X-ray ptychography is a coherent diffraction imaging technique that allows for the quantitative retrieval of both the amplitude and phase information of a sample in diffraction-limited resolution. However, traditional reconstruction algorithms require a large number of iterations to obtain phase and amplitude images exactly, and the expensive computation precludes real-time imaging. To solve the inverse problem of ptychography data, PtychoNN uses deep convolutional neural networks for real-time imaging. However, its model is relatively simple, and its accuracy is limited by the size of the training dataset, resulting in lower robustness. To address this problem, a series of W-Net neural network models have been proposed which can robustly reconstruct the object phase information from the raw data. Numerical experiments demonstrate that our neural network exhibits better robustness, superior reconstruction capabilities and shorter training time with high-precision ptychography imaging.

Abstract The crystalline lens makes an important contribution to the peripheral refraction of the human eye, which may affect the development and progression of myopia. However, little has been known about the peripheral optical features of the crystalline lens and its impacts on the peripheral ocular refraction. This study aims to investigate the relationship between the structural parameters of the crystalline lens and its peripheral power profile over a wide visual field. The peripheral power profile is defined with respect to the entrance and exit pupil centers along the chief rays. Analysis is performed by three-dimensional ray tracing through the gradient refractive index (GRIN) lens models built from measurement data. It has been found that the vergence of the wavefronts at the entrance and the exit pupil centers of the lens show an approximate linear correlation to each other for each field angle. The exponent parameters of the axial refractive index profile and the axial curvature profile, and the asphericity of the posterior lens surface are found to be the most influential parameters in the peripheral power profiles. The study also shows that there can be significantly different, sometimes unrealistic, power profiles in the homogeneous lens model compared with its corresponding GRIN model with the same external geometry. The theoretical findings on the peripheral lens properties provide a new perspective for both wide-field eye modelling and the design of intraocular lenses to achieve normal peripheral vision.

Abstract Magnetic levitation (MagLev) is a density-based method which uses magnets and a paramagnetic medium to suspend multiple objects simultaneously as a result of an equilibrium between gravitational, buoyancy, and magnetic forces acting on the particle. Early MagLev setups were bulky with a need for optical or fluorescence microscopes for imaging, confining portability, and accessibility. Here, we review design criteria and the most recent end-applications of portable smartphone-based and self-contained MagLev setups for density-based sorting and analysis of microparticles. Additionally, we review the most recent end applications of those setups, including disease diagnosis, cell sorting and characterization, protein detection, and point-of-care testing.

Abstract Waveguide technology has great prospects of development in optical see-through near-eye displays with larger field of view, lower thickness and lighter weight than other conventional optical technologies. However, the stray light is usually inevitable in current optical design and manufacturing, causing a poor imaging quality. In this paper, the principle and structures of stray light generation are analyzed, and the causes are discussed by non-sequential ray-tracing with mass precision calculation. From the ray-tracing, the suppression of stray light by optimizing design and manufacturing are achieved. A 2 mm-thickness geometrical waveguide with partially reflective mirror array is designed. The field of view of the optimized geometrical waveguide reaches 47° with 10  mm at exit pupil diameter and 20  mm at eye relief.

Abstract Driven by greatly increased applications, the optical see-through displays have been developing rapidly in recent decades. As a result, some innovative technologies have emerged toward making the display more compact and lighter with better performance. This paper serves as a systematical review on the advances in developing optical see-through displays, including the physical principles, optical configurations, performance parameters and manufacturing processes. The design principles, current challenges, possible solutions and future potential applications are also discussed in the paper.

AbstractEvaporation concentration of target analytes dissolved in a water droplet based on superhydrophobic surfaces could be able to break the limits for sensitive trace substance detection techniques (e.g. SERS) and it is promising in the fields such as food safety, eco-pollution, and bioscience. In the present study, polytetrafluoroethylene (PTFE) surfaces were processed by femtosecond laser and the corresponding processing parameter combinations were optimised to obtain surfaces with excellent superhydrophobicity. The optimal parameter combination is: laser power: 6.4 W; scanning spacing: 40 μm; scanning number: 1; and scanning path: 90 degree. For trapping and localising droplets, a tiny square area in the middle of the surface remained unprocessed for each sample. The evaporation and concentration processes of droplets on the optimised surfaces were performed and analyzed, respectively. It is shown that the droplets with targeted solute can successfully collect all solute into the designed trapping areas during evaporation process on our laser fabricated superhydrophobic surface, resulting in detection domains with high solute concentration for SERS characterisation. It is shown that the detected peak intensity of rhodamine 6G with a concentration of 10−6m in SERS characterisation can be obviously enhanced by one or two orders of magnitude on the laser fabricated surfaces compared with that of the unprocessed blank samples.

Abstract We implement slow-light under electromagnetically induced transparency condition to measure the motion of cold atoms in an optical lattice undergoing Bloch oscillation. The motion of atoms is mapped out through the phase shift of light without perturbing the external and internal state of the atoms. Our results can be used to construct a continuous motional sensor of cold atoms.

Abstract In order to realize the mass production of the large-area flexible transparent film heater (FTFH) at low-cost, this paper presents a novel method which can achieve the direct fabrication of the large-area FTFH with Ag-grid by using an electric-field-driven jet deposition micro-scale 3D printing. The effects of the line width and the pitch of the printed Ag-grids on the optical transmittance and the sheet resistance are revealed. A typical FTFH with area of 80 mm × 60 mm, optical transmittance of 91.5% and sheet resistance of 4.7 Ω sq−1 is fabricated by the nano-silver paste with a high silver content (80 wt.%) and high viscosity (up to 20 000 mPa · s). Temperature-time response profiles and heating temperature distribution show that the heating performance of the FTFH has good thermal and mechanical properties. Furthermore, the adhesive force grade between the Ag-grid and the PET substrate measured to be 4B by 3M scotch tape. Therefore, the FTFH fabricated here is expected to be widely used in industry, such as window defroster of vehicles and display or touch screens owing to its striking characteristics of large area and low cost fabrication.

Abstract The Absorbing Aerosol Sensor (AAS) will be launched aboard the GaoFen-5B satellite in China. The main purpose of AAS is to monitor absorbing aerosols by measuring the solar backscatter radiation. AAS is an ultraviolet-visible imaging spectrometer that uses a single charge coupled device to capture both the spectrum and the cross-track direction with a 114° wide swath. The large field of view enables daily global coverage with 4-km spatial resolution. The spectral range of the instrument extends from 340 to 550 nm with spectral resolution (full width at half maximum) of 2 nm. This paper provides details of the instrument design, including system design, optical design, and mechanical design, as well as detector and calibration unit on orbit. The numerous simulations show that all design results satisfy the specification and vibration requirements of the instrument.

Abstract Three multilayer interference optical filters, including a UV band-pass, a VIS dual-band-pass and a notch filter, were designed by using Ta2O5, Nb2O5, Al2O3 and SiO2 as high- and low-index materials. During the design of the coating process, a hybrid optical monitoring and RATE-controlled layer thickness control scheme was adopted. The coating process was simulated by using the optical monitoring system (OMS) Simulator, and the simulation result indicated that the layer thickness can be controlled within an error of less than ±0.1%. The three filters were manufactured on a plasma-assisted reactive magnetic sputtering (PARMS) coating machine. The measurements indicate that for the UV band-pass filter, the peak transmittance is higher than 95% and the blocking density is better than OD6 in the 300–1100 nm region, whereas for the dual-band-pass filter, the center wavelength positioning accuracy of the two passbands are less than ±2 nm, the peak transmittance is higher than 95% and blocking density is better than OD6 in the 300–950 nm region. Finally, for the notch filter, the minimum transmittance rates are >90% and >94% in the visible and near infrared, respectively, and the blocking density is better than OD5.5 at 808 nm.

Abstract Ytterbium fluoride (YbF3) single thin films were prepared on sapphire and monocrystalline silicon substrates through conventional thermal evaporation and ion beam-assisted deposition (IAD), at bias voltages ranging from 50 to 160 V of the Leybold advanced plasma source (APS). By using the Cauchy dispersion model, the refractive index and thickness of the YbF3 thin films were obtained by fitting the 400–2500 nm transmittance of the monolayer YbF3 thin films on the sapphire substrate. At the same time, the refractive index and thickness of the YbF3 thin films on the monocrystalline silicon substrates were also measured using the VASE ellipsometer at wavelength from 400 to 2200 nm. The results showed that the refractive index deviation of the YbF3 thin films between the fitted values by the transmittance spectra and the measured values by the VASE ellipsometer was <0.02 and the relative deviation of the thickness was <1%. Furthermore, the refractive index of the YbF3 thin films increased with increasing APS bias voltage. The conventional YbF3 thin films and the IAD thin films deposited at low bias voltage revealed a negative inhomogeneity, and a higher bias voltage is beneficial for improving the homogeneity of YbF3 thin films.

Abstract The explosive growth of data centers, cloud computing and various smart devices is limited by the current state of microelectronics, both in terms of speed and heat generation. Benefiting from the large bandwidth, promising low power consumption and passive calculation capability, experts believe that the integrated photonics-based signal processing and transmission technologies can break the bottleneck of microelectronics technology. In recent years, integrated photonics has become increasingly reliable and access to the advanced fabrication process has been offered by various foundries. In this paper, we review our recent works on the integrated optical signal processing system. We study three different kinds of on-chip signal processors and use these devices to build microsystems for the fields of microwave photonics, optical communications and spectrum sensing. The microwave photonics front receiver was demonstrated with a signal processing range of a full-band (L-band to W-band). A fully integrated microwave photonics transceiver without the on-chip laser was realized on silicon photonics covering the signal frequency of up 10 GHz. An all-optical orthogonal frequency division multiplexing (OFDM) de-multiplier was also demonstrated and used for an OFDM communication system with the rate of 64 Gbps. Finally, we show our work on the monolithic integrated spectrometer with a high resolution of about 20 pm at the central wavelength of 1550 nm. These proposed on-chip signal processing systems potential applications in the fields of radar, 5G wireless communication, wearable devices and optical access networks.

Abstract Hydrogen peroxide (H2O2) detection was demonstrated with multi-pass absorption spectroscopy using a commercial 76-m astigmatic multi-pass absorption cell. An ∼7.73-μm continuous wave, distributed feedback quantum cascade laser (CW DFB-QCL) was employed for targeting a strong H2O2 line (1296.2 cm-1) in the fundamental absorption band. Wavelength modulation spectroscopy combined with a second harmonic detection technique was utilized to increase the signal-to-noise ratio. By optimizing the pressure inside the multi-pass cell and the wavelength modulation depth, a minimum detection limit (1σ) of 13.4 ppbv was achieved for H2O2 with a 2-s sampling time. From an Allan-Werle deviation plot, the detection limit could be improved to 1.5 ppbv with an averaging time of 200 s. Interference effects of atmospheric air components are also discussed.

AbstractA wavelength-modulated heterodyne grating shearing interferometry using a birefringent crystal is proposed for two-dimensional displacement measurement. There is a difference in the optical path lengths of the p- and s- polarizations of the light beam in the birefringent crystal because of the double refraction caused by the birefringence. By passing through the unequal-path-length optical configuration, the wavelength-modulated light beam is converted into a heterodyne light beam having two frequencies. The modulated heterodyne light beam is further combined with grating-shearing interferometry based on the quasi-common-optical-path (QCOP) design concept. According to the working principle and the Jones calculation, the displacement information of a moving grating can be obtained by means of the optical phase variation resulting from the grating. Theoretical analysis shows that the measurement sensitivity of the proposed method is about 0.134°/nm. The experimental results indicate that the resolution is about 10 nm for the centimetric-level measurement range.