Curved Waveguide Evanescent Coupling for Photonic Integrated Circuits
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Solution Overview
Problem
High refractive index contrast photonic integrated circuits face challenges in efficiently coupling light due to small mode field diameters, leading to poor coupling performance, high insertion losses, narrow spectral bandwidth, and polarization dependence, particularly when interfacing with optical fibers.
Innovation Solution
The use of a glass or amorphous material substrate with 3D laser-inscribed waveguides and a curved section to enhance evanescent coupling, allowing for improved alignment tolerances, reduced polarization dependence, and broad spectral bandwidth transmission, while maintaining low insertion losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If high refractive index contrast platforms (silicon or indium phosphide) are used to reduce device size and improve integration, then device compactness and integration density are improved, but mode field diameter becomes small leading to poor optical coupling efficiency
Solution Approach 1:
The patent introduces an intermediate coupling structure comprising a first waveguide in a glass substrate and a second waveguide in the PIC platform, with a curved section that enables evanescent coupling. This intermediary structure bridges the mismatch between optical fibers and high-index-contrast PIC waveguides, achieving above 95% total evanescent coupling efficiency while maintaining the compactness of the high-index-contrast platform.
2Quantity of substance
If grating couplers are used to provide optical coupling, then mode size matching with optical fibers is improved, but insertion losses increase and spectral bandwidth becomes narrow
Solution Approach 1:
The patent employs a curved section in the first waveguide that extends in a plane parallel to the propagation direction of the evanescently coupled optical signal. This curvature is specifically designed to enhance evanescent coupling between the first and second waveguides, achieving low insertion losses while maintaining broad spectral bandwidth, unlike conventional grating couplers.
3Quantity of substance
If grating couplers are used for optical coupling, then mode size compatibility is improved, but polarization dependence increases
Solution Approach 1:
The patent changes the coupling mechanism from grating-based diffraction to evanescent wave coupling through a curved waveguide section. This parameter change in the coupling physics eliminates the polarization selectivity inherent in grating couplers, enabling the system to accept both TE and TM polarizations with comparable efficiency, thus reducing polarization dependence.
4Quantity of substance
If edge couplers with spot size converters are used to expand mode size, then coupling compatibility with optical fibers is improved, but alignment tolerances become stringent and lensed fibers are required
Solution Approach 1:
The patent introduces a first waveguide in a glass substrate as an intermediary element that performs mode size expansion through its curved geometry and evanescent coupling mechanism. This intermediary approach achieves relaxed alignment tolerances compared to direct edge coupling, eliminating the need for lensed fibers while maintaining coupling compatibility with standard optical fibers.
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 enables efficient optical coupling with high refractive index contrast platforms, achieving above 95% total evanescent coupling efficiency and facilitating the integration of compact photonic components with reduced manufacturing complexity.
Implementation Method 1
the first waveguide comprises a curved section configured to provide evanescent coupling of an optical signal from the first waveguide to the second waveguide
Data Source
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Figure 5~6b
AI summary
Optical apparatus and methods of manufacture thereof An optical apparatus (20) for evanescently coupling an optical signal across an (interface (30) is described. The optical apparatus (20) comprises a first substrate (22) and a second substrate (24). The optical signal is evanescently coupled between a first waveguide (26) formed by laser inscription of the first substrate (22) and a second waveguide (28) of the second substrate (22). The first waveguide (26) comprises a curved section (34) configured to provide evanescent coupling of the optical signal between the first and second waveguides (26, 28) via the interface (30).