Photonic switching architectures with logic cells

Possible switching architectures, with Optically Programmable Logic Cells - OPLCs - will be reported in this paper. These basic units, previously employed by us for some other applications mainly in optical computing, will be employed as main elements to switch optical communications signals. The main aspect to be considered is that because the nternal components of these cells have nonlinear behaviors, namely either pure bistable or SEED-like properties, several are the possibilities to be obtained. Moreover, because their properties are dependent, under certain condition, of the signal wavelength, they are apt to be employed in WDM systems and the final result will depend on the orresponding optical signal frequency. We will give special emphasis to the case where self-routing is achieved, namely to structures of the Batcher or Banyan type. In these cases, as it will be shown, there is the possibility to route any packet input to a certain direction according to its first bits. The number of possible outputs gives the number of bits needed to route signals. An advantage of this configuration is that a very versatile behavior may be allowed. The main one is the possibility to obtain configurations with different kinds of behavior, namely, Strictly Nonblocking, Wide-Sense Nonblocking or Rearrangeably Nonblocking as well as to eliminate switching conflicts at a certain intermediate stages.

Teaching digital control of switch mode power supplier

This paper explains the methodology followed to teach the subject `Digital control of power converters'. This subject belongs to the research master on `Industrial Electronics' of the Universidad Politécnica de Madrid. The subject is composed of several theoretical lessons plus the development of an actual digital control. For that purpose an ad hoc dc-dc converter has been designed and built. The use of this board together with some software tools seems a very powerful way for the students to learn the concepts from the design to the real world

Efficient design and optimization of bio-photonic sensing cells (BICELLs) for label free biosensing

In previous works we demonstrated the benefits of using micro–nano patterning materials to be used as bio-photonic sensing cells (BICELLs), referred as micro–nano photonic structures having immobilized bioreceptors on its surface with the capability of recognizing the molecular binding by optical transduction. Gestrinone/anti-gestrinone and BSA/anti-BSA pairs were proven under different optical configurations to experimentally validate the biosensing capability of these bio-sensitive photonic architectures. Moreover, Three-Dimensional Finite Difference Time Domain (FDTD) models were employed for simulating the optical response of these structures. For this article, we have developed an effective analytical simulation methodology capable of simulating complex biophotonic sensing architectures. This simulation method has been tested and compared with previous experimental results and FDTD models. Moreover, this effective simulation methodology can be used for efficiently design and optimize any structure as BICELL. In particular for this article, six different BICELL's types have been optimized. To carry out this optimization we have considered three figures of merit: optical sensitivity, Q-factor and signal amplitude. The final objective of this paper is not only validating a suitable and efficient optical simulation methodology but also demonstrating the capability of this method for analyzing the performance of a given number of BICELLs for label-free biosensing.

Photonic Logic Based on Molecular Reorientation of Nematic Liquid Crystals

A new type of photonic logic, based on the use of nematic liquid crystals is proposed. The system takes advantage of the refractive-index changes induced by laser beams. Examples of AND, OR and NOR functions are presented.

Learning from the living bodies: New principles and techniques for photonic sensing

Signal processing in any living being is much more complex than the one performed in artificial systems. Cortex architecture, although only partly known, gives some useful ideas to be employed in sensing technology. To analyze some of these structures is the objective of this paper. Among the points to be analyzed are the parallel transfer of information, the similarity of the different systems and the massive amount of data analyzed by physical techniques. As an example of these concepts, the possibility to transmit images in a parallel way will be reported.

Photonic processing subsystem based on visual cortex architecture

Optical signal processing in any living being is more complex than the one obtained in artificial systems. Cortex architecture, although only partly known, gives some useful ideas to be employed in communications. To analyze some of these structures is the objective of this paper. One of the main possibilities reported is handling signals in a parallel way. As it is shown, according to the signal characteristics each signal impinging onto a single input may be routed to a different output. At the same time, identical signals, coming to different inputs, may be routed to the same output without internal conflicts. This is due to the change of some of their characteristics in the way out when going through the intermediate levels. The simulation of this architecture is based on simple logic cells. The basis for the proposed architecture is the five layers of the mammalian retina and the first levels of the visual cortex.

Integrable high order UWB pulse photonic generator based on cross phase modulation in a SOA-MZI

We propose and experimentally demonstrate a potentially integrable optical scheme to generate high order UWB pulses. The technique is based on exploiting the cross phase modulation generated in an InGaAsP Mach-Zehnder interferometer containing integrated semiconductor optical amplifiers, and is also adaptable to different pulse modulation formats through an optical processing unit which allows to control of the amplitude, polarity and time delay of the generated taps.

Tunable liquid crystal-photonic crystal fiber interferometer

In this work, we present a novel interferometer based on liquid crystal and photonic crystal fiber technology. The objective of this project is the development of a tunable (switchable) modal (Mach-Zehnder) interferometer for optical communications or sensing.

Conductivity variations of multi-walled carbon nanotubes oriented in liquid crystal cells

The control of carbon nanotubes conductivity is generating interest in several fields since it may be relevant for a number of applications. The self-organizing properties of liquid crystals may be used to impose alignment on dispersed carbon nanotubes,thus control-ling their conductivity and its anisotropy. This leads to a number of possible applications in photonic and electronic devices such as electrically controlled carbon nanotube switch- es and crossboards. In this work, cells of liquid crystals doped with multi-walled nanotubes have been prepared in different configurations. Their conductivity variations upon switching have been investigated. It turns out that conductivity evolution depends on the initial configuration (either homogeneous, homeotropic or in-plane switching), the cell thickness and the switching record. The control of these manufacturing paramenters allows the modulation of the electrical behavior of carbon nanotubes.

Photonic liquid crystal fiber intermodal interferometer

In this work, we present a novel interferometer based on liquid crystal and photonic crystal fiber technology. The objective of this project is the development of a tunable (switchable) modal (Mach-Zehnder) interferometer for optical communications or sensing. This interferometer has been manufactured splicing a short portion (between 15 and 30 mm) of photonic crystal fiber with two single mode fiber pigtails. The study shows a high sensitivity of the interferometer to the polarization of the launching light.

Some relations between visual perception and non-linear photonic structures

The main objective of this work is to present a way to emulate some functions of the mammalian visual system and a model to analyze subjective sensations and visual illusions

High isolation series-shunt photoconductive microwave switch

This article presents a wide band compact high isolation photoconductive switch, which is based on the series-shunt switch design with three photoconductive switches made of diced high-resistivity silicon wafer placed over a microstrip gap and activated by 808-nm near-infrared laser diodes. The switch shows an insertion loss of 1.2 dB and an isolation of 44.8 dB at 2 GHz. It is easy to operate and control by light, high-speed, electromagnetically transparent and it does not require any biasing circuits.

Polarization properties of polymer-based photonic crystal fibers

Selectively filled photonic crystal fibers with polydimethylsiloxane (PDMS), a silicon-type material, have been studied. Is has been demonstrated that polarization properties of these hybrid devices and the properties of the guided light in relation with the temperature changes, finding that the state of polarization (SOP) change with the increasing temperature but remains constant for a wide spectrum of wavelengths for a determinate temperature.

Infiltration of a photonic crystal fiber with cholesteric liquid crystal and blue phase

Photonic crystal fibers (PCF) have been selectively filled with a cholesteric liquid crystal (ChLC) with special interest in the blue phase (BP) of the liquid crystal. It has been observed thermal tuning of the guided light in the visible region. A dramatically enhance appears when the phase of the liquid crystal changes from cholesteric to blue phase I (BPI). When a thermal range of the blue phase I is achieved, no changes are observed while increasing temperature from BPI through BPII and to the isotropic phase.

Silicon oxides as alignment surfaces for vertically-aligned nematics in photonic devices

A comparative study on alignment performance and microstructure of inorganic layers used for liquid crystal cell conditioning has been carried out. The study has focused on two specific materials, SiOx and SiO2, deposited under different conditions. The purpose was to establish a relationship between layer microstructure and liquid crystal alignment. The surface morphology has been studied by FESEM and AFM. An analysis on liquid crystal alignment, pretilt angle, response time, contrast ratio and the conditions to develop backflow effect (significant rise time increase due to pure homeotropic alignment) on vertically-aligned nematic cells has been carried out. A technique to overcome the presence of backflow has been identified. The full comparative study of SiOx and SiO2 layer properties and their influence over liquid crystal alignment and electrooptic response is presented.