Advanced Photonics Research最新文献

Diffractive neural networks (DNNs) are emerging as a new machine learning hardware based on optical diffraction with parallel and high-throughput information processing. The optical inputs to DNNs are spatially modulated by propagating through passive diffractive layers that work in succession to achieve an inference. Herein, visible wavelength classification using single- and two-layer DNNs fabricated using direct laser writing is demonstrated. The proposed DNN approach accepts the point spread function of two different wavelengths modeled after a microscope objective as the input and modulates the input field toward the target detector for classification. Of the three models trained to classify different wavelength pairs, the highest performance observed is for the classification of 561 and 785 nm, achieving over 90% accuracy. This work demonstrates the potential of all-optical artificial neural networks for applications requiring visible wavelengths, from visible light beam shaping to spectral analysis and optical imaging.

The impact of three different pulse durations (100 fs, 1, and 10 ps) on the formation of laser hyperdoped black silicon with respect to surface morphology, sub-bandgap absorptance, the sulfur concentration profile, and the effective minority carrier lifetime after Al₂O₃ surface passivation is investigated. The current flow behavior is compared through the hyperdoped layer by I–V measurements after hyperdoping with different pulse durations. For conditions that give the same absolute sub-bandgap absorptance, an increase in pulse duration from 100 fs to 10 ps results in a shallower sulfur concentration profile. Findings are explained by an increasing ablation threshold from 0.19 J cm⁻² for a pulse duration of 100 fs to 0.21 J cm⁻² for 1 ps and 0.34 J cm⁻² for 10 ps. The formation of an equally absorbing layer with a shallower doping profile results in a reduction in contact and/or sheet resistance. Despite the higher local sulfur concentration, the samples show no decrease in carrier lifetime measured by quasi-steady-state photoconductance decay on Al₂O₃ surface-passivated samples. The investigation shows that longer pulses of up to 10 ps during laser hyperdoping of silicon result in advanced layer properties that promise to be beneficial in a potential device application.

Super-resolution chip (SRC) made of fluorescent polymer film and polygon film waveguide can realize subdiffraction imaging. However, the propagation losses of evanescent waves impose a serious restriction on imaging performance. Meanwhile, the required redundant raw images hinder the imaging speed. Multiple-azimuths evanescent illumination at the same time can efficiently increase the illumination intensity and uniformity, and reduce the number of required raw images. But, the experimental realization is impeded by the complex spatial frequency mixing problem. Herein, an SRC microscopy method with counter-propagating evanescent illumination is demonstrated, which circumvents the influence of complex spatial frequency mixing, and efficiently enhances the reconstructed results. Meanwhile, the proposed method reduces the number of required raw images by half and saves the image acquisition time, which benefits the imaging speed enhancement of the SRC microscopy system and promotes its future practical application.

As numerous studies on highly efficient perovskite solar cells have been conducted on lead-based light absorbers, such as MAPbI₃ and FAPbI₃, increasing concerns are rising regarding toxicity and stability issues. One of the most prominent and promising lead-free alternatives is the double-perovskite Cs₂AgBiBr₆, which is well-suited for multi-junction solar cells considering its relatively large indirect bandgap of around 1.95–2.05 eV. Despite distinctive reports on its performance under ambient conditions, the demonstrated stability has not yet been conclusively clarified. Within this study, the degradation behavior of Cs₂AgBiBr₆ single crystals is investigated under different ambient environments, such as AM1.5g solar irradiation, aquatic conditions, and humidity. The corresponding samples are analyzed by using Raman, UV–vis, energy-dispersive X-Ray, and micro-photoluminescence spectroscopies together with X-Ray diffraction. High intrinsic stability of Cs₂AgBiBr₆ in ambient conditions and severe degradation in aquatic conditions are observed. Furthermore, surface morphology alterations are found during the simulated solar irradiation indicating photo-accelerated degradation behavior. In the results of this study, it is clearly implied that intense research efforts need to be put into sealing the Cs₂AgBiBr₆ layer in solar cells with the goal of protecting it from humidity and water intrusion simultaneously, therefore avoiding photo-accelerated degradation.

Printable colloidal photonic crystals (CPCs) with unique photonic bandgaps and elaborate shapes have attracted significant interest due to their characteristics, such as simplicity of fabrication, adjustable structural colors, photobleaching resistance, and stimulus-responsiveness. In this review, strategies for printing CPC patterns, including direct use of CPCs as inks, region-selective modification on responsive (solvent, force, and temperature) CPC papers, and printing combined with lithography, are first summarized. Second, based on the advantages of CPC printing technology, their applications in color displays, coatings, sensors, anticounterfeiting labels, and information storage, are discussed in detail. Finally, the current challenges and outlook regarding CPC printing technology are proposed.

Janus metasurfaces emerge as a promising platform for implementing multiple wave functionalities by fully exploiting the inherent propagation direction of electromagnetic waves. Their out-of-plane asymmetric structures enable different wave functions depending on the propagation direction. Herein, a multiplexed Janus metasurface is proposed, which operates in the microwave region to flexibly manipulate the transmission and reflection wavefronts for same linearly polarized (LP) incidence propagating along the two opposite directions. A meta-lens is constructed to validate the concept of full-space shared-aperture transmission-reflection-independent focusing of electromagnetic (EM) waves, exhibiting four distinct focusing performances. Experiments are conducted in the microwave region that agree well with the simulation results. The proposed full-space Janus metasurface may provide a platform for asymmetric imaging, multichannel information processing, and encrypted communication.

Herein, it is demonstrated that ultrashort spatially structured beams can sculpt a sample of gas-phase molecules like a 4D material to produce a spatial pattern of aligned molecules whose shape and temporal evolution allow to restore the spatial light information on a time-delayed reading pulse. To do so, the spatial phase and amplitude information of ultrashort light beams are encoded into rotational coherences of molecules by exploiting the interplay between spin angular momentum and orbital angular momentum. The field-free molecular alignment resulting from the interaction leads to an inhomogeneous spatial structuring of the sample allowing to transfer the encoded information into a time-delayed probe beam. The demonstration is conducted in $��{�\text{CO}�}_2�$ molecules. Besides applications in terms of THz bandwidth buffer memory, the strategy features interesting prospects for establishing versatile optical processing of orbital angular momentum (OAM) fields, for studying various molecular processes, or for designing new photonic devices enabling to impart superpositions of OAM modes to light beams.

Ascertainment of photonic stopband absolute topological character requires information regarding the Bloch eigenfunction spatial distribution. Consequently, the experimental investigations predominantly restrict themselves to the bulk-boundary correspondence principle and the ensuing emergence of topological surface state. Although capable of establishing the equivalence/inequivalence of bandgaps, the determination of their absolute topological identity remains out of its purview. The alternate method of reflection phase-based identification also provides only contentious improvements owing to the measurement complexities pertaining to the interferometric setups. To circumvent these limitations, the Kramers–Kronig amplitude-phase causality considerations are resorted to and an experimentally conducive method is proposed for bandgap topological character determination directly from the parametric reflectance measurements. Particularly, it is demonstrated that in case of 1D photonic crystals, polarization-resolved dispersion measurements suffice in qualitatively determining bandgaps’ absolute topological identities. By invoking the translational invariance of the investigated samples, a parameter “differential effective mass” is also defined, that encapsulates bandgaps’ topological identities and engenders an experimentally discernible bandgap classifier.