Spin-orbit optical Hall effect in π-vector fields.

Given the tremendous increase of data in digital era, vector vortex light with strongly coupled spin and orbital angular momenta of photons have attracted great attention for high-capacity optical applications. To fully utilize such rich degrees of freedom of light, it is highly anticipated to separate the coupled angular momentum with a simple but powerful method, and the optical Hall effect becomes a promising scheme. Recently, the spin-orbit optical Hall effect has been proposed in terms of general vector vortex light using two anisotropic crystals. However, angular momentum separation for π-vector vortex modes, another important part in vector optical fields, have not been explored and it remains challenging to realize broadband response. Here, the wavelength-independent spin-orbit optical Hall effect in π-vector fields has been analyzed based on Jones matrices and verified experimentally using a single-layer liquid-crystalline film with designed holographic structures. Every π-vector vortex mode can be decoupled into spin and orbital components with equal magnitude but opposite signs. Our work could enrich the fields of high-dimensional optics.

All-optically controlled beam splitting through asymmetric polarization-based holography.

All-optically controlled beam splitting is demonstrated by a tunable split ratio through polarization modulation. The beam splitters are essentially holographic gratings recorded by means of the interference of two 532 nm beams with asymmetric polarization states in an azobenzene liquid crystal film. It is found that the intensity ratio between zero and the first diffraction order is adjustable through the polarization manipulation of the recording light. An arbitrary split ratio from 0 to 1 is obtained with the photoinduced birefringence of the film being set to an appropriate value, which is independent on the polarization state of the probe light. Furthermore, the formation processes of the recorded beam splitters are contributed to the dual-grating coupling, and the tunable split ratio under various polarization conditions is discussed in terms of the Fresnel theory and Jones matrices.

Polarization modulation by means of tunable polarization gratings in an azobenzene side-chain liquid-crystalline polymer film.

Polarization modulation was achieved by means of a new type of grating recorded with two 532 nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged. With the polarization angle changing from 0 to 90 deg, the ± first-order diffraction efficiency increased from 5.15% to 10.53%. Diffraction properties of the recorded gratings were attributed to the combination of polarization holographic gratings and amplitude gratings based on the calculation of Jones matrices and polarization holographic theory.

Geometric-phase-based shearing interferometry for broadband vortex state decoding.

Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin-orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally.

All-optically phase-induced polarization modulation by means of holographic method.

Phase-induced polarization modulation has been achieved experimentally by means of the all-optical holographic method. An extra spiral phase is added to a Gaussian beam and then a holographic grating is recorded through the interference of a Gaussian beam and the phase-vortex beam with the same linear polarization state in an azobenzene liquid-crystalline film. We report here that the polarization state of the diffraction light from the recorded grating is different from that of the incident light, while no polarization variation occurs for the holographic grating recorded by two Gaussian beams. The phase-induced polarization modulation is mainly attributed to the formation of birefringence in the film generated by phase vortex, which is investigated through the ripple patterns resulting from the competition between photoinduced torques and analysed by the Jones matrix. The experimental results could enrich the connotation between optical parameters and offer a method to realize polarization modulation through phase control.