RSoft Application Note: Nanostructured Moth-Eye Anti-Reflective Coating

Tools Used: MOST, DiffractMOD, LightTools

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 𝐴𝑠2𝑆(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