JP2019194722A - Semiconductor Mach-Zehnder optical modulator and IQ modulator using the same - Google Patents

Abstract

To realize a semiconductor optical modulator in which modulation is fast and crosstalk is small.SOLUTION: The semiconductor optical modulator is a semiconductor Mach-Zehnder optical modulator comprising: first and second arm waveguides provided on a semiconductor substrate 213 and having a waveguide structure in which an n-InP layer 214, a first semiconductor clad layer 215, a semiconductor core layer 216 and a second semiconductor clad layer 217 are laminated in order; first and second signal electrodes 207, 208 formed along the respective arm waveguides; first and second phase adjustment electrodes 211, 212 branched from the respective signal electrodes and discretely formed in plurality on the arm waveguides; and first and second ground electrodes 209, 210 respectively formed along the first and second signal electrodes. The first and second signal electrodes are formed between the first and the second ground electrodes, and the n-InP layer is nonexistent below the first and second signal electrodes.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a semiconductor Mach-Zehnder optical modulator that modulates an optical signal with an electric signal and an IQ modulator using the same.

  In order to respond to the increasing demand for communication traffic, researches to increase the multiplicity of optical signals are being actively conducted. As a specific method for increasing the optical signal multiplicity, quaternary phase modulation method (QPSK) that doubles the transmission capacity by assigning two values (multiplicity 2) to one symbol, or four values (multiple) for one symbol. A multi-level optical modulation scheme such as a 16-value quadrature amplitude modulation scheme (16QAM) is known in which the transmission capacity is quadrupled by assigning the severity 4). A method of doubling the transmission capacity by optical polarization multiplexing is also known.

  When performing such multilevel optical modulation, an IQ modulator is used as the optical modulator. The I / Q modulator is also called a quadrature modulator, and is a modulator that can independently generate orthogonal optical electric field components (I channel, Q channel), and is a Mach-Zehnder (MZ) modulator (hereinafter, referred to as a MZ). , MZM) are connected in parallel. In recent years, miniaturization and low drive voltage of optical transmitter modules have become issues, and research and development of semiconductor MZ modulators that are small and capable of low drive voltages are being actively pursued.

  FIG. 1 shows an example of a conventional MZM as shown in Non-Patent Documents 1 and 2. In FIG. 1A, an input waveguide 101 for inputting a light wave, an optical demultiplexer 102 for demultiplexing a light wave guided through the input waveguide 101, and an optical demultiplexer 102 are used. Arm waveguides 103 and 104 that guide the light waves that have been waved, an optical multiplexer 105 that combines the light waves guided through the arm waveguides 103 and 104, and the optical waves that are combined by the optical multiplexer 105. An MZM including an output waveguide 106 to output, coplanar strip lines 107 and 108, and phase adjustment electrodes 109 and 110 formed on the arm waveguides 103 and 104, respectively, is shown.

  The input waveguide 101, the optical demultiplexer 102, the arm waveguides 103 and 104, the optical multiplexer 105, and the output waveguide 106 constitute a Mach-Zehnder interferometer. By applying a voltage to the arm waveguides 103 and 104, a refractive index change occurs due to an electro-optic effect in the semiconductor core layer, and as a result, the phase of light changes. At this time, by applying a voltage difference to the arm waveguides 103 and 104, the interference state of the light in the optical multiplexer 5 can be changed and modulated (the output light of the output waveguide 106 is turned on or turned off). )

  When one of the coplanar strip lines 107 and 108 is connected to the input electrical signal (S), the other has an SG configuration in which the other is connected to the reference potential or the ground (G).

  Microwaves propagating through the coplanar strip lines 107 and 108 are applied to the arm waveguides 103 and 104 by the phase adjustment electrodes 109 and 110, respectively. The phase adjustment electrodes 109 and 110 act as electrodes for applying a voltage to the waveguide, and form a traveling wave type electrode as a whole including the coplanar strip lines 107 and 108. That is, the velocity of the light wave guided through the arm waveguides 103 and 104 and the velocity of the microwave propagating through the traveling wave electrode are matched as much as possible so that the phase matching between the two can be achieved, thereby reducing the modulation band. It is an electrode structure intended to increase.

  Note that if there is no microwave loss and the optical wave and microwave velocity matching conditions are fully satisfied, the modulation bandwidth becomes infinite, but in practice microwave loss and phase shifts occur. The modulation band is limited. In addition, the impedance between the coplanar strip lines 107 and 108 is designed to be 50Ω, but if the impedance deviates from 50Ω, electrical reflection occurs and microwaves cannot be applied efficiently. Furthermore, the arm waveguides 103 and 104 have a so-called push-pull configuration in which voltages having opposite phases are applied to each other.

  FIG.1 (b) is Ib-Ib sectional drawing of MZM shown by Fig.1 (a). FIG. 1B shows an SI-InP substrate 111, an n-InP layer 112 formed on the SI-InP substrate 111, a lower semiconductor cladding layer 113 formed on the n-InP layer 112, An MZM including a semiconductor core layer 114 on which a light wave propagates formed on a semiconductor clad layer 113 and an upper semiconductor clad layer 115 formed on the semiconductor core layer 114 is shown. The MZM shown in FIG. 1 acts as an optical modulator when microwaves propagate through the coplanar strip lines 107 and 108 and a voltage is applied to the semiconductor core layer 114 via the phase adjustment electrodes 109 and 110. .

  As shown in FIG. 1B, the upper cladding 115, the semiconductor core layer 14, and the lower semiconductor cladding layer 113 are present under the phase adjustment electrodes 109 and 110, so that a certain element capacitance exists. That is, in FIG. 1A, the phase adjustment electrodes 109 and 110 are in a form (capacitance loaded type) in which capacitance is added to the coplanar strip lines 107 and 108. That is, by optimally designing the number of electrodes, the interval, and the contact length to the waveguide, it becomes possible to freely design the additional amount of capacitance.

In a general electrical transmission line model, the impedance Z ₀ propagation constant γ is expressed by the following (Equation 1).

Here, R represents resistance per unit length, G represents conductance, L represents inductance, and C represents capacitance. In the case of ωL >> R and ωC >> G, Z ₀ and γ can be expressed as in the following (Formula 2).

  At this time, the electric velocity v and the effective refractive index n can be expressed as shown in the following (Equation 3).

This model can also be applied to traveling wave electrodes. That is, this indicates that the impedance and the speed of electricity can be adjusted by qualitatively controlling the capacitance component of the optical modulator. That is, in the conventional MZM shown in FIG. 1, the electrodes 109 and 110 are used as capacitors for adjusting impedance and electric speed. Further, the frequency band Δf due to the difference between the speed of light and electricity is expressed by the following (Equation 4) using the light velocity c and the group velocity v ₀ electrode length l of light propagating through the optical waveguide.

From the above (Equation 4), it can be seen that the maximum frequency band can be obtained when the group velocity v _{0 of} light and the velocity of electricity v coincide. However, since the above (Equation 4) is an approximate expression when there is no propagation loss and impedance matching is matched, in practice, it is greatly affected by propagation loss and impedance matching.

  As described above, by designing the optimum addition amount of the capacity, it is possible to improve the speed matching between the light wave and the microwave, and also to obtain the impedance matching to 50Ω, and as a result, the high-speed modulation is achieved. Is possible.

L. Morl et al., “A traveling wave electrode Mach-Zehnder 40 Gb / s demultiplexer based on strain compensated GaInAs / AlInAs tunnellingbarrier MQW structure,” 1998 International Conference on Indium Phosphide and Related Materials, pp. 403-406, 1998) H.N.Klein et al., “1.55μm Mach-ZehnderModulators on InP for optical 40/80 Gbit / s transmission networks,” OFC2006, pp. 171-173

  However, in the conventional MZM shown in FIG. 1, when an IQ modulator in which semiconductor Mach-Zehnder optical modulators indispensable for multilevel optical modulation are connected in parallel is realized on one chip, crosstalk between two MZMs. However, it is difficult to install two MZMs close to each other, and there is a problem that the chip size becomes large.

  The present invention achieves high-speed modulation by satisfying impedance matching by a capacitive loading structure, which is a characteristic of a conventional modulator, and phase matching between microwaves and light waves, and a crosstalk problem between a plurality of MZMs, which has been a problem. It is an object of the present invention to provide a semiconductor optical modulator that can solve the above problem.

  In order to achieve such an object, a semiconductor Mach-Zehnder optical modulator according to an embodiment of the present invention includes first and second arm waveguides, and parallel and adjacent to the first and second arm waveguides. The first and second signal electrodes respectively formed, and branched from the first signal electrode, and a plurality of discretely formed on the first arm waveguide along the first signal electrode A first phase adjusting electrode and a second phase branched from the second signal electrode and discretely formed on the second arm waveguide along the second signal electrode A semiconductor Mach-Zehnder optical modulator comprising an adjustment electrode and first and second ground electrodes formed along the first and second signal electrodes, respectively, wherein the first and second signal An electrode is formed on the first graph. Characterized in that it is formed between the the cathode electrode second ground electrode.

  In a semiconductor Mach-Zehnder optical modulator according to another embodiment of the present invention, the first and second arm waveguides include an n-InP layer, a first semiconductor clad layer, and a non-doped semiconductor core on a semiconductor substrate. A waveguide structure formed by sequentially laminating a layer and a second semiconductor cladding layer, and the first and second signal electrodes are formed on a dielectric layer formed on the semiconductor substrate. It is characterized by being.

  In a semiconductor Mach-Zehnder optical modulator according to still another embodiment of the present invention, the first and second phase adjustment electrodes in the first and second arm waveguides are not formed in the second The semiconductor clad layer is a non-doped semiconductor clad layer.

  In a semiconductor Mach-Zehnder optical modulator according to still another embodiment of the present invention, the first and second signal electrodes and the first and second ground electrodes are on the same plane on the dielectric layer. It is formed.

  In a semiconductor Mach-Zehnder optical modulator according to still another embodiment of the present invention, one of the first semiconductor clad layer and the second semiconductor clad layer is composed of an n-type semiconductor, and the other is p. It is characterized by comprising a type semiconductor.

  In a semiconductor Mach-Zehnder optical modulator according to still another embodiment of the present invention, both the first semiconductor clad layer and the second semiconductor clad layer are formed of an n-type semiconductor, and the semiconductor core layer and the first semiconductor clad layer A third conductive semiconductor cladding layer made of a p-type semiconductor is inserted between the semiconductor cladding layer and at least one of the semiconductor core layer and the second semiconductor cladding layer. It is characterized by.

  An IQ modulator according to an embodiment of the present invention is characterized in that two semiconductor Mach-Zehnder optical modulators according to any one of claims 1 to 6 are arranged in parallel.

  A polarization multiplexing IQ modulator according to an embodiment of the present invention is characterized in that two IQ modulators according to claim 7 are arranged in parallel.

  According to the present invention, by arranging the signal electrode between the ground electrodes in the MZM, the impedance matching by the capacitive loading structure, which is the feature of the conventional modulator, and the phase matching between the microwave and the light wave are satisfied and high-speed modulation is performed. Since it is possible to suppress the crosstalk without increasing the physical distance between the MZMs, it is possible to realize a small I / Q modulator with a small crosstalk.

It is a figure which shows the conventional MZM. It is a figure which illustrates MZM which concerns on Example 1 of this invention. It is a figure which shows the other example of MZM which concerns on Example 1 of this invention. It is a figure which illustrates MZM which concerns on Example 2 of this invention. It is a figure which shows the other example of MZM which concerns on Example 2 of this invention. It is a figure which shows the further another example of MZM which concerns on Example 2 of this invention. It is a figure which shows the further another example of MZM which concerns on Example 2 of this invention. It is a figure which illustrates MZM which concerns on Example 3 of this invention. It is a figure which shows the other example of MZM which concerns on Example 3 of this invention. It is a figure which shows the other example of MZM which concerns on Example 3 of this invention. It is a figure which illustrates the IQ modulator which concerns on Example 4 of this invention. It is a figure which shows the other example of IQ modulator which concerns on Example 4 of this invention. It is a figure which shows the other example of IQ modulator which concerns on Example 4 of this invention. It is a figure which illustrates the polarization multiplexing IQ modulator which concerns on Example 5 of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
<Example 1>
FIG. 2 shows an MZM according to Embodiment 1 of the present invention. FIG. 2A shows an input waveguide 201 for inputting a light wave, an optical demultiplexer 202 for demultiplexing the light wave guided through the input waveguide 201, and an optical demultiplexer 202. Arm waveguides 203 and 204 for guiding the light waves that have been waved, an optical multiplexer 205 that combines the light waves guided through the arm waveguides 203 and 204, and the optical waves that are combined by the optical multiplexer 205 An MZM comprising an output waveguide 206 for output, signal electrodes 207 and 208, ground electrodes 209 and 210, and phase adjustment electrodes 211 and 212 formed on arm waveguides 203 and 204, respectively, is shown. Yes.

  The input waveguide 201, the optical demultiplexer 202, the arm waveguides 203 and 204, the optical multiplexer 205, and the output waveguide 206 constitute a Mach-Zehnder interferometer. By applying an electrical signal to the arm waveguides 203 and 204, the output light of the output waveguide 206 is modulated.

  The signal electrodes 207 and 208 are formed in parallel and adjacent to the arm waveguides 203 and 204, respectively. The phase adjustment electrodes 211 and 212 are branched from the signal electrodes 207 and 208, respectively, and a plurality of phase adjustment electrodes 211 and 212 are discretely formed along the signal electrodes 207 and 208. The ground electrodes 209 and 210 are formed along the signal electrodes 207 and 208, respectively.

  In the present invention, a GSSG (Ground, Signal, Signal, Ground) differential line (coplanar line) in which the signal electrodes 207 and 208 are arranged between the ground electrodes 209 and 210 by the signal electrodes 207 and 208 and the ground electrodes 209 and 210. Therefore, unlike the conventional structure, the structure is strong against crosstalk. At this time, from the viewpoint of crosstalk, it is desirable to design so that (double the distance between signal electrodes) ≦ (distance between ground electrode and signal electrode).

  Microwaves having opposite phases are propagated to the signal electrodes 207 and 208, and differential signals are inputted and outputted. Microwaves propagating through the signal electrodes 207 and 208 are branched into a plurality of phase adjustment electrodes 211 and 212 that are periodically arranged, and applied to the arm waveguides 203 and 204. The phase adjustment electrodes 211 and 212 act as electrodes for applying a voltage to the arm waveguides 203 and 204, and form a traveling wave electrode as a whole including the signal electrodes 207 and 208 and the ground electrodes 209 and 210. That is, capacitance is added to the signal electrodes 207 and 208 and the ground electrodes 209 and 210 by the phase adjustment electrodes 211 and 212. By optimally designing the number, interval, and length of the phase adjustment electrodes 211 and 212, the additional amount of capacitance can be freely designed, and the speed of the light wave guided through the arm waveguides 203 and 204, The velocity of the microwave propagating through the traveling wave electrode can be matched. Further, considering the connection with a general differential 100Ω line, if the impedance deviates from 100Ω, electrical reflection occurs and the modulation band deteriorates. Therefore, the traveling wave electrode is designed to have a differential of 100Ω from the viewpoint of impedance matching. As a result, high-speed modulation is possible.

  Although the number of phase adjustment electrodes 211 and 212 is three in the first embodiment, the number may be one, two, or more. Further, the positions of the phase adjustment electrodes 211 and 212 may have a vertically asymmetric configuration.

  Further, as shown in FIG. 2A, when the MZM according to the present embodiment is divided into an input wiring part 221, a phase modulation part 222, and an output wiring part 223, in particular, the input wiring part 221 and the output wiring part. Since an asymmetrical section such as a bent portion is generated in 223, it is important not only to design the differential mode 100Ω, but also to use a line design in which the common mode impedance is 25Ω. As for the input wiring part 221 and the output wiring part 223, as an example in FIG. 2, the input / output wirings are drawn up and down. However, the input wiring part 221 and the output wiring part 223 are installed on the left and right. Output may be set.

  Next, each cross-sectional structure of the MZM according to the first embodiment will be described. As shown in FIG. 2A, the cross-sectional structure of the phase modulation unit 222 is composed of two cross-sectional structures, a IIb cross-section (part contributing to phase modulation) and a IIc cross-section (part not contributing to phase modulation). .

  FIG. 2B is a IIb cross-sectional view of the MZM according to the first embodiment. As shown in FIG. 2B, in the IIb cross section of the phase modulation unit 222, the n-InP layer 214, the lower semiconductor cladding layer 215, the semiconductor core layer 216, and the upper semiconductor cladding layer 217 are formed on the SI-InP substrate 213. These layers are embedded in a dielectric layer 218. On the upper semiconductor clad layer 217 and the dielectric layer 218, signal electrodes 207 and 208, phase adjustment electrodes 211 and 212, and ground electrodes 209 and 210 are formed.

  For the n-InP layer 214, the width from the mesa portion formed by the lower semiconductor cladding layer 215, the semiconductor core layer 216, and the upper semiconductor cladding layer 217 to about 10 μm greatly affects the modulation band. This is important in terms of reducing wiring loss. That is, it is important that the n-InP layer 214 does not exist under the signal electrodes 207 and 208.

  FIG. 2C illustrates a IIc cross-sectional view of the MZM according to the first embodiment. As shown in FIG. 2C, the IIc cross section of the phase modulation unit 222 has the same structure as the IIb cross section, and does not contribute to phase modulation because the phase adjustment electrodes 211 and 212 on the mesa are not present. . The upper semiconductor clad layer 217 in the IIc cross section of the MZM according to the first embodiment needs to be non-doped InP or semi-insulating InP in order to reduce electrical isolation and waveguide loss.

  The differential impedance is 100Ω in total in the phase modulation section. However, when attention is paid only to the individual cross-sectional structure, each differential impedance is smaller than 100Ω in the IIb cross section and larger than 100Ω in the IIc cross section. ing.

  FIG. 2D shows a IId cross-sectional view of the MZM according to the first embodiment. As shown in FIG. 2D, signal electrodes 207 and 208 and ground electrodes 209 and 210 are formed on the SI-InP substrate 213 with the dielectric layer 218 interposed therebetween.

  In order to realize high-speed modulation, it is necessary to reduce the propagation loss of the microwave. Therefore, the dielectric layer 218 is not a semiconductor material such as InP but a desired impedance line when designed from the viewpoint of characteristics. In order to reduce the electrode loss, it is desirable to use a low dielectric constant material such as an organic material such as polyimide or BCB. The thicker the dielectric layer, the better. Further, the dielectric layer 218 shown in FIGS. 2B and 2C and the dielectric layer 218 shown in FIG. 2D can be formed of different film thicknesses and materials. However, from the viewpoint of manufacturing, the dielectric layers 218 shown in FIGS. 2B to 2D are preferably made of the same film thickness and material.

  FIG. 3 shows another example of the MZM according to the first embodiment. 3A is a top view of an MZM according to another example of the first embodiment, and FIGS. 3B to 3D are cross-sectional views taken along lines IIIb to d of the MZM according to the other example of the first embodiment, respectively. The figure is shown.

  In the configuration shown in FIG. 3, compared to the configuration shown in FIG. 2, the dielectric layer 218 is simply thickened, and the SI-InP substrate 213 is etched to increase the thickness of the dielectric layer 218. . As a result, since the ratio of the low dielectric constant material is increased, the signal electrodes 207 and 208 can be made thicker in realizing the desired impedance and speed matching, so that the microwave propagation loss can be reduced. In addition, it is effective in that impedance / speed matching can be adjusted by the thickness of the dielectric layer. When the ratio of the dielectric layer 218 is increased, the capacitance component of the signal line is reduced, so that it is also effective to increase the ratio of the capacity loading section, that is, to increase the length of the phase modulation section 222.

  Further, as shown in FIG. 3, it is most effective to increase the thickness of the dielectric layer 218 and to relatively increase the thickness of the dielectric layer 218 by etching the SI-InP substrate 213. It is also possible to apply only one of them.

In order to further improve the characteristics, in order to reduce the propagation loss of the microwave, the film thickness of the n-InP layer 214 can be made as thin as, for example, about 1 or 2 μm. It is desirable that the thickness be as thick as possible, and the doping concentration is 2 × 10 ¹⁸ or more.

  In the present invention, the signal electrodes 207 and 208 are arranged between the ground electrodes 209 and 210 to form a GSSG differential line configuration capable of adjusting the capacitance component, thereby satisfying phase matching and impedance matching and realizing high-speed modulation. In addition, the coupling between the signal electrodes is strengthened. As a result, the present invention solves the problem of crosstalk, which has been a problem with the conventional structure, and allows a plurality of MZMs to be integrated on one chip without increasing the chip size as compared with the conventional structure.

  As the semiconductor core layer 216, for example, a material system such as InGaAsP or InGaAlAs is used, and a single composition quaternary mixed crystal bulk layer or multiple quantum well layer is formed, or a band gap is formed above and below the multiple quantum well layer. It is also possible to use a structure having an optical confinement layer having a value larger than that of the multiple quantum well layer and smaller than that of the upper and lower semiconductor cladding layers. The band gap wavelength of the quaternary mixed crystal bulk layer or the multiple quantum well layer may be set so that the electro-optic effect works effectively and the light absorption does not become a problem at the light wavelength used.

  In the present invention, an InP-based material is mainly used. However, the present invention is not limited to an InP-based material, and for example, a material system that matches a GaAs substrate may be used. One of the lower semiconductor clad layer 215 and the upper semiconductor clad layer 217 may be an n-type semiconductor and the other may be a p-type semiconductor. On the other hand, both the lower semiconductor clad layer 215 and the upper semiconductor clad layer 217 are n-type semiconductors, and between the semiconductor core layer 216 and the upper semiconductor clad layer 217 or between the lower semiconductor clad layer 215 and the semiconductor core layer 216, 3 p-type semiconductor clad layers may be inserted.

<Example 2>
FIG. 4 shows an MZM according to Embodiment 2 of the present invention. FIG. 4A shows a top view of the MZM according to the second embodiment, and FIGS. 4B to 4D show sectional views of IVZ through d of the MZM according to the second embodiment, respectively. Since the operation principle and basic structure are the same as those in the first embodiment, a description thereof will be omitted.

  As shown in FIG. 4A, the MZM according to the second embodiment is different from the MZM according to the first embodiment in that signal electrodes 307 and 308 are formed inside the arm waveguides 303 and 304, respectively. As a result, the MZM according to the second embodiment has a feature that the distance between the signal electrodes can be further shortened compared to the MZM according to the first embodiment, and thus is more resistant to crosstalk. However, as shown in FIGS. 4B to 4D, since the n-InP layer 314 exists below the signal electrodes 307 and 308, the propagation loss of microwaves is larger than that in the first embodiment. There is a drawback of becoming.

  FIG. 5 shows another example of the MZM according to the second embodiment. FIG. 5A is a top view of an MZM according to another example of the second embodiment, and FIGS. 5B to 5D are Vb to d cross-sections of the MZM according to another example of the second embodiment, respectively. The figure is shown. As shown in FIG. 5, increasing the dielectric layer thickness is effective for improving the characteristics. However, unlike the first embodiment, the SI-InP substrate 313 cannot be etched and the dielectric layer 318 cannot be thickened due to the structure.

  6 and 7 show still another example of the MZM according to the second embodiment. 6 and 7A are top views of an MZM according to still another example of the second embodiment, and FIGS. 6 and 7B to 7D are still other examples of the second embodiment. The VIb thru | or d sectional drawing and VIIb thru | or d sectional drawing of MZM which concern on are shown.

As shown in FIGS. 6 and 7B to 7D, ground electrodes 309 ₂ and 310 ₂ are formed on the n-InP layer 314 below the ground electrodes 309 ₁ and 310 ₁ . . The MZM shown in FIGS. 6 and 7 is different from the MZM shown in FIGS. 4 and 5 in that the n-InP layer 314 is not present under the signal electrodes 307 and 308. Thereby, an increase in propagation loss of microwaves can be avoided.

  Since the SI-InP substrate 313 can be etched, the dielectric layer 318 is made thick by etching the SI-InP substrate 313 under the signal electrodes 307 and 308 as shown in FIG. Can do.

<Example 3>
FIG. 8 shows an MZM according to Embodiment 3 of the present invention. FIG. 8A illustrates a top view of the MZM according to the third embodiment, and FIGS. 8B to 8D illustrate cross-sectional views of the MZM according to the third embodiment, which are VIIIb to d, respectively. Since the operation principle and basic structure are the same as those in the first embodiment, a description thereof will be omitted. As shown in FIG. 8, the MZM according to the third embodiment basically has a GSGSG (Ground, Signal, Ground, Signal, etc.) in which the ground electrode 420 is provided on the n-InP layer 414 in the configuration shown in FIG. 2. , Ground) differential line configuration.

  In order to reduce the crosstalk, in the GSSG differential line configuration as in the first and second embodiments, it is assumed that the distance between the signal electrodes is made closer. However, in the GSSG differential line configuration as in the third embodiment, the reverse It is necessary to ensure a sufficient width for providing the central ground electrode by sufficiently separating the distance between the signal electrodes. Therefore, in the MZM according to the third embodiment, it is necessary to make a sufficient distance between the two optical waveguides as compared with the first and second embodiments, so that the chip size tends to increase.

  However, considering the connection with the RF driver, since the output from the RF driver is an output corresponding to the GSSGSG differential line configuration, the GSSG differential line configuration is different from the GSSG differential line configuration in the structures of the first and second embodiments. A conversion mechanism for a moving line configuration is required. Therefore, it is desirable to adopt a GSSGSG differential line configuration as in the third embodiment.

  9 and 10 show another example of the MZM according to the third embodiment of the present invention. FIGS. 9 and 10 (a) are top views of other examples of the MZM according to the third embodiment, and FIGS. 9 and 10 (b) to (d) show other examples of the MZM according to the third embodiment. Example IXb thru | or d sectional drawing and Xb thru | or d sectional drawing are shown. The configuration shown in FIG. 9 corresponds to the configuration in which the ground electrode 420 is added to the configuration shown in FIG. 3, and the configuration shown in FIG. 10 corresponds to the configuration in which the ground electrode 420 is added to the configuration shown in FIG. Description of the operation principle and basic structure is omitted.

<Example 4>
FIG. 11 illustrates an IQ modulator according to the fourth embodiment of the present invention. In FIG. 11, an input waveguide 501 for inputting a light wave, an optical demultiplexer 502 for demultiplexing a light wave guided through the input waveguide 501 into two, and an optical demultiplexer 502 are demultiplexed. the arm waveguide 503 ₁ and 503 ₂ for guiding light waves, the optical demultiplexer 504 ₁ and 504 ₂ for demultiplexing the arm waveguide 503 ₁ and 503 ₂ to the two light waves coming guided respectively, light Arm waveguides 505 ₁ and 506 ₁ , 505 ₂ and 506 ₂ for guiding the light waves demultiplexed by the demultiplexers 504 ₁ and 504 ₂ , and arm waveguides 505 ₁ and 506 ₁ and 505 ₂ and 506 ₂ are provided. each optical multiplexer 507 ₁ and 507 ₂ for multiplexing light waves coming guided, the light waves are multiplexed respectively by the optical multiplexer 507 ₁ and 507 ₂ and arm waveguide 508 ₁ and 508 ₂ for guiding, the arm waveguide 508 ₁ and 508 ₂ which Re and optical multiplexer 509 for multiplexing the light waves coming guided, and the output waveguides 510 for outputting the multiplexed light waves by the optical multiplexer 509, a signal electrode 511 ₁ and 512 ₁ and 511 ₂ and 512 ₂ , IQ having a ground electrode 513, 514 and 515, the arm waveguide 505 ₁ and 506 ₁ and 505 ₂ and 506 ₂ phase adjustment electrode 516 formed respectively on ₁ and 517 ₁ and 516 ₂ and 517 _2, the A modulator 500 is shown.

  As shown in FIG. 11, the IQ modulator according to the fourth embodiment corresponds to a configuration in which two MZMs according to the present invention are arranged in parallel.

  According to the fourth embodiment, since crosstalk can be suppressed without increasing the physical distance between MZMs, a small IQ modulator that suppresses crosstalk between MZMs can be realized. .

12 and 13 show another example of the IQ modulator according to the fourth embodiment of the present invention. The IQ modulator shown in FIGS. 12 and 13 has a structure in which the electrode arrangement is different from that of the IQ modulator shown in FIG. In the IQ modulator shown in FIG. 12, the ground electrodes 513, 514, and 515 in the IQ modulator shown in FIG. 11 are integrated to form the ground electrode 520. In the IQ modulator shown in FIG. The phase adjustment electrodes 516 ₁ and 517 ₁ and the phase adjustment electrodes 516 ₂ and 517 ₂ are arranged at different positions in the upper and lower MZMs.

  The configuration shown in FIG. 11 is ideal because it is better to make the differential lines equal in length. However, even in the configurations shown in FIGS. 12 and 13, the difference between the line lengths is actually small, so that the high-speed modulation and the small crosstalk IQ. A modulator can be realized.

<Example 5>
FIG. 14 illustrates a polarization multiplexed IQ modulator according to the fifth embodiment of the present invention. As illustrated in FIG. 14, the polarization multiplexing IQ modulator 600 according to the fifth embodiment has a configuration in which two IQ modulators 500 illustrated in FIG. 11 are arranged in parallel.

  According to the fifth embodiment, since crosstalk can be suppressed without increasing the physical distance between MZMs, a small-sized polarization multiplexing IQ modulator that suppresses crosstalk between MZMs is realized. be able to.

Input waveguide 101, 201, 301, 401, 501
Optical demultiplexer 102, 202, 302, 402, 502, 504
Arm waveguide 103, 104, 203, 204, 303, 304, 403, 404, 503, 505, 506, 508
Optical multiplexer 105, 205, 305, 405, 507, 509
Output waveguide 106, 206, 306, 406, 510
Coplanar stripline 107,108
Phase adjustment electrode 109, 110, 211, 212, 311, 312, 411, 412, 516, 517
Signal electrode 207, 208, 307, 308, 407, 408, 511, 512
Ground electrodes 209, 210, 309, 310, 409, 410, 420, 513, 514, 515, 520
SI-InP substrate 213, 313, 413
n-InP layers 214, 314, 414
Lower semiconductor clad layer 215, 315, 415
Semiconductor core layer 216, 316, 416
Upper semiconductor clad layer 217, 317, 417
Dielectric layer 218, 318, 418
Input wiring part 221
Phase modulator 222
Output wiring part 223
IQ modulator 500
Polarization multiplexing IQ modulator 600

Claims (9)

The first and second waveguide structures are provided on a semiconductor substrate and have a waveguide structure in which an n-InP layer, a first semiconductor cladding layer, a semiconductor core layer, and a second semiconductor cladding layer are sequentially stacked . Two arm waveguides;
First and second signal electrodes respectively formed along the first and second arm waveguides;
A first phase adjusting electrode branched from the first signal electrode and discretely formed on the first arm waveguide;
A second phase adjusting electrode branched from the second signal electrode and discretely formed on the second arm waveguide;
First and second ground electrodes respectively formed along the first and second signal electrodes;
A semiconductor Mach-Zehnder optical modulator comprising:
The first and second signal electrodes are formed between the first ground electrode and the second ground electrode,
The semiconductor Mach-Zehnder optical modulator, wherein the n-InP layer does not exist under the first and second signal electrodes . The n-InP layer has a thickness of 2 μm or more and a doping concentration of 2 × 10 ¹⁸ The semiconductor Mach-Zehnder optical modulator according to claim 1, which is as described above. 3. The semiconductor Mach-Zehnder optical modulator according to claim 1, wherein the first and second signal electrodes are formed on a dielectric layer formed on the semiconductor substrate . The second semiconductor clad layer is a non-doped semiconductor clad layer in a portion of the first and second arm waveguides where the first and second phase adjustment electrodes are not formed. The semiconductor Mach-Zehnder optical modulator according to claim 1 . 4. The semiconductor Mach-Zehnder light according to claim 3 , wherein the first and second signal electrodes and the first and second ground electrodes are formed on the same plane on the dielectric layer. Modulator. Of the first semiconductor cladding layer and said second semiconductor cladding layer, either that one is composed of an n-type semiconductor and the other of claims 1, characterized in that it is composed of a p-type semiconductor of 5 The semiconductor Mach-Zehnder optical modulator according to any one of the above. Both the first semiconductor clad layer and the second semiconductor clad layer are made of an n-type semiconductor, and between the semiconductor core layer and the first semiconductor clad layer, and between the semiconductor core layer and the first semiconductor clad layer. the semiconductor Mach-Zehnder according to any one of claims 1 to 5 in which the third conductive semiconductor cladding layer, characterized in that it is inserted, which is constituted by the p-type semiconductor with at least one of between the second semiconductor cladding layer Light modulator. IQ modulator, wherein the semiconductor Mach-Zehnder optical modulator according is configured by arranging two parallel to one of claims 1 to 7. 9. A polarization multiplexing IQ modulator comprising two IQ modulators according to claim 8 arranged in parallel.

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