Ring Resonators with Sagnac Loops for Photonic Processing in DWDM Backbone Networks

In this paper, optical configurations based on ring resonators (RR) with an internal Sagnac (SG) loop in the feedback path, are analyzed in terms of their amplitude response and dispersive properties for filtering and chromatic dispersion managing in digital transmission systems over amplified single- mode fiber (SMF) spans in DWDM backbone networks. Design issues for the architecture as regards quadratic dispersion and magnitude distortion are provided. The RR+SG compound filter provides frequency tunability of the amplitude and dispersion peaks by adjusting a coupling coefficient of an optical coupler, with no need for using integrated thermo-optic nor current- injection based phase shifters. The configuration can be employed as an additional structure for a general RR-based design and synthesis architecture, allowing bandwidth increase of dispersion compensators and flexibility. The performance of a compound filter consisting of a two RR in series stage and a RR+SG filter are reported as a more compact and effective solution for existing multi-channel SMF backbone links operating at high bit rates. Design guidelines of an integrated ring resonator based on polymer technology for showing feasibility of the proposal is reported.This work was partially supported by Spanish CICYT (TEC2006-13273-C03-03-MIC), European project NoE EPhoton/One+, CAM (FACTOTEM-CM:S-0505/ESP/000417), FENIS-CCG06-UC3MITIC-0619.Publicad

Radio-frequency ring resonators for self-referencing fiber-optic intensity sensors

A theoretical and experimental study of radiofrequency ring resonators (RR) for referencing and improving the sensitivity of fiber-optic intensity sensors (FOS) is reported. The separation between lead and transducer losses in the FOS is solved by converting the light intensity fluctuations to be measured into RR losses that produce high amplitude variations in the proximity of the RR resonance frequencies. Two different self-referencing techniques are developed. Via the definition of the measurement parameter RM , sensor linearity and sensitivity are analyzed. A calibration using an optical attenuator is reported to validate the model.Publicad

Minimal formulation of the linear spatial analysis of capillary jets: Validity of the two-mode approach

A rigorous and complete formulation of the linear evolution of harmonically stimulated capillary jets should include infinitely many spatial modes to account for arbitrary exit conditions [J. Guerrero et al., J. Fluid Mech. 702, 354 (2012)]. However, it is not rare to find works in which only the downstream capillary dominant mode, the sole unstable one, is retained, with amplitude determined by the jet deformation at the exit. This procedure constitutes an oversimplification, unable to handle a flow rate perturbation without jet deformation at the exit (the most usual conditions). In spite of its decaying behavior, the other capillary mode (subdominant) must be included in what can be called a “minimal linear formulation.” Deformation and mean axial velocity amplitudes at the jet exit are the two relevant parameters to simultaneously find the amplitudes of both capillary modes. Only once these amplitudes are found, the calculation of the breakup length may be eventually simplified by disregarding the subdominant mode. Simple recipes are provided for predicting the breakup length, which are checked against our own numerical simulations. The agreement is better than in previous attempts in the literature. Besides, the limits of validity of the linear formulation are explored in terms of the exit velocity amplitude, the wave number, the Weber number, and the Ohnesorge number. Including the subdominant mode extends the range of amplitudes for which the linear model gives accurate predictions, the criterion for keeping this mode being that the breakup time must be shorter than a given formula. It has been generally assumed that the shortest intact length happens for the stimulation frequency with the highest growth rate. However, we show that this correlation is not strict because the amplitude of the dominant mode has a role in the breakup process and it depends on the stimulation frequency.Ministerio de Economía, Industria y Competitividad, Spain, under Contract No. FIS2014-25161Junta de Andalucía under Contract No. P11-FQM-791

On the Minimum Order of Extremal Graphs to have a Prescribed Girth

We show that any n‐vertex extremal graph G without cycles of length at most k has girth exactly $k+1$ if $k\ge 6$ and $n>(2(k-2)^{k-2}+k-5)/(k-3)$. This result provides an improvement of the asymptotical known result by Lazebnik and Wang [J. Graph Theory, 26 (1997), pp. 147–153] who proved that the girth is exactly $k+1$ if $k\ge 12$ and $n\ge 2^{a^2+a+1}k^a$, where $a=k-3-\lfloor(k-2)/4\rfloor$. Moreover, we prove that the girth of G is at most $k+2$ if $n>(2(t-2)^{k-2}+t-5)/(t-3)$, where $t=\lceil (k+1)/2\rceil\ge 4$. In general, for $k\ge 5$ we show that the girth of G is at most $2k-4$ if $n\ge 2k-2$

Phage Lysins for Fighting Bacterial Respiratory Infections: A New Generation of Antimicrobials

Lower respiratory tract infections and tuberculosis are responsible for the death of about 4.5 million people each year and are the main causes of mortality in children under 5 years of age. Streptococcus pneumoniae is the most common bacterial pathogen associated with severe pneumonia, although other Gram-positive and Gram-negative bacteria are involved in respiratory infections as well. The ability of these pathogens to persist and produce infection under the appropriate conditions is also associated with their capacity to form biofilms in the respiratory mucous membranes. Adding to the difficulty of treating biofilm-forming bacteria with antibiotics, many of these strains are becoming multidrug resistant, and thus the alternative therapeutics available for combating this kind of infections are rapidly depleting. Given these concerns, it is urgent to consider other unconventional strategies and, in this regard, phage lysins represent an attractive resource to circumvent some of the current issues in infection treatment. When added exogenously, lysins break specific bonds of the peptidoglycan and have potent bactericidal effects against susceptible bacteria. These enzymes possess interesting features, including that they do not trigger an adverse immune response and raise of resistance is very unlikely. Although Gram-negative bacteria had been considered refractory to these compounds, strategies to overcome this drawback have been developed recently. In this review we describe the most relevant in vitro and in vivo results obtained to date with lysins against bacterial respiratory pathogens

Construction of an Instrument for Measuring the Perceived Usefulness of the ICT Used when Teaching by Building Engineering Students

Se ha realizado una investigación acerca del uso del ordenador y de los objetos de aprendizaje que utilizan los estudiantes en una asignatura de Arquitectura Técnica de la Universidad de Alicante. Para ello, se ha creado un instrumento que analiza la utilidad percibida de los objetos de aprendizaje en la adquisición de las competencias y las actitudes de los estudiantes hacia el uso del ordenador. Los análisis realizados indican que el instrumento de medición elaborado es fiable y válido. La validez de contenido del instrumento se analizó a través del juicio de expertos (validez general del cuestionario = .912, p-valor = .000). La validez de constructo se estudió a través del análisis de su estructura interna, sometiendo a un análisis factorial los ítems de la versión definitiva del cuestionario (se identificaron cuatro factores que juntos explicaron el 45.65% de la varianza). La fiabilidad del instrumento se analizó calculando su consistencia interna por medio del coeficiente alpha de Cronbach (? para el total de la escala = .90).This paper aims to evaluate the learning objects used by the students enrolled in a Building Engineering subject of the University of Alicante. An instrument was created to achieve that aim which analyzes the perceived usefulness of learning objects when it comes to competence acquisition and students' attitudes towards computer use. The analyses performed suggest that the measuring instrument developed is reliable and valid. Content validity for this instrument was examined through expert judgment (questionnaire general validity = .912, p-value = .000). In turn, construct validity was studied through the examination of its internal structure, applying factor analysis to the items contained on the final questionnaire version (four factors were identified which jointly explained 45.65% of variance). As for instrument reliability, it was analyzed through a calculation of its internal consistency by means of Cronbach's alpha coefficient (? for the scale total = .90).Universidad de Alicant

Measurements On Passive Tunable Optical Filters For DWDM

WFOPC 2002 IEEE/LEOS Workshop on Fibre and Optical Passive Components, University of Glasgow, Scotland, on 5th-6th June 2002.Measurements on a passive optical fibre tunable filter are presented. The device is based on a loop mirror in a ring resonator. The loop mirror allows tuning by changing the coupling coefficient of a coupler. The novel filter structure allows planar optical integration for having higher free spectral ranges. Novel and simple design equations for the filter parameters and the tuning process are reported. There is a good agreement between measurements and theory.Universidad Carlos III de MadridPublicad

Tunable Optical Filters Using Compound Ring Resonators for DWDM

The device is based on a loop mirror in a ring resonator. The loop mirror allows tuning by changing the coupling coefficient of a directional coupler. The loop mirror is implemented using a Sagnac configuration to have the same optical path between the signals to be interfered (copropagating and counterpropagating ones). The filter structure allows optical integration for having higher free-spectral ranges. Simple design equations for the filter parameters and the tuning are reported. Measurements on a passive optical fiber tunable filter are presented. There is a good agreement between measurements and theory.Publicad

On the λ'-optimality of s-geodetic digraphs

For a strongly connected digraph D the restricted arc-connectivity λ'(D) is defined as the minimum cardinality of an arc-cut over all arc-cuts S satisfying that D − S has a non trivial strong component D1 such that D − V (D1) contains an arc. Let S be a subset of vertices of D. We denote by ω+(S) the set of arcs uv with u ∈ S and v ∈ S, and by ω−(S) the set of arcs uv with u ∈ S and v ∈ S. A digraph D = (V,A) is said to be λ'-optimal if λ'(D) = ξ'(D), where ξ'(D) is the minimum arc-degree of D defined as ξ(D) = min{ξ'(xy) : xy ∈ A}, and ξ'(xy) = min{|ω+({x, y})|, |ω−({x, y})|, |ω+(x)∪ω−(y)|, |ω−(x)∪ω+(y)|}. In this paper a sufficient condition for a s-geodetic strongly connected digraph D to be λ'-optimal is given in terms of its diameter.Further we see that the h-iterated line digraph Lh(D) of a s-geodetic digraph is λ'-optimal for certain iteration h.Peer Reviewe

On the connectivity and restricted edge-connectivity of 3-arc graphs

A 3−arc of a graph G is a 4-tuple (y, a, b, x) of vertices such that both (y, a, b) and (a, b, x) are paths of length two in G. Let ←→G denote the symmetric digraph of a graph G. The 3-arc graph X(G) of a given graph G is defined to have vertices the arcs of ←→G. Two vertices (ay), (bx) are adjacent in X(G) if and only if (y, a, b, x) is a 3-arc of G. The purpose of this work is to study the edge-connectivity and restricted edge-connectivity of 3-arc graphs.We prove that the 3-arc graph X(G) of every connected graph G of minimum degree δ(G) ≥ 3 has edge-connectivity λ(X(G)) ≥ (δ(G) − 1)2; and restricted edge- connectivity λ(2)(X(G)) ≥ 2(δ(G) − 1)2 − 2 if κ(G) ≥ 2. We also provide examples showing that all these bounds are sharp.Peer Reviewe