Optical control element, optical modulation device using the same, and optical transmission apparatus

Abstract

Provided is an optical control element capable of arranging an input portion and an output portion of an optical waveguide on the same side of a substrate in which the optical waveguide is formed, and capable of reducing differences in the configuration of each branch waveguide while minimizing optical path differences between branch waveguides. The optical control element has a substrate (1) having an electro-optic effect, an optical waveguide (2) formed in the substrate, and a control electrode that controls an optical wave propagating in the optical waveguide, characterized in that an input portion (incident light (L1)) and an output portion (emitted light (L2)) of the optical waveguide are formed on the same side of the substrate, the optical waveguide has at least one Mach-Zehnder type optical waveguide portion (MZ) having two branch waveguides (21, 22) branched from one optical waveguide and recombining the two branch waveguides to form one optical waveguide, and the branch waveguides have an even number of return portions (A1, A2).

Description

Technical Field

[0001] The present invention relates to an optical control element, an optical modulation device using the optical control element, and an optical transmission device, and particularly to an optical control element having an input portion and an output portion having an optical waveguide on the same side of a substrate. Background Technology

[0002] In the fields of optical communication and optical measurement, optical control elements are widely used. These elements consist of an optical waveguide and control electrodes that control the propagation of light waves within the waveguide, on a substrate with electro-optic effects, such as lithium niobate (LN). Optical modulators, as one type of optical control element, require broadband speeds exceeding 400 Gbps and miniaturization.

[0003] Specifically, to suppress signal propagation loss when inputting a high-frequency signal to the optical control element, it is preferable to arrange the drive circuit that generates the high-frequency signal close to the optical control element and to configure the signal line as a straight line. Therefore, an optical modulator is proposed that inputs a high-frequency signal from one end face of the housing housing the optical control element and outputs a light wave from the opposite end face.

[0004] Furthermore, as a means to achieve miniaturization of the optical control element itself, Patent Document 1 proposes a method to shorten the element length by bending the optical waveguide within the optical modulator multiple times. Moreover, Patent Document 2 discloses a technique of arranging the optical input end and the optical output end on the same side of the optical modulator and bending the optical waveguide within the optical modulator only once.

[0005] On the other hand, the optical waveguide inserted into the optical control element uses a Mach-Zehnder type optical waveguide, which modulates the light by utilizing the optical path difference between the light waves propagating in the two branch waveguides. As shown in Patent Document 2, if the Mach-Zehnder type optical waveguide is folded back, the optical path difference between the two branch waveguides becomes different, and therefore the operating bias point voltage of the Mach-Zehnder type optical waveguide changes depending on the wavelength of the propagating light wave. Therefore, whenever the wavelength changes, a significant change in the bias voltage is required to adjust the bias point.

[0006] To eliminate the aforementioned problems, Patent Document 3 proposes a scheme to incorporate a delay waveguide section in one of the branch waveguides to ensure that the optical path lengths of the two branch waveguides are equal. However, this approach is constrained by the bending radius of the optical waveguides, making it difficult to compactly construct a delay waveguide that suppresses the increase in optical waveguide loss and compensates for the optical path difference between the outer and inner branch waveguides of the folded-back section. Furthermore, if the structures of the bent waveguides between the branch waveguides differ, differences in optical loss occur in each branch waveguide, leading to problems such as a deterioration in the on / off extinction ratio of Mach-Zehnder type optical waveguides.

[0007] Prior art literature

[0008] Patent documents

[0009] Patent Document 1: International Publication No. WO2019 / 039215

[0010] Patent Document 2: Japanese Patent Application Publication No. 2019-95698

[0011] Patent Document 3: Japanese Patent Publication No. 2018-534627 Summary of the Invention

[0012] Summary of the invention

[0013] The problem that the invention aims to solve

[0014] The present invention aims to solve the aforementioned problems by providing an optical control element that allows the input and output portions of an optical waveguide to be arranged on the same side of a substrate on which an optical waveguide is formed, thereby reducing the structural differences between the branch waveguides and minimizing the optical path difference between the branch waveguides. Furthermore, the present invention provides an optical modulation device and an optical transmission apparatus using this optical control element.

[0015] Solution for solving the problem

[0016] In order to solve the above-mentioned problems, the optical control element, optical modulation device and optical transmission device of the present invention have the following technical features.

[0017] (1) An optical control element comprising: a substrate having an electro-optic effect; an optical waveguide formed on the substrate; and a control electrode for controlling an optical wave propagating in the optical waveguide, wherein the optical control element is characterized in that an input portion and an output portion of the optical waveguide are formed on the same side of the substrate, the optical waveguide has at least one Mach-Zehnder type optical waveguide portion, the Mach-Zehnder type optical waveguide portion having two branch waveguides branching from an optical waveguide and combining the two branch waveguides to form an optical waveguide, the branch waveguide having an even number of foldback portions.

[0018] (2) In the optical control element described in (1) above, the optical path length of the branch waveguide is set to be equal to that of each other.

[0019] (3) In the optical control element described in (1) or (2) above, the characteristic is that multiple optical waveguides are branched from one optical waveguide, and the Mach-Zehnder type optical waveguide portion is provided in each branched optical waveguide. When the Mach-Zehnder type optical waveguide portions are arranged side by side, the branch waveguide of the Mach-Zehnder type optical waveguide portion has an even number of foldback portions.

[0020] (4) In any of the optical control elements described in (1) to (3) above, the control electrode is characterized in that the control electrode has a modulation electrode and a bias electrode, and the modulation electrode and the bias electrode are disposed in different intervals for a plurality of intervals divided by the foldback portion of the branch waveguide.

[0021] (5) An optical modulation device, characterized in that it comprises: any of the optical control elements described in (1) to (4) above; a housing for accommodating the optical control element; and an optical fiber for inputting and outputting optical waves to the optical control element.

[0022] (6) In the optical modulation device described in (5) above, the characteristic is that an electronic circuit is provided inside the housing to amplify the modulation signal input to the optical control element.

[0023] (7) An optical transmitting device, characterized in that it comprises: an optical modulation device described in (5) or (6) above; and an electronic circuit that outputs a modulation signal that causes the optical modulation device to perform modulation operation.

[0024] Invention Effects

[0025] According to the present invention, an optical control element is provided, comprising: a substrate having an electro-optic effect; an optical waveguide formed on the substrate; and a control electrode for controlling light waves propagating in the optical waveguide. The input and output portions of the optical waveguide are formed on the same side of the substrate. The optical waveguide includes at least one Mach-Zehnder type optical waveguide portion, which has two branch waveguides branching from a single optical waveguide. The two branch waveguides are combined to form a single optical waveguide. Each branch waveguide has an even number of foldback portions. Therefore, the input and output portions of the optical waveguide can be arranged on the same side of the substrate on which the optical waveguide is formed, reducing the structural differences between the branch waveguides and minimizing the optical path difference between the branch waveguides. As a result, the wavelength dependence of the operating bias voltage of the Mach-Zehnder type optical waveguide can be suppressed, as can the propagation loss of light waves in each branch waveguide, achieving a high on / off extinction ratio. Attached Figure Description

[0026] Figure 1 This is a top view showing a first embodiment of the light control element of the present invention.

[0027] Figure 2 This is a top view showing a second embodiment of the light control element of the present invention.

[0028] Figure 3 This is a top view showing a third embodiment of the light control element of the present invention.

[0029] Figure 4 This is a top view showing a fourth embodiment of the light control element of the present invention.

[0030] Figure 5 This is a top view showing a fifth embodiment of the light control element of the present invention.

[0031] Figure 6 This is a top view showing a sixth embodiment of the light control element of the present invention.

[0032] Figure 7 This is a top view showing a seventh embodiment of the light control element of the present invention.

[0033] Figure 8 This is a top view showing the eighth embodiment of the light control element of the present invention.

[0034] Figure 9 This is a top view showing the ninth embodiment of the light control element of the present invention.

[0035] Figure 10 This is a top view showing the optical modulation device and optical transmission apparatus of the present invention. Detailed Implementation

[0036] Hereinafter, the present invention will be described in detail using preferred embodiments.

[0037] like Figures 1 to 9 As shown, the present invention relates to an optical control element comprising: a substrate 1 having an electro-optic effect; an optical waveguide 2 formed on the substrate; and control electrodes (M, B1 to B2, etc.) for controlling light waves propagating in the optical waveguide. The optical control element is characterized in that the input portion (incident light L1) and the output portion (outgoing light L2) of the optical waveguide are formed on the same side of the substrate, the optical waveguide has at least one Mach-Zehnder type optical waveguide portion (MZ), the Mach-Zehnder type optical waveguide portion (MZ) has two branch waveguides (21, 22) branching from one optical waveguide and combining the two branch waveguides to form one optical waveguide, the branch waveguide having an even number of foldback portions (A1, A2).

[0038] As the substrate 1 with electro-optic effect, it can be a substrate such as lithium niobate (LN), lithium tantalate (LT), PLZT (lead lanthanum zirconate titanate), or a vapor-grown film based on these materials, or a composite substrate formed by bonding these materials to a different type of substrate.

[0039] Alternatively, various materials such as semiconductor materials or organic materials can be used as optical waveguides.

[0040] As a method for forming an optical waveguide, a convex ridge-shaped optical waveguide can be formed by etching the surface of a substrate other than the optical waveguide or by forming grooves on both sides of the optical waveguide. Furthermore, a high-refractive-index portion can be formed on the substrate surface using methods such as thermal diffusion or proton exchange to form an optical waveguide. Composite optical waveguides can also be formed by diffusing high-refractive-index materials into the ridge-shaped optical waveguide portion.

[0041] In order to achieve speed matching between the microwave and light waves of the modulation signal, the thickness of the substrate with the optical waveguide is set to be 10 μm or less, more preferably 5 μm or less.

[0042] Furthermore, the ratio h / t of the height h of the ridge waveguide (from the bottom edge of the grooves on both sides of the ridge waveguide to the top edge of the ridge waveguide protrusion) to the substrate thickness t of the ridge waveguide portion (from the bottom surface of the substrate to the top edge of the ridge waveguide protrusion) is set to 0.8 or less. For example, when the substrate thickness t is 1 μm or less, h / t is set to the range of 0.6 to 0.8. Moreover, a vapor-grown film can be formed on the reinforcing substrate 1, and this film can be processed into the shape of the waveguide described above.

[0043] To improve mechanical strength, the substrate forming the optical waveguide is directly bonded to or bonded to a reinforcing substrate via an adhesive layer such as resin. As the reinforcing substrate for direct bonding, a material with a lower refractive index than the optical waveguide or the substrate forming the optical waveguide, and a thermal expansion coefficient close to that of the optical waveguide, such as quartz, is preferred. Furthermore, when bonding to the reinforcing substrate via a low-refractive-index intermediate layer, the same material as the substrate forming the optical waveguide, such as an LN substrate, can be used as the reinforcing substrate, or a substrate with a high refractive index, such as silicon, can be used.

[0044] The light control element of the present invention is characterized in that, as Figure 1 As shown, the optical waveguide 2 formed on the substrate 1 has at least one Mach-Zehnder type optical waveguide section (MZ). Furthermore, the optical path difference between the branch waveguides (21, 22) located between the branch section 20 and the combiner section 23 constituting the Mach-Zehnder type optical waveguide section (MZ) is minimized.

[0045] To minimize the optical path difference between the branch waveguides (21, 22), such as Figure 1 As shown, an even number of fold-back sections (A1, A2) are formed in the branch waveguides. Furthermore, by forming the optical waveguides at fold-back sections A1 and A2 with the same shape, not only can the optical path lengths of the branch waveguides be set to be equal, but the propagation losses of the optical waveguides can also be set to be the same. As a result, the loss difference between the branch waveguides is reduced, and the degradation of the on / off extinction ratio of the Mach-Zehnder type optical waveguide can be suppressed.

[0046] Figure 2 and Figure 3 Possessing and Figure 1 The optical waveguide shape is the same as that of the optical control element, thus revealing the modulation electrode M and the bias electrodes (B1, B2) as control electrodes. Figure 2 and Figure 3 The common technical feature is that, for those made by Figure 1 The multiple sections of the branch waveguides (21, 22) divided by the foldback section (A1, A2) shown are used to set the modulation electrode M and the bias electrode (B1, B2) in different sections.

[0047] exist Figure 1 The structure is divided into three sections: the first section of the front segment of the return section A1 (the section from branch 20 to return section A1), the second section between return sections A1 and A2 (the section from return section A1 to return section A2), and the third section of the rear segment of return section A2 (the section from return section A2 to the wave combiner 23). Figure 2 and Figure 3 In the first interval, the modulation electrode M is configured in the second interval, the bias electrode B1 is configured in the third interval, and the bias electrode B2 is configured in the third interval.

[0048] The modulation electrode M propagates a high-frequency signal, therefore minimizing electrode bending is preferable for reducing high-frequency signal degradation. Therefore, the modulation signal M is configured to be contained within a single interval. Figure 2 In this circuit, the modulation signal S1 is introduced from a direction perpendicular to the extension direction (left-right direction in the figure) of the modulating electrode M (the part where the electric field acts on the optical waveguide), specifically from the upper side of the substrate 1. Therefore, a portion of the introduction portion of the modulation electrode (the part between the input portion of the modulation signal and the active portion) needs to be bent. To suppress the degradation of the high-frequency signal caused by this bending portion, such as... Figure 3 As shown, the modulation signal S1 is introduced by forming a straight line from the input part to the action part of the modulation electrode M. As a result, the bending of the introduction part of the modulation electrode can be reduced, and the degradation of high-frequency signal can be further suppressed.

[0049] The modulation signal S2 is derived from the terminal side of the modulation electrode, but the derived modulation signal S2 is introduced into a terminator including a terminating resistor. Regarding the bending of the electrode in the portion further back than the active part of the modulation electrode, since the degradation of high-frequency signals such as bending loss will not affect the frequency band of electro-optic modulation, a high degree of design freedom can be set. Moreover, in order to reduce the effects of signal leakage or reflection caused by bending, it can be designed as a structure in which the terminator is placed on the substrate or a structure such as a resistive film is made on the substrate.

[0050] like Figure 3Since no bias electrodes (B1, B2) are configured along the propagation direction of the modulation signal S1 in the modulation electrode M, it is possible to suppress the situation where the leakage signal from the modulation electrode is coupled to the bias electrode and is given high-frequency noise, thus making the optical modulation signal unstable.

[0051] The bias electrodes (B1, B2) can effectively utilize the regions where no modulation electrodes are configured. Although only one of the bias electrodes, B1 and B2, functions, it can be achieved through methods such as... Figure 2 and Figure 3 The bias electrode shown occupies multiple sections and is positioned along the length of the optical waveguide, which can reduce the bias voltage and also helps to suppress DC drift. In addition, although the electro-optic efficiency is poor, the light loss caused by the bias electrode can be reduced by moving the bias electrode away from the optical waveguide.

[0052] exist Figure 2 and Figure 3 The example shown is an example of a substrate 1 using a substrate (e.g., an X-cut LN substrate; hereinafter referred to as an X-plate) where signal electrodes are arranged between optical waveguides. Of course, it is self-evident that the present invention can also be applied to examples using substrates where signal electrodes are arranged on optical waveguides (e.g., a Z-cut LN substrate; hereinafter referred to as a Z-plate). Furthermore, even materials other than LN, such as semiconductors, can be used as long as the optical waveguide / electrode arrangement is as described above. It should be noted that... Figure 2 and Figure 3 In order to simplify the accompanying drawings, the description of the grounding electrode has been omitted.

[0053] Furthermore, when the bias electrodes are formed in two different regions, the bias electrodes are made in the same way by having the same sign for the phase change before and after the fold-back section, for example... Figure 2 or Figure 3 (a) Configured as described above.

[0054] Figure 3 (b) and (c) show examples of using a Z-plate, with particular examples of the configuration patterns of the bias electrodes (B1, B2). Figure 3 In (c), the region PR enclosed by the dashed line represents the polarization reversal region.

[0055] Furthermore, when electrodes are configured on the optical waveguide, a dual-electrode modulator structure can be adopted, which achieves zero chirp in the modulation function of the Mach-Zehnder type optical waveguide section, with electrodes configured on the two branch waveguides respectively, or a structure in which a modulation electrode is configured alternately in the two branch waveguides using polarization reversal.

[0056] Figure 4An example of a nested optical waveguide is shown, in which secondary Mach-Zehnder waveguides (MZ1, MZ2) are nested within the primary Mach-Zehnder waveguide. In such a structure, the modulation electrodes can be arranged in multiple intervals (two intervals in this case) to reduce the driving voltage of the modulation electrodes. In this case, a polarization reversal region is set in the section enclosed by the dashed line (one interval) so that the signs of the phase changes of the light waves before and after the foldback are the same.

[0057] The light control element of the present invention can also be applied to, for example... Figure 4 The following diagram illustrates a structure where a single optical waveguide branches into multiple optical waveguides, with Mach-Zehnder type waveguide sections (MZ1, MZ2) set up in each branched waveguide. The branching of the optical waveguide is not limited to a single occurrence; it can branch across multiple segments. Furthermore, the number of branch waveguides in a single branch is not limited to two; it can be three or more. The Mach-Zehnder type waveguide sections set up in the branched waveguides are easily implemented by arranging the branch waveguides of each Mach-Zehnder type waveguide section in a parallel configuration and setting an even number of foldbacks in each branch waveguide.

[0058] Regarding the shape of the optical waveguides at each foldback section, it is preferable to set them to the same shape. Specifically, the radii of curvature of the multiple branch waveguides arranged in parallel are set from the inside to R, R+r, R+2r, ..., R+nr (R and r are constants, and n is a natural number). Moreover, in order to obtain a larger radius of curvature R, the bending angle of the foldback can be set to be larger than 180 degrees (adjacent intervals are considered parallel) (see reference figure). However, it is self-evident that the shapes at different foldback sections should be set to be the same.

[0059] exist Figure 4 In this design, two modulation electrodes (M1, M2) are configured for the secondary Mach-Zehnder waveguides (MZ1, MZ2), and two modulation signals (S11, S12) are input. Furthermore, regarding the bias electrodes, bias electrode BM is configured for the primary Mach-Zehnder waveguide, and bias electrodes BS1 and BS2 are configured for the secondary Mach-Zehnder waveguides. Sufficient space is ensured for each bias electrode (BM, BS1, BS2), thus reducing the bias voltage.

[0060] It can also be like Figure 4 Instead of separately setting up bias electrodes, the bias electrode BM is configured in the main Mach-Zehnder type optical waveguide and the bias electrodes (BS1, BS2) are configured in the secondary Mach-Zehnder type optical waveguide. Instead, the modulation signal applied to the modulation electrode is applied with a DC bias.

[0061] Figure 5This diagram shows two nested optical waveguides arranged side-by-side. The four side-by-side Mach-Zehnder waveguides (MZ1 to MZ4) are configured with modulation electrodes (M1 to M4) and bias electrodes (BS1 to BS4) for each Mach-Zehnder waveguide. Furthermore, bias electrodes (BM1 and BM2) are also provided corresponding to the main Mach-Zehnder waveguide of each nested waveguide.

[0062] Figure 5 This illustrates an optical control element with polarization combining function. Incident light L1 is directed into the optical waveguide within the substrate 1 via lens 30, which is disposed on optical block 3. The incident light is split into two midway, each modulated by a nested optical waveguide, outputting two modulated signal lights. The two light waves emitted from substrate 1 are directed into optical fiber F via lenses (31, 32, 36). At this time, one light wave undergoes a polarization surface rotation via half-wave plate 33, and is then combined with other light waves via reflection unit 34 and polarization combining unit 35, resulting in a single output light. Figure 5 The diagram illustrates the synthesis process using space optics, but polarized wave synthesis can also be performed using waveguide elements.

[0063] exist Figure 5 In this design, the optical path lengths of each optical waveguide, from branching the input-side waveguide into two to being directed into each nested waveguide, are different. Therefore, it is essential to precisely adjust the timing of the modulation signals (S11, S12, S13, S14) applied to the optical waveguides at the active parts (M1, M2, M3, M4) of the modulation electrodes. To achieve this, the modulation signals are adjusted using a digital signal processor (DSP; not shown), the phase difference is adjusted, and the output signal is amplified by a drive circuit (not shown) and applied as a modulation signal to the optical control element.

[0064] Figure 6 It possesses and Figure 5 The same optical control element with polarization synthesis function. Figure 6 In this configuration, for an input waveguide where incident light is incident, two nested waveguides are configured on the left and right sides of the input waveguide after the waveguide is branched into two. This configuration is consistent with... Figure 5 Compared to the previous embodiment, there is a disadvantage that the distance between the output lenses 30 and 32 in the attached figure becomes larger, making it difficult to align the polarized wave synthesis during installation. However, the active parts (M1 to M4) of the modulation electrodes can be arranged separately from each other, thus suppressing crosstalk between modulation signals.

[0065] Figure 7 yes Figure 6 In a variation of the embodiment, the positions of the incident light L1 and the emitted light (L21, L22) are arranged separately. Along with this, modulation electrodes (M1 to M4) are arranged near the input waveguide.

[0066] In this structure, with Figure 6 Compared to other structures, the modulation electrodes of the two structures are positioned close to each other, thus suppressing the transmission loss of the modulation signal before it is input to the modulation electrodes.

[0067] It should be noted that, Figure 7 Although the polarized wave synthesis function is not illustrated, it can be configured. Furthermore, in Figure 7 From now on, only the positions of the modulating electrode and the bias electrode will be shown; the lead-in parts of each electrode will be omitted.

[0068] Figure 8 yes Figure 7 In a variation of the embodiment, the incident light L1 is positioned at the upper portion of the substrate 1, nested optical waveguides are stacked, one outgoing light L21 is positioned near the center of the substrate 1, and another outgoing light L22 is positioned at the lower portion of the substrate 1.

[0069] Figure 9 With Figure 8 Unlike previous embodiments, the modulation electrode and bias electrode are arranged in a direction perpendicular to the incident direction of the light wave (the left-right direction in the attached figure). This provides a high degree of design freedom for the optical waveguide of the optical control element of the present invention, allowing for various design approaches.

[0070] like Figure 10 As shown, the optical control element 1 of the present invention is housed within a housing 4 made of metal or the like, and the exterior of the housing is connected to the optical control element 1 via an optical fiber F, thereby providing a compact optical modulation device MD. Of course, the optical fiber can be directly connected not only to the incident or exit portion of the optical waveguide on the substrate 1, but also optically connected via a space optical system.

[0071] An electronic circuit (digital signal processor DSP) that outputs a modulation signal to modulate the optical modulator MD is connected to the optical modulator MD, thereby constructing an optical transmitting device OTA. The modulation signal applied to the optical control element needs to be amplified, therefore a driver circuit DRV is used. The driver circuit DRV and the digital signal processor DSP can be configured outside the housing 4, or they can be configured inside the housing 4. In particular, by configuring the driver circuit DRV inside the housing, the propagation loss of the modulation signal from the driver circuit can be further reduced.

[0072] Industrial availability

[0073] As described above, according to the present invention, an optical control element can be provided that allows the input and output portions of an optical waveguide to be arranged on the same side of a substrate on which an optical waveguide is formed, thereby reducing the structural differences between the branch waveguides and minimizing the optical path difference between the branch waveguides. Furthermore, an optical modulation device and an optical transmission apparatus using this optical control element can be provided.

[0074] Explanation of reference numerals in the attached figures

[0075] 1 substrate

[0076] 2 Optical waveguide

[0077] 21 and 22 branch waveguides

[0078] A1, A2 Return Section

[0079] B1 and B2 bias electrodes (active parts)

[0080] M Modulation electrode (Actuating part)

[0081] MD optical modulation device

[0082] MZ Mach-Zehnder type optical waveguide

[0083] OTA optical transmission device

Claims

1. An optical control element comprising: a substrate having an electro-optic effect; an optical waveguide formed on the substrate; and a control electrode for controlling a light wave propagating in the optical waveguide. The optical control element is characterized in that... The input and output portions of the optical waveguide are formed on the same side of the substrate. The optical waveguide has at least four Mach-Zehnder type optical waveguide sections, each of which has two branch waveguides branching from a single optical waveguide, and the two branch waveguides are combined to form a single optical waveguide. Two nested optical waveguides are arranged side by side. These nested waveguides are formed by arranging the branch waveguides of the master Mach-Zehnder waveguide in a nested manner to form a secondary Mach-Zehnder waveguide. The optical path lengths of each optical waveguide, from the branching of the input-side optical waveguide into two to the input of each nested optical waveguide, are different. This Mach-Zehnder type optical waveguide has an even number of foldbacks, and the adjacent intervals divided by these foldbacks are parallel, and the optical path lengths of the branch waveguides are set to be equal. The control electrode has at least a modulation electrode. The modulation electrode has an input section for inputting a modulation signal, an active section for applying an electric field to the optical waveguide, and a guide section for the portion between the input section and the active section. The modulated signal is adjusted for phase difference and then output using a digital signal processor. The line from the input section to the operating section is straight.

2. The optical control element according to claim 1, characterized in that, A single optical waveguide branches into multiple optical waveguides, and each branch is provided with a Mach-Zehnder type optical waveguide section. When the Mach-Zehnder type optical waveguide sections are arranged side by side, each branch waveguide of the Mach-Zehnder type optical waveguide section has an even number of foldbacks.

3. The optical control element according to claim 1 or 2, characterized in that, The control electrode also has a bias electrode, and for multiple intervals divided by the foldback of the branch waveguide, the modulation electrode and the bias electrode are located in different intervals.

4. An optical modulation device, characterized in that, It comprises: an optical control element as described in any one of claims 1 to 3; a housing for housing the optical control element; and an optical fiber for inputting and outputting optical waves to the optical control element.

5. The optical modulation device according to claim 4, characterized in that, Inside the housing is an electronic circuit that amplifies the modulation signal input to the light control element.

6. An optical transmitting device, characterized in that, It comprises: the optical modulation device as described in claim 4 or 5; and an electronic circuit that outputs a modulation signal that causes the optical modulation device to perform modulation.

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