JP6288153B2 - 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 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, since high performance, high density, and miniaturization of the optical modulator are contradictory requirements, a contrivance for achieving both of these is required.

The following invention is proposed regarding such an optical modulator.
For example, in Patent Document 1, a first light modulation unit and a second light modulation unit are provided in parallel in the width direction on a substrate, and adjacent to one side of the substrate, an electric signal for modulation is provided. An optical modulator having a structure in which a relay substrate for relaying is disposed.

JP2015-172630A

  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 propagates on the substrate 1 having the electro-optic effect, the optical waveguide 2, the control electrode 3 for controlling the light wave propagating through the optical waveguide 2 by the control signal, and the optical waveguide 2. And a light receiving element 4 for detecting a light wave to be detected. The control electrode 3 includes an RF electrode 3a to which an RF signal (modulation signal) as a kind of control signal is applied, and DC electrodes 3b and 3c to which a DC signal (bias voltage) as a kind of control signal is applied. Is done.

The optical waveguide 2 in each of the light modulation regions M1 and M2 has a structure in which Mach-Zehnder type optical waveguides are arranged in a nested manner, and a large 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 (not shown) 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 optical waveguide is combined by the polarization beam combiner. Output to the optical fiber connected to. The same applies to the light modulation region M2. The polarization combining unit includes a structure that performs polarization combining using a spatial optical system and a structure that performs polarization combining using an optical waveguide.

  A high-frequency signal relay substrate 11 that relays an RF signal to the RF electrode 3a adjacent to the side of the substrate 1 on the light modulation region M2 side, a DC signal to the DC electrodes 3b and 3c, and light reception detected by the light receiving element 4. A relay board 12 for low frequency signals that relays signals is disposed. A termination substrate 13 for terminating an RF signal for the RF electrode 3a in the light modulation region M1 is disposed on the side of the substrate 1 on the light modulation region M1 side, and on the side of the substrate 1 on the light modulation region M2 side. A termination substrate 14 for terminating an RF signal for the RF electrode 3a in the light modulation region M2 is disposed.

  When the relay boards 11 and 12 are arranged on one side of the board 1 as described above, input / output terminals (DC pins and RF connectors) connected to the relay board 11 for high-frequency signals and the relay board 12 for low-frequency signals. Etc.) can be arranged on the same side surface of the housing 6, so that there is an advantage that it becomes easy to handle the optical modulator. However, in a substrate (chip) on which a large number of control electrodes 3 (3a, 3b, 3c) and light receiving elements 4 are arranged, the degree of freedom of wiring of signal lines (electric lines) connected to those components is small. In particular, in the light modulation region M2 on the side close to the relay substrates 11 and 12, not only the signal line for the light modulation region M2 but also a part of the signal line for the light modulation region M1 is provided. Complexity becomes remarkable. As a result, the length of the signal line with respect to the control electrode 3 (3a, 3b, 3c) tends to vary. For example, variation in length occurs in each of the signal lines 5a and 5b with respect to the RF electrode 3a, thereby causing a skew (time delay) in the RF signal with respect to each RF electrode 3a or causing a difference in propagation loss between the signal lines. There are concerns that arise. In addition, when the length of the signal line is increased, there is a problem that propagation loss may increase or crosstalk may occur between the signal lines.

  The problem to be solved by the present invention is to provide an optical modulator that solves the above problems and suppresses the variation in the length of the signal line with respect to the control electrode.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) A housing, two substrates having an electro-optic effect disposed inside the housing, and an optical waveguide formed on each of the two substrates and a light wave propagating through the optical waveguide are controlled by a control signal. An optical modulator having a control electrode for performing a relay substrate on which a relay signal line is formed between the two substrates, the control electrode and the relay signal line being electrically connected, and The control signal is input through the relay signal line.

(2) The optical modulator according to the above (1), on the bottom surface of the housing outside is disposed pins connected to the relay signal line path, said control signal is inputted via the pins It is characterized by that.

(3) In the optical modulator described in (2) above, the control signal is a modulated signal of 20 Gbps or more.

(4) In the optical modulator according to (2) or (3), the connection structure with the signal line outside the modulator on the side where the control signal of the pin is input is a connector.

The optical modulator according to (5) above (1), a flexible substrate a flexible signal line is formed is disposed on the bottom side of the housing outside one end of the flexible signal line to the relay signal line path Electrically connected, the control signal is input through the other end of the flexible signal line.

(6) In the optical modulator described in (5), the skew of the control signal is adjusted by the flexible signal line disposed on the flexible substrate.

(7) In the optical modulator according to any one of (1) to (6), the control electrodes of the two substrates are arranged symmetrically with respect to a center line between the two substrates. Features.
(8) In the optical modulator according to any one of (1) to (7), a light receiving element that receives a part of a light wave propagating through each optical waveguide of the two substrates is provided, and A relay board arranged between the two is used for relaying when a light reception signal detected by the light receiving element is output to the outside of the casing.

An optical modulator according to the present invention includes a housing, two substrates having an electro-optic effect disposed inside the housing, an optical waveguide formed on each of the two substrates, and an optical wave propagating through the optical waveguide. In the optical modulator having a control electrode for controlling the control signal by a control signal, a relay substrate having a relay signal line is disposed between the two substrates, and the control electrode and the relay signal line are electrically connected to each other. Since the control signal is input via the relay signal line , it is possible to provide an optical modulator that suppresses variations in the length of the signal line with respect to the control electrode.

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 sectional drawing explaining the optical modulator which concerns on 1st Example of this invention. It is sectional drawing explaining the optical modulator which concerns on 2nd Example of this invention.

Hereinafter, the optical modulator according to the present invention will be described in detail.
For example, as shown in FIG. 2, the optical modulator according to the present invention includes a housing 6, two substrates 1A and 1B having an electro-optic effect disposed inside the housing, and two substrates 1A and 1B. Each has an optical waveguide 2 and a control electrode 3 for controlling a light wave propagating through the optical waveguide by a control signal. Relay boards 11 and 12 having relay signal lines (not shown) are disposed between the two boards 1A and 1B, the control electrode 3 and the relay signal line are electrically connected, and the control signal is transmitted to the relay signal line. Is input through .

The substrates 1A and 1B may be any substrate that can form an optical waveguide such as quartz or semiconductor, and in particular, a substrate having an electrooptic effect, such as LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate) or PLZT. A substrate using any single crystal of (lead lanthanum zirconate titanate) can be suitably used.

The optical waveguide 2 formed on the substrates 1A and 1B 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 substrates 1A and 1B are provided with a control electrode 3 for controlling a light wave propagating through the optical waveguide 2 with a control signal. 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 signal. 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 optical waveguide 2 constituting each of the optical modulation regions of the substrates 1A and 1B 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 corresponding to this are arranged. 4 is provided. In the figure, four RF electrodes 3a, six DC electrodes 3b and 3c, and two light receiving elements 4 are provided on each of the substrates 1A and 1B.

  The main feature of the optical modulator according to the present invention is that relay boards 11 and 12 each having a relay signal line (not shown) are disposed between the boards 1A and 1B, and the control electrode 3 and the relay signal line are electrically connected. The control signal is input / output from one end of the relay signal line. 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. Hereinafter, a detailed description will be given with reference to examples. 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 cross-sectional view taken along line AA ′ in FIG.
The optical modulator of this example has two substrates 1A and 1B arranged in parallel in the Y direction on the inner bottom surface of the housing 6 (the surface inside the housing facing the bottom surface outside the housing). Between the substrate 1A and the substrate 1B, a high-frequency signal relay substrate 11 that relays an RF signal to the RF electrode 3a and a low-frequency signal relay substrate 12 that relays a DC signal to the DC electrodes 3b and 3c are arranged. The The relay substrate 12 can also be used for relaying when a light reception signal detected by the light receiving element 4 is output to the outside.

  Relay signal lines (not shown) are formed on the relay boards 11 and 12. One end of the relay signal line is electrically connected to the signal line for the control electrodes 3 of the substrates 1A and 1B, and the pin 21 is connected to the other end. That is, the relay signal line is electrically connected to the control electrode 3 and relays the control signal input / output from the pin 21 to / from the control electrode 3. In FIG. 2, the signal line 5a for the RF electrode 3a of the substrate 1A and the signal line 5b for the RF electrode 3a of the substrate 1B are shown, but the other signal lines are omitted.

  Thus, by arranging the relay boards 11 and 12 that relay control signals for these boards between the boards 1A and 1B, the signal lines are not concentrated locally as in the prior art. That is, it is not necessary to arrange a part of the signal line for the other light modulation region (M1) in one light modulation region (M2). Further, the length of the signal line can be adjusted by the way of arranging the relay signal line on the relay boards 11 and 12. For this reason, it becomes easy to arrange the length of the signal line, and the skew (phase shift) of the control signal due to the variation in the length of the signal line can be suppressed.

  Further, since the length of the signal line can be adjusted by the relay signal line on the relay boards 11 and 12, the propagation loss in the entire signal line can be reduced by shortening the signal line on the boards 1A and 1B having a large propagation loss as much as possible. And the occurrence of crosstalk between signal lines can be suppressed. Further, by forming a structure in which the chips are separated as in this example instead of forming a large number of light modulation regions on one substrate (chip), an effect of improving the yield of chip manufacture can be obtained.

  In the optical modulator of this example, the relay signal lines formed on the relay boards 11 and 12 have pins extending from the relay boards 11 and 12 so as to penetrate the bottom surface of the housing 6 as shown in FIG. One end of 21 is electrically connected. The other end of the pin 21 is connected to a signal line outside the modulator for input / output of a control signal. As a connection structure with the signal line outside the modulator on the other end side (the side where the control signal is input) of the pin 21, the pin 21 may be used as it is when the control signal is a DC signal. When the control signal is an RF signal, the structure on the other end side of the pin 21 may be a connector such as GPPO or G3PO.

  In this way, by adopting a configuration in which the control signal is input / output via the pin 21 protruding from the bottom surface of the housing 6, the length of the signal line extending from the other end of the pin 21 to the control electrode 3 can be shortened. As a result, effects such as a reduction in skew, a reduction in propagation loss between signal lines, and a reduction in propagation loss as a total signal line can be obtained.

  Further, in the optical modulator of this example, each control electrode 3 on the substrate 1A and each control electrode 3 on the substrate 1B are axisymmetric with respect to a center line between the substrates 1A and 1B (dashed line C in the figure). Is arranged. For this reason, even when a thermal stress is generated on the substrate 1A or the substrate 1B due to a temperature change outside or inside the optical modulator, the thermal stress on the substrate 1A or the substrate 1B is generated symmetrically with respect to the alternate long and short dash line C. Variation in optical characteristics and electrical characteristics between the substrate 1B and the substrate 1B can be suppressed. Further, since the relay boards 11 and 12 are not arranged on the same side of the inner wall side of the board 1A or the board 1B as in the prior art, the relay boards 11 and 12 are arranged between the board 1A and the board 1B. Combined with the above configuration, a synergistic effect can be obtained. Further, when the optical waveguides on the substrate 1A and the substrate 1B are also arranged symmetrically with respect to the alternate long and short dash line C, the above effect can be further enhanced.

FIG. 4 is a cross-sectional view for explaining an optical modulator according to the second embodiment of the present invention.
In the optical modulator of this example, a flexible substrate 23 on which a signal line (flexible signal line) is formed is arranged on the bottom surface side outside the housing 6. One end of a pin 21 extending from the relay boards 11 and 12 so as to pass through the bottom surface of the housing 6 is electrically connected to the relay signal line formed on the relay boards 11 and 12. The other end of the pin 21 is electrically connected to one end of the flexible signal line. A control signal for the control electrode 3 is input / output from the other end of the flexible signal line.

  Thus, by forming a part of the signal path of the control signal for the control electrode 3 with a flexible signal line having a propagation loss smaller than that of the substrate 1A or the substrate 1B, the propagation loss of the control signal can be reduced. In particular, by increasing the proportion of sections formed by flexible signal lines in the signal path and minimizing the signal lines on the substrates 1A and 1B, it is possible to reduce the propagation loss as a total signal line. In addition, by adjusting the skew in the flexible signal line section where wiring is easy, wiring on the substrates 1A and 1B can be simplified, and design flexibility can be improved.

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 an example, a DC signal and an RF signal can be input and output from pins and connectors arranged on different surfaces of the housing.
In this case, for example, pins and connectors arranged on different surfaces of the housing are arranged so that the propagation direction of the DC signal and the propagation direction of the RF signal are orthogonal to each other in a portion connected to the signal line outside the modulator. It is good also as a structure. By doing so, since the propagation direction of the DC signal and the propagation direction of the RF signal are orthogonal, the crosstalk between the DC signal and the RF signal can be suppressed. In addition, since the distance between the pin and the connector can be increased as compared with the conventional configuration in which the pin and the connector are arranged on the same surface of the housing, the propagation direction of the DC signal and the propagation direction of the RF signal are orthogonal to each other. Due to the synergistic effect, crosstalk between the DC signal and the RF signal can be effectively suppressed.

In addition, for example, pins and connectors are arranged on the bottom and side surfaces of the housing, DC signals are input and output from pins and connectors arranged on the side surfaces of the housing, and RF signals are pins arranged on the bottom surface of the housing. Alternatively, it may be configured to input / output from a connector. Even in such a configuration, the length of the signal line of the RF signal can be shortened, and effects such as reduction in skew, variation in propagation loss between signal lines, and reduction in propagation loss as a total of signal lines can be obtained. Can be obtained.
The effect of the present invention can be obtained even when the modulation signal is less than 20 Gbps. However, when the modulation signal is 20 Gbps or more, the suppression of propagation loss in the entire signal line and the suppression of occurrence of crosstalk between signal lines. With this, even higher effects can be achieved.

  Further, the fixed surfaces of the substrates 1A and 1B and the relay substrates 11 and 12 with the surface inside the housing may not be the entire surface of the substrate or the relay substrate. For example, by making a part of the board or relay board a fixed surface, it is possible to mitigate the generation of stress on the board or relay board due to a change in the environmental temperature, and therefore it is possible to suppress the deterioration of the modulation characteristics with respect to the environmental temperature. . Further, the substrates 1A and 1B and the relay substrates 11 and 12 arranged inside the housing may be fixed to the surface inside the housing with an adhesive, solder, or the like, or the substrate or relay substrate and the surface inside the housing. You may fix via another member between.

  As described above, according to the present invention, it is possible to provide an optical modulator that suppresses variations in the length of the signal line with respect to the control electrode.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Control electrode 3a RF electrode 3b, 3c DC electrode 4 Light receiving element 5a, 5b Signal line 6 Housing 11, 12 Relay substrate 13, 14 Termination substrate 21 Pin 23 Flexible substrate

Claims (8)

A housing,
Two substrates having an electro-optic effect disposed inside the housing;
In each of the optical modulators formed on the two substrates, each having an optical waveguide and a control electrode for controlling a light wave propagating through the optical waveguide by a control signal,
A relay board on which a relay signal line is formed is disposed between the two boards,
The control electrode and the relay signal line are electrically connected,
The optical modulator, wherein the control signal is input via the relay signal line. The optical modulator according to claim 1.
Pin that is connected to the relay signal line path is arranged in the casing outside of the bottom surface,
The optical modulator, wherein the control signal is input through the pin. The optical modulator according to claim 2.
The optical modulator, wherein the control signal is a modulation signal of 20 Gbps or more. The optical modulator according to claim 2 or 3,
An optical modulator characterized in that a connection structure with a signal line outside the modulator on the side where the control signal of the pin is input is a connector. The optical modulator according to claim 1.
A flexible substrate on which a flexible signal line is formed is disposed on the bottom side outside the housing,
One end of the flexible signal line is electrically connected to the relay signal line path,
The optical modulator, wherein the control signal is input via the other end of the flexible signal line. The optical modulator according to claim 5.
An optical modulator characterized in that the skew of the control signal is adjusted by the flexible signal line disposed on the flexible substrate. The optical modulator according to any one of claims 1 to 6,
The light modulator, wherein the control electrodes on the two substrates are arranged symmetrically with respect to a center line between the two substrates.   8. The optical modulator according to claim 1, wherein a light receiving element that receives a part of a light wave propagating through each optical waveguide of the two substrates is provided, and is disposed between the two substrates. An optical modulator, wherein the relay substrate is used for relaying when a light reception signal detected by the light receiving element is output to the outside of the housing.

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