508… Driver circuit, 1600… Optical transmission device, 1604… Light source, 1606… Modulator drive unit, 1608… Modulation signal generation unit, 2136… Electrode. Detailed Implementation Manner

[0054] As a countermeasure to reduce the stress acting on the substrate from the SiO2 film in the above prior art, it can be considered to form the SiO2 film not on the entire surface of the substrate but only on the substrate portion where the optical waveguide and the electrode intersect, and form the electrode on the upper part of the SiO2 film.

[0055] Figure 17 This is a top view of the substrate surface at the intersection of a conventional optical waveguide element that forms the SiO2 film only at the intersection on the substrate. Moreover, Figure 18 is Figure 17 Cross-sectional view taken along the XVIII-XVIII plane of the intersection shown, Figure 19 The upper figure (upper figure) ofFigure 17 Cross-sectional view XIX-XIX of the intersection shown. Moreover, Figure 19 The lower diagram (lower diagram) shows a graph of the change in the effective refractive index of the optical waveguide along the waveguide direction of the optical waveguide in the cross-sectional view XIX-XIX.

[0056] As Figure 18 shown, the substrate 2130 is, for example, an LN substrate with a reduced thickness of 10 μm, and is fixed to the support substrate 2144 via the bonding layer 2142. The support substrate 2144 is, for example, a glass substrate, an LN substrate, a Si substrate, etc.

[0057] As Figure 17 shown, on the substrate 2130, an optical waveguide 2134 extending along the Y direction shown in the figure is formed by, for example, Ti thermal diffusion, and an electrode 2136 extending along the Z direction shown in the figure and made of, for example, gold (Au) is formed. At the intersection 2140 of the optical waveguide 2134 and the electrode 2136 ( Figure 17 the portion surrounded by the rectangle of the single-dot chain line shown in the figure), as Figure 18 and Figure 19 shown in the upper diagram, an SiO2 film 2138 as a buffer layer is formed on the upper part of the optical waveguide 2134, and the electrode 2136 is formed on the upper part of the SiO2 film 2138.

[0058] Due to the presence of the SiO2 film 2138, at the intersection 2140, the optical absorption loss of the waveguide light of the optical waveguide 2134 caused by the metal Au of the electrode 2136 can be suppressed.

[0059] However, in the case of such a configuration, the SiO2 film 2138 is formed only on a part of the optical waveguide 2134, that is, the part corresponding to the intersection 2140. As a result, the stress from the SiO2 film 2138 and the electrode 2136 is concentratedly applied to the part of the optical waveguide 2134 corresponding to the intersection 2140.

[0060] Especially in an optical modulation element that performs high-speed optical modulation exceeding 100G, generally, the signal electrode is configured to be relatively thick, with a thickness of 20 μm to 40 μm in order to reduce its conductor loss, etc. On the other hand, the SiO2 film as a buffer layer provided for reducing the above-mentioned optical absorption loss is formed with a thickness sufficient for its purpose, that is, a thin thickness of 0.3 μm to 0.5 μm. Therefore, especially in a configuration where the electrode 2136 is a signal electrode, the stress accumulated in the metal Au during the formation of the electrode 2136 or the stress remaining at the interface between the electrode 2136 and the SiO2 film 2138 is applied to the optical waveguide 2134 via the SiO2 film 2138 formed with a thickness of 1 μm or less.

[0061] And, the above stress asFigure 19 As shown in the lower part of the figure, the effective refractive index n1 in the optical waveguide 2134 increases by, for example, Δn9 at the intersection 2140 through the photoelastic effect of the LN constituting the substrate 2130, and changes sharply to n9. Figure 19 In the lower figure, the vertical axis represents the effective refractive index n of the optical waveguide 2134. eff The horizontal axis represents the waveguide direction of the optical waveguide 2134, that is, the position in the Y direction.

[0062] Such a sudden change in the effective refractive index causes a sudden change in the propagation mode of light within the optical waveguide 2134 at the intersection 2140 (for example, a sudden change in the mode field diameter of the propagation mode). This mode change causes light leakage at the boundary portion of the intersection 2140. As a result, in conventional optical waveguide elements such as those described above, this light leakage causes an increase in optical waveguide loss or a degradation in the extinction ratio.

[0063] In particular, optical waveguide components using thinner substrates to improve electric field efficiency are more susceptible to stress than optical waveguide components using thicker substrates. This mode shift, which causes increased light leakage-related losses and a more pronounced degradation of the extinction ratio, is more pronounced. Furthermore, when the intersection 2140 between the optical waveguide 2134 and the electrode 2136 is located near the optical waveguide portion that forms a Y-shaped optical branching or combining section, this mode shift can cause uneven optical branching or combining, significantly impacting the extinction ratio.

[0064] It should be noted that the change in the effective refractive index at the intersection 2140 of the optical waveguide 2134 depends on the direction of the stress applied to the intersection 2140 (the direction relative to the crystal axis of the substrate), and there are cases where the effective refractive index n1 increases or decreases relative to the other parts of the optical waveguide 2134. That is, the sign of Δn9 is as follows: Figure 19 As shown in the example in the lower figure of FIG, the refractive index may be positive (i.e., the refractive index increases) or negative (i.e., the refractive index decreases). When the effective refractive index decreases sharply at the intersection 2140, as described above, light leakage occurs due to a change in the propagation mode within the optical waveguide 2134, which may increase the optical waveguide loss and degrade the extinction ratio.

[0065] The optical waveguide element of the present invention does not cause degradation or worsening of the optical characteristics of the optical waveguide element that may be caused by changes in the propagation mode at the intersection, and effectively reduces the optical absorption loss of the waveguide light caused by the electrode metal at the intersection.

[0066] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0067] [First Embodiment]

[0068] Figure 1 FIG. 1 is a diagram showing the configuration of a modulator 100 using an optical waveguide element, i.e., an optical modulation element 104, according to the first embodiment of the present invention. The modulator 100 includes a housing 102, an optical modulation element 104 housed in the housing 102, and a relay substrate 106. The optical modulation element 104 is, for example, a DP-QPSK modulator. The housing 102 is finally hermetically sealed by fixing a cover (not shown) as a plate body to its opening.

[0069] The modulator 100 further includes signal pins 110a, 110b, 110c, 110d for inputting high-frequency electrical signals used in the modulation of the optical modulation element 104, and a feed through portion 108 for guiding these signal pins 110a, 110b, 110c, 110d into the housing 102.

[0070] In addition, the modulator 100 has an input optical fiber 114 for inputting light into the housing 102 and an output optical fiber 120 for guiding the light modulated by the optical modulation element 104 to the outside of the housing 102 on the same surface of the housing 102.

[0071] Here, the input optical fiber 114 and the output optical fiber 120 are respectively fixed to the housing 102 via supports 122 and 124 as fixing members. The light input from the input optical fiber 114 is collimated by a lens 130 disposed in the support 122 and then input to the optical modulation element 104 via a lens 134. However, this is an example, and the input of light to the optical modulation element 104 may also be performed according to the prior art, for example, by introducing the input optical fiber 114 into the housing 102 via the support 122 and connecting the end face of the introduced input optical fiber 114 to the end face of the substrate 230 of the optical modulation element 104.

[0072] The modulator 100 further includes an optical unit 116 for polarization synthesis of two beams of modulated light output from the optical modulation element 104. The polarization-synthesized light output from the optical unit 116 is condensed by a lens 118 disposed in the support 124 and coupled to the output optical fiber 120.

[0073] The relay substrate 106 relays high-frequency electrical signals input from the signal pins 110a, 110b, 110c, and 110d to the optical modulator 104 via a conductor pattern (not shown) formed on the relay substrate 106. The conductor patterns on the relay substrate 106 are connected to pads (described later) at one end of the signal electrodes of the optical modulator 104, for example, by wire bonding. Furthermore, the optical modulator 100 includes two terminators 112a and 112b having a predetermined impedance within the housing 102.

[0074] Figure 2 It means in Figure 1 FIG2 shows an example of the structure of the optical modulator 104, an optical waveguide element housed within the housing 102 of the optical modulator 100. The optical modulator 104 is constructed using optical waveguides (shown as bold dashed lines) formed on a substrate 230 made of, for example, LN, and performs, for example, 200G DP-QPSK modulation. These optical waveguides can be formed by thermally diffusing Ti onto the surface of the substrate 230.

[0075] The substrate 230 is, for example, rectangular and has two sides 280a and 280b extending in the vertical direction and facing each other in the figure, and two sides 280c and 280d extending in the horizontal direction and facing each other in the figure. Figure 2 As shown in the coordinate axis in the upper left part of the figure, the direction Figure 2 The normal direction of the depth of the paper (from the surface to the inside) is set as the X direction, the right direction in the figure is set as the Y direction, and the bottom direction in the figure is set as the Z direction.

[0076] The optical modulator 104 includes an input waveguide 232, which receives input light (indicated by an arrow pointing rightward in the figure) from the input optical fiber 114, located on the lower side of the left-hand side 280b of the substrate 230, and a branching waveguide 234, which branches the input light into two beams having equal light intensity. Furthermore, the optical modulator 104 includes two modulation sections, so-called nested Mach-Zehnder optical waveguides 240a and 240b (each enclosed by a dashed-dotted line in the figure), which modulate the respective beams branched by the branching waveguide 234.

[0077] The nested Mach-Zehnder optical waveguides 240a and 240b respectively include two Mach-Zehnder optical waveguides 244a (the part within the dotted line shown in the figure), 246a (the part within the long-dashed double-dotted line shown in the figure), 244b (the part within the dotted line shown in the figure), and 246b (the part within the long-dashed double-dotted line shown in the figure) provided in two waveguide parts constituting a pair of parallel waveguides. Thus, after the nested Mach-Zehnder optical waveguides 240a and 240b respectively perform QPSK modulation on the input light branched into two beams by the optical branching waveguide 23, the modulated light (output) is output to the left in the figure from the respective output waveguides 248a and 248b.

[0078] These two output light beams are then polarization-combined by the optical unit 116 disposed outside the substrate 230 and aggregated into one light beam. Hereinafter, the input waveguide 232, the branching waveguide 234, and the nested Mach-Zehnder optical waveguides 240a and 240b formed on the substrate 230 of the optical modulation element 104 and the Mach-Zehnder optical waveguides 244a, 246a, 244b, and 246b included therein are collectively referred to as the optical waveguides 232 and the like.

[0079] On the substrate 230, signal electrodes 250a, 252a, 250b, and 252b are provided for respectively performing modulation operations on the total four Mach-Zehnder optical waveguides 244a, 246a, 244b, and 246b constituting the nested Mach-Zehnder optical waveguides 240a and 240b. The left sides of the signal electrodes 250a and 252a are bent and extended to the upper side 280c of the substrate 230 shown in the figure and are connected to the pads 254a and 256a. Moreover, the right sides of the signal electrodes 250a and 252a are extended to the right side 280a of the substrate 230 shown in the figure and are connected to the pads 258a and 260a.

[0080] Similarly, the left sides of the signal electrodes 250b and 252b are extended to the lower side 280d of the substrate 230 shown in the figure and are connected to the pads 254b and 256b, and the right sides of the signal electrodes 250b and 252b are extended to the right side 280a of the substrate 230 shown in the figure and are connected to the pads 258b and 260b. The pads 258a, 260a, 258b, and 260b are connected to the above-mentioned relay substrate 106 by wire bonding or the like.

[0081] It should be noted that the signal electrodes 250a, 252b, 250b, and 252b, in accordance with the prior art, together with a ground conductor pattern (not shown) formed on the substrate 230, constitute a coplanar transmission line having a predetermined impedance, for example. The ground conductor pattern is provided, for example, in a manner not formed on the optical waveguides 232 and the like, and the multiple regions formed by being divided by the optical waveguides 232 and the like in the ground conductor pattern can be connected to each other by wire bonding or the like.

[0082] The pads 254a, 256a and 254b, 256b are connected to the above-mentioned terminators 112a and 112b. Thus, the high-frequency electrical signals input from the relay substrate 106 connected to the pads 258a, 260a, 258b, 260b become traveling waves and propagate in the signal electrodes 250a, 252a, 250b, 252b, and the light waves propagating in the Mach-Zehnder type optical waveguides 244a, 246a, 244b, 246b are respectively modulated.

[0083] Here, in order to further enhance the interaction between the electric field formed by the signal electrodes 250a, 252a, 250b, 252b in the substrate 230 and the waveguide light propagating in the Mach-Zehnder type optical waveguides 244a, 246a, 244b, 246b and enable high-speed modulation operation at a lower voltage, the substrate 230 is formed to have a thickness of 20 μm or less, preferably 10 μm or less. It should be noted that the back surface of the substrate 230 (the surface opposite to the Figure 2 shown surface) is bonded via an adhesive layer to a support substrate such as glass (not shown in Figure 2 . In the following Figure 4 etc., it is described as the adhesive layer 490 and the support substrate 492).

[0084] The optical modulation element 104 is also provided with bias electrodes 262a, 264a and 262b, 264b for compensating for the variation of the bias point caused by so-called DC drift. The bias electrodes 262a, 262b are each composed of two sets of electrode pairs and are respectively used for compensating for the variation of the bias point of the Mach-Zehnder type optical waveguides 244a, 246a and 244b, 246b. Moreover, the bias electrodes 264a and 264b are respectively used for compensating for the variation of the bias point of the nested Mach-Zehnder type optical waveguides 240a and 240b.

[0085] These bias electrodes 262a, 264a and 262b, 264b also respectively extend to the edges 280c and 280d of the substrate 230, and in the vicinity of these edges 280c and 280d, they are connected to a bias control circuit outside the housing via pins (not shown) provided on the bottom surface of the housing 102. Thus, the bias electrodes 262a, 264a, 262b, 264b are driven by this bias control circuit to compensate for the variation of the bias point of the corresponding Mach-Zehnder type optical waveguides. Hereinafter, the signal electrodes 250a, 252a, 250b, 252b and the bias electrodes 262a, 264a, 262b, 264b are collectively referred to as the electrodes 250a, etc.

[0086] The optical modulation element 104 configured as described above includes a large number of crossing portions where the optical waveguide 232, etc. cross the electrodes 250a, etc. From Figure 2The records are easy to understand. Figure 2 All intersections between the bold dashed line representing the optical waveguide 232 and the strip-shaped portion representing the electrode 250a are intersections between the optical waveguide 232 and the electrode 250a. In this embodiment, the optical modulation element 104 includes 50 intersections.

[0087] Figure 3 、 Figure 4 and Figure 5 The first example of the structure of such an intersection portion is shown, where the input waveguide 232 and the signal electrode 250b intersect. Figure 2 Here is a detailed diagram of the structure of part A in the figure. Figure 3 This is a top view of section A. Figure 4 yes Figure 3 The IV-IV cross-sectional view of the portion A shown. Figure 5 The upper part of the picture is Figure 3 The VV cross-sectional view of the A portion shown, Figure 5 The lower part of the figure is Figure 5 The upper figure corresponds to a diagram showing the change in the effective refractive index inside the input waveguide 232 along the waveguide direction of the input waveguide 232. Figure 3 、 Figure 4 and Figure 5 The prior art depicts the intersection of Figure 17 、 Figure 18 and Figure 19 The corresponding figure.

[0088] It should be noted that Figure 3 、 Figure 4 、 Figure 5 The illustrated structure is an example of a structure of a portion where the optical waveguide 232 and the like intersect with the electrode 250 a and the like in the light modulator 104 , and can be similarly applied to any portion other than the A portion where the optical waveguide 232 and the like intersect with the electrode 250 a and the like.

[0089] exist Figure 3 In FIG, the input waveguide 232 extending in the left-right direction (Y direction) and the signal electrode 250b extending in the up-down direction (Z direction) intersect with each other to form an intersection 370 (the portion surrounded by the single-dot dashed rectangle in the figure). Figure 4 In the embodiment, the substrate 230 is fixed to the support substrate 492 via the adhesive layer 490. Here, the adhesive layer 490 is made of, for example, a thermosetting resin, and the support substrate 492 is made of, for example, a glass substrate, an LN substrate, or a Si substrate.

[0090] Further, at the intersection 370, the signal electrode 250b is formed as a multi-layer structure including a plurality of metal layers 450-1 and 450-2 made of a metal material, and a resin layer 452 made of a resin material is formed between the signal electrode 250b and the substrate 230. It should be noted that the number of metal layers forming the above multi-layer structure is not limited to 2, and may be 3 or more. Moreover, the resin layer may be at least 1, and may be 2 or more in number.

[0091] In addition, the above-mentioned plurality of metal layers 450-1 and 450-2 may be metals of different types, or may be the same metal but with different manufacturing methods for the metal layers (the same applies to the case of including 3 or more metal layers). For example, when the metal layers 450-1 and 450-2 are set as metals of different types, the metal layer 450-1 may be made of titanium (Ti), and the metal layer 450-2 may be made of gold (Au). Moreover, when the metal layers 450-1 and 450-2 are the same metal but with different manufacturing methods for the metal layers, the metal layer 450-1 may be made of gold (Au) formed by sputtering, and the metal layer 450-2 may be made of gold (Au) formed by electroplating. It should be noted that from the viewpoint of dispersing stress at the interface between the metal layers 450-1 and 450-2, the two metal layers forming the boundary line, such as the metal layers 450-1 and 450-2, are preferably set as metals of different types.

[0092] It should be noted that the signal electrode 250b including the metal layers 450-1 and 450-2 is usually formed in such a way that the overall thickness is in the range of 20 μm to 40 μm in the optical modulation element 104 that performs broadband operation with a modulation speed exceeding 100 Gbps. Moreover, usually, the metal layer 450-1 is formed as a base layer for forming the metal layer 450-2 with a thickness of about 0.1 to 0.3 μm. That is, the thickness of the signal electrode 250b is substantially determined by the thickness of the metal layer 450-2. Therefore, the main cause of the stress acting on the substrate 230 from the signal electrode 250b is the upper metal layer 450-2. It should be noted that the bias electrodes 262a, 262b, 264a, and 264b are usually formed with an overall thickness in the range of 1 μm to 5 μm. In this case, the base metal layer constituting these bias electrodes is usually formed with a thickness of about 0.1 to 0.3 μm. Therefore, in the case of the bias electrodes, the upper metal layer also becomes the main cause of the stress on the substrate 230.

[0093] As Figure 5As shown in the upper diagram, in the present embodiment, the metal layers 450-1 and 450-2 of the signal electrode 250b are formed with the same width Le, and the width Ly1 of the resin layer 452 becomes the same width as the width Le of the above metal layer. However, this is an example, and the width Ly1 of the resin layer 452 can be set to any width larger than the width of the metal layer 450-1 in order to avoid contact between the upper metal layer 450-1 and the input waveguide 232. Moreover, the width of the upper metal layer 450-2 can be formed smaller than the width of the lower metal layer 450-1, or can be formed larger than the width of the lower metal layer 450-1.

[0094] Figure 5 The lower diagram is showing Figure 5 In the configuration shown in the upper diagram, a graph of the change in the effective refractive index of the input waveguide 232 along the waveguide direction (Y direction) of the input waveguide 232. Similar to Figure 19 the lower diagram, Figure 5 the vertical axis of the lower diagram represents the effective refractive index n eff of the input waveguide 232, and the horizontal axis represents the position in the waveguide direction of the input waveguide 232, i.e., the Y direction.

[0095] As Figure 5 shown in the upper diagram, at the crossing portion 370, a resin layer 452 is formed between the metal layer 450-1 and the substrate 230, so that it is possible to prevent waveguide light propagating in the input waveguide 232 from generating optical absorption loss caused by the metal layer 450-1 at the crossing portion 370. Moreover, the signal electrode 250a at the crossing portion 370 is composed of a multilayer structure including a plurality of metal layers 450-1 and 450-2. Since there is a resin layer 452 between the signal electrode 250a and the substrate 230, the stress transmitted from the upper metal layer 450-2 to the input waveguide 232 at the crossing portion 370 is alleviated through the interface between the metal layer 450-2 and the lower metal layer 450-1 and / or the lower metal layer 450-1, and is further alleviated by the resin layer 452 with low rigidity. Therefore, in the optical modulation element 104, compared with the conventional optical waveguide element in which a buffer layer made of SiO2 is formed on the entire surface or the crossing portion of the substrate 230, the stress applied to the crossing portion 370 of the substrate 230 is alleviated.

[0096] Therefore, in the optical modulation element 104, as Figure 5 shown in the lower diagram, the change amount Δn4 of the effective refractive index of the input waveguide 232 at the crossing portion 370 is suppressed to be smaller than the value in the configuration of the prior art using SiO2 as the buffer layer ( Figure 19 Δn9 shown), and the degree of change in the propagation mode of the waveguide light in the input waveguide 232 that would occur at the crossing portion 370 can also be alleviated.

[0097] As a result, in the optical modulation element 104, it is possible to suppress the generation of light leakage caused by the change in the propagation mode at the crossing portion 370, etc., prevent or suppress the deterioration or degradation of optical characteristics, and effectively reduce the light absorption loss caused by the signal electrode 250b.

[0098] As described above, Figure 3 , Figure 4 , Figure 5 The configuration shown can also be similarly applied to other crossing portions where the optical waveguide 232, etc. cross the electrode 250a, etc. outside the portion A. That is, in the optical modulation element 104, depending on the degree of suppression required for the light absorption loss caused by the electrode metal and the degree of leakage light suppression required for suppressing the deterioration of the extinction ratio, for all or part of the crossing portions of the optical waveguide 232, etc. and the electrode 250a, etc., a configuration similar to the configuration shown in Figure 3 , Figure 4 , Figure 5 can be applied.

[0099] It should be noted that in the above configuration, the resin constituting the resin layer 452 can be, for example, a resin formed by a crosslinking reaction. Such a resin is constituted by, for example, a polymer material containing a crosslinking agent and can be formed by heat-processing the polymer material. Moreover, such a resin constituting the resin layer 452 can form a resin having a low Young's modulus of 1 to 2 GPa, which is one order of magnitude smaller than the Young's modulus of SiO2 of 72 GPa to 74 GPa.

[0100] In addition, in Figure 3 , Figure 4 , Figure 5 In the configuration shown, the resin layer 452 forms a rectangle having a length Lz and a width Ly1 and extending along the signal electrode 250b in its plan view (i.e., Lz > Ly1) (see Figure 3 ), but it is not limited thereto. The plan view of the resin layer 452 may have a size that can cover the crossing portion 370 and may be formed as a rectangle extending along the input waveguide 232 (i.e., Lz < Ly1).

[0101] In addition, at the portion A, which is an example of the crossing portion and is shown in Figure 2 , the crossing angle between the input waveguide 232 and the signal electrode 250b is a right angle, but it is not limited thereto. The crossing angle can be set to any angle, and the plan view shape of the resin layer 452 may have a size that can cover the portion where the input waveguide 232 and the signal electrode 250b cross and may be any shape.

[0102] In addition, in Figures 3 - 5In the configuration shown, the signal electrode 250b is composed of two metal layers 450-1 and 450-2, but it is not limited thereto. The signal electrode 250b may be formed of three or more metal layers as described above. For example, the signal electrode at the crossing portion 370 may be composed of four metal layers 650-1, 650-2, 650-3, and 650-4 as shown in the signal electrode 250b'. In this case, at least two adjacent metal layers may be composed of different types of metals or the same type of metals formed by different methods. Figure 6 In the configuration shown, the signal electrode 250b' is composed of four metal layers 650-1, 650-2, 650-3, and 650-4. In this case, at least two adjacent metal layers may be composed of different types of metals or the same type of metals formed by different methods.

[0103] In such a configuration, at the interfaces between the metal layers formed of the metal layers 650-1, 650-2, 650-3, and 650-4, the propagation of stress from the metal layer formed in the upper part to the metal layer formed in the lower part can be suppressed. Moreover, in such a configuration, the thickness of each metal layer can be thinner than that of an electrode composed of a smaller number of layers, so that the stress that may be generated inside each metal layer itself can be further reduced. As a result, in the configuration shown, the stress applied from the signal electrode 250b' to the substrate 230 can be further alleviated. Figure 6 In the configuration shown, the stress applied from the signal electrode 250b' to the substrate 230 can be further alleviated.

[0104] It should be noted that at the crossing portion of the electrode 250a or the like and the optical waveguide 232 or the like, when the electrode 250a or the like is composed of a multilayer structure including three or more metal layers, it is preferably configured such that at least one layer (for example, 650-4) of the above metal layers other than the metal layer closest to the substrate 230 (for example, 650-1), that is, the lowermost layer, is thicker than the lowermost layer. Thus, the internal stress of the metal layer formed thicker than the lowermost layer is effectively dispersed at the interface between the lowermost layer formed thinner than it and the upper metal layer, and the stress applied to the optical waveguide 232 or the like on the substrate 230 and the refractive index change caused by the stress can be effectively alleviated.

[0105] In addition, in Figure 6 In the configuration shown, the metal layers 650-1, 650-2, 650-3, and 650-4 are formed with the same width, but it is not limited thereto. All or part of the metal layers 650-1, 650-2, 650-3, and 650-4 may be formed with different widths.

[0106] Next, a second configuration example of the crossing portion of the optical waveguide 232 or the like and the electrode 250a or the like used in the optical modulation element 104 of the optical modulator 100 in the present embodiment will be described.

[0107] Figure 7 , Figure 8 and Figure 9 are diagrams showing a second configuration example of the crossing portion. Specifically, they show Figure 2Partial detailed view of the structure of section B where the input waveguide 232 shown intersects with the signal electrode 252b. Here, Figure 7 is Figure 2 a top view of section B shown, Figure 8 is Figure 7 a sectional view taken along the VIII-VIII plane of section B shown. Moreover, Figure 9 the upper diagram of Figure 7 is Figure 9 a sectional view taken along the IX-IX plane of section B shown, Figure 7 and Figure 8 and Figure 9 the upper diagram of Figure 9 and Figure 2 the lower diagram of Figure 3 and Figure 4 and Figure 5 correspond to the upper diagrams of Figure 5 the A section shown respectively. Moreover, Figure 9 the middle diagram of Figure 9 is a diagram showing the change in the stress applied to the input waveguide 232 along the waveguide direction of the input waveguide 232 (the Y direction in this embodiment). In Figures 3 - 5 the middle diagram of

[0108] for comparison, the level of the peak stress acting on the input waveguide 232 in the structure of the A section shown in Figure 7 and Figure 8 and Figure 9 is recorded as the value p4. Figure 3 and Figure 4 and Figure 5 For the components that are the same as those shown in Figure 3 and Figure 4 and Figure 5 the same symbols as those in Figure 3 and Figure 4 and Figure 5 are used to denote them, and the description of the above

[0109] is cited. Figure 7 and Figure 8 and Figure 9 The structure of section B shown is another example of the structure of the part where the optical waveguide 232 etc. in the optical modulation element 104 intersects with the electrode 250a etc., and it can be used in section A instead of Figure 3 and Figure 4 and Figure 5 the structure shown, and it can also be equally applicable to any other part where the optical waveguide 232 etc. intersects with the electrode 250a etc. other than section A and section B.

[0110] In Figure 7 this structure, an input waveguide 232 extending in the left - right direction (Y - direction) as shown in the figure intersects with a signal electrode 252b extending in the up - down direction (Z - direction) as shown in the figure to form an intersection 770.

[0111] At the intersection 770 in part B, similar to the intersection 370 in part A shown in Figure 3 and Figure 4 the signal electrode 252b is composed of multiple segments including a plurality of metal layers 850 - 1, 850 - 2, and a resin layer 852 made of a resin material is formed between the signal electrode 252b and the substrate 230. However, as shown in the upper diagram of Figure 9 the structure of part B is different from the structure of part A shown in the upper diagram of Figure 5 and the lengths of the metal layers 850 - 1, 850 - 2 and the resin layer 852 along the waveguide direction of the input waveguide 232 are different from each other.

[0112] Specifically, the length Ly2 of the resin layer 852 along the waveguide direction (or the extending direction, which is the Y - direction in this embodiment) of the input waveguide 232 is formed to be longer than the length Le1 of the adjacent metal layer 850 - 1 along the waveguide direction of the input waveguide 232. Moreover, the length Le1 of the metal layer 850 - 1 adjacent to the resin layer 852 along the waveguide direction of the input waveguide 232 is formed to be longer than the length Le2 of the other metal layer 850 - 2 adjacent to the metal layer 850 - 1 along the waveguide direction of the input waveguide 232. That is, Le2 < Le1 < Ly.

[0113] In the above - mentioned structure, since Le2 < Le1 < Ly, the stress transmitted from the metal layer 850 - 2, which is usually thicker than the lower metal layer 850 - 1 and is the main cause of stress generation, to the substrate 230 is dispersed by the lower metal layer 850 - 1 and the resin layer 852 with lengths longer than Le2 and reaches the substrate 230. Similarly, the stress from the metal layer 850 - 1 to the substrate 230 is dispersed by the resin layer 852 with a length longer than Le1 and reaches the substrate 230. Therefore, the peak value of the stress acting on the substrate 230 at the intersection 770 is reduced from the peak value p4 of the intersection 370 shown in Figure 5 to p3. Therefore, the change in the effective refractive index generated in the input waveguide 232 at the intersection 770 also becomes gentle, and the peak value of the effective refractive index is reduced from the peak value n4 at the intersection 370 shown in Figure 5 to n3.

[0114] In addition, in the above - mentioned structure, since Le2 < Le1 < Ly, the change in the stress applied to the substrate 230 at the intersection 770 along the waveguide direction of the input waveguide 232 is as shown inFigure 9 The middle section shown in the figure becomes stepped. Therefore, the change in the effective refractive index generated in the input waveguide 232 at the intersection 770 also becomes stepped as shown in the lower figure of Figure 9 The change in the effective refractive index in the extending direction of the input waveguide 232 is gentler than the case where only the peak value of the effective refractive index decreases.

[0115] Therefore, the change in the propagation mode of the waveguide light in the input waveguide 232 that may occur at the intersection 770 also becomes gentle, and the amount of leakage light that may be generated due to the change in the propagation mode of the waveguide light in the input waveguide 232 in the B part including the intersection 770 can be lower than that in the Figures 3 - 5 shown A part. As a result, in the configuration of the B part shown in Figures 7 - 9 compared with the configuration of the A part shown in Figures 3 - 5 the influence of deterioration or degradation of the optical characteristics of the light modulation element 104 due to the generation of leakage light can be further reduced.

[0116] It should be noted that in the above configuration of the B part, Le2 < Le1 < Ly, but it is not limited thereto. For example, as long as the length Ly2 of the resin layer 852 is formed longer than the length Le1 of the adjacent metal layer 850-1, the length Le1 of the metal layer 850-1 adjacent to the resin layer 852 can be formed to be equal to the length Le2 of the other adjacent metal layer 850-2 (that is, Le2 = Le1 < Ly2). In such a configuration, the resin layer 852 that is formed longer than the lengths of the metal layers 850-1 and 850-2 also disperses the stress from the metal layers 850-1 and 850-2 and transfers it to the substrate 230. Therefore, the effective refractive index of the input waveguide 232 at the intersection 770 can be reduced to a certain extent, thereby suppressing the generation of leakage light.

[0117] It should be noted that as described above, in order to effectively change the effective refractive index of the optical waveguide 232 according to the stepped position change of the stress applied to the substrate 230 or the optical waveguide 232, it is preferable to set the distance of the stepped change of the stress to be equal to or greater than the wavelength of the light propagating in the optical waveguide 232. Therefore, it is preferable that the lengths Le11 and / or Le12 along the waveguide direction of the optical waveguide 232 of the portion of the resin layer 852 where the adjacent metal layer 850-1 is not formed (refer to Figure 9It is longer than the wavelength λ of the light propagating in the optical waveguide 232 (i.e., Le11, Le12 ≥ λ). Further, preferably, the length L21 and / or L22 in the waveguide direction of the optical waveguide 232 of the portion where no other metal layer 850-2 adjacent to the metal layer 850-1 is formed in the metal layer 850-1 adjacent to the resin layer 852 is longer than the wavelength λ of the light propagating in the optical waveguide 232 (i.e., Le21, Le22 ≥ λ).

[0118] It should be noted that in the description of the configuration of part A, as described above, the electrode 250a etc. at the crossing part can be constituted by two or more metal layers. For example, in the configuration of part B above, the signal electrode 252b can have a third metal layer provided on the upper part of the metal layer 850-2. Further, the above-described effect can be obtained similarly even when the length of the third metal layer measured in the waveguide direction is longer than Le2.

[0119] In addition, in the configuration of part B above, in order to further reduce the stress transmitted from the signal electrode 252b to the substrate 230, a slit can be provided in the metal layer 850-1. Figure 10 FIG. shows an alternative configuration of part B showing the metal layer 850-1' formed by providing such a slit 1054, and corresponds to Figure 9 the upper diagram of. In Figure 10 , regarding the constituent elements the same as those in the upper diagram of Figure 9 , the same reference numerals as those in the upper diagram of Figure 9 are used.

[0120] In Figure 10 , the inside of the slit 1054 is, for example, a cavity. By providing the slit 1054 in the metal layer 850-1', the stress transmitted from the upper metal layer 850-2 is released at the slit 1054, and thus the stress transmitted from the metal layer 850-2 to the substrate 230 is further reduced than in the Figures 7 - 9 shown configuration. As a result, the change in the effective refractive index at the input waveguide 232 caused by this stress becomes smoother, the leakage light from part B is further reduced, and the deterioration of the optical characteristics of the optical modulation element 104 caused by this leakage light is further suppressed.

[0121] It should be noted that the length of the slit 1054 in the extending direction of the signal electrode 250b is preferably equal to or greater than the width of the input waveguide 232 from the viewpoint of stress release. Further, in the Figure 10 shown configuration, the slit 1054 formed in the metal layer 850-1' is provided midway in the thickness direction of the metal layer 850-1', but is not limited thereto. The slit 1054 can also be provided so as to penetrate the metal layer 850-1' until it reaches the surface of the resin layer 852.

[0122] In addition, the slit 1054 is formed in the metal layer 850-1' sandwiched by the two layers of the resin layer 852 and the metal layer 850-2 in the configuration shown, but is not limited thereto. For example, when the signal electrode 252b' is composed of three or more metal layers, a slit such as the slit 1054 can be provided in the metal layer sandwiched by any two layers (including any two layers of the three or more metal layers and the resin layer on the substrate 230). That is, the slit can be formed in at least one metal layer other than the uppermost metal layer among the metal layers constituting the multilayer structure of the signal electrode 252b'. Figure 10

[0123] In addition, in Figure 9 the configuration of part B shown in the upper diagram, as a configuration for making the change in the effective refractive index of the input waveguide 232 gentler, the thickness of the left and right end portions of the resin layer 852 can be made thinner as it separates from the crossing portion 770. Figure 11 FIG. is a diagram showing another alternative configuration of part B using the resin layer 852' formed such that the end portions along the waveguide direction of the input waveguide 232 become thinner as they separate from the crossing portion 770, and is equivalent to Figure 9 the upper diagram of Figure 11 . In Figure 9 , for the same components as those in the upper diagram of Figure 9 , the same reference numerals as those in the upper diagram of

[0124] In Figure 11 the configuration shown, since the thickness of the end portions of the resin layer 852' becomes thinner as it separates from the crossing portion 770, the stress applied to the substrate 230 via the above-mentioned end portions decreases as it separates from the crossing portion 770. Therefore, the change in the effective refractive index of the input waveguide 232 at the end portions is gentler than the change in the effective refractive index at the end portions of the resin layer 852 in the configuration shown in Figure 9 .

[0125] Therefore, in Figure 11 the configuration shown, compared with the configuration shown in the upper diagram of Figure 9 , the change in the propagation mode of the input waveguide 232 at part B becomes gentler, and the generation of light leakage at part B is further suppressed. As a result, in Figure 11 the configuration shown, compared with the configuration shown in the upper diagram of Figure 9 , the deterioration of the optical characteristics of the optical modulation element 104 due to light leakage that may occur at part B can be further suppressed. It should be noted that during the formation process of the resin layer 852', by making the heat treatment time longer than usual and / or making the heating temperature higher than usual, the viscosity of the resin before curing that constitutes the resin layer 852' is increased, whereby it is possible to easily form​Figure 11 a shape like the resin layer 852’ shown

[0126] In addition, by including a crosslinking agent in the above resin and causing a crosslinking reaction to occur, it is also possible to easily form Figure 11 a shape like the resin layer 852’ shown. Note that in Figure 11 , the thickness of the resin layer 852’ becomes thinner starting from the crossing portion 770, but it is not limited thereto. For example, the thickness of the resin layer 852’ may be substantially the same from the crossing portion 770 to a certain range and then gradually become thinner.

[0127] Next, a third configuration example of the crossing portion between the optical waveguide 232 and the electrode 250a, etc., used in the optical modulation element 104 of the optical modulator 100 in the present embodiment will be described.

[0128] Figure 12 and Figure 13 are diagrams showing a third configuration example of the crossing portion. Specifically, it is a partial detailed diagram showing the configuration of portion C where the optical waveguide 244b-1, which is one of the parallel waveguides constituting the Mach-Zehnder type optical waveguide 244b, crosses the signal electrode 252b. Here, Figure 2 the upper diagram of Figure 12 is a top view of portion C, Figure 12 the middle diagram of Figure 12 is a diagram showing the change in the stress applied to the optical waveguide 244b-1 along the waveguide direction (Y direction in the present embodiment) of the optical waveguide 244b-1, Figure 13 and the lower diagram of Figure 12 is a diagram showing the change in the effective refractive index inside the optical waveguide 244b-1 along the waveguide direction of the optical waveguide 244b-1. Moreover,

[0129] Figure 12 the upper diagram of Figure 3 and Figure 7 correspond to Figure 12 and respectively show portions A and B Figure 9 The middle diagram of Figure 12 corresponds to the middle diagram of Figure 9 showing portion B, Figure 13 and the lower diagram of Figure 5 and Figure 9 correspond to the lower diagram of

[0130] Note that in Figure 12 and Figure 13 , regarding the components and values that are the same as the components and values shown in Figures 3 - 11 , the same reference numerals asFigures 3 - 11 The symbols with the same symbols in Figures 3 - 11 shall refer to the description mentioned above regarding

[0131] It should be noted that Figure 12 and Figure 13 the structure of part C shown in Figures 3 - 5 is an example of the structure of the part where the optical waveguide 232 etc. cross the electrode 250a etc., and it can be used in part A instead of Figures 7 - 9 the structure shown in Figure 12 and can be used in part B instead of Figures 7 - 9 the structure shown in Figure 12 and Figure 13 the structure of part C shown in Figure 12 and Figure 13 can also be similarly applied to any other cross - section part where the optical waveguide 232 etc. cross the electrode 250a etc. other than part A and part B.

[0132] In the upper diagram of Figure 12 , the optical waveguide 244b - 1 extending in the left - right direction (Y - direction) shown in the diagram crosses the signal electrode 252b extending in the up - down direction (Z - direction) shown in the diagram to form a cross - section part 1270. In Figure 13 , the structure of the signal electrode 252b at the cross - section part 1270 of part C is the same as that of the signal electrode 252b at the cross - section part 770 of part B shown in the upper diagram of Figure 9 , and is a multi - layer structure including multiple metal layers 1350 - 1, 1350 - 2. However, as shown in the upper diagram of Figure 12 , at the cross - section part 1270, a resin layer 1352 with a shape different from the resin layer 852 shown in the upper diagram of Figure 9 is formed between the lower metal layer 1350 - 1 and the substrate 230. It should be noted that the metal layers 1350 - 1 and 1350 - 2 are electrically connected to the metal layers 850 - 1 and 850 - 2 shown in the upper diagram of Figure 9 respectively as part of the signal electrode 252b.

[0133] The resin layer 1352 has the same uniform thickness as the resin layer 852 shown in the upper diagram of Figure 9 , but its top view is different from that of the resin layer 852 composed of rectangles (refer to the upper diagrams of Figure 7 and Figure 12 ). That is, as shown in the upper diagram of Figure 12 , the resin layer 1352 is formed such that at both ends in the waveguide direction of the optical waveguide 244b - 1 (i.e., the left - right direction shown in the diagram), the width in the direction orthogonal to the waveguide direction is less than or equal to the width of the optical waveguide 244b - 1 and becomes narrower as it separates from the cross - section part 1270. Specifically, for example, the resin layer 1352 has a polygon with vertices at both ends in the waveguide direction ( Figure 12 the left - right ends shown in the upper diagram of Figure 12 ) as its top - view shape.

[0134] In Figure 12 In the middle and lower diagrams, regions where the width of the resin layer 1352 is formed narrower than the width of the optical waveguide 244b-1 as it separates from the intersection portion 1270 are shown as regions from position y90 to y92 and from position y94 to y96 in the Y-axis direction.

[0135] In these regions, the range in which the resin layer 1352 covers the optical waveguide 244b-1 in the width direction of the optical waveguide 244b-1 varies along the waveguide direction (Y-axis direction). Therefore, the stress applied from the signal electrode 252b to the portion of the optical waveguide 244b-1 of the substrate 230 via the resin layer 1352 also varies along the waveguide direction (Y-axis direction).

[0136] Specifically, as shown in the middle diagram of Figure 12 , the stress applied to the portion of the optical waveguide 244b-1 gradually increases from y96 toward y94 and gradually decreases from y92 toward y90 along the propagation direction of the waveguide light (the direction from right to left in the figure). Therefore, due to the photoelastic effect, the effective refractive index of the optical waveguide 244b-1 also gradually increases from y96 toward y94 and gradually decreases from y92 toward y90 as shown in the lower diagram of Figure 12 . As a result, the change in the effective refractive index of the optical waveguide 244b-1 in the range from position y96 to position y90 is smoother than the change in the effective refractive index of the input waveguide 232 in the A portion shown in Figures 3 - 5 and the B portion shown in Figures 6 - 8 , and the change in the propagation mode of the waveguide light is also smoother.

[0137] In addition, the range in which the resin layer 1352 covers the optical waveguide 244b-1 is wider than the range in which the resin layer 852 covers the input waveguide 232 at the B portion shown in Figures 7 - 9 . Therefore, the peak p2 of the stress applied to the optical waveguide 244b-1 is smaller than the peak p3 of the stress of the input waveguide 232 at the B portion (refer to the middle diagram of Figure 12 ), and the peak n2 of the effective refractive index of the optical waveguide 244b-1 is also smaller than the peak n3 of the effective refractive index of the input waveguide 232 at the B portion (refer to the lower diagram of Figure 12 ).

[0138] Therefore, the change in the propagation mode at the C portion of the optical waveguide 244b-1 is smoother than the change in the propagation mode at the B portion of the input waveguide 232. As a result, the degree of generation of leakage light at the C portion due to the change in the propagation mode is more suppressed than in the A and B portions, and the influence on the optical characteristics of the light modulation element 104 due to the generation of this leakage light can be further reduced.

[0139] Note that in Figure 12In the upper diagram, as an example, a resin layer 1352 is shown whose top view shape is a polygon having vertices at both ends (the left and right ends in the drawing) in the above-mentioned waveguide direction. However, the shape of the resin layer 1352 is not limited to this. The resin layer 1352 is formed such that as long as the width in the direction orthogonal to the waveguide direction at both ends in the waveguide direction of the optical waveguide 244b-1 is equal to or less than the width of the optical waveguide 244b-1 and becomes narrower as it separates from the crossing portion 1270, it can be formed of other shapes. Such a shape can be, for example, a shape in which the left and right ends shown in the drawing are formed of curves. It should be noted that not only the ends of the resin layer 1352 but also other corners of the resin layer 1352 can be formed of curves.

[0140] Figure 14 This is a diagram showing an alternative configuration of part C using such a resin layer 1352' whose top view shape has ends formed of curves, and is equivalent to Figure 12 the upper diagram of. In Figure 14 , regarding the same constituent elements as Figure 12 and Figure 13 , the same symbols as those in Figure 12 and Figure 13 are used. In the configuration shown in Figure 14 , also at both ends shown on the left and right in the resin layer 1352', the width in the direction orthogonal to the waveguide direction of the optical waveguide 244b-1 is formed to be narrower than the width of the optical waveguide 244b-1 as it separates from the crossing portion 1270. Therefore, the change in the propagation mode of the optical waveguide 244b-1 can be made gentle, and the generation of light leakage can be effectively suppressed.

[0141] [Second Embodiment]

[0142] Next, a second embodiment of the present invention will be described. This embodiment is an optical modulation module 1500 using the optical modulation element 104 included in the optical modulator 100 of the first embodiment. Figure 15 This is a diagram showing the configuration of the optical modulation module 1500 of this embodiment. In Figure 15 , regarding the same constituent elements as those of the optical modulator 100 of the first embodiment shown in Figure 1 , the same symbols as those shown in Figure 1 are used to represent them, and the above description regarding Figure 1 is incorporated by reference.

[0143] The optical modulation module 1500 has the same as Figure 1The optical modulator 1500 has the same configuration as the optical modulator 100 shown above, but is different from the optical modulator 100 in that it includes a circuit board 1506 instead of the relay board 106. The circuit board 1506 includes a drive circuit 1508. Based on, for example, a modulation signal supplied from the outside via signal pins 110a, 110b, 110c, and 110d, the drive circuit 1508 generates a high-frequency electrical signal for driving the optical modulation element 104, and outputs the generated high-frequency electrical signal to the optical modulation element 104.

[0144] Similar to the optical modulator 100 of the first embodiment above, the optical modulation module 1500 having the above configuration includes, at the crossing portions of the optical waveguide 232 and the like and the electrodes 250a and the like, an optical modulation element 104 having the Figures 3 - 14 configuration shown above. Therefore, in the optical modulation module 1500, similar to the optical modulator 100, deterioration or degradation of the optical characteristics of the optical modulation element 104 is not caused, and the optical absorption loss of the waveguide light that may occur at the crossing portions of the optical waveguide 232 and the like and the electrodes 250a and the like on the substrate 230 can be effectively reduced, achieving good modulation characteristics and enabling good optical transmission.

[0145] [Third Embodiment]

[0146] Next, a third embodiment of the present invention will be described. This embodiment is an optical transmission device 1600 equipped with the optical modulator 100 of the first embodiment. Figure 16 FIG. shows the configuration of the optical transmission device 1600 of this embodiment. The optical transmission device 1600 includes an optical modulator 100, a light source 1604 that makes light enter the optical modulator 100, a modulator drive unit 1606, and a modulation signal generation unit 1608. It should be noted that the above optical modulation module 1500 may be used instead of the optical modulator 100 and the modulator drive unit 1606.

[0147] The modulation signal generation unit 1608 is an electronic circuit that generates an electrical signal for causing the optical modulator 100 to perform a modulation operation. Based on transmission data given from the outside, it generates a modulation signal, which is a high-frequency signal for causing the optical modulator 100 to perform an optical modulation operation according to the modulation data, and outputs it to the modulator drive unit 1606.

[0148] The modulator drive unit 1606 amplifies the modulation signal input from the modulation signal generation unit 1608, and outputs four high-frequency electrical signals for driving the four signal electrodes 250a, 252a, 250b, and 252b of the optical modulation element 104 included in the optical modulator 100.

[0149] These four high-frequency electrical signals are input to signal pins 110a, 110b, 110c, and 110d of the optical modulator 100 to drive the optical modulation element 104. As a result, the light output from the light source 1604 is modulated by the optical modulator 100, for example, DP-QPSK, and output from the optical transmitter 1600 as modulated light.

[0150] In particular, the optical transmitter 1600 uses the optical modulator 100 including the optical modulation element 104 that effectively reduces light absorption loss at intersections between the optical waveguide 232 and the electrode 250a, thereby achieving good modulation characteristics and performing good optical transmission.

[0151] It should be noted that the present invention is not limited to the configurations of the above-described embodiments and their alternative configurations, and can be implemented in various forms without departing from the spirit and scope of the present invention.

[0152] For example, in the first embodiment described above, in the optical modulator 104, the portion A, which is the intersection of the input waveguide 232 and the signal electrode 250b, the portion B, which is the intersection of the input waveguide 232 and the signal electrode 252b, and the portion C, which is the intersection of the optical waveguide 244b-1 and the signal electrode 252b, respectively have Figures 3 - 6 、 Figures 7 - 11 ,and Figures 12 - 14 The configuration shown is, but not limited to, this.

[0153] Regarding a part or all of the intersection of the optical waveguide 232 and the electrode 250a, the optical modulation element 104 as an optical waveguide element may have Figures 3 - 6 、 Figures 7 - 11 ,and Figures 12 - 14 Therefore, for example, the A portion representing the intersection of the signal electrode 250b and the input waveguide 232 may be replaced with Figures 3 - 6 Any of the configurations shown is applicable to the intersection of the bias electrode 264 b and the input waveguide 232 .

[0154] In addition, in order to make it easy for those skilled in the art to understand, the alternative structure of the A part is shown. Figure 6 The multi-layer structure of the signal electrode 250b' can be Figures 7 - 14 The composition combination of the B part or the C part shown. Figure 10 The slit 1054 and Figure 11 The thickness of the resin layer 852' can be varied with Figures 3 - 6 The composition of the A part shown or Figures 12 - 14The component combination of part C shown. By performing the above combination, it is possible to further alleviate the change in the effective refractive index of the optical waveguide 232 or the like that crosses the electrode 250a or the like, avoid the deterioration of the optical characteristics of the optical modulation element 104 caused by light leakage from the crossing portion, and reduce the light absorption loss at the optical waveguide 232 or the like caused by the crossing electrode 250a or the like.

[0155] In addition, in the above first embodiment, the resin layers 452, 852, etc., and 1352, etc. at the portions A, B, and C of the crossing portion between the optical waveguide 232 or the like and the electrode 250a or the like are separately formed for each crossing portion, but it is not limited thereto. These resin layers may be formed across (or connected to) at least two crossing portions (for example, at least two adjacent crossing portions). For example, at the portions A and B which are two adjacent crossing portions, the resin layer 452 of the portion A and the resin layer 852 of the portion B may be continuously formed as one resin layer. In this case, the portion of the continuously formed resin layer other than the portions corresponding to the resin layer 452 and the resin layer 852 may be formed with a different thickness (for example, thinner) from the resin layer 452 and the resin layer 852. Or, when the resin layer 452 and the resin layer 852 have the same thickness, the continuously formed resin layer may also be formed with the same thickness as that thickness.

[0156] Thereby, it is possible to make the effective refractive index changes caused by stress generation between waveguides or between waveguides of the same interference system equivalent, and it is possible to increase the contact area between the resin layer 452 or the like and the substrate 230, and improve the adhesion of the resin layer 452 or the like to the substrate 230.

[0157] In addition, in the above embodiment, as an example of the optical waveguide element, the optical modulation element 104 formed of the substrate 230 which is LN (LiNbO3) is shown, but the optical waveguide element may also be formed using a substrate such as InP or Si.

[0158] As described above, the optical modulator 100 of the above first embodiment includes the optical modulation element 104. The optical modulation element 104 as the optical waveguide element includes the substrate 230, the optical waveguide 232 or the like formed on the substrate 230, and the electrode 250a or the like that controls the light wave propagating in the optical waveguide 232 or the like. Moreover, the optical waveguide 232 or the like and the electrode 250a or the like have crossing portions 370 or the like where they cross each other. At the crossing portions 370 or the like, the electrode 250a or the like forms a multilayer structure including a plurality of metal layers made of a metal material, and a resin layer 452 or the like made of a resin material is formed between the electrode 250a or the like and the substrate 230.

[0159] According to this configuration, it will not cause deterioration or degradation of the optical characteristics of the optical modulation element 104, and can effectively reduce the optical absorption loss of the waveguide light caused by the electrode metal that may occur at the intersection 370 between the optical waveguide 232 and the like on the substrate 230 and the electrode 250a and the like.

[0160] In addition, in the optical modulation element 104, the multilayer structure of the electrode may be configured such that at least one layer of the metal layers other than the metal layer closest to the substrate, that is, the lowermost layer, is thicker than the lowermost layer. According to this configuration, the internal stress of the metal layer formed thicker than the lowermost layer is effectively dispersed at the interface between the lowermost layer formed thinner than it and the upper metal layer, and the stress applied to the optical waveguide 232 and the like on the substrate 230 and the refractive index change caused by this stress can be effectively alleviated.

[0161] In addition, in the optical modulation element 104, a resin layer 852 can be used. The length Ly2 of the resin layer 852 in the waveguide direction of the input waveguide 232 is formed longer than the length Le1 of the metal layer 850-1 adjacent to the resin layer 852 in the above waveguide direction. Here, the lengths Le11 and / or Le12 of the portions of the resin layer 852 where the adjacent metal layer 850-1 is not formed in the waveguide direction of the input waveguide 232 are preferably configured to be longer than the wavelength λ of the light propagating in this input waveguide.

[0162] In addition, in the optical modulation element 104, the length Le1 of the metal layer 850-1 adjacent to the resin layer 852 in the waveguide direction of the input waveguide 232 can be formed to be equal to the length Le2 of the other metal layer adjacent to the metal layer 850-1, that is, the metal layer 850-2, in the above waveguide direction or longer than Le2. Here, the lengths Le21 and / or Le22 of the portions of the metal layer 850-1 adjacent to the resin layer 852 where the other metal layer, that is, the metal layer 850-2, is not formed in the waveguide direction of the input waveguide 232 are configured to be longer than the wavelength of the light propagating in this input waveguide 232.

[0163] In addition, in the optical modulation element 104, a resin layer 1352 or a resin layer 1352' can be used. The resin layers 1352 and 1352' are formed such that at both end portions in the waveguide direction of the optical waveguide 244b-1, the width in the direction orthogonal to the waveguide direction is equal to or less than the width of the optical waveguide 244b-1 and becomes narrower as it separates from the intersection 1270.

[0164] In addition, in the optical modulation element 104, a resin layer 852' can be used. The resin layer 852' is formed such that its thickness becomes thinner as it separates from the intersection 770 at both end portions in the waveguide direction of the input waveguide 232.

[0165] In addition, in the optical modulation element 104, at the crossing portion such as the slit 1054 at the crossing portion 770, in the metal layer of the multilayer structure constituting the electrode 250a or the like, at least one metal layer other than the metal layer formed on the uppermost layer can form a slit.

[0166] According to the above configuration, it is possible to make the change in the effective refractive index of the input waveguide 232 at the portion B including the crossing portion 770 smoother, thereby better maintaining the optical characteristics of the optical modulation element 104.

[0167] In addition, in the optical modulation element 104, the resin layer 452 or the like can be formed across at least two of the crossing portions in the crossing portion between the electrode 250a or the like and the optical waveguide 232 or the like. According to this configuration, it is possible to make the effective refractive index changes due to stress generation equivalent between adjacent waveguides or between waveguides in the same interference system, and moreover, it is possible to increase the contact area between the resin layer 452 or the like and the substrate 230, and improve the adhesion of the resin layer 452 or the like to the substrate 230.

[0168] In addition, the optical modulation module 1500 of the second embodiment includes an optical modulation element 104 that modulates light as an optical waveguide element, and a drive circuit 1508 that drives the optical modulation element 104.

[0169] In addition, the optical transmission device 1600 of the third embodiment includes the optical modulator 100 or the optical modulation module 1500, and a modulation signal generation unit 1608, which is an electronic circuit that generates an electrical signal for causing the optical modulation element 104 to perform a modulation operation.

[0170] According to the above configuration, it is possible to realize an optical modulation module 1500 or an optical transmission device 1600 having good characteristics.

Claims

1. An optical waveguide element, comprising: a substrate; an optical waveguide formed on the substrate; and an electrode for controlling light waves propagating in the optical waveguide, wherein the optical waveguide and the electrode have an intersection where they cross each other, at the intersection, the electrode forms a multilayer structure including a plurality of metal layers made of a metal material, and a resin layer made of a resin material is formed between the electrode and the substrate, the metal layer adjacent to the resin layer is formed to have a length in the waveguide direction of the optical waveguide longer than the lengths in the waveguide direction of the optical waveguide of the other metal layers adjacent to this metal layer, the metal layer adjacent to the resin layer is configured such that the length in the waveguide direction of the optical waveguide of the portion where the other metal layers adjacent to this metal layer are not formed is longer than the wavelength of the light propagating in the optical waveguide.

2. The optical waveguide element according to claim 1, wherein in the multilayer structure of the electrode, at least one layer of the metal layers other than the metal layer closest to the substrate, i.e., the lowermost layer, is thicker than the lowermost layer.

3. The optical waveguide element according to claim 1 or 2, wherein the resin layer is formed to have a length in the waveguide direction of the optical waveguide longer than the lengths in the waveguide direction of the optical waveguide of the adjacent metal layers.

4. The optical waveguide element according to claim 3, wherein the resin layer is configured such that the length in the waveguide direction of the optical waveguide of the portion where the metal layer adjacent to this resin layer is not formed is longer than the wavelength of the light propagating in the optical waveguide.

5. The optical waveguide element according to claim 1 or 2, wherein the resin layer is formed such that, at both ends in the waveguide direction of the optical waveguide, the width in the direction orthogonal to the waveguide direction is equal to or less than the width of the optical waveguide and becomes narrower as it separates from the intersection.

6. The optical waveguide element according to claim 1 or 2, wherein the resin layer is formed such that its thickness becomes thinner as it separates from the intersection at both ends in the waveguide direction of the optical waveguide.

7. The optical waveguide element according to claim 1 or 2, wherein at least one of the metal layers in the metal layers constituting the multilayer structure, other than the metal layer formed at the uppermost part, is formed with a slit.

8. The optical waveguide element according to claim 1 or 2, wherein the resin layer is formed to straddle at least two of the intersections.

9. An optical modulator, comprising: the optical waveguide element according to any one of claims 1 to 8 as an optical modulation element for modulating light; a housing for accommodating the optical waveguide element; an optical fiber for inputting light to the optical waveguide element; and an optical fiber for guiding the light output from the optical waveguide element to the outside of the housing.

10. An optical modulation module, comprising: the optical waveguide element according to any one of claims 1 to 8 as an optical modulation element for modulating light; and a drive circuit for driving the optical waveguide element.

11. An optical transmission device, comprising: The optical modulator according to claim 9 or the optical modulation module according to claim 10; and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform a modulation operation.

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