Millimeter Grating Coupler Uniform Output Profile
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Solution Overview
Problem
Existing millimeter-scale grating couplers face challenges in achieving uniform spatial output profiles due to high index contrast between silicon and SiO2, leading to strong gratings that limit grating length and increase beam divergence, making it difficult to fabricate long gratings with low strength for applications like LIDAR systems.
Innovation Solution
A millimeter-scale weak grating coupler is designed by varying the duty cycle of Si3N4 bars along the length of the grating, reducing index contrast and grating strength, and using a thin Al2O3 stop layer to protect the silicon during etching, allowing for a uniform output profile and robust fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high index contrast between silicon and SiO2 is used, then grating coupling strength is increased, but grating length is limited and beam divergence increases
Solution Approach 1:
The patent applies local quality by varying the duty cycle of grating bars along the length of the grating structure. The duty cycle is higher at the input end and lower at the output end, creating a tapered profile that locally adjusts the coupling strength to compensate for light intensity decay, thereby enabling long grating lengths with uniform output
Solution Approach 2:
The patent implements dynamics by making the grating structure tunable through variable duty cycle modulation. The grating bars are designed with different widths at different positions, allowing the coupling strength to be dynamically adjusted along the propagation direction to maintain uniform light extraction over millimeter-scale lengths
2Strength
If high index contrast between silicon and SiO2 is used, then grating coupling strength is increased, but beam divergence increases
Solution Approach 1:
The tapered duty cycle profile locally reduces coupling strength at the output end where light intensity is already diminished, preventing excessive beam divergence and maintaining a collimated output profile over long grating lengths
3Ease of manufacture
If constant duty cycle is used, then fabrication is simplified, but output profile becomes exponential and non-uniform
Solution Approach 1:
The patent varies the duty cycle locally along the grating length, with higher values at the input and lower values at the output, to compensate for the exponential decay of light intensity in the waveguide and achieve a uniform output profile
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 achieves a uniform and low grating strength along the entire millimeter structure, enhancing the near-field output uniformity and reducing beam divergence, making it suitable for high-resolution optical phased arrays.
Implementation Method 1
a millimeter scale weak grating coupler comprising a silicon waveguide having a plurality of bars of overlay material of length (a) disposed periodically at a period (A) adjacent the silicon waveguide
Data Source
AI summary
A millimeter scale weak grating coupler comprising a silicon waveguide having bars of overlay material of length (a) disposed periodically at a period (∧) adjacent the silicon waveguide whereby a uniform grating output is achieved.