Bilayer Silicon Nitride Polarization Rotator for Low-Loss Mode Conversion
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Solution Overview
Problem
Polarization splitters/rotators (PSRs) in optical receivers suffer from high loss due to materials like crystalline silicon and poly-silicon, leading to limited performance and application in high optical power environments.
Innovation Solution
A polarization rotator using silicon nitride for bus and upper waveguides, employing mode hybridization to convert TM0 mode light to TE1 mode light, reducing device length and loss, and eliminating silicon-based materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If silicon-based materials (crystalline silicon, poly-silicon) are used in PSR, then mode conversion function is achieved, but insertion loss increases due to intrinsic scattering and absorption
Solution Approach 1:
The patent extracts and removes silicon-based materials from the waveguide structure, replacing them with silicon nitride. This eliminates the source of intrinsic scattering and absorption losses while maintaining the mode conversion functionality through a different material platform.
Solution Approach 2:
The patent changes the material parameter from silicon-based to silicon nitride, fundamentally altering the optical properties of the waveguide. This material substitution reduces scattering and absorption coefficients, directly addressing the insertion loss problem while enabling high-power operation.
2Loss of energy
If poly-silicon is used for mode conversion, then TM0 to TE1 conversion is achieved, but return loss deteriorates due to large back scattering
Solution Approach 1:
The patent removes poly-silicon from the structure, eliminating the source of back scattering that degrades return loss. The mode conversion functionality is preserved through silicon nitride waveguide design, maintaining manufacturing feasibility while improving optical performance.
3Device complexity
If silicon-based PSR is used, then polarization splitting function is achieved, but device complexity and footprint increase due to long modemux length
Solution Approach 1:
The patent changes the material composition to silicon nitride, which enables more compact mode converter designs. This material platform allows achieving the same mode conversion function with reduced device length, thereby reducing both footprint and associated insertion losses.
4Loss of energy
If silicon-based materials are used, then PSR functionality is achieved, but polarization-dependent loss increases due to asymmetric mode conversion efficiency
Solution Approach 1:
The patent changes the material parameters by substituting silicon with silicon nitride, which provides more symmetric and efficient mode conversion for both TE and TM modes. This material substitution reduces the asymmetry in conversion efficiency between different polarization modes, thereby reducing PDL.
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 achieves low loss and low polarization-dependent loss, enabling high-power handling and efficient operation across the O-band with a compact design.
Implementation Method 1
employing mode hybridization to convert TM0 mode light to TE1 mode light
Implementation Method 2
A polarization rotator includes a bus waveguide disposed on a first layer of the substrate... a first upper waveguide and a second upper waveguide disposed on a second layer, above the first layer
Data Source
AI summary
A polarization rotator includes a bus waveguide disposed on a first layer having a longitudinal axis, a first end, and a second end, and a first upper waveguide and a second upper waveguide disposed on a second layer, above the first layer, the first upper waveguide and the second upper waveguide widening as the first upper waveguide and the second upper waveguide extend from the first end to the second end. The first upper waveguide and the second upper waveguide may also symmetrically bend toward each other and then away from each other proximate the second end.