Sidelobe suppression for accelerating beams.

Although the control of trajectory, amplitude and beam-width in accelerating beams have been extensively investigated, sidelobes manipulation of such beams, which is required in many applications, has been surprisingly under-researched. This paper presents an approach for the generating of accelerating beams with significantly reduced sidelobes. The proposed method encompasses a two-step angular spectrum design, including employing a general model to establish the phase distribution and applying a stochastic parallel gradient descent (SPGD) algorithm to optimize the binary amplitude modulation.

Mechanical-scan-free multicolor super-resolution imaging with diffractive spot array illumination.

Point-scanning microscopy approaches are transforming super-resolution imaging. Despite achieving parallel high-speed imaging using multifocal techniques, efficient multicolor imaging methods with high-quality illumination are currently lacking. In this paper, we present for the first time Mechanical-scan-free multiColor Super-resolution Microscopy (MCoSM) with spot array illumination, which enables mechanical-scan-free super-resolution imaging with adjustable resolution and a good effective field-of-view based on spatial light modulators.

Periodic diffractive optical element for high-density and large-scale spot array structured light projection.

Structured light projection has been widely used for depth sensing in computer vision. Diffractive optical elements (DOEs) play a crucial role in generating structured light projected onto objects, and spot array is a common projection pattern. However, the primary metrics of the spot array, including density and field of view, are restricted by the principle of diffraction and its calculation.

Compact structured illumination microscopy with high spatial frequency diffractive lattice patterns.

Structured illumination microscopy (SIM) enables live-cell super-resolution imaging with wide field of view (FOV) and high imaging speed, but the illumination system is usually bulky. With the advantages of small structure and high efficiency, lattice patterns assisted by diffractive optical elements (DOEs) have been used for structured illumination in SIM. But it is still challenging to raise the spatial frequency of diffractive lattice patterns when using traditional DOE design method, and thus the super-resolution imaging performance is restricted.

Fluorescence Enhanced Optical Resonator Constituted of Quantum Dots and Thin Film Resonant Cavity for High-Efficiency Reflective Color Filter.

Conventional color filters selectively absorb a part of the backlight while reflecting or transmitting other light, resulting in the problem of low efficiency and energy wasting. For this problem, a new concept of fluorescence enhanced optical resonator was proposed and verified in this paper. The new structure consists of structural color filter and light-conversion material.

Metasurface for Structured Light Projection over 120° Field of View.

Structured light projection is a widely adopted approach for depth perception in consumer electronics and other machine vision systems. Diffractive optical element (DOE) is a key component for structured light projection that redistributes a collimated laser beam to a spot array with uniform intensity. Conventional DOEs for laser spot projection are binary-phase gratings, suffering from low efficiency and low uniformity when designed for a large field of view (FOV).

Effective Fresnel diffraction field extension of diffractive optical elements with plane wave incidence.

Diffractive optical elements (DOEs) are widely used to realize special diffraction fields today, but the size of the effective Fresnel diffraction field of the DOEs with plane wave incidence is limited by the wavelength of the incident beam, sampling interval of the DOE, and distance between the DOE and the output plane. In this paper, a method is proposed to extend the size of the effective Fresnel diffraction field with an introduced intermediate plane and two-step diffraction calculation. Zero padding is used on the DOE plane, the sampling interval on the intermediate plane is correspondingly decreased, and the size of the Fresnel diffraction field on the output plane is finally extended.

Multiring pure-phase binary optical elements to extend depth of focus.

Multiring pure-phase binary optical elements (BOEs) are widely used to extend the depth of focus (DOF) in many optical applications. Although researchers have designed various BOEs to extend the DOF, few theories and experiments have been reported to validate the performances of different N-ring pure-phase BOEs to realize the DOF as long as possible. In this paper, aberration theory is used to obtain the simple and straightforward initial phase, and a novel modified Gerchberg-Saxton algorithm is presented for generating N-ring 0-π-phase BOEs to optimally extend the DOF.

Future changes in Yuan River ecohydrology: Individual and cumulative impacts of climates change and cascade hydropower development on runoff and aquatic habitat quality.

The eco-hydrological system in southwestern China is undergoing great changes in recent decades owing to climate change and extensive cascading hydropower exploitation. With a growing recognition that multiple drivers often interact in complex and nonadditive ways, the purpose of this study is to predict the potential future changes in streamflow and fish habitat quality in the Yuan River and quantify the individual and cumulative effect of cascade damming and climate change. The bias corrected and spatial downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Model (GCM) projections are employed to drive the Soil and Water Assessment Tool (SWAT) hydrological model and to simulate and predict runoff responses under diverse scenarios.

Design of two-dimensional diffractive optical elements for beam shaping of multicolor light-emitting diodes.

To achieve a cellular network in visible light communication, the illumination areas covered by red, green, and blue light-emitting diodes (LEDs) forming a white LED should be of the same size with uniform intensity distribution. In this paper, the iterative algorithm for the design of multicolor-oriented two-dimensional diffractive optical elements (DOEs) is improved. Simulation results indicate that almost the same size of the diffraction patterns of the DOE illuminated by multicolor LEDs is achieved with good uniformity of the intensity distribution.

Design of diffractive optical elements for subdiffraction spot arrays with high light efficiency.

Spot arrays beyond the diffraction limit are required in many optical applications, and the shaping of a light beam into subdiffraction spot arrays can be implemented by diffractive optical elements (DOEs). However, the low light efficiency of spot arrays is undesired in many applications. In this paper, a modified Gerchberg-Saxton algorithm is presented for generating DOEs to realize subdiffraction spot arrays with higher light efficiency.

Holographic projection with higher image quality.

The spatial resolution limited by the size of the spatial light modulator (SLM) in the holographic projection can hardly be increased, and speckle noise always appears to induce the degradation of image quality. In this paper, the holographic projection with higher image quality is presented. The spatial resolution of the reconstructed image is 2 times of that of the existing holographic projection, and speckles are suppressed well at the same time.

Image magnification in lensless holographic projection using double-sampling Fresnel diffraction.

Since the diffraction angle is limited by the spatial resolution of the spatial light modulator (SLM), the size of the optical image of the lensless holographic projection with a SLM is very small. Using a divergent spherical beam to illuminate a SLM is an effective method to physically increase the projection angle; nevertheless, the sampling ranges of the existing Fresnel diffraction algorithms with fast Fourier transform keep unchanged. In this paper, a double-sampling Fresnel diffraction algorithm to enlarge the sampling range is proposed when using a divergent spherical beam to illuminate a SLM, and the magnification of the optical image is realized in lensless holographic projection.

Diffractive optical element with same diffraction pattern for multicolor light-emitting diodes.

The wavelength-division multiplexing technique can be utilized in visible light communication to increase the channel capacity when a multicolor mixed white LED is used as light source. In such an application, the illumination area of LEDs should be invariant to the incident wavelength, so as to decrease interference within the adjacent regions. Diffractive optical elements (DOEs) can be used in the optical transmitter system to shape the diffraction patterns into polygons.

Precise design of two-dimensional diffractive optical elements for beam shaping.

Diffractive optical elements (DOEs) for beam shaping are widely used in many fields, and there are many kinds of optimization algorithms to design the DOEs for beam shaping. However, only the intensity distribution of the selected sampling points is controlled by these optimization algorithms. The intensity distribution of other points on the output plane is always far away from the ideal distribution.

Real-time phase error compensation in phase sensitive scanning near-field optical microscopy.

Phase measurements are critical for investigations on the optical properties of surface plasmon polariton (SPP) nanostructures. In this paper, a real-time phase error compensation method based on a phase sensitive scanning near-field optical microscopy (SNOM) measurement system is proposed. The method adopts the common optical path configuration and CMR (common-mode rejection) principle.

Interferometric spherical surface testing with unknown phase shifts.

A general method is presented for spherical surface testing with unknown phase shifts based on a physical model of the interferometer cavity, which describes the phase shifts taking into account the rigid cavity motions and the radial imaging distortion of the interferometer. The captured interferograms are processed frame by frame with the regularized frequency-stabilizing method, so as to get the phase shifts between the frames. These phase shift data are subsequently fitted, and the initial estimations for the wavefront, direct current and interference contrast terms are calculated by the least-squares method.

Two-step resonant diffraction grating designed for three-color separation in Fresnel diffraction region.

A two-step resonant diffraction grating is designed to separate the distributions of the wavelengths of 633, 532, and 488 nm in the Fresnel diffraction field using an analytical solution of the modal method, which can give a physical explanation for mode propagation in the grating region and interference at the interfaces. The energy efficiencies are 76.1% for 633 nm, 83.

M-shaped grating by nanoimprinting: a replicable, large-area, highly active plasmonic surface-enhanced Raman scattering substrate with nanogaps.

Plasmonic nanostructures separated by nanogaps enable strong electromagnetic-field confinement on the nanoscale for enhancing light-matter interactions, which are in great demand in many applications such as surface-enhanced Raman scattering (SERS). A simple M-shaped nanograting with narrow V-shaped grooves is proposed. Both theoretical and experimental studies reveal that the electromagnetic field on the surface of the M grating can be pronouncedly enhanced over that of a grating without such grooves, due to field localization in the nanogaps formed by the narrow V grooves.

Accurate geometric characterization of gold nanorod ensemble by an inverse extinction/scattering spectroscopic method.

Aspect ratio, width, and end-cap factor are three critical parameters defined to characterize the geometry of metallic nanorod (NR). In our previous work [Opt. Express 21, 2987 (2013)], we reported an optical extinction spectroscopic (OES) method that can measure the aspect ratio distribution of gold NR ensembles effectively and statistically.

Phase extraction from interferograms with unknown tilt phase shifts based on a regularized optical flow method.

A novel method is presented to extract phase distribution from phase-shifted interferograms with unknown tilt phase shifts. The proposed method can estimate the tilt phase shift between two temporal phase-shifted interferograms with high accuracy, by extending the regularized optical flow method with the spatial image processing and frequency estimation technology. With all the estimated tilt phase shifts, the phase component encoded in the interferograms can be extracted by the least-squares method.

Fast statistical measurement of aspect ratio distribution of gold nanorod ensembles by optical extinction spectroscopy.

Fast and accurate geometric characterization and metrology of noble metal nanoparticles such as gold nanorod (NR) ensembles is highly demanded in practical production, trade, and application of nanoparticles. Traditional imaging methods such as transmission electron microscopy (TEM) need to measure a sufficiently large number of nanoparticles individually in order to characterize a nanoparticle ensemble statistically, which are time-consuming and costly, though accurate enough. In this work, we present the use of optical extinction spectroscopy (OES) to fast measure the aspect ratio distribution (which is a critical geometric parameter) of gold NR ensembles statistically.

Dual-polarity plasmonic metalens for visible light.

Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light.

Dispersionless phase discontinuities for controlling light propagation.

Ultrathin metasurfaces consisting of a monolayer of subwavelength plasmonic resonators are capable of generating local abrupt phase changes and can be used for controlling the wavefront of electromagnetic waves. The phase change occurs for transmitted or reflected wave components whose polarization is orthogonal to that of a linearly polarized (LP) incident wave. As the phase shift relies on the resonant features of the plasmonic structures, it is in general wavelength-dependent.

Color separation of high-density dielectric rectangular grating in the Fresnel diffraction region.

A high-density dielectric rectangular grating is designed for color separation in a Fresnel diffraction field. The Fresnel field distribution is analyzed and the optimization conditions for color separation are given. The process of the modes propagating and energy exchanging with the diffraction orders are expressed by modal method.