Photonics and Nanostructures-Fundamentals and Applications最新文献

In this study, a grating with a Gaussian distribution was used to increase the absorption of light by amorphous silicon thin film solar cells. A grating is an effective structure for trapping light inside the active layer of a cell, so a two-dimensional Gaussian grating with a rectangular structure was placed on the front surface of the cell. The results obtained by using the finite element method showed that the Gaussian grating significantly enhanced the absorption of light in the visible and near-infrared ranges by a cell with a thickness of 0.5 μm compared with a cell without gratings and a cell with normal gratings. The maximum average light absorption by the cell with a Gaussian grating was 84.8%, which was 90% higher compared with the reference cell. In addition, the short-circuit current density and efficiency were determined as 34.2 and 17.6 mA/cm², respectively, which were 72% and 72.5% higher, respectively, compared with the reference cell. The proposed structure could be used in a cell to convert more light into electricity.

Optical excited photoconductive antennas are a central technology for the Terahertz (THz) domain, crucial for both emitting and detecting THz radiation. This work proposes and experimentally realises a new approach in digitated photoconductive antennas (d-PCAs) based on a single digitated high resistivity metal contact with integrated resistances as voltage dividers. This permits a uniform applied electric field over a large surface area and a single step device processing procedure, simplifying the device realisation. This concept is further combined with digitated plasmonic nano-antennas that permits to enhance the light-matter interaction. Through femtosecond optical excitation of such structures, THz pulses can be generated efficiently through this device. Further, for the plasmonic d-PCA, the detected THz electric field of the device shows the effect of polarisation of the incident IR beam, highlighting the role of the nanostructured digitated contacts. This work is supported by electromagnetic simulations showing the optical and THz response of this new type of photoconductive antenna with integrated resistances.

Thermoelectrically-coupled nanoantennas (TECNAs)—nanoantennas that use the Seebeck effect to detect radiation—are a promising modality for spectrally resolved detection in the infrared. By tailoring the geometry of a nanoantenna coupled to a micro-cavity, their responsivity and spectral selectivity can be carefully designed. However, to date no measurements have directly established the spectral response of these detectors over a large frequency span in the infrared regime, particularly from 2 μm to 20 μm. In this work, we provide a comprehensive analysis of the spectral selectivity of TECNAs operating within the mid- and long-wave infrared (MWIR and LWIR) regions. We engineer arrays of detectors at 5.5 μm, 10.6 μm, and 14 μm, and we verify their selectivity using polarization-dependent Fourier-transform infrared spectroscopy (FTIR). We also show that the response can be tailored using a combination of antenna and cavity design. Our results not only underscore the potential of TECNAs in advancing sensing applications within the MWIR and LWIR domains, but also offer a promising direction for enhancing other detector modalities.

This study investigates the enhancement and nanofocusing of a radially polarized electric field by a conical plasmonic structure (CPS). The CPS is a dielectric cone with nanometer metal cladding on a dielectric substrate. Concentric circular slanted grooves are etched on the surface of the dielectric substrate. These grooves converge the incident field on the structure. Angled periodic gratings are engraved on the CPS metal surface near the tip, creating a plasmonic momentum and contributing to the field enhancement above the apex. The symmetry of the incident radially polarized light and the structure significantly boosts nanofocusing and field enhancement. The optimal width of the nanofocusing and the electric field enhancement factor obtained are approximately 9 nm and 30000, respectively. Because of its impressive effects, this scheme is a valuable tool for plasmonic, optics, and laser applications.

Miniaturized spectrometers are attracting widespread interest due to the rising demand for portable spectroscopic applications. While the chip-scale spectrometers are widely investigated using silicon photonics technology, few research have addressed the need for a mid-infrared (MIR) integrated chip-scale spectrometer due to the lack of an effective reconfigurable photonics approach. In this paper, we present a novel solution using silicon photonics MEMS technology in the MIR region (3.6–5 µm wavelength range). We adopt a computational spectrometry scheme using the digitalized control of cascaded MEMS-tunable waveguide couplers. The MEMS waveguide couplers are operated in digital on/off mode, thus making the device immune to driving voltage fluctuations and robust for on-chip field sensing applications. Moreover, a comprehensive numerical analysis method is discussed to systematically evaluate the performance of the computational spectrometer, including its resolution and operational bandwidth. As a proof-of-concept, a chip-scale spectrometer realized by seven cascaded MEMS-actuated waveguide coupler is demonstrated. The sparse spectral reconstruction is demonstrated in the wavelength range from 3.65 to 4.1 µm and the dual-peaks reconstruction results indicate a resolution of 8 nm. Besides, response time and power consumption of the proposed device are experimentally characterized. Benefitting from good scalability, the spectral resolution can be further improved by increasing the number of waveguide coupler stages. The proposed work has the potential to realize lab-on-a-chip applications with advances in MIR silicon photonics. © 2001 Elsevier Science. All rights reserved.

Integrated sensors based on guided optical devices can efficiently and selectively detect molecules in the mid-infrared (mid-IR) spectral range, exploiting the vibrational and rotational modes of these molecules at these wavelengths. In this work, a ridge waveguide based on porous silicon (PSi) layers was developed by electrochemical etching followed by a photolithographic process. The ridge waveguide is capable of propagating light in the mid-IR range (3.90–4.35 µm) with optical losses of approximately 10 dB/cm. An oxidation study was performed to stabilize the porous structure and identify the optimal oxidation degree, that allow mid-IR light to propagate in a ridge waveguide based on PSi material for sensing application. The results showed that the ridge waveguide remains capable of propagating light after undergoing partial oxidation at 300 °C and 600 °C (15% and 36% of the oxidation degree respectively) with optical losses of around 30 dB/cm and 60 dB/cm at the wavelength of 4.1 µm, respectively.

A novel direct binary search algorithm based on rotation (RDBS) is proposed in this paper. A 1*2 ultra-compact 2.4*3.6µm² multimode wavelength demultiplexer (DEMUX) is designed in reverse, which is roughly two orders of magnitude smaller than the size of a conventional waveguide device. It can simultaneously perform wavelength demultiplexing and mode conversion. This DEMUX separates the 1310 and 1550 nm wavelengths while converting the input light from the fundamental transverse electric mode (TE0) to the first-order transverse electric mode (TE1). The simulation results using RDBS show that the insertion loss($IL$) of the upper channel (wavelength 1310 nm) is −0.9644 dB, the $IL$ of the lower channel (wavelength 1550 nm) is −0.9752 dB, and the crosstalk values(CT) are −10.079 dB and −9.261 dB, respectively.

The present study employs a cost-effective laser ablation technique in combination with the RF sputtering method to successfully synthesize silver nanoparticles encapsulated by zinc oxide on a silicon (Si) substrate. This synthesis approach aims to enhance the efficiency of photodetector devices while concurrently reducing material expenses, thereby promoting advancements in photodetector applications. The incorporation of various plasmonic nanoparticles (NPs) into the photodetector's architecture is demonstrated as a means to substantially improve the photoresponse of UV photodetectors. Three distinct samples, denoted as AgNPs/Si, AgNPs/ZnO/Si, and ZnO/AgNPs/Si, underwent comprehensive analysis and characterization of their morphological attributes, crystal structures, elemental composition, and optical properties. The UV photodetection efficacy of these samples was evaluated by subjecting them to 385 nm UV light at different bias voltages. The current-voltage (I-V) characteristics of the ZnO/AgNPs/Si photodetector revealed significantly enhanced conductivity in comparison to the AgNPs/Si and AgNPs/ZnO/Si counterparts. Remarkably, the ZnO/AgNPs/Si photodetector exhibited the highest responsivity value of 132 A/W, accompanied by quantum efficiency of 429.88, sensitivity of 31,400%, gain of 315, detectivity of 18 × 10¹⁰ Jones, and a noise equivalent power (NEP) of 0.556 × 10^–13 W. These findings underscore the efficacy of our innovative broadband photodetector, highlighting its potential for practical implementation. This research offers valuable insights into the enhancement of photodetector performance and its applicability in real-world scenarios.

In this work, a novel solar absorber with wide angle tolerance and insensitivity to polarization is proposed. The upper layer of the absorber comprises two polygonal structures, which can achieve an absorption rate of 94.2% across a broad wavelength range of 2218 nm (584 nm - 2802 nm). The performance of the absorber is simulated and verified using the finite difference time domain (FDTD) method combined with impedance matching theory. Through examining the electromagnetic field distribution at absorption peaks, the physical mechanism is elucidated. Moreover, incorporating refractory metals and nonmetallic materials in its design enhances the stability of the absorber, making it suitable for various extreme environments. This indicates its potential applications in solar energy storage and solar thermal photovoltaic systems.

We report mid-infrared photoconductive atomic-force microscopy (AFM) of a graphene sheet with doped-diamond AFM probes illuminated with a quantum cascade laser. The diamond probe ensures high mechanical and electrical stability. We observe a prominent photoconduction at finite biases that we interpret as the overcoming of a potential barrier formed at the graphene-diamond junction by free carriers excited by mid-infrared photons (220 meV photon energy). Moreover, we observe a small photo-thermoelectric effect of graphene under zero applied bias. We demonstrate that the use of diamond AFM probes for mid-infrared photoconductive AFM has great potential to investigate the nanometric inhomogeneities of the Fermi level and of the work function across integrated semiconductor devices.