Silicon Nitride Polarization Splitter-Rotator for High-Power TM-TE Conversion
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Solution Overview
Problem
Conventional polarization management techniques in LiDAR systems struggle to operate under high optical power and have limited power handling capability, as they are difficult to rotate the polarization state of a transverse magnetic (TM)-polarized optical beam to a transverse electric (TE)-polarized optical beam efficiently.
Innovation Solution
An integrated silicon nitride (Si3N4) polarization splitter-rotator (PSR) with a silicon nitride based waveguide, featuring a first segment with tapered widths and a second segment with a silicon nitride adiabatic coupler, is used to split and rotate optical beams, enabling efficient conversion of TM0 mode to TE1 mode and vice versa, while being CMOS-compatible and maintaining low power density and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional polarization management techniques are used, then the device complexity is low, but the power handling capability is limited and two-photon absorption occurs under high optical power
Solution Approach 1:
The patent changes the material parameter from conventional silicon-based waveguides to silicon nitride (Si3N4) waveguides. This material substitution fundamentally alters the optical properties, reducing the nonlinear absorption coefficient and enabling high-power operation without two-photon absorption. The silicon nitride material maintains low loss while providing the necessary polarization rotation functionality at high power levels.
Solution Approach 2:
The patent employs a composite waveguide structure consisting of silicon nitride core with surrounding cladding layers. This composite material approach allows optimization of both the core material for low nonlinear absorption and the cladding materials for mechanical support and optical confinement, achieving high power handling capability while maintaining device functionality.
2Power
If silicon nitride based waveguide is used, then the power handling capability is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The waveguide structure is segmented into distinct layers: silicon nitride core layer, upper cladding layer, and lower cladding layer. Each layer can be fabricated independently using separate deposition processes, allowing optimization of each layer's properties while maintaining overall compatibility with CMOS manufacturing. The segmented structure simplifies the integration of silicon nitride with existing silicon-based photonic platforms.
3Productivity
If adiabatic coupler is used for mode conversion, then the polarization rotation efficiency is improved, but the device length increases
Solution Approach 1:
The patent employs an adiabatic coupler where the coupling between modes evolves dynamically along the waveguide length. The coupling coefficient varies continuously, allowing efficient mode conversion through gradual energy transfer rather than abrupt switching. This dynamic approach maximizes conversion efficiency while minimizing the required interaction length by optimizing the taper profile of the coupler.
Solution Approach 2:
The patent utilizes the cross-sectional dimension of the waveguide by varying the width and height of the silicon nitride core in the adiabatic coupler section. By changing the geometric dimensions in the transverse plane along the propagation direction, the effective index difference between modes is dynamically adjusted, enabling efficient coupling over a compact length.
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 silicon nitride PSR enhances power handling capability and thermal stability, allowing operation under high optical power with improved power threshold and reduced two-photon absorption, thus overcoming the limitations of conventional systems.
Implementation Method 1
the second silicon nitride segment includes a silicon nitride adiabatic coupler. The silicon nitride adiabatic coupler includes a first arm and a second arm. The first arm is extended from the first silicon nitride segment. The first arm includes a first silicon nitride taper with tapered widths along a longitudinal direction.
Implementation Method 2
the first silicon nitride segment including a first layer and a second layer, the first silicon nitride segment having tapered widths along a longitudinal direction. The first section extends from a first end of the first silicon nitride segment to a converging plane with increasing widths, and the second section extends from the converging plane to a second end of the first silicon nitride segment with decreasing widths.
Data Source
AI summary
A polarization splitter-rotator (PSR) is described. The PSR having a silicon nitride based waveguide including a first silicon nitride segment comprising a tapered width in a longitudinal direction and a ridge extending in a transverse direction and an adiabatic coupler coupled with the first silicon nitride segment.