A concise, efficient, and practical direct-view scheme is presented to generate arbitrary cylindrical vector (CV) beams, including CV beams, vortex beams, and cylindrical vector vortex (CVV) beams, by a vortex half-wave plate (VHP). Six kinds of first-order and other high-order CV beams, such as azimuthally polarized (AP) beams, antivortex radial polarization mode beams, and three-order AP beams, are formed by simply rotating a half-wave plate. The Stokes parameters and double-slit interference of multitype CV beams are investigated in detail. The polarization parameters, including degree of polarization, polarization azimuth, and ellipticity, are obtained, which demonstrates the efficient generation of CV beams. In addition, the double-slit interference experiment is introduced in the setup, and fringe misplacement and tilt appear for CVV beams, in which the misplacement number M is 2 P + 1 for P ≤ 2 and 2 P − 1 for P ≥ 3 , where P is the polarization order number, and the fringe tilt offset is positively related to the topological charge number l of CVV beams. In addition, new types of VHPs can be formed by cascading two or more VHPs when the types of available VHPs are limited, assisting in more flexible generation of multitype CV beams. It is experimentally demonstrated that arbitrary CV beams with high quality are effectively achieved by the proposed setup, and the double-slit interference method can be utilized to determine and analyze CV beams rapidly and concisely by practical performance, which shows the potential to be implemented as a commercial device.

We report on the nonlinear characterizations of the titanium dioxide micro-ring resonators (TiO₂ MRRs). By utilizing optimized fabrication processes, high quality factors (Q∼1.4 × 10⁵) doubling that of the previous work are achieved here for TiO₂ MRRs with high-confinement TiO₂ waveguides. The four-wave mixing (FWM) experiment results with low and high signal power demonstrate that, the fabricated TiO₂ MRRs can perform broadband (∼40 nm) wavelength conversion and cascaded FWMs. These achievements pave the way for key nonlinear photonic applications with TiO₂ waveguides and provide an efficient platform for various integrated photonic devices.

A practical direct-view scheme for generating arbitrary high-order cylindrical vector (HCV) beams by cascading vortex half-wave plates (VHPs) is presented. The combination of odd number 2n-1 VHPs for n≥1 can realize (m_2n-1-m_2n-2+…+m₁)-order CV beams, in which m is the order number of VHP and the corresponding subscript 2n-1 represents the arrangement number of VHPs, and the cascading of even number 2n ones can obtain (m_2n-m_2n-1+…+m₂-m₁)-order CV beams. All 1-12 order CV beams, including the high-order anti-vortex CV (ACV) beams, are generated only by selectively cascading the VHPs with m=1, 3 and 8. The polarization properties of the generated HCV beams are investigated by measuring the corresponding Stokes parameters. It is experimentally demonstrated that arbitrary HCV beams are effectively achieved by the proposed method. The order numbers of CV beams can be greatly expanded by cascading limited types of VHPs.

Target images recorded with range-gated laser imaging systems and conventional passive imaging systems through rapidly changing turbid mediums inevitably suffer from inhomogeneous degradations. Consequently, this makes the images partly or entirely different from their true targets and eventually has adverse effects on target identification. To date, the inhomogeneous degradations are still not finely eliminable despite utilizing adaptive optical methods and pure mathematical signal improvement techniques. Herein, we demonstrate an image restoration method involving intrinsic physical evolution of light beams based on the backscattering images of a turbid medium. The corresponding mathematical signal processing algorithms are applied for restoring the true target images in the presence of rapidly changing inhomogeneous degradations. This technique would benefit target imaging through moving cloud/mist in air and flowing muddy masses under water.

Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide ( TiO 2 ) MRRs with sub-10-μm radii are experimentally demonstrated. Thanks to the large refractive index of TiO 2 , the quality factors up to ∼ 7.9 × 10 4 and ∼ 4.4 × 10 4 are achieved for TiO 2 MRRs with radii of 10 μm and 6 μm, respectively, which result in large nonlinear power enhancement factors ( > 113 ) and large Purcell factors ( > 56 ). The four-wave mixing (FWM) measurements indicate that, compared to the large MRR, the FWM conversion efficiency of the ultracompact TiO 2 MRRs can be greatly improved (e.g., − 25 dB versus − 31 dB ), a harbinger of significant superiorities. Demonstrations in this work provide more arguments for the TiO 2 waveguides as a promising platform for various on-chip photonic devices.

Titanium dioxide ( T i O 2 ) microring resonators (MRRs) with high quality factors (Qs) are demonstrated by using a new, to the best of our knowledge, bottom-up fabrication method. Pattern platforms with a T-shaped cross section are first defined by etching a thin top layer of silicon nitride and a thick bottom layer of silica and partially undercutting the silica. Then, T i O 2 is deposited on the platforms to form the T i O 2 waveguides and devices. T i O 2 MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic Q ( Q i n t ) is achieved to be ∼ 1.1 × 10 5 at the telecommunication wavelengths, corresponding to a bend waveguide loss of 3.9 dB/cm while the compact MRR with a radius of 10 µm can still sustain a Q i n t of ∼ 10 5 . These results not only unfold the feasibilities of the proposed bottom-up method for fabricating T i O 2 waveguides and MRRs with high Qs and compact footprints but also suggest a new approach for fabricating waveguides in other materials, of which direct etching is not easily accessible.