Asymmetric Grating Coupler Structure for Reflection Suppression
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Solution Overview
Problem
In grating couplers, a significant portion of input light is reflected and emitted from the end face, reducing output efficiency and potentially causing optical element failure due to reverse entry of light, and light travels in undesirable directions, leading to losses.
Innovation Solution
A grating coupler with modified refractive index regions having a refractive index different from the base member, designed to suppress the ratio of light reflected in a 180° direction, with a ratio of second coupling coefficient to first coupling coefficient |κ2|/|κ1| of 3 or more, ensuring efficient light output and reducing reverse entry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional grating couplers with grooves or holes are used, then light diffraction and coupling with optical elements can be achieved, but a significant portion of input light is reflected back from the end face, reducing output efficiency and potentially causing optical element failure
Solution Approach 1:
The patent introduces asymmetric modified refractive index regions with different coupling coefficients for forward and backward light propagation. The ratio |κ2|/|κ1| ≥ 3 ensures that light traveling in the first direction has much stronger coupling to the second direction than vice versa, creating directional asymmetry that suppresses reflected light while maintaining forward coupling efficiency
Solution Approach 2:
The patent modifies the refractive index distribution by introducing regions with specifically engineered refractive indices different from the base member. By controlling the coupling coefficients κ1 and κ2 through these refractive index modifications, the system achieves asymmetric light coupling that suppresses reflection while maintaining transmission
2Productivity
If light travels in directions different by 180° from the intended path, then coupling with optical elements can occur, but light traveling in undesirable directions becomes a loss
Solution Approach 1:
The asymmetric coupling coefficients create a preferred propagation direction where light traveling in the first direction couples efficiently to the second direction (|κ2| ≥ 3|κ1|), while light attempting to propagate in the opposite direction experiences strong suppression, thereby minimizing energy loss from undesirable propagation paths
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 significantly enhances light output efficiency by minimizing light reflection and reverse entry, thereby improving the grating coupler's performance and reducing the risk of optical element failure.
Implementation Method 1
light having a specific wavelength corresponding to a period of grooves, holes, or the like among light input (incident) from an end face of a base member is diffracted and output (emitted) from a surface of the base member
Implementation Method 2
a part of the light input from the end face is reflected by the grooves or the holes in both the trapezoidal hole type and the isosceles triangle hole type, so that reflected light having a traveling direction changed by 180° is generated
Data Source
AI summary
A grating coupler includes a grating including a plate-shaped base member and modified refractive index regions having a refractive index different from that of the base member and either being point-like and periodically disposed two-dimensionally or one-dimensionally in the base member, or being linear and periodically disposed one-dimensionally in the base member, where the modified refractive index regions each have a planar shape in which a ratio |κ2|/|κ1| of an absolute value |κ2| of a second coupling coefficient to an absolute value |κ1| of a first coupling coefficient is 3 or more, the first coupling coefficient being an index indicating intensity at which light traveling in a first direction parallel to the base member is reflected in a second direction different by 180° from the first direction, the second coefficient being an index indicating intensity at which light traveling in the second direction is reflected in the first direction.