Schottky graphene/Si photodetector based on metal-dielectric hybrid hollow-core photonic crystal fibers.

This Letter presents a new family of Schottky graphene/silicon (Si) photodetectors (PDs) based on hollow-core photonic crystal fibers (HPCFs), working at both optical communication and room temperature. The proposed structure has the advantage of plasmonic HPCFs in a slow-light regime, and the absorption mechanism is based on an internal photoemission effect. The main feature of this structure is that the enhanced electric field is strongly localized in the hollow core of the guided core mode with the surface plasmon modes at the surface metal wires embedded in the photonic crystal structure. For the proposed graphene/silicon Schottky PD, numerical simulation predicts responsivity of ∼0.39 A/W, and continuous-wave sensitivity of -59 dBm, which reveals substantial improvements compared to that of typical metal/Si Schottky PDs.

Midinfrared supercontinuum generation via As2Se3 chalcogenide photonic crystal fibers.

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.

Design of an ultracompact low-power all-optical modulator by means of dispersion engineered slow light regime in a photonic crystal Mach-Zehnder interferometer.

We present the design procedure for an ultracompact low-power all-optical modulator based on a dispersion-engineered slow-light regime in a photonic crystal Mach-Zehnder interferometer (PhC MZI), selectively infiltrated by nonlinear optical fluids. The dispersionless slow-light regime enhancing the nonlinearities enabled a 22 µm long PhC MZI to operate as a modulator with an input power as low as 3 mW/µm. Simulations reveal that the switching threshold can be controlled by varying the optofluidic infiltration.

Design and numerical simulation of an optofluidic pressure sensor.

We present a numerical design procedure for an all-optical compact sensor by means of integrating the optofluidic switch polymer interferometers to measure the microfluidic air pressure and flow rate. The design is based on a flexible air gap optical cavity that can generate an interference pattern when illuminated by a monochromatic light. The optical interference pattern directly depends on the pressure. In our numerical simulations, we take the effects of fluid flow rate, solid deformation, and the light interference into account. We use the beam propagation method for simulating the optics and the finite element method for simulating the mechanics. The significance of the proposed sensor lies with its low power consumption, compactness, low cost, and short length. This sensor can operate under pressure range of 0-60±6% Pa at a constant temperature of 20 °C.

Proposal for enhancing the transmission efficiency of photonic crystal 60° waveguide bends by means of optofluidic infiltration.

We are proposing a procedure to enhance the transmission efficiency of 60° photonic crystal (PhC) waveguide bends by means of selective optofluidic infiltration of an air hole, which is created as a point defect at the center of the conventional 60° PhC bend. Numerical studies demonstrate that by varying the defect radius and indices of optical fluids, one may enhance the bend transmission level and tune its 3 dB bandwidth over a substantial range of 88-138 nm. In order to perform the numerical simulations, we have used two-dimensional (2D) finite difference time domain plane wave method, keeping in mind that the spectral features obtained by these 2D calculations are about 15% redshifted from those of real three-dimensional structures.

Slow light enhancement of nonlinear effects in silicon engineered photonic crystal waveguides.

We report nonlinear measurements on 80microm silicon photonic crystal waveguides that are designed to support dispersionless slow light with group velocities between c/20 and c/50. By launching picoseconds pulses into the waveguides and comparing their output spectral signatures, we show how self phase modulation induced spectral broadening is enhanced due to slow light. Comparison of the measurements and numerical simulations of the pulse propagation elucidates the contribution of the various effects that determine the output pulse shape and the waveguide transfer function. In particular, both experimental and simulated results highlight the significant role of two photon absorption and free carriers in the silicon waveguides and their reinforcement in the slow light regime.

Swing effect of spatial solitons propagating through Gaussian and triangular waveguides.

We report the behavior of spatial optical solitons propagating through inhomogeneous waveguides with Gaussian, single triangular, and double-triangular refractive index profiles. In a given Gaussian profile, as the soliton amplitude decreases below a certain value, its behavior deviates from that of a particlelike soliton. Dependence of the swing period of a spatial soliton in a single triangular index profile on its amplitude, eta, is less significant than that in a Gaussian profile. We also report the interacting behavior of two solitons propagating simultaneously through a waveguide with a double-triangular index profile. Furthermore, we present the effects of the solitons' initial phase factors and amplitude on their behavior.

The effects of cognitively demanding dual-task driving condition on elderly people's driving performance; Real driving monitoring.

BACKGROUND: Using in-vehicle audio technologies such as audio systems and voice messages is regarded as a common secondary task. Such tasks, known as the sources of non-visual distraction, affect the driving performance. Given the elderly drivers' cognitive limitations, driving can be even more challenging to drivers. The current study examined how listening to economic news, as a cognitively demanding secondary task, affects elderly subjects' driving performance and whether their comprehension accuracy is associated with these effects. METHODS: Participants of the study (N=22) drove in a real condition with and without listening to economic news. Measurements included driving performance (speed control, forward crash risk, and lateral lane position) and task performance (comprehension accuracy). RESULTS: The mean driving speed, duration of driving in unsafe zones and numbers of overtaking decreased significantly when drivers were engaged in the dual-task condition. Moreover, the cognitive secondary task led to a higher speed variability. Our results demonstrate that there was not a significant relationship between the lane changes and the activity of listening to economic news. However, a meaningful difference was observed between general comprehension and deep comprehension on the one hand and driving performance on the other. Another aspect of our study concerning the drivers' ages and their comprehension revealed a significant relationship between age above 75 and comprehension level. Drivers aging 75 and older showed a lower level of deep comprehension. CONCLUSION: Our study demonstrates that elderly drivers compensated driving performance with safety margin adoption while they were cognitively engaged. In this condition, however, maintaining speed proved more demanding for drivers aging 75 and older.