**5. Conclusion**

method and read by plasmonic effect. **Figure 12(b)** illustrates a quick response (QR) code, which links to the website of the author's laboratory (LPQM). Bar code (1D) or QR code (2D) is a fast, easy, and accurate data storage method enabling products to be tracked efficiently and accurately. In particular, QR code attracts more attention in e-commerce because it also

Furthermore, as mentioned previously, the DLW technique allows production of any structures at nanoscale. **Figure 13** shows the result of a real image: a real "experiment book" of French laboratories. The real photo was imported to a MATLAB image, and each pixel was transferred to an exact dose of the light exposure, resulting in a plasmonic image of this "experiment book" at microscale. The image color is quite faithful to the original one, but theoretically and experimentally limited in the green and yellow color domain. That could be explained by the result shown in the simulation section, which predicted that the plasmonic resonance shifts only about 48 nm when the particles size changes from 20 to 100 nm. It is theoretically expected that a variety of colors could be obtained by organizing these Au NIs in order, like 1D and 2D PNSs [10, 11]. The combination of LSPR and PNS will offer a large

The magneto-optical (MO) sensors are a powerful sensing platform based on the Faraday or Kerr effects, that is, the rotation of linearly polarized light when it passes through or reflects from a magnetic thin film under influence of an external magnetic field [40]. However, conventional MO sensor cannot be used as a refractometer since it is not sensitive to minute

**Figure 13.** The color printed image fabricated by the DLW method on Au film. Left: a real "experiment book". Right: a

improves mobile user experience by convenient and easy operation.

**4.3. About resonantly enhanced plasmonic magneto-optics**

possibility to tune the color.

80 Plasmonics

plasmonic image of corresponding book at microscale.

In summary, this chapter reports systematically most aspects related to arbitrary plasmonic nanostructures, in particular those realized by the direct laser writing technique. In the first section, the optical properties of very basic nanostructures are completely investigated by using a well-known FDTD simulation method. Real fabricated metallic structures are also imported to a simulation model and calculated accurately. These investigations offer a short but understandable image of plasmonic properties of various nanostructures and guide for applications of plasmonic nanostructures in different domains. In the second section, the direct laser writing technique is demonstrated as an excellent method for realization of desired plasmonic nanostructures on demand. The fabrication of plasmonic nanostructures is demonstrated in two ways: indirectly via the use a polymeric template and directly by exploiting the optically induced local thermal effect. Any plasmonic microstructures with desired size, shape, and color were obtained by controlling the writing pattern and the exposure doses (laser power and writing speed). Finally, several important applications of plasmonic nanostructures, in particular those realized by direct laser writing method, have been demonstrated. Namely, the nano-holes arrays are demonstrated as excellent optical bandpass filters and also sensitive plasmonics-based sensor. The plasmonic nano-islands realized by optically induced thermal effect offered an excellent way for data storage and color nanoprinter. It is clear that those fabricated structures could be useful for a wide range of applications in numerous fields (physics, chemistry, biology, etc.).
