查看更多>>摘要：We propose a multimode planar waveguide with polymer core of negative photoresist AZ15nXT with an upper cladding of electrically tunable 4-cyano-4'-pentylbiphenyl (5CB) nematic liquid crystal. The waveguide is realized on indium tin oxide (ITO) coated glass substrates using a simple, cost-effective photolithography fabrication technique. The refractive index of LC cladding changes with the applied voltage, which affects the propagation of transverse magnetic (TM) modes of light in the core. We experimentally achieved a relatively low threshold voltage of 1.08 V and the maximum required operating voltage of 4 V-pp (peak to peak) at 633 nm wavelength. An extinction ratio of 12 dB for TM modes is obtained at an applied voltage of 4 V-pp. A theoretical and experimental analysis is done to present the device as a low threshold electro-optic switch and optical attenuator for TM polarization.
查看更多>>摘要：Magneto-optical traps based on grating chips can simplify cold atom physical package architectures significantly. Here we report the design and fabrication of a high-diffraction-efficiency grating magneto-optical trap (GMOT). The numerical simulation is performed with an optimized profile and measured refractive index of the gold film. In the design, the fabrication tolerance is also considered. The fabricated grating chip achieved a diffraction efficiency of up to 40%. Up to 2.8 x 10(7) are trapped with the chip, and the characterization of the GMOT is performed. High absorption contrast CPT resonance signal was also obtained. The proposed atom chip can be leveraged to realize compact cold atom clocks and other cold atom-based quantum sensors.
查看更多>>摘要：As a potential high-energy laser, optically pumped metastable rare gas laser (OPRGL) has drawn attention worldwide. In this article, a stack-pumped metastable argon laser was demonstrated at 800 mbar of Ar/He mixture. The metastable particles were produced by repetitively pulsed discharge in the gas mixture, and laser oscillation was realized in a planar-concave cavity with the gain medium longitudinally or transversely pumped by the pumping source of a diode-stack with an external cavity of gratings. Maximum averaged power of 750 mW was obtained with transverse pumping in a repetition rate of 30 kHz of pulsed discharge. Compared to longitudinal pumped OPRGLs, extraction ability and pumping uniformity would be improved at transverse pumping configuration. And it is found that the average output power similar to that of longitudinal pumping can be achieved at a shorter gain length with transverse pumping, which is linearly proportional to the discharge repetition rate. This demonstration implies that power scaling of OPRGL is feasible by combining diode-stacks and multi-pass transverse pumping.
查看更多>>摘要：Shift error of modulation frequency generated from the refractive-index dispersion of a transparent glass plate and the nonlinear properties of phase modulation during wavelength tuning need to be suppressed for determining the homogeneity in optical thickness of the glass plate with wavelength tuning. In this study, we develop a new method to eliminate the dispersive error of refractive index and the nonlinear error of the phase modulation simultaneously. Moreover, a new 21-sample phase-extraction algorithm is derived using the proposed method. Characteristics of the newly designed algorithm are visualized in the frequency domain and on the complex plane. Numerical analysis show that the 21-sample algorithm has a greater error-suppression ability than other classical algorithms. The homogeneity in optical thickness of the transparent glass plate is determined by combining the proposed 21-sample algorithm and Fizeau-type interferometer. The standard deviation of thickness profiling measurement is 5.658 nm. This is significantly smaller than the standard deviation of other algorithms. Furthermore, the two-dimensional thickness distributions demonstrated that the proposed 21-sample algorithm can suppress residual ripples more effectively compared with other algorithms.
查看更多>>摘要：Here we theoretically investigate the third-harmonic generation of phase change material (Ge2Sb2Te5-GST) nanodisks, and analyze the nonlinear optical contributions from different Mie resonances including electric dipole, anapole states, and higher-order anapole states. Moreover, dynamically tuning the THG intensity and wavelength of the GST nanodisks has been demonstrated by switching the phase states among amorphous, crystalline and intermediate states. This study provides a new platform for the design of nanodevices with active nonlinear optical properties.
查看更多>>摘要：As a lensless imaging technology, coherent modulation imaging (CMI) can reconstruct the complex amplitude of the object from the measured intensity distribution. In this paper, a new CMI scheme is proposed. A random binary amplitude mask is introduced between the light source and the object. The incident light is modulated by the mask and the speckle field is generated to illuminate the object. The object can then be accurately recovered with the iterative phase retrieval algorithm by means of moving the mask several times in the axial direction and recording the corresponding diffraction pattern. Compared to the existing CMI schemes, the experimental system of the proposed method is simple and compact. No spatial light modulator or phase plate is required. Both numerical simulations and experiments are performed to verify the feasibility of the method. The influence of moving times, moving interval and pixel size of the mask on the reconstruction accuracy are analyzed in detail. In addition, the image registration encountered in the experiment is discussed.
查看更多>>摘要：Sampling frequency offset (SFO) between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) will severely degrade the transmission performance of orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system. In this paper, a novel SFO mitigation scheme based on rotated K-means clustering is proposed, which differs from traditional SFO compensation based on phase estimation and feedback. When SFO causes the constellation points to deviate from their original positions, this scheme can adaptively update the clustering centroids to achieve the correct symbol demapping without phase estimation and compensation. Experimental results indicate that after 3.5 m free-space transmission, the SFO tolerance of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM) can reach +/- 130 and +/- 65 ppm with a bit error rate (BER) less than the hard-decision forward error correction (HD-FEC) threshold of 3.8e-3, respectively.
查看更多>>摘要：In this novel scheme of terahertz (THz) generation, the effect of cross-focusing of Gaussian laser beams in the array of vertically aligned anharmonic carbon nanotubes (CNTs) has been studied. The static magnetic field is applied transverse to the axis of CNTs to magnetize the CNTs. The nonlinearity in the system arises due to the ponderomotive force exerted by the laser beams on the electrons of CNTs. The plasma in the CNTs rearranges itself due to this ponderomotive nonlinearity, which gives rise to the cross-focusing of both laser beams. The nonlinear current at THz frequency appears in the array of CNTs on account of the ponderomotive nonlinearity and anharmonicity of the system. The anharmonicity plays a pivotal role in the enhancement of THz generation. The normalized amplitude of THz radiation shows a notable enhancement with the increase of the externally applied static magnetic field (90 kG to 330 kG), dimensions of CNTs, and inter-tube separation. The cross-focusing of two laser beams in the magnetized collisional plasma makes a significant enhancement in the THz generation with the help of anharmonicity.
查看更多>>摘要：The angle of Degenerate and Non-Degenerate Conical Emission in BK-7 glass is measured in the emission span of +3000 to -2000 cm(-1 )produced from an 800 nm 50 fs source laser beam. The measured emission angle is compared to three different mathematical models. These models are the Alfano-Shapiro Model, the Luther Model, and the Faccio X-Wave model. Experimental results demonstrate the existence of Degenerate Conical Emission at a frequency shift of zero (delta omega & nbsp;= 0) from the source beam. Of the three tested models this is only predicted by the Alfano-Shapiro model, which relates it directly to the Kerr nonlinear index. The relationship shows that the Kerr index has transitioned to a nearly pure electron cloud response due to the temporal nature of the laser pulse. The experimental methods demonstrated here could be used in the future as a means of measuring the response of the Kerr nonlinear index and studying the importance of pulse duration in nonlinear optics.
Chen, ChaoliangShi, WeisongYang, Victor X. D.Gao, Wanrong...
6页
查看更多>>摘要：Bulk motions occurred during in vivo scanning could modulate the backscattered light signals with the same mechanism of moving scatterers (such as red blood cells), so bulk motion suppression plays a key role for optical coherence tomographic angiography (OCTA) applications. One classic method to overcome this issue is to compensate the bulk motions with image registration algorithms before calculating vascular signals, which is however computationally intensive and makes real-time screening (a key feature for clinical devices) challenging. In this work, we investigated the influence of the time interval (between consecutive B-scans) on the microvascular images calculated with the recently proposed differential standard deviation of logscale intensity (DSDLI) algorithm. An optimized time interval was successfully found and in vivo experiments were implemented for performance verification. The results showed that bulk-motion-suppressed high-contrast microvascular images could be obtained without image registration during data processing.
NSTL
Elsevier