Photodetector Notched Light-Absorbing Layer Reduces Back Reflection
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Solution Overview
Problem
Photodetectors in photonics chips suffer from back reflection due to index mismatches between the light-absorbing layer and the waveguide core, leading to poor responsivity and quantum efficiency.
Innovation Solution
A photodetector structure is introduced with a light-absorbing layer having a sidewall with a notch, and a waveguide core section adjacent to the notch, which helps in reducing back reflection by minimizing index mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional photodetector structure with a light-absorbing layer and waveguide core is used, then the device can perform basic light-to-electrical signal conversion, but back reflection occurs due to index mismatches leading to poor responsivity and quantum efficiency
Solution Approach 1:
The light-absorbing layer is segmented by introducing a notch that divides it into two separate sections. This segmentation allows each section to have optimized optical properties, with the first section having a first refractive index and the second section having a second refractive index, thereby reducing back reflection at the interface between the light-absorbing layer and the waveguide core
Solution Approach 2:
Different regions of the light-absorbing layer are given different local optical properties through the notch structure. The first and second light-absorbing sections have different refractive indices tailored to their specific positions and functions, with the first section optimized for light coupling and the second section optimized for light absorption and signal generation
2Reliability
If the light-absorbing layer material is changed to improve absorption, then quantum efficiency may improve, but index mismatch with the waveguide core worsens causing increased back reflection
Solution Approach 1:
The light-absorbing layer is divided into two sections with different materials or compositions, allowing each section to be optimized for different functions. The first section can be optimized for minimal index mismatch with the waveguide core to reduce reflection, while the second section can be optimized for high quantum efficiency
Solution Approach 2:
The light-absorbing layer uses composite material structure with two different materials or compositions in the first and second sections. This allows combining the benefits of different materials - one with refractive index matched to the waveguide core and another with superior light absorption properties
3Loss of energy
If a notch is introduced in the light-absorbing layer sidewall, then back reflection is reduced, but the device structure becomes more complex
Solution Approach 1:
The notch introduces a controlled segmentation that, while adding structural complexity, creates distinct optical zones that systematically address the reflection problem through refractive index management
Solution Approach 2:
The notch structure enables precise control and change of the refractive index parameter across different sections of the light-absorbing layer, allowing optimization of optical performance by adjusting material composition, thickness, or density in each section
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 proposed structure significantly reduces optical reflection loss and insertion loss while maintaining high coupling efficiency and responsivity, enhancing the performance of photodetectors in photonics chips.
Implementation Method 1
A photodetector may include a light-absorbing layer and a waveguide core that is configured to transfer light to the light-absorbing layer
Data Source
AI summary
Structures for a photonics chip that include a photodetector and methods of forming such structures. The structure comprises a photodetector that is disposed on a substrate and that includes a light-absorbing layer. The light-absorbing layer includes a sidewall and a notch in the sidewall. The structure further comprises a waveguide core including a section adjacent to the notch in the sidewall of the light-absorbing layer.