JP2018077545A - Optical transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmitter capable of keeping down implementation area including a driver element for outputting a control signal.SOLUTION: An optical transmitter includes an optical modulator including a casing 6, substrates 1A and 1B arranged inside the casing and having an electro-optic effect, and a control electrode 3 formed on the substrates 1A and 1B for controlling an optical waveguide 2 and optical waves propagating on the optical waveguide by a control signal. The optical transmitter further includes a driver element 22 for outputting the control signal and a printed circuit board 21 having the casing arranged thereon. The driver element 22 is arranged on an opposite face to the face having the casing mounted of the printed circuit board, and electrically connected with the control electrode 3.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical transmission device, and more particularly to an optical transmission device including 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 an optical transmission device including 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.

  Such an optical modulator is used by being incorporated in the optical transmission device as one of components constituting the optical transmission device. In general, an optical modulator is mounted on a printed circuit board 21 of an optical transmission device and operates based on a control signal from a driver element 22 disposed on the same surface as the mounting surface. That is, the optical modulator receives a control signal from the driver element 22 outside (outside the housing 6) and performs optical modulation according to the control signal.

  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, since the driver element 22 is arranged in parallel to the side of the housing 6, the mounting area thereof is increased, and it is difficult to reduce the size of the optical transmission device.

  In addition, if the control electrode 3 (3a, 3b, 3c) and the light receiving element 4 are arranged on the substrate (chip) as described above, the signal lines (electrical lines) connected to these components can be freely wired. Less degree. 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 disposed, and the signal line is locally Because of the concentration, the signal line becomes more complicated. 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 transmission apparatus that solves the above-described problems and reduces the mounting area of the optical modulator and the driver element.

In order to solve the above problems, the optical transmission device of the present invention has the following technical features.
(1) A housing, a substrate having an electro-optic effect disposed inside the housing, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating through the optical waveguide by a control signal And a driver element that outputs the control signal, and includes a printed circuit board on which the casing is disposed, and the driver element includes the casing of the printed circuit board. It is disposed on the surface opposite to the mounted surface (hereinafter also referred to as “bottom surface outside the housing”), and is electrically connected to the control electrode.

(2) In the optical transmission device according to (1), the substrate is provided with a plurality of control electrodes, and electrical connection from the driver element to each control electrode is made with respect to the traveling direction of the light wave on the substrate. The substrate is provided so as to go around from both sides of the substrate.

(3) In the optical transmitter according to (2), the electrical connection uses a pin that penetrates the bottom surface of the housing.

(4) In the optical transmission device according to (2) or (3), the electrical connection uses relay boards arranged on both sides of the board.

(5) In the optical transmission device according to any one of (1) to (4), the optical waveguide includes a plurality of Mach-Zehnder optical waveguides arranged in parallel, and each Mach-Zehnder optical waveguide includes On the other hand, the control electrode is provided.

  The optical transmission device of the present invention controls a housing, a substrate having an electro-optic effect disposed inside the housing, an optical waveguide formed on the substrate, and a light wave propagating through the optical waveguide by a control signal. In an optical transmission device comprising an optical modulator having a control electrode for controlling and a driver element for outputting the control signal, the driver element is disposed on the bottom side outside the casing, Therefore, it is possible to provide an optical transmission device that reduces the mounting area of the optical modulator and the driver element.

It is a top view which shows the structural example of the optical transmission apparatus provided with the conventional 2 wavelength integrated DP-QPSK modulator. It is a top view explaining the optical transmitter which concerns on 1st Example of this invention. It is sectional drawing explaining the optical transmitter which concerns on 1st Example of this invention. It is a top view explaining arrangement | positioning of the driver element in 1st Example of this invention. It is a top view explaining the optical transmitter which concerns on 2nd Example of this invention. It is sectional drawing explaining the optical transmitter which concerns on 2nd Example of this invention.

Hereinafter, the optical transmission apparatus according to the present invention will be described in detail.
As shown in FIGS. 2 and 3, for example, the optical transmission device 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. , 1B, each having an optical modulator having an optical waveguide 2 and a control electrode 3 for controlling a light wave propagating through the optical waveguide by a control signal. The optical transmission device further includes a driver element 22 that outputs the control signal. The driver element 22 is disposed on the bottom surface outside the housing and is electrically connected to the control electrode 3.

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 31, 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 transmitter according to the present invention is that the driver element 22 that outputs a control signal for the control electrode 3 is arranged on the bottom surface outside the housing of the optical modulator. In this specification, the length direction of the substrate is “X direction”, the width direction of the substrate is “Y direction”, and the thickness direction of the substrate is “Z 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 the direction of the substrate plane (the direction of the arrow Y in the figure) is the Y direction. The direction of the Z mark Z in the middle is the Z direction. Hereinafter, a detailed description will be given with reference to examples. The schematic configuration of the optical transmission device and the optical modulator is the same as that of the conventional one described with reference to FIG.

  FIG. 2 is a plan view for explaining the optical transmission apparatus according to the first embodiment of the present invention, and FIG. 3 is a sectional view of the optical transmission apparatus as viewed in the X direction. FIG. 4 is a plan view for explaining the arrangement of the driver elements 22. In FIG. 3, (a) is a diagram showing a state before the optical modulator is mounted on the printed circuit board of the optical transmission device, and FIG. 3 shows the optical modulator mounted on the printed circuit board of the optical transmission device. It is a figure which shows the mode of later.

  The optical modulator in the optical transmitter 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). is there. 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.

  The optical modulator of this example is used by being incorporated in the optical transmission device as one of the components constituting the optical transmission device. Specifically, the optical modulator of this example is mounted on the printed circuit board 21 of the optical transmitter, and is controlled from the driver element 22 disposed on the surface (lower surface) opposite to the mounting surface (upper surface). Operates based on the signal. That is, the driver element 22 that outputs a control signal is arranged on the bottom surface side outside the housing of the optical modulator.

  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 other end is electrically connected to pins 7a and 7b which are examples of electrical connection means. Connected. The pins 7 a and 7 b are formed so as to penetrate the bottom surface of the housing 6 from the relay boards 11 and 12. Further, the pins 7 a and 7 b are configured such that the length of the portion protruding from the bottom surface of the housing 6 is at least the thickness of the printed circuit board 21.

  The printed circuit board 21 is formed with through holes 23a and 23b through which the pins 7a and 7b can be inserted at positions where the pins 7a and 7b are located when the optical modulator is mounted. Further, output terminals 24 a and 24 b extending from the driver element 22 toward the through holes 23 a and 23 b are provided on the lower surface of the printed circuit board 21. When the optical modulator is mounted on the printed board 21, a part of the pins 7 a and 7 b protrude from the through holes 23 a and 23 b of the printed board 21. By connecting the protruding portions and the output terminals 24a and 24b with solder or the like, the relay signal lines of the relay boards 11 and 12 and the output terminals 24a and 24b of the printed board 21 can be electrically connected. The interval between the output terminals 24a, 24b and the through holes 23a, 23b is widened, and a signal line is formed between the output terminals 24a, 24b and the through holes 23a, 23b, and the pins 7a, 7b are connected via the signal lines. The output terminals 24a and 24b may be electrically connected.

  The output terminal 24a is a terminal for outputting a control signal supplied from the driver element 22 to the substrate 1A side. The output terminal 24b is a terminal for outputting a control signal supplied from the driver element 22 to the substrate 1B side. That is, for example, an RF signal for the substrate 1A is transmitted from the driver element 22 to the RF electrode 3a on the substrate 1A side through the output terminal 24a, the pin 7a, the signal line 5a, and the like. Also, for example, an RF signal for the substrate 1B is transmitted from the driver element 22 to the RF electrode 3b on the substrate 1B side through the output terminal 24b, the pin 7b, the signal line 5b, and the like. 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 other signal lines are omitted.

  As described above, in the optical transmission device of this example, the driver element 22 is arranged on the bottom surface outside the housing of the optical modulator, so that the size of the printed circuit board 21 can be reduced as compared with the conventional configuration. Thereby, it is possible to provide an optical transmission device in which the mounting area of the optical modulator and the driver element 22 is suppressed.

  Further, in the optical transmission device of this example, the relay signal line for electrically connecting the driver element 22 and the control electrode 3 is formed on the relay substrates 11 and 12 disposed between the substrate 1A and the substrate 1B. Thus, local concentration of signal lines as in the prior art can be suppressed. 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 (time delay) 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 with the relay signal line on the relay boards 11 and 12 and the signal line on the printed board 21, the signal lines on the boards 1A and 1B having a large propagation loss are made as short as possible. Thus, it is possible to suppress the propagation loss in the entire signal line and to suppress the occurrence of crosstalk between the signal lines. Furthermore, instead of forming a large number of light modulation regions on a single substrate (chip), a structure in which the chips are separated as in this example allows a fine pattern of waveguides and electrodes mounted on one chip. Since the number is reduced, an effect of improving the yield of chip manufacturing due to a defect of a putter or the like can be obtained.

  Further, in the optical transmission device of this example, at a position where it can be connected to the driver element 22 arranged on the bottom side outside the housing as seen from the center line (the one-dot chain line C in the figure) between the substrate 1A and the substrate 1B, Pins 7a and 7b are provided. For this reason, the length of the signal line from the driver element 22 to the control electrode 3 can be shortened efficiently. For this reason, the further reduction of the propagation loss of a control signal is realizable. In order to optimize the wiring of the signal line for each control electrode 3 of the substrates 1A and 1B, the center of the driver element 22 and the center line C are aligned when viewed in the Z direction as shown in FIG. 3 and FIG. It is desirable that the driver element 22 be arranged at the position.

  Here, in order to reduce the propagation loss of the control signal, it is preferable that the center of the driver element 22 and the center line C are aligned in the Z direction as described above. The driver element 22 may be arranged at a position shifted from the center line C toward the substrate 1A or the substrate 1B. However, from the viewpoint of suppressing variation in the length of the signal line, when viewed in the Z direction, the relay boards 11 and 12 on one side of the printed board 7 and the driver element on the other side of the printed board 7 It is desirable that the shift amount be arranged at a position overlapping with 22.

In the driver element 22 in FIG. 4A, control signal output terminals 24a and 24b are arranged on the left and right sides, and the output extending to the through hole 23a on the substrate 1A side and the output extending to the through hole 23b on the substrate 1B side. The terminal 24b is arranged symmetrically with respect to the center line C. Similarly, when the output terminals 24a and 24b are arranged only on one side of the driver element 22 as shown in FIG. 4B, the output terminal 24a extending through the through hole 23a on the substrate 1A side and the through on the substrate 1B side are similarly formed. The output terminal 24b extending to the hole 23b may be arranged symmetrically with respect to the center line C.
Needless to say, these arrangements related to the driver element 22 can be similarly adopted in the second embodiment described later.
The structure in which the driver element 22 is disposed on the bottom surface outside the housing is preferably applied when the control signal is 20 Gbps or higher.

FIG. 5 is a cross-sectional view illustrating an optical transmission apparatus according to the second embodiment of the present invention, and FIG. 6 is a cross-sectional view of the optical transmission apparatus viewed in the X direction.
The optical modulator in the optical transmitter 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). is there. On the side of the substrate 1A opposite to the substrate 1B, a high-frequency signal relay substrate 11A for the substrate 1A is disposed adjacent to the substrate 1A. Also, on the side of the substrate 1B opposite to the substrate 1A, a high-frequency signal relay substrate 11B for the substrate 1B is disposed adjacent to the substrate 1B.

Similar to the first embodiment, the optical modulator of this example is also used as one of the components constituting the optical transmission device. Specifically, the optical modulator of this example is mounted on the printed circuit board 21 of the optical transmitter, and is controlled from the driver element 22 disposed on the surface (lower surface) opposite to the mounting surface (upper surface). Operates based on the signal. That is, the driver element 2 that outputs a control signal is arranged on the bottom surface side outside the housing of the optical modulator.
Although the low-frequency signal relay board is not shown, like the high-frequency signal relay board, the side of the board 1A opposite to the board 1B and the board 1A of the board 1B are the same. It may be provided individually on both sides of the opposite side, or a common relay board may be provided only on one side.

  Even with such a configuration, the driver element 22 can be disposed on the bottom surface outside the casing of the optical modulator, so that it is possible to provide an optical transmission apparatus that reduces the mounting area of the optical modulator and the driver element 22. Also, as in the first embodiment, avoiding local concentration of the signal line, suppression of control signal skew (phase shift) due to variations in the length of the signal line, improvement of propagation loss in the entire signal line, etc. An effect can also be obtained.

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.
For example, in the above description, the example in which the optical modulator is mounted on the upper side of the printed circuit board 21 and the driver element 22 is mounted on the lower side has been described, but these may be reversed.
In the above description, the optical modulator configured such that the driver element 22 can be connected afterwards has been described. However, the driver element 22 may be connected to the optical modulator in advance. In this case, an opening may be provided on the printed circuit board 21 in a region where the driver element 22 is located when the optical modulator is disposed. Thus, when the optical modulator is arranged on the printed board 21, the driver element 22 appears from the opening, so that other circuit elements of the printed board 21 can be electrically connected to the driver element 22 in the opening.

  As described above, according to the present invention, it is possible to provide an optical transmission device in which the mounting area of the optical modulator and the driver element is suppressed.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Optical waveguide 3 Control electrode 3a RF electrode 3b, 3c DC electrode 4 Light receiving element 5a, 5b Signal line 6 Case 7a, 7b Pin 11, 11A, 11B, 12 Relay board 13, 14 Termination board 21 Print board 22 Driver Element 23a, 23b Through hole 24a, 24b Output terminal

Claims (5)

A housing, a substrate having an electro-optic effect disposed inside the housing, and an optical waveguide formed on the substrate and a control electrode for controlling a light wave propagating through the optical waveguide by a control signal An optical modulator;
In an optical transmission device comprising a driver element that outputs the control signal,
A printed circuit board on which the housing is mounted;
The driver device is disposed on a surface of the printed circuit board opposite to the surface on which the housing is mounted, and is electrically connected to the control electrode. The optical transmission device according to claim 1,
The substrate is provided with a plurality of control electrodes,
An optical transmission device characterized in that electrical connection from the driver element to each control electrode is provided so as to go around from both sides of the substrate with respect to the traveling direction of the light wave of the substrate. The optical transmission device according to claim 2,
The electrical connection uses a pin that penetrates the bottom surface of the casing. In the optical transmission device according to claim 2 or 3,
The optical connection apparatus uses a relay board disposed on both sides of the board for the electrical connection. The optical transmission device according to any one of claims 1 to 4,
The optical waveguide has a plurality of Mach-Zehnder optical waveguides arranged in parallel,
An optical transmitter characterized in that the control electrode is provided for each Mach-Zehnder type optical waveguide.

Images