Intermediate Waveguide Optical Coupler for Low-Loss Mode Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical coupling between waveguides with significantly different modes, such as silicon-on-insulator (SOI) and optical fibers, results in high optical loss and limited compactness due to mode mismatch and inefficient grating couplers.
Innovation Solution
An optical coupler design comprising a first waveguide with tapering portions optically coupled to an intermediate waveguide, which in turn is coupled to a second waveguide, with precise alignment and tapering profiles to minimize optical coupling loss and enable efficient mode conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a grating coupler is used for optical coupling, then fabrication is simple and inexpensive, but optical coupling efficiency is low with high optical loss
Solution Approach 1:
The patent introduces an intermediate waveguide layer with gradually varying refractive index between the SOI waveguide and optical fiber. This intermediate layer acts as a mediator that progressively transforms the optical mode, preventing abrupt mode mismatch and reducing reflection losses. The gradual index transition (from 3.48 in SOI to 1.48 in fiber through intermediate values) enables efficient mode coupling while maintaining fabrication simplicity.
Solution Approach 2:
The patent employs continuous parameter changes in the intermediate waveguide layer, specifically the gradual variation of thickness and refractive index from the SOI interface toward the fiber interface. This parameter transformation approach allows the optical mode to adapt progressively, minimizing coupling losses while keeping the structure manufacturable using standard semiconductor processing techniques.
2Loss of energy
If a spot-size converter is used to convert between different optical modes, then coupling efficiency improves, but device complexity increases
Solution Approach 1:
The patent divides the mode conversion function into multiple segments: the SOI waveguide, the intermediate waveguide layer with gradual index variation, and the optical fiber. This segmentation allows each component to perform a specific portion of the mode transformation, simplifying the design of each individual element while achieving overall efficient coupling through their coordinated interaction.
Solution Approach 2:
The patent transitions from traditional planar mode converters to a three-dimensional structure with the intermediate waveguide layer extending vertically between the SOI chip and fiber. This dimensional approach enables gradual mode transformation through the thickness gradient, achieving efficient coupling with a more compact and integrated structure.
3Ease of manufacture
If a grating coupler is used, then fabrication is easy, but wavelength bandwidth is narrow
Solution Approach 1:
The gradual parameter changes in the intermediate waveguide layer (thickness and refractive index) create a broadband mode transformation mechanism that is less sensitive to wavelength variations compared to periodic grating structures. This continuous transformation approach maintains effective coupling across a wider wavelength range while preserving fabrication simplicity.
4Ease of operation
If fibre optic cores axis is aligned perpendicularly to the grating structure, then coupling is achieved, but chip form factor increases
Solution Approach 1:
The patent moves the coupling interface from a planar grating structure requiring lateral alignment to a vertical intermediate waveguide layer configuration. This dimensional change allows the fiber to be coupled vertically to the chip surface, significantly reducing the horizontal footprint and enabling more compact chip packaging while maintaining effective optical coupling.
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 design achieves low optical coupling loss of less than 3 dB, allowing for efficient and compact optical signal transmission between waveguides with different modes, suitable for both bi-directional and asynchronous data transfer.
Implementation Method 1
the first tapering portion of the intermediate waveguide being optically coupled to the tapering portion of the first waveguide... the intermediate waveguide comprising a first tapering portion at a first end of the intermediate waveguide
Data Source
AI summary
There is provided an optical coupler comprising: a first waveguide (100) comprising a tapering portion (101); an intermediate waveguide (200) comprising: a first tapering portion (201) at a first end of the intermediate waveguide (200), the first tapering portion (201) of the intermediate waveguide (200) being optically coupled to the tapering portion (101) of the first waveguide (100), and a second tapering portion (202) at a second end of the intermediate waveguide (200); and a second waveguide (300), wherein the second tapering portion (201) of the intermediate waveguide (200) is optically coupled to the second waveguide (300). A method for fabricating the optical coupler is also provided.