We propose the graphene film with trapezoid-shaped nanoparticles (GTNAs) to transport particles. In our design, the conversion of plasmon surface resonances can be realized without changing the excitation light source. By sequentially activating three closely packed potential wells, nanoparticles can be transported between adjacent traps in a creeping manner. Three adjacent potential wells form a linearly repeating array structure, forming a nano-optical conveyor belt. When the resonant wavelength is 5.5 μm, and the power density is 0.4 mW/μm 2 , we verified that the target particle can move along the direction of the hot spots. In addition, the movement of nanoparticles in a liquid environment will be interfered with by viscous resistance and the random Brownian motion process. Since particles produce hysteresis or derailment during transmission, we also analyzed the time interval of switching the Fermi level to manipulate the particle in real-time. The three-dimensional finite-difference time-domain method has been used to verify that the design of this paper provides a conveyor belt in tunable graphene without rotating the polarization angle of the light source and has broad application prospects in biomedical diagnostics.
We experimentally demonstrate a stable polarization mode operation in long-wavelength tunable vertical-cavity surface-emitting lasers over a 65-nm tuning range and the entire output power range (< 14.6 mW) at room temperature. The polarization mode control was achieved by utilizing anisotropic gain properties of quantum wells due to the difference in bond lengths between the constituent atoms at the interfaces combined with uni-axial external strain induced by a stressor. The experiments were conducted to verify this newly proposed polarization control scheme based on the spin flip model (SFM) developed to incorporate the detailed gain properties, cavity standing wave effect, self-heating effect, and strain effect. The experimental results on the tuning characteristics of polarization switching behavior and output powers were reproduced in highly agreeable manner by simulations. The relative importance of the external strain, interfacial strain at quantum wells, and the wavelength dependence of gain anisotropy are also discussed. It is also shown that the fast spin relaxation times for InP-based vertical-cavity surface-emitting lasers (VCSELs) was responsible for the inhibition of elliptic polarization states often observed for GaAs-based VCSELs. The effectiveness of the polarization control scheme was highlighted by the observed high polarization suppression ratio of 34 dB maintained for the entire wavelength and pump power ranges during the reliability testing over 2000 h. The influence of the elliptic polarization state for the optical pump laser was detected which could be explained as a memory effect of the spin-polarized electrons, supporting the validity of the SFM.
A model simplification method for linear discrete systems is presented to determine both numerator and denominator coefficients of a simplified model by differential evolution algorithm in order to minimize the root mean squared error between the step responses of original and simplified models. The performance of the proposed method was demonstrated by two examples with different orders and the results show that the method can yield a good approximation of the original system.
Based on the balance between the scattering force and the trapping force of an evanescent field of a standing wave on silicon waveguides, we propose a structure for controllable trapping and releasing of nanoparticles, which can act as pause operation for nanoparticle flow control. The design is realized by the cascade of an optical switch with a structure of a ring-assisted Mach-Zehnder interferometer (RAMZI) and a Sagnac loop reflector which connects to one output of the switch. Through thermal tuning, with a tiny refractive index change of 4.3×10-4 on a ring resonator, the output of a RAMZI can be switched between two ports. As for the release state of the nanoparticle flow, the light is guided to the port without a reflector. There is no standing wave or traps formed on a waveguide. Therefore, the scattering force dominates, which drives particles moving forward to output ports. Otherwise, for trapping a state, the light will be reflected by the Sagnac loop and form a stationary standing wave which provides an array of traps for nanoparticles. Most importantly, the structure can switch its state to trap or sequentially release particles without losing the control of samples which, to the best of our knowledge, has not been realized before. With the statistical description of particle motion, the balance between trapping and releasing is distinguished by the trapping time and tuned by reflectance. The feasibility of our design is verified using the three-dimensional finite-difference time domain and Maxwell stress tensor methods. Our structure possesses the merits of high compactness and time effectiveness and, thereby, it is highly suitable for on-chip optical manipulation of nanoparticle flow control, which brings great potential in integrated on-chip optofluidics.
In this Letter, we have proposed an optically levitated conveyor belt based on periodic arrays of a polarization-dependent nanoslit-based metasurface lens (NBML) that is capable of realizing far-field capture, transport, and sorting. The NBML in arrays can be lit up in a relay way by rotating the polarization angle of the excitation beam and thereby provide a better stiffness for transporting particles. When excited at the wavelength of 1064 nm and power density of 0.3 mW/µm2, the particles will follow the directional movement of hot spots with an alternative switch of polarization angle and the success ratio of transport can be up to 97.0% with the consideration of Brownian motion. Furthermore, the influence of polarization switching time and incident optical power densities on the efficiency of transport are investigated numerically from a statistical point of view. The sorting of particles with different sizes has also been proved in a given power density. With the analysis of numerical results, our research provides a new approach, to the best of our knowledge, for particle trapping and transport, which is beneficial to on-chip optofluidic applications.
In this letter, we propose a plasmonic conveyor belt based on a periodically arranged graphene nanorings (GNRs) with different size, on which the hot spots could be continuously lighted up by electrically tuning the Fermi level of graphene and could be used for the trapping and transporting of nanoparticles even under a uniform Mid-infrared or terahertz light excitation. Graphene nano-structure supports surface plasmon resonance, and its resonance condition is not only related with its size, but also could be adjusted by its Fermi level, as well as the applied gate voltage. In this way, a periodically arranged GNRs with different size can be excited in turn, thus realizing the function of transporting nanoparticles without reconfiguring the light excitation. In light of the rotational symmetry of GNRs, our polarization-independent design approach obviously has more advantages than the ones consisting of the graphene strips. In addition, the feasibility of the particle-separation is demonstrated. As confirmed by the numerical analysis, our design offers an optimized scheme for polarization-independent and electrically tunable plasmonic conveyor belt, which could be used in many on-chip optofluidic applications.
Abstract This case study in Kerala, India explores the positive impacts of community participation on economic, socio-cultural and environmental factors through responsible tourism initiatives in Kumarakom destination. This research evaluates the effectiveness, fundamental elements and conceptual foundation of participatory design in the case study destination. The results of the case study indicate that participatory design can accelerate local community development, innovative initiatives, leadership, employment opportunities, demand for local products and sustainable development in the destination.
Lab-on-a-chip, or microfluidics large-scale integration (mLSI), enables the fabrication of chips containing hundreds or more of these functions using well-established lithography techniques, similar in principle to electronic LSI in the semiconductor industry. Logic manipulation is critical for large scale integration of optofluidics system. Based on two different ways for the light excitation namely waveguide mode coupling method and perpendicular focused beam method, here we demonstrate this kind of manipulation achieved by silicon photonic and plasmonic nanostructures in nanofluidics. The logic manipulation of optofluidic system will make the chip dynamically configurable and scalable. It will be a critical function unit for systems with a high degree of automation.
We developed a novel lab-on-a-chip device with the capability of rapidly pre-concentrating for Raman detection that use gold bead as the solid carrier of biomolecules. The device combines an array of patterned plasmonic surface (i.e. gold nano-ellipses), as the bead manipulation element. The purpose of gold bead manipulation is to provide sample pre-concentration in close proximity of the Raman detecting region. In the presence of an external uniform electric field, the gold ellipses create local electric field gradients (which is usually called hot spots) that capture the gold beads. The location of hot spots within a plasmonic nanostructure is polarization dependent, and inhomogeneous electric field between two adjacent nano-ellipses perpendicular to each other leads to highly unbalanced trap potential that give the chance of transferring trapped particles in a given direction through rotating the polarization. Nano-optical conveyor belts with staircase pattern of nano-ellipses were arranged with their terminus collected at detection area to gather biomolecules. With the capacity to transfer biomolecules precisely, our design offers an attractive scheme for rapid, high throughput and highly sensitive sensing of low abundance analytes.
A tunable metal surface composed of periodically arranged graphene nanodisks (GNDs) has been designed to achieve precise regulation of two-dimensional light fields. Since the distribution of hot spots (i.e., locally enhanced light fields) around GND is closely related to the polarization state, it can be reconfigured by rotating the polarization direction to transport trapped particles along the edge of the disk. By adjusting the Fermi level to activate the corresponding GND, the directional transmission of target particles between adjacent GND is realized. The rotation of the polarization direction determines the particle movement trajectory around GND. The target particle can move around GND in any direction by synchronously adjusting the Fermi energy level and the polarization angle. This innovative optical transport mechanism with high structural scalability can be widely used in on-chip optical fluid technology.
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