Suspended Ridge Oxide Waveguide Mode Matching
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Solution Overview
Problem
Efficient coupling of silicon photonic devices with optical fibers is hindered by a large mismatch between the highly-confined silicon waveguide mode and the optical fiber mode, leading to interference from higher-order modes, which degrades performance.
Innovation Solution
A single-mode suspended ridge waveguide is employed, featuring a core with a refractive index lower than the inversely tapered waveguide, surrounded by air cladding, to facilitate optical mode conversion and coupling, reducing interference from higher-order modes by designing the waveguide to support only the fundamental mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a highly-confined silicon waveguide mode is used, then the optical signal can be efficiently guided within the waveguide, but the mode mismatch with optical fiber leads to higher-order mode interference and degraded coupling performance
Solution Approach 1:
The patent introduces an intermediate suspended ridge waveguide layer that bridges the gap between the planar silicon waveguide and the optical fiber in the vertical dimension. This intermediate structure provides a gradual transition from the highly-confined silicon mode to the optical fiber mode, resolving the mode mismatch problem by adding a dimensional transition zone.
Solution Approach 2:
The suspended ridge waveguide acts as an intermediary structure between the silicon waveguide and the optical fiber. It has a refractive index and mode profile that is intermediate between the high-index silicon waveguide and the lower-index fiber mode, enabling efficient mode conversion and reducing higher-order mode interference.
2Adaptability or versatility
If the waveguide supports multiple modes, then it can accommodate various optical signals, but higher-order modes cause interference and degrade coupling efficiency
Solution Approach 1:
The suspended ridge waveguide is designed with specific local dimensions (ridge width, height, and spacing) that are optimized to support only the fundamental mode at the operating wavelength. By carefully controlling the local geometric parameters, the waveguide achieves single-mode operation while maintaining efficient coupling to the optical fiber.
3Productivity
If the core refractive index is higher than the cladding, then total internal reflection occurs and confines the optical signal, but a large index difference increases mode confinement and exacerbates mode mismatch
Solution Approach 1:
The patent carefully selects and optimizes the refractive index parameters of the suspended ridge waveguide materials and dimensions to achieve an intermediate effective index between the silicon waveguide and the optical fiber. This parameter optimization enables gradual mode transformation while maintaining sufficient optical confinement within the waveguide structure.
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 approach enhances coupling efficiency by ensuring single-mode optical signal propagation, reducing coupling loss to less than 3 decibels for both TE and TM modes, and allows for efficient optical edge coupling between silicon photonic devices and optical fibers.
Implementation Method 1
an air cladding disposed adjacent to the core along the axis of optical signal propagation
Implementation Method 2
a refractive index of the core is lower than a refractive index of the inversely tapered waveguide
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A waveguide comprising a single-mode optical core configured to carry an optical signal between an inversely tapered waveguide and an optical fiber, wherein the core extends longitudinally along an axis of optical signal propagation between the inversely tapered waveguide and the optical fiber, and an air cladding disposed adjacent to the core along the axis of optical signal propagation.