Side acceptance of tapered waveguides.

A) 2D schematic representation of ray acceptance within a tapered waveguide (thick black boundaries). Note that for visualization purpose the taper angle was exaggerated in this illustration. B) Critical accepted incidence angle θ_1c as a function of the taper angle θ. Rays with incidence angles ranging from θ_1c to 90° will be accepted in the waveguide (parameters were fixed as follows: R = 100 µm, R_f =5 µm, r_c =60 µm, r_cf = 3 µm, n₀ = 1 (air), n₀ = 1.35 (tissue) n₁ = 1.47 and n₂ = 1.45).