Convenient noncooperative speckle-correlation imaging method

For speckle-correlation-based scattering imaging,an iris is generally used next to the diffuser to magnify the speckle size and enhance the speckle contrast,which limits the light flux and makes the setup cooperative.Here,we experimentally demonstrate a non-iris speckle-correlation imaging method associated with an image resizing process.The experimental results demonstrate that,by estimating an appropriate resizing factor,our method can achieve high-fidelity noncooperative speckle-correlation imaging by digital resizing of the raw captions or on-chip pixel binning without iris.The method opens a new door for noncooperative high-frame-rate speckle-correlation imaging and benefits scattering imaging for dynamic objects hidden behind opaque barriers.

Concise and efficient direct-view generation of arbitrary cylindrical vector beams by a vortex half-wave plate

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 2P+1 for P ≤ 2 and 2P-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.

Ultra-compact titanium dioxide micro-ring resonators with sub-10-μm radius for on-chip photonics

Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here,ultracompact titanium dioxide (TiO2) 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 10μm and 6μm,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 TiO2 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.