Optical modulator and optical transmission apparatus using the same

Abstract

Provided is an optical modulator capable of suppressing crosstalk of a modulation signal even when a wiring substrate is arranged overlapping a modulation substrate. The optical modulator includes a modulation substrate (1) having an optical waveguide and a modulation electrode (10) for modulating an optical wave propagating in the optical waveguide, and a wiring substrate (2) provided with a wiring (22) for relaying a modulation signal applied to the modulation electrode (10). The optical modulator is characterized in that the wiring substrate is arranged overlapping the modulation substrate in a manner of covering an acting portion modulated by the modulation electrode, and an electric wave absorbing member (SH) is arranged at least a portion of a position of the wiring substrate opposite the acting portion.

Description

Technical Field

[0001] The present invention relates to an optical modulator and an optical transmitting apparatus using the optical modulator, and particularly to an optical modulator comprising a modulation substrate and a wiring substrate, the modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide, and the wiring substrate having wiring for relaying the modulation signal applied to the modulation electrode. Background Technology

[0002] In the fields of optical communication and optical measurement, optical modulators are commonly used. These modulators utilize a modulation substrate, which has an optical waveguide and modulation electrodes that modulate the light waves propagating in the waveguide. Recent demands for optical modulators include broadband or miniaturization, enabling the simultaneous application of multiple different high-frequency signals to a single modulator.

[0003] When the modulation signal is a microwave above 60 GHz, the signal straightness is high, and the transmission loss increases when the modulation electrodes are electrically connected to the modulation substrate via wire bonding. Therefore, Patent Document 1 proposes a structure in which the wiring substrate is arranged overlapping the modulation substrate.

[0004] When the wiring direction changes due to bending or vias in the wiring board, or when wiring from the wiring board is connected to the modulation electrode of the modulation board, a portion of the modulation signal may be emitted externally, causing interference with the modulation electrode. This crosstalk becomes particularly significant when the wiring board and modulation board are positioned close together. Furthermore, when processing multiple different modulation signals simultaneously, or when the electric field generated by the modulation electrode acts on multiple active parts of the optical waveguide in close proximity, crosstalk cancellation becomes an important challenge.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-191250 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The problem to be solved by the present invention is to provide an optical modulator that can suppress crosstalk of the modulation signal even when a wiring substrate is disposed overlapping with the modulation substrate, thereby solving the problems described above. Furthermore, an optical transmission device using these optical modulators is provided.

[0010] Solution for solving the problem

[0011] In order to solve the above-mentioned problems, the optical modulator and optical transmission device of the present invention have the following technical features.

[0012] (1) An optical modulator comprising: a modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide; and a wiring substrate having wiring provided for relaying a modulation signal applied to the modulation electrode, the optical modulator being characterized in that the wiring substrate is disposed overlapping the modulation substrate in such a way as to cover an active portion, the active portion being modulated by the modulation electrode, and an electromagnetic wave absorbing member is disposed on at least a portion of the wiring substrate at a position opposite to the active portion.

[0013] (2) In the optical modulator described in (1) above, the characteristic is that the electromagnetic wave absorbing member is connected to either the grounding wiring of the wiring board or the grounding electrode of the modulation electrode.

[0014] (3) In the optical modulator described in (1) or (2) above, the characteristic is that a plurality of Mach-Zehnder type optical waveguides are arranged side by side in the working part, and a modulation electrode is arranged corresponding to each Mach-Zehnder type optical waveguide.

[0015] (4) In any of the optical modulators described in (1) to (3) above, the modulation electrode is characterized in that the modulation electrode has a signal electrode and a ground electrode arranged in such a way as to sandwich the signal electrode, and the distance between the signal electrode and the electromagnetic wave absorbing member is greater than the interval between the signal electrode and the ground electrode.

[0016] (5) In the optical modulator described in (3) above, the modulation electrode is characterized by being composed of a signal electrode and a ground electrode, and the ground electrode and the electromagnetic wave absorption member are arranged opposite to each other between a specific Mach-Zehnder type optical waveguide and other adjacent Mach-Zehnder type optical waveguides.

[0017] (6) In the optical modulator described in (5) above, the ground electrode and the electromagnetic wave absorbing member are, when viewed from above, disposed inside the ground electrode, and using the width W of the signal electrode adjacent to the ground electrode and the spacing G between the signal electrode and the ground electrode, the distance S between the sides of the electromagnetic wave absorbing member and the ground electrode satisfies the following formula:

[0018] S≥2G+W... formula.

[0019] (7) In the optical modulator described in (5) or (6) above, the characteristic is that the electromagnetic wave absorbing member extends along the signal electrode beyond the active part.

[0020] (8) In any of the optical modulators described in (1) to (7) above, the characteristic is that a terminator is disposed on the wiring substrate, the terminator being electrically connected to the modulation electrode.

[0021] (9) In any of the optical modulators described in (1) to (8) above, a driving circuit element is disposed adjacent to the modulation substrate, the driving circuit element generates a modulation signal applied to the modulation electrode, and the output terminal of the driving circuit element is connected to the wiring of the wiring substrate.

[0022] (10) An optical transmitting apparatus, characterized in that it comprises: an optical modulator as described in any of (1) to (9) above; and a signal generator for generating a modulation signal input to the driving circuit element.

[0023] Invention Effects

[0024] According to the present invention, an optical modulator includes: a modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide; and a wiring substrate having wiring provided for relaying a modulation signal applied to the modulation electrode. The wiring substrate is disposed overlapping the modulation substrate in a manner that covers an active portion, the active portion being modulated by the modulation electrode. At least a portion of the wiring substrate at a position opposite to the active portion is provided with an electromagnetic wave absorbing member. Therefore, an optical modulator is provided that can effectively suppress crosstalk of the modulation signal even when the wiring substrate is disposed overlapping the modulation substrate. Attached Figure Description

[0025] Figure 1 This is a diagram illustrating an example of the optical modulator of the present invention.

[0026] Figure 2 It is Figure 1 An enlarged side view of a portion of the optical modulator.

[0027] Figure 3 This is a diagram illustrating the wiring substrate used in another embodiment of the optical modulator of the present invention.

[0028] Figure 4 This is an explanation Figure 3 A diagram of the modulation substrate used in an optical modulator.

[0029] Figure 5 yes Figure 3 and 4 A side view of an optical modulator.

[0030] Figure 6 yes Figure 5 The cross-sectional view of the optical modulator shown by the dashed lines A1 to A3.

[0031] Figure 7 This is a diagram showing an example of a configuration pattern for an electromagnetic wave absorbing component.

[0032] Figure 8 yes Figure 7 The cross-sectional view at the dashed line A3.

[0033] Figure 9 yes Figure 8 A magnified view of a portion of the diagram illustrates the placement of the electromagnetic wave absorbing components.

[0034] Figure 10 This is a diagram illustrating yet another embodiment of the optical modulator of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail using preferred embodiments.

[0036] like Figures 1 to 10 As shown, the present invention relates to an optical modulator comprising: a modulation substrate 1 having an optical waveguide and a modulation electrode 10 for modulating an optical wave propagating in the optical waveguide; and a wiring substrate 2 having wiring 22 for relaying a modulation signal applied to the modulation electrode 10. The wiring substrate is characterized in that it overlaps with the modulation substrate in a manner that covers an active portion, the active portion being modulated by the modulation electrode, and an electromagnetic wave absorbing member SH is disposed on at least a portion of the wiring substrate at a position opposite to the active portion.

[0037] Figure 1 This is a top view illustrating an example of an optical modulator. Previously, the mainstream approach was to introduce input light into one end face of the optical modulator and derive output light from the other end face. However, in recent years, such as... Figure 1 As shown, the input collimator 6 for the input light L1 and the output collimator 60 for the output light L2 are both positioned on one side of the optical modulator (right side of the figure) to facilitate the connection of optical signals. An optical waveguide is formed on the modulation substrate 1 to allow the input light L1 to be incident and the output light L2 to be output.

[0038] On the other hand, an input terminal 4 for the input modulation signal Sin is provided on the opposite side of the input / output section of the light wave. The input terminal 4 is constructed from flexible wiring or connector terminals, etc. Furthermore, the modulation signal Sin is generated by a digital signal processor (DSP) or similar device disposed outside the housing. The modulation signal Sin input from the input terminal 4 is input to the drive circuit element 3 via the circuit board 40. The drive circuit element 3 is a multi-stage structure of signal amplifiers, outputting the amplified modulation signal. The modulation signal output from the drive circuit element 3 is applied to the modulation electrode of the modulation board 1 via the wiring board 2.

[0039] The drive circuit element 3 can be housed inside the housing 5 in the same way as the modulation substrate 1, but it can also be disposed outside the housing 5. Furthermore, reference numeral 50 indicates a cover member for hermetically sealing the housing 5.

[0040] As a modulation substrate, a strong dielectric substrate with electro-optic effect, such as lithium niobate (LN) or lithium tantalate (LT), PLZT (lead lanthanum zirconate titanate), can be used, or a structure in which a vapor-phase grown film based on these materials is formed on a reinforcing substrate.

[0041] Alternatively, substrates made of various materials such as semiconductor materials like InP or organic materials can be used.

[0042] As a method for forming an optical waveguide, a convex ridge-shaped optical waveguide can be formed on the substrate by etching the surface of the substrate other than the optical waveguide or by forming grooves on both sides of the optical waveguide. Furthermore, an optical waveguide can also be formed by forming a high-refractive-index portion on the substrate surface using methods such as thermal diffusion or proton exchange on Ti. A composite optical waveguide can also be formed by diffusing a high-refractive-index material in the ridge-shaped optical waveguide portion.

[0043] The thickness of the modulation substrate on which the optical waveguide is formed can be 10 μm or less, more preferably 5 μm or less, to achieve velocity matching between the microwave and light waves of the modulation signal. Furthermore, the height of the ridge-shaped optical waveguide is set to 2 μm or less, more preferably 1 μm or less. Additionally, a vapor-grown film can be formed on the reinforcing substrate and then processed into the shape of an optical waveguide.

[0044] The modulation substrate, made of a thin plate, has improved mechanical strength, and can therefore be directly bonded or bonded to a reinforcing substrate via an adhesive layer such as resin. For direct bonding, a material with a lower refractive index than the optical waveguide or the substrate in which the optical waveguide is formed, and a thermal expansion coefficient close to that of the optical waveguide, such as quartz, is preferred as the reinforcing substrate. Furthermore, when bonding to the reinforcing substrate via an adhesive layer, the same material as a thin plate such as an LN substrate can also be used as the reinforcing substrate.

[0045] Modulation electrodes or bias electrodes are formed along the optical waveguide. As a method of forming electrodes, Au can be deposited onto a substrate metal such as Au or Ti using a plating method.

[0046] Figure 2 yes Figure 1 An enlarged view of the dashed box portion in (b) shows that the wiring 22 (25) for propagating the modulation signal is formed on the wiring substrate 2. The wiring substrate 2 uses an insulating substrate made of alumina or aluminum nitride ceramic. Figure 2 Electrical wiring is formed on the upper or lower surface of the wiring board 2. Furthermore, a terminator T for modulation signals is also formed on the wiring board 2.

[0047] Through-holes 23 and 24 are provided on the wiring substrate 2, and wiring is connected on the opposite side of the substrate. The connection between the wiring substrate (the connection wiring portion (pad portion) formed on the back side of the wiring substrate) and the modulation electrode 10 of the modulation substrate 1 is performed by flip-chip bonding. Specifically, there are methods such as forming the pad portion of the wiring substrate with Au electrode pads and connecting it to the Au electrode of the modulation electrode by pressure bonding based on heat / vibration application, or bump connection based on conductive adhesive B, etc.

[0048] like Figure 2 As shown, the modulation signal is introduced from wiring 22 through via hole 23 and bump B to modulation electrode 10. Then, it reaches wiring 25 through bump and via hole 24, and then reaches the terminator T, which is composed of terminating resistors, etc. Since the terminator T becomes a heat source, it can be kept as far away from the substrate 1 as possible.

[0049] like Figure 2 As shown, the optical modulator of the present invention is characterized by the arrangement of an electromagnetic wave absorbing member SH on the wiring substrate 2 at a position opposite to the modulation substrate 1 (the functional part of the modulation electrode 10). The electromagnetic wave absorbing member can be made of a ferrite sintered material using iron, carbon, nickel, Kovar alloy, etc.

[0050] The electromagnetic wave absorbing component can be connected to either the grounding wire of the wiring formed on the wiring board 2 or the grounding electrode (part of the modulation electrode) of the modulation electrode 1, and set to the grounding potential.

[0051] Figures 3-9 This is a diagram illustrating an example of an optical waveguide using two nested optical waveguides. Figure 3 The wiring substrate 2 is shown, with the dotted line WG indicating the optical waveguide formed on another modulation substrate. Reference numeral 3 is a driving circuit element that transmits the modulation signal from the output terminal 30 formed on the upper surface to the pad portion 21 of the wiring on the wiring substrate 2 via wire bonding WB. The modulation signal is guided from the pad portion 21 to the back side of the wiring substrate 2 via the wiring 22 and the via 23.

[0052] like Figure 5 As shown, the modulation signal via the via 23 is connected to the wiring 230 formed on the back side of the wiring substrate 2 and transmitted to the modulation electrode 10 of the modulation substrate 1 via the bump connection B1. Figure 4 This is a top view of the modulation substrate 1. An optical waveguide WG or modulation electrode 10 and bias electrode 11 are formed on the modulation substrate 1. For simplicity, the ground electrode, which is formed across the modulation electrode, is omitted from the drawing.

[0053] The modulation signal, passing through the modulation electrode 10, propagates via the bump connection B2 to the wiring 240 of the wiring board 2, and then reaches the terminator T via the via 24 and wiring 25. The terminator T is configured with a circuit structure incorporating terminating resistors, etc., and converts the modulation signal into heat energy, becoming a heat source. Figure 1 As in (b), the wiring board 2 and the modulation board 1 are hermetically sealed in the metal housing 5, so that the terminal T can be arranged away from the modulation board 1, especially the active part of the modulation electrode 10.

[0054] A bias electrode 11 is formed on the modulation substrate 1 to control the bias voltage of the optical modulation, but the voltage supply to the bias electrode 11 can also be achieved via... Figure 3 and 5 The wiring board 2 has wiring 27, through hole 28, wiring 280, and bump connection B3.

[0055] like Figure 3 and Figure 4 As shown, multiple Mach-Zehnder type optical waveguides are arranged side-by-side in the active portion where the modulation electrode 10 applies an electric field to the optical waveguide. Furthermore, modulation electrodes are arranged corresponding to each Mach-Zehnder type optical waveguide. Different modulation signals are applied to each modulation electrode 10, resulting in crosstalk between them. In this invention, as... Figure 5 As shown, an electromagnetic wave absorbing member SH is disposed on the wiring substrate 2 corresponding to the working portion of the modulation electrode 10. This electromagnetic wave absorbing member SH can suppress the mixing of a portion of the modulation signal leaking from the wiring substrate 2 side into the modulation electrode 10. It should be noted that the electromagnetic wave absorbing member SH is formed on the surface of the wiring substrate 2; however, if necessary, a recess can also be formed in the wiring substrate 2 to embed the member within the recess.

[0056] Figure 6 (a) to (c) show Figure 5 Part of the sectional views at the dashed lines A1 to A3. Here, Figure 6 The labels WG1 and WG2 depicted in (b) and (c) represent branch waveguides of a Mach-Zehnder type optical waveguide WG.

[0057] Especially as Figure 6 As shown in (c), the modulation electrode includes a signal electrode 10 and a ground electrode GND arranged to sandwich the signal electrode 10. The distance H between the signal electrode 10 and the electromagnetic wave absorbing member SH is set to be greater than the interval G between the signal electrode 10 and the ground electrode GND. This is to avoid the presence of the electromagnetic wave absorbing member from hindering the electric field formed between the signal electrode and the ground electrode.

[0058] exist Figure 6The example shown depicts an embodiment where an electromagnetic wave absorbing member SH is positioned above the signal electrode. However, in this case, a portion of the electric field formed by the signal electrode and the ground electrode is absorbed by the electromagnetic wave absorbing member, potentially weakening the electric field applied to the branch waveguides WG1 and WG2. To eliminate this undesirable situation, in Figures 7-9 The present invention describes an embodiment in which an electromagnetic wave absorbing member is configured opposite to a ground electrode configured between signal electrodes 10.

[0059] Figure 7 The arrangement pattern of the electromagnetic wave absorbing member SH on the wiring board 2 is made to coincide with the pattern of the arrangement pattern of the member SH. Figure 4 The figure shows the modulation substrate 1. Electron wave absorbing components SH are disposed between adjacent Mach-Zehnder type optical waveguides or between signal electrodes.

[0060] Figure 8 yes Figure 7 The cross-sectional view is shown at the dashed line A3. A ground electrode GND is disposed between adjacent Mach-Zehnder type optical waveguides (between signal electrodes), and an electromagnetic wave absorbing member SH is disposed on the wiring substrate 2 opposite to this ground electrode. The electromagnetic wave absorbing member SH and the ground electrode GND effectively suppress crosstalk of the modulation signal applied to the active portion of the adjacent Mach-Zehnder type optical waveguides. Moreover, since the electromagnetic wave absorbing member SH is not disposed on the upper side of the signal electrode, the absorption of the electric field formed by the signal electrode can also be suppressed.

[0061] Figure 9 It is Figure 8 A further enlarged view of a portion of the image. For reference, bump B, which electrically connects the ground electrode GND to the grounding wiring provided on the wiring board 2, is also shown. The height H of bump B is approximately 50 μm.

[0062] Viewed from above in the attached diagram Figure 9 In the case of a ground electrode GND and an electromagnetic wave absorbing member SH, the electromagnetic wave absorbing member SH is disposed inside the ground electrode GND. Furthermore, the distance S between their sides is set so as not to affect the electric field forming the signal electrode 10 (SIG1 or SIG2) as much as possible. Specifically, it is set in a manner that satisfies the following formula using the width W of the signal electrode adjacent to the ground electrode and the distance G between the signal electrode and the ground electrode.

[0063] S≥2G+W……Formula

[0064] In addition, such as Figure 7As shown, by extending the length of the modulation signal propagation direction (along the direction of the signal electrode 10) of the electromagnetic wave absorbing member SH beyond the working portion of the signal electrode 10, crosstalk signals emitted from the connection portion, i.e., the bump connection B1, between the wiring 230 formed on the back side of the wiring board 2 and the modulation electrode 10 of the modulation board 1 can be effectively blocked. It should be noted that... Figure 7 The area of ​​the active part (the lateral width in the attached figure) is approximately the same as the length of the signal electrode 10. Figure 7 In the process, the length of the radio wave shielding component SH is longer than the length of the signal electrode 10.

[0065] Figure 10 yes Figure 5 In a modified example, wiring 22 is provided on the back side of the wiring substrate 2. Furthermore, a drive circuit element 3 that generates a modulation signal applied to the modulation electrode 10 is disposed adjacent to the modulation substrate 1, and the wiring 22 of the wiring substrate 2 is connected to an output terminal formed on the upper surface of this drive circuit element. Thus, Figure 5 The wire bonding (WB) is also omitted, simplifying wiring. Figure 10 In this configuration, the terminator T is positioned on the lower surface of the wiring substrate 2, but it can, of course, be connected to... Figure 5 Similarly, it is also disposed on the upper surface of the wiring board 2.

[0066] By providing the aforementioned optical modulator and a signal generator that generates a modulation signal input to the drive circuit elements within the optical modulator, an optical transmitting device with the same effect can also be provided.

[0067] Industrial applicability

[0068] As described above, according to the present invention, it is possible to provide an optical modulator that can suppress crosstalk of the modulation signal even when a wiring substrate is disposed overlapping with the modulation substrate. Furthermore, it is also possible to provide an optical transmission device using these optical modulators.

[0069] Label Explanation

[0070] 1. Modulation substrate

[0071] 2 Wiring board

[0072] 3. Drive circuit components

[0073] SH radio wave absorbing components

Claims

1. An optical modulator, comprising: A modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide; and A wiring board is provided with wiring that relays the modulation signal applied to the modulation electrode. The optical modulator is characterized in that... The wiring board is disposed overlapping the modulation board in such a way that it covers the entire functional part, which is modulated by the modulation electrode. At least a portion of the wiring board at a position opposite to the functional part is provided with an electromagnetic wave absorbing member.

2. The optical modulator according to claim 1, characterized in that, The electromagnetic wave absorbing component is connected to either the grounding wiring of the wiring board or the grounding electrode of the modulation electrode.

3. The optical modulator according to claim 1 or 2, characterized in that, Multiple Mach-Zehnder type optical waveguides are arranged side by side in the functional part, and modulation electrodes are arranged corresponding to each Mach-Zehnder type optical waveguide.

4. The optical modulator according to claim 1 or 2, characterized in that, The modulation electrode has a signal electrode and a ground electrode arranged to sandwich the signal electrode, and the distance between the signal electrode and the electromagnetic wave absorbing member is greater than the distance between the signal electrode and the ground electrode.

5. The optical modulator according to claim 3, characterized in that, The modulation electrode consists of a signal electrode and a ground electrode, and the ground electrode and the electromagnetic wave absorption component are arranged opposite each other between a specific Mach-Zehnder type optical waveguide and other adjacent Mach-Zehnder type optical waveguides.

6. The optical modulator according to claim 5, characterized in that, When viewing the grounding electrode and the electromagnetic wave absorbing member from above, the electromagnetic wave absorbing member is disposed inside the grounding electrode. Using the width W of the signal electrode adjacent to the grounding electrode and the spacing G between the signal electrode and the grounding electrode, the distance S between the sides of the electromagnetic wave absorbing member and the grounding electrode satisfies the following formula: S≥2G+W… formula.

7. The optical modulator according to claim 5 or 6, characterized in that, The electromagnetic wave absorbing component extends along the signal electrode beyond the functional portion.

8. The optical modulator according to claim 1 or 2, characterized in that, A terminator is provided on the wiring board, and the terminator is electrically connected to the modulation electrode.

9. The optical modulator according to claim 1 or 2, characterized in that, A driving circuit element is disposed adjacent to the modulation substrate. The driving circuit element generates a modulation signal applied to the modulation electrode. The output terminal of the driving circuit element is connected to the wiring of the wiring substrate.

10. An optical transmitting device, characterized in that, The device comprises: an optical modulator as described in any one of claims 1 to 9; and a signal generator for generating a modulated signal input to the driving circuit element.

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