JP2017181851A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator whose size increase can be suppressed.SOLUTION: An optical modulator includes: a substrate 1 with an electro-optical effect; a first optical modulation region M1 for modulating the phase polarization or the quadrature amplitude to modulate the light with a wavelength of λ1 and a second optical modulation region M2 for modulating the phase polarization or the quadrature amplitude to modulate the light with a wavelength of λ2, which are formed on the substrate 1; an electrode (control electrode 3) for the modulation, which is provided in the optical modulation regions M1 and M2; and an external substrate 21 where a wiring circuit to be electrically connected to the electrode is formed. The optical modulation region M1 and the optical modulation region M2 are disposed in parallel in the width direction of the substrate 1, and the external substrate 21 is disposed right above the substrate 1. The electrode and the wiring circuit are electrically connected in a portion where the substrate 1 and the substrate 21 face each other.SELECTED DRAWING: Figure 2

Description

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

  As the speed and capacity of optical communication systems are increasing, the performance and density of optical modulators used therein are increasing. In addition, with the demand for miniaturization of optical modulators, miniaturization of substrates constituting the optical modulators is also being promoted. However, high performance, high density, and miniaturization of optical modulators are contradictory requirements, and a device for achieving both of these is required.

The following invention is proposed regarding such an optical modulator.
For example, Patent Document 1 discloses an optical waveguide, a waveguide substrate provided with a plurality of electrodes to which an electrical signal is applied to the optical waveguide, a relay substrate disposed adjacent to the waveguide substrate, and opposite to the relay substrate. An optical modulator is disclosed in which a termination substrate disposed 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 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 second wiring portions branched, and the other branched wiring portion is connected to the wiring of the carrier substrate via a bias resistor, and the waveguide It passes under the substrate and extends to the DC electrode for bias adjustment on the relay substrate.

Japanese Patent Laying-Open No. 2015-55840

  In recent years, highly integrated optical modulators such as a two-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 region M1 to which an optical wave having a wavelength λ1 is input, and an optical modulation region M2 to which an optical wave having a wavelength λ2 different from the wavelength λ1 is input. M2 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 through the optical waveguide 2, and a light wave propagating through the optical waveguide 2 on a substrate 1 having an electro-optic 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 arranged in a nested manner, and a number of control electrodes 3 and light receiving elements 4 are provided accordingly. Yes. 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 beam combiner 5 is disposed downstream of the light modulation region M1, and the light wave propagating through the output side arm portion of the main Mach-Zehnder type waveguide is combined by the polarization beam combiner 5 to produce the optical fiber 6 Output to. The same applies to the light modulation region M2. The polarization combining unit 5 includes a structure that performs polarization combining using a spatial optical system and a structure that performs polarization combining using an optical waveguide.

As described above, a 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 has been a problem that the wiring (managing) of electric wires (not shown) connected to these components increases and the substrate size increases.
In addition, the structure is such that an external substrate such as a termination substrate is disposed adjacent to the side of the chip, and a plane area in which not only the chip but also the external substrate can be disposed is required, so that the size of the optical modulator is likely to increase. There was a trend.

  The problem to be solved by the present invention is to provide an optical modulator capable of solving the above-described problems and 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-optic 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 second A second light modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of a wavelength, and an electrode 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, wherein the first light modulation region and the second light modulation region are parallel to the width direction of the substrate. The external substrate is disposed immediately above the substrate, and the electrode and the wiring circuit are electrically connected at a portion where the substrate and the external substrate face each other.

(2) In the optical modulator according to (1), 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. The arrangement order of the DC electrode and the RF electrode in the length direction of the substrate is different between the region and the second light modulation region.

(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 shifted in the length direction of the substrate. Features.

  In the light modulator of the present invention, the first light modulation region and the second light modulation region are disposed in parallel in the width direction of the substrate, the external substrate is disposed immediately above the substrate, the electrode on the substrate and the external substrate Since the wiring circuit is electrically connected at the portion where the substrate and the external substrate face each other, an optical modulator capable of suppressing an increase in the size of the optical modulator can be provided.

It is a top view which shows the structural example of the conventional 2 wavelength integrated 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. It is an enlarged plan view which shows the structure of each termination | terminus part in 1st Example of this invention. It is a top view which shows arrangement | positioning of each termination | terminus part in 2nd Example of this 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 which concerns on 4th Example of this 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-optic effect and phase polarization modulation or quadrature amplitude modulation that is formed on the substrate 1 and modulates light of wavelength λ1. The first light modulation region M1, the second light modulation region M2 for phase polarization modulation or quadrature amplitude modulation for modulating the light of wavelength λ2, and the modulation provided in the light modulation regions 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 disposed immediately above the substrate 1, and the substrate 1 and the external substrate 21 face each other with the electrodes and the wiring circuit. Electrically connected at the part. The light modulation regions M1 and M2 are not necessarily formed on the same substrate 1, and may be formed on different substrates.

The substrate 1 may be any substrate that can form an optical waveguide such as quartz or semiconductor, and in particular, is a substrate having an electro-optic effect, such as LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate) or PLZT (zircon). A substrate using any single crystal of lead lanthanum titanate) can be suitably 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 that becomes an optical waveguide and a ridge-type waveguide in which the optical waveguide portion is convex can be used. Further, the present invention can also be applied to an optical circuit in which optical waveguides are formed on different waveguide substrates such as PLC 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. The control electrode 3 includes an RF electrode 3a constituting a modulation electrode, a ground electrode (not shown) surrounding the modulation electrode, and DC electrodes 3b and 3c for applying a DC voltage. These control electrodes 3 can be formed by forming a Ti / Au electrode pattern on the substrate surface and using a gold plating method or the like. Furthermore, a buffer layer such as a dielectric SiO ₂ can be provided on the substrate surface after the formation of the optical waveguide, if necessary.

  The main feature of the optical modulator according to the present invention is that the external substrate 21 is disposed immediately above the substrate 1, and 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. It 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 “X direction”, and the width direction of the substrate is “Y direction”. The X direction corresponds to the traveling direction of the light wave (the direction of the arrow X in the figure), and the direction orthogonal to this (the direction of the arrow Y in the figure) is the Y direction. The schematic configuration of the optical modulator is the same as that of the conventional optical modulator described with reference to FIG.

FIG. 2 is a plan view for explaining an optical modulator according to the first embodiment of the present invention, and FIG. 3 is a side view thereof. FIG. 4 is an enlarged plan view showing the structure of each terminal portion in the first embodiment.
The optical modulator of this example has a first optical modulation region M1 for phase polarization modulation or quadrature amplitude modulation for modulating light of wavelength λ1, and phase polarization for modulating light of wavelength λ2, on a substrate 1. A second light modulation region M2 for modulation or quadrature amplitude modulation is formed. The light modulation regions M1 and M2 are arranged in parallel in the Y direction (substrate width direction).
In the light modulation regions M1 and M2, as the control electrode 3, an RF electrode 3a, DC electrodes 3b and 3c, and the like are arranged. 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 constituting the termination portion of the high-frequency signal are integrated, is disposed so as to at least partially overlap all the RF electrodes 3 a. The external substrate 21 is configured such that the RF electrode 3a and the wiring circuit of the external substrate 21 can be electrically connected at a portion facing the substrate 1.
That is, the termination portion 22 composed of a plurality of connection pads 23, termination resistors 24, and the like is disposed at a position corresponding to each RF electrode 3a on the lower surface of the external substrate 21 (surface on the substrate 1 side). In the example of FIG. 4, three connection pads 23 and two termination resistors 24 are provided for each element of the termination portion 22. Each connection pad 23 of the end portion 22 is provided with a bump 25 that is a protruding terminal formed of Au or the like. The RF electrode 3 a 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 portion where the bump 25 is formed.

A heat radiating structure (heat sink) 31 can also be disposed immediately above the external substrate 21. As the heat dissipation structure 31, a metal or a heat conductive sheet with good heat conduction can be used, and it is connected to the housing of the optical modulator. When a metal is used for the heat dissipation structure 31, a separate metal block may be used.
Further, when a bias tee (Bias Tee) function is incorporated in the external substrate 21 instead of a resistor alone, those elements may be mounted on the upper surface of the substrate. In this case, the heat dissipation structure 31 is further disposed thereon.

  By using a substrate having 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 with high mechanical reliability at the connection portion between the substrate 1 and the external substrate 21. For this reason, it is preferable to use the same material for the substrate 1 and the external substrate 21.

  Thus, by arranging the external substrate 21 immediately above the substrate 1, a plane necessary for the arrangement of the substrate 1 and the external substrate 21 as compared with the structure in which the external substrate 21 is arranged adjacent to the side portion of the substrate 1. Since the area can be reduced, an increase in the size of the optical modulator can be suppressed. Further, since the electrodes of the substrate 1 and the wiring circuit of the external substrate 21 are configured to be electrically connected at the opposing portions of these substrates, the wiring from the RF electrode 3a to the termination resistor 24 can be shortened or simplified. Can be realized.

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

  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. Needless to say, the arrangement of the terminal portions 22 shown in FIG. 5 is merely an example, and other arrangements may be used.

FIG. 6 is a plan view showing a modification of the external substrate in the second embodiment of the present invention.
In this modification, a dummy pad 27 that 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 for explaining an optical modulator according to the third embodiment of the present invention.
In the optical modulator of this example, the external substrate 21 is bonded and fixed to the substrate 1 with an adhesive resin 41. Bonding / fixing with the adhesive resin 41 is preferably performed at a site other than the action portion of the RF electrode 31 (the site 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 action portion of the RF electrode 31, there is a concern about the loss of high-frequency modulation, the impedance change, and the deterioration of the speed matching of the light modulation due to the change in the refractive index of the microwave.

  In the optical modulator of this example, outflow prevention patterns 42 and 43 are provided 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 adhesive resin 41 from flowing out in the Y direction and an outflow preventing pattern 43 for preventing the adhesive resin 41 from flowing out in the X direction are provided. These outflow prevention patterns may be provided on the substrate 1, may be provided on the external substrate 21, or may be provided on both of them.

  According to such a structure, it is possible to suppress deterioration in speed matching of light modulation due to high-frequency loss, impedance change, and microwave refractive index change due to the inflow of the adhesive resin 41 to the action part of the RF electrode 31. it can. Further, the outflow prevention patterns 42 and 43 can also serve as alignment for accurately arranging the external substrate 21 with respect to the substrate 1.

FIG. 8 is a plan view for explaining an optical modulator according to the fourth embodiment of the present invention.
In the light modulator of this example, the light modulation regions M1 and M2 are formed on different substrates. Specifically, the light modulation region M1 is formed on the substrate 1A, and the light modulation region M2 is formed on the substrate 1B. In addition, the light modulation areas M1 and M2 are 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 is also shifted in the X direction, and the wiring of the electric wire connected to each control electrode 3 is also shifted in the X direction. For this reason, since it can suppress that the wiring of an electric wire concentrates locally, the crosstalk between electric wires can be suppressed. Further, since it is not necessary to route the electric wire so as to go around other electric wires, the wiring can be shortened or simplified.

  The light modulator of this example is arranged in the order of the RF electrode 3a, the DC electrode 3b, and the DC electrode 3c from the upstream in the X direction toward the downstream in the light modulation region M1 located on the upstream side in the X direction. Yes. 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 in the X direction to the downstream. That is, the arrangement order of the DC electrode and the RF electrode in the X direction is different between the light modulation region M1 and the light modulation region M2. For this reason, the shift amount in the X direction of 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 shift amount in the X direction of the light modulation regions M1 and M2. Thus, each electric power from the RF connector to the RF electrode for inputting a high-frequency signal can be suppressed while suppressing an increase in the length of the optical modulator in the X direction by reducing the amount of shift in the X direction of the light modulation regions M1 and M2. Wires can be wired with a margin.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described contents, and it is needless to say that the design can be changed as appropriate without departing from the gist of the present invention.

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

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Control electrode 3a RF electrode 3b, 3c DC electrode 4 Light receiving element 5 Polarization combining part 6 Optical fiber 21 External substrate (termination substrate)
22 termination part 23 connection pad 24 termination resistor 25 bump 26 insulating film 27 dummy pad 31 heat dissipation structure 41 adhesive resin 42, 43 outflow prevention pattern

Claims (3)

A substrate having an electro-optic effect;
A first optical modulation region for modulating phase polarization or quadrature amplitude modulation, which is formed on the substrate, and phase polarization modulation for modulating light of the second wavelength; A second light modulation region for quadrature amplitude modulation;
An electrode for modulation 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 immediately above the substrate;
The optical modulator, wherein the electrode and the wiring circuit are electrically connected at a portion where the substrate and the external substrate face each other. The optical modulator according to claim 1.
A DC electrode and an RF electrode are respectively formed in the first light modulation region and the second light modulation region,
The optical modulator, wherein the arrangement order of the DC electrode and the RF electrode in the length direction of the substrate is different between the first light modulation region and the second light modulation region. The optical modulator according to claim 1 or 2,
The optical modulator, wherein the first optical modulation region and the second optical modulation region are arranged so as to be shifted in the length direction of the substrate.

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