Optical Applications Research Articles

Novel polymorph of 2-amino-6-methyl pyridinium-4-methyl benzoate (2A6MP4MB) single crystals: Synthesis, crystal structure, optical, spectroscopic and self-defocusing capabilities for nonlinear optical applications

By using the slow evaporation solution growth technique, the 2-amino 6-methyl pyridinium 4-methyl benzoate (2A6MP4MB) is crystallized in a single, high-quality crystal. Single crystal X-ray diffraction (SXRD) was used to determine the crystal structure. The different functional groups of the substances were identified using Fourier Transform Infrared Spectroscopy (FTIR) analysis. The 2A6MP4MB crystal exhibits a significant optical transmittance throughout the complete visible spectrum and a lowered UV cutoff wavelength, according to studies conducted using UV-Vis spectrometers. The optical band gap energy (Eg) of a single crystal of 2A6MP4MB is 4.768[Formula: see text]eV. The compound’s photoluminescence (PL) spectrum in the title illustrates the green emission technique. We analyze the produced single crystal’s dielectric tensorial behavior at various frequencies. The produced 2A6MP4MB crystal’s third-order susceptibility, nonlinear refraction, and nonlinear absorption coefficient were evaluated using the [Formula: see text]-scan technique. A Vickers hardness tester was used to assess the created crystal’s mechanical stability.

Correlation between structural – Optical – Magnetic properties of cobalt based double perovskite, Sr2TiCo1-yO6-δ

The influence of charge disorders, non-stoichiometry and oxygen vacancy on the physical properties such as optical properties and magnetic properties of Sr2TiCo1-yO6-δ exhibiting simple cubic (space group Pm-3m) structure has been investigated in the article. An analysis of energy dispersive X-ray spectrum reveals a deficiency of cobalt ions. Variable range hopping conduction mechanism is observed below 100 K. X-ray photoelectron spectroscopy results indicated the presence of oxygen deficiency accompanied by multiple valent cobalt ions (Co4+ and Co3+) in the material. The optical features of the material are noteworthy, with a wide range of significant optical absorption occurring in the UV range, characterized by a band gap of ∼3.03 eV. In addition, huge photoluminescence emission in the visible range and at room temperature was observed. In this context, Sr2TiCo1-yO6-δ is a potential material for optical applications due to its high thermal stability with respect to temperature in air environment. Magnetic studies indicate the presence of mixed exchange magnetic interactions among the cobalt ions with different valence states generated during the synthesis. The weak ferromagnetic exchange interactions involved Co3+-O-Co4+ ions.

Enhanced imaging with binary circular Dammann Fresnel zone plate

We introduce a novel approach in optical engineering by combining Dammann gratings with binary Fresnel zone plates to create a unique hybrid optical element with enhanced energetic efficiency of its focal spots. Traditionally, binary Fresnel zone plates focus light at multiple points with varying intensities, while Dammann gratings are renowned for their efficient and uniform light splitting capabilities. Our innovation lies in merging these two elements and generating a binary circular Dammann (varying along the radial direction) Fresnel zone plate that concentrates most of the incident light into a small and desired number of focused points with equal intensities, rather than distributing light’s energy non-equally across multiple points. This novel design significantly enhances the efficiency and precision of light manipulation. It opens new possibilities in applications requiring high-intensity focal points, such as in advanced medical imaging and in accurate scientific measurements. By redefining the conventional roles of these optical elements, our research contributes an advancement to the field, paving the way for innovative solutions in various optical applications.

Novel third order nonlinear optical stilbazolium crystal replaced with 3-methoxy benzaldehyde as donor for optical device applications

A novel organic nonlinear optical stilbazolium group single crystal of 1-methyl-2-[2-(3-methoxystyryl)]-pyridinium iodide (subsequently referred to as MSMI) was grown by the solution growth technique using the method of slow evaporation at ambient temperature. The Single-crystal XRD investigation indicates that the MSMI crystal belongs to a monoclinic crystal system with a centrosymmetric space group. CHN elemental analyser confirms the weight percentage of carbon (C = 51.00 %) hydrogen (H = 4.55 %) and nitrogen (N = 3.94 %) in the MSMI crystal structure. The presence of 16 hydrogen atoms and 15 carbon atoms in the MSMI was affirmed by the Nuclear Magnetic Resonance (NMR) spectroscopic analysis. Fourier Transform Infrared (FTIR) studies confirmed the fundamental vibrations for different functional groups found in the MSMI crystal. The Hirsfeld surface analysis figured out the hydrogen bond interaction and π…π interaction which supports the stability of the crystal structure. The crystal is found to exhibit transmittance of wavelength above 400 nm and has a band gap of 3.05 eV ascertained from UV–Vis-NIR spectroscopic analysis. Photoluminescence (PL) studies reveal that the title crystal has an emission wavelength of 572 nm. The surface characteristics of the title crystal were examined by Atomic Force Microscopy (AFM), and etching studies. The value of Meyer's number is n = 1.8 which is determined by the Vickers microhardness studies. The value of the third-order nonlinear refractive index (n2) is 4.662×10−8 cm2/W, the nonlinear absorption coefficient (β) is 1.305×10−3 cm/W, nonlinear susceptibility (χ(3)) is 9.297×10−5 esu and the optical limiting threshold is 11.43 J/cm2 was ascertained form the Z-scan technique. The results indicate that the MSMI crystal is a potential optical limiter and has promising applications in nonlinear optical devices.

Simulated Channel Length Variation Effects on Regulated Cascode Input Stage-Based Transimpedance Amplifier for Fiber Optics Applications

A proposed transimpedance amplifier with channel length variation is simulated. The amplifier consists of a regulated cascode input stage followed by a common gate-common source configuration. A channel length series (45 nm, 90 nm and 130 nm) in CMOS technology was introduced within the proposed amplifier in order to achieve comparative performance analysis. There are two key findings from this study. On one hand, it was found that the trade off in gain versus bandwidth and input referred noise current still applies when channel length is moved upward from 45 nm up to 130 nm. A series of transimpedance amplifier gains (42.16 dBΩ, 44.34 dBΩ and 46.25 dBΩ) that correspond to (1.80 GHz, 1.33 GHz and 1.06 GHz) of bandwidths is reported corresponding to the above channel length series respectively with an input referred noise current spectral density series (16.35 pA/sqrt(Hz), 12.17 pA/sqrt(Hz) and 10.60 pA/sqrt(Hz)) of reduction. On the other hand, a reduction in power consumption occurred as channel length is moved upward for the same proposed topology. A total power consumption series (0.611 mW, 0.287 mW and 0.173 mW) was reported that corresponds to the above channel length series.

Crystal structure, optical properties, Hirshfeld surface analysis and antibacterial activity of a new organic-inorganic metal halide: 4-nitrobenzyl-4-methylpyridinium tetrachlorocobaltate(II)

This paper presented the synthesis, composition analysis, and structural characterization of a new organo-inorganic metal halide, 4-nitrobenzyl-4-methylpyridinium tetrachlorocobaltate(II) [4NO2Bz-4-MePy]2[CoCl4](1). The single-crystal X-ray diffraction analysis displayed that the compound crystallized in the monoclinic space group P21/c, consisting of two [4NO2Bz-4-MePy]+ cations and a [CoCl4]2− anion. The energy gap between the HOMO and LUMO orbitals, the polarizability, and the first hyperpolarizability were carried out based on the DFT calculation. The HOMO-LUMO energy gap and UV-visible diffuse reflectance spectrum illustrated the charge transfer interactions between the [CoCl4]2− anions and the [4NO2Bz-4-MePy]+ cations. In addition, the low band gap values (1.64 eV for the Tauc formula, 1.62 eV for the truncated line method, and 2.73 eV for the calculated value) indicated that the crystal was appropriate for optical applications. The first hyperpolarizability (βtot) was 342 times higher than that of standard KDP crystal (βKDP = 6.85 × 10−31 esu), suggesting that crystal 1 was a premium material for NLO applications. The scanning electron microscopy and energy dispersive spectrometer determined the morphology and elemental distribution of the crystal. Hirshfeld surface analysis was performed to quantify the contributions of the different intermolecular interactions. The result of antimicrobial experiments displayed that the compound had excellent antimicrobial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli).

Improving photon number resolvability of a superconducting nanowire single-photon detector array using a level comparator circuit

Photon number resolving (PNR) capability is very important in many optical applications, including quantum information processing, fluorescence detection, and few-photon-level ranging and imaging. Superconducting nanowire single-photon detectors (SNSPDs) with a multipixel interleaved architecture give the array an excellent spatial PNR capability. However, the signal-to-noise ratio (SNR) of the PNR (SNRPNR) of the array will be degraded with increasing the element number due to the electronic noise in the readout circuit, which limits the PNR resolution as well as the maximum PNR number. In this study, a 16-element interleaved SNSPD array was fabricated, and the PNR capability of the array was investigated and analyzed. By introducing a level comparator circuit (LCC), the SNRPNR of the detector array was improved over a factor of four. In addition, we performed a statistical analysis of the photon number on this SNSPD array with LCC, showing that the LCC method effectively enhances the PNR resolution. Besides, the system timing jitter of the detector was reduced from 90 ps to 72 ps due to the improved electrical SNR.

Polymer-based three-waveguide polarization beam splitter with reduced crosstalk for optical circuitry

Polarization beam splitters are pivotal in manipulating polarized light within photonic integrated circuits for various optical applications. This study introduces a single-mode polarization beam splitter comprising three waveguides realized with polymer materials. The device optimization process employed the beam propagation method, explicitly using the RSoft CAD BeamProp solver. Our proposed beam splitter performs exceptionally well with 99% complete and null light transmission efficiency. In particular, it demonstrates minimal insertion loss (0.04 dB for complete transmission and 0.07 dB for null transmission) and low coupling loss (0.03 dB and 0.04 dB for complete transmission, 21.9 dB and 36.3 dB for null transmission from input to bridge and bridge to output waveguides, respectively). Additionally, the beam splitter showcases significantly reduced crosstalk: −27dB and −26.98dB for TE modes during complete light transfer, and −36.28dB and −33.61dB for TM modes during null light transfer. These results underscore its potential for advancing integrated optical systems.

First-principles quantum computational study to investigate radiation energy-dependent effect on optoelectronic properties of bismuth oxyhalides BiOX (X= I, Br)

Metal oxyhalides are potential candidates for fundamental and technological interest in pharmaceutical, biological, optical, photoluminance, sensing, energy, and photocatalyst applications. In this study, using first-principles density functional quantum computational approach, we investigate the electronic and optical properties of two members of bismuth oxyhalides, BiOX (X = I, Br). The study is mainly aimed to characterize and examine the light radiation energy-dependent optical properties of the compounds by using mBJ desnty functional with the full potential linearized augmented plane wave method. The oxyhalides show indirect bandgap semiconductor nature having bandgaps of 2.2 eV for BiOI and 3.5 eV for BiOBr. Besides, these are p-type materials owing to a large hole-like carrier density of states in the valence bands close to the Fermi level. The energy bands show considerable dispersion of particles. The increasing reflectivity at high light energy shows the potential of the materials as good reflectors in shielding screens or glasses to avoid damage from the ultraviolet radiation.

Gate-Tunable Multiband van der Waals Photodetector and Polarization Sensor.

A single photodetector with tunable detection wavelengths and polarization sensitivity can potentially be harnessed for diverse optical applications ranging from imaging and sensing to telecommunications. Such a device will require the combination of multiple material systems with different structures, band gaps, and photoelectrical responses, which is extremely difficult to engineer using traditional epitaxial films. Here, we develop a multifunctional and high-performance photosensor using all van der Waals materials. The device features a gate-tunable spectral response that is switchable between near-infrared/visible and short-/midwave infrared, as well as broad-band operation, at room temperature. The linear polarization sensitivity in the telecommunication O-band can also be directly modulated between horizontal, vertical, and nonpolarizing modes. These effects originate from the balance of photocurrent generation in two of the active layers that can be manipulated by an electric field. The photodetector features high detectivity (>109 cmHz1/2W-1) together with fast operation speed (∼1 MHz) and can be further exploited for dual visible and infrared imaging.

Barium chalcogenides for nonlinear optics in the mid-IR: Properties and applications

The essential properties of BaGa4S7 (BGS), BaGa4Se7 (BGSe), BaGa2GeS6 (BGGS), BaGa2GeSе6 (BGGSe), and Ba2Ga8GeS16 (B2GGS) are reviewed, together with all nonlinear optical applications of these non-centrosymmetric crystals realized so far.

Optical trapping and manipulating with a transmissive and polarization-insensitive metalens

Abstract Trapping and manipulating micro-objects and achieving high-precision measurements of tiny forces and displacements are of paramount importance in both physical and biological research. While conventional optical tweezers rely on tightly focused beams generated by bulky microscope systems, the emergence of flat lenses, particularly metalenses, has revolutionized miniature optical tweezers applications. In contrast to traditional objectives, the metalenses can be seamlessly integrated into sample chambers, facilitating flat-optics-based light manipulation. In this study, we propose an experimentally realized transmissive and polarization-insensitive water-immersion metalens, constructed using adaptive nano-antennas. This metalens boasts an ultra-high numerical aperture of 1.28 and achieves a remarkable focusing efficiency of approximately 50 % at a wavelength of 532 nm. Employing this metalens, we successfully demonstrate stable optical trapping, achieving lateral trapping stiffness exceeding 500 pN/(μm W). This stiffness magnitude aligns with that of conventional objectives and surpasses the performance of previously reported flat lenses. Furthermore, our bead steering experiment showcases a lateral manipulation range exceeding 2 μm, including a region of around 0.5 μm exhibiting minimal changes in stiffness for smoothly optical manipulation. We believe that this metalens paves the way for flat-optics-based optical tweezers, simplifying and enhancing optical trapping and manipulation processes, attributing ease of use, reliability, high performance, and compatibility with prevalent optical tweezers applications, including single-molecule and single-cell experiments.

Multiplexing near- and far-field functionalities with high-efficiency bi-channel metasurfaces

Propagating waves and surface waves are two distinct types of light-transporting modes, the free control of which are both highly desired in integration photonics. However, previously realized devices are bulky in sizes, inefficient, and/or can only achieve one type of light-manipulation functionality with a single device. Here, we propose a generic approach to design bi-channel meta-devices, constructed by carefully selected meta-atoms possessing reflection phases of both structural-resonance and geometric origins, which can exhibit two distinct light-manipulation functionalities in near-field (NF) and far-field (FF) channels, respectively. After characterizing the scattering properties of basic meta-atoms and briefly stating the theoretical strategy, we design/fabricate three different meta-devices and experimentally characterize their bi-channel wave-control functionalities in the telecom regime. Our experiments show that the first two devices can multiplex the generations of NF and FF optical vortices with different topological charges, while the third one exhibits anomalous surface plasmon polariton focusing in the NF and hologram formation in the FF simultaneously. Our results expand the wave-control functionalities of metasurfaces to all wave-transporting channels, which may inspire many exciting applications in integration optics.

Ultrafast laser inscription of 2D confinement MMI-based beam splitters with tunable splitting ratio in Nd:YAG crystal

The multimode-interference (MMI) devices based on the principle of self-imaging show great potential for applications in different scenarios. The research interest in two-dimensional confinement MMI devices has surged enormously due to the broader areas of applications compared with the one-dimensional confinement MMI devices. In this paper, we report on the characteristics of two-dimensional confinement 2 × 2 output MMI-based beam splitters which were achieved by femtosecond laser direct writing technology in a Nd:YAG crystal. The propagation features with different splitting ratios have been simulated by the beam propagation method. Two splitters with beam division performances of 2 × 2 output have been further demonstrated through an end-face coupling system and investigated with a laser beam at 532 nm wavelength, which have achieved two splitting ratios including 73 %: 12.5 %: 12.5 %: 2 % with a deviation less than 3 %, and 25 %: 25 %: 25 %: 25 % with a deviation less than 5 %. These performances with high consistency manifest that these devices can emerge into kinds of 3D optical applications with the ability of 3D spatial optical signal processing. Moreover, our work further proves that femtosecond laser direct writing technology presents absolute advantages in processing 3D micro-nano devices in transparent materials for on-chip integration.

Nano-kirigami/origami fabrications and optical applications

Emerging nano-kirigami/origami technology enables the flexible transformations of 2D planar patterns into exquisite 3D structures in situ and has aroused great interest in the areas of nanophotonics and optoelectronics. This paper briefly reviews some milestone research and breakthrough progresses in nano-kirigami/origami from the aspects of stimuli approaches and application directions. Versatile stimuli for kirigami/origami, including capillary force, residual stress, mechanical force, and irradiation-induced stress, are introduced in the micro/nanoscale region. Appealing optical applications and reconfigurable schemes of nano-kirigami/origami structures are summarized, offering effective routes to realize tunable nanophotonic and optoelectronic devices. Future challenges and promising pathways are also envisioned, including design methods, innovative materials, multi-physics field driving, and reprogrammable devices.

Advanced linear axial wavelength spreading through cascaded double hyperchromats

This study explores the design and optimization of cascaded double-hyperchromatic optical systems (i.e., 2×2 lenses), focusing on achieving an extremely linear axial spectral decomposition characterized by an exceptionally low equivalent Abbe number. The investigation involves two double hyperchromats, considering both purely refractive systems and hybrid configurations that combine refractive and diffractive elements. For purely refractive systems, alternating focal length signs of divergent and collective lenses are crucial to achieve significant axial chromatic dispersion. In hybrid systems, the position of the diffractive optical element (DOE) and the selection of focal lengths play key roles in obtaining extremely low equivalent Abbe numbers. The optimized systems demonstrate absolute equivalent Abbe numbers of 0.983 for purely refractive and 0.65 for hybrid systems—more than four times lower than the absolute Abbe number of a single diffractive element. Notably, even systems using standard materials exhibit significantly low equivalent Abbe numbers of 2.5 and 1.4 for pure refractive and hybrid configurations, respectively. These results offer promising opportunities for improving optical applications based on axial spectral decomposition, overcoming previous limitations of axial chromatic spreading.

Glass bonding of YAG/Nd:YAG and Sapphire/Nd:YAG windows

Transparent ceramic assemblies are of great interest and challenge for many optical applications. Lead silicate-based glass was successfully utilized to bond YAG/Nd:YAG and sapphire/Nd:YAG substrates at 850 °C in air. The glass's thermal characteristics and refractive index were measured and found to be comparable to those of YAG and sapphire. Microstructure and composition analysis of the glass bonding interface reveals no evidence of flaws or reaction products. The in-line transmission results of the YAG/Nd:YAG and sapphire/Nd:YAG assemblies are equivalent to those of the initial Nd:YAG ceramics throughout a wide wavelength range (450–1200 nm). The reported findings establish an efficient approach for future design and implementation of complex optical systems with enhanced optical and thermal properties.

Crystal structure, electronic structure and thermal stability of new phosphate Sr2In(PO4)(P2O7)

Searching for new phosphates is of special significance to enrich the basic database of the structure and properties for developing inorganic materials. Here, we present a new phosphate Sr2In(PO4)(P2O7) which crystallizes to a monoclinic cell (S.G. P21/c), with the lattice parameters of a = 6.5832(3) Å, b = 6.8984(3) Å, c = 19.813(1) Å, β=99.562(1)°, V = 887.3(1) Å3, and Z = 2. The three-dimensional frame of this structure is made of InO6, PO4, P2O7, SrO8, and SrO9 units. The co-existence of P2O7 and PO4 was confirmed by IR spectra assignment. The VB maximum and CB minimum of Sr2In(PO4)(P2O7) are dominated by In-s and O-p state, respectively. Combining the calculated electronic structure with measured UV–Vis diffuse reflectance spectrum, this phosphate shows a wide indirect energy band-gap. DTA indicates that its melt point is about 1245 °C. The large band gap and high thermal stability would be catering for the material requirement in futural optical or other functional application fields.

Wavelength-tuned transformation between photonic skyrmion and meron spin textures

Topological spin textures, among which skyrmions and merons are typical examples, have with their swirling vectorial structures triggered enormous interest in physical systems including elementary particles and magnetic materials. Manipulating their symmetry and topology is important for understanding the mechanisms that underlie their topological phase transformation as well as offering tunable degrees of freedom to encode information, which has already been demonstrated in magnetic materials. Recently, the photonic counterparts of skyrmions and merons were constructed in a 2D wave system with deep-subwavelength features promising for optical sensing, imaging, and information decoding. However, their experimental realization relied on stringent excitation conditions that only support a single spin texture type on a specific structure. Here, we demonstrate for the first time the transformation between photonic skyrmion and meron spin lattices on the same metallic meta-surface having a well-designed structural period. We show experimentally the wavelength-tuned symmetry transformation of the photonic spin lattices, which are also found to be robust against disorder in the structure to a certain degree. This work provides new insights into controlling the electromagnetic field symmetry and topology, as well as in developing applications in spin optics and topological photonics.

Scattering matrix for chiral harmonic generation and frequency mixing in nonlinear metasurfaces

We generalize the concept of optical scattering matrix (S-matrix) to characterize harmonic generation and frequency mixing in planar metasurfaces in the limit of undepleted pump approximation. We show that the symmetry properties of such nonlinear S-matrix are determined by the metasurface symmetries at the macroscopic and microscopic scale. We demonstrate that for description of degenerate frequency mixing processes such as optical harmonic generation, the multidimensional S-matrix can be replaced with a reduced two-dimensional S-matrix. We show that for metasurfaces possessing specific point group symmetries, the selection rules determining the transformation of the reduced nonlinear S-matrix are simplified substantially and can be expressed in a compact form. We apply the developed approach to analyze chiral harmonic generation in nonlinear metasurfaces with various symmetries including rotational, inversion, in-plane mirror, and out-of-plane mirror symmetries. For each of those symmetries, we confirm the results of the developed analysis by full-wave numerical calculations. We believe our results provide a new paradigm for engineering nonlinear optical properties of metasurfaces which may find applications in active and nonlinear optics, biosensing, and quantum information processing.