TWI708984B - Semiconductor Mach-Zehnder optical modulator and IQ modulator - Google Patents

Abstract

The phase modulation electrode circuit of the semiconductor Mach-Zehnder optical modulator is formed along the waveguide. The output-side lead line is bent in a direction crossing the extending direction of the waveguide in the plane of the dielectric layer, and is connected to a terminating resistor. The output-side lead line is formed with a certain width corresponding to the desired impedance, and the width is narrower than the certain width only in the curved part and the part that crosses the waveguide.

Description

Semiconductor Mach-Zehnder optical modulator and IQ modulator Invention field

The present invention relates to a semiconductor Mach-Zehnder optical modulator that modulates optical signals with electrical signals, and an IQ modulator that uses a semiconductor Mach-Zehnder optical modulator.

In order to meet the needs of increased communication traffic, high-speed optical modulators corresponding to high-level optical modulation methods are required. In particular, multi-value optical modulators using digital coherent technology play a significant role in realizing high-capacity transceivers exceeding 100Gbps. In these multi-value optical modulators, in order to add independent signals to the amplitude and phase of the light, a MZ: Mach-Zehnder interference-type zero-chirp (zero chirp) driven optical modulator.

In recent years, the miniaturization and low driving voltage of optical transmission modules have become issues, and efforts have been made to research and develop semiconductor MZ optical modulators that can be miniaturized and low driving voltage (see Non-Patent Document 1, Non-Patent Document) 2). 8A and 8B show an example of a conventional semiconductor MZ optical modulator. Fig. 8A is a plan view of the semiconductor MZ optical modulator, and Fig. 8B is a cross-sectional view taken along line c-c' of Fig. 8A.

In Figure 8A and Figure 8B, 101 is the semiconductor MZ optical modulation The input waveguide of the filter, 102 is the output waveguide, 103 is an optical splitter that splits the light wave propagating in the input waveguide 101 to the two waveguides 104 and 105, and 106 is the light wave propagating through the two waveguides 104 and 105 toward the output The waveguide 102 multiplexes the optical multiplexer. 109 and 110 are coplanar striplines, and 111 and 112 are used to apply voltage to the electrodes of the waveguides 104 and 105.

In FIG. 8B, 113 is an n-InP layer, 114 is a lower cladding layer composed of InP, 115 is a semiconductor core layer for light wave propagation, 116 is an upper cladding layer composed of InP, and 117 is an SI-InP substrate.

The input waveguide 101, the output waveguide 102, the optical splitter 103, the waveguides 104, 105, and the optical multiplexer 106 constitute an MZ interferometer. In the MZ interferometer, a voltage is applied to the waveguides 104 and 105, whereby the refractive index changes in the semiconductor core layer 115 by the electro-optical effect, and as a result, the phase of light changes. At this time, by imparting a potential difference to the waveguides 104 and 105, the interference state of the light in the optical multiplexer 106 is changed, and the light can be modulated (that is, the output light of the output waveguide 102 sometimes becomes on, sometimes Become off).

In the case where one of the two coplanar strip lines 109 and 110 is connected to the input electrical signal (S), the other is connected to the reference potential or ground (G), which is an SG configuration.

The microwaves propagating on the coplanar strip lines 109 and 110 are applied to the waveguides 104 and 105 through the electrodes 111 and 112. The electrodes 111, 112 and the coplanar strip lines 109, 110 integrally form a traveling wave electrode. That is, the following electrode structure is intended: as far as possible, the speed of the light waves propagating in the waveguides 104 and 105 is consistent with the speed of the microwave propagating in the above-mentioned traveling wave electrode, and the light waves and The phase matching of the microwave improves the electrode structure of the modulation bandwidth. As long as there is no loss of microwaves and the speed matching conditions of light waves and microwaves are fully satisfied, the modulation bandwidth will become infinite.

However, in fact, due to microwave loss or impedance mismatch, microwave reflection and phase shift between light waves and microwaves will occur. Therefore, the modulation bandwidth is limited for these reasons.

As described above, since the upper coating layer 116, the semiconductor core layer 115, and the lower coating layer 114 exist under the electrodes 111 and 112, there is a certain element capacitance. That is, in FIG. 8A, the electrodes 111 and 112 add capacitance to the coplanar strip lines 109 and 110.

In other words, by optimally designing the number and spacing of the electrodes 111, 112, and the contact length to the waveguide 104, 105, the additional capacitance of the coplanar strip lines 109, 110 can be freely designed, and the total The impedance matching of the noodle strip lines 109 and 110 and the speed of the microwave are designed to be arbitrary values. In addition, in order to reduce the loss of microwaves and achieve a wider frequency band, the coplanar strip lines 109 and 110 are designed to be thicker than 100 μm.

As mentioned above, in the semiconductor MZ optical modulator with a capacitive load structure, by designing the optimal amount of additional capacitance for the coplanar strip lines 109 and 110, the speed matching of light waves and microwaves can be improved, and the speed matching of light waves and microwaves can also be improved. Acquiring impedance matching to 50Ω, as a result, high-speed optical modulation becomes possible.

Although the semiconductor MZ optical modulator of the configuration shown in Fig. 8A and Fig. 8B is single-phase drive, if the connection with the differential drive driver and power consumption are considered, it is advisable to set the optical modulator side as Differential drive type (for example, GSSG configuration) (see Non-Patent Document 3).

Furthermore, unlike the single-phase drive type, the differential drive type optical modulator is excellent in the suppression of crosstalk, so it is advantageous in realizing a polarization multiplexed IQ modulator integrated on 1 chip of. Considering the layout of the modulator chip, in order to connect the signal line to the driver and the terminal resistor, a certain part must be bent to make the signal line reach the chip end. However, when the optical modulator is a differential drive type, as in the case of a single-phase drive IQ modulator disclosed in Non-Patent Document 4, there is the following problem: The formed signal line is bent at approximately a right angle, and a large phase difference occurs between the two signal lines forming a differential pair, which deteriorates the differential characteristics and excites the noise component that is the common mode, which deteriorates the transmission characteristics of the modulator. Subject.

FIG. 9 is a plan view of a conventional single-phase drive type IQ modulator disclosed in Non-Patent Document 4. The single-phase drive type IQ modulator is composed of the following: input waveguide 200; 1×2 multimode interference (MMI: MultiMode Interference) coupler 201, which divides the light propagating on the input waveguide 200 into two systems; waveguide 202 , 203, waveguide the two lights divided by the 1×2MMI coupler 201; 1×2MMI coupler 204, divide the light propagating in the waveguide 202 into 2 systems; 1×2MMI coupler 205, will propagate The light splitting in the waveguide 203 is a two-system; waveguides 206 and 207 are used to waveguide the two lights split by the 1×2 MMI coupler 204; the waveguides 208 and 209 are split by the 1×2 MMI coupler 205 The two light beams are guided; the signal lines 210~213 are used to apply voltage to the waveguides 206~209; the electrodes 214~217 are used to apply the voltage supplied from the signal lines 210~213 to the waveguides 206~209; the phase adjustment electrode 218~ 221, used to adjust the propagation in the waveguide 206~209 The phase of the modulated signal light; 2×1 MMI coupler 222 will combine the signal light propagating in the 2 systems of waveguides 206 and 207; 2×1 MMI coupler 223 will propagate the signal of 2 systems in the waveguide 208, 209 Optical multiplexing; waveguide 224, which guides the output light of the 2×1 MMI coupler 222; waveguide 225, which guides the output light of the 2×1 MMI coupler 223; phase adjustment electrodes 226, 227, to adjust the propagation in the waveguide 224, The phase of the signal light of 225; the 2×1 MMI coupler 228, which combines the signal light propagating in the two systems of waveguides 224 and 225; and the output waveguide 229. One end of the signal lines 210 to 213 is connected to the drivers 230 and 231, and the other end of the signal lines 210 to 213 is connected to a terminating resistor (not shown).

The reason why it becomes difficult to bend the signal line in the case of a differential drive is that in the case of a semiconductor MZ optical modulator with a capacitive load structure, the width of the signal line is about 100μm thick, so if the 2 A signal line will generate an electrical length difference between the two signal lines. With the electrical length difference, the frequency characteristics of the differential mode will be degraded and the common mode that is the cause of the noise will be excited. And mixed mode (mixed mode). Therefore, it is necessary to have a structure that does not excite the common mode and does not degrade the frequency characteristics of the differential mode, and can bend the signal line of the differential configuration.

In addition, as in Non-Patent Document 4, a modulator for single-phase drive may be connected to the driver and set as differential (SS) drive. However, due to the following doubts, it is less suitable: In this case, since the common mode cannot be propagated in the high-frequency line of the semiconductor MZ optical modulator, the common mode will be completely between the driver and the semiconductor MZ optical modulator. Reflection and become the cause of crosstalk etc. Because of this, it becomes the cause of the decrease in frequency characteristics and the driving force of the driver.

[Advanced Technical Literature] [Non-Patent Literature]

[Non-Patent Document 1] L. Morl et al., "A travelling wave electrode Mach-Zehnder 40 Gb/s demultiplexer based on strain compensated GaInAs/AlInAs tunnelling barrier MQW structure", 1998 International Conference on Indium Phosphide and Related Materials, pp .403-406, 1998

[Non-Patent Document 2] H.N. Klein et al., "1.55μm Mach-Zehnder Modulators on InP for optical 40/80 Gbit/s transmission networks", OFC2006, pp.171-173, 2006

[Non-Patent Document 3] K. Prosyk et al., "Travelling Wave Mach-Zehnder Modulators", IPRM2013, MoD3-1, 2013

[Non-Patent Document 4] S. Lange et al., "Low Power InP-Based Monolithic DFB-Laser IQ Modulator With SiGe Differential Driver for 32-GBd QPSK Modulation", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.34, NO.8, APRIL 15, 2016

[Summary of the invention]

The present invention was made to solve the above-mentioned problems, and its purpose is to provide The following semiconductor Mach-Zehnder optical modulators and IQ modulators, that is, in the semiconductor Mach-Zehnder optical modulator with a differential drive type capacitive load structure, it is necessary to connect the terminal resistor at the output end of the signal line In the high-frequency wiring of the conventional structure, the characteristic degradation caused by the phase difference of the differential mode in the bent part that is a problem in the conventional structure, and the excitation of the common mode accompanying the bent part are suppressed, and the high-frequency characteristic of the modulator can be solved Deteriorated, semiconductor Mach-Zehnder optical modulator and IQ modulator with excellent transmission characteristics.

The semiconductor Mach-Zehnder optical modulator of the present invention is provided with: the first and second arm waveguides are formed on a substrate; the first input-side lead-out line is formed on the dielectric layer on the substrate, and one end is supplied Modulation signal input; the second input side lead-out circuit is formed on the aforementioned dielectric layer adjacent to the first input side lead-out circuit, and one end of which is for the signal input complementary to the aforementioned modulation signal; first, second The phase modulation electrode circuit is formed on the dielectric layer, and one end is connected to the other end of the first and second input-side lead-out circuits respectively; the first and second output-side lead-out circuits are formed on the dielectric layer And one end is connected to the other end of the first and second phase modulation electrode circuits; the first and second electrodes apply the modulation signals propagating to the first and second phase modulation electrode circuits respectively To the first and second arm waveguides; the first ground line, along the propagation direction of the modulation signal, is formed on the first input side lead-out line, the first phase modulation electrode line, and the first output side On the dielectric layer on the outer side of the lead-out circuit; the second ground wire is formed along the propagation direction of the modulation signal and formed on the second input-side lead-out circuit and the second phase modulation electrode line Circuit, on the dielectric layer outside the second output-side lead-out circuit; and a terminating resistor connected to the other end of the first and second output-side lead-out circuits, and the first and second phase modulation electrode circuits It is formed along the first and second arm waveguides, and the first and second output-side lead lines are bent in a direction that intersects the extension direction of the first and second arm waveguides in the plane of the dielectric layer, and Connect with the aforementioned terminal resistance.

According to the present invention, the first and second phase modulation electrode lines are formed along the first and second arm waveguides, and the first and second output side lead lines are directed toward the surface of the dielectric layer and the first and second arms The extending direction of the waveguide is bent and connected to the terminating resistor. This solves the problem of the deterioration of high frequency characteristics in the conventional structure, and realizes a semiconductor Mach-Zehnder optical modulator with a wide frequency band and excellent connection with the driver. .

10, 10a, 101, 200: input waveguide

11, 14, 15, 204, 205: 1×2MMI coupler

12, 13, 16, 17, 18, 19, 42, 43, 104, 105, 202, 203, 206, 207, 208, 209, 224, 225: waveguide

20, 21, 22, 23: input side lead wire

24, 25, 26, 27: phase modulation electrode circuit

28, 29, 30, 31: output side lead wire

32, 33, 34, 35, 111, 112, 214, 215, 216, 217: electrodes

36, 37, 38, 39, 44, 45, 218, 219, 220, 221, 224, 225: phase adjustment electrode

40, 41, 46, 222, 223, 228: 2×1 MMI coupler

47, 102, 229: output waveguide

48, 49, 50: ground wire

51, 52, 53, 54: terminal resistance

55, 56: Wire

60, 113: n-InP layer

61, 114: Lower coating layer

62, 115: Semiconductor core layer

63, 116: Upper coating layer

64, 117: SI-InP substrate

65: Dielectric layer

70, 71: Melody

72, 73: wedge

80: Ground electrode

81, 82, 83, 84: ground vias

85, 86: Line

103: Optical Demultiplexer

106: Optical combiner

109, 110: Coplanar strip line

201:1×2 multimode interference coupler (1×2MMI coupler)

210, 211, 212, 213: signal line

230, 231: Drive

I: I modulation signal

:與I調變訊號互補的訊號

: A signal complementary to the I modulation signal

Q: Q modulation signal

:與Q調變訊號互補的訊號

: A signal complementary to the Q modulated signal

W1: certain width

W2: width

λ _eff : wavelength in the tube

Fig. 1 is a plan view showing the configuration of an IQ modulator according to a first embodiment of the present invention.

Fig. 2 is a cross-sectional view of the IQ modulator according to the first embodiment of the present invention.

Fig. 3 is an enlarged plan view of a part of a lead-out line on the output side of the IQ modulator of the first embodiment of the present invention.

4 is a cross-sectional view of the curved portion of the lead-out line on the output side of the IQ modulator of the first embodiment of the present invention.

Fig. 5 is a plan view showing a wire connecting ground wires in the first embodiment of the present invention.

Figure 6 is a diagram showing the connection between ground wires in the first embodiment of the present invention A plan view of a ground via.

Fig. 7 is a plan view showing the configuration of an IQ modulator according to a second embodiment of the present invention.

Fig. 8A is a plan view showing the configuration of a conventional semiconductor Mach-Zehnder light modulator.

Fig. 8B is a cross-sectional view showing the configuration of a conventional semiconductor Mach-Zehnder light modulator.

Fig. 9 is a plan view showing the configuration of a conventional single-phase drive type IQ modulator.

[Form to implement the invention] [First Embodiment]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a plan view showing the configuration of an IQ modulator according to a first embodiment of the present invention. The IQ modulator is equipped with: input waveguide 10; 1×2 MMI coupler 11, which divides the light propagating in the input waveguide 10 into 2 systems; waveguides 12 and 13, to the 2 by 1×2 MMI coupler 11 The strip of light is waveguided; 1×2MMI coupler 14 separates the light propagating in the waveguide 12 into 2 systems; 1×2 MMI coupler 15 divides the light propagating in the waveguide 13 into 2 systems; waveguides 16, 17 ( The first and second arm waveguides) are used to guide the two lights divided by the 1×2 MMI coupler 14; the waveguides 18 and 19 (the first and second arm waveguides) are paired by the 1×2 MMI coupler 15 The two split-wave lights are waveguided; the input-side lead-out lines 20 and 21 (the first and second input-side lead-out lines) are used to apply the I modulation signal to the waveguides 16, 17, and are composed of conductors; the input side Lead lines 22, 23 (No. 1, The second input side lead-out circuit) is used to apply the Q modulated signal to the waveguides 18 and 19, and is composed of conductors; the phase modulation electrode circuits 24, 25 (the first and second phase modulation electrode circuits), and The lead lines 20 and 21 on the input side are connected and are composed of conductors; the phase modulation electrode lines 26 and 27 (the first and second phase modulation electrode lines) are connected to the lead lines 22 and 23 on the input side and are connected by conductors. Composition; output side lead lines 28, 29 (first and second output side lead lines), connected to phase modulation electrode lines 24, 25, and are composed of conductors; output side lead lines 30, 31 (first and second lead lines) 2 output-side lead circuit), connected to phase modulation electrode circuits 26, 27, and composed of conductors; electrodes 32, 33 (first and second electrodes), I supplied from phase modulation electrode circuits 24, 25 The modulated signal is applied to the waveguides 16, 17 and is composed of conductors; and the electrodes 34, 35, the Q modulated signals supplied from the phase modulation electrode lines 26, 27 are applied to the waveguides 18, 19, and are composed of conductors .

Furthermore, the IQ modulator is equipped with: phase adjustment electrodes 36~39 for adjusting the phase of the modulated signal light propagating in the waveguides 16~19, and is composed of conductors; 2×1 MMI coupler 40, will propagate Optically multiplex the signals of the 2 systems of waveguides 16, 17; 2×1 MMI coupler 41, optically multiplex the signals propagating in the 2 systems of waveguides 18, 19; Waveguide 42, waveguide the output light of the 2×1 MMI coupler 40 ; Waveguide 43, to guide the output light of the 2×1MMI coupler 41; Phase adjustment electrodes 44, 45 to adjust the phase of the signal light propagating in the waveguides 42, 43, and are composed of conductors; 2×1MMI coupler 46. Optically multiplex the signals propagating in the two systems of waveguides 42, 43; output waveguide 47; ground wire 48, arranged on the input side lead line 20, the phase modulation electrode line 24, and the output side lead line 28 The ground wire 49 is arranged on the input side lead line 21, the phase modulation electrode line 25 and the output side lead line 29, and the input side lead line 22, the phase modulation electrode line 26 and the output Between the side lead lines 30 and are composed of conductors; the ground line 50 is arranged on the input side lead line 23, the phase modulation electrode line 27, and the output side lead line 31 outside, and is composed of conductors; and terminal The resistors 51 to 54 are connected to the ends of the lead lines 28 to 31 on the output side.

Fig. 2 is a cross-sectional view of a-a' of the IQ modulator of this embodiment. In Figure 2, 60 is the n-InP layer, 61 is the lower cladding layer composed of InP, 62 is the semiconductor core layer, 63 is the upper cladding layer composed of InP, 64 is the SI-InP substrate, and 65 is formed on The dielectric layer above the n-InP layer 60.

As shown in FIG. 2, the input-side lead lines 20-23, the phase modulation electrode lines 24-27, the output-side lead lines 28-31, and the ground lines 48-50 are formed on the dielectric layer 65.

Next, these high-frequency line patterns will be described in further detail. The high-frequency line pattern of this embodiment is based on a GSSG (Ground-Signal-Signal-Ground) differential coplanar strip line composed of two signal lines and two ground lines formed on the dielectric layer 65. The aforementioned dielectric layer 65 is composed of a material with a low dielectric constant.

However, in this embodiment, a semiconductor MZ optical modulator with an I modulation signal as input and a semiconductor MZ modulator with a Q modulation signal as input are arranged on the substrate, and are made into I modulation. The high-frequency circuit pattern of the MZ optical modulator and the semiconductor on the Q modulated signal side The high-frequency line pattern of the MZ optical modulator shares the central ground 49.

The signal line is formed by three parts of the input side lead lines 20-23, the phase modulation electrode line 24-27 part, and the output side lead lines 28-31. The entire part becomes the acquired impedance. Matched differential line structure (GSSG structure). Due to the differential circuit configuration, the modulator can be driven by a differential input signal (differential driver) with high energy efficiency.

Lead out the line 20 on the input side, input the I modulation signal from the differential driver (not shown) formed on the SI-InP substrate 64, and input the complementary I modulation signal (bar I) from the differential driver Lead wire 21 to the input side. Similarly, the line 22 is drawn on the input side, the Q modulated signal is input from the differential driver, and the complementary Q modulated signal (bar Q) is input from the differential driver to the lead line 23 on the input side.

The respective ends of the output-side lead lines 28 to 31 are terminated via terminating resistors 51 to 54.

One end of the ground wires 48-50 (the left end in FIG. 1) is connected to the ground of the differential driver.

1×2MMI coupler 14, waveguides 16, 17, input-side lead lines 20, 21, phase modulation electrode lines 24, 25, output-side lead lines 28, 29, electrodes 32, 33, and 2×1MMI coupler 40 The semiconductor MZ optical modulator on the signal side of the I modulation signal. The semiconductor MZ light modulator responds to the I modulation signal applied to the waveguides 16 and 17 from the electrodes 32 and 33 to modulate the phase of the light propagating in the waveguides 16 and 17.

Similarly, 1×2 MMI coupler 15, waveguide 18, 19, Input-side lead lines 22, 23, phase modulation electrode lines 26, 27, output-side lead lines 30, 31, electrodes 34, 35, and 2×1 MMI coupler 41 constitute a semiconductor MZ optical modulator on the Q modulation signal side . The semiconductor MZ light modulator modulates the phase of the light propagating through the waveguides 18 and 19 in response to the Q modulated signals applied to the waveguides 18 and 19 from the electrodes 34 and 35.

The 2×1 MMI coupler 40 optically multiplexes the modulated signals propagating in the waveguides 16 and 17. The 2×1 MMI coupler 41 optically multiplexes the modulated signals propagating in the waveguides 18 and 19. By applying voltage to the phase adjustment electrodes 44 and 45, the phase can be adjusted so that the signal light on the I side output from the 2×1 MMI coupler 40 and the signal light on the Q side output from the 2×1 MMI coupler 41 are in phase The difference becomes 90 degrees.

The 2×1 MMI coupler 46 optically combines the signal light propagating on the I side of the waveguide 42 and the signal propagating on the Q side of the waveguide 43 to obtain an optical IQ modulated signal. In this way, in this embodiment, an IQ modulator can be realized.

Next, the features of the present embodiment will be described in order. The phase modulation electrode lines 24-27 are arranged in parallel with the waveguides 16-19 constituting the semiconductor MZ optical modulator.

The input-side lead wires 20-23 connected with the phase modulation electrode circuits 24-27 must be formed on the same straight line with the phase modulation electrode circuits 24-27. In addition, it is desirable to have a structure without any bending. The reason is that in the lead-out lines 20 to 23 on the input side, if there is a bend in the differential line structure, the phase difference caused by the bend may be affected by: common mode is generated, and the differential transmission characteristics associated with it are large. Deterioration, resonance generation, and signal reflection in the curved part, that is, return to the driver side, which greatly deteriorates the driving force of the driver 化.

In addition, if the lead wires 20 to 23 on the input side are bent, the line becomes longer and the transmission loss increases compared to the straight line. In addition, bending loss occurs, so the high-frequency characteristics of the differential signal will deteriorate. In particular, the loss in the lead-out lines 20-23 on the input side is directly related to the degradation of the frequency modulation bandwidth. Therefore, it is important to minimize the loss in the lead-out lines 20-23 on the input side in order to achieve broadband.

In order to minimize the loss of the input-side lead lines 20-23, not only the input-side lead lines 20-23 and the phase modulation electrode lines 24-27 must be formed on the same straight line as described above, but also the waveguides 16-19 must be formed. Optimized the configuration of the lead wires 20-23 on the input side and the phase modulation electrode wires 24-27.

For example, if the configuration as in this embodiment is adopted, the length of the lead wires 20 to 23 on the input side can be minimized. In this embodiment, the input waveguide 10 and the 1×2 MMI coupler 11 are formed as the light propagation direction of the input waveguide 10 (up and down direction in FIG. 1) and the light input and output direction of the 1×2 MMI coupler 11 (up and down direction in FIG. 1) The extending direction of the waveguide 16-19 (the left-right direction in Fig. 1) is orthogonal, and the 1×2 MMI couplers 14, 15 and 2×1 MMI couplers 40, 41, 46 are formed into 1×2 MMI couplers 14, 15 And the light input and output directions of the 2×1 MMI couplers 40, 41, 46 (the left-right direction in FIG. 1) are the same direction with respect to the extending direction of the waveguides 16-19. In this way, the waveguide pattern has an L-shaped layout.

According to such a layout, the length of the lead-out lines 20 to 23 on the input side can be made 700μm or less, which is consistent with the literature "N.Kono et al., Compared with the conventional structure described in "Compact and Low Power DP-QPSK Modulator Module with InP-Based Modulator and Driver ICs", OFC2013, OW1G.2, 2013, it can be shortened by about 1mm.

Next, the phase modulation electrode lines 24 to 27 will be described. The phase modulation electrode lines 24 to 27 and the electrodes 32 to 35 connected thereto have a differential capacitive load structure (GSSG configuration) that is excellent in impedance matching and the speed matching of microwave and light waves. That is, it is arranged as follows: ground wire 48; phase modulation electrode circuit 24, input with I modulation signal; electrode 32, supplied with I modulation signal from phase modulation electrode circuit 24; electrode 33, input with A signal complementary to the I modulation signal (bar I); phase modulation electrode line 25, which supplies the signal to electrode 33; ground line 49; phase modulation electrode line 26, which has a Q modulation signal input; electrode 34, which is supplied The Q modulation signal from the phase modulation electrode circuit 26; the electrode 35, which inputs a signal complementary to the Q modulation signal (bar Q); the phase modulation electrode circuit 27, which supplies the signal to the electrode 35; and the ground wire 50.

By optimally designing the number, spacing, and length of the electrodes 32~35 of the capacitive load part, the additional capacitance of the phase modulation electrode circuit 24~27 can be freely designed, so the phase modulation electrode circuit can be changed The impedance of 24~27 and the speed of the microwave propagating on the phase modulation electrode lines 24~27 are designed to be arbitrary values. The electrodes 32~35 of the aforementioned capacitive load part are branched from the main line, that is, the phase modulation electrode lines 24~27. Periodically formed.

Therefore, it becomes an electrode structure that can realize impedance matching and the speed matching of microwave and light waves at the same time, and can realize the wideband operation of the modulator above 30 GHz. In addition, in order for the semiconductor MZ optical modulator to perform broadband operation, it must be designed so that the electrodes 32~35 can be regarded as wave-shaped electrodes. Therefore, the electrodes 32~35 of each signal must be regarded as a distributed constant. The period of λ _{eff in} the tube is set to less than 1/4 of the lowest limit of the wavelength λ _{eff in} the tube, ideally below 1/8. The wavelength λ _eff in the tube is the maximum frequency propagating in the phase modulation electrode circuit 24~27 and the electrode 32~35 The in-tube wavelength of the modulated signal.

Since the electrodes 32 to 35 are periodically arranged along the extending direction of the waveguides 16 to 19, the Bragg frequency must also be considered in general. However, in this embodiment, since the Bragg frequency is higher than the frequency corresponding to the above-mentioned tube wavelength, the period of the electrodes 32 to 35 of each signal is set as the tube wavelength λ _eff . If the above conditions are met at least 1/4 or less (ideally 1/8 or less), the Bragg frequency does not have to be considered.

Next, the output-side lead lines 28 to 31 will be described. Fig. 3 is an enlarged plan view of the output-side lead lines 28 to 31. The output-side lead lines 28 to 31 are in the plane of the dielectric layer 65 (in the paper surface of FIG. 3) and the extension direction of the waveguides 16 to 19 (the input-side lead lines 20 to 23 and the phase modulation electrode lines 24 to 27 extend The direction) intersecting the direction (the orthogonal direction in this embodiment) is curved. Since the high-frequency line pattern of this embodiment is a GSSG differential line structure as described above, the bending method of the output-side lead lines 28 to 31 becomes important.

For example, set the width of lines 28 to 31 on the output side If the width of the impedance is arbitrary, and the output-side lead lines 28 to 31 are directly bent at right angles with this width, signals will be generated between the two differentially formed lines 28 and 29 and between the lines 30 and 31. The electrical length is different, and a large phase difference occurs. Due to the phase difference and the asymmetry of the bending, the high frequency characteristics of the common mode and the differential mode will be degraded, and the frequency modulation bandwidth will be degraded and the transmission characteristics will be degraded, so it is not suitable.

Therefore, in this embodiment, the output-side lead lines 28 to 31 are formed with a certain width W1 corresponding to the desired impedance, and are made to be closer to the phase modulation from the curved part (70, 71 in FIG. 3) In the wedge-shaped portion (72, 73 in Fig. 3) with a length of about 50 μm from the position of the electrode lines 24 to 27, the width of the output-side lead-out lines 28 to 31 gradually narrows, and the output-side lead-out line 28 in the curved parts 70 and 71 The width of ~31 is narrower than the aforementioned certain width W1. In addition, the distance between the output-side lead lines 28 and 29 and the distance between the output-side lead lines 30 and 31 are set to be greater than the distance between the phase modulation electrode lines 24 and 25, and the phase modulation electrode lines 26 and 27 The distance between is short. Furthermore, in the curved parts 70 and 71, the distance between the output-side lead line 28 and the ground 48, the distance between the output-side lead line 29 and the ground 49, the distance between the output-side lead line 30 and the ground 49, And the distance between the output side lead wire 31 and the ground wire 50 is made shorter than the distance between the output side lead wire and the ground wire in other parts. However, at this time, the width of the ground wires 48 to 50 is different from the width of the output-side lead wires 28 to 31, and the curved portion and the straight portion have the same width. The reason is to make the co-modeling good and to ensure crosstalk characteristics.

In this way, in this embodiment, for the wavelength of the curved part, the line width is narrowed only in a small enough (1/4 or less) minute interval. Therefore, regardless of whether it is differential mode or common mode, even if the output side lead lines 28 to 31 are made high impedance, the output side lead lines 28 to 31 can be bent without performance degradation caused by impedance mismatch. .

In the curved parts 70 and 71, the width of the output-side lead lines 28 to 31 is made narrow, so that the electrical length difference and phase difference between the output-side lead lines 28 and 29, and the electrical length of the output-side lead lines 30 and 31 can be reduced. The length difference and the phase difference are sufficiently reduced, so that the occurrence of common mode and the deterioration of the high-frequency characteristics of the differential mode can be suppressed.

In this embodiment, compared with the conventional structure in which the width of the lead-out line on the output side is wired as it is, the transmission characteristic (Sdd21) can be improved, for example, by about 0.5 dB at 50 GHz. In other words, the display can be changed from Sdc21, which converts the differential mode to the common mode (excitation of the common mode), is improved by, for example, 10 dB.

In addition, in order to prevent the deterioration of the common mode characteristics, it is preferable to minimize the asymmetry of the structure and keep the width W2 of the ground wire 48-50 constant.

Furthermore, a clothoid is used as the trajectory of the edges of the curved portions 70 and 71 of the output-side lead lines 28 to 31, thereby further improving the high-frequency characteristics. If the Crosseau curve is used, for example, the differential reflection characteristic (Sdd11) can be improved by several dB compared with a normal curve.

In this embodiment, as described above, the widths of the output-side lead lines 28 to 31 in the curved portions 70 and 71 are made narrower than the constant width W1 of the linear portion where impedance matching has been achieved. However, when the transmission distance of the curved part is too long, it will be caused by narrowing the width of the lead lines 28 to 31 on the output side. Due to the influence of impedance mismatch, the curved parts 70 and 71 may become signal reflection points, which may degrade the high-frequency characteristics. In order to suppress the influence of impedance mismatch, the propagation length of the curved portions 70 and 71 should be less than 1/4 of the wavelength λeff in the tube, and if possible, should be less than 1/8. In addition, from the viewpoint of shortening the length, the propagation length of the wedge portions 72 and 73 is preferably 50 μm or less.

Furthermore, basically, the output-side lead lines 28 to 31 are formed on the dielectric layer 65. However, as shown in FIG. 4 showing the cross-sectional view taken along line b-b' of FIG. 3, by bending the output-side lead-out lines 28 to 31, it occurs that the output-side lead-out lines 28 to 31 are formed on the waveguides 16-19. In other words, compared with benzocyclobutene (BCB), which is an example of the low-dielectric material constituting the dielectric layer 65, it traverses a semiconductor with a dielectric constant of approximately 4 times. The line width on the electrical body layer 65 is formed on the waveguides 16-19, and the impedance of the output-side lead lines 28-31 will drop significantly, which may cause impedance mismatch.

Therefore, even in the crossing places other than the curved parts 70 and 71 (74 in FIGS. 3 and 4), the width of the output-side lead lines 28 to 31 can be made to correspond to that of the curved parts 70 and 71. The certain width W1 for the desired impedance matching is narrower, and the distance between the output side lead lines 28 and 29, the distance between the output side lead line 28 and the ground line 48, and the output side lead line 29 and the ground line 49 The distance is shortened.

With such a structure, the output-side lead lines 28 to 31 can cross the waveguides 16 to 19, which greatly reduces the impedance of the output-side lead lines 28 to 31 and reduces the possibility of impedance mismatch. but, The structure of the output-side lead lines 28~31 and the ground wires 48, 49 in the crossing as above is not an essential component of the present invention. The output-side lead lines 28~31 cross the waveguide 16~19 In the case of a small area, since the influence of impedance mismatch is not visible, this structure is not required.

Furthermore, in this embodiment, compared with the phase modulation electrode lines 24-27, the distance between the output-side lead lines 28 and 29 and the distance between the output-side lead lines 30 and 31 are shortened, and It can be made into a structure with strong electrical sealing, which can prevent electromagnetic waves from leaking toward the substrate and substrate resonance.

In addition, the ends of the output-side lead lines 28 to 31 are connected to terminal resistors 51 to 54 satisfying the desired differential mode impedance and common mode impedance, and are differentially terminated.

In addition, as shown in Fig. 5, actually, it is advisable to provide wires 55 and 56 electrically connecting the ground wires 48-50. The wire 55 connects the ground wires 48 and 49. The wire 56 connects the ground wires 49 and 50. Without the wires 55 and 56, the potential of the ground wires 48-50 will be unstable and swing, so resonance will occur at any frequency dependent on the propagation length. Therefore, it is difficult to implement a broadband modulator. In order to suppress this resonance, it is advisable to set the ground wire 48 with a period short enough for the signal wavelength, that is, a period less than 1/4 to 1/8 of the wavelength λ _eff in the tube, along the propagation direction of the signal. Connecting wires 55, 56 between ~50.

In the example of FIG. 5, the wires 55 and 56 are provided only where the lines 28 to 31 are drawn on the output side, but the same applies to the places where the lines 20 to 23 and the phase modulation electrode lines 24 to 27 are drawn on the input side. On the ground line 48~50 Conductors 55, 56 are arranged between.

By arranging wires 55 and 56, the potentials of the ground wires 48-50 on both sides of the lead wires 20-23 on the input side, the phase modulation electrode wires 24-27, and the lead wires 28-31 on the output side can be stabilized, and The resonance of the potential of the ground wire 48-50 is suppressed, and a broadband modulator can be realized. When the wires 55 and 56 are arranged at a period longer than 1/4 to 1/8 of the wavelength λ _eff in the tube, although the amount of ripple can be reduced, the resonance of the potential of the ground wire 48 to 50 cannot be completely suppressed.

Also, as shown in FIG. 6, the ground wires 48 to 50 can be connected through the ground electrode 80 provided on the back surface of the semiconductor substrate (SI-InP substrate 64) and the ground through holes 81 to 84 made by processing the semiconductor substrate. By connecting indirectly, the potential of the ground wires 48-50 can be stabilized. The ground via 81 connects the ground wire 48 and the ground electrode 80. The ground vias 82 and 83 connect the ground wire 49 and the ground electrode 80. The ground via 84 connects the ground wire 50 and the ground electrode 80.

In FIG. 6, in order to make the structure easy to understand, a line 85 connecting a pair of ground through holes 81, 82 is drawn. The ground through holes 81, 82 are 1/4 to 1/8 or less of the wavelength λ _eff in the tube. It is periodically set at the ground 48 and 49 in a period of time. Similarly, draw a line 86 connecting a pair of ground through holes 83 and 84. The ground through holes 83 and 84 are periodically placed on the ground at a period of 1/4 to 1/8 or less of the wavelength λ _eff in the tube. Line 49, 50.

As with FIG. 5, in FIG. 6, grounding through holes 81 to 84 are provided only at the output side lead lines 28 to 31, but regarding the input side lead lines 20 to 23 and phase modulation electrode lines 24 to 27 It is also advisable to set ground through holes 81 to 84 in the ground wires 48 to 50.

In addition, in the example of FIG. 6, although the ground electrode 80 is formed on the back surface of the semiconductor substrate, a dielectric layer may be formed on the structure shown in FIGS. 1 to 4, and a ground electrode may be formed on the dielectric layer 80.

[Second embodiment]

Next, the second embodiment of the present invention will be described. FIG. 7 is a plan view showing the structure of the IQ modulator of the second embodiment of the present invention, and the same structure as in FIG. 1 is attached with the same reference numeral. In the first embodiment, the light propagation direction of the input waveguide 10 is orthogonal to the extending direction of the waveguides 16 to 19 (the left-right direction in FIG. 1).

In contrast, in this embodiment, light enters the input waveguide 10 a from a direction parallel to the extending direction of the waveguides 16 to 19, and the input waveguide 10 a is bent slightly forward of the connection with the 1×2 MMI coupler 11. In this way, the waveguide pattern is composed of a U-shaped layout. Other configurations are as described in the first embodiment.

In this embodiment, the length of the lead-out lines 20 to 23 on the input side can also be made 700 μm or less, and is consistent with the document "N.Kono et al.," Compact and Low Power DP-QPSK Modulator Module with InP-Based Modulator and Driver ICs", OFC2013, OW1G.2, 2013" can reduce the length by about 1mm compared to the conventional structure described in "Driver ICs".

In addition, in the first and second embodiments, the waveguides 16 to 19 of the semiconductor MZ optical modulator are constructed as follows: on the SI-InP substrate 64, a lower coating layer 61 composed of InP is laminated in this order, and a non-doped Between the non-doped semiconductor core layer 62 and the upper cladding layer 63 composed of InP structure. The same applies to the other waveguides 10, 10a, 12, 13, 42, 43, 47.

The semiconductor core layer 62 functions as an optical waveguide layer, and is composed of materials such as InGaAsP and InGaAlAs, for example. The semiconductor core layer 62 can also be composed of a single-composition quaternary mixed crystal bulk layer and multiple quantum well layers. In addition, a structure forming a light confinement layer can also be used as the semiconductor core layer 62. The aforementioned light confinement layer is above and below the multiple quantum well layer. The energy gap is larger than that of the multiple quantum well layer and compared with the lower coating layer 61 and the upper coating layer. 63, the energy gap is small.

The energy gap wavelength of the bulk layer and the multiple quantum well layer of the quaternary mixed crystal is set to: in the light wavelength used, the electro-optic effect will effectively work, and will not become a problem of light absorption.

From a characteristic point of view, when the desired impedance line has been designed, since the electrode loss can be reduced, the dielectric layer 65 is preferably made of low dielectric constant materials such as organic materials such as polyimide and BCB. composition. In addition, the present invention is not limited to InP series materials, and for example, a material series compatible with GaAs substrates may be used.

Either the upper coating layer 63 and the lower coating layer 61 may be an n-type semiconductor and the other may be a p-type semiconductor.

Alternatively, both the upper coating layer 63 and the lower coating layer 61 may be n-type semiconductors, and the second coating layer may be inserted between the upper coating layer 63 and the semiconductor core layer 62, or between the lower coating layer 61 and the semiconductor core layer 62. 3p-type coating layer structure.

[Industrial use possibility]

The present invention can be applied to a semiconductor Mach-Zehnder optical modulator that modulates optical signals with electrical signals.

10: Input waveguide

11, 14, 15:1×2MMI coupler

12, 13, 16, 17, 18, 19, 42, 43: waveguide

20, 21, 22, 23: output side lead wire

24, 25, 26, 27: phase modulation electrode circuit

28, 29, 30, 31: output side lead wire

32, 33, 34, 35: electrodes

36, 37, 38, 39, 44, 45: Phase adjustment electrode

40, 41, 46: 2×1MMI coupler

47: output waveguide

48, 49, 50: ground wire

51, 52, 53, 54: terminal resistance

I: I modulation signal

:與I調變訊號互補的訊號

: A signal complementary to the I modulation signal

Q: Q modulation signal

:與Q調變訊號互補的訊號

: A signal complementary to the Q modulated signal

Claims (9)

A semiconductor Mach-Zehnder optical modulator, which is characterized by having: first and second arm waveguides formed on a substrate; a first input-side lead-out line formed on the dielectric layer on the substrate, and wherein One end is for modulating signal input; the second input side lead-out circuit is formed on the aforementioned dielectric layer adjacent to the first input side lead-out circuit, and one end is used for signal input complementary to the aforementioned modulation signal; The second phase modulation electrode circuit is formed on the dielectric layer, and one end is connected to the other end of the first and second input-side lead-out circuits respectively; the first and second output-side lead-out circuits are formed on the aforementioned dielectric On the electrical body layer, one end of which is respectively connected to the other end of the first and second phase modulation electrode lines; the first and second electrodes will propagate the modulation signals of the first and second phase modulation electrode lines Applied to the first and second arm waveguides respectively; the first ground wire is formed along the propagation direction of the modulation signal on the first input side lead-out line, the first phase modulation electrode line, and the first output The second ground line is formed on the second input side lead line, the second phase modulation electrode line, and the second output along the propagation direction of the modulation signal. On the aforementioned dielectric layer outside the side lead-out circuit; and The terminating resistor is connected to the other end of the first and second output side lead lines, the first and second phase modulation electrode lines are formed along the first and second arm waveguides, and the first and second The output-side lead line is bent in a direction that intersects the extending direction of the first and second arm waveguides in the plane of the dielectric layer, and is connected to the terminating resistor. Such as the semiconductor Mach-Zehnder optical modulator of claim 1, wherein the aforementioned first and second output-side lead lines are formed with a certain width corresponding to the desired impedance, and only in the curved part, the width and the line The distance is narrower than the aforementioned certain width. For example, the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, wherein the first and second input side lead lines and the first and second phase modulation electrode lines are formed on the same straight line. For example, the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, which is further provided with a plurality of wires or ground vias for electrically connecting the aforementioned first and second ground wires, and the aforementioned plurality of wires or ground vias are The wavelength in the tube is set at a period less than 1/4 of the wavelength in the tube, and the wavelength in the tube is the wavelength in the tube of the modulation signal of the maximum frequency propagating in the first and second phase modulation electrode lines. For example, the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, wherein the first and second output-side lead lines, except for the aforementioned curved part, have a width that is greater than the aforementioned constant across the first and second arm waveguides Narrow width, The distance between the first and second output side lead lines is shorter than the distance between the first and second phase modulation electrode lines, and the ground line is in a state where the width is constant. The curved portion of the output-side lead-out line and the portion where the first and second output-side lead-out lines traverse the first and second arm waveguides have a short distance from the first and second output-side lead-out lines. For example, the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, wherein the plane trajectory of the edge of the curved part of the first and second output side lead-out lines is drawn by the Crossau curve. For example, in the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, wherein the first and second ground wires of the portions where the first and second output sides lead out the wires always maintain a constant circuit width. For example, the semiconductor Mach-Zehnder optical modulator of claim 1 or 2, wherein the first and second electrodes are respectively along the extending direction of the first and second arm waveguides, and are less than 1/4 of the wavelength in the tube A plurality of wavelengths are arranged periodically, and the wavelength in the tube is the wavelength in the tube of the modulation signal of the maximum frequency propagating in the first and second phase modulation electrode lines. An IQ modulator, characterized in that it is provided with two semiconductor Mach-Zehnder optical modulators of any one of claims 1 to 8, and is provided with: an input waveguide formed on the aforementioned substrate; and a demultiplexer formed On the aforementioned substrate, the light propagating on the aforementioned input waveguide is split into two systems for the input of the aforementioned two semiconductor Mach-Zehnder optical modulators, The aforementioned semiconductor Mach-Zehnder optical modulator with an I modulation signal as input and the aforementioned semiconductor Mach-Zehnder optical modulator with a Q-modulated signal as input are arranged on the substrate. The input waveguide and the aforementioned sub The wave device is formed such that the light propagation direction of the input waveguide and the light input and output direction of the demultiplexer cross the extension directions of the first and second arm waveguides of the two semiconductor Mach-Zehnder optical modulators. .

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