JP2007264063A - Optical waveguide modulator and optical fiber gyro - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve an optical waveguide modulator of a simple configuration preventing an electric field from being caused by a pyroelectric effect. <P>SOLUTION: The optical waveguide modulator comprises: a base material 11; optical waveguises 12, 13, 14 prepared directly under the upper surface of the base material 11; and control electrodes 15A, 15B, 16A, 16B provided to both sides of the optical waveguides 13, 14 on the upper surface of the base material, and comprises: two grounding electrodes 21, 22 provided to both sides of the control electrodes on the upper surface of the base material 11; and bonding wires 23 for connecting the two grounding electrodes 21, 22. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical waveguide modulator provided on an electro-optic crystal substrate such as lithium niobate and an optical fiber gyro using the same.

  Optical modulators utilizing the electro-optic effect are widely used in optical fiber gyros and optical communication devices. An explanation will be given by taking an optical modulator used in an optical fiber gyro as an example.

  FIG. 1 is a diagram showing a schematic configuration of an optical fiber gyro described in Patent Document 1. As shown in FIG. The light emitted from the light source 1 is branched into two paths through an optical coupler 2, a polarizer (polarizer) 3, and further an optical waveguide modulator 4 through an optical fiber. Light propagates in both the clockwise direction (CW direction) and the counterclockwise direction (CCW direction). When an angular velocity is applied to the optical fiber loop 5 around the center of the loop of the optical fiber loop 5 in such a light propagation state, an angular velocity called a so-called sagnac effect is generated between the CW and CCW light. A phase difference proportional to is generated. The optical fiber gyro detects the change in the interference light intensity with respect to the angular velocity by the optical coupler 2 by utilizing the change in the intensity of the interference light in the CW direction and the CCW direction according to the phase difference. The output obtained as an optical output by the light receiver 6 via the system fiber is converted into an electrical output by photoelectric conversion to obtain a detection output.

  Here, when the phase difference between the CW light and the CCW light is φ, the intensity P of the interference light is expressed by the following equation.

P = Kp (1 + COSφ)
Here, Kp is a constant. The intensity output P of such interference light exhibits a cosine (COS) output curve in the output change corresponding to the change in the angular velocity. There is a drawback of being slow. For this purpose, electrical processing for applying sinusoidal phase modulation is performed in the detection system for the intensity P of the interference light. A sine wave generation circuit 7 shown in FIG. 1 applies sine wave modulation to light through the electrodes 4 a and 4 b of the optical waveguide modulator 4. When the modulated interference light is detected and demodulated by the demodulator 8, the angular velocity component of the output becomes a sine function of the angular velocity. However, since the range in which a linear output can be obtained is limited as it is, the output Vp of the light receiver 6 is further narrowed by performing feedback processing by a closed loop circuit having a limiting circuit 9 and a sawtooth wave generating circuit 10. I try to keep it down.

  FIG. 2 is a diagram illustrating a configuration example of the optical waveguide modulator 4 illustrated in FIG. 1. This optical waveguide modulator is formed on a base material 11 of lithium niobate crystal. As shown in the figure, the upper surface of the substrate 11 is a YZ plane, and a proton exchange type optical waveguide 12 is formed in the Y-axis direction immediately below the upper surface, and the optical waveguide 12 is branched into two optical waveguides 13 and 14. . The light entrance / exit surface (XZ plane) of the optical waveguide 13 is inclined with respect to the Z-axis direction. A pair of electrodes 15A and 15B are formed on the upper surface of the base material 11 on both sides along the optical waveguide 13, and a set of electrodes 16A and 16B are formed on the upper surface of the base material 11 on both sides along the optical waveguide 14. Is done. Further, connection electrode pads 17A and 17B, 18A and 18B are provided on the upper surface of the substrate 11, and are connected to the corresponding electrodes 15A and 15B, 16A and 16B, respectively. The connection electrode pads 17A and 17B, 18A and 18B are connected to terminals of an external drive circuit by bonding wires or the like. Since the manufacturing method of the optical waveguide modulator is widely known as described in Patent Document 2 and the like, description thereof is omitted.

  The optical fiber gyro described in Patent Document 1 and the optical waveguide modulator used therein have been described above, but the present invention is not limited to this.

  The optical waveguide modulator formed on the base material 11 of the lithium niobate crystal has a so-called pyroelectric effect in which charges of opposite polarity are charged on the opposite surface perpendicular to the Z-axis direction due to temperature change or stress application. As is known, an electric field is generated in the Z-axis direction as indicated by a broken arrow in FIG. The electric field due to the pyroelectric effect is unstable, and there is a problem that the intensity of light passing through the optical waveguide fluctuates due to this electric field. Such a problem occurs when using a base material having a pyroelectric effect as well as a base material of lithium niobate crystal.

  In order to prevent the influence of such a problem, for example, in the manufacturing process of an optical fiber gyro using an optical waveguide modulator, various adjustments were performed after stabilizing a light amount variation by taking a long temperature cycle. . However, since the fluctuation of the electric field due to the pyroelectric effect cannot be completely removed, the adjustment is started when the fluctuation of the electric field due to the pyroelectric effect is reduced to an allowable level. The same applies to the case where an optical fiber gyro is used, and it takes time to stabilize.

  In order to solve such a problem, for example, Patent Document 3 discloses that in order to stabilize a lithium niobate device, a silicon titanium oxynitride layer is formed on the upper surface on which the optical waveguide is formed, and the other surface of the base material is formed. Is provided with a connection layer for interconnection.

  Further, Patent Document 4 describes that a silicon film having a resistance value that does not conduct but can eliminate the potential difference is provided so as to contact each electrode.

Japanese Patent Laid-Open No. 10-221088 JP 2003-66257 A Special table 2005-515485 JP 11-118857 A

  In the configuration described in Patent Document 3, it is necessary to provide a connection layer not only on the upper surface of the base material but also on other surfaces, and it is necessary to change the orientation of the surface of the base material and perform a process of forming the connection layer. There is a problem that the manufacturing process becomes complicated.

  Further, in the configuration described in Patent Document 4, it is necessary that the silicon film does not conduct but has a resistance value that can eliminate the potential difference, and it is difficult to form a silicon film having a resistance value that satisfies such requirements. There was a problem.

  The present invention solves such a problem, and an object thereof is to realize an optical waveguide modulator that prevents the generation of an electric field due to the pyroelectric effect with a simple configuration.

  In order to achieve the above object, an optical waveguide modulator according to the present invention is provided with two ground electrodes on both sides of a control electrode that modulates the phase of light passing through the optical waveguide on the upper surface of the substrate. Are connected to each other by a bonding wire or a connection pattern on the upper surface. The connection of the two ground electrodes by the bonding wire can be performed in the same process as the wire bonding to the connection electrode pad, and the number of processes does not increase. Further, the connection pattern for connecting the two ground electrodes can be performed in the same process as the formation of other electrodes, and the number of processes does not increase.

  The present invention is applicable not only to a lithium niobate base material but also to a base material having a pyroelectric effect.

  The two ground electrodes are preferably formed along the entire length of the optical waveguide to the edge of the upper surface of the substrate.

  The present invention is also applied to an optical waveguide modulator in which an optical waveguide as shown in FIG. 2 is branched in a substrate, and two sets of control electrodes are provided for each branched optical waveguide. One ground electrode is provided further outside the two sets of control electrodes.

  Furthermore, the optical waveguide modulator of the present invention is suitable for use in the optical fiber gyro shown in FIG.

  According to the present invention, it is possible to realize an optical waveguide modulator and an optical fiber gyro capable of removing the influence of the pyroelectric effect and performing stable operation without increasing the number of manufacturing steps with a simple configuration.

  FIG. 3 is a plan view of the optical waveguide modulator according to the first embodiment of the present invention, and FIG. 4 is a cross-sectional view of a portion provided with control electrodes of two branched optical waveguides in FIG. This optical waveguide modulator is used as the optical modulator 4 of the optical fiber gyro shown in FIG.

  As apparent from the comparison with FIG. 2, the optical waveguide modulator of the first embodiment is provided with ground electrode patterns 21 and 22 at both edges along the extending direction of the optical waveguides 12, 13 and 14 on the upper surface. Unlike the conventional example of FIG. 2, the other parts are the same except that they are connected to each other by bonding wires 23.

  As shown in FIGS. 3 and 4, the light input / output port of the optical waveguide is formed on the surface close to the XZ plane, with the YZ plane of the lithium niobate crystal substrate 11 as the upper surface, and this plane is on the Y axis. On the other hand, it is slightly inclined from the vertical. Embedded optical waveguides 12, 13, and 14 are formed on the surface of the substrate 11 by a proton exchange method including a proton exchange treatment and an annealing treatment. The optical waveguide 12 is branched into optical waveguides 13 and 14 on the way. The light traveling through the optical waveguide 12 is split at the branching point and travels through the optical waveguides 13 and 14. The light traveling in the reverse direction through the optical waveguides 13 and 14 is combined at the branching point and enters the optical waveguide 12.

  Control electrodes 15A, 15B and 16A and 16B are formed on the upper surfaces on both sides of the branched optical waveguides 13 and 14 by sequentially vapor-depositing chrome or titanium, platinum and gold. At this time, the electrode patterns for connecting the connection electrode pads 17A and 17B, 18A and 18B, the control electrodes 15A, 15B and 16A and 16B to the connection electrode pads 17A and 17B, and 18A and 18B, and the ground electrode patterns 21, 22 Form. In this way, all the electrodes and electrode patterns are produced simultaneously in one process. As illustrated, the ground electrode patterns 21 and 22 are formed along the entire length of the optical waveguide and extend to the edge of the upper surface of the substrate 11. Accordingly, the control electrodes 15A, 15B and 16A and 16B and the connection electrode pads 17A and 17B, 18A and 18B are arranged between the two ground electrode patterns 21 and 22.

  As shown in FIG. 4, the two ground electrode patterns 21 and 22 are connected by a bonding wire 23. The connection electrode pads 17A and 17B and 18A and 18B are connected to an external circuit by wire bonding. At least one of the two ground electrode patterns 21 and 22 is connected to a ground (ground) terminal of an external circuit by wire bonding. The bonding wire 23 is attached in the same process.

  In the optical waveguide modulator of the first embodiment, since the optical waveguides 12, 13, and 14 are disposed between the two grounded electrode patterns 21 and 22, they are opposed to each other perpendicular to the Z axis of the substrate 11. Even if an electric field is formed by accumulating charges on the surface to be subjected to the pyroelectric effect, the electric field is shielded, and both sides of the optical waveguides 12, 12, 14 are always at the same potential, so that the influence can be eliminated or reduced. Further, since the charges accumulated on the opposing surfaces are easily neutralized through the ground electrode patterns 21 and 22 and the bonding wires 23, the accumulation of charges is also suppressed.

  As described above, the optical waveguide modulator of the first embodiment can be manufactured without increasing the number of conventional processes, and the influence of the electric field due to the pyroelectric effect can be removed.

  FIG. 5 is a plan view of an optical waveguide modulator according to the second embodiment of the present invention. In the optical waveguide modulator of the first embodiment, the two ground electrode patterns 21 and 22 are connected by the bonding wire 23, whereas in the optical waveguide modulator of the second embodiment, the ground electrode patterns 21 and 22 are connected. The connection is different in the pattern 24. Since the connection pattern 24 is formed simultaneously with other electrodes and electrode patterns, the number of processes does not increase compared to the conventional example.

  FIG. 6 is a diagram showing experimental results comparing the influence of the pyroelectric effect in the optical waveguide modulators of the first and second embodiments with the conventional example. This figure shows a measurement system that detects the amount of light emitted from a fixed amount of light incident on the optical waveguide. As indicated by the broken line, the temperature of the optical waveguide modulator changes between -35 ° C and + 85 ° C in a cycle of 4 hours. FIG. 3 is a graph showing a change (solid line) in the amount of emitted light when it is applied, (A) shows the measurement result in the conventional example of FIG. 2, and (B) shows the measurement result in the optical waveguide modulator of the first and second embodiments. Indicates. As shown in the figure, it can be seen that in the conventional example, the amount of emitted light changes greatly with the temperature change, whereas in the first and second embodiments, a stable and constant change is shown.

  As described above, the optical waveguide modulators of the first and second embodiments are used as the optical modulator of the optical fiber gyro of FIG. 1, and the optical waveguide modulators of the first and second embodiments are used. The optical fiber gyro has a very short time until it can be used stably, and a stable and highly accurate output can be obtained even if the temperature changes.

  As mentioned above, although the Example of this invention was described, this invention is not limited to these Examples, and it cannot be overemphasized that various modifications are possible.

  The present invention can be applied to any apparatus as long as it is an optical waveguide modulator using a base material having a pyroelectric effect and an apparatus using such an optical waveguide modulator.

It is a figure which shows schematic structure of an optical fiber gyroscope. It is a top view of the prior art example of an optical waveguide modulator. It is a top view of the optical waveguide modulator of 1st Example of this invention. It is sectional drawing of the optical waveguide modulator of 1st Example. It is a top view of the optical waveguide modulator of 2nd Example of this invention. It is a figure which shows the experimental result which shows the effect of this invention compared with the prior art example.

Explanation of symbols

11 Lithium niobate crystal substrate 12, 13, 14 Optical waveguide 15A, 15B, 16A, 16B Control electrode 17A, 17B, 18A, 18B Connection electrode pad 21, 22 Ground electrode pattern 23 Bonding wire 24 Connection pattern

Claims (7)

A substrate;
An optical waveguide provided directly below the upper surface in the substrate;
A control electrode provided on both sides of the optical waveguide on the upper surface of the substrate, and an optical waveguide modulator comprising:
Two ground electrodes provided on both sides of the control electrode on the upper surface of the substrate;
An optical waveguide modulator comprising: a bonding wire that connects the two ground electrodes. A substrate;
An optical waveguide provided directly below the upper surface in the substrate;
A control electrode provided on both sides of the optical waveguide on the upper surface of the substrate, and an optical waveguide modulator comprising:
Two ground electrodes provided on both sides of the control electrode on the upper surface of the substrate;
An optical waveguide modulator comprising: a connection electrode pattern provided on an upper surface of the base so as to connect the two ground electrodes.   The optical waveguide modulator according to claim 1, wherein the base material is a lithium niobate base material.   4. The optical waveguide modulator according to claim 1, wherein the two ground electrodes are formed along the entire length of the optical waveguide up to an edge of the upper surface of the base material. 5. The optical waveguide is branched in the substrate;
Two sets of the control electrodes are provided for each branched optical waveguide,
5. The optical waveguide modulator according to claim 1, wherein the two ground electrodes are provided further outside the two sets of the control electrodes. 6. An optical fiber loop, a light source, an optical coupler that guides light from the light source to a connection path to the optical fiber loop and separates light returning from the optical fiber loop through the connection path, and provided in the connection path An optical fiber gyro, comprising: an optical modulator formed by the optical coupler; and a light receiver that detects light separated by the optical coupler,
6. The optical fiber gyro according to claim 1, wherein the optical modulator is an optical waveguide modulator according to any one of claims 1 to 5. The optical modulator branches the connection path;
The two branched connection paths are connected to both ends of the optical fiber loop;
The optical fiber gyro according to claim 6, wherein the optical modulator adjusts a phase of light passing through the two branched connection paths.

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