Search

Contains fulltext : 221738.pdf (postprint version ) (Open Access)

Contains fulltext : 221738.pdf (postprint version ) (Open Access)

Contains fulltext : 221738.pdf (postprint version ) (Open Access)

Contains fulltext : 203335.pdf (publisher's version ) (Closed access)

Contains fulltext : 203335.pdf (publisher's version ) (Closed access)

We analyze the small- and large-signal response of a photonic crystal Fano laser (PhC-FL). Conventional current modulation, as well as modulation of the laser via the mirror, is investigated using a numerical approach as well as linear smallsignal analysis. The results show that the amplitude modulation bandwidth of one of the laser ports (the through-port) and the frequency modulation (FM) bandwidth of another port (the cross-port) extend to the THz region. Large-signal simulations of the laser response to a 500 Gbit/s pseudo-random bit sequence modulation of the nanocavity are in good agreement with the predictions of the small-signal analysis. Finally, it is investigated how the design of the Fano mirror, in particular, the qualityfactor (Q) of the nanocavity, affects the modulation properties.

Given a real number $t>1$, a geometric $t$-spanner is a geometric graph for a point set in $\mathbb{R}^d$ with straight lines between vertices such that the ratio of the shortest-path distance between every pair of vertices in the graph (with Euclidean edge lengths) to their actual Euclidean distance is at most $t$. An imprecise point set is modeled by a set $R$ of regions in $\mathbb{R}^d$. If one chooses a point in each region of $R$, then the resulting point set is called a precise instance of~$R$. An imprecise $t$-spanner for an imprecise point set $R$ is a graph $G=(R,E)$ such that for each precise instance $S$ of $R$, graph $G_S=(S,E_S)$, where $E_S$ is the set of edges corresponding to $E$, is a $t$-spanner. In this paper, we show that, given a real number $t>1$, there is an imprecise point set $R$ of $n$ straight-line segments in the plane such that any imprecise $t$-spanner for $R$ has $\Omega(n^2)$ edges. Then, we propose an algorithm that computes a Well-Separated Pair Decomposition (WSPD) of size ${\cal O}(n)$ for a set of $n$ pairwise disjoint $d$-dimensional balls with arbitrary sizes. Given a real number $t>1$ and given a set of $n$ pairwise disjoint $d$-balls with arbitrary sizes, we use this WSPD to compute in ${\cal O}(n\log n+n/(t-1)^d)$ time an imprecise $t$-spanner with ${\cal O}(n/(t-1)^d)$ edges for balls.

Let $G=(V, E)$ be a simple and undirected graph. For some integer $k\geq 1$, a set $D\subseteq V$ is said to be a k-dominating set in $G$ if every vertex $v$ of $G$ outside $D$ has at least $k$ neighbors in $D$. Furthermore, for some real number $\alpha$ with $0<\alpha\leq1$, a set $D\subseteq V$ is called an $\alpha$-dominating set in $G$ if every vertex $v$ of $G$ outside $D$ has at least $\alpha\times d_v$ neighbors in $D$, where $d_v$ is the degree of $v$ in $G$. The cardinality of a minimum $k$-dominating set and a minimum $\alpha$-dominating set in $G$ is said to be the $k$-domination number and the $\alpha$-domination number of $G$, respectively. In this paper, we present some approximability and inapproximability results on the problem of finding $k$-domination number and $\alpha$-domination number of some classes of graphs. Moreover, we introduce a generalization of $\alpha$-dominating set which we call an $f$-dominating set. Given a function $f:\mathbb{N}\rightarrow \mathbb{R}$, where $\mathbb{N}=\{1, 2, 3, \ldots\}$, a set $D\subseteq V$ is said to be an $f$-dominating set in $G$ if every vertex $v$ of $G$ outside $D$ has at least $f(d_v)$ neighbors in $D$. We prove NP-hardness of the problem of finding a minimum $f$-dominating set in $G$, for a large family of functions $f$.

We propose an efficient planar all-Si internal photoemission photodetector operating at the telecommunication wavelength of 1550 nm and numerically investigate its optical and electrical properties. The proposed polarization-sensitive detector is composed of an appropriately engineered subwavelength grating structure topped with a silicide layer of nanometers thickness as an absorbing material. It is shown that a nearly-perfect light absorption is possible for the thin silicide layer by its integration to the grating resonator. The absorption is shown to be maximized when the critical coupling condition is satisfied. Simulations show that the external quantum efficiency of the proposed photodetector with a 2-nm-thick PtSi absorbing layer at the center wavelength of 1550 nm can reach up to ∼60%.

It is easier to understand an algorithm when it can be seen in interactive mode. The current study implemented four algorithms to construct geometric spanners; the path-greedy, gap-greedy, Theta-graph and Yao-graph algorithms. The data structure visualization framework (http://www.cs.usfca.edu/~galles/visualization/) developed by David Galles was used. Two features were added to allow its use in spanner algorithm visualization: support point-based algorithms and export of the output to Ipe drawing software format. The interactive animations in the framework make steps of visualization beautiful and media controls are available to manage the animations. Visualization does not require extensions to be installed on the web browser. It is available at http://cs.yazd.ac.ir/cgalg/AlgsVis/.

It is easier to understand an algorithm when it can be seen in interactive mode. The current study implemented four algorithms to construct geometric spanners; the path-greedy, gap-greedy, Theta-graph and Yao-graph algorithms. The data structure visualization framework (http://www.cs.usfca.edu/~galles/visualization/) developed by David Galles was used. Two features were added to allow its use in spanner algorithm visualization: support point-based algorithms and export of the output to Ipe drawing software format. The interactive animations in the framework make steps of visualization beautiful and media controls are available to manage the animations. Visualization does not require extensions to be installed on the web browser. It is available at http://cs.yazd.ac.ir/cgalg/AlgsVis/.

In this thesis selected applications of both minority and majority carrier conductor- thin insulator - semiconductor (CIS) tunnel structures to microelectronic devices such asbipolar and field-effect transistors are studied. Minority carrier CIS structures have propertieswhich approach those of an ideal p-n junction diode when the insulator issufficiently thin to allow a large current to flow through it. The effective junction depth ofsuch a CIS diode is of the order of the thickness of the electrostatically induced inversionlayer at the semiconductor-insulator interface. On the other hand, majority carrier CIStunnel diodes have shown interesting properties such as an internal current gain.First, by replacing the normally diffused emitters of silicon bipolar transistors withmetallic conductor CIS heterojunction tunneling emitters, significant improvements in thecurrent gain and in the breakdown voltage of super gain silicon bipolar transistors havebeen obtained. Current gains above 3xl04 have been achieved for devices with a breakdownvoltage in excess of 30V. Lateral bipolar transistors having such CIS emitters andcollectors have been fabricated. These are shown to possess lower leakage and highercurrent gains than those previously reported.Then, the emitter of a newly proposed transistor structure, the bipolar inversionchannelfield-effect transistor (BICFET), is replaced by a majority carrier CIS tunnelemitter. Experimental BICFETs of this type are fabricated more simply than originallyproposed and are shown to possess characteristics of the general form predicted. Both Aland n + poly have been used as the conductor overlying the tunnel insulator. In the lattercase, where a self-aligned scheme is implemented, a good quality interfacial oxide isshown to have an essential role in device operation.The shallow junction depth of the minority carrier CIS structures has been used toadvantage by replacing the normally diffused source and drain regions of a MOSFET withsuch