Silicon Optical Modulator Trench Structure for Compact Footprint
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Solution Overview
Problem
Conventional silicon modulators for optical communications have large device footprints and limited modulation bandwidth due to small effective index variation of the optical mode, requiring long device lengths for sufficient phase change.
Innovation Solution
A modulator apparatus with a first silicon layer having trenches, a dielectric layer lining the trenches, and a second silicon layer filling them, creating an enlarged surface charge region with both horizontal and vertical portions for enhanced optical confinement, allowing a reduced device footprint and increased modulation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional silicon modulator uses a thin surface charge region to induce phase change, then the modulation mechanism is simple, but the overlap between optical mode and surface charge region is very small, leading to limited effective index variation and requiring very long device length
Solution Approach 1:
The patent transitions from a conventional planar surface charge region to a vertically structured modulator design. The surface charge region is formed at the interface between the silicon layer and the underlying layer, creating a vertical field effect that extends through the silicon thickness. This vertical dimension enhances the overlap between the optical mode and the surface charge region, increasing effective index variation without requiring longer device length.
Solution Approach 2:
The modulator employs a composite structure consisting of a silicon layer combined with an underlying layer (such as silicon dioxide or other dielectric materials). This composite structure creates a well-defined interface for surface charge formation while providing optical confinement. The combination of silicon's high refractive index and the underlying layer's properties enables enhanced modulation efficiency within a compact footprint.
2Speed
If the surface charge region thickness is kept very thin to achieve fast modulation response, then the modulation bandwidth is improved, but the overlap between optical mode and surface charge region becomes very small, reducing modulation efficiency
Solution Approach 1:
By forming the surface charge region vertically at the silicon interface rather than horizontally in a thin planar layer, the patent achieves both thin effective charge region thickness (for fast response) and strong optical mode overlap (for high efficiency). The vertical field penetration through the silicon thickness provides sufficient interaction length while maintaining fast modulation characteristics.
Solution Approach 2:
The patent concentrates the surface charge formation at the specific interface region between silicon and the underlying layer, creating a localized high-field region where modulation occurs. This localized charge region provides strong modulation effect where the optical mode has maximum intensity, while keeping the overall charge region thickness small for fast response.
3Reliability
If a long device length is used to achieve sufficient accumulative phase change, then the phase modulation depth is sufficient, but the device footprint becomes very large
Solution Approach 1:
The vertical interface structure enables strong phase modulation within a short horizontal distance. The surface charge region extends vertically through the silicon thickness, providing continuous phase modulation across the entire optical mode profile. This allows sufficient accumulative phase change to be achieved in a compact device length, reducing the overall footprint.
Solution Approach 2:
The patent changes the effective index modulation parameter by creating a vertical surface charge region that penetrates through the silicon layer. This vertical charge distribution creates a more uniform and stronger effective index change across the optical mode profile, increasing the phase modulation depth per unit length and reducing the required device footprint.
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
The solution enables enhanced optical confinement and reduced modulator footprint by increasing the overlap of the optical mode with the surface charge region, leading to improved modulation efficiency and smaller device size.
Implementation Method 1
A phase shift is induced in the optical mode of light propagating through the capacitor 100 when the refractive index of the silicon is modified, e.g., due to a surface charge produced by applied voltage
Data Source
AI summary
The present invention is a method and an apparatus for optical modulation, for example for use in optical communications links. In one embodiment, an apparatus for optical modulation includes a first silicon layer having one or more trenches formed therein, a dielectric layer lining the first silicon layer, and a second silicon layer disposed on the dielectric layer and filling the trenches.