Polarization Properties Of Porous Anodic Alumina With Metal Nanowires

The porous anodic alumina (PAA) film with metal nanowires has exhibited a better property of polarization in near infrared region. Compared with other kinds of polarizers, this one has many advantages, such as smaller volume, simpler fabrication method and lower cost. Firstly, having analyzed the polarization mechanism of the PAA with metal nanowires, a new theoretical model has been put forward to research the relation between the polarization and the template parameter. Secondly, the PAA with Cu nanowires has been fabricated by the electrochemistry method, and its property of polarization has also been studied. Finally, the PAA with Y-branched junction structure has been obtained through two-step anodization process; with this template, the Y-branched Cu nanowires have been synthesized and the polarization spectrum of this compound structure has been measured. Through using this structure, we are intended to improve the extinction ratio of this kind of micropolarizers.Based on the polarization principle of the metal wire-grid polarizer, we have analyzed the polarization mechanism of the PAA with metal nanowires thoroughly. Starting from the different loss mechanisms to the P and S light components, we have established a new theoretical model. Taking a row of nanowires as the investigation object, we have calculated the optical loss of the P and S light components when vertical incidence occurs. Under the condition of fixing the wavelength, we have calculated the relation between the transmittance of the P and S light components, the extinction ratio of this kind of structure and the aperture of the PAA template by using the Mathematic 4.0.In dilute solution of sulfuric acid, porous alumina templates with different apertures have been fabricated by increasing the anodic oxidation voltage and pore widening, and then Cu nanowires have been synthesized in porous alumina templates by alternating current deposition method. The effects of changing the aperture on the polarization have also been studied. The extinction ratio can be improved by increasing the oxidation voltage of the template, and the larger the templates' pore diameter is, the higher the extinction ratio is. Although the pore widening method also can increase the Cu nanowires' diameter, it cannot enhance the polarization performance of the micropolarizer.Porous anodic alumina templates with branches structure have been fabricated by the two-step anodic oxidation processes, and then the Y-branched Cu nanowires have been synthesized in the templates. The SEM image of the upside and downside templates and the cross-section of the samples indicate that the micropolarizer of PAA with Y-branched Cu nanowires has been obtained. We have measured the transmission spectrum and the polarization spectrum of the samples. The results show that PAA films with Y-branched Cu nanowires have better transmittance reaching 90% in the near infrared region, hence, it can be taken as a template of polarizer in the near infrared region; the porous alumina films with Y-branched Cu nanowires have tetter transmittance in the near infrared region. An extinction ratio of 15 to 18 dB and an insertion loss of 0.1 to 0.4 dB have been obtained in our experiment.