Advanced Photonics Research最新文献

It is shown here how encapsulated graphene devices can be laterally coupled to plasmonic metasurfaces via 1D edge contacts, preserving the high mobility of encapsulated graphene while enhancing optical coupling. The device is used for photodetection applications where high responsivities in the range of 100 A W⁻¹ for most of the visible spectrum are reported. The device exhibits a photogating effect which is attributed to defect states in the encapsulating hBN layers. The results highlight a new configuration to couple graphene with plasmonic structures and points to a new type of device based on defect states and graphene's excellent transport properties to achieve photodetectors with ultrahigh responsivities.

The photonic neural network is emerging as a promising technology for fast and power-efficient computing. So far, optics mainly perform linear transformations, and it remains challenging to integrate nonlinear activation function. The cover image shows an optical neural chip with only one multimode waveguide and a few electrodes. Though extremely simple, this chip constructs a modular network with both linear and nonlinear transformations. This work (see article number 2300253 by Ziyang Zhang and co-workers) offers an alternative route to exploiting the modulated multimode interference for photonic computing applications.

Zhiwei Fang, Min Wang, Ya Cheng and co-workers have fabricated an on-chip 8-channel thin-film lithium-niobate arrayed waveguide grating (AWG) by using photolithography-assisted chemo-mechanical etching technique (see article number 2300228). On-chip loss as low as 3.32 dB, a single-channel bandwidth of 1.6 nm, and a total-channel bandwidth of 12.8 nm are obtained. The cross talk between adjacent channels is measured to be below –3.83 dB and the cross talk between nonadjacent channels is below –15 dB.

Nanoparticles (NPs) generated by pulsed-laser ablation in liquids (PLAL) have benefited many key applications due to their versatility, enlarged surface area, and high purity. However, scaling up NPs production represents one of the main requisites to commercialize this technology. The established upscaling strategy demands high power and repetition rate laser source with fast scanning systems, which are not widely available and costly. Herein, a cost-effective alternative is proposed, the addition of static diffractive optical elements to achieve parallel processing through the multi-beam PLAL (MB-PLAL). In MB-PLAL, the optimum repetition rate is reduced to compensate laser energy splitting, hence achieving a higher interpulse distance, reducing pulse shielding, and increasing NPs productivity. MB-PLAL with 11 beams reached a factor 4 productivity increase for iron–nickel alloy (Fe₅₀Ni₅₀) NPs compared to the single-beam setup (0.4–1.6 g h⁻¹), and a factor 3 increase for gold (Au) NPs (0.32–0.94 g h⁻¹). The scalability of the proposed MB-PLAL technique setup is confirmed by Au and Fe₅₀Ni₅₀ NPs productivity experiments using 1, 6, and 11 beams, showing a linear increase in productivity.

Helical microstructures exhibit unprecedented chiroptical responses particularly interesting for emerging applications such as broadband photonic components. To explore their chiral behaviors, the micro-helixes composed of polymer cores and platinum shells are proposed and realized via a two-step process combining two-photon polymerizations and sputter coating. Thanks to the core–shell multi-material configurations, the micro-helixes packed in a dense array generate an ideal chiral lineshape. Overspanning a wide range from 3 to 7 μm, the reflection-based g factors approach the upper amplitude limits. Numerical modeling reveals that polarization-induced spectra result from overlapping modes similar to the previously reported solid metal helixes. The further chiral spectrum comparisons confirm that the core–shell spirals exhibit a 25% bandwidth increase compared to solid platinum helixes of same sizes. Interestingly, the asymmetrically distributed platinum shell may further expand the operational band. Overall, comprehensive studies are performed on multi-material micro-helixes, which could provide additional flexibility to tailor their chiroptical properties, enabling the production of high-performance chiral microstructures for diverse applications.

A novel approach for image formation in optical coherence tomography (OCT) and microscopy is presented. The depth resolution of OCT, including recently developed nanosensitive OCT (nsOCT), is limited by the spectral bandwidth of the light source used for illumination. The proposed approach, synthetic OCT (synOCT), permits label-free, depth-resolved quantitative visualization of the subwavelength-sized structures with nanosensitivity. Using synOCT it is possible to estimate the contribution of axial Fourier components of an object's structure in image formation at each small volume within the image. The size of such areas can be smaller than the resolution limit of the imaging system that provides potential for super-resolution imaging. Visualization of the subwavelength periodic structures and quantitative visualization of the subwavelength internal structures of highly scattering biological samples, within voxels smaller than resolution limit of the imaging system, are demonstrated. In contrast to nsOCT, the trade-off between spectral and spatial resolution is removed which results in dramatic improvement of both spectral and spatial resolution in synOCT relative to nsOCT.

Amorphous tin oxide (a-SnO_x) is a potential transparent oxide semiconductor candidate for future large-area electronic applications. The thin-film transistor (TFT) mobilities reach ≈100 cm² Vs⁻¹, a mobility higher than other multiple cation-based oxide semiconductor TFTs. Few optical properties have been reported so far and therefore both the effect of visible light and negative bias illumination stress (NBIS) on a-SnO_x TFT performances, known to dramatically impact oxide semiconductor-based TFTs, have been investigated. The variation of density of states (DOS) due to NBIS by device simulation is analyzed, and a fourfold increase of the donor-like states and a decrease in the band edge DOS from 2.3 to 2.0 × 10¹⁹ cm⁻³ eV⁻¹ are showed. The evaluation of the effect of neutral, singly, and doubly ionized oxygen vacancies by density functional theory using 95 atoms reveals not only states in the gap of SnO₂, but also variations in the electron density, and modifications in the crystal parameters compared to a structure without an oxygen vacancy. Material and device simulation analysis reveal that the oxygen vacancies have a dramatical impact on the DOS in the gap of SnO₂ and can explain the NBIS phenomenon observed in a-SnO_x TFT.

With strong electron–phonon coupling, self-trapped excitons (STEs) are typically formed in perovskite materials, and radiative recombination of STEs can produce broadband emission with large Stokes shifts. STEs are essential to further improve the optoelectronic properties of materials. Surprisingly, 2D system is the edge case, with low even no self-trapping barriers, leading to effortless formation of STEs. In this work, 2D strontium titanate (SrTiO₃) with defects is prepared using supercritical carbon dioxide (SC CO₂) and its carrier transport and transition are studied. The appearance of wide photoinduced positive absorption signals in the femtosecond transient absorption spectra is direct evidence for the formation of STEs. The presence of STEs is further supported by the increased Stokes shift and full width at half maximum in the steady-state photoluminescence spectra.