Jianying Zhou

Minimized spot of annular radially polarized focusing beam

We have experimentally demonstrated the measurement of a tighter focal spot generated by a radially polarized narrow-width annular beam with the double-knife-edge method. The reconstructed spot profiles indicate that sharper focus cannot be achieved by shrinking the annular aperture further. The smallest focal spot (0.0711λ(2)) is obtained in experiment with an annular factor of 0.91. An apodization function has been introduced with the consideration of the diffraction effect, which achieves good agreement with the experimental data. Our result shows that the diffraction effect should be considered with small topography structures of the incident beam.

Polarization control of multiply scattered light through random media by wavefront shaping

We show that the polarization state of coherent light propagating through an optically thick multiple scattering medium can be controlled by wavefront shaping, that is, by controlling only the spatial phase of the incoming field with a spatial light modulator. Any polarization state of light at any spatial position behind the scattering medium can be attained with this technique. Thus, transforming the random medium to an arbitrary optical polarization component becomes possible.

Ultralong pure longitudinal magnetization needle induced by annular vortex binary optics

In this Letter, based on the Richards and Wolf diffraction theory, an ultralong optical needle with pure transverse polarization is numerically generated by tightly focusing an azimuthally polarized beam through an annular vortex binary filter. Such an ultralong transversely polarized optical needle is generated through the π phase shift between adjacent rings of the binary filter. We show that such a pure transverse optical needle can induce pure longitudinal magnetization with a subwavelength lateral size (0.38λ) and an ultralong longitudinal depth (7.48λ) through the inverse Faraday effect. The corresponding needle aspect ratio of 20 is twice as large as that of the longitudinal magnetization needle generated by electron beam lithography.

All-optically configuring the inverse Faraday effect for nanoscale perpendicular magnetic recording

Nanoscale reversal of the longitudinal magnetization (Mz) is highly desired in the ultrahigh density perpendicular magnetic recording. In this paper, an all-optical method to realize the reversal of Mz with an ultrasmall lateral size through configuring the inverse Faraday effect (IFE) is numerically proposed. This feature is achieved by optical coherent configuration of the IFE in the central and peripheral regions of the focal spot with opposite signs. By increasing the intensity of the peripheral regions to produce destructive interference, the lateral size of the reversed Mz smaller than 30 nm in one dimension in the central region can be achieved. This result is of vital importance for realizing ultrafast nanoscale perpendicular magnetic recording.

Ultrafast optical bistable behaviors of vanadyl phthalocyanine-doped polymer film quasi-waveguide and waveguide

Abstract Picosecond optical bistable behaviors in an optical quasi-waveguide and a planar waveguide made with metallophthalocyanine-doped polymer films were demonstrated. Input–output curves with hysteresis characteristics were measured at 532 nm. In the quasi-waveguide through the observation on the bistabilities of the reflected light at various offset angles, the responsibility of high-order modes for the bistable behaviors was investigated by using the mode spectra. The non-linearity giving rise to optical bistability was predominantly electronic in origin.

Picosecond optical bistability in metallophthalocyanine-doped polymer film waveguides

Ultrafast optical bistability was observed in a planar optical waveguide made with a 2,9,16,23-tetraoctadecanoylamido-substituted vanadyl phthalocyanine-doped polystyrene film. Input-output curves with hysteresis characteristics were measured with laser pulses of 60-ps pulse width at 532 nm. The switchup and switchdown times were less than 10 and 20 ps, respectively. The origin of the nonlinearity giving rise to optical bistability was predominantly electronic effects.

Reshaping ultrashort light pulses in resonant photonic crystals

Ultrashort light pulses propagating through a resonant photonic crystal can be reshaped to shorter duration output through self-induced transparency. The reshaping process is shown to result from the unique transmission behavior of light pulses through the photonic structure. Pulse compression and pulse merging, with which multipeak optical pulses can be evolved to give rise to a single-peak, high-quality transmitted pulse output, are obtained. The pulse propagation in a resonant photonic crystal is compared with that in a bulk atomic medium, which shows that the effect of pulse reshaping is much more powerful in the former than in the latter.

Effect of polarization purity of cylindrical vector beam on tightly focused spot

The tightly focused spots of cylindrical vectors (CVs) are dependent on polarization composition. We experimentally demonstrate the effect of polarization purity (PP) of the CV beam on the tightly focused spot quantitatively, which should be strictly controlled for the effective applications of the CV beam. The focal spots measured by a knife-edge scanning method showed that the azimuthally polarized (AP) component increases the transverse field and the size of the focal spots, while the radially polarized component results in a nonzero intensity distribution at the center of the focus even in a high PP AP beam.

Pancharatnam-phase-based characterization for the diffraction of an optical vortex beam

We present an interferometric method to recover the phase diffraction patterns of a Gaussian optical vortex (OV) beam with different topological charges. The patterns are encoded and converted into polarization information, which can be decoded and measured by an analyser and a camera. Helical diffraction structures due to the spiral phase plates are obtained by a Mach–Zehnder interferometer. A numerical method based on angular spectrum representation is developed to simulate both the polarization and the distorted phase pattern of the OV beam through propagation. Simulation results show good agreement with the experiment.

Nonlinear dynamics of negatively refracted light in a resonantly absorbing Bragg reflector

The evolution of nonlinear light fields traveling inside a resonantly absorbing Bragg reflector is studied by use of Maxwell-Bloch equations. Numerical results show that a pulse initially resembling a light bullet may effectively experience negative refraction and anomalous dispersion in the resonantly absorbing Bragg reflector.