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Thermodynamic upper bound on broadband light coupling with photonic structures.
Zongfu Yu1, Aaswath Raman, Shanhui Fan
1Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
Physical Review Letters
|December 11, 2012
Summary
The second law of thermodynamics sets a fundamental limit on how efficiently light can couple to optical devices. This discovery impacts the design of photonic structures and solar absorbers.
Area of Science:
- Physics
- Optics
- Thermodynamics
Background:
- The performance of optical devices is heavily dependent on the interaction between light and optical media.
- Understanding the coupling of free space radiation to optical modes is crucial for device efficiency.
Purpose of the Study:
- To establish a fundamental upper bound on the external coupling rates of optical modes in any photonic structure.
- To apply this bound to determine the theoretical limit of light absorption in broadband solar absorbers.
Main Methods:
- Derivation of an upper bound for the sum of external coupling rates based on the second law of thermodynamics.
- Application of the derived bound to analyze light absorption in solar absorber systems.
Main Results:
- A universal upper bound exists for the total external coupling rate of optical modes in a given photonic structure.
- This bound is dictated by fundamental thermodynamic principles.
Conclusions:
- The efficiency of light coupling into photonic structures is fundamentally limited.
- The derived thermodynamic bound provides a critical parameter for optimizing light absorption in devices like solar absorbers.
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