Fig. 6.

a) Schematic diagram of an FP etalon integrated in an optical fibre illuminated by a diverging beam focussed using a GRIN lens; b) reflection-mode ITFs obtained using the ABCD model for different lengths of GRIN lens (h_g = 0 µm, h_g = 50 µm and h_g = 100 µm); and c) ITFs obtained for different lengths of NCF (z_off = 10, 30 and 60 µm). For the simulations, the etalon parameters were n₀ = 1.444, h_g = 102 µm, z_off = 10 µm, and MFD = 10.4 µm