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Wave localization by flatband mechanisms underlies prominent moiré physics and relevant applications. While typically studied in periodic superlattices, the wave-confining capability of finite-size superlattices is important both fundamentally and practically. Here, we investigate wave localization in few-cell moiré superlattices through fine tuning of band offset, which is accomplished by jointly adjusting structural parameters of constitutive lattice. Remarkably, the quality factor Q, which reflects the capability of few-cell superlattices to localize wave, can reach quite high levels with appropriate band offset. Thus, superior wave localization is feasible in few-cell superlattices, indicated by the very high Q up to 10 4 − 10 5 for single-cell superlattices and extremely high Q up to > 10 7 for double-cell superlattices. Moreover, the Q patterns are distinct for different flatband resonances and different number of cells, while narrow high-Q (∼ 10 8 ) branches appear for the triple-cell superlattices. The narrow high-Q branches are hard to be reached in practice, since it requires stringent control on structural parameters. In this respect, the double-cell superlattices are promising for exploiting unconventional effects induced by wave localization, since it can achieve extremely high-Q (> 10 7 ) resonances within a sufficiently large tuning range. These results demonstrate the profound role of band-offset tuning in achieving strong wave localization in few-cell superlattices, which is useful for on-chip applications such as lasing, optical filters, and optical harmonic generation. [ABSTRACT FROM AUTHOR]

The control of multiply-scattered light has greatly boosted the understanding of optics in complex photonic systems, leading to many applications including imaging, information processing, random lasing, to name just a few. Here, we demonstrate a real-time feedback approach to realize multiple focusing of multiply-scattered light, which is more robust to the inherent background field compared to the time reversal approach. Our method retrieves the optimized wavefront by aligning the high-dimensional vector of the measured pattern with that of the target pattern. Our theoretical simulations and experimental results show that the feedback approach is capable of constructing homogeneous diffraction-limited spots at predefined positions. Moreover, the peak-to-background ratio exhibits a sub- 1 / m decay with m being the number of focuses, indicating the excellent capability of the proposed approach to focus scattered light at multiple positions. This efficient approach provides a promising avenue toward complex control on scattered light in complex photonic media, and therefore would be useful in relevant applications such as optical imaging and optical manipulation. • A real-time feedback approach is developed for realizing diffraction-limited spots at a few predefined positions with multiply-scattered light. • The realized multiple focuses are robust to the random perturbation caused by inherent background light. • The peak-to-background ratio exhibits ∼ 1 / m 0. 62 decay (m: the number of focuses), slower than the well-known 1/m decay. [ABSTRACT FROM AUTHOR]

We propose a two-photon imaging scheme with a thin dynamic scattering layer as the crucial imaging element. The constructive two-photon interference for direct imaging is built when the object is properly illuminated by an entangled two-photon source. We show that the proposed imaging scheme can be used for imaging an amplitude object with incoherent two-photon illumination, and the resolution reaches Heisenberg limit. Besides, the imaging for a phase object can also be achieved in the proposed imaging scheme with coherent two-photon illumination. [ABSTRACT FROM AUTHOR]

• We realize nearly perfect dual-band absorption in one dimensional Octonacci sequences containing Dirac semimetal. • Dual-band absorptions are dynamically tunable by changing the Fermi energy of DSs and the incident angle of the wave. • The absorption can be flexibly tuned from bidirectional to unidirectional by controlling the conductivity of the VO 2 layer. The dual-band absorption properties of one-dimensional ternary Octonacci sequences, comprising dielectric, Dirac semimetal (DS), and Vanadium dioxide (VO 2), are investigated theoretically and numerically using transfer matrix method, full-wave simulations, and impedance match theory. The photonic quasi-periodic multilayers exhibit bidirectional dual-band high absorption properties, attributed to strong electric field localization. Interestingly, this dual-band absorption can be spectrally tuned to the desired frequencies by adjusting the Fermi energy of the DS, changing the structure's parameters, the choice of dielectric, and the angle of incidence. Furthermore, the addition of a VO 2 layer at the bottom of the Octonacci sequence enables the realization of dynamically tunable bidirectional and unidirectional dual-band absorption by modulating the conductivity of VO 2. Remarkably, the absorption response remains insensitive to the polarization of the incident wave. These unique properties, together with the ease of manufacturing, make our proposed structures a promising candidate for wide applications in tunable optical devices. [ABSTRACT FROM AUTHOR]

The exploration of structured light created through autofocusing beams has attracted widespread attention in optical manipulation. Here, we investigate the propagation dynamics of chirped multi-Pearcey beams (CMPBs) in theory and experiment, especially exploring the impact of chirped factors on the autofocusing characteristics of CMPBs. It is found that the autofocusing characteristics of the beams can be significantly modulated by introducing first-order and second-order chirped factors. Specifically, the first-order chirped factor greatly improves the autofocusing coefficient of CMPBs, while the second-order chirped factor introduces multiple autofocusing propagations. By analyzing the transverse power flow of CMPBs both without and with chirped factors, we explain why the chirped factors can remarkably strengthen the autofocusing performance of CMPBs. Finally, our theoretical analysis on trapping force on Rayleigh particles indicates that the introduction of chirped factors optimizes the intensity gradient and trapping capability of CMPBs, potentially enabling multiple longitudinal trapping positions. These findings offer a comprehensive insight into the propagation dynamics of CMPBs, opening avenues for flexible optical manipulation of multiple particles. • The autofocusing characteristics of the CMPBs can be significantly modulated by introducing chirped factors. • The theoretical analysis on trapping force on Rayleigh particles indicates that chirped factors optimize the intensity gradient and trapping capability of CMPBs, potentially enabling multiple longitudinal trapping positions. [ABSTRACT FROM AUTHOR]

The self-focusing transmissions of light beams in five food dye suspensions including Red 40, Red 2, Red 4, Yellow 6, Blue 1 are studied. We qualitatively analyze the key influencing factors of the self-focusing phenomenon with five widely-used food dyes, including the concentration of suspensions, the input-beam power and the kinds of the food dyes. It is found that, the self-focusing phenomenon is mainly attributed to the shift of focus caused by thermal effects. Particularly, Red 40 presents a best nonlinear performance with a 5 cm self-focusing propagation at the wavelength of 532 nm. The significant difference of the self-focusing effects of the five food dyes are further explained by investigating their optical absorption and optical nonlinearity including nonlinear refractive index and absorption coefficient. It is found that a stronger absorption and nonlinearity, originated from the kinds of the dyes or the concentration of the dyes, leads to a stronger nonlinear self-focusing effect. Our work provides a systematic study on the quantitative analysis of the synthetic food colorants with optical nonlinearity, demonstrating a strong nonlinear self-focusing propagation and high nonlinear refractive index in red 40, red 2, red 4. This may have potential applications in nonlinear optics with soft matters. [ABSTRACT FROM AUTHOR]

Low scattering and deep penetration of infrared light in colloidal materials are critical in many biomedical applications. Cu x S nanoparticles (NPs) play an important role on this due to their localized surface plasmonic resonant (LSPR) wavelength located at near infrared (NIR) range. In this work, tunable nonlinear responses of Cu x S NP suspensions are investigated by analyzing self-focusing propagation of infrared light. Cu x S NPs are firstly synthesized by hot-injection method with stoichiometric ratio controlled in range of 1.01 ≤ x ≤ 1.91, realizing an appropriate free hole densities for tuning their LSPR absorption wavelengths from 1170 nm to 1640 nm. Then, by changing concentration and stoichiometric ratio to adjust the polarizability, tunable nonlinear self-focusing effects of NIR light in various Cu x S NP/chloroform suspensions are observed, which are induced by optical nonlinearity of these Cu x S NPs. Particularly, a larger concentration and a lower stoichiometric ratio lead to a stronger nonlinearity, which results from the optical force-mediated dynamics and the LSPR absorption interactions. Our results not only provide new candidates for realizing LSPR nonlinearities and curious nonlinear optical phenomena, but also imply new possible tantalizing biomedical applications of Cu x S NPs such as biomedical imaging and medical diagnosis or therapy. • This study presents that near-infrared (NIR) light within the optical windows of biological tissue can be self-focused in suspensions containing self-doped Cu x S nanoparticles (NPs). • It relies on the optical nonlinearities of Cu x S NPs induced by localized surface plasmonic resonant (LSPR), and a smaller free carrier density to their metallic counterparts such as gold NPs. • Thus, we believe that our study makes a significant contribution to the literature because it provides a new strategy to realize deep penetration of light in biological tissue, which also take the advantage of NIR LSPR absorption of Cu x S NPs in applications such as photoacoustic imaging and photothermal therapy. [ABSTRACT FROM AUTHOR]