Evanescently Coupled Germanium Ring Resonator for Extended Wavelength Detection
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Solution Overview
Problem
Conventional germanium photodetectors face challenges in detecting wavelengths beyond 1.55 μm due to increased dark current and limited interaction length when detector size is increased, and strained germanium has a short interaction length, limiting efficiency at longer wavelengths.
Innovation Solution
A germanium layer is evanescently coupled to a resonator, allowing for efficient light absorption and conversion into electrical signals without increasing detector size, with the resonator's quality factors matched to enhance absorption efficiency, enabling detection across the S, C, and L bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the detector size is increased to detect wavelengths beyond 1.55 μm, then the detection wavelength range is extended, but the dark current increases and speed performance deteriorates
Solution Approach 1:
The patent transitions from conventional planar photodetector geometry to a resonant cavity structure with evanescent field coupling. The germanium layer is positioned adjacent to the resonator where the evanescent field extends, creating a three-dimensional interaction volume that increases effective interaction length without increasing the detector's planar footprint, thereby extending wavelength detection capability without proportionally increasing dark current
Solution Approach 2:
The resonator serves as an intermediary structure that mediates between the incident light and the germanium photodetector. The resonator's evanescent field couples light into the germanium layer, enabling enhanced light absorption at extended wavelengths while the resonator's high quality factor ensures that this coupling occurs efficiently without requiring a large germanium volume that would increase dark current
2Adaptability or versatility
If the detector size is increased to detect wavelengths beyond 1.55 μm, then the detection wavelength range is extended, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The resonator structure serves multiple functions simultaneously: it acts as a wavelength-selective filter, an optical cavity for enhancing light-matter interaction, and a coupling mechanism to the germanium photodetector. This multi-functionality allows the same structure to enable extended wavelength detection while maintaining compatibility with standard silicon photonic fabrication processes, thereby reducing overall device complexity
Solution Approach 2:
The patent utilizes parameter changes in the resonator design, specifically matching the resonator's quality factors (internal and external) to optimize coupling conditions. By adjusting the resonator geometry and material properties to achieve critical coupling, the system maximizes light absorption in the germanium layer at extended wavelengths while maintaining a compact structure that is manufacturable using existing CMOS-compatible processes
3Adaptability or versatility
If strained germanium is used to perform photodetection beyond 1.55 μm, then the detection wavelength range is extended, but the interaction length remains short and detection efficiency is limited
Solution Approach 1:
The resonator is designed to support optical resonance, creating a standing wave pattern with high field intensity within the cavity. This resonant enhancement effectively increases the interaction time between light and the germanium layer, compensating for the short physical interaction length of strained germanium and thereby improving detection efficiency at extended wavelengths
Solution Approach 2:
The resonator acts as an intermediary that enhances the weak interaction between light and strained germanium. By confining light in the resonator cavity and creating a strong evanescent field that couples to the germanium layer, the resonator amplifies the effective interaction strength, enabling efficient photodetection at wavelengths beyond 1.55 μm despite the inherently short absorption length of strained germanium
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 maintains low dark current and achieves high responsivity and extended detection wavelength range up to 1630 nm, facilitating simultaneous detection in multiple optical communication bands with improved power detection and wavelength filtering.
Implementation Method 1
A germanium layer is evanescently coupled to a resonator, allowing for efficient light absorption and conversion into electrical signals
Implementation Method 2
The germanium layer absorbs at least a portion of the light guided by the resonator
Implementation Method 3
The germanium layer converts the at least a portion of the light into an electrical signal
Data Source
AI summary
A photodetector includes a germanium layer evanescently coupled to a ring resonator. The ring resonator increases the interaction length between light guided by the ring resonator and the germanium layer without increasing the size of the photodetector, thereby keeping the photodetector's dark current at a low level. The germanium layer absorbs the guided light and converts the absorbed light into electrical signals for detection. The increased interaction length in the resonator allows efficient transfer of light from the resonator to the germanium layer via evanescently coupling. In addition, the internal and external quality factors (Q) of the ring resonator can be matched to achieve (nearly) full absorption of light in the germanium with high quantum efficiency.