Walter Margulis

Walter Margulis
Pontifícia Universidade Católica do Rio de Janeiro · Center for Science and Technology (CTC)

PhD

About

292
Publications
14,234
Reads
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3,476
Citations
Additional affiliations
January 2004 - present
KTH Royal Institute of Technology
Position
  • Guest professor

Publications

Publications (292)
Article
Full-text available
In this work, we report on a twin-core fiber sensor system that provides improved spectral efficiency, allows for multiplexing and gives low level of crosstalk. Pieces of the referred strongly coupled multicore fiber are used as sensors in a laser cavity incorporating a pulsed semiconductor optical amplifier (SOA). Each sensor has its unique cavity...
Conference Paper
The operation of a Hybrid Electronic Addressable Random laser is analyzed. The laser operates as a ϕ-OTDR distributed vibration sensor in a transform-limited mode-locked regime with 41 MHz FWHM bandwidth and <7-kHz mode linewidth.
Article
Full-text available
Electrical corona discharge is employed in this work to deposit ions on the surface of an optical fiber, creating a strong electric field that is used for poling. Green laser light propagating in the core frees photocarriers that are displaced by the poling field. The technique presented can induce a higher optical nonlinearity than previously obta...
Article
Full-text available
Microfluidics has emerged rapidly over the past 20 years and has been investigated for a variety of applications from life sciences to environmental monitoring. Although continuous-flow microfluidics is ubiquitous, segmented-flow or droplet microfluidics offers several attractive features. Droplets can be independently manipulated and analyzed with...
Article
Full-text available
We demonstrate the use of the electrooptic effect to control the propagation constant of the guided modes in silicate few mode fibers with internal electrodes. The electrooptic effect induces a perturbation of the fiber's refractive index profile that controls intermodal interference. To increase the electrooptic effect the silicate fibers are pole...
Conference Paper
The electrooptic effect is used in a few-mode fiber to control intermodal interference. The fiber has internal electrodes and is poled to increase its electrooptic coefficient. The response time is in the nanosecond range.
Article
Full-text available
The hybrid electronically addressable random (HEAR) laser is a novel type of random fiber laser that presents the remarkable property of selection of the fiber section with lasing emission. Here we present a joint analysis of the correlations between intensity fluctuations at distinct wavelengths and replica symmetry breaking (RSB) behavior of the...
Preprint
Full-text available
An all-fiber separation component capable of sorting and counting micron-sized particles based on size is presented. A sequence of silica fiber capillaries with various diameters and longitudinal cavities were used to fabricate the component for separation and detection in an uninterrupted flow. Fluorescence microparticles of 1 micrometer and 10 mi...
Article
In this work, we present a quantitative (statistical) 3D morphological characterization of optical fibers used in electric field sensing. The characterization technique employs propagation-based X-ray phase-contrast microcomputed tomography (micro-CT). Particularly, we investigate specialty optical fibers that contain microstructured holes that are...
Conference Paper
Sensitive bending and vibration sensors based on a coupled-core optical fiber with Bragg gratings are proposed and demonstrated. The interrogation of such sensors is cost effective without comprising the sensors performance.
Article
Full-text available
In this work, we explore the interrogation of an array of fiber Bragg gratings as part of a laser cavity. A semiconductor optical amplifier in a sigma-shaped fiber cavity provides gain and is gated periodically at a rate that matches the roundtrip time associated with each grating of the array. The interrogator exhibits clear laser properties such...
Article
Full-text available
Nowadays there is an increasing demand for the cost-effective monitoring of potential threats to the integrity of high-voltage networks and electric power infrastructures. Optical fiber sensors are a particularly interesting solution for applications in these environments, due to their low cost and positive intrinsic features, including small size...
Article
Full-text available
We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obta...
Article
We present a novel C-cavity concept for tunable lasers. The laser is based on a semiconductor optical amplifier (SOA), serving both as a gain medium as well as a modulator, and a chirped fiber Bragg grating (C-FBG) which acts as the end mirrors on both cavity ends. Driving the SOA with a pulse pair with variable delay enables wavelength tuning by t...
Conference Paper
Full-text available
Using various fiber capillaries with different diameters and multiple holes we develop an optofluidic component capable of separating micron-sized beads emulating cells and bacteria, exploiting particle focusing in a viscoelastic fluid and analyzed optically.
Conference Paper
Full-text available
A compact fiber capillary based microflow cytometer capable of detecting side- scattered-light is demonstrated by using a 45 ⁰ angle-cleaved metal coated optical fiber tip.
Conference Paper
This work describes the use of FBGs inscribed in optical fiber with electrodes for voltage sensing. The results show a quadratic voltage dependence. The device can be explored for a multipoint, single-ended voltage sensing device.
Article
We describe a simple, narrow-linewidth, tunable fiber-based laser with a high degree of tuning accuracy. A polarization independent semiconductor optical amplifier (SOA) is used as the gain medium in a unidirectional fiber ring cavity with a circulator connected to a 6-meter long chirped fiber Bragg grating (CFBG). The laser wavelength is chosen by...
Article
A second-order nonlinearity was induced in silica fibers poled by exposure to ultraviolet (UV) radiation and simultaneous high voltage applied to internal electrodes. The UV light source was a tubular lamp with spectral peak at 254 nm. The highest second-order nonlinear coefficient measured through the linear electro-optic effect was 0.062 pm/V. Th...
Preprint
Full-text available
Joule effect and thermal response of several carbon-coated fibers are modelled and analysed. An electro-thermally driven all-fiber phase modulator based on these principles is proposed and a proof of concept of it is characterized. This kind of fibers could be the basis for developing all-fiber components aimed to operate in environments where the...
Article
Full-text available
Optical fibers are inherently designed to allow no interaction between the guided light and the surrounding optical radiation. Thus, very few optical fiber-based technologies exist in the field of optical radiation sensing. Accomplishing fully-distributed optical radiation sensing appears then as even more challenging since, on top of the lack of s...
Conference Paper
We demonstrate a tunable narrow-linewidth laser based on a semiconductor optical amplifier and a linearly chirped FBG. High tuning resolution and small power variation over 40 nm tuning range were achieved by optimizing the drive current.
Conference Paper
Silicate fibers with internal electrodes are optically poled without a laser by side-exposure to radiation from a UV tubular lamp. Electrooptic coefficients χ(2) ~ 0.04 pm/V and Vπ = 810 V are obtained.
Poster
Full-text available
CONCLUSIONS • It was shown a proof-of-concept of the operation of a distributed bolometer over conventional fibers; • The sensor was readily demonstrated to be able to measure absolute values of irradiance with sensitivities of 10 W/m2, equivalent to ≈1% of the reference solar spectral irradiance on earth at surface level. • It has a high potential...
Article
An approach has been developed for incorporating optoelectronic devices into polymer fibres, which can be woven into fabrics. Such materials could have applications in both telecommunication and health monitoring. An approach has been developed for incorporating optoelectronic devices into polymer fibres, which can be woven into fabrics. Such mater...
Conference Paper
A fiber probe traps single micrometer-particles by fluid suction into a hollow microstructure and enables optical identification by the fluorescence light collected in a fiber core. The probe finds applications in life-science and environmental monitoring.
Conference Paper
Full-text available
Certain applications of fiber sensors (e.g. avionics, oil industry) imply extreme operating conditions spurring the development of hermetic all-fiber devices. We present a hermetic all-fiber phase modulator based on Joule heating in a carbon-coated fiber.
Conference Paper
Full-text available
A distributed bolometer operating over transparent-coated and carbon-coated optical fibers is proposed. The detection of light with irradiance sensitivities of in the order of 1% of the reference solar irradiance is readily demonstrated.
Article
A fiber probe is presented that traps single micro-sized particles and allows detection of their optical properties. The trapping mechanism used is based on fluid suction with a micro-structured optical fiber that has five holes along its cladding. Proof-of-principle experiments with a diluted solution of fluorescently labeled particles are perform...
Article
Full-text available
Flow cytometry is currently the gold standard for analysis of cells in the medical laboratory and biomedical research. Fuelled by the need of point-of-care diagnosis, a significant effort has been made to miniaturize and reduce cost of flow cytometers. However, despite recent advances, current microsystems remain less versatile and much slower than...
Article
Full-text available
We demonstrate the digital electric field induced switching of plasmonic nanorods between 1 and 0 orthogonal aligned states using an electro-optic fluid fiber component. We show by digitally switching the nanorods, that thermal rotational diffusion of the nanorods can be circumvented, demonstrating an approach to achieve submicrosecond switching ti...
Article
As information technologies move from electron-to photon-based systems, the need to rapidly modulate light is of paramount importance. Here, we study the evolution of the electric-field-induced alignment of gold nanorods suspended in organic solvents. The experiments were performed using an all-fiber optofluidic device, which enables convenient int...
Article
Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-op...
Conference Paper
Distributed sensors based on phase-optical time-domain reflectometry (φ-OTDR) are suitable for aircraft health monitoring due to electromagnetic interference immunity, small dimensions, low weight and flexibility. These features allow the fiber embedment into aircraft structures in a nearly non-intrusive way to measure vibrations along its length....
Article
Full-text available
The use of an optical fiber as a real-time distributed microphone is demonstrated employing a phase-OTDR with direct detection. The method comprises a sample-and-hold circuit capable of both tuning the receiver to an arbitrary section of the fiber considered of interest and to recover in real-time the detected acoustic wave. The system allows liste...
Conference Paper
Towards a portable point of care flow cytometry platform, we present here an integrated all optical fiber-based optofluidic system capable of counting and discriminating fluorescent particles and cells. The robust and compact device incorporates optical fibers and circular capillaries to build an all-fiber opto- fluidic device to enable counting pa...
Conference Paper
Full-text available
Recent progress in thermal poling of silica fibers is reviewed. It is demonstrated that poled fibers can be used in a number of practical applications. Challenges for further development of poled fibers are discussed and possible solutions proposed.
Conference Paper
Herein, we demonstrated a T-shaped whispering gallery modes (WGMs) excitation system including a tapered single mode fiber (SMF), a tapered microstructured optical fiber (MOF) and a BaTiO3 microsphere for efficient light coupling and routing between the two fibers. The BaTiO3 microsphere is semi-immersed into the capillary of a tapered MOF, while t...
Article
We demonstrate the addition of time gating to a standard optical spectrum analyzer (OSA) operating in the spectral region similar to 1.06 mu m. This is accomplished by opening for 7 ns the optical input to the OSA with an electrically driven poled fiber in a Sagnac loop. The sequential interrogation with nanosecond resolution of the reflection from...
Conference Paper
Optofluidics is exploited in an all-fiber component to detect and identify through fluorescence particles flowing at high rate and inertially focused in a capillary. The system represents a first step towards an in-fiber flow cytometer.
Conference Paper
Optical properties of nanorods in the presence of external electric field when confined to a special optical fiber was investigated, showing an increase of the longitudinal absorption peak in the presence of the field.
Article
By solving the two-dimensional Poisson equation for fibers with circular internal electrodes, we show that the parallelplate approximation incurs significant error in the determination of the electric field applied to the fiber core. This also affects the value of χ(3) measured in electro-optical fibers. The exact solution of Poisson's equation is...
Conference Paper
Full-text available
An optical fiber component and setup were developed to insert and remove gases from hollow-core optical fibers, allowing gas/light mixing over the length of the fiber for gas sensing applications. Transmitted signals acquired at the output of the fiber contain information regarding absorption occurring inside the fiber, providing a spectroscopic si...
Article
The visibility of graphene is greatly increased by illuminating samples deposited on transparent dielectrics at the substrates' Brewster angle. Using a commercial ellipsometer, the reflectivity of monolayers of chemical vapour deposition (CVD) graphene is found to be up to 33 times higher than that of the substrate, i.e., an optical contrast as hig...
Article
A micro-structured fiber-based system for identification and collection of fluorescent particles is demonstrated. An optical fiber probe with longitudinal holes in the cladding is used to retrieve fluorescent particles by exerting microfluidics forces. Laser induced fluorescent (LIF) is carried out by the fiber probe and an optical setup. When a pa...
Article
Full-text available
We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (~10 8 V/m) is comparable to that...
Article
An alignment free all-fiber pulse-picker running at variable repetition-rate for selecting pulses from an 86 MHz mode-locked Yb-fiber laser at 0-0.6 MHz with better than 35 dB extinction ratio is presented.
Article
Optofluidic dye lasers may play a significant role in future laser applications in numerous areas, combining wavelength flexibility with integration and ease of operation. Nevertheless, no all-fiber integrated dye lasers have been demonstrated so far. In this paper, we report on a series of optofluidic all-fiber Rhodamine optical sources operating...
Conference Paper
The integration of a microspherical whispering gallery mode (WGM) resonator inside a microstructured optical fiber taper is demonstrated. Preliminary WGM spectra of this in-fiber resonator in transmission mode are presented and discussed.
Conference Paper
A tunable single-wavelength Erbium-doped all-fiber laser was experimentally demonstrated. The tuning is obtained with a stress-optic phase modulator based on a twin-hole fiber and a chirped fiber Bragg grating in a medium birefringence fiber.
Conference Paper
Silica fibers with internal electrodes biased with HV are poled when simultaneously excited by green light. The chi2 induced measured through the Pockels effect at 1.55 µm reaches ~0.11 pm/V. Poling and erasure are studied.
Conference Paper
We illuminate particles in a solution using fibers with cladding holes. Particles sufficiently near the fiber tip and with the correct optical signature are collected into the holes with good specificity, mimicking cell-collection for diagnostics.
Article
Gold nanoparticles have been used since antiquity for the production of red-colored glasses. Contemporarily, it was determined that this color is caused by plasmon resonance, which, additionally, increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold n...