Silicon Electro-Optic Modulator With Lateral Extensions
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Solution Overview
Problem
Existing electro-optic phase modulators, particularly those of the SISCAP type, face challenges such as increased dimensions and beam confinement issues due to the need for significant waveguide width to prevent transverse electric mode rotation and ensure proper beam confinement, which complicates their design and functionality.
Innovation Solution
A silicon electro-optic phase modulator design featuring a waveguide with a doped single-crystal silicon strip and a polysilicon strip of opposite conductivity type, separated by an insulating interface layer, with lateral extensions and a silicon-germanium layer, allowing for better beam confinement and reduced dimensions through optimized etching and doping processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the waveguide width is increased to prevent transverse electric mode rotation and ensure proper beam confinement, then beam confinement is improved, but the device dimensions increase
Solution Approach 1:
The patent changes the geometric parameters of the waveguide structure by introducing lateral extensions that protrude from the main waveguide body. These extensions have optimized dimensions (width and length) that enhance beam confinement through improved mode matching and reduced diffraction effects, allowing for better optical performance without proportionally increasing the overall device footprint.
Solution Approach 2:
The patent adds lateral extensions that protrude from the sides of the main waveguide, utilizing the lateral dimension to improve beam confinement. This dimensional approach allows the extensions to interact with the optical mode from the sides, enhancing confinement without requiring a uniform increase in waveguide width throughout the entire device structure.
2Reliability
If lateral extensions are added to improve beam confinement, then optical performance is improved, but device complexity increases
Solution Approach 1:
The waveguide structure is segmented into a main waveguide body and separate lateral extensions. This segmentation allows each component to be independently optimized and fabricated using standard CMOS processes, reducing overall manufacturing complexity while achieving improved beam confinement through the combined structure.
Solution Approach 2:
The lateral extensions are designed with rounded corners and smooth transitions to the main waveguide body, avoiding sharp angles that would cause mode scattering. This curved geometry simplifies the optical mode profile and reduces fabrication complexity while maintaining effective beam confinement.
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 proposed modulator achieves better beam confinement and reduced dimensions compared to traditional designs, enabling more efficient phase shifting and improved optical performance without rotating transverse electric modes, thus enhancing the modulator's efficiency and compactness.
Implementation Method 1
The charge density in portions 17 and 19 is modified by applying a potential difference between contacts 21 and 22. This results in a modification of the optical index of the waveguide and thus in a phase shift of the laser beam propagating in the waveguide.
Implementation Method 2
A portion 17 of strip 15 covers a portion 19 of strip 13, portions 17 and 19 being separated from each other by an interface layer made of a dielectric material (not shown), which forms a capacitor.
Implementation Method 3
The assembly of strips 13 and 15 is encapsulated in a dielectric material (not shown) having a smaller optical index than strips 13 and 15. Portions 17 and 19 thus form a waveguide 23 capable of propagating a laser beam along a direction orthogonal to the plane of the sheet.
Data Source
AI summary
An E/O phase modulator may include a waveguide having an insulating substrate, a single-crystal silicon strip and a polysilicon strip of a same thickness and doped with opposite conductivity types above the insulating substrate, and an insulating interface layer between the single-crystal silicon strip and polysilicon strip. Each of the single-crystal silicon strip and polysilicon strip may be laterally continued by a respective extension, and a respective electrical contact coupled to each extension.