Optical waveguide components, optical modulators, optical modulation modules, and optical transmission devices

Abstract

This invention provides an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmitting device, which simultaneously suppresses optical absorption loss of the optical waveguide and signal propagation loss of the high-frequency signal electrode at multiple intersections between the convex optical waveguide and the high-frequency signal electrode, thereby achieving good operating characteristics. The optical waveguide element includes: a substrate on which the optical waveguide is formed; and electrodes formed on the substrate and having intersections that cross the optical waveguide. The optical waveguide includes protrusions extending on the substrate, and at the intersections adjacent to the electrodes, there is a resin-containing intermediate layer that fills the spaces between the protrusions along the electrodes and covers the upper portion of the protrusions.

Description

Technical Field

[0001] This invention relates to an optical waveguide element, an optical modulator, an optical modulation module, and an optical transmission device. Background Technology

[0002] In high-speed / high-capacity optical fiber communication systems, optical modulators are often used, incorporating optical modulation elements that function as optical waveguides. These waveguides consist of an optical waveguide formed on a substrate and control electrodes that control the light waves propagating within it. Optical modulation elements using LiNbO3 (hereinafter also referred to as LN), which exhibits photoelectric effects, as the substrate are widely used in high-speed / high-capacity optical fiber communication systems due to their low light loss and ability to achieve broadband optical modulation characteristics.

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

[0004] In addition, in recent years, in order to further enable low-voltage driving and high-speed modulation of optical modulators themselves, optical modulators using rib-type or ridge-type optical waveguides (hereinafter collectively referred to as convex optical waveguides) are also being put into practical use. The rib-type or ridge-type optical waveguides are constructed by forming strip-shaped protrusions on the surface of an LN substrate (e.g., with a thickness of 20 μm or less) that has been thinned to further enhance the interaction between the signal electric field in the substrate and the guided wave light.

[0005] Optical modulators performing QPSK modulation (QPSK optical modulators) or DP-QPSK modulation (DP-QPSK optical modulators) include multiple Mach-Zehnder waveguides forming a nested bushing structure, each of which includes at least one high-frequency signal electrode. Additionally, optical modulators using such Mach-Zehnder waveguides typically also include a bias electrode to compensate for variations in the bias point caused by direct current (DC) drift.

[0006] These high-frequency signal electrodes or bias electrodes (hereinafter collectively referred to as electrodes) are formed extending to the vicinity of the outer periphery of the LN substrate for connection to electrical circuits outside the substrate. Therefore, multiple optical waveguides and multiple electrodes intersect in a complex manner on the substrate, forming multiple intersections where electrodes traverse the optical waveguides.

[0007] If the intersection is formed with the optical waveguide in direct contact with the electrode, the light propagating in the optical waveguide is absorbed by the metal constituting the electrode in these intersections, resulting in optical loss (optical absorption loss). Furthermore, when a convex optical waveguide intersects with a high-frequency signal electrode that propagates a high-frequency electrical signal, unevenness is generated along the cross-sectional shape of the convex waveguide on the upper and lower surfaces of the high-frequency signal electrode on the substrate at the intersection. The high-frequency electrical signal leaks from the edges of these unevennesses through radiation, thereby increasing the signal propagation loss in the high-frequency signal electrode. Especially in optical modulation elements achieving modulation speeds exceeding 100G, the high-frequency electrical signal propagated by the high-frequency signal electrode becomes a microwave frequency signal. Due to the skin effect, it propagates near the surface of the high-frequency signal electrode and is therefore susceptible to adverse effects (propagation loss, etc.) caused by the unevenness of the surface.

[0008] Moreover, these optical losses or signal propagation losses may, for example, create an optical loss difference between the two parallel waveguides constituting a Mach-Zehnder type optical waveguide, thus degrading the extinction ratio of the modulated light. The higher the modulation speed required by the optical modulator, the more stringent the requirements for the extinction ratio become. Therefore, it is expected that this degradation of the extinction ratio will become increasingly pronounced with the increase in transmission capacity and the increase in modulation speed.

[0009] Furthermore, the aforementioned cross-section can also be formed in various optical waveguide elements, such as those using InP or other semiconductors as substrates (not limited to LN substrates) or silicon photonic waveguide devices using Si as substrates. Moreover, such optical waveguide elements can be not only optical modulators using Mach-Zehnder waveguides, but also optical modulators using optical waveguides that form directional couplers or Y-branches, or various other optical waveguide elements such as optical switches.

[0010] Furthermore, as optical waveguide components become more miniaturized, multi-channel, and / or highly integrated, the optical waveguide patterns and electrode patterns become more complex. The increasing number of intersections on the substrate may become a major factor that cannot be ignored, thus limiting the performance of the optical waveguide components.

[0011] As a technique to reduce light absorption loss caused by electrode metal formed on the optical waveguide, it is known to provide a buffer layer containing an inorganic material such as SiO2 on the surface of the substrate on which the optical waveguide is formed, and to form the electrode metal on top of the buffer layer (for example, Patent Document 3). When this structure is applied to an optical waveguide element including a convex optical waveguide, the intersection of the convex optical waveguide and the electrode can be as follows: Figure 14 That's how it's structured.

[0012] Figure 14 This is a cross-sectional view of the substrate 1200 along the length of the high-frequency signal electrode 1206 formed on the substrate 1200. Figure 14 In the middle, the high-frequency signal electrode 1206, for example, is perpendicular to the direction along which the high-frequency signal electrode 1206 is located ( Figure 14 Four convex optical waveguides 1202a, 1202b, 1202c, and 1202d (hereinafter collectively referred to as convex optical waveguides 1202) extending in the direction normal to the paper intersect to form intersection portions 1204a, 1204b, 1204c, and 1204d (hereinafter collectively referred to as intersection portions 1204), respectively. Convex optical waveguides 1202a, 1202b, 1202c, and 1202d each include protrusions 1208a, 1208b, 1208c, and 1208d (hereinafter collectively referred to as protrusions 1208) formed on the surface of the substrate 1200. Furthermore, a buffer layer 1210 containing SiO2 is formed on the substrate 1200 along the shape of the protrusions 1208, and a high-frequency signal electrode 1206 is formed thereon.

[0013] However, even with an inorganic buffer layer 1210 on the substrate 1200, the unevenness of the upper and lower surfaces of the high-frequency signal electrode 1206 at the intersection with the convex waveguide 1202 is not mitigated, making it difficult to reduce signal propagation loss. Alternatively, increasing the thickness of the high-frequency signal electrode 1206 could be considered to alleviate the unevenness of the upper surface caused by the cross-sectional shape of the convex waveguide 1202, but there is a limit to the reduction of the upper surface unevenness within a practical thickness range, and the unevenness of the lower surface of the high-frequency signal electrode 1206 (the surface closest to the convex waveguide 1202) is not completely reduced, thus failing to be a sufficiently effective countermeasure.

[0014] [Existing technical documents]

[0015] [Patent Literature]

[0016] Patent Document 1: Japanese Patent Application Publication No. 2007-264548

[0017] Patent Document 2: International Publication No. 2018 / 031916

[0018] Patent Document 3: Japanese Patent Application Publication No. 2009-181108 Summary of the Invention

[0019] [The problem the invention aims to solve]

[0020] Based on the aforementioned background, in an optical waveguide element having multiple intersections of a convex optical waveguide and electrodes that propagate high-frequency electrical signals, it is required to simultaneously suppress the optical absorption loss of the optical waveguide in the intersections and the signal propagation loss of the high-frequency signal electrodes in order to achieve good operating characteristics.

[0021] [Technical means to solve the problem]

[0022] One embodiment of the present invention is an optical waveguide element comprising: a substrate on which an optical waveguide is formed; and an electrode formed on the substrate and having an intersection portion intersecting the optical waveguide, wherein the optical waveguide element includes protrusions extending on the substrate, and a resin-containing intermediate layer is provided at the intersection portion adjacent to the electrode, which fills the spaces between the protrusions along the electrode and covers the upper portion of the protrusions.

[0023] According to another embodiment of the invention, the intermediate layer is strip-shaped along the electrode when viewed from above.

[0024] According to another embodiment of the invention, the upper surface of the intermediate layer is substantially flat from the upper part of the protrusion closest to the end of the intermediate layer to the end.

[0025] According to another embodiment of the present invention, the thickness of the intermediate layer measured from the upper surface of the protrusion is greater than the height of the protrusion from the surface of the substrate.

[0026] According to another embodiment of the present invention, the intermediate layer comprises multiple layers.

[0027] According to another embodiment of the present invention, the plurality of layers constituting the intermediate layer include a layer and other layers disposed above the layer, the other layers comprising other resins having a higher adhesion to the substrate than a resin constituting the layer.

[0028] According to another embodiment of the present invention, the optical waveguide includes two waveguide groups, each comprising a plurality of optical waveguides adjacent to each other, the electrode and each of the optical waveguides of the two different waveguide groups forming the intersection, and in each of the two waveguide groups, an intermediate layer is provided at the intersection adjacent to the electrode, the intermediate layer of the two waveguide groups being part of a common layer that extends along the electrode to the space between the two waveguide groups and appears as a strip connected together in top view.

[0029] According to another embodiment of the present invention, a buffer layer comprising inorganic material is provided between the intermediate layer and the electrode.

[0030] According to another embodiment of the present invention, a buffer layer comprising inorganic material is provided between the upper surface of the protrusion and the intermediate layer.

[0031] Another embodiment of the present invention is an optical modulator, comprising: any one of the optical waveguide elements, which is an optical modulation element for modulating light; a frame for housing 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 frame.

[0032] Another embodiment of the present invention is an optical modulation module, comprising: any one of the optical waveguide elements, which is an optical modulation element for modulating light; and a driving circuit for driving the optical waveguide element.

[0033] Another embodiment of the present invention is an optical transmitting device, comprising: the optical modulator or the optical modulation module; and electronic circuitry for generating an electrical signal for modulating the optical waveguide element.

[0034] In addition, this specification contains the full contents of Japanese Patent Application / Treasury Application No. 2020-160537, filed on September 25, 2020.

[0035] [The effects of the invention]

[0036] Through this invention, in an optical waveguide element having multiple intersections of a convex optical waveguide and a high-frequency signal electrode for propagating high-frequency electrical signals, the optical absorption loss of the optical waveguide in the intersections and the signal propagation loss of the high-frequency signal electrode can be suppressed simultaneously, thereby achieving good operating characteristics. Attached Figure Description

[0037] Figure 1 This is a diagram showing the structure of the optical modulator according to the first embodiment of the present invention.

[0038] Figure 2 It means Figure 1 A diagram showing the structure of the optical modulation element used in the optical modulator.

[0039] Figure 3 yes Figure 2 A detailed view of part A of the optical modulation element shown.

[0040] Figure 4 yes Figure 3 The plan view of section B is shown.

[0041] Figure 5 yes Figure 4Arrow view of section VV of part B shown.

[0042] Figure 6 yes Figure 5 The first variation of the structure of part B shown.

[0043] Figure 7 yes Figure 5 The second variation of the structure of part B shown.

[0044] Figure 8 yes Figure 5 The third variation of the structure of part B shown.

[0045] Figure 9 yes Figure 5 The fourth variation of the structure of part B shown.

[0046] Figure 10 yes Figure 3 The plan view of section C is shown.

[0047] Figure 11 yes Figure 10 Arrow view of section XI-XI of part C shown.

[0048] Figure 12 This is a diagram showing the structure of the optical modulation module according to the second embodiment of the present invention.

[0049] Figure 13 This is a diagram showing the structure of the optical transmitting device according to the third embodiment of the present invention.

[0050] Figure 14 This is a diagram illustrating an example of the cross-sectional structure of an existing optical waveguide element.

[0051] [Explanation of Symbols]

[0052] 100: Optical modulator

[0053] 102: Frame

[0054] 104: Optical modulation element

[0055] 106: Relay substrate

[0056] 108, 110: Signal pins

[0057] 112: Terminal

[0058] 114: Input fiber optic cable

[0059] 116: Optical Unit

[0060] 118, 130, 134: Lenses

[0061] 120: Output fiber optic cable

[0062] 122, 124: Braces

[0063] 230, 1200: substrate

[0064] 232: Input waveguide

[0065] 234: Branched waveguide

[0066] 240a, 240b: Nested Mach-Zehnder type optical waveguides

[0067] 244a, 244b, 246a, 246b: Mach-Zehnder type optical waveguides

[0068] 244a-1, 244a-2, 244b-1, 244b-2, 246a-1, 246a-2, 246b-1, 246b-2: Parallel waveguides

[0069] 248a, 248b: Output waveguides

[0070] 250a, 250b, 252a, 252b: High-frequency signal electrodes

[0071] 254a, 254b, 256a, 256b, 258a, 258b, 260a, 260b: Padding

[0072] 262, 262a, 262b, 262c: Bias electrodes

[0073] 400, 400-1, 400-2, 800-1, 800-2: Intermediate layer

[0074] 400-2a, 400-2b: End range

[0075] 402a, 402b, 402c, 402d, 702a, 702b, 702c, 702d, 704a, 704b, 704c, 704d, 1204a, 1204b, 1204c, 1204d: Intersection

[0076] 404b-1, 404b-2, 406b-1, 406b-2, 706a, 706a-1, 706a-2, 706a-3, 706a-4 , 706b, 706b-1, 706b-2, 706b-3, 706b-4, 1208a, 1208b, 1208c, 1208d: convex part

[0077] 408a, 408b, 408c, 708a, 708b, 708c, 710a, 710b, 710c: concave portion

[0078] 410a, 410b: Side panels

[0079] 412, 712a, 712b: First layer

[0080] 414, 714a, 714b: Second layer

[0081] 500, 600a, 600b, 600c, 600d: Buffer layers

[0082] 590: Adhesive layer

[0083] 592: Support substrate

[0084] 700a, 700b: Waveguide group

[0085] 810: Shared Layer

[0086] 1000: Optical Modulation Module

[0087] 1006: Circuit board

[0088] 1008: Drive Circuit

[0089] 1100: Optical Transmitting Device

[0090] 1104: Light source

[0091] 1106: Modulator driver unit

[0092] 1108: Modulation signal generation unit

[0093] 1202, 1202a, 1202b, 1202c, 1202d: Convex optical waveguides

[0094] 1206: High-frequency signal electrode

[0095] 1210: Buffer layer Detailed Implementation

[0096] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0097] [1. First Implementation Method]

[0098] Figure 1 This diagram illustrates the structure of an optical modulator 100, which uses an optical modulation element as an optical waveguide element in a first embodiment of the present invention. The optical modulator 100 includes a frame 102, an optical modulation element 104 housed within the frame 102, and a relay substrate 106. The optical modulation element 104 is, for example, a DP-QPSK modulator structure. The frame 102 is finally fixed to its opening with a cover (not shown) that serves as a plate, the interior of which is hermetically sealed.

[0099] Additionally, the optical modulator 100 has: a signal pin 108 for inputting a high-frequency electrical signal used in the modulation of the optical modulator 104; and a signal pin 110 for inputting an electrical signal used in adjusting the operating point of the optical modulator 104.

[0100] Furthermore, on the same side of the housing 102, the optical modulator 100 has an input optical fiber 114 for inputting light into the housing 102 and an output optical fiber 120 for guiding light modulated by the optical modulator element 104 to the outside of the housing 102.

[0101] Here, the input optical fiber 114 and the output optical fiber 120 are fixed to the frame 102 via brackets 122 and 124, which serve as fixing members, respectively. Light input from the input optical fiber 114 is collimated by a lens 130 disposed within the bracket 122 and then input to the optical modulation element 104 via a lens 134. However, this is just one example; the input of light to the optical modulation element 104 can also be performed according to the prior art, for example, by guiding the input optical fiber 114 into the frame 102 via the bracket 122 and connecting the end face of the guided input optical fiber 114 to the end face of the substrate 230 (described later) of the optical modulation element 104.

[0102] Additionally, the optical modulator 100 has an optical unit 116 that polarizes and combines two modulated beams of light output from the optical modulator 104. The polarized and combined light output from the optical unit 116 is focused by a lens 118 disposed within a bracket 124 and coupled to the output optical fiber 120.

[0103] The relay substrate 106 relays the high-frequency electrical signal input from signal pin 108 and the operating point adjustment electrical signal input from signal pin 110 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, for example, to pads (described later) at one end of the electrodes constituting the optical modulator 104 via wire bonding. Furthermore, the optical modulator 100 includes a terminator 112 with a specified impedance within the housing 102.

[0104] Figure 2 It means to be housed in Figure 1This diagram illustrates an example of the structure of the optical modulation element 104 within the frame 102 of the optical modulator 100. The optical modulation element 104 includes an optical waveguide (shown as a bold dashed line in the diagram) formed on a substrate 230, for example, performing 200G DP-QPSK modulation. The substrate 230 is, for example, a thin-film LN substrate with photoelectric effect, processed to a thickness of 20 μm or less (e.g., 2 μm). Furthermore, the optical waveguide is a convex waveguide (e.g., a ribbed or ridged waveguide) with protrusions extending in a strip-like pattern formed on the surface of the thin-film substrate 230. Here, when stress is applied to the LN substrate, the refractive index undergoes localized changes due to the photoelastic effect. Therefore, to enhance the overall mechanical strength of the substrate, it is generally bonded to a support substrate such as a Si (silicon) substrate, a glass substrate, or an LN substrate. In this embodiment, as described later, the substrate 230 is bonded to the support substrate 592 via an adhesive layer 590.

[0105] The substrate 230 is, for example, rectangular, having two opposing sides 280a and 280b extending in the vertical direction as shown in the figure, and two opposing sides 280c and 280d extending in the horizontal direction as shown in the figure, and also facing each other. Furthermore, Figure 2 In the middle, as shown by the coordinate axis in the upper left of the diagram, it will face towards Figure 2 The normal direction inside the paper (from the surface to the back) is defined as the X direction, the right direction in the illustration is defined as the Y direction, and the down direction in the illustration is defined as the Z direction. These coordinate axes correspond, for example, to the crystal axes of the substrate 230, which serves as the LN substrate, namely the X-axis, Y-axis, and Z-axis.

[0106] The optical modulation element 104 includes: an input waveguide 232, located on the upper side of the left edge 280b of the substrate 230 in the illustration, receiving input light from the input optical fiber 114 (arrow pointing to the right in the illustration); and a branch waveguide 234, which branches the input light into two beams of light with the same amount of light. Additionally, the optical modulation element 104 includes so-called nested Mach-Zehnder type optical waveguides 240a and 240b, which serve as two modulation sections for modulating the individual beams branched by the branch waveguide 234.

[0107] Nested Mach-Zehnder type optical waveguides 240a and 240b respectively include two Mach-Zehnder type optical waveguides 244a, 246a and 244b, 246b respectively disposed in the two waveguide sections forming a pair of parallel waveguides. Thus, nested Mach-Zehnder type optical waveguides 240a and 240b fold back the propagation direction of the input light, which is branched into two beams by branch waveguide 234, by 180 degrees and then perform QPSK modulation, and output these modulated lights (outputs) from their respective output waveguides 248a and 248b to the left of the figure.

[0108] Then, the two output beams are polarized and combined into a single beam by the optical unit 116 disposed outside the substrate 230. Hereinafter, the input waveguide 232, branch waveguide 234, and nested Mach-Zehnder type optical waveguides 240a, 240b, and their constituent Mach-Zehnder type optical waveguides 244a, 246a, 244b, and 246b, etc., formed on the substrate 230 of the optical modulation element 104, will also be collectively referred to as optical waveguides 232, etc. As described above, these optical waveguides 232, etc., are convex optical waveguides containing a strip-shaped protrusion extending on the substrate 230.

[0109] On substrate 230, high-frequency signal electrodes 250a, 252a, 250b, and 252b are provided. These electrodes are used to modulate the four Mach-Zehnder waveguides 244a, 246a, 244b, and 246b that constitute nested Mach-Zehnder waveguides 240a and 240b, respectively, and to receive high-frequency electrical signals. Here, the high-frequency electrical signals input to the high-frequency signal electrodes 250a, 252a, 250b, and 252b refer to microwave band electrical signals, specifically electrical signals containing signal components above, for example, the G-band frequency, as defined by the Institute of Electrical and Electronics Engineers (IEEE) standards, specifically above 0.2 GHz.

[0110] The high-frequency signal electrodes 250a, 252a, 250b, and 252b extend to the right edge 280a of the substrate 230 as shown in the illustration, and are connected to pads 258a, 260a, 258b, and 260b. Additionally, the high-frequency signal electrodes 250a, 252a, 250b, and 252b bend downwards from the left edge of the substrate 230 as shown in the illustration and extend to the edge 280d of the substrate 230, and are connected to pads 254a, 256a, 254b, and 256b.

[0111] Furthermore, according to the prior art, the high-frequency signal electrode 250a, high-frequency signal electrode 252b, high-frequency signal electrode 250b, and high-frequency signal electrode 252b together with the ground conductor pattern (not shown) formed on the substrate 230 constitute a coplanar transmission line having, for example, a specified impedance. The ground conductor pattern is provided, for example, not formed on the optical waveguide 232, etc., and the multiple regions formed by the optical waveguide 232, etc., in the ground conductor pattern can be interconnected, for example, by wire bonding.

[0112] Pads 258a, 260a, 258b, and 260b, located on the right side of edge 280a in the figure, are connected to the relay board 106 via lead bonding or the like. Additionally, pads 254a, 256a, 254b, and 256b, located on the lower side of edge 280d in the figure, are connected to the four terminating resistors (not shown) constituting the terminator 112. Thus, the high-frequency electrical signal input from signal pin 108 via relay substrate 106 to pads 258a, 260a, 258b, and 260b becomes a traveling wave, which propagates in high-frequency signal electrodes 250a, 252a, 250b, and 252b, modulating the light waves propagating in Mach-Zehnder type optical waveguides 244a, 246a, 244b, and 246b respectively.

[0113] Here, in order to further enhance the interaction between the electric field formed within the substrate 230 by the high-frequency signal electrodes 250a, 252a, 250b, and 252b and the waveguide light propagating in the Mach-Zehnder type optical waveguides 244a, 246a, 244b, and 246b, thereby enabling high-speed modulation at a lower voltage, the substrate 230 is formed with a thickness of 20 μm or less, preferably 10 μm or less. In this embodiment, for example, the thickness of the substrate 230 is 1.2 μm, and the height of the protrusions constituting the optical waveguide 232, etc., is 0.8 μm. Furthermore, the back surface of the substrate 230 (and...) Figure 2 The facing surfaces shown are bonded to a support substrate such as glass via an adhesive layer. Figure 2 Not illustrated in the text; will be discussed later. Figure 5 (As described in the document, it is an adhesive layer 590 and a support substrate 592).

[0114] Additionally, the optical modulation element 104 is provided with bias electrodes 262a, 262b, and 262c to adjust the operating point by compensating for bias point variations caused by so-called DC drift. Bias electrode 262a is used to compensate for bias point variations in nested Mach-Zehnder waveguides 240a and 240b. Furthermore, bias electrodes 262b and 262c are used to compensate for bias point variations in Mach-Zehnder waveguides 244a, 246a, 244b, and 246b, respectively.

[0115] These bias electrodes 262a, 262b, and 262c extend to the upper edge 280c of the substrate 230 as shown in the figure, and are connected to any of the signal pins 110 via the relay substrate 106. The corresponding signal pins 110 are connected to a bias control circuit located outside the frame 102. Thus, the bias control circuit drives the bias electrodes 262a, 262b, and 262c to adjust the operating point in a manner that compensates for variations in the bias point of each corresponding Mach-Zehnder waveguide. Hereinafter, the high-frequency signal electrodes 250a, 252a, 250b, and 252b will be collectively referred to as high-frequency signal electrode 250a, etc. Furthermore, the bias electrodes 262a, 262b, and 262c will be collectively referred to as bias electrode 262.

[0116] The bias electrode 262 is an electrode to which a DC or low-frequency electrical signal is applied. For example, when the thickness of the substrate 230 is 20 μm, it is formed with a thickness ranging from 0.3 μm to 5 μm. In contrast, the high-frequency signal electrodes 250a, 252b, and 252b are formed with a thickness ranging from 20 μm to 40 μm to reduce conductor loss of the applied high-frequency electrical signal. Furthermore, in order to set the impedance or microwave effective refractive index to a desired value, the thickness of the high-frequency signal electrodes 250a, etc., can be determined according to the thickness of the substrate 230; it can be made thicker when the substrate 230 is thicker, and thinner when the substrate 230 is thinner.

[0117] The optical modulation element 104, configured as described above, includes multiple intersections where a high-frequency signal electrode 250a or a bias electrode 262 crosses (traverses) an optical waveguide 232 or the like. According to... Figure 2 The records are easy to understand. Figure 2The portions where the thick dashed lines representing optical waveguides 232, etc., intersect with the strip-shaped portions representing high-frequency signal electrodes 250a, etc., or bias electrodes 262, are all intersections where the high-frequency signal electrodes 250a, etc., or bias electrodes 262 intersect on the optical waveguides 232, etc. In this embodiment, the optical modulation element 104 includes a total of 61 intersections between the optical waveguides 232, etc., and the high-frequency signal electrodes 250a, etc.

[0118] Figure 3 yes Figure 2 A detailed view of part A of the optical modulation element 104 shown.

[0119] The following is taken as Figure 3 Taking sections B and C of the intersection as examples, the structure of these intersections will be explained. Here, as... Figure 3 As shown, the Mach-Zehnder type optical waveguide 244a includes two parallel waveguides 244a-1 and 244a-2, and the Mach-Zehnder type optical waveguide 246a includes two parallel waveguides 246a-1 and 246a-2. Additionally, the Mach-Zehnder type optical waveguide 244b includes two parallel waveguides 244b-1 and 244b-2, and the Mach-Zehnder type optical waveguide 246b includes two parallel waveguides 246b-1 and 246b-2. Furthermore, parallel waveguides 244a-1, 244a-2, 246a-1, 246a-2, 244b-1, 244b-2, 246b-1, and 246b-2 are also configured as convex optical waveguides.

[0120] [1-1. Structure of Part B]

[0121] First, regarding the first structural example as the intersection part, Figure 3 The structure of part B shown will be explained. Figure 4 and Figure 5 This is a partially detailed diagram showing the structure of section B, where the high-frequency signal electrode 252b intersects with parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2. Here, Figure 4 This is the floor plan of Section B. Figure 5 yes Figure 4 Arrow view of section VV of part B shown.

[0122] also, Figure 4 , Figure 5 The structure shown is an example of the structure of the part where the optical waveguide 232 and the high-frequency signal electrode 250a intersect in the optical modulation element 104, and can also be used in any part other than part B where the optical waveguide 232 and the high-frequency signal electrode 250a intersect.

[0123] The high-frequency signal electrode 252b intersects on parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 to form intersections 402a, 402b, 402c, and 402d, respectively. For example... Figure 5 As shown, parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 are convex optical waveguides containing convex portions 404b-1, 404b-2, 406b-1, and 406b-2, respectively. Furthermore, in Figure 5 In the diagram, the ellipses of dashed lines depicting the cross-sections of parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 schematically represent guided light propagating in these parallel waveguides. Figures 6 to 9 and Figure 11 Similarly, the waveguide light is represented by a dashed ellipse.

[0124] also, Figure 5 In this configuration, substrate 230 is fixed to support substrate 592 via adhesive layer 590. Here, adhesive layer 590 is made of, for example, thermosetting resin, and support substrate 592 includes, for example, glass substrate, LN substrate, Si substrate, etc.

[0125] In particular, in this embodiment, such as Figure 5 As shown, an intermediate layer 400 (shown in the figure) containing resin is formed along the intersections 402a, 402b, 402c, and 402d adjacent to the high-frequency signal electrode 252b, and between these intersections, in a manner that fills between protrusions 404b-1, 404b-2, 406b-1, and 406b-2 along the high-frequency signal electrode 252b and covers the upper part of these protrusions. The resin constituting the intermediate layer 400 may be a resin that is applied to the substrate 230 in a viscous liquid state and then cured, such as a photoresist. Furthermore, in this embodiment, the intermediate layer 400 extends to the left side portion 410a of the protrusion 404b-1 located at the left end of the figure, and the right side portion 410b of the protrusion 406b-2 located at the right end of the figure.

[0126] In part B of the optical modulation element 104 having the aforementioned structure, an intermediate layer 400 is formed by embedding recesses 408a, 408b, and 408c formed between protrusions 404b-1, 404b-2, 406b-1, and 406b-2 of adjacent intersections 402a, 402b, 402c, and 402d along the high-frequency signal electrode 252b. This suppresses the generation of unevenness on the lower surface (the surface on the substrate 230 side) and upper surface of the high-frequency signal electrode 252b formed thereon. Consequently, in part B of the optical modulation element 104, signal propagation losses such as radiation loss caused by the unevenness of the high-frequency signal electrode 252b can be suppressed in the intersections 402a, 402b, 402c, and 402d.

[0127] Furthermore, in part B of the optical modulation element 104, the intermediate layer 400 is formed in such a way that it covers the upper parts of the protrusions 404b-1, 404b-2, 406b-1, and 406b-2. Therefore, the light absorption loss caused by the presence of the high-frequency signal electrode 252b in the parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 formed by these protrusions can also be suppressed.

[0128] Therefore, in the optical modulation element 104, by applying the same structure as part B in other intersections, the optical absorption loss of the optical waveguides and the signal propagation loss of the high-frequency signal electrodes in these intersections can be suppressed simultaneously, so as to achieve good optical modulation characteristics.

[0129] Here, the thickness of the intermediate layer 400, measured from the upper surfaces of protrusions 404b-1, 404b-2, 406b-1, and 406b-2, can be set to a thickness that, while improving the flatness of the upper surface of the intermediate layer 400 and suppressing signal propagation losses caused by radiation losses in the high-frequency signal electrode 252b, also suppresses light absorption losses in the parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2, and is as thin as possible. This allows for the suppression of the amount of resin remaining on the substrate 230 while maintaining good electrical and optical properties, thereby reducing the amount of gas released from the resin after the frame 102 is hermetically sealed.

[0130] In particular, in this embodiment, the intermediate layer 400 contains, for example, a resin such as a photoresist. Therefore, by adjusting the viscosity of the resin before hardening, the flatness of the resin surface when filling the recesses 408a, 408b, and 408c, and / or the adhesion of the resin in the side portions 410a and 410b can be easily adjusted.

[0131] As an example, the intermediate layer 400 can be formed by applying a photoresist with a viscosity of 100 cP or less to the surface of the substrate 230 on which the optical waveguide 232 is formed, to a desired thickness covering the upper part of the protrusions 404b-1, etc., using a spin coater, and removing the photoresist from the portion other than where the high-frequency signal electrode 252b is formed by conventional photolithography. By adjusting the rotation speed of the spin coater during coating, the photoresist remains thick in the recesses 408a, 408b, and 408c due to its viscosity and surface tension, and is coated thinly away from the side portions 410a and 410b.

[0132] In this embodiment, the intermediate layer 400 is formed in a strip shape when viewed from above along the high-frequency signal electrode 252b (see reference). Figure 4 By forming the intermediate layer 400 as a strip along the high-frequency signal electrode 252b, the amount of resin remaining on the substrate 230 can be suppressed, thereby reducing the amount of gas released from the resin after the frame 102 is hermetically sealed, thus enabling stable long-term operation as an optical modulator.

[0133] Next, a modified example of part B of the optical modulation element 104 will be described.

[0134] [1-1-1. First variation of the structure of part B]

[0135] First, we will explain the first variation of the structure in part B. Figure 6 This is a diagram showing the structure of part B in the first modified example, and it is equivalent to showing... Figure 4 VV section diagram in Figure 5 The image. Furthermore, in Figure 6 In China, for the sake of Figure 5 The constituent elements shown are the same as those used in the diagram. Figure 5 The same symbol as the one in the text, and references the one described. Figure 5 Related explanations.

[0136] Figure 6 The structure of part B shown is similar to Figure 5 The structure shown is the same, but the difference is that an intermediate layer 400-1 is used instead of intermediate layer 400. Intermediate layer 400-1 has the same structure as intermediate layer 400, but the difference is that it includes three first layers 412 that respectively fill the recesses 408a, 408b, and 408c, and a second layer 414 located on the upper part of the first layer 412 and on the upper part of the protrusions 404b-1, 404b-2, 406b-1, and 406b-2.

[0137] Here, the first layer 412 and the second layer 414, like the intermediate layer 400, are resins that are applied to the substrate 230 in a viscous liquid state and then cured, such as photoresist. The resins constituting the first layer 412 and the second layer 414 can be resins with different adhesion when applied to the substrate 230. For example, the second layer 414 may contain other resins with higher adhesion when applied to the substrate 230 than a resin constituting the first layer 412.

[0138] Therefore, in Figure 6 In the structure of part B shown, for example, by using a first layer 412 with low viscosity and good wettability during coating to fill the recesses 408a, 408b, and 408c without gaps and then hardening it, a second layer 414 with higher viscosity and surface tension during coating is applied. Figure 5 Compared to the structure shown, the flatness of the upper surface of the second layer 414 can be improved.

[0139] Therefore, in Figure 6 In the structure of part B shown, with Figure 5 Compared to the structure shown, the height (or depth) of the unevenness on the upper and lower surfaces of the high-frequency signal electrode 252b generated in the intersections 402a, 402b, 402c, and 402d can be further reduced. As a result, signal propagation losses such as radiation loss in the high-frequency signal electrode 252b caused by the unevenness can be further suppressed, thereby achieving better optical modulation operation.

[0140] Figure 6 The structure shown, for example, is characterized by high heights of protrusions 404b-1, 404b-2, 406b-1, and 406b-2, or by wide spacing between these protrusions. Figure 5 The single-layer intermediate layer 400 shown is effective in mitigating the unevenness of the lower surface of the high-frequency signal electrode 252b when it is insufficient. Additionally, Figure 6 The structure shown is effective, for example, in cases where light absorption loss occurs because the resin cannot be coated with sufficient thickness between the upper surfaces of the protrusions 404b-1, 404b-2, 406b-1, and 406b-2 and the lower surface of the high-frequency signal electrode 252b, or where the resulting light absorption loss causes manufacturing deviations.

[0141] Figure 6 The intermediate layer 400-1 of the illustrated double-layer structure can be formed as follows. First, for example, using the... Figure 5Using the same method as the intermediate layer 400, a resin with a viscosity of, for example, about 100 cP is coated onto the substrate 230, and then cured and patterned to form a first layer 412. Then, a resin with a viscosity higher than that of the first layer 412 (for example, a viscosity of 200 cP or more) is coated onto the substrate 230, and then cured and patterned to form a second layer 414.

[0142] Furthermore, the first layer 412 only needs to be formed to approximately fill the recesses 408a, 408b, and 408c, and its thickness can be either thicker or thinner than the heights of the protrusions 404b-1, 404b-2, 406b-1, and 406b-2. That is, the first layer 412 can be as follows: Figure 6 As shown, it may not be formed on the upper surfaces of protrusions 404b-1, 404b-2, 406b-1, and 406b-2, but it may also be formed on the upper surfaces of these protrusions.

[0143] The viscosity of the resins constituting the first layer 412 and the second layer 414 during coating, as well as the rotation speed of the spin coater, can be adjusted to achieve the desired flatness of the upper surface of the second layer 414 while minimizing the overall thickness of the intermediate layer 400-1. This reduces the amount of resin remaining on the substrate 230, reduces the amount of gas generated from the resin after the frame 102 becomes airtight, and ensures high long-term reliability as the optical modulator 100.

[0144] [1-1-2. Second variation of the structure of part B]

[0145] Next, a second variation of the structure in section B will be explained. Figure 7 This is a diagram showing the structure of part B in the second variation, and it is equivalent to showing... Figure 4 VV section diagram in Figure 5 The image. Furthermore, in Figure 7 In China, for the sake of Figure 5 The same constituent elements shown are used as the constituent elements. Figure 5 The same symbol as the one in the text, and references the one described. Figure 5 Related explanations.

[0146] Figure 7 The structure of part B shown is similar to Figure 5The structure shown is the same, but the difference is that an intermediate layer 400-2 is used instead of intermediate layer 400. Intermediate layer 400-2 has the same structure as intermediate layer 400, but the upper surface of intermediate layer 400-2 includes a non-buckling surface (e.g., a generally flat surface) in the range from the upper part of the protrusions 404b-1 and 406b-2 closest to the left and right ends of the intermediate layer 400-2 in the illustration to the end range closest to them (end range 400-2a and end range 400-2b in the illustration).

[0147] Generally, electrodes formed over a step on the substrate will experience signal propagation loss at the step portion. In contrast, in Figure 7 In the structure of section B shown, the end regions 400-2a and 400-2b of the intermediate layer 400-2 include non-buckling surfaces (e.g., generally flat surfaces), thus reducing the radiation loss of electrical signals in the high-frequency signal electrodes 252b formed in the end regions 400-2a and 400-2b, thereby reducing signal propagation loss. Therefore, in Figure 7 In the structure shown, with Figure 5 and Figure 6 Compared to the structure shown, the thickness of the intermediate layer 400-2 can be increased while suppressing signal propagation loss, so as to further suppress the generation of unevenness in the upper surface of the intermediate layer 400-2 or the lower surface of the high-frequency signal electrode 252b caused by the presence of protrusions 404b-1, 404b-2, 406b-1, and 406b-2.

[0148] From the viewpoint of reducing the unevenness generated on the upper surface of the intermediate layer 400-2 due to the presence of protrusions 404b-1, 404b-2, 406b-1, and 406b-2, and thus reducing signal propagation losses such as radiation loss in the high-frequency signal electrode 252b, it is ideal that the thickness d1 of the intermediate layer 400-2, measured from the upper surface of protrusions 404b-1, 404b-2, 406b-1, and 406b-2, is greater than the value of the height t1 of these protrusions measured from the surface of the substrate 230 (i.e., d1>t1).

[0149] This thick intermediate layer 400-2 can be easily formed, for example, using a resist with a relatively high viscosity (e.g., above 200 cP) when coated onto the substrate 230. Furthermore, the non-buckling (e.g., generally flat) upper surface of the intermediate layer 400-2 in the end ranges 400-2a and 400-2b can be formed by heat treatment at a relatively high temperature (e.g., 200°C) and / or a fast heating rate (e.g., 5°C / min) of 1°C or higher after hardening and patterning the coated resist, or by plasma ashing.

[0150] Furthermore, regarding the length w2 of the end range 400-2b, it is ideally greater than the sum of the width w1 of the protrusion 406b-2 closest to the end range 400-2b, and the distance k1 between the protrusion 406b-2 and its adjacent protrusion 406b-1 (and therefore the width of the recess 408c) (i.e., w2 > w1 + k1). The same applies to the length of the end range 400-2a. This suppresses sharp oscillations in the vertical direction of the surface of the substrate 230 of the electrical signal propagating in the high-frequency signal electrode 252b, thereby further reducing signal propagation losses such as radiation loss.

[0151] about Figure 7 The structure shown allows for easy formation of an intermediate layer 400-1 from a single thick layer, even when multiple optical waveguides 232 are close together and the protrusions constituting these waveguides 232 are arranged close together. This reduces light absorption loss and signal propagation loss, thus offering advantages in terms of manufacturing process and yield.

[0152] [1-2-3. The third variation of the structure of part B]

[0153] Next, the third variation of the structure in Part B will be explained. Figure 8 This is a diagram showing the structure of part B in the third variation, and it is equivalent to showing... Figure 4 VV section diagram in Figure 5 The image. Furthermore, in Figure 8 In China, for the sake of Figure 5 The same constituent elements shown are used as the constituent elements. Figure 5 The same symbol as the one in the text, and references the one described. Figure 5 Related explanations.

[0154] Figure 8 The structure of part B shown is similar to Figure 5 The structure shown is the same, but the difference is that a buffer layer 500 containing inorganic material is formed between the intermediate layer 400 and the high-frequency signal electrode 252b. In this modified example, the inorganic material constituting the buffer layer 500 is, for example, SiO2.

[0155] exist Figure 8 In the structure shown, a buffer layer 500 containing inorganic material is formed between the protrusions 404b-1, 404b-2, 406b-1, and 406b-2 constituting parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 and the high-frequency signal electrode 252b. Therefore, the electrical and / or optical properties of the inorganic material can be utilized to improve the characteristics of the optical modulation element 104 or increase the degree of design freedom.

[0156] For example, in the optical modulation element 104 of this embodiment using a substrate 230 containing LN, the buffer layer 500 is constructed using SiO2, which has high electrical insulation properties, as the inorganic material. This is suitable for designs requiring higher withstand voltage characteristics, such as those with narrow electrode spacing and applied high electric fields. Furthermore, since the dielectric constant of SiO2 is lower than that of LN constituting the substrate 230, by using SiO2 to form the buffer layer 500, the speed of light waves propagating in parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2, or the speed of high-frequency electrical signals propagating in the high-frequency signal electrode 252b, can be adjusted, thereby increasing the design freedom of the high-frequency signal electrode 252b.

[0157] [1-1-4. Fourth variation of the structure of part B]

[0158] Next, the fourth variation of the structure in Part B will be explained. Figure 9 This is a diagram showing the structure of part B in the fourth variation, and it is equivalent to showing... Figure 4 VV section diagram in Figure 5 The image. Furthermore, in Figure 9 In China, for the sake of Figure 5 and Figure 6 The same constituent elements shown are used as the constituent elements. Figure 5 and Figure 6 The same symbol as the one in the text, and references the one described. Figure 5 and Figure 6 Related explanations.

[0159] Figure 9 The structure of part B shown is similar to Figure 6 The structures shown are the same, but the difference lies in that buffer layers 600a, 600b, 600c, and 600d, containing inorganic materials, are formed between the upper surfaces of protrusions 404b-1, 404b-2, 406b-1, and 406b-2 and the intermediate layer 400-1. In this modified example, the inorganic material constituting buffer layers 600a, 600b, 600c, and 600d is SiO2.

[0160] exist Figure 9 The structure shown includes buffer layers 600a, 600b, 600c, and 600d, each containing inorganic materials, thus... Figure 8 Similarly, in the third variation shown, the electrical and / or optical properties of the inorganic material can be utilized to improve the properties of the optical modulation element 104 or increase the degree of design freedom.

[0161] Especially in Figure 9 In the structure shown, a buffer layer 500 is provided on the entire upper part of the intermediate layer 400. Figure 8 The structures shown differ, except that buffer layers 600a, 600b, 600c, and 600d are formed only on the upper parts of protrusions 404b-1, 404b-2, 406b-1, and 406b-2. Therefore, in Figure 9 In the structure shown, with Figure 8 Compared to other structures, this structure can suppress the stress applied to the substrate 230 from highly rigid inorganic materials (e.g., SiO2), thereby reducing the degradation of the extinction ratio in the nested Mach-Zehnder waveguides 240a, 240b, 244a, 246a, 244b, and 246b caused by deformation of the optical modulation element 104 or uneven stress on the substrate 230.

[0162] [1-2. Structure of Part C]

[0163] Subsequently, regarding the second structural example as the intersection, Figure 3 The structure of section C shown will be explained. Figure 10 This is the floor plan of section C. Figure 11 yes Figure 10 The arrow view of section XI-XI. Waveguide group 700a, which includes four parallel waveguides 244a-1, 244a-2, 246a-1, and 246a-2 that are adjacent to each other, and waveguide group 700b, which includes four parallel waveguides 244b-1, 244b-2, 246b-1, and 246b-2 that are adjacent to each other, are formed in part C to serve as optical waveguide 232, etc.

[0164] Here, parallel waveguides 244a-1, 244a-2, 246a-1, 246a-2, 244b-1, 244b-2, 246b-1, and 246b-2 are all convex optical waveguides, and each contains convex portions 706a-1, 706a-2, 706a-3, 706a-4, 706b-1, 706b-2, 706b-3, and 706b-4, respectively. Hereinafter, convex portions 706a-1, 706a-2, 706a-3, and 706a-4 will be collectively referred to as convex portion 706a, and convex portions 706b-1, 706b-2, 706b-3, and 706b-4 will be collectively referred to as convex portion 706b.

[0165] In addition, in section C, the high-frequency signal electrode 250b and the parallel waveguides 244a-1, 244a-2, 246a-1, 246a-2 and 244b-1, 244b-2, 246b-1, 246b-2, and 246b-2 belonging to two different waveguide groups 700a and 700b constitute cross-sections 702a, 702b, 702c, 702d and 704a, 704b, 704c, and 704d. Hereinafter, cross-sections 702a, 702b, 702c, and 702d will be collectively referred to as cross-section 702, and cross-sections 704a, 704b, 704c, and 704d will be collectively referred to as cross-section 704.

[0166] In addition, in section C, in waveguide group 700a, there is an intermediate layer 800-1 between the protrusions 706a of the intersection 702 adjacent to the high-frequency signal electrode 250b and above the protrusions 706a; and in waveguide group 700b, there is an intermediate layer 800-2 between the protrusions 706b of the intersection 704 adjacent to the high-frequency signal electrode 250b and above the protrusions 706b.

[0167] Furthermore, in section C, the intermediate layers 800-1 and 800-2 of the two waveguide groups 700a and 700b respectively are composed of a common layer that extends in a strip shape when viewed from above along the high-frequency signal electrode 250b.

[0168] Specifically, intermediate layers 800-1 and 800-2 have the same characteristics as... Figure 6 The structure is the same as the first variation of part B shown. That is, the intermediate layer 800-1 includes three first layers 712a that are respectively filled between three recesses 708a, 708b, and 708c formed between four adjacent protrusions 706a, and a second layer 714a located on the upper part of the first layer 712a and the upper part of the four protrusions 706a. Similarly, the intermediate layer 800-2 includes three first layers 712b that are respectively filled between three recesses 710a, 710b, and 710c formed between four adjacent protrusions 706b, and a second layer 714b located on the upper part of the first layer 712b and the upper part of the four protrusions 706b.

[0169] And, as Figure 10 , Figure 11 As shown, the second layer 714a of intermediate layer 800-1 and the second layer 714b of intermediate layer 800-2 are formed as part of a common layer 810 that extends along the high-frequency signal electrode 250b to the space between the two waveguide groups 700a and 700b and appears as a strip when viewed from above.

[0170] The second layer 714a and the second layer 714b of the C portion having the aforementioned structure are formed as part of a common layer 810, which extends between the two waveguide groups 700a and 700b. Therefore, the lower surface of the high-frequency signal electrode 250b will not drop to the surface of the substrate 230 at the position between the waveguide group 700a and the waveguide group 700b, and can maintain a height that is approximately the same as the height of the protrusions 706a and 706b.

[0171] Therefore, in the structure of section C, the up-and-down (normal direction of the surface of the substrate 230) oscillation of the high-frequency electrical signal propagating in the high-frequency signal electrode 250b can also be suppressed between the two waveguide groups 700a and 700b (i.e., between parallel waveguide 246a-2 and parallel waveguide 244b-1), thereby further suppressing signal propagation loss caused by radiation loss, etc.

[0172] [2. Second Implementation]

[0173] Next, a second embodiment of the present invention will be described. This embodiment is an optical modulation module 1000, which uses the optical modulation element 104 included in the optical modulator 100 of the first embodiment. Figure 12 This is a diagram showing the structure of the optical modulation module 1000 in this embodiment. Figure 12 In China, for the sake of Figure 1 The optical modulator 100 of the first embodiment shown has the same constituent elements as the one shown, and uses the same... Figure 1 The same symbols as those shown are used to represent and reference the symbols described. Figure 1 Related explanations.

[0174] The optical modulation module 1000 has the same characteristics as... Figure 1 The optical modulator 100 shown has the same structure, but differs from the optical modulator 100 in that it includes a circuit board 1006 instead of a relay board 106. The circuit board 1006 includes a driving circuit 1008. The driving circuit 1008 generates a high-frequency electrical signal to drive the optical modulator 104 based on a modulation signal supplied from the outside via signal pin 108, and outputs the generated high-frequency electrical signal to the optical modulator 104.

[0175] The optical modulation module 1000 having the aforementioned structure, like the optical modulator 100 of the first embodiment, includes a portion in which the optical waveguide 232, etc., intersects with the high-frequency signal electrode 250a, etc. Figures 4 to 11 The optical modulation element 104 has the structure shown. Therefore, in the optical modulation module 1000, similar to the optical modulator 100, the optical absorption loss of the optical waveguide 232 and the signal propagation loss of the high-frequency signal electrode 250a in the cross section can be suppressed at the same time, thereby achieving good operating characteristics.

[0176] [Third Implementation Method]

[0177] Next, a third embodiment of the present invention will be described. This embodiment is an optical transmitting device 1100 equipped with the optical modulator 100 of the first embodiment. Figure 13 This diagram illustrates the structure of the optical transmitting apparatus 1100 according to this embodiment. The optical transmitting apparatus 1100 includes an optical modulator 100, a light source 1104 that incident light onto the optical modulator 100, a modulator driving unit 1106, and a modulation signal generation unit 1108. Alternatively, the optical modulation module 1000 may be used instead of the optical modulator 100 and the modulator driving unit 1106.

[0178] The modulation signal generation unit 1108 is an electronic circuit that generates an electrical signal for causing the optical modulator 100 to perform modulation operations. 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 optical modulation operations according to the modulation data, and outputs it to the modulator drive unit 1106.

[0179] The modulator drive unit 1106 amplifies the modulation signal input from the modulation signal generation unit 1108 and outputs four high-frequency electrical signals for driving the four high-frequency signal electrodes 250a, 252a, 250b, and 252b of the optical modulation element 104 included in the optical modulator 100. Alternatively, as described above, an optical modulation module 1000 can be used instead of the optical modulator 100 and the modulator drive unit 1106. The optical modulation module 1000 includes, for example, a drive circuit 1008 containing circuitry equivalent to the modulator drive unit 1106 inside the housing 102.

[0180] The four high-frequency electrical signals are input to the signal pins 108 of the optical modulator 100, driving 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, by DP-QPSK, becoming modulated light and output from the optical transmitting device 1100.

[0181] In particular, in the optical transmitting device 1100, similar to the optical modulator 100 of the first embodiment, a device including [missing information] is used in the portion where the optical waveguide 232, etc., intersects with the high-frequency signal electrode 250a, etc. Figures 4 to 11 The optical modulator 100 or optical modulator module 1000 with the optical modulation element 104 shown in the diagram can achieve good modulation characteristics, thereby enabling good optical transmission.

[0182] Furthermore, the present invention is not limited to the structure of the described embodiments and its alternative structures, and may be implemented in various embodiments without departing from its spirit.

[0183] For example, in the first embodiment, with Figure 3 The structure of the intersection between the high-frequency signal electrode 250a and the optical waveguide 232, etc., shown in sections B and C, has been explained using examples. Figures 4 to 11 The structure shown is not limited to parts B and C, but can also be applied to any intersection of high-frequency signal electrode 250a and optical waveguide 232.

[0184] Furthermore, in the first embodiment, it is provided that a high-frequency signal electrode 250a, etc., on which a high-frequency electrical signal is input, and an optical waveguide 232, etc., are present at the intersection. Figures 4 to 11 The structures shown are not limited to high-frequency signal electrodes 250a, etc. For example, when a high-frequency signal such as a jitter signal is applied to the bias electrode 262, the intersections of these bias electrodes 262 and the optical waveguide 232, etc., are also used. Figures 4 to 11 The structure shown reduces light absorption loss and signal propagation loss.

[0185] In addition, Figure 6 In the first modified example of part B shown, the intermediate layer 400-1 is configured to include two layers, a first layer 412 and a second layer 414. The intermediate layer can be configured to include any number of multiple layers. In this case, from the viewpoint of reducing the unevenness of the electrode surface, it is ideal that the layers further away from the substrate 230 contain a resin with a higher viscosity during coating.

[0186] Additionally, as will be readily understood by those skilled in the art, it can be configured to... Figures 4 to 11 The characteristic parts of the structure shown are combined and applied to the intersection of the optical waveguide 232, etc., with any of the high-frequency signal electrode 250a, etc., and / or the bias electrode 262. For example, it can also be used in... Figure 6 Combination in structure Figure 8 or Figure 9 The structure forms a buffer layer containing SiO2 on the upper part of the second layer 414 of the intermediate layer 400-1 or on the upper part of the protrusion 404b-1, etc.

[0187] Alternatively, it can also be in Figure 6 Combination in structure Figure 7 The structure, such as the intermediate layer 400-2, forms a second layer 414 in such a way that the portions corresponding to the end ranges 400-2a and 400-2b do not contain buckled surfaces, and the second layer 414 is formed after the first layer 412 is formed.

[0188] Alternatively, it can also be in Figure 10 and Figure 11 In the structure shown, intermediate layer 800-1 and / or intermediate layer 800-2 are configured to be... Figure 5 The middle layer 400 or Figure 7The intermediate layer 400-2 has the same structure, and therefore, it can also be set as follows: Figure 8 A buffer layer 500 as shown or such Figure 9 Buffer layers such as 600a are shown.

[0189] In addition, as an example of an optical waveguide element described above, an optical modulation element 104 formed using a substrate 230 of LN (LiNbO3) is shown. However, it is not limited to this. The optical waveguide element can be configured as an element with arbitrary functions (such as optical switching, optical directional couplers, etc., in addition to optical modulation) made of a substrate of any material (such as InP, Si, etc., besides LN). Such an element can be, for example, a so-called silicon photonic waveguide device.

[0190] Furthermore, in the described embodiment, as an example, the substrate 230 is an X-cut LN substrate (so-called an X-plate) with the substrate normal direction being the X-axis of the crystal axis, but a Z-cut LN substrate can also be used as the substrate 230. In both the X-cut and Z-cut LN substrates, because the directions of the electric fields applied to the Mach-Zehnder waveguides 244a, 244b, 246a, and 246b are different, the arrangement of the high-frequency signal electrodes formed along these Mach-Zehnder waveguides 244a, 244b, 246a, and 246b can differ from that of the high-frequency signal electrodes 250a, 250b, 252a, and 252b in the described embodiment. However, even when the substrate 230 is a Z-cut LN substrate, the intersection of the high-frequency signal electrode and the waveguide 232, etc., can be different. Figures 4 to 11 It is constructed in the same way.

[0191] As explained above, the optical modulation element 104, which constitutes the optical waveguide element of the optical modulator 100 of the first embodiment, includes, for example, a substrate 230 on which parallel waveguides 244b-1 are formed; and a high-frequency signal electrode 252b, which is an electrode formed on the substrate 230 and has a cross portion 402a or the like that intersecting the parallel waveguides 244b-1. The parallel waveguides 244b-1 include protrusions 404b-1 extending on the substrate 230, and have an intermediate layer 400 containing resin at the cross portion 402a or the like adjacent to the high-frequency signal electrode 252b, which fills between the protrusions 404b-1 and the like along the high-frequency signal electrode 252b and covers the upper part of the protrusions 404b-1.

[0192] According to the structure, in an optical waveguide element having multiple intersections of a convex optical waveguide and an electrode for propagating high-frequency electrical signals, the optical absorption loss of the optical waveguide in the intersection and the signal propagation loss of the high-frequency signal electrode can be suppressed simultaneously, thereby achieving good operating characteristics.

[0193] Furthermore, in the optical modulation element 104, the intermediate layer 400 appears as a strip along the high-frequency signal electrode 252b when viewed from above. This structure suppresses the amount of resin remaining on the substrate 230, thus reducing the amount of gas released from the resin after the frame 102 is hermetically sealed, thereby achieving stable long-term operation as an optical modulator.

[0194] Furthermore, in the optical modulation element 104, as with the intermediate layer 400-2, the upper surface of the intermediate layer is formed by a non-buckling surface (e.g., a generally flat surface) in a range from the upper part of the protrusion closest to the end of the intermediate layer to the end (e.g., end range 400-2a and / or end range 400-2b). This structure reduces the radiation loss of the electrical signal in the high-frequency signal electrode 252b formed in the end ranges 400-2a and 400-2b, thereby reducing signal propagation loss. Additionally, since the thickness of the intermediate layer 400-2 can be increased while suppressing signal propagation loss, the generation of unevenness in the upper surface of the intermediate layer 400-2 and the lower surface of the high-frequency signal electrode 252b caused by the presence of the protrusion can be further suppressed.

[0195] Furthermore, regarding the intermediate layer 400-2, for example, the thickness d1 measured from the upper surface of the protrusion 406b-2 is greater than the value t1 of the height of the protrusion 406b-2 from the surface of the substrate 230. This structure effectively suppresses the generation of unevenness on the upper surface of the intermediate layer 400-2 or the lower surface of the high-frequency signal electrode 252b.

[0196] Additionally, for example, intermediate layer 400-1 comprises multiple layers (e.g., first layer 412 and second layer 414). Intermediate layer 400-1 also includes a first layer 412 and a second layer 414 disposed above the first layer 412. The second layer 414 comprises other resins whose adhesion to the substrate 230 during coating is higher than that of a resin constituting the first layer 412. Based on these structures, by utilizing the first layer 412, which has low adhesion and good wettability during coating, to seamlessly fill the recesses 408a, 408b, and 408c and then harden it, and then applying the second layer 414, which has higher adhesion during coating and higher surface tension than the first layer 412, the flatness of the upper surface of the second layer 414 can be improved.

[0197] Furthermore, the optical waveguide 232, for example, includes two waveguide groups 700a and 700b, each comprising multiple parallel waveguides adjacent to each other. The high-frequency signal electrode 250b and each of the parallel waveguides constituting waveguide group 700a and waveguide group 700b form an intersection. Waveguide group 700a and waveguide group 700b each have an intermediate layer 800-1 and an intermediate layer 800-2 along the adjacent intersection of the high-frequency signal electrode 250b. Moreover, the intermediate layers 800-1 and 800-2 of waveguide group 700a and waveguide group 700b constitute part of a shared layer 810 that extends along the high-frequency signal electrode 250b to the space between the two waveguide groups 700a and 700b, appearing as a strip when viewed from above.

[0198] According to the structure, at the intermediate position between waveguide group 700a and waveguide group 700b, the lower surface of the high-frequency signal electrode 250b will not drop to the surface of the substrate 230 due to the common layer 810, and can maintain a height that is approximately the same as the height of the protrusions 706a and 706b. Therefore, at the intermediate position, the oscillation of the electrical signal propagating in the high-frequency signal electrode 250b in the normal direction of the substrate 230 can also be suppressed, thereby further suppressing signal propagation loss caused by radiation loss, etc.

[0199] Additionally, in the optical modulation element 104, for example, a buffer layer 500 containing inorganic material may be provided between the intermediate layer 400 and the high-frequency signal electrode 252b. Furthermore, in the optical modulation element 104, for example, a buffer layer 600a containing inorganic material may be provided between the upper surface of the protrusion 404b-1 and the intermediate layer 400-1.

[0200] Based on these structures, the speed of light waves propagating in parallel waveguides 244b-1 or the speed of high-frequency electrical signals propagating in high-frequency signal electrodes 252b can be adjusted by means of the electrical and / or optical properties of inorganic materials, thereby increasing the design freedom of high-frequency signal electrodes 252b.

[0201] In addition, the optical modulation module 1000 of the second embodiment includes: an optical modulation element 104, which is an optical waveguide element for modulating light; and a driving circuit 1008 for driving the optical modulation element 104.

[0202] In addition, the optical transmitting device 1100 of the third embodiment includes: an optical modulator 100 or an optical modulation module 1000; and a modulation signal generation unit 1108, which is an electronic circuit for generating an electrical signal for causing the optical modulation element 104 to perform modulation operation.

[0203] These structures enable the realization of an optical modulator 100, an optical modulation module 1000, or an optical transmitting device 1100 with good characteristics.

Claims

1. An optical waveguide element, comprising: A substrate having an optical waveguide formed thereon; and Electrodes are formed on the substrate and have intersections that cross on the optical waveguide, wherein the optical waveguide element, The optical waveguide includes a protrusion extending on the substrate. The intersection has an intermediate layer between the optical waveguide and the electrodes crossing on the optical waveguide. The intermediate layer extends along the electrode to between adjacent intersections, filling the spaces between adjacent protrusions below the electrode, and The intermediate layer beneath the electrode appears as a strip along the extension direction of the electrode when viewed from above.

2. The optical waveguide element according to claim 1, wherein... The upper surface of the intermediate layer is generally flat from the upper part of the protrusion closest to the end of the intermediate layer to the end.

3. The optical waveguide element according to claim 2, wherein... The thickness of the intermediate layer, measured from the upper surface of the protrusion, is greater than the height of the protrusion from the surface of the substrate.

4. The optical waveguide element according to any one of claims 1 to 3, wherein The intermediate layer comprises multiple layers.

5. The optical waveguide element according to claim 4, wherein... The plurality of layers constituting the intermediate layer includes one layer and other layers disposed above the one layer. The other layers comprise other resins that have a higher adhesion to the substrate when coated than a resin constituting the other layer.

6. The optical waveguide element according to any one of claims 1 to 3, wherein The optical waveguide comprises two waveguide groups, each containing a plurality of adjacent optical waveguides. The electrode and each of the optical waveguides of the two different waveguide groups constitute the intersection. In each of the two waveguide groups, an intermediate layer is provided at the intersection adjacent to the electrodes. The intermediate layer of the two waveguide groups is part of a shared layer that extends along the electrodes to the space between the two waveguide groups and appears as a strip connected together when viewed from above.

7. The optical waveguide element according to any one of claims 1 to 3, wherein A buffer layer containing inorganic material is provided between the intermediate layer and the electrode.

8. The optical waveguide element according to any one of claims 1 to 3, wherein A buffer layer containing inorganic material is provided between the upper surface of the protrusion and the intermediate layer.

9. An optical modulator, comprising: The optical waveguide element according to any one of claims 1 to 8 is an optical modulation element for modulating light; The frame houses the optical waveguide element; An optical fiber that inputs light to the optical waveguide element; and An optical fiber that guides the light output from the optical waveguide element to the outside of the frame.

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

11. An optical transmitting device, comprising: The optical modulator according to claim 9, or the optical modulation module according to claim 10; as well as The electronic circuit generates an electrical signal for modulating the optical waveguide element.

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