JP2017173365A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of reflection points in a Mach-Zehnder type light modulator connected to a differential type open-collector driver, and to suppress reflection at a terminal resistance.SOLUTION: An optical modulator includes: a differential type open-collector driver; a Mach-Zehnder type light modulator with a pair of RF electrodes that is connected to the differential type open-collector driver; and a terminal resistance connected to the Mach-Zehnder type light modulator. Signal lines are isometric that respectively connect: a pair of differential output terminals of the differential type open-collector driver; and input pads of a pair of RF electrodes. Signal lines are isometric that respectively connect: output pads of a pair of RF electrodes; and a pair of input terminals connected respectively to a pair of resistances of the terminal resistances. Electrodes are arranged so that a center line between the pair of RF electrodes, a center line between the input pads of the pair of RF electrodes, and a center line between the output pads of the pair of RF electrodes are substantially parallel to each other.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an optical modulator used in an optical communication system and an optical information processing system. More specifically, the present invention relates to an optical modulator integrated with a modulator driver IC and having low power consumption and excellent frequency characteristics. It relates to a structure for providing.

  A Mach-Zehnder (MZ) type optical modulator has a structure in which light incident on an optical waveguide is split into two optical waveguides at an intensity of 1: 1, the branched light is propagated for a certain length, and then multiplexed again. Have. The phase modulation unit provided in the optical waveguide branched into two changes the phase of the two lights incident on the optical waveguide, changes the interference condition of the light when the two lights are combined, The intensity and phase can be modulated.

In the Mach-Zehnder type optical modulator, a dielectric such as LiNbO ₃ or a semiconductor such as InP, GaAs, and Si (silicon) is used as a material constituting the optical waveguide. An electrode is arranged in the vicinity of an optical waveguide made of these materials, and a phase of light propagating through the optical waveguide is changed by inputting a modulated electric signal to the electrode and applying a voltage to the optical waveguide.

As the principle of changing the phase of light, the Pockels effect is mainly used in LiNbO ₃ , the Pockels effect and the quantum confined stark effect (QCSE) are mainly used in InP and GaAs, and the carrier plasma effect is mainly used in Si. Used for.

  In order to perform optical communication with high speed and low power consumption, an optical modulator having a high modulation speed and a low driving voltage is required. In order to perform optical modulation with an amplitude voltage of several volts at a high speed of 10 Gbps or more, the high-speed electrical signal and the speed of light propagating in the phase modulator are matched, and the interaction is performed while propagating. A traveling wave electrode is required. An optical modulator using a traveling wave electrode having an electrode length of several millimeters to several tens of millimeters has been put into practical use (for example, Non-Patent Document 1). In an optical modulator using a traveling wave electrode, an electrode structure and an optical waveguide structure with low loss and low reflection are required so that an electric signal and light propagating through the optical waveguide can be transmitted without being reduced.

As the Mach-Zehnder type optical modulator, there is a Si optical modulator in which an optical waveguide is made of Si. The Si optical modulator is composed of an SOI (Silicon on Insulator) substrate in which a Si thin film is pasted on an oxide film (BOX) layer obtained by thermally oxidizing the surface of a Si substrate. After the Si thin film is processed into a thin line on the oxide film (BOX) layer so that light can be guided through the SOI layer, a dopant is injected into the thin Si thin film so as to become p-type and n-type semiconductors. It is fabricated by depositing SiO ₂ which will be the cladding layer of this, forming electrodes, and the like. At this time, the optical waveguide needs to be designed and processed so as to reduce the optical loss. It is necessary to perform p-type and n-type doping and to create an electrode so as to suppress the generation of light loss and to suppress reflection and loss of high-speed electrical signals.

FIG. 1 is a diagram showing a cross section in a direction perpendicular to the light guiding direction of an optical waveguide 100 which is the basis of a conventional Si optical modulator. The optical waveguide 100 in FIG. 1 includes a SiO ₂ cladding layer 110, a Si layer 120 formed on the SiO ₂ cladding layer 110, and a SiO ₂ cladding layer 130 formed on the Si layer 120.

The Si layer 120 has a structure called a rib waveguide having a difference in thickness in order to confine light, and includes a rib portion 101 serving as a core layer at a central thick portion, and slab portions 102 on both sides of the rib portion 101. And a slab portion 103. The rib portion 101 confines light propagating in the direction perpendicular to the paper surface by utilizing the difference in refractive index with the surrounding SiO ₂ cladding layers 110 and 130.

  The end of the slab portion 102 of the Si layer 120 opposite to the rib portion 101 is a high-concentration p-type semiconductor region 123, and the end of the slab portion 103 of the Si layer 120 opposite to the rib portion 101 is high. A concentration n-type semiconductor region 124 is formed. In addition, the rib portion 101 side of the slab portion 102 of the Si layer 120 and the slab portion 102 side of the rib portion 101 form a medium concentration p-type semiconductor region 121. In addition, the rib portion 101 side of the slab portion 103 of the Si layer 120 and the slab portion 103 side of the rib portion 101 form an intermediate concentration n-type semiconductor region 122.

  The boundary between the high-concentration p-type semiconductor region 123 and the medium-concentration p-type semiconductor region 121 is in contact, and the boundary between the high-concentration n-type semiconductor region 124 and the medium-concentration n-type semiconductor region 122 is also in contact. These boundaries may overlap and be doped. The rib portion 101 has a pn junction structure in which the medium concentration p-type semiconductor region 121 and the medium concentration n-type semiconductor region 122 are in contact with each other. As another example, a pin junction structure in which an i-type (intrinsic) semiconductor region is sandwiched between a medium-concentration p-type semiconductor region 121 and a medium-concentration n-type semiconductor region 122 may be employed.

  Although not shown in FIG. 1, a metal electrode in contact with the high-concentration p-type semiconductor region 123 and a metal electrode in contact with the high-concentration n-type semiconductor region 124 are provided, and the pn junction is reversed together with an RF (high frequency) modulated electric signal from the metal electrode. A bias electric field (from right to left in FIG. 1) is applied. Thereby, the carrier density inside the core layer of the optical waveguide 100 can be changed, the refractive index of the optical waveguide can be changed (carrier plasma effect), and the phase of light can be modulated.

  Since the waveguide dimension depends on the refractive index of the material to be the core / cladding, it cannot be uniquely determined, but includes the rib portion (core layer) and the slab portions 102 and 103 of the optical waveguide 100 as shown in FIG. As an example of a rib waveguide structure, the rib part 101 width (waveguide core width) 400 to 600 (nm) × height 150 to 300 (nm) × slab part thickness 50 to 200 ( nm) × number of lengths (mm).

  FIG. 2 is a plan view showing a conventional Si optical modulator 200. FIG. 3 is a cross-sectional view taken along the line AA ′ of FIG. The Si optical modulator 200 in FIG. 2 is a Mach-Zehnder optical modulator having a structure called a single electrode (see, for example, Non-Patent Document 2), and the light from the input optical waveguide 211 and the input optical waveguide 211 is branched and guided. The optical waveguides 212 and 213 to be waved, and the output optical waveguide 214 that combines the light from the optical waveguide 212 and the light from the optical waveguide 213 are provided. A high-frequency line (RF electrode) 221 for inputting a differential modulation electric signal (RF signal) is formed on the side of the substrate edge side of the optical waveguide 212, and a differential RF is also formed on the side of the substrate side of the optical waveguide 213. Signal) is formed, and a DC electrode 223 for applying a common bias voltage is formed between the optical waveguides 212 and 213. The optical waveguides 212 and 213 have a structure in which two optical waveguides having the same cross-sectional structure as the optical waveguide 100 in FIG.

  Light from the input optical waveguide 211 is branched into optical waveguides 212 and 213. The light guided through the optical waveguide 212 is phase-modulated by a modulated electric signal (RF signal) applied between the RF electrode 221 and the DC electrode 223, and the light guided through the optical waveguide 213 is Phase modulation is performed by a modulated electric signal (RF signal) applied between the DC electrodes 223. The phase-modulated light guided through the optical waveguide 212 and the optical waveguide 213 is combined and output from the output optical waveguide 214.

Referring to FIG. 3, the Si optical modulator 200 includes a SiO ₂ cladding layer 110, a Si layer 120 formed on the SiO ₂ cladding layer 110, and a SiO ₂ cladding layer 130 formed on the Si layer 120. .

  The Si layer 120 includes a first rib portion 101-1 serving as a first core layer, a second rib portion 101-2 serving as a second core layer, and a second rib portion 101-1. The first slab portion 102-1 disposed on the opposite side of the rib portion 101-2 and the first slab portion 102-1 disposed on the opposite side of the second rib portion 101-2 from the first rib portion 101-2. 2 slab portions 102-2, and a third slab portion 103 disposed between the first rib portion 101-1 and the second rib portion 101-2.

  The opposite side of the first slab part 102-1 of the Si layer 120 to the first rib part 101-1 is a high-concentration p-type semiconductor region 123-1, and the first rib of the third slab part 103 is the first rib. The side opposite to the portion 101-1 is a high concentration n-type semiconductor region 124. Also, the first rib portion 101-1 side of the first slab portion 102-1 and the first slab portion 102-1 side of the first rib portion 101-1 are in the medium concentration p-type semiconductor region 121. -1. Further, the first rib portion 101-1 side of the third slab portion 103 and the third slab portion 103 side of the first rib portion 101-1 become the intermediate concentration n-type semiconductor region 122-1. .

  On the other hand, the end of the second slab portion 102-2 of the Si layer 120 opposite to the second rib portion 101-2 becomes the high-concentration p-type semiconductor region 123-2, and the third slab portion 103 is formed. The end opposite to the second rib portion 101-2 becomes a high-concentration n-type semiconductor region 124. In addition, the second rib portion 101-2 side of the second slab portion 102-2 and the second slab portion 102-2 side of the second rib portion 101-2 include the medium concentration p-type semiconductor region 121. -2. Further, the second rib portion 101-2 side of the third slab portion 103 and the third slab portion 103 side of the second rib portion 101-2 become the intermediate concentration n-type semiconductor region 122-2. .

  The RF electrode 221 is in contact with the high-concentration p-type semiconductor region 123-1, the RF electrode 222 is in contact with the high-concentration p-type semiconductor region 123-2, and the DC electrode 223 is in contact with the high-concentration n-type semiconductor region 124. ing. By applying a positive voltage to the DC electrode 223 relative to the RF electrodes 221 and 222, a reverse bias can be applied to the two pn junctions on both sides of the DC electrode 223.

  FIG. 4 is a plan view showing a conventional optical modulator 400. FIG. 5 is a cross-sectional view taken along the line BB ′ of FIG. 4 is a Si Mach-Zehnder optical modulator having a structure called a dual electrode, and includes an input optical waveguide 411 and optical waveguides 412 and 413 in which light from the input optical waveguide 411 is branched and guided. And an output optical waveguide 414 that multiplexes the light from the optical waveguide 412 and the light from the optical waveguide 413. An RF electrode 421 for inputting a differential RF signal is formed on the side of the optical waveguide 412 on the substrate center side, and an RF electrode for inputting a differential RF signal on the side of the optical waveguide 413 on the substrate center side is formed. An electrode 422 is formed. A ground electrode 423 is formed on the side of the substrate edge side of the optical waveguide 412, and a ground electrode 424 is also formed on the side of the substrate side of the optical waveguide 413. A ground electrode 425 is formed between the RF electrodes 421 and 422. The optical waveguides 412 and 413 have a structure in which two optical waveguides having the same cross-sectional structure as the optical waveguide 100 in FIG.

  Light from the input optical waveguide 411 is branched into optical waveguides 412 and 413. The light guided through the optical waveguide 412 is phase-modulated by a modulated electric signal (RF signal) applied between the RF electrode 421 and the ground electrode 423, and the light guided through the optical waveguide 413 is transmitted to the RF electrode 422. Phase modulation is performed by a modulated electric signal (RF signal) applied between the ground electrodes 424. The phase-modulated light guided through the optical waveguide 412 and the optical waveguide 413 is combined and output from the output optical waveguide 414.

Referring to FIG. 5, the optical modulator 400 includes a SiO ₂ cladding layer 410, a Si layer 420 formed on the SiO ₂ cladding layer 410, and a SiO ₂ cladding layer 430 formed on the Si layer 420.

  The Si layer 420 includes a first rib portion 101-1 serving as a first core layer, a first slab portion 102-1 disposed on the substrate edge side of the first rib portion 101-1, The second slab portion 103-1 is disposed on the substrate center side of the rib portion 101-1.

  The opposite side of the first slab part 102-1 of the Si layer 420 to the first rib part 101-1 is the high-concentration p-type semiconductor region 123-1, and the first slab part 103-1 has the first The side opposite to the rib portion 101-1 is a high-concentration n-type semiconductor region 124-1. Also, the first rib portion 101-1 side of the first slab portion 102-1 and the first slab portion 102-1 side of the first rib portion 101-1 are in the medium concentration p-type semiconductor region 121. -1. Further, the first rib portion 101-1 side of the second slab portion 103-1 and the second slab portion 103-1 side of the first rib portion 101-1 are the medium concentration n-type semiconductor region 122. -1.

  The RF electrode 421 is in contact with the high concentration n-type semiconductor region 124-1, and the ground electrode 423 is in contact with the high concentration p-type semiconductor region 123-1. Although the ground electrode 425 is not in contact with the semiconductor layer, by forming a GSG high-frequency transmission line with the ground electrodes 423 and 425 with respect to the RF electrode 421, the characteristic impedance can be adjusted and the transmission characteristics can be improved. . In addition, since the RF electrode is surrounded by the ground electrode, it is possible to form an optical modulator with less signal leakage and less crosstalk and propagation loss.

  The characteristic impedance of the Si optical modulator as a high-frequency transmission line is greatly influenced by the capacitance of the pn junction of the Si layer. Therefore, the characteristic impedance of the single-electrode Si Mach-Zehnder type optical modulator is about 25Ω at the single end, and can be set to about 50Ω by differential driving. On the other hand, the dual-electrode Si Mach-Zehnder type optical modulator is relatively easy to adjust the characteristic impedance, and can be about 50Ω at a single end and about 100Ω at a differential drive. Characteristic impedance higher than that of the device.

  In order to perform optical communication with large capacity and low power consumption, an optical modulator capable of modulating light at high speed and a modulator drive driver IC with low power consumption are required. The characteristic impedance of the single-electrode Si Mach-Zehnder type optical modulator shown in FIG. 2 is about 25Ω at a single end and about 50Ω by differential driving, but is a back termination that is a general modulator driver IC. Since the type of driver generally has a single-ended 50Ω and a differential of 100Ω, a 50Ω resistor is added to the sending end resistor to obtain a 50Ω output. For this reason, an unbalanced-balanced conversion circuit (balun circuit) or the like for converting a 50Ω driver signal output at a single end into a 50Ω differential signal is required.

  On the other hand, the open collector driver does not have a sending end resistor and can be connected to an optical modulator having any impedance. For this reason, when an open collector driver is used, the power consumed by the sending end resistor can be reduced, and a differential drive driver IC can be used, providing an optical modulator with high power efficiency and low power consumption. can do.

  FIG. 6 is a circuit diagram showing a configuration of a general open collector driver. 6 includes a final-stage transistor 601, an input terminal 602 connected to the base (gate) of the transistor 601, an output terminal 603 connected to the collector (drain) of the transistor 601, A resistor 604 connected to the emitter (source), a current source 605 connected to the resistor 604, and a ground terminal 606 connected to the current source 605 are provided. The output terminal 603 is connected to the driven body 610.

  The open collector driver 600 is generally known to have high power efficiency because the power consumed by the terminal resistor is reduced as compared with a back-termination type driver (for example, Non-Patent Document 3). Further, only the driven body 610 to be connected is handled as a load of the transistor 601. Therefore, it is known that the driven body need not be designed in accordance with the impedance of the sending end resistor unlike the back termination type driver, and it is known that the driven body is highly designed.

  On the other hand, since the output terminal 603 which is a collector terminal is released, the open collector driver 600 viewed from the driven body 610 has a very high impedance. Therefore, when the driven body 610 is connected to the open collector driver 600, the open collector driver 600 has a high impedance with respect to the driven body 610, and the RF signal input to the open collector driver 600 is largely reflected at the output terminal 603. In addition, since the driven body 610 has a low impedance with respect to the open collector driver 600, the input from the open collector driver 600 to the connected body 610 is also reflected at the connection point 611 of the driven body 610. Therefore, resonance of the input signal occurs due to both reflections, causing oscillation.

  In order to suppress the influence of the reflection of the input signal, the connection distance between the driven body 610 and the open collector driver 600 (the distance between the output terminal 603 and the connection point 611 in FIG. 6) is sufficiently shorter than the wavelength of the RF signal. (Generally about 1/10 to 1/20). When the connection distance is sufficiently shorter than the wavelength of the RF signal, the driven body 610 can be driven without being affected by reflection regardless of the impedance.

Kazuhiro Goi, Kenji Oda, Hiroyuki Kusaka, Kensuke Ogawa, Tsung-Yang Liow, Xiaoguang Tu, Guo-Qiang Lo, Dim-Lee Kwong, “20 Gbps binary phase modulation characteristics of Si Mach-Zehnder push-pull modulator” 2012 IEICE Society Conference, C-3-50, 2012. Po Dong, Long Chen, and Young-kai Chen, `` High-speed low-voltage single-drive push-pull silicon Mach-Zehnder modulators '' Opt.Express vol.20, no.6, pp.6163-6169, 2012. N. Wolf, L. Yan, J.-H. Choi, T. Kapa, S. Wunsch, R. Klotzer, K.-O. Velthaus, H.-G. Bach, M. Schell, `` Electro-Optical Co -Design to Minimize Power Consumption of a 32 GBd Optical IQ-Transmitter Using InP MZ-Modulators '' 2015 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS 2015), H.3, pp.117, 2015.

  FIG. 7 is a plan view showing a configuration of an optical modulator in which a differential open collector driver is connected to a Mach-Zehnder optical modulator. A differential output terminal 711 of the differential open collector driver 710 is connected to an input pad 723 of a high frequency transmission line (RF electrode) 721 of a Mach-Zehnder optical modulator 720, and an RF electrode 722 is connected to the differential output terminal 712. The input pad 724 is connected. The RF electrode 721 of the Mach-Zehnder optical modulator 720 is connected to the resistor 731 via the input terminal 734 of the termination resistor 730, and the RF electrode 722 is connected to the resistor 732 via the input terminal 735 of the termination resistor 730. At this time, the driven bodies of the differential open collector driver 710 are the RF electrodes 721 and 722 and the resistors 731 and 732. Further, in order to match the operating point of the open collector driver 710, a potential (Vcc) is applied to the RF electrodes 721 and 722 and the resistors 731 and 732 at the terminal 733.

  When the characteristic impedance of the RF electrodes 721 and 722 of the Mach-Zehnder type optical modulator 720 matches the impedance of the resistors 731 and 732, the reflection point of the input signal from the open collector driver 710 is the input pad of the RF electrode 721. 723 and the input pad 724 of the RF electrode 722. In this case, the connection distance between the open collector driver 710 and the RF electrodes 721 and 722 (the distance between the differential output terminal 711 and the input pad 723, and the distance between the differential output terminal 712 and the input pad 724). ) Is sufficiently shorter than the wavelength of the RF signal applied to the RF electrodes 721 and 722, the influence of reflection at the input pads 723 and 724 can be suppressed. At this time, the characteristic impedance of the RF electrodes 721 and 722 and the impedance of the resistors 731 and 732 may have any values as long as they match.

  On the other hand, when the characteristic impedance of the RF electrodes 721 and 722 and the impedance of the resistors 731 and 732 do not coincide with each other, and when the reflection occurs in the middle of the RF electrodes 721 and 722, or the RF electrodes 721 and 722 If there is a defect portion 727 which is a structural defect, the signal reflection points from the driver are the resistance reflection points 731 and 732 and the structural reflection points in the middle of the RF electrodes 721 and 722, or the defect portion 727.

  In general, since the RF electrode of the Mach-Zehnder type optical modulator has a length exceeding the order of mm, the distance at which resonance due to reflection occurs (the distance between the differential output terminal 711 and the defect portion 727 or the input terminal 734, and the differential output). The distance between the terminal 712 and the input terminal 735, or the distance between the differential output terminals 711 and 712 and the structural reflection point in the middle of the RF electrodes 721 and 722) is not sufficiently shorter than the wavelength of the RF signal. . Therefore, when an RF signal in the GHz band is input, between the differential output terminal 711 and the input terminal 734, the reflection of the signal at the defective portion 727 in the middle of the RF electrode 721, the reflection of the signal at the differential output terminal 711, and the like. Resonance occurs between the two. When resonance due to reflection occurs, the high-frequency signal propagating through the RF electrode 721 (and 722) deteriorates propagation characteristics such as energy leakage, increased reflection, and increased transmission loss. Furthermore, the resonance that occurs at a specific frequency causes a change in the amount of reflection in the open collector driver 710, causing abnormal operation due to unintended oscillation of the driver IC, an increase in noise, and the like. Therefore, the characteristic impedance values of the RF electrodes 721 and 722 of the Mach-Zehnder type optical modulator 720 and the impedance values of the resistors 731 and 732 are perfectly matched, and the RF electrodes 721 and 722 and the resistors 731 and 732 are between It is desirable that there is no reflection point.

  The present invention has been made in view of such problems, and its object is to reduce reflection points in the phase modulation section of a Mach-Zehnder optical modulator connected to a differential output open collector driver. It is another object of the present invention to provide a Mach-Zehnder type optical modulator that suppresses the deterioration of frequency response characteristics and the deterioration of driver characteristics by suppressing reflection at the terminating resistor.

  In order to achieve such an object, a first aspect of the present invention provides a Mach-Zehnder optical modulation comprising a differential open collector driver and a set of RF electrodes connected to the differential open collector driver. And a termination resistor connected to the Mach-Zehnder type optical modulator, comprising: a set of differential output terminals of the open collector driver; and an input pad of the set of RF electrodes. The signal lines to be connected are of equal length, and the signal lines to connect the output pads of the set of RF electrodes and the input terminals of the set connected to the set of resistors of the termination resistor, respectively, are of equal length. A center line between the set of RF electrodes, a center line between the input pads of the set of RF electrodes, and a center line between output pads of the set of RF electrodes, Electricity so that it is approximately parallel Wherein the but are arranged.

  According to a second aspect of the present invention, there is provided the optical modulator according to the first aspect, wherein one set of RF electrodes of the Mach-Zehnder optical modulator is in a direction perpendicular to the signal output end face of the driver IC. It is arranged.

  According to a third aspect of the present invention, there is provided the optical modulator according to the first aspect, wherein the Mach-Zehnder type optical modulator is a Mach-Zehnder type optical modulator having a single electrode structure. Or the optical modulator of 2.

  According to a fourth aspect of the present invention, there is provided the optical modulator of the first or second aspect, wherein the Mach-Zehnder type optical modulator is a Mach-Zehnder type optical modulator having a dual electrode structure. The optical modulator according to claim 1.

  According to a fifth aspect of the present invention, there is provided the optical modulator according to any one of the first to fourth aspects, wherein the optical waveguide of the Mach-Zehnder optical modulator is formed of silicon. And

  According to a sixth aspect of the present invention, there is provided the optical modulator according to any one of the first to fifth aspects, wherein the differential open collector driver includes two or more sets of differential output terminals, The Mach-Zehnder type optical modulator includes two or more sets of RF electrodes connected to the two or more sets of differential output terminals, respectively, and the termination resistors are two or more sets connected to the two or more sets of RF electrodes, respectively. The two or more RF electrodes of the Mach-Zehnder type optical modulator are arranged in a direction perpendicular to the signal output end face of the driver IC, and the two or more RF electrodes of the Mach-Zehnder type optical modulator are The high-frequency transmission line is formed in a linear shape.

  In the Mach-Zehnder type optical modulator according to the present invention, abnormal operation due to unintended oscillation of the driver due to fluctuations in reflection amount, deterioration of driver characteristics such as increase in noise, and high-speed modulation due to deterioration of frequency response characteristics of the optical modulator. It is possible to prevent deterioration of waveform quality. Furthermore, it is possible to improve adverse effects such as an increase in crosstalk of signals within a transmission optical signal or between transmission and reception. Therefore, it is possible to provide an optical modulator having excellent high frequency characteristics and good waveform quality.

It is a figure which shows the cross section of the direction perpendicular | vertical to the light-guiding direction of the light of the optical waveguide used as the basis of the conventional Si optical modulator. It is a top view which shows the conventional single electrode Mach-Zehnder type | mold optical modulator. It is sectional drawing in AA 'of FIG. It is a top view which shows the conventional dual electrode Mach-Zehnder type | mold optical modulator. It is sectional drawing in BB 'of FIG. It is a circuit block diagram which shows the conventional open collector driver. It is a top view which shows the Mach-Zehnder type | mold optical modulator which uses a differential type open collector driver. 1 is a plan view showing a Mach-Zehnder optical modulator according to a first embodiment of the present invention. It is sectional drawing in CC 'of FIG. FIG. 5 is a plan view showing a conventional Mach-Zehnder type optical modulator in which a bent portion is provided in an RF electrode and an optical input / output unit and an RF signal input / output unit are arranged at different locations. It is a top view which shows the Mach-Zehnder type | mold optical modulator which concerns on the 2nd Embodiment of this invention. It is sectional drawing in DD 'of FIG. It is a top view which shows the Mach-Zehnder type | mold optical modulator which concerns on the 3rd Embodiment of this invention. It is a top view which shows the Mach-Zehnder type | mold optical modulator which concerns on the modification of embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 8 is a plan view showing the configuration of the optical modulator according to the first embodiment of the present invention. 8 is connected to a differential open collector driver 810, a single-electrode Si Mach-Zehnder optical modulator 820 connected to the differential open collector driver 810, and a Mach-Zehnder optical modulator 820. Terminal resistor 830. The Mach-Zehnder optical modulator 820 includes an input optical waveguide 801, optical waveguides 802 and 803 into which light from the input optical waveguide 801 is branched, and light from the optical waveguide 802 and light from the optical waveguide 803. And an output optical waveguide 804 for combining the two.

  A high-frequency line (RF electrode) 821 for inputting a differential modulation electric signal (RF signal) is formed on the side of the substrate edge side of the optical waveguide 802, and a differential RF is also provided on the side of the substrate side of the optical waveguide 803. An RF electrode 822 for inputting a signal is formed. Further, a DC electrode 823 for applying a common bias voltage is formed between the optical waveguides 802 and 803. An input pad 824 is formed on the differential open collector driver 810 side of the RF electrode 821 and is connected to the differential output terminal 811 of the differential open collector driver 810 by a signal line (wire) 841. An output pad 826 is formed on the termination resistor 830 side of the RF electrode 821, and is connected to the input terminal 834 of the termination resistor 830 by a signal line 843. An input pad 825 is formed on the RF electrode 822 on the differential open collector driver 810 side, and is connected to the differential output terminal 812 of the differential open collector driver 810 by a signal line 842. An output pad 827 is formed on the termination resistor 830 side of the RF electrode 822, and is connected to the input terminal 835 of the termination resistor 830 by a signal line 844.

  The input terminal 834 of the termination resistor 830 is connected to the terminal 833 through the resistor 831, and the input terminal 835 is connected to the terminal 833 through the resistor 832. The terminal 833 applies a potential (VCC) to the RF electrodes 821 and 822 and the resistors 831 and 832 in order to match the operating point of the differential open collector driver 810.

FIG. 9 is a cross-sectional view taken along the line CC ′ of the Mach-Zehnder optical modulator 820. Referring to FIG. 9, the Mach-Zehnder optical modulator 820 includes an SiO ₂ cladding layer 910, an Si layer 920 formed on the SiO ₂ cladding layer 910, and an SiO ₂ cladding layer 930 formed on the Si layer 920. Is provided.

  In addition, the Si layer 920 includes a first rib portion 921-1 serving as a first core layer, a second rib portion 921-2 serving as a second core layer, and a first rib portion 921-1. The 1st slab part 922-1 arrange | positioned on the opposite side to the 2nd rib part 921-2, and the 1st rib part 921-1 of the 2nd rib part 921-2 are arrange | positioned on the opposite side. The second slab portion 922-2, and the third slab portion 923 disposed between the first rib portion 921-1 and the second rib portion 921-2.

  The first slab part 922-1 of the Si layer 920 of the Mach-Zehnder optical modulator 820 is opposite to the first rib part 921-1 in the high-concentration p-type semiconductor region 943-1. On the opposite side of the slab portion 923 from the first rib portion 921-1, a high-concentration n-type semiconductor region 944 is formed. The first rib portion 921-1 side of the first slab portion 922-1 and the first slab portion 922-1 side of the first rib portion 921-1 are an intermediate concentration p-type semiconductor region 941. -1. Further, the first rib portion 921-1 side of the third slab portion 923 and the third slab portion 923 side of the first rib portion 921-1 become the intermediate concentration n-type semiconductor region 942-1. .

  On the other hand, the end of the second slab part 922-2 of the Si layer 920 opposite to the second rib part 921-2 is a high-concentration p-type semiconductor region 943-2, and the third slab part 923 is formed. The side opposite to the second rib portion 921-2 is a high-concentration n-type semiconductor region 944. Further, the second rib portion 921-2 side of the second slab portion 922-2 and the second slab portion 922-2 side of the second rib portion 921-2 are the medium concentration p-type semiconductor region 941. -2. Further, the second rib portion 921-2 side of the third slab portion 923 and the third slab portion 923 side of the second rib portion 921-2 become the intermediate concentration n-type semiconductor region 942-2. .

  The RF electrode 821 is in contact with the high-concentration p-type semiconductor region 943-1, the RF electrode 822 is in contact with the high-concentration p-type semiconductor region 943-2, and the DC electrode 823 is in the high-concentration n-type semiconductor region 944. Is in contact with By applying a positive voltage to the DC electrode 823 relative to the RF electrodes 821 and 822, a reverse bias can be applied to the two pn junctions on both sides of the DC electrode 823.

  A Mach-Zehnder type optical modulator using an open collector driver has a connection point between an open collector driver and an RF electrode, and an RF electrode and a termination resistance when the characteristic impedance of the RF electrode and the impedance of the termination resistance do not match. Resonance due to reflection occurs between the connection points. Even if there is a reflection point of the RF signal such as a defect point of the high-frequency transmission line in the connection wiring between the open collector driver and the RF electrode or in the RF electrode and the termination resistor and the connection wiring, In some cases, the high-frequency signal may resonate with the reflection at the connection end with the open collector driver as a node.

In addition, since the Si optical modulator can make the bending radius of the optical waveguide as small as about 10 μm, the optical multiplexing / demultiplexing circuit and the bending portion can be made small. For this reason, it is easy to arrange the optical input / output unit of the optical modulator at a location different from the open collector driver and the termination resistor. On the other hand, in an optical modulator composed of a material other than Si, such as LiNbO ₃ or InP, it is difficult to reduce the bending radius of the optical waveguide. The input / output unit and the RF signal input / output unit are arranged at different locations. FIG. 10 is a diagram showing a configuration of a Mach-Zehnder optical modulator in which a bent portion is provided in an RF electrode and an optical input / output unit and an RF signal input / output unit are arranged at different locations.

  The optical modulator 1000 of FIG. 10 is provided with a curved portion on the input side of the RF electrodes 1021 and 1022 of the Mach-Zehnder optical modulator 1020, the electrode ends of the RF electrodes 1021 and 1022, and the differential output of the differential open collector driver 1010. Terminals 1011 and 1012 are separated from the input optical waveguide 1001. Further, curved portions are also provided on the output sides of the RF electrodes 1021 and 1022 of the Mach-Zehnder optical modulator 1020, and the electrode ends of the RF electrodes 1021 and 1022 and the input terminals 1034 and 1035 of the termination resistor 1030 are separated from the output optical waveguide 1004. ing.

  However, when the RF electrode of the Mach-Zehnder type optical modulator is provided with a curved part and the high-frequency transmission line is bent, the curved part in the high-frequency transmission line becomes a reflection point of the RF signal, and reflection and open at that part. There is a possibility that resonance of a high-frequency signal having a node at the reflection of the connection end with the collector driver. Further, in a Mach-Zehnder type optical modulator for propagating a differential signal, if the RF electrode which is a high-frequency transmission line has a curved portion and there is a difference in the length of the two RF electrodes, the signal of the differential signal to be paired There is a phase difference between them. A state in which there is a phase difference between signals can be considered as a state in which two modes, ie, a differential mode that is an original differential signal and a common mode that causes noise are mixed in a propagating differential signal. When a signal is propagated to a long RF electrode in a state in which a differential mode and a common mode are mixed, the two modes are maintained even if the RF electrode is bent in the opposite direction to the bent direction to eliminate the difference in propagation line length. Then, since the propagation speed is different, the common mode cannot be eliminated. Since the value of the characteristic impedance is different between the differential mode and the common mode, common mode reflection occurs in the termination resistor. This reflection may cause resonance of a high-frequency signal having a node at the connection between the open collector driver and the Mach-Zehnder optical modulator.

  As described above, the Mach-Zehnder type optical modulator using the open collector driver has a large reflection between the differential output terminal of the signal of the differential open collector driver and the RF electrode. In such a case, and when there is reflection at the terminating resistor, resonance of the high-frequency signal is likely to occur between the signal output terminal and the RF reflection point.

  On the other hand, the optical modulator 800 of this embodiment shown in FIG. 8 includes a Mach-Zehnder optical modulator from a differential output terminal 811 that is a connection point between the differential open-collector driver 810 and the Mach-Zehnder optical modulator 820. The input terminal 834 which is a connection point between the terminal 820 and the terminating resistor 830 is configured to have a linear shape in terms of high-frequency propagation. Further, from a differential output terminal 812 that is a connection point between the differential open collector driver 810 and the Mach-Zehnder optical modulator 820 to an input terminal 835 that is a connection point between the Mach-Zehnder optical modulator 820 and the termination resistor 830. It is configured to have a linear shape in terms of high-frequency propagation. When this portion is configured to have a straight shape without a bent portion in the RF electrode, the propagation direction of the high-frequency signal is always constant.

  Further, in order to prevent the occurrence of common mode, the distance between the differential output terminal 811 of the differential open collector driver 810 and the input pad 824 of the RF electrode 821 of the Mach-Zehnder optical modulator 820 and the differential output terminal 812 The distance between the input pad 825 and the input pad 825 is equal, and the signal line 841 connecting the differential output terminal 811 and the input pad 824 and the signal line 842 connecting the differential output terminal 812 and the input pad 825 are of equal length. It is. Further, the distance between the output pad 826 of the RF electrode of the Mach-Zehnder type optical modulator 820 and the input terminal 834 of the termination resistor 830 and the distance between the output pad 827 and the input terminal 835 are arranged at equal distances. The signal line 843 that connects the input terminal 834 and the signal line 844 that connects the output pad 827 and the input terminal 835 have the same length. Therefore, the RF electrodes 821 and 822 are arranged in a direction perpendicular to the signal output end surface of the differential open collector driver 810 (a line connecting the differential output terminals 811 and 812).

  Here, the phase modulation unit of the Mach-Zehnder type optical modulator 820, wiring other than the phase modulation unit of the Mach-Zehnder type optical modulator 820, input pads 824 and 825 for connection to the differential type open collector driver 810, and the termination resistor 830 The output pads 826 and 827 for connecting to the electrode have the characteristic impedance matched to a constant value, so that the electrode spacing and the electrode width are adjusted as appropriate. Since the electrode spacing and electrode width are changed in each region, the outer periphery and center line of the electrode are not straight, but if the propagation direction of the high-frequency signal is constant, it is said that the high-frequency propagation is a straight line be able to.

  Since the RF electrodes 821 and 822 of the Mach-Zehnder type optical modulator 820 are configured so that the high-frequency transmission line portion is a straight line, the RF signal is not reflected by the curved portion. Further, since a time lag between the differential signals between the two RF electrodes does not occur as in the case where the curved portion is provided in the RF electrode, the occurrence of the common mode can be prevented. Therefore, due to the resonance of the RF signal due to these reflections, due to fluctuations in the amount of reflection, abnormal operation due to unintended oscillation of the driver IC, deterioration of driver characteristics such as increase in noise, and deterioration of frequency response characteristics of the optical modulator, It is possible to prevent deterioration of waveform quality during high-speed modulation. Furthermore, it is possible to improve adverse effects such as an increase in crosstalk of signals within a transmission optical signal or between transmission and reception. Therefore, it is possible to provide an optical modulator having excellent high frequency characteristics and good waveform quality.

[Second Embodiment]
FIG. 11 is a plan view showing a configuration of an optical modulator according to the second embodiment of the present invention. The optical modulator 1100 of FIG. 11 is connected to a differential open collector driver 1110, a dual-electrode Si Mach-Zehnder optical modulator 1120 connected to the differential open collector driver 1110, and a Mach-Zehnder optical modulator. And a terminating resistor 1130.

  The Mach-Zehnder optical modulator 1120 includes an input optical waveguide 1101, optical waveguides 1102 and 1103 in which light from the input optical waveguide 1101 is branched and guided, light from the optical waveguide 1102, and light from the optical waveguide 1103. And an output optical waveguide 1104 for combining the two.

  A high-frequency transmission line (RF electrode) 1121 for inputting a differential modulated electric signal (RF signal) is formed on the side of the optical waveguide 1102 on the substrate center side. An RF electrode 1122 for inputting a dynamic RF signal is formed. A ground electrode 1123 is formed on the side of the substrate edge side of the optical waveguide 1102, and a ground electrode 1124 is formed on the side of the substrate side of the optical waveguide 1103. A ground electrode 1125 is formed between the RF electrodes 1121 and 1124. An input pad 1126 is formed on the RF electrode 1121 on the differential open collector driver 1110 side, and is connected to the differential output terminal 1111 of the differential open collector driver 1110 by a signal line 1141. An output pad 1128 is formed on the termination resistor 1131 side of the RF electrode 1121, and is connected to an input terminal 1134 of the termination resistor 1130 by a signal line 1143. An input pad 1127 is formed on the RF electrode 1122 on the differential open collector driver 1110 side, and is connected to the differential output terminal 1112 of the differential open collector driver 1110 by a signal line 1142. An output pad 1129 is formed on the termination resistor 1130 side of the RF electrode 1122, and is connected to an input terminal 1135 of the termination resistor 1130 by a signal line 1144.

  The input terminal 1134 of the termination resistor 1130 is connected to the terminal 1133 via the resistor 1131, and the input terminal 1135 is connected to the terminal 1133 via the resistor 1132. The terminal 1133 applies a potential (Vcc) to the RF electrodes 1121 and 1122 and the resistors 1131 and 1132 in order to match the operating point of the differential open collector driver 1110.

FIG. 12 is a cross-sectional view taken along the line DD ′ of the Mach-Zehnder optical modulator 1120. Referring to FIG. 12, a Mach-Zehnder optical modulator 1120 includes an SiO ₂ cladding layer 1210, an Si layer 1220 formed on the SiO ₂ cladding layer 1210, and an SiO ₂ cladding layer 1230 formed on the Si layer 1220. Is provided.

  Further, the Si layer 1220 includes a first rib portion 1221-1 serving as a first core layer, a first slab portion 1222-1 disposed on the substrate edge side of the first rib portion 921-1, And a second slab portion 1223-1 disposed on the substrate center side of one rib portion 1221-1.

  The first slab part 1222-1 of the Si layer 1220 of the Mach-Zehnder type optical modulator 1120 is opposite to the first rib part 1221-1 to form a high-concentration p-type semiconductor region 1243-1. The opposite side of the slab portion 1223-1 to the first rib portion 1221-1 is a high-concentration n-type semiconductor region 1244-1. Further, the first rib portion 1222-1 side of the first slab portion 1222-1 and the first slab portion 1222-1 side of the first rib portion 1222-1 are an intermediate concentration p-type semiconductor region 1241. -1. In addition, the first rib portion 1221-1 side of the second slab portion 1223-1 and the second slab portion 1223-1 side of the first rib portion 1221-1 are an intermediate concentration n-type semiconductor region 1242. -1.

  The RF electrode 1121 is in contact with the high-concentration n-type semiconductor region 1244-1, and the ground electrode 1123 is in contact with the high-concentration p-type semiconductor region 1243-1. Although the ground electrode 1125 is not in contact with the semiconductor region, the GSG high-frequency transmission line is formed with the ground electrodes 1123 and 1125 with respect to the RF electrode 1121, thereby adjusting the characteristic impedance and improving the transmission characteristics. . In addition, since the RF electrode is surrounded by the ground electrode, it is possible to form an optical modulator with less signal leakage and less crosstalk and propagation loss.

  The optical modulator 1100 of this embodiment is connected to the Mach-Zehnder optical modulator 1120 and the termination resistor 1130 from a differential output terminal 1111 that is a connection point between the differential open-collector driver 1110 and the Mach-Zehnder optical modulator 1120. The input terminal 1134, which is a point, is configured to have a linear shape. Further, from the differential output terminal 1112 that is a connection point between the differential open collector driver 1110 and the Mach-Zehnder optical modulator 1120 to the output terminal 1135 that is a connection point between the Mach-Zehnder optical modulator 1120 and the termination resistor 1130. It is configured to have a linear shape in terms of high-frequency propagation. When this portion is configured to have a straight shape without a bent portion in the RF electrode, the propagation direction of the high-frequency signal is always constant.

  Since the RF electrodes 1121 and 1122 of the Mach-Zehnder optical modulator 1120 are configured to be straight, no RF signal is reflected by the curved portion. Further, since a time lag between the differential signals between the two RF electrodes does not occur as in the case where the curved portion is provided in the RF electrode, the occurrence of the common mode can be prevented. Therefore, due to the resonance of the RF signal due to these reflections, due to fluctuations in the amount of reflection, abnormal operation due to unintended oscillation of the driver IC, deterioration of driver characteristics such as increase in noise, and deterioration of frequency response characteristics of the optical modulator, It is possible to prevent deterioration of waveform quality during high-speed modulation. Furthermore, it is possible to improve adverse effects such as an increase in crosstalk of signals within a transmission optical signal or between transmission and reception. Therefore, it is possible to provide an optical modulator having excellent high frequency characteristics and good waveform quality.

[Third Embodiment]
FIG. 13 is a plan view showing a configuration of an optical modulator according to the third embodiment of the present invention. The optical modulator 1300 of FIG. 13 includes a differential open collector driver 1310, a Mach-Zehnder optical modulator array 1320 connected to the differential open-collector driver 1310, and a termination connected to the Mach-Zehnder optical modulator array 1320. A resistor 1330.

  The differential open collector driver 1310 includes four sets of differential output terminals 1311-1 to 1311-4 and 1312-1 to 1312-4. The Mach-Zehnder optical modulator array 1320 includes four single-electrode Mach-Zehnder optical modulators 1320-1 to 1320-4, and each of the Mach-Zehnder optical modulators 1320-1 to 1320-4 is the first embodiment. The optical modulator 800 has the same configuration as the Mach-Zehnder type optical modulator 820. The Mach-Zehnder optical modulator 1320-1 is connected to the differential output terminals 1311-1 and 1312-1, the Mach-Zehnder optical modulator 1320-2 is connected to the differential output terminals 1311-2 and 1312-2, and the Mach-Zehnder optical modulator 1320 is connected. -3 is connected to the differential output terminals 1311-3 and 1312-3, and the Mach-Zehnder optical modulator 1320-4 is connected to the differential output terminals 1311-4 and 1312-4, respectively. The Mach-Zehnder optical modulator 1320-1 is connected to the input terminal 1331-1 and the terminal 1332-1 of the termination resistor 1330. The Mach-Zehnder optical modulator 1320-2 is connected to the input terminal 1331-2 and the terminal 1332-2 of the termination resistor 1330. The Mach-Zehnder optical modulator 1320-3 is connected to the input terminal 1331-3 and the terminal 1332-3 of the termination resistor 1330. The Mach-Zehnder optical modulator 1320-4 is connected to the input terminal 1331-4 and the terminal 1332-4 of the termination resistor 1330.

  The optical modulator 1300 of the present embodiment has a linear shape from the differential output terminals 1311-1 to 1311-4 of the differential open collector driver 1310 to the input terminals 1331-1 to 1331-4 of the termination resistor 1330. It is comprised so that it may become. The differential open collector driver 1310 is configured to have a linear shape from the differential output terminals 1312-1 to 1312-4 to the input terminals 1332-1 to 1332-4 of the termination resistor 1330. When this portion is configured to have a straight shape without a bent portion in the RF electrode, the propagation direction of the high-frequency signal is always constant.

  Since the RF electrodes of the Mach-Zehnder optical modulators 1320-1 to 1320-4 are configured to be straight, no RF signal is reflected by the curved portion. Further, since a time lag between the differential signals between the two RF electrodes does not occur as in the case where the curved portion is provided in the RF electrode, the occurrence of the common mode can be prevented. Therefore, due to the resonance of the RF signal due to these reflections, due to fluctuations in the amount of reflection, abnormal operation due to unintended oscillation of the driver IC, deterioration of driver characteristics such as increase in noise, and deterioration of frequency response characteristics of the optical modulator, It is possible to prevent deterioration of waveform quality during high-speed modulation. Furthermore, it is possible to improve adverse effects such as an increase in crosstalk of signals within a transmission optical signal or between transmission and reception. Therefore, it is possible to provide an optical modulator having excellent high frequency characteristics and good waveform quality.

  The optical modulator shown in FIG. 13 can be a single-electrode Mach-Zehnder optical modulator or a dual-electrode Mach-Zehnder optical modulator.

[Modification]
FIG. 14 is a plan view showing an optical modulator according to a modification of the first to third embodiments of the present invention. An optical modulator 1400 shown in FIG. 14A is a first modification, and is an example in which the input pads and the output pads of the RF electrode of the optical modulator 800 of the first embodiment are spaced apart. That is, the input pad 1423 of the RF electrode 1421 and the input pad 1424 of the RF electrode 1422 are separated from each other, and the output pad 1425 of the RF electrode 1421 and the output pad 1426 of the RF electrode 1422 are separated from each other. Thereby, impedance can be matched.

  An optical modulator 1500 shown in FIG. 14B is a second modification, and the differential open collector driver 810 of the optical modulator 800 of the first embodiment includes a ground terminal in addition to the differential output terminal. It is an example. The differential open collector driver 1510 of the optical modulator 1500 is provided with differential output terminals 1511 and 1512 and ground terminals 1513 to 1515. The termination resistor 1530 is provided with input terminals 1531 and 1532 and ground terminals 1533 to 1535. Even in such a configuration, the signal line connecting the differential output terminal and the input pad of the RF electrode is the same length, and the signal line connecting the output pad of the RF electrode and the input terminal of the termination resistor is also the same length. I just need it.

  An optical modulator 1600 shown in FIG. 14C is a third modification, and is an example in which the positions of the input pads and the output pads of the RF electrode of the optical modulator 800 according to the first embodiment are changed. Specifically, the input pad 1623 of the RF electrode 1621 and the input pad 1624 of the RF electrode 1622 of the Mach-Zehnder optical modulator 1620 are shifted in parallel, and the output pad 1625 of the RF electrode 1621 and the output pad 1626 of the RF electrode 1622 are shifted. Are shifted in parallel. In the case of the third modification and the first modification described above, a curved portion exists between the RF electrode, the input pad, and the output pad, but there is a time lag between the differential signals. By shifting the input pad and the output pad of the optical modulator in parallel from the RF electrode so as not to occur, the arrangement in the element can be adjusted. That is, a center line between a set of RF electrodes (1621 and 1622), a center line between a set of RF electrode input pads (1623 and 1624), and a set of RF electrode output pads (1625 and 1626) should be substantially parallel to the center line.

  An optical modulator 1700 in FIG. 14D is a fourth modification example, and the differential open collector driver 1110 of the optical modulator 1100 of the second embodiment has a ground terminal in addition to the differential output terminal. It is an example. The differential open collector driver 1710 of the optical modulator 1700 is provided with differential output terminals 1711 and 1712 and ground terminals 1713 to 1715. The termination resistor 1730 is provided with RF electrode input terminals 1731 and 1732 and ground terminals 1733 to 1735. The input pad of the RF electrode 1721 of the Mach-Zehnder optical modulator 1720 is connected to the differential output terminal 1711, and the output pad of the RF electrode 1721 is connected to the input terminal 1731 of the termination resistor 1730. The input pad of the RF electrode 1722 of the Mach-Zehnder optical modulator 1720 is connected to the differential output terminal 1712, and the output pad of the RF electrode 1722 is connected to the input terminal 1732 of the termination resistor 1730. The input pad of the ground electrode 1723 of the Mach-Zehnder optical modulator 1720 is connected to the ground terminal 1713, and the output pad of the ground electrode 1723 is connected to the input terminal 1733 of the termination resistor 1730. The input pad of the ground electrode 1724 of the Mach-Zehnder optical modulator 1720 is connected to the ground terminal 1714, and the output pad of the ground electrode 1724 is connected to the input terminal 1734 of the termination resistor 1730. The input pad of the ground electrode 1725 of the Mach-Zehnder optical modulator 1720 is connected to the ground terminal 1715, and the output pad of the ground electrode 1725 is connected to the input terminal 1735 of the termination resistor 1730.

100, 211-214, 411-414, 801-804, 1001-1004, 1101-1104 Optical waveguide 101, 101-1, 101-2, 921-1, 921-2, 1221-1, 1221-2 Rib part 102, 102-1, 102-2, 103-1, 103-2, 922-1, 922-2, 923, 1222-1, 1222-2, 1223-1, 1223-2 Slab parts 110, 130, 410 430, 910, 930, 1210, 1220 Si cladding layer 120, 420, 920, 1220 Si layer 120, 121-1, 121-2, 941-1, 941-2, 1241-1, 1241-2 Medium concentration p Type semiconductor regions 122, 122-1, 122-2, 942-1, 942-2, 1242-1, 1242-2 Medium-concentration n-type semiconductor regions 123, 123-1, 123-2, 943-1, 943-2, 1243-1, 1243-2 High-concentration p-type semiconductor regions 124, 124-1, 124-2, 944, 1244-1, 1244-2 High-concentration n-type semiconductor region 200, 400 Optical modulator 221, 222, 421, 422, 721, 722, 821, 822, 1021, 1022, 1121, 1122, 1421, 1422, 1621, 1622, 1721, 1722 RF electrode 223 , 823 DC electrodes 423 to 425, 1123 to 1125, 1723 to 1725 Ground electrodes 600 Open collector driver 601 Transistors 602, 603, 606, 733, 833, 1033, 1133, terminal 604 Resistance 605 Current source 610 Driven object 611 Connection point 710, 810, 1010, 1 110, 1310, 1410, 1510, 1610, 1710 Differential open collector drivers 711, 712, 811, 812, 1011, 1012, 1111, 1112, 1311-1 to 1311-4, 1312-1 to 1312-4, 1511 , 1522, 1711, 1712 Differential output terminals 720, 820, 1020, 1120, 1320, 1320-1 to 1320-4, 1420, 1520, 1620, 1720 Mach-Zehnder type optical modulators 723, 724, 824, 825, 1126, 1127, 1423, 1424, 1623, 1624 Input pad 727 Defect 730, 830, 1030, 1130, 1330, 1430, 1530, 1630, 1730 Termination resistor 731, 732, 831, 832, 1031, 1032, 1131 1132 Resistance 734, 735, 833, 834, 1034, 1035, 1134, 1135, 1331-1 to 1331-4, 1332-1 to 1332-4, 1531, 1532, 1731, 1732 Input terminals 826, 827, 1128, 1129 , 1425, 1426, 1625, 1626 Output pads 841-832, 1141-1144 Signal lines 1523-1525, 1533-1535, 1713-1715, 1733-1735 Ground terminals

Claims (6)

An optical device comprising: a differential open collector driver; a Mach-Zehnder optical modulator including a pair of RF electrodes connected to the differential open collector driver; and a termination resistor connected to the Mach-Zehnder optical modulator. A modulator,
The signal lines connecting the pair of differential output terminals of the differential type open collector driver and the input pads of the pair of RF electrodes are equal in length,
The signal lines that connect the output pads of the one set of RF electrodes and the one set of input terminals respectively connected to the one set of resistors of the termination resistor are equal in length,
A center line between the set of RF electrodes, a center line between the input pads of the set of RF electrodes, and a center line between output pads of the set of RF electrodes are substantially parallel to each other. An optical modulator, wherein electrodes are arranged so as to be.   2. The optical modulator according to claim 1, wherein the set of RF electrodes of the optical modulator is arranged in a direction perpendicular to a signal output end face of the differential open collector driver.   3. The optical modulator according to claim 1, wherein the Mach-Zehnder optical modulator is a single-electrode Mach-Zehnder optical modulator.   The optical modulator according to claim 1, wherein the Mach-Zehnder optical modulator is a dual-electrode Mach-Zehnder optical modulator.   5. The optical modulator according to claim 1, wherein an optical waveguide of the Mach-Zehnder optical modulator is made of silicon. The differential open collector driver has two or more sets of differential output terminals,
The Mach-Zehnder type optical modulator includes two or more sets of RF electrodes respectively connected to the two or more sets of differential output terminals,
The termination resistor comprises two or more sets of resistors respectively connected to the two or more sets of RF electrodes,
Two or more sets of RF electrodes of the optical modulator are arranged in a direction perpendicular to the signal output end face of the driver IC,
The optical modulator according to any one of claims 1 to 5, wherein the two or more RF electrodes of the optical modulator have a high-frequency transmission line formed in a linear shape.