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

Abstract

The utility model provides an optical waveguide element, an optical modulator and an optical transmitting device which can restrain phase deviation of differential modulation signals transmitted in electrodes. An optical waveguide element in which two modulation electrodes for applying differential modulation signals are disposed on each of two branch waveguides constituting a Mach-Zehnder optical waveguide, each of the modulation electrodes is composed of a plurality of proximity electrodes disposed in a divided manner along the branch waveguide, a signal electrode for transmitting the modulation signal, and a bypass electrode for connecting the proximity electrodes and the signal electrode, and a ground electrode is disposed so as to sandwich the two modulation electrodes. A capacity adjustment mechanism for adjusting the phase velocity of a modulation signal transmitted in the modulation electrode is provided between the modulation electrode and the ground electrode that are adjacent to each other.

Description

Technical Field

[0001] This invention relates to optical waveguide elements, optical modulation devices using optical waveguide elements, and optical transmission devices, particularly to an optical waveguide element that forms on a substrate at least one Mach-Zehnder type optical waveguide and has two modulation electrodes for applying differential modulation signals disposed on each of the two branch waveguides constituting the Mach-Zehnder type optical waveguide. Background Technology

[0002] In the fields of optical communication and optical measurement, optical waveguide elements, such as optical modulators, are often used, where optical waveguides are formed on a substrate. In recent years, optical modulators included in transmitters of optical transceivers have been required to be miniaturized, have lower power consumption, and offer wider drive signals and lower drive voltages. To address miniaturization and wider drive signals, thin substrates with optical waveguides are used, typically a few μm or less. Furthermore, to reduce the drive voltage, differential modulation signals are used to drive the optical waveguide elements.

[0003] Patent document 1 discloses driving an optical waveguide element utilizing such a thin plate by using a differential modulation signal. Figure 1 and Figure 2 This is a top view showing a portion of the optical waveguide element disclosed in Patent Document 1. Figure 1 In the design, optical waveguide 10 consists of two branch waveguides forming a Mach-Zehnder type optical waveguide. Each branch waveguide 10 is driven by a push-pull method through electrodes E1 and E2, which are subjected to differential modulation signals. The structure of electrodes E1 and E2 consists of multiple "T"-shaped or "H"-shaped micro electrodes (segmented electrodes) connected to the strip-shaped signal electrodes LE1 and LE2 for transmitting the modulation signal.

[0004] In addition, such as Figure 2 As shown, a scheme is also proposed in which the signal electrodes LE1 and LE2 are connected together to form an "H"-shaped segmented electrode. Each segmented electrode consists of a proximity electrode (PE1~PE22) that is positioned close to the optical waveguide (branch waveguide) 10 and applies an electric field to the optical waveguide, and a bypass electrode (BE1, BE2) that connects the proximity electrode to the signal electrodes (LE1, LE2).

[0005] The differential modulation signal is transmitted to each electrode E1 and E2. Therefore, in the same optical waveguide 10, the proximity electrodes (e.g., PE1 and PE21, or PE1 and PR22) need to be always subjected to a modulation signal with opposite phase. However, the segmented electrodes connected to electrodes E1 and E2 may not be of the same shape, thus causing a gradual phase shift in the differential modulation signal transmitted in electrodes E1 and E2.

[0006] exist Figure 1 In the process, the segmented electrodes are shaped like the letter "T" and "H," and the shapes vary, but in... Figure 2 In the process, each segment electrode is the same "H" shape, but the spacing between the proximity electrodes (PE11 and PE12, PE21 and PE22) is different, the transmission speed of the differential modulation signal is different, and the phase of the modulation signal becomes deviated.

[0007] Prior technology literature

[0008] [Patent Documents]

[0009] [Patent Document 1] Chinese Patent Publication CN115586663A Utility Model Content

[0010] [Summary of the Utility Model]

[0011] [The problem that the utility model aims to solve]

[0012] The present invention aims to solve the aforementioned problems by providing an optical waveguide element capable of suppressing phase deviation of differential modulation signals transmitted in electrodes. Furthermore, it provides an optical modulation device and an optical transmission apparatus using such an optical waveguide element.

[0013] [Solutions for solving the problem]

[0014] To address the aforementioned issues, the optical waveguide element, optical modulation device, and optical transmission device of this invention have the following technical features.

[0015] (1) An optical waveguide element, wherein an optical waveguide comprising at least one Mach-Zehnder type optical waveguide is formed on a substrate, and two modulation electrodes for applying a differential modulation signal are provided for each of the two branch waveguides constituting the Mach-Zehnder type optical waveguide, characterized in that each modulation electrode is composed of a plurality of proximity electrodes arranged along the branch waveguide, a signal electrode for transmitting the modulation signal, and a bypass electrode connecting the proximity electrode and the signal electrode, a ground electrode is arranged in such a way that the two modulation electrodes are sandwiched, and a capacity adjustment mechanism is provided between adjacent modulation electrodes and the ground electrode, the capacity adjustment mechanism being used to adjust the phase velocity of the modulation signal transmitted in the modulation electrode.

[0016] (2) In the optical waveguide element described in (1) above, the characteristic is that the capacity adjustment mechanism is a dummy electrode, which is formed on a part of the modulation electrode or the ground electrode and does not generate an electric field applied to the branch waveguide.

[0017] (3) In the optical waveguide element described in (2) above, the dummy electrode has a first dummy electrode disposed on the modulation electrode and a second dummy electrode disposed on the ground electrode, and the distance from the signal electrode to the portion of the first dummy electrode furthest from the signal electrode is longer than the distance from the signal electrode to the portion of the second dummy electrode closest to the signal electrode.

[0018] (4) In the optical waveguide element described in (2) above, the dummy electrode has a first dummy electrode disposed on the modulation electrode and a second dummy electrode disposed on the ground electrode, and the distance from the signal electrode to the portion of the first dummy electrode furthest from the signal electrode is shorter than the distance from the signal electrode to the portion of the second dummy electrode closest to the signal electrode.

[0019] (5) In the optical waveguide element described in (2) above, the dummy electrode is a first dummy electrode disposed on the modulation electrode, and the ground electrode has a shape that surrounds a portion of the first dummy electrode.

[0020] (6) In the optical waveguide element described in (2) above, the length λ1 of the dummy electrode along the signal electrode and the distance λ0 between the adjacent bypass electrode are different from each other.

[0021] (7) In the optical waveguide element described in (1) above, the capacity adjustment mechanism has a structure for adjusting the interval between adjacent modulation electrodes and ground electrodes.

[0022] (8) In the optical waveguide element described in (1) above, a buffer layer is formed on the substrate, the proximity electrode is disposed between the substrate and the buffer layer, and a portion of the signal electrode and the bypass electrode are disposed on the buffer layer.

[0023] (9) In the optical waveguide element described in (1) above, the characteristic is that a dummy optical waveguide that does not transmit light waves is disposed between the adjacent modulation electrode and the ground electrode.

[0024] (10) In the optical waveguide element described in (1) above, a capacitor is formed in a part of the modulation electrode or a part of the signal line electrically connected to the modulation electrode to separate the DC component of the modulation signal.

[0025] (11) An optical modulation device, characterized in that the optical waveguide element described in any one of (1) to (10) above is housed in a housing, and the optical modulation device has an optical fiber for inputting or outputting optical waves relative to the optical waveguide.

[0026] (12) In the optical modulation device described in (11) above, the optical waveguide element is characterized in that the optical waveguide element has a modulation electrode for modulating the light wave transmitted in the optical waveguide, and an electronic circuit is provided inside the housing, which amplifies the modulation signal input to the modulation electrode of the optical waveguide element.

[0027] (13) An optical transmitting device, characterized in that the optical transmitting device has an optical modulator and an electronic circuit as described in (11) or (12) above, wherein the electronic circuit outputs a modulation signal that causes the optical modulator to perform a modulation operation.

[0028] [Utility Model Effect]

[0029] In this invention, an optical waveguide element comprising at least one Mach-Zehnder type optical waveguide is formed on a substrate. Each of the two branch waveguides constituting the Mach-Zehnder type optical waveguide is provided with two modulation electrodes for applying a differential modulation signal. Each modulation electrode consists of a plurality of proximity electrodes arranged along the branch waveguide, a signal electrode for transmitting the modulation signal, and a bypass electrode connecting the proximity electrode and the signal electrode. A ground electrode is arranged to sandwich the two modulation electrodes. A capacity adjustment mechanism is provided between adjacent modulation electrodes and the ground electrode to adjust the phase velocity of the modulation signal transmitted in the modulation electrode. Therefore, an optical waveguide element capable of suppressing phase deviation of the differential modulation signal transmitted in the electrode can be provided. Furthermore, an optical modulation device and an optical transmission device with the same excellent characteristics can be provided by using this optical waveguide element. Attached Figure Description

[0030] Figure 1 This is a top view showing an example of the optical waveguide element disclosed in Patent Document 1.

[0031] Figure 2 This is a top view showing another example of the optical waveguide element disclosed in Patent Document 1.

[0032] Figure 3 This is a top view illustrating an example of an optical waveguide element using segmented electrodes.

[0033] Figures 4A-4C It means Figure 3 An example of a cross-sectional view along the dashed lines A to C.

[0034] Figures 5A-5C It means Figure 3 Another example of a cross-sectional view along the dashed lines A to C.

[0035] Figure 6 This is a top view illustrating the first embodiment of the optical waveguide element of this utility model.

[0036] Figure 7 This is a top view illustrating a second embodiment of the optical waveguide element of this utility model.

[0037] Figure 8 This is a diagram illustrating an example of adjusting the spacing between the modulation electrode and the ground electrode.

[0038] Figure 9 This is a diagram illustrating an example of changing the spacing between the modulation electrode and the ground electrode.

[0039] Figure 10 This is a diagram illustrating a "T"-shaped dummy electrode set on the grounding electrode.

[0040] Figure 11 This is a diagram illustrating the relationship between the length λ1 of the dummy electrode set on the ground electrode and the spacing λ0 of the bypass electrode.

[0041] Figure 12 This is a diagram illustrating an example of a first dummy electrode disposed on a modulation electrode and a second dummy electrode disposed on a ground electrode being arranged opposite each other.

[0042] Figure 13 This diagram illustrates an example of arranging "T"-shaped dummy electrodes, located on both the modulation electrode and the ground electrode, in an alternating manner.

[0043] Figure 14 This diagram illustrates an example of how roughly "H"-shaped dummy electrodes, located on both the modulation electrode and the ground electrode, are arranged in an alternating manner.

[0044] Figure 15 This diagram illustrates an example of arranging "L"-shaped dummy electrodes, located on both the modulation electrode and the ground electrode, in an alternating manner.

[0045] Figure 16 This is a diagram illustrating an example of setting the shape of a ground electrode in such a way that it surrounds a portion of a dummy electrode that is used to modulate the electrode.

[0046] Figure 17 This is a top view illustrating the structure that improves the symmetry of the two modulation electrodes (E1 and E2) and the ground electrode in the optical waveguide element of this utility model.

[0047] Figure 18 This is an explanation Figure 17 The diagram shows an application example of the optical waveguide element.

[0048] Figure 19 This is a top view illustrating an example of using a dummy optical waveguide in the optical waveguide element of this utility model.

[0049] Figure 20 This is a top view illustrating an example of dummy electrodes, located on both the modulation electrode and the ground electrode, being separately arranged along the thickness direction of the substrate.

[0050] Figure 21 It means Figure 20 An example of a cross-sectional view at point A (dashed line).

[0051] Figure 22 This is a diagram illustrating the optical transmitting device of this utility model.

[0052] Figure 23 This is a diagram illustrating an example of a capacitor being locally arranged on the modulation electrode of an optical waveguide element.

[0053] Figure 24 This diagram illustrates an example of a signal wiring configuration with a capacitor connected to the modulation electrode of an optical waveguide element.

[0054] [Label Explanation]

[0055] 1 Optical waveguide substrate

[0056] 10. Optical waveguide (branch waveguide)

[0057] E1, E2 modulation electrodes

[0058] Electrodes for LE1 and LE2 signals

[0059] BE1, BE2 bypass electrodes

[0060] PE11~PE22 proximity electrodes

[0061] LET11~LET12, GT11~GT12 Dummy Electrodes

[0062] DW1 and DW2 are virtual optical waveguides Detailed Implementation

[0063] The present invention will now be described in detail using preferred embodiments.

[0064] For example Figure 6As shown, this utility model relates to an optical waveguide element, wherein an optical waveguide comprising at least one Mach-Zehnder type optical waveguide is formed on a substrate. For each of the two branch waveguides 10 constituting the Mach-Zehnder type optical waveguide, two modulation electrodes (E1, E2) for applying differential modulation signals are respectively arranged. The characteristic feature is that each modulation electrode consists of a plurality of proximity electrodes (PE11~PE22) arranged along the branch waveguide, a signal electrode (LE1, LE2) for transmitting the modulation signal, and a... The proximity electrode and the bypass electrode (BE1, BE2) connected to the signal electrode are configured such that the ground electrode (G1, G2) is arranged in such a way that the two modulation electrodes (E1, E2) are sandwiched. A capacity adjustment mechanism LET11~LET12 (LET21~LET22) is provided between the adjacent modulation electrode E1 (E2) and the ground electrode G1 (G2). The capacity adjustment mechanism LET11~LET12 (LET21~LET22) is used to adjust the phase speed of the modulation signal transmitted in the modulation electrode.

[0065] First, the structure of the optical waveguide element using segmented electrodes will be explained. Figure 3 It means that it was used. Figure 2 A top view of a portion of the segmented electrode optical waveguide element. Two modulation electrodes (E1, E2) are configured for the two branch waveguides 10 of the Mach-Zehnder type optical waveguide. Proximity electrodes (PE11~PE22) are configured such that each modulation electrode can always apply an electric field based on the modulation signal to both branch waveguides. Furthermore, ground electrodes (G1, G2) are configured to sandwich the two modulation electrodes (E1, E2).

[0066] Figures 4A-4C and Figures 5A-5C Show Figure 3 A portion of the cross-section along the dashed lines A~C. Figures 4A-4C and Figures 5A-5C In this design, a lower layer UL, made of a material with a lower refractive index than the optical waveguide substrate 1, is disposed on the lower surface side of the optical waveguide substrate 1, where the ribbed optical waveguide 10 is provided. When a retaining substrate is located below the lower layer UL, the lower layer UL is sometimes also referred to as an intermediate layer. Furthermore, a buffer layer BL, made of a material with a lower refractive index than the optical waveguide substrate 1, is disposed on the upper surface side of the optical waveguide substrate 1.

[0067] exist Figures 4A-4C In the buffer layer BL, modulation electrodes (E1, E2) are arranged on the upper surface side. The signal electrodes (LE1, LE2), bypass electrodes (BE1, BE2), and proximity electrodes (PE11~22) constituting the modulation electrodes are all located on the upper side of the buffer layer BL.

[0068] In contrast, Figures 5A-5CIn this configuration, proximity electrodes (PE11~PE22) are disposed between the optical waveguide substrate 1 and the buffer layer BL. By arranging the electrodes close to the optical waveguide 10, an electric field can be efficiently applied to the optical waveguide. However, signal electrodes (LE1, LE2) are disposed on the upper surface of the buffer layer BL, and bypass electrodes (BE1, BE2) penetrate the buffer layer BL to connect the signal electrodes to the proximity electrodes. Since the signal electrodes are disposed on the upper surface of the optical waveguide substrate, a portion of them sometimes intersects with the optical waveguide 10. Therefore, in order to suppress the absorption or scattering of light waves propagating in the optical waveguide, they are separated from each other by the buffer layer BL.

[0069] There are no particular limitations on the optical waveguide element of this utility model. Figures 4A-4C or Figures 5A-5C Any configuration can be selectively applied. Figures 5A-5C The structure described above is efficient in applying an electric field, but it complicates the manufacturing process. Therefore, appropriate structures are selected with these factors in mind.

[0070] The optical waveguide substrate 1 used as the optical waveguide element of this invention can utilize a substrate with an electro-optic effect. Specifically, it can be a single-crystal material such as lithium niobate (LN), lithium tantalate (LT), or PLZT (lead lanthanum zirconate titanate), or a material doped with MgO or the like. Furthermore, these materials can be formed into films using vapor phase growth methods such as sputtering, evaporation, or CVD. Alternatively, a substrate with an electro-optic effect can be used where the substrate has been bonded to another substrate and then thin-film processing has been performed on the substrate with the electro-optic effect. In addition, substrates made of organic materials such as semiconductor substrates or EO polymers can also be used.

[0071] As an optical waveguide 10, it can be an optical waveguide in which a high refractive index material such as Ti has been thermally diffused into the optical waveguide substrate 1, an optical waveguide formed by proton exchange, or an optical waveguide formed by etching the substrate 1 outside the optical waveguide or forming grooves on both sides of the optical waveguide, etc. Figures 4A-4C or Figures 5A-5C The diagram shows a ribbed optical waveguide 10 on a substrate, with the portion corresponding to the optical waveguide being convex. Alternatively, corresponding to the ribbed optical waveguide, Ti or similar materials can be diffused to the substrate surface using methods such as thermal diffusion or proton exchange, thereby further increasing the refractive index. The dimensions of the ribbed optical waveguide are designed to be micro-structured with a width and height of approximately 1 μm or less to improve light containment.

[0072] To achieve velocity matching between the microwave and light waves in the modulation signal, the thickness (maximum thickness) of the optical waveguide substrate 1 on which the optical waveguide 10 is formed is set to 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. Furthermore, the height of the ribbed optical waveguide 10 (the height of the portion protruding from the slab waveguide) is set to 80% or less of the maximum thickness of the optical waveguide substrate; specifically, it is set to 4 μm or less, more preferably 3 μm or less, and even more preferably 0.8 μm or less or 0.4 μm or less.

[0073] A lower layer is provided on the lower surface of the optical waveguide substrate 1 on which the optical waveguide is formed. To improve the mechanical strength of the optical waveguide element, a holding substrate can be bonded to the lower surface of the optical waveguide substrate 1. The optical waveguide substrate 1 and the holding substrate are directly bonded or bonded together via an adhesive layer such as resin. As for the holding substrate for direct bonding, it is preferable that the refractive index is lower than that of the optical waveguide or the substrate on which the optical waveguide is formed, but it is not limited to this. It should be noted that in the case of direct bonding, an intermediate layer such as a metal oxide or a metal can be included in the bonding portion. Moreover, the holding substrate can be made of a material with a thermal expansion coefficient close to that of the optical waveguide substrate 1, such as glass, crystal, fused silica, synthetic silica, Eagle Glass, alkali glass, alkali-free glass, lead glass, borosilicate glass, sodium glass, sapphire, alumina, and other SiO2-based or Al2O3-based low dielectric constant substrates containing oxide layers. Alternatively, an LN substrate identical to the optical waveguide substrate 1, a composite substrate with a silicon oxide layer formed on a silicon substrate abbreviated as SOI or LNOI, or a composite substrate with a silicon oxide layer formed on an LN substrate can also be used. While maintaining a higher refractive index than the optical waveguide substrate 1, a layer (intermediate layer) with a lower refractive index than the optical waveguide substrate 1 is provided between the optical waveguide substrate 1 and the holding substrate.

[0074] For example, a glass-based substrate is used as the holding substrate, and a bonding layer (intermediate layer) such as SiO2 is formed on the upper surface of the holding substrate via an adhesive layer such as Si, thereby enabling the optical waveguide substrate 1 to be disposed. Furthermore, a buffer layer BL is disposed on the upper side of the optical waveguide substrate 1.

[0075] In the optical waveguide element of this invention, the buffer layer BL sandwiching the optical waveguide substrate 1 and the lower layer UL function as cladding for the optical waveguide 10. Therefore, a dielectric material with a lower refractive index and higher transparency than the optical waveguide substrate 1 is used. Specifically, oxides or fluorides of metal elements from groups 1 to 17 of the periodic table, such as SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, CaF2, and Y2O3, can be used.

[0076] The electrodes (E1, E2) disposed on the upper side of the optical waveguide substrate 1 can be metals such as Au and Cu. Furthermore, to improve the bonding strength between the optical waveguide substrate, the buffer layer, and the electrodes, the electrodes can be constructed using a multilayer structure of the upper electrode and the substrate layer. The upper electrode is formed by covering the substrate layer using electroplating, electroless plating using resist patterns, vapor deposition, sputtering, or combinations thereof. The substrate layer material can be Ti, Nb, Ni, Cr, or Al, and is formed on the upper surface of the optical waveguide substrate, etc., by sputtering, vapor deposition, or other methods.

[0077] The optical waveguide element of this invention is characterized in that a capacity adjustment mechanism is provided on at least one of the two modulation electrodes (E1, E2), which is used to adjust the phase velocity of the modulation signal transmitted in the modulation electrode.

[0078] As mentioned above, the structure of the line transmitting the differential modulation signal, i.e., the two modulation electrodes (E1, E2), is asymmetrical, resulting in differences in the capacitance of each modulation electrode. The phase velocity of the high-frequency signal depends on the capacitance of the line (e.g., the approximate solution for the transmission speed v is v = 1 / (LC)). 1 / 2 (where L is the inductance of the line and C is the capacitance of the line). Therefore, by locally adjusting the capacitance of the modulation electrode, the phase velocity of the differential modulation signal transmitted in the two lines can be matched.

[0079] When the capacitance of the modulation electrode changes, the characteristic impedance of the circuit also changes. Therefore, the capacitance adjustment mechanism of this invention can also be used for characteristic impedance matching and transmission speed matching of optical waves and modulation signals. The characteristic impedance of the modulation electrode (signal electrode) is set to 80~120Ω, preferably 90~110Ω, and more preferably 95~105Ω.

[0080] As for the specific structure of the capacity adjustment mechanism, there are no particular restrictions as long as it is a structure that can adjust the phase speed of the modulation signal transmitted in the electrode. The following structure can be exemplified.

[0081] (1) Set up a dummy electrode that does not generate an electric field applied to the optical waveguide. The dummy electrode is positioned between the adjacent modulation electrode and the ground electrode and can be connected to either electrode.

[0082] (2) Locally adjust the spacing between adjacent modulation electrodes and grounding electrodes.

[0083] (3) Moreover, as another configuration location of the dummy electrode, it can also be configured to be connected to at least one of the proximity electrode, bypass electrode or signal electrode.

[0084] (4) Moreover, it is also possible to address this by changing the electrode width or electrode thickness of at least a portion of the proximity electrode, bypass electrode, or signal electrode.

[0085] The following is a detailed description focusing on (1) and (2) above. Of course, (1) to (4) above can also be combined.

[0086] The following uses Figures 6 to 21 To illustrate a specific example of a capacity adjustment mechanism.

[0087] Figure 6 This is a top view showing the first embodiment of the optical waveguide element of this utility model. As a capacity adjustment mechanism, dummy electrodes LET11~LET12 (LET21~LET22) are connected between the modulation electrode E1 (E2) and the ground electrode G1 (G2), and more specifically, on the ground electrode G1 (G2) side of the signal electrode LE1 (LE2) constituting the modulation electrode.

[0088] exist Figure 6 Although a "T"-shaped dummy electrode is illustrated, as will be discussed later, the shape of the dummy electrode is not limited to this. Moreover, the capacitance can be fine-tuned by changing the dimensions of each part of the "T"-shaped dummy electrode.

[0089] Figure 7 This is a second embodiment of the optical waveguide element of this utility model, in which a dummy electrode GT11~GT12 (GT21~GT22) is provided between the modulation electrode E1 (E2) and the ground electrode G1 (G2) and connected to the ground electrode G1 (G2).

[0090] In addition, as another example of a capacity adjustment mechanism, such as Figure 8 As shown, the line capacity can also be changed by adjusting the distance d between the signal electrode LE, which constitutes the modulation electrode, and the adjacent ground electrode G. It should be noted that the reference numeral BE indicates the bypass electrode that constitutes the segmented electrode.

[0091] Figure 9 This diagram illustrates an example of progressively changing the distance between the signal electrode LE and the ground electrode G. At each section (GS1~GS3) of the ground electrode, the distance between it and the signal electrode LE is varied (d1~d3). As the distance (d1~d3) increases, the resulting capacity decreases. By locally adjusting the distance between the ground electrode and the signal electrode, the capacity adjustment mechanism can function effectively. It should be noted that the distance can also be changed... Figure 9 The length of each part (GS1~GS3) along the signal electrode can also make the interval change continuously rather than stepwise.

[0092] use Figure 10This section explains the effect of shape variations on the dummy electrodes (GS4~GS6) placed on the ground electrode. All dummy electrodes (GS4~GS6) have the same spacing between the ground electrode G and the signal electrode LE. Therefore, the capacitance of the circuit formed by each dummy electrode is essentially similar. However, even a slight change in the thickness of the upper horizontal line portion GT1 of the "T" shape forming the dummy electrode can finely adjust the capacitance. This is because the electric field distribution between the signal electrode LE and the dummy electrode changes depending on the thickness of the horizontal line portion GT1. However, if the thickness (t1, t2) is larger than the spacing between the signal electrode LE and the ground electrode G, the change in electric field distribution almost disappears, essentially becoming unchanged compared to the dummy electrode GS6. Furthermore, variations in the thickness of the vertical line portion GT2 of the "T" shape also slightly affect capacitance adjustment, but the effect is greater for the dummy electrodes formed on the signal electrode compared to the ground electrode.

[0093] Next, use Figure 11 This paper explains the effect of varying the length λ1 of the dummy electrodes (GS7~GS8) along the signal electrode LE. Because the optical waveguide element of this invention periodically arranges multiple segmented electrodes on the modulation electrode, resonance is prone to occur when a modulation signal is applied. Therefore, by making the spacing λ0 of the bypass electrodes BE, which serves as the spacing between the segmented electrodes, inconsistent with the length λ1 of the dummy electrodes (GS7~GS8), this resonance phenomenon can be suppressed. The length λ1 can be n times the spacing λ0, or it can be 1 / n times (n is a natural number or a decimal).

[0094] Regarding the length λ1 of the dummy electrode, besides Figure 11 In addition, such as Figure 6 and Figure 7 As shown, the same effect can be expected for the length λ1 of the horizontal part (LET11, GT11) of the "T"-shaped dummy electrode.

[0095] Figure 12 This diagram illustrates an example where dummy electrodes are provided on both the modulation electrode and the ground electrode. By arranging the dummy electrodes (LET1~LET2, GT1~GT2) opposite to each other, the circuit capacity of the modulation electrode can be adjusted more finely. Specifically, the length α1 and width α3 of the horizontal portion (LET1, GT1) of the "T" shape of each dummy electrode, and the width α2 of the vertical portion (LET2, GT2) are adjusted. It should be noted that the shapes of the opposing dummy electrodes do not need to be symmetrical, nor are they limited to a "T" shape. Moreover, one dummy electrode can be shaped like a "T," while the other dummy electrode can be shaped in other ways.

[0096] exist Figure 12The following is an example of a situation where a dummy electrode has a dummy electrode (first dummy electrode) disposed on a modulation electrode and a dummy electrode (second dummy electrode) disposed on a ground electrode, and the distance from the signal electrode to the portion of the first dummy electrode furthest from the signal electrode LE is shorter than the distance from the signal electrode to the portion of the second dummy electrode closest to the signal electrode.

[0097] The following explains the situation (the so-called state of dummy electrode interleaving): In the dummy electrode, the distance from the signal electrode to the part of the first dummy electrode that is furthest from the signal electrode is longer than the distance from the signal electrode to the part of the second dummy electrode that is closest to the signal electrode.

[0098] Figures 13-15 It is a state of dummy electrode crossing. Figure 16 This describes the state of the dummy electrode entering the ground electrode. Figures 13-16 The shape and configuration of the dummy electrodes help to further improve the ability to adjust the capacitance of the dummy electrodes. By using the ground electrode itself or a dummy electrode formed on the ground electrode to surround a portion of the dummy electrode formed on the signal electrode, the capacitance can be adjusted more finely. Specifically, in Figure 12 In this context, within a portion of the dummy electrode, such as the horizontal line portion in a "T" shape, the periphery close to the ground electrode only aids in capacity adjustment. In contrast, in... Figures 13-16 In this configuration, the portion surrounded by the ground electrode can facilitate capacity adjustment. Therefore, the shape of the dummy electrode and its spacing from the surrounding ground electrode (the dummy electrode connected to the ground electrode) affect capacity adjustment, enabling finer capacity adjustments.

[0099] Figure 13 It is a diagram in which the dummy electrodes of the modulation electrode (LET1~LET2) and the dummy electrodes of the ground electrode (GT1~GT2) are arranged in an alternating manner, with the "T" shape selected as the shape of the dummy electrodes.

[0100] Figure 14 Using an approximate "H" shape as a dummy electrode, and... Figure 13 Similarly, the dummy electrodes (LEH1~LEH4, GH1~GH4) are interleaved.

[0101] in addition, Figure 15 The “L”-shaped dummy electrodes (LEL1~LEL2, GL1~GL2) are arranged in an alternating manner.

[0102] exist Figure 16The image shows an example where the dummy electrode LEI of the modulation electrode is surrounded by the ground electrode body. An "I"-shaped structure is shown for the dummy electrode, but it is not limited to this; it can also be a "T"-shaped, roughly "H"-shaped, or "L"-shaped structure.

[0103] like Figure 17 As shown, multiple dummy electrodes (LEH1~LEH2, GH1~GH2) are added between the modulation electrode E1 (E2) and the ground electrode G1 (G2). The shape of the electrodes as a whole becomes approximately the same in both modulation electrodes, thereby ensuring that the capacitance of each line is identical and achieving phase velocity adjustment. Furthermore, by improving the symmetry of the shapes of the two modulation electrodes, the distribution of internal stresses exerted on the optical waveguide substrate by the electrodes due to thermal expansion becomes more uniform, which also helps to suppress temperature drift.

[0104] In addition, Figure 18 In this configuration, the position of the dummy electrode LEH14 (LEH24) is set to correspond to the position of the bypass electrode BE1 (BE2). This further improves the symmetry of the two modulation electrodes.

[0105] In addition, such as Figure 19 As shown, in addition to the optical waveguide (branch waveguide) 10 that transmits light waves, dummy optical waveguides DW1~DW2 that do not transmit light waves can be configured close to the optical waveguide (branch waveguide) 10. Due to the presence of these dummy optical waveguides DW1~DW2, the symmetry of the shapes of the two modulation electrodes is further improved, and the distribution of internal stresses exerted on the optical waveguide substrate by the electrodes due to thermal expansion and other factors becomes more uniform.

[0106] exist Figure 20 and Figure 21 The paper describes a method for stacking two dummy electrodes with a buffer layer between them. Compared to arranging the two dummy electrodes side by side on the same plane, this method improves the capacity adjustment capability. Figure 21 Show Figure 20 The cross-sectional view at dashed line A shows that the horizontal portions of the "T"-shaped dummy electrodes LET1 and GT1 are arranged to overlap each other along the thickness direction of substrate 1.

[0107] Figure 22 This diagram illustrates an example of an optical transmitting device. In recent years, optical modulation devices that integrate driver ICs and optical waveguide elements into the same housing, such as high-bandwidth-coherent driver modulators (HB-CDM), have attracted attention, leading to an increasing demand for structures suitable for miniaturization, such as the optical waveguide element of this invention.

[0108] In the optical modulation device of this invention, an optical waveguide element is disposed within a housing CA, such as a metal. Within the housing, input light L1 is input to the optical waveguide 10 formed on the optical waveguide element via an optical fiber FB or other optical components such as lenses. Conversely, light waves emitted from the optical waveguide element are input to another optical fiber F, becoming output light L2. During light output, optical components such as polarization synthesizers and lenses are used as needed. A modulation electrode (not shown) is formed on the substrate 1 of the optical waveguide element. Furthermore, reinforcing members RI for improving mechanical strength are disposed on the substrate of the input / output portion of the optical waveguide element as needed.

[0109] In an optical modulation device, a drive circuit element DRV is disposed adjacent to an optical waveguide element to generate an electrical signal S applied to the modulation electrode of the optical waveguide element, and the optical waveguide element and the drive circuit element DRV are housed in the same housing CA.

[0110] Alternatively, a signal generator (DSP) can be installed to generate the modulation signal So input to the drive circuit element DRV, thus configuring it as an optical transmission device. The housing CA and the signal generator DSP can also be mounted in a single base.

[0111] Alternatively, it can be like Figure 23 and Figure 24 As shown, a capacitor is placed on a part of the signal electrode of the modulation electrode or a part of the signal line supplying the modulation signal to the modulation electrode to separate the DC component contained in the modulation signal. Figure 23 A capacitor CS1 (CS2) is disposed on the input side of the modulation signal (differential modulation signal S+, S-) of the signal electrode LE1 (LE2). Furthermore, in Figure 24 In order to supply modulation signals to the signal electrodes, capacitors (CS3, CS4) are provided on the signal lines (LE11, LE21) of the relay board RS. Labels G11 and G21 are lines provided on the ground electrode of the relay board.

[0112] [Industry Applicability]

[0113] As described above, according to this invention, an optical waveguide element capable of suppressing phase deviation of a differential modulation signal transmitted in the electrodes can be provided. Furthermore, an optical modulation device and an optical transmission apparatus using such an optical waveguide element can also be provided.

Claims

1. An optical waveguide element in which an optical waveguide including at least one Mach-Zehnder type optical waveguide is formed on a substrate, two modulation electrodes for applying a differential modulation signal are provided for each of two branch waveguides constituting the Mach-Zehnder type optical waveguide, characterized in that each of the modulation electrodes is composed of a plurality of proximity electrodes provided so as to be divided along the branch waveguide, a signal electrode through which the modulation signal is transmitted, and a bypass electrode connecting the proximity electrodes and the signal electrode, a ground electrode is provided so as to sandwich the two modulation electrodes, and a capacity adjustment mechanism for adjusting the phase velocity of the modulation signal transmitted in the modulation electrode is provided between the adjacent modulation electrode and the ground electrode.

2. The optical waveguide element according to claim 1, characterized in that the capacity adjustment mechanism is a dummy electrode which is formed in a part of the modulation electrode or the ground electrode and does not generate an electric field applied to the branch waveguide.

3. The optical waveguide element according to claim 2, characterized in that the dummy electrode has a first dummy electrode provided in the modulation electrode and a second dummy electrode provided in the ground electrode, and the distance from the signal electrode to the part of the first dummy electrode farthest from the signal electrode is longer than the distance from the signal electrode to the part of the second dummy electrode closest to the signal electrode.

4. The optical waveguide element according to claim 2, characterized in that the dummy electrode has a first dummy electrode provided in the modulation electrode and a second dummy electrode provided in the ground electrode, and the distance from the signal electrode to the part of the first dummy electrode farthest from the signal electrode is shorter than the distance from the signal electrode to the part of the second dummy electrode closest to the signal electrode.

5. The optical waveguide element according to claim 2, characterized in that the dummy electrode is a first dummy electrode provided in the modulation electrode, and the ground electrode has a shape in which a part of the first dummy electrode is surrounded.

6. The optical waveguide element according to claim 2, characterized in that the length λl of the dummy electrode along the signal electrode and the interval λ0 of the adjacent bypass electrodes are different lengths from each other.

7. The optical waveguide element according to claim 1, characterized in that the capacity adjustment mechanism has a structure for adjusting the interval between the adjacent modulation electrode and the ground electrode.

8. The optical waveguide element according to claim 1, characterized in that a buffer layer is formed on the substrate, the proximity electrodes are provided between the substrate and the buffer layer, and a part of the signal electrode and the bypass electrode are provided on the buffer layer.

9. The optical waveguide element according to claim 1, characterized in that a dummy optical waveguide which does not transmit an optical wave is provided between the adjacent modulation electrode and the ground electrode.

10. The optical waveguide element according to claim 1, characterized in that a capacitor which blocks a DC component of the modulation signal is formed in a part of the modulation electrode or a part of a signal line electrically connected to the modulation electrode.

11. An optical modulation device characterized by comprising: the optical waveguide element as claimed in claim 1 is housed in a case, and the optical modulation device is provided with an optical fiber that inputs or outputs an optical wave with respect to the optical waveguide.

12. The optical modulation device as claimed in claim 11, characterized in that: the optical waveguide element is provided with a modulation electrode for modulating an optical wave transmitted in the optical waveguide, and the case has an electronic circuit inside, which amplifies a modulation signal input to the modulation electrode of the optical waveguide element.

13. An optical transmission apparatus characterized by comprising: the optical modulation device as claimed in claim 11 and an electronic circuit that outputs a modulation signal that causes the optical modulation device to perform a modulation action.

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