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 an optical waveguide including at least one Mach-Zehnder type optical waveguide is formed on a substrate, and in which two modulation electrodes for applying differential modulation signals are disposed for each of two branch waveguides constituting the Mach-Zehnder type 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. At least one of the two modulation electrodes is provided with a capacity adjustment mechanism for adjusting the phase velocity of a modulation signal transmitted through the modulation electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical waveguide element, an optical modulation device using the optical waveguide element, and an optical transmission apparatus, and particularly relates to an optical waveguide element in which an optical waveguide including 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 two branch waveguides constituting the Mach-Zehnder type optical waveguide. BACKGROUND

[0002] In the field of optical communication and optical measurement, optical waveguide elements in which an optical waveguide is formed on a substrate, such as an optical modulator, are used. In recent years, optical modulators included in a transmitter built in an optical transceiver apparatus are required to be downsized, low power consumption, wideband of a driving signal, and low driving voltage. In order to cope with the downsizing and the wideband of the driving signal, a substrate on which the optical waveguide is formed uses a thin plate of several μm or less. In addition, in order to reduce the driving voltage, the optical waveguide element is driven by a differential modulation signal.

[0003] Patent Document 1 discloses an optical waveguide element using such a thin plate driven by a differential modulation signal. Figure 1 and 2 is a plan view showing a part of the optical waveguide element disclosed in Patent Document 1. In Figure 1 , the optical waveguide 10 is two branch waveguides constituting a Mach-Zehnder type optical waveguide, and each branch waveguide 10 is driven in a push-pull manner by electrodes El and E2 to which a differential modulation signal is applied. As a structure of the electrodes El and E2, a structure in which a plurality of "T" shaped or "H" shaped fine electrodes (segmented electrodes) are connected to strip-shaped signal electrodes LEl and LE2 through which a modulation signal is transmitted is adopted.

[0004] In addition, as shown in Figure 2 , a structure in which the "H" shaped segmented electrodes are connected to the signal electrodes LEl and LE2 is also proposed. Each segmented electrode is composed of a proximity electrode (PEl to PE22) which is disposed in close proximity to the optical waveguide (branch waveguide) 10 and applies an electric field to the optical waveguide, and a bypass electrode (BEl, BE2) which connects the proximity electrode to the signal electrode (LEl, LE2).

[0005] The differential modulation signal is transmitted to each electrode El and E2. Therefore, in the same optical waveguide 10, the proximity electrodes (for example, PEl and PE21, or PEl and PR22) need to be always applied with modulation signals of opposite phases. However, the segmented electrodes connected to the electrodes El and E2 are not necessarily the same shape, and thus a phenomenon in which the phases of the differential modulation signals transmitted in the electrodes El and E2 gradually deviate can occur.

[0006] In Figure 1In the process, the segmented electrodes are in different "T" and "H" shapes, 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] [Solution to 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, and a capacity adjustment mechanism is provided on at least one of the two modulation electrodes for adjusting 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 in part of the modulation 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 is a first dummy electrode that extends from the proximity electrode to the opposite side of the bypass electrode.

[0018] (4) In the optical waveguide element described in (2) above, the dummy electrode is a second dummy electrode that extends from the bypass electrode.

[0019] (5) In the optical waveguide element described in (2) above, the characteristic is that the dummy electrode is a third dummy electrode extending from the signal electrode.

[0020] (6) In the optical waveguide element described in (5) above, the third dummy electrode is characterized by being composed of a plurality of micro electrodes disposed between adjacent bypass electrodes.

[0021] (7) In the optical waveguide element described in (1) above, the characteristic is that the capacity adjustment mechanism changes the electrode width of at least a portion of the proximity electrode, the bypass electrode or the signal electrode.

[0022] (8) In the optical waveguide element described in (1) above, the characteristic is that the capacity adjustment mechanism changes the electrode thickness of at least a portion of the bypass electrode or the signal electrode.

[0023] (9) In any of the optical waveguide elements described in (1) to (8) 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.

[0024] (10) In any of the optical waveguide elements described in (1) to (9) above, the characteristic is that a dummy optical waveguide that does not transmit optical waves is disposed close to the branch waveguide.

[0025] (11) In any of the optical waveguide elements described in (1) to (10) above, the characteristic is that 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 block the DC component of the modulation signal.

[0026] (12) An optical modulation device, characterized in that the optical waveguide element described in any one of (1) to (11) 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.

[0027] (13) In the optical modulation device described in (12) 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.

[0028] (14) 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.

[0029] [Utility Model Effect]

[0030] This invention provides an optical waveguide comprising at least one Mach-Zehnder type optical waveguide 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 capacity adjustment mechanism is provided on at least one of the two modulation electrodes 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, by using this optical waveguide element, an optical modulation device and an optical transmission device with equally excellent characteristics can be provided. Attached Figure Description

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

[0032] Figure 2 This is a top view showing another example of the optical waveguide element disclosed in Patent Document 1.

[0033] Figure 3 This is a top view illustrating an example of an optical waveguide element using segmented electrodes.

[0034] Figures 4A-4C It means Figure 3 An example of a cross-sectional view along the dashed lines A to C.

[0035] Figures 5A-5C It means Figure 3 Another example of a cross-sectional view along the dashed lines A to C.

[0036] Figure 6 This is a top view illustrating the first embodiment of the optical waveguide element of this utility model.

[0037] Figure 7 This is an explanation Figure 6 A diagram illustrating an application example of the first embodiment.

[0038] Figure 8 This is an explanation Figure 6 A diagram showing another application example of the first embodiment.

[0039] Figure 9 This is a top view illustrating a second embodiment of the optical waveguide element of this utility model.

[0040] Figure 10 This is a top view illustrating the third embodiment of the optical waveguide element of this utility model.

[0041] Figure 11 This is a top view illustrating the structure that improves the symmetry of the two electrodes (E1 and E2) in the optical waveguide element of this utility model.

[0042] Figure 12 This is a top view illustrating an example of using a dummy optical waveguide in the optical waveguide element of this utility model.

[0043] Figure 13 This is an explanation Figure 10 A top view of an application example of the third embodiment.

[0044] Figure 14 This is a top view illustrating the fourth embodiment of the optical waveguide element of this utility model.

[0045] Figures 15A-15C It means Figure 14 An example of a cross-sectional view along the dashed lines A to C.

[0046] Figure 16 This is a top view illustrating the fifth embodiment of the optical waveguide element of this utility model.

[0047] Figure 17 It means Figure 16 An example of a cross-sectional view at point A (dashed line).

[0048] Figure 18 This is a diagram illustrating the optical transmitting device of this utility model.

[0049] Figure 19 This is a diagram illustrating an example of a capacitor being locally arranged on the modulation electrode of an optical waveguide element.

[0050] Figure 20 This diagram illustrates an example of a signal wiring configuration with a capacitor connected to the modulation electrode of an optical waveguide element.

[0051] [Label Explanation]

[0052] 1 Optical waveguide substrate

[0053] 10. Optical waveguide (branch waveguide)

[0054] E1, E2 modulation electrodes

[0055] Electrodes for LE1 and LE2 signals

[0056] BE1, BE2 bypass electrodes

[0057] PE11~PE22 proximity electrodes

[0058] DE, DE1~21 Dummy electrodes

[0059] DW Virtual Optical Waveguide Detailed Implementation

[0060] The present invention will now be described in detail using preferred embodiments.

[0061] For example Figure 6 As shown, this utility model relates to an optical waveguide element, wherein an optical waveguide including at least one Mach-Zehnder type optical waveguide is formed on a substrate. Two modulation electrodes (E1, E2) for applying differential modulation signals are respectively arranged for two branch waveguides 10 constituting the Mach-Zehnder type optical waveguide. The optical waveguide element is characterized in that the modulation electrode is respectively composed 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 bypass electrode (BE1, BE2) connecting the proximity electrode and the signal electrode. A capacity adjustment mechanism (DE) is provided for at least one of the two modulation electrodes (E1, E2), and the capacity adjustment mechanism (DE) is used to adjust the phase velocity of the modulation signal transmitted in the modulation electrode.

[0062] First, the construction 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 a 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).

[0063] 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.

[0064] 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.

[0065] In contrast, Figures 5A-5C In this design, proximity electrodes (PE11~PE22) are positioned between the optical waveguide substrate 1 and the buffer layer BL, closer to the optical waveguide 10, thereby enabling the efficient application of an electric field to the optical waveguide. However, signal electrodes (LE1, LE2) are positioned 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 positioned on the upper surface of the optical waveguide substrate, a portion of them sometimes intersects with the optical waveguide 10. Therefore, 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.

[0066] In the optical waveguide element of this utility model, there are no particular limitations. Figures 4A-4C or Figures 5A-5C It can be selectively applied in any of the configurations. 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.

[0067] 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.

[0068] 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-5CThe 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 the like 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 or height of approximately 1 μm or less to improve light containment.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] As mentioned above, the circuit for transmitting differential modulation signals, i.e., the two modulation electrodes (E1, E2), is asymmetrically constructed, resulting in differences in the capacitance of each modulation electrode. The phase velocity of the high-frequency signal depends on the circuit capacitance (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.

[0076] 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.

[0077] 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.

[0078] (1) Provide a dummy electrode that does not generate an electric field applied to the optical waveguide. The dummy electrode is configured to be connected to at least one of the proximity electrode, bypass electrode, or signal electrode.

[0079] (2) Change the electrode width or electrode thickness of at least a portion of the proximity electrode, bypass electrode, or signal electrode. However, when the electrode thickness of the proximity electrode to which an electric field is applied to the optical waveguide is changed, the electric field distribution also changes, therefore in, for example... Figures 5A-5C In the case of such a configuration close to the electrodes (PE11~PE22), it is preferable not to change the electrode thickness.

[0080] (3) In addition, as another configuration position of the dummy electrode, it can be between the adjacent modulation electrode and the ground electrode, and connected to any electrode.

[0081] (4) In addition, the spacing between adjacent modulation electrodes and grounding electrodes is locally adjusted.

[0082] The following is a detailed description focusing on (1) and (2) above. Of course, the structures of (1) and (2) above can also be combined. Moreover, (1) to (4) above can also be used in combination.

[0083] The following uses Figures 6-19 This provides a specific example of a capacity adjustment mechanism.

[0084] Figure 6 This is a top view showing a first embodiment of the optical waveguide element of this utility model. As a capacity adjustment mechanism, a dummy electrode is connected to a portion of the modulation electrode, more specifically, near the electrode. For example... Figure 6 As shown, a first dummy electrode DE is configured to extend from the proximity electrode PE12 to the opposite side of the bypass electrode BE1.

[0085] Regarding the dummy electrode DE, the phase velocity of the modulation signal can be finely adjusted by adjusting its length α1 in the left-right direction of the attached drawing and its length α4 protruding downwards from the near electrode PE12. Furthermore, the phase velocity can also be changed by adjusting the thickness (width) α2 or α3 of the various parts constituting the dummy electrode. Additionally, the phase velocity can also be adjusted by adjusting the distance α5 or α6 between the electrode E2 side and the dummy electrode DE.

[0086] Furthermore, the phase velocity can also be changed by altering the thickness of the dummy electrode DE. Moreover, the shape of the first dummy electrode connected to the proximity electrode is not limited to... Figure 6 That T-shaped form can also be Figure 7 The I-shaped form shown (DE1) Figure 8 The outer periphery is a shape formed by curves, as shown in Figure (DE2).

[0087] Figure 6 The electrode width α2 is important when the dummy electrode DE spans the lower side of the optical waveguide 10. This is because, in an electrode-spanning-the-waveguide structure, the optical loss of the light wave propagating in the waveguide increases. Therefore, in order to set the optical loss generated by the electrode to be the same in both the upper and lower optical waveguides 10, the electrode width α2 is preferably set to be the same width as the bypass electrode BE1. This is in Figure 7 and Figure 8 The same can also be said to apply to China.

[0088] like Figure 8 In the case where the dummy electrode DE2 is configured as an electrode surrounded by a curve, no corners are formed around the electrode, and no area of ​​electric field concentration is generated. Therefore, it is also possible to suppress the dummy electrode from applying an electric field to the nearby optical waveguide, which can be said to be a more preferred shape for the dummy electrode.

[0089] Figure 9 This is a diagram showing the second dummy electrode DE3 connected to the bias electrode BE1.

[0090] Figure 10 This diagram shows the third dummy electrode DE4 (or DE5) connected to the signal electrode LE1 (or LE2). Thus, regardless of where the dummy electrode is connected to the electrode constituting electrode E1 or E2, it can function as a capacity adjustment mechanism. Furthermore, not only can a capacity adjustment mechanism be provided with a dummy electrode on only one electrode (E1 or E2), but it can also be implemented as follows: Figure 10 By configuring capacity adjustment mechanisms on both sides of the two modulation electrodes (E1 and E2), the phase velocity of the two modulation electrodes as a whole is made the same.

[0091] Alternatively, it can be like Figure 11 As shown, by adding dummy electrodes DE6 and DE7, the symmetry of the electrode shape observed in the overall electrode configuration is improved by the two modulation electrodes. The improved symmetry of the two modulation electrodes leads to a more uniform distribution of internal stresses exerted on the optical waveguide substrate by thermal expansion, which also helps to suppress temperature drift.

[0092] Alternatively, it can be like Figure 12 As shown, in addition to the optical waveguide (branch waveguide) 10 that transmits light waves, a dummy optical waveguide DW is also configured close to the optical waveguide (branch waveguide) 10 but does not transmit light waves. Due to the presence of this dummy optical waveguide DW, the dielectric constant of the surrounding area experienced by the dummy electrode DE3 becomes equal to the dielectric constant of the surrounding area experienced by the nearby electrode PE22, allowing the phase velocity to be adjusted to be more uniform. Of course, the unevenness of the internal stress applied by the electrodes to the optical waveguide can also be eliminated.

[0093] likeFigure 13 As shown, multiple dummy electrodes (microelectrodes) DE41 and DE42 (or DE91 and DE92) can also be configured between adjacent bypass electrodes BE1 (or BE2). These multiple microelectrodes can suppress the resonance phenomenon of the modulation electrode.

[0094] use Figures 14-17 This illustrates another example of a capacity adjustment mechanism.

[0095] Figure 14 and Figures 15A-15C This diagram shows how the segmented electrodes formed on the two modulation electrodes are arranged to overlap vertically in order to make the segmented electrodes have the same shape. Figure 14 It is a top view. Figures 15A-15C Show Figure 14 The cross-sectional view along the dashed lines A to C. Focusing on section A (dashed line), corresponding to the proximity electrodes (P21, PE11, PE12, PE22), dummy electrodes (DE10, DE12, DE13) are arranged on the upper side. Furthermore, focusing on section B (dashed line), the shape of the segmented electrode containing the proximity electrodes (PE11 and PE12) is exactly the same as the shape of the segmented electrode containing the dummy electrodes (DE12 and DE13) (symmetrical).

[0096] By making the segmented electrodes of each modulation electrode have the same shape, the phase velocity of each modulation electrode can be made the same.

[0097] Figure 16 and Figure 17 The diagram shows a dummy electrode DE20 (DE21) connected to the lower side of the signal electrode LE1 (LE2). This allows the dummy electrode to be positioned in a three-dimensional location. Of course, it is not limited to the signal electrode; dummy electrodes can also be placed above or below the bypass electrode, or, depending on the situation, above or below the adjacent electrode.

[0098] Figure 18 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] Alternatively, it can be like Figure 19 and Figure 20 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 19 In this configuration, capacitors CS1 (CS2) are positioned on the input side of the modulation signals (differential modulation signals S+, S-) of the signal electrodes LE1 (LE2). Furthermore, in... Figure 20 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.

[0103] [Industry Applicability]

[0104] 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 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 capacity adjustment mechanism for adjusting a phase velocity of the modulation signal transmitted in the modulation electrode is provided in at least one of the two modulation electrodes.

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

3. The optical waveguide element according to claim 2, characterized in that the dummy electrode is a first dummy electrode extending from the proximity electrode to the opposite side of the bypass electrode.

4. The optical waveguide element according to claim 2, characterized in that the dummy electrode is a second dummy electrode extending from the bypass electrode.

5. The optical waveguide element according to claim 2, characterized in that the dummy electrode is a third dummy electrode extending from the signal electrode.

6. The optical waveguide element according to claim 5, characterized in that the third dummy electrode is composed of a plurality of fine electrodes provided between adjacent bypass electrodes.

7. The optical waveguide element according to claim 1, characterized in that the capacity adjustment mechanism changes an electrode width of at least a part of the proximity electrode, the bypass electrode, or the signal electrode.

8. The optical waveguide element according to claim 1, characterized in that the capacity adjustment mechanism changes an electrode thickness of at least a part of the bypass electrode or the signal electrode.

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

10. The optical waveguide element according to claim 1, characterized in that a dummy optical waveguide not transmitting an optical wave is provided in proximity to the branch waveguide.

11. The optical waveguide element according to claim 1, characterized in that a capacitor for blocking 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.

12. An optical modulation device characterized in that the optical waveguide element according to claim 1 is housed in a housing, and the optical modulation device is provided with an optical fiber for inputting or outputting an optical wave with respect to the optical waveguide.

13. The optical modulation device according to claim 12, characterized in that the optical waveguide element is provided with a modulation electrode for modulating an optical wave transmitted in the optical waveguide, and an electronic circuit amplifying a modulation signal input to the modulation electrode of the optical waveguide element is provided in the inside of the housing.

14. An optical transmission apparatus characterized in that The optical transmission apparatus has the optical modulation device of claim 12 and an electronic circuit which outputs a modulation signal for causing the optical modulation device to perform a modulation operation.

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