Tapered Photodiode Evanescent Coupling Linear Absorption
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Solution Overview
Problem
Existing photodiodes face limitations in absorbing high-power optical signals without exceeding the maximum energy density, leading to reduced absorption capacity and increased response time due to exponential absorption profiles in germanium or SiGe cores.
Innovation Solution
A photodiode design with a tapered termination in the silicon waveguide and a germanium core, utilizing a ribbon for evanescent and modal coupling, achieves a linear absorption profile, allowing for greater power absorption without increasing core volume, thereby enhancing absorption efficiency and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the transverse dimensions of the germanium core are increased to reduce energy density and increase maximum absorbable power, then the volume of the germanium core increases and the photodiode response time slows down
Solution Approach 1:
The patent changes the absorption profile parameter from exponential to linear by introducing a tapered waveguide structure. This parameter change allows the photodiode to absorb higher power optical signals uniformly along the germanium core length without increasing core volume or slowing response time, thus resolving the contradiction between power handling and response speed
2Power
If the transverse dimensions of the germanium core are increased to distribute energy density, then the volume of the germanium core increases
Solution Approach 1:
The patent transforms the absorption profile from exponential to linear through the tapered waveguide design, enabling uniform energy distribution along the core length. This allows the photodiode to handle higher power signals with the same core volume, resolving the contradiction between power capacity and device compactness
3Power
If a linear absorption profile is achieved through tapered termination and evanescent coupling, then higher optical power can be absorbed with equal core dimensions, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by creating a tapered termination only at the end of the silicon waveguide where it interfaces with the germanium core. This localized structural modification generates evanescent coupling that produces the desired linear absorption profile, achieving higher power capacity without requiring complex changes throughout the entire device structure
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 photodiode effectively absorbs higher optical signal powers with even energy distribution along the germanium or SiGe core, improving absorption efficiency and reducing response time while maintaining compactness.
Implementation Method 1
a ribbon (24) made of the same material as the core (22) and encapsulated inside a layer (88) of silicon oxide, the ribbon (24) being directly in contact with the core (26) made of germanium or SiGe so that the optical signal is transferred, by evanescent coupling, from the core (22) to the core (26)
Implementation Method 2
the optical signal being transferred, by modal coupling then by evanescent coupling, from the core (22) to the core (26)
Implementation Method 3
Photodiode 2 converts the optical signal into an electrical signal generated between two contact sockets 10 and 12
Data Source
Figure 1~3
Figure 4~5
Figure 6~12
AI summary
This photodiode comprises: - a core (22) of a first waveguide terminating in a tapered end (30) extending above a germanium or SiGe core (26) of a second waveguide, - a matching strip (24) extending on one side opposite the tapered end (30) and, on the opposite side, opposite the core (26) of the second waveguide, this matching strip being optically coupled to the core (26) of the second waveguide by evanescent coupling and comprising a first zone (92) within which its effective propagation index is equal to the effective propagation index of a second zone (94) of the tapered end (30), these first and second zones optically coupling the tapered end to the matching strip by modal coupling, and - a low-index layer extending between the matching strip and the tapered end.