To measure the refractive index and fabricate optical devices,
LFAR was dissolved in cyclopentanone (CP) at concentration
of 60–80 wt.%.With the presence of 8 wt.% photoinitiator
PI, the solution filtered by a syringe through a
0.22 μm Teflon membrane filter was spin-coated on the silicon
wafer substrates at a spin rate of 2000 rpm for 30 s. The
resulting film (2∼7 μm) was baked in an oven at 95◦C for
30 min, and then was irradiated by UV light to get a highly
transparent film. The film was finally baked in an oven at
120◦C for 1 h.