CN-121978853-A - Silicon optical modulator and waveguide core layer thereof

Abstract

The invention discloses a silicon optical modulator and a waveguide core layer thereof, relating to the technical field of optical communication, the silicon optical modulator comprises a waveguide core layer and semiconductor doped regions arranged in the waveguide core layer, and is characterized in that the semiconductor doped regions are asymmetrically distributed about a geometric center line. Specifically, the difference of light absorption sensitivity of P type doping and N type doping is utilized, so that the middle doped P+ region is more greatly toward the center than the N+ region, or only the P+ region is widened toward the center on one side. On the premise of not obviously increasing the optical loss, the structure greatly reduces the microwave loss of the PN junction and obviously improves the photoelectric response bandwidth.

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

20260408

Claims (10)

1. 1. A waveguide core for a silicon optical modulator extending in an optical signal transmission direction, the waveguide core having a cross-section with a geometric centerline, comprising: The semiconductor doped region is arranged in the waveguide core layer and forms a PN junction, and at least comprises a lightly doped P region and a lightly doped N region which are distributed on two sides of the geometric center line, and a medium doped P+ region and a medium doped N+ region which are respectively positioned on the outer sides of the lightly doped P region and the lightly doped N region; The semiconductor doped region is asymmetrically distributed about the geometric center line, and the middle doped P+ region widens towards the geometric center line.
2. 2. The waveguide core according to claim 1, wherein the asymmetric distribution is such that the intermediate doped P+ region and the intermediate doped N+ region each widen in the direction of the geometric centerline, and the intermediate doped P+ region is closer to the geometric centerline than the intermediate doped N+ region is to the geometric centerline.
3. 3. The waveguide core according to claim 1, wherein said asymmetric distribution is such that only said moderately doped P+ region widens towards said geometric centerline, the boundary between said lightly doped P region and said moderately doped P+ region moves towards said geometric centerline, and the physical width of said lightly doped N region remains unchanged.
4. 4. A waveguide core according to any of claims 1 to 3, wherein the semiconductor doped region further comprises a heavily doped p++ region and a heavily doped n++ region located outside the moderately doped p+ region and the moderately doped n+ region, respectively, the outer boundaries of the heavily doped p++ region and the heavily doped n++ region remaining unchanged.
5. 5. A silicon optical modulator comprising a waveguide core according to any of claims 1 to 4.
6. 6. The silicon optical modulator of claim 5, further comprising a traveling wave electrode above the waveguide core layer for receiving externally fed radio frequency signals, wherein the traveling wave electrode adopts a ground-signal-ground coplanar waveguide structure and comprises a central signal line and ground wires symmetrically distributed on both sides of the central signal line.
7. 7. The silicon optical modulator of claim 6 wherein the traveling wave electrode comprises at least a continuous first section along the radio frequency signal transmission direction, the central signal line being configured to have a constant initial width within the first section.
8. 8. The silicon optical modulator of claim 7, wherein the traveling wave electrode is further connected to a second section continuously after the first section in the transmission direction of the radio frequency signal, and wherein the physical width of the center signal line is gradually increased in the transmission direction in the second section while the ground line is kept straight to be extended so that a local distance between the center signal line and the ground line is compressed and narrowed passively to maintain a local electric field strength after the radio frequency signal is attenuated.
9. 9. The silicon optical modulator of claim 8 wherein the physical width of the central signal line increases linearly and gradually along the transmission direction.
10. 10. The silicon optical modulator of claim 9, 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: When (when) When (1): When (when) When (1): Wherein, the For the length of the first section to be the same, For the length of the second section to be the same, To be the initial width for improving the front end characteristic impedance and satisfy , Slope coefficients that widen outwardly for the center signal line.

Description

Silicon optical modulator and waveguide core layer thereof Technical Field The invention relates to the technical field of optical communication, in particular to a silicon optical modulator and a waveguide core layer 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 being largely employed by virtue of 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 a silicon-based substrate layer 10, an oxygen-buried layer 20 and a waveguide core layer 30 from bottom to top in sequence from the sectional structure. Specifically, the bottommost silicon substrate layer 10 mainly provides a firm 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 realized 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, the optical signals are transmitted in the channel, and meanwhile, the position of semiconductor doped areas (such as a P area and an N area) is also located, and an external radio frequency electric field interacts with the optical signals to realize phase modulation. V1 and trapezoid structures connected with the semiconductor doped region are through holes, V2 is also a through hole, and rectangular structures such as M1, M2 and the like connected with the through holes are metal wiring layers. As shown in fig. 2, in conventional silicon optical modulator waveguide core designs, symmetrical semiconductor doping structures are commonly employed. Specifically, with the geometric center line of the waveguide as a symmetry axis, a lightly doped P region and an N region, a medium doped P+ region and an N+ region as transition, and a heavily doped P++ region and an N++ region which are positioned at the outermost side and used for connecting electrodes are sequentially distributed at two sides. This symmetrical structure is easy to implement in standardized fabrication in early silicon photochip designs and is capable of maintaining basic photoelectric conversion functions at a certain modulation rate. However, as optical communication networks evolve towards ultra-high rates and ultra-large capacities, systems place more stringent demands on the optoelectronic bandwidth of silicon optical modulators, and the performance bottlenecks of existing symmetrical doped structures are increasingly apparent. Under the above-mentioned symmetrical doping architecture, to further increase the bandwidth of the silicon optical modulator, there is a physical contradiction that is not tunable. First, in the dynamic modulation process, when an external driving rf signal is applied to the PN junction, since the carrier concentration span between the heavily doped region (p++ or n++) and the central lightly doped region (P or N) is extremely large, such severe concentration variation may generate an extremely large potential difference and voltage drop at the semiconductor interface. For example, an otherwise nominal 1 volt input drive voltage may be lost at 0.2 volts. The inefficient dissipation of this voltage is essentially due to the extremely high intrinsic radio frequency losses inside the PN junction. In order to reduce the microwave loss and the radio frequency loss and improve the bandwidth, an intuitive solution thinking is to widen the P+ region and the N+ region at two sides towards the geometric center line direction of the waveguide at the same time, so that the original partial lightly doped region is replaced, and the transmission dissipation path of radio frequency signals is shortened. However, this conventional symmetrical retraction approach toward the center causes a fatal technical disadvantage in that the light absorption loss increases sharply. Therefore, the radio frequency loss cannot be effectively reduced by simple symmetrical structure adjustment on the premise of not increasing the light absorption loss, which becomes a key technical problem for restricting the breakthrough of the bandwidth of the silicon optical modulator to a