Angled Optical Waveguide Facet with MMI for Reflectivity Reduction
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Solution Overview
Problem
Existing optical waveguiding parts face challenges with high reflectivity at output facets, leading to performance degradation in semiconductor laser components, particularly when coupling light to air or optical fibers, due to geometrical restrictions and mode shape distortions caused by anti-reflection coatings and window regions.
Innovation Solution
The optical waveguiding part features a ridge waveguide with an output facet angled between 2° and 14° relative to the main light direction, incorporating a Multi Mode Interferometer (MMI) to create an output image at the facet, which significantly reduces reflectivity and maintains coupling efficiency by filtering out higher order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the waveguide is disposed at an angle to the facet normal to reduce reflections, then modal reflectance is reduced, but the angle is limited by geometrical restrictions of the optical circuit
Solution Approach 1:
The waveguide system is segmented into two functional parts: an angled waveguide section that handles reflection management, and a perpendicular output section that provides flexibility for optical circuit coupling. This segmentation allows each section to optimize its specific function without compromising the other.
Solution Approach 2:
An intermediary optical element (such as a lens or prism) is introduced between the angled waveguide and the output facet to redirect the reflected light while maintaining the perpendicular orientation of the output facet relative to the optical circuit. This intermediary enables both reflection reduction and beam direction flexibility.
2Object-affected harmful factors
If a window region is created by etching and filling to reduce facet reflectivity, then modal facet reflectivity is reduced, but mode shape distortion occurs which reduces coupling efficiency
Solution Approach 1:
The problematic window region that causes mode distortion is completely removed from the design. Instead, a different approach using angled waveguide geometry is employed to achieve reflection reduction without introducing mode shape distortion that would harm coupling efficiency.
Solution Approach 2:
The waveguide angle parameter is optimized to a specific range (45-60 degrees) to achieve the optimal balance between reflection reduction and maintaining proper mode shape for coupling. This parameter change eliminates the need for window regions while controlling reflectivity.
3Object-affected harmful factors
If anti-reflection coatings are applied to the facet, then reflectivity is reduced, but manufacturing complexity increases
Solution Approach 1:
The optical coating approach is replaced with a geometric solution. By changing the physical orientation of the waveguide (mechanical/structural approach), the need for delicate anti-reflection coatings is eliminated, simplifying manufacturing while achieving the same reflection reduction goal.
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 configuration achieves a more than order-of-magnitude reduction in output facet optical power reflectance with minimal degradation in coupling efficiency to output waveguides, particularly optical fibers, and can be integrated into existing fabrication steps without additional processes.
Implementation Method 1
the output facet is set at an angle in relation to a main direction of light along the said waveguide, so that light travelling in the waveguide along said main direction has an angle of incidence towards the facet of between 2° and 14° and is reflected towards a first side of the said ridge
Implementation Method 2
the waveguide comprises an MMI (Multi Mode Interferometer), arranged to create an output image substantially at the output facet, wherein an output end of the MMI coincides with the output facet
Data Source
Figure 1a~2a
Figure 2b~2d
Figure 3~6
AI summary
Optical waveguiding part (300), which waveguiding part is arranged to convey light through an output facet (30) of the waveguiding part, which waveguiding part comprises a ridge waveguide comprising a semiconductor substrate (320) and a semiconductor light-conveying ridge, wherein the output facet is set at an angle (a) in relation to a main direction (z) of light along the said waveguide, so that light travelling in the waveguide along said main direction has an angle of incidence towards the facet of between 2° and 14° and is reflected towards a first side (301) of the said ridge, wherein the waveguide comprises an MMI (Multi Mode Interferometer) (310), arranged to create an output image substantially at the output facet.