The circular polarizers were mostly made of meta-atom based chiral metamaterials (CMMs). Here we propose an ultra-thin metallic grating based circular polarizer, which can convert any polarization into circular polarization. The circular polarizer consists of two layers: an ultra-thin metallic grating embedded in the substrate and a silicon grating on the substrate surface. The ultra-thin metallic grating, which is thinner than the skin depth and was shown to hold anomalous resonant reflection for transverse magnetic (TM) wave, functions as a quarter-wave plate. We show that the ultra-thin metallic grating based quarter-wave plate can transmit circular polarized wave when the incident linear polarized wave is oriented properly. The silicon grating acts as a linear polarizer which restricts the polarization of the light that reaches the metallic grating. Unlike some of the CMMs, our structure is independent of the incident polarization state. Moreover, the fabrication of our circular polarizer is easier than other double-layer-CMMs, in which the relative position between the two layers must be precisely controlled. Our structure can find its application integrated photonic devices.
Surface plasmons have been widely investigated in many fields due to the unique property. ATR (attenuated totalreflection)
is the common method to excite surface plasmons. We derive the Fano-type analysis to present the
reflection spectrum of ATR configuration derived from the three-layer Fresnel reflection equation, which are
asymmetric curves resulted from interference between direct reflectance and surface plasmons leaky radiation. In the
fitting progress, we obtain the relationship between surface plasmons leaky radiation and metal thickness. When the
metal thickness is greater than 25nm, surface plasmons leaky radiation rate is less than 0.07. We also compare the ATR
and grating coupler excitement mechanism, which provide a reference to evaluate their application.
A special kind of metal nanograting which has excellent performance on polarization state controlling, is fabricated by
means of interference lithography, reactive ion etching (RIE) and two-time-evaporation coating with metal. The MNG
can produce angle-free elliptically polarized light via rolling the direction of grating, so it will have wide and convenient
applications in the systems which need flexible polarization orientation. We fabricate the MNG and test its performances
on polarization state controlling, then we simulate the process with software.
We numerically study the splitting of light beam which carries orbital angular momentum (OAM) through single metal nano-scale hole. A light beam carrying with OAM has a helical phase distribution in the transverse plane, where the electric field has the form: E(r,θ)=E0exp(lθ), and l is the topological charge which denotes the value of OAM. The circular polarization state is corresponding to the spin angular momentum (SAM), where s=+1 represents the left-handed polarization and s=-1 the right-handed polarization. Simulation results show l dependent splitting of beam through nano metal hole. When l is odd, the transmitted far field splits while no splitting happens when l is even. This phenomenon is attributed to the interaction between OAM beam and plasmonic mode of metal nano-hole. It is revealed that different OAM beam can excite different transverse mode in the metal cavity, which means the interaction should obey an OAM section rule. We show that even l can excite transverse mode with zero total AM and odd l can excite transverse mode with non-zero total AM within the hole. Orbital-spin conversion is also revealed in the free wave/plasmon interaction.
Organic solar cells show a commercially viable future duo to their inherent advantages, such as light weight, flexibility,
and so on. Recently, a lot of progress has been made in every domain of organic solar cells. Among these, plasmonic
light trapping is regarded as a promising light management technology for improving the light absorption in organic
active layer. In this work, we numerically investigate the light enhancement in organic solar cell by embedding metal
gratings as electrodes, including the anode and cathode. The absorption enhancement mechanism is analyzed, and the
effects of grating parameters and incident angle are also investigated systematically. The results show the plasmonic
gratings, especially the bottom grating, have an obvious improvement for light harvesting in organic layer, and an optical
enhancement factor about 100% is obtained.