Sharif Digital Repository

An electromagnetically induced phase grating (EIG) controlled by coherent population trapping (CPT) in a fourlevel Y-type atomic system is studied. The CPT condition promotes significantly the dispersion of light into the first-order diffraction in constructing a phase modulation grating by transferring energy from zero-order to firstorder diffraction. The diffraction efficiency of the phase grating is enhanced by up to 30% of the total probe intensity at the first-order diffraction. The present atomic scheme takes full advantage of the microwave-driven field for generating the EIG, which induces the quantum coherence and controls linear and nonlinear behaviors of the present system.... 

In this paper, we propose a new architecture for nanophotonic Networks on Chip (NoC), named 2D-HERT, which consists of optical data and control planes. The proposed data plane is built upon a new topology and all-optical switches that passively route optical data streams based on their wavelengths. Utilizing wavelength routing method, the proposed deterministic routing algorithm, and Wavelength Division Multiplexing (WDM) technique, the proposed data plane eliminates the need for optical resource reservation at the intermediate nodes. For resolving end-point contention, we propose an all-optical request-grant arbitration architecture which reduces optical losses compared to the alternative... 

We propose a flexible four-wave mixing-based label recognition technique for low-weight spectral amplitude codes in optical packet-switched networks. We experimentally demonstrate label recognition, packet switching, and error-free transmission  

We propose and demonstrate a novel architecture for four-wave mixing (FWM)-based recognition of spectral amplitude code (SAC) labels in optical packet-switched networks. With a proper code design, a unique FWM idler for each SAC label, referred to as a label identifier (LI), is generated in a nonlinear medium. A serial array of fiber Bragg gratings is then used to reflect the LI wavelengths. Each LI is associated with a unique amount of delay between two optical signals received at two photodiodes (PDs). Label recognition is then achieved by measuring this unique time delay (referred to as the characteristic delay). The main advantages of the proposed method include the following: no... 

In this article we propose a novel mechano-optical switch and dual channel transmitter based on photonic crystal. The device consists of two waveguides and an elliptical cavity in a square lattice structure. Two optical signals at separate wavelengths are inserted in the input waveguide. The elliptical cavity can be rotated using a mechanical force, which results in the control of transmission efficiency at each of the wavelengths. In addition, rotation of the cavity can be considered as a switching action, which changes on-off states of the output signals  

This paper proposes CoNoC (Contention-free optical NoC) as a new architecture for on-chip routing of optical packets. CoNoC is built upon all-optical switches (AOSs) which passively route optical data streams based on their wavelengths. The key idea of the proposed architecture is the utilization of per-receiver wavelength in the data network to prevent optical contention at the intermediate nodes. Routing optical packets according to their wavelength eliminates the need for resource reservation at the intermediate nodes and the corresponding latency, power, and area overheads. Since passive architecture of the AOS confines the optical contention to the end-points, we propose an electrical... 

In this paper, a QoS differentiation framework is proposed for an optical burst switching (OBS) multiservice network. Furthermore, hybrid wavelength division multiplexing and optical code division multiplexing (WDM/OCDM) scheme is used to mitigate the blocking probability of OBS networks. In our study, the measurement criteria of QoS are the blocking probability, OBS network delay, transmission rate, and OCDM probability of error. In order to increase the bandwidth efficiency and control the multiplexing interference effect of OCDM, an advanced optical resource allocation strategy is introduced. The proposed strategy is also compared with a conventional strategy based on random allocation.... 

We investigate the potential of plasmonic resonance in metal nanocomposite materials for the design of photonic crystal all optical switches by numerical methods. We study the absorption effect of the plasmonic resonance on the Fano resonances of one dimensional photonic crystal slabs covered by a metal nanocomposite layer. It is shown that the absorption reduces the contrast of the Fano resonances. However, for adequate metal nanoparticle concentrations it is possible to achieve both sufficiently sharp Fano resonance and strong Kerr nonlinearity, which provides a suitable condition for the design of high contrast and low threshold switches  

Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite... 

In this work, an optimum frequency is found for the operation of single cavity photonic switches. At this optimum point, the transmission contrast of ON and OFF states takes its highest value, while keeping the device power threshold relatively low and the device speed acceptably high. Then, the dynamic behavior of a typical single cavity all optical switch is investigated in the optimum operation point through temporal Coupled Mode Theory. Switching speed and power are discussed, and the device is shown to be applicable for telecommunication and data processing applications. The analysis is quite general, and can be used for resonant structures, such as photonic crystals and microring... 

A switchable dual light- and temperature-responsive drug carrier using gold nanoparticles (Au NPs)-grafted poly(dimethylacrylamide-co-acrylamide)/poly acrylic acid [P(DMA-co-AAm)/PAAc] hydrogel was prepared by free radical polymerization procedure using N,N-methylenebisacrylamide as cross-linker and ammonium persulfate as initiator. Initial P(DMA-co-AAm) hydrogel and uniformly-distributed stable Au NPs, prepared by reduction of hydrogen tetrachloroaureate (III) hydrate in the presence of trisodium citrate, were synthesized separately. Then, the prepared P(DMA-co-AAm) and Au NPs were added to an acrylic acid solution along with the cross-linker and initiator to prepare PAAc hydrogel within... 

Laser assisted drug release from a synthesized plain polymer composed of poly (butyl methacrylate-co-acrylamide-co-methacrylic acid) [P(BMA-co-AAm-co-MAA)] and a metallo-polymer composed of silver nanoparticles (Ag NPs) grafted plain polymer (the nanocomposite) were studied to investigate their capability to serve as drug carriers. Positive temperature dependent swelling changes were observed for both carriers and their thermal sensitivity and thermal and optical switching properties were investigated in two buffered solutions. An acidic solution with pH = 1.2 to simulate stomach body condition and a neutral solution with pH = 7.4 to simulate intestine condition. Reversible phase transition... 

Spectrum conversion can improve the performance of orthogonal frequency division multiplexing (OFDM)-based elastic optical networks (EONs) by relaxing the continuity constraint and consequently reducing connection request blocking probability during routing and spectrum assignment process. We propose three different architectures for including spectrum conversion capability in bandwidth-variable wavelength cross-connects (BVWXCs). To compare the capability of the introduced architectures, we develop an analytical method for computing average connection request blocking probability in a spectrum-convertible OFDM-based EON in which all, part, or none of the BVWXCs can convert the spectrum. An... 

This study examined MQWs made of InGaAs/GaAs, InAlAs/InP, and InGaAs/InP in terms of their band structure and reflectivity. We also demonstrated that the reflectivity of MQWs under normal incident was at maximum, while both using a strong pump and changing incident angle reduced it. Reflectivity of the structure for a weak probe pulse depends on polarization, intensity of the pump pulse, and delay between the probe pulse and the pump pulse. So this system can be used as an ultrafast all-optical switch which is inspected by the transfer matrix method. After studying the band structure of the one-dimensional photonic crystal, the optical stark effect (OSE) was considered on it. Due to the OSE... 

We investigate the problem of energy-efficient resource allocation constrained to quality of service and physical requirements in orthogonal frequency division multiplexing (OFDM)-based elastic optical networks and propose a fast two-stage algorithm to solve it. The first stage of the proposed algorithm deals with routing, traffic grooming, and traffic ordering and mainly aims at minimization of the number of deployed optical amplifiers and transponders. We provide an integer linear program for routing and traffic grooming and propose a heuristic procedure, which yields its near-optimum solution in a shorter runtime. In the second stage, we optimize transponder parameters to minimize total... 

The internally coded time-hopping coherent ultra-short light pulse code division multiple access (CULP CDMA) scheme (recently introduced) with an optical amplifier is described and its performance in fibre-optic communication systems is analysed. In accordance with the important role of optical amplifiers in optical communication systems, a preamplifier at the input of the receiver is used in order to compensate the losses because of the spectral encoder, spectral decoder and optical fibre path. The authors evaluate the bit error rate of the system considering the effects of the multiple access interference, noise because of the optical amplifier and thermal noise using saddle point...