Among plenty of techniques proposed to realize photonic structures, direct laser writing (DLW) has been considered as an ideal one to create any desired submicrometric structure. Particularly, we have recently proposed and demonstrated a simple and low-cost method called low one-photon absorption (LOPA) DLW, which benefits the advantages of both one-photon absorption (OPA) and two-photon absorption (TPA) techniques, allowing us to fabricate arbitrary 2D and 3D submicro-structures. The LOPA fabrication technique is based on the use of an excitation laser with the wavelength located near the edge of the absorption band of the photoresist used. With this low absorption, the light beam can propagate deeply inside the material. By using a microscope lens of high numerical aperture, the laser beam is focused into small region with a very high intensity, which compensates for the low absorption of the photoresist. By scanning the focusing spot, any sub-wavelength structure can be created via local photopolymerization process. 1D, 2D, and 3D arbitrary structures, with sizes as small as 100 nm, have been fabricated using SU8 photoresist and a continuous-wave laser at 532 nm-wavelength with only a few milliwatts. Figures 1(a,b) illustrate the working principle of LOPA-based DLW technique and an example of fabricated 3D structures.

Furthermore, we have recently demonstrated that by using this LOPA-based DLW, and with a double-step process, it is possible to address most kinds of nanoparticles and to precisely embed them into desired polymeric photonic structures. Figures 1(c,d) show a 2D structure containing a single gold nanoparticle.