Sidewall Waveguide Coupler for Photodetector Mode Matching
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Solution Overview
Problem
Significant mode mismatch between waveguides with thin silicon cores and photodetectors with thick germanium or silicon germanium light absorption layers leads to degraded coupling efficiency and reduced photodetector performance.
Innovation Solution
A photonic structure with a waveguide-to-photodetector coupler oriented along the sidewall of a polarization-independent photodetector, featuring a tapered adiabatic optical coupler with stacked cores to facilitate mode matching and improve coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a waveguide with a thin silicon core is coupled to a photodetector with a thick germanium or silicon germanium light absorption layer, then the photodetector can absorb more light, but significant mode mismatch occurs leading to degraded coupling efficiency
Solution Approach 1:
The patent introduces an intermediary structure (the coupler with stacked cores) between the waveguide and photodetector to bridge the mode mismatch. The stacked cores progressively transform the optical mode from the thin waveguide core to match the thick photodetector absorption layer, enabling both high light absorption and efficient coupling.
Solution Approach 2:
The patent transitions from a single-plane coupling interface to a three-dimensional stacked core structure. By adding the vertical dimension with multiple stacked cores of varying dimensions, the system can progressively match modes between the thin waveguide core and thick absorption layer, resolving the contradiction between absorption capacity and coupling efficiency.
2Ease of manufacture
If the thick Ge or SiGe light absorption layer is epitaxially grown on a recessed section of a Si layer, then the photodetector structure is formed, but the mode mismatch is exacerbated
Solution Approach 1:
The coupler with stacked cores serves as a mediator that compensates for the mode mismatch introduced by the recessed section structure. The stacked cores provide a gradual transition that bridges the geometric discontinuity between the waveguide and the photodetector's recessed absorption layer.
3Device complexity
If a conventional direct coupling between waveguide and photodetector is used, then the structure is simple, but mode mismatch leads to reduced photodetector performance
Solution Approach 1:
The patent adds vertical stacking of cores to the coupling structure, transitioning from a simple planar interface to a multi-layered three-dimensional structure. This dimensional addition enables mode matching while maintaining manufacturability through standard semiconductor fabrication processes.
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 solution enhances coupling efficiency and photodetector performance by effectively matching modes between the waveguide and the photodetector, thereby improving the conversion of light signals into current.
Implementation Method 1
a tapered adiabatic optical coupler with stacked cores to facilitate mode matching
Implementation Method 2
allowing light signals (i.e., photons) from the waveguide to be received by the photodetector and converted into current
Data Source
AI summary
Disclosed are embodiments of a photonic structure with at least one tapered coupler positioned laterally adjacent and along the length of a sidewall of a layer, such as a light absorption layer (LAL), of a photodetector to facilitate mode matching. Some embodiments include a vertically oriented photodetector, which is on an insulator layer and has an LAL stacked between bottom and top semiconductor layers, and a coupler, which is on the insulator layer positioned laterally adjacent to the photodetector and has stacked cores with one of the cores being at the same level as the LAL. Other embodiments include a horizontally oriented photodetector, which is on an insulator layer and has an LAL on a recessed section of a bottom semiconductor layer between side sections, and coupler(s), which is/are above side section(s) of the bottom semiconductor layer and, thus, positioned laterally adjacent to one or both sides of the LAL.