JP2014112171A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator which operates at high speed, is low in driving voltage and is low in bias voltage.SOLUTION: An optical modulator includes: a substrate having an electro-optical effect; an optical waveguide formed on the substrate to guide light; a high-frequency electrode which is formed on one surface side of the substrate and applies a high-frequency electric signal that modulates light; and a bias electrode for applying a bias voltage to light. In the optical modulator which is formed of a nest type optical waveguide having a child Mach-Zehnder optical waveguide on branched optical waveguides of a parent Mach-Zehnder optical waveguide, respectively, the optical waveguide includes at least one inversion optical waveguide which makes a direction of propagating light into an approximately U shape, the high-frequency electrode is arranged on one U-shaped arm, and the bias electrode is arranged on another U-shaped arm.

Description

  The present invention belongs to the field of optical modulators that are high in speed, low in driving voltage, and low in bias voltage.

An optical waveguide and a traveling wave electrode are provided on a substrate having a so-called electro-optic effect (hereinafter, the lithium niobate substrate is abbreviated as an LN substrate) such as lithium niobate (LiNbO ₃ ) that changes its refractive index when an electric field is applied. The formed traveling-wave electrode type lithium niobate optical modulator (hereinafter abbreviated as LN optical modulator) is applied to a 2.5 Gbit / s, 10 Gbit / s large capacity optical transmission system because of its excellent chirping characteristics. Yes. Recently, application to an ultra large capacity optical transmission system of 40 Gbit / s is also being studied, and it is expected as a key device.

(First prior art)
In recent 40 Gbit / s, DQPSK and DPSK types are being used, and in 40 Gbit / s, DPSK type phase modulation is being used.

  A DQPSK type is considered as the first prior art. FIG. 10 shows a schematic top view of a DQPSK type LN optical modulator (or DQPSK optical modulator) disclosed in Patent Document 1. As can be seen from FIG. 10, the DQPSK optical modulator has a structure (nesting) in which two small Mach-Zehnder (or child Mach-Zehnder and child MZ) optical waveguides 7 are incorporated in a large Mach-Zehnder (or parent Mach-Zehnder or parent MZ) optical waveguide 8. It is also called a structure or a nested type). That is, the DQPSK optical modulator has a nested structure in which two child MZ optical modulators are incorporated in one parent MZ optical modulator.

Here, 1 is a z-cut LN substrate, 3 is an optical waveguide, 3 _in and 3 _out are an input optical waveguide and an output optical waveguide, 3a is a high-frequency electrical signal, and a bias signal for a child MZ optical waveguide interacts with light. An interactive optical waveguide, 4 is a high-frequency traveling wave electrode (RF electrode) having a length L _RF , and 5 is a length L _{DC (C)} to which a bias voltage for controlling the operating point of the child MZ optical modulator is applied. The child MZ bias electrode 6 has a length L _{DC (P)} for applying a bias voltage for controlling the operating point of the parent MZ optical modulator by interacting with the light propagating through the optical waveguide 3b of the parent MZ. This is a bias electrode for the parent MZ. Note that L _LN is the length of the LN substrate 1 in the longitudinal direction, and the limit length that can be used is determined by the wafer size to be used.

Here, the problems of the prior art will be considered. In the conventional technique, since the RF electrode 4, the child MZ bias electrode 5, and the parent MZ bias electrode 6 are arranged in the same direction in series, L _RF + L _{DC (C)} + L _{DC (P)} <L _LN is always satisfied. It had to be established, and there was a restriction on the setting of each length. For example, when a 4-inch wafer is used, the length L _LN of the LN substrate 1 is about 70 mm. At high frequencies such as 40 Gbit / s and 100 Gbit / s, the electrical output from the driver is limited to 4 V or less, so the RF voltage must be reduced to 3.5 V or less. Therefore, if the length L _RF of the RF electrode 4 is about 45 mm, the length L _LN of the LN substrate is about 70 mm. For example, the length L _{DC (C)} of the bias electrode 5 for the child MZ is about 6 mm, and the parent MZ The length L _{DC (P) of the} bias electrode 6 for use is automatically determined to be about 6 mm. The length obtained by subtracting the length L _{DC (C) of the} child MZ bias electrode 5 and the length L _{DC (P)} of the parent MZ bias electrode 6 from the length L _LN of the LN substrate is used for wiring. To do.

That is, at a high frequency such as 40 Gbit / s or 100 Gbit / s, since the electric output from the driver is limited, if the length L _RF of the RF electrode 4 is increased, the length L _{DC (C of the} child MZ bias electrode 5 is increased. ₎ Or the length L _{DC (P) of the} bias electrode 6 for the parent MZ is shortened as described above, and the bias voltage is increased to about 13V. In other words, there is a trade-off relationship between the RF drive voltage and the bias voltage of the child MZ and the parent MZ, and a high bias voltage is a big problem in long-term reliability from the viewpoint of the bias voltage for controlling the optical modulator. It was.

(Second prior art)
FIG. 11 shows a schematic top view of a DP-QPSK type optical modulator used at a high frequency such as 40 Gbit / s or 100 Gbit / s. Here, 9 is an optical waveguide, 9 _in and 9 _out are input optical waveguides and output optical waveguides, 9 a is an interactive optical waveguide in which light and high frequency electrical signals and bias signals interact, and 10 is high frequency progression of length L _RF A wave electrode (RF electrode), 11 is a bias electrode for a child MZ having a length L _{DC (C)} to which a bias voltage for controlling the operating point of the child MZ optical modulator is applied, and 12 is an optical waveguide 9b of the parent MZ. Is a bias electrode for the parent MZ having a length L _{DC (P)} to which a bias voltage that interacts with the light propagating through the light and controls the operating point of the parent MZ optical modulator is applied. Reference numeral 50 denotes a polarization rotator for converting the Y polarized wave propagating through the z-cut LN substrate 1 into an X polarized wave, and 51 denotes a polarization beam combiner for combining the X polarized wave and the Y polarized wave.

Also in this DP-QPSK type optical modulator, since the RF electrode 10, the child MZ bias electrode 11, and the parent MZ bias electrode 12 are arranged in the same direction in series, L _RF + L _{DC (C)} + L _{DC (P)} <L _LN must be satisfied, and the setting of each length is restricted. In other words, like the first prior art, there is a trade-off relationship between the RF drive voltage and the bias voltage of the child MZ and the parent MZ in the second prior art, so that it can be used in an actual optical communication system. There was a big problem in long-term reliability.

JP 2007-208472 A

  Thus, in the prior art, the length of the RF electrode and the bias electrode for the child MZ or the parent MZ are arranged in the same straight line. Therefore, since there is a trade-off relationship between the lengths, the child MZ bias electrode and the parent MZ bias electrode are shortened. As a result, the half-wave voltage that determines the operating point becomes high, and there is a problem in reliability in actually using the optical modulator.

  In order to solve the above problems, an optical modulator according to claim 1 of the present invention includes a substrate having an electro-optic effect, an optical waveguide for guiding light formed on the substrate, A high-frequency electrode for applying a high-frequency electrical signal for modulating the light; and a bias electrode for applying a bias voltage to the light; An optical modulator comprising a nested Mach-Zehnder optical waveguide having a parent Mach-Zehnder optical waveguide between the waveguide and the output optical waveguide, and having a child Mach-Zehnder optical waveguide on a branched optical waveguide of the parent Mach-Zehnder optical waveguide. Comprises at least one inverting optical waveguide whose propagation direction is substantially U-shaped, the high-frequency electrode is disposed on one U-shaped arm, and the other U-shaped arm has the above-mentioned Is characterized in that bias electrodes are disposed.

  An optical modulator according to a second aspect of the present invention is the optical modulator according to the first aspect, wherein the parent Mach-Zehnder optical waveguide or the child is arranged so that the arms of the parent Mach-Zehnder optical waveguide are equal in length. It is characterized in that at least one arm of the Mach-Zehnder optical waveguide is deformed.

  The optical modulator according to claim 3 of the present invention is the optical modulator according to claim 1 or 2, wherein the arms of the child Mach-Zehnder optical waveguide are made equal in length so that the arms of the child Mach-Zehnder optical waveguide are equalized. It is characterized by deforming the arm.

  An optical modulator according to a fourth aspect of the present invention is the optical modulator according to any one of the first to third aspects, wherein the bias electrode is a bias electrode for the parent Mach-Zehnder optical waveguide. It is said.

  An optical modulator according to a fifth aspect of the present invention is the optical modulator according to the fourth aspect, wherein the bias electrode includes a bias electrode for the child Mach-Zehnder optical waveguide.

  An optical modulator according to a sixth aspect of the present invention is the optical modulator according to any one of the first to third aspects, wherein the high-frequency electrode and the child are disposed on the U-shaped arm. A bias electrode for a Mach-Zehnder optical waveguide is disposed, and a bias electrode for the parent Mach-Zehnder optical waveguide is disposed on the other arm.

  An optical modulator according to a seventh aspect of the present invention is the optical modulator according to any one of the first to third aspects, wherein the high-frequency electrode is disposed on the one U-shaped arm. A bias electrode for the parent Mach-Zehnder optical waveguide and a bias electrode for the child Mach-Zehnder optical waveguide are arranged on the other arm.

  An optical modulator according to an eighth aspect of the present invention is the optical modulator according to any one of the first to seventh aspects, wherein the inversion optical waveguide is formed on the same substrate as the substrate having the electro-optic effect. It is characterized by being.

  An optical modulator according to a ninth aspect of the present invention is the optical modulator according to any one of the first to seventh aspects, wherein the inverted optical waveguide is separate from the substrate having the electro-optic effect. It is characterized by comprising a quartz optical waveguide circuit.

  In the present invention, by arranging the bias electrode for the parent MZ, the bias electrode for the child MZ, or both in the direction opposite to the RF electrode, the degree of freedom in setting the length of these bias electrodes is increased. I have to. As a result, since the bias voltage can be significantly reduced, the long-term reliability in an actual optical communication system can be drastically improved. In addition, since the lengths of the child MZ optical waveguide and the arm of the parent MZ optical waveguide are made equal in terms of the phase of the light, there is no filter characteristic with respect to the wavelength of the light in the optical insertion loss, and it is used in a wide wavelength band. It can be used and is easy to use.

Schematic top view of the first embodiment of the optical modulator of the present invention. The figure for demonstrating the principle of this invention The figure for demonstrating the principle of this invention The figure for demonstrating the principle of this invention Schematic top view of the second embodiment of the optical modulator of the present invention. Schematic top view of the third embodiment of the optical modulator of the present invention. Schematic top view of the fourth embodiment of the optical modulator of the present invention. Schematic top view of the fifth embodiment of the optical modulator of the present invention. Schematic top view of the sixth embodiment of the optical modulator of the present invention. Schematic top view of a first conventional optical modulator Schematic top view of the second conventional optical modulator

  Hereinafter, embodiments of the present invention will be described. Since the same numbers as those of the conventional embodiment shown in FIG. 10 correspond to the same function units, the description of the function units having the same numbers is omitted here.

(First embodiment)
FIG. 1 shows a schematic top view of a DQPSK type optical modulator to which the present invention is applied as a first embodiment. Here, 14 is an optical waveguide, 14 _in and 14 _out are an input optical waveguide and an output optical waveguide, 15 is an arm having a length L ₁₅ of the branched optical waveguide, and 16 is another arm of the branched optical waveguide. L ₁₆ and 14a are interaction optical waveguides in which light and high frequency electrical signals or bias signals interact, 4 ′ is a high frequency traveling wave electrode (RF electrode) having a length L _RF ′, and 5 ′ is an operation of a child MZ optical modulator. A bias electrode for a child MZ having a length L _{DC (C)} 'to which a bias voltage for controlling a point is applied, 17 is a first inversion having a length L ₁₇ provided to reverse the propagation direction of light. An optical waveguide, similarly, 18 is a second inversion optical waveguide having a length L ₁₈ provided to invert the light propagation direction. 6 ′ is a bias for the parent MZ of length L _{DC (P)} ′ for applying a bias voltage for controlling the operating point of the parent MZ optical modulator by interacting with the light propagating through the optical waveguide 40 of the parent MZ. Electrode. Reference numerals 13 and 13 'denote quartz optical waveguide circuits manufactured by depositing glass on a Si substrate and forming a core in the glass.

  What is important in the present invention is that the propagation direction of light propagating through the optical waveguide 40 as the parent MZ and the optical waveguide 14a to which the RF electrical signal is applied is substantially U from the input optical waveguide toward the output optical waveguide. Inverted in the shape of a letter, a bias electrode is provided in the optical waveguide 40 in which this direction is inverted, and the arms constituting the parent MZ optical waveguide are made equal in length.

This will be described in detail below with reference to the drawings. As can be seen from FIG. 1, the length L ₁₈ of the second inversion optical waveguide ₁₈ is longer than the length L _{17 of} the first inversion optical waveguide 17 (L ₁₇ <L ₁₈ ). However, when the lengths of the two arms constituting the Mach-Zehnder optical waveguide are different, so-called filter characteristics in which the insertion loss depends on the wavelength occur.

For this reason, in this embodiment, the length of the first inversion optical waveguide 17 is determined by using the optical waveguides 15 and 16 on the branch portion on the light incident side and the optical waveguides 19 and 20 on the branch portion on the light emission side. For the length L ₁₇ and the length L ₁₈ of the second inversion optical waveguide 18, the difference between the lengths ΔL _18-17 = L ₁₈ −L ₁₇ is corrected. That is, the optical waveguides _{15, 16, 19} , and 20 and the inverting optical waveguides 17 and 18 are configured so that the relational expression ΔL _18-17 = (L ₁₅ −L ₁₆ ) + (L ₁₉ −L ₂₀ ) holds. Yes. In this embodiment, the lengths are corrected by meandering the optical waveguides 15 and 19.

FIG. 2 shows the length L _{DC (P)} of the parent MZ electrode 5 and the half-wave voltage DC Vπ (P) as the parent MZ in the first prior art, and the length L of the parent MZ electrode 6 ′ in the present embodiment. The relationship between _{DC (P)} ′ and the half-wave voltage DC Vπ (P) ′ as the parent MZ is shown. As shown in FIG. 1, by applying the present invention, the length L _{DC (P)} of the parent MZ electrode 6, which is as short as about 6 mm, can be increased to the same extent as the length L _LN of the LN substrate 1. did it. As a result, as can be seen from FIG. 2, the half-wave voltage can be made extremely small as compared with the first prior art (specifically, it can be reduced from about 13 V to about 1 V).

FIG. 3 shows the length L _RF of the RF electrode 4 in the first prior art and the RF half-wave voltage RF Vπ during operation of 40 Gbit / s, and the length L _RF ′ of the RF electrode in this embodiment and during operation of 40 Gbit / s. The relationship with the RF half-wave voltage RF Vπ ′ in FIG. FIG. 4 shows the length L _{DC (C)} and half-wave voltage DC Vπ (C) of the child MZ electrode 5 in the first prior art, and the length L _{DC (C} of the child MZ electrode 5 ′ in this embodiment. ₎ ′ And the half-wave voltage DC Vπ (C) ′ during the bias operation. In this embodiment, the length of L _{DC (P)} of the parent MZ bias electrode 6 in the first prior art of FIG. 10 can be allocated to the RF electrode 4 ′ and the child MZ bias electrode 5 ′. For the half-wave voltage RF Vπ ′ and the half-wave voltage DC Vπ (C) ′, the half-wave voltage could be reduced by several tens of percent.

  Since the distance between the optical waveguides 40 whose directions are reversed is sufficient if it is about several tens of microns, the increase in the width direction of the LN substrate 1 by applying the present invention is as small as about 100 to 200 μm, The dimension in the substrate width direction does not become so large as to affect the number that can be taken from the wafer. And this can be said for all embodiments of the invention.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 5 is a schematic top view of the second embodiment of the present invention.

Here, 9 ′ is an optical waveguide, 9 ′ _in and 9 ′ _out are input optical waveguides and output optical waveguides, 21, 22, 23, 24, 25, 26, 31, and 32 are light beams constituting the arms of the branched optical waveguides. It is a waveguide (in other words, a parent MZ optical waveguide is formed in a nested structure). 9a ′ is an interactive optical waveguide in which light interacts with a high-frequency electrical signal or bias signal, 10 ′ is a high-frequency traveling wave electrode (RF electrode) having a length L _RF ′, and 11 ′ is an operating point of the child MZ optical modulator. The MZ bias electrodes 27, 28, 29, and 30 having a length L _{DC (C)} ′ to which a bias voltage for control is applied are provided for reversing the light propagation direction. Inverted optical waveguide. Reference numeral 12 'denotes a bias electrode for the parent MZ having a length L _{DC (P)} ' for applying a bias voltage for controlling the operating point of the parent MZ optical modulator by interacting with light propagating through the optical waveguide 60. .

  As can be seen from FIG. 5, the inverted optical waveguides 27, 28, 29 and 30 have different lengths. Although not shown in detail, in order to correct the length of the inverted optical waveguides 27, 28, 29, and 30, a part of the arm of the MZ optical waveguide was deformed as in the first embodiment. Length adjustment regions 70a, 70b, 70c, 70d, 70e, 70f, 70g, and 70h are provided to adjust the difference in length.

Similar to the first embodiment, also in this embodiment, the bias voltage of the parent MZ optical waveguide can be extremely reduced. Further, the length of L _{DC (P)} of the parent MZ bias electrode 12 in the second prior art of FIG. 11 can be allocated to the RF electrode 10 ′ and the child MZ bias electrode 11 ′. With respect to RF Vπ ′ and half-wave voltage DC Vπ (C) ′, the half-wave voltage could be reduced by several tens of percent.

(Third embodiment)
Next, a DQPSK type optical modulator as a third embodiment of the present invention will be described. FIG. 6 is a schematic top view of the third embodiment of the present invention.

Here, 80 is an optical waveguide, 80 _in and 80 _out are input optical waveguides and output optical waveguides, 14 a is an interactive optical waveguide in which high-frequency electrical signals and light interact, 4 ′ is a high-frequency traveling wave electrode (RF electrode), 85 is a bias electrode for a child MZ to which a bias voltage for controlling the operating point of the child MZ optical modulator is applied, and 81, 82, 83, and 84 are provided for reversing the light propagation direction, respectively. This is a fourth inverted optical waveguide. Reference numeral 86 denotes a parent MZ bias electrode for applying a bias voltage for controlling the operating point of the parent MZ optical modulator.

  As can be seen from FIG. 6, the inverted optical waveguides 81, 82, 83, and 84 have different lengths. Although not shown in detail, in order to correct the lengths of the inverted optical waveguides 81, 82, 83, and 84, a part of the arm of the MZ optical waveguide was deformed as in the first embodiment. Length adjustment regions are provided at 87 and 88 to adjust the difference in length.

  The present embodiment has a great feature that the bias voltage of both the parent MZ optical waveguide and the child MZ optical waveguide can be reduced to a fraction of that of the prior art, such as 1/3 to 1/4.

(Fourth embodiment)
Next, a DQPSK type optical modulator as a fourth embodiment of the present invention will be described. FIG. 7 is a schematic top view of the fourth embodiment of the present invention.

  In the present embodiment, a parent MZ bias electrode 89 is used in which the parent MZ bias electrode 86 in the third embodiment shown in FIG. 6 is simplified. And length adjustment area | regions 87 and 90 are provided similarly to 3rd Embodiment.

  Compared with the third embodiment of FIG. 6, the present embodiment shown in FIG. 7 has an advantage that the configuration of the bias electrode for the parent MZ is simplified, and thus the fabrication is easy.

(Fifth embodiment)
Next, a DP-QPSK type optical modulator as a fifth embodiment of the present invention will be described. FIG. 8 is a schematic top view of the fifth embodiment of the present invention.

Here, 91 is an optical waveguide, 91 _in and 91 _out are an input optical waveguide and an output optical waveguide, 9a ′ is an interaction optical waveguide in which a high-frequency electrical signal and light interact, and 10 ′ is a high-frequency traveling wave electrode (RF electrode). , 100 is a bias electrode for the child MZ to which a bias voltage for controlling the operating point of the child MZ optical modulator is applied, and 92, 92, 93, 94, 95, 96, 97, 98, 99 are light propagation directions. Are first to eighth inversion optical waveguides provided to invert the. Reference numeral 101 denotes a parent MZ bias electrode for applying a bias voltage for controlling the operating point of the parent MZ optical modulator.

  As can be seen from FIG. 8, the inverted optical waveguides 92, 92, 93, 94, 95, 96, 97, 98, 99 have different lengths. Although not shown in detail, in order to correct the lengths of the inverted optical waveguides 92, 92, 93, 94, 95, 96, 97, 98, and 99, as in the first embodiment, the MZ light guide is used. Length adjustment regions in which a part of the arm of the waveguide is deformed are provided at 102 and 103 to adjust the difference in length.

  According to this embodiment, the bias voltage of both the parent MZ optical waveguide and the child MZ optical waveguide can be reduced to a fraction of that of the prior art.

(Sixth embodiment)
Next, a DP-QPSK type optical modulator as a sixth embodiment of the present invention will be described. FIG. 9 is a schematic top view of the sixth embodiment of the present invention.

  In the present embodiment, a parent MZ bias electrode 104 is used, which is a simplified version of the parent MZ bias electrode 101 in the fifth embodiment shown in FIG. And length adjustment area | regions 102 and 105 are provided similarly to 5th Embodiment.

  Compared with the fifth embodiment of FIG. 8, the configuration of the bias electrode for the parent MZ is simplified in the present embodiment shown in FIG.

(About each embodiment)
In the first embodiment and the second embodiment, the length of the bias electrode for the parent MZ is remarkably increased. Further, in the quartz optical waveguide circuit of the first embodiment or the second embodiment, the multiplexing part as the child MZ optical waveguide is eliminated, and the direction of all the optical waveguides is inverted using the inverted optical waveguide (in FIG. 1). In other words, a configuration in which four U-shaped optical waveguides are formed in 13 '), and not only the parent MZ bias electrode but also the child MZ bias above the optical waveguide in the direction opposite to the optical waveguide below the RF electrode. Electrodes can also be formed (third to sixth embodiments). That is, in this case, the lengths of both the parent MZ bias electrode and the child MZ bias electrode can be increased, and the half-wave voltage of not only the parent MZ but also the child MZ can be significantly reduced. In this case, it is desirable not only to make the lengths of the arms of the parent MZ optical waveguide equal, but also to make the lengths of the arms of the child MZ optical waveguide equal. These are true for all embodiments of the present invention.

  In this specification, the inverted optical waveguide is described as not crossing, but this is to prevent an increase in insertion loss. In the case where the optical waveguide can be crossed with a low loss or the loss due to the crossing of the optical waveguide can be tolerated, the equalization of the optical waveguide becomes easier by adopting the crossing structure.

  Although DQPSK and DP-QPSK type structures have been described, the present invention is applicable to more complex nested structures. In this embodiment, branching and multiplexing on the light incident side, and the inverted optical waveguide is a quartz optical waveguide that can be easily used as an optical waveguide with a small radius of curvature. However, an LN optical waveguide using a ridge structure or the like may be used. It may be a waveguide. That is, the substrate that forms the RF interaction portion and the bias portion of the portion that performs light modulation and the substrate that forms the optical input / output optical waveguide and the inverted optical waveguide may be formed of the same type or the same substrate.

  In order to simplify the explanation, the branched optical waveguide is assumed to be Y-branch in the drawing, but it goes without saying that an MMI or a directional coupler may be used.

  Further, in order to reverse the light propagation direction, the substantially U-shaped inverted optical waveguide is used only on the right side of the drawing, that is, only once, but is additionally used on the left side again (in this case, the entire S Needless to say, the present invention belongs to the present invention even if it is repeatedly used. And, for example, in the case of an S-shaped optical waveguide as a whole, even if the optical waveguide located in the middle (the common arm in the U-shaped portion positioned above and below) is not arranged at all, It belongs to the scope of the present invention.

  It is apparent that the difference in length of the inverted optical waveguide can be corrected by deforming both the arms of the child Mach-Zehnder optical waveguide as well as the parent Mach-Zehnder optical waveguide. Of course, the inverted optical waveguide itself may be deformed.

  In the above embodiment, the z-cut substrate has been described. However, the crystal orientation of the crystal in the x-cut, y-cut or z-cut plane orientation, that is, the direction perpendicular to the substrate surface (cut plane). The present invention can be applied to a substrate having an x-axis, y-axis, or z-axis, and the plane orientation in each of the above-described embodiments is set as a main plane orientation, and other plane orientations are mixed as plane orientations subordinate to these. Also good. It goes without saying that not only the LN substrate but also other substrates such as lithium tantalate and semiconductors may be used.

1: z-cut LN substrate 3, 3a, 3b, 9, 9a, 9a ′, 9b, 9 ′, 14, 14a, 40, 60, 80, 91: optical waveguides 3 _in , 9 _in , 9 ′ _in , 14 _in , 80 _in , 91 _in : input optical waveguide 3 _out , 9 _out , 9 ′ _out , 14 _out , 80 _out , 91 _out : output optical waveguide 4, 4 ′, 10, 10 ′: RF electrode 5, 5 ′ 11, 11 ′, 85, 100: child MZ bias electrode 6, 6 ′, 12, 12 ′, 86, 89, 101, 104: parent MZ bias electrode 7: child MZ optical waveguide 8: parent MZ optical waveguide 13, 13 ': Quartz optical waveguide circuit 15, 16, 19, 20, 21, 22, 23, 24, 25, 26, 31, 32: Branch arm 17, 18, 27, 28, 29, 30, 81, 82, 83, 84, 92, 93, 94, 95, 96, 97, 98, 99: inverted optical waveguide Path 50: Polarization rotator 51: Polarization synthesizer 70a, 70b, 70c, 70d, 70e, 70f, 70g, 70h, 87, 88, 90, 102, 103, 105: Length adjustment region

Claims (9)

A substrate having an electro-optic effect, an optical waveguide for guiding light formed on the substrate, and a high-frequency electric signal formed on one surface side of the substrate for applying a high-frequency electric signal for modulating the light An electrode, and a bias electrode for applying a bias voltage to the light,
The optical waveguide is a nested optical waveguide having a parent Mach-Zehnder optical waveguide between the input optical waveguide and the output optical waveguide, each having a child Mach-Zehnder optical waveguide on the branch optical waveguide of the parent Mach-Zehnder optical waveguide. In the optical modulator,
The optical waveguide includes at least one inverted optical waveguide whose propagation direction is substantially U-shaped, the high-frequency electrode is disposed on one U-shaped arm, and the other U-shaped waveguide An optical modulator, wherein the bias electrode is disposed on an arm.   2. The optical modulation according to claim 1, wherein at least one arm of the parent Mach-Zehnder optical waveguide or the child Mach-Zehnder optical waveguide is deformed so that the arms of the parent Mach-Zehnder optical waveguide are equal in length. vessel.   3. The optical modulator according to claim 1, wherein the arms of the child Mach-Zehnder optical waveguide are deformed so that the arms of the child Mach-Zehnder optical waveguide are equal in length.   The optical modulator according to any one of claims 1 to 3, wherein the bias electrode is a bias electrode for the parent Mach-Zehnder optical waveguide.   The optical modulator according to claim 4, wherein the bias electrode includes a bias electrode for the child Mach-Zehnder optical waveguide.   The high-frequency electrode and the bias electrode for the child Mach-Zehnder optical waveguide are disposed on the U-shaped one arm, and the bias electrode for the parent Mach-Zehnder optical waveguide is disposed on the other arm. The optical modulator according to any one of claims 1 to 3.   The high-frequency electrode is disposed on the U-shaped one arm, and the bias electrode for the parent Mach-Zehnder optical waveguide and the bias electrode for the child Mach-Zehnder optical waveguide are disposed on the other arm. The optical modulator according to any one of claims 1 to 3.   The optical modulator according to claim 1, wherein the inverted optical waveguide is formed on the same substrate as the substrate having the electro-optic effect. 8. The optical modulator according to claim 1, wherein the inverted optical waveguide is formed of a quartz optical waveguide circuit that is separate from the substrate having the electro-optical effect.

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