JP2016012037A - Light modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light modulator that is improved in high-frequency characteristics and can suppress a pyroelectric effect, and to provide a light modulator that also suppresses generation of an internal stress on a substrate constituting the light modulator.SOLUTION: The light modulator includes a substrate, an optical waveguide (not shown in the figure) formed on an upper surface side of the substrate, control electrodes (2, 31, 32) to control light waves propagating in the optical waveguide, and an electric connecting part electrically connecting the control electrodes and a high-frequency line (not shown in the figure) out of the substrate. The control electrodes comprise a signal electrode 2 and a first ground electrode 31 and a second ground electrode 32 disposed to interpose the signal electrode. A conducting part 40 that electrically connects the first ground electrode and the second ground electrode and is spaced from the signal electrode 2 is formed on a side face of the substrate where the electric connecting part is disposed.

Description

  The present invention relates to an optical modulator, and in particular, a substrate, an optical waveguide formed on the upper surface side of the substrate, a control electrode for controlling a light wave propagating through the optical waveguide, the control electrode, and the outside of the substrate The present invention relates to an optical modulator having an electrical connection portion for electrically connecting the high-frequency line.

  In the optical communication field and the optical measurement field, an optical modulator, in particular, an optical modulator provided with a control electrode for controlling an optical waveguide and a light wave propagating through the optical waveguide on a substrate is frequently used. In recent years, higher modulation speeds and larger capacities have been demanded, and multi-level modulation schemes such as quadrature amplitude modulation (QAM) have come to be used. An optical band characteristic with a flat frequency response is required.

  As disclosed in Patent Documents 1 to 3, it is disclosed that a back surface and a side surface of a substrate are covered with a conductive film such as a metal film in order to improve high frequency characteristics. Moreover, in patent document 2, in order to strengthen grounding (GND) connection with a housing and a connector part, the part corresponding to the taper part formed in the input / output part of the signal electrode and the vicinity of the feeder part of the taper part edge are provided. A configuration in which the metal film is removed except that the connection is made by solder is disclosed.

  Furthermore, when an electro-optic crystal such as lithium niobate (LN) is used for the substrate of the optical modulator, a configuration is also disclosed in which a conductive film is formed of metal or the like on the side surface of the modulation element chip in order to suppress the pyroelectric effect. ing.

  If there is a metal portion on the side surface of the substrate as described above around the connection pad, the electric field distribution before and after the electrical connection is disturbed, and parasitic capacitance is generated between the signal line of the high-frequency line and the metal GND on the side surface of the substrate. . As a result, a dip occurs in the high frequency band in the transmission characteristic S21 of the electric signal, and the high frequency response in the optical band is deteriorated.

  In addition, as shown in Patent Document 2, when the ground electrode is fixed to the casing with solder in order to improve the GND connection, a distance of several tens of millimeters of the input / output portion of the control electrode is firmly attached to the casing. It will be fixed. As a result, the internal stress due to the difference in the linear expansion coefficient between the substrate constituting the optical modulator and the housing is applied to the substrate with respect to the change in the external environment temperature, and the bias point generated by the change in the substrate refractive index according to the internal stress. Shift, and in the worst case, the substrate is damaged.

JP-A-5-158002 Japanese Patent Laid-Open No. 10-239648 JP 2005-181537 A JP-A-4-214526

  The problem to be solved by the present invention is to provide an optical modulator capable of solving the above-described problems, improving high-frequency characteristics, and suppressing the pyroelectric effect. It is another object of the present invention to provide an optical modulator that suppresses generation of internal stress on a substrate constituting the optical modulator.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) Electrically connecting a substrate, an optical waveguide formed on the upper surface of the substrate, a control electrode for controlling a light wave propagating through the optical waveguide, and the high-frequency line outside the substrate In the optical modulator having an electrical connection portion to be connected, the control electrode includes a signal electrode and a first ground electrode and a second ground electrode arranged so as to sandwich the signal electrode. On the side surface on which the electrical connection portion is disposed, a conductive portion is formed that electrically connects the first ground electrode and the second ground electrode and is spaced apart from the signal electrode. It is characterized by.

(2) In the optical modulator described in (1) above, the interval W1 between the first ground electrode and the second ground electrode in the vicinity of the conductive portion is such that the conductive portion and each ground electrode are electrically connected. It is characterized in that it is set to be equal to or less than the interval w between the connected positions.

(3) In the optical modulator according to (1) or (2), the high-frequency line is disposed so as to sandwich a signal conductor electrically connected to the signal electrode, and the signal conductor. The ground conductor is electrically connected to the first and second ground electrodes, and the distance W2 between the ground conductors sandwiching the signal conductor is the position where the conductive portion and each ground electrode are electrically connected. It is characterized by being set to be equal to or less than the interval w.

(4) In the optical modulator according to any one of (1) to (3), the electrical connection portion is configured to be connected to the high-frequency line using an electrical connection means that suppresses generation of internal stress. It is characterized by being.

(5) The optical modulator according to any one of (1) to (4), wherein the substrate is made of a material having a pyroelectric effect.

  The present invention electrically connects a substrate, an optical waveguide formed on the upper surface of the substrate, a control electrode for controlling a light wave propagating through the optical waveguide, and the high-frequency line outside the substrate. The control electrode comprises a signal electrode, a first ground electrode and a second ground electrode arranged so as to sandwich the signal electrode, and the substrate includes: On the side surface on which the electrical connection portion is disposed, a conductive portion is formed that electrically connects the first ground electrode and the second ground electrode and is spaced apart from the signal electrode. Therefore, the electric field distribution before and after the electrical connection can be connected without being disturbed, and the high frequency response can be prevented from deteriorating.

In particular, the effects described above become more remarkable by setting the conditions shown in the following (a) or (b).
(A) The interval W1 between the first ground electrode and the second ground electrode in the vicinity of the conductive portion is equal to or equal to the interval w between the conductive portion and each ground electrode. Must be set to:
(B) The high-frequency line is a signal conductor that is electrically connected to the signal electrode, and a ground conductor that is disposed so as to sandwich the signal conductor and is electrically connected to the first and second ground electrodes. The interval W2 between the ground conductors sandwiching the signal conductor is set to be equal to or less than the interval w at the position where the conductive portion and each ground electrode are electrically connected.

  In the optical modulator of the present invention, the electrical connection portion is configured to be connected to the high-frequency line using an electrical connection means that suppresses the generation of internal stress, whereby internal stress is applied to the substrate itself. Therefore, it is possible to suppress the shift of the bias point of the optical modulator.

  Furthermore, even when the substrate is made of a material having a pyroelectric effect, since the ground electrode is formed on both side surfaces of the substrate, the generation of the pyroelectric effect can be effectively suppressed. Become.

It is a perspective view which shows an example of the board | substrate (chip) used for the optical modulator of this invention. It is a top view which shows an example of the optical modulator module used for the optical modulator of this invention. It is a top view which shows an example of the electrical connection part which connects the control electrode on a board | substrate, and the high frequency line outside a board | substrate. It is a figure explaining the mode of the side surface of the board | substrate 1 of FIG. It is a graph which shows the frequency characteristic of an optical modulator.

Hereinafter, the optical modulator of the present invention will be described in detail using preferred examples.
As shown in FIG. 1, the optical modulator of the present invention includes a substrate, an optical waveguide (not shown) formed on the upper surface side of the substrate, and a control electrode (for controlling a light wave propagating through the optical waveguide). 2, 31, 32) and an electrical modulator that electrically connects the control electrode and a high-frequency line (not shown) outside the substrate, the control electrode includes the signal electrode 2 and the signal electrode 2 The first ground electrode 31 and the second ground electrode 32 are disposed so as to sandwich the signal electrode, and the side surface of the substrate on which the electrical connection portion is disposed has the first ground electrode and A conductive portion 40 is formed which is electrically connected to the second ground electrode and is spaced apart from the signal electrode 2.

As the substrate used in the optical modulator of the present invention, a substrate having an electro-optic effect such as a single crystal of any one of LiNbO ₃ , LiTaO ₅ or PLZT (lead lanthanum zirconate titanate) can be suitably used. In particular, LiNbO ₃ and LiTaO ₅ frequently used in light control elements such as an optical modulator are preferable. Since these substrates are prone to the pyroelectric effect, as shown in Patent Document 4, not only the control electrodes formed on the surface of the substrate, but also the conductivity for suppressing the pyroelectric effect on the side surface and back surface of the substrate. It is preferable to form a film.

An optical waveguide is formed on the substrate. The optical waveguide formed on the substrate is formed, for example, by thermally diffusing titanium (Ti) or the like on a LiNbO ₃ substrate (LN substrate). A ridge-type optical waveguide in which irregularities along the optical waveguide are formed on the substrate can also be used. As the pattern shape of the optical waveguide, various shapes such as a Mach-Zehnder type waveguide and a nested waveguide obtained by combining a plurality of Mach-Zehnder type waveguides can be adopted depending on the use of the optical modulator.

As shown in FIG. 1, the control electrode is composed of a signal electrode 2 and a ground electrode (31, 32). A Ti / Au electrode pattern is formed on the substrate surface, and can be formed by a gold plating method or the like. is there. Furthermore, if necessary, a buffer layer such as a dielectric SiO ₂ may be provided on the substrate surface after the optical waveguide is formed, and a control electrode may be formed above the buffer layer. As shown in FIG. 1, the signal electrode is not limited to one signal electrode. When there are a plurality of modulation regions of the optical waveguide, a plurality of signal electrodes can be provided corresponding to the number of modulation regions. It is.

  The optical modulator of the present invention is characterized in that conductive films (40, 42) are also formed on the side and back surfaces of the substrate as shown in FIG. 1 in order to improve the high frequency characteristics and suppress the pyroelectric effect. . Conventionally, as shown in Patent Document 2 or 3, a conductive film is provided on the entire side surface of the substrate on which the electrical connection portion for electrically connecting the control electrode and the high-frequency line outside the substrate is disposed. Alternatively, the conductive film is not formed on the side surface portion corresponding to the position where the connection pad of the signal electrode is formed.

  In the present invention, as shown in FIG. 1, with respect to the first ground electrode 31 and the second ground electrode 32 arranged so as to sandwich the signal electrode 2 and the signal electrode, the conductive portion 40 on the side surface has the first electrode The ground electrode 31 and the second ground electrode 32 are electrically connected and spaced apart from the signal electrode 2. In the vicinity of the signal electrode 2, there is a region 41 where the conductive portion 40 is not formed. However, in the side surface, a portion (region 41) that electrically connects the first ground electrode 31 and the second ground electrode 32. Lower side) is formed.

  As in the present invention, the conductive portion 40 formed on the side surface of the substrate is provided with the region 41 where the conductive portion is not formed and also provided with a portion for electrically connecting the two ground electrodes, so that the control electrode, the high frequency line, Before and after the electrical connection, the electric field portion distribution is connected without disturbance, and the generation of parasitic capacitance between the signal line and the side surface GND portion can be suppressed. Thereby, it is possible to further improve the high frequency characteristics of the optical modulator.

  The conductive portion 40 on the side surface of the substrate is electrically connected to the housing GND by being electrically connected via the conductive film formed on the back surface of the substrate and the edge portion between the side surface of the substrate and the back surface of the substrate. By being electrically connected to a part of the lower part of the side surface and the housing GND, the connection to the housing GND is strengthened and the high frequency characteristics are further improved. Furthermore, since the conductive portion on the side surface also plays a role of connecting the ground electrodes arranged on both sides of the signal electrode at a short distance, even when using an electrical connection means such as wire bonding as described later, 10 GHz Therefore, good characteristics can be obtained even in a high frequency range exceeding 1, and an optical modulator excellent in high frequency characteristics can be obtained. In particular, when the thickness of the substrate is larger than the distance between the signal electrode and the ground electrode (the distance between both in the vicinity of the connection pad), the high frequency characteristics are higher due to the electrical connection of the ground electrodes by the conductive portion 40. Become.

  As a method for forming the conductive portion 40, after forming a control electrode by an optical waveguide or gold plating on a wafer-like substrate, the wafer substrate is cut into a chip shape. Thereafter, the conductor (40) is formed on the side surface of the chip by a film forming method such as vapor deposition or a plating method. The removal portion 41 can be formed by masking with a resist or the like before forming the conductor. Further, after forming the conductor, it may be removed by processing. Moreover, although the shape of the removal part 41 was made into semicircle shape in FIG. 1, the shape of a removal part is not restricted to this, A rectangle and a polygon may be sufficient.

  FIG. 2 shows an optical modulator module in which the chip 1 of the optical modulator of FIG. Optical fibers (91, 92) are connected corresponding to input / output portions of an optical waveguide (not shown) formed on the chip. In FIG. 2, only the signal electrodes (2, 21, 22) are shown in a simplified manner as the control electrodes of the optical modulator. Reference numerals 21 and 22 denote connection pads for signal electrodes.

  In FIG. 2, the relay substrate 6 having a high-frequency line and the RF connector portion 5 are directly and electrically connected to the input side of the control electrode on the chip 1. The center conductor 51 of the RF connector portion is connected to the signal conductor 61 of the relay board using sliding contact, wire bonding, or the like, and the signal conductor 61 and the signal electrode connection pad 21 are connected by the wire bonding 81. Yes. The grounding part, which is a peripheral conductor of the RF connector part, and the grounding conductor (not shown) of the relay board, and the grounding conductor and the grounding electrode of the chip 1 are connected by wire bonding or the like.

  Although the relay board 6 is used in FIG. 2, the present invention is not limited to this, and the RF connector portion 5 can be directly electrically connected to the control electrode of the chip 1. It is preferable that the electrical connection portion that connects the high-frequency line such as the relay substrate or the RF connector portion and the control electrode on the chip is configured to suppress the generation of internal stress due to thermal expansion or the like on the substrate of the chip 1. Specifically, it is preferable to connect with a flexible material such as wire bonding or a conductive ribbon. Further, when the chip 1 and the RF connector portion 5 or the housing 10 are firmly fixed, such as a sliding contact or solder, the fixing location is one location (either the input portion or the output portion of the control electrode). Thus, it is preferable to avoid the adverse effect of generating internal stress when a plurality of fixings are performed as in Patent Document 2.

  The termination substrate 7 is connected to the output connection pad 22 of the signal electrode via a wire bonding 82. If necessary, an RF connector part can also be arranged on the output side of the control electrode.

FIG. 3 is a diagram showing a state of the input side connection part A or the output side connection part B of FIG.
In the optical modulator of the present invention, the interval W1 between the first ground electrode 31 and the second ground electrode 32 constituting the control electrode shown in FIG. 3 is set to the conductive portion 40 and each ground electrode (31, 31) shown in FIG. 32) is set to be equal to or less than the interval w between the connected positions.

  Further, the high-frequency line shown in FIG. 3 is disposed so as to sandwich the signal conductor 61 electrically connected to the signal electrode 2 and the first and second ground electrodes (31, 32). It is composed of electrically connected ground conductors (62, 63), and the distance W2 between the ground conductors sandwiching the signal conductor is connected between the conductive portion 40 and each ground electrode (31, 32) shown in FIG. It is set to be equal to or less than the interval w between the positions.

  By satisfying the relationship described with reference to FIGS. 3 and 4 (w ≧ W1 or w ≧ W2), the electric field portion distribution before and after connection in the electrical connection portion is smoothly connected, and the parasitic capacitance between the signal line and the side GND portion is reduced. Generation | occurrence | production can be suppressed further.

  FIG. 5 shows frequency characteristics when the conductive portion removal region 41 is provided on the conductive portion 40 on the side surface of the substrate as shown in FIG. 4 (the present invention) and when the conductive portion removal region is not provided (entire metal). It is a graph. The input side connection portion was connected to the RF connector portion, and the output side connection portion was connected to a termination substrate composed of a high frequency substrate. The shape of the conductive part removal region is the semicircular shape shown in FIG. 1, and the width w of the conductive part removal region of the prepared sample is set to a range of 1.1 to 2 times w1 and w2.

  As can be seen from FIG. 5, when the conductive portion 40 as shown in FIG. 1 is provided, a smooth frequency response without dip is obtained.

  As described above, according to the present invention, it is possible to provide an optical modulator that can improve high-frequency characteristics and suppress the pyroelectric effect. Furthermore, it is possible to provide an optical modulator that suppresses the generation of internal stress on the substrate constituting the optical modulator.

1 chip (light modulation element)
2 Signal electrode 31, 32 Ground electrode 40, 42 Conductive part 41 Conductor removal region 5 RF connector part 6 Relay substrate 7 Termination substrate 9 Waveguide 10 Housing

Claims (5)

A substrate, an optical waveguide formed on the upper surface of the substrate, a control electrode for controlling a light wave propagating through the optical waveguide, and an electrical connection electrically connecting the control electrode and a high-frequency line outside the substrate In an optical modulator having a connection part,
The control electrode is composed of a signal electrode and a first ground electrode and a second ground electrode arranged so as to sandwich the signal electrode,
The first ground electrode and the second ground electrode are electrically connected to the side surface of the substrate on which the electrical connection portion is disposed, and the conductive material is disposed away from the signal electrode. An optical modulator characterized in that a portion is formed.   2. The optical modulator according to claim 1, wherein a gap W <b> 1 between the first ground electrode and the second ground electrode in the vicinity of the conductive portion is such that the conductive portion and each ground electrode are electrically connected. An optical modulator characterized by being set to be equal to or less than the position interval w.   3. The optical modulator according to claim 1, wherein the high-frequency line is disposed so as to sandwich a signal conductor electrically connected to the signal electrode, and the first and second grounds. The ground conductor is electrically connected to the electrode, and the distance W2 between the ground conductors sandwiching the signal conductor is equal to or equal to the distance w between the conductive portion and each ground electrode. An optical modulator having the following settings.   4. The optical modulator according to claim 1, wherein the electrical connection portion is configured to be connected to the high-frequency line using an electrical connection means that suppresses generation of internal stress. 5. An optical modulator.   5. The optical modulator according to claim 1, wherein the substrate is made of a material having a pyroelectric effect.

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