JP6728888B2 - Light modulator - Google Patents

Description

The present invention relates to an optical modulator, and more particularly to a structure of a highly integrated modulator such as a dual wavelength integrated type.

As the speed and capacity of optical communication systems are increasing, the performance and density of optical modulators used for them are increasing. In addition, with the demand for miniaturization of optical modulators, the miniaturization of substrates constituting the optical modulators has been promoted. However, there is a trade-off between high performance, high density, and miniaturization of the optical modulator, and a device for satisfying these requirements is required.

The following inventions have been proposed for such an optical modulator.
For example, in Patent Document 1, an optical waveguide, a waveguide substrate provided with a plurality of electrodes to which an electric signal is applied to the optical waveguide, a relay substrate disposed adjacent to the waveguide substrate, and an opposite substrate to the relay substrate. There is disclosed an optical modulator in which a termination substrate arranged on the side is mounted on a carrier substrate. In this optical modulator, the plurality of electrodes includes a first wiring portion extending from the relay substrate to the termination substrate via the waveguide substrate, and a second wiring portion extending from the first wiring portion and branched on the termination substrate. Wiring part. In addition, a capacitor and a terminating resistor are provided in one of the branched wiring portions of the second wiring portion, and the other branched wiring portion is connected to the wiring of the carrier substrate via the bias resistor, It passes under the substrate and extends to the DC electrode for bias adjustment on the relay substrate.

JP, 2005-55840, A

In recent years, highly integrated optical modulators such as a dual wavelength integrated type have been developed. FIG. 1 shows a configuration example of a conventional dual wavelength integrated DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulator. The optical modulator shown in the figure has an optical modulation area M1 into which an optical wave of wavelength λ1 is input and an optical modulation area M2 into which an optical wave of wavelength λ2 different from wavelength λ1 is input. M2s are configured to operate independently of each other.

Each of the light modulation regions M1 and M2 has an optical waveguide 2, a control electrode 3 for controlling a light wave propagating in the optical waveguide 2, and a light wave propagating in the optical waveguide 2 on a substrate 1 having an electro-optical effect. And a light receiving element 4 for detection. The control electrode 3 includes an RF electrode 3a to which a high frequency signal (modulation signal) is applied and DC electrodes 3b and 3c to which a DC voltage (bias voltage) is applied.

The optical waveguide 2 in each of the light modulation regions M1 and M2 has a structure in which Mach-Zehnder type waveguides are multiply arranged in a nested manner, and correspondingly a large number of control electrodes 3 and light receiving elements 4 are provided. There is. In the figure, four RF electrodes 3a, six DC electrodes 3b and 3c, and two light receiving elements 4 are provided in each of the light modulation regions M1 and M2.
A polarization wave synthesizing unit 5 is arranged downstream of the optical modulation region M1, and the light wave propagating through the output side arm portion of the main Mach-Zehnder waveguide is synthesized by the polarization wave synthesizing unit 5 to generate an optical fiber 6 Output to. The same applies to the light modulation area M2. The polarization beam combiner 5 has a structure for performing polarization wave combination by using a spatial optical system, a structure for performing polarization wave combination by using an optical waveguide, and the like.

As described above, the highly integrated optical modulator uses a substrate (chip) on which a large number of control electrodes and light receiving elements are arranged. For this reason, there is a problem in that the wiring (routing) of electric wires (not shown) connected to these components increases, and the board size increases.
In addition, since the external substrate such as the termination substrate is arranged adjacent to the side of the chip, and a flat area for arranging not only the chip but also the external substrate is required, it is easy to increase the size of the optical modulator. There was a tendency.

An object of the present invention is to solve the above problems and provide an optical modulator capable of suppressing an increase in the size of the optical modulator.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) A substrate having an electro-optical effect, a first light modulation region formed on the substrate for phase polarization modulation or quadrature amplitude modulation for modulating light of a first wavelength, and a second Second light modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of wavelength, and electrodes for modulation provided in the first light modulation region and the second light modulation region And an external substrate on which a wiring circuit electrically connected to the electrode is formed, the first light modulation region and the second light modulation region are arranged in parallel in the width direction of the substrate. And the external substrate is disposed directly on the substrate, the electrodes and the wiring circuit are electrically connected at a portion where the substrate and the external substrate face each other, and a heat dissipation structure is provided on the external substrate. Is further arranged, and the wiring circuit includes a plurality of terminal end portions corresponding to the respective arm portions of the main Mach-Zehnder waveguides included in each of the first optical modulation region and the second optical modulation region. The plurality of end portions are alternately arranged so that the positions in the length direction of the substrate are different between the adjacent arm portions .

(2) In the optical modulator described in (1) above, a DC electrode and an RF electrode are formed in the first light modulation region and the second light modulation region, respectively, and the first light modulation region is formed. In the area and the second light modulation area, the arrangement order of the DC electrode and the RF electrode in the length direction of the substrate is different.

(3) In the optical modulator according to (1) or (2), the first light modulation region and the second light modulation region are arranged so as to be offset from each other in the length direction of the substrate. Characterize.

In the optical modulator of the present invention, the first optical modulation region and the second optical modulation region are arranged in parallel in the width direction of the substrate, the external substrate is arranged directly above the substrate, and the electrodes on the substrate and the external substrate are arranged. Since the wiring circuit is electrically connected to the wiring circuit at a portion where the substrate and the external substrate face each other, it is possible to provide an optical modulator capable of suppressing an increase in size of the optical modulator.

It is a top view which shows the structural example of the conventional 2 wavelength integrated type DP-QPSK modulator. It is a top view explaining the optical modulator which concerns on 1st Example of this invention. It is a side view explaining the optical modulator which concerns on 1st Example of this invention. FIG. 3 is an enlarged plan view showing the structure of each terminal portion in the first embodiment of the present invention. It is a top view showing arrangement of each termination in a 2nd example of the present invention. It is a top view which shows the modification of the external substrate in 2nd Example of this invention. It is a top view explaining the optical modulator which concerns on 3rd Example of this invention. It is a top view explaining the optical modulator concerning the 4th example of the present invention.

Hereinafter, the optical modulator according to the present invention will be described in detail.
The optical modulator according to the present invention is, for example, as shown in FIG. 2, for a substrate 1 having an electro-optical effect, and for phase polarization modulation or quadrature amplitude modulation for modulating light of wavelength λ1 formed on the substrate 1. Of the first light modulation area M1 and the second light modulation area M2 for phase polarization modulation or quadrature amplitude modulation for modulating light of wavelength λ2, and modulation provided in the light modulation areas M1 and M2. Electrode (control electrode 3) and an external substrate 21 on which a wiring circuit electrically connected to the electrode is formed. The light modulation region M1 and the light modulation region M2 are arranged in parallel in the width direction of the substrate 1, the external substrate 21 is arranged immediately above the substrate 1, and the electrodes and the wiring circuits are opposed to each other. The parts are electrically connected. The light modulation regions M1 and M2 do not necessarily have to be formed on the same substrate 1, but may be formed on different substrates.

The substrate 1 may be a substrate such as quartz or a semiconductor that can form an optical waveguide, and in particular, a substrate having an electro-optical effect such as LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate) or PLZT (zircon). A substrate using any one of single crystals of lead lanthanum titanate) can be preferably used.

The optical waveguide 2 formed on the substrate 1 is formed, for example, by thermally diffusing a high refractive index material such as titanium (Ti) on a LiNbO ₃ substrate (LN substrate). Further, a rib type optical waveguide in which grooves are formed on both sides of a portion to be an optical waveguide or a ridge type waveguide in which the optical waveguide portion has a convex shape can be used. Further, the present invention can be applied to an optical circuit in which optical waveguides are formed on different waveguide substrates such as PLCs and these waveguide substrates are bonded and integrated.

The substrate 1 is provided with a control electrode 3 for controlling a light wave propagating through the optical waveguide 2. As the control electrode 3, there are an RF electrode 3a that constitutes a modulation electrode, a ground electrode (not shown) surrounding the RF electrode 3a, DC electrodes 3b and 3c that apply a DC voltage, and the like. These control electrodes 3 can be formed by forming a Ti/Au electrode pattern on the surface of the substrate and then using a gold plating method or the like. Further, if necessary, it is possible to provide a buffer layer such as a dielectric material SiO _{2 on the} surface of the substrate after forming the optical waveguide.

The main feature of the optical modulator according to the present invention is that the external substrate 21 is arranged immediately above the substrate 1, and the electrodes of the substrate 1 and the wiring circuits of the external substrate 21 are electrically connected at the opposing portions of these substrates. Is to be done. Hereinafter, a detailed description will be given with reference to examples. In this specification, the length direction of the substrate is referred to as “X direction” and the width direction of the substrate is referred to as “Y direction”. The X direction corresponds to the traveling direction of the light wave (direction of arrow X in the figure), and the direction orthogonal thereto (direction of arrow Y in the figure) is the Y direction. The schematic structure of the optical modulator is similar to that of the conventional optical modulator described with reference to FIG.

FIG. 2 is a plan view illustrating the optical modulator according to the first embodiment of the present invention, and FIG. 3 is a side view thereof. Further, FIG. 4 is an enlarged plan view showing the structure of each terminal portion in the first embodiment.
The optical modulator of this example includes a first optical modulation area M1 for phase polarization modulation or quadrature amplitude modulation for modulating light of wavelength λ1 and a phase polarization for modulating light of wavelength λ2 on a substrate 1. A second light modulation area M2 for modulation or quadrature amplitude modulation is formed. The light modulation regions M1 and M2 are arranged in parallel in the Y direction (width direction of the substrate).
RF electrodes 3a, DC electrodes 3b, 3c, etc. are arranged as control electrodes 3 in the light modulation regions M1, M2. In the figure, eight RF electrodes 3a are arranged in parallel in the Y direction, eight DC electrodes 3b are arranged in parallel in the Y direction, and four DC electrodes 3c are arranged in parallel in the Y direction.

Immediately above the substrate 1, an external substrate 21, which is a termination substrate in which wiring circuits that constitute the termination of high-frequency signals are integrated, is arranged so as to at least partially overlap all the RF electrodes 3a. The external substrate 21 is configured so that the RF electrode 3a and the wiring circuit of the external substrate 21 can be electrically connected to each other at a portion facing the substrate 1.
That is, the termination portion 22 including a plurality of connection pads 23 and termination resistors 24 is arranged at a position corresponding to each RF electrode 3a on the lower surface (the surface on the substrate 1 side) of the external substrate 21. In the example of FIG. 4, three connection pads 23 and two termination resistors 24 are provided for each element of the termination section 22. Each connection pad 23 of the terminal portion 22 is provided with a bump 25 which is a protruding terminal formed of Au or the like. The RF electrode 3a is connected to the connection pad 23 by flip chip connection using the bump 25. The lower surface of the external substrate 21 is covered with an insulating film 26, except for a part including a bump 25 forming portion.

A heat dissipation structure (heat sink) 31 may be further arranged directly on the external substrate 21. As the heat dissipation structure 31, a metal having a high heat conductivity or a heat conductive sheet can be used and is connected to the housing of the optical modulator. When a metal is used for the heat dissipation structure 31, it may be a separate metal block.
When the external substrate 21 incorporates a bias tee function instead of the resistance alone, these elements may be mounted on the upper surface of the substrate. In this case, the heat dissipation structure 31 will be further arranged on it.

By using a substrate made of a material having a linear expansion coefficient substantially equal to that of the substrate 1 as the substrate material of the external substrate 21, it is possible to realize an optical modulator having a high mechanical reliability at the connecting portion between the substrate 1 and the external substrate 21. Therefore, it is preferable to use the same material for the substrate 1 and the external substrate 21.

As described above, by disposing the external substrate 21 immediately above the substrate 1, as compared with the structure in which the external substrate 21 is disposed adjacent to the side portion of the substrate 1, a plane required for disposing the substrate 1 and the external substrate 21. Since the area can be reduced, it is possible to suppress an increase in the size of the optical modulator. Further, since the electrodes of the substrate 1 and the wiring circuit of the external substrate 21 are electrically connected at the facing portions of these substrates, the wiring from the RF electrode 3a to the terminating resistor 24 can be shortened or simplified. Can be realized.

FIG. 5 is a plan view showing the arrangement of each terminal portion in the second embodiment of the present invention.
In the optical modulator of this example, two RF electrodes 31 are provided on each arm of the main Mach-Zehnder waveguide that constitutes the optical modulation region M1, but the RF electrode 31 of one arm and the other RF electrode 31 are provided. The RF electrode 31 of the arm portion is arranged so as to be displaced in the X direction (the length direction of the substrate). Then, in order to match this, the terminal portions 22 of the external substrate 21 are also arranged so as to be shifted in the X direction.

According to such a structure, the heat generation of the terminal portion 22 is dispersed, so that the heat generation of the external substrate 21 can be suppressed. The arrangement of the terminal end portion 22 shown in FIG. 5 is merely an example, and it goes without saying that another arrangement may be used.

FIG. 6 is a plan view showing a modified example of the external substrate in the second embodiment of the present invention.
In this modification, a dummy pad 27, which is a dummy connection pad, is provided on the lower surface of the external substrate 21 in addition to the terminal end 22 corresponding to the RF electrode 31. In FIG. 6, dummy pads 27 are provided at the four corners of the lower surface of the external substrate 21. By arranging such a dummy pad 27, the connection strength with the substrate 1 can be improved.

FIG. 7 is a plan view illustrating an optical modulator according to the third embodiment of the present invention.
In the optical modulator of this example, the external substrate 21 is fixed to the substrate 1 by adhesion with the adhesive resin 41. Adhesion/fixing with the adhesive resin 41 is preferably performed at a portion other than the acting portion of the RF electrode 31 (the portion where the electric field from the RF electrode 31 acts on the optical waveguide 2). This is because if the adhesive resin 41 flows into the acting portion of the RF electrode 31, there is a concern that the high-frequency loss, the impedance change, and the change in the refractive index of the microwave may deteriorate the speed matching of the optical modulation.

In the optical modulator of this example, the outflow prevention patterns 42 and 43 are provided in order to prevent the adhesive resin 41 from flowing into the action portion of the RF electrode 31. In the figure, an outflow prevention pattern 42 for preventing the outflow of the adhesive resin 41 in the Y direction and an outflow prevention pattern 43 for preventing the outflow of the adhesive resin 41 in the X direction are provided. These outflow prevention patterns may be provided on the substrate 1, the external substrate 21, or both of them.

With such a structure, it is possible to suppress the deterioration of the speed matching of the light modulation due to the loss of the high frequency due to the inflow of the adhesive resin 41 into the acting portion of the RF electrode 31, the change of the impedance, and the change of the refractive index of the microwave. it can. In addition, the outflow prevention patterns 42 and 43 can also serve as alignment for accurately disposing the external substrate 21 with respect to the substrate 1.

FIG. 8 is a plan view illustrating an optical modulator according to the fourth embodiment of the present invention.
In the optical modulator of this example, the optical modulation regions M1 and M2 are formed on different substrates. Specifically, the light modulation area M1 is formed on the substrate 1A, and the light modulation area M2 is formed on the substrate 1B. Further, the light modulation areas M1 and M2 are arranged so as to be shifted in the X direction. Correspondingly, the arrangement position of the control electrode 3 arranged in each of the light modulation regions M1 and M2 also shifts in the X direction, and the wiring of the electric wire connected to each control electrode 3 also shifts in the X direction. For this reason, it is possible to suppress local concentration of the wiring of the electric lines, and thus it is possible to suppress crosstalk between the electric lines. Moreover, since it is not necessary to arrange the electric wires around the other electric wires, it is possible to shorten or simplify the wiring.

Further, in the optical modulator M1 located on the upstream side in the X direction, the optical modulator of the present example has the RF electrode 3a, the DC electrode 3b, and the DC electrode 3c arranged in this order from the upstream side to the downstream side in the X direction. There is. On the other hand, in the light modulation region M2 located on the downstream side in the X direction, the DC electrode 3c, the RF electrode 3a, and the DC electrode 3b are arranged in this order from the upstream side to the downstream side in the X direction. That is, the arrangement order of the DC electrode and the RF electrode in the X direction is different between the light modulation area M1 and the light modulation area M2. Therefore, the amount of deviation in the X direction between the RF electrode in the light modulation region M1 and the RF electrode in the light modulation region M2 can be made larger than the amount of deviation in the X direction between the light modulation regions M1 and M2. As a result, the amount of shift in the X direction between the light modulation regions M1 and M2 is reduced, and the increase in the length in the X direction of the light modulator is suppressed, while each electrical component from the RF connector for inputting a high frequency signal to the RF electrode is input. You will be able to wire with some margin.

Although the present invention has been described above based on the embodiments, it goes without saying that the present invention is not limited to the above-described contents and can be appropriately modified in design without departing from the spirit of the present invention.

As described above, according to the present invention, it is possible to provide an optical modulator capable of facilitating the routing of electric lines on a substrate.

1 substrate 2 optical waveguide 3 control electrode 3a RF electrodes 3b and 3c DC electrode 4 light receiving element 5 polarization combining unit 6 optical fiber 21 external substrate (termination substrate)
22 Termination Part 23 Connection Pad 24 Termination Resistor 25 Bump 26 Insulation Film 27 Dummy Pad 31 Heat Dissipation Structure 41 Adhesive Resins 42, 43 Outflow Prevention Pattern

Claims (3)

A substrate having an electro-optic effect,
A first optical modulation area for phase polarization modulation or quadrature amplitude modulation for modulating light of a first wavelength and a phase polarization modulation for modulating light of a second wavelength, which are formed on the substrate. A second light modulation region for quadrature amplitude modulation;
An electrode for modulation, which is provided in the first light modulation region and the second light modulation region,
In an optical modulator having an external substrate on which a wiring circuit electrically connected to the electrode is formed,
The first light modulation region and the second light modulation region are arranged in parallel in the width direction of the substrate,
The external substrate is disposed directly on the substrate,
The electrode and the wiring circuit are electrically connected at a portion where the substrate and the external substrate face each other,
A heat dissipation structure is further arranged on the external substrate ,
The wiring circuit includes a plurality of terminal end portions corresponding to the respective arm portions of the main Mach-Zehnder type waveguides included in each of the first light modulation region and the second light modulation region,
The optical modulator, wherein the plurality of terminating portions are arranged alternately so that the positions in the length direction of the substrate are different between the adjacent arm portions . The optical modulator according to claim 1,
DC electrodes and RF electrodes are formed in the first light modulation region and the second light modulation region, respectively.
In the first light modulation region and the second light modulation region, the arrangement order of the DC electrode and the RF electrode in the length direction of the substrate is different, and the light modulator. The optical modulator according to claim 1 or 2, wherein
The optical modulator, wherein the first light modulation region and the second light modulation region are arranged so as to be offset from each other in the length direction of the substrate.

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