Optics Frontier—The 10th International Conference on Information Optics and Photonics (CIOP 2018)
The surface plasmon polaritons (SPPs) is an electromagnetic wave that can be stimulated and then propagates over the surface of the preshaped metallic nanostructures or the interface between the surface of the metallic nanostructures and the substrate media due to a strong coupling of incident light and the surface free-electrons moving on the metallic nanostructure surface with a featured micrometer scale. As shown, through SPPs, incident light energy can be localized effectively in a sub-wavelength region or space, and thus so-called light diffraction limit can be break through easily. Therefore, it has demonstrated a good prospects for developing advanced functioned materials or devices such as light absorbing materials, optical antennas, and optical information storage modules. In this paper, we propose a special metallic nanostructures, which can be used to absorb a certain band of incident light by converting them into a kind of local free-electron oscillation, which means that SPPs can be generated and processed efficiently. As shown, the metallic nanostructures will present a lower reflectivity in the wavelength range, and through adjusting several key parameters such as the period of the metallic nanostructures, we can achieve an effective control of reflectivity because a valley of the reflectivity curve can be formed, which means a low reflectance at a specific wavelength band has been obtained.
To study the performance and microstructure of TC17 thin-walled parts in shock wave and its reflection wave induced by laser, TC17 titanium alloy samples are processed using YAG laser with the wavelength of 1064 nm, pulse energy of 7J and pulse width of 15ns. Thus, its residual stress, microhardness and microstructure of overlapping shock with different thickness are obtained. The results show that with the thickness increasing, the front micro-hardness increases, and the reverse micro-hardness increases firstly and then decreases. The variation of residual stress with the thickness is consistent with the micro-hardness. The front residual stress maximum reaches -496.5MPa at the thickness of 5mm, and the reverse residual stress maximum reaches -171.1MPa at the thickness of 2mm. With the increase of thickness, the distribution of surface dislocations is more uniform, the grain refinement effect is more obvious, and the strengthening effect is the better. The causes of the variation of the double-sided residual stress field with the thickness are explained by theoretical analysis of the propagation and reflection of the shock wave in the material. The conclusions of this investigation have significance for the optimization of laser shock peening thin-wall workpieces.
Surface ozone, an important secondary air pollutant, has become the primary pollutant in China during the summer. During the 18 days between August 24 and September 10, 2016, the ozone heavy pollution incident occurred four times in the Yangtze river delta(YRD), one of Chinese most developed areas. It lasting 2 to 5 days every time, the maximum concentration reaching to 550ppb. A high concentration of ozone pollution layer with vertical and horizontal transmission showing at altitude 1-2km, which has a significant impact of near-grounded ozone pollution. It has been observed simultaneously by two differential absorption lidars(DIAL). Diurnal variation in near-grounded ozone concentration of a single peak and single valley, the average minimum value is 75ppb, appearing at around 02:00 LST, and the average maximum value is 90ppb, appearing at around 12:00 LST. However, the daily ozone concentration of the upper air is not obvious. In order to obtain the temporal and spatial variation characteristics of ozone concentration in the whole YRD region and the influence of meteorological factors on ozone concentration, the WRF-Chem model is used to simulate the pollution process. The results show that the simulation results of ozone concentration are in good agreement with the lidar monitoring values. The meteorological elements play an important role in the change of ozone concentration. Strong solar radiation, high temperature and low relative humidity are favorable environmental conditions for ozone pollution, while high wind speed has a diffusion effect on ground ozone, and rainfall has a good effect on ozone removal.
Two-photon excitation fluorescence imaging (TPEFI) is a nonlinear optical imaging technique. Compared with the traditional single-photon imaging technology, it has many advantages such as little light damage, small bleaching area, high spatial resolution, high fluorescence collection efficiency, and high image contrast. Especially, two-photon microscopy is more suitable for the observation of thick specimen, and real-time three-dimensional or four-dimensional observations of living cells and even living tissue. However, some probes used to label living cells are toxic and will have an adverse effect on the living cells imaging. Squaraine dye is an organic dye with strong fluorescence and low cytotoxicity. In this study, we synthesized a squaraine organic dye with a significant fluorescent effect. OVCAR-3 ovarian cancer cells were labelled with the squaraine dye and detected by confocal laser scanning microscope Leica TCS SP8 for single-photon and two-photon imaging. The OVCAR-3 cells were co-incubated with the squaraine dye at 1 μmol L-1 for 0.5 h, washed with PBS 7.4 three times, and then detected with Leica TCS SP8. The excitation wavelength was 600 nm for single-photon imaging and 1000 nm for two-photon imaging. The results showed that two-photon imaging has better resolution and deeper imaging depth, suggesting its potential application in imaging of thick samples. In conclusion, two-photon imaging using squaraine dye is a potential imaging technique that may be widely applied in cancer diagnosis in the future.
Hyperspectral imaging typically produces huge data volume that demands enormous computational resources in terms of storage, computation and transmission, particularly when real-time processing is desired. In this paper, we study a low-complexity scheme for hyperspectral imaging completely bypassing high-complexity compression task. In this scheme, compressive hyperspectral data are acquired directly by a device similar to the single-pixel camera based on the principle of compressive sensing (CS). To decode the compressive data, we propose a flexible recovery strategy by taking advantage of the joint spatial-spectral correlation model of hyperspectral images. Moreover, a thorough investigation is analytically conducted on compressive hyperspectral data and we find that the compressive data still have strong spectral correlation. To make the recovery more accurate, an adaptive spectral band reordering algorithm is directly added to the compressive data before the reconstruction by making best use of spectral correlation. The real hyperspectral images are tested to demonstrate the feasibility and efficiency of the proposed algorithm. Experimental results indicate that the proposed recover algorithm can speed up the reconstruction process with reliable recovery quality.
A chiral plasmonic lens (CPL) suitable for circular polarization analyzer is designed and numerically investigated. It consists of two arrays of rectangular nanoslits milled into a gold film along Archimedes spirals. The CPL can couple circularly polarized illumination into two SPPs waves, which can interfere constructively or destructively according to both the structure of the CPL and the handedness of circular polarization possessed by incident beam. We demonstrate both theoretically and numerically that the designed structure can convert an incident circularly polarized light beam with prescribed chirality into a Bessel-like distributed focus, but the circularly polarized one with the opposite chirality cannot be transmitted and focused by the same CPL due to the alternative chirality. Further, three-dimensional finite-difference time-domain (FDTD) simulations show that an ultrahigh extinction ratio up to ten thousands of the CPL is numerically achieved with a device size less than 10 λspp, which is two orders higher than that of a conventional plasmonic circularization analyzer with single Archimedes-spiral groove. The designed structure can be widely used in miniature polarimeter and detection of spin angular momentum.
Recently, we propose a temporal ghost imaging scheme based on frequency correlation, which is a stable degree of freedom when photons propagate over fibers. We demonstrate its feasibility with both quantum light source and thermal light source.
The quantum temporal ghost imaging is based on a telecom-band quantum light source, which generates frequency-correlated photon pairs. It is realized by spontaneous four-wave mixing in a piece of silicon waveguide under continuous-wave pumping. The quantum state of the photon pairs has a broad spectrum, hence, the two photons in a pair has broadband frequency correlation. The signal and idler photons are separated by a filter system, which are centered at 1510 nm and 1550 nm, respectively, with a bandwidth of 16 nm at both sides.
The temporal GI scheme is based on frequency correlation of two beams, which can also be realized by thermal light sources. In the experiment, the thermal light source is realized by SFWM in the silicon waveguide, since both signal and idler photons generated by spontaneous four-wave mixing are under thermal statistics. The pump light of the source is generated by a mode-lock fiber laser with a repetitive rate of 40 MHz. Two optical filters are used to control the linewidth of the pulsed pump light and select the signal photons, by which the linewidth of the selected signal photons is 3 nm and they are under single-mode thermal state.
In this study, a kind of electronically controlled liquid-crystal microlens array (LCMLA) with plane swing focus and tunable focal length instead of a commonly microlens array with a fixed focal length and then focus distribution for high-resolution image acquisition, wavefront measurement, and distortion wavefront correction, is proposed. The LCMLA mainly consists of two glass substrates coated with a film of indium-tin-oxide (ITO) transparent material on one side. Each sub-unit top layer is composed of four sub-square electrodes, and the bottom layer is a circular electrode. The key technological steps in electrode fabrication contain an ultraviolet lithography, a dry etching (ICP etching), and final electron beam evaporation and overlay. The current LCMLA can be realized in three operating modes under external driving circuitry, including intensity image acquiring, wavefront measurement and distortion wavefront correction. The LCMLA is only in the image acquisition mode under the condition of no driving electrical signal. As the same driving electrical signals are applied onto the top four sub-electrodes of each sub-unit, the LCMLA is in the wavefront measurement mode. The LCMLA is in the key wavefront correction mode when different driving electrical signals are simultaneously applied onto the top four sub-electrodes of each sub-unit. Experiments show that the focal point of the LCMLA can be moved along the optical axis and over the focal plane by applying appropriate driving voltage signals.
A dispersive optics quantum key distribution (DO-QKD) utilizing a quantum light source based on spontaneous four wave mixing (SFWM) in a piece of silicon waveguide is demonstrated.
In DO-QKD schemes, the conjugate bases based on large group-velocity delay (GVD) of normal dispersion (ND) and anomalous dispersion (AD) modules are utilized for security test, which has already been proved to be secure against collective attacks. In Alice and Bob, photons are detected by these two bases randomly. Experimental results tell that the coincidence show excellent correlation when the photons are detected at Alice and Bob by the same bases. If not, the correlation would be degraded. By further measuring the covariance matrix associated with the correlation between Alice and Bob’s detection events, we can bound the information accessible to Eve. Any information that Alice and Bob share in excess of this bound will be secure.
For key generation, we bin the single photon events in Alice and Bob in large alphabet way to get high-dimension information from each coincidence. By optimization towards detection events, the bit error rate (BER) due to the jitter of the detector electronics can be reduced to ~1.7%.
At last, combined with the large alphabet time encoding and DO-QKD, a raw key rate of 50 kbps with 1.7% BER was achieved with an alphabet size of 4 and a bin width of 65 ps through optical fibers of 20 km, showing that silicon based quantum light sources have great potential on long distance QKD over optical fibers.
Over the years, many approaches have been proposed to overcome imaging through scattering medium. Memory effect, as a relatively simple method, has aroused great enthusiasm recently. However, researchers mainly focus on imaging in transillumination geometry. In a more general case, it’s necessary to exploit imaging in reflection geometry for the purpose of noninvasive imaging. As back-scattered light from the medium becomes additive noise and submerges the signal, a phase retrieval algorithm and bispectrum analysis will severely suffer from noise and very likely result in false reconstruction. Thus, a more robust and steady technique, which is less sensitive to experimental noise, is highly in need.
Based on memory effect, we propose a method of imaging reflective targets hidden behind a scattering layer with the auxiliary of a known reference object. The proposed method does not rely on the phase retrieval algorithm. Instead, it resorts to an a priori reference object in the neighborhood of the target. Because of the inherent connection between speckle patterns, the knowledge of an a priori reference object beside the target makes it possible to directly reconstruct the target image using
autocorrelation if the reference is point-like or deconvolution with the recorded speckle performed.
To demonstrate the superiority of our method, we make a comparison of our results with those reconstructed using the phase retrieval algorithm, and demonstrate that our method has good performance even under extremely difficult conditions that the phase retrieval algorithms may not work well.