Mode-Evolution Compound Converter for Photonic Integrated Circuits
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Solution Overview
Problem
Conventional optical converters for polarization and spatial mode conversion in photonic integrated circuits face challenges such as polarization-dependent effects, sensitivity to fabrication variations, and the need for complex combinations of mode-evolution and mode-coupling converters, which compromise bandwidth and fabrication simplicity.
Innovation Solution
A mode-evolution-based compound converter system using multiple mode-evolution converters, including polarization and spatial converters, to achieve broadband and fabrication-tolerant conversion of optical signals, simplifying the fabrication process and maintaining the benefits of mode-evolution devices like larger bandwidth and tolerance to variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If mode-coupling converters are used for polarization and spatial mode conversion, then the device length is reduced, but the converters become sensitive to fabrication variations and wavelength dependent
Solution Approach 1:
The invention segments the conversion process into two independent sequential stages: first a polarization converter transforms TM0 to TE1 mode, then a spatial mode converter transforms TE1 to TE0 mode. This segmentation allows each stage to be optimized independently, with both stages using mode-evolution converters that are fabrication-tolerant, thus achieving short length without sacrificing manufacturing precision.
Solution Approach 2:
The invention changes the operational parameters by using mode-evolution converters instead of mode-coupling converters. Mode-evolution converters rely on gradual geometric variation rather than abrupt junctions, making them insensitive to fabrication variations and wavelength changes, thereby resolving the contradiction between short length and fabrication tolerance.
2Manufacturing precision
If mode-evolution converters are used for polarization and spatial mode conversion, then the bandwidth and fabrication tolerance are improved, but the device length increases
Solution Approach 1:
By segmenting the conversion into two independent mode-evolution converters working in sequence, the invention achieves complete polarization and spatial mode conversion while keeping each converter section compact. The segmented approach allows optimization of each stage's length independently, reducing the total length compared to a single monolithic mode-evolution converter.
3Length of moving object
If compound converters combining mode-evolution and mode-coupling converters are used, then the device length is reduced, but the fabrication complexity increases due to different epitaxial-grown or etched structures
Solution Approach 1:
The invention applies universality by using the same mode-evolution converter design for both polarization conversion and spatial mode conversion. Both converters use identical epitaxial growth and etching processes, making them universally fabricable with the same工艺流程, thus reducing fabrication complexity while maintaining short device length.
Solution Approach 2:
The invention achieves homogeneity by making both converters in the compound structure use the same fabrication methodology (mode-evolution based on identical epitaxial and etching processes). This homogeneous fabrication approach eliminates the complexity of coordinating different fabrication processes, resolving the contradiction between short length and fabrication simplicity.
4Reliability
If asymmetric bi-level tapers are used for polarization conversion from TM0 to TE0, then the conversion is achieved, but the tolerance to fabrication variations becomes small
Solution Approach 1:
The invention extracts the polarization conversion function from the direct TM0-to-TE0 transformation and introduces an intermediate TE1 mode. By transforming TM0 to TE1 first (using asymmetric taper), then TE1 to TE0 (using symmetric Y-coupler), the system achieves reliable polarization conversion while the second stage's symmetry provides fabrication tolerance, resolving the contradiction between conversion efficiency and fabrication tolerance.
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 provides accurate polarization and spatial mode control with a large bandwidth and simplified fabrication, addressing the limitations of conventional converters by using only mode-evolution converters to achieve desired conversions, resulting in improved performance and reliability.
Implementation Method 1
The mode-evolution converters replace the abrupt transition with gradual variation of the waveguide geometries along the wave propagation direction. Along the converter, a mode in the first waveguide can evolve into another mode in the second waveguide with different polarization and spatial distribution without exciting other modes in the second waveguide.
Implementation Method 2
When the optical signal is coupled from the single mode fiber to the PICs, the signal decomposes into arbitrary compositions of two orthogonal polarization components, namely, a first component in a transverse electric (TE) mode and a second component in a transverse magnetic (TM) mode.
Data Source
AI summary
A mode-evolution compound converter for processing an optical signal that includes a first component having a fundamental transverse magnetic (TM) mode and a second component having a fundamental transverse electric (TE) mode is disclosed. The compound converter includes a set of multiple converters connected to form a compound converter, wherein each converter is a mode-evolution converter selected from a group including a polarization converter, a spatial converter, and combination thereof, wherein the polarization converter at least converts a mode of a polarization of at least one component of the optical signal, and the spatial mode converter at least converts a spatial mode order of at least one component of the optical signal.