Planar Grating Waveguide Coupling Optimization
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Solution Overview
Problem
Existing solutions for multimode waveguides have poor coupling efficiency due to the complexity and high cost of manufacturing slanted gratings, and previous methods for enhancing diffraction efficiency are limited to thin waveguides and specific light sources, making them unsuitable for applications requiring bulk waveguides and larger light spots.
Innovation Solution
A method for constructing a multimode waveguide with a periodic diffractive grating that couples light into the waveguide using the first and/or minus first diffraction order, allowing for high efficiency coupling even in thicker waveguides, without relying on resonance effects, and using a refractive enhancement layer to optimize coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If slanted gratings are used to enhance diffraction efficiency, then coupling efficiency is improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent changes the grating geometry from slanted to planar with optimized parameters (grating depth, period, and duty cycle) to achieve high coupling efficiency without the manufacturing complexity of slanted gratings. The planar grating structure can be fabricated using standard photolithography and etching processes, making it suitable for mass production while maintaining coupling efficiencies above 80%.
2Reliability
If resonance effects are used to enhance diffraction efficiency, then coupling efficiency is improved, but waveguide thickness is limited to thin structures
Solution Approach 1:
The patent extracts the resonance requirement from the coupling mechanism, achieving high coupling efficiency through planar grating diffraction without relying on waveguide resonance. This allows the use of thick waveguides (greater than 10 micrometers) that are suitable for bulk optical applications, image transmission, and integration with standard optical components, while maintaining coupling efficiencies above 80%.
3Ease of manufacture
If standard surface embossing is used for grating fabrication, then manufacturing ease is improved, but slanted grating structures cannot be produced
Solution Approach 1:
Instead of trying to make slanted gratings difficult to manufacture easier, the patent inverts the approach by making planar gratings the focus and optimizing their parameters to achieve the same high coupling efficiency. This allows standard surface embossing and photolithography techniques to be used effectively, enabling mass production while maintaining the ability to produce various grating structures with different periods, depths, and duty cycles.
4Reliability
If thin waveguides are used for resonance enhancement, then diffraction efficiency is improved, but applicability to bulk waveguides and large light spots is lost
Solution Approach 1:
The patent creates a universal planar grating coupling solution that works effectively for both thin and thick waveguides, and for various light source types including LEDs and lasers. The optimized planar grating parameters (depth, period, duty cycle) enable high coupling efficiency across different waveguide thicknesses and can couple large light spots (hundreds of micrometers), making it suitable for bulk optical applications, image transmission, and display technologies.
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
Achieves coupling efficiencies of 80% or more for thicker waveguides, enabling the efficient transport of coherent laser beams and entire images or light spots larger than a few microns, while being compatible with mass production techniques and reducing power consumption.
Implementation Method 1
The coupling structure is periodic and therefore produces diffraction of the incident light beam. Efficient coupling into the waveguide is achieved if only the first and/or the minus first diffraction order is coupled into the waveguide.
Implementation Method 2
Light may be confined in the internal layer of the waveguide by total internal reflection when the dielectric index of the internal layer is larger than that of the surrounding layers.
Data Source
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AI summary
The present invention concerns a method for constructing a light coupling system wherein a grating is manufactured on the surface of a multimode waveguide and defines the entrance of the waveguide for an incident light beam, said grating comprising a repetition of patterns. The grating is defined by a set of parameters comprising: • grating period (P), separating two adjacent patterns, • grating depth (d) between the highest and the lowest point of the pattern, • incident angle mean value (θ) of the incident light with respect to the waveguide. The method comprises a step of optimization of the set of parameters to obtain an optimized second set of parameters, in order to obtain a transmission efficiency (Ce) of the incident light into said waveguide for the first or the second diffractive order exceeding 35% for unpolarized light, or exceeding 50% for polarized light, at a given wavelength of the incident light.