Optical modulator and optical transmitter using same

Abstract

To provide an optical modulator that, even when the width of a signal electrode in an action unit of a light control board is reduced, can reliably perform electrical connection between the signal electrode and signal wiring of a wiring board.SOLUTION: An optical modulator comprises: a light control board 1 having an optical waveguide OW that includes at least a branch waveguide branching one light wave into two, and a control electrode for applying an electric field to the branch waveguide; and a wiring board provided with wiring that relays an electric signal applied to the control electrode or wiring that terminates the electric signal. The control electrode includes a signal electrode S. The wiring includes signal wiring. In a portion Sc electrically connecting the signal electrode S and the signal wiring with each other, the interval W1 in which the branch waveguide OW sandwiches the signal electrode is wider than the interval W2 in which the branch waveguide sandwiches the signal electrode in an action portion where the control electrode applies an electric field to the branch waveguide.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an optical modulator and an optical transmitting device using the same, and in particular to an optical modulator comprising an optical control substrate having an optical waveguide including at least a branching waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branching waveguide, and a wiring substrate provided with wiring that relays an electrical signal applied to the control electrode. [Background technology]

[0002] In the fields of optical communication and optical measurement, optical modulators using an optical control substrate having an optical waveguide and a control electrode for controlling the light wave propagating through the optical waveguide are widely used. In recent years, optical modulators have been required to have a wider bandwidth and be smaller in size, and for example, multiple different high-frequency signals are simultaneously applied to one optical modulator.

[0003] Furthermore, in order to simplify the layout of electrical wiring, relay substrates are used to apply electrical signals to each control electrode including the modulation electrodes. As shown in FIG. 1 and Patent Document 1, wire bonding WB is exclusively used for electrical connection from relay substrate 2 to optical control substrate 1 due to ease of wiring. However, in optical modulators with frequencies of several tens of GHz or more, particularly those exceeding 100 GHz, such as the 96GBaud-800G modulator, wire bonding causes large propagation loss of electrical signals.

[0004] Furthermore, as shown in FIG. 1, when multiple control electrodes (S1 to S4) are used, the lengths of the wiring from each input port located near the side of the optical control board on which the relay board is located to the action part of each control electrode (the range indicated by arrow A to the left of the dotted line in FIG. 1) differ, resulting in differences in electrical characteristics between each control electrode (each port).

[0005] In FIG. 2, in order to miniaturize the optical modulator, the optical input / output (Lin, Lout1, Lout2) sections are provided on the same side of the optical control substrate 1. Even in such an optical modulator, for the input electrical signal Sin, the range from each input port to the action section (part indicated by arrow A) of each control electrode (S1 to S4) differs between the control electrodes, and differences in electrical characteristics occur as in FIG. 1. In FIG. 2, only the signal electrode S is indicated by a dotted line. Symbol PD is an optical detection means for detecting a part of the radiated light emitted from the multiplexing section of the optical waveguide OW.

[0006] In order to place the relay board along the side of the optical control board, it is necessary to secure a separate space for placing the relay board, which makes it difficult to reduce the size of the housing that houses the optical control board, etc. Moreover, the relay board requires space for the path design for impedance adjustment, making miniaturization even more difficult.

[0007] As a method for solving these problems, Patent Document 2 also proposes a structure in which a wiring board is arranged so as to overlap the optical control board. However, in the electrical connection between the wiring board and the optical control board, it is difficult to sufficiently secure the electrical connection between the wiring board and the control electrode, especially between the signal wiring related to the modulation signal and the signal electrode. That is, as shown in FIG. 2, in order to reduce the size of the optical modulator, when the optical waveguide is bent sharply, a thin plate rib structure is proposed in which the width and thickness of the optical waveguide are set to about 1 μm or less in order to strengthen the confinement of the light wave by the optical waveguide. For this reason, the interval between the electrodes in which the signal electrode and the ground electrode are arranged so as to sandwich the optical waveguide becomes increasingly narrow, and the width of the signal electrode itself becomes extremely narrow, making it difficult to sufficiently secure the area of ​​the connection part between the signal wiring of the wiring board and the signal electrode. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5494704 [Patent Document 2] JP 2014-191250 A Summary of the Invention [Problem to be solved by the invention]

[0009] The problem to be solved by the present invention is to provide an optical modulator that solves the above-mentioned problems and can reliably establish electrical connection between a signal electrode and a signal wiring of a wiring board even when the width of the signal electrode in the action part of the optical control board is narrowed, and also to provide an optical transmission device using such an optical modulator. [Means for solving the problem]

[0010] In order to solve the above problems, the optical modulator and optical transmitter of the present invention have the following technical features. (1) An optical modulator comprising an optical control board having an optical waveguide including at least a branch waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branch waveguide, and a wiring board provided with wiring for relaying a modulated signal applied to the control electrode, the control electrode comprises a signal electrode and a ground electrode that sandwiches the signal electrode, the wiring comprises a signal wiring and a ground wiring, the signal electrode is sandwiched between the branched branch waveguides in a portion electrically connecting the signal electrode and the signal wiring, the distance at which the branch waveguide sandwiches the signal electrode is wider than the distance at which the two branched branch waveguides sandwich the signal electrode in an action portion where the control electrode applies an electric field to the branch waveguide, and the distance between the ground electrode and the ground wiring is larger than the distance at which the two branched branch waveguides sandwich the signal electrode in a direction in which the modulated signal travels. First Electrical connection And that rear On one side , the signal electrode and the signal wiring but Electrical connection Being It is characterized by the fact that (2) An optical modulator comprising an optical control board having an optical waveguide including at least a branch waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branch waveguide, and a wiring board provided with wiring that terminates a modulated signal applied to the control electrode, the control electrode comprises a signal electrode and a ground electrode that sandwiches the signal electrode, the wiring comprises a signal wiring and a ground wiring, the signal electrode is sandwiched between the branched branch waveguides in a portion electrically connecting the signal electrode and the signal wiring, the distance at which the branch waveguide sandwiches the signal electrode is wider than the distance at which the two branched branch waveguides sandwich the signal electrode in an action portion where the control electrode applies an electric field to the branch waveguide, and the distance between the signal electrode and the signal wiring is larger than the distance at which the signal electrode is sandwiched between the signal electrode and the signal wiring in a direction in which the modulated signal travels. First Electrical connection And that rear On one side , the ground electrode and the ground wiring but Electrical connection Being It is characterized by the fact that

[0011] ( 3 ) Above (1) Or (2) In the optical modulator according to the present invention, the wiring board includes modulation The wiring that relays the signal and the modulation The present invention is characterized in that a wiring for terminating a signal is formed together.

[0012] ( 4 ) Above (1) or (3) In the optical modulator described in the above, the electrically connected portion is electrically connected by using a flip chip connection.

[0013] ( 5 ) (1) to ( 4 ) The optical modulator according to any one of claims 1 to 4, wherein the optical waveguide is formed of a thin plate rib structure with protrusions having a height of 1 μm or less.

[0014] (6) The above (1)In the described optical modulator, a driver circuit element that generates an electrical signal to be applied to the control electrode is disposed adjacent to the optical control substrate, and the output terminal of the driver circuit element is connected to the wiring of the wiring substrate.

[0015] ( 7 ) the above (6) and a signal generator for generating a modulated signal to be input to the driver circuit element. Effect of the Invention

[0016] According to the present invention, in an optical modulator comprising an optical control board having an optical waveguide including at least a branch waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branch waveguide, and a wiring board provided with wiring for relaying an electrical signal applied to the control electrode, the control electrode comprises a signal electrode, the wiring comprises a signal wiring, and in a portion where the signal electrode and the signal wiring are electrically connected, the distance between the branch waveguide and the signal electrode is wider than the distance between the branch waveguide and the signal electrode in an action portion where the control electrode applies an electric field to the branch waveguide, so that a sufficient width of the signal electrode can be secured in the portion where the signal electrode and the signal wiring are electrically connected, and it is possible to reliably make an electrical connection between the two. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating an example of a conventional optical modulator. [Diagram 2] FIG. 13 is a diagram showing another example of a conventional optical modulator. [Diagram 3] 1 is a diagram showing an example of an optical modulator according to the present invention; [Figure 4] 4 is an enlarged view of a portion Sc of the control electrode in FIG. 3 to which an electrical signal is input. [Diagram 5] 4 is a diagram showing a state in which a wiring board (relay board) 20 is superimposed on the optical control board 1 of the optical modulator of FIG. 3. FIG. [Figure 6] FIG. 6 is a cross-sectional view showing the state of electrical connection between the signal electrode and the wiring board in FIG. 5. [Figure 7] FIG. 13 is a diagram showing another example of an optical modulator according to the present invention. [Figure 8] FIG. 8 is a diagram showing a state in which a wiring board (relay board) 20 and a wiring board (termination board) 21 are superimposed on the optical control board 1 of the optical modulator in FIG. [Figure 9] 1 is a diagram showing an optical transmitting device according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will now be described in detail with reference to preferred embodiments. As shown in Figures 3 to 8, the present invention is an optical modulator comprising an optical control substrate 1 having an optical waveguide OW including at least a branch waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branch waveguide, and a wiring substrate (20, 21) provided with wiring for relaying an electrical signal applied to the control electrode or wiring for terminating the electrical signal, wherein the control electrode comprises a signal electrode S, and the wiring comprises a signal wiring, and as shown in Figure 4, in a portion (signal electrode side is Sc) that electrically connects the signal electrode and the signal wiring, a distance W1 at which the branch waveguide sandwiches the signal electrode is wider than a distance W2 at which the branch waveguide sandwiches the signal electrode in an action portion (symbol A) where the control electrode applies an electric field to the branch waveguide.

[0019] Fig. 3 is a diagram showing an optical control substrate 1 constituting an optical modulator according to the present invention, in which an optical waveguide OW and a control electrode (signal electrode S and ground electrode are not shown) are formed. Fig. 4 is an enlarged view of a portion of the signal electrode S in Fig. 3 where an electrical signal is input. Furthermore, Fig. 5 shows a state in which a wiring substrate (relay substrate 20) having a line for relaying an electrical signal is superimposed on the optical control substrate 1 in Fig. 4. Also, Fig. 6 shows a part of a cross-sectional view taken along dashed line B-B' in Fig. 5.

[0020] As the optical control substrate 1 including the optical waveguide OW, a ferroelectric substrate having an electro-optic effect such as lithium niobate (LN), lithium tantalate (LT), or PLZT (lead lanthanum zirconate titanate) can be used, but it is also possible to use a substrate in which a vapor-deposited film made of these materials is formed on a reinforcing substrate. Furthermore, substrates made of various materials such as semiconductor materials such as InP and organic materials can also be used. Quartz, crystal, etc. can be used for the reinforcing substrate.

[0021] As a method for forming the optical waveguide, it is possible to use a rib-type optical waveguide in which the portion of the substrate corresponding to the optical waveguide is made convex by etching the substrate surface other than the optical waveguide (OW1, OW2) or by forming grooves on both sides of the optical waveguide, as shown in Fig. 6. Furthermore, in addition to forming the rib-type optical waveguide, it is also possible to use a composite optical waveguide, for example by forming a high refractive index portion on the substrate surface using Ti or the like by thermal diffusion method or proton exchange method.

[0022] The thickness of the substrate 100 on which the optical waveguide is formed is 5 μm or less, more preferably 3 μm or less, in order to achieve speed matching between the microwave and light waves of the modulating signal. The thin plate can be formed by directly bonding the substrate 100 to the reinforcing substrate 110 and polishing it thin, or by forming the substrate 100 on the reinforcing substrate 110 as a vapor-phase grown film. The height of the rib-type optical waveguides (OW1, OW2) is set to 2 μm or less, more preferably 1 μm or less.

[0023] The control electrodes that apply an electric field to the optical waveguides (OW1, OW2) include a combination of a signal electrode that propagates a microwave electric signal such as a modulation signal and a ground electrode, a bias electrode that applies a DC bias voltage, etc. The control electrodes can be formed along the optical waveguide by laminating Au on an underlying metal such as Au or Ti by plating.

[0024] As shown in Fig. 6, when the optical waveguide (OW1, OW2) has a rib structure of a thin plate with a height of the convex part of 1 μm or less, the control electrode, especially the modulation electrode consisting of the signal electrode S and the ground electrode GND, needs to be considered as a structure that applies an efficient electric field to the optical waveguide and a structure that matches the propagation speed of the electric signal and the light wave and reduces the propagation loss of the electric signal. For this reason, the signal electrode S and the ground electrode GND are each provided with a lower electrode part (Slp and Glp), and these lower electrode parts are arranged close to the optical waveguide (OW1, OW2). In addition, upper electrode parts (Sup and Gup) narrower than the lower electrode parts are arranged above the lower electrode parts (Slp and Glp), and the signal electrode S and the ground electrode GND are spaced apart, and a sufficient cross-sectional area is secured in the signal electrode, etc., so that the height of the upper electrode part is, for example, several tens of μm or more.

[0025] 3 is a plan view showing an example of the optical control substrate 1 used in the optical modulator of the present invention. The optical waveguide OW is configured so that the input light Lin passes through three branching sections to form eight branching waveguides, and then passes through two multiplexing sections to finally emit two output lights (Lout1, Lout2).

[0026] The dotted frame DC1 and DC2 indicate the regions where DC bias electrodes for bias control are arranged. The symbol C indicates the region where the optical waveguide is bent, and by setting the height and width of the optical waveguide to 1 μm or less, it is possible to strengthen the confinement of light and reduce the radius of curvature. The dotted frame A indicates the action part where an electric field is applied to the optical waveguide (branching waveguide) by the control electrode (modulation electrode). PD is a light receiving element that receives a part of the output light (Lout1, Lout2) before it is emitted. Instead of such a light receiving element, it is also possible to arrange a light receiving element to receive the radiation mode light in the multiplexing section, which is a technology well known to those skilled in the art.

[0027] In FIG. 3, only the signal electrode S in the control electrode is clearly shown. The input portion Sc of the signal electrode S is configured with a portion that is wider than the width of the signal electrode in the action portion, as shown in an enlarged view in FIG. 4. This functions as the connection portion on the signal electrode side when performing flip-chip connection as described later. As shown in FIG. 4, the width of the electrical connection portion Sc of the signal electrode S becomes wider, and the interval of the branch waveguide (OW) also becomes wider accordingly. Therefore, in the connection portion Sc of the signal electrode, the interval W1 where the branch waveguide (OW) sandwiches the signal electrode S is wider than the interval W2 where the branch waveguide sandwiches the signal electrode S in the action portion A. The reason why the optical waveguide can be bent sharply in this way is also due to the strong light confinement of the optical waveguide as described above.

[0028] In FIG. 4, the ground electrodes GND are also clearly shown to sandwich the signal electrode S. As with the signal electrode, the ground electrode also needs to be electrically connected to the wiring (ground wiring) of the wiring board, and in FIG. 4, the connection part of the ground electrode is clearly shown by the dotted line Gc. In general, it is possible to make the movement of the electric signal more stable by connecting the ground electrode first in the traveling direction of the modulated signal and then connecting the signal electrode. More preferably, it is also possible to provide multiple (for example, four) connection parts of the ground electrode so that the connection part of the signal electrode is sandwiched between the front and rear of the traveling direction of the modulated signal. L1 is the light input to the branching waveguide, and L2 is the light propagating through the branching waveguide.

[0029] The input portion Sc of the signal electrode S is configured with a portion that is wider than the width of the signal electrode in the action portion, but may be thicker (for example, 5 μm to 30 μm). By increasing the thickness, it is possible to prevent the signal electrode from breaking or peeling off when performing flip-chip connection, and to increase the connection strength.

[0030] Flip chip connection can improve the propagation loss of electrical signals compared to wire bonding connection.Flip chip connection can also make the wiring lengths of multiple signal electrodes the same to some extent, thereby reducing the difference in electrical characteristics between each control electrode.

[0031] A wiring board (intermediate board) 20 as shown in FIG. 5 is used to input an electric signal to the signal electrode S. The wiring board 20 is arranged so as to overlap the light control board 1, and the size of the housing itself that accommodates the light control board is reduced. As an example, the wiring board 20 has an input pad section 20P formed along one side of the wiring board 20, and the input pad section 20P is electrically connected to a wiring 20L arranged on the lower surface (the surface on the light control board side) of the wiring board 20. The wiring 20L includes a signal wiring and a ground wiring, and the other end of the wiring 20L is electrically connected to the signal electrode connection section Sc and the ground electrode connection section Gc shown in FIG. 3 or FIG. 4 at a flip chip connection section FC. FIG. 6 shows the state of connection with the wiring board 20 side (signal wiring is not shown) by the flip chip connection section FC in the signal electrode S. The size of the flip chip connection is, for example, about 30 to 60 μm in width, and the width of the connection section of the signal electrode is set to about 30 to 80 μm correspondingly.

[0032] The signal electrode S in Fig. 3 is configured such that, after passing through the action portion A, it is connected to an output pad portion arranged along the side of the light control substrate 1, as in the conventional example in Fig. 2, and outputs (Sout) an electrical signal (modulation signal) to the outside. In contrast, in Figs. 7 and 8, a portion (connection portion Sc2) thicker than the action portion is also formed at the end of the output side of the signal electrode, and it is also possible to configure it so as to be directly and electrically connected to the wiring substrate (termination substrate) 21. Fig. 7 is a modified example of Fig. 3, and Fig. 8 is a modified example of Fig. 5.

[0033] Reference numeral 21 in FIG. 8 denotes a termination substrate, on which output pads 21PS connected to signal electrodes are formed. It is also possible to provide output pads 21PG connected to ground electrodes. On the output side of the signal electrode S, generally, the signal electrode is connected first in the direction of propagation of the modulated signal, and then the ground electrode is connected, in order to suppress radiation of the modulated signal from the signal electrode. More preferably, it is also possible to provide a plurality of (for example, four) ground electrode connection parts so as to sandwich the connection part of the signal electrode before and after the direction of propagation of the modulated signal. A termination element TE such as a termination resistor is provided on the termination substrate 21, and is electrically connected to the output pads (21PS, 21PG).

[0034] In FIG. 8, the terminal substrate 21 is provided separately from the relay substrate 20, but it is also possible to form both substrates as an integrated wiring substrate. Of course, in the optical modulator of the present invention, the relay substrate can be the same as in the past, and only the terminal substrate can be arranged so as to be superimposed on the optical control substrate 1 as in FIG. 8. In addition, when the light receiving element PD is arranged close to the wiring substrate, it is preferable to set the shape of the wiring substrate and the arrangement of the light receiving element so that the wiring substrate (20, 21) and the light receiving element PD do not overlap. The light receiving element PD can be configured not only to detect the radiation light from the multiplexing portion of the optical waveguide OW, but also to branch and detect a part of the light wave propagating through the optical waveguide OW.

[0035] FIG. 9 is a diagram illustrating an example of an optical transmitting device. In the optical modulator, a driver circuit element DRV that generates an electric signal to be applied to the control electrode is disposed adjacent to the optical control substrate 1, and an output terminal of the driver circuit element is connected to the wiring of the wiring substrate 20 described above. An input light Lin is input to the optical control substrate 1 in Fig. 9 using an optical fiber F via an optical component such as a lens. On the other hand, the light waves output from the optical control substrate 1 are combined, for example, via a polarization combining means PC, and input to another optical fiber via an optical component such as a lens to become an output light Lout.

[0036] Furthermore, it is possible to provide a signal generator DSP that generates a modulated signal S0 to be input to the driver circuit element DRV, and configure it as an optical transmitter. It is also possible to incorporate the optical modulator and the driver circuit element into a case CS, and further to incorporate the case CS and the signal generator DSP into a single chassis. [Industrial Applicability]

[0037] As described above, according to the present invention, it is possible to provide an optical modulator that can reliably establish electrical connection between a signal electrode and a signal wiring of a wiring board even when the width of the signal electrode in the action portion of the optical control board is narrowed. It is also possible to provide an optical transmission device using such an optical modulator. [Explanation of symbols]

[0038] 1 Optical control board 20 Wiring board (relay board) 21 Wiring board (termination board) S signal electrode Sc Signal electrode connection part GND ground electrode Gc Ground electrode connection part OW Optical Waveguide

Claims

1. an optical control substrate having an optical waveguide including at least a branching waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branching waveguide; In an optical modulator having a wiring board provided with wiring for relaying a modulation signal applied to the control electrode, the control electrode includes a signal electrode and ground electrodes sandwiching the signal electrode; the wiring comprises a signal wiring and a ground wiring, In a portion where the signal electrode and the signal wiring are electrically connected, the signal electrode is sandwiched between the branched waveguides, and a distance between the branched waveguides and the signal electrode is wider than a distance between the two branched waveguides and the signal electrode in an action portion where the control electrode applies an electric field to the branched waveguide; an optical modulator characterized in that, in the direction of propagation of the modulation signal, the ground electrode and the ground wiring are electrically connected first, and then, behind that, the signal electrode and the signal wiring are electrically connected.

2. an optical control substrate having an optical waveguide including at least a branching waveguide that branches one optical wave into two, and a control electrode for applying an electric field to the branching waveguide; In an optical modulator having a wiring board provided with wiring for terminating a modulation signal applied to the control electrode, the control electrode includes a signal electrode and ground electrodes sandwiching the signal electrode; the wiring comprises a signal wiring and a ground wiring, In a portion where the signal electrode and the signal wiring are electrically connected, the signal electrode is sandwiched between the branched waveguides, and a distance between the branched waveguides and the signal electrode is wider than a distance between the two branched waveguides and the signal electrode in an action portion where the control electrode applies an electric field to the branched waveguide; an optical modulator characterized in that, in the direction of propagation of the modulation signal, the signal electrode and the signal wiring are electrically connected first, and then, behind that, the ground electrode and the ground wiring are electrically connected.

3. 3. The optical modulator according to claim 1, wherein said wiring board is formed with both a wiring for relaying said modulated signal and a wiring for terminating said modulated signal.

4. 4. The optical modulator according to claim 1, wherein the electrically connected portion is electrically connected by flip chip connection.

5. 5. An optical modulator according to claim 1, wherein said optical waveguide is formed of a thin plate having a rib structure with protrusions having a height of 1 [mu]m or less.

6. 2. The optical modulator according to claim 1, wherein a driver circuit element for generating an electrical signal to be applied to the control electrode is disposed adjacent to the optical control substrate, and an output terminal of the driver circuit element is connected to the wiring of the wiring substrate.

7. 7. An optical transmitter comprising: an optical modulator according to claim 6; and a signal generator for generating a modulating signal to be input to said driver circuit element.

Images