JPH09218384A - Optical control element and directions for use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make cross talk due to the electric coupling of an input/output part very small, to make the element small and suitable for integration and to enable high-speed operation by shifting input/output terminals of each traveling-wave electrode and arranging them. SOLUTION: In an optical control element arranging terminals for inputting or outputting an electric signal to two traveling-wave electrodes composed of signal electrodes 103, 104 and a grounded electrode 105 on both sides of an optical waveguide 102, the input/output part of the signal electrode 103 and the input/output part of the signal electrode 104 are arranged by 4mm apart from their opposed position in the traveling direction of light. Since the grounded electrode 105 is arranged in the opposed part of the input part of the signal electrode 103, coupling to the signal electrode 104 is least. Since the signal electrode 103 is arranged in the opposed part of the input part of the signal electrode 104 and its width and gap are narrow, the coupling of both electrodes is very weak. In the output part, quite reverse phenomenon holds. Consequently, cross talk between two signal electrodes is very small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control element for modulating a light wave, switching an optical path, etc., and more particularly to an optical control element having an extremely high operating speed and a method of using the same.

[0002]

2. Description of the Related Art In recent years, advances in optical fibers and laser light sources have been advanced.
With the development, various systems and devices applying optical technology such as optical communication have been put into practical use and widely used, and more and more, there has been an increasing demand for the development of advanced technology. In particular, due to the recent demand for high-speed optical communication systems,
Also in an optical transmitter that transmits an optical signal, development of an optical element that modulates light at high speed and low voltage is required. As such an element, a branched optical waveguide is provided on a substrate having an electro-optical effect such as lithium niobate (LiNbO ₃ ).
A Mach-Zehnder type optical modulator, which uses two traveling wave electrodes and performs a phase binary intensity modulation operation or push-pull drive, is considered promising.

In a conventional push-pull drive type optical modulator, a coplanar strip line (C
Optical modulator equipped with two PS (T.Namiki et al., IOOC'89, 19D
4-2) Alternatively, or an optical modulator (SKKoro) equipped with two Coppner waveguide (CPW) electrodes as traveling wave electrodes.
tky et al .: IPR'91, TuG2). Here, when a plurality of electrodes are formed on the same substrate, crosstalk between the electrodes becomes a problem. Since the ground electrode is disposed between the two signal electrodes in the CPW electrode, crosstalk between the electrodes can be significantly reduced as compared with the CPS electrode. A conventional example of a push-pull drive type optical modulator using two CPW electrodes is shown in FIGS.
Shown in 5 is a plan view, and FIG. 6 is a cross-sectional view taken along the line AA '.

In this example, a Mach-Zehnder type optical waveguide 102 is formed on a z-cut LiNbO ₃ substrate 101 having an electro-optical effect by Ti thermal diffusion. Its substrate 1
01, a SiO ₂ buffer layer 108 is formed, and a CPW-type first traveling wave electrode composed of a signal electrode 103 and a ground electrode 105, and a signal electrode 104 and a ground electrode. A second traveling wave electrode composed of 105 is formed. 106 is C
A terminating resistor connected between the signal electrode of the PW traveling wave electrode and the ground electrode, 107 is connected to the electrodes 103 and 104, and supplies a modulation microwave signal to these signal electrodes 103 and 104. It is a power supply line (coaxial line for power supply).

When drive power is supplied to the optical modulator from the signal source 109 via the amplifier 110 and the modulating microwave power feed line 107, between the first signal electrode 103 and the ground electrode 105, and An electric field is applied between the second signal electrode 104 and the ground electrode 105. LiNbO ₃ substrate 1
Since 01 has an electro-optical effect, the refractive index changes due to this electric field. As a result, the phase of the light propagating through the two optical waveguides 102 is deviated. This deviation is 2mπ (m
Is a whole number) radians, the guided mode is excited at the combining portion of the Mach-Zehnder type optical waveguide 102, and the light is turned on.
State. On the other hand, when the phase shift becomes (2m + 1) π radians, the higher-order mode is excited in the combining portion of the Mach-Zehnder type optical waveguide 102, and the light is turned off. In the case of this optical modulator, a CP having ground electrodes 105 on both sides of the signal electrodes 103 and 104 as traveling wave electrodes
The W electrode is used, and the interaction part has a central conductor width of 8μ.
m, the gap is about 15 μm, and the distance between the two signal electrodes is about 15 times the gap (250 μm). Therefore, the microwave signal for modulation propagating through the CPW electrode 103 and the modulation microwave signal propagating through the CPW electrode 104. There is almost no coupling with the wave signal.

[0006]

However, when the traveling wave electrode is connected to the coaxial line or the coaxial type terminating resistor, the microwave electric field mode is usually connected via a coaxial type connector. To CPW electrode mode. As shown in FIG. 5, in order to match the size of the coaxial connector at the input / output portion of the electrode on the substrate,
By providing a taper portion, the width of the signal electrode is expanded to about 300 μm and the gap is expanded to about 700 μm. In this part,
Since the gap is widened and the input ends and the output ends are arranged to face each other, the electric field radiated at the time of the coaxial mode-CPW mode conversion easily causes electrical coupling. In order to suppress this coupling below a certain level, in the conventional example, the distance between the input ends of the two traveling wave electrodes and the distance between the output ends of the two traveling wave electrodes had to be made sufficiently large.

An object of the present invention is to suppress a crosstalk due to electric coupling at an input / output portion of an electric signal, which is a problem in a conventional multi-electrode element, and is a small-sized wide band optical control element suitable for integration and its use. To provide a method.

[0008]

In order to solve the above problems, according to claim 1 of the present invention, a substrate having an electro-optical effect, an optical waveguide formed on one main surface of the substrate, and the main surface are provided. A buffer layer formed above and a plurality of traveling wave electrodes formed on the buffer layer, and terminals for inputting or outputting electric signals to the traveling wave electrodes are provided on both sides of the optical waveguide. In the arranged light control element, the terminals are arranged at different positions along the light guide direction. According to a second aspect, in the light control element according to the first aspect, the optical waveguide is an optical waveguide formed on a flat surface of the substrate or an optical waveguide formed on the substrate having a ridge. According to a third aspect of the present invention, in the light control element according to the first or second aspect, the light control element is an optical switch including a Mach-Zehnder type optical modulator or a directional coupler. According to a fourth aspect of the present invention, in the light control element according to the first to third aspects, the positions of the terminals are separated from each other by 250 μm or more along the light guiding direction. According to a fifth aspect of the invention, the optical control element is the optical switch including the Mach-Zehnder type optical modulator according to the third aspect, wherein traveling wave electrodes are respectively arranged in the two branched optical waveguides, and the traveling wave electrodes are disposed in the traveling wave electrodes. An electric signal having a different polarity and an equal intensity was applied.

According to the present invention, since the terminals for input and output of each traveling wave electrode are arranged in a staggered manner, crosstalk due to electrical coupling between the input and output portions as in the conventional example is extremely reduced. It is possible to provide a small-sized, small-sized, wide-band optical control element suitable for integration and a method of using the same.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a plan view of a Mach-Zehnder type optical modulator according to the first embodiment of the present invention. In this embodiment, as in the conventional example shown in FIG. 5 and FIG. 6, two traveling wave electrodes composed of the first signal electrode 103, the second signal electrode 104, and the ground electrode 105 are provided, Unlike the structure of the conventional example, the first signal electrode 10
The input / output unit 3 and the input / output unit of the second signal electrode 104 are arranged so as to be displaced by 4 mm in the traveling direction of the light from the position facing each other. Since the ground electrode 105 is arranged in the facing portion of the input portion of the first signal electrode 103, the coupling to the second signal electrode 104 is extremely small. Second signal electrode 104
The first signal electrode 103 is arranged at the opposite portion of the input part of the above, but the width and gap are narrow, so the coupling between the two is extremely small. In the output part, the exact opposite phenomenon holds. Therefore, the crosstalk between the two signal electrodes as in the conventional example is extremely small. Other configurations are the same as the conventional example.

FIG. 2 is a diagram showing the crosstalk characteristics of the modulation element of the first embodiment.

In FIG. 2, a microwave signal was applied to the input section of the first traveling wave electrode, and the power coupled to the output section of the second traveling wave electrode was measured with a network analyzer. 45
Measurement limit (-30d from MHz to 50 GHz
B) It can be seen that it is suppressed below.

FIG. 3 is a diagram showing a second embodiment of the present invention.

In this embodiment, Ti thermal diffusion is performed on the z-cut LiNbO ₃ substrate 101 having an electro-optical effect,
Four optical waveguides 114, 115, 116 and 117 are formed to form a directional coupler. A SiO ₂ buffer layer is formed on the substrate 101 (not shown),
Further, on the buffer layer, a CPW-type first traveling wave electrode composed of the signal electrode 103 and the earth electrode 105, and a CPW-type second traveling wave electrode composed of the signal electrode 104 and the earth electrode 105. A third traveling wave electrode composed of the signal electrode 118 and the ground electrode 105 is formed. 106 is a terminating resistor connected between the signal electrode of the CPW traveling wave electrode and the ground electrode, 107 is a microwave signal feed line (feeding coaxial line), 109 is a signal source,
110 is an amplifier.

When no drive power is supplied to this light control element, the light incident on the optical waveguide 115 is coupled to the optical waveguide 116 by the directional coupler section and further coupled to the optical waveguide 117. Here, when drive power is supplied to the first signal electrode 103 from the signal source 109 via the amplifier 110 and the modulation microwave feed line 107, an electric field is generated between the signal electrode 103 and the ground electrode 105. Join. Since the LiNbO ₃ substrate 101 has an electro-optic effect, this electric field causes a change in the refractive index. As a result, the phase of the light propagating through the optical waveguide 115 shifts. When this shift becomes 3 ^1/2 · π radians, the light propagates through the optical waveguide 115 as it is. Then, it is coupled to the optical waveguide 114 at the next directional coupler section and emitted. Similarly, by changing the power applied to each signal electrode, it operates as a 1-input / 4-output 1 × 4 optical switch.

In the case of this optical switch, as in the case of the first embodiment, there is almost no coupling between the signal electrodes, and the coupling of the input / output portions of the opposing second signal electrode 104 and third signal electrode 118. The connection between the input / output portions of the second signal electrode 104 and the third signal electrode 119 facing each other becomes a problem, but the input / output portion of the second signal electrode 104 and the input / output portion of the third signal electrode 118 are not present. It is arranged so as to be displaced from the position facing the output portion in the light traveling direction. Second signal electrode 1
Since the ground electrode 105 is arranged in the facing portion of the input portion 04, the coupling to the third signal electrode 118 is extremely small. The second signal electrode 104 is arranged at a portion facing the input portion of the third signal electrode 118. However, since the width and the gap are narrow, the coupling between the two is extremely small. In the output part, the exact opposite phenomenon holds. Therefore, 2
Crosstalk between two signal electrodes is extremely small.

FIG. 4 is a diagram showing a third embodiment of the present invention.

The structure of the modulator is the same as that of the first embodiment. In the figure, 112 and 113 are signal cables, one end of which is connected to the input ends of the first signal electrode 103 and the second signal electrode 104, respectively.
The other end of 12 is, for example, the phase and amplitude adjusting means 1
11, connected to an electric signal source 109 via an amplifier 110. 106 is a terminating resistor.

Here, the transmission time between the branch point D of the electric signal and the leading point C of the second traveling wave electrode is the time between the branch point D of the electrical signal and the leading point B of the first traveling wave electrode. The transmission time is delayed by the time required for light to travel between the leading points B and C, and at the same time, the phase and amplitude adjusting means are arranged so that the polarities of the electric signals applied to the respective electrodes are inverted. The adjustment of 111 and the setting of the length of the signal cable 113 are performed. The magnitude of the effective electric field that acts on the light on the branched optical waveguide depends on the component acting from the first traveling wave electrode 103,
Since the magnitude of the component acting from the second traveling wave electrode 104 is equal and the direction is opposite, the drive voltage of the modulator can be reduced.

In the above embodiment, z-cut LiNbO is used.
_{Although three} substrates are used, a LiNbO ₃ substrate having another plane orientation such as x-cut or y-cut may be used, or another substrate having an electro-optical effect such as LiTaO ₃ may be used. Further, in the above embodiment, the present invention is applied to the optical modulator having two traveling wave electrodes, but the degree of integration of the device is improved and three electrodes are used.
It may be applied to an optical matrix switch or the like having three or more. Further, although the embodiment has been described only for the planar waveguide as the optical waveguide, the present invention can of course be implemented even if it is a ridge waveguide.

[0022]

As described above, according to the present invention, since the input and output terminals of each traveling wave electrode are arranged so as to be displaced from each other, it is possible to electrically connect the input and output portions as in the conventional example. A cross-talk due to coupling can be extremely reduced, high-speed operation is possible, and a small-sized broadband optical control element suitable for integration and a method of using the same can be provided.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing crosstalk characteristics according to the first embodiment of the present invention.

FIG. 3 is a plan view showing a second embodiment of the present invention.

FIG. 4 is a plan view showing a third embodiment of the present invention.

FIG. 5 is a plan view of a conventional light modulator.

FIG. 6 is a cross-sectional view of a conventional light modulation element.

[Explanation of symbols]

101 ... Z-cut LiNbO ₃ substrate, 102 ... Ti thermal diffusion Mach-Zehnder type optical waveguide, 103 ... First signal electrode, 104 ... Second signal electrode, 105 ... Ground electrode, 1
06 ... Termination resistance, 107, 112, 113 ... Microwave signal feed line for modulation, 108 ... SiO ₂ buffer layer, 10
9 ... Signal source, 110 ... Amplifier, 111 ... Phase and amplitude adjusting means, 114, 115, 116, 117 ... Ti thermal diffusion directional coupler type optical waveguide, 118 ... Third signal electrode.

Claims (5)

[Claims] 1. A substrate having an electro-optical effect, an optical waveguide formed on one main surface of the substrate, a buffer layer formed on the main surface, and a plurality of buffer layers formed on the buffer layer. In a light control element having a traveling wave electrode, wherein terminals for inputting or outputting an electric signal to the traveling wave electrode are arranged on both sides of the optical waveguide, and the terminals are arranged in respective waveguide directions. A light control element, which is arranged at different positions along a line. 2. The optical waveguide according to claim 1, wherein the optical waveguide is an optical waveguide formed on a flat surface of the substrate or an optical waveguide formed on the substrate having a ridge. Control element. 3. The light control element according to claim 1, wherein the light control element is an optical switch including a Mach-Zehnder type optical modulator or a directional coupler. 4. The light control element according to claim 1, wherein the positions of the terminals are separated from each other by 250 μm or more along the light guiding direction. 5. The optical switch comprising the Mach-Zehnder type optical modulator according to claim 3, wherein the optical control element has traveling-wave electrodes disposed on each of the two branched optical waveguides, and each traveling-wave electrode is disposed on the traveling-wave electrode. A method of using a light control element, which comprises applying electric signals having different polarities and equal in intensity.