Asymmetric Grating Coupler for Wavelength Duplexing
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Solution Overview
Problem
Conventional 2D square lattice diffraction gratings in optical transceivers have limitations due to their symmetric structure, which requires additional efforts for wavelength duplexing and polarization independence, and they offer limited wavelength range performance.
Innovation Solution
A 2D asymmetric silicon waveguide grating with different periods along orthogonal directions is used, allowing for asymmetric access waveguides and enabling wavelength duplexing and polarization diversity, integrated on a silicon-on-insulator platform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional 2D square lattice diffraction grating is used, then the grating structure provides wavelength duplexing capability, but the symmetric structure requires additional efforts to match the projected Bragg condition and tilt the fiber along the symmetry axis
Solution Approach 1:
The patent employs an asymmetric grating structure where the grating period along the x-direction (Λx) is deliberately made different from the grating period along the y-direction (Λy). This asymmetry breaks the symmetry constraints of conventional square lattice gratings, allowing independent optimization of coupling conditions for different wavelengths without requiring fiber tilting along symmetry axes. The asymmetric design enables direct coupling of TE-polarized light from a single-polarization laser diode while maintaining wavelength duplexing functionality.
Solution Approach 2:
The patent applies different grating periods in different spatial directions to achieve local optimization of coupling characteristics. By setting Λx ≠ Λy, the grating provides direction-dependent phase matching conditions that are locally optimized for specific wavelength channels, eliminating the need for global symmetry-based phase matching and reducing overall device complexity.
2Adaptability or versatility
If a symmetric grating structure is used, then the four access waveguides are equally assigned to two wavelength channels, but the transmitter part with a single polarized LD output would only require a single access waveguide
Solution Approach 1:
The asymmetric grating structure creates asymmetric coupling strengths for different waveguide directions. This allows the transmitter side to use a single access waveguide optimized for TE-polarized light from a single-polarization laser diode, while the receiver side can utilize multiple access waveguides for polarization diversity detection. The asymmetry enables mismatched waveguide configurations between transmit and receive sides, optimizing each for its specific function.
Solution Approach 2:
The patent enables dynamic adaptation of the optical coupling characteristics by using the asymmetric grating to selectively couple different polarizations to different waveguides based on wavelength and polarization state. This dynamic coupling behavior allows the system to adapt the waveguide usage pattern according to the transmission mode (single-polarization transmit vs. polarization-diversity receive).
3Reliability
If polarization independence behavior is implemented over a limited wavelength range, then the grating coupler achieves polarization diversity, but the wavelength range coverage is restricted
Solution Approach 1:
The patent uses parameter optimization of the asymmetric grating structure, specifically tuning the grating periods Λx and Λy, grating depth, and waveguide dimensions to achieve broad wavelength coverage. By carefully selecting these parameters, the grating maintains effective coupling and polarization independence across an extended wavelength range beyond what conventional symmetric gratings achieve, enabling multi-wavelength operation while preserving polarization diversity 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
This design enhances wavelength range coverage, improves polarization independence, and simplifies phase matching conditions, providing efficient coupling between fibers and waveguides while reducing manufacturing complexity and costs.
Implementation Method 1
a grating arrangement including a plurality of grating elements, the plurality of grating elements being defined on one surface of the substrate, wherein the plurality of grating elements are arranged to have a first period along a first direction, and a second period along a second direction orthogonal to the first direction
Data Source
AI summary
According to embodiments of the present invention, an optical coupling device is provided. The optical coupling device includes a substrate, and a grating arrangement including a plurality of grating elements, the plurality of grating elements being defined on one surface of the substrate, wherein the plurality of grating elements are arranged to have a first period along a first direction, and a second period along a second direction orthogonal to the first direction, the first period being different from the second period. According to further embodiments of the present invention, a photonic integrated circuit and a method of forming an optical coupling device are also provided.