Academic literature on the topic 'Optical Modulation - Ultra Narrow Nanomaterials'

Abstract Compared with continuous wave lasers, ultrafast lasers have the advantages of ultra-short pulse width and ultra-high peak power, and have significant applications in optical communications, medical diagnostics, and precision machining. Saturable absorber (SA) technology is the most effective technique for the generation of ultra-fast lasers, which are based on artificial SAs and natural SAs. Among them, the semiconductor saturable absorber mirror has become the most commonly used form at present. Recently, basic research and application of nanomaterials such as carbon nanotubes (CNTs) and graphene have been developed rapidly. Researchers have found that nanomaterials exhibit extraordinary characteristics in ultrafast photonics, such as the low saturation intensity of CNTs, zero-band gap of graphene, and extremely high modulation depth of the topological insulator nano-films. Since graphene was first reported as an SA in 2009, many other nanomaterials have been successively explored, resulting in the rapid development of novel nanomaterial-based SAs. In this paper, we classified the nanomaterials used in SA mode-locking technology at 1.5 μm and reviewed their research progress with a particular focus on nonlinear optical properties, integration strategies, and applications in the field of ultrafast photonics.

A metallic nano-trench is a unique optical structure capable of ultrasensitive detection of molecules, active modulation as well as potential electrochemical applications. Recently, wet-etching the dielectrics of metal–insulator–metal structures has emerged as a reliable method of creating optically active metallic nano-trenches with a gap width of 10 nm or less, opening a new venue for studying the dynamics of nanoconfined molecules. Yet, the high surface tension of water in the process of drying leaves the nano-trenches vulnerable to collapsing, limiting the achievable width to no less than 5 nm. In this work, we overcome the technical limit and realize metallic nano-trenches with widths as small as 1.5 nm. The critical point drying technique significantly alleviates the stress applied to the gap in the drying process, keeping the ultra-narrow gap from collapsing. Terahertz spectroscopy of the trenches clearly reveals the signature of successful wet etching of the dielectrics without apparent damage to the gap. We expect that our work will enable various optical and electrochemical studies at a few-molecules-thick level.

Ultra-fast electrical switches activated with an optical-polarized light trigger, also called photo-polarized activated electrical switches, are presented. A set of new transistor circuits is switched by light from above, illuminating deep V-grooves, whose angle is sensitive to the polarization of the incident. Thus, this application may serve for encryption/decryption devices since the strongest electrical responsivity is only obtained for very specific spatial polarization directions of the illumination beam. When this V-groove is sufficiently narrow, the device mainly responds to one polarization and not to the other. In such a way, electrons are generated only for one specific polarization. While the nature of the data remains electronic, the modulation control is optic, creating a photo-induced current depending on the polarization direction. This coupled device acts as a polarization modulator as well as an intensity modulator. The article focuses on the integration of several devices in different configurations of circuitry: dual, triple, and multi-element. Case studies of several adjacent devices are presented with varying critical variables, such as the V-groove aperture dimensions. Analytical models and complementary numerical analyses are presented for the future smooth integration into Complementary Metal-Oxide-Semiconductor (CMOS) technology.

Organic–inorganic photocurable nanocomposite materials are a topic of intensive research nowadays. The wide variety of materials and flexibility of their characteristics provide more freedom to design optical elements for light and neutron optics and holographic sensors. We propose a new strategy of nanocomposite application for fabricating resonant waveguide structures (RWS), whose working principle is based on optical waveguide resonance. Due to their resonant properties, RWS can be used as active tunable filters, refractive index (RI) sensors, near-field enhancers for spectroscopy, non-linear optics, etc. Our original photocurable organic–inorganic nanocomposite was used as a material for RWS. Unlike known waveguide structures with corrugated surfaces, we investigated the waveguide gratings with the volume modulation of the RI fabricated by a holographic method that enables large-size structures with high homogeneity. In order to produce thin photosensitive waveguide layers for their subsequent holographic structuring, a special compression method was developed. The resonant and sensing properties of new resonant structures were experimentally examined. The volume waveguide gratings demonstrate narrow resonant peaks with a bandwidth less than 0.012 nm. The Q-factor exceeds 50,000. The sensor based on waveguide volume grating provides detection of a minimal RI change of 1 × 10−4 RIU. Here we also present the new theoretical model that is used for analysis and design of developed RWS. Based on the proposed model, fairly simple analytical relationships between the parameters characterizing the sensor were obtained.

Phase change materials (PCMs) are attracting more and more attentions as enabling materials for tunable nanophotonics. They can be processed into functional photonic devices through customized laser writing, providing great flexibility for fabrication and reconfiguration. Lithium Niobate (LN) has excellent nonlinear and electro-optical properties, but is difficult to process, which limits its application in nanophotonic devices. In this paper, we combine the emerging low-loss phase change material Sb2S3 with LN and propose a new type of high Q resonant metasurface. Simulation results show that the Sb2S3-LN metasurface has extremely narrow linewidth of 0.096 nm and high quality (Q) factor of 15,964. With LN as the waveguide layer, strong nonlinear properties are observed in the hybrid metasurface, which can be employed for optical switches and isolators. By adding a pair of Au electrodes on both sides of the LN, we can realize dynamic electro-optical control of the resonant metasurface. The ultra-low loss of Sb2S3, and its combination with LN, makes it possible to realize a new family of high Q resonant metasurfaces for actively tunable nanophotonic devices with widespread applications including optical switching, light modulation, dynamic beam steering, optical phased array and so on.

Nanotechnology is the science of designing, producing, and using structures and devices having one or more dimensions of about 100 millionth of a millimetre (100 nanometres) or less. It is going to be a major driving force behind the imminent technological revolution in the 21st century. Private and public sector companies are constantly in synthesizing nanomaterial based products. Nanotechnology has the potential of producing new materials and products that may revolutionize all areas of life. Meanwhile, its opponents believe that nanotechnology may cause serious health and environmental risks and advise that the prophylactic approach should command the blooming and distribution of such products. Nanotechnology pledges for producing novel materials with augmented properties and potential applications (Zeng and Sun, 2008). Nanoparticles and nanomaterials both terms are used interchangeably in scientific literature. However, according to British Standards Institution for the scientific terms: “Nanomaterial is a material with any internal or external structures on the nanoscale dimension, while Nanoparticle a is nano-object with three external nanoscale dimensions. According to the European Commission, nanoparticles can be defined as a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate with one or more external dimensions is in the size range 1 nm – 100nm. The size of nanoparticles is comparable to the size of cell organelles. Nanoparticles can have amorphous or crystalline form and their surfaces can act as carriers for liquid droplets or gases. They have at least one dimension between 1 and 100 nanometers and a narrow size distribution. The nanometric dimensions of these materials make them ideal candidates for surface engineering and functionalization. Due to the development of nanotechnology in recent years, engineered nanoparticles are being used in various fields, particularly in biomedical field. Various physico-chemical properties such as large surface area strength, mechanical, optical activity and chemical reactivity make nanoparticles unique and suitable candidates for various applications. Nanomaterials can be classified into natural and anthropogenic categories based on their origin. Natural sources include volcanic eruptions, forest fires, photochemical reactions, dust storms, etc., while anthropogenic sources include human activities, which can be of two types: Incidental nanomaterials that are generated unintentionally as a result of industrial activities. Combustion from vehicles, cooking, fuel petroleum and coal for power generation (Linak et al., 2000), aeroplanes engines, welding, ore refining and smelting are some of the incidental activities that lead to nanoparticle formation (Rogers et al., 2005). Engineered nanomaterials are designed and created intentionally for producing nanoparticles with specific characteristics. Due to its unusual tunable properties, these materials are widely used in electronics such as semiconductor chips, lighting technologies such as light-emitting diodes (LEDs), lasers, batteries, and fuel electronics etc. Scientists are using nanoparticles to target tumors, in drug delivery systems, and to improve medical imaging. Emerging engineered nanomaterials like quantum dots, nanobranches, nanocages, and nanoshells are presently being used in advance photovoltaic cells, drug delivery nanovehicles, and immunological sensing devices (Kahru and Dubourguier, 2010). Nanomaterials are also classified on the basis of morphology (rod, flower shaped, fiber, sphere and sheet), crystalline mature (amorphous and cristaline), dimension (0D, 1D, 2D, and 3D), and chemical nature (metal, semi-metal and non-metal). There are more than 1800 market products containing nanomaterials, including drugs, food products, food preservatives, clothing, sports items, cosmetics and electronic appliances (Chou et al., 2008; Vance et al., 2015). Nanoparticles are currently being used in biomedicine, bio-imaging, targeted drug delivery, assisted rreproductive technologies (ART), etc. Nanoparticle exposure to humans may be either incidental or accidental or occupational to the natural and manmade nanomaterials. Nanoparticles enter human bodies through inhalation, ingestion and skin, accumulate in the body organs and cause toxic effects on the biological system. The highly activated surfaces of nanoparticles have great potential to induce cytotoxic, genotoxic and carcinogenic activities (Seaton et al., 2010). In-vivo studies specify that the lung, spleen, liver, and kidney are the major distribution sites and target organs for nanomaterial exposure (Wang et al., 2013). They induce localized toxic effects such as cardiotoxicity, hepatotoxicity, nephrotoxicity, etc., in related organs (Du et al., 2013; Yan et al., 2012; Hussain et al., 2005). Several reports have described the adverse effects of nanoparticles on human and animal health, especially in context of reproductive health. The reproductive toxicity of nanoparticles is becoming an important part of nano-science research (Ema et al., 2010). Exposure to nanoparticles adversely affects male reproductive system including both structural and functional aspects. Metallic nanoparticles, generally below 30 nm, owing to their spherical nature and diameter easily cross blood testicular barrier causing considerable toxic changes in the testicular tissue. Hong et al. (2015) reported decreased sperm production in testis accompanied with changes in expression of spermatogenesis regulating genes due to exposure of metallic nanoparticle titanium dioxide (TiO2). A sub-chronic oral exposure of PVP-coated AgNPs to rats resulted in altered testicular histology and sperm morphological abnormalities. In a study, testicular toxicity due to silver nanoparticles was examined in Sprague Dawley rat. The results indicated a significant fall in testosterone level and hike in LH levels. Ultra structural examination revealed vaculations in Sertoli cells and abnormalities in spermatogenic cells, sperm viability and chromatin integrity were also affected adversely (Elsharkawy et al., 2019). Similarly, exposure to zinc oxide nanoparticles resulted in apoptosis in testicular cells and structural changes in seminiferous epithelium and sperm anomalies (Han et al., 2016). Accumulation of copper oxide nanoparticles in testis of mouse may affect sperm morphology (Kadammattil et al., 2018). Spherical shaped nickel nanoparticles of 90 nm size can change motility and decrease FSH and testosterone levels in rats. At higher dose, nickel nanoparticles induced significant structural damage to the testis (Kong et al., 2014). Iron oxide nanoparticles of 20-80 nm size adverse by affected the sperm and Leydig cells in mouse (Nasri et al., 2015). Recent testicular toxicity study conducted by Verma et al. (2022) demonstrated that low, medium and high doses (20, 40 and 80 mg kg-1) of spherically shaped, with an average diameter of 15-20 nm, super paramagnetic IONPs (Fe3O4) injected intra-peritoneally decreased sperm counts and motility in spermatozoa. With respect to the effects due to non-metallic or semi-metallic nanoparticles having different shapes, different outcomes have been reported. A study conducted by Nirmal et al. (2017) on Wistar rat, exposed to 2.0 and 10.0 mg kg-1 bwt doses of OH-f MWCNTs resulted in sperm dysfunction and degeneration in seminiferous tubules (Nirmal et al., 2017). In another study by the same group, Wistar rat exposed to high doses of nanoscale graphene oxide (NGO) intra-peritonially, showed reduced sperm motility and total sperm count and increased sperm abnormalities (Nirmal et al., 2017). It is thus apparent that nanoparticles have a considerable negative impact on testicular tissue including damage to Leydig cells, Sertoli cells, spermatogenesis and sperm quality. Various studies have revealed that the testicular toxicity is caused due to combination factors. Oxidative stress is a key factor responsible for nanoparticle mediated damage. It becomes more harmful, especially to the testes because of high metabolism, continuous sperm production and presence of high amount of unsaturated fatty acids (Aitken and Roman, 2008). With the expansion and production of nanometerials for industrial and medical applications, exposure chances are also increasing. Many research reports have documented the adverse effects of nanoparticles on animals and environment. The major concern with the widespread use of NPs is their toxicity to living cells. Therefore, alleviating or reducing NPs toxicity remains much coveted goal for researchers around the globe. It is the alertness and scientific awareness which can prevent these materials from becoming bane instead of boon for humanity. This editorial is written as a tribute to my beloved teacher Dr. R. C. Dalela who has been my mentor since 1985, when I was student of M.Sc. Zoology (1985-1987) and Ph.D (1987-1993) in D.A.V. P.G. College, Muzaffarnagar. He has played a vital role in moulding my career, from an average post-graduate student to the academician and a researcher I am today. I deeply cherish his guidance, encouragement and support. It was my privilege to meet him last November, so close to his sudden demise. The values inculcated by him continues to inspire me in my onward journey. I have been associated with JEB for the past 25 years as a reviewer and an Associate Editor. The articles published in this journal receive good citations, which reflect the popularity of this open access journal among the researchers of Environmental Biology and Toxicology. I must appreciate the present editorial team headed by Professor Divakar Dalela for their efforts in maintaining the standard of this journal. I wish all success and my sincere co-operation for the same in the coming years.

Abstract Metasurfaces, the ultrathin media with extraordinary wavefront modulation ability, have shown great promise for many potential applications. However, most of the existing metasurfaces are limited by narrow-band and strong dispersive modulation, which complicates their real-world applications, which usually require strict customized dispersion. To address this issue, we report a general methodology for generating ultra-broadband achromatic metasurfaces with prescribed ultra-broadband achromatic properties in a bottom-up inverse-design paradigm. We demonstrate three ultra-broadband functionalities, including acoustic beam deflection, focusing and levitation, with relative bandwidths of 93.3%, 120% and 118.9%, respectively. In addition, we reveal a relationship between broadband achromatic functionality and element dispersion. All metasurface elements have anisotropic and asymmetric geometries with multiple scatters and local cavities that synthetically support internal resonances, bi-anisotropy and multiple scattering for ultra-broadband customized dispersion. Our study opens new horizons for ultra-broadband high-efficient achromatic functional devices, with promising extension to optical and elastic metamaterials.

Abstract Two-dimensional materials hold a great promise for developing extremely fast, compact and inexpensive optoelectronic devices. A molybdenum disulphide (MoS2) monolayer is an important example which shows strong, stable and gate tunable optical response even at room temperature near excitonic transitions. However, optical properties of a MoS2monolayer are not documented well. Here, we investigate the electric field effect on optical properties of a MoS2 monolayer and extract the dependence of MoS2 optical constants on gating voltage. The field effect is utilised to achieve ~10% visible light modulation for a hybrid electro-optical waveguide modulator based on MoS2. A suggested hybrid nanostructure consists of a CMOS compatible Si3N4 dielectric waveguide sandwiched between a thin gold film and a MoS2 monolayer which enables a selective enhancement of polarised electro-absorption in a narrow window of angles of incidence and a narrow wavelength range near MoS2 exciton binding energies. The possibility to modulate visible light with 2D materials and the robust nature of light modulation by MoS2 could be useful for creation of reliable ultra-compact electro-optical hybrid visible-light modulators.

Abstract Recently, improving the sensing performance of refractive index sensors by using of the weak far-field radiation and strong local field enhancement properties of toroidal dipole resonances has been intensively studied. Transmission/reflection spectra with significant narrow linewidth resonance has a vital effect on improving the sensing performance. However, narrower linewidth always leads to smaller modulation depth of the resonance which hinders the sensing performance to be improved for experiments. In this paper, we design an ultrathin all-dielectric asymmetric X-type metasurface array where an extremely narrow linewidth and high modulation depth of transmission resonance in the near-infrared has been demonstrated with Mie lattice resonance formed by the coupling of the toroidal dipole with Rayleigh Anomalous diffraction. With optimized structure parameters, a transmission dip with a full width at half-maximum as narrow as 0.061 nm and a modulation depth as high as 99.24% is achieved at the wavelength of 943.33 nm with a corresponding Q factor of 15464. According to the analysis of the displacement current distributions and the scattered powers in far field at the resonant and non-resonant wavelengths, it is confirmed that the narrow linewidth resonance is originated from the coupling of the toroidal dipole with Rayleigh Anomalous diffraction. A sensitivity and a figure of merit of 321 nm/RIU and 5262 RIU-1 are numerically demonstrated respectively for a refractive index sensor based on the all-dielectric asymmetric X-type metasurface array.

AbstractTailored nanostructures provide at-will control over the properties of light, with applications in imaging and spectroscopy. Active photonics can further open new avenues in remote monitoring, virtual or augmented reality and time-resolved sensing. Nanomaterials with χ(2) nonlinearities achieve highest switching speeds. Current demonstrations typically require a trade-off: they either rely on traditional χ(2) materials, which have low non-linearities, or on application-specific quantum well heterostructures that exhibit a high χ(2) in a narrow band. Here, we show that a thin film of organic electro-optic molecules JRD1 in polymethylmethacrylate combines desired merits for active free-space optics: broadband record-high nonlinearity (10-100 times higher than traditional materials at wavelengths 1100-1600 nm), a custom-tailored nonlinear tensor at the nanoscale, and engineered optical and electronic responses. We demonstrate a tuning of optical resonances by Δλ = 11 nm at DC voltages and a modulation of the transmitted intensity up to 40%, at speeds up to 50 MHz. We realize 2 × 2 single- and 1 × 5 multi-color spatial light modulators. We demonstrate their potential for imaging and remote sensing. The compatibility with compact laser diodes, the achieved millimeter size and the low power consumption are further key features for laser ranging or reconfigurable optics.

Using an ensemble Monte Carlo simulation of coupled electrons and nonequilibrium slab mode polar optical phonons in single and multiple quantum well systems, we have studied the relaxation of photoexcited carriers in ultra-fast optical intersubband relaxation experiments. Here we study intersubband relaxation in three different types of systems: i) wide wells in which the intersubband separation is less than the optical phonon energy, ii) narrow wells in modulation doped multi-quantum well structures, and iii) coupled asymmetric quantum wells. Simulated results using self-consistent envelope functions in the quantum well system show the importance of nonequilibrium hot phonons and self-consistency in explaining the experimental results from time resolved Raman, intersubband absorption, and photoluminescence spectroscopy.

The photon echo is often the best technique for measuring ultra narrow homogeneous linewidths of an inhomogeneously broadened optical transition for which a higher spectral resolution than the laser bandwidth is required. Homogenous linewidths on the order of one kHz have been measured for Eu3+ and Pr3+ in different host materials at liquid helium temperature from the echo intensity as a function of the delay between the two excitation pulses. These linewidths arc three orders of magnitude narrower than the long term jitter bandwidth of the laser which was used for excitation.1 Here we present a novel spectroscopic method based on the modulation of a 2-pulsc photon echo or a stimulated echo by an externally applied field, for the accurate measurement of frequency shifting perturbations with sub-homogeneous linewidth resolution. This is illustrated by the Stark effect on the 7F0→5D0 transition of Eu3+:YAIO3. The basic idea is that two coherent preparation pulses create an excited state population grating in the frequency domain of an inhomogeneously broadened line, which then gives rise to the echo in the course of the free induction decay of the coherently prepared ions. Since the photon echo can be observed for pulse separations much larger than T2, it is possible to generate frequency gratings which have a periodic spacing smaller than the homogeneous linewidth.2 In the case of a centrosymmetric crystal there are two groups of ions with equal and opposite dipole moments. An applied electric field Es shifts the ground and excited state energy levels through interaction with the electric dipole moments of these states and hence leads to a linear frequency shift, Ω=δμ⇀⋅E⇀s/ℏ, for the two sets of ions in opposite directions, where δμ⇀ is the difference between the ground and excited state dipole moments. If the electric field is applied after the first pulse, the two sets of ions accumulate equal and opposite phase shifts Φ = ± Ωt during the time interval, t. The result of the second pulse is that an excited state population grating is created in the frequency domain with a period (t + τ)-1 where t is the time interval between the pulses and τ is the duration of one pulse. Since there arc two sets of ions with opposite phase shifts, we formally get two population gratings, one with the phase Φ = + Ωt and one with the phase Φ = − Ωt. with respect to the population grating that is caused without an applied field.