查看更多>>摘要：In this paper, we investigate the propagation properties of the Ince-Gaussian vector beams through atmospheric turbulence. For this type of generalized fundamental vector beams, the spatial structures of intensity and polarization are demonstrated to have the stability of transmission over kilometers. Analysis of scintillation index and spot centroid drift also supports this view. The von Karman type index power spectrum and the resulting random phase screens are used to simulate the atmospheric turbulence model. Owing to the strong quantum-like correlation between polarization and the spatial components, the Ince-Gaussian vector beams exhibit stable photon entanglement and high inseparability. In particular, the increasing complexity of light field structure will enhance this stability of structure transmission. Higher-order Ince-Gaussian vector beams have the longer decoherence time and longer identified distance. The fourth-order Ince-Gaussian vector beams have stronger transmission stability than the third-order Ince-Gaussian vector beams. Our work contributes to the understanding of the stable propagation of the vectorial structured light and improves imaging and free-space optical communication in perturbing media.
查看更多>>摘要：Optical nonreciprocity plays an important role in optical communication and signal processing. Here, we propose and demonstrate a magnetic-free optical nonreciprocal amplification based on a far-detuned four-wave mixing process in hot atoms. The absorption of the probe field can be significantly reduced by the large detuning. In our experiment, with just one pump field, an ultra-strong forward gain of 45 dB is achieved while the backward one keeps a near unit transmission. The experimental realization of ultra-strong nonreciprocal amplification may have applications for the generation of strong nonreciprocal quantum correlations.
查看更多>>摘要：Here we highlight enantioselective optical gradient forces present in 3D (non-paraxial) structured optical vortex tweezing systems. One chiral force originates from the circular polarization of the light, while remarkably the other is independent of the input polarization -even occurring for unpolarized light - and is not present in 2D structured light nor propagating plane waves. This latter chiral sorting mechanism allows for the enantioselective trapping of chiral particles into distinct rings in the transverse plane through conservative radial forces.
查看更多>>摘要：We propose a compact computational imaging system with adaptive weighted feedback amplitude-phase retrieval (awfAPR) algorithm, in which the traditional axial linear scanning method is replaced by periodic optical path modulation (OPM) strategy. The introduced adaptive feedback scenario can significantly suppress noise contamination. Specifically, OPM is achieved by the rotation of gradient thicknesses of the transparent optical medium. Compared with multi-distance/height scanning (MDPR), all system components in the OPM system are fixed at discrete lateral positions. Besides, according to the auxiliary of corresponding auto-focusing criterion and sub-pixel registration algorithms, the OPM system is also self-calibration and independent of the accuracy of rotation and thickness parameter. Furthermore, experimental results show that the adaptive weighted feedback strategy remarkably improves the stability and robustness toward the noise. OPM has flexible adaptability to optical path modulation method. The proposed optical system configuration has minimal hardware requirements and is anticipated to expand dynamic real-time imaging.
Malik, Karuna SindhuKumar, NagendraBoruah, Bosanta R.
7页
查看更多>>摘要：In this paper we first describe two existing schemes to construct binary amplitude or phase holograms for arbitrary complex amplitude modulation in the +1 order diffracted beam. We then propose another binarization scheme for complex amplitude modulation that uses a combination of fixed as well as statistically dependent threshold values for binarization. We perform a numerical investigation to compare the accuracy of the three binarization schemes to incorporate spatial intensity modulation in a laser beam and observe that the proposed scheme offers significant relative advantage in terms of aliasing. We present experimental results that supports the above observations.
查看更多>>摘要：Parameters including pump energy, beam waist radius, length of gain medium and beam divergence all affect the generation threshold and output pulse characteristics of lasers that utilize the stimulated Brillouin scattering (SBS) effect. In this paper, we investigate the effect that changes to the pump beam focusing parameters (namely beam divergence and beam waist) have on the output characteristics of the Stokes beam generated through the SBS process. This study is conducted both theoretically and experimentally using a single-cell SBS structure. The results highlight that pump beams with a small divergence angle at the focal point within the SBS cell are favorable for the generation of Stokes beams with short pulse lengths. Here, we demonstrate the generation of a Stokes beam with a pulse width of 854 ps using a pump pulse with a pulse width of 7.2 ns, which was focused to a spot with a divergence angle of 2.48 mrad.
查看更多>>摘要：In this article, a widely tunable graphene-liquid crystal photodetector is proposed and numerically investigated. The photodetector is composed of a single graphene layer on top of a silicon grating. Tunability is achieved by employing a liquid crystal layer which acts as a Fabry-Perot filter, yielding frequency selectivity. Detection mechanism is internal photoemission rising from Si/graphene Schottky junction. In the structure, Si grating determines the operation band, which can be tuned from less than 1.5 mu m to more than 1.7 mu m. For any specific Si grating, liquid crystal voltage controls the detection wavelength. It is shown that this tuning range can be as wide as 50 nm. Graphene fermi energy on the other hand, controls the absorption efficiency and detection linewidth. This independent separation of roles is a main advantage of the proposed structure, which makes the design process straightforward. Based on these functionalities, a tunable photodetector is designed at which the detection wavelength can be tuned from less than 1530 nm to more than 1570 nm covering the entire C communications band. For this tuning to take place, liquid crystal voltage is varied between 1.1 V and 4.2 V (RMS). Detection linewidth is as low as 2 nm making the photodetector ideal for optical communications, and the responsivity and quantum efficiency are 0.25 A/W and 20% respectively. Dependency of the photodetector characteristics on graphene fermi energy, liquid crystal voltage and Si grating parameters are fully discussed in the article.
查看更多>>摘要：The phenomenon of bound state in the continuum (BIC) has raised ever-increasing research interest as a new means of manipulating light-matter interactions. The ultra-high quality factors associated with BIC resonances also make them very vulnerable to any environmental turbulence. For example, very weak changes of the refractive index may lead to large spectral shift. In this work, we numerically investigate the spectral stability of the quasi-BIC resonances due to temperature changes supported by all-dielectric optical nanoantennas in the form of slotted silicon disk array. We find that due to the extremely-high quality factor of the quasi-BIC mode, the resonance is very sensitive to ambient temperatures with a wavelength shift rate around 0.077 nm/K, resulting from the thermo-optic effect of the constituent materials. This effect of thermal tunability can nevertheless be utilized to achieve an efficient thermo-optic modulator and we demonstrate that the transmittance at the original resonance frequency will change from 0 to 1 when the temperature increases by only 5 Kelvin, using an experimentally obtained thermo-optic coefficient of silicon and fused silica as 1.8 x 10(-4)/K and 8.5 x 10-(6)/K respectively.
查看更多>>摘要：As the performance of the silicon-based nanolaser is developing, further miniaturization of laser size is expected, and nanocavities will make it possible to avoid defects contained in the gain cavity. Hence, the miniaturization of the cavity is becoming necessary. In this letter, a photonic crystal cavity for the nanolaser grown on the patterned SOI substrate was proposed and analyzed in detail. The quality (Q) factor of 5 x 105 at a resonant wavelength of 1.516 mu m was demonstrated. And an insight into the variation of the resonant wavelength and the dependence of the Q-factor on the geometrical parameters of the laser cavity was obtained through simulation. For current injection, a pillar under the cavity region was introduced, the Q-factor over 104 was obtained as the length of the pillar was less than 160 nm. The effects of fabrication errors on the performance of cavities were also discussed by simulation.
查看更多>>摘要：The advantage of graphene nanomaterial to support strong plasmonic resonances in the THz frequency range makes it an ideal candidate in biosensing field where the ability of detecting molecules is becoming essential to improve the quality of human life. In this paper, a theoretical study of plasmon nanosensor based on silver metallic nanoparticles (Ag MNPs) placed near the surface of graphene nanodisk (GND) for blood components detection is analyzed and then the results are presented. The exploited nonlinear Kerr effect shows that the sensitivity (Se) is equal to 472 (nm/RIU) in THz frequency range while the selectivity (theta) is around 19.6 RIU-1. The proposed biosensor is characterized by a wide linear range sensor between 0.02mM-0.054 mM and a limit of detection (LoD) around 0.018 mM. It is mentioned that the chemical potential (mu) and the temperature (T) of graphene nanodisk essentially control the sensitivity of the proposed biosensor which represents a fundamental feature in optical sensor processing and leverages the CMOS compatibility necessary for various biological compounds detection.
NSTL
Elsevier