Evanescent Coupling Interface for Photonic Chip Waveguide Alignment
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Solution Overview
Problem
Transmitting optical signals between silicon-on-insulator (SOI) devices and external optical components is challenging due to the mismatch in mode sizes between fiber optic cables and sub-micron waveguides, resulting in low transmission efficiency and high coupling loss.
Innovation Solution
The implementation of an evanescent coupling method using tapered waveguides that align with corresponding waveguides on an external substrate, allowing optical signals to transfer between the photonic chip and external optical device with minimal coupling loss, through an adiabatic structure that maintains the optical mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If lenses are used to focus light from external fiber optic cables into sub-micron waveguides, then the optical signal can be efficiently transferred, but the device complexity increases and alignment precision requirements become more stringent
Solution Approach 1:
The patent removes the lens component from the optical coupling system. Instead of using lenses to focus light, the invention employs direct evanescent coupling between waveguides, eliminating the need for complex lens alignment and reducing device complexity while maintaining coupling efficiency.
Solution Approach 2:
The patent introduces an evanescent coupler as an intermediary structure between the fiber optic cable and sub-micron waveguide. This coupler enables gradual optical mode transformation through evanescent field interaction, allowing efficient coupling without requiring precise lens alignment or complex focusing mechanisms.
2Productivity
If lenses are used to adjust numerical aperture for efficient optical signal transfer, then transmission efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs a tapered waveguide structure where the waveguide width gradually changes along the propagation direction. This dynamic geometric transformation allows the optical mode to adaptively adjust its size, enabling efficient coupling over a broader range of alignment tolerances and reducing manufacturing precision requirements.
Solution Approach 2:
The patent changes the geometric parameters of the waveguide (width, height) along its length to create a tapered profile. This parameter variation enables continuous transformation of the optical mode size, matching the numerical aperture of external fiber cables to sub-micron waveguides without requiring high-precision lens alignment.
3Device complexity
If direct coupling between fiber optic cables and sub-micron waveguides is attempted, then device complexity is reduced, but coupling loss increases due to mode size mismatch
Solution Approach 1:
The patent implements a tapered waveguide structure that preliminarily transforms the optical mode size before the signal enters the sub-micron waveguide. This gradual mode transformation occurs along the tapered section, preparing the optical field for efficient coupling into the narrow waveguide without requiring complex lens systems.
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 transmission of optical signals with minimal loss, maintaining the optical mode and improving coupling efficiency between the SOI device and external optical components.
Implementation Method 1
an evanescent coupler spaced apart from the silicon waveguide along a direction normal to the insulation layer and active surface layer, where the evanescent coupler is optically coupled to the silicon waveguide
Implementation Method 2
through an adiabatic structure that maintains the optical mode
Data Source
AI summary
Embodiments herein describe a photonic chip which includes a coupling interface for evanescently coupling the chip to a waveguide on an external substrate. In one embodiment, the photonic chip includes a tapered waveguide that aligns with a tapered waveguide on the external substrate. The respective tapers of the two waveguides are inverted such that as the width of the waveguide in the photonic chip decreases, the width of the waveguide on the external substrate increases. In one embodiment, these two waveguides form an adiabatic structure where the optical signal transfers between the waveguides with minimal or no coupling of the optical signal to other non-intended modes. Using the two waveguides, optical signals can be transmitted between the photonic chip and the external substrate.