A Novel Strategy for Rapid Fluorescence Detection of FluB and SARS-CoV-2.

Undoubtedly, SARS-CoV-2 has caused an outbreak of pneumonia that evolved into a worldwide pandemic. The confusion of early symptoms of the SARS-CoV-2 infection with other respiratory virus infections made it very difficult to block its spread, leading to the expansion of the outbreak and an unreasonable demand for medical resource allocation. The traditional immunochromatographic test strip (ICTS) can detect one analyte with one sample. Herein, this study presents a novel strategy for the simultaneous rapid detection of FluB/SARS-CoV-2, including quantum dot fluorescent microspheres (QDFM) ICTS and a supporting device. The ICTS could be applied to realize simultaneous detection of FluB and SARS-CoV-2 with one test in a short time. A device supporting FluB/SARS-CoV-2 QDFM ICTS was designed and had the characteristics of being safe, portable, low-cost, relatively stable, and easy to use, ensuring the device could replace the immunofluorescence analyzer in cases where there is no need for quantification. This device does not need to be operated by professional and technical personnel and has commercial application potential.

Flexible broadband white light multimode interference coupler.

In recent years, with the development of micro broadband white light sources, micro white light devices have exhibited great potential application value in many fields. As the core component of broadband white light technology, the compact, efficient and flexible RGB coupler plays a vital role. However, the traditional RGB coupler is composed of discrete components. Realizing miniaturization, flexibility and high transmission efficiency of the device is difficult, which greatly limits the development of micro white light broadband devices. In this paper, we propose an RGB on-chip waveguide coupler that can meet the requirements of miniaturization, flexibility, and high transmission efficiency and study its performance. The research results show that the device size is reduced to 0.04 mm×3.6 mm, and the average transmission efficiency in RGB beam multiplexing/demultiplexing is as high as 94.6%. In addition, the use of the SU8 polymer as a waveguide material makes our design compatible with flexible optoelectronic technology, which will greatly promote the development of miniaturization and flexibility for micro white light devices in the future.

Microsphere-lens coupler with 100 nm lateral resolution accuracy in visible light.

We propose a microsphere-lens coupler that can successfully constrain the beam with near-field details to achieve ∼100nm lateral resolution accuracy. In theory, we use the finite-difference time-domain method to analyze the properties of the "photonic nanojet." The optimal focusing ability scope can be obtained by adjusting the focusing parameters, such as refractive index, paraxial optical intensity attenuation ratio, sizes of microspheres, and so forth. In experiment, the "non-brush scrubbing" cleaning technology is adopted to optimize the experimental results. Aiming to self-assemble properties of dielectric spheres, we introduce the deagglomeration method to produce homogeneous liquid. Meanwhile, by tiling a 5 µm-diameter microsphere-lens on a specimen, a traditional optical microscope can realize 100 nm lateral superresolution microimaging, which lays a certain foundation for further development of superresolution microimaging.

Microcavity-integrated graphene waveguide: a reconfigurable electro-optical attenuator and switch.

Graphene has been widely utilized in optoelectronic applications due to its high carrier mobility, and extremely fast optical response. Microcavity-integrated graphene waveguide structure is one basic module of integrated photonic devices which can greatly improve the light-matter interaction strength. The enhanced optical absorption in the undoped graphene layer results from the light trapping and the corresponding long light-graphene interaction length. Tuning the Fermi energy level of the graphene layer enables the electro-optical modulation. We report the realization of reconfigurable electro-optical attenuator and switch with unity-order modulation depth in light reflection and transmission at near-infrared frequency. The transformation from a lossy absorber to a quasi-perfect transparent condition of the monolayer graphene by tuning the Fermi level leads to the unity-order tunability of the electro-optical attenuator and switch. We investigate theoretically and numerically the absorption properties of the designed microcavity-integrated graphene with respect to different graphene Fermi levels. Electro-optical attenuator with attenuating coefficient from 10% to 98.29% is fulfilled. On-off electro-optical switching with a switching contrast larger than 21 dB is demonstrated. Our approach provides the possibilities of graphene photonics applied in communications, and sensing.

Tight focusing of a higher-order radially polarized beam transmitting through multi-zone binary phase pupil filters.

When the pupil filters are used to improve the performance of the imaging system, the conversion efficiency is a critical characteristic for real applications. Here, in order to take full advantage of the subwavelength focusing property of the radially polarized higher-order Laguerre-Gaussian (LG) beam, we introduce the multi-zone binary phase pupil filters into the imaging system to deal with the problem that the focal spot is split along the z axis for the small size parameter of the incident LG beam. We provide an easy-to-perform procedure for the design of multi-zone binary phase pupil filters, where the zone numbers of π phase are uncertain when the optimizing procedure starts. Based on this optimizing procedure, we successfully find the set of optimum structures of a seventeen-belt binary phase pupil filters and generate the excellent focal spot, where the depth of focus, the focal spot transverse size, the Strehl ratio, and the sidelobe intensity are 9.53λ, 0.41λ, 41.75% and 16.35% in vacuum, respectively. Most importantly, even allowing the power loss of the incident LG beam truncated by the pupil of the imaging system, the conversion efficiency is still as high as 37.3%. Theoretical calculations show that we succeed to have sufficient conversion efficiency while utilizing the pupil filters to decrease the focal spot and extend the depth of focus.

Near-field focusing of the dielectric microsphere with wavelength scale radius.

We focus on physically analyzing the origins of the numerical aperture (NA) and the spherical aberration of the microsphere with wavelength scale radius. We demonstrate that the microsphere naturally has negligible spherical aberration and high NA when the refractive index contrast (RIC) between the microsphere and its surrounding medium is about from 1.5 to 1.75. The reason is due to the spherical aberration compensation arising from the positive spherical aberration caused by the surface shape of the microsphere and the RIC and the negative spherical aberration caused by the focal shifts due to the wavelength scale dimension of the microsphere. We show that, only within the approximate region of 1.5 ≤ RIC ≤ 1.75 with the proper radius r of microsphere, the microsphere can generate a near-field focal spot with lateral resolution slightly beyond λ/2ns, which is also the lateral resolution limit of the dielectric microsphere. The r for each RIC can be obtained by optimizing r from 1.125λ/n o to 1.275λ/n o. Here λ, n s, and n o are the wavelength in vacuum and the refractive indices of microsphere and its surrounding medium, respectively. For the case of the near-field focusing, we also develop a simple transform formula used to calculate the new radius from the known radius of microsphere corresponding to the original illumination wavelength when the illumination wavelength is changed.

Control of the multifocal properties of composite vector beams in tightly focusing systems.

The numbers of the focal spots and the dominant field (i.e., whether the axial field or the transverse fields play dominant role in the focusing field) have significant effects on various applications. In this paper, we have derived the universal imaging model of the composite vector beam (CVB) composed of two orthogonally linearly polarized beams with inhomogeneous polarization modulation, which is also suitable for various polarized beams, such as linearly, circularly, radially, azimuthally, and vortex polarized beams. Moreover, the sin&cos amplitude modulation with arbitrary orders and the pupil filters with cylindrical symmetry are also involved in this imaging model. On the basis of this imaging model, the regulars to control the focal numbers and the dominant field are drawn. For the various applications, some important conclusions and constructive advices are given.

Multifocus with small size, uniform intensity, and nearly circular symmetry.

We investigate in detail the focusing properties of the composite vector beam (CVB) composed of two orthogonally linearly polarized beams with inhomogeneous polarization modulation. By optimizing the modulation factor, a multifocus with excellent quality is obtained, where the sizes of each focus are fairly smaller than that of the focusing spot of a radially polarized beam, the uniformity in the intensity of the focal spots is as high as 1, and the distributions of each focal spot have nearly circular symmetry. In order to decrease the power loss of the incident beam, the CVB formed by an annular beam is demonstrated as the substitute for the optimized CVB formed by a Gaussian beam. This work is important for high-resolution and high-speed imaging in biology and micro-nanofabrication.

Automatic waveguide-fiber coupling system based on a multiobjective evolutionary algorithm.

A method for the automated alignment of optical waveguides and fibers based on a multiobjective evolutionary algorithm is proposed. This algorithm reduces the number of parallel operations considerably compared to previous automation schemes. The automated alignment of a single-core input fiber with a channel waveguide and a single-core output fiber is completed using this system in less than 3 min. The alignment of a single-core input fiber with a 1x8 splitter coupler and an eight-core output fiber array is completed in less than 10 min. These results demonstrate the effectiveness of the proposed scheme for automated waveguide alignment, substantially outperforming previous automatic alignment methods.