Waveguide for efficient light trapping and absorption

A waveguide (10) on which an electromagnetic wave impinges, said electromagnetic wave having a wavelength λ included in a given interval Δλ of interest centered on a λcentr, said waveguide comprising:

• a film defining a surface on a plane (X,Y) on which said electromagnetic waves are apt to impinge, and having a thickness in a direction (Z) substantially perpendicular to said surface, said film being realized in a material having a first refractive index (nfilm);
• a plurality of scatterers (11), said scatterers being randomly distributed in two directions in at least a portion of said surface of said film, said scatterers having a substantially constant cross section along said substantially perpendicular direction (Z);
• said scatterers being realized in a material having a second refractive index (nscatt), said second refractive index being lower than said first refractive index (nfilm);
• wherein the wavelength of the incident electromagnetic waves is comprised between
• 0.1
• <
• Δλ
• λ
• centr
• ≤
• 3
• and wherein the area (Ascatt) of the cross section of said scatterers is comprised between π·(Φref/6)2≦Ascatt≦π·Φref2, where
• Φ
• ref
• =
• n
• scatt
• n
• film
• ·
• λ
• centr
• .