Optical Waveguide Transitions With Adiabatic Tapers for Low Reflection
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Solution Overview
Problem
The efficiency of coupling light between heterogeneous semiconductor materials in optical devices is limited by fabrication processes, leading to inefficiencies such as reflections and optical losses, which affect device performance by introducing noise and unintended lasing effects.
Innovation Solution
The implementation of high efficiency optical waveguide transitions using tapered regions with lateral offsets and passive or active structures to minimize reflections, such as angled tapers, star-shaped structures, and electrical contacts, which adiabatically transform the optical mode and enhance light coupling while reducing back-reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional fabrication processes are used for heterogeneous semiconductor materials, then device manufacturing is feasible, but light coupling efficiency deteriorates due to reflections and optical losses
Solution Approach 1:
An intermediate waveguide structure is introduced between the first and second waveguides formed from different semiconductor materials. This intermediate structure serves as a mediator that facilitates gradual mode transformation and reduces reflections, thereby improving light coupling efficiency while working within existing fabrication process constraints.
Solution Approach 2:
The waveguide transition structure modifies geometric parameters (such as width, height, and lateral position) along the propagation direction to create an adiabatic transition. This gradual parameter change enables efficient mode transformation between heterogeneous materials, reducing optical losses without requiring new fabrication processes.
2Object-generated harmful factors
If abrupt waveguide transitions are used between heterogeneous materials, then fabrication is simplified, but reflections increase causing noise and unintended lasing
Solution Approach 1:
The waveguide transition employs curved or tapered geometries instead of abrupt straight transitions. The curved profile enables adiabatic mode transformation, gradually changing the waveguide dimensions to minimize reflections and eliminate harmful back-reflections that cause noise and unintended lasing.
Solution Approach 2:
The transition structure utilizes additional spatial dimensions (such as lateral offset and vertical height changes) to achieve mode transformation. By expanding the solution space into multiple dimensions, the design achieves low-reflection transitions while managing the complexity through systematic geometric progression.
3Productivity
If tapered regions with small minimum dimensions are used, then light coupling efficiency is improved, but fabrication precision requirements increase
Solution Approach 1:
Instead of achieving the theoretically optimal minimum dimension, the design uses a partially sufficient dimension that is easier to fabricate. The transition length and profile are optimized to compensate for the larger minimum dimension, achieving acceptable coupling efficiency without requiring extreme fabrication precision that would increase manufacturing complexity and cost.
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 results in lower relative intensity noise and phase noise, improving the performance of optical devices by ensuring efficient light transfer between heterogeneous semiconductor materials, thereby enhancing the efficiency of optical waveguide transitions.
Implementation Method 1
taper 102 to adiabatically transform (i.e., laterally confine) the optical mode of light
Implementation Method 2
region 106 is to receive light from waveguide 100 that was not coupled into waveguide 110
Data Source
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AI summary
Embodiments describe high-efficiency optical waveguide transitions - i.e., creating heterogeneous transitions between Si and III-V semiconductor regions or devices with minimal reflections. This is advantageous for III-V device performance, e.g. for an on-chip lasers achieving lower relative intensity noise (RIN) and lower phase noise by avoiding reflections, higher gain and reduced gain-ripple from an semiconductor optical amplifier (SOA) by avoiding internal reflections in the SOA. Furthermore, in some embodiments, generated photocurrent can be used as a monitor signal for control purposes, thereby avoiding the use of separate tap-monitor photodetectors, which provide additional link loss.