Grating Coupler Bandwidth Efficiency Trade-off
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Solution Overview
Problem
Current grating couplers face a trade-off between optical bandwidth and coupling efficiency, where increasing bandwidth typically results in lower coupling efficiency and vice versa, limiting their effectiveness in single-channel applications.
Innovation Solution
A coupler system using multiple distinct sub-gratings and a combiner to split and combine radiation beams, with means for guiding them to ensure all radiation is coupled into substantially one direction, allowing for increased optical bandwidth without significant reduction in coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of grating periods is decreased to increase optical bandwidth, then bandwidth is improved, but coupling efficiency deteriorates due to reduced scattered power
Solution Approach 1:
The grating is divided into multiple segments (first and second gratings) with different numbers of periods. The first grating has N1 periods and the second grating has N2 periods, where N1 ≠ N2. This segmentation allows each grating segment to contribute differently to the overall coupling, enabling broader bandwidth while maintaining sufficient scattered power through the combined effect of multiple segments with optimized individual period counts.
2Power
If etch depth is increased to improve coupling strength, then coupling strength is improved, but overlap with fiber mode deteriorates due to radiation over short length
Solution Approach 1:
Different grating segments have different local properties, specifically different numbers of periods (N1 and N2). This allows each segment to be optimized for specific functions: one segment can provide stronger coupling while the other extends the radiation length for better mode overlap. The varying local characteristics across segments enable simultaneous optimization of coupling strength and mode overlap that cannot be achieved with a uniform grating.
3Loss of energy
If number of periods is increased to improve coupling efficiency, then coupling efficiency is improved, but optical bandwidth deteriorates
Solution Approach 1:
The grating structure is segmented into multiple gratings with different period counts. This segmentation strategy allows the system to achieve high coupling efficiency through the combined effect of multiple segments while the variation in period numbers across segments broadens the optical bandwidth. Each segment contributes to coupling efficiency, and the diversity in segment characteristics extends the operational bandwidth beyond what a single uniform grating could achieve.
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 higher optical bandwidth while maintaining coupling efficiency, as demonstrated by calculated coupling efficiencies of up to 36% and 1dB bandwidths exceeding 70 nm, compared to standard grating couplers.
Implementation Method 1
The coupling efficiency of a grating coupler (e.g. to a fiber) is determined by the amount of power scattered by the grating
Implementation Method 2
a splitter/combiner for splitting a received radiation beam from a photonic circuit in at least two radiation sub-beams
Implementation Method 3
or for combining at least two radiation sub-beams into one combined radiation beam into a photonic circuit
Data Source
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AI summary
The present invention relates to a coupler (100) for coupling radiation to one optical element. The coupler (100) comprises a splitter (110) for splitting a received radiation beam in at least two radiation sub-beams, at least two distinct sub-gratings (120a, 120b) adapted for directing radiation sub-beams such that all radiation is coupled out by the coupler into substantially one direction, and a means for guiding (130a, 130b) each of the radiation sub-beams between the splitter and a sub-grating (120a, 120b).