CN-121978852-A - Silicon light modulator and traveling wave electrode thereof

CN121978852ACN 121978852 ACN121978852 ACN 121978852ACN-121978852-A

Abstract

The invention discloses a silicon optical modulator and a traveling wave electrode thereof, relates to the technical field of optical communication, and aims to solve the problem that the modulation efficiency of the second half section of the electrode is low due to the fact that radio frequency signals of the existing silicon optical modulator are attenuated along a transmission path. The traveling wave electrode is divided into first and second sections in the transmission direction. In the first section, the distance between the central signal line and the ground line is kept constant to ensure high impedance matching feed-in of the signals, and in the second section, the distance between the central signal line and the ground line is gradually reduced along the transmission direction. Through the non-uniform geometric gradual change design, the local space is compressed passively at the second half section of the radio frequency voltage attenuation, and the local electric field intensity is maintained forcibly in a mode of sacrificing part impedance, so that the effective phase modulation is regenerated by the second half section of the waveguide which is disabled originally. According to the invention, on the premise of not increasing the process complexity, the performance redistribution of the impedance and the electric field is realized, and the overall modulation efficiency and the signal extinction ratio of the modulator are obviously improved.

Inventors

YANG LINGGANG
ZHANG YUJIA
SHI HUIQING
ZHU CHUNHUA

Assignees

可川光子技术(苏州)有限公司

Dates

Publication Date: 20260505
Application Date: 20260403

Claims (10)

1. The traveling wave electrode is used for a silicon optical modulator and is characterized by comprising a central signal line and at least one ground wire, wherein the central signal line and the ground wire extend along the transmission direction of radio frequency signals; Along the transmission direction, the traveling wave electrode at least comprises a first section and a second section which are continuous; within the first section, a spacing between the center signal line and the ground line is maintained at a constant value; In the second section, a distance between the center signal line and the ground line is gradually reduced along the transmission direction.
2. The traveling wave electrode according to claim 1, wherein the traveling wave electrode adopts a ground-signal-ground coplanar waveguide structure, and the ground line comprises a first ground line and a second ground line symmetrically distributed on both sides of the central signal line.
3. The traveling wave electrode according to claim 2, wherein a physical width of the center signal line is kept constant in both the first section and the second section, and the ground line is inclined to the side of the center signal line in the second section so that the pitch is gradually reduced.
4. A travelling wave electrode according to claim 3, wherein in the second section the pitch tapers in a linear progression with distance in the direction of transmission.
5. The traveling wave electrode according to claim 4, wherein said pitch Along with the coordinates along the direction of transmission The variation of (2) satisfies the following formula: Wherein, the For the length of the first section to be the same, Being a constant value of the spacing within the first section, A slope that is inclined inward for the ground line and satisfies 。
6. The traveling wave electrode according to claim 1 or 2, characterized in that in the first section the physical width of the central signal line is kept constant, and in the second section the ground line is kept straight extending in the transmission direction, the physical width of the central signal line being gradually increased so that the pitch is passively compressed.
7. The traveling wave electrode according to claim 6, wherein in said second section, a physical width of said central signal line gradually increases in a law of linear gradation with a distance in said transmission direction.
8. The traveling wave electrode of claim 7, wherein the physical width of the center signal line Along with the coordinates along the direction of transmission The variation of (2) satisfies the following formula: Wherein, the For the length of the first section to be the same, Is a constant value of the physical width of the center signal line within the first section, Slope coefficients that widen outwardly for the center signal line.
9. The traveling wave electrode according to any one of claims 1 to 5, wherein in the second section, the ground line is inclined to the side of the central signal line to narrow the pitch, and a physical width of the central signal line is also continuously narrowed in the transmission direction to compensate for a characteristic impedance drop due to the narrowing of the pitch.
10. A silicon optical modulator, comprising: A silicon-based substrate layer; the waveguide core layer is positioned above the silicon-based substrate layer, and a semiconductor doping area is arranged in the waveguide core layer and forms a PN junction; The traveling wave electrode of any one of claims 1 to 9, located above the waveguide core for receiving externally fed high-speed radio frequency signals and applying an alternating electric field to the optical signals in the waveguide core.

Description

Silicon light modulator and traveling wave electrode thereof Technical Field The invention relates to the technical field of optical communication, in particular to a silicon optical modulator and a traveling wave electrode thereof. Background The silicon optical modulator is used as a core active device in an optical communication and optical interconnection system, bears the key task of converting high-speed electric signals and loading the high-speed electric signals onto an optical carrier, and is a physical hub for realizing high-efficiency electro-optical conversion. In practical applications, silicon optical modulators are commonly used due to their compatibility with CMOS processes and high integration. However, as the requirements of modern communications on data transmission rate and bandwidth are continuously increasing, how to further increase the modulation efficiency of the silicon optical modulator, improve the extinction ratio and reduce the driving power becomes a core technical challenge to be solved in the field. As shown in fig. 1, the prior art silicon optical modulator generally adopts a planar traveling wave electrode structure. The device comprises, from bottom to top, in cross-sectional configuration, a silicon-based substrate layer 10, a buried oxide layer 20, a waveguide core layer 30, an isolation layer 40, and a top electrode structure 50. Specifically, the bottommost silicon substrate layer 10 mainly provides solid physical support for the whole chip, the buried oxide layer 20 is tightly attached to the silicon substrate layer, vertical limitation of an optical field is achieved by utilizing the material characteristics of the buried oxide layer to prevent optical signals from leaking to the bottom substrate, the waveguide core layer 30 is a core functional area of the whole device, optical signals are transmitted in the channel, meanwhile, the position of semiconductor doped areas (such as a P area and an N area) is located, an external radio frequency electric field interacts with the optical signals to achieve phase modulation, the isolation layer 40 covered above the waveguide mainly plays the dual roles of electric insulation and optical protection to avoid direct additional absorption loss of top metal on the optical signals, and finally, the electrode structure 50 located at the topmost part is responsible for receiving the externally fed high-speed radio frequency signals and applying an alternating electric field to the waveguide core layer area below so as to drive the whole modulation process. As can be further seen in conjunction with the top view of fig. 2, the top electrode structure 50 demonstrates a classical G-S-G (ground-signal-ground) coplanar traveling wave electrode configuration. This configuration consists of three parallel metal lines, centered on a central signal line 51 having a specific physical width W, and symmetrically distributed on both sides of the central signal line are a first ground line 52 and a second ground line 53, with a specific spacing G maintained between them. The design of the width W and the spacing G directly determines the impedance characteristics of the electrodes and the distribution of the local electric field. In normal operation, a high-speed radio frequency signal is fed from the input end of the traveling wave electrode and propagates along the transmission direction (assumed to be the Z-axis direction, left to right as shown in fig. 2) of the optical signal to achieve phase modulation. However, the rf signal is transmitted over the electrode with serious physical attenuation problems. Especially considering the semiconductor doping conditions of the waveguide region and the presence of the PN junction, the PN junction produces an additional electromagnetic absorption effect on the transmission path of the radio frequency signal, which makes the signal more rapidly lost than in pure metal or conventional coplanar waveguides (CPWs). For example, a high frequency signal having an initial amplitude of 3 volts at the input may have a significant attenuation in signal strength after about 0.5 mm along the electrode, and the amplitude of the radio frequency signal may have substantially attenuated to zero when transmitted to the end of about two mm. This sharp attenuation along the transmission path results in a core technical disadvantage in that the local electric field strength generated in the latter half of the row waveguide electrode is insufficient to produce an effective phase change of the optical signal in the waveguide core due to the very low amplitude of the radio frequency voltage. This not only causes the modulation efficiency of the entire modulator to exhibit serious discontinuities in the longitudinal direction, but also causes the latter half of the electrode to be a largely superfluous design. The ineffective second half structure cannot not only contribute to modulation efficiency, but also causes extra li