Intermediary Waveguide for Low-Loss Optical Coupling
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Solution Overview
Problem
Efficient optical signal coupling between low refractive index waveguides and high refractive index waveguides is challenging due to significant refractive index differences, leading to high coupling losses and fabrication complexities, particularly in integrating optical fibers with semiconductor waveguides in microelectronics and biosensors.
Innovation Solution
A two-step approach involving a low refractive index intermediary waveguide fabricated using standard micrometer resolution photolithographic techniques for easy alignment, followed by directional optical coupling into a high refractive index semiconductor waveguide, allowing efficient energy transfer through tunneling-like phenomena by matching effective refractive indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If butt-coupling is used between optical fibers and semiconductor waveguides, then alignment precision is improved, but coupling loss increases due to refractive index mismatches
Solution Approach 1:
The patent introduces an intermediary waveguide layer with refractive index n2 that is intermediate between the optical fiber (n1≈1.47) and the semiconductor waveguide (n3≈3.5-4.0). This intermediary layer acts as a mediator to gradually transition the optical mode from the low refractive index fiber to the high refractive index semiconductor waveguide, reducing the abrupt refractive index mismatch and minimizing reflection losses at the coupling interface.
Solution Approach 2:
The patent changes the refractive index parameter by introducing a material layer with intermediate refractive index properties. By adjusting the refractive index of the intermediary waveguide layer, the patent optimizes the coupling efficiency between the optical fiber and semiconductor waveguide, transforming the harsh refractive index mismatch into a manageable gradient transition.
2Loss of energy
If refractive index difference between waveguides is reduced, then coupling efficiency is improved, but material selection becomes more constrained
Solution Approach 1:
The patent employs a composite waveguide structure consisting of multiple materials with different refractive indices. The intermediary waveguide layer is formed from materials such as silicon nitride (n≈2.0) or silicon oxide (n≈1.45-1.5), which are commonly used in photonic integrated circuits. This composite approach allows the system to achieve optimal coupling efficiency while maintaining compatibility with standard CMOS fabrication processes and existing material libraries.
3Loss of energy
If waveguide geometry is matched between fiber and semiconductor waveguide, then coupling loss is reduced, but mode confinement requirements are compromised
Solution Approach 1:
The patent resolves the geometry mismatch by transitioning from direct spatial overlap (0D/2D coupling) to evanescent field coupling through the intermediary layer (3D field interaction). The optical mode from the fiber couples to the intermediary waveguide through evanescent fields, which then couple to the semiconductor waveguide. This dimensional transition allows different waveguide geometries to coexist while maintaining efficient energy transfer.
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 method simplifies the fabrication process, reduces alignment complexities, and achieves efficient optical signal coupling with minimal loss, making it compatible with standard CMOS fabrication processes and applicable to various photonic circuits.
Implementation Method 1
said high refractive index waveguide and said I/O waveguide being arranged substantially parallel and in proximity with an overlap therebetween to permit tunnel coupling of said at least one mode of said optical signal between said internal signal path and said external signal path
Data Source
AI summary
An optocoupler, an optical interconnect and method of manufacture providing same are provided for coupling an optical signal between a high refractive index waveguide of an integrated circuit and a waveguide external to the integrated circuit. The optocoupler includes a thinned high refractive index waveguide having a thickness configured to exhibit an effective refractive index substantially matching a refractive index of the external waveguide.