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Nanostructured Moth-Eye Anti-Reflective Coating
Tools Used: MOST, DiffractMOD
Microscale structures on the surface of optical interfaces have been known for over a century as an effective method of reducing Fresnel reflections. The eyes of a moth are covered with a natural anti-reflective nanostructured film.
- The moth-eye pattern is a pattern of subwavelength “bumps”; reduces reflection by creating an effective refractive index gradient between the air and the medium.
- The moth-eye structure is one of the most effective nanostructures to reduce reflection
- Moth-eye nanostructures can be patterned on surfaces to give them antireflection properties
- Moth-eye structures have several advantages over traditional thin-film AR coatings
- Environmental tolerance
- Surface adhesion
- Single-material fabrication
- Minimal surface preparation
- Higher laser-induced damage threshold
- Self cleaning (lotus effect)
- Moth-eye structures are especially useful for reducing reflections from and increasing transmission between materials with a large refractive index contrast
- Particularly important in high-power & low-loss applications
- Moth-eye AR structures have found uses in a number of applications, including laser systems, photovoltaics, LEDs, electronic displays, and fiber optics
The Challenge
In this work, we optimize the shape and dimensions of moth-eye structures for maximum output coupling through the endfaces of 𝐴𝑠2𝑆3 (n=2.45) chalcogenide optical fibers.
The Solution
Rigorous computational EM propagation methods, like FDTD and RCWA, can be used to accurately simulate the transmission/reflection from the moth-eye surface.
- For this particular moth-eye structure, RSoft’s DiffractMOD RCWA tool is utilized due to RCWA’s speed advantages over FDTD
- RSoft’s MOST Optimization and Scanning Utility is used in conjunction with DiffractMOD to optimize the reflection/transmission for the moth-eye AR pattern