Sharif Digital Repository

A simple analytic formula is derived to extract tiny dispersion fluctuations along highly nonlinear fibers from distributed measurements of parametric gain. A refined BOTDA scheme, suitable to track Kerr processes, enables low noise measurements  

A sensitive and accurate method for dispersion map extraction along an arbitrarily profiled highly nonlinear fiber (HNLF) is proposed. High sensitivity is achieved by positioning the wavelength of a signal at the band edge of the modulation instability (MI) spectrum generated by an intense degenerate four wave mixing (FWM) pump. In doing so, the to-be-extracted dispersion fluctuations leave a more drastic effect on the FWM-generated power since they either inflate or deflate the MI spectrum. The accuracy of the method is increased by monitoring the distribution of power along the fiber. Once the power distribution is measured along the fiber, dispersion map of the HNLF is extracted using an... 

We introduce a refinement of the Ozsváth-Szabó complex associated by Juhósz [Ju1] to a balanced sutured manifold (X,τ). An algebra (Formula Presented)τ is associated to the boundary of a sutured manifold. For a fixed class s of a Spinc structure over the manifold X, which is obtained from (Formula Presented) by filling out the sutures, the Ozsvóth-Szabó chain complex CF(X, τ, s) is then defined as a chain complex with coefficients in (Formula Presented)T and filtered by the relative Spinc classes in Spinc(X, τ). The filtered chain homotopy type of this chain complex is an invariant of (X,τ) and the Spinc class s Є Spinc(Formula Presented). The construction generalizes the construction of... 

A method to measure the signal power evolution along phase-sensitive parametric amplifiers is proposed using Brillouin optical time-domain analysis. Different evolutions along the fiber are reported by varying input wave phases, including amplification and de-amplification  

We propose a new system which can generate digital holograms using natural color information. The proposed system can generate about 10 digital holographic video frames per a second using about 6K light sources  

The performance of devices based on highly nonlinear fibers (HNLF) can be drastically impeded by even tiny fluctuations of the zero dispersion wavelength (ZDW) along the fiber. Being able to measure ZDW fluctuations along an HNLF is therefore essential for the design of efficient nonlinear optics based devices such as fiber optical parametric amplifiers (FOPA), regenerators and limiters. Different schemes using complex distributed sensing of localized nonlinear interactions have been used in order to derive the ZDW fluctuations along the fiber [1-2]. In [3], the distributed gain of a pulsed pump FOPA along an HNLF was measured using a Brillouin Optical-Time Domain Analysis (BOTDA) based... 

In this paper, we introduce a notion of quantum discrepancy, a non-commutative version of combinatorial discrepancy which is defined for projection systems, i.e. finite sets of orthogonal projections, as non-commutative counterparts of set systems. We show that besides its natural algebraic formulation, quantum discrepancy, when restricted to set systems, has a probabilistic interpretation in terms of determinantal processes. Determinantal processes are a family of point processes with a rich algebraic structure. A common feature of this family is the local repulsive behavior of points. Alishahi and Zamani (2015) exploit this repelling property to construct low-discrepancy point... 

A Brillouin probing method is proposed to extract the distribution of signal power along phase-sensitive parametric amplifiers. Operation near the zero-dispersion-wavelength shows enhanced sensitivity to dispersion fluctuations, allowing effective extraction of the dispersion map  

We propose and experimentally demonstrate a method based on Brillouin optical time-domain analysis to measure the longitudinal signal power distribution along phase-sensitive fiber-optical parametric amplifiers (PS-FOPAs). Experimental results show that the amplification of a PS-FOPA could go through different longitudinal profiles and yet finish with the same overall gain. This behavior is in sheer contrast with theoretical expectations, according to which longitudinal gain distribution should follow certain profiles determined by the initial relative phase difference but can never end up in the same overall gain. The gap between theory and experiment only becomes evident when the pump... 

In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (CDMA) as applied to wireless and optical communication systems under very general settings (of any size) for the user symbols and the signature matrix entries. The channel is modeled by real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether uniquely detectable overloaded matrices exist in the absence of additive noise under these general settings, and if so, whether there are any practical optimum detection algorithms. The second one is about the bounds for the sum channel capacity when user data and signature matrices employ any real... 

In this paper, we introduce a new class of codes for overloaded synchronous wireless and optical code-division multiple-access (CDMA) systems which increases the number of users for fixed number of chips without introducing any errors. Equivalently, the chip rate can be reduced for a given number of users, which implies bandwidth reduction for downlink wireless systems. An upper bound for the maximum number of users for a given number of chips is derived. Also, lower and upper bounds for the sum channel capacity of a binary overloaded CDMA are derived that can predict the existence of such overloaded codes. We also propose a simplified maximum likelihood method for decoding these types of... 

We consider one-hop communication in wireless networks with random connections. In the random connection model, the channel powers between different nodes are drawn from a common distribution in an i.i.d. manner. In a wireless network with n nodes, a simple one-hop scheme achieving the throughput scaling of order n 1/3-δ, for any arbitrarily small δ > 0, is proposed. This scheme is based on maximizing the number of successful concurrent transmissions. Such achievable throughput, along with the order n 1/3 upper bound derived by Cui et al., characterizes the throughput of one-hop schemes for the class of connection models with distribution having finite mean and variance  

We consider the problem of determining throughput of one-hop unicast transmissions in ad hoc wireless networks. We consider an interference-limited scenario in which wireless links between different nodes are modeled by independently and identically distributed random variables. The main decoding challenge for receive nodes is due to interference of nonintended concurrent transmissions. In this scenario, we consider a heuristic one-hop transmission strategy based on activating source-destination pairs with strongest direct links and forcing other pairs to be silent. We present a closed-form expression for throughput scaling of such strategy, for a completely general channel power... 

In this paper, enhanced spatial and temporal shifts in the reflection of Gaussian wave packets from twodimensional photonic crystal waveguides supporting above-the-light-line leaky modes are studied, for the first time to our best knowledge. Particular attention is given to two important special cases, namely, harmonic Gaussian beams and Gaussian-pulse uniform plane waves. Analytical expressions are given for enhanced spatial and temporal shifts when the stationary phase approximation holds and the incident wave excites above-the-light-line leaky modes. The enhanced spatial and temporal shifts of Gaussian wave packets are thereby related to each other via the group velocity of the excited... 

The spherical ensemble is a well-studied determinantal process with a fixed number of points on $2. The points of this process correspond to the generalized eigenvalues of two appropriately chosen random matrices, mapped to the surface of the sphere by stereographic projection. This model can be considered as a spherical analogue for other random matrix models on the unit circle and complex plane such as the circular unitary ensemble or the Ginibre ensemble, and is one of the most natural constructions of a (statistically) rotation invariant point process with repelling property on the sphere. In this paper we study the spherical ensemble and its local repelling property by investigating the... 

A new, fast, and efficient approach based on the differential transfer matrix idea, is proposed for analysis of nonuniform nonlinear distributed feedback structures. The a priori knowledge of the most-likely electromagnetic field distribution within the distributed feedback region is exploited to speculate and factor out the rapidly varying portion of the electromagnetic fields. In this fashion, the transverse electromagnetic fields are transformed into a new set of envelope functions, whereupon the numerical difficulty of solving the nonlinear coupled differential equations is partly imparted to the analytical factorization of the fields. This process renders a new set of well-behaved... 

This paper is devoted to the study of some asymptotic behaviors of Poisson-Voronoi tessellation in the Euclidean space as the space dimension tends to ∞. We consider a family of homogeneous Poisson-Voronoi tessellations with constant intensity λ in Euclidean spaces of dimensions n = 1, 2, 3,... First we use the Blaschke-Pètkantschin formula to prove that the variance of the volume of the typical cell tends to 0 exponentially in dimension. It is also shown that the volume of intersection of the typical cell with the co-centered ball of volume u converges in distribution to the constant λ-1 (1-e-λu). Next we consider the linear contact distribution function of the Poisson-Voronoi tessellation...