Germanium Laser With Evanescent Waveguide Cavity
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Solution Overview
Problem
Existing laser sources with suspended membranes made from germanium lack improved mechanical, optical, and electronic properties, as the mechanical tensile stress is not sufficient to directly alter the energy band structure for efficient light emission.
Innovation Solution
A laser source design featuring a semiconductor layer with a suspended membrane comprising a central portion strained in tension and tensor arms, integrated with a waveguide that forms a hybrid optical cavity, allowing for evanescent coupling and optimized stress distribution to achieve direct energy band structure and enhanced light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Bragg mirrors are integrated into the tension arms to form the optical cavity, then the optical cavity can be formed, but the mechanical properties of the suspended membrane deteriorate due to stress concentration
Solution Approach 1:
The patent extracts the optical cavity formation function from the tension arms by placing Bragg mirrors in separate sacrificial layers positioned adjacent to the membrane, rather than integrating them into the tension arms. This separation removes the harmful stress concentration effect while preserving the optical cavity function through evanescent coupling between the membrane and waveguide.
Solution Approach 2:
The patent introduces sacrificial layers as intermediary structures that hold the Bragg mirrors in position during fabrication, then are removed to create the final configuration. This intermediary approach allows the Bragg mirrors to be positioned optimally for optical coupling without being mechanically integrated into the stress-bearing tension arms.
2Device complexity
If the integrated waveguide is placed close to the tension arms for compact design, then device size is reduced, but optical losses increase due to mode leakage
Solution Approach 1:
The patent positions the Bragg mirrors and waveguide in a configuration where they are laterally adjacent rather than vertically stacked or overlapping. The mirrors are placed in sacrificial layers next to the membrane, creating a side-coupling geometry that reduces evanescent field overlap with the tension arms while maintaining coupling efficiency through the waveguide.
3Object-generated harmful factors
If tensile stress is applied to the germanium layer to change band structure, then direct bandgap is achieved for light emission, but mechanical stress concentration occurs at structural features
Solution Approach 1:
The patent applies different structural characteristics to different regions: the membrane has uniform thickness and material composition optimized for stress distribution and light emission, while the tension arms have varying thickness and material composition optimized for mechanical support. This local differentiation allows tensile stress to be applied effectively to the membrane for band structure conversion without creating stress concentrations at structural features.
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 design enhances the mechanical, optical, and electronic properties of the suspended membrane, leading to improved light emission efficiency and reduced optical losses by maintaining the tensor arms free from optical reflectors, thus preventing stress concentration and mode leakage.
Implementation Method 1
a coupling section, located opposite the optical amplification section, adapted to allow optical coupling to the latter by evanescent wave
Data Source
Figure 1~2A
Figure 2B~3B
Figure 4~5A
AI summary
The invention relates to a laser source (1) comprising a semiconductor layer (10) made of germanium, comprising a suspended membrane formed of a central portion (20) under tension and comprising an optical amplification section (21), and several tension arms (30). It comprises an integrated waveguide (40), participating in the formation of an optical cavity located at the level of the support layer (3) and at a distance from the suspended membrane, and comprising a coupling section (41) located opposite the optical amplification section (21), adapted to allow optical coupling to the latter by evanescent wave, and at least one curved section (42), extending from the coupling section (41), and arranged so that the integrated waveguide (40) is disposed at a distance, in orthogonal projection, from the tension arms (30).