Fabrication and characterization of near-field optical fiber nanoprobes with high resolution and high-transmission efficiency

Abstract

As one of the key components in scanning near-field optical microscopes (SNOM), optical fiber probes can be fabricated by use of either laser-heated pulling or chemical etching. For high-resolution near-field imaging, the near-field optical signal is rapidly attenuated as the aperture of probes decreases. It is thus important to fabricate probes optimized for aperture size and optical transmission. We present a two step fabrication method of 50 - 70% reproducibility to obtain probes with high optical transmission efficiency as well as small tip diameters. First, optic fiber probes with the transitional taper in hyperbolic or parabolic shape are produced by use of the simple home-made device for heating- pulling. Then, a rapid chemical etching with 40% buffered hydrofluoric acid is used to sharpen the tip while keeping the taper shape and the conic angle unchanged. The method renders us to achieve probes with tip diameters in the range of 20 nm - 200 nm and the tape angle near the tip apex in the range of 20 degree(s) - 60 degree(s). Particularly, the length of the non- propagating evanescent wave modes region decreases greatly to tens of micrometers or even less. In order to test the achieved probes, we give the photon tunneling decay curve and scanning near-field optical image of holographic grating by use of PSTM mode and collection-mode SNOM, respectively. In addition, an approach curve of shear force with hyperbolic probe is shown to verify its applicability to sample-tip distance regulation on basis of the principle of shear-force.