Steering The Polarization And Spin Hall Effect Of Light Via Man-made Microstructures

Polarization is an important property of light. It is always desirable to have full control of the polarization. In essence, manipulation of the polarization of light can be achieved by controlling the magnitude of its electric field components and their phase difference. Convention methods include anisotropic waveplates, polarizers, chiral media or gratings. Man-made microstructure is a kind of composite medium whose electromagnetic properties are depend on its structure rather than composition. It is composed of two or more kinds of media with its structure unit further less than a wavelength. It always has the properties further exceeded (or not possessed by) the conventional media, or has abnormal properties. One can obtain much larger anisotropy than convention anisotropic media via suitably tailoring the structure geometry of the man-made microstructure. Also, the desirable polarization or phase properties could be acquired by locally designing the structure units.The polarization will also affect another fundamental property of light, that is, coherence, so one can control the coherence of light by steering the polarization. High coherence is a striking property of lasers, which facilitate lasers to be widely applied in those fields requiring high coherent light sources. However, just as a coin has two sides, coherence is harmful to some laser application fields. High coherence usually results in unwanted speckle noise in laser display (or laser projection imaging or laser TV), thereby decreasing the imaging resolution. In laser fusion and laser heat processing, coherence makes the intensity distribution on the focal plane not uniform enough. In some spectroscopy experiments, a high coherence laser is also undesirable. Thus, in these applications, it is urgently needed to eliminate the laser coherence. On the other hand, as a hot topic in the recent years, the spin Hall effect light has attracted much attention. It is an analogy of the spin Hall effect in electronic system in which the spin photon corresponds to the spin electron and the refractive index gradient plays a role of external field. It manifests itself as the spin-dependent splitting of photon spin states. Therefore, in some way, manipulating the spin Hall effect of light is essentially control the polarization.Based on the above knowledge, we propose that man-made microstructures can be employed to manipulate the polarization and the spin Hall effect of light. Some creative work has done as in the follows. (i) We propose an inhomogeneous anisotropic microstructure for producing incoherent laser illumination. The structure can produce locally polarization change for the laser beam. In the far-field focal plane, the superposition beam is incoherent. Without loss of generality, we will exemplify our scheme numerically using a variation version of the typical L-shaped metamaterial, although the approach can be applied to an arbitrary metamaterial geometry offering enough number of free design parameters. The calculating results show that this structure can effectively suppress the speckle contrast and increase irradiation uniformity. The dimension of the structure can be confined to the order of a wavelength, which facilitates the metamaterial-base polarization control device to be potential applied in the future photonic integrated circuit.(ⅱ) We investigate the spin Hall effect of refractive light in two kinds of multi-layer films. The two films have symmetric and non-symmetric structure geometries, respectively, whose Fresnel coefficients can be tunable via changing the optical parameters of the films. We find that the spin-orbital interaction exhibits a sine-like oscillation in the range of negative-zero-positive valves due to the Fabry-perot resonance. Thus, we can significantly enhance or totally suppress the spin-dependent transverse shifts, and then the spin Hall effect of light. Further, we propose a one-dimensional photonic crystal with a defect layer to enhance the spin Hall effect of light. Under the condition of obliquely incidence, the defect modes have polarization-dependent transmission peaks (reflection valleys). Near the peaks, it is possible to acquire large ratio of the Fresnel coefficients, and thereby significantly enhancing the spin Hall effect of light to dozens of times of the ever observed values. At the same time, due to its close dependency on refractive index gradient, it is possible to develop the spin Hall effect as a precise metrology for investigating and describing the subwavelength variation of the structure geometries and refractive indices.(iii) We explore the unusual spin Hall effect of light in an anisotropic metamaterial. which manifests as non-symmetric spin-dependent splitting. In the previous researches, the observed splitting of left and right circular polarization components are all symmetric, that is, they reside on both sides of the incident plane with identical magnitudes. While we find that, due the non-symmetric geometrical phase induced by the strong anisotropy of the metamaterial. the non-symmetric splitting appears. It manifests as the same splitting direction and/or non-identical magnitudes. The asymmetry can be tunable via changing the optical parameters of the medium and the intersection angle between the incident plane and optics axis,(iv) Finally, we propose that the inhomogeneous anisotropic media with specified geometries can be used to manipulate the spin Hall effect of light. This medium can locally control the polarization of light, and apply a spin-dependent and space-variant geometrical phase to beam that passes through it. which cause the separation of the spin components of light. Interestingly, this spin-dependent splitting in the far field exhibits multi-lobe splitting patterns with alternatively left and right circular polarizations, described by the Stokes S3parameters. The lobe number depends upon the structure geometries of the media. So, this medium serves as a potential device to manipulate the spin-dependent splitting and photon spin states. Actually, the geometrical phase is not only associated with the medium properties, but also the incident polarization distribution. For different polarization angle of incident linear polarization, the splitting patterns will rotate. As far as we know, existing researches have concentrated their interests in the case of spatially homogeneous, linearly polarized incident light. We have investigated the case of axisymmetric linearly polarized light. Since the geometrical phase originates from the two kinds of contributions:medium property and polarization distribution, so the far-field splitting pattern can also be controlled by the incident polarization distribution. We believe that the incident polarization distribution servers as a new degree of freedom to manipulate the spin-dependent splitting of beam and photon spin states.