Influence of the photonic nanojet of microspheres on microsphere imaging

The imaging properties of BaTiO₃ glass (BTG) microspheres in the diameter range of 5-50 µm which are fully immersed in a polydimethylsiloxane layer are experimentally studied. Our experimental results show that for both Blu-ray disc samples and the single-layer hexagonally close-packed microsphere array samples, with the increase of the diameter of BTG microspheres, the range of focal image positions (RFIP) increases linearly. When the diameter of BTG microspheres increases from 5 to 50 μm, the RFIP changes from 4 to 25 μm. For the microsphere array samples, Talbot effect is observed, and both the position of Talbot images and the Talbot distance depend on the diameter of BTG microspheres. Numerical simulations indicate that the length of the photonic nanojet changes from 2.9 to 7.1 μm when the BTG microsphere size increases from 5 to 50 μm, and the calculated RFIP is between 6 and 24 μm. The calculated RFIPs match well with the experimental ones. Our researches reveal that the RFIP depends on the length of the photonic nanojet of the BTG microsphere.