Sub-wavelength Grating Polarization Converter for Phase Coherence
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Solution Overview
Problem
Existing polarization converters in photonic integrated circuits face challenges in maintaining polarization independence due to phase mismatches and the need for adaptive control mechanisms, which are limited by fabrication tolerances and rotational conversion capabilities.
Innovation Solution
A polarisation converter with a sub-wavelength grating structure that extends from the waveguide core, featuring a top section and lateral section with reducing width, enables efficient conversion of arbitrary polarization to a supported mode without adaptive control, using effective refractive index engineering and resonant excitation of interface waves to maintain phase and frequency coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarization splitters separate two orthogonal polarizations into different paths, then polarization separation is achieved, but phase mismatch occurs due to different effective optical paths
Solution Approach 1:
The patent merges the separation and recombination paths by using a polarization-maintaining beam splitter that directs orthogonal polarizations through different spatial paths while ensuring they recombine at the same output port with controlled phase relationship, eliminating the phase mismatch problem inherent in traditional polarization splitters
Solution Approach 2:
The patent introduces a polarization-maintaining beam splitter as an intermediary component that mediates between the input polarization and the waveguide, enabling controlled separation and recombination of orthogonal polarizations while maintaining phase coherence through its specific optical path design
2Adaptability or versatility
If adaptive polarization controllers are used to track and recover from polarization fluctuations, then polarization independence is improved, but device complexity and fabrication tolerance requirements increase
Solution Approach 1:
The patent implements a self-service mechanism where the polarization diversity receiver automatically tracks and compensates for polarization fluctuations through inherent optical path design and signal processing, eliminating the need for external adaptive polarization controllers and their associated complexity
Solution Approach 2:
The patent creates a universal polarization-independent receiver that can handle any input polarization state through fixed optical components and signal processing algorithms, replacing the need for specialized adaptive control mechanisms while maintaining polarization independence
3Reliability
If the two polarization paths are made identical to avoid phase differences, then phase coherence is maintained, but fabrication tolerances make this impossible to achieve
Solution Approach 1:
The patent deliberately designs asymmetric optical paths for the two orthogonal polarizations that compensate for fabrication tolerances, using different physical path lengths that result in equal effective optical paths when accounting for typical manufacturing variations, thereby maintaining phase coherence without requiring identical physical structures
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 allows for efficient polarization conversion and rotation without phase mismatch, adapting any incoming polarization to a single guided mode, enhancing the performance and reliability of photonic integrated circuits by eliminating the need for adaptive control mechanisms and reducing the footprint of polarization converters.
Implementation Method 1
using effective refractive index engineering and resonant excitation of interface waves to maintain phase and frequency coherence
Implementation Method 2
The proposed PSR consists of a taper integrated SWG coupler combined with a partially-etched waveguide between the input and output strip waveguides to make the input transverse-electric (TE) mode couple and convert to the output transverse-magnetic (TM) mode at the cross port
Implementation Method 3
using effective refractive index engineering and resonant excitation of interface waves to maintain phase and frequency coherence
Data Source
Figure 1~2
Figure 3(A)~4
Figure 5~6
AI summary
A polarisation converter (100) comprising a substrate (102) and a waveguide core (104) provided on the substrate. The waveguide core having a top surface (106) and a side surface (108). The polarisation converter (100) comprises a sub-wavelength grating structure (110) extending from the waveguide core, the sub-wavelength grating structure comprising a top section (112) extending outwardly from the top surface of the waveguide core and a lateral section (114) extending laterally from the side surface of the waveguide core and from the top section. A lateral width of one of the top section and the lateral section reduces along a length of the waveguide core.