Elongated Rectangular Optical Waveguide Core for Low Coupling Loss
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Solution Overview
Problem
Silicon thin-wire optical waveguides have a small core diameter and high light-confinement rate, requiring a long taper to enlarge spot size, which complicates the fabrication process and increases optical coupling loss with other waveguide elements.
Innovation Solution
An optical waveguide with a core layer formed into an elongated rectangular shape, having a cross-sectional aspect ratio of 10:1, and a tapered connection to a compound semiconductor amplifier, reducing light confinement and facilitating easier spot size enlargement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the core diameter is decreased to satisfy single mode condition in silicon thin-wire optical waveguides, then light confinement rate is improved, but spot size becomes too small causing increased optical coupling loss
Solution Approach 1:
The invention transitions from a conventional square cross-section core to an elongated rectangular cross-section core with aspect ratio of 10:1 or more. This dimensional change allows the core to maintain small dimensions in one direction (preserving light confinement) while extending in another direction (enlarging spot size for better coupling), effectively resolving the contradiction through geometric transformation.
Solution Approach 2:
The invention changes the geometric parameters of the core from a square cross-section to an elongated rectangular cross-section with specific aspect ratio (10:1 or more). This parameter change fundamentally alters the mode distribution and spot size characteristics, enabling simultaneous achievement of good light confinement and reduced coupling loss.
2Loss of energy
If a long taper is used to enlarge spot size in silicon thin-wire optical waveguides, then optical coupling loss is reduced, but fabrication process becomes complicated
Solution Approach 1:
The invention performs preliminary action by pre-designing the core with an elongated rectangular cross-section that inherently provides the desired spot size characteristics. This eliminates the need for subsequent complex taper fabrication processes, as the favorable coupling properties are built into the basic core structure from the beginning.
Solution Approach 2:
By changing the core cross-section from square to elongated rectangular with aspect ratio of 10:1 or more, the invention fundamentally alters the mode field distribution to achieve larger spot size without requiring additional taper structures, thereby simplifying the fabrication process while maintaining low coupling loss.
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 reduces scattering loss, improves optical coupling with other elements, stabilizes laser operation, and minimizes absorption loss, while allowing for adjustable beam diameter and reduced complexity in fabrication.
Implementation Method 1
a core layer which is disposed in the cladding member and is formed into an elongated body having a rectangular cross-sectional shape from a material having a refractive index higher than that of a material constituting the cladding member
Data Source
AI summary
Provided are: an optical waveguide that relatively easily expands a spot size and that can suppress an increase in optical coupling loss with another optical waveguide element; and an optical component and variable-wavelength laser that use the optical waveguide. The optical waveguide is provided with: a cladding member; and a core layer that is disposed within the cladding member and that is formed as an elongated body having a rectangular cross-sectional shape from a material having a higher refractive index than the material configuring the cladding member. Here, the cross-sectional shape of the core layer is characterized in having a rectangular shape in which the length in the lateral direction is at least 10 times the length in the vertical direction.