Dual-Polarization Grating Couplers for Tight-Pitch Multi-Core Fibers
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Solution Overview
Problem
Existing grating couplers for multi-core optical fibers are structurally incompatible with certain multi-core optical fibers due to small core-to-core separation distances, leading to a loss of polarization diversity, which is unacceptable for high-end communication systems.
Innovation Solution
A fiber coupler with a grating array and mode converters is designed to efficiently couple light from each core of a multi-core optical fiber to separate waveguides, maintaining polarization diversity by using polarization splitting gratings and mode converters that are compactly arranged to match the core arrangement, even with core-to-core separations less than 45 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If existing grating couplers are used for multi-core optical fibers with small core-to-core separation distances, then the coupling structure is simple, but polarization diversity is lost
Solution Approach 1:
The grating coupler is segmented into multiple independent polarization splitting gratings, each responsible for splitting two polarization modes from a specific core. This segmentation allows each grating to be optimized for its specific function while maintaining overall system compactness, resolving the contradiction between structural simplicity and polarization diversity preservation.
Solution Approach 2:
The patent utilizes three-dimensional mode converters with varying cross-sectional dimensions to transform optical modes between the fiber and waveguide domains. By operating in the dimensional domain, the design achieves compact coupling structures that preserve polarization diversity without requiring bulky conventional gratings.
2Reliability
If compact grating couplers are designed for small core-to-core separations, then polarization diversity is maintained, but device complexity increases
Solution Approach 1:
Multiple functional elements are merged into integrated photonic circuits on a single substrate. The polarization splitting gratings, mode converters, and waveguides are combined into a unified compact structure, reducing overall device complexity while maintaining polarization diversity through coordinated design of all elements.
Solution Approach 2:
The grating array is designed with universal polarization splitting gratings that can handle multiple cores and polarization modes using the same fundamental structure. This multi-functionality reduces device complexity by avoiding the need for different specialized gratings for each core, while still maintaining polarization diversity through proper geometric arrangement.
3Device complexity
If conventional waveguide tapers are used for coupling, then the coupling mechanism is simple, but the structure is too bulky for small core separations
Solution Approach 1:
The waveguide taper parameters are optimized with varying cross-sectional dimensions along their length, transitioning from large dimensions at the fiber interface to small dimensions at the waveguide interface. This parameter optimization enables compact coupler size suitable for small core separations while maintaining effective coupling through controlled dimensional changes.
Solution Approach 2:
The mode converters are designed with nested structures where waveguides are positioned within or adjacent to the grating structures. This nesting arrangement minimizes the overall coupler volume by eliminating wasted space between components, enabling compact design for small core-to-core separations while preserving the coupling mechanism functionality.
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 maintains polarization diversity and achieves high coupling efficiency, guiding multiple polarization modes into waveguides with efficiencies greater than or equal to −6.0 dB, suitable for high data rate applications and space-constrained systems.
Implementation Method 1
a first mode converter extending from a first side of each of the plurality of polarization splitting gratings to receive a first polarization mode of the optical signal scattered by the polarization splitting grating
Data Source
AI summary
A fiber coupler (135) for coupling a plurality of cores (160) of a multi-core optical fiber (105) to an integrated photonic device comprises a grating array comprising a plurality of polarization splitting gratings (180) arranged in a manner that corresponds to the plurality of cores (160) in the multi-core optical fiber (105). The fiber coupler (135) also comprises first and second mode converters (235, 240) extending from first and second sides of each of the plurality of polarization splitting gratings (180) to receive first and second polarization modes of the optical signal scattered by the polarization splitting grating (180). A plurality of waveguides (145-a, 145-b) extends from ends of each of the mode converters (235, 240) to guide a single polarization mode of one of the optical signals.