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The calibration of the slit width under an atomic force microscope, the other two experimental data to calibrate the resolution and calibration of penetration of the evanescent field.

Supplementary Document 1

Passive radiative cooling, which pumps heat to outer space via thermal radiation, has been a promising energy free technology to maintain the earth surface temperature. Nighttime radiative cooling technology is quite mature, while daytime radiative cooling still poses many challenges due to the requirement of minimization of incident solar absorption and maximization of the mid-infrared emissivity in the atmospheric transparency windows. However, the mid-infrared emissivity efficiency of natural materials is usually poor, providing a low cooling efficiency and the realization of a high performance daytime radiative cooler is still quite challenge. In this work, we design and numerically investigate a three dimensional (3D) all-dielectric pyramidal multilayer metamaterial (PMM), which not only avoids the problem of high absorptivity loss of metal materials to solar, but also provide extremely high infrared absorptivity due to the attenuation effect of moth-eye structure and the electromagnetic resonant absorption in the metamaterial, achieving the purpose of both extremely low solar spectrum absorption and strong infrared emissivity within the atmospheric windows under the direct sunlight. Eventually, our designed cooler presents the potential to achieve a net radiative cooling power exceeding 156 W/m2 at ambient temperature of 300 K under direct solar irradiation, leading to a temperature reduction of 42.4°C. At nighttime, the net cooling power is more than 199 W/m2 at ambient temperature, resulting in a temperature reduction of 58.5°C. Even considering the non-radiative heat exchange conditions, this metamaterial cooler can still cool down 9.6°C at the daytime and 12.3°C at the nighttime respectively. Therefore, this work further promotes the development of all-dielectric metamaterial based passive radiative coolers and is of great significance for energy conservation.

Bloch surface wave (BSW) can be considered as the dielectric analogue of surface plasmon polariton (SPP) with less loss since it is sustained at the surface of a truncated dielectric multilayer. As dielectric materials show nearly no ohmic loss, BSW can propagates much farther compared to SPP, and thus is beneficial for planar optical devices. In this paper, we study the spin-orbital interaction between incident beam and BSW. We demonstrate that due to the spin-orbital coupling, the near-field properties of generated BSW can be controlled with a meta-antenna structure. The meta-antenna is composed of two gold nano-antennas oriented at 45° and 135° as a near-field coupler. By careful design of the meta-antenna, the generated BSW can be guided and focused depending on the chirality of the incident beam. Three examples of meta-antennas are demonstrated for chiral sensitive focusing, directional switching and asymmetric focusing. The proposed method can be applied as a design method for low-loss on-chip photonic devices.

Polarization imaging finds applications in many areas, such as photoelasticity, ellipsometry, and biomedical imaging. A compact, snapshot, and high-efficiency imaging polarimeter is highly desirable for many applications. Here, based on a single multifunctional geometric phase optical element (GPOE), a new method is proposed for high-efficiency snapshot imaging polarimetry. With tailored spatially varying orientation of each anisotropic unit cell, the GPOE works highly efficiently as both a spin sorter and a half-wave plate, enabling snapshot retrieving of a full Stokes vector of incident light. The designed GPOE is implemented in the form of liquid crystal fabricated with a photo-alignment technology, and its application in imaging polarimetry is experimentally demonstrated by retrieving full Stokes parameters of a cylinder vector beam. This method can also work in the form of plasmonic or dielectric metasurfaces, enabling ultra-compact polarization detection systems by monolithic integration with other devices such as metalenses.

Structured illumination microscopy (SIM) is a powerful super-resolved imaging technique which enables to perform fast and in vivo imaging of bio-samples. In order to achieve a better resolution of a SIM system, evanescent waves with larger in-plane wave-vector are preferred for SIM, among which the total internal reflection (TIRF-SIM) and the plasmonic SIM (pSIM) configurations are widely studied. Here, we demonstrated a metal-dielectric waveguide (MDW) based SIM system - termed as MDW-SIM, which can achieve a good compromise between TIRF-SIM and pSIM. The MDW can support a low-loss waveguide mode at an aqueous environment, with an evanescent tail existing above the water/dielectric interface for SIM. A proof-of-concept imaging experiment was performed on fluorescent beads, where a spatial resolution of 86nm was achieved at a 473nm illumination wavelength and a 1.45 numerical aperture objective lens. The proposed MDW-SIM has a great potential for the bio-imaging applications.

Strong plasmonic focal spots, excited by radially polarized light on a smooth thin metallic film, have been widely applied to trap various micro- and nano-sized objects. However, the direct transmission part of the incident light leads to the scattering force exerted on trapped particles, which seriously affects the stability of the plasmonic trap. Here we employ a novel perfect radially polarized beam to solve this problem. Both theoretical and experimental results verify that such a beam could strongly suppress the directly transmitted light to reduce the piconewton scattering force, and an enhanced plasmonic trapping stiffness that is 2.6 times higher is achieved in experiments. The present work opens up new opportunities for a variety of research requiring the stable manipulations of particles.

The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum (OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM (de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM (de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.

Because of the fingerprint-like specificity of its characteristic spectrogram, Raman spectral imaging has been applied widely in various research areas. Using a combination of structured illumination with the surface-enhanced Raman scattering (SERS) technique, wide-field Raman imaging is developed with a significant improvement in spatial resolution. As a result of the relatively narrow Raman characteristic peaks, optically encoded SERS nanoparticles can be used to perform multiplexed imaging. The results show excellent superresolution wide-field multiplexed imaging performance. The developed technique has extraordinary potential for applications in biological imaging and other related fields.

We suggest a plasmonic nanodevice for performing the second-order spatial derivative of light fields. The device consists of five gold nanorods arranged to evanescently couple to each other so that emit cross-polarized output proportional to the second-order differentiation of the incident wave. A theoretical model based on the electrostatic eigenmode analysis is derived and numerical simulations using the finite-difference time-domain methods are provided as supporting evidence. It is shown in both the analytic and numerical methods that the proposed plasmonic circuit performs second-order differentiation of the phase of the incident light field in transmission mode with a subwavelength planar resolution. The resolution of 0.29 lambda(-1) is numerically demonstrated for a 20 nm thick circuit at the wavelength of 700 nm. The suggested plasmonic device has potential application in miniaturized systems for all-optical computation. Refereed/Peer-reviewed

Optical traps use focused laser beams to generate forces on targeted objects ranging in size from nanometers to micrometers. However, for their high coefficients of scattering and absorption, micrometer-sized metallic particles were deemed non-trappable in three dimensions using a single beam. This barrier is now removed. We demonstrate, both in theory and experiment, three-dimensional (3D) dynamic all-optical manipulations of micrometer-sized gold particles under high focusing conditions. The force of gravity is found to balance the positive axial optical force exerted on particles in an inverted optical tweezers system to form two trapping positions along the vertical direction. Both theoretical and experimental results confirm that stable 3D manipulations are achievable for these particles regardless of beam polarization and wavelength. The present work opens up new opportunities for a variety of in-depth research requiring metallic particles.

We propose a method to generate uniform optical cages with adjustable number and position along the optical axis in a low numerical aperture (NA) optical system. The uniform optical cages are the superposition of multiple dark and bright spots, which are of x- and y-polarized electric fields with the neglected axial component obtained, respectively, by focusing a quasi-x-polarized vortex beam with topological charge 1 and a quasi-y-polarized beam. By adjusting the number and position of the dark and bright spots with reversal radiation theory, valuable optical cages with uniformity up to 1, such as multiple optical cages, optical chain, and optical tube, can be realized. Moreover, the influences of the axial field to the quality of optical cages are also investigated. Numerical results show that an effective optical cage with uniformity up to 0.695 can be achieved even with an NA close to 0.75. The generated optical cages may find valuable application in optical trapping of samples with a large scale, which are difficult to be trapped under a high NA focusing condition.

Amplitude, phase and polarization are essential parameters of an optical field. In the past decade, with the enhancement of techniques in manipulating phase and polarization states in complex optical fields, optical vortices and vector beams are investigated in a closely coupled fashion in terms of efficient beam generation and manipulation, stable transmission and novel detection aimed at various applications. In this special issue 6 invited papers demonstrate a number of typical topics in the field, with emphasis on the vectorial beam generation and optical communication systems utilising orbital angular momentum (OAM).

Space-division multiplexing allows unprecedented scaling of bandwidth density for optical communication. Routing spatial channels among transmission ports is critical for future scalable optical network, however, there is still no characteristic parameter to label the overlapped optical carriers. Here we propose a free-space optical flow routing (OFR) scheme by using optical orbital angular moment (OAM) states to label optical flows and simultaneously steer each flow according to their OAM states. With an OAM multiplexer and a reconfigurable OAM demultiplexer, massive individual optical flows can be routed to the demanded optical ports. In the routing process, the OAM beams act as data carriers at the same time their topological charges act as each carrier's labels. Using this scheme, we experimentally demonstrate switching, multicasting and filtering network functions by simultaneously steer 10 input optical flows on demand to 10 output ports. The demonstration of data-carrying OFR with nonreturn-to-zero signals shows that this process enables synchronous processing of massive spatial channels and flexible optical network.

We theoretically demonstrate the generation and detection of broadband multi-channel Orbital Angular Momentum(OAM) by a micrometer-scale meta-reflectarray. The meta-reflectarray composed of patterned silicon bars on a silver ground plane can be designed to realize phase modulation and work as chip-level OAM devices. Compared to traditional methods of OAM generation and detection, our approach shows superiorities of very compact structure size, broadband working wavelength (1250-1750 nm), high diffraction efficiency (~70%), simultaneously handling multiplex OAMs, and tunable reflection angle (0-45°). These fascinating advantages provides great potential applications in photonic integrated devices and systems for high-capacity and multi-channel OAM communication.

We demonstrate an all-optical plasmonic structured illumination microscopy (PSIM) technique. A set of plasmonic standing-wave patterns is excited by amplitude-modified optical vortices (OVs), which have fractional topological charges for precise phase shift of {-2π/3, 0, 2π/3}. A specially designed optical aperture is introduced to modify the OVs in order to improve the uniformity of interference patterns. The imaging results of fluorescent beads reveal a sub-100nm resolving capability in aqueous environment. This PSIM technique as a structure-free, wide-field and super-resolved imaging technique is of great potential for low-cost biological dynamic imaging applications.

The hydrodynamic theory is a powerful tool to study the nonlocal effects in metallic nanostructures that are too small to obey classical electrodynamics while still too large to be handled with a full quantum-mechanical theory. The existing hydrodynamic model can give accurate quantitative predictions for the plasmonic resonance shifts in metallic nanoplasmonics, yet is not able to predict the spectral width which is usually taken as a pre-set value instead. By taking account the fact that due to electron density spill-out from a surface, the Coulomb interaction screening is less efficient close the surface thus leads to a higher electron-electron scattering rate in this paper, we study how the electron-density-related damping rate induced by such Coulomb interaction will affect the plasmonic spectral broadening. We perform the simulation on a Na nanowire, which shows that the absorption spectra width is wider when the size of the nanowire becomes smaller. This result is consistent well with the reported experiment. Therefore, our theoretical model extends the existing hydrodynamic model and can provide much more quantum insight about nonlocal effects in metallic nanostructures.

In this paper, the phase-stepping technique is applied to improve a phase-sensitive surface plasmon resonance biosensor based on differential interferometry between focused radially polarized and azimuthally polarized cylindrical vector beams. Detailed analysis is presented for the phase-stepping method, and the least squares unwrapping algorithm is employed to detect the phase distribution in correspondence to the refractive index of sample. Benefiting from the phase-stepping technique, both the measurement speed and sensitivity are improved significantly. The proposed sensor maintains high sensitivity of 9.4×10sup-7/sup RIU/1° and a wide dynamic range of 0.35 RIU simultaneously. Furthermore, the real-time binding reaction process of bovine serum albumin with antibody is monitored to verify the system for potential biological applications.

Based on vectorial diffraction theory, tight focusing properties of quasi-cylindrical polarized beams (QCPBs) composed of equal fan-shaped sectors with linear polarization are investigated. We find that, for quasi-radially polarized illumination, a weak azimuthal component emerges and the circular symmetry of focus is traded in when the total number of sector N is small, but when N≥8 it is approaching that of a perfect radially polarized beam with a deviation smaller than 5.3% and a ratio of maximum total intensity larger than 95.5%. Meanwhile, for quasi-azimuthal polarized illumination, although weak radial and longitudinal components emerge, it is also close to that of the perfect azimuthally polarized beam when N≥8 with deviation smaller than 5.3% and a ratio larger than 95.0%. These results not only reveal a deep understanding of the focusing properties of QCPBs, but also provide an important contribution toward optimization of the monolithic methods for generating vector beams.

We propose and experimentally demonstrate the singular surface plasmon beam that presents a dark channel generated by a point dislocation and a long diffraction-free propagation distance up to 70λsp. The singular surface beam is the result of the interference of two surface plasmon polariton (SPP) plane waves, which are launched by two coupling gratings with lateral displacement. An aperture-type near-field scanning optical microscope is used to map the intensity distribution of the singular SPP waves. The propagating point dislocation embedded in the beam is shown by full-wave calculations and is later verified by near-field interference in the experiment. Published version

We propose and experimentally demonstrate a new method for free-space optical (FSO) communication, where the transmitter encodes data into a composite computer-generated hologram and the receiver decodes through a retrieved array of sidelobe-modulated optical vortices (SMOVs). By employing the SMOV generation and detection technique, the usual stringent alignment and phase-matching requirement of the detection of optical vortices is released. In transmitting a gray-scale picture with 180×180 pixels, a bit error rate as low as 3.01×10(-3) has been achieved. Due to the orbital angular momentum multiplexing and spatial paralleling, this FSO communication method possesses the ability to greatly increase the capacity of data transmission.

A new real-time integral imaging pick-up and display method is demonstrated. This proposed method utilizes the dual-camera optical pick-up part to collect 3D information of real scene in real-time without pre-calibration. Elemental images are then provided by a computer-generated integral imaging part and displayed by a projection-type integral imaging display part. The theoretical analysis indicates the method is robust to the camera position deviation, which profits the real-time data processing. Experimental results show that the fully continuous, real 3D scene pick-up and display system is feasible with a throughput of 8 fps in real time. Further analysis predicts that the parallel optimization can be adopted by the proposed method for real-time 3D pick-up and display with a throughput of 25 fps.

Novel hybrid-polarized vector beams with radial and azimuthal polarization states in arbitrary fan-sectors are generated and studied for manipulating surface plasmon polaritons (SPPs). The method has high energy conversion efficiency based on an interferometric arrangement with a Dammann vortex phase grating. The polarization states of generated beams are measured by a linear polarizer and show excellent agreement with theoretical predictions. The manipulation properties of the hybrid-polarized beams on SPPs excitation and distribution are demonstrated by both experiments and simulations. The results show that focusing or standing wave patterns of SPPs can be obtained depending on the polarization of the beams. Published version

This article defines the tunable viewing scope (TVS) of three-dimensional integral imaging (3DII) considering the human eye's performance, which could provide a fine viewing effect without flipping or information missing. TVS required by different applications is achieved through an innovative method, attaching the reserved blank to the elemental images. The viewing comfort improvement resulting from TVS is verified by practical experiments, which indicates that it would be promising for future applications of 3DII.

We demonstrate an experimental result that shows the phase singularity of surface plasmon waves generated by the direct transform of optical vortices at normal incidence focused on a structureless metal surface. The near-field two-dimensional intensity distribution near the focal plane is experimentally examined by using near-field scanning optical microscopy and shows a good agreement with the finite-difference time-domain simulation result. The experimental realization demonstrates a potential of the proposed excitation scheme to be reconfigured locally with advantages over structures milled into optically thick metallic films for plasmonics applications involving plasmonic vortices.

We propose an approach to the generation of nondiffracting quasi-circularly polarized beams by a highly focusing azimuthally polarized beam using an amplitude modulated spiral phase hologram. Numerical verifications are implemented in the calculation of the electromagnetic fields and Poynting vector field near the focus based on the vector diffraction theory, and the polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the electric field, magnetic field, and Poynting vector field can simultaneously be uniform and nondiverging over a relatively long axial range of ~7.23λ. In the transverse plane, the ellipticity and azimuthal angle of the local polarization ellipse varies from point to point. No polarization singularity and phase singularity are found at the beam center, which makes the bright spot possible.

We report an approach to the increase of signal channels in free-space optical communication based on composed optical vortices (OVs). In the encoding process, conventional algorithm employed for the generation of collinearly superimposed OVs is combined with a genetic algorithm to achieve high-volume OV multiplexing. At the receiver end, a novel Dammann vortex grating is used to analyze the multihelix beams with a large number of OVs. We experimentally demonstrate a digitized system which is capable of transmitting and receiving 16 OV channels simultaneously. This system is expected to be compatible with a high-speed OV multiplexing technique, with potentials to extremely high-volume information density in OV communication.

Manipulation of surface plasmon polaritons (SPP) by phase modulation of incident light beams is proposed with analytical and numerical verifications when an optical vortex (OV) beam is employed as an example. Fundamental functionalities of a plasmonic chip such as in-plane focusing, coupling and multiplexing of SPP by sequentially varying the topological charge of OV beam are demonstrated. Complementary to the manually-controlled optical-path-different technique reported in literature, the proposed method reveals a direct phase transform from OV beam to SPP with dynamic and reconfigurable advantages.

This paper establishes explicit relations between the radial modulation and the optimal sidelobe expression effect in the Bessel-like modulation technique. It verifies that both central and outer ring areas of the phase plate result in sidelobes in the diffraction pattern, and the corresponding structural dimensions can be determined quantitatively. This approach gives rise to complete sidelobe suppression by taking optimal modulation parameters.

This is a reply to the comment [J. Opt. Soc. Am. A26, 2181 (2009)] on our paper that appeared in J. Opt. Soc. Am. A21, 1192 (2004). In the paper the Helmholtz equation was used to introduce the expression of Eq. (2), which generates the fractional Bessel beam (FBB) when n is a fractional number. The paper, however, did not convey whether the FBB is a solution of the Helmholtz equation.

Using micro-optical elements can be an effective, low-cost way to shape laser micro-beams, which are needed for optical trapping and manipulation. This article covers various designs of micro-optical elements that are used to generate the necessary optical vortices within a beam.

Phase-only elements are generally more desirable than complex-amplitude-modulated elements not only because of the higher diffraction efficiency but the readier implementation and fabrication. A novel iterative algorithm is proposed for generating multiple helical modes by a single phase-only element. A superposition of four helical modes is demonstrated experimentally by using a spatial light modulator.

We report a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft-lithography replication method, to fabricate conicoid refractive microlens arrays (MLAs), including hyperboloid, paraboloid, and ellipsoid MLAs in inorganic-organic hybrid SiO2-ZrO2 solgel material. The fabrication procedures involve two basic steps. First, a master of the conicoid MLA was made in photoresist by the sample-inverted reflow technique. Second, we built a negative mold of the master by casting polydimethylsiloxane (PDMS) onto a silicone elastomer against the master, and then the profile was imprinted onto the solgel glass. As a result, the fabricated solgel MLAs have been obtained with excellent smooth profiles, having negligible discrepancies from the profiles of ideal conicoid MLAs.

To improve the coupling efficiency between a laser diode and a single-mode fiber, we propose a two-microlens coupling scheme that uses two solgel spherical microlenses for high coupling efficiency. The conventional reflow technique was employed and extended to the inorganic-organic hybrid SiO2/ZrO2 solgel material to form the microlenses. Preliminary results show that the coupling efficiency was increased to--1.28 dB (74.5%) by the proposed scheme, compared with a coupling efficiency of--10.13 dB (9.7%) by the butt-joint method. The proposed fabrication technique demonstrates that use of a reflowed solgel spherical microlens is a cost-effective mass-production approach to application of micro-optical elements in optical communication.

We propose a novel fabrication method, which is referred to as the sample-inverted reflow technique, to fabricate a refractive microlens array (MLA) with a revolved-hyperboloid profile in a solgel material. The fabricated solgel MLA demonstrates an excellent smooth profile with a fabrication error much less than the difference between the revolved hyperboloid and the spherical surface. In an application of coupling a laser diode (LD) to a single-mode fiber (SMF), we propose a two-MLA coupling scheme in which two revolved-hyperboloid MLAs are used between the LD and the SMF. In this configuration the coupling efficiency achieves 81.7% (-0.88 dB).

We report a simple method for fabricating a concave refractive microlens array (MLA) in solgel glass by using a proximity-effect-assisted reflow technique. The solgel concave refractive MLA that we fabricated had excellent surface smoothness; good dimensional conformity, with an 8.23% nonuniformity of the microlens elements; and structural perfection, with a biggest deviation of 1% from a perfect concave spherical crown. The relative error between the measured and the designed values of the concave MLA's focal length was only 1.83%. Compared with the conventional fabrication techniques for concave MLAs, the proposed method has significant advantages including simplicity, low cost, good element conformity, and smooth device surface.

We demonstrate the experimental generation of a fractional Bessel beam by holographic means. Such fractional modes of Bessel beams possess an intrinsic opening gap across concentric intensity rings on propagation. We also show that the opening gaps within the fractional modes are diffraction free for a working distance while a fractional helical wave front is maintained.

A simple reflow technique is employed for the fabrication of elliptical refractive microlens arrays (MLAs) on a low-cost inorganic-organic SiO2/ZrO2 sol-gel glass. The measured results show that the fabricated elliptical microlenses in a 256 x 512 array have excellent surface and dimensional qualities in terms of smoothness and uniformity. It is also shown that the optical parameters of the MLAs, such as the focal length and aperture dimension, can be accurately controlled. The proposed technique requires only an ordinary binary photomask for pattern transfer. Furthermore, the sol-gel material is found to be feasible for high-volume production, because the fabrication of MLAs can be implemented by use of cheap sol-gel materials without an etching step.

A negative-tone sensitive SiO2/TiO2 organic-inorganic hybrid sol-gel material was synthesized and characterized for fabrication of multilevel micro-optical elements by direct electron-beam lithography. The exposure was carried out by an in-house modified electron-beam writing system using LEO SEM-982 with Elphy Quantum exposure beam-blanking control system at 25keV. The hybrid Sol-Gel material demonstrated a superb sensitivity for doses between 0.22microC/cm2 and 0.33microC/cm2.

Hybrid approaches that combine genetic algorithms (GA’s) with traditional gradient-based local search techniques are proposed for the optimization design of diffractive phase elements (DPE’s) for laser beam shaping. These hybrid methods exploit the global nature of the GA’s as well as the local improvement capabilities of the gradient-based local search techniques and will perform a more improved search in comparison with each of the individual approaches. The incorporated local search technique that we used here is the Davidon–Fletcher–Powell method. A cost function that can directly control the performance of the final solutions is also used. By performing the DPE design with different desired diffraction efficiencies, we obtain a set of results that approximately reflect the trade-off between the design objectives, namely, signal-to-noise ratio (SNR) and diffraction efficiency. Reasonable solutions can be chosen on the basis of the knowledge of the problem. Simulation computations are detailed for two rotationally symmetric beam-shaping systems, in which an incident Gaussian profile laser beam is converted into a uniform beam and a zero-order Bessel beam. Numerical results demonstrate that the proposed algorithm is highly efficient and robust. DPE’s that have high diffraction efficiency and excellent SNR can be achieved by using the algorithm that we propose.

The theoretical diffraction efficiency upper limit of diffractive phase elements (DPE's) with finite apertures is investigated. A successful numerical method of evaluating the efficiency upper bound of DPE's is proposed. The method includes a hybrid optimization procedure that combines a genetic algorithm with the conjugate gradient method. This efficient global optimization technique can also be used to design DPE's. Simulation computations are detailed for rotationally symmetric beam shaping in which a Gaussian profile laser beam is converted into a uniform beam. Numerical results demonstrate that the estimated diffraction efficiency upper bound is consistent with the design results.