Dual-Layer Polarization Splitter Rotator for Low-Reflection Mode Conversion
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Solution Overview
Problem
Current PSR designs suffer from high back reflections and large insertion losses due to the use of silicon, which complicates meeting return loss requirements and leads to inconsistent performance.
Innovation Solution
A PSR design with two layers separated by a dielectric layer, where the first layer is made of a lower refractive index material and the second layer of a higher refractive index material, with a controlled gap and thickness to minimize back reflections, allowing TM mode rotation without confinement in the second layer and enabling efficient TE mode conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon (especially poly-silicon) is used in PSR design, then efficient hybridization and mode rotation are achieved, but insertion loss increases and return loss deteriorates
Solution Approach 1:
The patent employs a composite structure combining silicon waveguide core with silicon nitride cladding layers. The silicon core provides efficient TM-to-TE mode conversion through strong optical confinement and hybridization, while the silicon nitride cladding layers reduce back reflections and insertion losses by providing impedance matching and reducing mode coupling to radiation modes. This composite material approach resolves the contradiction by leveraging the strengths of each material while mitigating their individual weaknesses.
2Reliability
If silicon (especially poly-silicon) is used in PSR design, then efficient hybridization and mode rotation are achieved, but return loss increases
Solution Approach 1:
The silicon nitride cladding layers act as intermediary layers between the silicon waveguide core and the surrounding environment. These intermediate layers provide gradual impedance transition, reducing abrupt refractive index changes that cause back reflections. The cladding layers mediate the optical field distribution, allowing efficient mode rotation in the silicon core while minimizing harmful back reflections at the waveguide interfaces.
3Reliability
If silicon is used in PSR design, then mode rotation is achieved, but performance variation increases
Solution Approach 1:
The patent utilizes precise control of structural parameters including cladding layer thicknesses, waveguide dimensions, and material compositions to optimize performance. By carefully designing these geometric and material parameters, the system achieves consistent mode rotation efficiency across fabrication tolerances. The parameter optimization ensures that the mode conversion ratio and back reflection levels remain stable, reducing performance variation while maintaining high mode rotation capability.
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 design achieves low back reflections and reduced insertion loss, facilitating efficient mode conversion and minimizing the need for additional material transitions, thereby enhancing performance and fabrication ease.
Implementation Method 1
a rotator that includes a first layer comprising a first waveguide formed from a lower refractive index material and a second layer comprising a second waveguide formed from a higher refractive index material where the rotator is configured to receive an optical signal including a first optical mode at an input of the first waveguide and, at an end of the rotator, the optical signal is primarily confined in the first waveguide and is rotated into a second optical mode
Data Source
AI summary
Embodiments herein describe a PSR that includes a rotator with two layers that are separated by a dielectric layer. A first layer of the rotator includes a first waveguide formed from a lower refractive index material (e.g., SiN) while a second layer of the rotator includes a second waveguide formed from a higher refractive index material (e.g., Si). An optical signal, which can include two optical modes (e.g., TE and TM modes), is then introduced into the first layer where the TM mode is rotated. At the end of the rotator, the first waveguide (which is the same waveguide that received the optical signal) includes the optical signal which is now in the same optical mode. That is, one of the optical modes is rotated so that the light is the same type of optical mode (e.g., TE).