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

Abstract

The present invention is an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmission device, and the object of the present invention is to effectively reduce the optical absorption loss of the waveguide light that may be generated at the intersection of the optical waveguide and the electrode in the optical waveguide element without causing degradation of the optical characteristics and reduction of the long-term reliability. The optical waveguide element of the present invention includes: an optical waveguide formed on a substrate; and an electrode that controls the light wave propagating in the optical waveguide, and the electrode has an intersection that intersects the optical waveguide, and the substrate includes a portion of the intersection, and a resin layer is partially provided between the optical waveguide and the electrode, and the corner of the resin layer on the electrode side in a cross section along the extension direction of the electrode is composed of a curve.

Description

Technical Field

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

[0002] In high-speed / large-capacity optical fiber communication systems, optical modulators are often used that incorporate optical modulation elements, which are optical waveguide elements composed of optical waveguides formed on a substrate. Among them, optical modulation elements that use LiNbO3 (hereinafter also referred to as LN) with a photoelectric effect as a substrate are widely used in high-speed / large-capacity optical fiber communication systems because they have low light loss and can achieve broadband optical modulation characteristics. In such optical modulation elements using an LN substrate, for example, a Mach-Zehnder type optical waveguide and a signal electrode are provided, and the signal electrode is used to apply a high-frequency electrical signal as a modulation signal to the optical waveguide.

[0003] In particular, regarding the modulation method of the optical fiber communication system, influenced by the trend of increasing transmission capacity in recent years, multi-value modulation such as Quadrature Phase Shift Keying (QPSK) or Dual Polarization-Quadrature Phase Shift Keying (DP-QPSK) or transmission formats that introduce polarization multiplexing into multi-value modulation have become mainstream. In addition to being used in backbone optical transmission networks, they are also gradually being introduced into metropolitan area networks (metro networks).

[0004] An optical modulator that performs QPSK modulation (QPSK optical modulator) or an optical modulator that performs DP-QPSK modulation (DP-QPSK optical modulator) includes a plurality of Mach-Zehnder optical waveguides, each of which has at least one signal electrode. In addition, an optical modulator using such a Mach-Zehnder optical waveguide is generally provided with a bias electrode for compensating for a change in a bias point caused by a so-called direct current (DC) drift.

[0005] These signal electrodes or bias electrodes (hereinafter also collectively referred to as electrodes) are formed to extend to the vicinity of the outer periphery of the LN substrate in order to connect to an electrical circuit outside the substrate. Therefore, on the substrate, a plurality of optical waveguides and a plurality of electrodes are complexly intersected, forming a plurality of intersections where the electrodes cross the optical waveguides.

[0006] If the optical waveguide and the electrode are directly in contact at the intersection, the light propagating in the optical waveguide is absorbed by the metal constituting the electrode at the intersection, thereby generating optical loss (optical absorption loss). The optical loss may, for example, cause an optical loss difference between two parallel waveguides constituting the Mach-Zehnder optical waveguide, thereby deteriorating the extinction ratio of the modulated light. The higher the modulation speed required by the optical modulator, the stricter the requirements for the extinction ratio. Therefore, it is expected that the degradation of the extinction ratio will become more and more obvious as the modulation speed increases with the increase in transmission capacity.

[0007] Furthermore, the intersections as described above are formed not only in optical modulators using Mach-Zehnder optical waveguides, but also in optical waveguide elements such as directional couplers, optical modulators using optical waveguides forming Y branches, and / or optical switches. In addition, as optical waveguide patterns and electrode patterns become more complex with further miniaturization, multi-channelization, and / or high integration of optical waveguide elements, the number of intersections on the substrate increases, which may become a cause of loss that cannot be ignored and limit the performance of the optical waveguide element.

[0008] As a technology for reducing the light absorption loss caused by the electrode metal formed on the optical waveguide, it is conventionally known to provide a buffer layer containing SiO2 on the surface of the substrate on which the optical waveguide is formed and to form the electrode metal on the upper part of the buffer layer (for example, Patent Document 1).

[0009] However, SiO2 is more rigid than the LN substrate, so when a SiO2 layer is formed on the LN substrate, stress is applied to the substrate not only from the SiO2 layer itself but also from the electrode metal formed on the upper portion thereof via the SiO2 layer. In addition, such stress may adversely affect the optical characteristics or electrical characteristics of the optical waveguide element through the photoelastic effect of the LN substrate.

[0010] In particular, in an optical waveguide element in which the LN substrate is formed to be thin (for example, a thickness of less than 20 μm) in order to further enhance the interaction between the signal electric field in the substrate and the waveguide light (i.e., to improve the electric field efficiency), the stress imparted to the substrate by the SiO2 layer and the electrode metal thereon may have a significant effect on the optical and / or electrical properties, and may also become a factor that induces damage such as cracking or disconnection of the SiO2 layer itself or the electrode thereon during manufacturing and / or over time due to local strain caused by the difference in linear expansion coefficient between the SiO2 layer and the LN substrate.

[0011] [Prior art literature]

[0012] [Patent Document]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 2009-181108 Summary of the invention

[0014] [Problems to be solved by the invention]

[0015] Against this background, it is required to effectively reduce light absorption loss of waveguide light caused by electrode metal that may occur at the intersection of an optical waveguide and an electrode in an optical waveguide element without causing degradation of the optical characteristics of the optical waveguide element and reduction of long-term reliability.

[0016] [Technical means to solve the problem]

[0017] One embodiment of the present invention is an optical waveguide element, comprising: an optical waveguide formed on a substrate; and an electrode that controls light waves propagating in the optical waveguide and has an intersection portion that intersects the optical waveguide, and in the optical waveguide element, a resin layer is locally provided between the optical waveguide and the electrode in a portion of the substrate including the intersection portion, and a corner of the resin layer on the electrode side in a cross section along an extension direction of the electrode is formed by a curved line.

[0018] According to another embodiment of the present invention, a distance of the resin layer from a starting point to an end of a curve constituting the corner in the cross section and measured along an extension direction of the electrode is greater than a height of the resin layer measured from a surface of the substrate.

[0019] According to another embodiment of the present invention, the resin layer is provided along the extending direction of the electrode at a distance greater than or equal to three times the width of the optical waveguide in the intersection.

[0020] According to another embodiment of the present invention, at the intersection, between the optical waveguide and the electrode, a plurality of the resin layers are stacked in a step-like manner along an extending direction of the electrode.

[0021] According to another embodiment of the present invention, an insulating layer including SiO 2 is formed between the optical waveguide and the resin layer at the intersection.

[0022] According to another embodiment of the present invention, the resin constituting the resin layer is a resin formed using a photoresist including a cross-linking agent.

[0023] According to another embodiment of the present invention, the resin layer is formed across the adjacent intersections.

[0024] According to another embodiment of the present invention, the electrode is formed thicker than 10 μm at least in the intersection.

[0025] According to another embodiment of the present invention, the substrate has a thickness of less than 20 μm.

[0026] Another embodiment of the present invention is an optical modulator, comprising: any one of the optical waveguide elements is an optical modulator that modulates light; a frame that accommodates the optical waveguide element; an optical fiber that inputs light to the optical waveguide element; and an optical fiber that guides the light output by the optical waveguide element to the outside of the frame.

[0027] Another embodiment of the present invention is an optical modulation module, comprising: any one of the optical waveguide elements is an optical modulation element for modulating light; and a driving circuit for driving the optical waveguide element.

[0028] Still another embodiment of the present invention is an optical transmission device, comprising: the optical modulator or the optical modulation module; and an electronic circuit for generating an electrical signal for causing the optical waveguide element to perform a modulation operation.

[0029] [Effects of the Invention]

[0030] According to the present invention, in an optical waveguide element, light absorption loss of waveguide light caused by electrode metal that may occur at the intersection of an optical waveguide and an electrode on a substrate can be effectively reduced without causing degradation of the optical characteristics of the optical waveguide element and reduction of long-term reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a diagram showing the structure of the optical modulator according to the first embodiment of the present invention.

[0032] Figure 2 To express Figure 1 A diagram showing the structure of a light modulation element used in the light modulator shown.

[0033] Figure 3 for Figure 2 A partial detailed view of portion A of the light modulation element shown.

[0034] Figure 4 for Figure 3 The plan view of Section B is shown.

[0035] Figure 5 for Figure 4 The VV cross-sectional arrow view of part B is shown.

[0036] Figure 6 for Figure 3 The VI-VI cross-sectional arrow view of section C is shown.

[0037] Figure 7 for Figure 3 The VII-VII cross-sectional arrow view of section D is shown.

[0038] Figure 8 for Figure 3The VIII-VIII cross-sectional arrow view of section E is shown.

[0039] Fig. 9 for Figure 3 The IX-IX cross-sectional arrow view of section F is shown.

[0040] Fig.10 It is a diagram showing the structure of an optical modulation module according to a second embodiment of the present invention.

[0041] Fig.11 It is a diagram showing the structure of an optical transmission device according to a third embodiment of the present invention.

[0042] Fig.12 FIG. 1 is a cross-sectional view of an intersection portion along an extending direction of the electrode, showing an example of a structure of an intersection portion between an optical waveguide and an electrode in a conventional optical waveguide element.

[0043] Fig.13 FIG. 1 is a cross-sectional view of another example of the structure of the intersection of an optical waveguide and an electrode in a conventional optical waveguide element, and is a view of the intersection along the extending direction of the electrode.

[0044] [Explanation of Symbols]

[0045] 100: Optical modulator

[0046] 102: Frame

[0047] 104: Light modulation element

[0048] 106: Relay substrate

[0049] 108: Feedthrough Department

[0050] 110a, 110b, 110c, 110d: signal pins

[0051] 112a, 112b: Terminal

[0052] 114: Input fiber

[0053] 116: Optical unit

[0054] 118, 130, 134: Lens

[0055] 120: Output fiber

[0056] 122, 124: Bracket

[0057] 230, 2130: Substrate

[0058] 232: Input waveguide

[0059] 234: Branched waveguide

[0060] 240a, 240b: Nested Mach-Zehnder waveguide

[0061] 244a, 244b, 246a, 246b: Mach-Zehnder type optical waveguide

[0062] 244a-1, 244b-1, 244b-2: Parallel waveguide

[0063] 248a, 248b: Output waveguide

[0064] 250a, 250b, 252a, 252b, 252b: signal electrodes

[0065] 254a, 254b, 254b-1, 256a, 256b, 258a, 258b, 260a, 260b: pad

[0066] 262a, 262b, 264a, 264b, 264b-1: Bias electrodes

[0067] 280a, 280b, 280c, 280d: Edge

[0068] 452, 652, 752-1, 752-2, 752-3, 852, 952: Resin layer

[0069] 452-1, 452-2, 652-1, 652-1, 852-1, 852-2, 952-1, 952-2: Curve

[0070] 470, 670, 770, 870, 970, 2140, 2140, 2240: intersection

[0071] 590, 2142: Adhesive layer

[0072] 592, 2144: Support substrate

[0073] 990, 2138: SiO2 layer

[0074] 1000: Optical modulation module

[0075] 1006: Circuit board

[0076] 1008: Driving circuit

[0077] 1100: Optical transmitter

[0078] 1104: Light Source

[0079] 1106: Modulator driver

[0080] 1108: Modulation signal generation unit

[0081] 2134: Optical waveguide

[0082] 2136, 2236: Electrode

[0083] 2150, 2152: Disconnection

[0084] 2254, 2256: Rupture DETAILED DESCRIPTION

[0085] As a countermeasure to reduce the stress applied to the substrate from the SiO2 layer in the structure of the prior art, the following structure is considered, namely, instead of providing the SiO2 layer on the entire surface of the substrate, the SiO2 layer is formed only on the portion of the substrate where the optical waveguide and the electrode intersect, and an electrode is formed on the upper portion of the SiO2 layer.

[0086] However, if Fig.12 As shown, in a case where a SiO2 layer 2138 is locally formed on the substrate 2130 in the intersection 2140, due to a sudden shape change of the step difference portion of the SiO2 layer 2138 or local strain caused by the difference in linear expansion coefficient between the SiO2 layer 2138 and the substrate 2130, broken lines 2150 and 2152 may occur near the corners of the SiO2 layer 2138 in the electrode 2136.

[0087] also, Fig.12 In the figure, the optical waveguide 2134 extends in the Y direction of the coordinate axis shown in the upper right corner of the figure. In addition, the electrode (or signal line) 2136 composed of a metal layer extends in the Z direction and intersects the optical waveguide 2134 to form an intersection 2140.

[0088] Furthermore, in the case where the electrode is formed thicker, as Fig.13 As shown, in the intersection 2240, cracks 2254 and 2256 may be generated at the corners of the SiO2 layer 2138 due to stress from the electrode 2236 (stress accumulated inside the metal layer or at the interface with the SiO2 layer 2138 when the electrode 2236 is formed as a metal layer, etc.) and / or due to local strain caused by the difference in linear expansion coefficient between the SiO2 layer 2138 and the substrate 2130.

[0089] also, Fig.13 In the figure, the optical waveguide 2134 extends in the Y direction of the coordinate axis shown in the upper right corner of the figure. In addition, the electrode 2236 composed of a metal layer extends in the Z direction and intersects the optical waveguide 2134 to form an intersection 2240.

[0090] also, Fig.12 and Fig.13In the embodiment, the substrate 2130 is an LN substrate thinned to a thickness of 20 μm or less (eg, 10 μm), and is fixed to a support substrate 2144 via an adhesive layer 2142. The support substrate 2144 is, for example, a glass substrate, an LN substrate, or a Si substrate.

[0091] In an optical modulation element using a Mach-Zehnder optical waveguide as in the embodiment shown below, electrodes for transmitting low-frequency signals such as bias electrodes are usually formed with a thickness of about 0.3 μm to 5 μm. Fig.12 In addition, the high-frequency signal electrode that transmits the modulated signal is usually formed with a thickness of about 20μm to 40μm, and there is a concern that Fig.13 Such a rupture of the SiO2 layer.

[0092] The optical waveguide element of the present invention prevents the occurrence of disconnection or cracking at the intersection of the optical waveguide and the electrode crossing the optical waveguide, and effectively reduces the optical absorption loss of the waveguide light caused by the electrode metal at the intersection without causing degradation of the optical characteristics of the optical waveguide element and reduction of the long-term reliability.

[0093] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0094] [First embodiment]

[0095] Figure 1 1 is a diagram showing the structure of an optical modulator 100, which uses an optical modulator element as an optical waveguide element according to the first embodiment of the present invention. The optical modulator 100 includes a housing 102, an optical modulator element 104 accommodated in the housing 102, and a relay substrate 106. The optical modulator element 104 is, for example, a DP-QPSK modulator. The housing 102 is finally fixed with a cover (not shown) as a plate body at its opening, and the interior thereof is hermetically sealed.

[0096] Moreover, the optical modulator 100 has: a signal pin 110a, a signal pin 110b, a signal pin 110c, and a signal pin 110d, which are used to input a high-frequency electrical signal used in the modulation of the optical modulator element 104; and a feed-through portion 108, which is used to introduce these signal pins 110a, 110b, 110c, and 110d into the frame 102.

[0097] Furthermore, the optical modulator 100 includes 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 .

[0098] Here, the input optical fiber 114 and the output optical fiber 120 are fixed to the frame 102 via the bracket 122 and the bracket 124 as fixing members, respectively. The light input from the input optical fiber 114 is collimated by the lens 130 arranged in the bracket 122, and then input to the light modulator 104 via the lens 134. However, this is an example, and the input of light to the light modulator 104 can also be performed according to the prior art, for example, by the following method: the input optical fiber 114 is introduced into the frame 102 via the bracket 122, and the end face of the introduced input optical fiber 114 is connected to the end face of the substrate 230 of the light modulator 104.

[0099] Furthermore, the optical modulator 100 includes an optical unit 116 for performing polarization combination on two modulated lights output from the optical modulation element 104. The polarization combined light output from the optical unit 116 is focused by a lens 118 disposed in a support 124 and coupled to an output optical fiber 120.

[0100] The relay substrate 106 relays the high-frequency electrical signals input from the signal pins 110a, 110b, 110c, and 110d to the optical modulator 104 using a conductor pattern (not shown) formed on the relay substrate 106. The conductor pattern on the relay substrate 106 is connected to pads (described later) at one end of a signal electrode constituting the optical modulator 104, respectively, by wire bonding or the like. In addition, the optical modulator 100 includes two terminators 112a and 112b having a predetermined impedance in the housing 102.

[0101] Figure 2 To indicate that it is housed Figure 1 FIG. 1 is a diagram showing an example of the structure of an optical modulator 104 as an optical waveguide element in a housing 102 of an optical modulator 100 shown in FIG. The optical modulator 104 is composed of an optical waveguide (bold dotted line in the figure) formed on a substrate 230 composed of LN, for example, and performs 200G DP-QPSK modulation, for example. These optical waveguides can be formed by thermally diffusing Ti on the surface of the substrate 230.

[0102] The substrate 230 is, for example, rectangular and has two sides 280a and 280b extending in the vertical direction and facing each other, and two sides 280c and 280d extending in the horizontal direction and facing each other. Figure 2 As shown in the coordinate axis shown in the upper left part of the figure, the direction Figure 2 The normal direction of the inner side of the paper (from the front to the back) is set as the X direction, the right direction in the figure is set as the Y direction, and the downward direction in the figure is set as the Z direction.

[0103] The optical modulator 104 includes an input waveguide 232 that receives input light (arrow pointing to the right in the figure) from the input optical fiber 114 at the lower side of the side 280b on the left side of the substrate 230, and a branching waveguide 234 that branches the input light into two lights having the same light amount. The optical modulator 104 includes a so-called nested Mach-Zehnder optical waveguide 240a and a nested Mach-Zehnder optical waveguide 240b (parts surrounded by a dashed line in the figure) as two modulation units that modulate the lights branched by the branching waveguide 234.

[0104] The nested Mach-Zehnder optical waveguide 240a and the nested Mach-Zehnder optical waveguide 240b respectively include two Mach-Zehnder optical waveguides 244a (part in the dashed line in the figure) and 246a (part in the two-dot chain line in the figure) and 244b (part in the dashed line in the figure) and 246b (part in the two-dot chain line in the figure) provided in two waveguide portions forming a pair of parallel waveguides. Thus, the nested Mach-Zehnder optical waveguide 240a and the nested Mach-Zehnder optical waveguide 240b respectively QPSK modulate the input light branched into two beams by the branching waveguide 234, and then output the modulated light (output) from the respective output waveguides 248a and 248b to the left in the figure.

[0105] Then, the two output lights are polarized and combined into one light beam by the optical unit 116 disposed outside the substrate 230. Hereinafter, the input waveguide 232, the branch waveguide 234, the nested Mach-Zehnder optical waveguide 240a, the nested Mach-Zehnder optical waveguide 240b, and the Mach-Zehnder optical waveguide 244a, the Mach-Zehnder optical waveguide 246a, the Mach-Zehnder optical waveguide 244b, the Mach-Zehnder optical waveguide 246b and other optical waveguides contained therein formed on the substrate 230 of the light modulator 104 are collectively referred to as optical waveguides 232 and the like.

[0106] On the substrate 230, signal electrodes 250a, 252a, 250b, and 252b are provided, and the signal electrodes 250a, 252a, 250b, and 252b are used to make the four Mach-Zehnder optical waveguides 244a, 246a, 244b, and 246b constituting the nested Mach-Zehnder optical waveguide 240a and the nested Mach-Zehnder optical waveguide 240b perform modulation operations. The signal electrodes 250a and 252a are bent to the left side in the figure, extending to the upper side 280c of the substrate 230 in the figure, and connected to the pads 254a and 256a. In addition, the signal electrodes 250a and 252a are extended to the right side 280a of the substrate 230 in the figure, and connected to the pads 258a and 260a.

[0107] Similarly, the signal electrodes 250b and 252b extend to the side 280d at the bottom of the substrate 230 in the figure, and are connected to the pads 254b and 256b, and the signal electrodes 250b and 252b extend to the side 280a at the right of the substrate 230 in the figure, and are connected to the pads 258b and 260b. The pads 258a, 260a, 258b, and 260b are connected to the relay substrate 106 described above by wire bonding or the like.

[0108] In addition, according to the prior art, the signal electrodes 250a, 252b, 250b, and 252b together with the 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 waveguide 232, etc., and a plurality of regions formed by dividing the optical waveguide 232, etc. in the ground conductor pattern can be connected to each other, for example, by wire bonding, etc.

[0109] The pads 254a, 256a, 254b, and 256b are connected to the terminators 112a and 112b described above. As a result, the high-frequency electric signal input from the relay substrate 106 connected to the pads 258a, 260a, 258b, and 260b becomes a traveling wave, propagates through the signal electrodes 250a, 252a, 250b, and 252b, and modulates the optical waves propagating through the Mach-Zehnder optical waveguides 244a, 246a, 244b, and 246b, respectively.

[0110] Here, in order to further enhance the interaction between the electric field formed by the signal electrodes 250a, 252a, 250b, and 252b in the substrate 230 and the waveguide light propagating in the Mach-Zehnder optical waveguides 244a, 246a, 244b, and 246b, and to 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. In addition, the back surface of the substrate 230 (which faces the substrate 230) is Figure 2 The surfaces facing each other as shown) are bonded to a supporting substrate such as glass via an adhesive layer ( Figure 2 Not shown in the figure. Figure 4 etc., recorded as adhesive layer 590 and supporting substrate 592).

[0111] In addition, the light modulator 104 is provided with bias electrodes 262a, 264a, 262b, 264b for compensating for the variation of the bias point due to the so-called DC drift. The bias electrodes 262a and 262b are respectively composed of two electrode pairs and are respectively used for compensating for the variation of the bias point of the Mach-Zehnder optical waveguide 244a, 246a and the Mach-Zehnder optical waveguide 244b, 246b. Furthermore, the bias electrodes 264a and 264b are respectively used for compensating for the variation of the bias point of the nested Mach-Zehnder optical waveguide 240a and the nested Mach-Zehnder optical waveguide 240b.

[0112] The bias electrodes 262a, 264a, 262b, and 264b also extend to the sides 280c and 280d of the substrate 230, respectively, and are connected to a bias control circuit outside the frame body via, for example, lead pins (not shown) provided on the side of the frame body 102 in the vicinity of the sides 280c and 280d. Thus, the bias electrodes 262a, 264a, 262b, and 264b are driven by the bias control circuit to compensate for the bias point variation of the corresponding Mach-Zehnder optical waveguides. Hereinafter, the signal electrodes 250a, 252a, 250b, and 252b and the bias electrodes 262a, 264a, 262b, and 264b are collectively referred to as electrodes 250a, etc.

[0113] The bias electrodes 262a, 264a, 262b, and 264b are electrodes to which a DC or low-frequency electric signal is applied, and are formed, for example, with a thickness in the range of 0.3 μm or more and 5 μm or less. In contrast, the signal electrodes 250a, 252b, 250b, and 252b are formed, for example, with a thickness in the range of 20 μm or more and 40 μm or less in order to reduce conductor loss of the high-frequency electric signal applied to the signal electrodes.

[0114] The light modulation element 104 configured as described above includes a plurality of intersections where the electrodes 250a and the like intersect (traverse) the optical waveguide 232 and the like. Figure 2 The records are easy to understand. Figure 2 All the intersections of the bold dotted line representing the optical waveguide 232 and the strip-shaped portion representing the electrode 250a are intersections where the electrode 250a and the like intersect the optical waveguide 232 and the like. In this embodiment, the light modulation element 104 includes a total of 50 intersections.

[0115] Figure 3 for Figure 2 A partial detailed view of portion A of the light modulation element 104 is shown.

[0116] Below, take as Figure 3 The structures of the intersection portions will be described by taking the B portion, C portion, D portion, E portion, and F portion of the intersection portion shown as examples.

[0117] First, as a first structural example of the intersection portion, Figure 3 The structure of the B portion shown will be described. Figure 4 and Figure 5 2 is a partial detailed diagram showing the structure of the B portion where the bias electrode 264b-1, which is a part of the bias electrode 264b, intersects the input waveguide 232. Here, Figure 4 This is the floor plan of Section B. Figure 5 for Figure 4 The VV cross-sectional arrow view of part B is shown.

[0118] also, Figure 4 , Figure 5 The structure shown is an example of the structure of the portion where the optical waveguide 232 etc. and the electrode 250a etc. intersect in the light modulation element 104, and can also be similarly applied to any portion other than the B portion where the optical waveguide 232 etc. and the electrode 250a etc. intersect.

[0119] Figure 4 In the figure, the bias electrode 264b-1 extending in the up-down direction (Z direction) intersects with the input waveguide 232 extending in the left-right direction (Y direction) to form an intersection 470 (a portion surrounded by a rectangle with a dashed line in the figure).

[0120] Especially Figure 5 As shown, in this embodiment, the resin layer 452 is partially provided between the input waveguide 232 and the bias electrode 264b-1 in the substrate portion including the intersection 470 in the substrate 230. In addition, the resin layer 452 has a cross section along the extension direction of the bias electrode 264b-1 (i.e., for example Figure 5 In the cross section shown in FIG. 4 , the corner on the bias electrode 264b-1 side is formed by the curves 452-1 and 452-2. That is, the resin layer 452 is formed in such a way that the boundary line with the bias electrode 264b-1 is connected to the end of the resin layer 452 by the curves 452-1 and 452-2.

[0121] Here, the resin layer 452 may be, for example, a photoresist used in the patterning process of the electrode 250a, etc. Furthermore, the portions of the curves 452-1 and 452-2 constituting the angle on the bias electrode 264b-1 side may be formed, for example, by setting the temperature rise rate of the photoresist during the high temperature treatment after patterning to a rate greater than the usual 1°C / min (for example, 5°C / min). Alternatively, the portions of the curves 452-1 and 452-2 may be formed, for example, by subjecting the photoresist constituting the resin layer 452 to plasma treatment (for example, ashing treatment).

[0122] Furthermore, as described above, the bias electrode 264 b - 1 is formed relatively thin with a thickness ranging from 0.3 μm to 5 μm, and thus the resin layer 452 is formed with a thickness ranging from 0.3 μm to 1 μm, which is about the same as the thickness of the SiO 2 layer in the related art.

[0123] also, Figure 5 In the embodiment, the substrate 230 is fixed to the support substrate 592 via the adhesive layer 590. Here, the adhesive layer 590 is made of, for example, a thermosetting resin, and the support substrate 592 includes, for example, a glass substrate, an LN substrate, a Si substrate, or the like.

[0124] In the B portion of the optical modulation element 104 having the above structure, the resin layer 452 is provided between the input waveguide 232 and the bias electrode 264b-1 in the intersection 470. This prevents the waveguide light of the input waveguide 232 from being absorbed by the metal constituting the bias electrode 264b-1.

[0125] In particular, the resin such as photoresist constituting the resin layer 452 has a Young's modulus of about 1 GPa to 2 GPa, which is one digit smaller than the Young's modulus of 72 GPa to 74 GPa of SiO2 used between the electrode and the optical waveguide in the prior art, and has lower rigidity than SiO2. Therefore, in the B portion of the light modulation element 104, the stress applied from the resin layer 452 itself to the substrate 230 is reduced compared to the structure of the prior art using the SiO2 layer, and the stress transmitted from the bias electrode 264b-1 to the substrate 230 is also reduced. In addition, due to the low rigidity of the resin layer 452 itself, the generation of local strain that may be generated near the end of the resin layer 452 due to the difference in linear expansion coefficient between the resin layer 452 and the substrate 230 can also be suppressed.

[0126] Furthermore, the resin layer 452 is Figure 5In the cross section along the extending direction of the bias electrode 264b-1 shown in the figure, the corner on the bias electrode 264b-1 side is formed by the curve 452-1 and the curve 452-2, so the continuity of the shape of the bias electrode 264b-1 around the corner is improved (that is, the sharp change of the shape is alleviated). Therefore, the bias electrode 264b-1 can be prevented from being broken, which is complementary to the suppression of strain due to the low rigidity of the resin layer 452. In addition to the suppression of the strain, the curves 452-1 and the curves 452-2 prevent the stress from concentrating on the corner of the resin layer 452 from the bias electrode 264b-1, so that the resin layer 452 can be prevented from being cracked.

[0127] As a result, in the optical modulator 104, by also using the same structure as that of part B for other intersections between the electrode 250a etc. and the optical waveguide 232 etc., light absorption loss of the waveguide light caused by the metal constituting the electrode 250a etc., which may be generated at the intersections between the optical waveguide 232 etc. on the substrate 230 and the electrode 250a etc., can be effectively reduced without causing degradation of the optical properties of the optical modulator 104 and a reduction in long-term reliability.

[0128] Furthermore, from the viewpoint of suppressing cracks at the corners of the resin layer 452 and suppressing disconnection of the bias electrode 264b-1 around the corners, it is desirable that the distances L1 and L2 measured along the extending direction of the bias electrode 264b-1 from the starting points of the curves 452-1 and 452-2 constituting the corners to the ends of the resin layer 452 are greater than the thickness t1 of the resin layer 452. That is, it is desirable that L1≧t1 and L2≧t1.

[0129] Next, as a second structural example of the intersection portion, Figure 3 The structure of the C portion shown will be described. Figure 6 This is a VI-VI cross-sectional arrow view of the C portion where the input waveguide 232 intersects the signal electrode 252 b .

[0130] also, Figure 6 The structure shown is an example of the structure of the portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect in the light modulation element 104 , and can be similarly applied to any portion other than the C portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect.

[0131] Figure 6 In the figure, the signal electrode 252b extending in the left-right direction (Z direction) crosses (crosses) the input waveguide 232 extending in the normal direction (Y direction) of the paper, forming an intersection 670 (a portion surrounded by a rectangle with a dashed line shown in the figure).

[0132] and Figure 5 The structure of the B part shown is similar, Figure 6 In the structure of the C portion shown, a substrate portion including the intersection portion 670 is included in the substrate 230 , and a resin layer 652 is partially provided between the signal electrode 252 b and the input waveguide 232 .

[0133] Generally speaking, the stress transmitted from the electrode 250a etc. to the substrate 230 increases as the thickness of the electrode 250a etc. increases. Therefore, it is ideal that the thicker the electrode 250a etc. is, the thicker the thickness t1 of the resin layer provided between the electrode 250a etc. and the optical waveguide 232 etc. is. As described above, the signal electrode 252b is formed with a thickness of about 20 μm to 40 μm, which is about one digit thicker than the bias electrode 264b etc. formed with a thickness of about 0.3 μm to 5 μm. Therefore, regarding Figure 6 The thickness t1 of the resin layer 652 shown is about one digit greater than the thickness of the SiO 2 layer in the related art, and is formed in the range of 2 μm to 7.5 μm, which is a very thick layer compared with the related art.

[0134] Moreover, with Figure 5 Similarly, the resin layer 452 shown in FIG. 6 is a cross-section of the resin layer 652 along the extending direction of the signal electrode 252 b (ie, for example, Figure 6 In the cross section shown in FIG. 1 , the corner on the signal electrode 252b side is formed by the curve 652-1 and the curve 652-2. That is, the resin layer 652 is formed in such a way that the boundary line with the signal electrode 252b is connected to the end of the resin layer 652 by the curve 652-1 and the curve 652-2.

[0135] Furthermore, as for the resin layer 652, as the above-mentioned ideal embodiment, the distance L1 and the distance L2 measured from the starting point to the end of the curve 652-1 and the curve 652-2 along the extension direction of the signal electrode 252b are formed to be greater than the thickness t1 of the resin layer 552 (that is, L1≧t1, L2≧t1). Figure 5 The intersection 470 shown can also improve the continuity of the shape of the signal electrode 252b to suppress disconnection of the signal electrode 252b near the corner of the resin layer 652, and suppress the concentration of stress from the signal electrode 252b to the corner of the resin layer 652 to prevent cracks in the corner.

[0136] Moreover, from the perspective of stabilizing the light propagation characteristics of the optical waveguide 232, etc., it is ideal that the stress applied from the resin layer 652 to the optical waveguide 232, etc. is uniform, so that the range corresponding to the upper part of the input waveguide 232 (i.e., the range of the width W shown in the figure) on the upper surface of the resin layer 652 (i.e., the surface in contact with the signal electrode 252b) is formed to be flat (i.e., the thickness of the resin layer 652 in the said range is constant).

[0137] In addition, as a particularly ideal structure of the resin layer 652, the length Lz measured along the extending direction of the signal electrode 252b is a value that is three times or more the width W of the input waveguide 232 in the intersection 670, that is, Lz≧3W. As a result, the contact area between the resin layer 652 and the substrate 230 in the intersection 670 is increased, and the stress transmitted from the signal electrode 252b to the input waveguide 232 via the resin layer 652 is further reduced. Therefore, for example, the following situation can be suppressed: the effective refractive index of the input waveguide 232 changes due to the stress due to the photoelastic effect of the substrate 230 composed of LN. As a result, even when the signal electrode 252b is formed to be thicker than 10 μm, the degradation or deterioration of the optical characteristics of the light modulator 104 caused by the stress from the thick electrode 252b can be prevented.

[0138] Furthermore, as an ideal structure of the resin layer 652, the distance L1 and the distance L2 measured from the starting point to the end of the curve 652-1 and the curve 652-2 along the extension direction of the signal electrode 252b are formed to be not only larger than the thickness t1 of the resin layer 552, but also larger than the width W of the input waveguide 232 in the intersection 670 (that is, L1≧W, L2≧W).

[0139] Thus, the corners of the resin layer 652 where the stress from the signal electrode 252 b is likely to be concentrated are away from the input waveguide 232 , so that the stress applied to the input waveguide 232 via the resin layer 652 can be further reduced.

[0140] In addition, the resin layer 652 can be formed by, for example, a cross-linking reaction caused by, for example, high-temperature heating using a photoresist containing a cross-linking agent. The resin formed by the photoresist containing a cross-linking agent can be deformed to a greater extent than a photoresist for ordinary micro-processing by a cross-linking reaction and a high-temperature treatment (for example, 200° C.), so that the corners of a resin layer formed with a thickness exceeding 1 μm, such as the resin layer 652, can be easily curved over a wide range. Since the shrinkage accompanying the cross-linking reaction is inevitable, the photoresist containing a cross-linking agent is not suitable for micro-processing requiring submicron precision, but since the physical property changes (deterioration) over time or the generation of gas is small, the resin layer 652, which does not require high-precision processing accuracy compared to the optical waveguide 232, is suitable as a resin for long-term use in an airtight frame such as the frame 102.

[0141] In addition to the above-mentioned high temperature treatment, the portions of curve 652-1 and curve 652-2 possessed by the resin layer 652 can be formed in the same manner as the resin layer 452 by setting the temperature rise rate during the high temperature treatment after patterning to a rate greater than the usual 1°C / minute (for example, 5°C / minute), and / or by plasma treating the photoresist constituting the resin layer 652 (for example, ashing treatment).

[0142] In the present embodiment, the signal electrodes 250 a , 252 b , 250 b , and 252 b are formed in a range of, for example, 20 μm to 40 μm, but the present invention is not limited thereto. Fig.13 The cracks 2254 and 2256 at the corners of the SiO2 layer shown in the figure may have a higher probability of occurrence when the thickness of the electrode on the top is thicker than 10 μm. Therefore, when the thickness of the electrode 250a is thicker than 10 μm at least in the intersection with the optical waveguide 232, etc., the cracks 2254 and 2256 at the corners of the SiO2 layer may have a higher probability of occurrence. Figure 5 or the following Figures 6 to 9 The structure shown can effectively prevent the degradation of the optical characteristics of the light modulator 104 and the reduction of the long-term reliability, and reduce the optical absorption loss of the waveguide light caused by the electrode 250a and the like.

[0143] Next, as a third structural example of the intersection portion, Figure 3 The structure of the D portion shown will be described. Figure 7 This is a VII-VII cross-sectional arrow view of the D portion where the input waveguide 232 intersects the signal electrode 250b. Figure 7 The structure shown is an example of the structure of the portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect in the light modulation element 104 , and can be similarly applied to any portion other than the D portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect.

[0144] Figure 7 , the signal electrode 250b extending in the horizontal direction (Z direction) shown in the figure crosses (crosses) the input waveguide 232 extending in the normal direction (Y direction) of the paper, forming an intersection 770 (a portion surrounded by a rectangle with a dashed line shown in the figure).

[0145] In addition, in the substrate portion of the substrate 230 including the intersection 770, a plurality of (for example, three) resin layers 752-1, 752-2, and 752-3 are partially provided between the signal electrode 250b and the input waveguide 232. In addition, the corners of the resin layers 752-1, 752-2, and 752-3 on the signal electrode 250b side are formed by curved lines. Moreover, the resin layers 752-1, 752-2, and 752-3 are stacked in a manner such that the height measured from the surface of the substrate 230 becomes a step shape along the extending direction of the signal electrode 250b. In addition, the ideal conditions of L1, L2, Lz, etc. described above can be applied to the resin layers 752-1, 752-2, and 752-3 respectively.

[0146] Figure 7 In the structure shown, the plurality of resin layers 752-1, 752-2, and 752-3 are formed in a step-like shape along the extending direction of the signal electrode 250b, and thus, the continuity of the shape of the signal electrode 250b at the intersection 770 can be further improved (i.e., the degree of change in shape can be further alleviated) in complement to the fact that the corners of these resin layers are formed by curves, and the signal electrode 250b at the intersection 770 can be further prevented from being disconnected. In addition, the resin layers 752-1, 752-2, and 752-3, whose corners are formed by curves, are formed in a step-like shape, and thus the stress from the signal electrode 250b is dispersedly applied to the corners of the resin layers, and the occurrence of cracks at these corners can be further prevented.

[0147] Furthermore, since a plurality of resin layers are used, the thickness of the resin layers 752-1, 752-2, and 752-3 can be set to a desired thickness, and the thickness of each of the resin layers 752-1, 752-2, and 752-3 can be set to a certain thickness or less. Therefore, for example, each resin layer can be formed using a common photoresist having sub-micron processing accuracy, and the positions or shapes of the resin layers 752-1, 752-2, and 752-3 can be determined with high accuracy, and the thickness of the resin layers can be set to a large value corresponding to the thickness of the signal electrode 250b.

[0148] Next, as a fourth structural example of the intersection portion, Figure 3 The structure of the portion E shown will be described below. In this structural example, one resin layer is provided across two intersection portions. Figure 8 1 is a VIII-VIII cross-sectional view of the E portion, which includes two intersection portions 870-1 and 870-2 where the signal electrode 252b intersects the two parallel waveguides 244b-1 and 244b-2 constituting the Mach-Zehnder optical waveguide 244b, respectively.

[0149] also, Figure 8The structure shown is applicable not only to the intersection of the parallel waveguide and the electrode constituting the Mach-Zehnder optical waveguide, but also to any intersection where the optical waveguide 232 and the electrode 250 a intersect and a plurality of adjacent intersections.

[0150] Figure 8 In the figure, the signal electrode 252b extending in the left-right direction (Z direction) crosses (intersects) the parallel waveguide 244b-1 and the parallel waveguide 244b-2 extending in the normal direction of the paper (Y direction), forming the intersection 870-1 and the intersection 870-2 respectively.

[0151] The resin layer 852 provided between the signal electrode 252b and the substrate 230 is formed to extend across the adjacent intersections 870-1 and 870-2. Thus, the resin layer 852 is provided between the signal electrode 252b and the parallel waveguides 244b-1 and 244b-2 in the intersections 870-1 and 870-2, respectively.

[0152] Furthermore, the cross section of the resin layer 852 along the extending direction of the signal electrode 252b (ie, for example Figure 8 In the cross section shown in FIG. 8 , the corner on the signal electrode 252b side is formed by the curve 852-1 and the curve 852-2. That is, the resin layer 852 is formed in such a way that the boundary line with the signal electrode 252b is connected to the end of the resin layer 852 by the curve 852-1 and the curve 852-2.

[0153] According to the structure, a resin layer 852 is provided across the plurality of intersections 870-1 and 870-2, thereby reducing the number of resin layers formed on the substrate 230 and improving the manufacturing yield. In addition, as a result of providing a resin layer 852 across the plurality of intersections 870-1 and 870-2, the area of ​​the portion of the resin layer 852 in contact with the surface of the substrate 230 becomes larger, thereby improving the adhesion of the resin layer 852 to the substrate 230.

[0154] Furthermore, when the resin layer 852 is formed across the intersection 870-1 and the intersection 870-2, the thickness of the resin layer 852 including the width Fw of the intersection 870-1 and the intersection 870-2 can be easily formed into a uniform thickness. Figure 8As shown in the structure, when two adjacent intersections 870-1 and 870-2 include parallel waveguides 244b-1 and 244b-2, the stress and other conditions that the two parallel waveguides 244b-1 and 244b-2 are subjected to from the resin layer 852 (and / or via the resin layer 852) can be made uniform, thereby suppressing the additional optical phase difference between the parallel waveguides 244b-1 and 244b-2 caused by the unevenness of the stress and other conditions, and suppressing the additional action point change of the Mach-Zehnder type optical waveguide 244b caused by the provision of the resin layer 852.

[0155] Next, the fifth structural example of the intersection portion is Figure 3 In this structural example, in order to reduce the light absorption loss caused by the electrode 250a, etc., a SiO2 layer similar to the prior art is provided on the optical waveguide 232, etc., and on this SiO2 layer, a Fig.12 , Fig.13 As shown, the resin layer serves as a protective layer for preventing the SiO2 layer from cracking and / or the electrode from disconnecting.

[0156] Fig. 9 FIG. 1 is a cross-sectional view of the F portion where the signal electrode 252a intersects one of the parallel waveguides 244a-1 of the Mach-Zehnder optical waveguide 244a. Fig. 9 The structure shown is an example of the structure of the portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect in the light modulation element 104 , and can be similarly applied to any portion where the optical waveguide 232 etc. and the electrode 250 a etc. intersect other than the F portion.

[0157] Fig. 9 In the figure, the signal electrode 252a extending in the left-right direction (Z direction) crosses (crosses) the parallel waveguide 244a-1 extending in the normal direction (Y direction) of the paper, forming an intersection 970 (the portion surrounded by the rectangle shown in the figure with a dashed line).

[0158] In the intersection 970, a SiO2 layer 990 is formed on the parallel waveguide 244a-1 in the same manner as in the prior art. However, unlike the prior art, a resin layer 952 is provided between the SiO2 layer 990 and the signal electrode 252a in the intersection 970. Figure 5Similarly to the intersection 470 shown in FIG. 1 , the intersection 970 has a structure in which a resin layer 952 is partially provided between the signal electrode 252a and the parallel waveguide 244a-1 in the substrate portion including the intersection 970. In addition, the corner of the resin layer 952 on the signal electrode 252a side is formed by the curve 952-1 and the curve 952-2. Here, similarly to the prior art, the thickness of the SiO2 layer is, for example, 0.5 μm, which is a sufficient thickness to reduce the light absorption loss of the parallel waveguide 244a-1 caused by the signal electrode 252a. Moreover, the resin layer 952 is formed with a thickness of, for example, 3 μm.

[0159] According to the above structure, in the intersection 970, the SiO2 layer 990 provided on the parallel waveguide 244a-1 is protected by the resin layer 952, and cracks can be prevented from occurring at the corners of the SiO2 layer 990 due to stress from the signal electrode 252a. Figure 5 The intersection 470 and Figure 6 Similarly, the intersection 670 shown can prevent the resin layer 952 from being cracked due to the stress from the signal electrode 252a and prevent the signal electrode 252a from being disconnected near the corner of the resin layer 952 by the curves 952-1 and 952-2 forming the corners of the resin layer 952.

[0160] Fig. 9 The structure shown is particularly suitable for the following case: it is necessary to utilize the high electrical insulation, transparency, and temporal stability of the SiO2 layer and to suppress the disconnection of the electrode 250a and the like at the intersection.

[0161] [Second Embodiment]

[0162] Next, a second embodiment of the present invention will be described. This embodiment is a light modulation module 1000 that uses the light modulation element 104 included in the light modulator 100 of the first embodiment. Fig.10 1 is a diagram showing the structure of the optical modulation module 1000 according to the present embodiment. Fig.10 In Figure 1 The same components as those of the optical modulator 100 of the first embodiment shown in FIG. Figure 1 The same symbols as those shown in the figure are used to represent Figure 1 Related instructions.

[0163] The optical modulation module 1000 has Figure 1The optical modulator 100 shown in FIG. 1 is similar in structure to the optical modulator 100 shown in FIG. 1 , but is different from the optical modulator 100 in that it includes a circuit substrate 1006 instead of the relay substrate 106. The circuit substrate 1006 includes a drive circuit 1008. The drive circuit 1008 generates a high-frequency electric signal for driving the optical modulator 104 based on, for example, a modulation signal supplied from the outside via the signal pins 110a, 110b, 110c, and 110d, and outputs the generated high-frequency electric signal to the optical modulator 104.

[0164] The optical modulation module 1000 having the above structure includes, similarly to the optical modulator 100 of the first embodiment, a plurality of optical waveguides 232 and the electrodes 250a and the like at the intersections thereof. Figures 4 to 9 Therefore, in the optical modulation module 1000, similarly to the optical modulator 100, it is possible to effectively reduce the optical absorption loss of the waveguide light that may be generated at the intersection of the optical waveguide 232 and the electrode 250a on the substrate 230 without causing the degradation of the optical characteristics of the optical modulation element 104 and the reduction of the long-term reliability, thereby achieving good modulation characteristics and performing good light transmission.

[0165] [Third Embodiment]

[0166] Next, a third embodiment of the present invention will be described. This embodiment is an optical transmission device 1100 equipped with the optical modulator 100 of the first embodiment. Fig.11 1 is a diagram showing the structure of an optical transmission device 1100 of the present embodiment. The optical transmission device 1100 includes an optical modulator 100, a light source 1104 for inputting light into the optical modulator 100, a modulator driver 1106, and a modulation signal generator 1108. In addition, the optical modulation module 1000 may be used instead of the optical modulator 100 and the modulator driver 1106.

[0167] The modulation signal generating unit 1108 is an electronic circuit that generates an electrical signal for causing the optical modulator 100 to perform a modulation action. Based on the transmission data given from the outside, it generates a modulation signal as a high-frequency signal for causing the optical modulator 100 to perform an optical modulation action according to the modulation data, and outputs it to the modulator driving unit 1106.

[0168] The modulator driving unit 1106 amplifies the modulation signal input from the modulation signal generating unit 1108 , and outputs four high-frequency electrical signals for driving the four signal electrodes 250 a , 252 a , 250 b , and 252 b of the optical modulation element 104 included in the optical modulator 100 .

[0169] The four high-frequency electrical signals are input to the 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 1104 is modulated by the optical modulator 100, for example, DP-QPSK, to become modulated light and output from the optical transmission device 1100.

[0170] In particular, in the optical transmitting device 1100, an optical modulator 100 including an optical modulation element 104 is used. The optical modulation element 104 can effectively reduce the light absorption loss at the intersection of the optical waveguide 232 and the electrode 250a, thereby achieving good modulation characteristics and performing good optical transmission.

[0171] In addition, 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 within the scope not departing from the gist of the present invention.

[0172] For example, in the first embodiment, in the optical modulator 104, the B portion which is the intersection of the input waveguide 232 and the bias electrode 264b-1, the C portion which is the intersection of the input waveguide 232 and the signal electrode 252b, the D portion which is the intersection of the input waveguide 232 and the signal electrode 250b, the E portion which includes two intersections of the parallel waveguide 244b-1 and the parallel waveguide 244b-2 and the signal electrode 252b, and the F portion which is the intersection of the parallel waveguide 244a-1 and the signal electrode 252a are provided respectively with Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 The structure shown is not limited to this.

[0173] The light modulator 104 as a light waveguide element may be configured to have a portion or all of the intersections between the light waveguide 232 and the electrode 250a. Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 Therefore, for example, the intersection of the signal electrode 250b, the signal electrode 252b or the signal electrode 252a may be Figures 6 to 9 Any of the structures shown is applicable to any intersection including the bias electrode 264b, etc.

[0174] Moreover, as will be readily appreciated by those skilled in the art, Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 The characteristic structural combination of the B part, C part, D part, E part, and F part shown in the figure is applicable to any intersection of the optical waveguide 232 and the electrode 250a. Figure 7 The structure and Fig. 9 In the structural combination, a plurality of resin layers stacked in multiple steps are formed at the intersection of the optical waveguide 232 and the like formed with the SiO2 layer and the electrode 250a and the like.

[0175] Furthermore, for example, Figure 7 The structure and Figure 8 The structure of the combination of the two intersections forms a plurality of resin layers stacked in multiple steps. Figure 8 and Fig. 9 In combination, a plurality of resin layers stacked in a multi-step manner are formed across two adjacent intersections of the optical waveguide 232 and the like formed with the SiO 2 layer and the electrode 250 a and the like.

[0176] and, Figure 7 In the structure of the D portion shown, as the multiple resin layers stacked in multiple steps, a structure including three resin layers, resin layer 752-1, resin layer 752-2, and resin layer 752-3 is shown, but the present invention is not limited thereto. The number of resin layers stacked in multiple steps may be two or more.

[0177] and, Fig. 9 In the structure of the F portion shown, a structure in which a SiO2 layer 990 is provided on the parallel waveguide 244a-1 is shown, but the present invention is not limited thereto. In addition to SiO2, an insulating layer or a transparent insulating layer (for example, a layer composed of SiN, etc.) made of any material having a greater refractive index and electrical insulation than the optical waveguide 232, etc. may be formed on the upper portion of the optical waveguide 232, etc.

[0178] Furthermore, in the first embodiment, the intersection including the B to F parts is formed by the electrode 250a and the like being orthogonal to the optical waveguide 232 and the like, but the present invention is not limited thereto. Figures 3 to 9 The structure of the intersection shown can also be applied to the following intersection, which is the intersection of the electrode 250a etc. and the optical waveguide 232 etc. formed by the electrode 250a etc. crossing the optical waveguide 232 etc., and the electrode 250a etc. crosses at an arbitrary angle relative to the optical waveguide 232 etc. (not parallel).

[0179] Moreover, in the above-described embodiment, as an example of an optical waveguide element, an optical modulator element 104 formed using a substrate 230 of LN (LiNbO3) is shown, but the present invention is not limited thereto, and the optical waveguide element may be an element formed by a substrate of any material (InP, Si, etc. other than LN) and having any function (optical switch, optical directional coupler, etc. other than optical modulation).

[0180] As described above, the optical modulator 100 of the first embodiment includes the optical modulator element 104. The optical modulator element 104, which is an optical waveguide element, includes: an optical waveguide 232, etc., formed on the substrate 230; and an electrode 250a, etc., which controls the light wave propagating in the optical waveguide 232, etc., and has an intersection 470, etc. that intersects the optical waveguide 232, etc. In addition, in the portion of the substrate 230 including the intersection 470, etc., a resin layer 452, etc. is partially provided between the optical waveguide 232, etc. and the electrode 250a, etc., and the corner of the resin layer 452, etc. on the side of the electrode 250a, etc. in the cross section along the extending direction of the electrode 250a, etc. is formed by a curved line.

[0181] According to the structure, the optical absorption loss of the waveguide light caused by the electrode metal that may be generated at the intersection 470 of the optical waveguide 232 on the substrate 230 and the electrode 250a can be effectively reduced without causing degradation of the optical characteristics of the optical modulation element 104 and a reduction in long-term reliability.

[0182] Furthermore, in the optical modulation element 104, the distance of the resin layer 452 etc. measured along the extension direction of the electrode 250a etc. from the starting point to the end of the curve constituting the corner in the cross section is greater than the value of the height of the resin layer 452 etc. measured from the surface of the substrate 230. According to the above structure, the corner of the resin layer 452 etc. can be formed by a curve having a curvature of a certain value or more, and the continuity of the shape of the electrode 250a etc. at the intersection 470 etc. can be further improved, and the stress applied from the electrode 250a etc. to the corner of the resin layer can be further dispersed. Therefore, it is possible to more effectively suppress the occurrence of disconnection of the electrode 250a etc. at the intersection 470 etc. or cracking of the corner of the resin layer 452 etc. As a result, it is possible to more effectively prevent the degradation of the optical characteristics of the optical modulation element 104 and the reduction of the long-term reliability, and reduce the optical absorption loss of the waveguide light caused by the electrode metal that may be generated at the intersection 470 etc. between the optical waveguide 232 etc. on the substrate 230 and the electrode 250a etc.

[0183] Furthermore, for example, the resin layer 652 of the optical modulation element 104 is provided at a distance of three times or more of the width of the input waveguide 232 in the intersection 670 along the extending direction of the signal electrode 252b. According to the above structure, the stress of the signal electrode 252b is suppressed from being concentrated on the optical waveguide, so that, for example, the change in the effective refractive index of the optical waveguide due to the photoelastic effect of the substrate 230 composed of LN can be suppressed. As a result, even when a thick signal electrode 252b is formed, for example, exceeding 10 μm, the degradation or deterioration of the optical characteristics of the optical modulation element 104 caused by the stress from the thick signal electrode 252b can be prevented.

[0184] Furthermore, for example, a plurality of resin layers 752-1, 752-2, and 752-3 are stacked in a step-like manner along the extending direction of the signal electrode 250b between the input waveguide 232 and the signal electrode 250b at the intersection 770 of the optical modulation element 104. With this structure, the continuity of the shape of the signal electrode 250b at or around the intersection 770 can be further improved, and the signal electrode 250b at the intersection 770 or the corner of the resin layer 752-1 can be further suppressed from being disconnected or cracked.

[0185] Furthermore, for example, at the intersection 970 of the light modulation element 104, a SiO2 layer 990 is formed as an insulating layer between the parallel waveguide 244a-1 and the resin layer 952. According to the above structure, the high electrical insulation, transparency, and temporal stability of SiO2 can be utilized, and disconnection of the signal electrode 252a can be suppressed, and cracks in the SiO2 layer 990 and the resin layer 952 can be prevented.

[0186] Furthermore, for example, the resin constituting the resin layer 652 of the light modulator 104 is formed using a photoresist containing a crosslinking agent. With this structure, a curved portion can be easily formed in a wide range at the corner of the resin layer 652 compared to the case of using a normal photoresist for microfabrication.

[0187] Furthermore, for example, the resin layer 852 of the optical modulation element 104 is formed across the adjacent intersections 870-1 and 870-2. According to the above structure, the contact area between the resin layer 852 and the substrate 230 can be enlarged, and the adhesion of the resin layer 852 to the substrate 230 can be improved. Moreover, the resin layer 852 can be easily formed with a uniform thickness in the range including the two intersections, so that, for example, the thickness of the resin layer 852 can be formed to be the same in the two intersections 870-1 and 870-2 including the two parallel waveguides 244b-1 and 244b-2 of the Mach-Zehnder optical waveguide 244b, respectively, so that the stress and other conditions received by the resin layer 852 of the two parallel waveguides can be uniform. As a result, the additional operating point variation of the Mach-Zehnder optical waveguide 244b can be suppressed, and good modulation characteristics can be achieved.

[0188] Furthermore, in the light modulation element 104, the electrode 250a and the like are formed thicker than 10 μm at least in the intersection with the optical waveguide 232 and the like. Furthermore, in the light modulation element 104, the substrate 230 has a thickness of 20 μm or less. According to these structures, even in the case of an electrode structure and a substrate structure in which the frequency of disconnection of the electrode or cracking of the corner of the SiO2 layer tends to become relatively high when a SiO2 layer is used as in the prior art, the occurrence of such disconnection and cracking can be effectively suppressed.

[0189] Moreover, the optical modulator of the first embodiment includes: any one of the optical modulator elements 104, which is an optical waveguide element; a frame 102, which accommodates the optical modulator element 104; an input optical fiber 114, which inputs light to the optical modulator element 104; and an output optical fiber 120, which guides the light output by the optical modulator element 104 to the outside of the frame 102.

[0190] Furthermore, the optical modulation module 1000 of the second embodiment includes: an optical modulation element 104 which is an optical waveguide element and modulates light; and a driving circuit 1008 which drives the optical modulation element 104 .

[0191] Furthermore, the optical transmission device 1100 of the third embodiment includes: the optical modulator 100 or the optical modulation module 1000; and a modulation signal generation unit 1108 which is an electronic circuit that generates an electrical signal for causing the optical modulation element 104 to perform a modulation operation.

[0192] According to these structures, the optical modulator 100, the optical modulation module 1000, or the optical transmission device 1100 having excellent characteristics can be realized.

Claims

1. An optical waveguide component, comprising: an optical waveguide formed on the substrate; as well as The electrode controls the light wave propagating in the optical waveguide and has an intersection portion intersecting the optical waveguide, and in the optical waveguide element, In a portion of the substrate including the intersection, a resin layer is partially provided between the optical waveguide and the electrode, and the resin layer has a cross section along the extending direction of the electrode. wherein the upper surface of the resin layer is in contact with the electrode, and the surface of the resin layer opposite to the upper surface is in contact with the upper surface of the optical waveguide, At an edge of the upper surface of the resin layer, the upper surface of the resin layer is bent downward toward the upper surface of the optical waveguide to form a curve.

2. The optical waveguide element according to claim 1, wherein A distance measured from a starting point to an end of the curved line constituting the electrode side in an extending direction of the electrode is greater than a height of the resin layer measured from a surface of the substrate.

3. The optical waveguide element according to claim 1 or 2, wherein: The resin layer is provided along the extending direction of the electrode at a distance equal to or greater than three times the width of the optical waveguide in the intersection.

4. The optical waveguide element according to claim 1 or 2, wherein: At the intersection, between the optical waveguide and the electrode, a plurality of the resin layers are stacked in a stepwise manner along an extending direction of the electrode.

5. The optical waveguide element according to claim 1 or 2, wherein: At the intersection, an insulating layer containing SiO 2 is formed between the optical waveguide and the resin layer.

6. The optical waveguide element according to claim 1 or 2, wherein: The resin constituting the resin layer is a resin formed using a photoresist containing a cross-linking agent.

7. The optical waveguide element according to claim 1 or 2, wherein: The resin layer is formed across the adjacent intersections.

8. The optical waveguide element according to claim 1 or 2, wherein: The electrode is formed thicker than 10 μm at least in the intersection.

9. The optical waveguide element according to claim 1 or 2, wherein: The substrate has a thickness of 20 μm or less.

10. An optical modulator, comprising: The optical waveguide element according to any one of claims 1 to 9, which is a light modulation element that modulates light; A frame housing the optical waveguide element; an optical fiber for inputting light into the optical waveguide element; and An optical fiber guides the light output from the optical waveguide element to the outside of the housing.

11. An optical modulation module, comprising: The optical waveguide element according to any one of claims 1 to 9, which is a light modulation element that modulates light; and a driving circuit for driving the optical waveguide element.

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

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