Optical Waveguide Surface Roughness for High-Order Mode Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical waveguide devices face challenges in efficiently removing high-order mode light beams while maintaining a small width or height, leading to manufacturing difficulties and incomplete removal of high-order modes, especially when integrating a driver circuit and requiring a 180-degree folded structure.
Innovation Solution
The optical waveguide device incorporates a rib type optical waveguide with a slab waveguide having a larger roughness on its upper surface than the rib waveguide, with the slab waveguide being disposed close to the rib waveguide, and optionally featuring multiple slab waveguides with varying heights and roughness levels to effectively scatter high-order modes, facilitating efficient removal of high-order mode light beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the width or height of the optical waveguide is set to 1 μm or less to strengthen light confinement, then light confinement is improved, but manufacturing precision becomes significantly more difficult
Solution Approach 1:
The patent changes the surface roughness parameter of the slab waveguide as a alternative approach. By controlling the roughness parameter (Ra value) of the slab waveguide surface rather than reducing the dimensional parameters (width/height) of the rib waveguide, the patent achieves mode filtering without the manufacturing precision challenges associated with sub-micron dimensional control.
2Object-generated harmful factors
If the height of the slab waveguide is set lower than the rib type optical waveguide to attenuate high-order modes, then high-order mode attenuation is improved, but manufacturing precision deteriorates due to the need for accurate dimensional control
Solution Approach 1:
The patent shifts from controlling geometric dimensional parameters (height differences between waveguides) to controlling surface physical parameters (roughness). By specifying Ra values (e.g., Ra1 ≥ 50 nm for rib waveguide, Ra2 ≥ 100 nm for slab waveguide), the patent achieves high-order mode attenuation while avoiding the manufacturing precision issues of precise height control.
Solution Approach 2:
The patent applies different surface roughness qualities to different components: the rib waveguide maintains a relatively smooth surface (Ra1 ≥ 50 nm) for low loss, while the slab waveguide has a deliberately roughened surface (Ra2 ≥ 100 nm) for high-order mode scattering. This local differentiation of surface quality achieves both mode filtering and low loss transmission.
3Adaptability or versatility
If the dimension of the optical waveguide is set to approximately 10 μm MFD, then the optical waveguide can support multiple modes, but high-order mode light beam cannot be completely removed
Solution Approach 1:
The patent uses surface roughness parameter changes in the slab waveguide to selectively scatter high-order modes while preserving fundamental mode propagation. By setting Ra2 ≥ 100 nm for the slab waveguide surface, the patent creates strong scattering for high-order modes (which have larger mode fields extending into the slab region) while the fundamental mode remains confined to the rib waveguide core.
Solution Approach 2:
The patent creates a composite waveguide structure combining a smooth rib waveguide (for low-loss fundamental mode transmission) with a rough slab waveguide (for high-order mode scattering). This composite structure integrates two different surface quality characteristics to simultaneously achieve low loss and effective high-order mode removal.
4Device complexity
If a folded structure with at least 180 degrees is employed to dispose input and output ports on one end surface, then device integration is improved, but light confinement must be further strengthened requiring smaller dimensions
Solution Approach 1:
The patent introduces surface roughness parameter control as an alternative method to achieve stronger light confinement without reducing waveguide dimensions. By setting Ra1 ≥ 50 nm for the rib waveguide and Ra2 ≥ 100 nm for the slab waveguide, the patent enhances mode confinement through surface scattering mechanisms, allowing the use of folded structures for integration without requiring sub-micron dimensional precision.
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 allows for efficient removal of high-order mode light beams while simplifying manufacturing and maintaining a small optical waveguide size, reducing coupling losses and enabling effective integration with driver circuits for high-frequency and compact optical modulators.
Implementation Method 1
roughness of at least a part of an upper surface of the slab waveguide is larger than roughness of a surface of a top portion of the rib type optical waveguide
Data Source
AI summary
A method of roughening the upper surface of the slab waveguide includes a method of locally forming roughness using an electron beam and a method of roughening the upper surface via etching. As an etching condition for the rough surface, processing is performed under a condition in which roughness is generated compared to a processing condition for the rib top portion. Particularly, since the surface can be simply locally roughened by etching, the rough surface can be formed much more simply than that of the unnecessary light beam removing unit in Patent Literature No. 1. Roughness of the rough surface is preferably 10 nm or larger in arithmetic average roughness Ra. Roughness of an upper surface of the rib type optical waveguide is normally set to 1 nm or less