ABSTRACT
We describe the spin-Hall effect of light (as well as the angular Goos-Hänchen effect) at a tilted linear-dichroic plate, such as a usual linear polarizer. Although the spin-Hall effect at a tilted polarizer was previously associated with the geometric spin-Hall effect of light (which was contrasted to the regular spin-Hall effect) [Phys. Rev. Lett.112, 113902 (2014) PRLTAO0031-900710.1103/PhysRevLett.112.113902], we show that the effect is actually an example of the regular spin-Hall effect that occurs at tilted anisotropic plates [Optica3, 1039 (2016) OPTIC82334-253610.1364/OPTICA.3.001039]. Moreover, our approach reveals the angular spin-Hall shift, which is absent in the "geometric" approach. We verify our theory experimentally using the method of quantum weak measurements.
ABSTRACT
In this Letter, we report the chiral dynamics of optical exceptional points (EPs), the singular axes in weakly absorbing biaxial crystal, arising due to a fine balance between the birefringence and dichroism. Taking advantage of the coincidence of the singular axes and C-point singularity, the EPs are characterized using conoscopic Stokes polarimetry. We observe that the two optic axes of the biaxial crystal split into two pairs of singular axes upon introducing weak dichroism which, upon application of a transverse electric field, follows a helical trajectory to coalesce and disappear. Our results show a fine control on the chiral behavior of EPs due to an electrogyration effect, which controls the retardance gradient and the fast-axis orientation in the crystal.
ABSTRACT
Electric-field applied perpendicular to the direction of propagation of paraxial beam through an optical crystal dynamically modifies the spin-orbit interaction (SOI), leading to the demonstration of controllable spin-Hall effect of light (SHEL). The electro- and piezo-optic effects of the crystal modifies the radially symmetric spatial variation in the fast-axis orientation of the crystal, resulting in a complex pattern with different topologies due to the symmetry-breaking effect of the applied field. This introduces spatially-varying Pancharatnam-Berry type geometric phase on to the paraxial beam of light, leading to the observation of SHEL in addition to the spin-to-vortex conversion. A wave-vector resolved conoscopic Mueller matrix measurement and analysis provides a first glimpse of the SHEL in the biaxial crystal, identified via the appearance of weak circular birefringence. The emergence of field-controllable fast-axis orientation of the crystal and the resulting SHEL provides a new degree of freedom for affecting and controlling the spin and orbital angular momentum of photons to unravel the rich underlying physics of optical crystals and aid in the development of active photonic spin-Hall devices.
ABSTRACT
Discovered in 1813, the conoscopic interference pattern observed due to light propagating through a crystal, kept between crossed polarizers, shows isochromates and isogyres, respectively containing information about the dynamic and geometric phase acquired by the beam. We propose and demonstrate a closed-fringe Fourier analysis method to disentangle the isogyres from the isochromates, leading us to the azimuthally varying geometric phase and its manifestation as isogyres. This azimuthally varying geometric phase is shown to be the underlying mechanism for the spin-to-orbital angular momentum conversion observed in a diverging optical field propagating through a z-cut uniaxial crystal. We extend the formalism to study the optical activity mediated uniaxial-to-biaxial transformation due to a weak transverse electric field applied across the crystal. Closely associated with the phase and polarization singularities of the optical field, the formalism enables us to understand crystal optics in a new way, paving the way to anticipate several emerging phenomena.
ABSTRACT
The realization of spiral phase optical elements on the cleaved end of an optical fiber by focused ion beam milling is presented. A focused Ga+ ion beam with an acceleration voltage of 30 keV is used to etch continuous spiral phase plates and fork gratings directly on the tip of the fiber. The phase characteristics of the output beam generated by the fabricated structures measured via an interference experiment confirmed the presence of phase singularity in the output beam. The devices are expected to be promising candidates for all-fiber beam shaping and optical trapping applications.
