Bilayer Silicon Nitride Polarization Rotator With Low Insertion Loss
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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, which limit their performance and application in high optical power environments, and modemux designs add complexity and insertion loss, particularly for TE1 mode light.
Innovation Solution
A polarization rotator using silicon nitride for bus and upper waveguides, with a symmetric design that hybridizes TM0 mode light to TE1 mode via mode hybridization, eliminating the need for separate TE0 and TE1 mode waveguides and reducing device length to 350-400 μm, resulting in low loss and high-power handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If crystalline silicon and poly-silicon are used in PSR, then the device can be manufactured with existing processes, but the insertion loss increases due to intrinsic scattering and absorption
Solution Approach 1:
The patent changes the material parameter from silicon-based to silicon nitride-based waveguides, fundamentally altering the optical loss characteristics while maintaining compatibility with standard semiconductor fabrication processes. This material substitution reduces intrinsic scattering and absorption, directly addressing the insertion loss problem.
Solution Approach 2:
The patent employs a composite structure with silicon nitride as the core waveguide material, combining it with silicon dioxide cladding layers. This composite approach leverages the low-loss properties of silicon nitride while using silicon dioxide for its excellent fabrication compatibility and optical confinement properties.
2Ease of manufacture
If poly-silicon is used in PSR, then the device can be manufactured, but the return loss decreases due to large back scattering
Solution Approach 1:
The patent changes the material parameter from poly-silicon to silicon nitride, which has fundamentally different scattering characteristics. Silicon nitride provides smoother waveguide walls and reduced back scattering, improving return loss while remaining manufacturable with standard processes.
3Ease of manufacture
If poly-silicon is used in PSR, then the device can be manufactured, but the application range is limited due to 2-photon absorption at high optical power
Solution Approach 1:
The patent changes the material parameter from poly-silicon to silicon nitride, which has a much higher damage threshold and does not exhibit 2-photon absorption at telecommunications wavelengths. This enables the PSR to be used in high-power applications such as optical transmitters, significantly expanding the application range.
4Reliability
If a modemux is added to convert TE1 mode to TE0 mode, then the polarization splitting function is completed, but the device length increases to 100-200 μm and complexity increases
Solution Approach 1:
The patent merges the polarization rotation function and the mode conversion function into a single integrated structure. The symmetric coupler design simultaneously achieves TM0 to TE1 rotation and TE1 to TE0 mode conversion, eliminating the need for a separate modemux component and reducing overall device complexity.
Solution Approach 2:
The silicon nitride waveguide structure serves multiple functions: it acts as the polarization rotator, the mode converter, and the polarization splitter all in one. This multi-functional design eliminates the need for separate components and reduces the overall device footprint.
5Reliability
If a modemux is added to convert TE1 mode to TE0 mode, then the polarization splitting function is completed, but the insertion loss increases particularly for TE1 mode
Solution Approach 1:
The patent merges the polarization rotation function and the mode conversion function into a single integrated structure. The symmetric coupler design simultaneously achieves TM0 to TE1 rotation and TE1 to TE0 mode conversion, eliminating the need for a separate modemux component and reducing overall device complexity.
6Reliability
If a modemux is added to convert TE1 mode to TE0 mode, then the polarization splitting function is completed, but the polarization-dependent loss increases
Solution Approach 1:
The patent employs asymmetric coupling between the bus waveguide and the two output waveguides, with different coupling lengths and positions. This asymmetric design enables differential phase shifting that compensates for the different propagation constants of TE0 and TE1 modes, achieving polarization-independent operation and 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 efficient operation across the O-band with minimal insertion loss and reduced device footprint.
Implementation Method 1
a polarization rotator using silicon nitride for bus and upper waveguides, with a symmetric design that hybridizes TM0 mode light to TE1 mode via mode hybridization
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.