Silicon-Photonic TM Rib Modulators for Low Optical Loss and High Bandwidth
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Solution Overview
Problem
Conventional silicon-photonic modulators face challenges in achieving high bandwidth and low drive voltage due to light leakage into the slab portion of the optical waveguide, which limits the doping concentration and increases optical loss.
Innovation Solution
The use of transverse-magnetic (TM) polarized light in rib waveguides with a height greater than the width, reducing light leakage into the slab and allowing for higher doping concentrations, thereby enhancing bandwidth without increasing optical loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional silicon-photonic modulators use standard rib waveguide configurations, then the structure is simple and easy to manufacture, but light leakage into the slab portion limits doping concentration and increases optical loss
Solution Approach 1:
The patent changes the geometric parameters of the rib waveguide, specifically setting the rib height greater than the rib width (e.g., height=220nm, width=150nm), which fundamentally alters the optical mode confinement characteristics. This parameter change enables TM-polarized light to be confined within the rib region, preventing light leakage into the slab and reducing optical loss, while maintaining manufacturing feasibility through standard semiconductor fabrication processes
Solution Approach 2:
The patent applies different doping concentrations to different regions of the waveguide structure. The rib region receives higher doping concentration (e.g., 1×10^19 to 1×10^20 atoms/cm³) compared to the slab region, creating local quality differences that enhance carrier confinement in the rib while managing optical loss. This localized doping strategy allows high doping levels where needed without uniformly increasing optical absorption throughout the entire structure
2Productivity
If higher doping concentration is applied to reduce series resistance and increase bandwidth, then bandwidth improves, but optical loss increases due to light leakage into the slab
Solution Approach 1:
By changing the waveguide geometry parameters (height > width) and polarization mode (to TM), the patent enables the system to tolerate higher doping concentrations without proportional increases in optical loss. The modified waveguide structure confines the optical mode within the highly-doped rib region, allowing bandwidth enhancement through high doping (e.g., 1×10^19 to 1×10^20 atoms/cm³) while maintaining acceptable optical loss levels
Solution Approach 2:
The patent segments the doping concentration across different spatial regions: the rib region is heavily doped (high carrier concentration for low series resistance and high bandwidth) while the slab region maintains lower doping. This segmentation allows the system to achieve high bandwidth through localized high doping in the rib without suffering proportional optical loss increases, since the optical mode is confined to the rib region
3Speed
If TM-polarized light is used with rib height greater than width, then light confinement is improved and bandwidth increases, but the waveguide geometry becomes more complex
Solution Approach 1:
The patent employs specific geometric parameters where the rib height exceeds the rib width (e.g., height=220nm, width=150nm, slab thickness=90nm). This parameter configuration creates strong vertical confinement for TM-polarized light modes while maintaining horizontal confinement through the rib structure. The resulting mode confinement enables high bandwidth operation with acceptable geometric complexity that can be fabricated using standard semiconductor processes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration results in a silicon-photonic modulator with higher bandwidth and lower drive voltage by confining light primarily within the rib waveguide, reducing series resistance, and maintaining low optical loss.
Implementation Method 1
each of the at least one optical waveguide is configured as a rib waveguide that includes a rib arranged on a slab
Implementation Method 2
The at least one optical waveguide is configured to propagate quasi-transverse-magnetic (quasi-TM) polarized light
Implementation Method 3
modulating a phase difference between quasi-TM polarized light in the first optical waveguide and quasi-TM polarized light in the second optical waveguide
Implementation Method 4
at least one electrode configured to apply at least one electric field to the quasi-TM polarized light in the at least one optical waveguide
Implementation Method 5
a Mach-Zehnder interferometer including the at least one optical waveguide
Data Source
AI summary
A silicon-photonic optical modulator includes at least one optical input and at least one optical waveguide that is connected to the at least one optical input. The at least one optical waveguide is configured to propagate quasi-transverse-magnetic (quasi-TM) polarized light, where each of the at least one optical waveguide is configured as a rib waveguide that includes a rib arranged on a slab. The silicon-photonic optical modulator also includes at least one electrode configured to apply at least one electric field to the quasi-TM polarized light in the at least one optical waveguide. In some implementations, a height of the rib waveguide is greater than 0.85 λ/n, where λ is a free-space wavelength of light and n is a refractive index of silicon in the silicon-photonic optical modulator, and a width of the rib waveguide is greater than a thickness of the slab.