Giant birefringence in anisotropically nanostructured silicon

Abstract

We performed a study of the in-plane birefringence of anisotropically nanostructured Si layers, which exhibit a greater difference in the main value of the anisotropic refractive index than that of natural birefringent crystals. The anisotropy parameters were found to be strongly dependent on the typical size of the Si nanowires used to assemble the layers. This finding opens the possibility of an application of birefringent Si retarders to a wide spectral range for control of the polarization state of light.

Giant optical birefringence in ensembles of semiconductor nanowires

“…Next to the natural birefringence of crystals, artificial birefringence occurs in materials containing aligned macroscopic scatterers. The phenomenon has been observed in various systems such as aligned carbon nanotube films, 5 porous silicon, 6,7 and liquid-crystal templated porous CdTe. 8 In this letter we show that giant birefringence can be achieved in dense collections of randomly positioned vertical nanowires by controlling their length, alignment and diameter, and thereby the semiconductor filling fraction.…”

“…The largest birefringent ensemble that we have measured has an extraordinary large birefringence of 0.8, exceeding the natural birefringence of quartz by a factor of 75 and that of inverted or porous materials by more than a factor of 2. 6,7 This is to our knowledge the strongest birefringent material to date based on randomly positioned scatterers in the long-wave limit.…”

“…7,9,10 The extremely large available surface area of the wires can be coated with additional layers of silicon or noble metals for compatibility with biological functionalization groups, 9,11 while local bottom-up growth of nanowire layers on optical waveguides will yield integrated optical sensors with improved sensitivity. 10 Other applications of giant-birefringence nanowire materials are anticipated in quantum optics as a source of entangled photons, 12 for polarization control in microphotonics, 13 and as propagation medium for surface waves on birefringent materials.…”

“…The value of ⌬n = 0.80 measured in GaP nanowires is more than a factor 2 higher than previously reported values in highly birefringent porous Si. 6,7 A parameter of considerable interest is the birefringence normalized to the in-plane refractive index n o , describing the relative difference of the phase velocity of the light between the two polarizations. We have represented this relative birefringence in Fig.…”

Epitaxial Growth of Aligned Semiconductor Nanowire Metamaterials for Photonic Applications

“…[1] One of these properties is optical formbirefringence, the difference in refractive index for different polarizations of light, resulting from the arrangement of anisotropic scatterers. [2] Optical form-birefringence has been observed in various systems such as aligned carbon nanotube films, [3] porous silicon, [4][5][6] and liquid-crystal templated porous CdTe. [7] In periodic structures like photonic crystals [8,9] and gratings, [10] large artificial birefringence occurs at certain frequencies near a resonance dictated by the periodicity.…”