Facet Optical Coupler With Undercut Region For Photonic Integrated Circuits
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Solution Overview
Problem
Coupling an optical fiber to a submicron silicon waveguide in photonic integrated circuits (PICs) is challenging due to the mismatch in mode field size, resulting in significant coupling loss, and existing techniques like grating couplers have narrow optical bandwidth and mechanical integrity issues.
Innovation Solution
A facet optical coupler with a layer of second material disposed on a silicon substrate and an offset undercut region is used, where the waveguide is embedded within the second material, reducing interference and enhancing mechanical integrity while allowing for efficient coupling by adjusting the refractive indices and dimensions to match the mode field of the optical fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a facet optical coupler uses direct coupling between optical fiber and submicron waveguide, then coupling efficiency is improved, but coupling loss increases due to mode field size mismatch
Solution Approach 1:
The patent introduces an intermediate layer of second material between the silicon substrate and the waveguide, which acts as a mediator to gradually transition the mode field size from the optical fiber to the submicron waveguide. This intermediate layer reduces the abrupt discontinuity in mode field dimensions, thereby reducing coupling loss without requiring precise direct alignment between fiber and waveguide.
Solution Approach 2:
The patent changes the refractive index parameter of the material layer (second material with refractive index between silicon and air) to optimize mode field transition. By adjusting the refractive index and thickness of this intermediate layer, the mode field size is gradually transformed, enabling efficient coupling between optical fiber and submicron waveguide while reducing coupling loss.
2Loss of energy
If grating couplers are used to couple optical fiber to waveguide, then coupling efficiency is improved, but optical bandwidth becomes narrow
Solution Approach 1:
The patent changes the geometric parameters (width and thickness) of the waveguide and intermediate layer to optimize mode field matching across a broader spectral range. By adjusting these dimensions, the coupler maintains efficient coupling over a wider optical bandwidth compared to grating couplers, which rely on diffraction conditions that are more sensitive to wavelength variations.
3Ease of manufacture
If the waveguide is directly on the silicon substrate, then manufacturing is simplified, but mechanical integrity deteriorates during production and packaging
Solution Approach 1:
The patent uses a composite structure consisting of the silicon substrate, an intermediate layer of second material, and the waveguide. This composite structure provides mechanical support and protection to the waveguide during production and packaging while maintaining optical performance. The intermediate layer acts as a protective barrier that enhances mechanical integrity without complicating the manufacturing process significantly.
4Strength
If the waveguide is embedded in the layer of second material, then mechanical integrity is improved, but coupling efficiency may be reduced due to additional material interfaces
Solution Approach 1:
The patent optimizes the refractive index and thickness parameters of the intermediate layer of second material to minimize optical loss at the interfaces. By carefully selecting these parameters, the patent achieves a balance where the waveguide is sufficiently embedded for mechanical protection while the optical interfaces remain transparent enough to maintain efficient coupling between the optical fiber and waveguide.
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 coupling loss and improves mechanical integrity, enabling efficient light coupling between optical fibers and submicron silicon waveguides while maintaining structural stability during device production and packaging.
Implementation Method 1
The waveguide is embedded within the layer of second material... The undercut region is disposed between a portion of the silicon substrate and the layer of second material
Implementation Method 2
adjusting the refractive indices and dimensions to match the mode field of the optical fiber... The silicon substrate having a first index of refraction... a region having a second index of refraction less than the first index of refraction
Data Source
AI summary
Techniques for forming a facet optical coupler to couple light at an edge of silicon substrate are described. The facet optical coupler includes a silicon substrate, a layer of second material disposed on the silicon substrate and in direct contact with the edge of the silicon substrate, and an undercut region disposed between a portion of the silicon substrate and the layer of second material. The undercut region is offset from the edge to provide mechanical integrity of the facet optical coupler to improve production of photonic integrated circuits having the facet optical coupler from a wafer.