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Using a plasmonic graphene ring resonator of resonant frequency 10.38 THz coupled to a plasmonic graphene waveguide, we design a lab-on-a-chip optophoresis system that can function as an efficient plasmonic force switch. Finite difference time domain numerical simulations reveal that an appropriate choice of chemical potentials of the waveguide and ring resonator keeps the proposed structure in on-resonance condition, enabling the system to selectively trap a nanoparticle. Moreover, a change of 250 meV in the ring chemical potential (i.e., equivalent to 2.029 V change in the corresponding applied bias) switches the structure to a nearly perfect off-resonance condition, releasing the trapped particle. The equivalent plasmonic switch ON/OFF ratio at the waveguide output is -15.519 dB. The designed system has the capability of trapping, sorting, controlling, and separating PS nanoparticles of diameters ≥30 nm with a THz source intensity of 14.78 mW/µm 2 and ≥22 nm with 29.33 mW/µm 2 .

We present theoretical and experimental studies of the plasmonic properties of hexagonal arrays of gold triangles, fabricated by angle-resolved nanosphere lithography method. Our numerical and experimental results both show that a change in the angle of gold deposition affects the size and the distance between the triangles, leading to a controlled shift in their absorption and scattering spectra. We calculate the force exerted on the polystyrene particles of 650 nm radii numerically while passing above the hexagonal arrays. Simulation results show that the presented hexagonal arrays of gold triangles can operate as efficient plasmonic tweezers with a controllable operating wavelength and high trap strength, owing to the additive interaction of the neighboring triangles. Moreover, we apply the realized plasmonic nanostructures in a conventional optical tweezers configuration and show that the optical tweezers stiffness can be effectively modulated by the plasmonic forces, at the IR wavelength of 1064 nm.

We numerically investigate and design a compact electrically pumped edge-emitting photonic crystal waveguide (PCW) quantum dot (QD) laser operating at room temperature. Use of a narrowband folded directional coupler as the output mirror has made the proposed structure an edge-emitting single-mode laser. Moreover, we propose a set of rate equations to model the performance of the PCW-QD laser. In the proposed model, we take the effects of the homogeneous and inhomogeneous broadenings and the slow-light effects on the modal gain and loss coefficient into account. Simulations show that threshold current as low as ∼26  μA can be achieved for the PCW-QD laser with a 50-μm-long cavity and output power in the range of micro-watts. The proposed low-threshold edge-emitting PCW-QD laser is a promising light source for the off-chip and on-chip photonic network applications.

We are introducing a new bias free CW terahertz photomixer emitter array. Each emitter consists of an asymmetric metal-semiconductor-metal (MSM) that is made of two side by side dis-similar Schottky contacts, on a thin layer of low temperature grown (LTG) GaAs, with barrier heights of difference (ΔΦ(B)) and a finite lateral spacing (s). Simulations show that when an appropriately designed structure is irradiated by two coherent optical beams of different center wavelengths, whose frequency difference (∆f) falls in a desired THz band, the built-in field between the two dis-similar potential barriers can accelerate the photogenerated carriers that are modulated by ∆ω, making each pitch in the array to act as a CW THz emitter, effectively. We also show the permissible values of s and ΔΦ(B) pairs, for which the strengths of the built-in electric field maxima fall below that of the critical of 50 V/μm- i.e., the breakdown limit for the LTG-GaAs layer. Moreover, we calculate the THz radiation power per emitter in an array. Among many potential applications for these bias free THz emitters their use in endoscopic imaging without a need for hazardous external biasing circuitry that reduces the patient health risk, could be the most important one. A hybrid numerical simulation method is used to design an optimum emitter pitch, radiating at 0.5 THz.

Using numerical analysis, we compare the results of optofluidic and rod filling techniques for the broadening of supercontinuum spectra generated by As2Se3 chalcogenide photonic crystal fibers (PCFs). The numerical results show that when air-holes constituting the innermost ring in a PCF made of As2Se3-based chalcogenide glass are filled with rods of As2Se3-based chalcogenide glass, over a wide range of mid-IR wavelengths, an ultra-flattened near-zero dispersion can be obtained, while the total loss is negligible and the PCF nonlinearity is very high. The simulations also show that when a 50 fs input optical pulse of 10 kW peak power and center wavelength of 4.6 μm is launched into a 50 mm long rod-filled chalcogenide PCF, a ripple-free spectral broadening as wide as 3.86 μm can be obtained.

We have obtained a simple numerical model that explains the temperature behavior of multi-quantum-dot (QD) nanophotonic devices whose operations are based on optical near-field (ONF) interactions between any two resonant QDs that are in thermal equilibrium. This model involves a set of coupled rate equations that govern the temporal behavior of the QDs' energy level occupancies. Under a certain operating condition, this simple model can substitute for the more complex density matrix (DM) approach in modeling the temperature dependence of the ONF energy transfer rate (R(ONF)) between any two resonant QDs in thermal equilibrium. The same applies for modeling the system state-filling time (tau(S)). Applying our simple model to a two-QD system, we have derived analytical formulas for the interdot and the intradot transfer rates at finite temperatures (T > or = 0). Furthermore, by assuming a unidirectional energy transport operating condition, we have also derived an analytic formula for calculating tau(S) for a two-QD system. To the best of our knowledge, this work is the first instance of reporting such analytic equations. Approximated values of tau(S) obtained from our simple analytic equation are in reasonable agreements with those calculated by the DM approach.

We propose a new numerical model to analyze heat induced by two-photon absorption and free-carrier absorption, while high intensity optical pulses propagate along silicon-on-insulator (SOI) nanowaveguides (NWGs). Using this model, we demonstrate that such induced heat causes a shift in the amount of wavelength conversion and hence deteriorates the converter output characteristics for pulses in the picosecond regime. The wavelength shift induced by a pulse with maximum input intensity and full width at half-maximum of I(max)=1.5x10(10) W x cm(-2) and T(FWHM)=30 ps, propagating along a SOI NWG with an effective cross-sectional area of a(eff)=0.15 microm(2), is shown to be Delta lambda(s) approximately 8 pm. We also demonstrate that such a shift can be compensated by tuning the pump intensity down by approximately 6.33%.

Chromatic dispersion compensation is an essential feature of high speed dense wavelength-division multiplexing (DWDM) systems. We propose a dispersion compensator structure whose characteristics meet the optical DWDM system requirements. The proposed structure is based on Fibonacci quasi-periodic multilayer structures composed of layers with large index differences. Studying the dispersive properties of Fibonacci structures with generation numbers j=3 and 4, and calculating group delay (GD) and group velocity dispersion (GVD) of their reflection bands, we have demonstrated that to have a smooth GD and almost a constant GVD in each band of a DWDM system, one needs not only to suitably chirp the structure refractive index profile, but also must properly apodize it. We also demonstrate the possibility of achieving high slope GDs and large GVDs by means of high order Fibonacci structures with thicker layers. Finally, by varying the layer dimensions and refractive indices as well as Fibonacci's order, one can design DWDM dispersion compensators suitable for distances as long as 220 km.