Low Index ARROW Optical Coupler for Large Mode Field Alignment
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Solution Overview
Problem
Existing optical couplers face challenges in efficiently coupling free space optical signals with large mode field diameters to high index waveguides due to back-reflections and mis-alignment issues, leading to signal loss and instability.
Innovation Solution
An optical coupler is formed using an antiresonant reflecting optical waveguide (ARROW) structure with an embedded nanotaper coupling waveguide, which traps energy and adiabatically transforms modes for efficient coupling into a single mode high index waveguide, relaxing alignment tolerances and enabling wider bandwidth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high index nanotaper tip is placed at the junction where the incoming signal couples into the optical substrate, then coupling efficiency is improved, but back-reflections are generated causing laser instability
Solution Approach 1:
The patent introduces a low index material layer (intermediary) between the high index nanotaper tip and the optical substrate. This intermediary layer acts as a buffer that reduces the abrupt refractive index contrast, thereby minimizing back-reflections while maintaining efficient light coupling into the waveguide.
Solution Approach 2:
The patent modifies the refractive index parameter at the coupling junction by using a low index material instead of the conventional high index material directly at the substrate interface. This parameter change (from high index to low index) reduces the reflection coefficient and eliminates the harmful back-reflections that cause laser instability.
2Reliability
If the nanotaper tip is recessed from the cleaved edge of the optical substrate, then back-reflections are reduced, but coupling efficiency decreases due to mis-alignment
Solution Approach 1:
The low index material layer serves as an intermediary that extends the interaction region between the incoming light and the nanotaper waveguide. This allows the light to couple efficiently into the recessed nanotaper tip without requiring precise alignment, as the low index layer provides a gradual transition zone.
Solution Approach 2:
The patent introduces an additional dimensional element (the low index material layer thickness) to the coupling structure. By adjusting this vertical dimension, the system achieves both reduced back-reflections and maintained coupling efficiency, effectively adding a degree of freedom to the coupling design.
3Loss of energy
If an auxiliary waveguide with larger dimensions and lower refractive index is used to transmit light to the nanotaper tip, then coupling efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges the auxiliary waveguide function with the existing nanotaper structure by placing the low index material layer directly at the nanotaper-substrate interface. This integration eliminates the need for a separate auxiliary waveguide structure, reducing device complexity while maintaining the benefits of improved coupling efficiency.
Solution Approach 2:
The low index material layer serves multiple functions simultaneously: it acts as an intermediary to reduce back-reflections, provides a gradual index transition for improved coupling, and enables the nanotaper to function effectively as both the waveguide and coupling structure, eliminating the need for separate auxiliary components.
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 solution achieves low loss and efficient mode conversion, reducing alignment sensitivity and allowing for broader bandwidth operation, while enabling wafer-scale fabrication and use of low index waveguides for improved optical signal coupling.
Implementation Method 1
an antiresonant reflecting optical waveguide (ARROW) structure with an embedded nanotaper coupling waveguide, which traps energy
Implementation Method 2
adiabatically transforms modes for efficient coupling into a single mode high index waveguide
Data Source
AI summary
An optical coupler is formed of a low index material and exhibits a mode field diameter suitable to provide efficient coupling between a free space optical signal (of large mode field diameter) and a single mode high index waveguide formed on an optical substrate. One embodiment comprises an antiresonant reflecting optical waveguide (ARROW) structure in conjunction with an embedded (high index) nanotaper coupling waveguide. Another embodiment utilizes a low index waveguide structure disposed in an overlapped arrangement with a high index nanotaper coupling waveguide. The low index waveguide itself includes a tapered region that overlies the nanotaper coupling waveguide to facilitate the transfer of the optical energy from the low index waveguide into an associated single mode high index waveguide. Methods of forming these devices using CMOS processes are also disclosed.